Electrical & Computer Engineering

Ο στόχος αυτού του εγγράφου είναι να εξηγηθεί πώς ένα τυπικό WSN λειτουργεί, ποιά είναι τα πλεονεκτήματα, τα μειονεκτήματα και τα τεχνικά χαρακτηριστικά του, καθώς επίσης και τα οικονομικά οφέλη από την εφαρμογή της τεχνολογίας αισθητήρων στον τομέα της Γεωργίας Ακριβείας. Επιπλέον προτείνεται μια νέα μέθοδος κατασκευής τοπολογίας δικτύων βασισμένη στις ζώνες ηλεκτρικής αγωγιμότητας και διαχείρισης του εδάφους.

In this paper we are going to propose a new way to build a wireless sensor network which is based on measuring the field's electrical conductivity, staying away from the classic network grid implementation. Furthermore we are going to explain the way a typical WSN works, which are the pros and cons and the technical characteristics, as well as how electrical conductivity can influence our decision to build the WSN topology and the advantage of this approach comparing to the typical ones. Figure 6: Grid Topology & Optimal nodes placement

Αν και οι μοντέρνες στρατηγικές σχεδίασης έχουν ώς κύρια κριτήριά τους την εφαρμογή ασφάλειας (security), επιδεξιότητας (manageability), εξελιξιμότητας (scalability), οι περιορισμοί στο εύρος ζώνης αποτελεί μέγιστο παράγοντα μείωσης της απόδοσης του δικτύου διότι όλη η πληροφορία μεταχειρίζεται με τον ίδιο τρόπο.

Στην εργασία αυτή παρουσιάζεται ένας αλγόριθμος τοποθέτησης αισθητήρων, ο οποίος με βάση τις ζώνες διαχείρισης που έχουν παραχθεί από τη μέτρηση της αγωγιμότητας σε ένα χωράφι, αρχικά τοποθετεί κόμβους στα κεντροειδή των ζωνών αυτών και μετά με βάση τον υπολογισμό του συνόλου και των τοποθεσιών των πιθανών πατέρων του κάθε κόμβου που απαιτούνται για τη δημιουργία ενός spanning tree, προτείνει το τελικό πλήθος και την τελική τοποθεσία των κόμβων που θα αποτελούν ουσιαστικά έναν άκυκλο γράφο. Έτσι, με λιγότερους κόμβους από όσους θα απαιτούνταν σε μία grid τοπολογία λαμβάνουμε εφάμιλλες ποιοτικές και ποσοτικές μετρήσεις, εξοικονομώντας ενέργεια και μειώνοντας το κόστος της λύσης.

Energy-aware connectivity in wireless sensor networks (WSNs) can increase their network lifetime. This can be achieved by optimizing the power control, a particular communication mechanism and the topology control. To this end, in this paper 1 , an energy-aware joint power, packet and topology optimization for WSNs is provided. More specifically, we assume power control based on feedback information, packet transmission through automatic-repeat-request(ARQ) mechanism and topology control assuming specific coverage constraints. This particular joint optimization problem is considered as NP-complete and heuristic methods are usually applied in such complicated cases. In particular, we employ Simulated Annealing (SA) for a step-by-step evaluation of the average energy consumption of sensor nodes, which is considered the objective function of our optimization problem. In each step of the SA algorithm, the resultant topology is evaluated and at the convergence point the near optimal transmit power and packet as well as node placements are obtained jointly.

Extending network lifetime is a primary design objective for a wireless sensor network (WSN). Efficient clustering among sensor nodes seems a promising solution to evenly balance energy consumption and thus extend node and network lifetime. One of the most dominant clustering algorithms for energy efficient cluster formation is LEACH, because it balances node energy consumption. However, stochastic cluster head election of LEACH poses problems. In this paper, we propose a new clustering algorithm, named Minimum Weighted Clustering Algorithm (MWCLA) and compare its effectiveness with LEACH. MWCLA functions as follows: 1) Selects cluster heads based on cost criterion and quantifies the suitability of candidate cluster head by applying weights and 2) Rotates cluster head roles among nodes in a deterministic way, based on residual energy levels. In our simulations, we compare MWCLA with LEACH in terms of network lifetime and we highlight the cases where MW-CLA is better in balancing node energy consumption, improving the efficiency in energy dissipation for communication and prolonging network lifetime. Our comparisons are based on three metrics: FND (First Node Dies), HND (Half Node Dies) and LND (Last Node Dies). MWCLA succeeds a network lifetime extension of 20% -30% as compared to LEACH.

