Littérature scientifique sur le sujet « Systolic geometry »
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Articles de revues sur le sujet "Systolic geometry"
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Redaelli, A., E. Di Martino, S. Mantero, A. Agazzi, E. Vangeri, A. Gamba et R. Fumero. « Optimisation of a Stentless Valve Prosthesis Based on an Analytic Parametric Model of the Aortic Valve ». International Journal of Artificial Organs 21, no 3 (mars 1998) : 161–70. http://dx.doi.org/10.1177/039139889802100307.
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An analytical mathematical model of a stentless aortic valve has been implemented. The valve is characterised by a trileaflet geometry, cilindrical leaflets; the aortic root is schematised by a conical surface which includes the leaflet attachments. The model Is defined through six geometric parameters: the base radius, the valve height, the commissure radius, the leaflet radial, circumferential and attachment line lengths. Five performance indexes have been used to optimise the valve geometry, namely: the systolic area, the leaflet circumferential stress in diastole, the leaflet bending strain in systole and two bending angles related to the rotation of the leaflets from the diastolic to the systolic configuration. The sensitivity analysis is carried out which can identify the influence of each geometric parameter on the performance indexes adopted for the optimum valve design. The analysis of the results provides the geometric configuration which optimises the overall function of the valve throughout the cardiac cycle.
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Adebayo, Rasaaq A., Olaniyi J. Bamikole, Michael O. Balogun, Anthony O. Akintomide, Victor O. Adeyeye, Luqman A. Bisiriyu, Tuoyo O. Mene-Afejuku, Ebenezer A. Ajayi et Olugbenga O. Abiodun. « Echocardiographic Assessment of Left Ventricular Geometric Patterns in Hypertensive Patients in Nigeria ». Clinical Medicine Insights : Cardiology 7 (janvier 2013) : CMC.S12727. http://dx.doi.org/10.4137/cmc.s12727.
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Left ventricular (LV) hypertrophy is an important predictor of morbidity and mortality in hypertensive patients, and its geometric pattern is a useful determinant of severity and prognosis of heart disease. Studies on LV geometric pattern involving large number of Nigerian hypertensive patients are limited. We examined the LV geometric pattern in hypertensive patients seen in our echocardiographic laboratory. A two-dimensional, pulsed, continuous and color flow Doppler echocardiographic evaluation of 1020 consecutive hypertensive patients aged between 18 and 91 years was conducted over an 8-year period. LV geometric patterns were determined using the relationship between the relative wall thickness and LV mass index. Four patterns of LV geometry were found: 237 (23.2%) patients had concentric hypertrophy, 109 (10.7%) had eccentric hypertrophy, 488 (47.8%) had concentric remodeling, and 186 (18.2%) had normal geometry. Patients with concentric hypertrophy were significantly older in age, and had significantly higher systolic blood pressure (BP), diastolic BP, and pulse pressure than those with normal geometry. Systolic function index in patients with eccentric hypertrophy was significantly lower than in other geometric patterns. Doppler echocardiographic parameters showed some diastolic dysfunction in hypertensive patients with abnormal LV geometry. Concentric remodeling was the most common LV geometric pattern observed in our hypertensive patients, followed by concentric hypertrophy and eccentric hypertrophy. Patients with concentric hypertrophy were older than those with other geometric patterns. LV systolic function was significantly lower in patients with eccentric hypertrophy and some degree of diastolic dysfunction were present in patients with abnormal LV geometry.
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Katz, Mikhail G., et Tahl Nowik. « A systolic inequality with remainder in the real projective plane ». Open Mathematics 18, no 1 (24 août 2020) : 902–6. http://dx.doi.org/10.1515/math-2020-0050.
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Abstract The first paper in systolic geometry was published by Loewner’s student P. M. Pu over half a century ago. Pu proved an inequality relating the systole and the area of an arbitrary metric in the real projective plane. We prove a stronger version of Pu’s systolic inequality with a remainder term.
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Babenko, Ivan, Florent Balacheff et Guillaume Bulteau. « Systolic geometry and simplicial complexity for groups ». Journal für die reine und angewandte Mathematik (Crelles Journal) 2019, no 757 (1 décembre 2019) : 247–77. http://dx.doi.org/10.1515/crelle-2017-0041.
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AbstractTwenty years ago Gromov asked about how large is the set of isomorphism classes of groups whose systolic area is bounded from above. This article introduces a new combinatorial invariant for finitely presentable groups called simplicial complexity that allows to obtain a quite satisfactory answer to his question. Using this new complexity, we also derive new results on systolic area for groups that specify its topological behaviour.
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Dehne, F., A. L. Hassenklover, J. R. Sack et N. Santoro. « Computational geometry algorithms for the systolic screen ». Algorithmica 6, no 1-6 (juin 1991) : 734–61. http://dx.doi.org/10.1007/bf01759069.
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Dranishnikov, Alexander N., Mikhail G. Katz et Yuli B. Rudyak. « Cohomological dimension, self-linking, and systolic geometry ». Israel Journal of Mathematics 184, no 1 (31 juillet 2011) : 437–53. http://dx.doi.org/10.1007/s11856-011-0075-8.
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Katz, M. « Local calibration of mass and systolic geometry ». Geometric And Functional Analysis 12, no 3 (1 août 2002) : 598–621. http://dx.doi.org/10.1007/s00039-002-8259-3.
