1,616 research outputs found
HadISD: a quality-controlled global synoptic report database for selected variables at long-term stations from 1973--2011
[Abridged] This paper describes the creation of HadISD: an automatically
quality-controlled synoptic resolution dataset of temperature, dewpoint
temperature, sea-level pressure, wind speed, wind direction and cloud cover
from global weather stations for 1973--2011. The full dataset consists of over
6000 stations, with 3427 long-term stations deemed to have sufficient sampling
and quality for climate applications requiring sub-daily resolution. As with
other surface datasets, coverage is heavily skewed towards Northern Hemisphere
mid-latitudes.
The dataset is constructed from a large pre-existing ASCII flatfile data bank
that represents over a decade of substantial effort at data retrieval,
reformatting and provision. These raw data have had varying levels of quality
control applied to them by individual data providers. The work proceeded in
several steps: merging stations with multiple reporting identifiers;
reformatting to netCDF; quality control; and then filtering to form a final
dataset. Particular attention has been paid to maintaining true extreme values
where possible within an automated, objective process. Detailed validation has
been performed on a subset of global stations and also on UK data using known
extreme events to help finalise the QC tests. Further validation was performed
on a selection of extreme events world-wide (Hurricane Katrina in 2005, the
cold snap in Alaska in 1989 and heat waves in SE Australia in 2009). Although
the filtering has removed the poorest station records, no attempt has been made
to homogenise the data thus far. Hence non-climatic, time-varying errors may
still exist in many of the individual station records and care is needed in
inferring long-term trends from these data.
A version-control system has been constructed for this dataset to allow for
the clear documentation of any updates and corrections in the future.Comment: Published in Climate of the Past, www.clim-past.net/8/1649/2012/. 31
pages, 23 figures, 9 pages. For data see
http://www.metoffice.gov.uk/hadobs/hadis
Composite Fermions and the Energy Gap in the Fractional Quantum Hall Effect
The energy gaps for the fractional quantum Hall effect at filling fractions
1/3, 1/5, and 1/7 have been calculated by variational Monte Carlo using Jain's
composite fermion wave functions before and after projection onto the lowest
Landau level. Before projection there is a contribution to the energy gaps from
the first excited Landau level. After projection this contribution vanishes,
the quasielectron charge becomes more localized, and the Coulomb energy
contribution increases. The projected gaps agree well with previous
calculations, lending support to the composite fermion theory.Comment: 12 pages, Revtex 3.0, 2 compressed and uuencoded postscript figures
appended, NHMFL-94-062
Nonperturbative Tests of Three-Dimensional Dualities
We test several conjectural dualities between strongly coupled superconformal
field theories in three dimensions by computing their exact partition functions
on a three-sphere as a function of Fayet-Iliopoulos and mass parameters. The
calculation is carried out using localization of the path integral and the
matrix model previously derived for superconformal N = 2 gauge theories. We
verify that the partition functions of quiver theories related by mirror
symmetry agree provided the mass parameters and the Fayet-Iliopoulos parameters
are exchanged, as predicted. We carry out a similar calculation for the mirror
of N = 8 super-Yang-Mills theory and show that its partition function agrees
with that of the ABJM theory at unit Chern-Simons level. This provides a
nonperturbative test of the conjectural equivalence of the two theories in the
conformal limit
Integer quantum Hall effect for hard-core bosons and a failure of bosonic Chern-Simons mean-field theories for electrons at half-filled Landau level
Field-theoretical methods have been shown to be useful in constructing simple
effective theories for two-dimensional (2D) systems. These effective theories
are usually studied by perturbing around a mean-field approximation, so the
question whether such an approximation is meaningful arises immediately. We
here study 2D interacting electrons in a half-filled Landau level mapped onto
interacting hard-core bosons in a magnetic field. We argue that an interacting
hard-core boson system in a uniform external field such that there is one flux
quantum per particle (unit filling) exhibits an integer quantum Hall effect. As
a consequence, the mean-field approximation for mapping electrons at
half-filling to a boson system at integer filling fails.Comment: 13 pages latex with revtex. To be published in Phys. Rev.
Possible Pairing-Induced Even-Denominator Fractional Quantum Hall Effect in the Lowest Landau Level
We report on our theoretical investigations that point to the possibility of
a fractional quantum Hall effect with partial spin polarization at .
