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- ItemOpen AccessSuper-resolution ultrasound imaging
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2022-10-31) Κοτσαρίνης, Νικόλαος; Kotsarinis, NikolaosRecently, research studies have shown a rapid increase of several types of cancer which are attributed to many factors such as air pollution, unhealthy diet, modern living, random mutations etc. An important type of cancer among men that is clearly accused of high death rate if it is not diagnosed in time, is prostate cancer. Prostate cancer is being diagnosed after following a specific protocol which of course includes a TRUS-guided biopsy, usually after having an MRI scan. US has been undoubtedly considered as an imaging modality which can compete with MRI due to its low cost, the real-time imaging possibility, its portability, its non-radiation effects and its relatively easy user’s operation. On the other hand, its poor spatial resolution, often an MRI or CT-scan is required to make an accurate diagnosis of a disease regarding soft tissues. CEUS has come to bridge this gap, since it introduces UCAs, non-linear scatterers of the sound wave. These agents, often called MBs, are infused in the blood in a specific region to be scanned. A US transducer produces sound waves at a specific frequency. The MBs reflect the transmitted signal, since they are strong scatterers of sound waves, and the reflected signal is received by the transducer again. This procedure is based on the piezoelectric effect of certain materials. This means that when an electric field is applied to them they produce sound waves, but also the opposite. Thus, an image with high contrast can be achieved. Of course there are several methods that utilize the non-linear effect of the MBs and distinguish it from the surrounding tissues, called the contrast-specific imaging techniques. Many of them take advantage of the high mechanical index, while others use the low mechanical index, especially when continuous real-time imaging is necessary. This modality can be used for visualizing the micro-vascularity of the prostate gland in super-resolution using accurate localization-based detection procedures. Since, it is known that there is high correlation between micro-vascularity and cancer growth, it is very important to create US images which can provide the clinician with information about the vascular bed and possibly a tumor growth at early or more progressive stages. After detecting these MBs in super-resolution images, there comes the part, where the tracking procedure is taking place. Usually, a frame sequence of the contrast-enhanced images of the prostate is available and the MBs detected using localization techniques, have to be linked in sequential frames in order to create the tracks of each MB and thus the vessels in which the MBs are flowing into. Several Algorithms have been developed for dealing with the tracking problem, mainly divided in two sub-categories, the deterministic and the probabilistic. The deterministic approach is assumed to be a more conservative method for dealing with tracking and it is based on the optimization of the assignment problem like the Nearest-Neighbor algorithm, after having accurately localized the targets. The probabilistic approaches, on the other hand, have been recently introduced to deal with the tracking problems and it seems that they lead to more accurate and reliable results than the previous ones, since they are based on the prediction of the trajectory using the prior knowledge of measurements like locations or velocities, thus creating realistic probabilities of a certain MB to be linked with another MB. In this study a new tracking algorithm is introduced, the BM3D plus Rho, which utilizes the correlation between MBs in sequential frames to form links inside tracks. Of course, a thorough investigation of MB size and other characteristics is preceded. The new algorithm uses data taken from manually collected tracks in a sample of the population in order to optimize the linking procedure on a link-based level. A new detection filter is also added which leads to even more accurate localizations. During the analysis, an evaluation procedure is taking place using synthetic data produced by an algorithm, and thus a more robust comparison can be achieved. In this study, It was found that the vector angle correlation between MBs inside the same track range from 0 to 23 (angle in degrees) for the sample and dataset SRI001, which of course can be used in other datasets such as SRI010, in which the resulting maps were clearly improved even if the maximum correlation value is not know from a respective sample, like in SRI001. Resulting track number maps, velocity maps and blood flow maps show that the vessels can be clearly separated and the noisy areas have been reduced compared to the previous version of the algorithm. Thus the micro-vascularity of the prostate in both datasets with different MB size distributions and PSFs is depicted clearly, and of course enhanced correctly in the expected areas. It was found also, that the long tracks which the algorithm calculated do not locate inside the cancer area, but in the healthy regions, and this information is important for assessing also the differences between the cancer and the healthy area. The detection due to the filter showed an almost 2% improvement in the detection part. The tracking was improved by a significant percent since the vessels in the maps are very well structured and also the areas which contain already confirmed vessels have greater amplitude than before. The mean link per track has risen about 6% while the total tracks and links formed have risen in SRI001 by 5.2% and 11.9% respectively, and the fact that the high density areas are enhanced, is a strong indicator that these rise in links and tracks includes correct additions.
- ItemOpen AccessModeling of the pathway of multiciliated cells' differentiation
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2022-11-10) Γκάντζου, Βασιλική; Gkatzou, VasilikiMulticiliogenesis constitutes an important biological process in which progenitor cells differentiate into multiciliated cells (MCCs). These cells are located in various biological systems, performing important biological functions such as: ensuring the circulation of cerebrospinal fluid in CNS (Central Nervous System), removing extraneous pollutants from the respiratory tract, transporting gametic cells during fertilization and many others. The aim of this diploma thesis is to study multiciliogenesis at the level of protein interactions. We examine whether our designed mathematical model is capable enough of describing the behavior of the proteins we have chosen as key factors of this biological phenomenon. More specifically, our mathematical model consists of ordinary differential equations (ODEs), each one expresses the rate of change in the concentration of one of the regulatory proteins: Geminin, Lynkeas, McIdas. For the parameter estimation of the model, we use experimental data and a calculated estimator as a comparison measurement. The results of the simulations we run, show that the designed for Geminin equation verifies with great precision qualitatively and quantitatively its behavior, as it is presented on the experimental data. On the other hand, the designed system of Lynkeas/McIdas equations, while qualitatively seems to follow the behavior seen in the experimental data, failed to quantitatively describe the experimental data. In this work, we decide to examine the simplest form of this mathematical model, where in the system of Lynkeas/McIdas equations, we integrate the negative effect of McIdas to Lynkeas in the simplest form. More complex forms of equations may describe more precisely the behavior of these proteins in the biological phenomenon under study.
