Δημοσιεύσεις
Δημοσιεύσεις¶
Διδακτορική Διατριβή: Αισθητήρες Αερίων Οξειδίων Μετάλλων και η χρήση τους σε Συστήματα Τεχνητής Όσφρησης ⤓ PDF
ΕΘνικό Μετσόβιο Πολυτεχνείο, Σχολή Ηλεκτρολόγων Μηχανικών και Μηχανικών Η/Υ, Ιούνιος 1996
Motion-Compensated PET Image Reconstruction via Separable Parabolic Surrogates
Nicholas E. Protonotarios, George A. Kastis, Andreas D. Fotopoulos, Andreas G. Tzakos, Dimitrios Vlachos and Nikolaos Dikaios
Abstract: The effective resolution of positron emission tomography (PET) can be significantly degraded by patient motion during data acquisition. This is especially true in the thorax due to respiratory motion. This study concentrates on the improvement of motion correction algorithms both in terms of image quality and computational cost. In this paper, we present a novel motion-compensated image reconstruction (MCIR) algorithm based on a parabolic surrogate likelihood function instead of the loglikelihood function of the expectation maximization (EM) algorithm. The theoretical advantage of the parabolic surrogate algorithm lies within the fact that its loglikelihood is upper bounded by the EM loglikelihood, thus it will converge faster than EM. This is of particular importance in PET motion correction, where reconstructions are very computationally demanding. Relaxation parameters were also introduced to converge closer to the maximum likelihood (ML) solution and achieve lower noise levels. Image reconstructions with embedded relaxation parameters actually converged to better solutions than the corresponding ones without relaxation. Motion-compensated parabolic surrogates were indeed shown to accelerate convergence compared to EM, without reaching a limit cycle. Nonetheless, with the incorporation of ordered subsets in the reconstruction setting, the improvement was less evident.
Cite as: Protonotarios, N.E.; Kastis, G.A.; Fotopoulos, A.D.; Tzakos, A.G.; Vlachos, D.; Dikaios, N. Motion-Compensated PET Image Reconstruction via Separable Parabolic Surrogates. Mathematics 2023,11,55. https://doi.org/10.3390/math11010055.
Nearest Neighbor Forecasting Using Sparse Data Representation
Dimitrios Vlachos and Dimitrios Thomakos
Abstract: The method of the nearest neighbors as well as its variants have proven to be very powerful tools in the non-parametric prediction and categorization of experimental measurements. On the other hand, the number of data available today as well as their dimensionality and complexity is growing rapidly in many scientific fields, such as economics, biology, chemistry, medicine, and others. Usually, the data and their characteristics have semantic dependence and a lot of noise. At this point, the sparse data representation that deals with these problems with great success is involved. In this paper we present the application of these two tried and tested techniques for prediction in various fields related to economics. New techniques are presented as well as exhaustive tests for the evaluation of the proposed methods. The results are encouraging to continue research into the possibilities of sparse representation combined …
Cite as: Vlachos, D., Thomakos, D. (2021). Nearest Neighbor Forecasting Using Sparse Data Representation. In: Parasidis, I.N., Providas, E., Rassias, T.M. (eds) Mathematical Analysis in Interdisciplinary Research. Springer Optimization and Its Applications, vol 179. Springer, Cham. https://doi.org/10.1007/978-3-030-84721-0_38. https://link.springer.com/chapter/10.1007/978-3-030-84721-0_38.
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Error Analysis Through Energy Minimization and Stability Properties of Exponential Integrators
Odysseas Kosmas and Dimitrios Vlachos
Abstract: In this article, the stability property and the error analysis of higher-order exponential variational integration are examined and discussed. Toward this purpose, at first we recall the derivation of these integrators and then address the eigenvalue problem of the amplification matrix for advantageous choices of the number of intermediate points employed. Obviously, the latter determines the order of the numerical accuracy of the method. Following a linear stability analysis process we show that the methods with at least one intermediate point are unconditionally stable. Finally, we explore the behavior of the energy errors of the presented schemes in prominent numerical examples and point out their excellent efficiency in long term integration.
Cite as: Kosmas, O., Vlachos, D. (2021). Error Analysis Through Energy Minimization and Stability Properties of Exponential Integrators. In: Rassias, T.M., Pardalos, P.M. (eds) Nonlinear Analysis and Global Optimization. Springer Optimization and Its Applications, vol 167. Springer, Cham. https://doi.org/10.1007/978-3-030-61732-5_13. https://link.springer.com/chapter/10.1007/978-3-030-61732-5_13.
Exponential Variational Integrators Using Constant or Adaptive Time Step
Odysseas Kosmas and Dimitrios Vlachos
Abstract: In this book article, at first we survey some recent advances in variational integrators focusing on the class of them known as exponential variational integrators, applicable in finite dimensional mechanical systems. Since these integrators are based on the space and time discretization, we start with a brief summary of the general development of the discrete mechanics and its application in describing mechanical systems with space-time integration algorithms. We, then, make an attempt to treat briefly in depth only the particular topic of adaptive time step exponential variational integrators. To this aim, the action integral along any curve segment is defined using a discrete Lagrangian that depends on the endpoints of the segment and on a number of intermediate points of interpolation. This Lagrangian is then, at any time interval, written as a weighted sum of the Lagrangians corresponding to a set of the chosen …
Cite as: Kosmas, O., Vlachos, D. (2020). Exponential Variational Integrators Using Constant or Adaptive Time Step. In: Raigorodskii, A.M., Rassias, M.T. (eds) Discrete Mathematics and Applications. Springer Optimization and Its Applications, vol 165. Springer, Cham. https://doi.org/10.1007/978-3-030-55857-4_10. https://link.springer.com/chapter/10.1007/978-3-030-55857-4_10.
Geometric derivation and analysis of multi-symplectic numerical schemes for differential equations
Odysseas Kosmas and Dimitrios Papadopoulos and Dimitrios Vlachos
Abstract: In the current work we present a class of numerical techniques for the solution of multi-symplectic PDEs arising at various physical problems. We first consider the advantages of discrete variational principles and how to use them in order to create multi-symplectic integrators. We then consider the nonstandard finite difference framework from which these integrators derive. The latter is now expressed at the appropriate discrete jet bundle, using triangle and square discretization. The preservation of the discrete multi-symplectic structure by the numerical schemes is shown for several one- and two-dimensional test cases, like the linear wave equation and the nonlinear Klein–Gordon equation.
Cite as: Kosmas, O., Papadopoulos, D., Vlachos, D. (2020). Geometric Derivation and Analysis of Multi-Symplectic Numerical Schemes for Differential Equations. In: Daras, N., Rassias, T. (eds) Computational Mathematics and Variational Analysis. Springer Optimization and Its Applications, vol 159. Springer, Cham. https://doi.org/10.1007/978-3-030-44625-3_12. https://link.springer.com/chapter/10.1007/978-3-030-44625-3_12.
A Metric Space Approach on the Molecular vs. Chemical Similarity of Some Analgesic and Euphoric Compounds
Demetrios Xenides and Dionisia Fostiropoulou and Dimitrios S Vlachos
Abstract: There is a relentless effort on gaining information on the reason why some compounds could cause similar effects though they are or not structural similar. That is the chemical similarity that plays an equally important role and we approach it via metric space theory on a set of analgesic drugs and euphoric compounds. The findings of the present study are in agreement to these obtained via traditional structural indices moreover are in accord with clinical findings.
Cite as: Xenides D, Fostiropoulou D, Vlachos DS. A Metric Space Approach on the Molecular vs. Chemical Similarity of Some Analgesic and Euphoric Compounds. ChemRxiv. Cambridge: Cambridge Open Engage; 2019. https://chemrxiv.org/engage/chemrxiv/article-details/60c73fe0bdbb896b88a380c5.
Comparing scrum and XP agile methodologies using dynamic simulation modeling
Nasiopoulos K Alexandros and Damianos P Sakas and DS Vlachos and Nasiopoulos K Dimitrios
Abstract: A software development process is designated as an aggregation of methods, practices, and techniques that are used to procure and substantiate software and its produced product (Wadhwa and Sharma, Adv Comput Sci Inf Technol 2:370–374, 2015). The majority of agile methods promote teamwork, cooperation, and adjustability through the life cycle of the developing procedure (Moniruzzaman and Hossain, Global J Comput Sci Technol 13, 2013). The first and maybe best known agile methods, between others, are Scrum and eXtreme Programming (XP) (Salo and Abrahamsson, Softw Process: Improv Pract 12, 2007). Scrum is more focused on management practices for software development, whereas XP emphasizes on the activities of software implementing (Mushtaq and Qureshi, Inf Technol Comput Sci 6, 2012). In this paper we explore the principles of two agile methodologies, XP and Scrum, and …
Cite as: Alexandros, N.K., Sakas, D.P., Vlachos, D.S., Dimitrios, N.K. (2017). Comparing Scrum and XP Agile Methodologies Using Dynamic Simulation Modeling. In: Kavoura, A., Sakas, D., Tomaras, P. (eds) Strategic Innovative Marketing. Springer Proceedings in Business and Economics. Springer, Cham. https://doi.org/10.1007/978-3-319-56288-9_52. https://link.springer.com/chapter/10.1007/978-3-319-56288-9_52.
Modeling and Simulation of Promotion Procedures for IT Companies Through Facebook
Tsiavos G Panagiotis and Pachtiti E Foteini and Nasiopoulos K Dimitrios and Damianos P Sakas and DS Vlachos
Abstract: The last years have seen a rapid increase both of the number of users on social media and particularly on Facebook and also, on the number of different types of applications available for use (Kluemper et al., Research in personnel and human resources management, Emerald Group Publishing Limited, Bingley, 2016). This paper attempts to model and simulate the promotion of new IT products processes. The study of the results obtained through simulation dynamic model, which was developed in order to test the potential profitability of a business.
Cite as: Panagiotis, T.G., Foteini, P.E., Dimitrios, N.K., Sakas, D.P., Vlachos, D.S. (2017). Modeling and Simulation of Promotion Procedures for IT Companies Through Facebook. In: Kavoura, A., Sakas, D., Tomaras, P. (eds) Strategic Innovative Marketing. Springer Proceedings in Business and Economics. Springer, Cham. https://doi.org/10.1007/978-3-319-56288-9_44
. https://link.springer.com/chapter/10.1007/978-3-319-56288-9_44.
Software Protection and Piracy Focusing on the 2008 Crisis: A Comparative Study and Simulation Modeling Regarding the Case of Greece, Germany, and England
John Hlias Plikas and Nasiopoulos K Dimitrios and Panagiotis Delis and DS Vlachos
Abstract: In this paper, the relationship between software security and piracy rates is been analyzed, by utilizing an information set for three European nations of extreme importance as regarding the 2008 economic crisis, Greece, Germany, and England. Having undergone thorough research and empirical analysis, taking into consideration Monte Carlo simulation technique we discover proof that research and development impacts negatively piracy rates. We likewise find that piracy rates are affected negatively by per capita income. The above discoveries are supportive to the consideration of different descriptors recommended by the empirical literature on piracy.
Cite as: Plikas, J.H., Nasiopoulos, D.K., Delis, P., Vlachos, D.S. (2017). Software Protection and Piracy Focusing on the 2008 Crisis: A Comparative Study and Simulation Modeling Regarding the Case of Greece, Germany, and England. In: Kavoura, A., Sakas, D., Tomaras, P. (eds) Strategic Innovative Marketing. Springer Proceedings in Business and Economics. Springer, Cham. https://doi.org/10.1007/978-3-319-56288-9_42. https://link.springer.com/chapter/10.1007/978-3-319-56288-9_42.
The development of new ideas for IT products, through social media
Pachtiti E Foteini and Nasiopoulos K Dimitrios and Damianos P Sakas and DS Vlachos
Abstract: In this research the question that will occupy us is the development of new ideas for IT products, through the social media. Thanks to the social media, every business can interact with its public, thus with its collaborators. One of the most important forms that appear is the Facebook. The Facebook pages present the possibilities with which the development of new ideas can be achieved, as they give the opportunity to the businesses to proceed to the analog environment and thereby to emerge. The development, however, of those ideas in order to bring the desired results is distinguished in certain phases, which must also be satisfied. These phases–steps will be analyzed in the continuation of our study.
Cite as: Foteini, P.E., Dimitrios, N.K., Sakas, D.P., Vlachos, D.S. (2017). The Development of New Ideas for IT Products, Through Social Media. In: Kavoura, A., Sakas, D., Tomaras, P. (eds) Strategic Innovative Marketing. Springer Proceedings in Business and Economics. Springer, Cham. https://doi.org/10.1007/978-3-319-56288-9_53. https://link.springer.com/chapter/10.1007/978-3-319-56288-9_53.
Modeling and Simulation for the Development of Innovative Ideas for Video Games in Smartphones
Tsomis Konstantinos and Koukouris Georgios and Damianos P Sakas and Nasiopoulos K Dimitrios and DS Vlachos
Abstract: In this research, paper will be highlighted the dominant role that the video games hold nowadays. It is undeniable that as time and technology go by, more and more people spend time playing games on their smartphones. As shown by recent studies, 44% of the game developers are working on a game that will be released on smartphone or tablet (Game Developers Conference 2016). This has led, in turn, to a growing number of companies taking interest in releasing video games for smartphones, increasing the competition. Due to the above, companies have realized the significance of importing more and more innovative ideas in their video games so they get more appealing to buyers, resulting in holding a bigger share in video games market. The impact of these innovations in a company’s function and the profit, or loss, they can cause will also be investigated. This will be examined via the modeling …
Cite as: Konstantinos, T., Georgios, K., Sakas, D.P., Dimitrios, N.K., Vlachos, D.S. (2017). Modeling and Simulation for the Development of Innovative Ideas for Video Games in Smartphones. In: Kavoura, A., Sakas, D., Tomaras, P. (eds) Strategic Innovative Marketing. Springer Proceedings in Business and Economics. Springer, Cham. https://doi.org/10.1007/978-3-319-56288-9_45
. https://link.springer.com/chapter/10.1007/978-3-319-56288-9_45.
