Academic literature on the topic 'Champ deformation'

Problems in surrounding rock displacement, roadway deformation and complex support are the hallmarks of the long wall mining system. Such problems seriously affect the safety and efficient production of coal mines. To control the deformation of the rocks around the roadway next to the goaf, to reduce the support pressure, in Vietnamese underground mines often leave supporting coal pillars. Identification of a reasonable design for roadway supporting pillars by a numerical simulation study was conducted under the geological and technical foundation of I-10- 2 working faces at the Khe Cham coal mine, Vietnam . The characteristics of stress and pressure distribution of roof layers on coal pillars are modeled under different pillar widths. The results show a great linear increase of the vertical stress on the narrow coal pillar and as the width of the coal pillar increases, the area of the elastic core area also increases and the level of stress increase tends to be stable without any apparent uptrend. Coal pillar deformation decreases with increasing coal pillar width, but it leads to large coal loss and waste of resources. Therefore, with the current supporting solutions to increase the stability of the coal pillar, the size range of a coal pillar is determined to be 6-8 m through numerical simulation. The conclusions obtained may provide a certain reference number to choose the logical location of the furnace lines under similar geological conditions.

The work is devoted to the search for new effective modifying additives that allow to purposefully regulate the technological properties of rubber compounds and physical-mechanical properties of rubbers based on combinations of non-polar rubbers and at the same time being cheaper and more affordable than traditional products, in particular, with resorcinol-urotropin complex (modifier RU -1). It was proposed to use as a modifier of frame rubbers based on a combination of isoprene (SKI-3) and butadiene-styrene (SCS-30ARKM-15) rubbers, chlorinated atactic polypropylene (CHAPP). It is shown that when the RU-1 modifier is replaced with this compound, the conditional stresses and tensile strength, tearing resistance, rebound elasticity, fatigue resistance in the regime of constant deformation amplitude, heat resistance, resistance to thermal aging of rubbers, as well as the strength of rubber bonding with rubber Textile cord, including at elevated temperatures are observed. Comparison of the CHAPP for the effectiveness of the action in the carcass gum with the previously proposed oligoefirmetacrylate epichlorhydrine, from the point of view of the provided complex of properties, showed the advantage of chlorinated atactic polypropylene for a number of priority indicators. From the comparative analysis of the modifying activity of chlorinated atactic polypropylene and oligoether methacrylate epichlorohydrin, it follows that the vulcanizates of rubber compounds containing instead of RU-1 chlorinated atactic polypropylene CHAPP are characterized by more improved parameters of hardness in TM-2, elasticity by rebound, the strength of the rubber-cord connection. It is also revealed that the main advantage of the proposed modifier is the low cost of the modifier used, as well as the use of secondary raw materials for its production.Forcitation:Mustafayeva R.E. Technological aspects of production and research of polymers composite materials with increased strength. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 10. P. 82-86

The structure and stability of the Li+Arn and K+Arn clusters are studied using pair additive potentials adapted to reproduce the ab initio calculations that we estimate as the most accurate for the Li+Ar, K+Ar, and Ar–Ar dimers. The exploration of the potential energy surfaces of the Li+Arn and K+Arn systems was carried out with Wales’ method, which includes Monte-Carlo and deformation methods. From a structural point of view, one identifies a construction mechanism in very good agreement with the interpretation of the mass spectrum done by Velegrakis, including a difference for the n = 10 case. The study of the relative stability of these structures yields magic numbers for n = 8, 10, 14, 16, 18, 20, 22, 30, 32, and 34, which are in good agreement with the experiment. [Journal translation]

Currently, the application of coal pillars to protect an adjacent roadway is a common method in Vietnam when exploiting according to the longwall system. Therefore, the width of a coal pillar is an important issue for the stability of a roadway. In order to reduce coal loss in these coal pillars, they tend to be designed in a narrow coal pillar style but still have to ensure that the adjacent roadway can meet safe coal production conditions. The stability of roadways and coal pillars is related to many factors such as technical mechanical characteristics, physical and mechanical properties of coal, stress environment and support methods. The bearing structure of the coal pillar and the around rock a roadway is analyzed and it has been shown that enhancing roadway support and improving the carrying capacity of coal pillars can control the deformation of the surrounding rock. A study related to the stability and safety of roadways and small coal pillars in the longwall mining system has been carried out. Stabilization factors have been considered, especially the state of stress in the coal pillars and the deformation of the roadway. By applying the numerical simulation method, the stress of the coal pillar and the deformation of the adjacent roadway under different supporting solutions were analyzed and evaluated. By using this method, the rock bolt roadway support solution combined with the long cable bolt in the roadway roof and the coal pillar was selected in the safe condition of the mining process. Because cable bolt can improve the flexibility of the coal pillar such as: reducing the size of the plastic area on both sides of the pillar; enhancing coal pillar stability in the core area by providing great drag and tensile for coal pillars; contributing to improving the anchor point fixation of rock bolt. The conclusions obtained may provide a certain reference parameters to improve mining efficiency and labor safety in underground coal mines.