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Vatnikov, Yury A., Andrey A. Rudenko, Boris V. Usha, Evgeny V. Kulikov, Elena A. Notina, Irina A. Bykova, Nadiya I. Khairova, Irina V. Bondareva, Victor N. Grishin et Andrey N. Zharov. « Left ventricular myocardial remodeling in dogs with mitral valve endocardiosis ». April-2020 13, no 4 (2020) : 731–38. http://dx.doi.org/10.14202/vetworld.2020.731-738.
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Background and Aim: Left ventricular myocardial remodeling could play an important role in the progression of chronic heart failure (CHF) syndrome in dogs with mitral valve endocardiosis. The aim of this study was to evaluate the left ventricular myocardial remodeling in dogs with mitral valve endocardiosis and to study the dependence of the incidence of this pathological phenomenon on the functional class (FC) of progression of the CHF syndrome. Materials and Methods: A total of 108 afflicted dogs and 36 clinically healthy dogs were examined using transthoracic echocardiography. The following structural and geometric parameters of the left ventricular remodeling were evaluated: Myocardial mass and its index, sphericity index at the end of systole and diastole, end-systolic and end-diastolic relative wall thickness, and integral remodeling index. Results: In all clinically healthy dogs, a normal type of the left ventricular chamber geometry was revealed, whereas, in dogs with mitral valve endocardiosis, the normal geometry of the left ventricle occurred in 56.4%, eccentric hypertrophy in 24.1%, concentric remodeling in 10.2%, and concentric hypertrophy in 9.3% of the cases. In patients with endocardiosis, there was no dilatation type of cardiac remodeling observed. Conclusion: When compared to the clinically healthy animals, the dogs with mitral valve endocardiosis presented with indicators of structural and geometric remodeling, such as increased myocardial mass, myocardial mass index, and sphericity index at the end of systole and diastole, as well as relatively reduced integral systolic index of remodeling and systolic relative thickness of the walls of the heart. The parameters of the left ventricular myocardial remodeling correlated significantly with the FC of CHF syndrome.
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Batra, S., et K. Rakusan. « Capillary length, tortuosity, and spacing in rat myocardium during cardiac cycle ». American Journal of Physiology-Heart and Circulatory Physiology 263, no 5 (1 novembre 1992) : H1369—H1376. http://dx.doi.org/10.1152/ajpheart.1992.263.5.h1369.
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Microvascular geometry was evaluated in rat left ventricular midmyocardium (male Sprague-Dawley, n = 14), arrested in systole (S) or diastole (D), by bolus injections of CaCl2 or KCl, respectively. The histological method employed in this study allowed for the visualization of capillary pathways from arteriole to venule. Capillary length, as directly measured from terminal arteriole to collecting venule, was not significantly different between S and D groups, averaging 606 +/- 15 microns (pooled mean +/- SE). The capillary length tortuosity, defined as the ratio of the capillary length to the direct arteriovenous distance, was significantly increased in systolic-arrested hearts (S = 1.31 +/- 0.03; D = 1.18 +/- 0.02, P < 0.01). At the level of individual capillary segments, however, there was no increase in tortuosity in systolic-arrested hearts (S = 1.17 +/- 0.03; D = 1.16 +/- 0.02). Intercapillary spacing was significantly more uniform in systolic-arrested hearts. These data suggest that in systole, capillary length and tortuosity are generally preserved, and capillary spacing is more uniform, serving to maintain geometric conditions for oxygen supply during the cardiac cycle.
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Osajda, Damian, et Piotr Przytycki. « Boundaries of systolic groups ». Geometry & ; Topology 13, no 5 (17 août 2009) : 2807–80. http://dx.doi.org/10.2140/gt.2009.13.2807.
Texte intégralThèses sur le sujet "Systolic geometry"
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Kowalick, Ryan. « Discrete Systolic Inequalities ». The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1384873457.
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Vesier, Carol Cockerham. « The role of papillary muscle-mitral valve geometry in systolic anterior motion of the mitral valve ». Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/10279.
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Mesmay, Arnaud de. « Topics in low-dimensional computational topology ». Paris, École normale supérieure, 2014. https://theses.hal.science/tel-04462650v1.