- ItemOpen AccessPhysical breast phantoms for X-ray imaging employing 3D printing techniques
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023) Πετράι, Άντζελα; Petrai, AntzelaCancer is one of the most severe diseases, and many studies have been conducted to investigate possible treatments for it. Cancer is characterized by abnormal cell growth and the ability to invade tissues and distant organs. Breast cancer is the leading cause of cancer death in women worldwide and the risk factors may vary according to several conditions. Menarche and the menstrual cycle, childbearing, menopause, diet, and exercise are some of these factors. The female breast is composed of adipose, glandular, and soft tissues and lymph nodes which create the lymphatic route, which is the main route for breast cancer metastasis. Breast cancer has always been studied by the scientific world and combined with the constant evolution of technology, important tools have been developed in order to detect and diagnose cancerous tumors. Conventional mammography and digital breast tomosynthesis are specialized medical imaging devices that display these abnormal masses of tissue. Three-dimensional printing is another excellent example of the evolution in the biomedical field, providing several applications. Physical breast phantoms are one of them. Physical breast phantoms are physical models of the breast developed by ‘mimicking’ materials to assess the image quality of the breast. This project mainly focuses on the study of the appropriate materials, suitable for the development of physical breast phantoms for breast X-ray imaging. Six thermoplastic materials were investigated and printed by employing the fused deposition modeling technique of 3D printing and two photopolymer resins by employing the stereolithography technique of 3D printing. 3D cubes made of ABS, PLA, PLA_Pro, Nylon, CPE, PET_G, Clear, and Purple were printed for optimal breast tissue imaging based on their attenuation coefficient (μ) and phase contrast. The X-ray exposure took place at Freiburg University Hospital and have been studied back at University of Patras.
- ItemOpen AccessDevelopment of virtual reality (VR) graphical user interface for learning the human body
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-02-10) Αλεξόπουλος, Δημήτριος; Alexopoulos, DimitriosIn this thesis we created a virtual environment for the users and a graphical user interface. Based on this environment a user can see the different parts of the human body. The circulatory system, the muscles, the nervous system, and the rest of the elements that make up the human body will be able to advance the user. The users have full control over what they see. Using virtual reality (VR) the users can see the human body unfold before them. They can rotate, grab, zoom and examine the parts of the human body in detail. After the creation of the app an evaluation was performed. During this evaluation the factors that affect the presence in virtual environments were measured. Also, an SUS questionnaire was used to measure the system usability. In total, 21 participants took place in the evaluation and filled the questionnaire. They results are interested and showed that, users who had previous virtual experiences performed better in our virtual environment. Our app is placed in a good place in the system usability scale through the SUS questionnaire. After the evaluation and the results, we performed some changes in the app to make users have a better experience.
- ItemOpen AccessCurrent insight into kidney fibrosis and the role of EGFR as a potential therapeutic target
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-02-17) Κουκουτσίδη, Παναγιώτα; Koukoutsidi, PanagiotaThe epidermal growth factor receptor (EGFR) is a member of the ErbB/HER family of receptors and its expression can be detected in almost every tissue of the human body. EGFR is a receptor tyrosine kinase with 11 known ligands. Over the years, researchers have conducted numerous experiments to determine the structure and the receptor’s potential implications in human physiology and pathophysiology. Renal fibrosis is the final common manifestation of a wide variety of chronic kidney diseases such as diabetic and obstructive nephropathy. Chronic kidney disease carries significant impact for the patients’ lives and its management poses a challenge for the physicians and the healthcare systems globally, especially due to its high prevalence. Τhis thesis presents a description of the normal ECM, the fibrotic process and its major mediators. Hereupon and based on the current literature, researchers argue that sustained or dysregulated activation of EGFR leads to renal fibrosis via the following mechanisms: a) activation and increased expression of TGF-β1, b) arrest of epithelial cells in the G2/M phase of cell cycle, and c) excessive production of cytokines and chemokines. Furthermore, the role of two EGFR ligands, amphiregulin and heparin-binding EGF, in the fibrotic process is explained. EGFR could be used as a therapeutic target for the treatment of chronic kidney disease. Nevertheless, extensive research has yet to be conducted to elucidate the exact molecular pathways implicated in EGFR activation. The aim of the thesis is to lay emphasis on the structural and functional complexity of the kidney and to explain the most prominent information about EGFR along with its role in chronic kidney disease. It also aims to highlight the absence of clinical trials that test specific anti EGFR agents as potential therapeutic agents for renal fibrosis. The interdisciplinary approach that was followed is essential for every scientist who wishes to dive into research and address elaborate clinical challenges.
