1. Διατριβές & Εργασίες | Theses & Dissertations

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Στην συλλογή αυτή συγκεντρώνονται συστηματικά όλες οι εργασίες των μεταπτυχιακών φοιτητών, δηλαδή οι πτυχιακές εργασίες υποψηφίων για Μεταπτυχιακό Δίπλωμα Ειδίκευσης (ΜΔΕ) και εργασίες για την απόκτηση διδακτορικού τίτλου (ΔΔ). Συγκεντρώνονται επίσης και πτυχιακές εργασίες για όσα Τμήματα έχουν ορίσει ως υποχρεωτική την υποβολή τους στο Αποθετήριο για τη λήψη πτυχίου

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Open Access
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(ΤΕΙ Δυτικής Ελλάδας, 12/30/1899) ΜΑΡΙΑ ΜΠΟΧΩΡΙΔΟΥ;
ΔΙΟΙΚΗΣΗ ΚΟΙΝΩΝΙΚΩΝ ΣΥΝΕΤΑΙΡΙΣΤΙΚΩΝ ΕΠΙΧΕΙΡΗΣΕΩΝ ΚΑΙ ΟΡΓΑΝΩΣΕΩΝ (ΔΕ)
Open Access
0 ΡΟΛΟΣ & Η ΣΗΜΑΣΙΑ ΕΦΑΡΜΟΓΗΣ ΤΟΥ ISO 9001:2000 ΣΤΙΣ ΕΠΙΧΕΙΡΗΣΕΙΣ ΠΑΡΑΓΩΓΗΣ ΠΡΟΪΟΝΤΩΝ (ΤΡΟΦΙΜΩΝ) & ΠΑΡΟΧΗΣ ΥΠΗΡΕΣΙΩΝ
(ΤΕΙ Δυτικής Ελλάδας, 06/01/2006) ΜΕΝΤΖΕΛΟΥ ΚΩΝΣΤΑΝΤΙΝΑ; ΜΠΙΤΣΑΚΗ ΕΥΔΟΚΙΑ; ΒΕΤΣΟΠΟΥΛΟΣ ΑΠΟΣΤΟΛΟΣ
ΔΙΟΙΚΗΣΗ ΚΟΙΝΩΝΙΚΩΝ ΣΥΝΕΤΑΙΡΙΣΤΙΚΩΝ ΕΠΙΧΕΙΡΗΣΕΩΝ ΚΑΙ ΟΡΓΑΝΩΣΕΩΝ (ΔΕ)
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 simulation of blood flow in the microcirculation
Ζαμπέλης, Δημήτριος; Zabelis, Dimitris
Τμήμα Χημικών Μηχανικών (ΔΕ)
This thesis concerns hemodynamics in the microcirculation. More specifically, it studies the effect of the hematocrit, vessel diameter and shear-rate on the relative apparent viscosity and velocity profile of blood and on the thickness of the cell-free layer in straight microvessels. In this regard, the theoretical framework, upon which the abovementioned dependences are based, consists of all the fundamental hemodynamical phenomena [1], that is, the formation of the cell-free layer, the Fahraeus and Fahraeus-Lindqvist effects and the shear-thinning behavior of blood [2]. To accomplish the above, this research employs the computing framework proposed by Závodszky et al. [1]. On the one hand, the blood cells, here only the red blood cells, are explicitly modeled as deformable membranes, that consist of networks of Lagrangian surface points [3, Ch. 4] and their responses to force fields are dictated by the constitutive model found in [1]. On the other hand, the suspending medium, in this case, the blood plasma, is represented using the lattice Boltzmann method [1], [3, Ch. 4]. Then, the collective blood behavior emerges as a product of the coupling of the aforementioned cellular and liquid components that the immersed boundary algorithm achieves [1], [3, Ch. 4]. Last, it should be noted that all simulations concern blood flows in straight microvessels with circular cross-sections and that the hemodynamical features are always calculated at steady flow conditions. The final results that stem from a systematic parametric study of approximately 70 simulations are presented in three different forms. First, for all three examined hemodynamical features the corresponding data are given in proper diagrams of those features against the shear-rate for various hematocrits or vessel diameters. Second, the microstructural configurations of some representative systems are displayed and third, whenever possible, the algebraic correlations derived from the non-linear fittings on the data are proposed as well. To conclude it should be highlighted that not only all the results are in qualitative agreement with the theoretical remarks mentioned above, but the quantitative comparison also demonstrates that they are in accordance with the few available data points provided in the literature [1], [4].
