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Τεκμήριο 3DSSE – A 3D Scene Search Engine: Exploring 3D scenes using keywords(2012) Koutsoudis, Anestis; Stavroglou, Konstantinos; Pavlidis, George; Chamzas, ChristodoulosThe evolution of real time 3D graphics technologies in combination with high bandwidth Internet connections and modern Web browsers enable users to explore complex 3D scenes. As a rule, a virtual visitor has to manually explore the geometrically complex 3D model in order to discover points of interest. This manual exploration is a time consuming process that, in some cases, can be assisted by sets of predefined points of interest. In this paper, we propose the annotation of 3D scenes in order to equip the user with a text based 3D scene search engine. The search engine provides a query mechanism that unburdens the user from the time consuming process of manually exploring vast 3D scenes. It responds to queries by exploiting the metadata of each 3D model and returns textual and visual information along with a group of links that correspond to relative points of interest within the 3D scene. The search engine allows the virtual visitor to automatically be transferred to a specific point of interest. We have built a Web accessible prototype system that is able to handle queries related to historical data, topological relationships and architectural properties of buildings. A number of 3D reconstructions covering urban areas of cultural importance located in Northern Greece have been annotated and used in the search engine as case studies. The prototype system is based on open source technologies and on a hybrid metadata schema that is derived from the MIDAS Heritage and MACE schemas.Τεκμήριο A Computational Model for Path Loss in Wireless Sensor Networks in Orchard Environments(2014-03) Anastassiu, Hristos T.; Vougioukas, Stavros; Fronimos, Theodoros; Regen, Christian; Petrou, Loukas; Zude, Manuela; Käthner, JanaA computational model for radio wave propagation through tree orchards is presented. Trees are modeled as collections of branches, geometrically approximated by cylinders, whose dimensions are determined on the basis of measurements in a cherry orchard. Tree canopies are modeled as dielectric spheres of appropriate size. A single row of trees was modeled by creating copies of a representative tree model positioned on top of a rectangular, lossy dielectric slab that simulated the ground. The complete scattering model, including soil and trees, enhanced by periodicity conditions corresponding to the array, was characterized via a commercial computational software tool for simulating the wave propagation by means of the Finite Element Method. The attenuation of the simulated signal was compared to measurements taken in the cherry orchard, using two ZigBee receiver-transmitter modules. Near the top of the tree canopies (at 3 m), the predicted attenuation was close to the measured one—just slightly underestimated. However, at 1.5 m the solver underestimated the measured attenuation significantly, especially when leaves were present and, as distances grew longer. This suggests that the effects of scattering from neighboring tree rows need to be incorporated into the model. However, complex geometries result in ill conditioned linear systems that affect the solver's convergence.Τεκμήριο A host/co-processor FPGA-based Architecture for Fast Image Processing(2007) Kalomiros, John; Lygouras, JohnA general system architecture for fast image processing, based on a Field Programmable Gate Array (FPGA) co-processor and a host computer, is presented and evaluated. Images are transferred to the FPGA board via a high speed USB2.0 channel, implemented with a standard macrocell. A LabVIEW host application controlling a frame grabber and an industrial camera is used to capture and exchange video data with the hardware co-processor. The FPGA accelerator is based on a Altera Cyclone II chip and is implemented as a system-ona- programmable-chip (SOPC) with the help of an embedded Nios II software processor. The SOPC system integrates the processor, external and on chip memory, the communication channel and a typical image filter appropriate for the evaluation of the system performance. Measured transfer rates over the communication channel and processing times for the implemented hardware filters are presented for various frame sizes. A range of applications is also discussed.Τεκμήριο A reconfigurable architecture for robotic stereo vision(2012) Kalomiros, John; Lygouras, JohnA reconfigurable architecture for dense stereo is presented as an observation framework for a real-time implementation of the simultaneous localization and mapping problem in robotics. The reconfigurable sensor detects point features as corners from stereo image pairs, in order to use them at the measurement update stage of the procedure. The main hardware blocks are a dense depth stereo accelerator, a left and right image corner detector and a stage performing left-right consistency check for the detected features. For the stereo-processor stage we have implemented and tested both a localmatching method based on the Sum of Absolute Differences (SAD) and a global-matching component based on a maximum-likelihood dynamic programming technique (MLDP). The system includes a Nios II processor for data control and a USB 2.0 interface for host communication. The proposed hardware is applied as the sensor part in a real-time robotic localization and mapping experiment with the help of a small guided vehicle.