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La topologie, c’est-à-dire l’étude qualitative des formes et des espaces, constitue un domaine classique des mathématiques depuis plus d’un siècle, mais il n’est apparu que récemment que pour de nombreuses applications, il est important de pouvoir calculer informatiquement les propriétés topologiques d’un objet. Ce point de vue est la base de la topologie algorithmique, un domaine très actif à l’interface des mathématiques et de l’informatique auquel ce travail se rattache. Les trois contributions de cette thèse concernent le développement et l’étude d’algorithmes topologiques pour calculer des décompositions et des déformations d’objets de basse dimension, comme des graphes, des surfaces ou des 3-variétés. Le premier problème auquel nous nous attaquons traite de déformations : comment peut-on tester si deux graphes dessinés sur une même surface sont isotopes, c’est-à-dire si l’on peut déformer continûment l’un en l’autre ? Ce type de question est relié à des problèmes pratiques que l’on rencontre par exemple dans les systèmes d’information géographique ou les métamorphoses (morphings). En nous appuyant sur des concepts de géométrie hyperbolique et de la théorie des mapping class groups, nous établissons d’abord un critère combinatoire pour caractériser l’isotopie, ce qui reprouve et améliore un résultat de Ladegaillerie de 1984. Ensuite, en combinant ceci avec des algorithmes antérieurs pour tester l’homotopie de courbes, nous fournissons des algorithmes efficaces pour résoudre ce problème d’isotopie de graphes. Nous déplaçons ensuite notre étude vers des problèmes de décompositions, en nous intéressant à la découpe de surfaces le long de courbes ou de graphes respectant certaines propriétés topologiques, ce qui est une routine importante en algorithmique des graphes ou en infographie, parmi d’autres domaines. En établissant une forte connexion avec le cas continu, ainsi qu’en étudiant un modèle discret de surfaces aléatoires, nous améliorons les meilleures bornes connues pour plusieurs schémas de découpe. Cela prouve en particulier une conjecture de Przytycka et Przytycki datant de 1993, et fournit également un nouvel algorithme pour calculer des décompositions en pantalons courtes. Enfin, nous montons d’une dimension, où les meilleurs algorithmes connus pour de nombreux problèmes topologiques (comme le célèbre problème du noeud) sont exponentiels. La plupart de ces algorithmes reposent sur les surfaces normales, un objet omniprésent pour étudier les surfaces plongées dans une 3-variété. Nous étudions une relaxation naturelle de cette notion, les surfaces normales immergées, dont la meilleure structure algébrique en fait de bons candidats pour obtenir des algorithmes polynomiaux pour des problèmes topologiques. Dans ce travail, nous montrons qu’utiliser des surfaces normales immergées mène naturellement à un problème de détection de singularités, et nous prouvons que celui-ci est NP-dur ; c’est un résultat notable car l’on dispose de très peu de preuves de difficulté en topologie en 3 dimensions. Notre réduction s’appuie sur une connexion avec une classe restreinte de problèmes de satisfaction de contraintes qui a été partiellement classifiée par FederTopology is the area of mathematics investigating the qualitative properties of shapes and spaces. Although it has been a classical field of study for more than a century, it only appeared recently that being able to compute the topological features of various spaces might be of great value for many applications. This idea forms the core of the blossoming field of computational topology, to which this work belongs. The three contributions of this thesis deal with the development and the study of topological algorithms to compute deformations and decompositions of low-dimensional objects, such as graphs, surfaces or 3-manifolds. The first question we tackle concerns deformations: how can one test whether two graphs embedded on the same surface are isotopic, i. E. , whether one can be deformed continuously into the other? This kind of problems is relevant to practical problems arising with morphings or geographic information systems, for example. Relying on hyperbolic geometry and ideas from the theory of mapping class groups, we first establish a combinatorial criterion to characterize isotopy, reproving and strengthening a result of Ladegaillerie (1984). Combined with earlier algorithms on the homotopy of curves, this allows us in turn to provide efficient algorithms to solve this graph isotopy problem. We then shift our focus to decompositions, by investigating how to cut surfaces along curves or graphs with prescribed topological properties, which is an important routine in graph algorithms or computer graphics, amongst others domains. By establishing a strong connection with the continuous setting, as well as studying a discrete model for random surfaces, we improve the best known bounds for several instances of this problem. In particular, this proves a conjecture of Przytycka and Przytycki from 1993, and one of our new bounds readily translates into an algorithm to compute short pants decompositions. Finally, we move up one dimension, where the best known algorithms for many topological problems, like for example unknot recognition, are exponential. Most of these algorithms rely on normal surfaces, a ubiquitous tool to study the surfaces embedded in a 3-manifold. We investigate a relaxation of this notion called immersed normal surfaces, whose more convenient algebraic structure makes them good candidates to solve topological problems in polynomial time. We show that when working with immersed normal surfaces, a natural problem on the detection of singularities arises, and we prove it to be NP-hard – this is noteworthy as hardness results are very scarce in 3-dimensional topology. Our reduction works by establishing a connection with a restricted class of constraint satisfaction problems which has been partially classified by Feder
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Ren, Jiajun Carleton University Dissertation Computer Science. « Geometric characterizations of fault patterns in linear systolic arrays ». Ottawa, 1994.
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Bulteau, Guillaume. « Sur des problèmes topologiques de la géométrie systolique ». Thesis, Montpellier 2, 2012. http://www.theses.fr/2012MON20148/document.
