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Littérature scientifique sur le sujet « Cover source mismatch »

Auteur : Grafiati

Publié le 25 janvier 2025

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Articles de revues sur le sujet "Cover source mismatch"

Giboulot, Quentin, Rémi Cogranne, Dirk Borghys et Patrick Bas. « Effects and solutions of Cover-Source Mismatch in image steganalysis ». Signal Processing : Image Communication 86 (août 2020) : 115888. http://dx.doi.org/10.1016/j.image.2020.115888.

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Yu, Lifang, Shaowei Weng, Mengfei Chen et Yunchao Wei. « RCDD : Contrastive domain discrepancy with reliable steganalysis labeling for cover source mismatch ». Expert Systems with Applications 237 (mars 2024) : 121543. http://dx.doi.org/10.1016/j.eswa.2023.121543.

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Hu, Donghui, Zhongjin Ma, Yuqi Fan, Shuli Zheng, Dengpan Ye et Lina Wang. « Study on the interaction between the cover source mismatch and texture complexity in steganalysis ». Multimedia Tools and Applications 78, n^o 6 (15 août 2018) : 7643–66. http://dx.doi.org/10.1007/s11042-018-6497-0.

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Kauko, Hanne, Daniel Rohde, Brage Rugstad Knudsen et Terje Sund-Olsen. « Potential of Thermal Energy Storage for a District Heating System Utilizing Industrial Waste Heat ». Energies 13, n^o 15 (31 juillet 2020) : 3923. http://dx.doi.org/10.3390/en13153923.

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The potential for utilizing industrial waste heat for district heating is enormous. There is, however, often a temporal mismatch between the waste heat availability and the heating demand, and typically fossil-based peak boilers are used to cover the remaining heat demand. This study investigates the potential of applying a thermal energy storage tank at the district heating supply system at Mo Industrial Park in Norway, where waste heat from the off-gas of a ferrosilicon production plant is the main heating source. To cover peak heating demands, boilers based on CO gas, electricity, and oil are applied. The reduction in peak heating costs and emissions is evaluated as a function of tank size for two different scenarios: (1) a scenario where CO gas, which is a byproduct from another nearby industry, is the main peak heating source; and (2) a scenario where no CO gas is available, and electricity is the main peak heating source. The highest economic viability is obtained with the smallest storage tank with a volume of 1000 m3, yielding a payback period of 7.1/16.2 years and a reduction in total heat production costs of 14.6/10.0% for Scenarios 1/2, respectively. The reduction in CO2 emissions is 19.4/14.8%, equal to 820/32 ton CO2 for the analyzed period. Sensitivity analysis shows a significant reduction in payback period for Scenario 2 with increasing electricity prices, while the payback period in Scenario 1 is most sensitive to the emission factors.

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Wang, Peipei, Yun Cao et Xianfeng Zhao. « Segmentation Based Video Steganalysis to Detect Motion Vector Modification ». Security and Communication Networks 2017 (2017) : 1–12. http://dx.doi.org/10.1155/2017/8051389.

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This paper presents a steganalytic approach against video steganography which modifies motion vector (MV) in content adaptive manner. Current video steganalytic schemes extract features from fixed-length frames of the whole video and do not take advantage of the content diversity. Consequently, the effectiveness of the steganalytic feature is influenced by video content and the problem of cover source mismatch also affects the steganalytic performance. The goal of this paper is to propose a steganalytic method which can suppress the differences of statistical characteristics caused by video content. The given video is segmented to subsequences according to block’s motion in every frame. The steganalytic features extracted from each category of subsequences with close motion intensity are used to build one classifier. The final steganalytic result can be obtained by fusing the results of weighted classifiers. The experimental results have demonstrated that our method can effectively improve the performance of video steganalysis, especially for videos of low bitrate and low embedding ratio.

