1,585 research outputs found
Ga NMR study of the local susceptibility in SrCr8Ga4O19: pseudogap and paramagnetic defects
We present the first Ga(4f) NMR study of the Cr susceptibility in the
archetype of Kagome based frustrated antiferromagnets,
SrCrGaO. Our major finding is that the susceptibility of the
frustrated lattice goes through a maximum around 50 K. Our data also supports
the existence of paramagnetic ``clusters'' of spins, responsible for the Curie
behavior observed in the macroscopic susceptibility at low T. These results set
novel features for the constantly debated physics of geometrically frustrated
magnets.Comment: 4 pages, 5 figures Submitted to Phys. Rev. Let
Evolution from a nodeless gap to d(x2-y2) form in underdoped La(2-x)SrxCuO4
Using angle-resolved photoemission (ARPES), it is revealed that the
low-energy electronic excitation spectra of highly underdoped superconducting
and non-superconducting La(2-x)SrxCuO4 cuprates are gapped along the entire
underlying Fermi surface at low temperatures. We show how the gap function
evolves to a d(x2-y2) form as increasing temperature or doping, consistent with
the vast majority of ARPES studies of cuprates. Our results provide essential
information for uncovering the symmetry of the order parameter(s) in strongly
underdoped cuprates, which is a prerequisite for understanding the pairing
mechanism and how superconductivity emerges from a Mott insulator.Comment: 5 pages, 4 figure
Spin Echo Decay in a Stochastic Field Environment
We derive a general formalism with which it is possible to obtain the time
dependence of the echo size for a spin in a stochastic field environment. Our
model is based on ``strong collisions''. We examine in detail three cases
where: (I) the local field is Ising-like, (II) the field distribution is
continuous and has a finite second moment, and (III) the distribution is
Lorentzian. The first two cases show a T2 minimum effect and are exponential in
time cubed for short times. The last case can be approximated by a
phenomenological stretched exponential.Comment: 11 pages + 3 postscript figure
Evidence of magnetic mechanism for cuprate superconductivity
A proper understanding of the mechanism for cuprate superconductivity can
emerge only by comparing materials in which physical parameters vary one at a
time. Here we present a variety of bulk, resonance, and scattering measurements
on the (Ca_xLa_{1-x})(Ba_{1.75-x}La_{0.25+x})Cu_3O_y high temperature
superconductors, in which this can be done. We determine the superconducting,
Neel, glass, and pseudopage critical temperatures. In addition, we clarify
which physical parameter varies, and, equally important, which does not, with
each chemical modification. This allows us to demonstrate that a single energy
scale, set by the superexchange interaction J, controls all the critical
temperatures of the system. J, in-turn, is determined by the in plane Cu-O-Cu
buckling angle.Comment: 17 pages, 13 figure
Discovery of Multiply Imaged Galaxies behind the Cluster and Lensed Quasar SDSS J1004+4112
We have identified three multiply imaged galaxies in Hubble Space Telescope
images of the redshift z=0.68 cluster responsible for the large-separation
quadruply lensed quasar, SDSS J1004+4112. Spectroscopic redshifts have been
secured for two of these systems using the Keck I 10m telescope. The most
distant lensed galaxy, at z=3.332, forms at least four images, and an Einstein
ring encompassing 3.1 times more area than the Einstein ring of the lensed QSO
images at z=1.74, due to the greater source distance. For a second multiply
imaged galaxy, we identify Ly_alpha emission at a redshift of z=2.74. The
cluster mass profile can be constrained from near the center of the brightest
cluster galaxy, where we observe both a radial arc and the fifth image of the
lensed quasar, to the Einstein radius of the highest redshift galaxy, ~110 kpc.
Our preliminary modeling indicates that the mass approximates an elliptical
body, with an average projected logarithmic gradient of ~-0.5. The system is
potentially useful for a direct measurement of world models in a previously
untested redshift range.Comment: 5 pages, 3 figures. Accepted by ApJL. High resolution version of the
paper can be found at: http://wise-obs.tau.ac.il/~kerens/papers.htm
Extracorporeal Shock Wave Therapy (ESWT) as a treatment for recurrent Neurogenic Heterotopic Ossification (NHO)
“This is an Accepted Manuscript of an article published by Taylor & Francis in Brain Injury on 5 Feb 2013, available online: http://www.tandfonline.com/10.3109/02699052.2012.729293."
