From extended phase space dynamics to fluid theory

We derive a fluid theory for spin-1/2 particles starting from an extended kinetic model based on a spin-projected density matrix formalism. The evolution equation for the spin density is found to contain a pressure-like term. We give an example where this term is important by looking at a linear mode previously found in a spin kinetic model.Comment: 4 page

On optical black holes in moving dielectrics

We study the optical paths of the light rays propagating inside a nonlinear moving dielectric media. For the rapidly moving dielectrics we show the existence of a distinguished surface which resembles, as far as the light propagation is concerned, the event horizon of a black hole. Our analysis clarifies the physical conditions under which electromagnetic analogues of the gravitational black holes can eventually be obtained in laboratory.Comment: 5 pages, 2 figures, revtex

Stability of Circular Orbits in General Relativity: A Phase Space Analysis

Phase space method provides a novel way for deducing qualitative features of nonlinear differential equations without actually solving them. The method is applied here for analyzing stability of circular orbits of test particles in various physically interesting environments. The approach is shown to work in a revealing way in Schwarzschild spacetime. All relevant conclusions about circular orbits in the Schwarzschild-de Sitter spacetime are shown to be remarkably encoded in a single parameter. The analysis in the rotating Kerr black hole readily exposes information as to how stability depends on the ratio of source rotation to particle angular momentum. As a wider application, it is exemplified how the analysis reveals useful information when applied to motion in a refractive medium, for instance, that of optical black holes.Comment: 20 pages. Accepted for publication in Int. J. theor. Phy

Factors associated with first return to work and sick leave durations in workers with common mental disorders

Background: Associations are examined between socio-demographic, medical, work-related and organizational factors and the moment of first return to work (RTW) (within or after 6 weeks of sick leave) and total sick leave duration in sick leave spells due to common mental disorders. Methods: Data are derived from a Dutch database, build to provide reference data for sick leave duration for various medical conditions. The cases in this study were entered in 2004 and 2005 by specially trained occupational health physicians, based on the physician's assessment of medical and other factors. Odds ratios for first RTW and sick leave durations are calculated in logistic regression models. Results: Burnout, depression and anxiety disorder are associated with longer sick leave duration. Similar, but weaker associations were found for female sex, being a teacher, small company size and moderate or high psychosocial hazard. Distress is associated with shorter sick leave duration. Medical factors, psychosocial hazard and company size are also and analogously associated with first RTW. Part-time work is associated with delayed first RTW. The strength of the associations varies for various factors and for different sick leave durations. Conclusion: The medical diagnosis has a strong relation with the moment of first RTW and the duration of sick leave spells in mental disorders, but the influence of demographic and work-related factors should not be neglected

Evaluation of the passive safety in cars adapted with steering control devices for disabled drivers

The purpose of this research is to analyse the influence of steering control devices for disabled people on passive safety. It is based on the advances made in the modelling and simulation of the driver position and in the suit verification test. The influence of these devices is studied through airbag deployment and/or its influence on driver safety. We characterise the different adaptations that are used in adapted cars that can be found mounted in vehicles in order to generate models that are verified by experimental test. A three-dimensional design software package was used to develop the model. The simulations were generated using a dynamic simulation program employing LS-DYNA finite elements. This program plots the geometry and assigns materials. The airbag is shaped, meshed and folded just as it is mounted in current vehicles. The thermodynamic model of expansion of gases is assigned, and the contact interfaces are defined. Static tests were carried out on the deployment of the airbag to contrast with and to validate the computational models and to measure the behaviour of the airbag when there are steering adaptations mounted in the vehicle. © 2011 Taylor & Francis.Masiá Vañó, J.; Eixerés Tomás, B.; Dols Ruiz, JF. (2011). Evaluation of the passive safety in cars adapted with steering control devices for disabled drivers. International Journal of Crashworthiness. 16(1):75-83. doi:10.1080/13588265.2010.514772S7583161Bedewi, N. E., Marzougui, D., & Motevalli, V. (1996). Evaluation of parameters affecting simulation of airbag deployment and interaction with occupants. International Journal of Crashworthiness, 1(4), 339-354. doi:10.1533/cras.1996.0025Chawla, A., Mukherjee, S., & Sharma, A. (2005). Development of FE meshes for folded airbags. International Journal of Crashworthiness, 10(3), 259-266. doi:10.1533/ijcr.2005.0343Cheng, Z., Rizer, A. L., & Pellettiere, J. A. (2003). Modeling and Simulation of OOP Occupant-Airbag Interaction. SAE Technical Paper Series. doi:10.4271/2003-01-0510Crandall, J. R., Bass, C. R., Pikey, W. D., Miller, H. J., Sikorski, J., & Wilkins, M. (1996). Thoracic response and injury with belt, driver side airbag, and force limited belt restraint systems. International Journal of Crashworthiness, 2(1), 119-132. doi:10.1533/cras.1997.0039Dalrymple, G. (1996). Effects of Assistive Steering Devices on Air Bag Deployment. SAE Technical Paper Series. doi:10.4271/960223Khan, M. U., & Moatamedi, M. (2008). A review of airbag test and analysis. International Journal of Crashworthiness, 13(1), 67-76. doi:10.1080/13588260701731674Khan, M. U., Moatamedi, M., Souli, M., & Zeguer, T. (2008). Multiphysics out of position airbag simulation. International Journal of Crashworthiness, 13(2), 159-166. doi:10.1080/13588260701788385Richert, J., Coutellier, D., Götz, C., & Eberle, W. (2007). Advanced smart airbags: The solution for real-life safety? International Journal of Crashworthiness, 12(2), 159-171. doi:10.1080/13588260701433461Ruff, C., Jost, T., & Eichberger, A. (2007). Simulation of an airbag deployment in out-of-position situations. Vehicle System Dynamics, 45(10), 953-967. doi:10.1080/0042311070153830

