2. Ερευνητικές - Επιστημονικές Δημοσιεύσεις του Ακαδημαϊκού Προσωπικού
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Πλοήγηση 2. Ερευνητικές - Επιστημονικές Δημοσιεύσεις του Ακαδημαϊκού Προσωπικού ανά Ημερομηνία έκδοσης
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Τεκμήριο Μη γραμμική ηλεκτρική αγωγιμότητα μονοκρυστάλλων V2O5(1991) Καλόμοιρος, ΙωάννηςΠαρασκευάστηκαν κρύσταλλοι V2O5 και μελετήθηκε η ηλεκτρική τους αγωγιμότητα στην περιοχή μεταξύ 200 - 300 Κ. Λήφθησαν χαρακτηριστικές Ι(103/T) και Ι(U). Οι τελευταίες αποτελούνται από μία ωμική και μία S-τύπου περιοχή με αρνητική διαφορική αντίσταση (NDR). Στην περιοχή NDR παρατηρήθηκαν περιοδικές, ημιπεριοδικές και χαοτικές ταλαντώσεις της τάσης. Η παραδοχή σχηματισμού νηματιδίων υψηλής συγκέντρωσης φορέων στο εσωτερικό του υλικού ερμηνεύει τα προηγούμενα φαινόμενα, τόσο ποιοτικά όσο και ποσοτικά, καθώς και την αύξηση της θερμοκρασίας του δείγματος που παρατηρήθηκε στην περιοχή NDR.Τεκμήριο Excitonic and other interband transitions in TlIn2 single crystals(1993) Kalomiros, John; Anagnostopoulos, AntoniosA study of the optical properties of the layered compound TlInS2 is presented. Reflection spectra were measured at room temperature, in the energy region 1.5-6.2 eV. Transmission spectra were measured in the temperature range 10-290K, in the energy region 1.5 to 3.5 eV. Two structures, at energy positions 2.57 and 2.87 eV (10K), are attributed to transitions to the ground exciton state, from valence states split because of the spin-orbit interaction, at the point G of the Brillouin zone. Lorentzian line shapes are used to fit the structures of excitonic origin. The temperature dependence of the peaks and their broadening parameters are also presented.Τεκμήριο Optical and photoelectrical properties of the TlGaS2 ternary compound(1996) Kalkan, Nevin; Kalomiros, John; Hanias, M.; Anagnostopoulos, AntoniosAbsorption and photoconductivity spectra of thin TlGaS2 layers are used to study tbe fundamental and other transitions of TlGaS2 in the energy region 1.0-3.0 eV and in the temperature range lo-300 K. One of the peaks resolved by photoconductivity measurements corresponds to the excitonic peak registered in the absorption spectrum of this compound. The temperature dependence of the critical energy and of the broadening parameter of this excitonic peak are presented. Most of the rest photoconductivity peaks are related to transitions from localized levels to the conduction band.Τεκμήριο Angular dependence of the NEXAFS structure in hexagonal and cubic GaN(1996) Kalomiros, John; Katsikini, Maria; Paloura, Eleni; Bressler, Patrick; Moustakas, T. N.Επιταξιακά υμένια κυβικού και εξαγωνικού GaN, μελετώνται με χρήση φασμάτων απορρόφησης ακτίνων Χ, στην περιοχή της ακμής (ΝEXAFS), μετρημένων υπό διάφορες γωνίες. Στην περίπτωση του κυβικού GaN οι εντάσεις των γραμμών συντονισμού είναι ανεξάρτητες από τη γωνία πρόσπτωσης, ενώ στην περίπτωση του εξαγωνικού GaN εμφανίζεται μια εξάρτηση της μορφής cos2θ. Προτείνεται ότι τα φάσματα NEXAFS μπορούν να χρησιμοποιηθούν για την ταυτοποίηση της συμμετρίας των υπο εξέταση κρυστάλλων.Τεκμήριο Finite element solution of planar waveguides with embedded networks(2000-11-09) Dillon, B. M.; Tsitsos, S.; Gibson, A.A.P.Planar microwave structures which combine electromagnetic fields and network parameter descriptions are analysed using the finite element (FE) method. The predicted performance of a nonsymmetrical three-port power divider with an embedded impedance network is presented and compares well with measured data.Τεκμήριο Pedestrian way design for the road safety of school students(2003) Panagiotopoulos, E.; Kariotis, G.; Theodoridou-Sotiriou, LilaThe years of school enrollment represent a crucial period of a person's life. The schooling experience forms the foundations of human evolution. The school day represents 30% of each school child's everyday activity experienced. Additionally, another important dimension that should be taken into account is that of time - space - school access safety. The pluralistic essence of the educational process is described as the sum total of actions exercised by various factors (family, school, state, the church, profession, society, etc.) aiming at the appropriate mental, physical and moral development as well as the culture and shaping of a country's citizens. The objective is to equip these persons in their effort for a harmonious adaptation to their physical, social and cultural environment. A relation between students and the environment is created, to be examined at three levels: student - school spaces, student - access means - safety and student - road traffic education and environment. The application of a Geographical System of Information (GIS) contributes to the qualitative improvement of the study, offers the potential for data updating and control over time, assists decision-making processes. In the areas where problems appear, political decisions and the related increased fund allocations result in the implementation of the necessary projects and activities aiming at upgrading the student - environment relationship. The supply of a pleasant and safe environment for walking is a necessary condition in order for the city to be friendly toward its student population and persons with special needs (the disadvantaged).