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Streckienė, Giedrė, et Salomėja Bagdonaitė. « MODELLING THE SIZE OF SEASONAL THERMAL STORAGE IN THE SOLAR DISTRICT HEATING SYSTEM / SEZONINĖS ŠILUMOS AKUMULIACINĖS TALPYKLOS TŪRIO MODELIAVIMAS CENTRALIZUOTOJE SAULĖS ŠILDYMO SISTEMOJE ». Mokslas - Lietuvos ateitis 5, n^o 4 (31 décembre 2012) : 499–506. http://dx.doi.org/10.3846/mla.2012.80.

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The integration of a thermal storage system into the solar heating system enables to increase the use of solar thermal energy in buildings and allows avoiding the mismatch between consumers’ demand and heat production in time. The paper presents modelling a seasonal thermal storage tank various sizes of which have been analyzed in the district solar heating system that could cover a part of heat demand for the district of individual houses in Vilnius. A biomass boiler house, as an additional heat source, should allow covering the remaining heat demand. energyPRO software is used for system modelling. The paper evaluates heat demand, climate conditions and technical characteristics. Santrauka Šilumos akumuliavimo sistemos integracija į saulės šildymo sistemą suteikia galimybę padidinti Saulės šiluminės energijos panaudojimą pastatuose, nes tai leidžia išvengti vartotojų poreikio ir šilumos gamybos nesutapimo laike. Šiame darbe modeliuojama sezoninė šilumos akumuliacinė talpykla, analizuojami įvairūs jos dydžiai centralizuotoje saulės šildymo sistemoje. Nagrinėjama sistema galėtų užtikrinti dalį individualių namų mikrorajono, esančio Vilniuje, šilumos poreikių. Kaip papildomas šilumos šaltinis modeliuojama biokuro katilinė, kuri leistų užtikrinti likusią šilumos poreikių dalį. Modeliavimas atliekamas energyPRO programa įvertinant pastatų poreikius, klimatines sąlygas ir technologines įrenginių charakteristikas.

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Kartini, Dede Sri, Neneng Yani Yuningsih et Iyep Saefulrahman. « Consistency between Political Party’s Program and Policy Product in Bandung Regency ». MIMBAR, Jurnal Sosial dan Pembangunan 33, n^o 2 (20 décembre 2017) : 267. http://dx.doi.org/10.29313/mimbar.v33i2.2330.

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After political parties win election, several political issues will be formulated into a series of alternate policy. Based on this system, political parties have a role to collect the will of society and then use it as consideration to make various public policies. Vision and mission of Golkar as the winner of 2010 elections, has become vision and mission of all SKPD even the village chief, the realization of the programs when Golkar’s candidate used rural development policy product as source of campaign in 2010-2015 local elections for Bandung Regent, have been consistent. In the other side, the obstacles are human resources in rural areas which frequently changed when trained by BPMPD, late disbursement in rural development and grants for Uninhabitable Houses (Rumah Tidak Layak Huni) are insufficient and not equally distributed. Moreover, the policy has been already consistent between Golkar’s programs with the product of public policy, particularly in the field of rural development. If the government is able to cover up weaknesses in the implementation of rural development programs, it should fulfill the needs of rural communities for employments on dry season as priority program for the followings years. Based on this research, it can be concluded that, in the micro policy level, the policies face a distortion because of mismatch between the tasks and functions BPMPD in reality,

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Wang, Mo, Furong Chen, Dongqing Zhang, Qiuyi Rao, Jianjun Li et Soon Keat Tan. « Supply–Demand Evaluation of Green Stormwater Infrastructure (GSI) Based on the Model of Coupling Coordination ». International Journal of Environmental Research and Public Health 19, n^o 22 (9 novembre 2022) : 14742. http://dx.doi.org/10.3390/ijerph192214742.