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Soit G un groupe de présentation finie. Un résultat de Gromov affirme l'existence de cycles géométriques réguliers qui représentent une classe d'homologie non nulle h dans le énième groupe d'homologie à coefficients entiers de G, cycles géométriques dont le volume systolique est aussi proche que souhaité du volume systolique de h. Ce théorème, dont aucune démonstration exhaustive n'avait été faite, a servi à obtenir plusieurs résultats importants en géométrie systolique. La première partie de cette thèse est consacrée à une démonstration complète de ce résultat. L'utilisation de ces cycles géométriques réguliers est connue sous le nom de technique de régularisation. Cette technique permet notamment de relier le volume systolique de certaines variétés fermées à d'autres invariants topologiques de ces variétés, tels que les nombres de Betti ou l'entropie minimale. La seconde partie de cette thèse propose d'examiner ces relations, et la mise en oeuvre de la technique de régularisation.La troisième partie est consacrée à trois problèmes liés à la géométrie systolique. Dans un premier temps on s'intéresse à une inégalité concernant les tores pleins plongés dans l'espace tridimensionnel. Puis, on s'intéresse ensuite aux triangulations minimales des surfaces compactes, afin d'obtenir des informations sur le volume systolique de ces surfaces. Enfin, on présente la notion de complexité simpliciale d'un groupe de présentation finie, et ses liens avec la géométrie systoliqueLet G be a finitely presented group. A theorem of Gromov asserts the existence of regular geometric cycles which represent a non null homology class h in the nth homology group with integral coefficients of G, geometric cycles which have a systolic volume as close as desired to the systolic volume of h. This theorem, of which no complete proof has been given, has lead to major results in systolic geometry. The first part of this thesis is devoted to a complete proof of this result.The regularizationtechnique consists in the use of these regular geometric cycles to obtain information about the class $h$. This technique allows to link the systolic volume of some closed manifolds to homotopical invariants of these manifolds, such as the minimal entropy and the Betti numbers. The second part of this thesis proposes to investigate these links.The third part of this thesis is devoted to three problems of systolic geometry. First we are investigating an inequality about embeded tori in $R^3$. Second, we are looking into minimal triangulations of compact surfaces and some information they can provide in systolic geometry. And finally, we are presenting the notion of simplicial complexity of a finitely-presented group and its links with the systolic geometry
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Karam, Steve. « Croissance du volume des boules dans les revêtements universels des graphes et des surfaces ». Phd thesis, Université François Rabelais - Tours, 2013. http://tel.archives-ouvertes.fr/tel-00914945.
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Dans le cadre de la géométrie riemannienne globale sans hypothèse de courbure en lien avec la topologie, nous nous intéressons au volume maximal des boules de rayon fixé dans les revêtements universels des graphes et des surfaces. Dans la première partie, nous prouvons que si l'aire d'une surface riemannienne fermée M de genre au moins 2 est suffisamment petite par rapport à son aire hyperbolique, alors pour chaque rayon R>0, le revêtement universel de M contient une R-boule d'aire au moins l'aire d'une cR-boule dans le plan hyperbolique, où c<1 est une constante universelle. En particulier (quitte à prendre l'aire de la surface encore plus petite), nous démontrons que pour chaque rayon R plus grand ou égal à 1, le revêtement universel de M contient une R-boule d'aire au moins l'aire d'une R-boule dans le plan hyperbolique. Ce résultat répond positivement pour les surfaces, à une question de L. Guth. Nous démontrons également que si Gamma est un graphe connexe de premier nombre de Betti b et de longueur su suffisamment petite par rapport à la longueur d'un graphe trivalent Gamma_b de premier nombre de Betti b dont la longueur de chaque arête est 1, alors pour chaque rayon R>0, le revêtement universel de Gamma contient une R-boule d'aire au moins c fois l'aire d'une R-boule dans le revêtement universel de Gamma_b, où c est dans l'intervalle (1/2 ,1). Dans la deuxième partie, nous généralisons un théorème de M. Gromov concernant le nombre maximal de courts lacets homotopiquement indépendants basés en un même point. Plus précisément, nous prouvons que sur toute surface riemannienne fermée M de genre g et d'aire normalisée à g, il existe au moins log(2g) lacets homotopiquement indépendants basés en un même point de longueur au plus C log(g), où C est une constante positive indépendante du genre. Comme corollaire immédiat de ce théorème, nous redémontrons l'inégalité systolique asymptotique sur la systole séparante. Nous démontrons également un théorème analogue pour les graphes métriques. Plus précisément, nous prouvons que sur chaque graphe métrique Gamma de premier nombre de Betti b et de longueur b, il existe au moins log(b) lacets homologiquement indépendants basés en un même point de longueur au plus 48 log(b). Ce résultat étend la borne en log(b) sur la systole homologique dûe à Bollobàs-Szemerédi-Thomason à au moins log(b) lacets homologiquement indépendants basés en un même point. En outre, nous donnons des exemples de graphes où notre résultat est optimal (à une constante multiplicative près).
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CHEN, HOUG-XIN, et 陳宏信. « Systolic algorithms for graph and geometry connectivity problems ». Thesis, 1986. http://ndltd.ncl.edu.tw/handle/58775912386612409940.
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Sanki, Bidyut. « Shortest Length Geodesics on Closed Hyperbolic Surfaces ». Thesis, 2014. http://etd.iisc.ac.in/handle/2005/3049.
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Given a hyperbolic surface, the set of all closed geodesics whose length is minimal form a graph on the surface, in fact a so called fat graph, which we call the systolic graph. The central question that we study in this thesis is: which fat graphs are systolic graphs for some surface -we call such graphs admissible. This is motivated in part by the observation that we can naturally decompose the moduli space of hyperbolic surfaces based on the associated systolic graphs.
A systolic graph has a metric on it, so that all cycles on the graph that correspond to geodesics are of the same length and all other cycles have length greater than these. This can be formulated as a simple condition in terms of equations and inequations for sums of lengths of edges. We call this combinatorial admissibility.
Our first main result is that admissibility is equivalent to combinatorial admissibility. This is proved using properties of negative curvature, specifically that polygonal curves with long enough sides, in terms of a lower bound on the angles, are close to geodesics.
Using the above result, it is easy to see that a subgraph of an admissible graph is admissible. Hence it suffices to characterize minimal non-admissible fat graphs. Another major result of this thesis is that there are infinitely many minimal non-admissible fat graphs (in contrast, for instance, to the classical result that there are only two minimal non-planar graphs).
