2,351 research outputs found
Exploring binary-neutron-star-merger scenario of short-gamma-ray bursts by gravitational-wave observation
We elucidate the feature of gravitational waves (GWs) from binary neutron
star merger collapsing to a black hole by general relativistic simulation. We
show that GW spectrum imprints the coalescence dynamics, formation process of
disk, equation of state for neutron stars, total masses, and mass ratio. A
formation mechanism of the central engine of short -ray bursts, which
are likely to be composed of a black hole and surrounding disk, therefore could
be constrained by GW observation.Comment: Accepted to PR
Gravitational waves and neutrino emission from the merger of binary neutron stars
Numerical simulations for the merger of binary neutron stars are performed in
full general relativity incorporating a finite-temperature (Shen's) equation of
state (EOS) and neutrino cooling for the first time. It is found that for this
stiff EOS, a hypermassive neutron star (HMNS) with a long lifetime (
ms) is the outcome for the total mass \alt 3.0M_{\odot}. It is shown that the
typical total neutrino luminosity of the HMNS is --
ergs/s and the effective amplitude of gravitational waves from the HMNS is
4-- at --2.5 kHz for a source distance of 100 Mpc. We
also present the neutrino luminosity curve when a black hole is formed for the
first time.Comment: 4 pages, 4 figures (Fig.2 is in low resolution), Accepted for
publication in PR
Gravitational waves from the Papaloizou-Pringle instability in black hole-torus systems
Black hole (BH)--torus systems are promising candidates for the central
engine of gamma-ray bursts (GRBs), and also possible outcomes of the collapse
of supermassive stars to supermassive black holes (SMBHs). By three-dimensional
general relativistic numerical simulations, we show that an
nonaxisymmetric instability grows for a wide range of self-gravitating tori
orbiting BHs. The resulting nonaxisymmetric structure persists for a timescale
much longer than the dynamical one, becoming a strong emitter of large
amplitude, quasiperiodic gravitational waves. Our results indicate that both,
the central engine of GRBs and newly formed SMBHs, can be strong gravitational
wave sources observable by forthcoming ground-based and spacecraft detectors.Comment: 4 pages, 4 figure, to be published in PR
Relativistic stars with purely toroidal magnetic fields
We investigate the effects of the purely toroidal magnetic field on the
equilibrium structures of the relativistic stars. The master equations for
obtaining equilibrium solutions of relativistic rotating stars containing
purely toroidal magnetic fields are derived for the first time. To solve these
master equations numerically, we extend the Cook-Shapiro-Teukolsky scheme for
calculating relativistic rotating stars containing no magnetic field to
incorporate the effects of the purely toroidal magnetic fields. By using the
numerical scheme, we then calculate a large number of the equilibrium
configurations for a particular distribution of the magnetic field in order to
explore the equilibrium properties. We also construct the equilibrium sequences
of the constant baryon mass and/or the constant magnetic flux, which model the
evolution of an isolated neutron star as it loses angular momentum via the
gravitational waves. Important properties of the equilibrium configurations of
the magnetized stars obtained in this study are summarized as follows ; (1) For
the non-rotating stars, the matter distribution of the stars is prolately
distorted due to the toroidal magnetic fields. (2) For the rapidly rotating
stars, the shape of the stellar surface becomes oblate because of the
centrifugal force. But, the matter distribution deep inside the star is
sufficiently prolate for the mean matter distribution of the star to be
prolate. (3) The stronger toroidal magnetic fields lead to the mass-shedding of
the stars at the lower angular velocity. (4) For some equilibrium sequences of
the constant baryon mass and magnetic flux, the stars can spin up as they lose
angular momentum.Comment: 13 figures, 7 tables, submitted to PR
Subsurface Flow Barriers to Reduce Nitrate Leaching
