2,659 research outputs found
Rotating black hole orbit functionals in the frequency domain
In many astrophysical problems, it is important to understand the behavior of
functions that come from rotating (Kerr) black hole orbits. It can be
particularly useful to work with the frequency domain representation of those
functions, in order to bring out their harmonic dependence upon the fundamental
orbital frequencies of Kerr black holes. Although, as has recently been shown
by W. Schmidt, such a frequency domain representation must exist, the coupled
nature of a black hole orbit's and motions makes it difficult to
construct such a representation in practice. Combining Schmidt's description
with a clever choice of timelike coordinate suggested by Y. Mino, we have
developed a simple procedure that sidesteps this difficulty. One first Fourier
expands all quantities using Mino's time coordinate . In particular,
the observer's time is decomposed with . The frequency domain
description is then built from the -Fourier expansion and the
expansion of . We have found this procedure to be quite simple to implement,
and to be applicable to a wide class of functionals. We test the procedure
using a simple test function, and then apply it in a particularly interesting
case, the Weyl curvature scalar used in black hole perturbation
theory.Comment: 16 pages, 2 figures. Submitted to Phys Rev D. New version gives a
vastly improved algorithm due to Drasco for computing the Fourier transforms.
Drasco has been added as an author. Also fixed some references and
exterminated a small herd of typos; final published versio
A diffusion Monte Carlo study of small para-Hydrogen clusters
Ground state energies and chemical potentials of parahydrogen clusters are
calculated from 3 to 40 molecules using the diffusion Monte Carlo technique
with two different pH2-pH2 interactions. This calculation improves a previous
one by the inclusion of three-body correlations in the importance sampling, by
the time step adjustement and by a better estimation of the statistical errors.
Apart from the cluster with 13 molecules, no other magic clusters are
predicted, in contrast with path integral Monte Carlo results
Spin Coulomb drag in the two-dimensional electron liquid
We calculate the spin-drag transresistivity
in a two-dimensional electron gas at temperature in the random phase
approximation. In the low-temperature regime we show that, at variance with the
three-dimensional low-temperature result [], the spin transresistivity of a two-dimensional {\it spin unpolarized}
electron gas has the form . In the
spin-polarized case the familiar form is
recovered, but the constant of proportionality diverges logarithmically as
the spin-polarization tends to zero. In the high-temperature regime we obtain
(where
is the effective Rydberg energy) {\it independent} of the density.
Again, this differs from the three-dimensional result, which has a logarithmic
dependence on the density. Two important differences between the spin-drag
transresistivity and the ordinary Coulomb drag transresistivity are pointed
out: (i) The singularity at low temperature is smaller, in the Coulomb
drag case, by a factor where is the Fermi wave vector and
is the separation between the layers. (ii) The collective mode contribution
to the spin-drag transresistivity is negligible at all temperatures. Moreover
the spin drag effect is, for comparable parameters, larger than the ordinary
Coulomb drag effect.Comment: 6 figures; various changes; version accepted for publicatio
The alpha-particle in nuclear matter
Among the light nuclear clusters the alpha-particle is by far the strongest
bound system and therefore expected to play a significant role in the dynamics
of nuclei and the phases of nuclear matter. To systematically study the
properties of the alpha-particle we have derived an effective four-body
equation of the Alt-Grassberger-Sandhas (AGS) type that includes the dominant
medium effects, i.e. self energy corrections and Pauli-blocking in a consistent
way. The equation is solved utilizing the energy dependent pole expansion for
the sub system amplitudes. We find that the Mott transition of an
alpha-particle at rest differs from that expected from perturbation theory and
occurs at approximately 1/10 of nuclear matter densities.Comment: 9 pages RevTex file, 1 figure, submitted to Phys. Lett.