- ItemOpen AccessSmart grid management on distributed generation systems with RES and storage units
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-03-01) Αλεξάκης, Ζάιντ; Alexakis, ZaintThe rapid integration of renewables into the daily production schedule has greatly increased the complexity of today’s contemporary power systems. These sources suffer significantly from variability in terms of production due to their large dependance on ambient conditions. As the main purpose of a power system is to ceaselessly supply the demand, in a supervised manner, renewables are usually installed in systems in ways that facilitate cooperation between them and conventional power sources. These systems are known as microgrids and they combine distinct renewables and conventional power sources to either supply local demand or inject power to the grid. The introduction of such complex systems has also led to the need of proper control algorithms that can accommodate their performance. The general notion of a microgrid is not a novel term, but had been first introduced in the late 1950s. Nevertheless, the conventional control systems that have been developed, mainly dismiss dynamic response and unfortunately these assumptions may lead to a system failure due to unaccounted parameters. In this frame, researchers mainly focused on model-based analysis and development of model-based control algorithms, that regulate these contemporary power systems dynamically, while only making mild assumptions that do not significantly restrict the operation bounds of the final system. Furthermore, the results of the control design are also exploited to appropriately select system parameters that can facilitate its operation and improve the response of the applied control scheme. The proportional and integral controllers constitute the main blueprint of these controllers and have been repeatedly proven to be quite efficient when regulating power systems, but without proper analysis, they may fail to control more complex installations such as those of the microgrids. Thus, a proper stability analysis is important when applying any type of control scheme that aims to regulate specific states of a larger system. Even though PI-based control schemes are usually able to achieve the control design goals, they unfortunately suffer from lack of adaptation and when they are applied in more complex systems, where strict transfer functions cannot be derived, it is almost impossible to control parameters such as overshoots, oscillations or even settling time. Solution to this problem is provided with the introduction of Artificial intelligence. More specifically, intelligent controllers such as neuro-fuzzy techniques and Neural Networks are able to adapt their output in a way that minimizes specific cost functions. Unfortunately, though, they lack vital stability foundations and that’s the main reason why researchers have not yet introduced effective AI-based control schemes. In this frame, main purpose of this thesis is to design, control and implement a novel microgrid that combines distinct renewable power sources that are regulated by an elaborate energy storage system. The microgrid consists a Permanent Magnet Synchronous Generator-based wind-turbine and a PV panel farm. The microgrid operates in two unique modes known as grid-following and grid-forming. In the former, the microgrid control design goal is to inject set amounts of active power to the grid, while the power sources are regulated to operate in maximum power point mode. In grid forming mode, the microgrid’s sole purpose is to supply local loads under nominal voltage and frequency conditions, whereas the power sources proportionally share the load power through a novel droop technique. Details on the modeling and design of the interface of the power system that provides the ability to control and interconnect the renewable power sources are also provided. Furthermore, based on the equivalent average model, a rigorous control system is developed that is based on the highly-efficient cascaded-PI scheme and relies on the time separation principle. Finally, to prove the efficiency of AI-based controllers, suitable Neural Networks were properly trained, under various circumstances, to improve the transient response of the conventional control technique. Hence, simulation results pertaining the response of the microgrid that took place on Matlab’s Simulink virtual environment, are provided for both the cascaded-PI scheme-based system and the Neural network one, to facilitate their comparison, where it is found that the later significantly, improves the system transient response and therefore the potential of AI-control algorithms on power system applications is established.
- ItemOpen AccessElectroencephalogram brain computer interface during inner speech
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-04-05) Ζαρμπούτης, Δημήτριος; Zarmpoutis, DimitriosThe scope of the present thesis was to investigate whether a set of electroencephalography data obtained from an already conducted study was suitable for Brain Computer Interface applications. Brain Computer Interfaces are a technology that allows the direct communication between the brain and an outside device which can be either a computer or any other artificial machinery. Brain Computer Interfaces achieve so by bypassing the normal physiological way in which the brain communicates the messaging and connecting it directly to the outer device. Regarding the experimental procedure, the data were acquired from ten healthy subjects in a study that was published by Argentinean researchers where the magnitudes such as Event Related Potentials, Inter Trial Coherence and Power Spectral Density were calculated for the total number of subjects. Subjects were presented with 4 visual cues which corresponded to the classes “up”, ”down”, ”right” and “left”. The experimental procedure was repeated both for imaging and for pronouncing the prompts. What was done was to compute the same magnitudes for each separate subject and for each separate class out of the four that were presented in the initial experiment. The conditions that we compared were two: inner speech and pronounced speech. After the extraction of the diagrams, the computational procedure was repeated but this time concentrating only in the channels that corresponded to Broca’s area which is the brain area that is mainly responsible for the production of speech. We used the MNE package written in python which is a computational tool for importing and processing electroencephalography data. It possesses significant advantages since it is open source and consequently can be implemented free of charge. The outcomes of our study showed significant differences in Event Related Potentials between each one of the subject. However, for the same subject and for each one of the separate classes the differences were negligible. As far as the inter trial coherence and power diagrams were concerned, again we observed significant similarities for the four classes but for the same subject and significant differences from subject to subject. It has to be mentioned that the outcomes for the selected channels being concentrated only in Broca’s area were more or less similar to the ones for the total number of channels. Additionally to the already acquired outcomes, a further statistical analysis was conducted which consisted firstly by the computation of the topographical display of the power for each one of the subjects and for the two separate conditions but simultaneously for all of the four classes. Secondly, the time frequency plots and the power spectral density plots were computed. The final part of this statistical analysis is the computation of event related synchronizations and desynchronizations and three series of diagrams were constructed in this computational process. Firstly, the event related synchronizations and desynchronizations in bands which were computed for the four classes in sum, secondly the event related synchronizations and desynchronizations analyzed through the time frequency responses and finally the violin plots of event related synchronizations and desynchronizations. After the further evaluation of the data through the statistical analysis it has to be stated the goal of drawing the conclusion that the data are suitable for a brain computer interface application in the inner speech modality has not been fully achieved.
