Μεταπτυχιακές Εργασίες

Permanent URI for this community

https://hdl.handle.net/10889/6

Browse

Now showing 1 - 20 of 7564

Open Access
1Μελέτη και εφαρμογή web based συστημάτων σύστασης επαφών και σχέσεων με βάση αθλητικά χαρακτηριστικά
Παπαδόπουλος, Γεώργιος; Papadopoulos, Georgios
Τμήμα Μηχανικών Η/Υ και Πληροφορικής (ΜΔΕ)
Η παρούσα διπλωματική στοχεύει στην μελέτη συστημάτων σύστασης προσωπικών επαφών και σχέσεων έχοντας ως βάση αθλητικά ενδιαφέροντα και κοινά χαρακτηριστικά. Πιο συγκεκριμένα μελετώνται συστήματα συστάσεων σχέσεων όπου και αναλύθηκε, σχεδιάστηκε και υλοποιήθηκε κατάλληλο σύστημα με αθλητικά στοιχεία. Η εφαρμογή που σχεδιάστηκε υποστηρίζει δύο ήδη χρηστών, τον διαχειριστή και τον απλό χρήστη. Το σύστημα σύστασης βασίζεται σε έναν αλγόριθμο ο οποίος βρίσκει ομοιότητες με βάση άλλους χρήστες και τους ταιριάζει. Τα κριτήρια που επιλέχθηκαν είναι οι ομάδες, η ηλικία, οι χώρες ομάδων και το φύλο. Τα κριτήρια είναι και συνδυαστικά.
Open Access
3-d cone beam αναπαράσταση με χρήση παράλληλης επεξεργασίας σε περιβάλλον MATLAB
(2009-02-09T08:06:04Z) Μπασαγιάννης, Γεώργιος; Παλληκαράκης, Νικόλαος; Κωστόπουλος, Γεώργιος; Παλληκαράκης, Νικόλαος; Μπεζεριάνος, Αναστάσιος
Τμήμα Ιατρικής (ΜΔΕ)
3d αναπαράσταση με παράλληλη επεξεργασία μέσω Matlab
Open Access
396 ημέρες, Αθήνα. Παρατηρώντας τα αστικά κελύφη συναρτήσει των ανθρώπινων δράσεων
Αδαμίδου, Ελένη; Ρόδη, Άλκηστις; Αίσωπος, Γιάννης; Πανέτσος, Γεώργιος; Δραγώνας, Πάνος; Κατσώτα, Δήμητρα; Adamidou, Eleni
Τμήμα Αρχιτεκτόνων Μηχανικών (ΜΔΕ)
Κατοικώντας σε ένα ρετιρέ στο κέντρο της Αθήνας αντιλαμβάνεσαι τον χρόνο, τις εποχές, τον κόσμο που αλλάζει. Τα πάντα από το διαμέρισμά στον 6ο φαίνονται να έχουν κάτι να πουν. Ακόμη και οι δορυφορικές κεραίες που σκορπίζονται βίαια όπου κοιτάζει το μάτι. Βγαίνοντας στο μπαλκόνι καταλάβαινες τη ζωή της Αθήνας σαν από ένα παρατηρητήριο. Από εκεί παρατηρείς τους γείτονες στα απέναντι μπαλκόνια, τα φώτα που ανάβουν, τα κρυμμένα από φυτά διαμερίσματα, τις τέντες, τον ήλιο που δύει και ξανανατέλλει.» Μια ιδιαίτερα συναισθηματική μελέτη που στηρίζεται στην περιέργεια του νέου αρχιτέκτονα ως παρατηρητή του αθηναϊκού τοπίου και αντιλαμβάνεται την σημαντικότητα του χρήστη πάνω στην αστική πολυκατοικία. Η συγκεκριμένη μελέτη στηρίζεται σε τρεις παραμέτρους: την πόλη ως ζωντανό οργανισμό και υποδοχέα της πολυκατοικίας, την πολυκατοικία ως πυρήνα της ελληνικής οικογένειας και υποδοχέα ζωής, και τον κάτοικο ως τον κεντρικό ήρωα κάθε δραστηριότητας ή σύγχρονης ανάγκης που λαμβάνει μέρος στο αθηναϊκό τοπίο. Το διαμέρισμα έρχεται σε αντιδιαστολή με το εξωτερικό περίβλημα. H ταράτσα, ως νέο αστικό έδαφος γίνεται υποδοχέας της ανθρώπινης εκτόνωσης και των σύγχρονων αναγκών. Περιγράφονται με έναν ιδιαίτερα προσωπικό και ποιητικό τρόπο οι ανθρώπινες δραστηριότητες που εντοπίζονται στα σημεία εκείνα που μεσολαβούν, πέραν των ορίων του οικείου χώρου ενός διαμερίσματος, στους εξώστες και τα δώματα. Καταγράφει χωρίς να εξηγήσει την τα επιστημονικά συστατικά των σημείων που απαρτίζουν τα κελύφη των κτιρίων κατοίκισης. Αυτό γίνεται στοχευμένα ώστε αποδείξει πως ο σύγχρονος κάτοικος αντιλαμβάνεται τι τον περιβάλλει και έχει την ευκαιρία να το εκμεταλλευτεί για να εξελίξει το δικό του προσωπικό «good living».
Open Access
3D joint kinematics quantification with 3D fluoroscopy : Implementation of algorithm proposed by Mahfouz MR
(2014-05-27) Πετρόπουλος, Γεώργιος; Παλληκαράκης, Νικόλαος; Παλληκαράκης, Νικόλαος; Stagni, Rita; Τσαγγάρης, Σωκράτης; Bliznakova, Kristina; Petropoulos, Georgios