Τεκμήριο Planning, implementation and evaluation of a new academic curriculum: the case of the Geoinformatics and Surveying Department at the TEI of Serres(2004) Theodoridou-Sotiriou, LilaIn this article, the author seeks to assess the design, development and three-year operation of a new course curriculum in applied technology in a Greek Technological Educational Institute (TEI). The constant increase in demand for spatial information and the technology for managing this information provided a challenge in forming an independent undergraduate academic curriculum in applied sciences, similar to other departments in peer European and worldwide academic institutions. In the article, the author analyses the structure of the curriculum and the methodology behind its design. Quantitative data from the first evaluation of the operation of the Department at the TEI of Serres is also presented, along with data from a survey was conducted on students of the Department. The survey explored the way that current students evaluated the academic curriculum’s structure and the benefits it afforded them. The results of the survey revealed that a strong appraisal of the new academic curriculum seemed to be the case for the student, academic and professional communities in Greece.Τεκμήριο Efficient minimization over products of simplices and its application to nonlinear multicommodity network problems(2004) Karakitsiou, Athanasia; Mavrommati, Athanasia; Migdalas, AthanasiosMany problems in portfolio selection, in traffic planning and in computer communication networks can be formulated as nonlinear problems involving minimization of a nonlinear function over simplices. Based on the concepts of regularization and partial linearization, we propose an efficient solution technique for such programs, prove its global convergence and discuss the possibilities for parallel implementation. We provide, as an application, an algorithm for traffic assignment which outperforms previous state-of-the-art codes.Τεκμήριο User Profiling for Fraud Detection in Telecommunication Networks(2005) Hilas, Constantinos S.; Sahalos, John N.Telecommunications fraud is increasing dramatically each year resulting in loss of a large amount of euros worldwide. A statistical machine learning method is presented that constructs user profiles for the detection of fraudulent activities in telecommunications networks. The approach presented here can be used for the detection of superimposed or hacking fraud, works well for mid-term decisions and cannot be used for on-line account comparison.Τεκμήριο Error Estimation of the Method of Auxiliary Sources (MAS) for Scattering from an Impedance Circular Cylinder(2005) Anastassiu, H.The purpose of this paper is a rigorous error estimation of the Method of Auxiliary Sources (MAS), when the latter is applied to electromagnetic scattering from a circular, coated, perfectly conducting cylinder, assumed to satisfy the Standard Impedance Boundary Condition (SIBC). The MAS matrix is inverted analytically, via eigenvalue analysis, and an exact expression for the discretization error in the boundary condition is derived. Furthermore, an analytical formula for the condition number of the linear system is also extracted, in addition to an asymptotic estimate for large scatterers, explaining the irregular behavior of the computational error resulting from numerical matrix inversion. Finally, the optimal location of the auxiliary sources is determined, on the grounds of error minimization.Τεκμήριο Information Services offered through the Hotel Web sites. A Comparative study between Cyprous and Greece(2005) Zafiropoulos, Costas; Vrana, VasilikiInformation provided through the hotels web sites can serve as a means for improving marketing and eCommerce for tourism companies. The article uses a conceptual framework which categorizes a wide range of offered information services into seven categories: Facilities information, Customer contact information, Reservation-price information, Surrounding area information, Management of the website, Company information and Communication. Also the property of interactivity is taken into account for the study of each category. A case study of hotels in Cyprus and Greece reveals differences in types of information services provided through the hotel web sites between these countries. Greek hotels mainly provide general and contact information while Cypriot hotels lead in providing reservation and area information services. Hotel class and chain membership have an effect on the volume of offered information in both countries but to different degrees.