- ItemOpen AccessΑνάλυση και έλεγχος ηλεκτρομηχανικού συστήματος έλξης με ελεγχόμενη υποστήριξη υπερπυκνωτή
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-04-06) Λαμπίρης, Σπυρίδων; Lampiris, SpyridonΗ ηλεκτροκίνηση κερδίζει συνεχώς έδαφος σε παγκόσμιο επίπεδο και τείνει να κυριαρχήσει έναντι των θερμικών κινητήρων. Το μεγαλύτερο μειονέκτημά της (και μάλλον το μοναδικό ) είναι η μικρή αυτονομία λόγω των συσσωρευτών. Προς λύση αυτού του θέματος διεξάγεται συνεχώς έρευνα σε παγκόσμιο επίπεδο με ενθαρρυντικά αποτελέσματα. Η παρούσα μεταπτυχιακή εργασία μελετά τη συμπεριφορά ενός Ηλεκτρομηχανικού Συστήματος Έλξης με Ελεγχόμενη Υποστήριξη Υπερπυκνωτή. Πρόκειται στην ουσία για την τροφοδότηση από συσσωρευτή και τον έλεγχο μέσω ηλεκτρονικών διατάξεων ελέγχου ενός σύγχρονου κινητήρα μόνιμου μαγνήτη που χρησιμοποιείται στα ηλεκτρικά αυτοκίνητα. Η διάταξη υποστηρίζεται από υπερπυκνωτή για κάλυψη επιπλέον ισχύος. Όσον αφορά τη δομή της εργασίας, αρχικά παρουσιάζεται μια ιστορική αναδρομή της ηλεκτροκίνησης όπου και γίνονται σαφής οι συνθήκες επικράτησης της ηλεκτροκίνησης στις μέρες μας. Ακολουθεί το μια ανάλυση των χαρακτηριστικών και των συσσωρευτών που χρησιμοποιούνται στην ηλεκτροκίνηση και των αντιστροφέων που χρησιμοποιήθηκαν στο σύστημα που υλοποιήθηκε. Στη συνέχεια παρουσιάζονται τα χαρακτηριστικά των σύγχρονων κινητήρων μόνιμου μαγνήτη και του διανυσματικού ελέγχου που αποτελεί μέθοδο ελέγχου των κινητήρων αυτών. Στη συνέχεια αναλύεται η δομή και η λειτουργία των υπερπυκνωτών. Τέλος παρουσιάζονται τα δομικά χαρακτηριστικά του υλοποιηθέντος συστήματος και τα αποτελέσματα της προσομοίωσής του.
- ItemOpen AccessΜελέτη λειτουργίας ανεμογεννήτριας
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-06-08) Καλλιανέζος, Παντελής Θωμάς; Kallianezos, Pantelis ThomasΣτόχος της παρούσας μεταπτυχιακής διπλωματικής εργασίας είναι ο έλεγχος ενός διασυνδεδεμένου συστήματος διεσπαρμένης παραγωγής ηλεκτρικής ενέργειας με το δίκτυο. Το σύστημα που μελετάται αρχικά, αποτελείται από μια ανεμογεννήτρια μεταβλητών στροφών, με τη γεννήτριά της να είναι μια σύγχρονη γεννήτρια μόνιμου μαγνήτη, η οποία συνδέεται στο δίκτυο μέσω 2 ηλετρονικών μετατροπέων ισχύος, ενός Ανορθωτή και στη συνέχεια ενός αντιστροφέα. Επιπλέον μελετάται το ίδιο σύστημα, πρoσθέτοντας κι έναν super capacitor, ο οποίος συνδέεται μέσω ενός back boost μετατροπέα στο dc link, δηλαδή ανάμεσα από τους 2 παραπάνω ηλεκτρονικούς μετατροπείς ισχύος του συστήματός μου. Ο έλεγχος του συστήματος πραγματοποιείται μέσω ειδικά σχεδιασμένων ελεγκτών, παράγοντας τα κατάλληλα σήματα για την παλμοδότηση των χρησιμοποιούμενων ηλεκτρονικών μετατροπέων ισχύος και αυτό που θέλει να πετύχει, είναι η μέγιστη απομάστευση ισχύος από τον άνεμο και ο καθορισμός των σημείων λειτουργίας τάσης και συχνότητας. Η απόκριση του συστήματος και η αποτελεσματικότητα των ελεγκτών του στις διάφορες καταστάσεις λειτουργίας, συμπεριλαμβανομένου και του σεναρίου με την προθήκη του super capacitor, εξετάζονται μέσω εκτεταμένω προσομοιώσεων με τη βοήθεια του matlab/simulink.