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Sanki, Bidyut. « Shortest Length Geodesics on Closed Hyperbolic Surfaces ». Thesis, 2014. http://hdl.handle.net/2005/3049.
Texte intégralRésumé :
Given a hyperbolic surface, the set of all closed geodesics whose length is minimal form a graph on the surface, in fact a so called fat graph, which we call the systolic graph. The central question that we study in this thesis is: which fat graphs are systolic graphs for some surface -we call such graphs admissible. This is motivated in part by the observation that we can naturally decompose the moduli space of hyperbolic surfaces based on the associated systolic graphs.
A systolic graph has a metric on it, so that all cycles on the graph that correspond to geodesics are of the same length and all other cycles have length greater than these. This can be formulated as a simple condition in terms of equations and inequations for sums of lengths of edges. We call this combinatorial admissibility.
Our first main result is that admissibility is equivalent to combinatorial admissibility. This is proved using properties of negative curvature, specifically that polygonal curves with long enough sides, in terms of a lower bound on the angles, are close to geodesics.
Using the above result, it is easy to see that a subgraph of an admissible graph is admissible. Hence it suffices to characterize minimal non-admissible fat graphs. Another major result of this thesis is that there are infinitely many minimal non-admissible fat graphs (in contrast, for instance, to the classical result that there are only two minimal non-planar graphs).
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Huang, Kuo Tai, et 黃國泰. « A systolic array architecture for the decoding of algebraic- geometric codes with modified Feng-Rao algorithm ». Thesis, 1996. http://ndltd.ncl.edu.tw/handle/95458916818186210050.
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碩士國立清華大學
電機工程研究所
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Feng-Rao algorithm is a successful algorithm for the decoding of algebraic-geometric (AG) codes. However, there is no implementation of this algorithm up to now. In this thesis, we have modified the Feng-Rao algorithm to have more parallelism and developed a systolic array architecture for VLSI implementation. The symmetry property of the syndrome matrix has been exploited to reduce the complexity of this architecture. The complexity of our proposed systolic array architecture is t^3/6+(1+g')t^2/2+[(g-3)g'/2-2/3+g]t, which is comparable to that elimination on a square matrix with matrix size equal to t, where t is the error-correcting capability of a code, g is the genus of the curve, and g'=\floor(g-1/2). The control circuit in oursimple. Besides, we have also proposed a circuitry to perform the majority voting scheme needed in the Feng-Rao algorithm with the consideration that the candidates are q-ary symbols.
Livres sur le sujet "Systolic geometry"
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Katz, Mikhail Gersh. Systolic geometry and topology. Providence, R.I : American Mathematical Society, 2007.
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Zoccali, Carmine, Davide Bolignano et Francesca Mallamaci. Left ventricular hypertrophy in chronic kidney disease. Sous la direction de David J. Goldsmith. Oxford University Press, 2018. http://dx.doi.org/10.1093/med/9780199592548.003.0107_update_001.
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Alterations in left ventricular (LV) mass and geometry and LV dysfunction increase in prevalence from stage 2 to stage 5 in CKD. Nuclear magnetic resonance is the most accurate and precise technique for measuring LV mass and function in patients with heart disease. Quantitative echocardiography is still the most frequently used means of evaluating abnormalities in LV mass and function in CKD. Anatomically, myocardial hypertrophy can be classified as concentric or eccentric. In concentric hypertrophy, the muscular component of the LV (LV wall) predominates over the cavity component (LV volume). Due to the higher thickness and myocardial fibrosis in patients with concentric LVH, ventricular compliance is reduced and the end-diastolic volume is small and insufficient to maintain cardiac output under varying physiological demands (diastolic dysfunction). In those with eccentric hypertrophy, tensile stress elongates myocardiocytes and increases LV end-diastolic volume. The LV walls are relatively thinner and with reduced ability to contract (systolic dysfunction). LVH prevalence increases stepwisely as renal function deteriorates and 70–80% of patients with kidney failure present with established LVH which is of the concentric type in the majority. Volume overload and severe anaemia are, on the other hand, the major drivers of eccentric LVH. Even though LVH may regress after renal transplantation, the prevalence of LVH after transplantation remains close to that found in dialysis patients and a functioning renal graft should not be seen as a guarantee of LVH regression. The vast majority of studies on cardiomyopathy in CKD are observational in nature and the number of controlled clinical trials in these patients is very small. Beta-blockers (carvedilol) and angiotensin receptors blockers improve LV performance and reduce mortality in kidney failure patients with LV dysfunction. Although current guidelines recommend implantable cardioverter-defibrillators in patients with ejection fraction less than 30%, mild to moderate symptoms of heart failure, and a life expectancy of more than 1 year, these devices are rarely offered to eligible CKD patients. Conversion to nocturnal dialysis and to frequent dialysis schedules produces a marked improvement in LVH in patients on dialysis. More frequent and/or longer dialysis are recommended in dialysis patients with asymptomatic or symptomatic LV disorders if the organizational and financial resources are available.
Chapitres de livres sur le sujet "Systolic geometry"
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Katz, Mikhail. « Systolic applications of integral geometry ». Dans Mathematical Surveys and Monographs, 43–49. Providence, Rhode Island : American Mathematical Society, 2007. http://dx.doi.org/10.1090/surv/137/06.
