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Dissertations / Theses on the topic 'Contraction'
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Murtada, Sae-Il. "Smooth muscle modeling activation and contraction of contractile units in smooth muscle /." Licentiate thesis, Stockholm : Skolan för teknikvetenskap, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11349.
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Sringeri, Vageeswara Abhijit. "Tensor Contraction Optimizations." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440399261.
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Njoya, Nadine Katia. "Contraction-Expansion Protocols." Digital Commons @ East Tennessee State University, 2008. https://dc.etsu.edu/etd/1971.
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An approach to a new class of compounds known as bridgehead dienone is described. The route is based on a tandem contraction-expansion event in which the contraction triggers the expansion. The two steps involved are a palladium-catalyzed Favorskii contraction and a cis-divinyl cyclopropanone rearrangement. Progress towards these goals is reported.
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Wang, Wei 1972 Oct 17. "Contraction and partial contraction : a study of synchronization in nonlinear networks." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/30343.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.<br>Includes bibliographical references (p. 121-128).<br>This thesis focuses on the study of collective dynamic behaviors, especially the spontaneous synchronization behavior, of nonlinear networked systems. We derives a body of new results, based on contraction and partial contraction analysis. Contraction is a property regarding the convergence between two arbitrary system trajectories. A nonlinear dynamic system is called contracting if initial conditions or temporary disturbances are forgotten exponentially fast. Partial contraction, introduced in this thesis, is a straightforward but more general application of contraction. It extends contraction analysis to include convergence to behaviors or to specific properties (such as equality of state components, or convergence to a manifold). Contraction and partial contraction provide powerful analysis tools to investigate the stability of large-scale complex systems. For diffusively coupled nonlinear systems, for instance, a general synchronization condition can be derived which connects synchronization rate to net- work structure explicitly. The results are applied to construct flocking or schooling models by extending to coupled networks with switching topology. We further study the networked systems with different kinds of group leaders, one specifying global orientation (power leader), another holding target dynamics (knowledge leader). In a knowledge-based leader-followers network, the followers obtain dynamics information from the leader through adaptive learning. We also study distributed networks with non-negligible time-delays by using simplified wave variables and other contraction-oriented analysis. Conditions for contraction to be preserved regardless of the explicit values of the time-delays are derived.<br>(cont.) Synchronization behavior is shown to be robust if the protocol is linear. Finally, we study the construction of spike-based neural network models, and the development of simple mechanisms for fast inhibition and de-synchronization.<br>by Wei Wang.<br>Ph.D.
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Corin, Karolina A. (Karolina Ann) 1981. "Inhibition of myofibroblast contraction." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32381.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.<br>Includes bibliographical references (p. 46-49).<br>Although current medical procedures cannot restore complete function of a transected nerve, inserting both of its ends in a tube helps it regenerate. The regenerate is inferior to the uninjured nerve: it has a smaller diameter and poorer electrical conduction. Layers of contractile cells known as myofibroblasts have been observed around regenerated nerve portions. An inverse relationship between the layer thickness and the quality of the regenerate has also been observed. These findings suggest that the cells are exerting contractile forces which prevent the regenerating nerve from fully developing. Inhibiting this contraction should thus improve the quality of nerve regeneration. Alpha smooth muscle actin ([alpha]-SMA) is a critical contractile protein. Its expression can be upregulated by the growth factor TGF-[beta]1, and blocked by the pharmacological agent PP2. To investigate whether blocking SMA expression alone can inhibit myofibroblast contraction, NR6 wild type fibroblasts were seeded into short cylindrical collagen-GAG matrices, and administered either media alone, media with TGF-[beta]1 (3ng/ml), or media with TGF-[beta]1 and PP2 (10 [mu]M). Non-seeded matrix samples were also prepared. The matrix diameters were measured every day for 12 days, after which the matrices were digested and the number of adhered cells were counted. The daily change in matrix diameter was calculated. The results showed that the cells contracted the matrices. TGF-[beta]1 increased cell contractility, while PP2 inhibited it..<br>(cont.) Normalizing the Day 12 diameter change measurements to cell number and the original matrix diameter showed that TGF-[beta] increased the strain generated by each cell ... relative to ... for untreated cells), and that PP2 counteracted this effect (...). Using the linear elastic constitutive relations, the average force exerted per cell was calculated for the untreated cells (...), TGF-[beta]1 stimulated cells (...), and TGF-[beta] + PP2 stimulated cells (...). The cell counts after Day 12 indicate that PP2 interferes with cell adhesion to the matrices. After 6 hours in culture, 21% of untreated cells, 25% percent of cells treated with TGF-[beta] 1, and 25% of cells treated with TGF-[beta]1 and PP2 had adhered. By Day 12, only 12% of the seeded untreated cells, 14% of cells treated with TGF-[beta] I, and 3.2% of cells treated with both TGF-[beta]1 and PP2 remained adhered. This study thus indicates that PP2 inhibits cellular contraction, possibly by preventing cell-substrate adhesion<br>by Karolina A. Corin.<br>S.M.
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Reis, Maurício Duarte Luís. "On theory multiple contraction." Doctoral thesis, Universidade da Madeira, 2011. http://hdl.handle.net/10400.13/255.
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The one which is considered the standard model of theory change was presented in
[AGM85] and is known as the AGM model. In particular, that paper introduced
the class of partial meet contractions. In subsequent works several alternative constructive models for that same class of functions were presented, e.g.: safe/kernel
contractions ([AM85, Han94]), system of spheres-based contractions ([Gro88]) and
epistemic entrenchment-based contractions ([G ar88, GM88]).
Besides, several generalizations of such model were investigated. In that regard
we emphasise the presentation of models which accounted for contractions by sets of
sentences rather than only by a single sentence, i.e. multiple contractions. However, until now, only two of the above mentioned models have been generalized in the
sense of addressing the case of contractions by sets of sentences: The partial meet
multiple contractions were presented in [Han89, FH94], while the kernel multiple
contractions were introduced in [FSS03].
In this thesis we propose two new constructive models of multiple contraction
functions, namely the system of spheres-based and the epistemic entrenchment-based
multiple contractions which generalize the models of system of spheres-based and of
epistemic entrenchment-based contractions, respectively, to the case of contractions
(of theories) by sets of sentences. Furthermore, analogously to what is the case
in what concerns the corresponding classes of contraction functions by one single
sentence, those two classes are identical and constitute a subclass of the class of
partial meet multiple contractions.
Additionally, and as the rst step of the procedure that is here followed to
obtain an adequate de nition for the system of spheres-based multiple contractions,
we present a possible worlds semantics for the partial meet multiple contractions
analogous to the one proposed in [Gro88] for the partial meet contractions (by one
single sentence).