Membrane Bioreactor and Promising Application for Textile Industry in Vietnam
Abstract A pilot-scale membrane bioreactor (MBR) was developed in order to run two membrane modules in parallel for the treatment of model textile wastewater (MTDW). Two independently operated commercially available ultrafiltration membrane modules called UP150 from Microdyn-Nadir where tested in the same activated sludge tank over a period of 70 days for their removal efficiency of the MTDW. In general the results of both membrane modules are in very good agreement. The water permeability ranged between 20 – 50 L/(m 2 .h.bar). Typically, the chemical oxygen demand (COD) removal efficiency indicated good biodegradation performance above 95%. The nitrification rate depended on the food to microorganism (F/M) ratio i.e. below 0.2 kg COD/(kg MLSS.d) the system showed complete nitrification. However, the color rejection for the model dyes was only around 20% to 60% what can be attributed to the low biodegradability of these chemicals. The next step is to run the MBR with novel nanostructured membranes in parallel with the commercially available membrane to compare their performances. This study contributes to sustainable development in the textile industry by improving water quality of treated textile wastewater what helps to reduce fresh water consumption and pollutant discharge
Electron Spin Injection at a Schottky Contact
We investigate theoretically electrical spin injection at a Schottky contact
between a spin-polarized electrode and a non-magnetic semiconductor. Current
and electron density spin-polarizations are discussed as functions of barrier
energy and semiconductor doping density. The effect of a spin-dependent
interface resistance that results from a tunneling region at the
contact/semiconductor interface is described. The model can serve as a guide
for designing spin-injection experiments with regard to the interface
properties and device structure.Comment: 4 pages, 4 figure
Impact of the relatively light fourth family neutrino on the Higgs boson search
The existence of a fourth fermion generation has mostly been considered as a
source of enhanced Higgs signals with respect to the 3 family Standard Model
predictions. However, a fourth Standard Model family neutrino could cause the
opposite situation. It is shown that relatively light fourth family neutrino
(2m_(nu_(4))<m_(H)) could drastically change the interpretation of the search
results for the Higgs boson, especially if m_(H)<170 GeV.Comment: 5 pages, 9 figure
Short time evolved wave functions for solving quantum many-body problems
The exact ground state of a strongly interacting quantum many-body system can
be obtained by evolving a trial state with finite overlap with the ground state
to infinite imaginary time. In this work, we use a newly discovered fourth
order positive factorization scheme which requires knowing both the potential
and its gradients. We show that the resultaing fourth order wave function
alone, without further iterations, gives an excellent description of strongly
interacting quantum systems such as liquid 4He, comparable to the best
variational results in the literature.Comment: 5 pages, 3 figures, 1 tabl
Vacuum creation of quarks at the time scale of QGP thermalization and strangeness enhancement in heavy-ion collisions
The vacuum parton creation in quickly varying external fields is studied at
the time scale of order 1 fm/ typical for the quark-gluon plasma formation
and thermalization. To describe the pre-equilibrium evolution of the system the
transport kinetic equation is employed. It is shown that the dynamics of
production process at times comparable with particle inverse masses can deviate
considerably from that based on classical Schwinger-like estimates for
homogeneous and constant fields. One of the effects caused by non-stationary
chromoelectric fields is the enhancement of the yield of quark
pairs. Dependence of this effect on the shape and duration of the field pulse
is studied together with the influence of string fusion and reduction of quark
masses.Comment: REVTEX, 11pp. incl. 4 figures, to be published in Phys. Lett.
Quantum linear mutual information and classical correlations in globally pure bipartite systems
We investigate the correlations of initially separable probability
distributions in a globally pure bipartite system with two degrees of freedom
for classical and quantum systems. A classical version of the quantum linear
mutual information is introduced and the two quantities are compared for a
system of oscillators coupled with both linear and non-linear interactions. The
classical correlations help to understand how much of the quantum loss of
purity are due to intrinsic quantum effects and how much is related to the
probabilistic character of the initial states, a characteristic shared by both
the classical and quantum pictures. Our examples show that, for initially
localized Gaussian states, the classical statistical mutual linear entropy
follows its quantum counterpart for short times. For non-Gaussian states the
behavior of the classical and quantum measures of information are still
qualitatively similar, although the fingerprints of the non-classical nature of
the initial state can be observed in their different amplitudes of oscillation.Comment: (16 pages, 4 figures
- …