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)
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Open Access
3D subject-specific subject specific modeling, finite element analysis and evaluation of biomechanics of the knee complex after anterior cruciate ligament reconstruction
Ρισβάς, Κωνσταντίνος; Risvas, Konstantinos
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογ. (ΔΕ)
The Anterior Cruciate Ligament (ACL) injury is one of the most common knee injuries during sports activities. Anterior Cruciate Ligament reconstruction (ACLR) is a surgical approach that has emerged as the golden standard treatment, where a graft is placed in the position of the torn ligament through tunnels that are drilled on the femur and tibia bones, close to the native ligament origin and insertion sites. Over the course of years, many ACLR techniques have been developed featuring a plethora of parameters like the number of the drilled tunnels, the tunnel positioning, the graft harvesting site, the graft pre-tensioning load and much more. To evaluate the results of each selected ACLR approach, follow up examination is required.The complex nature of these examinations and recent technological advances paved the way for computational biomechanics as an alternative and effective tool to the disposal of biomedical researchers. Finite Element Analysis (FEA) is a valuable modeling and simulation approach of computational biomechanics, that enables to capture the geometry and material effects on the response of the anatomical structures like the knee joint under various loading conditions. In this thesis, a workflow that generates subject-specific FEM models of the knee joint to assess knee biomechanics after ACLR is developed. The proposed pipeline includes modeling and simulation of all key steps of ACLR, from tunnel drilling to graft fixation. Furthermore, it provides simulation scenarios that represent daily life activities, such as gait, and clinical exams, such as the Lachman test, to evaluate the performance of the ACL reconstructed FEM knee models, laying the ground for performing "what if" scenarios in order to predict the effectiveness of the ACLR approach. In the confines of this work we evaluated the performance of Single and Double Channel, Anteromedial and Transtibial portal surgery techniques and the response of three different graft materials under various pre-tension loads and fixation angles in simulation scenarios representing the Lachman test and a gait trial. Despite the limitations regarding the FE models constraints and the inherent complex nature of FEM simulations, the present work provides the groundwork for developing an extended and fully featured ACLR modeling framework.
Open Access
3Δ ανίχνευση αντικειμένων σε νέφη σημείων με χρήση βαθιάς γεωμετρικής μάθησης
Ρωμανέλης, Ιωάννης; Romanelis, Ioannis
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογ. (ΔΕ)
Η 3D ανίχνευση αντικείμενων βρίσκει εφαρμογή σε προβλήματα που κυμαίνονται από την αυτόνομη οδήγηση έως τη ρομποτική όραση. Σε αυτά τα προβλήματα απαιτείται πολύ μεγάλη ακρίβεια, καθώς ένα λάθος μπορεί να έχει σοβαρές συνέπειες. Για το λόγο αυτό έχουν αναπτυχθεί πιο σύνθετοι αισθητήρες, όπως το LIDAR (Light Detection And Ranging), για την καλύτερη αναγνώριση του περιβάλλοντος. Στην εργασία αυτή μελετάται το πρόβλημα της 3D ανίχνευσης αντικειμένων σε σκηνές εξωτερικού χώρου, ως μέρος του γενικότερου προβλήματος της αυτόνομης οδήγησης. Για να δημιουργηθούν τα δεδομένα ένας LIDAR αισθητήρας τοποθετείται στην οροφή του οχήματος, το οποίος επιστρέφει ένα νέφος σημείων που περιγράφει το χώρο 360 μοίρες γύρω από αυτό. ́Οπως και στην 2D ανίχνευση δεδομένων έτσι και στην 3D οι αλγόριθμοι που έχουν ξεχωρίσει για αυτό το πρόβλημα είναι αυτοί βασισμένοι σε βαθιά νευρωνικά δίκτυα. Το πρόβλημα της γενίκευσης των δικτύων