9,372 research outputs found
Generalized Einstein or Green-Kubo relations for active biomolecular transport
For driven Markovian dynamics on a network of (biomolecular) states, the
generalized mobilities, i.e., the response of any current to changes in an
external parameter, are expressed by an integral over an appropriate
current-current correlation function and thus related to the generalized
diffusion constants. As only input, a local detailed balance condition is
required typically even valid for biomolecular systems operating deep in the
non-equilibrium regime.Comment: 4 page
Sublattice Asymmetric Reductions of Spin Values on Stacked Triangular Lattice Antiferromagnet CsCoBr
We study the reductions of spin values of the ground state on a stacked
triangular antiferromagnet using the spin-wave approach. We find that the spin
reductions have sublattice asymmetry due to the cancellation of the molecular
field. The sublattice asymmetry qualitatively analyzes the NMR results of
CsCoBr.Comment: 5pages, 5figure
Social disruption stress exacerbates alpha-galactosylceramide-induced hepatitis in mice
Objective: Psychosocial stress has been suggested as a possible aggravating factor in liver diseases, however, the underlying mechanism has yet to be clarified. Recently, our research revealed that electric foot-shock stress aggravated NK1.1 Ag+ T cell-dependent a-galactosylceramide (alpha-GalCer)-induced hepatitis in mice via a mechanism mediated by endogenous glucocorticoids. In this study, we examined whether or not such aggravation could be applied to a psychosocially stressful situation, e.g. social disruption stress. Methods: Male wildtype C57BL/6 (B6) or B6 hepatitis virus type B surface antigen transgenic (HBs-tg) mice, a hepatitis B virus carrier mouse model, were exposed 3 times in 1 week to social disruption stress in which an 8-month-old aggressive male intruder was placed into their home cage (5 mice per group) for 2 h. Twelve hours after the final exposure to the stress, the wild-type and HBs-tg mice were intravenously injected with alpha-GalCer. Results:The stress-exposed wild-type mice exhibited significantly reduced thymus weight loss compared with the control animals. Moreover, this stress regimen led to a significant increase in serum alanine aminotransferase levels in both the wild-type and the HBs-tg mice, although the increase in the HBs-tg mice was higher than that in the wild-type mice. Conclusion: These findings demonstrated that, similar to electric foot-shock stress, social disruption stress exacerbated alpha-GalCer-induced hepatitis. Copyright (C) 2005 S. Karger AG, Basel
The hepatic sympathetic nerve plays a critical role in preventing Fas induced liver injury in mice
Background: Although previous studies have shown that the hepatic sympathetic nerve controls various physiological functions in the liver, the role of this nerve in liver injury has yet to be clarified.Aims: The purpose of this study was to elucidate the role of this nerve, based on our newly developed technique for selectively removing the activities of the hepatic sympathetic nerve.Subjects and methods: Male C57BL/6 mice were operated on for hepatic sympathetic denervation. Thereafter, mice were intravenously administered 0.25 or 0.35 mg/g weight of the Fas agonist antibody, Jo-2, after which mortality by fulminant hepatitis was evaluated. Apoptosis in the liver was also examined by both terminal deoxynucleotidyl transferase mediated dUTP nick end labelling and caspase-3 assay.Results: Mortality in sympathectomised mice was significantly higher than that in sham operated mice following administration of Jo-2. This result was also supported by apoptosis data in which sympathectomised livers exhibited a significant elevation in the number of apoptotic hepatocytes and caspase-3 activity after Jo-2 treatment compared with sham operated livers. Moreover, pretreatment with norepinephrine dose dependently inhibited the hepatic sympathectomy induced increase in mortality after Jo-2 injection. Antiapoptotic protein levels of FLICE inhibitory protein, Bcl-xL, and Bcl-2 in the liver were significantly lower in sympathectomised mice at one and two hours following Jo-2 treatment than in sham operated animals. In addition, interleukin 6 supplementation dose dependently suppressed the hepatic sympathectomy induced increase in mortality after Jo-2 treatment.Conclusions: These results suggest that norepinephrine released from the hepatic sympathetic nerve plays a critical role in protecting the liver from Fas mediated fulminant hepatitis, possibly via mechanisms including antiapoptotic proteins and interleukin 6
Electric foot-shock stress drives TNF-alpha production in the liver of IL-6-deficient mice