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Katz, Mikhail. « Geometry and topology of systoles ». Dans Mathematical Surveys and Monographs, 3–11. Providence, Rhode Island : American Mathematical Society, 2007. http://dx.doi.org/10.1090/surv/137/01.
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Hofer, Helmut, Alberto Abbondandolo, Urs Frauenfelder et Felix Schlenk. « Remarks on the systoles of symmetric convex hypersurfaces and symplectic capacities ». Dans Symplectic Geometry, 775–800. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-031-19111-4_26.
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Fletcher, Nick. « Left ventricular systolic function ». Dans Oxford Textbook of Advanced Critical Care Echocardiography, sous la direction de Anthony McLean, Stephen Huang et Andrew Hilton, 83–92. Oxford University Press, 2020. http://dx.doi.org/10.1093/med/9780198749288.003.0006.
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Left ventricular systolic function assessment is an essential component of the echocardiographic assessment of the critically ill patient. A wide range of diseases from sepsis to coronary ischaemia can affect the left ventricle (LV). An understanding of the events and timings in LV systole within the cardiac cycle is important, together with an appreciation of LV anatomy and geometry. Advanced echocardiography requires the competence to obtain all the imaging planes relevant to the LV in transthoracic (TTE) and transoesophageal (TOE) echocardiography. Ejection fraction is currently regarded as the gold standard for LV function and biplane Simpson’s method is the most accurate way to measure this at the critical care bedside, although newer applications such as strain may become more widely used in future. Imaging can be technically difficult in critically ill patients and a detailed knowledge of sources of technical error and physiological confounders is crucial. For the same reason, a knowledge of the alternative methods of LV systolic assessment to employ is also important. Many intrinsic diseases of the heart will be encountered in daily practice and require communication and referral to cardiologists. It is important in this setting that both clinicians are able to converse in the universal language of echocardiography. A comprehensive knowledge of regional wall anatomy and function will enable prompt diagnosis and management of coronary syndromes, particularly as onset of dysfunction can be rapid and serious in critical illness. Finally, an understanding of LV function and assessment in the context of sepsis syndromes is a key concept.
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Badano, Luigi, et Denisa Muraru. « Functional anatomy of atria ». Dans ESC CardioMed, sous la direction de Yen Ho, 88–92. Oxford University Press, 2018. http://dx.doi.org/10.1093/med/9780198784906.003.0017.
Texte intégralRésumé :
The left and right atria are dynamic structures that play an integral role in cardiac performance by modulating the respective ventricular filling. This function is accomplished by their role as a reservoir for venous return during ventricular systole, a conduit for venous return during early ventricular diastole, and a booster pump for ventricular filling during late diastole. Recent advances in cardiac imaging allow the accurate assessment of the geometry and phasic functions of both atria. Two- and three-dimensional echocardiography enables a volumetric analysis of atrial function, and both Doppler tissue imaging and speckle-tracking echocardiography allow the assessment of the deformation of atrial myocardium.
Actes de conférences sur le sujet "Systolic geometry"
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Guth, Larry. « Metaphors in Systolic Geometry ». Dans Proceedings of the International Congress of Mathematicians 2010 (ICM 2010). Published by Hindustan Book Agency (HBA), India. WSPC Distribute for All Markets Except in India, 2011. http://dx.doi.org/10.1142/9789814324359_0072.
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AL-Rawi, Mohammad, Djelloul Belkacemi et Ahmed M. Al-Jumaily. « Mesh Independency Analysis for Aorta Geometry Using a Computational Modelling Approach ». Dans ASME 2023 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/imece2023-110446.
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Abstract Cardiovascular diseases have been investigated computationally by biomedical engineers to find new diagnoses for these diseases. Computationally simulating diseases occurring at the aorta artery and more specifically aortic arch, requires a comprehensive workstation computer with an advanced processor and graphics card to create a suitable mesh for the elements. The mesh process is essential: sufficient granularity of the mesh increases simulation accuracy, providing the ability to solve the governing partial differential equations in an increasingly realistic three-dimensional form in the allocated cell. For the complicated geometry of an artery, it is essential to reach a suitable mesh, validated with clinical data, to ensure the computational fluid dynamics model (CFD) has minimal error. Therefore, in this study we investigated different types of mesh, applying different element sizes, and comparing the results with clinical data for a healthy aorta using ANSYS 2021 R1-Fluent. Tetrahedral and Polyhedral meshes were applied for the same element size (1.0, 0.8 and 0.6 mm) with a growth rate of 1.2 and 10 boundary layers for the artery wall using the same boundary conditions to investigate the pressure, velocity waveforms and wall shear stress (WSS) at the aortic arch. The boundary conditions used in this study are the blood flow waveform applied at the ascending aorta and iliac pressure waveform applied at the iliac bifurcation based on clinical data. The results show that the Tetrahedral mesh obtained higher average pressure values with 2.8% at the systolic; however, the diastolic pressure values are the same for the 1 mm element size. Comparing that to the element size of 0.8 and 0.6 mm, the pressure difference was 2.9% and 3.1% respectively for the systolic pressure with a phase time of 0.01 s.
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Aristokleous, Nicolas, Yannis Papaharilaou, Ioannis Seimenis, Georgios C. Georgiou, Brigitta C. Brott et Andreas S. Anayiotos. « Head Rotation Effects on the Flow and Hemodynamics of the Human Carotid Bifurcation ». Dans ASME 2013 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/sbc2013-14708.
