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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

Monte-Carlo Simulations of the Dynamical Behavior of the Coulomb Glass

Wappler, T., Vojta, Th., Schreiber, M. 30 October 1998 (has links) (PDF)
We study the dynamical behavior of disordered many-particle systems with long-range Coulomb interactions by means of damage-spreading simulations. In this type of Monte-Carlo simulations one investigates the time evolution of the damage, i.e. the difference of the o ccupation numbers of two systems, subjected to the same thermal noise. We analyze the dependence of the damage on temperature and disorder strength. For zero disorder the spreading transition coincides with the equilibrium phase transition, whereas for finite disorder, we find an evidence for a dynamical phase transition well below the transition temperature of the pure system.
32

MPI-basierte Koppelrandkommunikation und Einfluß der Partitionierung im 3D-Fall

Grabowsky, L. 30 October 1998 (has links) (PDF)
In der vorliegenden Arbeit wird die Anwendung eines bereits im 2D-Fall benutzten Mechanismus zur MPI-basierten Koppelrandkommunikation auf das 3D-FEM-System SPC PMPo-3D beschrieben. Insbesondere soll der Einfluss der Partitionierung auf die Laufzeit im Vergleich mit den Resultaten für das Originalsystem, fuer das entsprechende Untersuchungen bereits in durchgefuehrt wurden, betrachtet werden. Weiterhin wird ein Ausblick auf weitere Optimierungsmöglichkeiten des Verfahrens gegeben.
33

On the preconditioning in the domain decomposition technique for the p-version finite element method. Part II

Ivanov, S. A., Korneev, V. G. 30 October 1998 (has links) (PDF)
P-version finite element method for the second order elliptic equation in an arbitrary sufficiently smooth domain is studied in the frame of DD method. Two types square reference elements are used with the products of the integrated Legendre's polynomials for the coordinate functions. There are considered the estimates for the condition numbers, preconditioning of the problems arising on subdomains and the Schur complement, the derivation of the DD preconditioner. For the result we obtain the DD preconditioner to which corresponds the generalized condition number of order (logp )2 . The paper consists of two parts. In part I there are given some preliminary results for 1D case, condition number estimates and some inequalities for 2D reference element. Part II is devoted to the derivation of the Schur complement preconditioner and conditionality number estimates for the p-version finite element matrixes. Also DD preconditioning is considered.
34

Caracterização de células mesenquimais-like diferenciadas a partir de células-tronco humanas de pluripotência induzida / Characterization of differentiated mesenchymal-like cells from induced pluripotent stem cell

