787 research outputs found
Low lying spectrum of weak-disorder quantum waveguides
We study the low-lying spectrum of the Dirichlet Laplace operator on a
randomly wiggled strip. More precisely, our results are formulated in terms of
the eigenvalues of finite segment approximations of the infinite waveguide.
Under appropriate weak-disorder assumptions we obtain deterministic and
probabilistic bounds on the position of the lowest eigenvalue. A Combes-Thomas
argument allows us to obtain so-called 'initial length scale decay estimates'
at they are used in the proof of spectral localization using the multiscale
analysis.Comment: Accepted for publication in Journal of Statistical Physics
http://www.springerlink.com/content/0022-471
Existence and uniqueness of the integrated density of states for Schr\"odinger operators with magnetic fields and unbounded random potentials
The object of the present study is the integrated density of states of a
quantum particle in multi-dimensional Euclidean space which is characterized by
a Schr\"odinger operator with a constant magnetic field and a random potential
which may be unbounded from above and from below. For an ergodic random
potential satisfying a simple moment condition, we give a detailed proof that
the infinite-volume limits of spatial eigenvalue concentrations of
finite-volume operators with different boundary conditions exist almost surely.
Since all these limits are shown to coincide with the expectation of the trace
of the spatially localized spectral family of the infinite-volume operator, the
integrated density of states is almost surely non-random and independent of the
chosen boundary condition. Our proof of the independence of the boundary
condition builds on and generalizes certain results by S. Doi, A. Iwatsuka and
T. Mine [Math. Z. {\bf 237} (2001) 335-371] and S. Nakamura [J. Funct. Anal.
{\bf 173} (2001) 136-152].Comment: This paper is a revised version of the first part of the first
version of math-ph/0010013. For a revised version of the second part, see
math-ph/0105046. To appear in Reviews in Mathematical Physic
Wegner estimate for discrete alloy-type models
We study discrete alloy-type random Schr\"odinger operators on
. Wegner estimates are bounds on the average number of
eigenvalues in an energy interval of finite box restrictions of these types of
operators. If the single site potential is compactly supported and the
distribution of the coupling constant is of bounded variation a Wegner estimate
holds. The bound is polynomial in the volume of the box and thus applicable as
an ingredient for a localisation proof via multiscale analysis.Comment: Accepted for publication in AHP. For an earlier version see
http://www.ma.utexas.edu/mp_arc-bin/mpa?yn=09-10
Potential Role of Protein Kinase B in Insulin-induced Glucose Transport, Glycogen Synthesis, and Protein Synthesis
Various biological responses stimulated by insulin
have been thought to be regulated by phosphatidylinosi-tol
3-kinase, including glucose transport, glycogen syn-thesis,
and protein synthesis. However, the molecular
link between phosphatidylinositol 3-kinase and these
biological responses has been poorly understood. Re-cently,
it has been shown that protein kinase B (PKB/c-Akt/
Rac) lies immediately downstream from phosphati-dylinositol
3-kinase. Here, we show that expression of a
constitutively active form of PKB induced glucose up-take,
glycogen synthesis, and protein synthesis in L6
myotubes downstream of phosphatidylinositol 3-kinase
and independent of Ras and mitogen-activated protein
kinase activation. Introduction of constitutively active
PKB induced glucose uptake and protein synthesis but
not glycogen synthesis in 3T3L-1 adipocytes, which lack
expression of glycogen synthase kinase 3 different from
L6 myotubes. Furthermore, we show that deactivation
of glycogen synthase kinase 3 and activation of rapamy-cin-
sensitive serine/threonine kinase by PKB in L6 myo-tubes
might be involved in the enhancement of glycogen
synthesis and protein synthesis, respectively. These re-sults
suggest that PKB acts as a key enzyme linking
phosphatidylinositol 3-kinase activation to multiple bi-ological
functions of insulin through regulation of
downstream kinases in skeletal muscle, a major target
tissue of insulin
Physiological and Biochemical Mechanisms of Plant Adaptation to Low-Fertility Acid Soils of the Tropics: The Case of Brachiariagrasses
Magnetoresistance of antidot lattices with grain boundaries
The magnetotransport properties of antidot lattices containing artificially
designed grain boundaries have been measured. We find that the grain boundaries
broaden the commensurability resonances and displace them anisotropically.