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The rational spatial allocation of Green Stormwater Infrastructure (GSI), which is an alternative land development approach for managing stormwater close to the source, exerts a crucial effect on coordinating urban development and hydrological sustainability. The balance between the supply and demand of urban facilities has been an influential standard for determining the rationality of this allocation. However, at this stage, research on evaluating planning from the perspective of supply–demand in GSI is still limited. This study proposed an evaluation method for assessing supply–demand levels in GSIs in Guangzhou, China, using the coupling coordination model consisting of Coupling Degree (CD) and Coupling Coordination Degree (CCD). Furthermore, the spatial distributions of supply–demand balance and resource mismatch were identified. The results indicated that the supply and demand levels of GSI exhibited significant spatial differences in distribution, with most streets being in short supply. The GSI exhibited a high CD value of 0.575 and a poor CCD value of 0.328, implying a significant imbalance in facility allocation. A lot of newly planned facilities failed to effectively cover the streets in need of improvement, so it became essential to adjust the planning scheme. The findings of this study can facilitate the decision-makers in assessing the supply–demand levels in GSI and provide a reference of facility allocation for the sustainable construction of Sponge City.

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FRANCIS, ELAINE J., et ETSUYO YUASA. « A multi-modular approach to gradual change in grammaticalization ». Journal of Linguistics 44, n^o 1 (5 février 2008) : 45–86. http://dx.doi.org/10.1017/s0022226707004951.

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Examining four constructions in three languages (English quantificational nouns, Japanese subordinating conjunctions, Cantonese coverbs, Japanese deverbal postpositions), this paper shows that semantic properties can change faster than syntactic properties in gradual processes of grammaticalization. In each of these cases, the syntactic properties of one category become associated with the semantic properties of a different category when an item undergoes semantic change, leading to the appearance of mixed categorial properties. We propose that this sort of change is best captured using a multi-modular framework (Sadock 1991, Yuasa 2005), which allows changes to affect semantics independently of syntax, and which shows clearly that the relevant items and constructions still conform to the separate structural constraints of syntax and semantics, despite the unusual combination of properties. These findings are important for theories of grammaticalization because they suggest that the cover term ‘decategorialization’ (the loss of grammatical properties associated with the source category) must be understood in terms of at least two separate processes: (1) the effects of semantic change on an item's distribution; and (2) the effects of frequency (Bybee & Hopper 2001) and Pressure for Structure–Concept Iconicity (Newmeyer 1998) on an item's syntactic categorization. Our case studies show that the first kind of decategorialization effects can occur even in the absence of the second kind. Implications of these findings, including possible reasons for both the instability and the long-term retention of mismatch constructions, are also considered.

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Lasch-Born, Petra, Felicitas Suckow, Christopher P. O. Reyer, Martin Gutsch, Chris Kollas, Franz-Werner Badeck, Harald K. M. Bugmann et al. « Description and evaluation of the process-based forest model 4C v2.2 at four European forest sites ». Geoscientific Model Development 13, n^o 11 (5 novembre 2020) : 5311–43. http://dx.doi.org/10.5194/gmd-13-5311-2020.

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Abstract. The process-based model 4C (FORESEE) has been developed over the past 20 years to study climate impacts on forests and is now freely available as an open-source tool. The objective of this paper is to provide a comprehensive description of this 4C version (v2.2) for scientific users of the model and to present an evaluation of 4C at four different forest sites across Europe. The evaluation focuses on forest growth as well as carbon (net ecosystem exchange, gross primary production), water (actual evapotranspiration, soil water content), and heat fluxes (soil temperature) using data from the PROFOUND database. We applied different evaluation metrics and compared the daily, monthly, and annual variability of observed and simulated values. The ability to reproduce forest growth (stem diameter and biomass) differs from site to site and is best for a pine stand in Germany (Peitz, model efficiency ME=0.98). 4C is able to reproduce soil temperature at different depths in Sorø and Hyytiälä with good accuracy (for all soil depths ME > 0.8). The dynamics in simulating carbon and water fluxes are well captured on daily and monthly timescales (0.51 < ME < 0.983) but less so on an annual timescale (ME < 0). This model–data mismatch is possibly due to the accumulation of errors because of processes that are missing or represented in a very general way in 4C but not with enough specific detail to cover strong, site-specific dependencies such as ground vegetation growth. These processes need to be further elaborated to improve the projections of climate change on forests. We conclude that, despite shortcomings, 4C is widely applicable, reliable, and therefore ready to be released to the scientific community to use and further develop the model.

