14,079 research outputs found
Quadrupole moment of a magnetically confined mountain on an accreting neutron star: effect of the equation of state
Magnetically confined mountains on accreting neutron stars are promising
sources of continuous-wave gravitational radiation and are currently the
targets of directed searches with long-baseline detectors like the Laser
Interferometer Gravitational Wave Observatory (LIGO). In this paper, previous
ideal-magnetohydrodynamic models of isothermal mountains are generalized to a
range of physically motivated, adiabatic equations of state. It is found that
the mass ellipticity drops substantially, from \epsilon ~ 3e-4 (isothermal) to
\epsilon ~ 9e-7 (non-relativistic degenerate neutrons), 6e-8 (relativistic
degenerate electrons) and 1e-8 (non-relativistic degenerate electrons)
(assuming a magnetic field of 3e12 G at birth). The characteristic mass M_{c}
at which the magnetic dipole moment halves from its initial value is also
modified, from M_{c}/M_{\sun} ~ 5e-4 (isothermal) to M_{c}/M_{\sun} ~ 2e-6,
1e-7, and 3e-8 for the above three equations of state, respectively. Similar
results are obtained for a realistic, piecewise-polytropic nuclear equation of
state. The adiabatic models are consistent with current LIGO upper limits,
unlike the isothermal models. Updated estimates of gravitational-wave
detectability are made. Monte Carlo simulations of the spin distribution of
accreting millisecond pulsars including gravitational-wave stalling agree
better with observations for certain adiabatic equations of state, implying
that X-ray spin measurements can probe the equation of state when coupled with
magnetic mountain models.Comment: 20 pages, 15 figures, to be published in MNRA
Gravitational waves from an accreting neutron star with a magnetic mountain
We calculate the amplitude of gravitational waves from a neutron star accreting symmetrically at its magnetic poles. The magnetic field, which is compressed into an equatorial belt during accretion, confines accreted matter in a mountain at the magnetic pole, producing gravitational waves. We compute hydromagnetic equilibria and the corresponding quadrupole moment as a function of the accreted mass, Ma, finding the polarization- and orientation- averaged wave strain at Earth to be h_c = 6.3 × 10^(–25)(M_a/10^(–5)M_☉)(ƒ/0.6kHz)^2(d/1kpc)^(–1) for a range of conditions, where ƒ is the wave frequency and d is the distance to the source. This is ~ 10^2 times greater than previous estimates, which failed to treat the mass-flux distribution self-consistently with respect to flux-freezin
A second eigenvalue bound for the Dirichlet Schroedinger operator
Let be the th eigenvalue of the Schr\"odinger
operator with Dirichlet boundary conditions on a bounded domain and with the positive potential . Following the spirit of the
Payne-P\'olya-Weinberger conjecture and under some convexity assumptions on the
spherically rearranged potential , we prove that . Here denotes the ball, centered at the
origin, that satisfies the condition .
Further we prove under the same convexity assumptions on a spherically
symmetric potential , that decreases
when the radius of the ball increases.
We conclude with several results about the first two eigenvalues of the
Laplace operator with respect to a measure of Gaussian or inverted Gaussian
density
Importance of many body effects in the kernel of hemoglobin for ligand binding
We propose a mechanism for binding of diatomic ligands to heme based on a
dynamical orbital selection process. This scenario may be described as bonding
determined by local valence fluctuations. We support this model using
linear-scaling first-principles calculations, in combination with dynamical
mean-field theory, applied to heme, the kernel of the hemoglobin metalloprotein
central to human respiration. We find that variations in Hund's exchange
coupling induce a reduction of the iron 3d density, with a concomitant increase
of valence fluctuations. We discuss the comparison between our computed optical
absorption spectra and experimental data, our picture accounting for the
observation of optical transitions in the infrared regime, and how the Hund's
coupling reduces, by a factor of five, the strong imbalance in the binding
energies of heme with CO and O_2 ligands.Comment: 5 pages, 4 figures. Supplementary material 12 pages, 5 figures. This
version (v2) matches that accepted for Physical Review Letters on 31 January
201
A Note on the Reliability Tests of Estimates from ARMS Data
USDA uses the concept of "publish-ability" rather than statistical reliability of an estimate for quality validation of USDA estimates, which is solely based on the sample size and the coefficient of variation (CV). We demonstrate conceptually how the reliability of the sample mean can be tested by estimating the upper and lower bounds of the confidence interval for an unknown population mean using the CV. However, the reliability test for the sample mean can be made only under the normality assumption. USDA multiple-way Agricultural Resource Management Survey (ARMS) estimates are used to illustrate the relative measure of precision for sample-based estimators.Research Methods/ Statistical Methods,
Vanadium dioxide : A Peierls-Mott insulator stable against disorder
Vanadium dioxide undergoes a first order metal-insulator transition at 340 K.
In this work, we develop and carry out state of the art linear scaling DFT
calculations refined with non-local dynamical mean-field theory. We identify a
complex mechanism, a Peierls-assisted orbital selection Mott instability, which
is responsible for the insulating M phase, and furthermore survives a
moderate degree of disorder.Comment: 5 pages, 4 figures. Supplementary material 8 pages, 4 figures. This
version (v2) matches that accepted for Physical Review Letters on 16th May
201
- …