Finally, we present yet an axiomatic characterization for the new class(es) of
multiple contraction functions that are here introduced.<br>Eduardo Fermé
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Makur, Anuran. "Information contraction and decomposition." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122692.
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This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Thesis: Sc. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2019<br>Cataloged from student-submitted PDF version of thesis.<br>Includes bibliographical references (pages 327-350).<br>Information contraction is one of the most fundamental concepts in information theory as evidenced by the numerous classical converse theorems that utilize it. In this dissertation, we study several problems aimed at better understanding this notion, broadly construed, within the intertwined realms of information theory, statistics, and discrete probability theory. In information theory, the contraction of f-divergences, such as Kullback-Leibler (KL) divergence, X²-divergence, and total variation (TV) distance, through channels (or the contraction of mutual f-information along Markov chains) is quantitatively captured by the well-known data processing inequalities.<br>These inequalities can be tightened to produce "strong" data processing inequalities (SDPIs), which are obtained by introducing appropriate channel-dependent or source-channel-dependent "contraction coefficients." We first prove various properties of contraction coefficients of source-channel pairs, and derive linear bounds on specific classes of such contraction coefficients in terms of the contraction coefficient for X²-divergence (or the Hirschfeld-Gebelein-Rényi maximal correlation). Then, we extend the notion of an SDPI for KL divergence by analyzing when a q-ary symmetric channel dominates a given channel in the "less noisy" sense. Specifically, we develop sufficient conditions for less noisy domination using ideas of degradation and majorization, and strengthen these conditions for additive noise channels over finite Abelian groups.<br>Furthermore, we also establish equivalent characterizations of the less noisy preorder over channels using non-linear operator convex f-divergences, and illustrate the relationship between less noisy domination and important functional inequalities such as logarithmic Sobolev inequalities. Next, adopting a more statistical and machine learning perspective, we elucidate the elegant geometry of SDPIs for X²-divergence by developing modal decompositions of bivariate distributions based on singular value decompositions of conditional expectation operators. In particular, we demonstrate that maximal correlation functions meaningfully decompose the information contained in categorical bivariate data in a local information geometric sense and serve as suitable embeddings of this data into Euclidean spaces.<br>Moreover, we propose an extension of the well-known alternating conditional expectations algorithm to estimate maximal correlation functions from training data for the purposes of feature extraction and dimensionality reduction. We then analyze the sample complexity of this algorithm using basic matrix perturbation theory and standard concentration of measure inequalities. On a related but tangential front, we also define and study the information capacity of permutation channels. Finally, we consider the discrete probability problem of broadcasting on bounded indegree directed acyclic graphs (DAGs), which corresponds to examining the contraction of TV distance in Bayesian networks whose vertices combine their noisy input signals using Boolean processing functions.<br>This generalizes the classical problem of broadcasting on trees and Ising models, and is closely related to results on reliable computation using noisy circuits, probabilistic cellular automata, and information flow in biological networks. Specifically, we establish phase transition phenomena for random DAGs which imply (via the probabilistic method) the existence of DAGs with logarithmic layer size where broadcasting is possible. We also construct deterministic DAGs where broadcasting is possible using expander graphs in deterministic quasi-polynomial or randomized polylogarithmic time in the depth. Lastly, we show that broadcasting is impossible for certain two-dimensional regular grids using techniques from percolation theory and coding theory.<br>by Anuran Makur.<br>Sc. D.<br>Sc.D. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science
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Corona, Benjamin T. "Junctophilin Damage Contributes to Early Force Deficits and Excitation-Contraction Coupling Failure after Performing Eccentric Contractions." Digital Archive @ GSU, 2009. http://digitalarchive.gsu.edu/kin_health_diss/4.
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Junctophilins (JP1 & JP2) are expressed in skeletal muscle and are the primary proteins involved in transverse (T)-tubule and sarcoplasmic reticulum (SR) membrane apposition. During the performance of eccentric contractions, the apposition of T-tubule and SR membranes may be disrupted, resulting in excitation-contraction (EC) coupling failure and thus reduced force-producing capacity. In this study, we made three primary observations: 1) Through the first three days after the performance of 50 eccentric contractions in vivo by the left hindlimb anterior crural muscles of female mice, both JP1 and JP2 were significantly reduced by ~50 and 35%, respectively, while no reductions were observed after the performance of non-fatiguing concentric contractions; 2) following the performance of a repeated bout 50 eccentric contractions in vivo, only JP1 was immediately reduced (~30%) but recovered by 3d post-injury in tandem with the recovery of strength and EC coupling; and 3) following the performance of 10 eccentric contractions at either 15 or 35˚C by isolated mouse EDL muscle, isometric force, EC coupling, and JP1 and JP2 were only reduced after the 35˚C eccentric contractions. Regression analysis of JP1 and JP2 content in TA and EDL muscles from each set of experiments indicated that JP damage is significantly associated with early (0 – 3d) strength deficits after performing eccentric contractions (R = 0.49; P < 0.001). As a whole, the results of this study indicate that JP damage plays in role in early force deficits due to EC coupling failure following the performance of eccentric contractions.
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Lohmiller, Winfried Stefan 1971. "Contraction analysis of nonlinear systems." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9793.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.<br>Includes bibliographical references (leaves 87-90).<br>This thesis derives new results in nonlinear system analysis using methods inspired from fluid mechanics and differential geometry. Based on a differential analysis of convergence, these results may be viewed as generalizing the classical Krasovskii theorem, as well as linear eigenvalue analysis. A central feature is that convergence and limit behavior are in a sense treated separately, leading to significant conceptual simplifications. We establish new combination properties of nonlinear dynamic systems and use them to derive simple controller and observer designs for mechanical systems such as aircraft, underwater vehicles, and robots. The method is also applied to chemical chain reactions and mixture processes. The relative simplicity of these designs stems from their effective exploitation of the systems' structural specificities. Next, we analyze and quantify the global stability properties of physical partial differential equations such as the heat equation, or the Schroedinger equation. Lyapunov exponents are not coordinate-invariant, and thus their exact physical meaning is somewhat questionable. As an alternative, we suggest an extension of linear eigenvalue analysis to nonlinear dynamic systems. Finally, the thesis derives new controller and observer designs for general nonlinear dynamic systems. In particular, an extension of feedback linearization is proposed when the corresponding integrability conditions are violated.<br>by Winfried Stefan Lohmiller.<br>Ph.D.
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Novel, Maxence. "Contraction de cônes complexes multidimensionnels." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS263/document.