Τμήμα Ιατρικής (ΜΔΕ)
Dynamic assessment of three-dimensional (3D) joint kinematics is essential for understanding normal joint function as well as the effects of injury or disease. The knowledge of one or two series of bi-dimensional fluoroscopic projections of the joint in motion (mono-planar or bi-planar fluoroscopy), and the 3D model of the joint segments, were claimed to be sufficient to reconstruct the absolute and relative 6 Degrees Of Freedom (DOFs) pose of bones or prostheses in the 3D space. The software MultiTrack was developed at the Health Sciences and Technologies - Interdepartmental Center for Industrial Research (HST - ICIR) for the joint kinematics estimation with 3D Video Fluoroscopy (3DF) [1] using C++ language with ITK [2] segmentation & registration toolkit and VTK [3] visualization toolkit. An optimization procedure finds the 6 degrees of freedom pose that optimizes a metric quantifying the matching of the 3D model and its relevant projections. The metric, currently implemented in the software, is based on the contour segmentation of the object to be tracked and on the use of 3D adaptive distance maps (ADM) [4,5]. However, the contour extraction is a time consuming procedure for the user. Different methods were proposed in the literature to reduce the user interaction, each with its proper pros and cons. In the current thesis a few of the for-mentioned methods are discussed in order to evaluate each of them in terms of accuracy, speed and user dependency. At the final step the algorithm proposed by Mafhouz et al. [6], initially proposed for prostheses, is implemented inside the MultiTrack framework. To be properly characterized, the above method is tested on in vivo datasets and under various sources of error.
Open Access
3D printing nano-resolution organic electronic drug delivery devices
Genedy, Hussein; Κλεπετσάνης, Παύλος; Κλεπετσάνης, Παύλος; Audrieux, Karine; Roques, Caroline
Τμήμα Φαρμακευτικής (ΜΔΕ)
Development of biocompatible electronic interfaces and systems that can control drug release is a rapidly emerging multidisciplinary scientific niche. Various materials are used for bioelectronic applications, including inorganic electronic materials (e.g. metals and alloys) and organic electronic materials (e.g. graphene, carbon nanotubes, and conducting polymers). We focused here on conducting polymers for biomedical applications and therapeutics. We report 3D printing of conductive polymeric materials in various dimensions and scales (mesoscale, microscale and nanoscale) to be applied as organic bioelectronic neural interfaces and stimuli responsive drug delivery devices. Conductive polymers were 3D printed onto a 3D material (Polydimethylsiloxane PDMS acting as a soft conformal interface) using two-photon polymerization (TPP) via a direct laser writing (DLW) instrument (Nanoscribe), paving the way for the administration of drugs from flexible organic electronic devices. The research was carried out using a polymer frequently used in bioelectronics (polypyrrole, PPy) because it has previously been reported to be non-immunogenic with no significant inflammation and with a positive biocompatibility profile with CNS parenchyma in vivo. This technology has the potential to be applied in therapeutic devices in the future as neural interfaces and implantable or topical drug delivery systems.
