1,721,126 research outputs found
Phonon and electron transport engineering for enhanced thermoelectric performance and the challenges of device integration [Dataset]
No full textThermoelectricity has long been recognized as a transformative technology for power generation and cooling, owing to its capability to convert heat directly into electricity and vice versa, thereby facilitating cost-effective and environmentally friendly energy conversion. Following a period of modest activity, the field has experienced a remarkable resurgence since 2000, driven by significant advancements in the development of a diverse array of new materials and compounds, alongside enhanced capabilities for controlled nanostructuring. This rapid growth and the innovative breakthroughs observed over the past two decades can be largely attributed to a deeper understanding of the physical properties at the nanoscale. Among the various thermoelectric materials, nanostructured variants exhibit the highest potential for commercial application due to their unprecedented thermoelectric performance, which arises from substantial reductions in thermal conductivity. However, further advancements will not rely solely on nanostructuring; they will also necessitate novel electronic structure design concepts that require a comprehensive understanding of the complexities of electronic and phonon transport. These developments present significant opportunities for thermoelectric energy harvesting, power generation, and cooling applications. This Dataset refers to the article which summarize and elucidate the breakthroughs reported in recent years, discuss future avenues that integrate nanostructuring concepts with the rich electronic structures of novel materials, and provide a critical overview of the future directions in thermoelectric materials research. Additionally, it offers a comprehensive overview of state-of-the-art thermoelectric materials and devices and a summary of the challenges associated with transitioning these materials into practical devices.This work was supported by a Grant named ERC Advanced (POWERbyU Grant Agreements No. 101052603) and ERC Starting Grant (NANOthermMA grant agreement No. 678763).Peer reviewe
Phonon and electron transport engineering for enhanced thermoelectric performance and the challenges of device integration
No full textThermoelectricity has long been recognized as a transformative technology for power generation and cooling, owing to its capability to convert heat directly into electricity and vice versa, thereby facilitating cost-effective and environmentally friendly energy conversion. Following a period of modest activity, the field has experienced a remarkable resurgence since 2000, driven by significant advancements in the development of a diverse array of new materials and compounds, alongside enhanced capabilities for controlled nanostructuring. This rapid growth and the innovative breakthroughs observed over the past two decades can be largely attributed to a deeper understanding of the physical properties at the nanoscale. Among the various thermoelectric materials, nanostructured variants exhibit the highest potential for commercial application due to their unprecedented thermoelectric performance, which arises from substantial reductions in thermal conductivity. However, further advancements will not rely solely on nanostructuring; they will also necessitate novel electronic structure design concepts that require a comprehensive understanding of the complexities of electronic and phonon transport. These developments present significant opportunities for thermoelectric energy harvesting, power generation, and cooling applications. This article aims to summarize and elucidate the breakthroughs reported in recent years, discuss future avenues that integrate nanostructuring concepts with the rich electronic structures of novel materials, and provide a critical overview of the future directions in thermoelectric materials research. Additionally, it offers a comprehensive overview of state-of-the-art thermoelectric materials and devices and a summary of the challenges associated with transitioning these materials into practical devices.This work was supported by a Grant named ERC Advanced (POWERbyU Grant Agreements No.
101052603) and ERC Starting Grant (NANOthermMA grant agreement No. 678763).Peer reviewe
Εφαρμογή υπαρχόντων αλγορίθμων συστάσεων, σε εκπαιδευτικά σύνολα δεδομένων, απο αποθετήρια μαθησιακών αντικειμένων
No full textΠεριέχει βιβλιογραφικές παραπομπές.Τα συστήματα συστάσεων στο διαδίκτυο, έχουν ως στόχο τη συλλογή των πληροφοριών, που θα αποτυπώσουν τις προτιμήσεις του εκάστοτε χρήστη και θα του προσφέρουν την ιδανικότερη για αυτόν σύσταση. Μελετήθηκε ο τομέας των συστημάτων συστάσεων στην εκπαίδευση. Κάθε σύστημα σύστασης στηρίζεται σε έναν αλγόριθμο, ο οποίος λαμβάνει ως είσοδο, δεδομένα και προτιμήσεις του χρήστη και παράγει την ιδανικότερη για αυτόν σύσταση. Αυτό που προσπαθεί να επιτύχει το κάθε σύστημα σύστασης, είναι η σειρά των αποτελεσμάτων που θα παράξει, να έχει άμεση σχέση και συνάφεια, με αυτό που ζήτησε ο χρήστης.