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L'objet de cette thèse est l'introduction, l'étude et l'utilisation des cônes complexes multidimensionnels. Dans un premier temps, nous étudions la grassmannienne des espaces de Banach. Nous définissons une notion de bonne décomposition pour les espaces de dimension p et nous démontronsl'équivalence entre la distance de Hausdorff sur la grassmannienne et la distance fournie par une norme sur l'algèbre extérieure.Dans un deuxième temps, nous définissons les cônes complexes p-dimensionnels ainsi qu'une jauge sur les sous-espaces de dimension p de ces cônes. Nous montrons alors un principe de contraction pour cette jauge. Cela nous permet de prouver, pour un opérateur contractant un tel cône, l'existence d'un trou spectral séparant les p valeurs propres dominantes du reste du spectre. Nous utilisons cette théorie pourdémontrer un théorème de régularité analytique pour les exposants de Lyapunov d'un produit aléatoire d'opérateurs contractant un même cône.Nous donnons également une comparaison entre la distance de Hausdorff entre espaces vectoriels et notre jauge.Enfin, nous introduisons une notion de cône dual pour les cônes p-dimensionnels. Dans ce cadre, nous prouvons que les propriétéstopologiques d'un cône se traduisent en propriétés topologiques sur son dual, et réciproquement. Nous complétons le théorème de régularitéprécédent en démontrant l'existence et la régularité d'une décomposition de l'espace en "espace lent" et "espace rapide"<br>The subject of this thesis is the introduction, the study and the applications of multidimensional complex cones. First, we study the grassmannian of Banach space. We define a notion of right decomposition for p-dimensional spaces and we prove the equivalence between theHausdorff distance on the grassmannian and the distance given by a norm on the exterior algebra.Then, we define p-dimensional complex cones and a gauge on the subspaces of dimension p of these cones. We show a contraction principle for thisgauge. This allows us to prove, for an operator contracting such a cone, the existence of a spectral gap which isolate the p leading eigenvaluesfrom the rest of the spectrum. We use this theory to prove a theorem of analytic regularity for Lyapunov exponents of a random product ofoperators contracting a cone. We also give a comparison between the Hausdorff distance for vector spaces and our gauge.Finally, we introduce a notion of dual cone for p-dimensional cones. In this setting, we prove that the topological properties of a cone translateinto topological properties for its dual and conversely. We complete the previous regularity theorem by proving the existence and the regularity ofa dominated splitting of the space into a "fast space" and a "slow space"
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Mazure, Ank. "Cell-mediated contraction in three-dimensional collagen matrices in relation to proliferative vitreoretinopathy and wound contraction." Thesis, Imperial College London, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320529.
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Sethi, Kamaljit Kaur. "Control of fibroblast-mediated collagen contraction : importance and mechanism of cell attachment in the contraction process." Thesis, University College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313283.
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Xu, Liqun. "Ontogeny of myocardial excitation-contraction coupling." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ51512.pdf.
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Korte, F. Steven. "Thick filament regulation of myocardial contraction." Diss., Columbia, Mo. : University of Missouri-Columbia, 2006. http://hdl.handle.net/10355/4383.
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Thesis (Ph. D.)--University of Missouri-Columbia, 2006.<br>The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Vita. "August 2006" Includes bibliographical references.
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Self, Brian P. "A control model of muscle contraction." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-03022010-020135/.
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HIRATA, Tomio, and Hideaki OTSUKI. "Inapproximability of the Edge-Contraction Problem." Institute of Electronics, Information and Communication Engineers, 2006. http://hdl.handle.net/2237/15066.
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Clas, David. "Nifedipine inhibits cholecystokinin induced gallbladder contraction." Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60499.
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The purpose of this study was to show that nifedipine, a calcium channel blocker, can decrease gallbladder contractility in guinea pigs and in man. Gallbladder contraction was measured in response to repeated injections of cholecystokinin both before and after the injection of nifedipine in three groups of five animals each. The mean amplitude of gallbladder contraction in response to cholecystokinin was decreased by 45, 73 and 67% (p $<$ 0.01) in response to intravenous nifedipine doses of 100, 200 and 300 $ mu$g respectively. In nine healthy human volunteers, gallbladder emptying was measured by radionuclide cholescintigraphy in response to cholecystokinin infusion before and after a 10 mg oral dose of nifedipine. Gallbladder ejection fraction was significantly decreased by 29% (p $<$ 0.001). These data demonstrate that nifedipine is a potent inhibitor of gallbladder contractility.
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Soto, Jonathan. "Nonlinear contraction tools for constrained optimization." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62538.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (p. 77-78).<br>This thesis derives new results linking nonlinear contraction analysis, a recent stability theory for nonlinear systems, and constrained optimization theory. Although dynamic systems and optimization are both areas that have been extensively studied [21], few results have been achieved in this direction because strong enough tools for dynamic systems were not available. Contraction analysis provides the necessary mathematical background. Based on an operator that projects the speed of the system on the tangent space of the constraints, we derive generalizations of Lagrange parameters. After presenting some initial examples that show the relations between contraction and optimization, we derive a contraction theorem for nonlinear systems with equality constraints. The method is applied to examples in differential geometry and biological systems. A new physical interpretation of Lagrange parameters is provided. In the autonomous case, we derive a new algorithm to solve minimization problems. Next, we state a contraction theorem for nonlinear systems with inequality constraints. In the autonomous case, the algorithm solves minimization problems very fast compared to standard algorithms. Finally, we state another contraction theorem for nonlinear systems with time-varying equality constraints. A new generalization of time varying Lagrange parameters is given. In the autonomous case, we provide a solution for a new class of optimization problems, minimization with time-varying constraints.<br>by Jonathan Soto.<br>S.M.