Open Access
3D scaffold development for tissue engineering
Πάντσιος, Πασχάλης; Δεληγιάννη, Δέσποινα; Αθανασίου, Γεώργιος; Μαυρίλας, Αθανάσιος; Pantsios, Paschalis
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)
During this thesis a novel perfusion bioreactor was constructed. Based on an existing bioreactor apparatus [1], investigating previous researches and using spare parts found in the Laboratory the bioreactor was designed and assembled. It was tested for functionality and non-toxicity by culturing cells in it and it passed. In association with Biomedical Research Foundations (Academy of Athens), Human Umbilical Artery specimens were tested. The ulterior purpose is to use HUA as grafts. Mesenchymal Stem Cells cultivated in decellularized HUA in incubator for one day and in the perfusion bioreactor for five days. The main parameter controlled was the flow rate, depending on the shear stress of the fluid (culture medium) flow. The results were significant. A successful recellularization was accomplished with a high cell density on the lumen of arteries. The results are depicted implementing Hematoxylin & Eosin Stain and confocal microscopy techniques processed at the BRFAA. The second experimental series consisted of ten-layered Polycaprolactone-Carbon Nanotubes scaffolds, manufactured in our Laboratory using a prototype Electrospinning unit. PCL-CNT scaffolds are considered promising tool for osteogenesis. Perfusion bioreactor MSC cultures, halting at one and three days, were compared to static cultures applying MTT assay. A strong indication was deducted that perfusion is quite more efficient to the proliferation of MSC, than in the case of static culture. Unfortunately, the time margins were narrow enough to be an obstacle to a more thorough investigation of the researches above. More days of culture and repetitive experiments are considered mandatory for a complete investigation. Finally, the next step should be the investigation of MSC differentiation to either endothelial cells, or osteocytes, regarding HUA and PCL-CNT scaffolds, respectively.
Open Access
3D segmentation of great vessels using active contours and morphological image processing techniques
(2010-05-25T06:15:31Z) Montejo Garcia, Cristina; Santos, Andres; Nikolaos, Pallikarakis
Τμήμα Ιατρικής (ΜΔΕ)
The scope of this project is to present a semi-automated vessels segmentation algorithm, to describe its usage and results. This will be achieved combining several segmentation algorithms to get proper vessel segmentation and visualization. Consequently, automatic segmentation can significantly reduce the scan-to-diagnosis time, thus helping the clinicians to reach the fundamental goal of efficient patient management. In order to complete our project, we can identify different phases: - Correct reading of CT and MR images and extraction of data needed for the post-processing. - Processing of these images using the most appropriate segmentation techniques to get the desired contour. - Visualization of the contour.