Instagram Company Page Creation Modeling and Simulation
AS Sarlis and DP Sakas and DP Vlachos and A Antoniou
Abstract: Instagram is the largest image-based social media platform. For this reason, it provides an excellent opportunity for companies to promote their products or services. The purpose of this project is to quantify the income of an organization/company arising from the utility of Instagram in accordance to the resources invested by modeling the promotional process. This paper begins by thoroughly analyzing Instagram platform in order to fully understand its function. After this is done, we set the objectives that need to take place in order for company to achieve its final goal. The main aim is no other than modeling the augmentation of interaction between organization and users, resulted in this way further mouth to mouth hearsay via Instagram. Subsequently, several actions are defined in order to accomplish these individual goals. However, these actions depend and rely in a plurality of factors, a situation that leads …
Cite as: Sarlis, A.S., Sakas, D.P., Vlachos, D.P., Antoniou, A. (2017). Instagram Company Page Creation Modeling and Simulation. In: Kavoura, A., Sakas, D., Tomaras, P. (eds) Strategic Innovative Marketing. Springer Proceedings in Business and Economics. Springer, Cham. https://doi.org/10.1007/978-3-319-56288-9_58. https://link.springer.com/chapter/10.1007/978-3-319-56288-9_58.
Mobile commerce and success factors. simulation and modeling of the problem
Aristotelis Chantzaras and Nasiopoulos K Dimitrios and DS Vlachos
Abstract: Mobile commerce (m-commerce) is a rapidly growing industry, which derives from e-commerce, and within the next few years is expected to conquer a great part of the global market share. There are several factors that can play a major role in the success of an m-commerce website. The ones that should be taken most into account can be distinguished in three categories. The first one is Security and Trust, which concerns safe transactions online and giving the user a sense of trust and no second thoughts when buying a product through his/her smartphone. Second, Personalization–Localization, which is about adjusting properly the content depending on the user’s preferences and local needs, trends, and conditions. Last but not least, user’s convenience, which can be described in three sub-categories: Speed, Accessibility, and Mobile Friendly Design. All of the above contribute in a pleasant online …
Cite as: Chantzaras, A., Dimitrios, N.K., Vlachos, D.S. (2017). Mobile Commerce and Success Factors. Simulation and Modeling of the Problem. In: Kavoura, A., Sakas, D., Tomaras, P. (eds) Strategic Innovative Marketing. Springer Proceedings in Business and Economics. Springer, Cham. https://doi.org/10.1007/978-3-319-56288-9_46. https://link.springer.com/chapter/10.1007/978-3-319-56288-9_46.
Businesses: The Association Between Their Export Performance and Information and Communication Technology Adoption
John Hlias Plikas and Nasiopoulos K Dimitrios and Eleni-Karveli Glynou and Damianos P Sakas and DS Vlachos
Abstract: Today’s world is characterized with rapid engineering and technological increase where enterprises search to develop competitive vantage based on the extensive use of information and communication technology, a crucial succeeder in today’s competitive market. Information and communication technology, a factor characterized as a foundation and complementary to innovation, affects business exploitation, exploration and market competitive presence in several ways. This paper aims at explaining how the Information and Communication Technology trajectory and its adoption affects the export intensity of business sphere along with other important variable factors using a large data sample of 3500 business firms using hybrid simulation with Anylogic 7.2 University and eventually analyzing empirically this relation through an economic based regression analysis model using E-Views 8. The explanatory …
Cite as: Plikas, J.H., Dimitrios, N.K., Glynou, EK., Sakas, D.P., Vlachos, D.S. (2017). Businesses: The Association Between Their Export Performance and Information and Communication Technology Adoption. In: Kavoura, A., Sakas, D., Tomaras, P. (eds) Strategic Innovative Marketing. Springer Proceedings in Business and Economics. Springer, Cham. https://doi.org/10.1007/978-3-319-56288-9_50. https://link.springer.com/chapter/10.1007/978-3-319-56288-9_50.
Modeling the promotion process of academic conferences through social media
John Hlias Plikas and Dimitrios K Nasiopoulos and Damianos P Sakas and Dimitrios S Vlachos
Abstract: Social networks are now a crucial part of today’s way of life. Academic conferences is another chapter, that give people the opportunity to explore new ideas and share them with the scientific world. Blending those two factors together in order to achieve a main purpose, could give a remarkable effect. The purpose of this paper is to analyze the promotion process of academic conferences through social media and use simulation models to model that analysis. The reason the paper was created, is to provide this optimal solution to all those seeking how to promote academic conferences effectively through social media. Thorough research through the paper revealed that social media, nowadays used by millions and millions of users can be successfully used to promote academic papers and with great appeal.
Cite as: Plikas, J.H., Nasiopoulos, D.K., Sakas, D.P., Vlachos, D.S. (2017). Modeling the Promotion Process of Academic Conferences Through Social Media. In: Kavoura, A., Sakas, D., Tomaras, P. (eds) Strategic Innovative Marketing. Springer Proceedings in Business and Economics. Springer, Cham. https://doi.org/10.1007/978-3-319-33865-1_60. https://link.springer.com/chapter/10.1007/978-3-319-33865-1_60.
Merchandizing IT products via social networks. modeling and simulation of the procedures
Theodora Papadopoulou and Dimitrios K Nasiopoulos and Dimitrios S Vlachos
Abstract: In this paper is going to be analyzed the different ways and results an IT company will gave if it would use simulation modeling for product merchandizing through social networks (Liu et al., Internet Research 25(2):300–316, 2015). All over through these years the companies are developing different ways of marketing methods on the Internet so they can sell more and more. In this research paper, is going to be presented the results which an IT company could have if it would changed the traditional way of selling and advertising products by social media marketing. A company that produces IT products is going to advertise and deliver these, through social networks, a daily habit in our lives and our routine (Dunne et al., Journal of Research in Interactive Marketing 4(1):46–58, 2010).
Cite as: Papadopoulou, T., Nasiopoulos, D.K., Vlachos, D.S. (2017). Merchandizing IT Products via Social Networks. Modeling and Simulation of the Procedures. In: Kavoura, A., Sakas, D., Tomaras, P. (eds) Strategic Innovative Marketing. Springer Proceedings in Business and Economics. Springer, Cham. https://doi.org/10.1007/978-3-319-33865-1_61
. https://link.springer.com/chapter/10.1007/978-3-319-33865-1_61.
A space-time geodesic approach for phase fitted variational integrators
Odysseas Kosmas and DS Vlachos
Abstract: The use of space-time geodesic approach of classical mechanics is investigated, in order to derive time adaptive high order phase fitted variational integrators. The proposed technique is employed for systems of which the Lagrangian is of separable form. To this end, first the unfolding of the standard Euler-Lagrange system to its space-time manifold is presented and then it is rewritten as a geodesic problem with zero potential energy. Preliminary simulation results (without optimizing the choice of step sizing) show that one can use the spacetime geodesic formulation to generate an adaptive scheme that still preserves some underlying geometric structure.
Cite as: Odysseas Kosmas and DS Vlachos (2016). A space-time geodesic approach for phase fitted variational integrators. Journal of Physics: Conference Series, vol 738 (1), (IOP Publishing). https://iopscience.iop.org/article/10.1088/1742-6596/738/1/012133/meta.
Modeling the development of the online conference’s services
Damianos P Sakas and Dimitrios S Vlachos and Dimitrios K Nasiopoulos
Abstract: – The integrated purpose of the libraries’ communication plan in general is to create and accomplish scientific events aiming, first of all, at covering the extensive demand for the scientific conferences. Their primary objective is to raise the prestigious brand name of their organisation, which constitutes the organizing authority. At the same time, this authority, except for its non-profit charitable profile, aims to financial gains by attracting participants for its sustainability. Furthermore, these academic events have contributed to the utmost dissemination of the library’s brand name to an expanding mass of people to the extent of attracting new visitors (Broady-Preston and Lobo, 2011). One of the qualitative academic events, among others, is the creation of academic-nature events, whose following-up is blocked by a multitude of financial barriers according to the new visitors’ viewpoint. Considering …
Cite as: Sakas, D.P., Vlachos, D.S. and Nasiopoulos, D.K. (2016), "Modeling the development of the online conference’s services", Library Review, Vol. 65 No. 3, pp. 160-184. https://doi.org/10.1108/LR-06-2015-0063. https://www.emerald.com/insight/content/doi/10.1108/LR-06-2015-0063/full/html.
Twitter’s tweet method modelling and simulation
Apostolos S Sarlis and Damianos P Sakas and DS Vlachos
Abstract: This paper seeks to purpose the concept of Twitter marketing methods. The tools that Twitter provides are modelled and simulated using iThink in the context of a Twitter media-marketing agency. The paper has leveraged the system’s dynamic paradigm to conduct Facebook marketing tools and methods modelling, using iThink™ system to implement them. It uses the design science research methodology for the proof of concept of the models and modelling processes. The following models have been developed for a twitter marketing agent/company and tested in real circumstances and with real numbers. These models were finalized through a number of revisions and iterators of the design, develop, simulate, test and evaluate. It also addresses these methods that suit most organized promotion through targeting, to the Twitter social media service. The validity and usefulness of these Twitter marketing methods …
Cite as: Apostolos S Sarlis and Damianos P Sakas and DS Vlachos (2015). Twitter’s tweet method modelling and simulation. AIP Conference Proceedings, vol 1644 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.4907856.
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Facebook’s personal page modelling and simulation
Apostolos S Sarlis and Damianos P Sakas and DS Vlachos
Abstract: In this paper we will try to define the utility of Facebook’s Personal Page marketing method. This tool that Facebook provides, is modelled and simulated using iThink in the context of a Facebook marketing agency. The paper has leveraged the system’s dynamic paradigm to conduct Facebook marketing tools and methods modelling, using iThink™ system to implement them. It uses the design science research methodology for the proof of concept of the models and modelling processes. The following model has been developed for a social media marketing agent/company, Facebook platform oriented and tested in real circumstances. This model is finalized through a number of revisions and iterators of the design, development, simulation, testing and evaluation processes. The validity and usefulness of this Facebook marketing model for the day-to-day decision making are authenticated by the management of the …
Cite as: Apostolos S Sarlis and Damianos P Sakas and DS Vlachos (2015). Facebook’s personal page modelling and simulation. AIP Conference Proceedings, vol 1644 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.4907855.
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Modeling of market segmentation for new IT product development
Dimitrios K Nasiopoulos and Damianos P Sakas and DS Vlachos and Amanda Mavrogianni
Abstract: Businesses from all Information Technology sectors use market segmentation[1] in their product development[2] and strategic planning[3]. Many studies have concluded that market segmentation is considered as the norm of modern marketing. With the rapid development of technology, customer needs are becoming increasingly diverse. These needs can no longer be satisfied by a mass marketing approach and follow one rule. IT Businesses can face with this diversity by pooling customers[4] with similar requirements and buying behavior and strength into segments. The result of the best choices about which segments are the most appropriate to serve can then be made, thus making the best of finite resources. Despite the attention which segmentation gathers and the resources that are invested in it, growing evidence suggests that businesses have problems operationalizing segmentation[5]. These problems …
Cite as: Dimitrios K Nasiopoulos and Damianos P Sakas and DS Vlachos and Amanda Mavrogianni (2015). Modeling of market segmentation for new IT product development. AIP conference proceedings, vol 1644 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.4907817.
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Simulation of generation of new ideas for new product development and IT services
Dimitrios K Nasiopoulos and Damianos P Sakas and DS Vlachos and Amanda Mavrogianni
Abstract: This paper describes a dynamic model of the New Product Development (NPD) process. The model has been occurring from best practice noticed in our research conducted at a range of situations. The model contributes to determine and put an IT company's NPD activities into the frame of the overall NPD process[1]. It has been found to be a useful tool for organizing data on IT company's NPD activities without enforcement an excessively restrictive research methodology refers to the model of NPD. The framework, which strengthens the model, will help to promote a research of the methods undertaken within an IT company's NPD process, thus promoting understanding and improvement of the simulation process[2]. IT companies tested many techniques with several different practices designed to improve the validity and efficacy of their NPD process[3]. Supported by the model, this research examines how widely …
Cite as: Dimitrios K Nasiopoulos and Damianos P Sakas and DS Vlachos and Amanda Mavrogianni (2015). Simulation of generation of new ideas for new product development and IT services. AIP conference proceedings, vol 1644 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.4907818.
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Modeling the scientific dimension of academic conferences
Nasiopoulos K Dimitrios and Damianos P Sakas and DS Vlachos
Abstract: The rapid spread of the Internet and the growing trend towards research are the leading factors and strong springboards, for the Industry of conference organizations, to proceed with further development. With the increase of shareholding in organizing events, the environment has become very complex. The Conference Organizing Committee is challenged to define a wide range of factors, in order to better serve the needs and objectives of the Conference.The main topic of this research is the study and modeling of the scientific dimension of Academic Conferences. We studied and recorded the basic procedures that govern the organization of scientific conferences. These are the procedures that affect the way that scientific conferences are conducted and eventually of course, the success or failure of those. Our research is engaged in the scientific aspect of these conferences, as the majority of the participants are …
Cite as: Nasiopoulos K Dimitrios and Damianos P Sakas and DS Vlachos (2014). Modeling the scientific dimension of academic conferences. Procedia-social and behavioral sciences, vol 147 pp (576-585), (Elsevier). https://www.sciencedirect.com/science/article/pii/S187704281404083X.
Modeling publications in academic conferences
Nasiopoulos K Dimitrios and Damianos P Sakas and DS Vlachos
Abstract: The growing trend towards research constitutes a strong springboard for organizing more and more scientific conferences. The global scientific community, now, recognizes the contribution of conferences to the promotion of research and knowledge. Due to the increasing participation of individuals in organizing events, the environment has become very complex. The organizing committee of the conference is now required to identify and respond to a wide range of determinants, in order to balance the needs and objectives of the conference.The main topic of this research is to study and model the publications of academic conferences. In this paper, we studied and recorded the procedures that are applied to the publications of scientific conferences, which affect the pattern and the success or failure of the conference. Our study deals with conferences of scientific nature, as the participants are highly qualified and …
Cite as: Nasiopoulos K Dimitrios and Damianos P Sakas and DS Vlachos (2014). Modeling publications in academic conferences. Procedia-social and behavioral sciences, vol 147 pp (467-477), (Elsevier). https://www.sciencedirect.com/science/article/pii/S1877042814040506.
