269 research outputs found
Exploiting Amorphous Data Parallelism to Speed-Up Massive Time-Dependent Shortest-Path Computations
No full textWe aim at exploiting parallelism in shared-memory multiprocessing systems, in order to speed up the execution time with as small redundancy in work as possible, for an elementary task that comes up frequently as a subroutine in the daily maintenance of large-scale time-dependent graphs representing real-world relationships or technological networks: the many-to-all time-dependent shortest paths (MATDSP) problem. MATDSP requires the computation of one time-dependent shortest-path tree (TDSPT) per origin-vertex and departure-time, from an arbitrary collection of pairs of origins and departure-times, towards all reachable destinations in the graph.
Our goal is to explore the potential and highlight the limitations of amorphous data parallelism, when dealing with MATDSP in multicore computing environments with a given amount of processing elements and a shared memory to exploit. Apart from speeding-up execution time, consumption of resources (and energy) is also critical. Therefore, we aim at limiting the work overhead for solving a MATDSP instance, as measured by the overall number of arc relaxations in shortest-path computations, while trying to minimize the overall execution time. Towards this direction, we provide several algorithmic engineering interventions for solving MATDSP concerning: (i) the compact representation of the instance; (ii) the choice and the improvement of the time-dependent single-source shortest path algorithm that is used as a subroutine; (iii) the way according to which the overall work is allocated to the processing elements; (iv) the adoption of the amorphous data parallelism rationale, in order to avoid costly synchronization among the processing elements while doing their own part of the work.
Our experimental evaluations, both on real-world and on synthetic benchmark instances of time-dependent road networks, provide insight how one should organize heavy MATDSP computations, depending on the application scenario. This insight is in some cases rather unexpected. For instance, it is not always the case that pure data parallelism (among otherwise totally independent processors) is the best choice for minimizing execution times. In certain cases it may be worthwhile to limit the level of data parallelism in favor of algorithmic parallelism, in order to achieve more efficient MATDSP computations
A Novel GO Analysis Tool for GRIN Lenses based on the Fast Sweeping Method
No full textAdditive manufacturing has facilitated the straightforward development and prototyping of Graded Index (GRIN) lenses. These lenses are constructed using inhomogeneous dielectric materials and leverage a refractive index gradient to manipulate the path of light within the lens. This technology allows for creating lenses with flat surfaces and a high level of design flexibility. The Fast Sweeping Method (FSM) is a numerical approach designed to efficiently address both wavefront propagation and field amplitude in GRIN lenses. The utility of the FSM is evaluated by establishing its accuracy and effectiveness, making it a viable alternative to traditional ray-tracing methods. Due to its robust performance, FSM emerges as a strong candidate for serving as the analytical engine in an optimization process for the automatic design of GRIN lenses
Data Set of PLOS Computational Paper PCOMPBIOL-D-18-02181R1
No full textFigures Data of PLOS Computational paper:Modeling of the axon plasma membrane structure and its effects on protein diffusionAuthors: Yihao Zhang, Anastasios V. Tzingounis, and George LykotrafitisCorresponding Author: George Lykotrafitis, Ph.D.University of ConnecticutStorss, CT UNITED STATES</div
GO Analysis of GRIN Lens Antennas by Combining in a Single ODE, Field and Wavefront-Curvature Transport to the Ray Tracing
No full textA novel very efficient algorithm based on geometrical optics (GO) is presented for the analysis of graded index (GRIN) lens antennas, namely, dielectric inhomogeneous lenses with a 3-D arbitrary varying refractive index. A family of curved ray paths are traced starting from a set of points defined on the lens input interface, which is illuminated by a feed antenna, up to a corresponding set of points on the output interface, i.e., the lens radiating aperture. The ray tracing is numerically performed in combination with the field transportation along the ray by exploiting an additional wavefront-curvature transport equation, thus providing a single independent vector ordinary differential equation (ODE) for