1,970 research outputs found
Increased plasma viscosity as a reason for inappropriate erythropoietin formation
The aim of this study was to examine whether altered plasma viscosity could contribute to the inappropriately low production rate of erythropoietin (EPO) observed in patients suffering from hypergammaglobulinemias associated with multiple myeloma or Waldenström's disease. We found that the EPO formation in response to anemia in these patients was inversely related to plasma viscosity. A similar inverse relationship between plasma viscosity and EPO production was seen in rats in which EPO formation had been stimulated by exchange transfusion and the plasma viscosity of which was thereby altered by using exchange solutions of different composition to alter plasma viscosity and thus whole blood viscosity independently from hematocrit. Raising the gammaglobulin concentration to approximately 40 mg/ml plasma in the rats almost totally blunted the rise in serum EPO levels despite a fall of the hematocrit to 20%. Determination of renal EPO mRNA levels by RNase protection revealed that the reductions in serum EPO levels at higher plasma viscosities were paralleled by reductions in renal EPO mRNA levels. Taken together, our findings suggest that plasma viscosity may be a significant inhibitory modulator of anemia-induced EPO formation. The increased plasma viscosity in patients with hypergammaglobulinemias may therefore contribute to the inappropriate EPO production, which is a major reason for the anemia developing in these patients
Cohomological tautness for Riemannian foliations
In this paper we present some new results on the tautness of Riemannian
foliations in their historical context. The first part of the paper gives a
short history of the problem. For a closed manifold, the tautness of a
Riemannian foliation can be characterized cohomologically. We extend this
cohomological characterization to a class of foliations which includes the
foliated strata of any singular Riemannian foliation of a closed manifold
Force balance and membrane shedding at the Red Blood Cell surface
During the aging of the red-blood cell, or under conditions of extreme
echinocytosis, membrane is shed from the cell plasma membrane in the form of
nano-vesicles. We propose that this process is the result of the
self-adaptation of the membrane surface area to the elastic stress imposed by
the spectrin cytoskeleton, via the local buckling of membrane under increasing
cytoskeleton stiffness. This model introduces the concept of force balance as a
regulatory process at the cell membrane, and quantitatively reproduces the rate
of area loss in aging red-blood cells.Comment: 4 pages, 3 figure
Exotic Differentiable Structures and General Relativity
We review recent developments in differential topology with special concern
for their possible significance to physical theories, especially general
relativity. In particular we are concerned here with the discovery of the
existence of non-standard (``fake'' or ``exotic'') differentiable structures on
topologically simple manifolds such as , \R and
Because of the technical difficulties involved in the smooth case, we begin
with an easily understood toy example looking at the role which the choice of
complex structures plays in the formulation of two-dimensional vacuum
electrostatics. We then briefly review the mathematical formalisms involved
with differentiable structures on topological manifolds, diffeomorphisms and
their significance for physics. We summarize the important work of Milnor,
Freedman, Donaldson, and others in developing exotic differentiable structures
on well known topological manifolds. Finally, we discuss some of the geometric
implications of these results and propose some conjectures on possible physical
implications of these new manifolds which have never before been considered as
physical models.Comment: 11 pages, LaTe
Probing the dynamics of quasicrystal growth using synchrotron live imaging
The dynamics of quasicrystal growth remains an unsolved problem in condensed
matter. By means of synchrotron live imaging, facetted growth proceeding by the
tangential motion of ledges at the solid-melt interface is clearly evidenced
all along the solidification of icosahedral AlPdMn quasicrystals. The effect of
interface kinetics is significant so that nucleation and free growth of new
facetted grains occur in the melt when the solidification rate is increased.
The evolution of these grains is explained in details, which reveals the
crucial role of aluminum rejection, both in the poisoning of grain growth and
driving fluid flow
Matrix-free calcium in isolated chromaffin vesicles
Isolated secretory vesicles from bovine adrenal medulla contain 80 nmol of Ca2+ and 25 nmol
of Mg2+ per milligram of protein. As determined with a Ca2+-selective electrode, a further accumulation
of about 160 nmol of Ca2+/mg of protein can be attained upon addition of the Ca2+ ionophore A23187.