The physics of the incompressible state proposed here involves p-wave pairing
of composite fermions in the spin reversed sector. The temperature and magnetic
field regimes for the realization of this state are estimated
The role of the chemokine receptor CXCR4 in infection with feline immunodeficiency virus
Infection with feline immunodeficiency virus (FIV) leads to the development of a disease state similar to AIDS in man. Recent studies have identified the chemokine receptor CXCR4 as the major receptor for cell culture-adapted strains of FIV, suggesting that FIV and human immunodeficiency virus (HIV) share a common mechanism of infection involving an interaction between the virus and a member of the seven transmembrane domain superfamily of molecules. This article reviews the evidence for the involvement of chemokine receptors in FIV infection and contrasts these findings with similar studies on the primate lentiviruses HIV and SIV (simian immunodeficiency virus)
Electron localization in sound absorption oscillations in the quantum Hall effect regime
The absorption coefficient for surface acoustic waves in a piezoelectric
insulator in contact with a GaAs/AlGaAs heterostructure (with two-dimensional
electron mobility at T=4.2K) via a small
gap has been investigated experimentally as a function of the frequency of the
wave, the width of the vacuum gap, the magnetic field, and the temperature. The
magnetic field and frequency dependencies of the high-frequency conductivity
(in the region 30-210 MHz) are calculated and analyzed. The experimental
results can be explained if it assumed that there exists a fluctuation
potential in which current carrier localization occurs. The absorption of the
surface acoustic waves in an interaction with two-dimensional electrons
localized in the energy "tails" of Landau levels is discussed.Comment: RevTeX 6 pages+6 EPS pic
Sound and Heat Absorption by a 2D Electron Gas in an Odd-Integer Quantized-Hall Regime
The absorption of bulk acoustic phonons in a two-dimensional (2D) GaAs/AlGaAs
heterostructure is studied (in the clean limit) where the 2D electron-gas
(2DEG), being in an odd-integer quantum-Hall state, is in fact a spin
dielectric. Of the two channels of phonon absorption associated with excitation
of spin waves, one, which is due to the spin-orbit (SO) coupling of electrons,
involves a change of the spin state of the system and the other does not. We
show that the phonon-absorption rate corresponding to the former channel (in
the paper designated as the second absorption channel) is finite at zero
temperature (), whereas that corresponding to the latter (designated as the
first channel) vanishes for . The long-wavelength limit, being the
special case of the first absorption channel, corresponds to sound (bulk and
surface) attenuation by the 2DEG. At the same time, the ballistic phonon
propagation and heat absorption are determined by both channels. The 2DEG
overheat and the attendant spin-state change are found under the conditions of
permanent nonequilibrium phonon pumping.Comment: 26 pages, 2 figure
Density Induced Interchange of Anisotropy Axes at Half-Filled High Landau Levels
We observe density induced 90 rotations of the anisotropy axes in
transport measurements at half-filled high Landau levels in the two dimensional
electron system, where stripe states are proposed (=9/2, 11/2, etc). Using
a field effect transistor, we find the transition density to be
cm at =9/2. Hysteresis is observed in the
vicinity of the transition. We construct a phase boundary in the filling
factor-magnetic field plane in the regime . An in-plane magnetic
field applied along either anisotropy axis always stabilizes the low density
orientation of the stripes.Comment: 1 revtex file, 3 eps figure
Cyclotron resonance of correlated electrons in semiconductor heterostructures
The cyclotron resonance absorption of two-dimensional electrons in
semiconductor heterostructures in high magnetic fields is investigated. It is
assumed that the ionized impurity potential is a dominant scattering mechanism,
and the theory explicitly takes the Coulomb correlation effect into account
through the Wigner phonons. The cyclotron resonance linewidth is in
quantitative agreement with the experiment in the Wigner crystal regime at
T=4.2K. Similar to the cyclotron resonance theory of the charge density waves
pinned by short-range impurities, the present results for the long-range
scattering also show the doubling of the resonance peaks. However, unlike the
case of the charge density waves, our theory gives the pinning mode independent
of the bulk compressibility of the substrate materials.Comment: 6 pages, 5 figure
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