Modelling strategic management for the development of competitive advantage, based on technology
Damianos Sakas and Dimitris Vlachos and Dimitris Nasiopoulos
Abstract: – The purpose of this research work is to find a methodology for the strategic development of competitive advantage for information technology (IT) companies (Mezger and Violani, 2011). The ultimate aim of this project is to develop a methodological approach on this issue, based on dynamic simulation models (DSM) (Wirahadikusumah and Abraham, 2003). With the aid of DSM, senior managements of organizations will have the opportunity to make decisions of assured success. This success shall be guaranteed by the realization of entrepreneurial activity in a safe and inexpensive computing environment before actual investment. – This paper highlights the advantages of the dynamic modelling of systems aiming at developing competitive advantage for IT companies (Ordóñez de Pablos, 2006). In this research, we have used …
Cite as: Sakas, D., Vlachos, D. and Nasiopoulos, D. (2014), "Modelling strategic management for the development of competitive advantage, based on technology", Journal of Systems and Information Technology, Vol. 16 No. 3, pp. 187-209. https://doi.org/10.1108/JSIT-01-2014-0005. https://www.emerald.com/insight/content/doi/10.1108/JSIT-01-2014-0005/full/html.
Evolutionary algorithm for optimal vaccination scheme
KJ Parousis-Orthodoxou and DS Vlachos
Abstract: The following work uses the dynamic capabilities of an evolutionary algorithm in order to obtain an optimal immunization strategy in a user specified network. The produced algorithm uses a basic genetic algorithm with crossover and mutation techniques, in order to locate certain nodes in the inputted network. These nodes will be immunized in an SIR epidemic spreading process, and the performance of each immunization scheme, will be evaluated by the level of containment that provides for the spreading of the disease.
Cite as: KJ Parousis-Orthodoxou and DS Vlachos (2013). Evolutionary algorithm for optimal vaccination scheme. Journal of Physics: Conference Series, vol 490 (1), (IOP Publishing). https://iopscience.iop.org/article/10.1088/1742-6596/490/1/012027/meta.
Modeling complex network epidemics using nodes' roles
DS Vlachos and KJ Parousis-Orthodoxou
Abstract: In this work we investigate the usefulness of node roles of complex systems in dynamical processes. More specifically, we use the characteristic equations of an SIS epidemic spreading in order to simulate an actual epidemic spreading. The equations that are used, encapsulate the degree correlations in comparison to the role distribution and the results are compared with an actual epidemic release simulation.
Cite as: DS Vlachos and KJ Parousis-Orthodoxou (2013). Modeling complex network epidemics using nodes' roles. Journal of Physics: Conference Series, vol 490 (1), (IOP Publishing). https://iopscience.iop.org/article/10.1088/1742-6596/490/1/012026/meta.
Simulation model for motivating the creation of entrepreneurship actions
Damianos P Sakas and DS Vlachos and SI Gikas
Abstract: The small and medium sized software enterprises should be encouraged to take a leading role in exploiting new opportunities. There is a need to develop, implement and emphasize the important role of engineering, technology and development of small and medium software enterprises on poverty reduction and sustainable social and economic development.In this paper, there is a scope to inform about the ways that can encourage the creation and establishment of a new software company and explain about the important role of creating new businesses in a developing and changing industry. There is also an analysis on computers with dynamic simulation models [1] (iThink) in order to simulate all the different situations and scenarios of encouraging new software enterprises and predict the outcome. Relevant studies have been devoted in computational methods, giving the impetus for further research in this …
Cite as: Damianos P Sakas and DS Vlachos and SI Gikas (2013). Simulation model for motivating the creation of entrepreneurship actions. Procedia-Social and Behavioral Sciences, vol 73 pp (354-362), (Elsevier). https://www.sciencedirect.com/science/article/pii/S1877042813003558.
The modeling of funding education as a strategic choice in increasing the brand name of companies
Damianos P Sakas and DS Vlachos and SI Gikas
Abstract: The successful distribution of business funds creates the foundation for the development of new products and services. Funding education is one of the most important sectors that a software company can invest, in order to achieve its growth and expansion, success of its products, establishment among the best companies in this kind of industry, increasing of its brand name [1] and ensuring its profit. It is explained how powerful a software company can be when the pool of available students is higher educated and specialized.In this paper, these funding actions are analyzed on computers [2] with the help of dynamic simulation models [3](i-think), so that a simulation of reality can be achieved, without investing the required capital, predict situations and create a tool for business decisions. Numerous studies have been developed with the aid of computational methods, as the literature reveals [4], [5], [6], [7], [8], [9], [10 …
Cite as: Damianos P Sakas and DS Vlachos and SI Gikas (2013). The modeling of funding education as a strategic choice in increasing the brand name of companies. Procedia-Social and Behavioral Sciences, vol 73 pp (345-353), (Elsevier). https://www.sciencedirect.com/science/article/pii/S1877042813003546.
Analysis of strategic leadership simulation models in non-profit organizations
Nasiopoulos K Dimitrios and Damianos P Sakas and DS Vlachos
Abstract: Leadership of a company may be the only management concept that receives more attention than a company's strategy lately. But there's little unanimity on what strategic leadership [1] is and how it should best be encountered. Organizational leadership [2] has been defined as an interpersonal process for influencing individuals and groups to achieve organizational goals.That's where the strategic leadership comes in. In the ideal case, strategic leadership supplies a widely shared sense of long-term direction and a fascinating project that drives the company through all the important and difficult situations of constant change to achieve the desired aims. But when we see examples of organizational “excellence” - such as Apple, IBM, Xerox, and Zenith - to have overcome the difficulties of restructuring and rightsizing, we’re reminded how difficult it is to preserve strategic leadership.Strategic Leadership is even more …
Cite as: Nasiopoulos K Dimitrios and Damianos P Sakas and DS Vlachos (2013). Analysis of strategic leadership simulation models in non-profit organizations. Procedia-Social and Behavioral Sciences, vol 73 pp (276-284), (Elsevier). https://www.sciencedirect.com/science/article/pii/S1877042813003467.
The role of information systems in creating strategic leadership model
Nasiopoulos K Dimitrios and Damianos P Sakas and DS Vlachos
Abstract: Recent articles claim that the management Information Systems (IS) [1] function should no longer be faced in its classic role, but in terms of a strategic role for exploiting IS-based competitive advantages. Rooted in such a strategic role perspective, this paper develops a research with the aid of a Dynamic Simulation Model [2] of IS and creates an effective plan of Strategic Leadership. Such modeling has been frequently used in similar studies [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17]. The effectiveness of this plan is the supporting mechanism to strategic management of an organization.In the research we conducted on this paper, we focus on the significant role that the IS function plays in the complete strategic management. Based on the requirements of the IS strategic role, an important planning system indicates the major factors which are identified to evolve a Dynamic Simulation Model of IS …
Cite as: Nasiopoulos K Dimitrios and Damianos P Sakas and DS Vlachos (2013). The role of information systems in creating strategic leadership model. Procedia-Social and Behavioral Sciences, vol 73 pp (285-293), (Elsevier). https://www.sciencedirect.com/science/article/pii/S1877042813003479.
Analysis of Strategic Leadership Models in Information Technology
Nasiopoulos K Dimitrios and Damianos P Sakas and DS Vlachos
Abstract: Strategic leadership of the company includes the strategic management of Information Technology (IT) [1] in the context of business relationships. Companies do not exist in isolation. Multiple constituents make up a relationship network that constitutes the vital resource needed to fulfil the mission of a business.To leverage a company's business relationships [2] basically, a relationship “lens” is needed that can act as a guiding process for strategy creation. In order to engage and manage each business relationship and to execute relationship strategies, the relationship engagement cycle creates the phases necessary to acquire, learn about and build memorable experiences with each relationship and to establish trust and loyalty with the most valuable relationships. IT, in many various forms, is a key strategic enabler of the relationship engagement cycle. The literature review reveals that such issues are often …
Cite as: Nasiopoulos K Dimitrios and Damianos P Sakas and DS Vlachos (2013). Analysis of Strategic Leadership Models in Information Technology. Procedia-Social and Behavioral Sciences, vol 73, (Elsevier). https://www.sciencedirect.com/science/article/pii/S1877042813003455.
Global vaccination strategies in Modular Networks
KJ Parousis-Orthodoxou and MM Stamos and DS Vlachos
Abstract: We study the effect of vaccinating networks with different growing strategies, using various techniques that require the complete knowledge of the network. The goal is to restrain the epidemic before it spreads throughout the network and target the few key nodes that will help contain it. Our target networks are chosen to have relatively large modularity index and various immunization techniques are applied to them.
Cite as: KJ Parousis-Orthodoxou and MM Stamos and DS Vlachos (2013). Global vaccination strategies in Modular Networks. Journal of Physics: Conference Series, vol 410 (1), (IOP Publishing). https://iopscience.iop.org/article/10.1088/1742-6596/410/1/012079/meta.
Evolution of Correlations in Complex Networks
MM Stamos and KJ Parousis-Orthodoxou and DS Vlachos
Abstract: We investigate in detail the mechanisms under which degree correlations evolve in complex networks. We consider the case where a vertex is entering the network at each time, carrying a predefined number of edges. We prove in this work, that the same elementary interactions which is responsible for emerging of scaling in complex networks, can give several patterns of degree corellations. As a test case, the effect of preferential attachement rule in degree correlations is studied in detail.
Cite as: MM Stamos and KJ Parousis-Orthodoxou and DS Vlachos (2013). Evolution of Correlations in Complex Networks. Journal of Physics: Conference Series, vol 410 (1), (IOP Publishing). https://iopscience.iop.org/article/10.1088/1742-6596/410/1/012093/meta.
Multi-step numerical methods derived using discrete Lagrangian integrators
DS Vlachos and OT Kosmas
Abstract: On the basis of the variational integrators theory, we initially examine the possibility of deriving multi-step numerical methods. Then, we propose an integration technique that approximates the action integral within one time interval by using appropriate expressions for the relevant configurations and velocities. These approximations depend on a specific number of known configurations defined at previous time nodes. Multi-step numerical methods can finally be deduced, by defining, as usually, the Lagrange function as a weighted sum over the discrete Lagrangians corresponding to each of the curve segments and using the discrete Euler-Lagrange equations.
Cite as: DS Vlachos and OT Kosmas (2013). Multi-step numerical methods derived using discrete Lagrangian integrators. Journal of Physics: Conference Series, vol 410 (1), (IOP Publishing). https://iopscience.iop.org/article/10.1088/1742-6596/410/1/012119/meta.
Symmetric Path Fitted Variational Integrators
DS Vlachos and OT Kosmas
Abstract: Recently, the benefits of variational integrators have been combined with efficient high order techniques. On the other hand, a special set of high order methods are the symmetric ones, those who preserve time reversal symmetry and show improved behavior in long term integration. In the present work, we will introduce a systematic way to construct symmetric variational integrators. The idea is to apply the variational principle not in a set of intermediate points but to a set of parameters that characterize a symmetric orbit between starting and ending points. The estimated symmetric orbit may be a polynomial or a general function that sometimes is indicated by the nature of the problem to solve. The results show excellent behavior in long term integration and acceleration of the method when special functions are used.
Cite as: DS Vlachos and OT Kosmas (2013). Symmetric Path Fitted Variational Integrators. Journal of Physics: Conference Series, vol 410 (1), (IOP Publishing). https://iopscience.iop.org/article/10.1088/1742-6596/410/1/012117/meta.
Evolutionary Processes in Complex Networks and Small Worlds
DS Vlachos and KJ Parousis-Orthodoxou
Abstract: In recent years, researchers discovered by empirical studies that the majority of networked systems that occurring in nature and society, exhibit an emerging behavior which is caused by the statistical properties of these systems. Two of the most important factors that characterize those complex systems is the degree distribution of the underlying network and the so called small world property. In this work, we examine the application of evolutionary processes on these systems in order to derive useful results for human dynamics modeling. Simulation experiments are used to explain universal properties observed recently in the vote distribution of proportional elections. Moreover, it has been founded that the hierarchical or modular nature of complex networks accelerates the convergent of a hybrid genetic algorithm applied in a rather complex search space.
Cite as: DS Vlachos and KJ Parousis-Orthodoxou (2013). Evolutionary Processes in Complex Networks and Small Worlds. Journal of Physics: Conference Series, vol 410 (1), (IOP Publishing). https://iopscience.iop.org/article/10.1088/1742-6596/410/1/012081/meta.
Random Walks and Optimal Stopping Strategies as a Model for Evolving Networks
DS Vlachos and KJ Parousis-Orthodoxou and MM Stamos
Abstract: In this work, a model for evolving networks is presented based on a Brownian particle. Each time, the Brownian particle enters the network through a randomly selected node. The random walk is terminated after having created m-links with visited nodes. Two strategies have been tested: in the first one, we used a generalized algorithm for the secretary problem in order to maximize the degree of the node with which the new node is connected, while in the second strategy, the Brownian particle creates links with nodes that meets twice. In all cases, scale free, modular, dissasortative networks are created.
Cite as: DS Vlachos and KJ Parousis-Orthodoxou and MM Stamos (2013). Random Walks and Optimal Stopping Strategies as a Model for Evolving Networks. Journal of Physics: Conference Series, vol 410 (1), (IOP Publishing). https://iopscience.iop.org/article/10.1088/1742-6596/410/1/012092/meta.
Population Induced Instabilities in Genetic Algorithms for Constrained Optimization
DS Vlachos and KJ Parousis-Orthodoxou
Abstract: Evolutionary computation techniques, like genetic algorithms, have received a lot of attention as optimization techniques but, although they exhibit a very promising potential in curing the problem, they have not produced a significant breakthrough in the area of systematic treatment of constraints. There are two mainly ways of handling the constraints: the first is to produce an infeasibility measure and add it to the general cost function (the well known penalty methods) and the other is to modify the mutation and crossover operation in a way that they only produce feasible members. Both methods have their drawbacks and are strongly correlated to the problem that they are applied. In this work, we propose a different treatment of the constraints: we induce instabilities in the evolving population, in a way that infeasible solution cannot survive as they are. Preliminary results are presented in a set of well known from the …
Cite as: DS Vlachos and KJ Parousis-Orthodoxou (2013). Population Induced Instabilities in Genetic Algorithms for Constrained Optimization. Journal of Physics: Conference Series, vol 410 (1), (IOP Publishing). https://iopscience.iop.org/article/10.1088/1742-6596/410/1/012078/meta.
The concept of roles in complex networks
KJ Parousis-Orthodoxou and M Stamos and DS Vlachos
Abstract: This paper is an analytic process of introducing the concept of roles in a complex network. Each node has a specific connectivity pattern to the rest of the nodes in the network. There are many nodes that have the same number of connections and also the same type. In this case we say that two nodes can have the same role. The work described here, shows the process of identifying the roles of all the nodes in a network and grouping them accordingly.