In this paper we outline the design and implementation of a product traceability system based on RFID technology, which is developed as a proof of concept for monitoring and control in agriculture and livestock application domains. In particular, our aim is to combine RFID/WSN monitoring technology and incorporate it to product, transport and disposal processes in order to guarantee quality product to the consumer. To this end, the proposed system requires the integration of network, telecommunication and monitoring technologies as well as the adjustment and customization to meet the very business needs of several entities of the region of Thessaly, Greece. However, our proposed system set-up is open to customization in order to be applied in other RFID applications such as livestock monitoring and production automation.

It has been claimed that robotics can provide new benefits to the learning process at all levels of education. The main ideas of the present study adhered to the constructionist theory, according to which the learning process is not only transmitted from teacher to pupil, but rather constructed in the mind of the pupil in the form of active learning. The purpose of the present study was to implement a robotic toy (Lego Mindstorms NXT TM ) in a Greek primary school, in order to teach twelve year-old children some of the basic concepts of geometry. The main hypothesis of the present study was that children that used the Lego Mindstorms NXT platform would score higher on an evaluation questionnaire than children that formed the control group. Descriptive statistical analysis was performed in order to evaluate the correct answers of the questionnaires. The statistical analysis revealed that children that participated in the experimental group performed better in the 21 items of the questionnaire. Moreover, they mentioned that the geometry course became more interesting and drew their attention in comparison to the courses that were taught through the standard teaching process. It is apparent that the present study follows the line of inquiries that supports that robotics can make a significant impact to education. Robots can be a tool that can enhance the skills of children.

This work aims to familiarize students of the last elementary classes with basic programming modules, through the design and implementation of a training programming scenario, which is based on educational robotics principles, and Lego WEDO / Scratch tools. During their learning process, students are required to design, construct and program their robotic flight simulation airplane mechanisms. In parallel, they will have the opportunity to learn and develop certain skills (e.g. analytical and critical thinking, creativity etc.), while playing and investigating, according to the principles of constructionism. Additionally, all proposed learning activities are based and inspired by the social-cultural theories of learning -by -doing, through cooperation and student interaction at all development stages. Within this framework, the use of educational robotics has positive effects to both cognitive and emotional domain (e.g. self-esteem and self-confidence), as well as to social domain (e.g. socialization and cooperativeness).

In this paper, we optimize the energy consumption and node placements of a wireless sensor network (WSN) using simulated annealing (SA). We propose an energy-aware optimization of the power control, the packet transmission and the topology control in WSNs. An optimization problem of minimizing the energy consumption, which incorporates the power control, the packet transmission through error correcting codes (ECC) and the topology control fulfilling specific coverage constraints is formulated. The considered joint optimization problem is proved NP-complete and for that reason a metaheuristic method based on SA is applied. The energy consumption is related to the average energy consumption of sensor nodes and sensing coverage in a crosslayer fashion. Using the SA algorithm, an updated topology is evaluated at any convergence point and thus a near-optimal transmit power and packet in conjunction with node placement is achieved jointly. From the results, it is inferred that the proposed near optimal topology deployment leads to greater network coverage as compared to the initial node deployment for different cooling schedules. We also compare our results with those obtained by a Random Sampling (RS) heuristic applied to the original problem highlighting that SA leads to better solution than RS since RS does not incorporate probabilistic hill climbing being caught in local minima producing near-optimal solutions. Finally, applying automatic-repeat-request (ARQ), forward error correction (FEC) and hybrid ARQ (HARQ), the results show that the HARQ performs better than the simple ARQ and simple FEC in terms of overall energy consumption.