Open Access
3D simultaneous algebraic reconstruction technique for cone-beam projections
(2010-06-15T13:48:14Z) Chlewicki, Wojciech; Παλληκαράκης, Νικόλαος; Παλληκαράκης, Νικόλαος
Τμήμα Ιατρικής (ΜΔΕ)
-
Open Access
A constitutive rheological model for agglomerating blood derived from non-equilibrium thermodynamics
Τσιμούρη, Ιωάννα; Μαυραντζάς, Βλάσιος; Τσαμόπουλος, Ιωάννης; Δημακόπουλος, Γιάννης; Tsimouri, Ioanna
Τμήμα Χημικών Μηχανικών (ΜΔΕ)
Many deaths are the result of cardiovascular diseases associated with unusual blood rheological properties in the circulatory system [Yilmaz and Gundogdu (2008)]. Therefore, understanding the rheological behavior of blood is paramount in providing insights on the causes of various diseases and the tailor-design of the transport of drug directly to the infected area [Yilmaz and Gundogdu (2008)]. Blood is mainly a suspension of elastic particulate cells, among which red blood cells (RBCs) dominate, in plasma, usually considered as a Newtonian fluid. Red blood cells tend to aggregate in the presence of plasma proteins, forming structures known as rouleaux which can be decomposed upon the applied tension induced by the flow. In this master thesis, we derive a constitutive rheological model for human blood which accounts for the formation and dissociation of rouleaux using the generalized bracket formulation of non-equilibrium thermodynamics [Beris and Edwards (1994)]. Similar to the model derived by Owens and coworkers [Owens (2006); Fang and Owens (2006); Moyers-Gonzalez et al. (2008)] through polymer network theory, each rouleau in our model is represented as a dumbbell; the corresponding structural variable is the conformation tensor of the dumbbell. The kinetics of rouleau formation and dissociation is treated as in German et al. (2013) by assuming a set of reversible reactions, each characterized by a forward and a reverse rate constant. The final set of evolution equations for the microstructure of each rouleau and the expression for the stress tensor turn out to be very similar to those of Owens and co-workers. However, by explicitly considering a mechanism for the formation and breakage of rouleaux, our model further provides expressions for the aggregation and disaggregation rates appearing in the final transport equations, which in the kinetic theory-based network model of Owens were absent and had to be specified separately. Despite this, the two models are found to provide similar descriptions of the experimental data collected by Mehri et al. (2013) on the size distribution of rouleaux.
Embargo
A cyber-physical system for quality assessment in welding electric vehicle batteries
Σαμπατακάκης, Κυριάκος; Sabatakakis, Kyriakos
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
The battery of an electric vehicle consists of cells assembled into modules which in turn are assembled to create a battery pack. Most of these connections are permanent and are made using a welding process. However, due to the involvement of non-ferrous, inhomogeneous and multilayer materials, the creation of welds with low electrical resistance, high strength and quality characteristics that can be reproduced with minimal deviation is a challenge. This fact combined with the assembly process, in which the interconnection of tens or even hundreds of cells take place, makes the existence even of a single joint that is out-of-spec, crucial for the safe and efficient operation of the battery, but also for its longevity. This fact makes quality inspection of every joint necessary, which cannot be achieved by using sample-based destructive or non-destructive methods. And while the scientific community has developed and described solutions and approaches for non-destructive real-time inspection and assessment in welding a very small amount of them concerns battery assembling applications and in general the welding of non-ferrous dissimilar metals. On the other hand, none of these studies yet has addressed the issue of inspecting or assessing the electrical quality of the joints. In this study based on the design practices of Cyber-Physical systems a novel quality assessment approach for the assembly of batteries in terms of electrical and mechanical quality is developed in the context of the Laser welding of aluminum and copper battery tabs. The assessment approach is based on infrared vision data using machine learning. The classification accuracy for the electrical and mechanical quality of the welds on the training and test data was set at 100% under specific conditions.
Open Access
A lexicological study of the linguistics terminology in Greek
Καλαμίδα, Φωτεινή; Ξυδόπουλος, Γιώργος Ι.; Ράλλη, Αγγελική; Μαρκόπουλος, Θεόδωρος; Kalamida, Foteini
Τμήμα Φιλολογίας (ΜΔΕ)
The present study aims at examining the adaptation of the English linguistics terminology into the Greek language. More specifically, in order to do this, after presenting the theoretical background regarding terminology, and especially linguistics terminology, its standardization and unification, a number of English linguistic terms are selected and discussed by consulting certain dictionaries so as to compare and contrast the translations of the terms into Greek; then, the translations are further examined by applying a set of evaluation criteria with ultimate aim to find and propose the best and most accurate translation of each term in Greek. Besides, the challenges and difficulties encountered when reviewing the translations of the terms are presented and finally, some general conclusions are drawn concerning the linguistics terminology in Greece.