Cite as: KJ Parousis-Orthodoxou and M Stamos and DS Vlachos (2013). The concept of roles in complex networks. Journal of Physics: Conference Series, vol 410 (1), (IOP Publishing). https://iopscience.iop.org/article/10.1088/1742-6596/410/1/012080/meta.
The role of open source leadership in developing high technology companies
Nasiopoulos K Dimitrios and Damianos P Sakas and Dimitrios S Vlachos
Abstract: The paper seeks to propose the concept of sustainable enterprise simulation models. The social, environmental and economic models are developed and simulated using iThink in the context of a high technology (high-tech) company. With the rapid growth of Social Networks [, Open source applications are increasingly invading the world of Web. High-tech companies must adapt to the world of open source, by the people who work in them, until their products. The paper has leveraged the systems dynamic paradigm to conduct sustainable enterprise modelling and iThink system to implement the models. It uses the design science research methodology for the proof of concept of the models and modelling processes. The models have been developed for a high-tech company and tested in the business settings. These models were finalised through a number of revisions and iterations of the design, develop …
Cite as: Dimitrios, Nasiopoulos K., Damianos P. Sakas, and D.S. Vlachos. “The Role of Open Source Leadership in Developing High Technology Companies.” Key Engineering Materials. Trans Tech Publications, Ltd., March 2013. . https://www.scientific.net/KEM.543.402.
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The contribution of dynamic simulation model of depiction of knowledge, in the leading process of high technology companies
Nasiopoulos K Dimitrios and Damianos P Sakas and Dimitrios S Vlachos
Abstract: The purpose of this paper is to examine the impact of knowledge [creation mode (eg goal-driven and goal-free) and organizational culture on knowledge creation and sharing performance in the context of high technology (high-tech) companies [with the contribution of Dynamic Simulation Model. Both goal-free and goal-framed creation modes are more likely to support knowledge creation, while the goal-driven mode is not likely to be favorable for knowledge creation. The paper has leveraged the systems dynamic paradigm to conduct sustainable enterprise modelling and iThink system to implement the models. High-tech companies who are frequently looking for new ideas for product design [and manufacturing technologies [are more likely to adopt the goal-free creation mode. High-tech companies who would like to emphasize goal achievement with respect to creation in manufacturing should form an …
Cite as: Dimitrios, Nasiopoulos K., Damianos P. Sakas, and D.S. Vlachos. “The Contribution of Dynamic Simulation Model of Depiction of Knowledge, in the Leading Process of High Technology Companies.” Key Engineering Materials. Trans Tech Publications, Ltd., March 2013. https://doi.org/10.4028/www.scientific.net/kem.543.406.. https://www.scientific.net/KEM.543.406.
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Local path fitting: a new approach to variational integrators
Odysseas T Kosmas and DS Vlachos
Abstract: A new approach for constructing variational integrators is presented. In the general case, the estimation of the action integral in a time interval [t k, t k+ 1] is used to construct a symplectic map (q k, q k+ 1)→(q k+ 1, q k+ 2). The basic idea, is that only the partial derivatives of the estimated action integral of the Lagrangian are needed in the general theory. The analytic calculation of these derivatives, gives rise to a new integral that depends on the Euler–Lagrange vector itself (which in the continuous and exact case vanishes) and not on the Lagrangian. Since this new integral can only be computed through a numerical method based on some internal grid points, we can locally fit the exact curve by demanding the Euler–Lagrange vector to vanish at these grid points. Thus, the integral vanishes, and the process dramatically simplifies the calculation of high order approximations. The new technique is tested in high …
Cite as: Odysseas T Kosmas and DS Vlachos (2012). Local path fitting: a new approach to variational integrators. Journal of Computational and Applied Mathematics, vol 236 (10), (North-Holland). https://www.sciencedirect.com/science/article/pii/S0377042711006352.
Simulated annealing for optimal ship routing
Odysseas T Kosmas and DS Vlachos
Abstract: In this article we present a simulated annealing based algorithm for the determination of optimal ship routes through the minimization of a cost function defined as a weighted sum of the time of voyage and the voyage comfort (safety is taken into account too). This cost function is dependent on the wind speed and its direction as well as on the wave height and its direction. The constructed algorithm at the beginning discretizes an initial route and then optimizes it by considering small deviations, which are accepted or rejected by utilizing the simulated annealing technique. Using calculus of variations, we prove a key theorem which tremendously accelerates the convergence of the proposed algorithm. For an illustration of the advantages of the constructed method, both computational and real experiments have been carried out which are presented and discussed.
Cite as: Odysseas T Kosmas and DS Vlachos (2012). Simulated annealing for optimal ship routing. Computers & Operations Research, vol 39 (3), (Pergamon). https://www.sciencedirect.com/science/article/pii/S0305054811001341.
Marketing dynamic simulation modelling in high tech laboratories
Marina C Terzi and Damianos P Sakas and Dimitrios Vlachos
Abstract: The paper considers the role of Integrated Marketing Communication in enhancing the brand awareness of high-tech laboratories. By acknowledging the great interaction of public and private laboratories with high-tech companies, the study is aimed at developing a simulation model to be incorporated in the marketing strategy of laboratories. The comprehensive dynamic simulation model that was developed highlights the emphasis that should be placed when B2B marketing activities are the matter of concern. Marketing Dynamic Simulation Modelling is based on the principles of Integrated Marketing. It has been tested in both private and public laboratories, concluding that marketing in the private sector receives more attention than in the public sector. The proposed model incorporates all the components for successfully marketing laboratories by taking their budget restrictions into consideration.
Cite as: Terzi, Marina C., Damianos P. Sakas, and Dimitrios Vlachos. “Marketing Dynamic Simulation Modelling in High Tech Laboratories.” Key Engineering Materials 495 (November 2011): 23–27. https://doi.org/10.4028/www.scientific.net/kem.495.23.. https://www.scientific.net/KEM.495.23.
Phase-fitted discrete Lagrangian integrators
Odysseas T Kosmas and DS Vlachos
Abstract: Phase fitting has been extensively used during the last years to improve the behavior of numerical integrators on oscillatory problems. In this work, the benefits of the phase fitting technique are embedded in discrete Lagrangian integrators. The results show improved accuracy and total energy behavior in Hamiltonian systems. Numerical tests on the long term integration (105 periods) of the 2-body problem with eccentricity even up to 0.95 show the efficiency of the proposed approach. Finally, based on a geometrical evaluation of the frequency of the problem, a new technique for adaptive error control is presented.
Cite as: Odysseas T Kosmas and DS Vlachos (2010). Phase-fitted discrete Lagrangian integrators. Computer Physics Communications, vol 181 (3), (North-Holland). https://www.sciencedirect.com/science/article/pii/S0010465509003531.
Algorithm 901: LMEF—A program for the construction of linear multistep methods with exponential fitting for the numerical solution of ordinary differential equations
DS Vlachos and Tom E Simos
Abstract: LMEF is a program written in MATLAB, to calculate the coefficients of a linear multi-step method (explicit, implicit or backward differentiation formulas) with algebraic and/or exponential fitting, for the numerical solution of first order ordinary differential equations. Moreover, LMEF calculates the local truncation error and in the case of exponential fitting, the Taylor expansions of the coefficients that are necessary for the implementation of the method.
Cite as: DS Vlachos and Tom E Simos (2010). Algorithm 901: LMEF—A program for the construction of linear multistep methods with exponential fitting for the numerical solution of ordinary differential equations. ACM Transactions on Mathematical Software (TOMS), vol 37 (1), (ACM). https://dl.acm.org/doi/abs/10.1145/1644001.1644013.
High order phase fitted multistep integrators for the Schrödinger equation with improved frequency tolerance
DS Vlachos and ZA Anastassi and TE Simos
Abstract: In this work we introduce a new family of 14-steps linear multistep methods for the integration of the Schrödinger equation. The new methods are phase fitted but they are designed in order to improve the frequency tolerance. This is achieved by eliminating the first derivatives of the phase lag function at the fitted frequency forcing the phase lag function to be ‘flat’ enough in the neighbor of the fitted frequency. The efficiency of the new family of methods is proved via error analysis and numerical applications.
Cite as: DS Vlachos and ZA Anastassi and TE Simos (2009). High order phase fitted multistep integrators for the Schrödinger equation with improved frequency tolerance. Journal of mathematical chemistry, vol 46 (4), (Springer Netherlands). https://link.springer.com/article/10.1007/s10910-008-9510-4.
A family of Runge-Kutta methods with zero phase-lag and derivatives for the numerical solution of the Schrödinger equation and related problems
ZA Anastassi and DS Vlachos and TE Simos
Abstract: We construct a family of two new optimized explicit Runge-Kutta methods with zero phase-lag and derivatives for the numerical solution of the time-independent radial Schrödinger equation and related ordinary differential equations with oscillating solutions. The numerical results show the superiority of the new technique of nullifying both the phase-lag and its derivatives.
Cite as: ZA Anastassi and DS Vlachos and TE Simos (2009). A family of Runge-Kutta methods with zero phase-lag and derivatives for the numerical solution of the Schrödinger equation and related problems. Journal of mathematical chemistry, vol 46 (4), (Springer Netherlands). https://link.springer.com/article/10.1007/s10910-008-9505-1.
High order multistep methods with improved phase-lag characteristics for the integration of the Schrödinger equation
DS Vlachos and ZA Anastassi and TE Simos
Abstract: In this work we introduce a new family of 12-step linear multistep methods for the integration of the Schrödinger equation. The new methods are constructed by adopting a new methodology which improves the phase lag characteristics by vanishing both the phase lag function and its first derivatives at a specific frequency. This results in decreasing the sensitivity of the integration method on the estimated frequency of the problem. The efficiency of the new family of methods is proved via error analysis and numerical applications.
Cite as: DS Vlachos and ZA Anastassi and TE Simos (2009). High order multistep methods with improved phase-lag characteristics for the integration of the Schrödinger equation. Journal of mathematical chemistry, vol 46 (2), (Springer Netherlands). https://link.springer.com/article/10.1007/s10910-008-9509-x.
A new methodology for the construction of numerical methods for the approximate solution of the Schrödinger equation
ZA Anastassi and DS Vlachos and TE Simos
Abstract: In the present paper we introduce a new methodology for the development of numerical methods for the numerical solution of the one-dimensional Schrödinger equation. The new methodology is based on the requirement of vanishing the phase-lag and its derivatives. The efficiency of the new methodology is proved via error analysis and numerical applications.
Cite as: ZA Anastassi and DS Vlachos and TE Simos (2009). A new methodology for the construction of numerical methods for the approximate solution of the Schrödinger equation. Journal of mathematical chemistry, vol 46 (2), (Springer Netherlands). https://link.springer.com/article/10.1007/s10910-008-9508-y.
A new methodology for the development of numerical methods for the numerical solution of the Schrödinger equation
ZA Anastassi and DS Vlachos and TE Simos
Abstract: In the present paper we introduce a new methodology for the construction of numerical methods for the approximate solution of the one-dimensional Schrödinger equation. The new methodology is based on the requirement of vanishing the phase-lag and its derivatives. The efficiency of the new methodology is proved via error analysis and numerical applications.
Cite as: ZA Anastassi and DS Vlachos and TE Simos (2009). A new methodology for the development of numerical methods for the numerical solution of the Schrödinger equation. Journal of mathematical chemistry, vol 46 (2), (Springer Netherlands). https://link.springer.com/article/10.1007/s10910-008-9507-z.
A new family of multistep methods with improved phase-lag characteristics for the integration of orbital problems
DS Vlachos and ZA Anastassi and TE Simos
Abstract: In this paper, we introduce a new family of 10-step linear multistep methods for the integration of orbital problems. The new methods are constructed by adopting a new methodology which improves the phase-lag characteristics by vanishing both the phase-lag function and its first derivatives at a specific frequency. The efficiency of the new family of methods is proved via error analysis and numerical applications.
Cite as: DS Vlachos and ZA Anastassi and TE Simos (2009). A new family of multistep methods with improved phase-lag characteristics for the integration of orbital problems. The Astronomical Journal, vol 138 (1), (IOP Publishing). https://iopscience.iop.org/article/10.1088/0004-6256/138/1/86/meta.
High order phase-fitted discrete Lagrangian integrators for orbital problems
OT Kosmas and DS Vlachos
Abstract: In this work, the benefits of the phase fitting technique are embedded in high order discrete Lagrangian integrators. The proposed methodology creates integrators with zero phase lag in a test Lagrangian in a similar way used in phase fitted numerical methods for ordinary differential equations. Moreover, an efficient method for frequency evaluation is proposed based on the eccentricities of the moving objects. The results show that the new method dramatically improves the accuracy and total energy behaviour in Hamiltonian systems. Numerical tests for the 2-body problem with ultra high eccentricity up to 0.99 for 1000000 periods and to the Henon-Heiles Hamiltonian system with chaotic behaviour, show the efficiency of the proposed approach.
Cite as: OT Kosmas and DS Vlachos (2009). High order phase-fitted discrete Lagrangian integrators for orbital problems. arXiv preprint arXiv:0904.0112. https://arxiv.org/abs/0904.0112.
Operational optimal ship routing using a hybrid parallel genetic algorithm
OT Kosmas and DS Vlachos
Abstract: Optimization of ship routing depends on several parameters, like ship and cargo characteristics, environmental factors, topography, international navigation rules, crew comfort etc. The complex nature of the problem leads to oversimplifications in analytical techniques, while stochastic methods like simulated annealing can be both time consuming and sensitive to local minima. In this work, a hybrid parallel genetic algorithm - estimation of distribution algorithm is developed in the island model, to operationally calculate the optimal ship routing. The technique, which is applicable not only to clusters but to grids as well, is very fast and has been applied to very difficult environments, like the Greek seas with thousands of islands and extreme micro-climate conditions.
Cite as: OT Kosmas and DS Vlachos (2009). Operational optimal ship routing using a hybrid parallel genetic algorithm. arXiv preprint arXiv:0811.2166. https://arxiv.org/abs/0811.2166.
The use of vertical and horizontal accelerations of a floating buoy for the determination of directional wave spectra in coastal zones
DS Vlachos and Christos Tsabaris
Abstract: A parametric method is presented for calculating the directional wave spectrum from vertical and horizontal accelerations of a floating buoy. These measurements are obtained from accelerometers attached on board the buoys of the POSEIDON network. The method assumes the superposition of two independent wave trains giving a better approach to the multidirectional nature of the wave field. A general purpose software module called WaveAna has been developed which can process horizontal and vertical displacements of floating buoys. The functionality of WaveAna is shown with the measured data from the POSEIDON network and the determination of wind generated waves and swell is demonstrated.