Objectives: Accumulating evidence has shown that interleukin-6 (IL-6) has pleiotropic effects on a variety of biological functions, including its antiapoptotic potential during liver injury. Our previous work demonstrated that restraint stress-induced elevation of plasma IL-6 negatively regulates plasma tumor necrosis factor-alpha (TNF-alpha). Herein, we further clarified the mechanism underlying the above finding and investigated the effect of IL-6 on liver apoptosis triggered by stress. Methods: Male C57BL/6J and IL-6-deficient C57BL/SV129 mice were exposed to 1 h of electric foot-shock stress. Thereafter, the serum, liver and spleen TNF-alpha levels were measured at several time points. Serum alanine aminotransferase (ALT), liver caspase-3 and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling ( TUNEL) activities were analyzed to evaluate the severity of liver injury and apoptosis. Results: The liver, but not the spleen, of the IL-6-deficient mice exhibited a significant increase in TNF-alpha level after stress in parallel with serum TNF-alpha elevation, whereas no such TNF-alpha responses were found in the wild animals. No significant differences in stress-induced elevation of serum ALT levels, liver caspase-3 activities and the number of TUNEL-positive hepatocytes were found between the wild and IL-6-deficient mice. Conclusions: Taken together, these results indicate that IL-6 may play a critical role in suppressing TNF-alpha production in the liver, thereby decreasing the blood TNF-alpha level. In contrast, IL-6 secretion was shown to have no protective effect on stress-triggered liver injury. Copyright (C) 2004 S. Karger AG, Basel
Carrier States and Ferromagnetism in Diluted Magnetic Semiconductors
Applying the dynamical coherent potential approximation to a simple model, we
have systematically studied the carrier states in Mn-type diluted
magnetic semiconductors (DMS's). The model calculation was performed for three
typical cases of DMS's: The cases with strong and moderate exchange
interactions in the absence of nonmagnetic potentials, and the case with strong
attractive nonmagnetic potentials in addition to moderate exchange interaction.
When the exchange interaction is sufficiently strong, magnetic impurity bands
split from the host band. Carriers in the magnetic impurity band mainly stay at
magnetic sites, and coupling between the carrier spin and the localized spin is
very strong. The hopping of the carriers among the magnetic sites causes
ferromagnetism through a {\it double-exchange (DE)-like} mechanism. We have
investigated the condition for the DE-like mechanism to operate in DMS's. The
result reveals that the nonmagnetic attractive potential at the magnetic site
assists the formation of the magnetic impurity band and makes the DE-like
mechanism operative by substantially enhancing the effect of the exchange
interaction. Using conventional parameters we have studied the carrier states
in GaMnAs. The result shows that the ferromagnetism is caused
through the DE-like mechanism by the carriers in the bandtail originating from
the impurity states.Comment: 20 pages, 14 figure
Electronic structure and resistivity of the double exchange model
The double exchange (DE) model with quantum local spins S is studied; an
equation of motion approach is used and decoupling approximations analogous to
Hubbard's are made. Our approximate one-electron Green function G is exact in
the atomic limit of zero bandwidth for all S and band filling n, and as n->0
reduces to a dynamical coherent potential approximation (CPA) due to Kubo; we
regard our approximation as a many-body generalisation of Kubo's CPA. G is
calculated self-consistently for general S in the paramagnetic state and for
S=1/2 in a state of arbitrary magnetization. The electronic structure is
investigated and four bands per spin are obtained centred on the atomic limit
peaks of the spectral function. A resistivity formula appropriate to the model
is derived from the Kubo formula and the paramagnetic state resistivity rho is
calculated; insulating states are correctly obtained at n=0 and n=1 for strong
Hund coupling. Our prediction for rho is much too small to be consistent with
experiments on manganites so we agree with Millis et al that the bare DE model
is inadequate. We show that the agreement with experiment obtained by Furukawa
is due to his use of an unphysical density of states.Comment: 20 pages, 8 figures, submitted to J. Phys.: Condens. Matte
Super and Sub-Poissonian photon statistics for single molecule spectroscopy
We investigate the distribution of the number of photons emitted by a single
molecule undergoing a spectral diffusion process and interacting with a
continuous wave laser field. The spectral diffusion is modeled based on a
stochastic approach, in the spirit of the Anderson-Kubo line shape theory.