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Anquetil, Patrick A. T. (Patrick Armand T. ). 1973. "Large contraction conducting polymer molecular actuators." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/30349.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, February 2005.<br>Vita. Leaf 239 blank.<br>Includes bibliographical references.<br>The development of powerful and efficient artificial muscles that mimic Nature will profoundly affect engineering sciences including robotics and prosthetics, propulsion systems, and microelectromechanical systems (MEMS). Biological systems driven by muscle out-perform human-engineered systems in many key aspects. For example, muscle endows animals with a level of dexterity and speed that has yet to be emulated by even the most complex robotic system to date. Conducting polymers were chosen for research as actuators, based on a review of the relevant properties of all known actuators and active materials. Key features of conducting polymer actuators include low drive voltages (1 - 2 V) and high active strength (10 - 40 MPa) but moderate active strains (2 %). Active strains of 20 %, which human skeletal muscle is capable of, are desirable for applications in life-like robotics, artificial prostheses or medical devices. This thesis focuses on two approaches to create large contraction in conducting polymer actuators. The first strategy utilizes polypyrrole (PPy), a conducting polymer actuator material that contracts and expands based on a bulk ion swelling mechanism. Optimization of the polymer activation environment via room temperature ionic liquids enables PPy actuators to generate large contractions (16.3 % recoverable strain at 2.5 MPa, 21 % max) at slow speeds (0.4 %/s). In addition, cycle life can reach 10⁵ cycles without significant polymer degradation. This thesis presents an in-depth characterization of the behavior of polypyrrole actuators in room temperature 1-butyl-3-methyl imidazolium tetrafluoroborate liquid salt electrolyte.<br>(cont.) The characterization includes the assessment of passive and electroactive mechanical properties as well as electrical and morphological properties. Using Nature's actin-myosin molecular engine as a source of inspiration, the second approach uses molecular mechanisms to create motion. In this bottom-up approach molecules are rationally designed from the molecular level for specific actuation properties. Such active molecular building blocks include shape changing, load bearing, passively deformable or hinge-like molecular elements. Several novel materials based on contractile molecular design were synthesized and their active properties characterized.<br>by Patrick A.T. Anquetil.<br>Ph.D.
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Otto, Oliver, Sebastian Sturm, Nadanai Laohakunakorn, Ulrich Keyser, and Klaus Kroy. "Rapid internal contraction boosts DNA friction." Diffusion fundamentals 20 (2013) 77, S. 1, 2013. https://ul.qucosa.de/id/qucosa%3A13665.
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Ould, Ahmed Salem Cheikh [Ahmadou]. "Approximation de points fixes d'une contraction." Montpellier 2, 1998. http://www.theses.fr/1998MON20035.
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Dans la premiere partie de cette these, nous considerons le probleme de recherche des zeros d'une somme de deux operateurs maximaux monotones. Ce probleme se ramene a un probleme de point fixe d'une contraction particuliere. La seconde partie est consacree a la recherche des points fixes d'une contraction quelconque. D'une part, nous introduisons la notion de bonne position, ainsi que le conditionnement pour ce type de problemes. Nous etudions les liens entre ces deux notions. D'autre part, nous presentons deux sortes de regularisations qui permettent la selection d'une solution particuliere. Cette etude est completee par des tests numeriques sur un exemple de recherche d'un point fixe commun a deux contractions fermes.
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Brady, Adrian J. B. "Nitric oxide and cardiac myocyte contraction." Thesis, University of Edinburgh, 1994. http://hdl.handle.net/1842/20215.
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Whether nitric oxide is implicated in the contractile function of isolated cardiac ventricular myocytes forms the major part of the work of this thesis. Contracting guinea-pig cardiac myocytes were studied in isolation <I>in vitro</I> using a videomicroscopy length detection system. Studies are presented which establish that nitric oxide attenuates contractility of cardiac ventricular myocytes, both when it is derived from exogenous sources, and when nitric oxide is released from adjacent endothelium in coculture with cardiac myocytes. The coronary microcirculation is in close proximity to cardiac myocytes within the myocardium, thus endothelium-derived nitric oxide may have an important tonic effect on myocardial contractility. This may be particularly important when the diffusing distance from endothelial cell to myocyte is altered in disease states. Myocardial contractility is impaired in endotoxic shock. The hypothesis that this is caused by production of nitric oxide within cardiac myocytes is examined. A model of endotoxic shock was developed. Contractility of cardiac myocytes was substantially impaired. Much of this impairment was caused by nitric oxide production within the cardiac myocytes themselves. Inhibition of nitric oxide synthesis in these cells restored contractility towards normal. Healthy myocytes did not produce effective amounts of nitric oxide. Induction of nitric oxide synthase activity within cardiac myocytes may account for much of the depressed contractility of endotoxic heart failure. Myocardial contractility is impaired following ischaemia-reperfusion. Experiments examining myocyte behaviour in this situation are discussed, but whether activation of nitric oxide synthase contributes to the impaired contractility of myocytes following ischaemia is not established.
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Otto, Oliver, Sebastian Sturm, Nadanai Laohakunakorn, Ulrich Keyser, and Klaus Kroy. "Rapid internal contraction boosts DNA friction." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-183656.
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Lagemann, Frederico. "Estudo da representação numérica do comportamento mecânico de músculos esqueléticos sujeitos à combinação de diferentes tipos de contrações." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/131057.
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Esta dissertação apresenta um estudo da caracterização numérica do comportamento mecânico de um músculo esquelético estriado sujeito à combinação de diferentes contrações. A partir dos mecânismos fisiológicos da contração do tecido muscular esquelético, são apresentadas as principais características da produção de força do músculo em diferentes tipos de contrações (isométrica, concêntrica, excêntrica) e suas combinações. A representação numérica da resposta mecânica do músculo esquelético foi investigada por diferentes autores. Dos diversos modelos encontrados na literatura, alguns foram escolhidos para a continuidade deste estudo, segundo sua capacidade representativa e facilidade de implementação em métodos numéricos de solução para grandes deformações. Os modelos disponíveis na literatura foram implementados e avaliados para diferentes sequências de contrações, sendo também realizado um ajuste de parâmetros para dados experimentais de contrações isométricas e isométricas-excêntricas-isométricas. Nenhuma das propostas avaliadas apresentou resultados satisfatórios. A principal deficiência dos modelos foi a incapacidade de reproduzir a dependência do histórico de carregamentos, ou seja, da combinação de contrações. Desta maneira, uma nova proposta de modelo constitutivo foi desenvolvida e implementada para testes uniaxiais e em um código de elementos finitos para testes tridimensionais. A partir destas implementações, foram executados testes numéricos para diferentes sequências de contrações, avaliando a capacidade representativa do modelo proposto neste trabalho. O modelo proposto apresentou bons resultados para contrações isométricas e a combinação de contrações com diferentes níveis de alongamento, ou encurtamento, a uma mesma velocidade. A principal contribuição deste modelo é a capacidade de representar a resposta associada à fadiga muscular e o ganho, ou perda de força, observados experimentalmente.<br>This work present a striated skeletal muscle numerical characterization subjected to different contractions. From the physiological contraction mechanism of the skeletal muscle tissue the force produced in different kinds of contraction (isometric, concentric and eccentric), and their combination, are presented. The numerical representation of these response was investigated by different authors. From the diverse models found in literature, some were selected to be studied according to their representation capability and the implementation ease in numerical methods for large strains. The models available in literature were implemented and evaluated for different contractions combinations and a parameter identification for experimental results of two isometric contraction and a isometric-eccentric-isometric contraction. None of the proposed models presented satisfactory results. The main deficiency of these models were the incapability of reproducing the loading history dependence, in other words, the contraction combination. In this way, a new material model was proposed and implemented to uniaxial and tridimensional finite element method tests. From these, different contractions sequences evaluated the proposed model representation capabilities. The proposed model present good results to isometric contraction, as well as contraction combination with different stretch, or shortening, level in the same speed. The main contribution of this model is the capability of represent the the response associated to the muscle fatigue and the force gain or loss, experimentally observed.