These phenomena are unexpectedly weak but differ characteristically from
isotropic, Gaussian disorder in the antidot positions. The observations are
interpreted in terms of semiclassical trajectories which tend to localize along
the grain boundaries within certain magnetic field intervals. Furthermore, our
results indicate how the transport through superlattices generated by
self-organizing templates may get influenced by grain boundaries.Comment: 6 pages, 3 figure
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Characterization of protein kinase C isoform's action on retinoblastoma protein phosphorylation, vascular endothelial growth factor-induced endothelial cell proliferation, and retinal neovascularization
Retinal neovascularization is a major cause of blindness and requires the activities of several signaling pathways and multiple cytokines. Activation of protein kinase C (PKC) enhances the angiogenic process and is involved in the signaling of vascular endothelial growth factor (VEGF). We have demonstrated a dramatic increase in the angiogenic response to oxygen-induced retinal ischemia in transgenic mice overexpressing PKCβ2 isoform and a significant decrease in retinal neovascularization in PKCβ isoform null mice. The mitogenic action of VEGF, a potent hypoxia-induced angiogenic factor, was increased by 2-fold in retinal endothelial cells by the overexpression of PKCβ1 or β2 isoforms and inhibited significantly by the overexpression of a dominant-negative PKCβ2 isoform but not by the expression of PKC α, δ, and ζ isoforms. Association of PKCβ2 isoform with retinoblastoma protein was discovered in retinal endothelial cells, and PKCβ2 isoform increased retinoblastoma phosphorylation under basal and VEGF-stimulated conditions. The potential functional consequences of PKCβ-induced retinoblastoma phosphorylation could include enhanced E2 promoter binding factor transcriptional activity and increased VEGF-induced endothelial cell proliferation
Regulation of Calcium-Permeable TRPV2 Channel by Insulin in Pancreatic β-Cells
OBJECTIVE—Calcium-permeable cation channel TRPV2 is expressed in pancreatic β-cells. We investigated regulation and function of TRPV2 in β-cells
ANK, a Host Cytoplasmic Receptor for the Tobacco mosaic virus Cell-to-Cell Movement Protein, Facilitates Intercellular Transport through Plasmodesmata
Plasmodesma (PD) is a channel structure that spans the cell wall and provides symplastic connection between adjacent cells. Various macromolecules are known to be transported through PD in a highly regulated manner, and plant viruses utilize their movement proteins (MPs) to gate the PD to spread cell-to-cell. The mechanism by which MP modifies PD to enable intercelluar traffic remains obscure, due to the lack of knowledge about the host factors that mediate the process. Here, we describe the functional interaction between Tobacco mosaic virus (TMV) MP and a plant factor, an ankyrin repeat containing protein (ANK), during the viral cell-to-cell movement. We utilized a reverse genetics approach to gain insight into the possible involvement of ANK in viral movement. To this end, ANK overexpressor and suppressor lines were generated, and the movement of MP was tested. MP movement was facilitated in the ANK-overexpressing plants, and reduced in the ANK-suppressing plants, demonstrating that ANK is a host factor that facilitates MP cell-to-cell movement. Also, the TMV local infection was largely delayed in the ANK-suppressing lines, while enhanced in the ANK-overexpressing lines, showing that ANK is crucially involved in the infection process. Importantly, MP interacted with ANK at PD. Finally, simultaneous expression of MP and ANK markedly decreased the PD levels of callose, β-1,3-glucan, which is known to act as a molecular sphincter for PD. Thus, the MP-ANK interaction results in the downregulation of callose and increased cell-to-cell movement of the viral protein. These findings suggest that ANK represents a host cellular receptor exploited by MP to aid viral movement by gating PD through relaxation of their callose sphincters
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