Cite as: DS Vlachos and Christos Tsabaris (2008). The use of vertical and horizontal accelerations of a floating buoy for the determination of directional wave spectra in coastal zones. Mathematical and computer modelling, vol 48 (11-12), (Pergamon). https://www.sciencedirect.com/science/article/pii/S089571770800071X.
Monte Carlo Simulation of Effective Coordination Mechanisms for e‐Commerce
DP Sakas and DS Vlachos and TE Simos
Abstract: Making decisions in a dynamic environment is considered extremely important in today’s market. Decision trees which can be used to model these systems, are not easily constructed and solved, especially in the case of infinite sets of consequences (for example, consider the case where only the mean and the variance of an outcome is known). In this work, discrete approximation and Monte Carlo techniques are used to overcome the aforementioned difficulties.
Cite as: DP Sakas and DS Vlachos and TE Simos (2008). Monte Carlo Simulation of Effective Coordination Mechanisms for e‐Commerce. AIP Conference Proceedings, vol 1060 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.3037116.
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PSEMA: An Algorithm for Pattern Stimulated Evolution of Music
AN Mavrogianni and DS Vlachos and G Harvalias
Abstract: An algorithm for pattern stimulating evolution of music is presented in this work (PSEMA). The system combines a pattern with a genetic algorithm for automatic music composition in order to create a musical phrase uniquely characterizing the pattern. As an example a musical portrait is presented. The initialization of the musical phrases is done with a Markov Chain process. The evolution is dominated by an arbitrary correspondence between the pattern (feature extraction of the pattern may be used in this step) and the esthetic result of the musical phrase.
Cite as: AN Mavrogianni and DS Vlachos and G Harvalias (2008). PSEMA: An Algorithm for Pattern Stimulated Evolution of Music. AIP Conference Proceedings, vol 1060 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.3037121.
Fuzzy neural networks for decision support in negotiation
DP Sakas and DS Vlachos and TE Simos
Abstract: There is a large number of parameters which one can take into account when building a negotiation model. These parameters in general are uncertain, thus leading to models which represents them with fuzzy sets. On the other hand, the nature of these parameters makes them very difficult to model them with precise values. During negotiation, these parameters play an important role by altering the outcomes or changing the state of the negotiators. One reasonable way to model this procedure is to accept fuzzy relations (from theory or experience). The action of these relations to fuzzy sets, produce new fuzzy sets which describe now the new state of the system or the modified parameters. But, in the majority of these situations, the relations are multidimensional, leading to complicated models and exponentially increasing computational time. In this paper a solution to this problem is presented. The use of fuzzy …
Cite as: DP Sakas and DS Vlachos and TE Simos (2008). Fuzzy neural networks for decision support in negotiation. AIP Conference Proceedings, vol 1060 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.3037115.
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Identification of critical moments in negotiation using Monte Carlo Simulation
DP Sakas and DS Vlachos and TE Simos
Abstract: A very important moment during negotiation is when one of the negotiators is willing or is driven to try something new. These moments in general produce some kind of uncertainty and surprise. Moreover, the result of the negotiation is strongly depended now on how comfortable feels the negotiator with this surprise. In order to overcome these situation, it would be fruitful to predict or identify these moments. In this work, a new technique is applied to attack this problem. A fuzzy model is adopted to characterize the state and the evolution of the negotiation process, while a Monte Carlo simulation is performed, translating membership function to probability distributions. The moments with the maximum uncertainty, that is those moments with the maximum deviation, can be considered as critical moments. A simple negotiation model is presented to demonstrate the new technique. Moreover, based on the results of the …
Cite as: DP Sakas and DS Vlachos and TE Simos (2008). Identification of critical moments in negotiation using Monte Carlo Simulation. AIP Conference Proceedings, vol 1060 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.3037114.
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Simulation of an Ant Colony Optimization Technique in Continuous Space‐Time
DS Vlachos
Abstract: The ant colony optimization system is an algorithm inspired by the ants’ foraging behavior. The good results obtained by this system on academic problems has made it appealing for applications in industrial settings, one of the current hot topics of the method is the application in continuous problems. In this work, a modified model is presented which is based on autonomous agents, the ants, which behave like the ants in the ant colony system. These agents communicate by the biological inspired pheromone mechanism in order to find sources of food which located near their nest (optimal solutions).
Cite as: DS Vlachos (2008). Simulation of an Ant Colony Optimization Technique in Continuous Space‐Time. AIP Conference Proceedings, vol 1060 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.3037120.
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Multi‐surface Pattern Separation of Interdigital Dielectrometry Data for Volume Detection
D Xenides and DS Vlachos and TE Simos
Abstract: The use of multi‐wavelength interdigital sensors for non‐destructive testing is based on the capability of the measuring system to classify the measured impendence according to some physical properties of the material under test. This is done mostly with computational techniques since the inverse problem is ill‐posed and sometimes leads to physical unaccepted solutions. Thus, the successful application of interdigital sensors are related to the construction of a set of measurements sufficient to classify the physical property of interest. A separable measuring data set consists of measurements obtained in a predefined set of M‐sensor wavelengths (multiples of a base wavelength) and in a predefined set of N‐frequencies. The classification of the M×N‐dimensional vectors obtained in this way can be used to detect volumes of different shapes and sizes inside a uniform medium. The multi‐surface pattern separation …
Cite as: D Xenides and DS Vlachos and TE Simos (2008). Multi‐surface Pattern Separation of Interdigital Dielectrometry Data for Volume Detection. AIP Conference Proceedings, vol 1060 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.3037113.
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Obstacle Bypassing in Optimal Ship Routing Using Simulated Annealing
OT Kosmas and DS Vlachos and TE Simos
Abstract: In this paper we are going to discuss a variation on the problem of finding the shortest path between two points in optimal ship routing problems consisting of obstacles that are not allowed to be crossed by the path. Our main goal are going to be the construction of an appropriate algorithm, based in an earlier work [16] by computing the shortest path between two points in the plane that avoids a set of polygonal obstacles.
Cite as: OT Kosmas and DS Vlachos and TE Simos (2008). Obstacle Bypassing in Optimal Ship Routing Using Simulated Annealing. AIP Conference Proceedings, vol 1060 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.3037118.
A Discrete Lagrangian Algorithm for Optimal Routing Problems
OT Kosmas and DS Vlachos and TE Simos
Abstract: The ideas of discrete Lagrangian methods for conservative systems are exploited for the construction of algorithms applicable in optimal ship routing problems. The algorithm presented here is based on the discretisation of Hamilton’s principle of stationary action Lagrangian and specifically on the direct discretization of the Lagrange‐Hamilton principle for a conservative system. Since, in contrast to the differential equations, the discrete Euler‐Lagrange equations serve as constrains for the optimization of a given cost functional, in the present work we utilize this feature in order to minimize the cost function for optimal ship routing.
Cite as: OT Kosmas and DS Vlachos and TE Simos (2008). A Discrete Lagrangian Algorithm for Optimal Routing Problems. AIP Conference Proceedings, vol 1060 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.3037117.
A Reaction‐Diffusion Technique for Community Structure Identification in Complex Networks
DS Vlachos and KJ Parousis‐Orthodoxou and TE Simos
Abstract: Many networks exhibit community structure which means that the vertices of the network can be classified into groups. The criterion of this classification can be everything (from connectivity between members of the same group to the value of some hidden variables characterizing the vertices of the network). One of the most important criterion for classification is the fact that connections are dense inside a group but between distinct groups they are sparser. In this work, a diffusion‐reaction technique is proposed to identify the community structure of a network. The algorithm, in some cases, gives better result than the most used algorithms found in the bibliography.
Cite as: DS Vlachos and KJ Parousis‐Orthodoxou and TE Simos (2008). A Reaction‐Diffusion Technique for Community Structure Identification in Complex Networks. AIP Conference Proceedings, vol 1048 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.3040244.
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Winner‐Takes‐All Strategies for Complex Network Evolution
DS Vlachos and KJ Parousis‐Orthodoxou and TE Simos
Abstract: In this work, we examine a realistic mechanism for evolution of complex networks which is based on Winner‐Takes‐All strategies. A new vertex, when entering the network, creates N random trial edges with the existing vertices, and then decides to keep only the best (the winner). A modification of this strategy is to force the new vertex to keep the m best edges. Degree distribution and degree correlation is examined through simulated experiments.
Cite as: DS Vlachos and KJ Parousis‐Orthodoxou and TE Simos (2008). Winner‐Takes‐All Strategies for Complex Network Evolution. AIP Conference Proceedings, vol 1048 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.3040246.
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The Use of Phase‐Lag Derivatives in the Numerical Integration of ODEs with Oscillating Solutions
ZA Anastassi and DS Vlachos and TE Simos
Abstract: In this paper we consider the fitting of the coefficients of a numerical method, not only due to the nullification of the phase‐lag, but also to its derivatives. We show that the method gains efficiency with each derivative of the phase‐lag nullified for various problems with oscillating solutions. The analysis of the local truncation error analysis and the stability of the methods show the importance of zero phase‐lag derivatives when integrating oscillatory differential equations.
Cite as: ZA Anastassi and DS Vlachos and TE Simos (2008). The Use of Phase‐Lag Derivatives in the Numerical Integration of ODEs with Oscillating Solutions. AIP Conference Proceedings, vol 1048 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.2990865.
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A New Multistep Integrator Based on Discrete Langrangian Formulation
OT Kosmas and DS Vlachos and TE Simos
Abstract: A multi‐step numerical method is formulated for the solution of discrete Lagrangian and Hamilton differential equations presented in previous works. As an application, the relative motion of the two body problem is treated with a multi‐step algorithm and its possibility to be used in other physics problems (e.g. Schrödinger equation) is discussed.
Cite as: OT Kosmas and DS Vlachos and TE Simos (2008). A New Multistep Integrator Based on Discrete Langrangian Formulation. AIP Conference Proceedings, vol 1048 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.3040248.
Gamma Ray Spectrum Unfolding Using Derivative Kernels
DS Vlachos and OT Kosmas
Abstract: The unfolding of a gamma ray spectrum experience many difficulties due to noise in the recorded data, that is based mainly on the change of photon energy due to scattering mechanisms (either in the detector or the medium), the accumulation of recorded counts in a fixed energy interval (the channel width of the detector) and finally the statistical fluctuation inside the detector. In order to deal with these problems, a new method is developed which interpolates the ideal spectrum with the use of special designed derivative kernels. Preliminary simulation results are presented and show that this approach is very effective even in spectra with low statistics.
Cite as: DS Vlachos and OT Kosmas (2008). Gamma Ray Spectrum Unfolding Using Derivative Kernels. arXiv preprint arXiv:0808.0311. https://arxiv.org/abs/0808.0311.
Phase Lag Sensitivity Analysis for Numerical Integration
DS Vlachos and ZA Anastassi and TE Simos
Abstract: In the field of numerical integration, methods specially tuned on oscillating functions, are of great practical importance. Such methods are needed in various branches of natural sciences, particularly in physics, since a lot of physical phenomena exhibit a pronounced oscillatory behavior. Among others, probably the most important tool used to construct efficient methods for oscillatory problems is the exponential (trigonometric) fitting. The basic characteristic of these methods is that their phase lag vanishes at a predefined frequency. In this work, we introduce a new tool which improves the behavior of exponentially fitted numerical methods. The new technique is based on the vanishing of the first derivatives of the phase lag function at the fitted frequency. It is proved in the text that these methods present improved characteristics in oscillatory problems.
Cite as: DS Vlachos and ZA Anastassi and TE Simos (2008). Phase Lag Sensitivity Analysis for Numerical Integration. arXiv preprint arXiv:0807.2939. https://arxiv.org/abs/0807.2939.
A family of multistep methods with zero phase-lag and derivatives for the numerical integration of oscillatory ODEs
ZA Anastassi and DS Vlachos and TE Simos
Abstract: In this paper we develop a family of three 8-step methods, optimized for the numerical integration of oscillatory ordinary differential equations. We have nullified the phase-lag of the methods and the first r derivatives, where r=1,2,3. We show that with this new technique, the method gains efficiency with each derivative of the phase-lag nullified. This is the case for the integration of both the Schrodinger equation and the N-body problem. A local truncation error analysis is performed, which, for the case of the Schrodinger equation, also shows the connection of the error and the energy, revealing the importance of the zero phase-lag derivatives. Also the stability analysis shows that the methods with more derivatives vanished, have a bigger interval of periodicity.
Cite as: ZA Anastassi and DS Vlachos and TE Simos (2008). A family of multistep methods with zero phase-lag and derivatives for the numerical integration of oscillatory ODEs. arXiv preprint arXiv:0807.2929. https://arxiv.org/abs/0807.2929.
Synchronization in complex systems following a decision based queuing process: rhythmic applause as a test case
D Xenides and DS Vlachos and TE Simos
Abstract: Living communities can be considered as complex systems, and are thus fertile grounds for studies related to statistics and dynamics. In this study we revisit the case of rhythmic applause by utilizing the model proposed by Vázquez et al (2006 Phys. Rev. E 73 036127) augmented with two opposing driving forces, namely the desires for individuality and companionship. To that end, after performing computer simulations with a large number of oscillators we propose an explanation on the following open questions:(a) Why does synchronization occur suddenly?(b) Why is synchronization observed when the clapping period (T c) is 1.5× T s< T c< 2.0× T s (T s is the mean self-period for the spectators) and lost after a time? Moreover, on the basis of the model, a weak preferential attachment principle is proposed which can produce complex networks obeying a power law in the distribution of the number of edges per …
Cite as: D Xenides and DS Vlachos and TE Simos (2008). Synchronization in complex systems following a decision based queuing process: rhythmic applause as a test case. Journal of Statistical Mechanics: Theory and Experiment, vol 2008 (07), (IOP Publishing). https://iopscience.iop.org/article/10.1088/1742-5468/2008/07/P07017/meta.
Image Recognition Techniques for Gamma Spectroscopy
DS Vlachos and CG Tsabaris
Abstract: Photons, after generated from a radioactive source and before they deposit their energy in a photo detector, are subsequent to multiple scattering mechanisms. As a result, the measured energy from the photo detector is different from the energy the photon had when generated. This is known as folding of the photon energy. Moreover, statistical fluctuation inside the detector contribute to energy folding. In this work, a new method is presented for unfolding the gamma ray spectrum. The method uses a 2‐dimensional representation of the measured spectrum (image) and then uses image recognition techniques, and especially differential edge detection, to generate the original spectrum.
