1,891 research outputs found
Two scales hydrodynamic limit for a model of malignant tumor cells
No full textWe consider a model introduced in [S. Luckhaus, L. Triolo, The continuum reaction-diffusion limit of a stochastic cellular growth model, Rend. Acc. Lincei (S.9) 15 (2004) 215-223] with two species (eta and xi) of particles, representing respectively malignant and normal cells. The basic motions of the eta particles are independent random walks, scaled diffusively. The xi particles move on a slower time scale and obey an exclusion rule among themselves and with the eta particles. The competition between the two species is ruled by a coupled birth and death process. We prove convergence in the hydrodynamic limit to a system of two reaction-diffusion equations with measure valued initial data. (c) 2006 Elsevier Masson SAS. All rights reserved
Ask questions, get sales : close the deak and create long-term relationships / Stephan Schiffman.
No full textIncludes index.v, 168 pages ;In Ask Questions, Get Sales, the author and sales guru Stephan Schiffman helps readers boost their careers to the gold-medal level by teaching them how to strengthen their questioning skills during the sales process. The premise is simple yet effective: In order to be successful, salespeople need to change their mindset from "need-orientated" to "do-orientated". The message of the book centers around six core "do" questions: What do you do? How do you do it? When and where do you do it? Why do you do it that way? Who do you do it with? How can we help you do it better? With this indispensable guide in their briefcase, salespeople will have information at the ready to score big sales over the short term and the long term
A stochastic selection principle in case of fattening for curvature flow
No full textConsider two disjoint circles moving by mean curvature plus a forcing term which makes them touch with zero velocity. It is known that the generalized solution in the viscosity sense ceases to be a curve after the touching (the so-called fattening phenomenon). We show that after adding a small stochastic forcing epsilondW, in the limit epsilon --> 0 the measure selects two evolving curves, the upper and lower barrier in the sense of De Giorgi. Further we show partial results for nonzero epsilon
Study of a model for reference-free plasticity
No full textIn meiner Doktorarbeit untersuche ich ein Kac-artiges Vielteilchen-Modell, das eine Beschreibung von plastischen Verformungen ohne Verwendung einer Referenz-Konfiguration ermöglicht. Im Rahmen des Modells wird die Verformung eines Körpers durch Angabe von Atompositionen beschrieben. Es wird eine Mesoskala zwischen der Mikroskala der Atom-Atom Abstände und der Makroskala des Körpers eingeführt. Um jeden Punkt wird die Konfiguration auf dieser Mesoscala mit einem Bravais-Gitters approximiert. Die Matrix, die dieses Gitter aufspannt, wird als Argument eines elastischen Energiefunktionals verwendet.
Auf diese Weise wird ein Energiefunktional definiert, das die Eigenschaften des Systems festlegt.
Im Ersten Teil meiner Doktorarbeit analysiere ich das Modell im Fall das eine Referenz-Konfiguration lokal existiert.
Ich schätze die Energiedichte einer solchen Konfiguration mit einer Störungsrechung von oben ab und erhalte eine obere Schranke für die Energiebarriere für plastische Relaxation in zwei Dimensionen. Im zweiten Teil untersuche ich Möglichkeiten Lagrange-Koordinaten im Rahmen des Modells zu konstruieren.
Ich beweise, dass für zwei Punkte deren Abstand klein genug sind und die bestimmte Regularitätseigenschaften erfüllen, die Gitterparameter der approximierenden Bravais-Gitter bis auf eine Reparametrisierung nahe beieinander liegen müssen. Dies erlaubt diskrete Ketten von regulären Punkten zur Definition
von Homotopieklassen zu benutzen die mit verallgemeinerten Burgers-Vektoren charakterisiert werden. Es ist mit dieser Technik auch möglich die Kernenergie von Versetzungen nach unten abzuschätzen. Schließlich passe ich eine Methode kontinuierliche Lagrange-Koordinaten, die von L. Mugnai und S. Luckhaus entwickelt wurden, an das Model an und verbessere sie dergestalt, dass ich die Energiedichte mit Hilfe eines Funktionales der Lagrange-Koordinaten nach unten abschätzen kann.I study a Kac-type many particle model that allows a reference-free description of plastic deformation.In the framework of the model the state of the body is given by a set of atom position. The typical atom-atom distance is the microscopic scale. The size of the body is the macroscopic scale. Around each point a lattice is fitted to the configuration on a mesoscopic scale. The lattice parameters are used as an argument of a non-linear elasticity energy functional. Hence, this procedure allows to define an free-energy functional of a particle configuration.
In the first part of my thesis I analyze the model in the case that a reference configuration exists locally. I bound the energy-density of such a configuration from above with a pertubative calculation and obtain an upper bound for the energy barrier of plastic deformation for dimension two.
In the second part I explore the possibility to construct Lagrangian coordinates in the framework of the model.
