52 research outputs found

    Modeling dislocation sources and size effects at initial yield in continuum plasticity

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    Size effects at initial yield (prior to stage II) of idealized micron-sized specimens are modeled within a continuum model of plasticity. Two different aspects are considered: specification of a density of dislocation sources that represent the emission of dislocation dipoles, and the presence of an initial, spatially inhomogeneous excess dislocation content. Discreteness of the source distribution appears to lead to a stochastic response in stress-strain curves, with the stochasticity diminishing as the number of sources increases. Variability in stress-strain response due to variations of source distribution is also shown. These size effects at initial yield are inferred to be due to physical length scales in dislocation mobility and the discrete description of sources that induce internal-stress-related effects, and not due to length-scale effects in the mean-field strain-hardening response (as represented through a constitutive equation)

    Osmotically Regulated Two-Compartment Asymmetric Membrane Capsules for Simultaneous Controlled Release of Anti-Hypertensive Drugs

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    In the present study, asymmetric membrane capsules (AMCs) with two compartments were successfully developed for simultaneous delivery of two poorly water-soluble drugs, Atenolol and Amlodipine Besylate, by using solubility modulation approach. Scanning electron microscopy (SEM) before dissolution showed presence of outer dense region and inner porous region for the prepared asymmetric membrane and the pore size increased after dissolution for both outer and inner layer. Diffuse reflectance spectroscopy (DRS) showed no incompatibility between the drug(s) and the excipients used in the study. The developed system was able to control the release of ATN and AMB by increasing the solubility through buffering agents of different strengths (0.25N to 1.0N). As the level of buffering agent was increased, the solubility of drugs also increased inside the asymmetric membrane capsule. The developed system was independent of the agitation intensity of the dissolution fluid but was dependent on the polymer diffusibility and osmotic pressure of the media, which clearly stated that osmotic pumping was the primary mechanism of drug(s) release from AMCs. The results of in-vitro demonstration of effect of membrane thickness on dissolution fluid entering AMCs showed that as the membrane thickness increased the volume of dissolution fluid entering into AMC decreased. The release kinetic studies of different formulations of AMCs showed that formulation code six, which consists of the highest amount of osmotic agents and optimum amount of buffering agents, was the best formulation, and it followed zero order release kinetics (r2=0.9990 for ATN and r2=0.9988 for AMB)

    Correlation between leukocytospermia and oxidative stress in male partners of infertile couples with leukocytospermia

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    Background: The last century has seen rapid advances in the diagnosis and management of male infertility but still the cause eludes us in a majority of cases. The World Health Organization (WHO) has defined leukocytospermia as >1 million WBC/mL of semen. However, the clinical significance of increased leukocyte infiltration in semen, that is, leukocytospermia, is currently a subject of controversy. Evidence from several recent studies indicates that leukocytospermia could significantly contribute to male infertility. Of the many causes of male infertility, oxidative stress has been identified as one factor that affects fertility status and thus, has been extensively studied in recent years. A study was conducted to evaluate the relationship between leukocytospermia and oxidative stress.  Methods: 88 men with leukocytospermia were included in the study. Semen parameters, no. of pus cells present and oxidative stress were noted. The correlation between leukocytospermia and ROS level was found using Pearson correlation coefficient.Results: Significant positive correlation (r = 0.882, P <0.001) was observed between leukocytospermia and oxidative stress suggesting leukocytes are the main source of Reactive Oxygen Species (ROS) in semen.  Conclusions: Significant positive correlation between oxidative stress and leukocytospermia was found in this study suggesting the need of further robust clinical trials to evaluate the role of antioxidants in improving the fertility outcome in infertile men with pyospermia