Cite as: DS Vlachos and CG Tsabaris (2008). Image Recognition Techniques for Gamma Spectroscopy. AIP Conference Proceedings, vol 963 (2), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.2836014.
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Optimized Derivative Kernels for Gamma Ray Spectroscopy
DS Vlachos and OT Kosmas and TE Simos
Abstract: In gamma ray spectroscopy, the photon detectors measure the number of photons with energy that lies in an interval which is called a channel. This accumulation of counts produce a measuring function that its deviation from the ideal one may produce high noise in the unfolded spectrum. In order to deal with this problem, the ideal accumulation function is interpolated with the use of special designed derivative kernels. Simulation results are presented which show that this approach is very effective even in spectra with low statistics.
Cite as: DS Vlachos and OT Kosmas and TE Simos (2008). Optimized Derivative Kernels for Gamma Ray Spectroscopy. AIP Conference Proceedings, vol 963 (2), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.2836015.
Fuzzy Neural Classifiers for Multi‐Wavelength Interdigital Sensors
D Xenides and DS Vlachos and TE Simos
Abstract: The use of multi‐wavelength interdigital sensors for non‐destructive testing is based on the capability of the measuring system to classify the measured impendence according to some physical properties of the material under test. By varying the measuring frequency and the wavelength of the sensor (and thus the penetration depth of the electric field inside the material under test) we can produce images that correspond to various configurations of dielectric materials under different geometries. The implementation of a fuzzy neural network witch inputs these images for both quantitative and qualitative sensing is demonstrated. The architecture of the system is presented with some references to the general theory of fuzzy sets and fuzzy calculus. Experimental results are presented in the case of a set of 8 well characterized dielectric layers. Finally the effect of network parameters to the functionality of the system is …
Cite as: D Xenides and DS Vlachos and TE Simos (2008). Fuzzy Neural Classifiers for Multi‐Wavelength Interdigital Sensors. AIP Conference Proceedings, vol 963 (2), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.2836018.
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Fuzzy constraint based model for efficient management of dynamic purchasing environments
DP Sakas and DS Vlachos and TE Simos
Abstract: This paper considers the application of a fuzzy constraint based model for handling dynamic environments where only one of possibly many bundles of items must be purchased and quotes for items open and close over time. Simulation results are presented and compared with the optimal solution.
Cite as: DP Sakas and DS Vlachos and TE Simos (2008). Fuzzy constraint based model for efficient management of dynamic purchasing environments. AIP Conference Proceedings, vol 963 (2), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.2836002.
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Adaptive techniques for online auctions
DP Sakas and DS Vlachos and TE Simos
Abstract: Online auctions consider a setting in which agents arrive dynamically and require that an allocation and payment decision is made before they depart. An auctioneer must take a decision having no knowledge about the time horizon and the strategy of the bidder agent. In this work, we present an utility theory based model which is capable of taking the auctioneer decision and adopt its assumptions about the bidders from the results of past auctions. Simulation results are presented in order to test the efficiency of the proposed model.
Cite as: DP Sakas and DS Vlachos and TE Simos (2008). Adaptive techniques for online auctions. AIP Conference Proceedings, vol 963 (2), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.2836004.
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Adaptive neural networks for automatic negotiation
DP Sakas and DS Vlachos and TE Simos
Abstract: The use of fuzzy logic and fuzzy neural networks has been found effective for the modelling of the uncertain relations between the parameters of a negotiation procedure. The problem with these configurations is that they are static, that is, any new knowledge from theory or experiment lead to the construction of entirely new models. To overcome this difficulty, we apply in this work, an adaptive neural topology to model the negotiation process. Finally a simple simulation is carried in order to test the new method.
Cite as: DP Sakas and DS Vlachos and TE Simos (2008). Adaptive neural networks for automatic negotiation. AIP Conference Proceedings, vol 963 (2), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.2836003.
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Symbolic Derivation of Order Conditions for Runge‐Kutta‐Nyström Methods
DS Vlachos and TE Simos
Abstract: The theory of bi‐coloured trees and some special properties of Runge‐Kutta‐Nyström methods are used to construct a simple algorithm for the symbolic derivation of the order conditions. The basic assumption is that there is a certain connection between the elementary weights of trees with black and white roots, which reduces the number of conditions only to those that are derived from trees with white roots. This connection is compatible with symplecticity.
Cite as: DS Vlachos and TE Simos (2007). Symbolic Derivation of Order Conditions for Runge‐Kutta‐Nyström Methods. AIP Conference Proceedings, vol 936 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.2790211.
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Discrete algorithms for optimization in ship routing problems
OT Kosmas and DS Vlachos and TH Simos
Abstract: Within the ideas of discretization of Lagrangian dynamics for conservative systems, we have constructed a discrete algorithm appropriate for optimal ship routing problems. This algorithm is an iterative optimization which produces optimal routes and optimal cost functions, by exploiting the advantages of the discrete Lagrangian methods.
Cite as: OT Kosmas and DS Vlachos and TH Simos (2007). Discrete algorithms for optimization in ship routing problems. AIP Conference Proceedings, vol 936 (1), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.2790141.
Construction of General Linear Methods with Parallel Stages
ZA Anastassi and DS Vlachos and TE Simos
Abstract: During the last years, several types of parallel methods for integrating non-stiff initial-value problems for first-order ordinary differential equation have been proposed. The majority of them are based on an implicit multistage method in which the implicit relations are solved by the predictor-corrector (or fixed point iteration) method. In the predictor-corrector approach the computation of the components of the stage vector iterate can be distributed over s processors, where s is the number of implicit stages of the corrector method. However, after each iteration, the processors have to exchange their just computed results. Given that the communication time between the processors is several orders greater that the computational time, this frequent communication between the processors is a serious drawback. Particularly on distributed memory computers, such a fine grain parallelism is not attractive. An alternative …
Cite as: ZA Anastassi and DS Vlachos and TE Simos (2006). Construction of General Linear Methods with Parallel Stages. Recent Progress in Computational Sciences and Engineering pp (5), (CRC Press). https://www.taylorfrancis.com/chapters/edit/10.1201/9780429070655-32/construction-general-linear-methods-parallel-stages-anastassi-vlachos-simos.
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PDSW: A program for the calculation of photon energy distribution resulting from radioactive elements in seawater
DS Vlachos and TE Simos
Abstract: Photons, when emitted from radioactive sources in seawater, are subsequent to multiple scattering mechanisms, namely the photoelectric effect, the Compton scattering and the pair production effect. Thus, the monoenergetic emission of photons in seawater will result in equilibrium in a distribution of photons with different energies. PDSW is a MATLAB program which calculates this distribution and can be found useful for the characterization of measured spectra obtained by gamma detectors such as NaI(Tl). PDSW has been developed as an autonomous MATLAB function in order to make possible to integrate it in other applications. All calculations are performed using a typical value for seawater salinity (3.5%).Title of program: PDSWCatalogue identifier: ADWWProgram summary URL: http://cpc.cs.qub.ac.uk/summaries/ADWWProgram obtainable from: CPC Program Library, Queen's University …
Cite as: DS Vlachos and TE Simos (2006). PDSW: A program for the calculation of photon energy distribution resulting from radioactive elements in seawater. Computer physics communications, vol 174 (5), (North-Holland). https://www.sciencedirect.com/science/article/pii/S0010465505005813.
A Method for the Separation of Wind Generated and Traveling Waves in Coastal Zones and its Use in Wave Height Prediction
DS Vlachos
Abstract: The most widely used and accepted method of studying wind generated waves is an examination of the spectra at a single point. This approach is based mostly on the assumption that recorded time series of the surface elevation, pressure or velocities are the results of linear superposition of small amplitude oscillations regardless of their directions of propagation. In this work, the vertical and horizontal accelerations of a floating buoy have been used in order to calculate the directional wave spectra in coastal zones. The method used is a parametric one, which incorporates two waves propagating in different directions. The resulting splitting of the incoming waves into two main directions is used for 24‐hours wave height prediction with an adaptive neural network. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cite as: DS Vlachos (2005). A Method for the Separation of Wind Generated and Traveling Waves in Coastal Zones and its Use in Wave Height Prediction. Applied Numerical Analysis & Computational Mathematics, vol 2 (1), (WILEY‐VCH Verlag). https://onlinelibrary.wiley.com/doi/abs/10.1002/anac.200410031.
Response function calculation of an underwater gamma ray NaI (Tl) spectrometer
DS Vlachos and C Tsabaris
Abstract: Autonomous measuring systems for radioactivity in the water environment require caution concerning the specifications of power consumption, stability, communication equipment, tolerance and efficiency. In addition, the calculation of the response function of the whole system is essential for suppressing the background of the measurement and for estimating the concentration of the involved radionuclides, especially given the greater probability of primary gamma photons undergoing multiple scattering events before they interact with the sensing device. In this work, a method is presented that can be used to calculate the response function of a NaI(Tl)-based spectrometer when it is used in the marine environment. The method takes into account both the scattering of photons in the water (analytical calculations) and the detection mechanism of the sensor (Monte-Carlo simulation). In order to validate the method, the …
Cite as: DS Vlachos and C Tsabaris (2005). Response function calculation of an underwater gamma ray NaI (Tl) spectrometer. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, vol 539 (1-2), (North-Holland). https://www.sciencedirect.com/science/article/pii/S0168900204022144.
Self-calibration techniques of underwater gamma ray spectrometers
DS Vlachos
Abstract: In situ continuous monitoring of radioactivity in the water environment has many advantages compared to sampling and analysis techniques but a few shortcomings as well. Apart from the problems encountered in the assembly of the carrying autonomous systems, continuous operation some times alters the response function of the detectors. For example, the continuous operation of a photomultiplier tube results in a shift in the measured spectrum towards lower energies, making thus necessary the re-calibration of the detector. In this work, it is proved, that when measuring radioactivity in seawater, a photo peak around 50 keV will be always present in the measured spectrum. This peak is stable, depends only on the scattering rates of photons in seawater and, when it is detectable, can be used in conjunction with other peaks (40K and/or 208Tl) as a reference peak for the continuous calibration of the detector.
Cite as: DS Vlachos (2005). Self-calibration techniques of underwater gamma ray spectrometers. Journal of environmental radioactivity, vol 82 (1), (Elsevier). https://www.sciencedirect.com/science/article/pii/S0265931X05000032.
On Frequency Determination in Exponential Fitting Multi-step Methods for ODEs
DS Vlachos and TE Simos
Abstract: The frequency determination in an exponential fitting multi-step method is a question without a definite answer. In most of the cases, the estimation of the frequency arises from the nature of the problem, as in the Schrödinger equation. Another approach is to select a frequency which increases the order of the method by zeroing the first non vanishing term of the linear truncation error. In this work, two general methods are exploited: the first is applicable to equations of the form y(x) = f(x,y) and relates the frequency with the coefficient of y in f(x, y) while the other connects the frequency with the curvature of the solution.
Cite as: DS Vlachos and TE Simos (2004). On Frequency Determination in Exponential Fitting Multi-step Methods for ODEs. International Conference of Computational Methods in Sciences and Engineering 2004 (ICCMSE 2004) pp (2), (CRC Press). https://www.taylorfrancis.com/chapters/edit/10.1201/9780429081385-136/frequency-determination-exponential-fitting-multi-step-methods-odes-vlachos-simos.
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Numerical and Monte-Carlo Calculation of Photon Energy Distribution in Sea Water
DS Vlachos
Abstract: Photons, when emitted in sea water, are subject to multiple scattering mechanisms, resulting in a shift in their initial energy. Consequently, a problem arises when measured spectra of radioactivity in sea water are processed, because the measured values do not reflect the initial photon energy but a distribution of energies. In this work a detailed analytical formulation of this distribution is performed and numerical results are compared to results from Monte-Carlo calculation.
Cite as: DS Vlachos (2004). Numerical and Monte-Carlo Calculation of Photon Energy Distribution in Sea Water. International Conference of Computational Methods in Sciences and Engineering 2004 (ICCMSE 2004) pp (14), (CRC Press). https://www.taylorfrancis.com/chapters/edit/10.1201/9780429081385-134/numerical-monte-carlo-calculation-photon-energy-distribution-sea-water-vlachos.
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A Hybrid Adaptive Neural Network for Sea Waves Forecasting
DS Vlachos
Abstract: The physical process of generation of wind waves is extremely complex, uncertain and not yet fully understood. Despite a variety of deterministic models presented to predict the heights and periods of waves from the characteristics of the generating wind, a large scope still exists to improve on the existing models or to provide alternatives to them. In this work, a hybrid adaptive neural network has been designed and used in order to predict the wave height. The system has been proved to produce a 95% successful 24 hours prediction of wave height after 2 months of operation.
Cite as: DS Vlachos (2004). A Hybrid Adaptive Neural Network for Sea Waves Forecasting. International Conference of Computational Methods in Sciences and Engineering 2004 (ICCMSE 2004) pp (24), (CRC Press). https://www.taylorfrancis.com/chapters/edit/10.1201/9780429081385-137/hybrid-adaptive-neural-network-sea-waves-forecasting-vlachos.
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Monte-Carlo Simulation of Clustering in a Plasma-Discharge Source
DS Vlachos and AC Xenoulis
Abstract: The assumption that the ionization and coagulation of metal plasma-generating cluster source can be described by the orbital limited motion theory, when it was examined by Monte Carlo calculations, was found inadequate. That assumption cannot firstly predict the modes of cluster ionization observed experimentally. Secondly, the effectiveness of coagulation was found to depend on the initial size of the condensing particles. Specifically, the coagulation of dust particles proceeds in a satisfactory degree. The coagulation of single atoms in a cluster source, however, saturates at about 140 atoms per cluster, in serious underestimation of relevant experimental data.
Cite as: DS Vlachos and AC Xenoulis (2004). Monte-Carlo Simulation of Clustering in a Plasma-Discharge Source. International Conference of Computational Methods in Sciences and Engineering 2004 (ICCMSE 2004) pp (34), (CRC Press). https://www.taylorfrancis.com/chapters/edit/10.1201/9780429081385-135/monte-carlo-simulation-clustering-plasma-discharge-source-vlachos-xenoulis.