- ItemOpen AccessMedical device vigilance case study : breast implants
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-06-22) Μπαγουρδή, Κυριακή; Bagourdi, KyriakiBreast implants have been used for more than half a century and primarily in breast augmen-tation, one of the most popular procedures in the US. Breast implants as medical devices have, in some ways, contributed to the creation of the new medical device regulations, with stricter re-quirements in both the pre-approval and post-approval phases. This study includes bibliographic data obtained from databases such as Medline and EMBASE with the aim of providing an in-depth analysis of the evolution of breast implants as well as presenting the main adverse events that have been associated with them and have led to the updated European Medical Device Regulation of 2017. At first, specific characteristics of breast implants are presented, such as the filling material and the shell surface, their structure and shape, the place they are implanted as well as the manufacturing techniques depending on the desired texture of their surface. Moreover, a detailed history of the development and evolution of breast implants from their first market launch and their use for medical purposes, mainly for breast augmentation procedures, is presented. Adverse events observed in patients with breast implants are also reported in this chapter, and with start-ing point the PIP incident involving non-medical grade approved cases of silicone breast implants, their most important adverse events in patients worldwide are presented. Rupture and capsular contracture has been shown to be one of the most common adverse events caused by PIP breast implants. Through a more specific and thorough literature search, capsular contracture is investigated in relation to the surface topography of breast implants. The foreign body reaction of immune sys-tem, in an implantable implant, is proved to be one of the causes of capsular contracture and the role of biocompatibility appears crucial. The surface of textured implants is demonstrated to be associated with increased biocompatibility compared to implants that have a smooth surface, while the risk of capsular contracture is reduced in textured implants. However, the scientific community has been faced with a dilemma for the past decade or so. Anaplastic large cell lymphoma (ALCL) identified and recognized by health authorities in 2016 as a risk directly associated with textured breast implants has led to further studies of these types of implants. To this end, a thorough literature search was conducted along with data provided by the FDA safety database, MAUDE, with the aim of presenting the increasing incidence of ALCL associ-ated with textured breast implants. The statistics and studies presented confirm the dilemma that arises with the use of textured breast implants. Although they present a reduced risk of capsular contracture in the long term, the new risk of ALCL associated with them has led the scientific community as well as breast implant manufacturers to turn to other manufacturing techniques and innovations.
- ItemOpen AccessDocument representation for text clustering
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-06-23) Μπούργος, Νικόλαος; Bourgos, NikolaosClustering plays a crucial role in organizing and understanding large collections of documents. In this thesis, we conduct a comprehensive investigation of document clustering, examining clustering algorithms, text preprocessing techniques, similarity and distance measures, and evaluation metrics. We place significant emphasis on topic modeling and document representation methods, particularly those reliant on word embeddings, and conduct a detailed literature review to gain insight into the current state-of-the-art in document clustering. We conducted an experimental study on the 20newsgroups dataset, testing a range of document representation methods, including TF-IDF weighted bag-of-words, Doc2Vec, average and TF-IDF weighted average of Word2Vec, GloVe and FastText word embeddings with K-means clustering. We utilized both intrinsic and extrinsic evaluation metrics to assess the clustering performance of each of these representation methods. Moreover, Latent Dirichlet Allocation is also assessed in the context of document clustering. Our findings reveal the strengths and weaknesses of different document representation and topic modeling methods and offer insights into their effectiveness for document clustering. Despite some limitations, our study contributes to the understanding of document clustering, providing guidance on selecting and assessing document representation methods and implementing a complete clustering pipeline.
- ItemOpen AccessLarge scale deliberation : a comparison of visualization approaches
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-06-23) Ζαγκότα, Αργυρή; Ζagkota, ArgyriIn today's globalized and interconnected world, with advanced digital technology to support discussions and forums, progress has yet to be made in visualization support technology for large-scale deliberation. At least, there is no widely adopted alternative to overpass the limitations of traditional forums. Visualizing deliberation on a large scale is a challenging task. Many ideas have been implemented and proposed, and this thesis collects and describes the most successful examples found in literature and practice. It distinguishes five main representation styles, including argument map, argument tree, outline view, columnar view, and linear view, and uses them as a vehicle to explore design affordances. Additionally, it identifies eight factors influencing scaling, including ontology, representation style, moderation, participation, assessment, evidence, usability, community features, and contacts a comparative assessment. The contribution of this study is a summary of key features that future designers of large-scale deliberation tools should consider.
- ItemOpen AccessPseudo-haptic and self-haptic feedback during VR text entry
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-06-27) Κουναλάκη, Μαρία; Kounalaki, MariaThe use of virtual reality (VR) equipment is becoming increasingly common in people’s daily lives concerning a variety of applications and utilities. Text entry in the VR environment has always been a challenge and a main subject of research in HCI, especially when it comes to human-centered and user-friendly interfaces and implementations. To assist occasional text entry on small VR keyboards without specialised sensing equipment or external devices, we compare a single-finger text entry method relying on pseudo-haptic feedback, and a novel bimanual method that exploits the principles of self-haptic feedback. In a user study (n=24), we find that both methods have comparable performance but also distinct advantages and disadvantages, demonstrating good learnability and promising prospects for further refinement.