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The use of realistic anatomic human carotid artery bifurcation (CB) models with a realistic blood waveform leads to physiologically relevant numerical simulations. To study the effects of head posture on the geometry and hemodynamics of the CB, Magnetic resonance imaging (MRI) was used on six healthy volunteers in two different head postures: 1) the supine neutral (N) and 2) the prone with rightward head rotation (P) up to 80°. Geometric differences with posture change in both the left (LCA) and right (RCA) carotid arteries were reported before [1]. The blood velocity waveform for each individual was obtained using phase-contrast MRI (PCMRI) at five diameters upstream of CB. Results have shown that peak systolic blood flow rate is reduced, in the prone position for both RCA and LCA in all six volunteers. To investigate the effects of the reduced peak systolic flow on the hemodynamics of the CB, numerical simulations were performed for a volunteer that exhibited the most geometric changes for the prone position in comparison to the other five based on specific geometric parameters [1, 2]. For the two investigated head postures the observed measured input waveforms were used.
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Jhun, Choon-Sik, Mark B. Ratcliffe et Julius M. Guccione. « Ventricular Wall Stress and Pump Function of Ventricular Septal Defect of Congenital Heart Defects ». Dans ASME 2009 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2009. http://dx.doi.org/10.1115/sbc2009-206320.
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About 36,000 infants are born each year with a congenital heart defect (CHD) and charges for treatment surpass $2.2 billion for inpatient surgery alone. Of many different types of CHDs, ventricular septal defect (VSD) is the most common class (∼1/3 of CHDs) of heart deformity present at birth. Though many close spontaneously and rarely require treatment, VSD still accounts for ∼15% of defects requiring an invasive procedure within the first year of life [1]. Generally, the ventricular performance is indexed by geometry, shape, diastolic and systolic function, and myocardial contractility [2]. Ejection fraction (EF) and end-systolic (ES) wall stress also used to assess the ventricular function [3–5]. Ratcliffe and Guy suggested that the assessment of LV function focusing on indices of systolic function, such as EF and contractility (EES), is misleading because the shift of end-systolic pressure-volume relationship (ESPVR) and increase/decrease in EES and coincident shift of end-diastolic pressure-volume relationship (EDPVR) may result in pseudo increase/decrease of EF even though there may not be any significant change in true LV function (i.e., Starling relationship) [6]. Though Sagawa and associates proposed the ESPVR as a reliable index of intrinsic systolic function [7], it requires derivation of the pressure-volume relationship at different loading conditions by using a noninotropic vasoconstrictor or vasodilator. This may consequently enforce a significant burden on infants with a failing heart. Moreover, irreversible complication of muscle structure can be generated [8–10]. Thus, rigorous quantification of the pump function associated with mechanics has been hindered especially for infants.
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Chandra, Santanu, Vimalatharmaiyah Gnanaruban, Jaehoon Seong, Barry B. Lieber, Jose F. Rodriguez et Ender A. Finol. « Experimental Validation of a Computational Algorithm for the Zero Pressure Geometry Derivation of Blood Vessels ». Dans ASME 2013 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/sbc2013-14716.
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Patient-specific computational assessment of biomechanical parameters such as peak wall stress is a promising tool for rupture risk assessment of blood vessels. However, this assessment is dependent on image based modeling of the vasculature [1] and on either structural or fluid-structure interaction analyses performed with numerical models to compute the stress and strain in the vascular wall. Protocols have been successfully derived to develop 3D models of normal and pathological vessels from individual Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) [2]. While the image based models used for these simulations are essentially in a pressurized state (gated to diastolic pressure), the application of physiologic systolic and diastolic pressures to compute stresses and strains is debatable. Therefore, the derivation of a “simulation ready” computational geometry is of great importance to the research community as the accuracy of the computational results is dependent on it.
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Cheng, Allen, Frank Langer, Filiberto Rodriguez, John C. Criscione, George T. Daughters, D. Craig Miller et Neil B. Ingels. « Transmural LV Systolic Wall Thickening Gradients and Models of Heart Wall Mechanics ». Dans ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-61238.
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We implanted arrays of radiopaque markers to measure lateral equatorial wall transmural strains and global and regional LV geometry in 7 sheep. Without intervening procedures, one and eight weeks after surgery, 4-D datasets from stereo radiographic studies were processed to yield transmural strains from each heart. In accordance with previous theoretical predictions and experimental results, we hypothesized that systolic radial strain (i.e., wall thickening) would exhibit a transmural gradient, increasing from subepicardium to subendocardium, and, as previous work suggested that this was a fundamental mechanism, this gradient would be observed at both the one- and eight-week studies. The one-week studies yielded the expected gradient. This gradient, however, was not present in the eight-week studies, although LV shape and hemodynamics were virtually identical to their one-week values. We discuss the implications of these findings to mechanistic theories of heart wall mechanics.
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Roldán, Alejandro, Victor Haughton, Tim Osswald et Naomi Chesler. « Computational Analysis of Cerebrospinal Fluid Flow in the Normal and Obstructed Subarachnoid Space ». Dans ASME 2008 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2008. http://dx.doi.org/10.1115/sbc2008-192762.