    Geo-Mechanical Modelling for Optimization of Rock Slope in an Opencast Coal Mine

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    Jharia Coalfield, in India, is a prime storehouse of the coking coal. It contains as many as thirty contiguous seams. Multiplicity of seams has contributed to a number of problems, fire, inundated workings, goaf out area and disturbed strata condition. However, due to various geotechnical problems, it was not possible to fully extract coal by underground mining method. Opencast mining is now planned for extraction of virgin coal seams upto an ultimate depth of 500 m for ensuring maximum resources recovery. There are various modeling methods to analyze the behaviour of slopes. To achieve the objective for ensuring the safe slopes with steepest possible angle, the prototype of one of the mine was simulated in physical model i.e. Equivalent material model (EM) incorporating all the pertinent characteristics of rock mass, mining method and geological discontinuities properties. The results of EM are corroborated by Numerical method using Computer code FLAC- 2D. It was observed that when slope reached near the bottom seam the resultant vector of various monitoring points showed toppling tendency of slopes whereas high stress concentration was observed in the toe region and decreases towards the surface

    The development and validation of a scoring tool to predict the operative duration of elective laparoscopic cholecystectomy

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    Background: The ability to accurately predict operative duration has the potential to optimise theatre efficiency and utilisation, thus reducing costs and increasing staff and patient satisfaction. With laparoscopic cholecystectomy being one of the most commonly performed procedures worldwide, a tool to predict operative duration could be extremely beneficial to healthcare organisations. Methods: Data collected from the CholeS study on patients undergoing cholecystectomy in UK and Irish hospitals between 04/2014 and 05/2014 were used to study operative duration. A multivariable binary logistic regression model was produced in order to identify significant independent predictors of long (> 90 min) operations. The resulting model was converted to a risk score, which was subsequently validated on second cohort of patients using ROC curves. Results: After exclusions, data were available for 7227 patients in the derivation (CholeS) cohort. The median operative duration was 60 min (interquartile range 45–85), with 17.7% of operations lasting longer than 90 min. Ten factors were found to be significant independent predictors of operative durations > 90 min, including ASA, age, previous surgical admissions, BMI, gallbladder wall thickness and CBD diameter. A risk score was then produced from these factors, and applied to a cohort of 2405 patients from a tertiary centre for external validation. This returned an area under the ROC curve of 0.708 (SE = 0.013, p  90 min increasing more than eightfold from 5.1 to 41.8% in the extremes of the score. Conclusion: The scoring tool produced in this study was found to be significantly predictive of long operative durations on validation in an external cohort. As such, the tool may have the potential to enable organisations to better organise theatre lists and deliver greater efficiencies in care

    Apprentissage, sĂ©lection et codage de nouvelles transformĂ©es de blocs dans et pour la boucle d’optimisation de codeurs vidĂ©o

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    Transforms are a key element in block-based video coding systems which, in conjugation with quantization, is important for the overall compression efficiency of the system. This thesis explores multiple transform-based learning schemes.A first contribution of this work is dedicated to the evaluation of transform learning schemes with two flavors 1) online learning, and 2) offline learning. The two approaches are compared against each other and their respective appropriability is studied in detail. Some novel techniques are proposed in this work to 1) improve the stability of the learning scheme and 2) to reduce the signaling cost.In a second contribution of this thesis, the offline multiple-transform learning schemes already known in the literature are further extended with the aims to altogether 1) provide more generic transforms that are less biased towards specific classes of contents, 2) achieve higher compression gains, 3) reduce encoding and decodingcomputational complexity. An improved Mode Dependent Transform Competition (IMDTC) scheme is proposed which provides a considerable gain of over 5% compared to standard HEVC under All Intra (AI) configuration at a complexity just 2.9 times the standard HEVC.Finally, the content adaptability aspect of the offline learning is explored through a novel content-adapted pool-based transform learning approach where several multiple-transform sets are learned on different contents and pooled together. During the coding of a given region of an image, one transform set is selected locally from thepool. Numerical results show the high potential of this approach against the conservative online and offline approaches.Les transformĂ©es sont un Ă©lĂ©ment clĂ© dans les systĂšmes de codage vidĂ©o par blocs. Cette thĂšse approfondit les schĂ©mas d’apprentissage Ă  multiples transformĂ©es.Une premiĂšre contribution de ce travail est consacrĂ©e Ă  l’évaluation de schĂ©mas d’apprentissage de transformĂ©es de deux types en ligne et hors ligne. Les deux approches sont comparĂ©es en dĂ©tail et leur pertinence respective rĂ©vĂ©lĂ©es. Nous proposons ensuite plusieurs techniques afin d’amĂ©liorer la stabilitĂ© du systĂšme d’apprentissageet rĂ©duire le coĂ»t de la signalisation.Une seconde contribution concerne les schĂ©mas d’apprentissage multi-transformĂ©es hors ligne dĂ©jĂ  connus qui sont Ă©tendus avec pour objectifs de 1) fournir des transformĂ©es plus gĂ©nĂ©riques et moins biaisĂ©es, 2) obtenir des gains de compression plus Ă©levĂ©s, 3) rĂ©duire la complexitĂ© d’encodage et de dĂ©codage. On propose unschĂ©ma dit IMDTC (Improved Mode Dependent Transform Competition) qui offre un gain de codage trĂšs significatif, plus de 5% par rapport Ă  HEVC standard sous la configuration All Intra (AI), avec une augmentation de complexitĂ© raisonnable.Enfin, l’adaptabilitĂ© au contenu de l’apprentissage hors ligne est Ă©tendue en explorant une nouvelle approche d’apprentissage des transformĂ©es basĂ©e sur des jeux de transformĂ©es adaptĂ©es Ă  des contenus. Plusieurs ensembles contenant de multiples transformĂ©es sont appris sur diffĂ©rents contenus et regroupĂ©s en jeu. Lors du codage d’une rĂ©gion donnĂ©e d’une image, un ensemble de transformĂ©es est sĂ©lectionnĂ© localement Ă  partir du jeu. Les rĂ©sultats numĂ©riques montrent le potentiel Ă©levĂ© de cette approche par rapport aux approches classiques en ligne et hors ligne