- ItemOpen AccessHuman Robot interaction : development of user interface for control of a semi-autonomous robot
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-06-27) Γεωργακόπουλος, Θεόδωρος; Georgakopoulos, TheodorosHuman-Robot Interaction (HRI) has emerged as a multidisciplinary field aiming to improve the collaboration and communication between humans and robots. This thesis describes the setup and troubleshooting process to achieve the interaction with the robot Summit-XL, made by Robotniks. Firstly, an introduction to Human-Robot Interaction is presented, examining the various applications and research fields involved. The classification of robots and their usage is also portrayed to showcase how robots have evolved. A detailed analysis and presentation of this particular robot’s specifications and abilities is depicted along with a set of software libraries and tools called Robot Operating System (ROS) which enable the user to engage with the robot and perform the desired actions. The process of achieving the interaction with the Summit-XL is then analyzed by a detailed description of each step taken to enable the robot’s functionality and an installation of a ROS distribution to achieve connection and management of the robot via a remote personal computer. Lastly, various use cases and tutorials are logged to aid future users in executing certain use case scenarios seamlessly with the robot.
- ItemOpen AccessThe effect of strike pattern on the cushioning capacity of technical midsole footwear
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-06-28) Τζοβλά, Αικατερίνη; Tzovla, AikateriniNumerous research studies have highlighted the interconnection between footwear and running strike patterns . The processes that govern these adjustments in movement patterns are generally acknowledged to depend on the perception and transmission of impact forces through the musculoskeletal system of runners . Consequently, a variety of midsole technologies have been developed in recent years to cater to the requirements of both professional and regular runners. Despite extensive efforts dedicated to understanding the intricacies of running biomechanics and mitigating impact, the impact of foot placement on the cushioning capacity of specific midsole systems remains poorly understood. The purpose of this project was to determine the extent to which Finite Element (FE) modelling techniques can determine how different strike patterns relate the energy absorption capacity of technical footwear. To obtain detailed information about a commercial running shoe, a micro-Computed Tomography device (Werth TomoScope® HV Compact-225 3D CNC) was utilized for scanning purposes. The gel-based midsole of the shoe was accurately reverse-engineered with a precision of 200μm. Subsequently, the obtained model was processed using ANSA software by BETA CAE Systems S.A., where the meshing of the model was performed. Convergence studies were conducted to ensure the grid's accuracy and independence, resulting in a mesh that met the desired quality criteria. For the analysis, two distinct strike patterns were taken into account: heel-strike (HS) and forefoot strike (FFS). To capture the plantar pressure distributions during running for both strike patterns, a Footscanner insole 2.39 system (Niceville, FL 32578, USA) was utilized. Additionally, the shoe-ground contact duration, which varies with time, was obtained from high-speed camera measurements using the MotionBLITZ EoSens® mini. Data collection was focused on female endurance athletes, with an average weight of 51 kg ± 0.82 kg. All recorded data underwent a filtering process and were statistically normalized to ensure accuracy and consistency. Under dynamic conditions, load and boundary conditions were applied to both the superior and inferior surfaces of the 3D midsole. The Finite Element (FE) analysis specifically considered four key phases of the running cycle: touchdown, impact peak, end of mid-stance, and toe-off. Based on the evaluation process, it was determined that during forefoot strike (FFS), the maximum ground reaction force was found to be 6.7% higher compared to heel strike (HS). Additionally, the support phase duration for HS was slightly prolonged by approximately 9.2%. These findings indicate that FFS involves a more energy-intensive foot-strike, which aligns with existing literature .
- ItemOpen AccessArtificial intelligence applications in breast imaging
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-06-28) Δημητρίου, Ευγενία; Dimitriou, EugeniaBreast cancer is one of the leading health concerns, that affects millions of women worldwide. Breast cancer detection plays a vital role in improving patient outcomes and survival rates. In recent years, Computer-Aided Diagnosis (CAD) systems have emerged as powerful tools in medical imaging, leveraging advanced deep learning algorithms to assist radiologists in accurately identifying potential cancerous lesions. This thesis focuses on the implementation and evaluation of two CAD systems, UNet and YOLOv5, for breast cancer detection. The thesis begins by providing an overview of breast cancer, highlighting its prevalence and the limitations of traditional diagnostic methods. It emphasizes the need for advanced Computer-Based systems to augment radiologists’ expertise and improve diagnostic accuracy. UNet and YOLOv5, both widely recognized in computer vision tasks, are implemented in order to aid breast cancer detection. The technical aspects of UNet and YOLOv5, including their architectures and training procedures, are discussed in detail. The thesis addresses the challenges specific to medical imaging, such as data preprocessing and augmentation techniques, and highlights the potential benefits of integrating these models into the diagnostic workflow. An extensive evaluation is conducted using a subset of digital mammograms of the INbreast dataset. Metrics including Precision, Recall and F1-Score are used to measure their effectiveness. Comparative analyses provide insights into the strengths and weaknesses of both networks. Specifically, the best results can be summarized on average for the UNet as Precision: 85.87%, Recall: 85.10% and F1-Score: 84.25%. For the UNet CLAHE as Precision: 89.73%, Recall: 84.12% and F1- Score: 85.13%. Lastly for the YOLOv5 as Precision: 92.30%, Recall: 90.60% and F1-Score: 91.20%. Recommendations and further improvements, such as model optimization are also included. The conclusions drawn from this thesis highlight the potential of UNet and YOLOv5 in breast cancer detection. The implemented CAD systems demonstrate the ability to accurately detect cancerous lesions in medical images, aiding radiologists in making timely and informed diagnoses. The findings emphasize the importance of comprehensive and diverse datasets, as well as collaboration between medical professionals and computer scientists, to optimize CAD systems and drive advancements in breast cancer detection. Overall, this thesis contributes to the research on CAD systems, and their potential to improve the accuracy and efficiency of breast cancer diagnosis. Continued research in this field holds promise for further advancements, ultimately leading to enhanced patient outcomes and a significant reduction in breast cancer-related morbidity and mortality.
