570 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
La fouille du terrain Yannopoulos et les établissements de bains à Thasos (IIIe-VIe s.)
No full textΗ ανασκαφή του οικόπεδου Γιαννόπουλου και τα λουτρικά συγκροτήματα στη Θάσο (3ος-6ος αι. μ. Χ.)
Το άρθρο πραγματεύεται το λουτρικό συγκρότημα που ερευνήθηκε στο οικόπεδο Γιαννόπουλου στη Θάσο, τα κατασκευαστικά χαρακτηριστικά, τα ευρήματα και την ένταξή του στο αστικό περιβάλλον. Πρόκειται για ένα κτήριο ορθογώνιας κάτοψης, με 12 χώρους και τρεις οικοδομικές φάσεις. Αναγνωρί-στηκαν δύο praefurnia, δύο υπόκαυστοι και οκτώ μη-θερμαινόμενοι χώροι. Με αφορμή το λουτρό στο οικόπεδο Γιαννόπουλου, επιχειρείται μια παρουσίαση όλων των λουτρικών εγκαταστάσεων, δημόσιας και ιδιωτικής χρήσης, που έχουν εντοπιστεί στη Θάσο, εντός και εκτός του άστεως. Με βάση την έρευνά μας, διαπιστώθηκε ότι τα κτήρια στα γειτνιάζοντα οικόπεδα Γιαννόπουλου και Βέλλιου ανήκουν σε ένα ενιαίο λουτρικό οικοδόμημα. Η χρονολόγηση των εγκαταστάσεων επιβεβαιώνει τη χρήση λουτρών στη Θάσο καθ’ όλη τη διάρκεια της ρωμαϊκής και της πρωτοβυζαντινής εποχής.The excavation of the Yannopoulos plot and the bathing establishments at Thasos (3rd-6th c.)
This article concerns the bathing establishment excavated on the Yannopoulos property in the city of Thasos, its architectural particularities, the finds recovered, and its insertion in the urban environment. The twelve-room building, of rectangular plan, has three architectural phases. Two praefurnia, two hypocausts, and eight non-heated rooms have been distinguished. The study of this baths offers an occasion to present the totality of bathing establishments, public and private, identified on the island, in the city as well as outside. During our research it has become clear that the buildings on the neighbouring Yannopoulos and Vellios plots belong to a single complex. The dating of the installations confirms the use of baths at Thasos throughout the roman and protobyzantine periods.Cet article traite de l’établissement de bains fouillé dans le terrain Yannopoulos à Thasos, de ses particularités architecturales, des trouvailles qui y ont été faites et de son insertion dans l’environnement urbain. Ce bâtiment de douze pièces, de plan rectangulaire, comporte trois phases architecturales. On y a reconnu deux praefurnia, deux hypocaustes et huit pièces non chauffées. L’étude de ce bain est l’occasion d’essayer de présenter l’ensemble des établissements balnéaires, publics et privés, qui ont été localisés à Thasos, aussi bien dans la ville qu’en dehors. Lors de notre recherche, il est apparu que les bâtiments des terrains Yannopoulos et Vellios, voisins, appartiennent à un seul et même complexe. La datation des installations confirme l’usage des bains à Thasos pendant toute la durée des époques romaine et protobyzantine.Oulkeroglou Anastasios, Papadopoulos Stratis. La fouille du terrain Yannopoulos et les établissements de bains à Thasos (IIIe-VIe s.). In: Bulletin de correspondance hellénique. Volume 138, livraison 2, 2014. pp. 467-507
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
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
Measurement of damage growth in ultrasonic spot welded joint
No full textUltrasonic spot welding is a joining technique for thermoplastic composites with great potential regarding processing speed and cost. To investigate the damage tolerance and possible inherent damage arresting behavior of multi-spot welded joints, a technique is necessary to measure damage growth in the joints under cyclic loading. Visual inspection is not possible because the damage is not located on the outside surface and conventional techniques such as C-scan are not practical during a fatigue test because the specimen would have to be removed from the setup. This paper details a methodology for quantifying damage growth rates in singlespot welded joints using surface strain measurements made by Digital Image Correlation. This represents the first step towards developing a methodology for quantifying damage progression behavior in complex multi-spot welded joints.Structural Integrity & CompositesAerospace Structures & Computational Mechanic
Development and characterization of hybrid thin-ply composite materials
No full textThin-ply composites are recognized as a key solution for the manufacturing of high-performance composite structures due to the unique mechanical properties and the increased design versatility that they offer. They are obtained with state-of-the-art fiber spreading methods where high-count (6-24K filaments) tows of technical fibers (carbon, glass) are thinned by spreading into flat unidirectional tapes which are then combined with a polymer matrix to create pre-impregnated (prepregs) tapes of reduced thickness. In recent years, the industrialization of fiber spreading and impregnation processes enabled the large-scale production of homogenous thin-ply prepregs with thicknesses down to about 15μm per ply, which attracted the interest of the research community. However, the high production cost due to the complexity of the manufacturing methods and the inherent brittleness of thin-ply composites limit their wider adoption by the composites industry[1]. Fiber hybridization (i.e combining at least two types of fibers in a common matrix) is emerging as a promising approach for alleviating these drawbacks towards laminates with balanced characteristics in terms of mechanical properties and cost-efficiency. Currently, most studies on thin-ply hybrids employ simple interlayer (ply-by-ply) configurations mainly due to difficulties in manufacturing of more complex hybrid architectures[2]. However, simulation tools predict that notable improvements can be obtained from more complex intralayer (tow-by-tow) and intrayarn (fiber-by-fiber) hybrid architectures[3]. This work focuses on the study of existing fiber spreading methodologies, the development of equipment, and the optimization of composite processing at North Thin Ply Technology (NTPT) Renens, Switzerland, that allowed the manufacturing of hybrid composites with a high degree of fiber dispersion and controlled microstructure. Hybrid prepregs were produced by combining various ratios of dissimilar fibers following different processing routes. Composite