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Pasquet, Benjamin. "Etude de la spécificité de la commande motrice et de sa régulation pendant différents types de contractions musculaires." Doctoral thesis, Universite Libre de Bruxelles, 2009. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210280.
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Le but de cette dissertation doctorale était de mieux comprendre les mécanismes de contrôle tant centraux que périphériques qui sont à l’origine de la régulation neuromusculaire lors de mouvement impliquant des contractions de type excentrique. Lors d’une première étude réalisée sur le muscle jambier antérieur, nous avons montré qu’un exercice utilisant des contractions excentriques présentait une meilleure résistance à la fatigue que lorsque des contractions concentriques étaient impliquées puisque celui-ci conduit à une moindre diminution du couple de force et de l’activité électromyographique. L’absence de fatigue nerveuse centrale et l’observation d’un comportement spécifique du couple de force et de l’activité électromyographique lors de ces épreuves de fatigue semblait traduire la mise en jeu de processus périphériques différents. La plus grande fatigue observée lors de l’épreuve concentrique suggérait une activation plus importante que pour l’épreuve excentrique, dont les conséquences métaboliques renforcent les altérations du couplage excitation-contraction. Dans un second temps, nous avons étudié l’effet des modifications de longueur de fascicule du muscle jambier antérieur sur le comportement spécifique des unités motrices (ordre, fréquence et seuil de recrutement) lors de contractions isométriques. Nous avons ensuite analysé le comportement d’unités motrices selon les différentes modalités de contractions (concentrique vs. excentrique) sur ce même muscle. Pour y répondre, différentes techniques d’analyse ont été utilisées dont l’enregistrement électromyographique intramusculaire et l’ultrasonographie. Enfin, nous avons cherché à analyser l’évolution des différents mécanismes de régulation d’origine périphérique et /ou central susceptible de modifier l’excitabilité du pool de motoneurone lors de contractions concentriques et excentriques. Pour y répondre, les modulations d’une part, du réflexe de Hoffmann (réflexe H) par stimulation électrique et d’autre part, celles du potentiel moteur évoqué (MEP) par stimulation magnétique transcorticale, ont été investiguées. Ces réponses ont été enregistrées à différents angles de la plage articulaires étudiée lors des contractions concentriques et excentriques, ainsi qu’aux deux extrémités angulaires lors de contraction isométriques. Notre travail indique que l’ordre de recrutement des unités motrices entre les contractions concentriques et excentriques étant identique, le système nerveux n’utilise qu’une seule et même stratégie d’activation liée à la taille des motoneurones impliqués dans ces deux types de contractions. En outre, les contractions excentriques lorsqu’elles sont réalisées à vitesse constante, sont associées à une modulation spécifique de la fréquence de décharge des unités motrices. Ce comportement diffère de celui observé lors de contractions concentriques, malgré une modification linéaire et similaire de la longueur des fascicules et du couple de force au cours de ces deux tâches. Les modulations du recrutement des unités motrices semblent davantage dépendre de la longueur musculaire tandis que les modulations de fréquence prédominent pendant les contractions en raccourcissement. Ce comportement spécifique semble dépendant de mécanismes de régulation principalement localisés au niveau spinal. Ainsi, le degré d’inhibition des afférences fusoriales affectant le pool de motoneurones du muscle tibial antérieur lors de sollicitations actives du muscle, dépend davantage de l’angle articulaire et donc de la longueur du muscle plutôt que du mode de contraction. Lors de sollicitations isométriques, le retour sensoriel Ia est principalement contrôlé au niveau présynaptique en fonction de la longueur du muscle. Lors de sollicitations concentriques et excentriques, ces mécanismes présynaptiques réguleraient l'excitabilité spinale de manière similaire entre les deux modes. Néanmoins, bien que l'inhibition présynaptique soit probablement plus marquée lors des sollicitations excentriques, ce mode de contraction semble également régulé par des mécanismes d'inhibition intervenant au niveau postsynaptique tel que l'inhibition récurrente de Renshaw. Ce mécanisme localisé au niveau postsynaptique permettrait de réguler la fréquence de pulsation des unités motrices lors de sollicitations excentriques dans le but le faciliter l'exécution du mouvement. L'originalité de notre travail a été d’étudier le comportement d’une même unité dans les deux modes de contractions alors que la méthode d’analyse généralement adoptée consistait à comparer des populations d’unités motrices entre-elles. De plus, les changements de la longueur du muscle au cours du mouvement ainsi que les vitesses de raccourcissement ou d'allongement ont été estimés à partir de la mesure directe de la longueur des fascicules musculaires. Cette dernière présente l’avantage de fournir une information de longueur et de vitesse sur la portion de muscle à partir de laquelle les enregistrements d’unités motrices ont été obtenus. Enfin, étant donné les modulations possibles tant au niveau spinal que supraspinal des mécanismes nerveux mis en jeu, il semblait important d’analyser celles-ci pendant le mouvement et aux différents angles investigués. Cette précision méthodologique a permis d'élargir la discussion concernant les possibles modifications de la balance "excitation-inhibition" lors de sollicitations excentriques, qui, jusqu’à présent, n'avaient été analysées que pour un angle articulaire donné.<br>Doctorat en Sciences de la motricité<br>info:eu-repo/semantics/nonPublished
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Kawano, Yoji, Takeshi Yoshimura, and Kozo Kaibuchi. "Smooth muscle contraction by small GTPase Rho." Nagoya University School of Medicine, 2002. http://hdl.handle.net/2237/5374.
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Wadsworth, R. M. "Regulation of contraction of arterial smooth muscle." Thesis, University of Strathclyde, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248764.
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Griffiths, R. H. ugh. "Modelling the Regulation of Skeletal Muscle Contraction." Thesis, University of Kent, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.499839.
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Catana, Leo. "The concept of contraction in Bruno's philosophy." Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397591.
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Grocott-Mason, Richard Michael. "Endothelium derived nitric oxide and myocardial contraction." Thesis, King's College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307580.