A modernidade iniciou a crítica dos antigos promovendo a ruptura entre o público e o privado, retirando do primeiro a idéia de princípios ético-morais universais, substituindo-os por interesses. Assim a modernidade vai transformar-se no auto da razão, em nome do perseguir de interesses ligados à razão instrumental. Este fato justifica a "crise " de valores que perpassa as sociedades contemporâneas. Decorrente disto, no campo da análise, da pesquisa, è de suma importância a busca de recomposição de saberes para além da razão instrumental. Neste texto, a educação é pensada pelo autor como princípio formador de vontade política, no contexto de produção democrática da cultura. Aí a educação encontra seu papel de mediador político. Categorizado como processo de desideologização, o ato pedagógico torna-se um instrumento deformação democrática da vontade política: elimna por ato de reflexão as vontades que nascem das contradições da realidade e, através de um processo discursivo, revela o lado oculto da ideologia, produzindo desejos que se manifestam em atos práticos concretos da ação política. Diante da crise dos paradigmas científicos na área da sociologia, especialmente na de política, o autor refuta os referenciais teóricos de autores que realizaram análises do tema educação na rota de exames e (re)exames das relações entre educação e estrutura econômico-social capitalista. A compreensão da conexão entre forças produtivas e relações de produção, em que o papel político da educação é analisado segundo um modelo dualista de classes sociais, não responde mais à atual realidade social e política de um capitalismo "renovado". Isso instiga um (re)pensar da educação. Abstract Modernity started a criticism of the old, causing the rupture between the public and the private, removing from the first the idea of universal ethical-moral principles, substituting them for interests. This modernity becomes the cuit of reason, under the purpose of pursuing interests linked to the instrumental reason. This fact justifies the "crisis" of values that contemporary societies undergo. Asa residi, (in the analysis and researches developed) it is extremely important to search for the rearrangement of knowledge beyond the instrumental reason. In this text, education is wiewed by the author as a principle able to shape politic will in the context of democratic production of culture. Education has the role of political mediator. The pedagogic act, considered a "desideologización" process, becomes an instrument for democratic shaping of the politic will: it removes through reflexion the wills that emerge from contradictions of reality and trough a discursive process discloses the occult face of ideology, producing wishes that show themselves trough concrete practical acts. Given the crisis of scientific paradigms in (he area of the sociology, especially in Political Science, the author denies theoretical approaches of authors who developed studies in education through the analysis of the relationships between Education in the Capitalist Social-Economical Structure. The understanding of the connection between productive forces and production relations where the political role of education is analized according to a dualistic model of social classes does not grasp any more the social and political reality of a "renewed" capitalism. This induces to (re)think Education. Résumé La modernité a comencé la critique aux antiques en provoquant la rupture entre le public et le privé, en retirant du premier l'idée de principes éthico-morals universels en les remplaçant pour des intérêts liés à la raison instrumentale. Ce fait justifie la "crise" de valeurs qui touche les sociétés contemporaines. A cause de cela, dans le domaine de l'analyse et de la recherche, c 'est très important la recherche de récomposition de savoirs pour au-delà de la raison instrumentale. En ce texte l'éducation est pensée par l'auteur comme principe formateur de volonté politique dans le contexte de production démocratique de la culture. Alors, l'éducation trouve son rôle, c 'est-à-dire elle va devenir la médiatrice politique et s'assume catégoriquement comme un processus de désidéologisation. Ainsi, l'actepédagogique est devenu un instrument deformation démocratique de la volonté politique: l'éducation élimine par l'acte de réflexion les volontés qui naissent des contradictions de la réalité et à travers un processus discursif qui dévoile le côté oculte de l'idéologie en produisant des souhaits qui se manifestent en actes pratiques concrets de l'action politique. Devant cette crise des paradigmes scientifiques, dans le domaine de la sociologie, spécialement dans le champ politique, l'auteur refuse les références théoriques d'auteurs qui ont réalisé des analyses sur le même thème éducatif dans les sens d'examens et (re)examens des relations entre l'éducation et la structure économique-sociale capitaliste. La compréhension de ¡a connexion forces productives et relations de production dont le rôle politico-social est analysé selon un modèle dualiste de classes sociales qui ne répond plus à l'actuelle réalité sociale el politique d'un capitalisme "renouvelé". Cela provoque en nous un (re)penser de l'éducation. Resumen La modernidad empezó la crítica de los antiguos promoviendo la ruptura entre el público y el privado, retirando del primer la idea de principios ético-morales universales substituiendo-lospor intereses. Así, la modernidad va a transformarse en el culto de la razón, en nombre del perseguir de intereses ligados a la razón instrumental. Este hecho justifica la crisis de valores queperpasa las sociedades contemporáneas. A causa de esto, en el campo de la análisis, de la pesquisa, es muy importante la busca de recomposición de saberes a los lejos de la razón instrumental. En este texto la educación es pensada por el autor como principio formador de volontadpolítica en el contexto de producción democrática de la cultura. Ahi, la educación encuentra su tarea de mediador político. Categorizado como proceso de desideologización, el acto pedagógico va a ser un instrumento deformación democrático de la volontad política: elimina por acto de reflexión las volontades que nacen de las contradicciones de la realidad y através de un proceso discursivo revela el lado oculto de la ideologia produciendo deseos que se manifestán en actos prácticos concretos de la acción política. Frente la crisis de paradigmas científicos en la area de la sociologia, especialmente en la de política, el autor rechaza los referenciales teóricos de autores que realizaran algunas análises del tema educación en el rumo de examenes y (re)examenes de las relaciones entre Educación y Estructura Economicasocial capitalista. La comprensión de la conexión fuerzas productivas y relaciones de producción onde el papel político de la educación es analizado según un modelo dualista de clases sociales que no responde más a la actual realidad social y política de un capitalismo (renovado). Esto instiga un (re)pensar de la Educación.