I prove that for two points that are close to each other and that fulfill certain regularity assumptions the fitted lattice parameters are close to each other up to a reparametrisation. This allows to use discrete chains of regular points for homotopy type arguments and define a generalized Burgers vector as a topological quantity. I also use this method to get a lower bound for the core energy of a dislocation.
Finally, I adapt a method to construct continuous Lagrangian coordinates presented in by L.Mugnai and S.Luckhaus to my model and improve it to a point where I can use a functional of these Lagrangian coordinate as a lower bound for the energy of the model
Unemployment Benefits and Unemployment Rates of Low-Skilled and Elder Workers in West Germany: A Search Equilibrium Approach
No full textApproach Author & abstract Download 16 References 1 Citations Related works & more Corrections Author Listed: Launov, Andrey ([email protected]) (University of Kent) Wolff, Joachim ([email protected]) (Institute for Employment Research (IAB), Nuremberg) Klasen, Stephan ([email protected]) (University of Göttingen) Registered: Stephan Klasen Abstract In this paper we investigate whether the extension of the entitlement to unemployment benefits in the mid 80s can explain the increase in the unemployment rates of unskilled and elder workers in western Germany. To answer this question we estimate a version of the Burdett-Mortensen search equilibrium model and analyze how workers’ search behaviour responded to these reforms. We try both nonparametric and fully-parametric estimation methods and identify the cases in which the nonparametric approach cannot be applied. We find that the entitlement reforms are largely responsible for the increase of unemployment among unskilled workers
Unemployment Benefits and Unemployment Rates of Low-Skilled and Elder Workers in West Germany: A Search Equilibrium Approach
No full textApproach Author & abstract Download 16 References 1 Citations Related works & more Corrections Author Listed: Launov, Andrey ([email protected]) (University of Kent) Wolff, Joachim ([email protected]) (Institute for Employment Research (IAB), Nuremberg) Klasen, Stephan ([email protected]) (University of Göttingen) Registered: Stephan Klasen Abstract In this paper we investigate whether the extension of the entitlement to unemployment benefits in the mid 80s can explain the increase in the unemployment rates of unskilled and elder workers in western Germany. To answer this question we estimate a version of the Burdett-Mortensen search equilibrium model and analyze how workers’ search behaviour responded to these reforms. We try both nonparametric and fully-parametric estimation methods and identify the cases in which the nonparametric approach cannot be applied. We find that the entitlement reforms are largely responsible for the increase of unemployment among unskilled workers
Measuring Vulnerability to Poverty Using Long-Term Panel Data
No full textMeasuring Vulnerability to Poverty Using Long-Term Panel Data Author & abstract Download & other version 16 References 4 Citations Related works & more Corrections Author Listed: Katja Landau (Georg-August-University Göttingen) Stephan Klasen (Georg-August-University Göttingen) Walter Zucchini (Georg-August-University Göttingen) Registered: Stephan Klasen Abstract We investigate the accuracy of ex ante assessments of vulnerability to income poverty using cross-sectional data and panel data. We use long-term panel data from Germany and apply di fferent regression models, based on household covariates and previous-year equivalence income, to classify a household as vulnerable or not. Predictive performance is assessed using the Receiver Operating Characteristics (ROC), which takes account of false positive as well as true positive rates. Estimates based on cross-sectional data are much less accurate than those based on panel data, but for Germany, the accuracy of vulnerability predictions is limited even when panel data are used. In part this low accuracy is due to low poverty incidence and high mobility in and out of poverty
Measuring Vulnerability to Poverty Using Long-Term Panel Data
No full textMeasuring Vulnerability to Poverty Using Long-Term Panel Data Author & abstract Download & other version 16 References 4 Citations Related works & more Corrections Author Listed: Katja Landau (Georg-August-University Göttingen) Stephan Klasen (Georg-August-University Göttingen) Walter Zucchini (Georg-August-University Göttingen) Registered: Stephan Klasen Abstract We investigate the accuracy of ex ante assessments of vulnerability to income poverty using cross-sectional data and panel data. We use long-term panel data from Germany and apply di fferent regression models, based on household covariates and previous-year equivalence income, to classify a household as vulnerable or not. Predictive performance is assessed using the Receiver Operating Characteristics (ROC), which takes account of false positive as well as true positive rates. Estimates based on cross-sectional data are much less accurate than those based on panel data, but for Germany, the accuracy of vulnerability predictions is limited even when panel data are used. In part this low accuracy is due to low poverty incidence and high mobility in and out of poverty
Evaluation of in-store processes related to returnable packaging services offered in grocery stores - the store management perspective
No full textAuthor Stephan LehnerMasterarbeit Universität Linz 202
Evaluation of in-store processes related to returnable packaging services offered in grocery stores - the store management perspective
No full textAuthor Stephan LehnerMasterarbeit Universität Linz 202
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