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Constraints on velocity anisotropy of spherical systems with separable augmented densities  [PDF]
J. An
Physics , 2011, DOI: 10.1088/0004-637X/736/2/151
Abstract: If the augmented density of a spherical anisotropic system is assumed to be multiplicatively separable to functions of the potential and the radius, the radial function, which can be completely specified by the behavior of the anisotropy parameter alone, also fixes the anisotropic ratios of every higher-order velocity moment. It is inferred from this that the non-negativity of the distribution function necessarily limits the allowed behaviors of the radial function. This restriction is translated into the constraints on the behavior of the anisotropy parameter. We find that not all radial variations of the anisotropy parameter satisfy these constraints and thus that there exist anisotropy profiles that cannot be consistent with any separable augmented density.
Equilibrium models of radially anisotropic spherical stellar systems with softened central potentials  [PDF]
E. V. Polyachenko,V. L. Polyachenko,I. G. Shukhman
Physics , 2013, DOI: 10.1093/mnras/stt1236
Abstract: We study a new class of equilibrium two-parametric distribution functions of spherical stellar systems with radially anisotropic velocity distribution of stars. The models are less singular counterparts of the so called generalized polytropes, widely used in works on equilibrium and stability of gravitating systems in the past. The offered models, unlike the generalized polytropes, have finite density and potential in the center. The absence of the singularity is necessary for proper consideration of the radial orbit instability, which is the most important instability in spherical stellar systems. Comparison of the main observed parameters (potential, density, anisotropy) predicted by the present models and other popular equilibrium models is provided.
Dynamic Monte Carlo Simulations of Anisotropic Colloids  [PDF]
Sara Jabbari-Farouji,Emmanuel Trizac
Physics , 2012, DOI: 10.1063/1.4737928
Abstract: We put forward a simple procedure for extracting dynamical information from Monte Carlo simulations, by appropriate matching of the short-time diffusion tensor with its infinite-dilution limit counterpart, which is supposed to be known. This approach --discarding hydrodynamics interactions-- first allows us to improve the efficiency of previous Dynamic Monte Carlo algorithms for spherical Brownian particles. In a second step, we address the case of anisotropic colloids with orientational degrees of freedom. As an illustration, we present a detailed study of the dynamics of thin platelets, with emphasis on long-time diffusion and orientational correlations.
A Spherical Relativistic Anisotropic Compact Star Model  [PDF]
Prakash Chandra Fulara, Archana Sah
International Journal of Astronomy and Astrophysics (IJAA) , 2018, DOI: 10.4236/ijaa.2018.81004
Abstract: We provide solutions to Einsteins field equations for a model of a spherically symmetric anisotropic fluid distribution, relevant to the description of compact stars. The central matter-energy density, radial and tangential pressures, red shift and speed of sound are positive definite and are decreasing monotonically with increasing radial distance from the center of matter distribution of astrophysical object. The causality condition is satisfied for complete fluid distribution. The central value of anisotropy is zero and is increasing monotonically with increasing radial distance from the center of the distribution. The adiabatic index is increasing with increasing radius of spherical fluid distribution. The stability conditions in relativistic compact star are also discussed in our investigation. The solution is representing the realistic objects such as SAXJ1808.4-3658, HerX-1, 4U1538-52, LMC X-4, CenX-3, VelaX-1, PSRJ1614-2230 and PSRJ0348+0432 with suitable conditions.
Gravothermal Catastrophe in Anisotropic Spherical Systems  [PDF]
M. Magliocchetti,G. Pucacco,E. Vesperini
Physics , 1998, DOI: 10.1046/j.1365-8711.1998.01939.x
Abstract: In this paper we investigate the gravothermal instability of spherical stellar systems endowed with a radially anisotropic velocity distribution. We focus our attention on the effects of anisotropy on the conditions for the onset of the instability and in particular we study the dependence of the spatial structure of critical models on the amount of anisotropy present in a system. The investigation has been carried out by the method of linear series which has already been used in the past to study the gravothermal instability of isotropic systems. We consider models described by King, Wilson and Woolley-Dickens distribution functions. In the case of King and Woolley-Dickens models, our results show that, for quite a wide range of amount of anisotropy in the system, the critical value of the concentration of the system (defined as the ratio of the tidal to the King core radius of the system) is approximately constant and equal to the corresponding value for isotropic systems. Only for very anisotropic systems the critical value of the concentration starts to change and it decreases significantly as the anisotropy increases and penetrates the inner parts of the system. For Wilson models the decrease of the concentration of critical models is preceded by an intermediate regime in which critical concentration increases, it reaches a maximum and then it starts to decrease. The critical value of the central potential always decreases as the anisotropy increases.