Liver segmentation is relevant for several clinical applications. Automatic liver segmentation using convolutional neural networks (CNNs) has been recently investigated. In this paper, we propose a new approach of combining a largest connected component (LCC) algorithm, as a post-processing step, with CNN approaches to improve liver segmentation accuracy. Specifically, in this study, the algorithm is combined with three well-known CNNs for liver segmentation: FCN-CRF, DRIU and V-net. We perform the experiment on a variety of liver CT images, ranging from non-contrast enhanced CT images to low-dose contrast enhanced CT images. The methods are evaluated using Dice score, Haudorff distance, mean surface distance, and false positive rate between the liver segmentation and the ground truth. The quantitative results demonstrate that the LCC algorithm statistically significantly improves results of the liver segmentation on non-contrast enhanced and low-dose images for all three CNNs. The combination with V-net shows the best performance in Dice score (higher than 90%), while the DRIU network achieves the smallest computation time (2 to 6 seconds) for a single segmentation on average. The source code of this study is publicly available at https://github.com/kennyha85/Liver-segmentation. Keywords: Liver segmentations, CNNs, Connected Components, Post processing Reference [1] K.A. McGlynn, J.L. Petrick, W.T. London, Global epidemiology of hepatocellular carcinoma: An emphasis on demographic and regional variability. Clinics in liver disease 19(2) (2015) 223-238. [2] M. Mohammadian, N. Mahdavifar, A. Mohammadian-Hafshejani, H. Salehiniya, Liver cancer in the world: epidemiology, incidence, mortality and risk factors, World Cancer Res J. 5(2) (2018) e1082. [3] T.T. Hong, N. Phuong Hoa, S.M. Walker, P.S. Hill, C. Rao, Completeness and reliability of mortality data in Viet Nam: Implications for the national routine health management information system, PloS one 13(1) 2018) e0190755. https://doi.org/10.1371/journal.pone.0190755. [4] T. Pham, L. Bui, G. Kim, D. Hoang, T. Tran, M. Hoang, Cancers in Vietnam-Burden and Control Efforts: A Narrative Scoping Review. Cancer Control 26(1) (2019) 1073274819863802. [5] M. Borner, M. Castiglione, J. Triller, H.U. Baer, M. Soucek, L. Blumgart, K. Brunner, Arena: Considerable side effects of chemoembolization for colorectal carcinoma metastatic to the liver, Annals of oncology 3(2) (1992) 113-115. [6] K. Memon, R.J. Lewandowski, L. Kulik, A. Riaz, M.F. Mulcahy, R. Salem, Radioembolization for primary and metastatic liver cancer, In Seminars in radiation oncology, WB Saunders. 21(4) (2011) 294-302. [7] I. Gory, M. Fink, S. Bell, P. Gow, A. Nicoll, V. Knight, W. Kemp, Radiofrequency ablation versus resection for the treatment of early stage hepatocellular carcinoma: A multicenter Australian study, Scandinavian journal of gastroenterology 50(5) (2015) 567-576. [8] H.M. Luu, C. Klink, W. Niessen, A. Moelker, T. Van Walsum, Non-rigid registration of liver CT images for CT-guided ablation of liver tumors. PloS one, 11(9) 92016) e0161600. [9] G. Gunay, M.H. Luu, A. Moelker, T. Van Walsum, S. Klein, Semiautomated registration of pre‐and intraoperative CT for image‐guided percutaneous liver tumor ablation interventions, Medical physics 44(7) (2017) 3718-3725. [10] A. Gotra, L. Sivakumaran, G. Chartrand, N. Vu, F. Vandenbroucke-Menu, C. Kauffmann, A. Tang, Liver segmentation: Indications, techniques and future directions, Insights into imaging 8(4) (2017) 377-392. https://doi.org/10.1007/s13244-017-0558-1. [11] T. Heimann, B. Van Ginneken, M.A. Styner, Y. Arzhaeva, V. Aurich, C. Bauer, F. Bello, Comparison and evaluation of methods for liver segmentation from CT datasets, IEEE transactions on medical imaging 28(8) (2009) 1251-1265. [12] O. Ronneberger, P. Fischer, T. Brox, U-net: Convolutional networks for biomedical image segmentation, In International Conference on Medical image computing and computer-assisted intervention, Springer, Cham, 2015, pp. 234-241. [13] F. Milletari, N. Navab, S.A. Ahmadi, October, V-net: Fully convolutional neural networks for volumetric medical image segmentation, In 2016 Fourth International Conference on 3D Vision (3DV) IEEE, 2016, pp. 565-571. [14] P.F. Christ, F. Ettlinger, F. Grün, M.A. Elshaera, J. Lipkova, S. Schlecht, M. Rempfler, Automatic liver and tumor segmentation of CT and MRI volumes using cascaded fully convolutional neural networks, arXiv preprint arXiv:1702.05970, 2017. [15] P.F. Christ, M.E.A. Elshaer, F. Ettlinger, S. Tatavarty, M. Bickel, P. Bilic, H. Sommer, Automatic liver and lesion segmentation in CT using cascaded fully convolutional neural networks and 3D conditional random fields. In International Conference on Medical Image Computing and Computer-Assisted Intervention, Springer, Cham, 2016, pp. 415-423. [16] H. Meine, G. Chlebus, M. Ghafoorian, I. Endo, A. Schenk, Comparison of U-net-based Convolutional Neural Networks for Liver Segmentation in CT. arXiv preprint arXiv, 2018, pp. 1810.04017. [17] X. Li, H. Chen, X. Qi, Q. Dou, C.W. Fu, P.A. Heng, H-DenseUNet: hybrid densely connected UNet for liver and tumor segmentation from CT volumes, IEEE transactions on medical imaging, 37(12) (2018) 2663-2674. [18] M. Bellver, K.K. Maninis, J. Pont-Tuset, X. Giró-i-Nieto, J. Torres, L. Van Gool, Detection-aided liver lesion segmentation using deep learning, ArXiv preprint arXiv:1711.11069, 2017. [19] H.S. Hoang, C.P. Pham, D. Franklin, T. Van Walsum, M.H. Luu, An Evaluation of CNN-based Liver Segmentation Methods using Multi-types of CT Abdominal Images from Multiple Medical Centers, In 2019 19th International Symposium on Communications and Information Technologies (ISCIT), IEEE, September, 2019, pp. 20-25. [20] H. Samet, M. Tamminen, Efficient component labeling of images of arbitrary dimension represented by linear bintrees, IEEE Transactions on Pattern Analysis and Machine Intelligence, 10(4) (1988) 579-586. [21] P. Bilic, P.F. Christ, E. Vorontsov, G. Chlebus, H. Chen, Q. Dou, S. Kadoury, The liver tumor segmentation benchmark (lits), ArXiv preprint arXiv, 2019, 1901.04056. [22] H.M. Luu, A. Moelker, S. Klein, W. Niessen, T. Van Walsum, Quantification of nonrigid liver deformation in radiofrequency ablation interventions using image registration, Physics in Medicine & Biology 63(17) (2018) 175005. [23] A.A. Novikov, D. Major, M. Wimmer, D. Lenis, K. Bühler, Deep Sequential Segmentation of Organs in Volumetric Medical Scans, IEEE transactions on medical imaging, 2018. [24] Y. Huo, J.G. Terry, J. Wang, S. Nair, A. Lasko, B.I. Freedman, B.A. Landman, Fully Automatic Liver Attenuation Estimation combing CNN Segmentation and Morphological Operations, Medical physics, 2019. [25] N. Gruber, S. Antholzer, W. Jaschke, C. Kremser, M. Haltmeier, A Joint Deep Learning Approach for Automated Liver and Tumor Segmentation, ArXiv preprint arXiv, 2019, pp. 1902.07971. [26] S. Chen, K. Ma, Y. Zheng, Med3D: Transfer Learning for 3D Medical Image Analysis, ArXiv preprint arXiv, 2019, pp. 1904.00625. [27] W. Tang, D. Zou, S. Yang, J. Shi, DSL: Automatic Liver Segmentation with Faster R-CNN and DeepLab, In International Conference on Artificial Neural Networks, Springer, Cham, 2018, pp. 137-147.