Costa, Péricles Natan Mendes da 09 March 2017 (has links)
As células-tronco de pluripotência induzida (iPSC) representam uma fonte de maior disponibilidade para obtenção de células estromais mesenquimais (MSC). Além disso, as células mesenquimais derivadas de iPSC, as MSC-like, demonstram in vitro uma atividade parácrina e uma taxa de proliferação que as apontam como uma candidata em potencial à terapia celular. Em paralelo, a terapia celular dispõe das propriedades terapêuticas das células estromais mesenquimais do cordão umbilical (UC-MSC), uma população celular de fácil isolamento, rendimento notável, alta capacidade de proliferação e ausência de tumorigenecidade. Assim, perante a relevância das iPSC como fonte alternativa para obtenção de MSC e do desempenho in vitro demonstrado pelas MSC-like, tornou-se necessário a comparação destas com as UC-MSC. Para tanto, iPSC reprogramadas a partir de células mononucleares do sangue periférico (iPS-PBMC) foram diferenciadas em MSC-like e estas por sua vez foram caracterizadas, segundo à aderência ao plástico, expressão de genes e proteínas de pluripotência, expressão de antígenos de superfície CD73, CD90, CD105, CD14, CD19, CD34, CD45 e HLA-DR; capacidade de diferenciação in vitro em adipócitos e osteócitos e posteriormente comparadas as UC-MSC frente a capacidade de proliferação e imunomodulação. As MSC-like obtidas mostraram-se aderentes ao plástico, não pluripotentes e com morfologia fibroblastoide. Demonstraram um perfil imunofenotípico negativo (menos de 2% de células positivas) para marcadores hematopoéticos e HLA-DR, mais de 90% para CD73 e CD90 e menos de 80% para CD105. Ademais, exibiram capacidade de diferenciação osteogênica e adipogênica. Quando comparadas às UC-MSC, em relação à capacidade de proliferação, as MSC-like apresentaram uma taxa de proliferação duas vezes menor. A comparação da capacidade imunomodulatória entre as duas linhagens demonstrou que as UC-MSC foram capazes de conter a proliferação de linfócitos T CD8+ mas não de linfócitos T CD4+. As MSC-like não foram capazes de conter a proliferação de ambas as populações de linfócitos. Os resultados indicam que o protocolo de indução utilizado foi capaz de gerar MSC-like com antígenos de superfície clássico em mesenquimais, baixa expressão de marcadores de pluripotência, hematopoéticos e HLA-DR e com habilidade de se diferenciar em linhagens mesodérmicas, porém, com menor capacidade de proliferação e ausência de propriedades imunomodulatórias. A funcionalidade das MSC-like geradas neste trabalho pode ser proveniente de fatores genéticos e epigenéticos do doador e pelas metodologias de reprogramação da célula somática à iPSC, bem como pela indução da iPSC à MSC. A investigação futura destes fatores pode contribuir para a obtenção de MSC-like funcionalmente semelhante às UC-MSC. / Induced pluripotent stem cells (iPSC) are an easily available mesenchymal stromal cell (MSC) source. Moreover, iPSC-derived mesenchymal cells (MSC-like) demonstrated an in vitro proliferation rate and paracrine activity that make them a potential candidate for cell therapy. Currently the cell therapy uses the therapeutic properties of umbilical cord-derived mesenchymal cells (UC-MSC), an effortlessly isolated cell population with remarkable yield, high proliferation capacity, and absence of tumorigenecity. Thus, considering the iPSC relevance as an alternative MSC source and their in vitro performance, it has become necessary to compare them with UC-MSC. The iPSC reprogrammed from peripheral blood mononuclear cells (iPS-PBMC) were differentiated in MSC-like and these cells were characterized according their adherence to plastic; pluripotency genes and proteins expression; surface antigens expression such CD73, CD90, CD105, CD14, CD19, CD34, CD45, and HLA-DR; in vitro differentiation capacity into adipocytes and osteocytes; and were compared with the UC-MSC proliferation and immunomodulation capacity. The obtained MSC-like were adherent to plastic, not pluripotent, and with fibroblastoid morphology. They demonstrated an immunophenotypic profile with less than 2% hematopoietic and HLA-DR positive cell markers, over 90% of CD73 and CD90, and less than 80% were CD105 positives. They also exhibited osteogenic and adipogenic differentiation capacity. When proliferation rate was compared between the two cell lineages, MSC-like showed a proliferation rate twice smaller than UC-MSC. The UC-MSC immunomodulatory activity contained the proliferation of T CD8+ lymphocytes but did not of T CD4+. MSC-like did not show immunomodulatory activity in the proliferation of CD4+ and CD8+. These results allow the assumption that the applied induction protocol was able to generate MSC-like with the classic mesenchymal surface markers, low pluripotency, hematopoietic, and HLA-DR surface markers expression and with mesodermal lineage differentiation potential, however, with lower proliferation rate and absence of immunomodulatory properties. The MSC-like functionality could be influenced by donor genetic and epigenetic factors as well as by as well as the methodologies of reprogramming of somatic cells to the iPSC and the induction of iPSC to the mesenchymal phenotype. These influential factors should be investigated in deep detail in order to make the generated MSC-like functionally similar to UC-MSC.
35

Near Infrared Spectroscopy : An Introductory Study On Measurement Techniques And Tools For Analysing Moisture Content In Pulp And Paper Media

Dahlman, Niclas January 2012 (has links)
The growing technique of near infrared spectroscopy is used to build fundamental knowledge of how the method might be applied for moisture determination in pulp and paper media. Filter paper was used to investigate the angle and distance dependence, otherwise obscured by the uneven surface of pulp or dry fibers. For contact measurements both filter paper and CTMP-fibers were used. The angle and distance evaluation is based on visual spectral interpretation to later incorporate preprocessing methods of the data followed by a multivariate analysis using PLS. With the knowledge built before the experimental startup, the acquired spectra are known to have many co-linearities and hence, for the purpose of determining the moisture content abundant information which might enable the reduction of data points for evaluation. The distance and angle experiments gave results indicating that the intensity of the reflected light change the information gathered and must be accounted for in calibration. Turning the measuring probe 30 degrees or more at 5 mm distance reduced the effect of high intensity specular reflection. Temperature displayed differences in the spectra, cold samples giving less response than warm samples although no clear correlation was found. Multivariate analysis of the contact measurement samples gave most accurate result after multiple signal correction preprocessing. Distance measurements on fiber rendered models with high RMSEC values and gave no reasonable base for prediction.
36

