Landau quantization and neutron emissions by nuclei in the crust of a magnetar

Magnetars are neutron stars endowed with surface magnetic fields of the order of $10^{14}-10^{15}$~G, and with presumably much stronger fields in their interior. As a result of Landau quantization of electron motion, the neutron-drip transition in the crust of a magnetar is shifted to either higher or lower densities depending on the magnetic field strength. The impact of nuclear uncertainties is explored considering the recent series of Brussels-Montreal microscopic nuclear mass models. All these models are based on the Hartree-Fock-Bogoliubov method with generalized Skyrme functionals. They differ in their predictions for the symmetry energy coefficient at saturation, and for the stiffness of the neutron-matter equation of state. For comparison, we have also considered the very accurate but more phenomenological model of Duflo and Zuker. Although the equilibrium composition of the crust of a magnetar and the onset of neutron emission are found to be model dependent, the quantum oscillations of the threshold density are essentially universal.Comment: 7 pages, 2 figure

Polarization of Thermal X-rays from Isolated Neutron Stars

Since the opacity of a magnetized plasma depends on polarization of radiation, the radiation emergent from atmospheres of neutron stars with strong magnetic fields is expected to be strongly polarized. The degree of linear polarization, typically ~10-30%, depends on photon energy, effective temperature and magnetic field. The spectrum of polarization is more sensitive to the magnetic field than the spectrum of intensity. Both the degree of polarization and the position angle vary with the neutron star rotation period so that the shape of polarization pulse profiles depends on the orientation of the rotational and magnetic axes. Moreover, as the polarization is substantially modified by the general relativistic effects, observations of polarization of X-ray radiation from isolated neutron stars provide a new method for evaluating the mass-to-radius ratio of these objects, which is particularly important for elucidating the properties of the superdense matter in the neutron star interiors.Comment: 7 figures, to be published in Ap

Predictive models of glucose control : roles for glucose-sensing neurones

© 2014 The Authors. Acta Physiologica published by John Wiley & Sons Ltd on behalf of Scandinavian Physiological Society.Peer reviewedPublisher PD

Spin-Kick Correlation in Neutron Stars: Alignment Conditions and Implications

Recent observations of pulsar wind nebulae and radio polarization profiles revealed a tendency of the alignment between the spin and velocity directions in neutron stars. We study the condition for spin-kick alignment using a toy model, in which the kick consists of many off-centered, randomly-oriented thrusts. Both analytical considerations and numerical simulations indicate that spin-kick alignment cannot be easily achieved if the proto-neutron star does not possess some initial angular momentum, contrary to some previous claims. To obtain the observed spin-kick misalignment angle distribution, the initial spin period of the neutron star must be smaller than the kick timescale. Typically, an initial period of a hundred milliseconds or less is required.Comment: 17 pages, 8 figures. Accepted by Ap

Photon assisted tunneling in pairs of silicon donors

Shallow donors in silicon are favorable candidates for the implementation of solid-state quantum computer architectures because of the promising combination of atomiclike coherence properties and scalability from the semiconductor manufacturing industry. Quantum processing schemes require (among other things) controlled information transfer for readout. Here we demonstrate controlled electron tunneling at 10 K from P to Sb impurities and vice versa with the assistance of resonant terahertz photons

New constraints for heavy axion-like particles from supernovae

We derive new constraints on the coupling of heavy pseudoscalar (axion-like) particles to photons, based on the gamma ray flux expected from the decay of these particles into photons. After being produced in the supernova core, these heavy axion-like particles would escape and a fraction of them would decay into photons before reaching the Earth. We have calculated the expected flux on Earth of these photons from the supernovae SN 1987A and Cassiopeia A and compared our results to data from the Fermi Large Area Telescope. This analysis provides strong constraints on the parameter space for axion-like particles. For a particle mass of 100 MeV, we find that the Peccei-Quinn constant, f_a, must be greater than about 10^{15} GeV. Alternatively, for fa=10^{12} GeV, we exclude the mass region between approximately 100 eV and 1 GeV.Comment: 14 pages, 4 figures. Version published in JCAP. Major changes in the exposition. Added a figure. Added appendix. Minor changes in the results. Some changes in the bibliograph

Integrability of anisotropic and homogeneous Universes in scalar-tensor theory of gravitation

In this paper, we develop a method based on the analysis of the Kovalewski exponents to study the integrability of anisotropic and homogeneous Universes. The formalism is developed in scalar-tensor gravity, the general relativistic case appearing as a special case of this larger framework. Then, depending on the rationality of the Kovalewski exponents, the different models, both in the vacuum and in presence of a barotropic matter fluid, are classified, and their integrability is discussed.Comment: 16 pages, no figure, accepted in CQ

Analogue of the Kubo Formula for Conductivity of Spatially Inhomogeneous Systems and Electric Fields

The average of densities of currents and charges, induced by a weak electromagnetic field in spatially inhomogeneous are calculated at final temperatures. The Kubo formula for a conductivity tensor is generalized for spatially inhomogeneous systems and fields. The contributions containing electric fields and derivative from fields on coordinates are allocated. The Semiconductor quantum wells, wires and dots may be considered as spatially inhomogeneous systems.Comment: 10 page