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Kane, Christopher. "Heterocellular regulation of cardiomyocyte excitation-contraction coupling." Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/53120.
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Our understanding of cardiomyocyte electrophysiology and function has been built from experimentation on the single, isolated cardiomyocyte. As a result, a significant body of work has been accumulated describing the mechanisms underlying cardiomyocyte function in health, and how they are altered in disease. The heart however is a sophisticated syncytium of which cardiomyocytes comprise only one third of the cellular content, supported by a number of other cell types. It is the summation of these parts which underlies the effectiveness and adaptability of the heart as an organ, however our understanding of how the non-myocyte niche supports and regulates cardiomyocyte function is limited. Cardiac fibroblasts represent a significant portion of the non-myocyte component of the myocardium, intrinsically linked to extracellular matrix synthesis and turnover as well as secreting significant amounts of bioactive molecules. Multiple aspects of cardiac fibroblast function have been demonstrated to have significant effects on cardiomyocyte electrophysiology, but how these multiple threads combine into a coherent syncytium, as in vivo, is unclear. In this thesis, we investigated the hypothesis that cardiac fibroblasts regulate excitation-contraction coupling in cardiomyocytes, and the effect of this regulation is dependent on the modality of interaction. To do this we utilised cardiac fibroblasts from failing human hearts, and induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) as a surrogate of human cardiomyocytes. Initial work investigating the optimal conditions for iPSC-CM culture conditions identified a significant effect of environment, specifically iPSC-CM seeding density, on their structure and electrophysiological properties. Confluent monolayers of iPSC-CMs were more consistent, stable and functional than isolated cells. As such these formed the basis of further experimentation. iPSC-CM - fibroblast co-cultures were designed in ways to limit the pathways of interaction available between the two cell types. Three were used: fibroblast conditioned medium alone, co-culture in the same well but kept physically separate to allow two-way paracrine interaction, and finally in direct contact with fibroblasts seeded directly on iPSC-CM monolayers. We found that the first two culture conditions broadly slowed iPSC-CM Ca2+ transient properties, while in contrast, physical contact between the two resulted in the opposite, with significantly faster Ca2+ transient kinetics. Assessing these changes in iv more detail with caffeine experiments, we demonstrated that this change in properties was a result of a four-fold increase in sarcoplasmic reticulum Ca2+ uptake when the iPSC-CMs and fibroblasts were in contact, as well as an enhanced ratio of sarcolemmal Ca2+ flux and sarcoplasmic reticulum Ca2+ release. Investigating the potential mechanisms bringing about these changes, we identified a number of cytokines present in the supernatant of the co-cultures that had potential cardio-active effects, however none of these were responsible for the observed contact-induced effects. As fibroblasts actively secrete extracellular matrix, we proceeded to investigate the possible contribution of fibroblast-derived extracellular matrix in this interaction using a small peptide-based model of integrin stimulation. Treatment of the iPSC-CMs with the fibronectin binding sequence peptide GRGDS recapitulated the contact-induced changes in iPSC-CM Ca2+ handling properties as well as significantly shortening the action potential. We further identified that the mechanism through which GRGDS acts was partially a result of stimulation of actin polymerisation and not integrin-associated kinase signalling. This work supports the growing understanding of the fundamental role non-myocytes play in supporting and regulating cardiomyocyte function. In particular we have demonstrated that cardiac fibroblasts stimulate the engagement of the sarcoplasmic reticulum in the process of excitation-contraction coupling in iPSC-CMs. This is not only relevant for the applications of iPSC-CMs in translational medicine and cardiovascular research, but also to understand and target the excitation-contraction coupling machinery in development, health and disease.
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Combescot, Caroline 1976. "A study of contraction theory and oscillators." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/89298.
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Patterson, Tiffany. "Flow contraction matching in the human heart." Thesis, King's College London (University of London), 2017. https://kclpure.kcl.ac.uk/portal/en/theses/flow-contraction-matching-in-the-human-heart(7be09606-52cc-4b0d-9331-9d7c970e0a85).html.
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Introduction: Induction of myocardial ischaemia results in a cascade of left ventricular haemodynamic effects, resulting in myocyte necrosis, scar formation and eventual heart failure, for which treatment is limited. Fundamental to enhancing our understanding of cardiovascular pathophysiology and therapeutics is the assessment of ventricular pump properties. The main aim of this work was to gain a greater understanding of the myocardial-coronary and ventricular-arterial interaction in humans in health and diseased states. Methods: Simultaneous invasive left ventricular (LV) pressure-volume (PV) (by use of a conductance catheter) and intra-coronary haemodynamic assessment (dual-sensor pressure-flow wire) were performed in the catheterisation laboratory. A novel software system was developed to perform simultaneous analysis of PV loop and coronary haemodynamic data. In-vitro and in-vivo studies were performed for calibration; PV loop recordings from patients were used for validation. Results: 1) Using wave intensity analysis, the origin of the coronary wave energies were described, and their temporal relationship with the cardiac cycle was established. In the absence of autoregulation a direct relationship was found to exist between LV elastance and coronary flow velocity. 2) Assessment of coronary haemodynamics and LV PV measurements were performed during supine exercise to provoke ischaemia, with a control group comparator. Ischaemia led to a rightward shift in end-systolic and end-diastolic PV relations; VA interaction was adversely affected during ischaemia compared to control. 3) The effects of nitrates in patients with coronary artery disease were examined. Nitrates induced vasodilatation of the systemic vasculature and coronary circulation, decreasing myocardial oxygen consumption and inducing stenosis dilatation. 4) 3D speckle tracking echocardiography was performed in patients with preserved LV function and coronary artery disease followed by PV loop assessment. Parameters of strain correlated well with contractility indices in-vivo; thus has potential for use in prognostication and risk stratification. 5) The haemodynamic mechanisms of percutaneous ventricular restoration (PVR) therapy are not understood. Patients underwent PVR implantation and LV PV loops were recorded pre- and post-PVR and at 6-month follow up. PVR decreased dyssynchrony, LV volumes and induced reverse remodelling with improved contractility. Conclusions: Development of software enabled understanding of the cardiac-coronary interaction: coronary wave energies were shown to be dependent on V-A interaction rather than myocardial-coronary interaction. Coronary systolic flow was directly related to LV elastance on abolition of autoregulation. Systemic response to demand ischaemia was described, as were the anti-anginal effects of nitrates; 3D deformation imaging was validated as a prognostic tool for subclinical heart disease and PVR was shown to induce reverse remodelling.
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Khabbaza, Elias Joseph. "Regulation of contraction in porcine coronary arteries /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487325740717536.