Η παρούσα διπλωματική εργασία επιχειρεί μια εμβάθυνση στο τομέα των συστάσεων, μέσα από βιβλιογραφική ανασκόπηση και παράλληλα γίνεται μία προσπάθεια παρουσίασης, των τεχνικών που χρησιμοποιούνται για να συσταθούν τα συστήματα, στα οποία αναπτύσσονται. Γίνεται μια ανάλυση τριών κατηγοριών αλγορίθμων συστάσεων, των αλγορίθμων συστάσεων που εστιάζουν στο περιεχόμενο, των αλγορίθμων συνεργατικών φίλτρων και των αλγορίθμων συστάσεων ανάλυσης γράφων.
Παρουσιάζεται μια πλήρης περιγραφή των εκπαιδευτικών συνόλων δεδομένων, στα οποία εφαρμόζονται οι αλγορίθμοι συστάσεων. Μελετήθηκε η μορφή τους καθώς και ο τρόπος με τον οποίο συλλέγονται οι πληροφορίες που τα απαρτίζουν. Αναλύθηκαν οι μέθοδοι με τις οποίες αυτά διαχωρίζονται και διαιρούνται σε κλάσεις και στην συνέχεια πως επεξεργάζονται.
Χρησιμοποιήθηκε το λογισμικό recommender101, για την εφαρμογή των αλγορίθμων στα σύνολα δεδομένων MovieLens 100K, 1M, 10M, και για τη εξαγωγή των αποτελεσμάτων. Οι αλγόριθμοι που επιλέχθηκαν ώστε να αξιολογηθούν είναι ο Κ-ΝΝ, Slope One, Funk SVD, BPRMF Naïve Bayes.
Η εκτέλεση τους, σε διαφορετικά σύνολα δεδομένων, η δομή και το περιεχόμενο των οποίων περιγράφεται αναλυτικά στην εργασία, απέδειξε ότι οι γράφοι ανήκουν στην κατηγορία εκείνη των αλγορίθμων που σημειώνουν τα μεγαλύτερα ποσοστά. Παρουσίασαν διακυμάνσεις στην επίδοσή τους γεγονός το οποίο οφείλεται στα ιδιαίτερα χαρακτηριστικά των συνόλων δεδομένων. Αξιολογήθηκαν διάφορες μετρικές, από τα αποτελέσματα του κάθε αλγορίθμου, πάνω σε διαφορετικά σύνολα δεδομένων, για να γίνουν γνωστές οι συνθήκες υπό τις οποίες λειτουργούν καλύτερα.Recommender systems came up having as main purpose the collection of all the available information in order to provide the user with the best suitable for him recommendation. Beyond all existing applications, the area of recommender systems seems to be invading the world of education. As described above, each and any of the recommender systems use an efficient algorithm in order to gather all the necessary information about the user and offer him as a result the most effective and appropriate solution regarding his research. The outcome of the algorithm should produce an immediate connection among user and suggestion in order for it to cover completely his necessity.
The present thesis begins with a description of the above described field as well as with what it represents. There was made a serious effort in order clarify the nature of recommender systems in combination with their present route, their acceptance from the users and their future. Through a thorough literature review there was made a serious attempt of deepening in this specific area. Attempt an analysis of three classes of recommendations algorithms, “Content-Based Recommender Algorithms”, “Collaborative Filtering Algorithms” and “Graph-Based Recommender Algorithms”.
In addition to this, the thesis contains a thorough research in the world of the datasets that basically consist the main tool of the recommender systems. Topics such as the formulation of dataset, the information included as well as the way that the information becomes part of a dataset were extensively investigated and presented. Furthermore, the present thesis tried to analyze all methods used in datasets in order to separate them and divide them into classes.
