1,010 research outputs found
Experimental Demonstration of Fermi Surface Effects at Filling Factor 5/2
Using small wavelength surface acoustic waves (SAW) on ultra-high mobility
heterostructures, Fermi surface properties are detected at 5/2 filling factor
at temperatures higher than those at which the quantum Hall state forms. An
enhanced conductivity is observed at 5/2 by employing sub 0.5 micron wavelength
SAW, indicating a quasiparticle mean-free-path substantially smaller than that
in the lowest Landau level. These findings are consistent with the presence of
a filled Fermi sea of composite fermions, which may pair at lower temperatures
to form the 5/2 ground state.Comment: 11 pages, 4 figure
Circular polarization dependent study of the microwave photoconductivity in a two-dimensional electron system
The polarization dependence of the low field microwave photoconductivity and
absorption of a two-dimensional electron system has been investigated in a
quasi-optical setup in which linear and any circular polarization can be
produced in-situ. The microwave induced resistance oscillations and the zero
resistance regions are notedly immune to the sense of circular polarization.
This observation is discrepant with a number of proposed theories. Deviations
only occur near the cyclotron resonance absorption where an unprecedented large
resistance response is observed.Comment: 5 pages, 3 figure
Possibility of p-wave pairing of composite fermions at
We find that for the pure Coulomb repulsion the composite Fermi sea at
is on the verge of an instability to triplet pairing of composite
fermions. It is argued that a transition into the paired state, described by a
Pfaffian wave function, may be induced if the short-range part of the
interaction is softened by increasing the thickness of the two-dimensional
electron system.Comment: 14 pages, 3 eps figures include
The Kerr-Newman-Godel Black Hole
By applying a set of Hassan-Sen transformations and string dualities to the
Kerr-Godel solution of minimal D=5 supergravity we derive a four parameter
family of five dimensional solutions in type II string theory. They describe
rotating, charged black holes in a rotating background. For zero background
rotation, the solution is D=5 Kerr-Newman; for zero charge it is Kerr-Godel. In
a particular extremal limit the solution describes an asymptotically Godel BMPV
black hole.Comment: 12 pages, LaTeX, no figures; v2: one reference added, very minor
changes; to appear in CQ
Nonequilibrium evolution of Phi**4 theory in 1+1 dimensions in the 2PPI formalism
We consider the out-of-equilibrium evolution of a classical condensate field
and its quantum fluctuations for a Phi**4 model in 1+1 dimensions with a
symmetric and a double well potential. We use the 2PPI formalism and go beyond
the Hartree approximation by including the sunset term. In addition to the mean
field phi= the 2PPI formalism uses as variational parameter a time
dependent mass M**2(t) which contains all local insertions into the Green
function. We compare our results to those obtained in the Hartree
approximation. In the symmetric Phi**4 theory we observe that the mean field
shows a stronger dissipation than the one found in the Hartree approximation.
The dissipation is roughly exponential in an intermediate time region. In the
theory with spontaneous symmetry breaking, i.e., with a double well potential,
the field amplitude tends to zero, i.e., to the symmetric configuration. This
is expected on general grounds: in 1+1 dimensional quantum field theory there
is no spontaneous symmetry breaking for T >0, and so there should be none at
finite energy density (microcanonical ensemble), either. Within the time range
of our simulations the momentum spectra do not thermalize and display
parametric resonance bands.Comment: 14 pages, 18 encapsulated postscript figures; v2 minor changes, new
appendix, accepted for publication in Phys.Rev.
