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Search Results: 1 - 10 of 9827 matches for " Stefan Horatschek "
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Uniformly Rotating Homogeneous Rings in post-Newtonian Gravity
Stefan Horatschek,David Petroff
Physics , 2010, DOI: 10.1111/j.1365-2966.2010.17241.x
Abstract: In this paper uniformly rotating relativistic rings are investigated analytically utilizing two different approximations simultaneously: (1) an expansion about the thin ring limit (the cross-section is small compared with the size of the whole ring) (2) post-Newtonian expansions. The analytic results for rings are compared with numerical solutions.
Uniformly Rotating Homogeneous Rings in Newtonian Gravity
Stefan Horatschek,David Petroff
Physics , 2008,
Abstract: In this paper, we describe an analytical method for treating uniformly rotating homogeneous rings without a central body in Newtonian gravity. We employ series expansions about the thin ring limit and use the fact that in this limit the cross-section of the ring tends to a circle. The coefficients can in principle be determined up to an arbitrary order. Results are presented here to the 20th order and compared with numerical results.
Uniformly Rotating Polytropic Rings in Newtonian Gravity
David Petroff,Stefan Horatschek
Physics , 2008, DOI: 10.1111/j.1365-2966.2008.13540.x
Abstract: An iterative method is presented for solving the problem of a uniformly rotating, self-gravitating ring without a central body in Newtonian gravity by expanding about the thin ring limit. Using this method, a simple formula relating mass to the integrated pressure is derived to the leading order for a general equation of state. For polytropes with the index n=1, analytic coefficients of the iterative approach are determined up to the third order. Analogous coefficients are computed numerically for other polytropes. Our solutions are compared with those generated by highly accurate numerical methods to test their accuracy.
A Roche Model for Uniformly Rotating Rings
Stefan Horatschek,David Petroff
Physics , 2008, DOI: 10.1111/j.1365-2966.2008.14122.x
Abstract: A Roche model for describing uniformly rotating rings is presented and the results are compared with numerical solutions to the full problem for polytropic rings. In the thin ring limit, the surfaces of constant pressure including the surface of the ring itself are given in analytic terms, even in the mass-shedding case.
Uniformly Rotating Rings in General Relativity
Thomas Fischer,Stefan Horatschek,Marcus Ansorg
Physics , 2005, DOI: 10.1111/j.1365-2966.2005.09629.x
Abstract: In this paper, we discuss general relativistic, self-gravitating and uniformly rotating perfect fluid bodies with a toroidal topology (without central object). For the equations of state describing the fluid matter we consider polytropic as well as completely degenerate, perfect Fermi gas models. We find that the corresponding configurations possess similar properties to the homogeneous relativistic Dyson rings. On the one hand, there exists no limit to the mass for a given maximal mass-density inside the body. On the other hand, each model permits a quasistationary transition to the extreme Kerr black hole.
Comparison of Different Control Algorithms for a Gantry Crane System  [PDF]
Stefan Bruins
Intelligent Control and Automation (ICA) , 2010, DOI: 10.4236/ica.2010.12008
Abstract: For a gantry crane system, this paper presents a comparison between four control algorithms. These algo-rithms are being compared on simplicity, stability and robustness. Goal for the controller is to move the load on a gantry crane to a new position with minimal overshoot of the load and maximal speed of the load. An-other goal is to provide an insight in the behaviour of the possible controllers. In this article a parallel P-controller, cascade P-controller, fuzzy controller and an internal model controller are used. To be able to validate and design the controllers a model is derived from the gantry crane. The controllers and the model are being implemented in Matlab Simulink. Finally the controllers are validated and tuned in Labview on a laboratory gantry scrane scale model. Main conclusion is that all presented controllers can be used as a con-troller for the gantry crane system but the fuzzy controller is showing the best performance.
Simulation and Injection Molding of Ring-Shaped Polymer Bonded Nickel Braze Metal Composite Preforms Based on Rheological and Thermal Analyses  [PDF]
Stefan Kirchberg
Open Journal of Composite Materials (OJCM) , 2013, DOI: 10.4236/ojcm.2013.32004

Rheological and thermal properties of LD-PE and LD-PE + 65 vol% Ni composite were examined by viscosity, pvt and thermal conductivity measurements at a wide range of shear rate, temperature and pressure. The typical shear-thinning viscosity of LD-PE polymer melt was enhanced up to four times by adding 65 vol% Ni braze metal particles. LD-PE show increasing specific volume versus temperature, decreasing with pressure and braze particle filler content. Variation of specific volume of LD-PE was reduced to 5% by admixing 65 vol% rigid Ni braze metal particles. Thermal conductivity of LD-PE was increased up to 15 times in the composite, reduced by decreasing pressure at temperature exceeding 80. Furthermore, thermal analysis was performed in modulated DSC to determine the specific heat capacity in wide temperature range. Viscosity and pvt-data were fitted using Cross-WLF equation and 2-domain Tait-pvt model, respectively. Simulation of LD-PE and LD-PE + 65 vol% Ni composite was performed based on rheological and thermal properties to define processing parameters. Simulation and injection molding of ring-shaped LD-PE + 65 vol% Ni composite braze metal preforms were performed successfully.

Creating a Strategic Partnership for Educating Nurse Practitioner Students about Sexual Health  [PDF]
Stefan Rowniak
Creative Education (CE) , 2014, DOI: 10.4236/ce.2014.515156

Sexual health is an essential and often neglected component of primary care. Nurse practitioners are ideal members of the healthcare team to be providing sexual health information, diagnoses, and treatments. Unfortunately, this is an area that has been lacking in the education of all healthcare providers. This paper describes a program that incorporates sexual health into the curriculum for nurse practitioner students through collaboration between the university school of nursing and the local health department. Given the increasing shortage of clinical sites and the need to train nurse practitioners to be competent in the delivery of sexual health, this is a model that could benefit other schools of nursing.

On the Stability of Stochastic Jump Kinetics  [PDF]
Stefan Engblom
Applied Mathematics (AM) , 2014, DOI: 10.4236/am.2014.519300
Abstract: Motivated by the lack of a suitable constructive framework for analyzing popular stochastic models of Systems Biology, we devise conditions for existence and uniqueness of solutions to certain jump stochastic differential equations (SDEs). Working from simple examples we find reasonable and explicit assumptions on the driving coefficients for the SDE representation to make sense. By “reasonable” we mean that stronger assumptions generally do not hold for systems of practical interest. In particular, we argue against the traditional use of global Lipschitz conditions and certain common growth restrictions. By “explicit”, finally, we like to highlight the fact that the various constants occurring among our assumptions all can be determined once the model is fixed. We show how basic long time estimates and some limit results for perturbations can be derived in this setting such that these can be contrasted with the corresponding estimates from deterministic dynamics. The main complication is that the natural path-wise representation is generated by a counting measure with an intensity that depends nonlinearly on the state.
Product Repositioning in the UK Newspaper Industry  [PDF]
Stefan Behringer
Theoretical Economics Letters (TEL) , 2016, DOI: 10.4236/tel.2016.65099
Abstract: This paper investigates the alleged predatory behaviour in the UK quality newspaper industry in the 1990s in terms of product repositioning using a horizontal differentiation model and industry data. It supports the call for an effects based approach to competition law by showing that non-price conduct can be a critical and less visible, complementary means to achieve a predatory goal than mere price cuts.
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