Open Access
A method for the in-situ measurement of the water content of atmospheric particles
Τσιλιγιάννης, Επαμεινώνδας; Πανδής, Σπύρος; Κουτσούκος, Πέτρος; Κορνάρος, Μιχαήλ; Tsiligiannis, Epameinondas
Τμήμα Χημικών Μηχανικών (ΜΔΕ)
The hygroscopic behavior of atmospheric aerosols influences their size, composition, lifetime, chemical reactivity, and light scattering. Hygroscopic growth plays an important role in a number of air pollution problems including visibility impairment, climate change, acid deposition, longrange transport and the ability of particles to penetrate the human respiratory system. The absorption of water by aerosol particles often exhibits a hysteresis. Thus, the physical state (liquid or solid) of particles and the amount of aerosol water at a specific relative humidity (RH) are uncertain, as they depend on the history of these particles. In this work, the reduced version of the Dry Ambient Aerosol Size Spectrometer (DAASS) that measures the water content of atmospheric aerosols has been redesigned and optimized. The DAASS measures the number distribution of the aerosols at ambient conditions and at low RH thus drying the particles. A comparison of these distributions allows the determination of the physical state of the particles and their water content. The new version of the DAASS is capable of operating at higher RH values than its predecessor. The instrument has been characterized regarding particle wall losses, in a set of smog chamber experiments using (NH4)2SO4 particles. An algorithm checking the consistency of the measurements and the applicability of the assumptions used in the data analysis was developed. The water concentrations observations were compared to the predictions of the aerosol thermodynamics model EAIM. Ambient measurements, using the original and the improved version of DAASS, were conducted during two different time periods in a suburban area in Patras. These tests allowed the testing and assessment of the operation of the DAASS and also the examination of the hygroscopic behavior of particulate matter. The original version was used during a moderate RH period, in which the water content of the aerosol represented 0-50% of the fine aerosol mass. The improved DAASS operated during high RH conditions. The particles retained water throughout the duration of the measurements. The measured volume growth factors were quite higher than the measured ones during the moderate RH period. The water concentrations observations were compared to the predictions of the aerosol thermodynamics model EAIM.
Open Access
A new medical decision support system (MDSS) for the diagnosis of coronary artery disease (CAD) using fuzzy cognitive maps (FCM)
Αποστολόπουλος, Ιωάννης; Apostolopoulos, Ioannis
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογιστών (ΜΔΕ)
Cardiovascular Diseases, which the Coronary Artery Disease is part of, are the leading cause of death worldwide, despite the progress made in prognosis and treatment. Accurate, noninvasive diagnosis of the disease is impossible to achieve, due to the constrained accuracy of the diagnostic tests and the complexity of the parameters affecting the risk of suffering from the disease. Hence, humans are forced to undergo the invasive way of diagnosis and treatment, the Coronary Angiography. It is proven that 30% to 50% of the candidates that undergo the Coronary Angiography were healthy. This is the reason why a lot of research has been going on regarding the prognosis and the automatic diagnosis of CAD. Recently, several approaches have been employed, reclaiming the advances in Data Mining and Machine Learning of the past years. In this work, we approach the problem with Fuzzy Modelling, Machine Learning, and Deep Learning approaches. Based on the Diploma Thesis for the BSc Degree of Electrical and Computer Engineering, an improved method of modelling Coronary Artery Disease with Fuzzy Cognitive Maps is presented in this thesis. Next, Machine Learning and Deep Learning methods are examined. For Machine Learning, state-of the art classifiers are employed to perform the diagnosis. Utilizing the Myocardial Perfusion images from the database, Deep Learning with Convolutional Neural Networks is examined for the classification of the medical images. The state-of-the-art Convolutional Neural Network, called Virtual Geometry Group (VGG) was employed to perform the classification task. The three methods are compared, and conclusions regarding their advantages and drawbacks are discussed.