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A Local Supervised Learning Algorithm For Multi‐Layer Perceptrons
DS Vlachos
Abstract: The back propagation of error in multi‐layer perceptrons when used for supervised training is a non‐local algorithm in space, that is it needs the knowledge of the network topology. On the other hand, learning rules in biological systems with many hidden units, seem to be local in both space and time. In this work, a local learning algorithm is proposed which makes no distinction between input, hidden and output layers. Simulation results are presented and compared with other well known training algorithms. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cite as: DS Vlachos (2004). A Local Supervised Learning Algorithm For Multi‐Layer Perceptrons. Applied Numerical Analysis & Computational Mathematics, vol 1 (2), (WILEY‐VCH Verlag). https://onlinelibrary.wiley.com/doi/abs/10.1002/anac.200410016.
Optimal ship routing based on wind and wave forecasts
DS Vlachos
Abstract: Short term accurate wind and wave forecasts can be used for optimal ship routing. In this work, a method is presented for manipulating the POSEIDON [1] system forecasts for the Greek seas and for producing optimal routes for small and medium size ships. The method is composed from a geometrical calculation of all possible routes between two points and from an iterative algorithm which approximates the optimal (or an almost optimal) route. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cite as: DS Vlachos (2004). Optimal ship routing based on wind and wave forecasts. Applied Numerical Analysis & Computational Mathematics, vol 1 (2), (WILEY‐VCH Verlag). https://onlinelibrary.wiley.com/doi/abs/10.1002/anac.200410018.
Partitioned Linear Multistep Method for Long Term Integration of the N‐Body Problem
DS Vlachos and TE Simos
Abstract: In this paper an exponential fitted partitioned linear multistep method is developed for the long term integration of the N‐body problem. The new method integrates exactly any linear combination of the functions 1, x, x2, x3 ,…, x2k–1, exp(±wx) for the coordinates and any linear combination of the functions 1, x, x2, x3,…, x2k–3, exp(±wx) for the velocities. Numerical results are produced and compared with a set of well known symplectic and single step methods. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cite as: DS Vlachos and TE Simos (2004). Partitioned Linear Multistep Method for Long Term Integration of the N‐Body Problem. Applied Numerical Analysis & Computational Mathematics, vol 1 (2), (WILEY‐VCH Verlag). https://onlinelibrary.wiley.com/doi/abs/10.1002/anac.200410017.
Adaptive neural network for wave forecasting
DS Vlachos and A Papadopoulos
Abstract: The physical process of generation of wind waves is extremely complex, uncertain and not yet fully understood. Despite a variety of deterministic models presented to predict the heights and periods of waves from the characteristics of the generating wind, a large scope still exists to improve on the existing models or to provide alternatives to them. In this work, an adaptive neural network has been designed and used in order to predict the wave height. The system has been proved to produce a 90% successful 24 hour prediction of wave height after 2 months of operation.
Cite as: D.S. Vlachos, A. Papadopoulos, Adaptive neural network for wave forecasting, Editor(s): H. Dahlin, N.C. Flemming, K. Nittis, S.E. Petersson, Elsevier Oceanography Series, Elsevier, Volume 69, 2003,Pages 403-406. https://www.sciencedirect.com/science/article/pii/S0422989403800673.
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Monte Carlo simulation of Nal (TI) gamma-spectra in sea water
DS Vlachos and C Tsabaris
Abstract: In the field of gamma spectroscopy, detection systems such as NaI(Tl), HPGe, CdZnTe, Csl, BaF2, BGO, GaAs are widely known. In a marine environment only the NaI(Tl) and HPGe detectors have been used for in situ monitoring of radioactivity due to their high efficiency and to their capability of detecting in a wide energy range. HPGe detectors have been used for a number of applications in seawater, but these detectors could only function for limited period of time (2 hours) due to overheating of the crystal. On the other hand, NaI(Tl) based detectors suffer from high background radiation, so that the real information consists of the gamma ray emission from various radionuclides. The most significant contribution to the background is produced by the natural constituent of the seawater 40K, which has an abundance of 0.012% and emits gamma rays at 1461 keV with approximate activity of 12000 Bqm3.In this work …
Cite as: DS Vlachos and C Tsabaris (2003). Monte Carlo simulation of Nal (TI) gamma-spectra in sea water. Elsevier Oceanography Series, vol 69, (Elsevier). https://www.sciencedirect.com/science/article/pii/S0422989403800612.
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Polis: Poseidon on-line information system
DS Vlachos
Abstract: POLIS is a user-friendly information system that is exported to the World Wide Web. The system provides routing information for the Aegean Sea. The user can draw his route by selecting waypoints, defining the mean speed and time of departure. The system answers with a detailed report, which contains initial routing recommendations and information about the weather and sea condition along this route. Optional field equipment is available for continuous monitoring, providing corrections on the initial route recommendation. The system is connected with the POSEIDON system, which contains a network of observation buoys and a specialised operational centre for the processing of the data collected and the production of forecasts. POLIS can be found very valuable especially in small and medium size ship cruise programming.
Cite as: DS Vlachos (2003). Polis: Poseidon on-line information system. Elsevier Oceanography Series, vol 69, (Elsevier). https://www.sciencedirect.com/science/article/pii/S0422989403801083.
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Development and application of an underwater gamma ray spectrometer for radioactivity measurements
C Tsabaris and DS Vlachos and CT Papadopoulos and R Vlastou and CA Kalfas
Abstract: The set up and control of an underwater measuring instrument for radioactivity pollution in marine environment is described, by using a simple, low consumption, long-term monitoring and stable detection system. This sytem is a Nal scintillator (RADAM III) with special specifications for the use in the marine environment. The sensor before its deployment has been calibrated in the laboratory by using a big tank (5.5 m super(3)) for energy, energy resolution and total efficiency in the water. These calibrations have been performed, by using the gamma rays of a known activity liquid source ( super(137)Cs at 661keV) and the gamma ray emission of known mass KCI, by the decay of super(40)K at 1461 keV. The measured spectra from the tank (laboratory analysis) were compared with spectra from the same detector as acquired in the field. The analysis of the parallel measurement gave satisfactory agreement for the …
Cite as: C Tsabaris and DS Vlachos and CT Papadopoulos and R Vlastou and CA Kalfas (2001). Development and application of an underwater gamma ray spectrometer for radioactivity measurements. INTERREG Meeting, North Aegean system functioning and inter-regional pollution, Kavala, Greece, 28-30 May 2001.. https://scholar.google.com/scholar?cluster=3533217543871183668&hl=en&oi=scholarr.
In-situ calibrations of oceanographic sensors in the framework of the Poseidon project.
V Zervakis and O Gotsis-Skretas and E Krasakopoulou and C Diamanti and P Renieris and E Papageorgiou and S Lyng and G Noesen and D Ballas and A Mallios and A Morfis and D Vlachos and S Barmpetseas and G Chronis
Abstract: Στην παρούσα εργασία περιγράφεται η πρώτη προσπάθεια του Ε.Κ.Θ.Ε. για ποιοτική αξιολόγηση και -εάν κρίνεται σκόπιμο- βελτίωση της ποιότητας των μετρήσεων αγωγιμότητας, διαλυμένου οξυγόνου και φθορισμού χλωροφύλλης-α που συλλέγονται από τους αντίστοιχους αισθητήρες των πλωτών ωκεανογραφικών μετρητικών σταθμών (ΠΩΜΣ) του προγράμματος "ΠΟΣΕΙΔΩΝ".
Cite as: V Zervakis and O Gotsis-Skretas and E Krasakopoulou and C Diamanti and P Renieris and E Papageorgiou and S Lyng and G Noesen and D Ballas and A Mallios and A Morfis and D Vlachos and S Barmpetseas and G Chronis,In-situ calibrations of oceanographic sensors in the framework of the Poseidon project, Technical Report, HCMR, 1999. https://okeanos-dspace.hcmr.gr/bitstream/handle/123456789/3285/577.pdf?sequence=1.
The conditions for effective clustering in a plasma-discharge source identified via Monte-Carlo simulations
DS Vlachos and AC Xenoulis and Th Tsakalakos
Abstract: The assumption that the ionization and coagulation of metal particles in a plasma-generating cluster source can be described by the orbital limited motion theory, examined by Monte Carlo calculations, was found inadequate. That assumption cannot firstly predict the modes of cluster ionization observed experimentally. Secondly, the effectiveness of coagulation was found to depend on the initial size of the condensing particles. Specifically, the coagulation of dust particles proceeds in a satisfactory degree. The coagulation of single atoms in a cluster source, however, saturates at about 140 atoms per cluster, in serious underestimation of relevant experimental data.
Cite as: DS Vlachos and AC Xenoulis and Th Tsakalakos (1999). The conditions for effective clustering in a plasma-discharge source identified via Monte-Carlo simulations. Nanostructured Materials, vol 12 (5-8), (Pergamon). https://www.sciencedirect.com/science/article/pii/S0965977399002779.
The size distribution of metal clusters produced in plasma-discharge hollow-cathode source
AC Xenoulis and G Doukellis and C Potiriadis and N Boukos and DS Vlachos and Th Tsakalakos
Abstract: The mean size of Cu clusters produced in a hollow-cathode, dc plasma-discharge source, increases significantly with decreasing flow rate and less pronouncedly with increasing Ar/He abundance ratio and increasing discharge current. The effect of pressure is mixed. Between 0.4 and 0.6 mbar the size is not affected. Above 0.6 mbar, the size increases significantly with increasing pressure. With the help of the above parameters, the mean cluster size can be shifted at will between 20 and 250 Å. Implications concerning the mechanisms associated with clustering in plasma are discussed.
Cite as: AC Xenoulis and G Doukellis and C Potiriadis and N Boukos and DS Vlachos and Th Tsakalakos (1999). The size distribution of metal clusters produced in plasma-discharge hollow-cathode source. Nanostructured Materials, vol 12 (1-4), (Pergamon). https://www.sciencedirect.com/science/article/pii/S0965977399001245.
Gas detection sensitivity and cluster size
DS Vlachos and AC Xenoulis
Abstract: A theoretical investigation of the dependence of gas sensitivity of nanostructured semiconductor gas sensors on cluster size is presented. The clusters are represented as spheres and the adsorbed gas as a surface state density. The sensitivity is calculated as a change in conductivity over a change of surface state density. The results show that there is a critical cluster size, which is material dependent, at which the sensitivity is maximal. The cluster size for maximum sensitivity of several metal oxide gas sensors of practical interest, such as ZnO, SnO2, TiO2 and In2O3, is predicted and discussed.
Cite as: DS Vlachos and AC Xenoulis (1998). Gas detection sensitivity and cluster size. Nanostructured Materials, vol 10 (8), (Pergamon). https://www.sciencedirect.com/science/article/pii/S0965977399000057.
The unfolding procedure of the alpha particle spectra of the 58Ni (n, α) 55Fe reaction
C Tsabaris and D Vlachos and CA Kalfas
Abstract: The correction of the alpha particle energy spectra which is required because of the alpha particle energy loss, due to the thickness of the sample, is described by an analytical-empirical retrospective relation. This relation can yield a spectrum as it was produced in the sample from a corresponding measured spectrum. The alpha decays of the reaction 58Ni(n, α)55Fe were used as the source of the alpha particle spectra. The projectile neutrons were produced via the T(p,n) and D(d,n) reactions in the energy range from 2 to 9 MeV. The validity of our assumption for the correctness of the alpha particle spectra was checked by comparing the measured spectrum with the spectrum produced by folding the corrected spectrum with the response function of the system. The calculated folded spectrum appeared to be consistent with the experimental data of the measured spectrum. Typical results are given at the neutron …
Cite as: C Tsabaris and D Vlachos and CA Kalfas (1997). The unfolding procedure of the alpha particle spectra of the 58Ni (n, α) 55Fe reaction. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, vol 401 (2-3), (North-Holland). https://www.sciencedirect.com/science/article/pii/S0168900297009984.
An adaptive neural network topology for degradation compensation of thin film tin oxide gas sensors
DS Vlachos and DK Fragoulis and JN Avaritsiotis
Abstract: A hybrid neural network for gas sensing application is presented, which is based on adaptive resonance theory. The network may use as an input one or more gas sensors. The basic feature of the proposed topology is its ability to learn a new pattern or form a new pattern category at any point of its operation. At the same time it retains knowledge of previously learned patterns or pattern categories. This adaptation ability helps the network to solve many of the problems encountered with tin oxide gas sensors, like instabilities and degradation. The functionality of the network is presented in the two cases of one and four input providing gas sensors. The experimental results show that the effect of sensor degradation maybe compensated by the proposed network topology.
Cite as: DS Vlachos and DK Fragoulis and JN Avaritsiotis (1997). An adaptive neural network topology for degradation compensation of thin film tin oxide gas sensors. Sensors and Actuators B: Chemical, vol 45 (3), (Elsevier). https://www.sciencedirect.com/science/article/pii/S0925400597003092.
A technique for suppressing ethanol interference employing Seebeck effect devices with carrier concentration modulation
DS Vlachos and CA Papadopoulos and JN Avaritsiotis
Abstract: Thin sputtered indium oxide films with an additive deposited on the half of their surface are considered as Seebeck effect devices for sensing of methane and ethanol. The electron concentration of the oxide film is controlled with an applied voltage perpendicular to the film with the use of a buried gate under it, in the same way the channel conductance in a MOS device is controlled by the gate voltage. Due to the different chemisorption mechanisms of methane and ethanol, a gate voltage modulating the free electron concentration of the oxide film enhances sensitivity to methane, whereas it does not influence sensitivity to ethanol.
Cite as: DS Vlachos and CA Papadopoulos and JN Avaritsiotis (1997). A technique for suppressing ethanol interference employing Seebeck effect devices with carrier concentration modulation. Sensors and Actuators B: Chemical, vol 44 (1-3), (Elsevier). https://www.sciencedirect.com/science/article/pii/S0925400597002153.
Characterisation of the catalyst-semiconductor interaction mechanism in metal-oxide gas sensors
DS Vlachos and CA Papadopoulos and JN Avaritsiotis
Abstract: Catalysts may affect the intergranular contact regions in polycrystalline metal-oxide films with two mechanisms: spillover and Fermi energy control. In this work, a simple experimental method is proposed consisting of monitoring sensor resistance as a function of oxygen partial pressure, in order to distinguish which of these mechanisms is dominant in certain catalyst-metal oxide interfaces. Interpretation of experimental results, using the theoretical background for these two mechanisms in the case of InOx sensors with palladium and platinum catalysts, indicates that the electronic interaction of Fermi energy control dominates in the case of palladium, while the chemical interaction of spillover dominates in the case of platinum. These results are also confirmed by Monte Carlo simulation of the spillover process.