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Torstenson, Bodil. "Contraction gaps around dental composite resin restorations." Stockholm : Kongl. Carolinska Medico Chirurgiska Institutet, 1988. http://books.google.com/books?id=_vNpAAAAMAAJ.
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McSherry, Iain Neil. "Endothelial cell modulation of smooth muscle contraction." Thesis, University of Bath, 2005. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423481.
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Ronceray, Pierre. "Contraction active de réseaux de fibres biologiques." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS154/document.
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Le fonctionnement des organismes vivants requiert la production deforces à grande échelle, pour des processus biologiques aussi diversque la motilité cellulaire, le développement embryonnaire, lacicatrisation ou encore la contraction musculaire. Dans de telssystèmes, les forces générées à l'échelle moléculaire par des moteursprotéiques sont transmises par des réseaux de fibres désordonnés,menant à des tensions actives à grande échelle. Les propriétésmacroscopiques passives de ces réseaux de fibres sont biencaractérisées. En revanche, ce problème de production de stress pardes unités actives microscopiques n'est pas résolu. Cette Thèseprésente une étude approfondie, par des méthodes théoriques etnumériques, de la transmission de forces dans les réseaux élastiquesde biopolymères. Je montre que la réponse linéaire, à faible force,des réseaux est remarquablement simple : elle est déterminée par laseule la géométrie des unités actives exerçant les forces. Aucontraire, lorsque les forces actives sont suffisamment importantespour provoquer le flambage non-linéaire des fibres, ces forces sontrectifiées par le réseau, et deviennent isotropiquementcontractiles. La contraction émergente qui en résulte est amplifiéepar la transmission de forces non-linéaire à travers le réseau. Cetteamplification du stress macroscopique est renforcée par le caractèredésordonnée du réseau, mais sature lorsque la densité d'unités activesest grande. Nos prédictions sont en accord quantitatifs avec desrésultats expérimentaux sur des tissus reconstitués et des réseauxd'actomyosine in vitro, et apportent un éclairage nouveau surl'influence de l'architecture microscopique des réseaux sur structuredes stress à l'échelle de la cellule et du tissu<br>Large-scale force generation is essential for biological functionssuch as cell motility, embryonic development, wound healing and musclecontraction. In these processes, forces generated at the molecularlevel by motor proteins are transmitted by disordered fiber networks,resulting in large-scale active stresses. While fiber networks arewell characterized macroscopically, this stress generation bymicroscopic active units is not well understood. In this Thesis, Ipresent a comprehensive theoretical and numerical study of forcetransmission in elastic fiber networks. I show that the linear,small-force response of the networks is remarkably simple, as themacroscopic active stress depends only on the geometry of theforce-exerting unit. In contrast, as non-linear buckling occurs aroundthese units, local active forces are rectified towards isotropiccontraction, making the local geometry of force exertion irrelevant.This emergent contractility is amplified by non-linear forcetransmission through the network. This stress amplification isreinforced by the networks' disordered nature, but saturates for highdensities of active units. Our predictions are quantitativelyconsistent with experiments on reconstituted tissues and actomyosinnetworks, and that they shed light on the role of the networkmicrostructure in shaping active stresses in cells and tissue
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Marcucci, Lorenzo. "Un modèle mécanique de la contraction musculaire." Palaiseau, Ecole polytechnique, 2009. http://www.theses.fr/2009EPXX0001.
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The thesis describes the skeletal muscle contraction from a purely (micro)mechanical point of view. The fast time scale processes related to the power stroke event is firstly described as diffusion in a non-convex energy which leads to an overcoming of some drawbacks of the classical Huxley and Simmons model. The new model allows the description of the power stroke in the same framework of the Brownian ratchet theory, already used to describe the slower process of the attachment detachment of the myosin head from the actin sites. A global model is finally presented, able to reproduce not only the main features of the muscle contraction, but also to interpret the main phases of the whole cross bridge cycle. The efforts to maintain the modeling in the purely mechanical framework represent a first step to the possible construction of artificial machines based on skeletal muscle mechanics, more than a limitation on the physical interpretation of the chemical events.
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De, Soete Franz. "Ecoulement de gouttes couvertes dans une contraction." Electronic Thesis or Diss., Université Paris sciences et lettres, 2021. http://www.theses.fr/2021UPSLS082.
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L’écoulement de gouttes d'huile dans l’eau à travers la contraction d’un canal présente un intérêt pour de nombreuses applications telles que l’extraction de pétrole ou la microfluidique. Dans la littérature, la condition de bouchage d’un pore soumis à un gradient de pression a été largement étudiée pour les gouttes et les bulles. La relation entre le débit et la pression fait intervenir la différence des pressions de Laplace à l'avant et à l'arrière de la goutte : elle dépend donc des tensions interfaciales à l’avant et à l’arrière. La présence d'espèces adsorbées à la surface abaissant la tension interfaciale, comme des tensioactifs ou des particules colloïdales, modifie donc non seulement le seuil de bouchage mais également la valeur du débit au-dessus de ce seuil. L’objectif de cette thèse est d’étudier l’écoulement, sous gradient de pression imposé, de gouttes dont la surface est initialement saturée de tensioactifs (au-dessus de la CMC) ou de particules à travers la contraction d’un capillaire cylindrique. Nous montrons comment la mesure du débit par analyse d’images permet d’accéder sous certaines hypothèses à une mesure des tensions interfaciales. Dans le cas des tensioactifs, nous mesurons ainsi une augmentation de la tension interfaciale à l’avant qui résulte d’une compétition entre l’effet de l’accroissement de surface et celui d’un transport par effet Marangoni. Dans le cas des gouttes couvertes de particules, nous montrons que la vitesse de la goutte et le rayon des particules adsorbées à sa surface contrôlent le régime d’écoulement. A faible vitesse, le mouillage de l’huile sur la paroi du canal est observé à l’avant de la goutte ; aux vitesses plus élevées, le régime dépend de la taille des particules comparée à l’épaisseur du film de lubrification, suivant les cas, un frottement des particules sur la paroi du canal, ou un régime de lubrification visqueuse sont observés. Ces régimes sont responsables d’une accumulation plus ou moins importante des particules à l’arrière de la goutte, y diminuant la tension interfaciale et donnant lieu à différents mécanismes de déstabilisation de l’interface. Pour les deux systèmes, nous montrons que la présence d’espèces adsorbées affecte peu la condition de bouchage. En revanche, nous mesurons une augmentation du temps de passage des gouttes couvertes de tensioactifs ou de particules résultant du couplage entre l’écoulement de la goutte et les dynamiques interfaciales<br>The flow of oil drops in water through a constricted channel is of interest for many applications such as oil extraction or microfluidics. In the literature, the condition of pore clogging under a pressure gradient has been extensively studied for drops and bubbles. The relation between flowrate and pressure involves the difference in Laplace pressures at the front and back of the drop, and thus the interfacial tensions at the front and the back. The presence of species adsorbed on the surface lowering the interfacial tension, such as surfactants or colloidal particles, therefore modifies not only the clogging threshold but also the value of the flowrate above this threshold. The objective of this thesis is to study the flow, under an imposed pressure gradient, of drops whose surface is initially saturated with surfactants (above the CMC) or with particles, through cylindrical constricted capillaries. We show how measurements of flowrate by image analysis can provide measurements of the interfacial tensions. In the case of surfactant-laden drops, we measure an increase in the interfacial tension at the front which results from a competition between the surface expansion effects and the transport by a Marangoni effect. In the case of particle-laden drops, we show that both the velocity of the drop and the radius of the particles adsorbed on its surface control the flow regime. At low velocities, the wetting of oil on the capillary walls is observed at the front of the drop; at larger velocities, the flow depends on the particle size compared to the thickness of the lubricating film, according to this criterion either the occurence of friction of the particles on the channel walls or a viscous lubrication regime are observed. These regimes are responsible for a greater or lesser accumulation of particles at the back of the drop, decreasing the back interfacial tension and giving rise to various mechanisms of interface destabilization. For both systems, we show that the presence of adsorbed species has little effect on the clogging condition. Nevertheless, we measure an increase in the passage time of the drops covered with surfactants or particles, which results from the coupling of interfacial dynamics and flow through the contraction
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Laurens, Pascale. "Modélisation et simulation numérique de l'écoulement coronarien : effets de la contraction cardiaque." Toulouse 3, 1994. http://www.theses.fr/1994TOU30052.