Open Access
A nonnegative least squares solver for multiple right-hand sides for approximating the nonnegative matrix factorization
(2022-11-04) Κολώνιας, Λεωνίδας; Kolonias, Leonidas
Τμήμα Μηχανικών Η/Υ και Πληροφορικής (ΜΔΕ)
Nonnegative Least Squares (NNLS) problems, where the variables are restricted to take only nonnegative values, often arise in many applications and are also at the core of most approaches to solve the nonnegative matrix factorization (NMF), a low-rank matrix approximation problem with nonnegativity constraints. NMF is a data analysis technique used in a great variety of applications such as text mining, image processing, hyperspectral data analysis, computational biology, and clustering. In more detail, the nonnegative factors can be interpreted as data e.g., as images described by pixel intensities or texts represented by vectors of word counts. The mathematical formulation for NMF appears as a non-convex optimization problem, and various types of algorithms have been devised to solve the problem. The first goal of this thesis is to propose a new eﬀicient, yet simple to implement, approach to solve nonnegative linear least squares problems for multiple right-hand sides. More precisely, we study and use properties of global algorithms for least squares problems which are then combined with rules that enforce nonnegativity and lead to novel techniques for solving the aforementioned problem by a flexible Krylov subspace method. Comparisons of the state of the art algorithms using datasets and examples that come from real life applications as well as those artificially generated show that the proposed new algorithm presents a satisfactory behaviour and in some cases outperforms existing ones in computational speed and accuracy. Our second goal is to study extensively the NMF, its properties and applications and dive into the existing algorithms and methodologies used in order to approximate a solution for it. Moreover, using our new approach, tuned to solve large scale nonnegative least squares problems for multiple right-hand sides we present a novel algorithm for NMF based on the alternating nonnegative least squares (ANLS) framework. Extensive experiments on document clustering, images and synthetic datasets indicate the effectiveness of our approach.
Open Access
A novel time-dependent model for route planning in public transit networks
(2021-10-21) Μαχαίρα, Παρασκευή-Μαρία-Μαλεβή; Machaira, Paraskevi-Maria-Malevi
Τμήμα Μηχανικών Η/Υ και Πληροφορικής (ΜΔΕ)
In this thesis, the non-FIFO time-dependent model with REalistic vehicle eXchange times (REX) is introduced for schedule-based public transport systems, along with two novel query al- gorithms for computing optimal multimodal journeys for either a single criterion (earliest arrivals) or two criteria (plus number of transfers). The REX model is a considerable en- hancement of the simple time-dependent model, with additional features towards handling non-negligible exchanges from one vehicle to another, as well as supporting non-FIFO in- stances which are typical in public transport, without compromising the space e ciency of the model. Apart from the novelty of the model, REX is also accompanied with two novel query algorithms, whose rationale is some short of “trip-targeted” label-correction propagation process: the rst algorithm, TRIP-based Label-correction propagation Algorithm (TRIPLA), efficiently solves the realistic earliest-arrival routing problem; the second algo- rithm, Multi-criteria TRIP-based Label-correction propagation Algorithm (McTRIPLA), solves the bicriteria variant of the problem, where apart from the earliest-arrival objective, the commuters also care for minimizing the number of vehicle exchanges. The set of Pareto- optimal journeys is discovered when all the arrival-times are bounded. We conduct a thor- ough experimental evaluation on real-world public transit networks which demonstrates that TRIPLA query algorithm for the REX model outperforms signi cantly all state-of-art query algorithms for multimodal routing in schedule-based public transport models, while McTRIPLA is competitive.