Τεκμήριο Computational cost estimations and comparisons for three methods of applied electromagnetics (MoM, MAS, MMAS)(2005) Avdikos, G. K.; Anastassiu, H. T.The computational costs of three numerical techniques used in electromagnetics, namely the moment method (MoM), the method of auxiliary sources (MAS), and its modified version (MMAS), are estimated for various calculation schemes and configurations. Both surface and volumetric problems are considered. The number of multiplications required for the system-matrix fill is calculated and added to the algorithmic cost of the matrix inversion. The Green's function singularity extraction is also taken into account, particularly for the MoM. The original integrals are transformed into the local (area or volume) coordinate systems, and are subsequently evaluated on the basis of standard numerical quadrature schemes. For the surface integral equation (SIE), some calculations using either the well-known Duffy transformations or some analytical-numerical integration schemes are also presented (expressions are available only for the scalar potential integral case). For the MAS and MMAS, the matrix fill is shown to be much faster, since no time-consuming integrations are involved. The analysis is applied to various objects, such as a perfectly conducting (PEC) parallelpiped, a PEC sphere, and a microstrip patch antenna, and useful conclusions are drawn on the relative efficiency of the three methods.Τεκμήριο Estimating and Visualising Factors Affecting Traffic Noise Propagation, by use of Advanced GIS Techniques(2005) Evangelidis, Konstantinos E.; Konstantinidis, Alexandros P.; Nikolaou, Konstantinos I.This paper proposes a methodology through which advanced Geographic Information Systems’ (GIS) techniques are applied in the study of environmental traffic-related noise. The spatial nature of the factors affecting traffic noise propagation necessitates the use of GIS, a field of applications offering by default specialised analytical tools and functionalities for managing spatial information. In this respect contemporary GIS tools have been employed in order to estimate and visualise the impacts of the above factors, on the noise generated by road traffic. GIS capabilities such as spatial analysis and geographical processing, were integrated with proven methods used for calculating road traffic noise, with the aim to enhance the study of factors such as distance from the noise source, screening form intervening obstacles and reflections from buildings facade. Separate maps representing the impacts of each individual factor, on the basic noise level were produced providing a comprehensive view of traffic noise propagation. All of the analysis was based on splitting the study area into a high-density grid, where each grid-cell corresponded to a reception point. By combining each individual factor’s contribution for every separate grid-cell, yielded to the global traffic noise sound field of the entire study area.Τεκμήριο Designing simplicity: usability perspectives on Learning Management Systems(2005) Fotaris, Panagiotis; Politis, Anastasios; Manitsaris, AthanasiosThis paper presents an experimental Learning Management System (LMS).The usability aspect of its functions serves as the main focus of this system because the potential for usability problems seems to be especially severe in LMSs, due to their ability to implement complex features and intricate interactions. In order to establish a more efficient e-learning environment, an LMS should have intuitive interfaces and clear information design, allowing learners to concentrate on learning and instructors on learning strategies. The proposed LMS includesall the important functions of delivering learning material, tracking learning activities and managing community tasks, yet by following recent usability techniques it manages to hide all this complexity. Moreover, providing a comprehensive idea of content organization and management along with a simple navigationtool, it allows learnersto focus on their learning activities without excessive hassleandinstructors, especially those unfamiliar withInformation Technologies,to profitably exploittheir learning resources.Τεκμήριο In what sense Regional Convergence? A case study for the Prefecture of Greece 1970-2000(2005) Paschaloudis, D.; Alexiadis, S.This paper explicitly seeks to confront theory with fact regarding regional convergence taking the prefectures of Greece as a case study. The maίn question to be tackled ίη this paper is whether prefectures of Greece converge under conditions of s or b-convergence. The concept of s-convergence is approxίmated empirically by the measures of standard deviation, coefficient of variation and the Herfindahl ratio. The techniques proposed by Baumol and subsequently by Friedman are used for the assessment of b-convergence. The empirical assessment is carried out for the period 1970 to 2000. Empirical results reject the hypothesis of b-convergence, while provide support to s-convergence.