Groundwater is a very important natural resource which directly affects many human lives. In the United States, groundwater is the source of about 22 percent of the freshwater used. About 53 percent of the total population and 97 percent of the rural population use groundwater supplies for their drinking water (Moody, 1990). Although contamination of groundwater can occur naturally, agriculture is considered to be one of the most widespread nonprofit sources of groundwater contamination. Among agricultural chemicals, nitrogen-fertilizer has been used most extensively, especially by com producers. About one million tons of nitrogen-fertilizer are used annually in Iowa. In some studies, more than 50 percent of the applied fertilizer nitrogen is not removed by the crop or stored in the soil, and leaching as a form of nitrate is thought to be a major reason for the losses (Blackmer, 1987). Leached nitrate may enter groundwater supplies. Nitrate-nitrogen concentrations found in unsaturated soil below the rootzone of agricultural fields are in the range of 5 to 100 mg!L (Bouwer, 1990). Nitrate-nitrogen concentrations in tile drainage below row crops often exceed 10 mg/L, the U.S.A. drinking water standard (Gast et al., 1978; Baker and Johnson, 1981; Timmons and Dylla, 1981; Baker et al., 1985)
Critical Current Properties in Longitudinal Magnetic Field of YBCO Superconductor with APC
The critical current density (Jc) properties of the Artificial Pinning Center (APC) introduced YBa2Cu3O7 (YBCO) films in the longitudinal magnetic field were measured. Y2O3 or Y2BaCuO5 (Y211) was introduced as APCs to YBCO, and YBCO films with APC were fabricated on SrTiO3 single crystal substrate. The sizes of Y2O3 and Y211 were 5—10 nm and 10—20 nm, respectively. As a result, Jc enhancement in the longitudinal magnetic field was observed in Y2O3 introduced YBCO films. However, it was not observed in Y211 introduced YBCO films. Therefore, it was considered that Jc properties in the longitudinal magnetic field were affected by introducing of small size APC, and it was necessary that APC does not disturb the current pathway in the superconductor.28th International Symposium on Superconductivity, ISS 2015, November 16-18, 2015, Tokyo, Japa
Hydraulic properties of soil cores from untrafficked and trafficked areas
The hydraulic conductivity is an important soil parameter that is both difficult and time consuming to measure directly. Several methods have been proposed to estimate soil hydraulic conductivity indirectly. This paper focuses on one method of predi.:ting hydraulic conductivity from knowledge of the soil water retention curve. Water retention curves were measured for 15 undisturbed soil cores. Unsaturated hydraulic conductivity of the same 15 soil cores also was determined directly by using unit gradient measurements. An equation was fitted to each of the retention curves, and a procedure using the fitting parameters was implemented to predict hydraulic conductivity of each core. Predicted and observed hydraulic conductivities are compared. The procedure describes hydraulic conductivity relationships better when observed values of unsaturated hydraulic conductivity are included in the curve fitting process, than when the saturated hydraulic conductivity alone is used as a matching point. Analysis of a data set taken from the literature indicates that observed air permeabilities may also be useful for estimating the unsaturated hydraulic conductivity
Raman and fluorescence contributions to resonant inelastic soft x-ray scattering on LaAlO/SrTiO heterostructures
We present a detailed study of the Ti 3 carriers at the interface of
LaAlO/SrTiO heterostructures by high-resolution resonant inelastic soft
x-ray scattering (RIXS), with special focus on the roles of overlayer thickness
and oxygen vacancies. Our measurements show the existence of interfacial Ti
3 electrons already below the critical thickness for conductivity and an
increase of the total interface charge up to a LaAlO overlayer thickness of
6 unit cells before it levels out. By comparing stoichiometric and oxygen
deficient samples we observe strong Ti 3 charge carrier doping by oxygen
vacancies. The RIXS data combined with photoelectron spectroscopy and transport
measurements indicate the simultaneous presence of localized and itinerant
charge carriers. However, it is demonstrated that the relative amount of
localized and itinerant Ti electrons in the ground state cannot be deduced
from the relative intensities of the Raman and fluorescence peaks in excitation
energy dependent RIXS measurements, in contrast to previous interpretations.
Rather, we attribute the observation of either the Raman or the fluorescence
signal to the spatial extension of the intermediate state reached in the RIXS
excitation process.Comment: 9 pages, 6 figure
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