In this work, we use an unequal energy distribution algorithm, with which we succeed to extend network lifetime. In the sequel, we, we provide the best effort coverage by ar- ranging the nodes using topology control principles. We formulate an optimization prob- lem and define an objective function that incorporates both network coverage and lifetime that should be both maximized. Such a complex problem can be solved in polynomial time through Simulated Annealing (SA). An updated topology is evaluated in each convergence point and a near optimal node placement together with near optimal unequal energy allo- cation charge scheme is achieved. Results reveal that the proposed near optimal topology leads to greater coverage and lifetime as compared to several random deployments. We complete this work by providing a reliability study of the results, which is carried out by analysing the survival function of the derived statistical propertied of the proposed objective function.

In this paper, we study the aggregation between the frequency division duplex
and time division duplex (TDD) spectrum bands within the context of 3GPP LTE-A
system. To be specific, we first provide a cross-layer design analysis to obtain the
achievable throughput using the TDD mode for transmission in LTE-A system. Under
particular QoS requirements and certain channel conditions, the achievable throughput is derived and evaluated. The QoS requirements required from the upper layers, where the file size, the TCP window size and the latency for efficient transmission are incorporated in the final formulation. Having obtained the formulation, simulation results highlight the impact of the QoS parameters to different TDD frame format, wherein the number of DL and UL subframes vary. Having taken into account this design aspects, we propose a framework for TDD frame adaptation within the LTE-A system. The aim of this framework is to provide the dynamic configuration of different TDD frame formats by calculating the DL:UL subframes ratio under certain channel conditions and QoS requirements. We also provide flowchart procedures of how such a solution could be implemented within the 3GPP LTE-A context. Simulation results are carried out, which reveal the probability of choosing the different TDD frame formats from the system under certain channel conditions and QoS requirements.

Στην παρούσα διδακτική – διερευνητική πρόταση που λαμβάνει τη μορφή διαθεματικού project, οι μαθητές/-τριες καλούνται, μέσω ενός προτύπου ταξινόμησης (ταξινόμηση κατά Hubble), να ταξινομήσουν ένα αριθμό γαλαξιών ως προς τη μορφή τους. Καλούνται, επίσης, με τη βοήθεια μαθηματικών μεθόδων, να κατανοήσουν την έννοια της πλάτυνσης ελλειψοειδούς και να την προσδιορίσουν στην πράξη μετρώντας σχετικές διαστάσεις από εικόνες γαλαξιών, με το χάρακα.
Επίσης, μέσω επαναληπτικών διαδικασιών, να σχεδιάσουν πρότυπα σπειροειδών γαλαξιών με τη βοήθεια χάρακα και διαβήτη. Οι επαναληπτικές διαδικασίες σχεδίασης ενός σπειροειδούς γαλαξία πραγματοποιήθηκαν με ακόμη μεγαλύτερη
ακρίβεια και αυστηρότητα μέσω αλγοριθμικών διαδικασιών σχεδίασης σε προγραμματιστικό περιβάλλον της γλώσσας Logo. Το προγραμματιστικό περιβάλλον της Logo ανήκει στην κατηγορία των εκπαιδευτικών λογισμικών που είναι κατάλληλα για την ανάπτυξη συνθετικών εργασιών. Στο τελευταίο στάδιο του project, καλούνται να κατανοήσουν τη δημιουργία σπειρών σε ένα γαλαξία με τη βοήθεια του προτύπου διαφορικής περιστροφής καθώς και την διαπίστωση της ίδιας της διαφορικής περιστροφής μέσω του φαινομένου Doppler.

Συμμετοχή μου στην ομάδα των συγγραφέων στο παρακάτω βιβλίο, το οποίο είναι προς έκδοση από τον εκδοτικό όμιλο ΤΖΙΟΛΑΣ
Τίτλος: ARDUINO και RASPBERRY στην ΕΚΠΑΙΔΕΥΣΗ: Για Παιδαγωγούς και Εκπαιδευτικούς
Σύντομη Περιγραφή:
Το βιβλίο αυτό διαπραγματεύεται εργαλεία physical computing όπως Arduino, Raspberry, εκπαιδευτικής ρομποτικής, τα οποία στηρίζουν STEM διδακτικά σενάρια. Δίνεται πληθώρα παραδειγμάτων και εξετάζονται σενάρια εφαρμογής.