laminates were manufactured and a versatile microstructural analysis tool was developed that enabled correlations between the manufacturing route, the resulting microstructural features describing the degree of co-dispersion, and the mechanical performance of the final part. Acknowledgments The research leading to these results has been performed within the framework of the HyFiSyn project and has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 765881. Delamination growth in fibre reinforced polymer composites is generally evaluated with experiments that have been standardized for quasi-static load conditions. These tests characterize unidirectional delamination growth in mode I (DCB), mode II (ELS or ENF) of mixed mode conditions (MMB). However, little attention is paid in literature to the applicability of these tests to in-service delamination problems that are generally characterized by planar delamination growth. In this study, the relation between planar delamination growth, induced by transverse quasi-static indentation loading, and these unidirectional delamination tests was investigated. To that aim, prior planar delamination growth tests reported in literature, performed at EPFL, were analysed to identify up to what extent this planar growth could be correlated to the concepts of strain energy release and strain energy density. Once this appeared to successful, an experimental setup was designed to measure the delamination boundary during the transverse indentation loading of planar delamination specimens made of nontransparent carbon fibre reinforced polymer composites. With that set-up, quasi-static and fatigue planar delamination growth experiments were performed, and delamination contours could be successfully captured. While the quasi-static tests revealed limited growth, evaluation with numerical simulations revealed that the indentation force required to extend the delamination quasi-statically would cause damage to the specimen. This is attributed to the increasing length of the delamination contour when delaminations expand, which is not the case with standard unidirectional specimen. With the fatigue tests, however, delamination growth was achieved, but interestingly enough two phases were observed; first the delamination propagated in a planar fashion, while at some point in time work did not exceed an apparent threshold. Instead of no growth, however, the delamination still increased but then in a transverse manner. What makes this study of particular interest, is that the strain energy density as criterion could capture the strain energy offered (work) along the entire delamination contour, while the strain energy release rate described the resistance to delamination growth. This latter observation is in agreement with the original concept employed by Griffith when he formulated the basis of linear elastic fracture mechanics. This presentation present the experiments performed, the analysis of results, and will conclude with a proposal how to relate standard unidirectional tests to planar growth, considering that these standard tests contain little to no information on transverse phenomena with respect to strain energy density (work) and strain energy release (dissipation).Aerospace Manufacturing Technologie
The role of matrix boundary in the microstructure of unidirectional composites
No full textFinding new ways to evaluate the variability of microstructures, and its effect on macroscopic properties such as permeability and mechanical performance [1,2] is of increasing interest in the composite field. The variability of microstructural features at a three-dimensional level is not fully understood and its effect on macroscale properties is not well established, and mostly analyzed at a phenomenological level [3]. We introduced in recent work a method based on X-ray Computed Tomography for the threedimensional reconstruction of the fibrous microstructure of unidirectional tapes at a single fibre resolution [4]. A schematic of the workflow is represented in Figure 1. Three descriptors are introduced in the work to describe increasing level of complexity in the microstructural organization, from a single fiber path level with differential tortuosity, to group behavior with collective motion, to fibre network connectivity with length of contact. These descriptors and their interdependence highlight local effects like edge-core segregation in microstructural characteristics. However, in order to achieve a more complete definition of the unidirectional tape domain, understanding of matrix-based features and its interrelation with fiber architecture descriptors is needed. In this work, we expand the methodology of Gomarasca et al. [4], to account for matrix-based phenomena such as tape boundary variability, and void formation and morphology. This will be showcased on a unidirectional composite tape including both fiber-based and matrix-based analysis. These methods enable advanced characterization and modelling of microstructural formation and evolution during composite manufacturing.Aerospace Manufacturing TechnologiesAerospace Structures & Computational Mechanic
Deep learning based prediction of fibrous microstructure permeability
No full textKnowledge of permeability of fibrous microstructures is crucial for predicting the mold fill times and resin flow path in composite manufacturing. Herein we report a method to rapidly predict the permeability of 3D fibrous microstructures. Our method relies on predicting the permeability of 2D cross-sections via deep neural networks and extending this capability to 3D microstructures via circuit analogy as a means of reduced order modeling. Approximately 50% of the permeability predictions of 2D cross-sections have 10% or less deviation from the permeability results obtained via flow simulations in Geodict. Computational time required for predicting the permeability of 3D microstructures is reduced from hours to less than 10 seconds. This framework enables fast and accurate prediction of micro-permeability and serves as the first building block towards prediction of fabric mesostructures’ permeability via deep learning based methods.Aerospace Manufacturing Technologie
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