στα νέφη σημείων έγκειται στο πως θα δεχτούν τα νέα δεδομένα, καθώς σε αντίθεση με την εικόνα όπου τα εικονοστοιχεία είναι διατεταγμένα σε ένα πλέγμα, τα σημεία βρίσκονται στο συνεχή χώρο. Για να υπερκεραστεί αυτό το πρόβλημα γίνεται χρήση της αναπαράστασης των αραιών voxel, καθώς με αυτά μπορούν να δημιουργηθούν δίκτυα εκτελέσιμα σε πραγματικό χρόνο, διατηρώντας μικρές απαιτήσεις μνήμης. Το πρώτο δίκτυο που μελετάται αποτελεί επανυλοποίηση ενός από τα σημαντικότερα δίκτυα που έχουν προταθεί για το πρόβλημα της 3D ανίχνευσης. Το δίκτυο αυτό χρησιμοποιεί ανά σημείο πλήρως συνδεδεμένα επίπεδα για να εξάγει τα χαρακτηριστικά των voxel, το μέρος αυτό της αρχιτεκτονικής καλείται Voxel Feature Extractor (VFE). Τα voxel αυτά εισέρχονται σε μία σειρά από αραιά συνελικτικά επίπεδα για να εξαχθούν τα 3D χαρακτηριστικά, τα οποία γίνονται προβολή σε Bird’s Eye View (BEV) εικόνα και ένας 2D συνελικτικό δίκτυο εξάγει τις τελικές προβλέψεις. Η αρχιτεκτονική αυτή δοκιμάζεται για δεδομένα εισόδου σε καρτεσιανές αλλά και κυλινδρικές συντεταγμένες. Στη δεύτερη αρχιτεκτονική το δίκτυο διαμορφώνεται ώστε να αφαιρεθεί ο VFE, χρησιμοποιώντας απευθείας αραιές συνελίξεις στο κβαντισμένο νέφος. Για την αρχιτεκτονική αυτή γίνονται, επίσης, εκτεταμένα πειράματα ως προς τα δεδομένα εισόδου της αλλά και τον αλγόριθμο βελτιστοποίησής της. Το υλοποιημένο δίκτυο εκπαιδεύτηκε στο σύνολο δεδομένων KITTI. Για την αξιο- λόγηση του έγινε διαχωρισμός του συνόλου σε δύο υποσύνολα, ένα για εκπαίδευσης και ένα για αξιολόγηση των αποτελεσμάτων. Το τελικό δίκτυο καταφέρνει να εξάγει αποτελέσματα συγκρίσιμα με τις state-of-the-art μεθόδους.
Open Access
A cognition-centered personalization framework for cultural-heritage applications
Ράπτης, Γεώργιος; Raptis, George
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογ. (ΔΔ)
Cultural-heritage applications provide the visitors with high volume of cultural information and therefore there is a need for personalizing the visit experience to help visitors understand and perceive the provided cultural content according to the characteristics of their cognitive style. However, the current research and design attempts do not consider the diversity of the visitors, in terms of their cognitive styles, as an important design and evaluation factor. Cognitive styles influence the way people seek, collect, organize, process, and recall information and are expected to have an impact on the cultural-heritage domain, which is enriched in cultural information. The results presented in the PhD thesis revealed that visitors with different cognitive styles behave differently when interacting with cultural-heritage applications. Theses differences influence the visit experience, in terms of content understanding and immersion. The current cultural-heritage applications do not consider the diversity of the visitors in terms of cognitive styles, and thus, they unintentionally led to experience imbalances between visitors with different cognitive styles. The PhD thesis presents CogniCHeF, which is a framework that aims to help designers to deliver personalized cultural-heritage applications tailored to the visitors’ cognitive styles, aiming to offer them an enhanced visit experience. Moreover, the results presented in the PhD thesis revealed that the cognitive styles can be elicited automatically with high accuracy during the first stages of interaction between the visitors and the cultural-heritage applications through the use f eye-tracking data. Furthermore, the results presented in the PhD thesis revealed that CogniCHeF can be efficiently used by cultural-heritage designers to implement personalized applications tailored to the visitors’ cognitive styles. Finally, the results presented in the PhD thesis revealed that cognition-centered personalization improved the overall visit experience.