- ItemOpen AccessOnline platform to support victims of natural disasters
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-06-28) Χρόνη, Αίγλη; Chroni, AigliThis thesis presents the development and evaluation of an online platform aimed at providing support to individuals affected by natural disasters. Through a user-centered design approach, the platform addresses common challenges faced by victims during the post-disaster recovery phase. The platform offers a centralized information hub, real-time updates on relief efforts, and a community support system. The platform was developed through sequential phases starting with requirement analysis followed by interface design, evaluations and concluding with code development. The structure of the thesis consists of the following chapters and sections: Chapter 1: Introduction Subject analysis and purpose of the thesis are presented providing an overview of the research objectives and scope. Chapter 2: Analysis of Application’s Requirements and Specifications Focus on the analysis, starting with personas representing different user roles such as victims of natural disasters, organization employees, and volunteers. Storyboards illustrating on-site and application scenarios are included. Use case scenarios for employees, volunteers, and victims are also explored. Chapter 3: Database Design Database design, including the procedure of creation of the database and analysis of its structure. Chapter 4: Design of the Application's Interface Interface design aspects, beginning with a hierarchical task analysis (HTA) and its description. A site map is presented to provide an overview of the application's structure. Chapter 5: Initial Designs Initial designs of the web application, including the general structure of the application. The specific pages of the application are, also presented. Chapter 6: Evaluations & Redesigns Various evaluation methods, including heuristic evaluation, think-aloud evaluation, and questionnaires, to assess the usability and user experience of the application. Based on theses evaluation results, redesigns are proposed. Chapter 7: Technologies Used Overview of the technologies used in the design and development of the application. Front-end, database, back-end, and hosting aspects. Chapter 8: Conclusion and Future Work Summary of the findings and conclusions of the thesis. Potential future work and roll out of the application. Annexes Parts of the source code that was implemented in order to develop the web application. Usability testing and user feedback demonstrate positive experiences and increased feelings of support and resilience. The thesis contributes to the field by providing an innovative solution to enhance post-disaster support and inform future research in disaster management.
- ItemOpen AccessInvestigating the reasons of annoyance in online ads
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-06-28) Τριανταφύλλη, Αγγελική; Triantafilli, AggelikiThe analysis and research of online advertising has been an extremely and widely discussed topic over the past few decades. The intense and rapid growth of online advertising due to the covid pandemic creates an even bigger incentive to research and therefore understand what contributes to the better user perception and experience towards ads. Researchers focus on understanding and identifying the elements that generate annoyance, with the aim of minimizing fatigue, increasing engagement and user acceptance that will lead to more responsive and profitable results. Furthermore, the broader understanding of user behavior in the digital advertising landscape will also lead to higher user satisfaction and less ignorance towards advertising. Variables, which are presented in this thesis and are also usually analyzed when trying to get a better overview of the advertising challenges are the existence of intense graphics and formats, unpredictable and abrupt interruptions of a process and excessive frequency. This thesis aims to investigate user reactions towards online ads as well as presenting the reasons behind user’s annoyance. That happens by presenting the relevant research of previous years while also analyzing data from a questionnaire filled in by universitystudents on the annoyance created from online ads. The questionnaire included a total of 109 participants, consisting of 76 males and 33 females, all within the age range of 20-24. Participants were asked to watch annoying ads and then to fill in the questionnaire. Each participant completed 3-4 questionnaires, corresponding to the number of the ads they watched, resulted in a total of 349 data points. Our objective with this questionnaire was to analyze the following factors: the ability and ease of closing the ad, coverage of page contents, coverage of browser window, ad expansion, automatic ad activation, video/animation, sound, and ad targeting based on recent browsing history. Based on our data analysis, we reached the conclusion that higher levels of annoyance are created from ads that are triggered automatically as well as from ads with the automatic start of sound and dynamic expansion. The ad’s overlay to part or the whole browser’s page also creates high levels of annoyance along with the inclusion of video. The thesis begins with the objective and significance of online advertising. It resumes with the literature review, the display of different methods and types of online advertising, while also exploring the consumer attitude. In Chapter 2 the available ad avoidance techniques are presented along with factors that contribute and enhance it. In Chapter 3 the research methodology, research questions and method of data collection are presented and analyzed. Continuing in Chapter 4 the statistical analysis of the survey results is thoroughly explained along with the conclusions that are combined with the previously presented bibliography. The last chapter, Chapter 5, focuses on the main conclusions, limitations and proposals for future work.