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Thèses sur le sujet "Cover source mismatch"

Abecidan, Rony. « Stratégies d'apprentissage robustes pour la détection de manipulation d'images ». Electronic Thesis or Diss., Centrale Lille Institut, 2024. http://www.theses.fr/2024CLIL0025.

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Aujourd'hui, la manipulation d'images à des fins non éthiques est courante, notamment sur les réseaux sociaux et dans la publicité. Les utilisateurs malveillants peuvent par exemple créer des images synthétiques convaincantes pour tromper le public ou dissimuler des messages dans des images numériques, posant des risques pour la sécurité nationale. Les chercheurs en analyse forensique d'image travaillent donc avec les forces de l'ordre pour détecter ces manipulations. Les méthodes d'analyse forensique les plus avancées utilisent notamment des réseaux neuronaux convolutifs pour les détecter. Cependant, ces réseaux sont entraînés sur des données préparées par des équipes de recherche, qui diffèrent largement des données réelles rencontrées en pratique. Cet écart réduit considérablement l'efficacité opérationnelle des détecteurs de manipulations d'images. Cette thèse vise précisément à améliorer l'efficacité des détecteurs de manipulation d'images dans un contexte pratique, en atténuant l'impact de ce décalage de données. Deux stratégies complémentaires sont explorées, toutes deux issues de la littérature en apprentissage automatique : 1. Créer des modèles capables d'apprendre à généraliser sur de nouvelles bases de données ou 2. Sélectionner, voire construire, des bases d'entraînement représentatives des images à examiner. Pour détecter des manipulations sur un grand nombre d'images non étiquetées, les stratégies d'adaptation de domaine cherchant à plonger les distributions d'entraînement et d'évaluation dans un espace latent où elles coïncident peuvent se révéler utiles. Néanmoins, on ne peut nier la faible efficacité opérationnelle de ces stratégies, étant donné qu'elles supposent un équilibre irréaliste entre images vraies et manipulées parmi les images à examiner. En plus de cette hypothèse problématique, les travaux de cette thèse montrent que ces stratégies ne fonctionnent que si la base d'entraînement guidant la détection est suffisamment proche de la base d'images sur laquelle on cherche à évaluer, une condition difficile à garantir pour un praticien. Généraliser sur un petit nombre d'images non étiquetées est encore plus difficile bien que plus réaliste. Dans la seconde partie de cette thèse, nous abordons ce scénario en examinant l'influence des opérations de développement d'images traditionnelles sur le phénomène de décalage de données en détection de manipulation d'images. Cela nous permet de formuler des stratégies pour sélectionner ou créer des bases d'entraînement adaptées à un petit nombre d'images. Notre contribution finale est une méthodologie qui exploite les propriétés statistiques des images pour construire des ensembles d'entraînement pertinents vis-à-vis des images à examiner. Cette approche réduit considérablement le problème du décalage de données et permet aux praticiens de développer des modèles sur mesure pour leur situation
Today, it is easier than ever to manipulate images for unethical purposes. This practice is therefore increasingly prevalent in social networks and advertising. Malicious users can for instance generate convincing deep fakes in a few seconds to lure a naive public. Alternatively, they can also communicate secretly hidding illegal information into images. Such abilities raise significant security concerns regarding misinformation and clandestine communications. The Forensics community thus actively collaborates with Law Enforcement Agencies worldwide to detect image manipulations. The most effective methodologies for image forensics rely heavily on convolutional neural networks meticulously trained on controlled databases. These databases are actually curated by researchers to serve specific purposes, resulting in a great disparity from the real-world datasets encountered by forensic practitioners. This data shift addresses a clear challenge for practitioners, hindering the effectiveness of standardized forensics models when applied in practical situations.Through this thesis, we aim to improve the efficiency of forensics models in practical settings, designing strategies to mitigate the impact of data shift. It starts by exploring literature on out-of-distribution generalization to find existing strategies already helping practitioners to make efficient forensic detectors in practice. Two main frameworks notably hold promise: the implementation of models inherently able to learn how to generalize on images coming from a new database, or the construction of a representative training base allowing forensics models to generalize effectively on scrutinized images. Both frameworks are covered in this manuscript. When faced with many unlabeled images to examine, domain adaptation strategies matching training and testing bases in latent spaces are designed to mitigate data shifts encountered by practitioners. Unfortunately, these strategies often fail in practice despite their theoretical efficiency, because they assume that scrutinized images are balanced, an assumption unrealistic for forensic analysts, as suspects might be for instance entirely innocent. Additionally, such strategies are tested typically assuming that an appropriate training set has been chosen from the beginning, to facilitate adaptation on the new distribution. Trying to generalize on a few images is more realistic but much more difficult by essence. We precisely deal with this scenario in the second part of this thesis, gaining a deeper understanding of data shifts in digital image forensics. Exploring the influence of traditional processing operations on the statistical properties of developed images, we formulate several strategies to select or create training databases relevant for a small amount of images under scrutiny. Our final contribution is a framework leveraging statistical properties of images to build relevant training sets for any testing set in image manipulation detection. This approach improves by far the generalization of classical steganalysis detectors on practical sets encountered by forensic analyst and can be extended to other forensic contexts

