40,354 research outputs found
A Novel Method for the Solution of the Schroedinger Eq. in the Presence of Exchange Terms
In the Hartree-Fock approximation the Pauli exclusion principle leads to a
Schroedinger Eq. of an integro-differential form. We describe a new spectral
noniterative method (S-IEM), previously developed for solving the
Lippman-Schwinger integral equation with local potentials, which has now been
extended so as to include the exchange nonlocality. We apply it to the
restricted case of electron-Hydrogen scattering in which the bound electron
remains in the ground state and the incident electron has zero angular
momentum, and we compare the acuracy and economy of the new method to three
other methods. One is a non-iterative solution (NIEM) of the integral equation
as described by Sams and Kouri in 1969. Another is an iterative method
introduced by Kim and Udagawa in 1990 for nuclear physics applications, which
makes an expansion of the solution into an especially favorable basis obtained
by a method of moments. The third one is based on the Singular Value
Decomposition of the exchange term followed by iterations over the remainder.
The S-IEM method turns out to be more accurate by many orders of magnitude than
any of the other three methods described above for the same number of mesh
points.Comment: 29 pages, 4 figures, submitted to Phys. Rev.
Suaeda japonica Makino Attenuates Lipopolysaccharide- Induced Neuro-Inflammatory Responses in BV-2 Microglia via NF-kappa B Signaling
Purpose: To evaluate in vitro anti-oxidant and anti-neuro-inflammatory activities of Suaeda japonica extract (SJE) in lipopolysaccharide (LPS)-stimulated BV-2 microglial cells.Methods: 1, 1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging assay was used to study the antioxidant effects. 3-(4, 5-dimethylthiazol-2-yl)-2, 5- diphenyl-tetrazolium bromide (MTT) assay was used to study cell viabilities. LPS-stimulated BV- microglial cells were used to study the geneexpression and production of inflammatory mediators determined by Western blot analysis.Results: SJE significantly inhibited the DPPH generated free radicals, and suppressed LPS-induced expression of inducible nitric oxide synthase (iNOS) and production of nitric oxide (NO) in a concentration-dependent manner. It decreased LPS-induced expression of some inflammatorymediators and pro-inflammatory cytokines (cyclooxygenase-2 and interleukin (IL)-6). This suppression of inflammatory mediators was nuclear factor kappa-B (NF-êB)-dependent.Conclusion: Our findings imply that SJE may be a potential therapeutic agent in regulating microgliamediated neuroinflammatory responses observed in several neurodegenerative diseases.Keywords: Suaeda japonica, Antioxidant activity, Anti-inflammatory activity, Microglial Cells, iNOS, IL-6
Distribution of equilibrium free energies in a thermodynamic system with broken ergodicity
At low temperatures the configurational phase space of a macroscopic complex
system (e.g., a spin-glass) of interacting particles may split
into an exponential number of
ergodic sub-spaces (thermodynamic states). Previous theoretical studies assumed
that the equilibrium collective behavior of such a system is determined by its
ground thermodynamic states of the minimal free-energy density, and that the
equilibrium free energies follow the distribution of exponential decay. Here we
show that these assumptions are not necessarily valid. For some complex
systems, the equilibrium free-energy values may follow a Gaussian distribution
within an intermediate temperature range, and consequently their equilibrium
properties are contributed by {\em excited} thermodynamic states. This work
will help improving our understanding of the equilibrium statistical mechanics
of spin-glasses and other complex systems.Comment: 7 pages, 2 figure
Efficiency of Nonlinear Particle Acceleration at Cosmic Structure Shocks
We have calculated the evolution of cosmic ray (CR) modified astrophysical
shocks for a wide range of shock Mach numbers and shock speeds through
numerical simulations of diffusive shock acceleration (DSA) in 1D quasi-
parallel plane shocks. The simulations include thermal leakage injection of
seed CRs, as well as pre-existing, upstream CR populations. Bohm-like diffusion
is assumed. We model shocks similar to those expected around cosmic structure
pancakes as well as other accretion shocks driven by flows with upstream gas
temperatures in the range K and shock Mach numbers spanning
. We show that CR modified shocks evolve to time-asymptotic states
by the time injected particles are accelerated to moderately relativistic
energies (p/mc \gsim 1), and that two shocks with the same Mach number, but
with different shock speeds, evolve qualitatively similarly when the results
are presented in terms of a characteristic diffusion length and diffusion time.
For these models the time asymptotic value for the CR acceleration efficiency
is controlled mainly by shock Mach number. The modeled high Mach number shocks
all evolve towards efficiencies %, regardless of the upstream CR
pressure. On the other hand, the upstream CR pressure increases the overall CR
energy in moderate strength shocks (). (abridged)Comment: 23 pages, 12 ps figures, accepted for Astrophysical Journal (Feb. 10,
2005
Non-local Control of the Kondo Effect in a Double Quantum Dot-Quantum Wire Coupled System
We have performed low-temperature transport measurements on a double quantum
dot-quantum wire coupled device and demonstrated non-local control of the Kondo
effect in one dot by manipulating the electronic spin states of the other. We
discuss the modulation of the local density of states in the wire region due to
the Fano-Kondo antiresonance, and the Ruderman-Kittel-Kasuya-Yoshida (RKKY)
exchange interaction as the mechanisms responsible for the observed features.Comment: 4 pages, 4 figure
Interference through quantum dots
We discuss the effect of quantum interference on transport through a quantum
dot system. We introduce an indirect coherent coupling parameter alpha, which
provides constructive/destructive interference in the transport current
depending on its phase and the magnetic flux. We estimate the current through
the quantum dot system using the non-equilibrium Green's function method as
well as the master equation method in the sequential tunneling regime. The
visibility of the Aharonov-Bohm oscillation is evaluated. For a large inter-dot
Coulomb interaction, the current is strongly suppressed by the quantum
interference effect, while the current is restored by applying an oscillating
resonance field with the frequency of twice the inter-dot tunneling energy.Comment: 10 pages, 3 figure
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