each ray. This scheme allows a complete parallelization of the algorithm by assigning any ray to a different thread. Crossing the lens input–output interfaces at the two end points of the curved ray is accomplished by augmenting the refraction Snell’s law and the Fresnel transmission coefficients with a novel compact closed-form dyadic formula for the transmitted wavefront curvature. The ODE output provides the field aperture distribution on the output lens interface, permitting the far-field calculation as a radiation integral. To this end, an ad hoc quadrature rule is exploited, which requires an aperture sampling rate corresponding to the slowly varying part of the integrand, while the rapid phase variation is accounted for analytically, thus resulting in an extremely efficient and frequency-independent scheme. The effectiveness and accuracy of the algorithm are shown by resorting to a couple of well-known analytical benchmarks and to two more general examples with real-life antennas: a spaceborne weather radar lens antenna and a feed antenna with a zero-focal lens
The state of modern Greek language as spoken in Victoria
No full textDeposited with permission of the author. © 1986 Dr. Anastasios TamisThis thesis reports a sociolinguistic study, carried out between 1981 and 1984, of the state of the Modern Greek (MG) language in Australia, as spoken by native-speaking first-generation Greek immigrants in Victoria. Particular emphasis is given to the analysis of those characteristics of the linguistic behaviour of these Greek Australians which can be attributed to the contact with English and to other environmental, social and linguistic influence. (For complete abstract open document
New historical evidence for Anastasios Emm. Papas
No full textNo AbstractThe author’s attention has been drawn to the existence of this historicalevidence in the National Archives of Vienna, by his friend the writer EteoclesGregoriadis together with the numbers of the relevant files. Most of the documents were written in the old German script. Thus the author asked for the help of his friend and former colleague at the University of Thessaloniki and director of the Goethe Institute, Graf Kurt v. Posadowsky, for reading andstudying those documents. Without his help this study would have been impossible. This new evidence concerns the sojourn of Anastasios Papas·—son of Emmanuel Papas, leading figure of the Greek Revolution—in Austria andGermany between the 3rd January and 11th March 1822. There is informationabout his short imprisonment in Trieste, after his arival from Vienna. He then visits various towns in Germany and after negotiations with the Philhellene professor Fr. Thiersch in Munich, he purchases large quantities of ammunition to be despatched to Greece. He finally arrives in Greece early in 1824, and takes part—together with his three brothers who were already fighting—in the struggle for the liberation of the common great fartheland
3-D Printed All-Dielectric GRIN Lens Antenna With an Integrated Feeder
No full textIn this paper we present the design, fabrication, and experimental verification of a new type of Graded-index (GRIN) lens antenna with an integrated feeder. The continuously varying refractive index distribution is chosen appropriately to offer the rays collimation at the lens aperture. It is practically implemented by varying the material density in a host medium, thus realizing a new type of all-dielectric high gain antenna, entirely using 3D printing. This solution can find application to high gain wireless communication and measurement systems. This GRIN lens antenna is printed in one monolithic process and does not require the feeder to be placed at a focal distance, thus complying with more strict space requirements. It accepts interchangeable feeds that can cover a wide frequency range. The directivity and gain are evaluated using near-field measurements in the Ku-band. A 40% measured aperture efficiency is achieved at 14GHz. The challenges and performance limitations that come with 3D printing, as compared to the design of idealized continuous distribution GRIN lenses are discussed
Body-centric wireless communications: wearable antennas, channel modelling, and near-field antenna measurements
No full textThis thesis provides novel contribution to the field of body-centric wireless communications (BCWC) with the development of a measurement methodology for wearable antenna characterisation on the human body, the implementation of fully-textile wearable antennas and the on-body channel modelling considering different antenna types and user's dynamic effects.