L'analyse de la polarisation des ondes s d'un grand nombre de repliques enregistrees apres les seismes d'erzincan (turquie) en 1992, d'aigion (grece) en 1995 et d'agios-pandes (grece) en 1997, a revele une birefringence des ondes s tres claire, que nous avons interprete en terme d'anisotropie sismique crustale. Dans le bassin d'erzincan, la direction de polarisation des ondes s est tournee par rapport a la direction de la contrainte regionale. Au bord sud du bassin, la direction de la s rapide differe significativement de la direction de la contrainte regionale. Nous avons interprete ces deux rotations par l'activite des failles qui controleraient et deformeraient localement le champ de contrainte. Ce modele permet de proposer un retard de glissement du segment de faille nab (active en 1992) par rapport au segment nae. Cette hypothese est en accord avec la sismicite historique de la region. Les etudes de birefringence des ondes s dans le golfe de corinthe montrent deux directions differentes d'anisotropie. La premiere est perpendiculaire a la direction quasi-ns de l'extension du golfe, en agrement avec le modele eda. La seconde, observee pour tous les sites situes sur la rive nord du golfe, est significativement tournee par rapport a la direction de la contrainte regionale. Pour quelques sites, situes proche des failles actives, les directions observees sont quasi-paralleles a l'azimut de ces failles suggerant un controle local du champ de contrainte par leur activite. Au site psal, la direction observee en 1995, apres le seisme d'aigion qui a rompu une faille normale situee sous le site, est tournee par rapport a sa direction anterieure obtenue en 1991-1992 par bouin et al. , 1996 et par rapport a la direction de l'anisotropie electrique observee en 1995. La rotation temporelle suggere que des nouvelles fissures ont ete generees par le seisme de 1995.