Open Access
A computational study of blood flow in the left atrium of patients with atrial fibrillation
Βάρσος, Παύλος; Varsos, Pavlos
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχανικ. (ΔΕ)
The main object of this Diploma Thesis is the computational study of blood flow in the left atrium of patients with Atrial Fibrillation. Atrial Fibrillation is the most frequent cardiac arrhythmia worldwide, since it affects 1 to 2% of the general population, while it is accompanied by high mortality rates. Like any other arrhythmia, Atrial Fibrillation refers to cases in which the electrical activity of the heart involves abnormalities, which are often not completely treated with neither medication nor surgery. A critical treatment method, minimally invasive, is catheter ablation which is simultaneously conducted with the procedure of electrophysiological mapping of the left atrium. The scope of this project is to create a framework for the comparison of mappings of multiple wall shear stress indices (which according to experiments are associated with the cardiac electrical activity) with electrophysiological mappings, using patient-specific data provided by doctors. Possible correlations can supply doctors with crucial information in a direction of improving the ablation process outcomes. Reconstruction techniques are implemented to convert two-dimensional MRI images into three-dimensional models of the left atrium. Following the optimization of the 3D model, the mesh generation and the solution of the cardiac flow procedures take place. Both of these processes are performed in the open-source software, OpenFOAM ®, as we take advantage of the countless capabilities offered. After generating the mesh, a procedure of paramount importance for a computational study, the mesh independence study is carried out under steady state conditions using the simpleFoam solver, aiming to obtain the most suitable model for the present project. At the same time, various turbulence models and boundary conditions are tested in order to detect any possible differences in blood flow behavior. Finally, a transient flow simulation of a realistic cardiac cycle is conducted, utilizing the pisoFoam solver, since our main goal is to visualize the distribution of a variety of hemodynamic parameters, such as the Oscillatory Shear Index, as well as indices for indicating blood stasis in high-risk areas of the left atrium, like the Left Atrial Appendage.
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.
Open Access
A constructionist view of complex interactions between inflection and derivation: the case of SMG and Griko
(2014-09-15) Κουτσούκος, Νικόλαος; Ράλλη, Αγγελική; Booij, Geert; Iacobini, Claudio; Γαβριηλίδου, Ζωή; Μανωλέσσου, Ιώ; Ευθυμίου, Αγγελική; Ξυδόπουλος, Γεώργιος; Koutsoukos, Nikolaos
Τμήμα Φιλολογίας (ΔΔ)
One of the most difficult, but -at the same time- interesting questions in morphological theory is the relation between inflection and derivation. This question lies at the heart of the problem of the architecture of the morphological component and thus raises important issues such as: (a) the relation between the lexicon and the grammar, and (b) the model which best accounts for the relevant facts. In the present thesis, the aim is to examine certain morphological phenomena which reveal the close relation between the two processes, and to show that both should be accounted for in the morphological component. Three aspects of the problem are exhaustively discussed, drawing data from Standard Modern Greek and Griko: (a) the relation between conversion and inflectional classes in Standard Modern Greek, (b) the evolution of derivational affixes into inflectional ones in Griko and (c) the appearance of inflection inside derivation in both Griko and Standard Modern Greek. The analysis of the data is given within a Construction Morphology (CM) framework. CM offers important insights into the problem since it has a strong lexicalist orientation with both inflection and word formation within the lexicon, and the proposed word-formation schema (construction) is applicable to both derivation and inflection. The CM framework provides effective solutions to the problems discussed in the relevant chapters and paves the way for the analysis of similar phenomena. It should be mentioned that the contribution of the present thesis to the relevant discussion can be described in two points: (a) it presents some data that have not been described before and offers an up-to-date analysis, (b) it examines the relation between the two processes within the CM framework.