More specifically, a measurement methodology is developed for characterising wearable antennas on different locations of the human body. A cylindrical near-field (CNF) technique is employed, which facilitates wearable antenna measurements on a full-body solid anthropomorphic mannequin (SAM) phantom. This technique allows the fast extraction of the full spherical radiation pattern and the corresponding radiation efficiency, which is an important parameter for optimising wearable system design. It appears as a cost- effective and easy to implement solution that does not require expensive positioning systems to rotate the phantom, in contrast to conventional roll-over-azimuth far-field systems.
Furthermore, a flexible fully-textile wearable antenna is designed, fabricated and measured at 2.4 GHz that can be easily integrated in smart clothing. It supports surface wave propagation and exhibits an omni-directional radiation pattern that makes it suitable for on-body communications. It is based on a multilayer low-profile higher-mode patch antenna (HMMPA) design with embroidered shorting vias. Emphasis is given to the fabrication process of the textile vias with conductive sewing thread that play an important role in generating the optimal mode for on-body radiation. The radiation pattern shape of the proposed fully-textile antenna was found to be similar to a copper rigid antenna, exhibiting a high on-body radiation efficiency of 50 %. The potential of the embroidery technique for creating wearable antennas is also demonstrated with the fabrication of a circularly polarised spiral antenna that achieves a broadband performance from 0.9-3 GHz, which is suitable for off-body communications. By testing the textile spiral antenna on the SAM phantom, the antenna-body interaction is examined in a wide frequency range.
Finally, a statistical characterisation of on-body communication channels is undertaken both with EM simulations and channel measurements including user's dynamic movement (walking and running). By using antenna types of different polarisation, the on-body channels are examined for different propagation conditions. Four on-body channels are examined with the one part fixed on the waist of the human body while the other part located on the chest, back, wrist and foot. Channel path gain is derived, while large-scale and small-scale fading are modelled by best-fit statistical distributions
Ασύρματες επικοινωνίες με επίκεντρο το ανθρώπινο σώμα: φορετές κεραίες, μοντελοποίηση τηλεπικοινωνιακού καναλιού, και μετρήσεις κεραίας στο κοντινό πεδίο
No full textThis thesis provides novel contribution to the field of body-centric wireless communications (BCWC) with the development of a measurement methodology for wearable antenna characterisation on the human body, the implementation of fully-textile wearable antennas and the on-body channel modelling considering different antenna types and user’s dynamic effects. More specifically, a measurement methodology is developed for characterising wearable antennas on different locations of the human body. A cylindrical near-field (CNF) technique is employed, which facilitates wearable antenna measurements on a full-body solid anthropomorphic mannequin (SAM) phantom. This technique allows the fast extraction of the full spherical radiation pattern and the corresponding radiation efficiency, which is an important parameter for optimising wearable system design. It appears as a cost- effective and easy to implement solution that does not require expensive positioning systems