Etude de la variation apparente de l'energie de rupture observee dans le beton et attribuee a un effet d'echelle, pour la relier a la fissuration et a la microfissuration non decelee; tentative non reussie d'etablir un parametre unique d'energie de rupture pour caracteriser la resistance du beton a la propagation de fissure, en mode i

Les proprietes des atomes en champ magnetique relevent de plusieurs domaines comme l'astrophysique, la physique de la matiere condensee, la physique des plasmas, la physique atomique ou la physique des solides. Le but de cette these est de resoudre l'equation de schrodinger en presence d'un champ magnetique arbitrairement fort. Nous avons fait le choix de la methode hartree-fock pour resoudre notre probleme. En general, dans ce type de methode, les fonctions de base sont des orbitales de slater ou des gaussiennes. Nous avons decide d'utiliser des fonctions solutions de l'atome sans champ. Pour cela, on resout les equations de kohn-sham. Le changement de symetrie provoque par le champ (spherique cylindrique, de 0 a 10#7 t) oblige l'utilisation de bases de plus en plus importantes. Pour reduire le nombre de fonctions dans le developpement, nous avons simule l'effet du champ magnetique sur l'anisotropie de la fonction d'onde en multipliant les fonctions de base par un facteur gaussien. On peut se restreindre ainsi a une base limitee aux seuls etats electroniques occupes. On a pu proceder a des calculs de structures electroniques pour de l'helium, du lithium et du carbone mais aussi de l'oxygene et du neon. Les valeurs sont en accord avec les quelques resultats publies. Nous avons aussi calcule quelques elements de matrice de transition optique entre etats lies ainsi que des courants de probabilites.

Description du magnetodisque de jupiter dans laquelle les gradients de pression et les forces d'inertie agissent sur le plasma et engendrent des courants perpendiculaires au champ magnetique et le deforment. Les observations effectuees par les sondes spatiales sont en accord avec cette description. La ou les courants perpendiculaires sont divergents ils creent des courants alignes qui se referment dans l'ionosphere conductrice en deformant le champ electrique. On propose un mecanisme tenant compte de la perte d'electrons par diffusion en angle d'attaque, compatible avec les observations du radar eiscat de la distorsion du champ electrique

L'objectif de mon travail de these aura ete d'etudier les relations entre un reseau de failles et la deformation globale consecutive a son fonctionnement. Ma recherche se sera deroulee en quatre temps. Une premiere approche du probleme a ete realisee par l'analyse d'experiences de cisaillement simple progressif. J'ai propose de nouvelles relations entre la deformation globale d'un champ de failles, et diverses caracteristiques telles que leurs longueurs, leurs rejets cumules, ou encore la quantite de rotation rigide des failles, etc. Une deuxieme approche aura ete effectuee par l'etude d'une deformation progressive faisant varier des pourcentages respectifs de cisaillements simple et pur. Les failles reparties en domaines bien distincts, sont soumises a des rotations respectivement aux axes principaux de la deformation globale. Lorsque ces rotations rigides deviennent importantes, les failles vont jusqu'a se confondre avec les directions predites par le modele de kink band, voire les directions de cisaillement maximum. La troisieme approche aura donc ete l'ecriture d'un programme dans le but d'estimer la deformation globale (forme et intensite) a partir des failles, en prenant comme modele, le fait que les stries accumulent des quantites maximales de cisaillement fini. Le quatrieme approche est une application du programme sur des champs de failles du nord-ouest argentin en confrontant les resultats obtenus numeriquement a ceux acquis par l'experimentation. Les pourcentages de raccourcissement et d'allongement trouves revelent une deformation de la region, non negligeable. Le reequilibrage isostatique de ce raccourcissement relativement important (de plus de 10% a travers le bassin de pipanaco, et de presque 20% a travers le bassin de arenal) a certainement du accentuer la surrection des sierras pampeanas les plus septentrionales, contemporaine au soulevement du plan de subduction il y a 10 ma.

On exploite les mesures des deformations longitudinales de l'armature, au cours d'un essai d'arrachement axisymetrique pour en tirer une formulation mathematique servant d'hypothese de depart a une mise en equations des champs de contraintes, deformations et deplacements. Mise en equations en faisant l'hypothese d'uniaxialite de l'etat de contrainte dans l'armature. Reponse de la formulation mathematique en tenant compte de l'effet des efforts transversaux exerces par le beton d'enrobage sur la barre. Comparaison des resultats obtenus a ceux des mesures realisees au cours d'experience (ecart relatif inferieur a 5%). Introduction dans la formulation mathematique triaxiale d'une loi de frottement simple au contact acier-beton. Les resultats obtenus par cette nouvelle formulation permettent de decrire l'evolution du deplacement de la barre au cours de l'essai

Cette these concerne l'etude theorique du champ de pression et du tenseur de correlation pression-deformation dans les ecoulements turbulents homogenes en rotation. Elle comprend deux parties: dans la premiere partie sont etudiees les caracteristiques du spectre de pression en ecoulement turbulent axisymetrique en rotation. Les resultats phenomenologiques et numeriques obtenus montrent que le spectre de pression presente un comportement bidimensionnel dans la region equatoriale de l'espace spectral et un comportement tridimensionnel dans la region polaire. Lorsque le nombre de reynolds augmente, le domaine de comportement bidimensionnel s'accroit. Dans la deuxieme partie, les travaux portent sur l'etude du terme lineaire du tenseur des correlations pression-deformation. L'originalite de cette etude consiste a suivre une voie differente de la demarche usuelle selon laquelle une modelisation de ce tenseur est proposee a partir de l'etude de l'equation regissant l'evolution du tenseur de reynolds ; ici, la nature des differentes contributions determinant le tenseur de correlation pression-deformation est analysee directement dans l'espace spectral, la turbulence etant supposee homogene, axisymetrique. - dans le cadre de la distorsion rapide, le terme lineaire ne necessite aucune hypothese de fermeture. - en turbulence semi-axisymetrique, il ne depend que du deviateur complexe. - en turbulence faiblement anisotrope, une rotation uniforme ou une rotation liee a un ecoulement moyen jouent des roles identiques dans leur action sur cette partie lineaire, dans le cadre d'une modelisation a l'ordre un en b pour u#i#j (k)