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Chapitres de livres sur le sujet "Cover source mismatch"

Zhang, Xunpeng, Xiangwei Kong, Pengda Wang et Bo Wang. « Cover-Source Mismatch in Deep Spatial Steganalysis ». Dans Digital Forensics and Watermarking, 71–83. Cham : Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-43575-2_6.

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Hu, Donghui, Zhongjin Ma, Yuqi Fan et Lina Wang. « A Study of the Two-Way Effects of Cover Source Mismatch and Texture Complexity in Steganalysis ». Dans Digital Forensics and Watermarking, 601–15. Cham : Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-53465-7_45.

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Mahto, Rakeshkumar, et Reshma John. « Modeling of Photovoltaic Module ». Dans Solar Cells [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.97082.

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A Photovoltaic (PV) cell is a device that converts sunlight or incident light into direct current (DC) based electricity. Among other forms of renewable energy, PV-based power sources are considered a cleaner form of energy generation. Due to lower prices and increased efficiency, they have become much more popular than any other renewable energy source. In a PV module, PV cells are connected in a series and parallel configuration, depending on the voltage and current rating, respectively. Hence, PV modules tend to have a fixed topology. However, in the case of partial shading, mismatching or failure of a single PV cell can lead to many anomalies in a PV module’s functioning. If proper attention is not given, it can lead to the forward biasing of healthy PV cells in the module, causing them to consume the electricity instead of producing it, hence reducing the PV module’s overall efficiency. Hence, to further the PV module research, it is essential to have an approximate way to model them. Doing so allows for understanding the design’s pros and cons before deploying the PV module-based power system in the field. In the last decade, many mathematical models for PV cell simulation and modeling techniques have been proposed. The most popular among all the techniques are diode based PV modeling. In this book chapter, the author will present a double diode based PV cell modeling. Later, the PV module modeling will be presented using these techniques that incorporate mismatch, partial shading, and open/short fault. The partial shading and mismatch are reduced by incorporating a bypass diode along with a group of four PV cells. The mathematical model for showing the effectiveness of bypass diode with PV cells in reducing partial shading effect will also be presented. Additionally, in recent times besides fixed topology of series–parallel, Total Cross-Tied (TCT), Bridge Link (BL), and Honey-Comb (H-C) have shown a better capability in dealing with partial shading and mismatch. The book chapter will also cover PV module modeling using TCT, BL, and H-C in detail.

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Actes de conférences sur le sujet "Cover source mismatch"

Quentin, Giboulot, Bas Patrick, Cogranne Remi et Borghys Dirk. « The Cover Source Mismatch Problem in Deep-Learning Steganalysis ». Dans 2022 30th European Signal Processing Conference (EUSIPCO). IEEE, 2022. http://dx.doi.org/10.23919/eusipco55093.2022.9909553.

