599 research outputs found
Alcohol Increases Microglial Expression of Chemokine MIP-1 and MCP-1 mRNA
Fetal exposure to alcohol can lead to extensive pathology in the CNS causing fetal alcohol syndrome or alcohol-related neurodevelopmental disorder. Our previous research has revealed that alcohol has detrimental effects on development of neurons and glial cells, including microglia. However, the effects of alcohol on microglial function as well as interactions between microglia and neurons remain relatively unexplored. Microglia produce immunomodulatory cytokines and chemokines that directly control the survival, development, and function of neurons and glia. In this study, mouse N9 microglial cells were treated with 0.5% (w/v) ethanol for 12-48 hr with or without subsequent challenge with the cellular activator lipopolysaccharide. Microglial expression of the cytokines IL1,IL6,IL10,IL12, TNFcc, IFNy, and MIF, and the chemokines MCP-1, MIP-loc,MIP-1p, MIP-2, IP-10, TCA-3, and RANTES was quantified by ribonuclease protection assay of cellular RNA. The mRNA levels of MIP-1P, MlP-la, and MCP-1 RNA were increased 94% (
Fermi Edge Singularities and Backscattering in a Weakly Interacting 1D Electron Gas
The photon-absorption edge in a weakly interacting one-dimensional electron
gas is studied, treating backscattering of conduction electrons from the core
hole exactly. Close to threshold, there is a power-law singularity in the
absorption, , with where is the forward scattering
phase shift of the core hole. In contrast to previous theories, is
finite (and universal) in the limit of weak core hole potential. In the case of
weak backscattering , the exponent in the power-law dependence of
absorption on energy crosses over to a value above an energy scale , where is a dimensionless measure of the
electron-electron interactions.Comment: 8 pages + 1 postscript figure, preprint TPI-MINN-93/40-
Coulomb blockade of strongly coupled quantum dots studied via bosonization of a channel with a finite barrier
A pair of quantum dots, coupled through a point contact, can exhibit Coulomb
blockade effects that reflect an oscillatory term in the dots' total energy
whose value depends on whether the total number of electrons on the dots is
even or odd. The effective energy associated with this even-odd alternation is
reduced, relative to the bare Coulomb blockade energy for uncoupled dots, by a
factor (1-f) that decreases as the interdot coupling is increased. When the
transmission coefficient for interdot electronic motion is independent of
energy and the same for all channels within the point contact (which are
assumed uncoupled), the factor (1-f) takes on a universal value determined
solely by the number of channels and the dimensionless conductance g of each
individual channel.
This paper studies corrections to the universal value of (1-f) that result
when the transmission coefficent varies over energy scales of the size of the
bare Coulomb blockade energy. We consider a model in which the point contact is
described by a single orbital channel containing a parabolic barrier potential,
and we calculate the leading correction to (1-f) for one-channel (spin-split)
and two-channel (spin-degenerate) point contacts in the limit where the single
orbital channel is almost completely open. By generalizing a previously used
bosonization technique, we find that, for a given value of the dimensionless
conductance g, the value of (1-f) is increased relative to its value for a
zero-thickness barrier, but the absolute value of the increase is small in the
region where our calculations apply.Comment: 13 pages, 3 Postscript figure
Dynamical electron transport through a nanoelectromechanical wire in a magnetic field
We investigate dynamical transport properties of interacting electrons moving
in a vibrating nanoelectromechanical wire in a magnetic field. We have built an
exactly solvable model in which electric current and mechanical oscillation are
treated fully quantum mechanically on an equal footing. Quantum mechanically
fluctuating Aharonov-Bohm phases obtained by the electrons cause nontrivial
contribution to mechanical vibration and electrical conduction of the wire. We
demonstrate our theory by calculating the admittance of the wire which are
influenced by the multiple interplay between the mechanical and the electrical
energy scales, magnetic field strength, and the electron-electron interaction
Control of Ovulation Rate in Beef Cattle.
