20,362 research outputs found
On some further properties of nonzero-sum diffential games
Optimality principle and open loop-closed loop control relations in nonzero-sum differential game
Atmospheres and radiating surfaces of neutron stars with strong magnetic fields
We review the current status of the theory of thermal emission from the
surface layers of neutron stars with strong magnetic fields G, including formation of the spectrum in a partially ionized
atmosphere and at a condensed surface. In particular, we describe recent
progress in modeling partially ionized atmospheres of central compact objects
in supernova remnants, which may have moderately strong fields G. Special attention is given to polarization of thermal
radiation emitted by a neutron star surface. Finally, we briefly describe
applications of the theory to observations of thermally emitting isolated
neutron stars.Comment: 27 pages, 5 figures, invited review at the conference "The Modern
Physics of Compact Stars 2015" (Yerevan, Armenia, Sept. 30 - Oct. 3, 2015),
edited by R. Avagyan, A. Saharian, and A. Sedrakian. In v.2, a citation
(Ref.114) is correcte
Opacities and spectra of hydrogen atmospheres of moderately magnetized neutron stars
There is observational evidence that central compact objects (CCOs) in
supernova remnants have moderately strong magnetic fields G.
Meanwhile, available models of partially ionized hydrogen atmospheres of
neutron stars with strong magnetic fields are restricted to
G. We extend the equation of state and radiative opacities, presented in
previous papers for 10^{12}\mbox{ G}\lesssim B \lesssim 10^{15} G, to weaker
fields. An equation of state and radiative opacities for a partially ionized
hydrogen plasma are obtained at magnetic fields , temperatures , and
densities typical for atmospheres of CCOs and other isolated neutron
stars with moderately strong magnetic fields. The first- and second-order
thermodynamic functions, monochromatic radiative opacities, and Rosseland mean
opacities are calculated and tabulated, taking account of partial ionization,
for 3\times10^{10}\mbox{ G}\lesssim B\lesssim 10^{12} G, K K, and a wide range of densities. Atmosphere models and spectra
are calculated to verify the applicability of the results and to determine the
range of magnetic fields and effective temperatures where the incomplete
ionization of the hydrogen plasma is important.Comment: 11 pages, 7 figures, accepted for publication in A&
Binding Energies and Scattering Observables in the ^3He^4He_2 Atomic System
The ^3He^4He_2 three-atomic system is studied on the basis of a hard-core
version of the Faddeev differential equations. The binding energy of the
^3He^4He_2 trimer, scattering phase shifts, and the scattering length of a ^3He
atom off a ^4He dimer are calculated using the LM2M2 and TTY He-He interatomic
potentials.Comment: Contribution to Proceedings of the 17th International IUPAP
Conference on Few-Body Problems in Physics (Durham, North Carolina, USA, June
5-10, 2003
Two--Electron Atoms in Short Intense Laser Pulses
We discuss a method of solving the time dependent Schrodinger equation for
atoms with two active electrons in a strong laser field, which we used in a
previous paper [A. Scrinzi and B. Piraux, Phys. Rev. A 56, R13 (1997)] to
calculate ionization, double excitation and harmonic generation in Helium by
short laser pulses. The method employs complex scaling and an expansion in an
explicitly correlated basis. Convergence of the calculations is documented and
error estimates are provided. The results for Helium at peak intensities up to
10^15 W/cm^2 and wave length 248 nm are accurate to at least 10 %. Similarly
accurate calculations are presented for electron detachment and double
excitation of the negative hydrogen ion.Comment: 14 pages, including figure
Magnetic Hydrogen Atmosphere Models and the Neutron Star RX J1856.5-3754
RX J1856.5-3754 is one of the brightest nearby isolated neutron stars, and
considerable observational resources have been devoted to it. However, current
models are unable to satisfactorily explain the data. We show that our latest
models of a thin, magnetic, partially ionized hydrogen atmosphere on top of a
condensed surface can fit the entire spectrum, from X-rays to optical, of RX
J1856.5-3754, within the uncertainties. In our simplest model, the best-fit
parameters are an interstellar column density N_H \approx 1x10^20 cm^-2 and an
emitting area with R^infty \approx 17 km (assuming a distance to RX
J1856.5-3754 of 140 pc), temperature T^infty \approx 4.3x10^5 K, gravitational
redshift z_g \sim 0.22, atmospheric hydrogen column y_H \approx 1 g cm^-2, and
magnetic field B \approx (3-4)x10^12 G; the values for the temperature and
magnetic field indicate an effective average over the surface. We also
calculate a more realistic model, which accounts for magnetic field and
temperature variations over the neutron star surface as well as general
relativistic effects, to determine pulsations; we find there exist viewing
geometries that produce pulsations near the currently observed limits. The
origin of the thin atmospheres required to fit the data is an important
question, and we briefly discuss mechanisms for producing these atmospheres.
Our model thus represents the most self-consistent picture to date for
explaining all the observations of RX J1856.5-3754.Comment: 11 pages, 8 figures; MNRAS, accepte
The effect of screening long-range Coulomb interactions on the metallic behavior in two-dimensional hole systems
We have developed a technique utilizing a double quantum well heterostructure
that allows us to study the effect of a nearby ground-plane on the metallic
behavior in a GaAs two-dimensional hole system (2DHS) in a single sample and
measurement cool-down, thereby maintaining a constant disorder potential. In
contrast to recent measurements of the effect of ground-plane screening of the
long-range Coulomb interaction in the insulating regime, we find surprisingly
little effect on the metallic behavior when we change the distance between the
2DHS and the nearby ground-plane.Comment: 5 pages, 4 figures, accepted for publication in PR
Ballistic transport in induced one-dimensional hole systems
We have fabricated and studied a ballistic one-dimensional p-type quantum
wire using an undoped AlGaAs/GaAs heterostructure. The absence of modulation
doping eliminates remote ionized impurity scattering and allows high mobilities
to be achieved over a wide range of hole densities, and in particular, at very
low densities where carrier-carrier interactions are strongest. The device
exhibits clear quantized conductance plateaus with highly stable gate
characteristics. These devices provide opportunities for studying spin-orbit
coupling and interaction effects in mesoscopic hole systems in the strong
interaction regime where rs > 10.Comment: 6 pages, 4 figures (accepted to Applied Physics Letters
Optimization of Growth Medium for Efficient Cultivation of Lactobacillus salivarius i 24 using Response Surface Method
Production of Lactobacillus salivarius i 24, a probiotic strain for chicken, was studied in batch fermentation using 500 mL Erlenmeyer flask. Response surface method (RSM) was used to optimize the medium for efficient cultivation of the bacterium. The factors investigated were yeast extract, glucose and initial culture pH. A polynomial regression model with cubic and quartic terms was used for the analysis of the experimental data. Estimated optimal conditions of the factors for growth of L. salivarius i 24 were; 3.32 % (w/v) glucose, 4.31 % (w/v) yeast extract and initial culture pH of 6.10
Quantum Hall Ferromagnets
It is pointed out recently that the quantum Hall states in bilayer
systems behave like easy plane quantum ferromagnets. We study the
magnetotransport of these systems using their ``ferromagnetic" properties and a
novel spin-charge relation of their excitations. The general transport is a
combination of the ususal Hall transport and a time dependent transport with
time average. The latter is due to a phase slippage process in
and is characterized by two topological constants. (Figures will be
provided upon requests).Comment: 4 pages, Revtex, Ohio State Universit
- …