188,704 research outputs found

    Neutrinos and the Supernova Origin of the Elements

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    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

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    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

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    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 ∼112.2yr\sim112.2 \textbf{\textrm{yr}} cyclic variation with an amplitude of ∼0.1977days\sim0.1977\textbf{\textrm{days}}. The cyclic oscillation can be attributed to the LTTE via a third body with a mass no less than 6.43M⊙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

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    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

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    Brownian ratchet like stochastic theory for the electrochemical membrane system of Hodgkin-Huxley (HH) is developed. The system is characterized by a continuous variable Qm(t)Q_m(t), representing mobile membrane charge density, and a discrete variable KtK_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 QmQ_m is a more natural dynamic variable than potential VmV_m; our formalism treats QmQ_m-dependent conformational transition rates λij\lambda_{ij} as intrinsic parameters. Therefore in principle, λij\lambda_{ij} vs. VmV_m is experimental protocol dependent,e.g., different from voltage or charge clamping measurements. For constant membrane capacitance per unit area CmC_m and neglecting membrane potential induced by gating charges, Vm=Qm/CmV_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 epe_p. For rapidly fluctuating channels, an expression for epe_p is obtained.Comment: 8 pages, two figure

    rHARM: Accretion and Ejection in Resistive GR-MHD

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    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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