Nonequilibrium corrections in the pressure tensor due to an energy flux

The physical interpretation of the nonequilibrium corrections in the pressure tensor for radiation submitted to an energy flux obtained in some previous works is revisited. Such pressure tensor is shown to describe a moving equilibrium system but not a real nonequilibrium situation.Comment: 4 pages, REVTeX, Brief Report to appear in PRE Dec 9

Effect of Boundary Conditions on a Non-Equilibrium Transient Marshak Wave Problem

Transient processes in radiative transfer have recently become of interest in the modeling of astrophysical phenomena, particularly with regard to the brightness of novae, supernovae, and perhaps even galactic clouds adjacent to quasars. Analytic solutions to a particular class of Marshak wave problems are presented with and without the Marshak (Milne) boundary condition. The choice of boundary condition can have a decisive effect on the coupling of radiative energy to the material energy in the vicinity of a material boundary. The analytic solution obtained can be useful as a tool for calibrating numerical calculation techniques

Monte Carlo analysis of the backscattering of radiation from a sphere to a plane

A Monte Carlo method is described for computing the backscattering of radiation from a sphere situated above an emitting plane. Numerical results are given and compared with analytic bounds for this problem which were previously reported in this journal.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28732/1/0000558.pd

A photon transport problem with a time-dependent point source

We consider a time-dependent problem of photon transport in an interstellar cloud with a point photon source modeled by a Dirac δ functional. The existence of a unique distributional solution to this problem is established by using the theory of continuous semigroups of operators on locally convex spaces coupled with a constructive approach for producing spaces of generalized functions

Information theory in the study of anisotropic radiation

Information theory is used to perform a thermodynamic study of non equilibrium anisotropic radiation. We limit our analysis to a second-order truncation of the moments, obtaining a distribution function which leads to a natural closure of the hierarchy of radiative transfer equations in the so-called variable Eddington factor scheme. Some Eddington factors appearing in the literature can be recovered as particular cases of our two-parameter Eddington factor. We focus our attention in the study of the thermodynamic properties of such systems and relate it to recent nonequilibrium thermodynamic theories. Finally we comment the possibility of introducing a nonequilibrium chemical potential for photons.Comment: 1 eps figure upon request by e-mail, to appear in Journal of Physics

Neutrino-Nucleon Interactions in Magnetized Neutron-Star Matter: The Effects of Parity Violation

We study neutrino-nucleon scattering and absorption in a dense, magnetized nuclear medium. These are the most important sources of neutrino opacity governing the cooling of a proto-neutron star in the first tens of seconds after its formation. Because the weak interaction is parity violating, the absorption and scattering cross-sections depend asymmetrically on the directions of the neutrino momenta with respect to the magnetic field. We develop the moment formalism of neutrino transport in the presence of such asymmetric opacities and derive explicit expressions for the neutrino flux and other angular moments of the Boltzmann transport equation. For a given neutrino species, there is a drift flux of neutrinos along the magnetic field in addition to the usual diffusive flux. This drift flux depends on the deviation of the neutrino distribution function from thermal equilibrium. Hence, despite the fact that the neutrino cross-sections are asymmetric throughout the star, asymmetric neutrino flux can be generated only in the outer region of the proto-neutron star where the neutrino distribution deviates significantly from thermal equilibrium. In addition to the asymmetric absorption opacity arising from nucleon polarization, we find the contribution of the electron (or positron) ground state Landau level. For neutrinos of energy less than a few times the temperature, this is the dominant source of asymmetric opacity. Lastly, we discuss the implication of our result to the origin of pulsar kicks: in order to generate kick velocity of a few hundred km/s from asymmetric neutrino emission using the parity violation effect, the proto-neutron star must have a dipole magnetic field of at least $10^{15}-10^{16}$ G.Comment: 35 pages, no figures, submitted to Phys.Rev.

Instabilities in the Envelopes and Winds of Very Massive Stars

The high luminosity of Very Massive Stars (VMS) means that radiative forces play an important, dynamical role both in the structure and stability of their stellar envelope, and in driving strong stellar-wind mass loss. Focusing on the interplay of radiative flux and opacity, with emphasis on key distinctions between continuum vs. line opacity, this chapter reviews instabilities in the envelopes and winds of VMS. Specifically, we discuss how: 1) the iron opacity bump can induce an extensive inflation of the stellar envelope; 2) the density dependence of mean opacity leads to strange mode instabilities in the outer envelope; 3) desaturation of line-opacity by acceleration of near-surface layers initiates and sustains a line-driven stellar wind outflow; 4) an associated line-deshadowing instability leads to extensive small-scale structure in the outer regions of such line-driven winds; 5) a star with super-Eddington luminosity can develop extensive atmospheric structure from photon bubble instabilities, or from stagnation of flow that exceeds the "photon tiring" limit; 6) the associated porosity leads to a reduction in opacity that can regulate the extreme mass loss of such continuum-driven winds. Two overall themes are the potential links of such instabilities to Luminous Blue Variable (LBV) stars, and the potential role of radiation forces in establishing the upper mass limit of VMS.Comment: 44 pages, 13 figures. Chapter to appear in the book "Very Massive Stars in the Local Universe", Springer, J.S. Vink, e

Radiation transport in diffractive media

We consider radiation transport theory applied to non-dispersive but refractive media. This setting is used to discuss Minkowski's and Abraham's electromagnetic momentum, and to derive conservation equations independent of the choice of momentum definition. Using general relativistic kinetic theory, we derive and discuss a radiation gas energy-momentum conservation equation valid in arbitrary curved spacetime with diffractive media.Comment: 10 pages, typos and equation numbers corrected, version to appear in J. Phys. A: Math. Ge

High Resolution Detection and Analysis of CpG Dinucleotides Methylation Using MBD-Seq Technology

Methyl-CpG binding domain protein sequencing (MBD-seq) is widely used to survey DNA methylation patterns. However, the optimal experimental parameters for MBD-seq remain unclear and the data analysis remains challenging. In this study, we generated high depth MBD-seq data in MCF-7 cell and developed a bi-asymmetric-Laplace model (BALM) to perform data analysis. We found that optimal efficiency of MBD-seq experiments was achieved by sequencing ∼100 million unique mapped tags from a combination of 500 mM and 1000 mM salt concentration elution in MCF-7 cells. Clonal bisulfite sequencing results showed that the methylation status of each CpG dinucleotides in the tested regions was accurately detected with high resolution using the proposed model. These results demonstrated the combination of MBD-seq and BALM could serve as a useful tool to investigate DNA methylome due to its low cost, high specificity, efficiency and resolution