Le but de cette thèse est d’utiliser le langage des champs pour étudier les espaces de Teichmüller dans un cadre analytique. L’approche classique de Kodaira et Spencer dans la théorie des déformations infinitésimales et le théorème d’existence de déformation verselle de Kuranishi ne permettent pas en effet une étude de l’espace de Teichmüller comme objet analytique global. Lathéorie des champs est particulièrement adaptée à l’étude des espaces de modules et des quotients mais elle n’a été essentiellement employée que dans un cadre algébrique. Après la présentation de son adaptation au cadre analytique on s’attachera à l’utiliser sur l’exemple simple mais néanmoins pertinent des surfaces de Hopf, premier exemple de variété compacte complexe non Kählérienne, dont l’espace de Teichmüller n’est ni séparé, ni une orbifold. On donne en particulier deux atlas concrets de ce champ et on calcul certain groupe d’homotopie et de cohomologie. Enfin, on donne des applications aux classes d’homotopies de déformations de surfaces de Hopf
The goal of this phd thesis is to use stacks to study Teichmüller spaces in an analytic framework. Kodaira Spencer theory of infinitesimal deformations is not enough to describe teichmüller space as a global analytic object. Stack theory is very well adapted tostuying moduli spaces and quotients. however it is essentially developped in an algebraic context. We adapt this theory to an analytic framework and we use it on simple but interesting example of Hopf surfaces. In particular we give two concrete atlases of the Teichmüller stack of Hopf surfaces. We compute some of its homotopy groups and homology groups. Finally we give some applications to homotopy classes of deformations of Hopf surfaces

La généralisation de données géographiques est l'opération de simplification de ces données effectuée lors de la diminution de leur échelle de représentation. Cette thèse s'appuie sur le modèle de généralisation automatique à base d'agents de (Ruas et Duchêne, 2007), qui a été mis en oeuvre avec succès pour la généralisation des objets géographiques discrets (bâtiments, routes, etc.). L'objectif est de permettre une prise en compte d'un nouveau type de thèmes, appelés "thèmes champ", comme le relief ou l'occupation du sol. Ces thèmes ont pour particularité d'être définis en tout point de l'espace. Nous souhaitons permettre une préservation des relations pouvant exister entre les objets géographiques et les champs, comme par exemple le fait qu'un cours d'eau s'écoule sur le relief. Pour répondre à cet objectif, nous proposons le modèle de généralisation GAEL (Généralisation à base d'Agents Elastiques) qui permet d'appliquer des déformations aux champs pour préserver les relations objet-champ. Les champs sont modélisés comme des agents, dits élastiques, qui ont la capacité de se déformer pour amortir les opérations de généralisation appliquées aux objets géographiques (bâtiments, routes, etc.). Ces déformations sont obtenues en s'appuyant sur une décomposition des champs en petits éléments contraints (points, segments, triangles, etc.) et sur une modélisation des points composant les champs sous forme d'agents. Couplé au modèle de (Ruas et Duchêne, 2007), le modèle GAEL permet de disposer d'un modèle de généralisation hybride, capable d'effectuer à la fois des opérations discrètes et continues

Developpement d'un modele moleculaire semi-empirique pour les ions d**(5). L'application aux calculs des coefficients de couplage orbite-reseau et des coefficients de couplage spin-reseau a donne de tres bons resultats

The concept of the finite-element procedure may be dated back to 1943 when Courant approximated the warping function linearly in each of an assemblage of triangular elements to the St. Venant torsion problem and proceeded to formulate the problem using the principle of minimum potential energy. Similar ideas were used later by several investigators to obtain the approximate solutions to certain boundary-value problems. It was Clough who first introduced the term “finite elements” in the study of plane elasticity problems. The equivalence of this method with the well-known Ritz method was established at a later date, which made it possible to extend the applications to a broad spectrum of problems for which a variational formulation is possible. Since then numerous studies have been reported on the theory and applications of the finite-element method. In this and next chapters the finite-element formulations necessary for the deformation analysis of metal-forming processes are presented. For hot forming processes, heat transfer analysis should also be carried out as well as deformation analysis. Discretization for temperature calculations and coupling of heat transfer and deformation are discussed in Chap. 12. More detailed descriptions of the method in general and the solution techniques can be found in References [3-5], in addition to the books on the finite-element method listed in Chap. 1. The path to the solution of a problem formulated in finite-element form is described in Chap. 1 (Section 1.2). Discretization of a problem consists of the following steps: (1) describing the element, (2) setting up the element equation, and (3) assembling the element equations. Numerical analysis techniques are then applied for obtaining the solution of the global equations. The basis of the element equations and the assembling into global equations is derived in Chap. 5. The solution satisfying eq. (5.20) is obtained from the admissible velocity fields that are constructed by introducing the shape function in such a way that a continuous velocity field over each element can be denned uniquely in terms of velocities of associated nodal points.