to rotate the phantom, in contrast to conventional roll-over-azimuth far-field systems. The CNF measurement method is evaluated by using a printed dipole antenna in vertical and horizontal polarisation in three on-body locations, namely on chest, head and shoulder, at 2.4 and 5.8 GHz ISM band. Moreover, two textile wearable patch antennas are examined with distinct radiation characteristics, which are suitable for on-body and off-body communications. Apart from the 3D far-field antenna performance, the measured near-field is graphically presented on the human body outline, which gives an insight of the on-body propagation. The accuracy of the available measurement results is validated with EM simulations using an equivalent numerical phantom. Hence, this measurement system can be used as a repeatable test-bed for evaluating the performance of wearable antennas. Furthermore, a flexible fully-textile wearable antenna is designed, fabricated and measured at 2.4 GHz that can be easily integrated in smart clothing. It supports surface wave propagation and exhibits an omni-directional radiation pattern that makes it suitable for on-body communications. It is based on a multilayer low-profile higher-mode patch antenna (HMMPA) design with embroidered shorting vias. Emphasis is given to the fabrication process of the textile vias with conductive sewing thread that play an important role in generating the optimal mode for on-body radiation. The radiation pattern shape of the proposed fully-textile antenna was found to be similar to a copper rigid antenna, exhibiting a high on-body radiation efficiency of ≈ 50%.The potential of the embroidery technique for creating wearable antennas is also demonstrated with the fabrication of a circularly polarised spiral antenna that achieves a broadband performance from 0.9-3 GHz, which is suitable for off-body communications. By testing the textile spiral antenna on the SAM phantom, the antenna-body interaction is examined in a wide frequency range. Finally, a statistical characterisation of on-body communication channels is undertaken both with EM simulations and channel measurements including user’s dynamic movement (walking and running). By using antenna types of different polarisation, the on-body channels are examined for different propagation conditions. Four on-body channels are examined with the one part fixed on the waist of the human body while the other part located on the chest, back, wrist and foot. Channel path gain is derived, while large-scale and small-scale fading are modelled by best-fit statistical distributions.Αυτή η διατριβή παρέχει μια πρωτότυπη συμβολή στον τομέα των ασυρμάτων επικοινωνιών με επίκεντρο το ανθρώπινο σώμα με την ανάπτυξη μιας νέας μεθοδολογίας μετρήσεων για τον χαρακτηρισμό κεραιών πάνω στο ανθρώπινο σώμα,. Παράλληλα, πρσφέρει νέα δεδομένα ως προς την υλοποίηση πλήρως υφασμάτινων κεραιών και τη μοντελοποίηση ασύρματων καναλιών επικοινωνίας πάνω στο σώμα λαμβάνοντας υπόψη τους διαφορετικούς τύπους κεραιών και τα αποτελέσματα της δυναμικής κίνησης του χρήστη.Πιο συγκεκριμένα, αναπτύσσεται μια μεθοδολογία μέτρησης για τον χαρακτηρισμό φορετών (wearable) κεραιών σε διαφορετικές θέσεις του ανθρώπινου σώματος. Αυτή η μεθοδολογία βασίζεται στη τεχνική μετρήσεων κεραιών στο κοντινό πεδίο σε κυλινδρικές συντεταγμένες (Cylindrical Near Field, CNF), η οποία διευκολύνει τις μετρήσεις φορετών κεραιών όταν χρησιμοποιείται ένα ολόσωμο συμπαγές ανθρωπόμορφο μανεκέν (SAM human body model). Αυτή η τεχνική επιτρέπει τη γρήγορη εξαγωγή του τρισδιάστατου (3D) σφαιρικού διαγράμματος ακτινοβολίας (full spherical radiation pattern) και την αντίστοιχη απόδοση ακτινοβολίας, που είναι μια σημαντική παράμετρος για τη βελτιστοποίηση του σχεδιασμού των φορετών συστημάτων κεραιών. Εμφανίζεται ως οικονομικά αποδοτική και εύκολη στην εφαρμογή λύση που δεν απαιτεί ακριβή συστήματα τοποθέτησης και περιστροφής (positioners) του ανθρωπίνου σώματος, σε αντίθεση με το συμβατικό σύστημα χαρακτηρισμού κεραιών στο μακρινό πεδίο.