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Borghys, Dirk, Patrick Bas et Helena Bruyninckx. « Facing the Cover-Source Mismatch on JPHide using Training-Set Design ». Dans IH&MMSec '18 : 6th ACM Workshop on Information Hiding and Multimedia Security. New York, NY, USA : ACM, 2018. http://dx.doi.org/10.1145/3206004.3206021.

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Mallet, Antoine, Patrick Bas et Rémi Cogranne. « Statistical Correlation as a Forensic Feature to Mitigate the Cover-Source Mismatch ». Dans IH&MMSEC '24 : ACM Workshop on Information Hiding and Multimedia Security. New York, NY, USA : ACM, 2024. http://dx.doi.org/10.1145/3658664.3659638.

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Li, Zhenyu, et Adrian G. Bors. « Selection of robust features for the Cover Source Mismatch problem in 3D steganalysis ». Dans 2016 23rd International Conference on Pattern Recognition (ICPR). IEEE, 2016. http://dx.doi.org/10.1109/icpr.2016.7900302.

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Kodovský, Jan, Vahid Sedighi et Jessica Fridrich. « Study of cover source mismatch in steganalysis and ways to mitigate its impact ». Dans IS&T/SPIE Electronic Imaging, sous la direction de Adnan M. Alattar, Nasir D. Memon et Chad D. Heitzenrater. SPIE, 2014. http://dx.doi.org/10.1117/12.2039693.

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Méreur, Arthur, Antoine Mallet et Rémi Cogranne. « Are Deepfakes a Game-changer in Digital Images Steganography Leveraging the Cover-Source-Mismatch ? » Dans ARES 2024 : The 19th International Conference on Availability, Reliability and Security. New York, NY, USA : ACM, 2024. http://dx.doi.org/10.1145/3664476.3670893.

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Benes, Martin, Nora Hofer et Rainer Bohme. « The Effect of the JPEG Implementation on the Cover-Source Mismatch Error in Image Steganalysis ». Dans 2022 30th European Signal Processing Conference (EUSIPCO). IEEE, 2022. http://dx.doi.org/10.23919/eusipco55093.2022.9909711.

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Oliveira, Daniel, Paolo Rech et Philippe Olivier Navaux. « Hardening Strategies for HPC Applications ». Dans XX Simpósio em Sistemas Computacionais de Alto Desempenho. Sociedade Brasileira de Computação - SBC, 2019. http://dx.doi.org/10.5753/wscad_estendido.2019.8708.

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HPC devices reliability is one of the major concerns for supercomputers today and for the next generation. In fact, the high number of devices in large data centers makes the probability of having at least a device corrupted to be very high. In this work, we first evaluate the problem by performing radiation experiments. The data from the experiments give us realistic error rate of HPC devices. Moreover, we evaluate a representative set of algorithms deriving general insights of parallel algorithms and programming approaches reliability. To understand better the problem, we propose a novel methodology to go beyond the quantification of the problem. We qualify the error by evaluating the criticality of each corrupted execution through a dedicated set of metrics. We show that, as long as imprecise computing is concerned, the simple mismatch detection is not sufficient to evaluate and compare the radiation sensitivity of HPC devices and algorithms. Our analysis quantifies and qualifies radiation effects on applications output correlating the number of corrupted elements with their spatial locality. We also provide the mean relative error (dataset-wise) to evaluate radiation-induced error magnitude. Furthermore, we designed a homemade fault-injector, CAROL-FI, to understand further the problem by collecting information using fault injection campaigns that is not possible through radiation experiments. We inject different fault models to analyze the sensitivity of given applications. We show that portions of applications can be graded by different criticalities. Mitigation techniques can then be relaxed or hardened based on the criticality of the particular portions. This work also evaluates the reliability behaviors of six different architectures, ranging from HPC devices to embedded ones, with the aim to isolate code- and architecture-dependent behaviors. For this evaluation, we present and discuss radiation experiments that cover a total of more than 352,000 years of natural exposure and fault-injection analysis based on a total of more than 120,000 injections. Finally, Error-Correcting Code, Algorithm-Based Fault Tolerance, and Duplication With Comparison hardening strategies are presented and evaluated on HPC devices through radiation experiments. We present and compare both the reliability improvement and imposed overhead of the selected hardening solutions. Then, we propose and analyze the impact of selective hardening for HPC algorithms. We perform fault-injection campaigns to identify the most critical source code variables and present how to select the best candidates to maximize the reliability/overhead ratio.