End of Project ReportUnder intensive production systems, the greatest potential for effecting increases
in production and economic efficiency in the beef cow herd lies in the possibility
of increasing the frequency of twin births. Embryo transfer is technically a
successful method of inducing twin births in cattle. While an embryo transfer
approach is too costly to allow commercial twinning, it has been used to show
that ovulation rate and not uterine capacity is the limiting factor in increasing the
reproductive rate of the cow. While ovulation of one or more viable oocytes is
central to normal reproduction, knowledge of the control of ovulation and of
folliculogenesis on which ovulation depends, is limited. In spite of the fact that
many follicles are subjected to the same endogenous hormonal environment and
theoretically should all be capable of ovulating, only a tiny proportion do. While
gonadotrophic hormones play a central role in ovarian follicle development and
ovulation, their action at the ovarian level seems to be controlled by intra-ovarian
factors. This intra-ovarian control of ovulation is thought to be exerted partly by
the hormone inhibin and partly by other, as yet, unidentified compounds in
follicular fluid. This project focused on identification and isolation of ovarian
compounds involved in the control of ovulation rate, followed by immunisation
against these compounds in order to study the effect on ovulation and the twin
calving rates. The main results are summarised here and detailed results have
been published in the papers listed at the end of this report
Spin- and charge-density oscillations in spin chains and quantum wires
We analyze the spin- and charge-density oscillations near impurities in spin
chains and quantum wires. These so-called Friedel oscillations give detailed
information about the impurity and also about the interactions in the system.
The temperature dependence of these oscillations explicitly shows the
renormalization of backscattering and conductivity, which we analyze for a
number of different impurity models. We are also able to analyze screening
effects in one dimension. The relation to the Kondo effect and experimental
consequences are discussed.Comment: Final published version. 15 pages in revtex format including 22
epsf-embedded figures. The latest version in PDF format is available from
http://fy.chalmers.se/~eggert/papers/density-osc.pd
Soluble `Supersymmetric' Quantum XY Model
We present a `supersymmetric' modification of the -dimensional quantum
rotor model whose ground state is exactly soluble. The model undergoes a
vortex-binding transition from insulator to metal as the rotor coupling is
varied. The Hamiltonian contains three-site terms which are relevant: they
change the universality class of the transition from that of the ()--- to
the -dimensional classical XY model. The metallic phase has algebraic ODLRO
but the superfluid density is identically zero. Variational wave functions for
single-particle and collective excitations are presented.Comment: 12 pages, REVTEX 3.0, IUCM93-00
Low-temperature nonequilibrium transport in a Luttinger liquid
The temperature-dependent nonlinear conductance for transport of a Luttinger
liquid through a barrier is calculated in the nonperturbative regime for
, where is the dimensionless interaction constant. To
describe the low-energy behavior, we perform a leading-log summation of all
diagrams contributing to the conductance which is valid for .
With increasing external voltage, the asymptotic low-temperature behavior
displays a turnover from the to a universal law.Comment: 13 pages RevTeX 3.0, accepted by Physical Review
Electron spin coherence in semiconductors: Considerations for a spin-based solid state quantum computer architecture
We theoretically consider coherence times for spins in two quantum computer
architectures, where the qubit is the spin of an electron bound to a P donor
impurity in Si or within a GaAs quantum dot. We show that low temperature
decoherence is dominated by spin-spin interactions, through spectral diffusion
and dipolar flip-flop mechanisms. These contributions lead to 1-100 s
calculated spin coherence times for a wide range of parameters, much higher
than former estimates based on measurements.Comment: Role of the dipolar interaction clarified; Included discussion on the
approximations employed in the spectral diffusion calculation. Final version
to appear in Phys. Rev.
Effective action and interaction energy of coupled quantum dots
We obtain the effective action of tunnel-coupled quantum dots, by modeling
the system as a Luttinger liquid with multiple barriers. For a double dot
system, we find that the resonance conditions for perfect conductance form a
hexagon in the plane of the two gate voltages controlling the density of
electrons in each dot. We also explicitly obtain the functional dependence of
the interaction energy and peak-splitting on the gate voltage controlling
tunneling between the dots and their charging energies. Our results are in good
agreement with recent experimental results, from which we obtain the Luttinger
interaction parameter .Comment: 5 pgs,latex,3 figs,revised version to be publshed in Phys.Rev.
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