1,341 research outputs found
N-Cadherin cleavage during activated hepatic stellate cell apoptosis is inhibited by tissue inhibitor of metalloproteinase-1. [In supplement: 11th International Symposium on the Cells of the Hepatic Sinusoid and their Relation to Other Cells]
Apoptosis of hepatic stellate cells (HSC) has previously been shown to occur during spontaneous resolution of experimental liver fibrosis. TIMP-1 has also been shown to have a key role because of its ability to inhibit apoptosis of HSC via matrix metalloproteinase (MMP) inhibition. This has led to further study of novel substrates for MMPs that might impact on HSC survival. N-Cadherin is known to mediate cell-cell contacts in fibroblasts. In this study we demonstrate that N-Cadherin is expressed by activated rat HSC. Furthermore, during apoptosis of HSC, the N-Cadherin is cleaved into smaller fragments. Apoptosis of HSC may be inhibited by TIMP-1. This is associated with reduced fragmentation of N-Cadherin. N-Cadherin may have an important role in supporting HSC survival while N-Cadherin cleavage may play a part in promoting HSC apoptosis in recovery from liver fibrosis
Quantum Lifetime of Two-Dimensional Holes
The quantum lifetime of two-dimensional holes in a GaAs/AlGaAs double quantum
well is determined via tunneling spectroscopy. At low temperatures the lifetime
is limited by impurity scattering but at higher temperatures hole-hole Coulomb
scattering dominates. Our results are consistent with Fermi liquid theory, at
least up to r_s = 11. At the highest temperatures the measured width of the
hole spectral function becomes comparable to the Fermi energy. A new,
tunneling-spectroscopic, method for determining the in-plane effective mass of
the holes is also demonstrated.Comment: 5 pages, 4 figures. Published versio
Tunneling ``zero-bias'' anomaly in the quasi-ballistic regime
For the first time, we study the tunneling density of states (DOS) of the
interacting electron gas beyond the diffusive limit. A strong correction to the
DOS persists even at electron energies exceeding the inverse transport
relaxation time, which could not be expected from the well-known
Altshuler-Aronov-Lee (AAL) theory. This correction originates from the
interference between the electron waves scattered by an impurity and by the
Friedel oscillation this impurity creates. Account for such processes also
revises the AAL formula for the DOS in the diffusive limit.Comment: 4 pages, 2 .eps figures, submitted to Phys. Rev. Let
Breakdown of Particle-Hole Symmetry in the Lowest Landau Level Revealed by Tunneling Spectroscopy
Tunneling measurements on 2D electron gases at high magnetic field reveal a
qualitative difference between the two spin sublevels of the lowest Landau
level. While the tunneling current-voltage characteristic at filling factor
is a single peak shifted from zero bias by a Coulomb pseudogap, the
spectrum at shows a well-resolved double peak structure. This
difference is present regardless of whether and occur at
the same or different magnetic fields. No analogous effect is seen at and 7/2 in the first excited Landau level.Comment: 5 pages, 4 figure
Lifetime of Two-Dimensional Electrons Measured by Tunneling Spectroscopy
For electrons tunneling between parallel two-dimensional electron systems,
conservation of in-plane momentum produces sharply resonant current-voltage
characteristics and provides a uniquely sensitive probe of the underlying
electronic spectral functions. We report here the application of this technique
to accurate measurements of the temperature dependence of the electron-electron
scattering rate in clean two-dimensional systems. Our results are in
qualitative agreement with existing calculations.Comment: file in REVTEX format produces 11 pages, 3 figures available from
[email protected]
Persistent Currents and Dissipation in Narrow Bilayer Quantum Hall Bars
Bilayer quantum Hall states support a flow of nearly dissipationless
staggered current which can only decay through collective channels. We study
the dominant finite-temperature dissipation mechanism which in narrow bars is
driven by thermal nucleation of pseudospin solitons. We find the
finite-temperature resistivity, predict the resulting staggered current-voltage
characteristics, and calculate the associated zero-temperature critical
staggered current and gate voltage.Comment: 4 pgs. REVTeX, 3 eps figure
Electron-electron interactions and two-dimensional - two-dimensional tunneling
We derive and evaluate expressions for the dc tunneling conductance between
interacting two-dimensional electron systems at non-zero temperature. The
possibility of using the dependence of the tunneling conductance on voltage and
temperature to determine the temperature-dependent electron-electron scattering
rate at the Fermi energy is discussed. The finite electronic lifetime produced
by electron-electron interactions is calculated as a function of temperature
for quasiparticles near the Fermi circle. Vertex corrections to the random
phase approximation substantially increase the electronic scattering rate. Our
results are in an excellent quantitative agreement with experiment.Comment: Revtex style, 21 pages and 8 postscript figures in a separate file;
Phys. Rev. B (in press
Skyrmion Excitations in Quantum Hall Systems
Using finite size calculations on the surface of a sphere we study the
topological (skyrmion) excitation in quantum Hall system with spin degree of
freedom at filling factors around . In the absence of Zeeman energy, we
find, in systems with one quasi-particle or one quasi-hole, the lowest energy
band consists of states with , where and are the total orbital and
spin angular momentum. These different spin states are almost degenerate in the
thermodynamic limit and their symmetry-breaking ground state is the state with
one skyrmion of infinite size. In the presence of Zeeman energy, the skyrmion
size is determined by the interplay of the Zeeman energy and electron-electron
interaction and the skyrmion shrinks to a spin texture of finite size. We have
calculated the energy gap of the system at infinite wave vector limit as a
function of the Zeeman energy and find there are kinks in the energy gap
associated with the shrinking of the size of the skyrmion. breaking ground
state is the state with one skyrmion of infinite size. In the presence of
Zeeman energy, the skyrmion size is determined by the interplay of the Zeeman
energy and electron-electronComment: 4 pages, 5 postscript figures available upon reques
Experimental Stage Separation Tool Development in NASA Langley's Aerothermodynamics Laboratory
As part of the research effort at NASA in support of the stage separation and ascent aerothermodynamics research program, proximity testing of a generic bimese wing-body configuration was conducted in NASA Langley's Aerothermodynamics Laboratory in the 20-Inch Mach 6 Air Tunnel. The objective of this work is the development of experimental tools and testing methodologies to apply to hypersonic stage separation problems for future multi-stage launch vehicle systems. Aerodynamic force and moment proximity data were generated at a nominal Mach number of 6 over a small range of angles of attack. The generic bimese configuration was tested in a belly-to-belly and back-to-belly orientation at 86 relative proximity locations. Over 800 aerodynamic proximity data points were taken to serve as a database for code validation. Longitudinal aerodynamic data generated in this test program show very good agreement with viscous computational predictions. Thus a framework has been established to study separation problems in the hypersonic regime using coordinated experimental and computational tools
Correlations, compressibility, and capacitance in double-quantum-well systems in the quantum Hall regime
In the quantum Hall regime, electronic correlations in double-layer
two-dimensional electron systems are strong because the kinetic energy is
quenched by Landau quantization. In this article we point out that these
correlations are reflected in the way the partitioning of charge between the
two-layers responds to a bias potential. We report on illustrative calculations
based on an unrestricted Hartree-Fock approximation which allows for
spontaneous inter-layer phase coherence. The possibility of studying
inter-layer correlations by capacitive coupling to separately contacted
two-dimensional layers is discussed in detail.Comment: RevTex style, 21 pages, 6 postscript figures in a separate file;
Phys. Rev. B (in press
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