Open Access
A containerized monitoring toolkit to measure performance in 5G/NFV networks
(2022-10-12) Σαμαράς, Κωνσταντίνος; Samaras, Konstantinos
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογ. (ΔΕ)
Nowadays network connectivity touches almost every aspect of our daily lives which means the use of mobile data keeps growing thus creating the need for a more sophisticated mobile technology, 5G. The next generation of wireless technology, 5G is based on a cloud-native core (5GC), can utilize virtualization technologies and follow a Service-based architecture thus taking advantage of all their benefits. However, even on 5G networks, in order to fulfill the Quality of Service (QoS) requirements, it is crucial for network providers to monitor various points in the network and detect any faults. Testing network performance and collecting metrics helps a service provider to define network resource utilization, predict future traffic demands, identify abnormal traffic patterns, and offer suggestions for enhancing network performance. Network administrators traditionally use monitoring tools to measure and analyze the network, for instance a tool that uses client-server approach. Moreover, one of 5G’s key technology is virtualization and while hypervisor-based virtualization is the prevailing technology, the environment is altering recently, as a new form of virtualization that has existed for a long-time gains popularity, called containerization. Since enterprises grow more and more their adoption of Cloud Computing solutions, they also move towards containerized technologies and microservices concepts because of the wide range of benefits they offer, as better uptime, faster deployments, better hardware utilization and lower costs are only a few of them. The purpose of this thesis is to describe the basic concepts of these technologies, then create a containerized and orchestrated toolkit, with which we could monitor and make measurements throughout a 5G container-centric Cloud infrastructure to test the network performance and collect metrics. To achieve that, Docker and Kubernetes as the container technologies are used, along with a set of free open-source monitoring tools like Iperf3 and Ookla Speedtest, resulting in a lightweight and easily configurable implementation.
Open Access
A contribution to the theoretical study and numerical calculation of edge diffraction
Νικολάου, Πέτρος; Μενούνου, Πηνελόπη; Μενούνου, Πηνελόπη; Σκαρλάτος, Δημήτριος; Ταρουδάκης, Μιχαήλ; Μουρτζόπουλος, Ιωάννης; Παπαδόπουλος, Πολύκαρπος; Πολύζος, Δημοσθένης; Κωστόπουλος, Βασίλειος; Nikolaou, Petros
Τμήμα Μηχανολόγων και Αεροναυπηγών Μηχαν. (ΔΔ)
The subject of the present thesis is the sound field around solid obstacles and specifically, the diffraction field generated as sound reaches the edges of the obstacles. Consider, for example, the edge of a half-plane or of a wedge. Diffraction is important in many practical problems, such as noise barriers, sonic boom propagation around buildings, room acoustics, volcanic explosions or ancient theater acoustics. The present work aims to derive new analytical solutions and/or to extend existing models in both time and frequency domain. The purpose of the work is to provide new physical insight in the study of diffraction and to accelerate its computation. The analysis begins in the frequency domain, where an existing analytical model, the Directive Line Source Model (DLSM), is extended in areas where it was not valid before. The new model has a unified form for all types of incident radiation, being exact for plane incident waves and approximate for cylindrical and spherical incident waves. It is shown that the diffraction field can be interpreted as radiation from a directional line source (as stipulated by the original DLSM) irrespective of the receiver proximity to a shadow boundary, provided that the directivity of the virtual line source is appropriately modified. The properties of the new directivity function are investigated, its parameters recast and appropriate simpler asymptotic forms presented. Based on the new directivity function a new, precisely defined separation of the diffraction field around the shadow boundaries is proposed, which also provides a computational advantage for large scale simulations. Further, the proposed reformulation of the diffraction solution and of its parameters enables the application of the model to two cases of practical interest: (i) directional sound sources and (ii) diffraction by wedges, where the proposed formulation is considerably faster to compute than well-established solutions. In time domain a new solution in the form of impulse response is also derived as the Fourier transform of the proposed frequency domain solution. The proposed impulse response, as its frequency counterpart, has a unified form for all types of incident signals, is exact for plane incident signals, and approximate for cylindrical and spherical incident signals. The investigation of the derived formulation leads to the derivation of a generator curve that embodies the impulse response at any source–receiver configuration. The generator curve is function of a single variable, namely the diffraction