- ItemOpen AccessUncovering themes and trends in HCI
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-06-28) Μούλιας, Θεόδωρος; Moulias, TheodorosThis thesis aims to identify the trends in the field of Human Computer Interaction. In the context of this work, a python tool was developed which, through the search for keywords and the number of their occurrences, in publications of selected sessions per year, receives as input the pdf files with the publications of each conference that we wish to evaluate, processes them by isolating the words we are looking for and then records the number of their occurrences in each year for the conference we are looking at. The data from this processing are exported, for their better management, to an Excel and then with the help of SPSS we proceed to evaluate them and extract the results to identify trends that will concern us in the future years in the field of HCI or even topics that are on the decline in the industry and we won't need to waste resources investigating them.
- ItemOpen AccessEffect of printing parameters on the mechanical properties of 3D-printed specimen
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)(2023-06-28) Χαρισιάδης, Δημήτριος; Charisiadis, Dimitrios3D printing is an ever-growing manufacturing process, gaining a lot of popularity in the last years, with potential for application in a multitude of fields, particularly in the medical field on the subject of prosthetics and orthotics. Its ease of accessibility and both time and cost effectiveness make it an attractive alternative to current manufacturing processes. Due to its recency, however, as well as insufficient documentation for the thermoplastic materials it commonly uses (compared to more conventional materials like metals), there is an information gap, regarding how the plethora of pre-process configurations and parameters can potentially affect the mechanical properties of the 3D-printed parts. The goal of this thesis is to fill this gap, as well as provide a guideline for future studies regarding this subject. To achieve this goal, a number of specimen was printed, following the guidelines from ASTM D638 standard, which would be tested for their tensile properties. The standard procedure is to input the CAD file of the specimen into the slicer program of the 3D printer, and after some configurations, an STL file is exported, which can be read by the 3D printer, and the part is produced. These configurations have to do with the 3D printing procedure, from nozzle temperatures to specific instructions on how the printer will fill the volume of the part. The latter is very important, as it creates an internal geometry, which greatly affects the mechanical behavior and load response of the 3D printed part, and this is what is tested in this thesis. To do that, control specimen were created, with specific values for four printing parameters that were to be tested: Infill Density, Perimeter Thickness, Shell Thickness and Layer Height. The rest of the specimen had the value of one parameter changed, while the rest remained as they were, in order to test the effect of each parameter individually. For the creation of the specimen, four common 3D-printing materials (PLA, PETG, CPE and ABS) were used, to determine the potential effect that the parameters had on each one. The specimen were then tested on a tensile testing apparatus, to determine their tensile properties, and more specifically, Modulus of Elasticity and Tensile Strength, and compared to determine their differences, taking into consideration the printing time and the cost of their manufacturing. This indicated the effectiveness of each parameter and whether applying that change would be worthwhile, which is especially useful information in large scale operations. The tensile tests showed that perimeter thickness had the greatest effect on the mechanical properties on the specimen, regardless of the material used, and that by increasing it, both modulus of elasticity and tensile strength would improve significantly, with minimal change in printing time and cost. Shell thickness came second on this matter, also having a noticeable effect on the mechanical properties of the specimen. Increasing the infill density did increase the modulus of elasticity for the specimen, but had a small effect on the tensile strength. In addition, these improvements came with a substantial increase in both printing time and cost, making other adjustments, like the ones mentioned above, more attractive. Finally, in all cases, layer height had a small effect on both modulus of elasticity and tensile strength, compared to the other parameters, while increasing printing time drastically, making it a suboptimal choice, and thus not recommended for improving the mechanical properties of a part, unless required by its geometry. To validate these experimental results, a Finite Element Analysis model of the tensile specimen was created, which was used in a simulation tensile test. At first, a CAD model of the 3D-printed part, which included the internal geometry, was created in Autodesk Fusion 360, and was then imported in ANSYS Mechanical Student ver., the software used for the simulations. Since ANSYS does not have material data for plastics, they were created from scratch for each material used. With the creation for the materials done, a mesh was then constructed for the specimen, which essentially breaks the model into Finite Elements, to be used in the analysis. Finally, boundary conditions and loads that replicated the tensile tests were configured, the simulation setup was ready. Same simulations were run multiple times with increasing number of FE used, to reach mesh convergence, and the converged data was used to extract the information required (tensile strength and modulus of elasticity), to be compared with the experimental results. Unfortunately, it should be kept in mind that factors like FE usage license limitations, as well as material data inaccuracies by manufacturers and difficulty in finding appropriate material models to express the mechanical behavior of plastics in ANSYS have lowered the quality of the simulation model and its results. The simulated tensile tests’ results were overall close to their experimental counterparts, indicating that the model was accurate, but lacked precision. There were only a few exceptions, regarding the tensile strength of the specimen, where the model was not able to accurately predict the specimen’s tensile behavior. In addition, the simulation model was more accurate predicting the behavior of PETG and CPE than ABS and especially PLA, which showed larger differences between results. In the end, however, this model was able to predict up to a point, the mechanical properties of 3D-printed specimen, thus validating the experimental results. Narrow time margins prevented the further improvement of the FEA model. Testing the simulation model without license limitations, as well as a more refined material model would be some basic directions for further research on the FEA part. As far as the experiments go, more parameters like printing orientation and infill patterns, as well as other mechanical tests, like fatigue and compression, would expand the scope of this study and are necessary, in order to have a clearer picture on 3D-printing as a whole.