12,849 research outputs found
Anisotropic Superconducting Properties of MgB2 Single Crystals
In-plane electrical transport properties of MgB2 single crystals grown under
high pressure of 4-6 GPa and temperature of 1400-1700oC in Mg-B-N system have
been measured. For all specimens we found sharp superconducting transition
around 38.1-38.3K with transition width within 0.2-0.3K. Estimated resistivity
value at 40K is about 1 mkOhmcm and resistivity ratio R(273K)/R(40K) of about
4.9. Results of measurements in magnetic field up to 5.5T perpendicular to Mg
and B planes and up to 9T in parallel orientation show temperature dependent
anisotropy of the upper critical field with anisotropy ratio increasing from
2.2 close to Tc up to about 3 below 30K. Strong deviation of the angular
dependence of Hc2 from anisotropic mass model has been also found.Comment: 10pages, including 5 figures,submitted to Physica C (in press
Mucus Sugar Content Shapes the Bacterial Community Structure in Thermally Stressed Acropora muricata
It has been proposed that the chemical composition of a coral’s mucus can influence the associated bacterial community. However, information on this topic is rare, and non-existent for corals that are under thermal stress. This study therefore compared the carbohydrate composition of mucus in the coral Acropora muricata when subjected to increasing thermal stress from 26°C to 31°C, and determined whether this composition correlated with any changes in the bacterial community. Results showed that, at lower temperatures, the main components of mucus were N-acetyl glucosamine and C6 sugars, but these constituted a significantly lower proportion of the mucus in thermally-stressed corals. The change in the mucus composition coincided with a shift from a γ-Proteobacteria- to a Verrucomicrobiae- and α-Proteobacteria-dominated community in the coral mucus. Bacteria in the class Cyanobacteria also started to become prominent in the mucus when the coral was thermally stressed. The increase in the relative abundance of the Verrucomicrobiae at higher temperature was strongly associated with a change in the proportion of fucose, glucose and mannose in the mucus. Increase in the relative abundance of α-Proteobacteria were associated with GalNAc and glucose, while the drop in relative abundance of γ-Proteobacteria at high temperature coincided with changes in fucose and mannose. Cyanobacteria were highly associated with arabinose and xylose. Changes in mucus composition and the bacterial community in the mucus layer occurred at 29°C, which were prior to visual signs of coral bleaching at 31°C. A compositional change in the coral mucus, induced by thermal stress could therefore be a key factor leading to a shift in the associated bacterial community. This, in turn, has the potential to impact the physiological function of the coral holobiont
Characterization of bipartite states using a single homodyne detector
We suggest a scheme to reconstruct the covariance matrix of a two-mode state
using a single homodyne detector plus a polarizing beam splitter and a
polarization rotator. It can be used to fully characterize bipartite Gaussian
states and to extract relevant informations on generic states.Comment: 7 pages, 1 figur
The half-filled Landau level - composite fermions and dipoles
The composite-fermion approach as formulated in the fermion Chern-Simons
theory has been very successful in describing the physics of the lowest Landau
level near Landau level filling factor 1/2. Recent work has emphasized the fact
that the true quasiparticles at these filling factors are electrically neutral
and carry an electric dipole moment. In a previous work, we discussed at length
two formulations in terms of dipolar quasiparticles. Here we briefly review one
approach - termed electron-centered quasiparticles - and show how it can be
extended from 1/2 to nearby filling factors where the quasiparticles carry both
an electric dipole moment and an overall charge.Comment: 10 pages, minor improvements of notation and referencin
Finite-Wavevector Electromagnetic Response of Fractional Quantized Hall States
A fractional quantized Hall state with filling fraction can
be modeled as an integer quantized Hall state of transformed fermions,
interacting with a Chern-Simons field. The electromagnetic response function
for these states at arbitrary frequency and wavevector can be calculated using
a semiclassical approximation or the Random Phase Approximation (RPA). However,
such calculations do not properly take into account the large effective mass
renormalization which is present in the Chern-Simons theory. We show how the
mass renormalization can be incorporated in a calculation of the response
function within a Landau Fermi liquid theory approach such that Kohn's theorem
and the -sum rules are properly satisfied. We present results of such
calculations.Comment: 19 pages (REVTeX 3.0), 5 figures available on request; HU-CMT-93S0
Hamiltonian Description of Composite Fermions: Aftermath
The Lowest Landau Level (LLL), long distance theory of Composite Fermions
(CF) developed by Murthy and myself is minimally extended to all distances,
guided by very general principles. The resulting theory is mathematically
consistent, and physically appealing: we clearly see the electron and the
vortices binding to form the CF. The meaning of the constraints, their role in
ensuring compressibility of dipolar objects at , and the
observability of dipoles are clarified.Comment: Revised for publication in PRL, 4 - epsilon page
Finite Temperature Magnetism in Fractional Quantum Hall Systems: Composite Fermion Hartree-Fock and Beyond
Using the Hamiltonian formulation of Composite Fermions developed recently,
the temperature dependence of the spin polarization is computed for the
translationally invariant fractional quantum Hall states at and
in two steps. In the first step, the effect of particle-hole
excitations on the spin polarization is computed in a Composite Fermion
Hartree-Fock approximation. The computed magnetization for lies above
the experimental results for intermediate temperatures indicating the
importance of long wavelength spin fluctuations which are not correctly treated
in Hartree-Fock. In the second step, spin fluctuations beyond Hartree-Fock are
included for by mapping the problem on to the coarse-grained
continuum quantum ferromagnet. The parameters of the effective continuum
quantum ferromagnet description are extracted from the preceding Hartree-Fock
analysis. After the inclusion of spin fluctuations in a large-N approach, the
results for the finite-temperature spin polarization are in quite good
agreement with the experiments.Comment: 10 pages, 8 eps figures. Two references adde
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