Τεκμήριο Acceleration of image processing algorithms using minimal resources of custom reconfigurable hardware(2012) Vourvoulakis, John; Kalomiros, John; Lygouras, JohnThe hardware/software implementation of a custom vision board using minimal resources out of a reconfigurable platform is described. Demanding robotic vision applications in most cases require dedicated hardware for reliable operation. The designed system is based on a Cyclone IV Altera FPGA device that constitutes the main processing unit of the reconfigurable hardware and on a 32–bit Microchip PIC32 microcontroller as a complementary processor. The main goal of this research is to implement image processing algorithms using only minimal resources of the FPGA device. The microcontroller serves peripheral control tasks, relieving valuable resources from FPGA. Video images are captured using a CMOS image sensor. USB connectivity with a personal computer is provided using a FIFO-to-USB module. Operational tasks such as frame grabbing, image filtering and USB communication are integrated to the system by implementing custom-designed controllers in VHDL. Image processing functions are accelerated using a fully parallel pipeline which is described analytically. A host computer interface has also been developed in order to test the overall system in action. The system is evaluated in terms of resource usage and the advantages emanating from the proposed architecture are discussed.Τεκμήριο An accounting comparison of the post-merger economic performance of greek acquiring listed firms in domestic versus international M&As at Southeast Europe(2011) Agorastos, Konstantinos; Pazarskis, MichailThis study examines the impact of M&As on the economic performance of merger-involved firms in Greece at domestic and international M&As using accounting data (financial ratios). The post-merger performance of a sample of acquiring listed firms involved in domestic M&As is compared with an equivalent sample of firms with similar characteristics involved in international M&As. The results revealed in general that the international M&As have provided a better post-merger economic performance for the acquiring firms than the domestic M&As, and in contrast to the general economic performance of all listed firms in this period also have had a superior performance.Τεκμήριο An accounting examination of the long-run performance of greek acquiring firms(2011) Pazarskis, Michail; Lyroudi, Katerina; Pantelidis, Panagiotis; Christodoulou, PetrosThis paper examines empirically the impact of M&As on the post-merger performance of Greek merger-involved firms in the long-run perspective. Τhe post-merger performance of an extensive sample of acquiring listed firms is investigated with accounting data analysis. For the purpose of the study, an explanatory set of 24 financial ratios (divided into five main groups) is employed, in order to measure firms’ post-merger performance. The results revealed that six out of all the examined ratios had decreased and showed, in general, deterioration in several business functions of merger-involved firms’ performance in the post-merger period.Τεκμήριο Affine transformation invariant image watermarking using moment normalization and radial symmetry transform(2011-09) Nikolaidis, A.A novel technique for image watermarking aiming at robustness against geometrical attacks is proposed in the current paper. The first stage relies on computing a normalized version of the original image using image moments. A radial symmetry transform is then applied to the normalized image, followed by a non-maxima suppression step. The feature points extracted this way act as centers of the area where the watermark is to be embedded. To minimize image distortion, we embed the inversely normalized watermark (initially formed in the DCT domain) in the original image. The detection process consists of normalizing the input image, applying the radial symmetry transform and extracting the feature points, after which a correlation detector is employed to detect the possibly inserted watermark in the normalized image. Experimental results prove the robustness of the method against affine geometrical transform attacks, as well as other image processing operations.Τεκμήριο Alfven modes driven nonlinearly by metric perturbations in Anisotropic Magnetized Cosmologies(2007) Kuiroukidis, Apostolos; Kleidis, Kostas; Papadopoulos, Demetrios B.We consider anisotropic magnetized cosmologies filled with conductive plasma fluid and study the implications of metric perturbations that propagate parallel to the ambient magnetic field. It is known that in the first-order (linear) approximation with respect to the amplitude of the perturbations no electric field and density perturbations arise. However when we consider the nonlinear coupling of the metric perturbations with their temporal derivatives, certain classes of solutions can induce steeply increasing in time, electric field perturbations. This is verified both numerically and analytically. The source of these perturbations can be either high-frequency quantum vacuum fluctuations, driven by the cosmological pump field, in the early stages of the evolution of the Universe, or astrophysical processes, or a nonlinear isotropization process, of an initially anisotropic cosmological space–time.Τεκμήριο Analysis of quantitative profiles of GI Education: towards an analytical basis for EduMapping(Springer Berlin Heidelberg, 2011) Rip, Frans; Grinias, Elias; Kotzinos, DimitrisThere is an ongoing discussion among the members of the GI educational community about the possibility to find a common way to describe a course taught as part of a GI curriculum (anywhere in the world) with the final goal of being able to automatically identify similar courses and define their equivalence. EduMapping is such an initiative that started recently, which used the BoK concepts as its basic labeling scheme. Based on this work we extended the analysis provided by the EduMapping initiative by suggesting and applying an analytical method that is capable of clustering the courses into classes based on (dis)similarity metrics, which are in turn calculated based on the course assessments done by their instructors using the BoK concepts. In this paper, we present and discuss the preliminary results obtained while applying the suggested method on the EduMapping data. We also provide some pointers for further research in an area that has very few contributions so far.