Scalar quantum kinetic theory for spin-1/2 particles: mean field theory

Starting from the Pauli Hamiltonian operator, we derive a scalar quantum kinetic equations for spin-1/2 systems. Here the regular Wigner two-state matrix is replaced by a scalar distribution function in extended phase space. Apart from being a formulation of principal interest, such scalar quantum kinetic equation makes the comparison to classical kinetic theory straightforward, and lends itself naturally to currently available numerical Vlasov and Boltzmann schemes. Moreover, while the quasi-distribution is a Wigner function in regular phase space, it is given by a Q-function in spin space. As such, nonlinear and dynamical quantum plasma problems are readily handled. Moreover, the issue of gauge invariance is treated. Applications (e.g. ultra-dense laser compressed targets and their diagnostics), possible extensions, and future improvements of the presented quantum statistical model are discussed.Comment: 21 pages, 2 figure

Spin kinetic theory - quantum kinetic theory in extended phase space

The concept of phase space distribution functions and their evolution is used in the case of en enlarged phase space. In particular, we include the intrinsic spin of particles and present a quantum kinetic evolution equation for a scalar quasi-distribution function. In contrast to the proper Wigner transformation technique, for which we expect the corresponding quasi-distribution function to be a complex matrix, we introduce a spin projection operator for the density matrix in order to obtain the aforementioned scalar quasi-distribution function. There is a close correspondence between this projection operator and the Husimi (or Q) function used extensively in quantum optics. Such a function is based on a Gaussian smearing of a Wigner function, giving a positive definite distribution function. Thus, our approach gives a Wigner-Husimi quasi-distribution function in extended phase space, for which the reduced distribution function on the Bloch sphere is strictly positive. We also discuss the gauge issue and the fluid moment hierarchy based on such a quantum kinetic theory.Comment: 10 pages, to appear in Transport Theory and Statistical Physics, proceedings of Vlasovia III, 200

Spin and magnetization effects in plasmas

We give a short review of a number of different models for treating magnetization effects in plasmas. In particular, the transition between kinetic models and fluid models is discussed. We also give examples of applications of such theories. Some future aspects are discussed.Comment: 18 pages, 1 figure. To appear in Plasma Physics and Controlled Fusion, Special Issue for the 37th ICPP, Santiago, Chil

Kinematic self-similar locally rotationally symmetric models

A brief summary of results on kinematic self-similarities in general relativity is given. Attention is focussed on locally rotationally symmetric models admitting kinematic self-similar vectors. Coordinate expressions for the metric and the kinematic self-similar vector are provided. Einstein's field equations for perfect fluid models are investigated and all the homothetic perfect fluid solutions admitting a maximal four-parameter group of isometries are given.Comment: 12 pages, LaTeX, final version, to appear in Class. Quantum Gra