Τεκμήριο Sizing stand-alone photovoltaic systems(2005) Balouktsis, A.; Karapantsios, T. D.; Antoniadis, A.; Paschaloudis, D.; Bezergiannidou, A.; Bilalis, N.A method of sizing stand-alone photovoltaic systems regarding the reliability to satisfy the load demand, economy of components, and discharge depth exploited by the batteries is presented in this work. Solar radiation data simulated by an appropriate stochastic time series model, and not actual measurements, are used in the sizing procedure. This offers two distinct advantages: (a) sizing can be performed even for locations where no actual data exist, (b) the influence of the variation of the statistical parameters of solar radiation in sizing can be examined. The method has been applied and tested for several representative locations all over Greece for which monthly daily average values of solar radiation are given by ELOT (Hellenic Organization of Standardization).Τεκμήριο Exploiting Concept Mapping in a Semantic Web Environment(2005) Giouvanakis, Thanasis; Fragidis, Garyfallos; Kehris, Eyaggelos; Samaras, HaidoOntologies provide a formal representation of a conceptualization of a specific domain. This paper proposes an easy and natural way to create ontologies through concept mapping. We also present the well-grounded theoretical framework, which supports concept mapping as a valuable educational activity and as a navigational tool.Τεκμήριο Establishing effective Learning Management Systems through simplicity(2005) Mastoras, Theodoros; Fotaris, Panagiotis; Politis, Anastasios; Manitsaris, AthanasiosDesigning a Learning Management System (LMS) is a combination of pedagogical design, usability and information architecture. E-Learning systems should have intuitive interfaces and clear information design, allowing learners to concentrate on learning and course developers on learning strategies, thus making e-learning more efficient. Hence, effective LMSs should include sophisticated and advanced functions, yet their interface should hide their complexity. In this paper we present the key features of an experimental LMS which follows recent usability techniques in order to accomplish simplicity. The usage of computer file management as a metaphor for management and navigation between Learning Objects (LOs) along with a clear and unambiguous user interface allow users to focus on their learning activities without excessive hassle.Τεκμήριο Optimization of the Method of Auxiliary Sources (MAS) for Scattering by an Infinite Cylinder Under Oblique Incidence(2005) Tsitsas, N. L.; Alivizatos, E. G.; Anastassiu, H. T.; Kaklamani, D. I.This paper presents a rigorous accuracy analysis of the method of auxiliary sources (MAS) for the problem of oblique incidence plane wave scattering by a perfectly conducting, infinite circular cylinder. For this particular scattering geometry, it is shown that the MAS matrix is inverted analytically, via eigenvalue analysis, and an exact mathematical expression for the discretization error is derived. Furthermore, the computational error, resulting from numerical matrix inversion, is calculated and compared to the analytical one, showing perfect fit for a wide range of the auxiliary sources' locations. The irregular behavior of the computational error for small values of the auxiliary sources' radii is explained by the corresponding high values of the linear system's condition number. It is also demonstrated that specific source locations, associated with the characteristic eigenvalues of the scattering problem, should be avoided, because then both computational and analytical error increase very abruptly. The dependence of the computational and analytical error on the angle of incidence is thoroughly investigated. Finally, the optimal location of the auxiliary sources is determined on the grounds of error minimization.Τεκμήριο The Business Strategy Perspective on the Development of Decision Support Systems(2005) Fragidis, G.; Tarabanis, K.This article examines the support that information systems may provide to the strategy process in business organisations. Being the process through which organizations make decisions for their future, strategy is very important in organisations. Early enough, systems that supported decision making were developed. In the mid of 1980s a new stream of information systems aimed at addressing the specific needs of executives. However, these systems used to serve as general purpose systems for top management needs and did not focus on the business strategy process per se. There is plentiful evidence that these systems do not, in fact, meet the expectations of business strategists. Based on a literature survey in the field of business strategy, this article identifies the needs of the business strategy process, demonstrates the shortcomings of current approaches in the development of information systems that support strategic decision making and proposes implications for the development of information systems that support business strategy.