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Patients with Chiari I malformations have increased cerebrospinal fluid (CSF) velocities compared to subjects without the malformation. Improved methods of analyzing the CSF fluid dynamics are needed to evaluate the impact of increased fluid velocities on pressure differentials in the upper cervical spinal canal and the potential impact of surgery on flow dynamics in patient-specific geometries. Here, a numerical technique based on the boundary elements method (BEM) for modeling the CSF flow within the spinal canal is presented. Results for velocity and pressure throughout the spinal canal were obtained at flow rates representative of different phases of the cardiac cycle for a healthy geometry and a Chiari model. In the healthy geometry, peak CSF velocities occurred anterolateral to the spinal cord at all flow rates. Partially obstructing the subarachnoid space increased peak systolic and diastolic velocities and shear stresses anteriorly. In addition, in the obstructed (Chiari) model, stagnation regions were evident posteriorly. The effects of surgical treatment on these CSF flow patterns warrant further study.
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Moghaddaszade-Kermani, Ahmad, Peter Oshkai et Afzal Suleman. « Fluid-Structure Interaction Simulation of Blood Flow Inside a Diseased Left Ventricle With Obstructive Hypertrophic Cardiomyopathy in Early Systole ». Dans ASME 2009 Fluids Engineering Division Summer Meeting. ASMEDC, 2009. http://dx.doi.org/10.1115/fedsm2009-78381.
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Mitral-Septal contact has been proven to be the cause of obstruction in the left ventricle with hypertrophic cardiomyopathy (HC). This paper presents a study on the fluid mechanics of obstruction using two-way loosely coupled fluid-structure interaction (FSI) methodology. A parametric model for the geometry of the diseased left ventricular cavity, myocardium and mitral valve has been developed, using the dimensions extracted from magnetic resonance images. The three-element Windkessel model [1] was modified for HC and solved to introduce pressure boundary condition to the aortic aperture in the systolic phase. The FSI algorithm starts at the beginning of systolic phase by applying the left ventricular pressure to the internal surface of the myocardium to contract the muscle. The displacements of the myocardium and mitral leaflets were calculated using the nonlinear finite element hyperelastic model [2] and subsequently transferred to the fluid domain. The fluid mesh was moved accordingly and the Navier-Stokes equations were solved in the laminar regime with the new mesh using the finite volume method. In the next time step, the left ventricular pressure was increased to contract the muscle further and the same procedure was repeated for the fluid solution. The results show that blood flow jet applies a drag force to the mitral leaflets which in turn causes the leaflet to deform toward the septum thus creating a narrow passage and possible obstruction.
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Bale-Glickman, J., K. Selby, D. Saloner et O¨ Savas¸. « Physiological Flow Studies in Exact-Replica Atherosclerotic Carotid Bifurcations ». Dans ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-41281.
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Some results from a series of physiological flow experiments in a model of an atherosclerotic carotid bifurcation are presented. The flow model exactly replicates the lumen of the plaque excised intact from a patient with severe carotid atherosclerosis. Flow visualization (FV) and particle image velocimetry (PIV) are employed as the tools for this study. The complex internal geometry of the diseased artery combined with the pulsatile input flows gives rise to complex flow patterns. The flow fields are highly three-dimensional and chaotic with details varying from cycle to cycle. These flow patterns also include internal jets, three-dimensional shear layers, numerous separation/recirculation zones and stagnation lines. The vorticity and streamline maps confirm this complex and three-dimensional nature of the flow. Planar streamline maps show the three-dimensional flow by the multiple sources/sinks throughout the model. Wall shear stresses (WSS) are estimated to range form about −7 Pa to 34 Pa at the stenotic neck over time with the peak at peak systolic. These WSS also exhibit chaotic behavior during pulsatile flow cycles.
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Ford, Matthew D., Ugo Piomelli, Richard Y. Cao, Colin D. Funk et Andrew Pollard. « Numerical Simulations of the Intra-Aneurysmal Vortex Shedding in Induced Mouse Abdominal Aortic Aneurysms ». Dans ASME 2010 3rd Joint US-European Fluids Engineering Summer Meeting collocated with 8th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30546.
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A feature of particular interest observed in vivo in murine abdominal aortic aneurysm (AAA) is the presence of a vortex shed from the proximal edge of the abdominal aortic aneurysm. It is unclear whether the occurrence of the shed vortex is due to the periodic nature of the flow-rate waveform, to geometric features, or to the compliant nature of the vessel tissue. Numerical simulations were performed on 3D semi-idealized and 2D axi-symmetric models of the abdominal aortic aneurysm at a mean Reynolds number of 63 and a Womersley number of 2 (for unsteady inflow conditions). The numerical results from the 3D model showed good agreement with the flows visualized by Doppler Ultrasound with respect to the development of the observed shed vortex. The idealized axi-symmetric models under steady flow conditions showed no signs of vortex shedding. Under unsteady inflow conditions, however, shear-layer roll-up occurred near the peak systolic velocity. The presence of a proximal lip was found to lead to vortex separation (from the wall) earlier in the cardiac cycle, and the presence of the proximal narrowing led to the earliest vortex separation. The sensitivity to the inflow waveform shape also showed that the presence of the shedding, in the model with proximal narrowing, disappeared when the peak-to-mean velocity ratio was reduced by approximately half. Therefore, we conclude that the observed intra-aneurysmal vortex shedding is a shear-layer rollup phenomenon; however, the geometry can act to enhance further the observed vortex shedding.