1,492 research outputs found
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
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
Hydrogen atom in a magnetic field: The quadrupole moment
The quadrupole moment of a hydrogen atom in a magnetic field for field
strengths from 0 to 4.414e13 G is calculated by two different methods. The
first method is variational, and based on a single trial function. The second
method deals with a solution of the Schroedinger equation in the form of a
linear combination of Landau orbitals.Comment: 4 pages, 1 figure, 1 table; RevTeX. Final (proofs-stage) version of
the text; corrected numbers in Table 1 and in Eq.(15
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
Folding Under Inequilibrium Conditions as a Possible Reason for Partial Irreversibility of Heat-Denatured Proteins: Computer Simulation Study
Using computer simulations we have studied possible effects of heating and cooling at different scan rates on unfolding and refolding of macromolecules. We have shown that even the simplest two-state reversible transition can behave irreversibly when an unfavorable combination of cooling rate, relaxation time and activation energy of refolding occurs. On the basis of this finding we suppose that apparent irreversibility of some proteins denatured by heat may result from slow relaxation on cooling rather than thermodynamic instability and/or irreversible alterations of the polypeptide chain. Using this kinetic reversible two-state model, we estimated the effects of the scan rate and kinetic parameters of the macromolecule on its unfolding–refolding process. A few recommendations are suggested on how to reach maximal possible recovery after denaturation if refolding appears to be under kinetic control
Testing cosmological variability of fundamental constants
One of the topical problems of contemporary physics is a possible variability
of the fundamental constants. Here we consider possible variability of two
dimensionless constants which are most important for calculation of atomic and
molecular spectra (in particular, the X-ray ones): the fine-structure constant
\alpha=e^2/\hbar c and the proton-to-electron mass ratio \mu=m_p/m_e. Values of
the physical constants in the early epochs are estimated directly from
observations of quasars - the most powerful sources of radiation, whose spectra
were formed when the Universe was several times younger than now. A critical
analysis of the available results leads to the conclusion that present-day data
do not reveal any statistically significant evidence for variations of the
fundamental constants under study. The most reliable upper limits to possible
variation rates at the 95% confidence level, obtained in our work, read:
|\dot\alpha/\alpha| < (1.4e-14)/yr,
|\dot\mu/\mu| < (1.5e-14)/yr
on the average over the last ten billion years.Comment: 9 pages, 2 figures, 2 tables, LaTeX using aipproc.sty (included). In:
X-ray and Inner-Shell Processes, R.W. Dunford, D.S. Gemmel, E.P. Kanter, B.
Kraessig, S.H. Southworth, L. Young (eds.), AIP Conf. Proc. (AIP, Melville,
2000) vol. 506, p. 50
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