1,996 research outputs found
Ionization equilibrium and equation of state of hydrogen plasmas in strong magnetic fields
We study hydrogen plasmas at magnetic fields B ~ 10^{12}-10^{13} Gauss,
densities ~ 10^{-3}-10^3 g/cc and temperatures T ~ 10^{5.5}-10^{6.5} K, typical
of photospheres of middle-aged cooling neutron stars. We construct an
analytical free energy model of the partially ionized plasma, including into
consideration the decentred atomic states, which arise due to the thermal
motion across the strong field. We show that these states, neglected in
previous studies, may contribute appreciably into thermodynamics of the outer
atmospheric layers at density below 1 g/cc and typical B and T. We take into
account Coulomb non-ideality of the ionized component of the plasma affected by
intense magnetic field. Ionization degree, occupancies and equation of state
are calculated, and their dependences on the temperature, density and magnetic
field are studied.Comment: 4 pages, 1 figure, LaTeX using cpp.sty (included) and epsf.sty. Proc.
of the Workshop on Nonideal Plasmas PNP-9, Rostock, Germany, 7-11 Sept. 1998.
To be published in Contrib. Plasma Phy
Partially ionized atmospheres of neutron stars with strong magnetic fields
We construct hydrogen atmosphere models for strongly magnetized neutron stars
in thermodynamic equilibrium, taking into account partial ionization. The
presence of bound states affects the equation of state, absorption
coefficients, and polarizability tensor of a strongly magnetized plasma.
Therefore the partial ionization influences the polarization vectors and
opacities of normal electromagnetic waves, and thus the spectra of outgoing
radiation. Here we review a model suitable for the most typical neutron-star
atmospheres and focus on the problems that remain to be solved for its
extension to other atmospheric parameters.Comment: 7 pages, 1 figure, Adv. Sp. Res., in pres
Electron conduction along quantizing magnetic fields in neutron star crusts. I. Theory
Transport properties of degenerate relativistic electrons along quantizing
magnetic fields in neutron star crusts are considered. A kinetic equation is
derived for the spin polarization density matrix of electrons. Its solution
does not depend on the choice of basic electron wave functions unlike previous
solutions of the traditional kinetic equation for the distribution function.
The density matrix formalism shows that one can always reach high accuracy with
the traditional method by a proper choice of the basic functions. Electron
Coulomb scattering on ions is considered in liquid matter, and on
high-temperature phonons or on charged impurities in solid matter. In the solid
regime, the Debye -- Waller reduction of phonon scattering can strongly enhance
the longitudinal thermal or electric conductivity. An efficient numerical
method is proposed for calculating the transport properties of electron gas at
any magnetic field of practical interest.Comment: 12 pages, A&A-LaTeX (l-aa.sty included), 2 PostScript figures. A
misprint in Eq. (B3) correcte
Corrections to linear mixing in binary ionic mixtures and plasma screening at zero separation
Using the results of extensive Monte Carlo simulations we discuss corrections
to the linear mixing rule in strongly coupled binary ionic mixtures. We analyze
the plasma screening function at zero separation, H_{jk}(0), for two ions (of
types j=1,2 and k=1,2) in a strongly coupled binary mixture. The function
H_{jk}(0) is estimated by two methods: (1) from the difference of Helmholtz
Coulomb free energies at large and zero separations; (2) by fitting the Widom
expansion of H_{jk}(x) in powers of interionic distance x to Monte Carlo data
on the radial pair distribution function g_{jk}(x). These methods are shown to
be in good agreement. For illustration, we analyze the plasma screening
enhancement of nuclear burning rates in dense stellar matter.Comment: 4 pages, 2 figures, pre-peer reviewed version of the article accepted
for publication in Contrib. Plasma Phys. (2009). The results can be applied
to plasma screening enhancement of nuclear burning rates in dense stellar
matte
Atmospheres and radiating surfaces of neutron stars
The early 21st century witnesses a dramatic rise in the study of thermal
radiation of neutron stars. Modern space telescopes have provided a wealth of
valuable information which, when properly interpreted, can elucidate the
physics of superdense matter in the interior of these stars. This
interpretation is necessarily based on the theory of formation of neutron star
thermal spectra, which, in turn, is based on plasma physics and on the
understanding of radiative processes in stellar photospheres. In this paper,
the current status of the theory is reviewed with particular emphasis on
neutron stars with strong magnetic fields. In addition to the conventional deep
(semi-infinite) atmospheres, radiative condensed surfaces of neutron stars and
"thin" (finite) atmospheres are considered.Comment: 43 pages, 13 figures, 1 table. In v.3, there are more than 50 minor
corrections (typos, wording, style) and one important typo fix (the sign in
Eq.(61)). In v.4, beside a few minor improvements, ionization equilibrium
equation (58) is corrected. In v.5, a typo in Eq.(12) is fixe
Cyclotron harmonics in opacities of isolated neutron star atmospheres
Some of X-ray dim isolated neutron stars (XDINS) and central compact objects
in supernova remnants (CCO) show absorption features in their thermal soft
X-ray spectra. It has been hypothesized that these features could be due to the
periodic peaks in free-free absorption opacities, caused by either Landau
quantization of electron motion in magnetic fields B<10^{11} G or analogous
quantization of ion motion in magnetic fields B>10^{13} G. Here, I review the
physics behind cyclotron quantum harmonics in free-free photoabsorption,
discuss different approximations for their calculation, and explain why the ion
cyclotron harmonics (beyond the fundamental) cannot be observed.Comment: 12 pages, 5 figures. In v.5, a typo (missed sign factor) in Eq.(9) is
fixe
On the Stabilizing Action of Protein Denaturants: Acetonitrile Effect on Stability of Lysozyme in Aqueous Solutions
Stability of hen lysozyme in the presence of acetonitrile (MeCN) at different pH values of the medium was studied by scanning microcalorimetry with a special emphasis on determination of reliable values of the denaturational heat capacity change. It was found that the temperature of denaturation decreases on addition of MeCN. However, the free energy extrapolation showed that below room temperature the thermodynamic stability increases at low concentrations of MeCN in spite of the general destabilizing effect at higher concentrations and temperatures. Charge-induced contribution to this stabilization was shown to be negligible (no pH-dependence was found); therefore, the most probable cause for the phenomenon is an increase of hydrophobic interactions at low temperatures in aqueous solutions containing small amounts of the organic additive. The difference in preferential solvation of native and denatured states of lysozyme was calculated from the stabilization free energy data. It was found that the change in preferential solvation strongly depends on the temperature in the water-rich region. At the higher MeCN content this dependence decreases until, at 0.06 mole fractions of MeCN, the difference in the preferential solvation between native and denatured lysozyme becomes independent of the temperature over a range of 60 K. The importance of taking into account non-ideality of a mixed solution, when analyzing preferential solvation phenomena was emphasized
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