Minimum Norm Regularization of Descriptor Systems by Output Feedback

Chu, D., Mehrmann, V. 30 October 1998 (has links) (PDF)
We study the regularization problem for linear, constant coefficient descriptor systems $E x^. = AX + Bu, y_1 = Cx, y_2=\Gamma x^.$ by proportional and derivative mixed output feedback. Necessary and sufficient conditions are given, which guarantee that there exist output feedbacks such that the closed-loop system is regular, has index at most one and $E +BG\Gamma$ has a desired rank, i.e. there is a desired number of differential and algebraic equations. To resolve the freedom in the choice of the feedback matrices we then discuss how to obtain the desired regularizing feedback of minimum norm and show that this approach leads to useful results in the sense of robustness only if the rank of E is decreased. Numerical procedures are derived to construct the desired feedbacks gains. These numerical procedures are based on orthogonal matrix transformations which can be implemented in a numerically stable way.
37

Interpolation of non-smooth functions on anisotropic finite element meshes

Apel, Th. 30 October 1998 (has links) (PDF)
In this paper, several modifications of the quasi-interpolation operator of Scott and Zhang (Math. Comp. 54(1990)190, 483--493) are discussed. The modified operators are defined for non-smooth functions and are suited for the application on anisotropic meshes. The anisotropy of the elements is reflected in the local stability and approximation error estimates. As an application, an example is considered where anisotropic finite element meshes are appropriate, namely the Poisson problem in domains with edges.
38

Using POMDP-based Reinforcement Learning for Online Optimization of Teaching Strategies in an Intelligent Tutoring System

Zhang, Pengfei 05 September 2013 (has links)
This thesis is an investigation of "Using POMDP-based Reinforcement Learning for Online Optimization of Teaching Strategies in an Intelligent Tutoring System". A challenge in building an intelligent tutoring system (ITS) is to create and maintain an optimal teaching strategy. We cast an ITS as a partially observable Markov decision process (POMDP), and apply a reinforcement learning (RL) algorithm to learn the optimal teaching strategy through interactions between the system and the students. The optimal teaching strategy is chosen correctly and e ciently in tutoring a student, it is also learned and maintained in an online model. We present an RL algorithm based on POMDP for learning optimal teaching strategy, then describe the experiments and analyse the experimental results. The experiment has showed that the technique can remarkably improve an ITS's teaching performance / Using POMDP-based Reinforcement Learning for Online Optimization of Teaching Strategies in an Intelligent Tutoring System
39

Some Remarks on the Constant in the Strengthened C.B.S. Inequality: Application to $h$- and $p$-Hierarchical Finite Element Discretizations of Elasticity Problems

Jung, M., Maitre, J. F. 30 October 1998 (has links) (PDF)
For a class of two-dimensional boundary value problems including diffusion and elasticity problems it is proved that the constants in the corresponding strengthened Cauchy-Buniakowski-Schwarz (C.B.S.) inequality in the cases of h -hierarchical and p -hierarchical finite element discretizations with triangular meshes differ by the factor 0.75. For plane linear elasticity problems and triangulations with right isosceles tri- angles formulas are presented that show the dependence of the constant in the C.B.S. inequality on the Poisson's ratio. Furthermore, numerically determined bounds of the constant in the C.B.S. inequality are given for three-dimensional elasticity problems discretized by means of tetrahedral elements. Finally, the robustness of iterative solvers for elasticity problems is discussed briefly.
40

Elliptic problems in domains with edges: anisotropic regularity and anisotropic finite element meshes

Apel, T., Nicaise, S. 30 October 1998 (has links) (PDF)
This paper is concerned with the anisotropic singular behaviour of the solution of elliptic boundary value problems near edges. The paper deals first with the description of the analytic properties of the solution in newly defined, anisotropically weighted Sobolev spaces. The finite element method with anisotropic, graded meshes and piecewise linear shape functions is then investigated for such problems; the schemes exhibit optimal convergence rates with decreasing mesh size. For the proof, new local interpolation error estimates in anisotropically weighted spaces are derived. Moreover, it is shown that the condition number of the stiffness matrix is not affected by the mesh grading. Finally, a numerical experiment is described, that shows a good agreement of the calculated approximation orders with the theoretically predicted ones.

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