Τεκμήριο Analytical Estimation of Economic Loss for Buildings in the Area Struck by the 1999 Athens Earthquake and Comparison with Statistical Repair Costs(2007-05) Kappos, A.; Lekidis, V.; Panagopoulos, G.; Sous, I.; Theodulidis, N.; Karakostas, Ch.; Anastasiadis, T.; Salonikios, T.; Margaris, B.Reliable loss assessment (in monetary terms) for buildings struck by an earthquake is an essential factor in the development of seismic risk scenarios for a given urban area. The evaluation of loss due to building damage in a certain region depends both on seismic hazard and the vulnerability of the building stock in the area. The study presented herein consists of predicting the loss to selected groups of buildings struck by the 1999 Athens earthquake using an analytical methodology and comparison with statistical repair costs collected after the earthquake. Since no near-field strong ground motion recordings from the main shock were available, a pilot methodology was used for its analytical evaluation for different soil conditions. Different suites of motions were derived, based on various theoretical and semi-empirical approaches, and were then used in analytical investigations of the seismic behavior of the buildings in the examined area, aiming at the prediction of economic losses. An in-situ survey of about 10% of the total building stock was performed, and data regarding the structural type, actual earthquake damage, and corresponding repair costs were collected. The statistically derived repair cost for the area was compared with the economic loss estimation obtained using the analytical procedure and various estimates of the seismic action in the area considered, and was found to agree with it reasonably for some of the seismic hazard scenarios.Τεκμήριο Analytical modeling of masonry infills with openings(2009-03-10) Kakaletsis, DimitriosIn order to perform a step-by-step force-displacement response analysis or dynamic time-history analysis of large buildings with masonry infilled R/C frames, a continuous force-deformation model based on an equivalent strut approach is proposed for masonry infill panels containing openings. The model, which is applicable for degrading elements, can be implemented to replicate a wide range of monotonic force-displacement behaviour, resulting from different design and geometry, by varying the control parameters of the model. The control parameters of the proposed continuous model are determined using experimental data. The experimental program includes fifteen 1/3-scale, single-story, single-bay reinforced concrete frame specimens subjected to lateral cyclic loading. The parameters investigated include the shape, the size, the location of the opening and the infill compressive strength. The actual properties of the infill and henceforth the characteristics needed for the diagonal strut model are based on the assessment of its lateral resistance by the subtraction of the response of the bare frame from the response of the infilled frame.Τεκμήριο Analyzing value co-creation in service systems: contribution from GORE(2011-03) Fragidis, Garyfallos; Tarabanis, KonstantinosService systems are characterized mostly by the co-creation of value in the interactions between service providers and customers. In this paper we examine the possibility to use GORE methodologies and techniques for the analysis of value cocreation in service systems. We regard value co-creation as an abstract, high-end goal of the customer that is accomplished through the integration of service from providers and the complementary application of proprietary resources from the customer and examine the possibility to analyze it with AND/OR goal diagrams. In addition, we examine six GORE methodologies and assess their relevance to the requirements analysis of value co-creation. The results show that GORE can provide a promising methodological foundation for the analysis of value co-creation. In particular, softgoals and “satisficing” objectives are extremely useful in analyzing value co-creation and the representation of services as nodes in AND/OR graphs can elicit both the valuerelated and the activity-related properties of the notion.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 Application of optimal control in man power planning(2010-02-01) Mouza-Lazaridi, Anna-MariaMany techniques are met in the literature (see for instance Bartholomew and Forbes (Statistical Techniques for Manpower Planning. wiley, New York 1979); Gunz (Organiz. Stud. 9(4), 529–554, 1988); Becker and Huselid (Human Resour. Manage. 38, 287–301, 1999); Wagner et al. (J. Manage. Med. 14(5/6), 383–405, 2000); Harris and Ogbonna (J. Business Res. 51, 157–166, 2001); Rogg et al. (J. Manage. 