Cite as: DS Vlachos and CA Papadopoulos and JN Avaritsiotis (1997). Characterisation of the catalyst-semiconductor interaction mechanism in metal-oxide gas sensors. Sensors and Actuators B: Chemical, vol 44 (1-3), (Elsevier). https://www.sciencedirect.com/science/article/pii/S0925400597001500.
Effect of surface catalysts on the long-term performance of reactively sputtered tin and indium oxide gas sensors
CA Papadopoulos and DS Vlachos and JN Avaritsiotis
Abstract: Long term performance of tin and indium oxide thin films with palladium and platinum deposited on their surface as catalysts was studied using a standardization method proposed recently by other researchers. A simple gas classification algorithm was used to investigate the validity of the standardization method proposed and to study the effect of doping type and thickness onto the surface of SnOx and InOx films on their selectivity and stability characteristics. It was found that: (a) the proposed method is reliable for the assessment of sensor degradation- and (b) sensors with relatively thick additive layer are more reliable.
Cite as: CA Papadopoulos and DS Vlachos and JN Avaritsiotis (1997). Effect of surface catalysts on the long-term performance of reactively sputtered tin and indium oxide gas sensors. Sensors and Actuators B: Chemical, vol 42 (2), (Elsevier). https://www.sciencedirect.com/science/article/pii/S0925400597001901.
A comparative study of tin and indium oxide gas sensors based on Seebeck effect
Costas A Papadopoulos and Demetrios S Vlachos and John N Avaritsiotis
Abstract: A comparative study on the response of tin and indium oxide thin sputtered films to different reducing gases is presented. The operation of the sensors is based on the Seebeck effect. Platinum has been deposited on half of the films- thus as the rates of gas reaction on the two halves of the films are expected to be different (inducing a temperature gradient), a Seebeck voltage is developed as the response signal. Different responses experimentally observed for tin and indium oxide sensors are qualitatively explained with the aid of the well established theory of chemisorption of reducing gases on metal oxides and the different electronic properties of tin and indium oxide films. The target gases used were 2000 ppm CO, 10,000 ppm CRi and 26 ppm C2H5OH diluted in zero-grade air (ZGA).
Cite as: Costas A Papadopoulos and Demetrios S Vlachos and John N Avaritsiotis (1997). A comparative study of tin and indium oxide gas sensors based on Seebeck effect. Sensors and Materials, vol 9, (SCIENTIFIC PUBLISHING DIVISION MYU). https://www.myukk.org/SM2017/sm_pdf/SM274.pdf.
Dependence of sensitivity of SnOx thin‐film gas sensors on vacancy defects
DS Vlachos and CA Papadopoulos and JN Avaritsiotis
Abstract: Oxygen flow during dc reactive sputtering of SnOx thin films affects film conductivity in zero grade air and gas sensitivity to carbon monoxide and ethanol. The experimental results show that an increase in oxygen flow during film deposition produces films exhibiting higher conductivity in zero grade air and lower gas sensitivity. A theoretical model is presented that explains this behavior. The proposed model takes into account both the dependence of conductivity on the potential barrier height at grain boundaries of the film and the dependence of chemisorption rate of oxygen on free‐electron availability. The theoretical analysis is in good qualitative agreement with experiment.
Cite as: DS Vlachos and CA Papadopoulos and JN Avaritsiotis (1996). Dependence of sensitivity of SnOx thin‐film gas sensors on vacancy defects. Journal of Applied Physics, vol 80 (10), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.363562.
A new planar device based on Seebeck effect for gas sensing applications
CA Papadopoulos and DS Vlachos and JN Avaritsiotis
Abstract: A new planar sensor structure has been developed, which takes advantage of the differential temperature appearing between the two halves of a tin or an indium oxide film, one half of which is covered with a catalyst, in the presence of a combustible gas. Since the rates of reaction of the combustible gas on the two halves of the film are expected to be different, different amounts of heat are delivered at the two halves of the film, resulting in a temperature gradient across the film. According to the Seebeck effect, this temperature gradient produces a voltage difference at the two edges of the film. Different Seebeck voltage values have been recorded when the structure is exposed to various gases, due to the different heat of adsorption or combustion delivered from each gas at the two portions of the film.
Cite as: CA Papadopoulos and DS Vlachos and JN Avaritsiotis (1996). A new planar device based on Seebeck effect for gas sensing applications. Sensors and Actuators B: Chemical, vol 34 (1-3), (Elsevier). https://www.sciencedirect.com/science/article/pii/S0925400597800226.
On the electronic interaction between additives and semiconducting oxide gas sensors
DS Vlachos and CA Papadopoulos and JN Avaritsiotis
Abstract: A model for the electronic interaction between additives and semiconducting oxide gas sensors is presented. The model is based on the depletion layer that is created due to the metal–semiconductor contact forced by the presence of a metallic additive. This depletion layer corresponds to an active grain size that is smaller than the geometrical one. Thus, the work function of the metal is connected to the change of sensor characteristics. Moreover, the dependence of the sensitivity on the amount of the deposited additive is explained on the same basis. Experimental results are presented in the case of tin oxide thin film gas sensors with Pd, Pt, and Ni in the presence of zero grade air and carbon monoxide. The experimental results are in excellent qualitative agreement with the proposed model.
Cite as: DS Vlachos and CA Papadopoulos and JN Avaritsiotis (1996). On the electronic interaction between additives and semiconducting oxide gas sensors. Applied physics letters, vol 69 (5), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.117794.
Fuzzy neural networks for gas sensing
Dimitrios Vlachos and John Avaritsiotis
Abstract: The implementation of a fuzzy neural network with an array of tin oxide based gas sensors for both quantitative and qualitative gas sensing is demonstrated. The architecture of the system is presented with some references to the general theory of fuzzy sets and fuzzy calculus. Experimental results are presented in the case of gas identification between CO, ethanol and methane and in the case of CO detection in different levels of relative humidity. Finally the effect of network parameters to the functionality of the system is discussed, especially in the case of functions evaluating the fuzzy AND and OR operations.
Cite as: Dimitrios Vlachos and John Avaritsiotis (1996). Fuzzy neural networks for gas sensing. Sensors and Actuators B: Chemical, vol 33 (1-3), (Elsevier). https://www.sciencedirect.com/science/article/pii/092540059601917X.
Comparative study of various metal-oxide-based gas-sensor architectures
CA Papadopoulos and DS Vlachos and JN Avaritsiotis
Abstract: Reactively sputtered SnOx and InOx thin films, plain and surface doped with Pt, have been covered with layers of various insulating films and catalysts. Test gases used are carbon monoxide, methane, ethanol, butane and propane. Filters used are alumina (Al2O3), silicon oxide (SiO2) and tungsten trioxide (WO3). Palladium has also been added on the surface of alumina filters, while platinum is added on the surface of metal-oxide sensor films. Response to hydrocarbons, and especially to butane and propane is found to be enhanced with the addition of noble metals on the sensing film or on the filter. It is also found that a WO3 filter improves the carbon monoxide sensitivity at low working temperatures and reduces the sensor response to ethanol with respect to other test gases. The behaviour of indium-oxide-based sensors is qualitatively very similar to that of tin-oxide-based sensors.
Cite as: CA Papadopoulos and DS Vlachos and JN Avaritsiotis (1996). Comparative study of various metal-oxide-based gas-sensor architectures. Sensors and Actuators B: Chemical, vol 32 (1), (Elsevier). https://www.sciencedirect.com/science/article/pii/0925400596801109.
Simulation of the effect of fractional dimension on tin-oxide-based gas sensors
DS Vlachos and JN Avaritsiotis
Abstract: The effect of the fractional dimension of a tin-oxide surface on the sensing mechanism is studied by means of Monte Carlo simulation in the case of CO. The dimension of the active surface has been found to be connected to both the sensitivity and the recovery rate of sensor resistance after CO removal. A method of producing fractal surfaces with different dimensions is presented. Experimentally observed large recovery times are explained on the basis of a small fractal dimension. On the other hand, the observed instabilities of tin-oxide-based thick-film gas sensors are explained by considering the change of surface dimension caused by local reduction of tin oxide in the presence of CO.
Cite as: DS Vlachos and JN Avaritsiotis (1995). Simulation of the effect of fractional dimension on tin-oxide-based gas sensors. Sensors and Actuators B: Chemical, vol 25 (1-3), (Elsevier). https://www.sciencedirect.com/science/article/pii/0925400595851062.
The effect of film oxygen content on SnOitx gas-sensor selectivity
DS Vlachos and CA Papadopoulos and JN Avaritsiotis
Abstract: The effect of the oxyen content in tin oxide films on selectivity in gas detection has been studied. The experimental results show that sensors with different Sn:O ratios exhibit different behaviour in response to CO and ethanol. A theoretical explanation of this phenomenon is presented, which is based on the density of oxygen vacancies at the surface. Moreover, a simple parametric method using three sensors with different Sn:O ratios has been tested to distinguish between CO and ethanol.
Cite as: DS Vlachos and CA Papadopoulos and JN Avaritsiotis (1995). The effect of film oxygen content on SnOitx gas-sensor selectivity. Sensors and Actuators B: Chemical, vol 25 (1-3), (Elsevier). https://www.sciencedirect.com/science/article/pii/0925400595851941.
The effect of humidity on tin-oxide thick-film gas sensors in the presence of reducing and combustible gases
DS Vlachos and PD Skafidas and JN Avaritsiotis
Abstract: The effect of humidity on tin-oxide thick-film gas sensors has been studied in the case of carbon monoxide, methane, methanol, butane and propane. The results are qualitatively explained under the assumption that water molecules dissociate on the tin-oxide surface and produce hydroxyl species capable of acting as electron donors. Moreover, palladium and vanadium, when used as additives, affect the overall behaviour of sensors in the presence of water vapour. To reduce the effect of humidity, thin organometallic films have been deposited on top of thick tin-oxide-based sensors in order to act as filters. The results show that both the sensitivity of these sensors and the effect of humidity are decreased.
Cite as: DS Vlachos and PD Skafidas and JN Avaritsiotis (1995). The effect of humidity on tin-oxide thick-film gas sensors in the presence of reducing and combustible gases. Sensors and Actuators B: Chemical, vol 25 (1-3), (Elsevier). https://www.sciencedirect.com/science/article/pii/0925400595851054.
Modelling and simulation of abnormal behaviour of thick-film tin oxide gas sensors in CO
PD Skafidas and DS Vlachos and JN Avaritsiotis
Abstract: A new model is proposed that takes into account oxygen vacancies in tin oxide resistive-type, assuming that lattice oxygen modifies the rate of oxygen adsorption. Applying this hypothesis in a Monte Carlo simulation, effects observed in thick-film samples are explained. Morevoer, computational techniques have been used in order to simulate different thick-film structures, and the role of both surface coverage and reduction in the sensing mechanism is investigated. The simulation results are in good qualitative agreement with the experimental results obtained from our samples. In particular, phenomena like undershoot and overshoot of the sample's resistance, very long recovery times and poisoning of the sensor surface are discussed.
Cite as: PD Skafidas and DS Vlachos and JN Avaritsiotis (1994). Modelling and simulation of abnormal behaviour of thick-film tin oxide gas sensors in CO. Sensors and Actuators B: Chemical, vol 21 (2), (Elsevier). https://www.sciencedirect.com/science/article/pii/092540059480012X.
Modelling and simulation of tin oxide based thick-film gas sensors using Monte Carlo techniques
PD Skafidas and DS Vlachos and JN Avaritsiotis
Abstract: An advanced model has been developed to explain the experimental results obtained from tin oxide sensors in the presence of carbon monoxide and/or water vapor. The basic principles of the proposed model applied to the simulation are that (a) there is a reduction of the tin oxide surface by both CO and wter vapor, (b) at low temperatures,the oxygen vacancies cannot be refilled, (c) in the presence of both CO and water vapor, formate species are formed which, when they desorb, increase the sensor's resistance, and (d) hydroxyl species increase the electron availability and thus the sensitivity in CO. Simulation results are in excellent qualitative agreement with the experimental ones.
Cite as: PD Skafidas and DS Vlachos and JN Avaritsiotis (1994). Modelling and simulation of tin oxide based thick-film gas sensors using Monte Carlo techniques. Sensors and Actuators B: Chemical, vol 19 (1-3), (Elsevier). https://www.sciencedirect.com/science/article/pii/092540059301222P.
Modelling and simulation of abnormal behavior of thick-film tin oxide gas sensors in CO
JN Avaritsiotis and PD Skaidas and DS Vlachos
Abstract: A new model is proposed that takes into account oxygen vacancies in tin oxide resistive-type gas sensors, assuming that lattice oxygen modifies the rate of oxygen adsorption. Applying this hypothesis in a Monte Carlo simulation, effects observed in thick-film samples are explained. Moreover, computational techniques have been used in order to simulate different thickfilm structures, and the role of both surface coverage and reduction in the sensing mechanism is investigated. Tbe simulation results are in good qualitative agreement with the experimental results obtained from our samples. In particular, phenomena like undershoot and overshoot of the sample’s resistance, very long recovery times and poisoning of the sensor surface are discussed.
Cite as: JN Avaritsiotis and PD Skaidas and DS Vlachos (1994). Modelling and simulation of abnormal behavior of thick-film tin oxide gas sensors in CO. Sensors and Actuators B, vol 21 (2), (Elsevier). https://www.academia.edu/download/48124130/0925-4005_2894_2980012-x20160817-23091-98sx4m.pdf.
Transient effects of tin oxide CO sensors in the presence of water vapor
DS Vlachos and PD Skafidas and JN Avaritsiotis
Abstract: During the experimental study of CO sensitivity of SnO2 resistive‐type gas sensors in the presence of water vapor, a transient effect was observed which elucidates the CO sensing mechanism in tin oxide. More precisely, after the removal of CO, an increase of the measured conductance was observed, depending on substrate temperature. An explanation of this phenomenon is proposed, which is based on the conductance modulation due to three different mechanisms: Formate desorption, occupation of lattice sites by oxygen molecules, and diffusion of lattice oxygen vacancies to sensor’s bulk.
Cite as: DS Vlachos and PD Skafidas and JN Avaritsiotis (1993). Transient effects of tin oxide CO sensors in the presence of water vapor. Applied physics letters, vol 63 (13), (American Institute of Physics). https://aip.scitation.org/doi/abs/10.1063/1.110706.