Essential Constants for Spatially Homogeneous Ricci-flat manifolds of dimension 4+1
The present work considers (4+1)-dimensional spatially homogeneous vacuum
cosmological models. Exact solutions -- some already existing in the
literature, and others believed to be new -- are exhibited. Some of them are
the most general for the corresponding Lie group with which each homogeneous
slice is endowed, and some others are quite general. The characterization
``general'' is given based on the counting of the essential constants, the
line-element of each model must contain; indeed, this is the basic contribution
of the work. We give two different ways of calculating the number of essential
constants for the simply transitive spatially homogeneous (4+1)-dimensional
models. The first uses the initial value theorem; the second uses, through
Peano's theorem, the so-called time-dependent automorphism inducing
diffeomorphismsComment: 26 Pages, 2 Tables, latex2
Skipping orbits and enhanced resistivity in large-diameter InAs/GaSb antidot lattices
We investigated the magnetotransport properties of high-mobility InAs/GaSb
antidot lattices. In addition to the usual commensurability features at low
magnetic field we found a broad maximum of classical origin around 2.5 T. The
latter can be ascribed to a class of rosetta type orbits encircling a single
antidot. This is shown by both a simple transport calculation based on a
classical Kubo formula and an analysis of the Poincare surface of section at
different magnetic field values. At low temperatures we observe weak
1/B-periodic oscillations superimposed on the classical maximum.Comment: 4 pages, 4 Postscript figures, REVTeX, submitted to Phys Rev
The O(N) linear sigma model at finite temperature beyond the Hartree approximation
We study the O(N) linear sigma model with spontaneous symmetry breaking,
using a Hartree-like ansatz with a classical field and variational masses. We
go beyond the Hartree approximation by including the two-loop contribution, the
sunset diagram, using the 2PPI expansion. We have computed numerically the
effective potential at finite temperature. We find a phase transition of second
order, while it is first order in the Hartree approximation. We also discuss
some implications of the fact that in this order, the decay of the sigma into
two pions affects the thermal diagrams.Comment: 22 pages, 14 figures. v2: minor corrections, some more references.
v3: added new set of data, new appendix. Submitted to Phys.Rev.
Selective digestive and oropharyngeal decontamination in medical and surgical ICU patients:individual patient data meta-analysis
Objectives: Selective digestive decontamination (SDD) and selective oropharyngeal decontamination (SOD) improved intensive care unit (ICU), hospital and 28-day survival in ICUs with low levels of antibiotic resistance. Yet it is unclear whether the effect differs between medical and surgical ICU patients.& para;& para;Methods: In an individual patient data meta-analysis, we systematically searched PubMed and included all randomized controlled studies published since 2000. We performed a two-stage meta-analysis with separate logistic regression models per study and per outcome (hospital survival and ICU survival) and subsequent pooling of main and interaction effects.& para;& para;Results: Six studies, all performed in countries with low levels of antibiotic resistance, yielded 16 528 hospital admissions and 17 884 ICU admissions for complete case analysis. Compared to standard care or placebo, the pooled adjusted odds ratios for hospital mortality was 0.82 (95% confidence interval (CI) 0.72-0.93) for SDD and 0.84 (95% CI 0.73-0.97) for SOD. Compared to SOD, the adjusted odds ratio for hospital mortality was 0.90 (95% CI 0.82-0.97) for SDD. The effects on hospital mortality were not modified by type of ICU admission (p values for interaction terms were 0.66 for SDD and control, 0.87 for SOD and control and 0.47 for SDD and SOD). Similar results were found for ICU mortality.& para;& para;Conclusions: In ICUs with low levels of antibiotic resistance, the effectiveness of SDD and SOD was not modified by type of ICU admission. SDD and SOD improved hospital and ICU survival compared to standard care in both patient populations, with SDD being more effective than SOD. (C) 2017 The Author(s). Published by Elsevier Ltd on behalf of European Society of Clinical Microbiology and Infectious Diseases
Effective Mass of the Four Flux Composite Fermion at
We have measured the effective mass () of the four flux composite
fermion at Landau level filling factor (CF), using the
activation energy gaps at the fractional quantum Hall effect (FQHE) states
= 2/7, 3/11, and 4/15 and the temperature dependence of the Shubnikov-de
Haas (SdH) oscillations around . We find that the energy gaps show a
linear dependence on the effective magnetic field (), and from this linear dependence we obtain and
a disorder broadening 1 K for a sample of density /cm. The deduced from the temperature dependence of
the SdH effect shows large differences for and . For
, . It scales as with the mass
derived from the data around and shows an increase in as , resembling the findings around . For ,
increases rapidly with increasing and can be described by . This anomalous dependence on is
precursory to the formation of the insulating phase at still lower filling.Comment: 5 pages, 3 figure
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