© 2013 Informa UK Ltd.Primary objective: To describe the effects of extracorporeal shock wave therapy (ESWT) on neurogenic heterotopic ossification (NHO).
Research design: A single case study was considered the most appropriate methodology in this situation.
Methods and procedures: The subject was a 43 year old female 10 years post-traumatic brain injury with recurring NHO around the hip joint. Baseline assessments of pain using a 10-point VAS, range of motion of the hip using a goniometer and walking ability (number of steps over a standard distance) were conducted. Four applications of ESWT using a Minispecâ„¢ Extracorporeal Shock Wave Lithotripsy machine (Medispec Int. USA) administered over 6 weeks to the anterolateral aspect of the right hip. Follow-up assessments were conducted weekly over the period of intervention and then monthly for 5 months.
Main outcomes and results: Immediately following treatment, pain was reduced to 0 on the VAS scale; hip range of motion increased and the number of steps over a standard distance reduced, indicating increased step length. At 5-month follow-up, without further ESWT intervention, these results were maintained.
Conclusion: This case study suggests that ESWT may be a non-invasive, low risk intervention for the management of NHO
The Imprinted Retrotransposon-Like Gene PEG11 (RTL1) Is Expressed as a Full-Length Protein in Skeletal Muscle from Callipyge Sheep
peer-reviewedMembers of the Ty3-Gypsy retrotransposon family are rare in mammalian genomes despite their abundance in invertebrates and some vertebrates. These elements contain a gag-pol-like structure characteristic of retroviruses but have lost their ability to retrotranspose into the mammalian genome and are thought to be inactive relics of ancient retrotransposition events. One of these retrotransposon-like elements, PEG11 (also called RTL1) is located at the distal end of ovine chromosome 18 within an imprinted gene cluster that is highly conserved in placental mammals. The region contains several conserved imprinted genes including BEGAIN, DLK1, DAT, GTL2 (MEG3), PEG11 (RTL1), PEG11as, MEG8, MIRG and DIO3. An intergenic point mutation between DLK1 and GTL2 causes muscle hypertrophy in callipyge sheep and is associated with large changes in expression of the genes linked in cis between DLK1 and MEG8. It has been suggested that over-expression of DLK1 is the effector of the callipyge phenotype; however, PEG11 gene expression is also strongly correlated with the emergence of the muscling phenotype as a function of genotype, muscle type and developmental stage. To date, there has been no direct evidence that PEG11 encodes a protein, especially as its anti-sense transcript (PEG11as) contains six miRNA that cause cleavage of the PEG11 transcript. Using immunological and mass spectrometry approaches we have directly identified the full-length PEG11 protein from postnatal nuclear preparations of callipyge skeletal muscle and conclude that its over-expression may be involved in inducing muscle hypertrophy. The developmental expression pattern of the PEG11 gene is consistent with the callipyge mutation causing recapitulation of the normal fetal-like gene expression program during postnatal development. Analysis of the PEG11 sequence indicates strong conservation of the regions encoding the antisense microRNA and in at least two cases these correspond with structural or functional domains of the protein suggesting co-evolution of the sense and antisense genes
Ultrafast optical nonlinearity in quasi-one-dimensional Mott-insulator
We report strong instantaneous photoinduced absorption (PA) in the
quasi-one-dimensional Mott insulator in the IR spectral
region. The observed PA is to an even-parity two-photon state that occurs
immediately above the absorption edge. Theoretical calculations based on a
two-band extended Hubbard model explains the experimental features and
indicates that the strong two-photon absorption is due to a very large
dipole-coupling between nearly degenerate one- and two-photon states. Room
temperature picosecond recovery of the optical transparency suggests the strong
potential of for all-optical switching.Comment: 10 pages, 4 figure
Properties of a classical spin liquid: the Heisenberg pyrochlore antiferromagnet
We study the low-temperature behaviour of the classical Heisenberg
antiferromagnet with nearest neighbour interactions on the pyrochlore lattice.
Because of geometrical frustration, the ground state of this model has an
extensive number of degrees of freedom. We show, by analysing the effects of
small fluctuations around the ground-state manifold, and from the results of
Monte Carlo and molecular dynamics simulations, that the system is disordered
at all temperatures, T, and has a finite relaxation time, which varies as 1/T
for small T.Comment: 4 pages revtex; 3 figures automatically include
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