27, 431–449, 2001), among others), for planning the manpower resources. However, we haven’t seen in the literature an empirical study regarding the proper application of optimal control, which considered to be the most efficient method for multi-objective programming. With this in mind, we analyse in this paper the way of applying optimal control for manpower planning. For this purpose, and in order to facilitate the presentation, we first adopted a comparatively simple dynamic system (plant), with analytical presentation of stocks and flows. Next we proceed to the formulation of an optimal control problem, aiming to achieve in the most satisfactory way some preassigned targets. These targets mainly refer to a desirable trajectory of the plant stocks over time, in order to fully satisfy the needs for human resources over the planning horizon. Finally we present a method of solution of the formulated control problem which is based on the use of the generalized inverse Lazaridis (Qual. Quan. 120, 297–306, 1986). We believe that it is very important for successful management, that the policy makers have to know the effect of their polices and to determine the optimal path of the state variables (i.e. the ones describing the system) before the realization of the plan, so as to be able to reform their strategies, reallocate the resources and arrange the infrastructure accordingly, if all these are necessary, as it can be depicted from the optimal control solution.Τεκμήριο An application of supervised and unsupervised learning approaches to telecommunications fraud detection(2008-10) Hilas, Constantinos S.; Mastorocostas, Paris A.This paper investigates the usefulness of applying different learning approaches to a problem of telecommunications fraud detection. Five different user models are compared by means of both supervised and unsupervised learning techniques, namely the multilayer perceptron and the hierarchical agglomerative clustering. One aim of the study is to identify the user model that best identifies fraud cases. The second task is to explore different views of the same problem and see what can be learned form the application of each different technique. All data come from real defrauded user accounts in a telecommunications network. The models are compared in terms of their performances. Each technique’s outcome is evaluated with appropriate measures.Τεκμήριο Application of the symmetry eigenvalue approach to the analysis of a PCS-type ceramic monoblock filter(2007) Tsitsos, S.; Kyriazidis, P.; Gibson, A. A. P.The symmetry concept for the analysis of symmetrical waveguide discontinuities using the eigenvalue approach is applied to the analysis of a 3-pole monoblock ceramic PCS-type filter. It is demonstrated how the symmetry technique substantially reduces simulation times and improves accuracy.Τεκμήριο Applying QE-DEA in the evaluation of the Greek public sector: the case of the agencies for aliens and immigration of the Decentralized Administration of Macedonia and Thrace(2013) Dimitriadis, Sotirios; Karakitsiou, Athanasia; Mitsopoulou, OlgaThe public administration is entering a new area of rapid reform and restructuring aiming at enhancing its efficiency and effectiveness. The purpose of the present work is to investigate the degree of effectiveness of the Greek public sector applying the QE-DEA model. The results reveal those departments that more efficiently carry out their activities as well as those found to be relatively less effective. For the latter, QE-DEA can recommend specific potential improvements if they wish to operate at what appears to be the best practice.Τεκμήριο Are acquiring firms better off after an acquisition? Evidence from a knowledge-intensive industry in Greece(2011-07) Pazarskis, Michail; Alexandrakis, Alexandros; Notopoulos, Panagiotis; Kydros, DimitriosThis study examines the impact of mergers and acquisitions (M&As) on the post-merger operating performance of merger-involved firms in Greece at information technology industry, a knowledge-intensive industry. Using accounting data (financial ratios), the post-merger performance of all the Greek companies, listed on the Athens Stock Exchange at information technology industry, that executed one merger or acquisition in the period from 2004 to 2007 as acquirers (a sample of five firms), is investigated and the degree their successful knowledge transfer to the new merged firm is evaluated. For the purpose of the study, a set of eleven ratios is employed, in order to measure acquiring firms’ operating performance and to compare pre- and post-merger operating performance for two years before and after the M&A announcements. The results revealed that M&As had a negative impact on the post-merger performance of the mergerinvolved firms from a knowledge-intensive industry, concerning their total debt analysis, two years after the M&A transaction. Also there were not some other positive or negative impacts at any other examined ratio, which reveals a possible successful transfer of knowledge, but not the creation of potential synergies or cost reductions.Τεκμήριο Assembly line balancing and group working: A heuristic procedure for workers’ groups operating on the same product and workstation(2006-09) Dimitriadis, Sotirios G.In this paper, we examine an assembly line balancing problem that differs from the conventional one in the sense that there are multi-manned workstations, where workers’ groups simultaneously perform different assembly works on the same product and workstation. This situation requires that the product is of sufficient size, as for example in the automotive industry, so that the workers do not block each other during the assembly work. The proposed approach here results in shorter physical line length and production space utilization improvement, because the same number of workers can be allocated to fewer workstations. Moreover, the total effectiveness of the assembly line, in terms of idle time and production output rate, remains the same. A heuristic assembly line balancing procedure is thus developed and illustrated. Finally, experimental results of a real-life automobile assembly plant case and well-known problems from the literature indicate the effectiveness and applicability of the proposed approach in practice.