Software such as “recommender101” was used to apply a number of different algorithms over different datasets, like MovieLens 100K, 1M and 100M. The algorithms were chosen to be assessed are K-Nearest Neighbor, Naive Bayes (BPRMF), Funk SVD and Slope One. Datasets used were completely different in structure and content as their use had as main purpose the evaluation of the algorithms. Graphs proved out, to be the most reliable source, as they scored the highest percentages, in terms of prediction. Fluctuations their performance which is due to the specific characteristics of the data sets. Evaluated the results of each algorithm, on most important metrics, through different data sets, to be known the conditions under which they work best
Ο ρόλος των ακαδημαϊκών προσόντων στην επαγγελματική επιτυχία του ατόμου στην κύπρο: Συνέπειες
No full textΠεριέχει βιβλιογραφικές παραπομπές.Η επαγγελματική επιτυχία είναι ένα από τα πλέον ουσιώδη θέματα που προβληματίζουν τόσο τους ίδιους τους εργαζόμενους, τους οργανισμούς που τους απασχολούν αλλά και την ευρύτερη κοινωνία στο σύνολο της. Ο ρόλος των ακαδημαϊκών προσόντων στην επαγγελματική επιτυχία του ατόμου στην Κύπρο αποτελεί το βασικό ερευνητικό αντικείμενο της διατριβής μας, σε μια ομολογουμένως δύσκολη οικονομική συγκύρια για ολόκληρο τον κόσμο, με τον τομέα της απασχόλησης να αντιμετωπίζει ιδιαίτερα σοβαρά προβλήματα.
Βασικός σκοπός της παρούσας εργασίας ήταν να διερευνήσει την ύπαρξη επαγγελματικής επιτυχίας ανάμεσα στους εργαζόμενους στην Κύπρο και πιο συγκεκριμένα να εξετάσει κατά πρώτο και κύριο λόγο σε ποιο βαθμό μπορεί να συσχετιστεί με τα ακαδημαϊκά προσόντα και κατά δεύτερο με μια σειρά από άλλους παράγοντες που επιδρούν τόσο στην αντικειμενική όσο και στην υποκειμενική επαγγελματική επιτυχία. Αναφορά γίνεται επίσης και στα αποτελέσματα που προκύπτουν από αυτή την κατάσταση.
Η θέση της διατριβής είναι ότι τα ακαδημαϊκά προσόντα καθορίζουν αλλά δεν διασφαλίζουν την επαγγελματική επιτυχία στην Κύπρο. Συνδέονται θετικά με τα περισσότερα αντικειμενικά κριτήρια επαγγελματικής επιτυχίας, με την σημαντικότερη συσχέτιση να εντοπίζεται ως προς τον μισθό, ενώ για την υποκειμενική επαγγελματική επιτυχία τα αποτελέσματα είναι κάπως ασαφή, χωρίς ιδιαίτερα σημαντικές συσχετίσεις. Όσον αφορά τους υπολοίπους παράγοντες που επιδρούν στην επαγγελματική επιτυχία, οι σημαντικότερες συσχετίσεις αφορούν την καθοδήγηση και την ύπαρξη εμπιστοσύνης προς τους ανώτερους, ενώ σχετικά με τα αποτελέσματα που προκύπτουν, η αφοσίωση στον οργανισμό, η κοινωνική αναγνώριση, το χαρακτηριστικό της Organizational Citizenship Behavior και η μειωμένη συστηματική απουσία επίσης συνδέονται θετικά με την ύπαρξη ακαδημαϊκών προσόντων, κάτι που συνάδει με τα αποτελέσματα προηγούμενων ερευνών.
Δεν παρουσιαστήκαν σημαντικές στατιστικές συσχετίσεις ανάμεσα στην ύπαρξη ακαδημαϊκών προσόντων και την ικανοποίηση που προκύπτει από το μισθό, αν τα άτομα κάνουν στην εργασία τους πράγματα που τους ευχαριστούν, τις προσωπικές φιλοδοξίες και την ύπαρξη εμπιστοσύνης ανάμεσα σε συναδέλφους.Career success is one of the most substantial issues that concern the employees, employers and the whole society including them. The influence of academic qualifications on the career success of an individual in Cyprus is our basic subject, in a difficult financial timing for the whole world and especially the section of employment which is facing serious problems.
The main purpose of this study was to examine career success between the individuals in Cyprus and more specifically the influence of the academic qualifications and some other factors on the achievement of objective and subjective career success. There is also reference to the outcomes from where this applies.
Our conclusion is that academic qualifications are defining but they do not secure career success. Correlation analysis has revealed that academic qualifications were positively related with objective career success, especially with the level of pay while on subjective career success the results were inconclusive. Regarding the other factors, the most important correlations founded on the effect of mentoring, trust on management and regarding the outcomes Organizational Citizenship Behavior, commitment, social recognition and low absenteeism were positively related with academic qualifications in accordance with other studies.
