188,704 research outputs found

### Neutrinos and the Supernova Origin of the Elements

Intense fluxes of neutrinos are emitted by the hot neutron star produced in a
supernova. The electron neutrino and antineutrino capture reactions on neutrons
and protons, respectively, provide heating to drive a wind from the hot neutron
star. The same reactions also determine the neutron-richness of the wind
material. Nucleosynthesis via rapid neutron capture, the r-process, may occur
in the wind material as it expands away from the neutron star. The
neutron-richness of the wind material, and hence, the r-process nucleosynthesis
therein, are sensitive to mixing between the muon (or tauon)
neutrino/antineutrino and the electron (or sterile) neutrino/antineutrino.
Indirect arguments and direct tests for the supernova origin of the r-process
elements are discussed with a goal to establish supernova r-process
nucleosynthesis as an important probe for neutrino mixing.Comment: 6 pages including 2 figures, to appear in the Proceedings of Neutrino
200

### Statistical Thermodynamics of General Minimal Diffusion Processes: Constuction, Invariant Density, Reversibility and Entropy Production

The solution to nonlinear Fokker-Planck equation is constructed in terms of
the minimal Markov semigroup generated by the equation. The semigroup is
obtained by a purely functional analytical method via Hille-Yosida theorem. The
existence of the positive invariant measure with density is established and a
weak form of Foguel alternative proven. We show the equivalence among
self-adjoint of the elliptic operator, time-reversibility, and zero entropy
production rate of the stationary diffusion process. A thermodynamic theory for
diffusion processes emerges.Comment: 23 page

### The most plausible explanation of the cyclical period changes in close binaries: the case of the RS CVn-type binary WW Dra

We searched the orbital period changes in 182 EA-type (including the 101
Algol systems used by \cite{hal89}), 43 EB-type and 53 EW-type binaries with
known both the mass ratio and the spectral type of their secondary components.
We reproduced and improved the same diagram as Hall's (1989) according to the
new collected data. Our plots do not support the conclusion derived by
\cite{hal89} that all cases of cyclical period changes are restricted to
binaries having the secondary component with spectral types later than F5. The
presence of period changes also among stars with secondary component of early
type indicates that the magnetic activity is one cause, but not the only one,
for the period variation. It is discovered that cyclic period changes, likely
due to the presence of a third body are more frequent in EW-type binaries among
close binaries. Therefore, the most plausible explanation of the cyclical
period changes is the LTTE via the presence of a third body. By using the
century-long historical record of the times of light minimum, we analyzed the
cyclical period change in the Algol binary WW Dra. It is found that the orbital
period of the binary shows a $\sim112.2 \textbf{\textrm{yr}}$ cyclic variation
with an amplitude of $\sim0.1977\textbf{\textrm{days}}$. The cyclic oscillation
can be attributed to the LTTE via a third body with a mass no less than $6.43
M_{\odot}$. However, no spectral lines of the third body were discovered
indicating that it may be a candidate black hole. The third body is orbiting
the binary at a distance shorter than 14.4 AU and it may play an important role
in the evolution of this system.Comment: 9 pages, 5 figures, published by MNRA

### Neutrino Gravitational Redshift and the Electron Fraction Above Nascent Neutron Stars

Neutrinos emitted from near the surface of the hot proto-neutron star
produced by a supernova explosion may be subject to significant gravitational
redshift at late times. Electron antineutrinos decouple deeper in the
gravitational potential well of the neutron star than do the electron
neutrinos, so that the electron antineutrinos experience a larger redshift
effect than do the electron neutrinos. We show how this differential redshift
can increase the electron fraction Ye in the neutrino-heated ejecta from the
neutron star. Any r-process nucleosynthesis originating in the neutrino-heated
ejecta would require a low Ye, implying that the differential redshift effect
cannot be too large. In turn, this effect may allow nucleosynthesis to probe
the nuclear equation of state parameters which set the neutron star radius and
surface density scale height at times of order tpb = 10 to 25 s after core
bounce.Comment: 4 pages, uses espcrc2.sty, contribution to Festschrift for G. E.
Brown on the occasion of his 70th birthda

### Stochastic Dynamics of Electrical Membrane with Voltage-Dependent Ion Channel Fluctuations

Brownian ratchet like stochastic theory for the electrochemical membrane
system of Hodgkin-Huxley (HH) is developed. The system is characterized by a
continuous variable $Q_m(t)$, representing mobile membrane charge density, and
a discrete variable $K_t$ representing ion channel conformational dynamics. A
Nernst-Planck-Nyquist-Johnson type equilibrium is obtained when multiple
conducting ions have a common reversal potential. Detailed balance yields a
previously unknown relation between the channel switching rates and membrane
capacitance, bypassing Eyring-type explicit treatment of gating charge
kinetics. From a molecular structural standpoint, membrane charge $Q_m$ is a
more natural dynamic variable than potential $V_m$; our formalism treats
$Q_m$-dependent conformational transition rates $\lambda_{ij}$ as intrinsic
parameters. Therefore in principle, $\lambda_{ij}$ vs. $V_m$ is experimental
protocol dependent,e.g., different from voltage or charge clamping
measurements. For constant membrane capacitance per unit area $C_m$ and
neglecting membrane potential induced by gating charges, $V_m=Q_m/C_m$, and
HH's formalism is recovered. The presence of two types of ions, with different
channels and reversal potentials, gives rise to a nonequilibrium steady state
with positive entropy production $e_p$. For rapidly fluctuating channels, an
expression for $e_p$ is obtained.Comment: 8 pages, two figure

### rHARM: Accretion and Ejection in Resistive GR-MHD

Turbulent magnetic diffusivity plays an important role for accretion disks
and the launching of disk winds. We have implemented magnetic diffusivity,
respective resistivity in the general relativistic MHD code HARM. This paper
describes the theoretical background of our implementation, its numerical
realization, our numerical tests and preliminary applications. The test
simulations of the new code rHARM are compared with an analytic solution of the
diffusion equation and a classical shock tube problem. We have further
investigated the evolution of the magneto-rotational instability (MRI) in tori
around black holes for a range of magnetic diffusivities. We find indication
for a critical magnetic diffusivity (for our setup) beyond which no MRI
develops in the linear regime and for which accretion of torus material to the
black hole is delayed. Preliminary simulations of magnetically diffusive thin
accretion disks around Schwarzschild black holes that are threaded by a
large-scale poloidal magnetic field show the launching of disk winds with mass
fluxes of about 50% of the accretion rate. The disk magnetic diffusivity allows
for efficient disk accretion that replenishes the mass reservoir of the inner
disk area and thus allows for long-term simulations of wind launching for more
than 5000 time units.Comment: 21 pages, 43 figures, accepted by Ap

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