Open Access
A radiomics extraction parameterization analysis for machine learning based regression models
(2023-02-24) Λαμπρινάκος, Ιωάννης; Lamprinakos, Ioannis
Τμήμα Ιατρικής (ΜΔΕ)
Neuroendocrine Tumors (NETs) are inhomogeneous neoplasms, the most common origin sites of which being the gastrointestinal and pulmonary system. Many treatment methods have been developed to treat this type of cancer, as well as combinations of these are applied. One of these methods is Peptide Receptor Radionuclide Therapy (PRRT) that uses radiation, which is delivered continuously at a decreasing rate to cause retention and/or tumor cell death. Lutathera®, or 177Lu-DOTA-TATE as scientifically named, is a radiolabeled somatostatin analog that is both FDA and EMA approved for PRRT. Radiomics, a non-invasive and quantitative mining medical imaging information tool, are used to extract information from medical images and contribute to diagnosis as well as cancer prognosis, by improving diagnostic accuracy, assisting differential diagnosis between benign and malignant lesions, as well as classifying the risk of disease progression. These quantitative characteristics, which are known as Radiomic Features, can be thus extracted and used for theragnostic reasons. This thesis aims to investigate the ability of the radiomic features that were extracted from images of 68Ga-DOTA-TOC and 177Lu-DOTA-TATE from 21 patients with NETs who underwent therapy with 177Lu-DOTA-TATE to predict the post-therapeutic doses. Four different experiments were conducted and every time parameter values such as Voxel Size and Bin Width changed. Then, in every experiment, image filters named “Wavelets” were once extracted and once omitted. Therefore, 3412 features were extracted from each ROI, including wavelets and 436 features were extracted, excluding wavelets. Moreover, features were selected by following a strict pipeline including Mutual Information regression, efficiency with Pearson and Spearman correlations and, lastly, Backward Elimination Sequential Feature Selection (SFS) and Recursive Feature Elimination (RFE) were used as wrapper methods. Then, a predictive machine learning regression model that included 9 algorithms, both linear and nonlinear, was developed. The performance of this model was judged by taking into account two different metrics, Mean Absolute Error (MAE) and R2. The analysis of our results revealed that when the parameter values (Bin Width, Voxel Size) decreased, more accurate results were acquired. Also, we observed that linear based algorithms seemed to be more efficient than nonlinear ones, with Ridge algorithm being the most prevailing in every experiment for both metrics, and Linear Regression algorithm being the second most prevailing. We also concluded that wavelets-based features were of great importance in our study, since when they were included in our model, better results were yielded.
Open Access
A review on sediment samples from a deep hypersaline anoxic basin : Tyros
Νικητίδου, Αγγελική; Γεραγά, Μαρία; Γεραγά, Μαρία; Nikitidou, Angeliki
Τμήμα Γεωλογίας (ΜΔΕ)
The Tyros basin is a presently deep hypersaline anoxic depression in the eastern part of the Mediterranean Sea. Its presence attributes to a combination of submarine dissolution of outcropping or subcropping evaporates (Messinian) which accumulate at the slopes of the basin and at its tectonic subsidence (pull-apart mechanism) that occurs in the western Strabos trench. Therefore, this unique environment consists of two major factors. The first one is a high density stagnant bottom-water column and the second is the preservation of the organic-rich sediments of the area due to the anoxic conditions. The core (TYRO5) that was retrieved from that basin had a total length of 285cm and comprises a complex lithostratigraphic sequence due to the strong geodynamic regime of the area. The analysis conducted on sediment samples from the core TYR05 included granulometry, mineralogy, micropaleontology, bulk geochemistry and total CHNS/organic carbon (TOC). The grain size distribution along with the planktonic foraminifera presents fluctuations which coincide with changes in the lithology of the core. The mineralogical composition of the sediments confirm the evaporate influence developed on the bottom of the basin, while both geochemistry and total CHNS/TOC verify the present anoxic conditions and the existence of organic-rich sediments. The synthesis of all the above analysis suggests that the sediment core consist mostly of sapropel to sapropelic layers and that it has a rather homogeneous character, because of its high re-sedimentation rate. Subsequently, it is indicated that the sapropel units refer to an S1 type, but further analyses are needed in order to be safely determine, such as radiocarbon dating C14 and stable isotopes of O, C.
