Disks Surviving the Radiation Pressure of Radio Pulsars

The radiation pressure of a radio pulsar does not necessarily disrupt a surrounding disk. The position of the inner radius of a thin disk around a neutron star can be estimated by comparing the electromagnetic energy density generated by the neutron star with the kinetic energy density of the disk. Inside the light cylinder, the near zone electromagnetic field is essentially the dipole magnetic field, and the inner radius is the conventional Alfven radius. Far outside the light cylinder, in the radiation zone, $E=B$ and the electromagnetic energy density is $/c \propto 1/r^2$ where $S$ is the Poynting vector. Shvartsman (1970) argued that a stable equilibrium can not be found in the radiative zone because the electromagnetic energy density dominates over the kinetic energy density, with the relative strength of the electromagnetic stresses increasing with radius. In order to check whether this is true also near the light cylinder, we employ global electromagnetic field solutions for rotating oblique magnetic dipoles (Deutsch 1955). Near the light cylinder the electromagnetic energy density increases steeply enough with decreasing $r$ to balance the kinetic energy density at a stable equilibrium. The transition from the near zone to the radiation zone is broad. The radiation pressure of the pulsar can not disrupt the disk for values of the inner radius up to about twice the light cylinder radius if the rotation axis and the magnetic axis are orthogonal. This allowed range beyond the light cylinder extends much further for small inclination angles. We discuss implications of this result for accretion driven millisecond pulsars and young neutron stars with fallback disks.Comment: Accepted by Astrophysical Journal, final version with a minor correctio

Maximum Mass-Radius Ratios for Charged Compact General Relativistic Objects

Upper limits for the mass-radius ratio and total charge are derived for stable charged general relativistic matter distributions. For charged compact objects the mass-radius ratio exceeds the value 4/9 corresponding to neutral stars. General restrictions for the redshift and total energy (including the gravitational contribution) are also obtained.Comment: 6 pages, 2 figures, RevTex. To appear in Europhys. Let

Nonstationary heat conduction in one-dimensional models with substrate potential

The paper investigates non-stationary heat conduction in one-dimensional models with substrate potential. In order to establish universal characteristic properties of the process, we explore three different models --- Frenkel-Kontorova (FK), phi4+ ($\phi^4$+) and phi4- ($\phi^4-$). Direct numeric simulations reveal in all these models a crossover from oscillatory decay of short-wave perturbations of the temperature field to smooth diffusive decay of the long-wave perturbations. Such behavior is inconsistent with parabolic Fourier equation of the heat conduction and clearly demonstrates the necessity of hyperbolic models. The crossover wavelength decreases with increase of average temperature. The decay patterns of the temperature field almost do not depend on the amplitude of the perturbations, so the use of linear evolution equations for temperature field is justified. In all model investigated, the relaxation of thermal perturbations is exponential -- contrary to linear chain, where it follows a power law. However, the most popular lowest-order hyperbolic generalization of the Fourier law, known as Cattaneo-Vernotte (CV) or telegraph equation (TE) is not valid for description of the observed behavior of the models with on-site potential. In part of the models a characteristic relaxation times exhibit peculiar scaling with respect to the temperature perturbation wavelength. Quite surprisingly, such behavior is similar to that of well-known model with divergent heat conduction (Fermi-Pasta-Ulam chain) and rather different from the model with normal heat conduction (chain of rotators). Thus, the data on the non-stationary heat conduction in the systems with on-site potential do not fit commonly accepted concept of universality classes for heat conduction in one-dimensional models.Comment: 9 pages, 7 figures, corrected versio

Poling and annealing of piezoelectric poly(vinylidene fluoride) micropillar arrays

R.S. acknowledges the financial support from the Russian Science Foundation (project #18-73-10050)

Nonadiabatic charged spherical gravitational collapse

We present a complete set of the equations and matching conditions required for the description of physically meaningful charged, dissipative, spherically symmetric gravitational collapse with shear. Dissipation is described with both free-streaming and diffusion approximations. The effects of viscosity are also taken into account. The roles of different terms in the dynamical equation are analyzed in detail. The dynamical equation is coupled to a causal transport equation in the context of Israel-Stewart theory. The decrease of the inertial mass density of the fluid, by a factor which depends on its internal thermodynamic state, is reobtained, with the viscosity terms included. In accordance with the equivalence principle, the same decrease factor is obtained for the gravitational force term. The effect of the electric charge on the relation between the Weyl tensor and the inhomogeneity of energy density is discussed.Comment: 23 pages, Latex. To appear in Phys. Rev. D. Some references correcte

Quantitative phase separation in multiferroic Bi0.88Sm0.12FeO3 ceramics via piezoresponse force microscopy

BiFeO3 (BFO) is a classical multiferroic material with both ferroelectric and magnetic ordering at room temperature. Doping of this material with rare-earth oxides was found to be an efficient way to enhance the otherwise low piezoelectric response of unmodified BFO ceramics. In this work, we studied two types of bulk Sm-modified BFO ceramics with compositions close to the morphotropic phase boundary (MPB) prepared by different solid-state processing methods. In both samples, coexistence of polar R3c and antipolar P-bam phases was detected by conventional X-ray diffraction (XRD); the non-polar P-nma or P-bnm phase also has potential to be present due to the compositional proximity to the polar-to-non-polar phase boundary. Two approaches to separate the phases based on the piezoresponse force microscopy measurements have been proposed. The obtained fractions of the polar and non-polar/anti-polar phases were close to those determined by quantitative XRD analysis. The results thus reveal a useful method for quantitative determination of the phase composition in multi-phase ceramic systems, including the technologically most important MPB systems. (C) 2015 AIP Publishing LLC