During this process protons are released from the vesicles, in exchange for Ca2+ ions, as indicated by the
decrease of the pH in the incubation medium or the release of 9-aminoacridine previously taken up by the
vesicles. Intravesicular Mg2+ is not released from the vesicles by A23 187, as determined by atomic emission
spectroscopy. In the presence of N H Q , which causes the collapse of the secretory vesicle transmembrane
proton gradient (ApH), Ca2+ uptake decreases. Under these conditions A23 187-mediated influx of Ca2+
and efflux of H+ cease at Ca2+ concentrations of about 4 pM. Below this concentration Ca2+ is even released
from the vesicles. At the Ca2+ concentration at which no net flux of ions occurs the intravesicular matrix
free Ca2+ equals the extravesicular free Ca2+. In the absence of NH4C1 we determined an intravesicular
pH of 6.2. Under these conditions the Ca2+ influx ceases around 0.15 pM. From this value and the known
pH across the vesicular membrane an intravesicular matrix free Ca2+ concentration of about 24 pM was
calculated. This is within the same order of magnitude as the concentration of free Ca2+ in the vesicles
determined in the presence of NH4C1. Calculation of the total Ca2+ present in the secretory vesicles gives
an apparent intravesicular Ca2+ concentration of 40 mM, which is a factor of lo4 higher than the free
intravesicular concentration of Ca2+. It can be concluded, therefore, that the concentration gradient of free
Ca2+ across the secretory vesicle membrane in the intact chromaffin cells is probably small, which implies
that less energy is required to accumulate and maintain Ca2+ within the vesicles than was previously
anticipated
Scanning Tunneling Microscope-Induced Luminescence Spectroscopy on Semiconductor Heterostructures
Scanning tunneling microscope (STM)-induced luminescence is explored as a technique for the characterization of semiconductor quantum wells and quantum wire heterostructures. By injecting minority carriers into the cleaved cross section of these structures, luminescence excitation on a nanometer scale is demonstrated. Using spectrally resolved STM-induced luminescence for the tip placed at various positions across the cleaved heterostructure, it is possible to obtain local spectroscopic information on closely spaced quantum structures
Transferring Learning from External to Internal Weights in Echo-State Networks with Sparse Connectivity
Modifying weights within a recurrent network to improve performance on a task has proven to be difficult. Echo-state networks in which modification is restricted to the weights of connections onto network outputs provide an easier alternative, but at the expense of modifying the typically sparse architecture of the network by including feedback from the output back into the network. We derive methods for using the values of the output weights from a trained echo-state network to set recurrent weights within the network. The result of this “transfer of learning” is a recurrent network that performs the task without requiring the output feedback present in the original network. We also discuss a hybrid version in which online learning is applied to both output and recurrent weights. Both approaches provide efficient ways of training recurrent networks to perform complex tasks. Through an analysis of the conditions required to make transfer of learning work, we define the concept of a “self-sensing” network state, and we compare and contrast this with compressed sensing
Association of Hepatitis C Virus—Specific CD8+ T Cells with Viral Clearance in Acute Hepatitis C
CD8+ T lymphocytes play a major role in antiviral immune defense. Their significance for acute hepatitis C is unclear. Our aim was to correlate the CD8+ T cell response with the outcome of infection. Eighteen patients with acute hepatitis C and 19 normal donors were studied. Hepatitis C virus (HCV)—specific CD8+ T cells were identified in the enzyme-linked immunospot assay by their interferon-γ (IFN-γ) production after specific stimulation. The highest numbers of IFN-γ—producing HCV-specific CD8+ T cells were found in patients with acute hepatitis C and a self-limited course of disease during the first 6 months after onset of disease, but these numbers dropped thereafter to undetectable levels. The differences in responsiveness between patients with self-limited disease versus patients with a chronic course were statistically significant (P < .001). Our data show that the number of IFN—γ-producing HCV-specific CD8+ T cells during the first 6 months after onset of disease is associated with eradication of the HCV infectio
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