13,467 research outputs found
Cyclosporine augments hepatic regenerative response in rats
A number of mechanisms participate in the hepatic injury that occurs during and following liver transplantation. A normal allograft regenerative response is probably essential for a successful transplant outcome. In this study, the effect of cyclosporine, a potent immunosuppressant used routinely after liver transplantation, on the regenerative response of the liver after partial hepatectomy was investigated. Male Wistar rats were pretreated for one week with either cyclosporine or the olive oil vehicle and were subjected to either a two-thirds partial hepatectomy or a sham operation. Animals were sacrificed at various times postoperatively and the remnant livers were weighed to determine the liver weight to body weight ratio, two biochemical measures of a regenerative response (cytosolic ornithine decarboxylase activity and thymidine kinase activity), and the hepatic content of estrogen and androgen receptors, as the content of these receptors has been shown to modulate, at least in part, the subsequent hepatic regenerative response. The preoperative hepatic cytosol content of ornithine decarboxylase, thymidine kinase, and estrogen receptor was significantly greater (P<0.05) in rats pretreated with cyclosporine than in those treated with the vehicle alone. A significant increase in ornithine decarboxylase and thymidine kinase activities occurred after partial hepatectomy in both the cyclosporine-pretreated and vehicle-pretreated animals. The absolute levels for each parameter were also greater in the cyclosporine-treated animals than in the vehicle-treated controls at 24 hr after partial hepatectomy (P<0.05). The pattern of change in the hepatic cytosolic content of estrogen and androgen receptors in both groups of animals was comparable with those described previously for regenerating liver. These data suggest that cyclosporine may predispose the liver to respond to either a regenerative signal or perceived need and thereby fortuitously enhance liver graft performance after successful surgical implantation. © 1989 Plenum Publishing Corporation
Magnetic phase diagram of a frustrated ferrimagnetic ladder: Relation to the one-dimensional boson Hubbard model
We study the magnetic phase diagram of two coupled mixed-spin
Heisenberg chains as a function of the frustration parameter related to
diagonal exchange couplings. The analysis is performed by using spin-wave
series and exact numerical diagonalization techniques. The obtained phase
diagram--containing the Luttinger liquid phase, the plateau phase with a
magnetization per rung , and the fully polarized phase--is closely
related to the generic phase diagram of the one-dimensional boson
Hubbard model.Comment: 4 pages, 2 figure
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The super greenhouse effect in a changing climate
In all outputs of the 1%/yr increase inCO2 climate model experiments archived under the World Climate
Research Programme’s (WCRP) phase 5 of the Coupled Model Intercomparison Project (CMIP5), regions
exist in the low latitudes where both the clear-sky and all-sky OLR decrease with surface warming. These are
identified as regions of positive longwave feedback and are regions of a super greenhouse effect (SGE). These
SGE regions are identified from feedback analysis of the 4X CO2 abrupt experiments of CMIP5, and despite
their existence, there is little agreement across models as to the magnitude of the effect. The general effects of
clouds on the SGE are to amplify the clear-sky SGE, but there is also poor agreement on the magnitude of the
amplification that varies by an order of magnitude across models. Sensitivity analyses indicate that localized
SGE regions are spatially aligned with a large moistening of the upper troposphere. The reduction in clear-sky
OLR arises from a reduction in emission in the far IR with nonnegligible contributions from mid-IR emission
from the midtroposphere. When viewed in the broader context of meridional heat transport, it is found that of
the 1.03-PW rate of heat gained globally, 0.8 PW is absorbed in the tropics and is contributed almost equally
by reductions in clear-sky longwave emission (i.e., the clear-sky SGE) and increased absorbed clear-sky solar
radiation associated with increased water vapor. The processes that define the clear-sky SGE are shown to be
fundamental to the way models accumulate heat and then transport it poleward
Disk Formation by AGB Winds in Dipole Magnetic Fields
We present a simple, robust mechanism by which an isolated star can produce
an equatorial disk. The mechanism requires that the star have a simple dipole
magnetic field on the surface and an isotropic wind acceleration mechanism. The
wind couples to the field, stretching it until the field lines become mostly
radial and oppositely directed above and below the magnetic equator, as occurs
in the solar wind. The interaction between the wind plasma and magnetic field
near the star produces a steady outflow in which magnetic forces direct plasma
toward the equator, constructing a disk. In the context of a slow (10 km/s)
outflow (10^{-5} M_sun/yr) from an AGB star, MHD simulations demonstrate that a
dense equatorial disk will be produced for dipole field strengths of only a few
Gauss on the surface of the star. A disk formed by this model can be
dynamically important for the shaping of Planetary Nebulae.Comment: 14 pages, 8 figures, 1 table, accepted by Ap
Universality of the Gunn effect: self-sustained oscillations mediated by solitary waves
The Gunn effect consists of time-periodic oscillations of the current flowing
through an external purely resistive circuit mediated by solitary wave dynamics
of the electric field on an attached appropriate semiconductor. By means of a
new asymptotic analysis, it is argued that Gunn-like behavior occurs in
specific classes of model equations. As an illustration, an example related to
the constrained Cahn-Allen equation is analyzed.Comment: 4 pages,3 Post-Script figure
Anisotropy effects in a mixed quantum-classical Heisenberg model in two dimensions
We analyse a specific two dimensional mixed spin Heisenberg model with
exchange anisotropy, by means of high temperature expansions and Monte Carlo
simulations. The goal is to describe the magnetic properties of the compound
(NBu_{4})_{2}Mn_{2}[Cu(opba)]_{3}\cdot 6DMSO\cdot H_{2}O which exhibits a
ferromagnetic transition at . Extrapolating our analysis on the
basis of renormalisation group arguments, we find that this transition may
result from a very weak anisotropy effect.Comment: 8 pages, 10 Postscript figure
Chaos in resonant-tunneling superlattices
Spatio-temporal chaos is predicted to occur in n-doped semiconductor
superlattices with sequential resonant tunneling as their main charge transport
mechanism. Under dc voltage bias, undamped time-dependent oscillations of the
current (due to the motion and recycling of electric field domain walls) have
been observed in recent experiments. Chaos is the result of forcing this
natural oscillation by means of an appropriate external microwave signal.Comment: 3 pages, LaTex, RevTex, 3 uuencoded figures (1.2M) are available upon
request from [email protected], to appear in Phys.Rev.
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