General spherical anisotropic Jeans models of stellar kinematics: including proper motions and radial velocities  [PDF]
Michele Cappellari
Physics , 2015,
Abstract: Cappellari (2008) presented a flexible and efficient method to model the stellar kinematics of anisotropic axisymmetric and spherical stellar systems. The spherical formalism could be used to model the line-of-sight velocity second moments allowing for essentially arbitrary radial variation in the anisotropy and general luminous and total density profiles. Here we generalize the spherical formalism by providing the expressions for all three components of the projected second moments, including the two proper motion components. A reference implementation is now included in the public JAM package available at http://purl.org/cappellari/software
Spherical Infall Model in a Cosmological Background Density Field  [PDF]
A. Taruya,J. Soda
Physics , 1999, DOI: 10.1046/j.1365-8711.2000.03615.x
Abstract: We discuss the influence of the cosmological background density field on the spherical infall model. The spherical infall model has been used in the Press-Schechter formalism to evaluate the number abundance of clusters of galaxies, as well as to determine the density parameter of the universe from the infalling flow. Therefore, the understanding of collapse dynamics play a key role for extracting the cosmological information. Here, we consider the modified version of the spherical infall model. We derive the mean field equations from the Newtonian fluid equations, in which the influence of cosmological background inhomogeneity is incorporated into the averaged quantities as the {\it backreaction}. By calculating the averaged quantities explicitly, we obtain the simple expressions and find that in case of the scale-free power spectrum, the density fluctuations with the negative spectral index make the infalling velocities slow. This suggests that we underestimate the density parameter $\Omega$ when using the simple spherical infall model. In cases with the index $n>0$, the effect of background inhomogeneity could be negligible and the spherical infall model becomes the good approximation for the infalling flows. We also present a realistic example with the cold dark matter power spectrum. There, the anisotropic random velocity leads to slowing down the mean infalling velocities.
Spherical Model for Anisotropic Ferromagnetic Films  [PDF]
D. A. Garanin
Physics , 1998, DOI: 10.1088/0305-4470/29/10/006
Abstract: The corrections to the Curie temperature T_c of a ferromagnetic film consisting of N layers are calculated for N \gg 1 for the model of D-component classical spin vectors in the limit D \to \infty, which is exactly soluble and close to the spherical model. The present approach accounts, however, for the magnetic anisotropy playing the crucial role in the crossover from 3 to 2 dimensions in magnetic films. In the spatially inhomogeneous case with free boundary conditions the D=\infty model is nonequivalent to the standard spherical one and always leads to the diminishing of T_c(N) relative to the bulk.
Collapse of spherical charged anisotropic fluid spacetimes  [PDF]
F. Cipolletta,R. Giambò
Physics , 2012, DOI: 10.1088/0264-9381/29/24/245008
Abstract: A class of spherical collapsing exact solutions with electromagnetic charge is derived. This class of solutions -- in general anisotropic -- contains however as a particular case the charged dust model already known in literature. Under some regularity assumptions that in the uncharged case give rise to naked singularities, it is shown that the process of shell focusing singularities avoidance -- already known for the dust collapse -- also takes place here, determing shell crossing effects or a completely regular solution.
Density Functional for Anisotropic Fluids  [PDF]
Giorgio Cinacchi,Friederike Schmid
Physics , 2002, DOI: 10.1088/0953-8984/14/46/323
Abstract: We propose a density functional for anisotropic fluids of hard body particles. It interpolates between the well-established geometrically based Rosenfeld functional for hard spheres and the Onsager functional for elongated rods. We test the new approach by calculating the location of the the nematic-isotropic transition in systems of hard spherocylinders and hard ellipsoids. The results are compared with existing simulation data. Our functional predicts the location of the transition much more accurately than the Onsager functional, and almost as good as the theory by Parsons and Lee. We argue that it might be suited to study inhomogeneous systems.
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