This chapter is concerned with the formulations and solutions for plane plastic flow. In plane plastic flow, velocities of all points occur in planes parallel to a certain plane, say the (x, y) plane, and are independent of the distance from that plane. The Cartesian components of the velocity vector u are ux(x, y), uy(x, y), and uz = 0. For analyzing the deformation of rigid-perfectly plastic and rate-insensitive materials, a mathematically sound slip-line field theory was established (see the books on metal forming listed in Chap. 1). The solution techniques have been well developed, and the collection of slip-line solutions now available is large. Although these slip-line solutions provide valuable insight into deformation modes and forming loads, slip-line field analysis becomes unwieldy for nonsteady-state problems where the field has to be updated as deformation proceeds to account for changes in material boundaries. Furthermore, the neglect of work-hardening, strain-rate, and temperature effects is inappropriate for certain types of problems. Many investigators, notably Oxley and his co-workers, have attempted to account for some of these effects in the construction of slip-line fields. However, by so doing, the problem becomes analytically difficult, and recourse is made to experimental determination of velocity fields, similarly to the visioplasticity method. Some of this work is summarized in Reference [2]. The applications of the finite-element method are particularly effective to the problems for which the slip-line solutions are difficult to obtain. The finite-element formulation specific to plane flow is recapitulated here.

The design, control, and optimization of forming processes require (1) analytical knowledge regarding metal flow, stresses, and heat transfer, as well as (2) technological information related to lubrication, heating and cooling techniques, material handling, die design and manufacture, and forming equipment. The purpose of using analysis in metal forming is to investigate the mechanics of plastic deformation processes, with the following major objectives. • Establishing the kinematic relationships (shape, velocities, strain-rates, and strains) between the undeformed part (billet, blank, or preform) and the deformed part (product); i.e., predicting metal flow during the forming operation. This objective includes the prediction of temperatures and heat transfer, since these variables greatly influence local metal-flow conditions. • Establishing the limits of formability or producibility; i.e., determining whether it is possible to perform the forming operation without causing any surface or internal defects (cracks or folds) in the deforming material. • Predicting the stresses, the forces, and the energy necessary to carry out the forming operation. This information is necessary for tool design and for selecting the appropriate equipment, with adequate force and energy capabilities, to perform the forming operation. Thus, the mechanics of deformation provides the means for determining how the metal flows, how the desired geometry can be obtained by plastic deformation, and what the expected mechanical properties of the produced part are. For understanding the variables of a metal-forming process, it is best to consider the process as a system, as illustrated in Fig. 2.1 in Chap. 2. The interaction of most significant variables in metal forming are shown, in a simplified manner, in Fig. 3.1. It is seen that for a given billet or blank material and part geometry, the speed of deformation influences strain-rate and flow stress. Deformation speed, part geometry, and die temperature influence the temperature distribution in the formed part. Finally, flow stress, friction, and part geometry determine metal flow, forming load, and forming energy. In steady-state flow (kinematically), the velocity field remains unchanged, as is the case in the extrusion process; in nonsteadystate flow, the velocity field changes continuously with time, as is the case in upset forging.

The main concern here is the analysis of plastic deformation processes in the warm and hot forming regimes. When deformation takes place at high temperatures, material properties can vary considerably with temperature. Heat is generated during a metal-forming process, and if dies are at a considerably lower temperature than the workpiece, the heat loss by conduction to the dies and by radiation and convection to the environment can result in severe temperature gradients within the workpiece. Thus, the consideration of temperature effects in the analysis of metal-forming problems is very important. Furthermore, at elevated temperatures, plastic deformation can induce phase transformations and alterations in grain structures that, in turn, can modify the flow stress of the workpiece material as well as other mechanical properties. Since materials at elevated temperatures are usually rate-sensitive, a complete analysis of hot forming requires two considerations—the effect of the rate-sensitivity of materials and the coupling of the metal flow and heat transfer analyses. A material behavior that exhibits rate sensitivity is called viscoplastic. A theory that deals with viscoplasticity was described in Chap. 4. It was shown that the governing equations for deformation of viscoplastic materials are formally identical to those of plastic materials, except that the effective stress is a function of strain, strain-rate, and temperature. The application of the finite-element method to the analysis of metal-forming processes using rigid-plastic materials leads to a simple extension of the method to rigid-viscoplastic materials. The importance of temperature calculations during a metal-forming process has been recognized for a long time. Until recently, the majority of the work had been based on procedures that uncouple the problem of heat transfer from the metal deformation problem. Several researchers have used the following approach. They determined the flow velocity fields in the problem either experimentally or by calculations, and they then used these fields to calculate heat generation. Examples of this approach are the works of Johnson and Kudo on extrusion, and of Tay et al. on machining. Another approach uses Bishop’s numerical method in which heat generation and transportation are considered to occur instantaneously for each time-step with conduction taking place during the time-step.

The theory of plasticity describes the mechanics of deformation in plastically deforming solids, and, as applied to metals and alloys, it is based on experimental studies of the relations between stresses and strains under simple loading conditions. The theory described here assumes the ideal plastic body for which the Bauschinger effect and size effects are neglected. The theory also is valid only at temperatures for which recovery, creep, and thermal phenomena can be neglected. The basic theory of classical plasticity is described by Hill, and also in References, in addition to the books listed in Chap. 1. A concise description of the general plasticity theory necessary for metal forming is given in the book by Johnson et al.. In this chapter, certain important aspects of the theory are presented in order to elucidate the developments of the finite-element solutions of metal-forming problems discussed in this book. First, various measures of stress and strain are introduced. Then, the governing equations for plastic deformation and principles that are the foundations for the analysis are described. The extension of the theory of plasticity to time-dependent theory of viscoplasticity is outlined in Section 4.8. Particular references are made, in Sections 4.3 through 4.7, to the books by Hill and by Johnson and Mellor, and to the section on general plasticity theory in the book by Johnson et al.. The basic quantities that may be used to describe the mechanics of deformation when a body deforms from one configuration to another under an external load are the stress, strain, and strain-rate. Various measures of these quantities are defined, depending upon how closely formulations represent actual situations. Although it is not possible to provide the complete mathematical formulations in one-dimensional deformation, these measures are introduced for the case of simple uniaxial tension. Consider the uniaxial tension test of a round specimen whose initial length is l0 and cross-sectional area is A0. The specimen is stretched in the axial direction by the force P to the length l and the cross-sectional area A at time t, as shown in Fig. 4.1. The response of the material is recorded as the load-displacement curve, and converted to the stress-strain curve as shown in the figure. The deformation is assumed to be homogeneous until necking begins.