    Simulating Dislocation Densities with Finite Element Analysis

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    A one-dimensional set of nonlinear time-dependent partial differential equations developed by Acharya (2010) is studied to observe how differing levels of applied strain affect dislocation walls. The framework of this model consists of a convective and diffusive term which is used to develop a linear system of equations to test two methods of the finite element method. The linear system of partial differential equations is used to determine whether the standard or Discontinuous Galerkin method will be used. The Discontinuous Galerkin method is implemented to discretize the continuum model and the results of simulations involving zero and non-zero applied strain are computed. The evolution in time of functions for plastic deformation, dislocation density, and internal shear stress are plotted and discussed

    Modeling Dislocation Sources and Plastic Flow through Grain Boundaries in Mesoscopic Field Dislocation Mechanics

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    This work involves the modeling and understanding of mechanical behavior of crystalline materials using a continuum approach, Phenomenological Mesoscopic Field Dislocation Mechanics (PMFDM; Acharya and Roy, 2006). Specifically, this thesis contains three major parts. The first part involves the modeling of some aspects of dislocation sources that represent the emission of dislocation dipoles. The developed strategy is then used to investigate the dependence of mechanical response on the external dimensions of idealized single crystalline cubical samples with varying source and initial excess dislocation density distribution. The second part involves the modeling of plastic flow through grain boundaries in polycrystalline materials. The model is then used to analyze dislocation microstructure development in polycrystalline thin films and its effect on the mechanical response. The effect of thickness and the presence/absence of surface passivation on the plastic deformation of thin films is also studied. Results from these simulations are found to be in good qualitative agreement with experimental observations. The last part involves the numerical implementation of finite deformation PMFDM theory. The developed computational tool is capable of analyzing the deformation of crystalline materials under geometric and material nonlinearity.</p

    Plastic deformation of multicrystalline thin films: Grain size distribution vs. grain orientation

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    A continuum model of plasticity, Mesoscopic Field Dislocation Mechanics (MFDM), is used to study the interplay between grain size and grain orientation on the mechanical response of multicrystalline thin films undergoing plane strain tension. It is shown that the grain size dependence in the case of multicrystals is controlled by those grains which are relatively more susceptible to plastic deformation. This effect is captured to some extent by conventional crystal plasticity theory; however, the explicit incorporation of polar dislocations in the MFDM model significantly enhances the overall mechanical response as demonstrated in the paper
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