600 research outputs found
Antiferromagnetic Order in Disorder-Induced Insulating Phase of SrRu_{1-x}Mn_xO_3 (0.4<x<0.6)
We have performed the powder neutron diffraction measurements on the solid
solutions of SrRu_{1-x}Mn_xO_3, and found that the itinerant ferromagnetic
order observed in pure SrRuO_3 changes into the C-type antiferromagnetic (AF)
order with nearly localized d electrons in the intermediate Mn concentration
between x=0.4 and 0.6. With increasing x, the AF moment is strongly enhanced
from 1.1 mB (x=0.4) to 2.6 mB (x=0.6), which is accompanied by the elongation
of the tetragonal c/a ratio. These results suggest that the substitution of Mn
for Ru suppresses the itinerant character of the d electrons, and induces the
superexchange interaction through the compression in the c plane. We have also
found that the magnetic and transport properties observed in our tetragonal
samples are quite similar to those of recently reported orthorhombic ones.Comment: 4 pages, 4 figure
Transport spin polarisation in SrRuO3 measured through Point Contact Andreev reflection
We report a study in which Andreev reflection using a Nb point contact is
used to measure the transport spin polarisation of the 4d itinerant ferromagnet
SrRuO3. By performing the study in high quality thin films with residual
resistivities less than 7micro-ohm-cm, we ensure that the study is done in the
ballistic limit, a regime which is difficult to reach in oxide ferromagnets.
The degree of transport spin polarisation that we find is comparable to that of
the hole doped rare-earth manganites. We conclude that the large transport spin
polarisation results mainly from a difference in the Fermi velocities between
the majority and minority spin channels in this material.Comment: Text and 2 Figure
Metamagnetism and critical fluctuations in high quality single crystals of the bilayer ruthenate Sr3Ru2O7
We report the results of low temperature transport, specific heat and
magnetisation measurements on high quality single crystals of the bilayer
perovskite Sr3Ru2O7, which is a close relative of the unconventional
superconductor Sr2RuO4. Metamagnetism is observed, and transport and
thermodynamic evidence for associated critical fluctuations is presented. These
relatively unusual fluctuations might be pictured as variations in the Fermi
surface topography itself. No equivalent behaviour has been observed in the
metallic state of Sr2RuO4.Comment: 4 pages, 4 figures, Revtex 3.
A dusty X-ray absorber in the Perseus Cluster ?
We have analyzed 0.35-7.5 keV X-ray spectra of the center of the Perseus
cluster collected using the Broad Band X-Ray Telescope (BBXRT) on the Astro-1
mission. These spectra are particularly useful for examining the nature of the
X-ray absorber in cooling flows because of BBXRT's sensitivity between 0.35 and
1.0 keV. We confirm that there is X-ray absorption above that expected from gas
in our own galaxy. Further, the absorbing medium is deficient in helium.
However, the energy of the K-edge of oxygen is consistent with neutral material
(at the redshift of the cluster) and is not consistent with any ionized state
of oxygen. It is not possible to completely ionize helium and have oxygen
neutral so the apparent helium deficiency cannot be due to ionization. We
propose that the X-ray absorption is due to dust grains that have condensed out
of a medium in which helium remains ionized. This model satisfies all the
observational constraints but is difficult to understand theoretically.Comment: 15 pages including 6 figures. Uses aaspp4 and psfig style
Transport properties of strongly correlated metals:a dynamical mean-field approach
The temperature dependence of the transport properties of the metallic phase
of a frustrated Hubbard model on the hypercubic lattice at half-filling are
calculated. Dynamical mean-field theory, which maps the Hubbard model onto a
single impurity Anderson model that is solved self-consistently, and becomes
exact in the limit of large dimensionality, is used. As the temperature
increases there is a smooth crossover from coherent Fermi liquid excitations at
low temperatures to incoherent excitations at high temperatures. This crossover
leads to a non-monotonic temperature dependence for the resistance,
thermopower, and Hall coefficient, unlike in conventional metals. The
resistance smoothly increases from a quadratic temperature dependence at low
temperatures to large values which can exceed the Mott-Ioffe-Regel value, hbar
a/e^2 (where "a" is a lattice constant) associated with mean-free paths less
than a lattice constant. Further signatures of the thermal destruction of
quasiparticle excitations are a peak in the thermopower and the absence of a
Drude peak in the optical conductivity. The results presented here are relevant
to a wide range of strongly correlated metals, including transition metal
oxides, strontium ruthenates, and organic metals.Comment: 19 pages, 9 eps figure
Hierarchical Hough all-sky search for periodic gravitational waves in LIGO S5 data
We describe a new pipeline used to analyze the data from the fifth science
run (S5) of the LIGO detectors to search for continuous gravitational waves
from isolated spinning neutron stars. The method employed is based on the Hough
transform, which is a semi-coherent, computationally efficient, and robust
pattern recognition technique. The Hough transform is used to find signals in
the time-frequency plane of the data whose frequency evolution fits the pattern
produced by the Doppler shift imposed on the signal by the Earth's motion and
the pulsar's spin-down during the observation period. The main differences with
respect to previous Hough all-sky searches are described. These differences
include the use of a two-step hierarchical Hough search, analysis of
coincidences among the candidates produced in the first and second year of S5,
and veto strategies based on a test.Comment: 7 pages, 2 figures, Amaldi08 proceedings, submitted to JPC
Phase Space Reduction and Vortex Statistics: An Anyon Quantization Ambiguity
We examine the quantization of the motion of two charged vortices in a
Ginzburg--Landau theory for the fractional quantum Hall effect recently
proposed by the first two authors. The system has two second-class constraints
which can be implemented either in the reduced phase space or
Dirac-Gupta-Bleuler formalism. Using the intrinsic formulation of statistics,
we show that these two ways of implementing the constraints are inequivalent
unless the vortices are quantized with conventional statistics; either
fermionic or bosonic.Comment: 14 pages, PHYZZ
A repurposing strategy for Hsp90 inhibitors demonstrates their potency against filarial nematodes
Novel drugs are required for the elimination of infections caused by filarial worms, as most commonly used drugs largely target the microfilariae or first stage larvae of these infections. Previous studies, conducted in vitro, have shown that inhibition of Hsp90 kills adult Brugia pahangi. As numerous small molecule inhibitors of Hsp90 have been developed for use in cancer chemotherapy, we tested the activity of several novel Hsp90 inhibitors in a fluorescence polarization assay and against microfilariae and adult worms of Brugia in vitro. The results from all three assays correlated reasonably well and one particular compound, NVP-AUY922, was shown to be particularly active, inhibiting Mf output from female worms at concentrations as low as 5.0 nanomolar after 6 days exposure to drug. NVP-AUY922 was also active on adult worms after a short 24 h exposure to drug. Based on these in vitro data, NVP-AUY922 was tested in vivo in a mouse model and was shown to significantly reduce the recovery of both adult worms and microfilariae. These studies provide proof of principle that the repurposing of currently available Hsp90 inhibitors may have potential for the development of novel agents with macrofilaricidal properties
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