2,601 research outputs found
Activated Transport in the individual Layers that form the =1 Exciton Condensate
We observe the total filling factor =1 quantum Hall state in a
bilayer two-dimensional electron system with virtually no tunnelling. We find
thermally activated transport in the balanced system with a monotonic increase
of the activation energy with decreasing below 1.65. In the
imbalanced system we find activated transport in each of the layers separately,
yet the activation energies show a striking asymmetry around the balance point.
This implies that the gap to charge-excitations in the {\em individual} layers
is substantially different for positive and negative imbalance.Comment: 4 pages. 4 figure
Exciton condensate at a total filling factor of 1 in Corbino 2D electron bilayers
Magneto-transport and drag measurements on a quasi-Corbino 2D electron
bilayer at the systems total filling factor 1 (v_tot=1) reveal a drag voltage
that is equal in magnitude to the drive voltage as soon as the two layers begin
to form the expected v_tot=1 exciton condensate. The identity of both voltages
remains present even at elevated temperatures of 0.25 K. The conductance in the
current carrying layer vanishes only in the limit of strong coupling between
the two layers and at T->0 K which suggests the presence of an excitonic
circular current
A new mechanism for exchange processes observed in the compounds [M(η-C_5H_5)_2(exo-η-RCH = CH_2)H], M = Nb and Ta
Dynamic n.m.r. studies of the exchange processes in the complexes [M(η-C_5H_5)(exo-η-RCH=CH_2)H], M = Nb, Ta, lead to the proposal of a new mechanism involving intermediates with agostic bonding
Coulomb Drag as a Probe of the Nature of Compressible States in a Magnetic Field
Magneto-drag reveals the nature of compressible states and the underlying
interplay of disorder and interactions. At \nu=3/2 a clear T^{4/3} dependence
is observed, which signifies the metallic nature of the N=0 Landau level. In
contrast, drag in higher Landau levels reveals an additional contribution,
which anomalously grows with decreasing T before turning to zero following a
thermal activation law. The anomalous drag is discussed in terms of
electron-hole asymmetry arising from disorder and localization, and the
crossover to normal drag at high fields as due to screening of disorder.Comment: 5 pages, 4 figure
Micro-SQUID technique for studying the temperature dependence of switching fields of single nanoparticles
An improved micro-SQUID technique is presented allowing us to measure the
temperature dependence of the magnetisation switching fields of single
nanoparticles well above the critical superconducting temperature of the SQUID.
Our first measurements on 3 nm cobalt nanoparticle embedded in a niobium matrix
are compared to the Neel Brown model describing the magnetisation reversal by
thermal activation over a single anisotropy barrier.Comment: 3 pages, 4 figures; conference proceeding: 1st Joint European
Magnetic Symposia (JEMS'01), Grenoble (France), 28th August - 1st September,
200
Is it better to treat chronic hepatitis B as early as possible?—Con
Ideally, treatment of chronic hepatitis B in its early stage prior to irreversible liver damage should be most effective in preventing adverse clinical outcome. However, currently available treatments have low efficacy in achieving sustained response among patients in the early phase of chronic hepatitis B infection when the immune response to hepatitis B virus is weak. This review will provide evidence why a ‘wait and monitor’ approach is appropriate for chronic hepatitis B patients who are in the immune tolerant phase.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73513/1/j.1440-1746.2004.03660.x.pd
Nonequilibrium Atom-Dielectric Forces Mediated by a Quantum Field
In this paper we give a first principles microphysics derivation of the
nonequilibrium forces between an atom, treated as a three dimensional harmonic
oscillator, and a bulk dielectric medium modeled as a continuous lattice of
oscillators coupled to a reservoir. We assume no direct interaction between the
atom and the medium but there exist mutual influences transmitted via a common
electromagnetic field. By employing concepts and techniques of open quantum
systems we introduce coarse-graining to the physical variables - the medium,
the quantum field and the atom's internal degrees of freedom, in that order -
to extract their averaged effects from the lowest tier progressively to the top
tier. The first tier of coarse-graining provides the averaged effect of the
medium upon the field, quantified by a complex permittivity (in the frequency
domain) describing the response of the dielectric to the field in addition to
its back action on the field through a stochastic forcing term. The last tier
of coarse- graining over the atom's internal degrees of freedom results in an
equation of motion for the atom's center of mass from which we can derive the
force on the atom. Our nonequilibrium formulation provides a fully dynamical
description of the atom's motion including back action effects from all other
relevant variables concerned. In the long-time limit we recover the known
results for the atom-dielectric force when the combined system is in
equilibrium or in a nonequilibrium stationary state.Comment: 24 pages, 2 figure
World-wide epidemiology of HBeAg-negative chronic hepatitis B and associated precore and core promoter variants
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72281/1/j.1365-2893.2002.00304.x.pd
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