number. The diffraction number is a universal diffraction parameter, which translates the generator curve into impulse response at all times and all source-receiver locations, according to a condition termed the similarity condition. The employment of the generator curve can provide considerable computational benefit compared to direct computations. A separation of the diffracted signal into precisely determined time stages is also proposed. Further, for the case of the spherical incident signal the concept of the generator curve is also extended for the case of the exact solution. The exact solution is embodied in the same generator curve as the approximate solution but with a different diffraction number and similarity condition. A separation of the diffracted signal based on the exact impulse response is also proposed. The work continues in the time domain with the study of the convolution between the impulse response and the incident signal, which is used to obtain the diffracted signal or diffraction response. The primitive functions of the proposed impulse response are employed to: (i) prove that the convolution of the impulse response with any bounded signal is bounded for all times, (ii) obtain analytically the diffraction response, as combination of elementary functions, for any incident signal approximated piecewise by fitting polynomials, (iii) improve the performance of the numerical convolution by orders of magnitude, and (iv) handle the convolution of very sparsely sampled incident signals. The analysis also handles the diffraction of spherical signals incident on edges of finite length. Existing finite length diffraction theory and the proposed impulse response for the infinite edge are combined to form a new impulse response for the finite edge. The new impulse response has a simple analytical form and as opposed to other analytical solutions does not require integration along the edge length to compute the diffracted signal. Because it is based on the impulse response for infinite edges, it inherits all afore mentioned benefits associated with its primitive functions. Furthermore, it offers substantial computational benefit compared to traditional integration formulas along the edge. In the frequency domain the Fourier transform of the new finite length impulse response can be approximated analytically. The resulting frequency formula does not require integration along the edge and offers physical insight on exactly how much different portions of the edge contribute to the total diffraction field.
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 decentralized API registration and discovery system on the Ethereum blockchain utilized for smart cities
(2023-03-02) Παππάς, Θωμάς; Pappas, Thomas
Τμήμα Ηλεκτρολ. Μηχαν. και Τεχνολ. Υπολογ. (ΔΕ)
The rapid emergence of the Internet of Things (IoT) technology has prospered the concept of smart city, which refers to an urban area that facilitates the coexistence of people, organizations, environment and technology. IoT plays a major role, as it enables the sensing of physical events that occur, along with actuating on various objects in a city, thus granting valuable information and services for the citizens. Usually, the architecture of a smart city IoT implementation can be conceptualized in five distinct layers. The realization of IoT in smart cities faces a significant obstacle in the form of interoperability challenges inside and between these five layers. Interoperability denotes the capacity of various systems to communicate and exchange data smoothly, without requiring manual intervention. The absence of interoperability between IoT devices and software systems can lead to information silos, wherein data cannot be accessed or utilized by other systems. This thesis focuses on the discoverability of Layer 3 platform systems by Layer 4 applications, without prior knowledge of them, in a complex city scenario. Layer 3 platforms abstract the sensor and networking layers from the end-user applications and are responsible for the registration, discovery and management of devices (sensors, actuators), security, semantics and communication management with other software systems. Generally, platforms expose RESTful northbound APIs, so applications can onboard and receive data and functionality. The proliferation of these APIs is a prominent issue and a common place for the accumulation of the API specifications of the platforms is necessary. After examining the importance of transparency of operations in a collaborative environment such as a smart city, the utilization of Peer-to-Peer systems is unfolded. Taking into consideration the advantages, but also the limitations of blockchain networks, the solution proposed is a decentralized API Directory that can be deployed in any Ethereum Virtual Machine (EVM) compatible public or private blockchain. This API Directory can be used as a common place for smart-city IoT platforms to publish their API specifications, formulated on the OpenAPI specification standard, and for end-user applications to discover them based on location and desired category. Finally, a smart parking use case is demonstrated as a proof of concept for the system.