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Bowling, Kim. « Geometry Detector Teardown Results at CSX ». Dans ASME 2009 Rail Transportation Division Fall Technical Conference. ASMEDC, 2009. http://dx.doi.org/10.1115/rtdf2009-18026.

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CSX Transportation has purchased, installed and integrated eight Optical Geometry Detector sites. These detectors measure the wheelset’s angle of attack and lateral position with respect to the tangent track upon which they pass. The objective of this project was to determine the source of extreme geometry measurements. CSX performed 19 teardowns of cars that were identified by the optical geometry system. Many other cars with geometry exceptions have also had close inspections at the repair tracks. This report will summarize how the defects found relate to the geometry exception. CSX has primarily looked at trucks with progressive and repeatable tracking problems, which cover 87% of the geometry exceptions. Key truck measurements recorded include: circumferential wheel tape size, digital wheel profiles, side bearing set up height, center bowl dimensions, side frame length and the distance between the thrust lugs. Many of the geometry exceptions seem to have been caused by mismatched (or asymmetrical worn) wheels. Differences in the circumference force the axle to shift laterally and allow the wheel to continually flange on the gauge side of the rail.

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Feneley, Adam, Apostolos Pesiridis et Hua Chen. « A One-Dimensional Gas Dynamics Code for Turbocharger Turbine Pulsating Flow Performance Modelling ». Dans ASME Turbo Expo 2017 : Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-64743.

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As governments around the world ramp up their efforts to reduce CO2 emissions, downsizing internal combustion engines has become a dominant trend in the automotive industry. Air charging systems are being utilised to increase power density and therefore lower emissions by downsizing internal combustion engines. Turbocharging represents the majority of these air charging systems, which are commonly adopted for commercial and passenger vehicles. The process of matching turbomachinery to an engine during early-stage development is important to achieving maximum engine performance in terms of power output and the reduction of emissions. Despite on-engine conditions providing highly unsteady gas flows, current turbocharger development commonly uses performance maps that are produced from steady state measurements. There are other significant sources of error to be found in early stage turbocharger performance prediction, such as the omission of heat transfer effects, and the use of data extrapolation methods to cover the entire operating range of a device from limited data sets. Realistic engine conditions provide a complex heat transfer scenario, which is dependent upon load history and the component layout of the engine bay. Heat transfer effects are particularly prevalent at low engine loads, whilst pulsating effects are significant at both high and low engine speeds (and therefore exhaust pulse frequency). Compressor maps are often provided by manufacturers with a level of heat transfer corresponding to a gas stand test, not realistic engine conditions. This causes a mismatch when using the aforementioned maps in commercial engine codes. This reduces the quality of overall engine performance predictions, since as the temperature of the exhaust gas on the turbine side rises, the performance prediction increasingly deviates from the usual adiabatic assumption used in simulations. In the present work, a one-dimensional unsteady flow model has been developed to predict the performance of a vaneless turbine under pulsating inlet conditions, with scope to account for heat transfer effects. Flow within the volute is considered to be one-dimensional and unsteady, with mass addition and withdrawal used to simulate the gas flow between the volute and rotor. Rotor passages are also treated as one-dimensional and unsteady, with the equations being solved by the method of characteristics. This model is able to simulate the circumferential feeding of the rotor from the casing, unlike many previous zero and one-dimensional models. Building upon previous work, the basis of this code has been constructed in C++ with future integration with other modern gas dynamics codes in mind. By providing the appropriate instantaneous operating conditions at specified time intervals, a code such as this could theoretically negate the need for maps produced by steady-state data.

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