We did not found any important correlations between academic qualifications and satisfaction arising from level of pay, things that employees do at their work that they like and make them happy, personal ambitions and trust in peers
Quantum and atomistic effects in nanoelectronic transport devices
No full textAs devices scale towards atomistic sizes, researches in silicon electronic device technology are investigating alternative structures and materials. As predicted by the International Roadmap for Semiconductors, (ITRS), structures will evolve from planar devices into devices that include 3D features, strong channel confinement, strain engineering, and gate all around placement for better electrostatic control on the channel. Alternative channel materials such as carbon nanotubes (CNT), nanowires (NW) and III-V based channel materials are considered to be possible candidates for future device technology nodes because of their potentially superior to silicon transport properties. For nanoscale dimensions, and under the operating conditions mentioned above, both atomistic and quantum effects become important in determining the electronic structure and transport properties of the devices. Detailed modeling and simulation that capture these new physics will be essential in providing understanding and guidance to the device operation and optimization. We have used the non-equilibrium Green\u27s function (NEGF) formalism for quantum transport simulations and real space atomistic tight-binding techniques (p z, sp3d5s*-SO) to investigate transport properties in CNT, NW and III-V HEMT field-effect transistors. Specifically, we have investigated the effect of atomistic defects such as atomic vacancies, and charged impurities in 1D CNT, and dangling bonds in NW channels. It was found that the presence of single defects, severely degrades the transport performance of 1D channels. We have further investigated the effect of physical quantization on the electronic structure of NW field-effect transistors and identified the main electronic structure factors that influence their performance. It was found that structural and quantization below 10nm can severely affect the electronic properties of NW channels by changing the effective masses and altering degeneracies through valley splitting. Different wire orientations have different transport properties. The [110] and secondly [100] oriented nanowires are found to perform better than the [111] wires in terms of ON-current capabilities for n-type wires, whereas the [111] and [110] significantly outperform the [100] wires in the case of p-type nanowires. Explanations for this behavior can be extracted from the non-parabolicity and anisotropy of the Si 3D bulk E(k). Finally, we present an analysis of recent experimental data for III-V HEMT devices using the NEGF formalism and address several issues related to the operation of HEMT devices. Interestingly, a 60nm HEMT device can be though to first order as a ballistic channel connected to two series resistances
Theory and simulation methods for electronic and phononic transport in thermoelectric materials
No full textThis book introduces readers to state-of-the-art theoretical and simulation techniques for determining transport in complex band structure materials and nanostructured-geometry materials, linking the techniques developed by the electronic transport community to the materials science community. Starting from the semi-classical Boltzmann Transport Equation method for complex band structure materials, then moving on to Monte Carlo and fully quantum mechanical models for nanostructured materials, the book addresses the theory and computational complexities of each method, as well as their advantages and capabilities. Presented in language that is accessible to junior computational scientists, while including enough detail and depth with regards to numerical implementation to tackle modern research problems, it offers a valuable resource for computational scientists and postgraduate researchers whose work involves the theory and simulation of electro-thermal transport in advanced materials
Low Dimensional Si Nanostructures for Efficient Thermoelectric Energy Conversion and Generation
No full textPhonon transport simulations in low-dimensional disordered graphene nanoribbons
Full text linkWe investigate the thermal conductance of one-dimensional periodic width-modulated graphene nanoribbons using lattice dynamics for the phonon spectrum and the Landauer formalism for phonon transport. We conduct a full investigation considering all relevant geometrical features, i.e., the various lengths and widths of the narrow and wide regions that form the channel. In all cases that we examine, we find that width-modulation suppresses the thermal conductance at values even up to ∼70% below those of the corresponding uniform narrow nanoribbon. We show that this can be explained by the fact that the phonon spectrum of the width-modulated channels acquires less dispersive bands with lower group velocities and several narrow bandgaps, which reduce the phonon transmission function significantly. The largest degradation in thermal conductance is determined by the geometry of the narrow regions. The geometry of the wider regions also influences thermal conductance, although modestly. Our results add to the ongoing efforts in understanding the details of phonon transport at the nanoscale, and our conclusions are generic and could also apply to other one-dimensional channel materials
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