Η μέθοδος μέτρησης CNF αξιολογείται χρησιμοποιώντας μια τυπωμένη κεραία διπόλου σε κάθετη και οριζόντια πόλωση σε τρεις θέσεις πάνω στο σώμα, συγκεκριμένα στο στήθος, το κεφάλι και τον ώμο, στη ζώνη συχνοτήτων ISM 2,4 και 5,8 GHz. Επιπλέον, δύο πλήρως υφασμάτινες φορετές κεραίες τύπου patch με διακριτά χαρακτηριστικά ακτινοβολίας εξετάζονται ξεχωριστά, οι οποίες είναι κατάλληλες για επικοινωνίες πάνω (on-body) και έξω (off-body) από το ανθρωπίνο σώμα αντίστοιχα. Εκτός από τα αποτελέσματα μετρήσεων των κεραιών και πιο συγκεκριμένα το 3D διάγραμμα ακτινοβολίας μακρινού πεδίου, το πεδίο στο κοντινό πεδίο (near-field) αποτυπώνεται γραφικά πάνω στο περίγραμμα του ανθρώπινου σώματος, το οποίο δίνει μια εικόνα της κατανομής του ηλεκτρικού πεδίου πάνω στο σώμα. Η ακρίβεια των διαθέσιμων αποτελεσμάτων μετρήσεων επιβεβαιώνεται με ηλεκτρομαγνητικές προσομοιώσεις χρησιμοποιώντας ένα ισοδύναμο αριθμητικό ανθρώπινο μοντέλο. Ως εκ τούτου, αυτό το σύστημα μέτρησης μπορεί να χρησιμοποιηθεί ως πρότυπο για την αξιολόγηση της απόδοσης φορετών κεραιών πάνω στο ανθρώπινο σώμα. Επιπλέον, σχεδιάζεται και κατασκευάζεται μια εύκαμπτη πλήρως υφασμάτινη φορετή κεραία η οποία χαρακτηρίζεται στα 2,4 GHz που μπορεί εύκολα να ενσωματωθεί σε έξυπνα ρούχα. Υποστηρίζει τη διάδοση επιφανειακών κυμάτων και παρουσιάζει μια ομοιοκατευθυντική ακτινοβολία (omnidirectional) που την καθιστά κατάλληλη για επικοινωνίες πάνω στο σώμα. Βασίζεται σε σχεδίαση κεραίας πολλαπλών στρωμάτων και χαμηλού προφίλ (HMMPA) με κεντημένες οπές βραχυκυκλωματος (conductive vias). Έμφαση δίνεται στη διαδικασία κατασκευής των υφασμάτικων οπών με αγώγιμη κλωστή που παίζουν σημαντικό ρόλο δημιουργώντας τη βέλτιστη λειτουργία για ακτινοβολία στο σώμα. Το χαρακτηριστικά ακτινοβολίας της προτεινόμενης πλήρως υφασμάτινης κεραίας βρέθηκαν παρόμοια με αυτά μιας συμπαγούς άκαμπτη χάλκινης κεραίας, που παρουσιάζει υψηλή απόδοση ακτινοβολίας πάνω στο σώμα ≈ 50%.Παράλληλα κατασκευάστηκε και μια πλήρως υφασμάτινη σπειροειδής κεραία με κυκλική πόλωση που επιτυγχάνει ευρυζωνική λειτουργία από 0.9-3 GHz, η οποία είναι κατάλληλη για επικοινωνίες εκτός σώματος. Μετρώντας την υφασμάτινη σπειροειδή κεραία πάνω στο SAM ανθρωπόμορφο μοντέλο, η αλληλεπίδραση κεραίας-σώματος εξετάζεται σε ένα ευρύ φάσμα συχνοτήτων. Τέλος, πραγματοποιείται ένας στατιστικός χαρακτηρισμός των καναλιών επικοινωνίας πάνω στο σώμα τόσο με προσομοιώσεις EM όσο και με μετρήσεις καναλιιού συμπεριλαμβανομένης της δυναμικής κίνησης του χρήστη (περπάτημα και τρέξιμο). Με τη χρήση τύπων κεραιών διαφορετικής πόλωση, τα κανάλια στο σώμα εξετάζονται για διαφορετικές συνθήκες διάδοσης. Τέσσερα κανάλια πάνω στο σώμα εξετάζονται με το ένα μέρος σταθερό στη μέση του ανθρώπινου σώματος ενώ το άλλο μέρος βρίσκεται στο στήθος, πλάτη, καρπός και πόδι. Το κέρδος διαδρομής καναλιού (channel path gain) καθώς και οι διαλείψεις μικρής και μεγάλης κλιμακας εξάγονται μετα από μια διαδικασία μετρήσεων με αναλυτη κυκλωμάτων (vector network analyzer VNA), και μοντελοποιούνται από στατιστικές κατανομές με την καλύτερη προσαρμογή (best-fit)
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