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Une des particularites de l'ecoulement sanguin coronarien est d'irriguer, tout en y cheminant, un muscle qui se contracte. Afin d'etudier l'effet de cette contraction sur l'ecoulement coronarien, un modele mathematique et numerique est propose. Cette modelisation est basee sur un nouveau concept assimilant la contraction cardiaque a une onde se propageant dans le myocarde a une vitesse finie. Cette approche differe d'autres modelisations basees sur la pression intraventriculaire ou sur la variation d'elastance du tissu myocardial. Le reseau vasculaire coronarien est simule par deux modules: un module de 11 tubes souples, representant les principales arteres et un autre schematisant le reseau peripherique, lui-meme divise en deux tubes en parallele dont l'un represente le reseau epicardial peripherique et l'autre le reseau intramyocardial. L'ecoulement instationnaire du sang dans le premier module est modelise a partir des equations globales de continuite, de quantite de mouvement et d'une loi de tube lineaire liant le mouvement de la paroi a la pression du fluide. Pour le reseau intramyocardial, cette derniere relation est remplacee par une relation, de type peristaltique, specifiant le mouvement de la paroi sous forme sinusoidale. Le reseau epicardial peripherique est considere successivement rigide, compliant, ou peristaltique. Pour une onde de contraction progressive, ces trois modelisations permettent d'obtenir une reduction du debit arteriel systolique ainsi que l'opposition de phase entre les debits arteriel et veineux, avec des allures comparables a celles obtenues in-vivo. Un couplage de deux ondes de contraction de sens oppose permet d'obtenir en plus des deux caracteristiques precitees, un debit arteriel systolique retrograde
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Lou, Fang. "A study of the contractile properties of vertebrate skeletal muscle with special reference to the force-velocity relationship and the cellular mechanisms of muscle fatigue /." Lund : Dept. of Pharmacology, University of Lund, 1994. http://books.google.com/books?id=zO9qAAAAMAAJ.
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Telley, Ivo Andreas. "The role of sarcomere dynamics in muscular contraction /." Zürich : ETH, 2005. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16381.
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Fadia, Tanvi N. "Gender differences in muscle fatigue during isometric contraction /." Connect to Online Resource-OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1187911454.
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Hudson, Tina Ann. "A biomorphic integrated-circuit implementation of muscular contraction." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/14976.
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Carey, Mara L. "An enhanced integrated-circuit implementation of muscular contraction." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/15507.
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Grace, Andrew Ashley. "The regulation of intracellular pH and cardiac contraction." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319389.
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Yeung, Wai Ella, and 楊慧. "Eccentric contraction-induced injury in mammalian skeletal muscle." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B29750313.
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Ferguson, Roisean Emily. "The regulatory domain of myosin in muscle contraction." Thesis, King's College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300319.
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McCloskey, Diana Teresa. "Adrenergic regulation of cardiac muscle contraction and relaxation." Thesis, King's College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324975.
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Mazelet, Lise. "The role of contraction in skeletal muscle development." Thesis, Queen Mary, University of London, 2015. http://qmro.qmul.ac.uk/xmlui/handle/123456789/8960.
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The aim of this project was to determine the role of contraction in skeletal muscle development. The role of the initial spontaneous contractions observed in zebrafish embryos from 17 to 24 hours post fertilisation was examined. Genetic and pharmacologic approaches were used to study paralysis-induced disruption of skeletal muscle structure and function and subsequently determine the role of contraction. The structural and functional characteristics of developing skeletal muscles were found to be regulated by a dual mechanism of both movement-dependent and independent processes, in vivo. Novel data demonstrates that contraction controls sarcomere remodelling, namely regulation of actin length, via movement driven localisation of the actin capping protein, Tropmodulin1. Myofibril length was also shown to be linked to the mechanical passive property, stretch, with lengthening leading to an increase of the muscle’s ability to stretch. In addition, myofibril bundling and the myofilament lattice spacing, responsible for active tension generation via cross-bridge formation, were shown to be unaffected by paralysis and thus, movement-independent processes. Furthermore, the mechanism of the contraction-driven myofibril organisation pathway at the focal adhesion complexes (FAC), was shown to be different in zebrafish compared to mammals, with mechanosensing revolving around the Src protein rather than Fak. In summary, the role of contraction was established as a critical driver of myofibril organisation and passive tension in the developing zebrafish skeletal muscle. Passive tension regulates muscle function by determining its operational range ensuring that the needs of locomotion are met. Furthermore, investigation of FAC’s role in the contractiondriven myofibril organisation pathway led to the discovery of a novel function for Src in zebrafish somitogenesis. These two findings (i) that contraction is a driver of myofibril organisation and (ii) that Src is a key protein of the skeletal muscle development provides the potential for new therapeutic approaches in humans.