According to Spies, the majority of forgings can be classified into three main groups. The first group consists of compact shapes that have approximately the same dimensions in all three directions. The second group consists of disk shapes that have two of the three dimensions (length and width) approximately equal and larger than the height. The third group consists of the long shapes that have one main dimension significantly larger than the two others. All axially symmetric forgings belong to the second group, which includes approximately 30% of all commonly used forgings. A basic axisymmetric forging process is compression of cylinders. It is a relatively simple operation and thus it is often used as a property test and as a preforming operation in hot and cold forging. The apparent simplicity, however, turns into a complex deformation when friction is present at the die–workpiece interface. With the finite-element method, this complex deformation mode can be examined in detail. In this chapter, compression of cylinders and related forming operations are discussed. Since friction at the tool–workpiece interface is an important factor in the analysis of metal-forming processes, this aspect is also given particular consideration. Further, applications of the FEM method for complex-shaped dies are shown in the examples of forging and cabbaging. Finite-element discretization with a quadrilateral element is similar to that given in Chap. 8. The cylindrical coordinate system (r, ϑ, z) is used instead of the rectangular coordinate system. The element is a ring element with a quadrilateral cross-section, as shown in Fig. 9.1. The ξ and η of the natural coordinate system vary from −1 to 1 within each element.

A majority of the finished products made by metal forming are geometrically complex and the metal flow involved is of a three-dimensional nature. Thus, any analysis technique will become more useful in industrial applications if it is capable of solving three-dimensional metal-flow problems. Nagpal and Altan introduced dual-stream functions for describing metal flow in three dimensions. This work showed that the proper selection of a flow function makes the incompressibility requirement automatically satisfied and provides general kinematically admissible velocity fields. Yang and Lee utilized the conformal transformation of a unit circle onto a cross-section in the analysis of curved die extrusion. They derived the stream-line equation from which a kinematically admissible velocity field was determined. The upper-bound method was then applied to determine the extrusion pressure for a rigid-perfectly plastic material. An important aspect of three-dimensional plastic deformation is the analysis of spread in metal-forming operations, such as spread in rolling or in flat tool forging, and spread in compression of noncircular disks. Solutions to such problems have been obtained by the use of Hill’s general method and the upper-bound method. The extension of the finite-element method to solve three-dimensional problems is natural and not new, particularly in the area of elasticity. However, the simulation of three-dimensional forming operations by the finite-element method is relatively recent. Park and Kobayashi described the formulation for the three-dimensional rigid-plastic finite-element method and the implementation of the boundary conditions. They applied this technique to the analysis of block compression between two parallel flat platens. For certain forming problems, such as those involving lateral spread, the use of a simplified three-dimensional element is efficient and some examples can be found for analysis of spread in rolling and flat tool forging. The matrices for evaluation of elemental stiffness equations are defined for a three-dimensional brick element in Chap. 6 and some of them are recapitulated in this section. A three-dimensional brick element used for the analysis is an eight-node hexahedral isoparametric element.

In the previous chapters we have discussed only the applications of flow formulation to the analysis of metal-forming processes. Lately, elastic-plastic (solid) formulations have evolved to produce techniques suitable for metal-forming analysis. This evolution is the result of developments achieved in large-strain formulation, beginning from the infinitesimal approach based on the Prandtl–Reuss equation. A question always arises as to the selection of the approach—“flow” approach or “solid” approach. A significant contribution to the solution of this question was made through a project in 1978, coordinated by Kudo, in which an attempt was made to examine the comparative merits of various numerical methods. The results were compiled for upsetting of circular solid cylinders under specific conditions, and revealed the importance of certain parameters used in computation, such as mesh systems and the size of an increment in displacement. This project also showed that the solid formulation needed improvement, particularly in terms of predicting the phenomenon of folding. For elastic-plastic materials, the constitutive equations relate strain–rate to stress–rates, instead of to stresses. Consequently, it is convenient to write the field equation in the boundary-value problem for elastic-plastic materials in terms of the equilibrium of stress rates. In this chapter, the basic equations for the finite-element discretization involved in solid formulations are outlined both for the infinitesimal approach and for large-strain theory. Further, the solutions obtained by the solid formulation are compared with those obtained by the flow formulation for the problems of plate bending and ring compression. A discussion is also given concerning the selection of the approach for the analysis. In conclusion, significant recent developments in the role of the finite-element method in metal-forming technology are summarized. The field equation for the boundary-value problem associated with the deformation of elastic-plastic materials is the equilibrium equation of stress rates. As stated in Chap. 1 (Section 1.3), the internal distribution of stress, in addition to the current states of the body, is supposed to be known, and the boundary conditions are prescribed in terms of velocity and traction-rate.