Open Access
A smart shop-floor monitoring system through Internet of Things and wireless sensor networks
Μήλας, Νικόλαος; Μούρτζης, Δημήτριος; Μούρτζης, Δημήτριος; Χρυσολούρης, Γεώργιος; Παπαδόπουλος, Χρήστος; Milas, Nikolaos
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικών (ΜΔΕ)
With the advent of the fourth industrial revolution manufacturing systems are transformed into digital ecosystems. In this transformation, the Internet of Things (IoT) and other emerging technologies pose a major role. Small and medium enterprises (SMEs) in manufacturing, often employ outdated equipment which does not have connectivity capabilities. Therefore, smart sensor systems are required to connect these resources into the digital world. To address this issue, this master thesis presents a monitoring framework and the development of a data acquisition device for machine-tools. The system is designed for installation into the electrical cabinet of the machine-tools and transmits the data related to their operation to a Cloud server via a wireless sensor topology. The data transmission is performed in two levels i.e. locally in the shop-floor using a star wireless sensor network topology coordinated by a microcomputer gateway, and from the microcomputer to Cloud using Internet protocols. The collected data provide information about the status of the resources, along with a set of performance indicators to support decision making. The developed system follows the IoT paradigm in terms of connecting the physical with the cyber world and offering integration capabilities with existing industrial systems. The gateway level supports connectivity with industrial networks through the OPC-UA standard, while the higher level supports integration with industrial software tools via Web-Services. The operation of the system was evaluated in a 3-axis machine-tool under actual machining operations. Moreover, the capabilities for knowledge reuse were validated through the case-based reasoning methodology in the subject of the energy consumption estimation.
Open Access
A study on the values and ethos of ancient Sparta, its modern reception and the use of digital media in the contemporary hellenic secondary education
Τσίκα, Μάρθα; Tsika, Martha
Τμήμα Ιστορίας - Αρχαιολογίας (ΜΔΕ)
The present dissertation aims at investigating the extend in which digital means are used in the Hellenic secondary school classes, determine the reasons behind poor digital means usage and propose new fields of research that the Covid-19 pandemic has presented the educational system with. To achieve its goal Zack Snyder’s film ‘300’ is used as a case study. The present thesis is divided into three main parts: The theoretical part: It includes i. a brief description of the Spartan society and structure at its peak, ii. the role of women in Sparta followed by iii. basic elements of Spartan warfare, including the armor, weaponry and war tactics. On a parallel level, the Persian army of the Acheamenid period is also described, compared and contrasted to the Spartan one. On this purpose, the battle of Marathon is mentioned so the reader can clearly comprehend how strategy and wit can win a battle despite numerical superiority. The case study part: It includes a critical presentation of the movie ‘300’, taking snapshots and comparing it to historical data so as to determine to which extend the movie is accurate. By using facts that were described in the previous chapters, the present chapter consolidates previous knowledge and puts it to the test in a rather exciting game of discovering real history behind Hollywood saga and exaggeration. The research part: Secondary school teachers of History (be it Greek language teachers, foreign language teachers or theologians) are asked their opinion on why History is not considered a popular school subject, why lack of digital means usage is so profound in the Hellenic class and how this has changed during the Covid-19 pandemic. Teachers are also asked to propose changes in the curriculum regarding teaching periods and material and evaluate the distant learning period during the pandemic.
Open Access
A two stage DEA model for measuring European regions’ innovative performance
Μαρκογιαννάκης, Χρυσοβαλάντης; Κουνετάς, Κωνσταντίνος; Τζαγκαράκης, Μανώλης; Τσεκούρας, Κωνσταντίνος; Markogiannakis, Chrysovalantis
Τμήμα Οικονομικών Επιστημών (ΜΔΕ)
In this dissertation we follow the methodological approach of measuring the European regions’ innovative performance in two stages. The present framework calculates the innovative behaviour of the European regions using the methodology of data envelopment analysis (DEA) in order to track down regions’ efficiencies. For this purpose, 232 European regions are being tested in a fourteen year time-span, from 2002 to 2015. Empirical results show that regions from France, Germany, United Kingdom and Spain take the best spots. In addition, the average efficiency of the innovative behaviour of the European regions shows improvement through the passage of time.