Στην παρούσα διδακτική – διερευνητική πρόταση, οι μαθητές/-τριες καλούνται, μέσω της ανάλυσης επιστημονικών δεδομέ-νων από το πείραμα LIGO, να κατανοήσουν την έννοια του βαρυτικού κύματος που παρήχθη από τη συγχώνευση δύο μαύ-ρων τρυπών, να κατανοήσουν τα μεγέθη που το χαρακτηρίζουν και να τα υπολογίσουν, να προσεγγίσουν το μηχανισμό ανίχνευσης του βαρυτικού κύματος και να εκτιμήσουν τα σφάλματα των μετρήσεων που γίνονται κατά την ανίχνευση. Κα-λούνται, επίσης, με τη βοήθεια κατάλληλων ιστογραμμάτων και γραφικών παραστάσεων που αναπτύχθηκαν μέσω των μο-ντέλων που προτάθηκαν για τη συγχώνευση των μαύρων τρυπών, να εκτιμήσουν το εύρος τιμών των μαζών των συγκρου-σθένων μαύρων τρυπών, την ενέργεια που εκλύθηκε από το φαινόμενο, καθώς και την ευαισθησία των οργάνων ανίχνευ-σης (LIGO). Τέλος, προτάθηκε στους μαθητές/-τριες, με τη βοήθεια αλγοριθμικών διαδικασιών, να πειραματισθούν με διά-φορα ζεύγη υποθετικά συγκρουομένων μαύρων τρυπών και να ελέγξουν τη «μάζα σφυρίγματος» καθώς και αν τα παραγό-μενα βαρυτικά κύματα μπορούν να ανιχνευθούν με την υπάρχουσα ευαισθησία των οργάνων του πειράματος LIGO.

Industrial Internet of Things (IIoT) automation should be based on a framework that guarantees flexible and energy efficient monitoring and control, without the need for frequent human intervention. The ability to analyse and process machine faults in real time is vital, however it poses many technical difficulties and challenges, mainly for industrial application environments. In our paper, we propose a novel, energy efficient, IoT and Cloud based decentralised framework for real time machine condition monitoring (MCM) and fault prediction, where computational demanding tasks are distributed across fog nodes and decision fusion rules are set and controlled by the Cloud. In particular, data acquisition phase is done by sensors distributed across machines, feature extraction and health condition classification is done by fog nodes, after receiving data and instructions as processed by the Cloud node. Our framework is based on collaboration and information flow among IoT, Fog and Cloud layers. To this purpose, we formulate a global consensus cross layer optimisation problem, concerning industrial healthy status monitoring, and we solve it in a distributed manner by applying asynchronous altering direction method of multipliers (ADMM) algorithm.

Computational Pedagogy is an instructional approach based on Computational Science and the Computational Experiment as well as on the CPACK model. Computational Science in Education engages students in computational modeling and simulation technology in alignment with the essential features of Inquiry based teaching and learning approach and the Computational Thinking dimensions (practices and skills). STEAM –content based epistemology- education is connected to Computational Pedagogy through the Computational Experiment leading to a proposed model called ‘Computational STEAM Content Pedagogy’ as a teaching and learning approach which can be implemented in a STEAM holistic interdisciplinary/trans-disciplinary epistemology approach to the curriculum for solving real computational problems.

The aim of this research is to suggest a didactic approach as to how students comprehend the growth and the activities of the two most well-known Ancient Greek civilizations (i.e. the Mycenaean and the Cycladic). The teaching approach is based on STEM perspective, the use of several digital technologies, as well as several learning theories. Digital technologies help students delve into the process of scientific discovery. The degree of new technology and STEM – based didactic approach appealing to students is evaluated through questionnaires. In particular, in our survey, 115 students participated and the questionnaires distributed to four schools of Volos and Veria Greece region. The Research was carried out with the consensus of their parents. According to our results, students expressed great interest in STEM activities that they were exposed to. Moreover, they expressed high interest in the integration of a classic history lesson with new technologies and they developed the abi...