Using a generating function formalism we solve the generalized optical Bloch
equations, and obtain an exact analytical formula for the line shape and
Mandel's Q parameter. The line shape exhibits well known behaviors, including
motional narrowing when the stochastic modulation is fast, and power
broadening. The Mandel parameter, describing the line shape fluctuations,
exhibits a transition from a Quantum sub-Poissonian behavior in the fast
modulation limit, to a classical super-Poissonian behavior found in the slow
modulation limit. Our result is applicable for weak and strong laser field,
namely for arbitrary Rabi frequency. We show how to choose the Rabi frequency
in such a way that the Quantum sub-Poissonian nature of the emission process
becomes strongest. A lower bound on is found, and simple limiting behaviors
are investigated. A non-trivial behavior is obtained in the intermediate
modulation limit, when the time scales for spectral diffusion and the life time
of the excited state, become similar. A comparison is made between our results,
and previous ones derived based on the semi-classical generalized
Wiener--Khintchine theorem.Comment: 14 Phys. Rev style pages, 10 figure
Classical orbital paramagnetism in non-equilibrium steady state
We report the results of our numerical simulation of classical-dissipative
dynamics of a charged particle subjected to a non-markovian stochastic forcing.
We find that the system develops a steady-state orbital magnetic moment in the
presence of a static magnetic field. Very significantly, the sign of the
orbital magnetic moment turns out to be {\it paramagnetic} for our choice of
parameters, varied over a wide range. This is shown specifically for the case
of classical dynamics driven by a Kubo-Anderson type non-markovian noise.
Natural spatial boundary condition was imposed through (1) a soft (harmonic)
confining potential, and (2) a hard potential, approximating a reflecting wall.
There was no noticeable qualitative difference. What appears to be crucial to
the orbital magnetic effect noticed here is the non-markovian property of the
driving noise chosen. Experimental realization of this effect on the laboratory
scale, and its possible implications are briefly discussed. We would like to
emphasize that the above steady-state classical orbital paramagnetic moment
complements, rather than contradicts the Bohr-van Leeuwen (BvL) theorem on the
absence of classical orbital diamagnetism in thermodynamic equilibrium.Comment: 6 pages, 4 figures, Has appeared in Journal of Astrophysics and
Astronomy special issue on 'Physics of Neutron Stars and Related Objects',
celebrating the 75th birth-year of G. Srinivasa
An expression for stationary distribution in nonequilibrium steady state
We study the nonequilibrium steady state realized in a general stochastic
system attached to multiple heat baths and/or driven by an external force.
Starting from the detailed fluctuation theorem we derive concise and suggestive
expressions for the corresponding stationary distribution which are correct up
to the second order in thermodynamic forces. The probability of a microstate
is proportional to where
is the excess entropy change.
Here is the difference between two kinds of conditioned
path ensemble averages of excess heat transfer from the -th heat bath whose
inverse temperature is . Our expression may be verified experimentally
in nonequilibrium states realized, for example, in mesoscopic systems.Comment: 4 pages, 2 figure
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