2,234 research outputs found
Direct observation of quantized interlayer vortex flow and vortex pinning distribution in high-Tc La_(1.87)Sr_(0.13)CuO_4 single crystals
A scanning superconducting quantum interference device (SQUID) microscope
(SSM) is used to study the magnetic imaging of dynamic motion of quantized
interlayer vortices induced by the Lorentz force in anisotropic high-Tc
La_(1.87)Sr_(0.13)CuO_4 single crystals. It is found that 3 modes of flux
motion switch depending on the transport current. By increasing the current a
transition from the creep-like behavior of vortices to a steady flow of
vortices was observed. Even higher current induced a continuous expansion of
vortex-flow area indicating an inhomogeneous distribution of various pinning
centers.Comment: 16 pages, 4 figure
Magnetic excitations in coupled Haldane spin chains near the quantum critical point
Two quasi-1-dimensional S=1 quantum antiferromagnetic materials, PbNi2V2O8
and SrNi2V2O8, are studied by inelastic neutron scattering on powder samples.
While magnetic interactions in the two systems are found to be very similar,
subtle differences in inter-chain interaction strengths and magnetic anisotropy
are detected. The latter are shown to be responsible for qualitatively
different ground state properties: magnetic long-range order in SrNi2V2O8 and
disordered ``spin liquid'' Haldane-gap state in PbNi2V2O8.Comment: 15 figures, Figs. 5,9, and 10 in color. Some figures in JPEG format.
Complete PostScript and PDF available from
http://papillon.phy.bnl.gov/publicat.ht
One-loop surface tensions of (supersymmetric) kink domain walls from dimensional regularization
We consider domain walls obtained by embedding the 1+1-dimensional
-kink in higher dimensions. We show that a suitably adapted dimensional
regularization method avoids the intricacies found in other regularization
schemes in both supersymmetric and non-supersymmetric theories. This method
allows us to calculate the one-loop quantum mass of kinks and surface tensions
of kink domain walls in a very simple manner, yielding a compact d-dimensional
formula which reproduces many of the previous results in the literature. Among
the new results is the nontrivial one-loop correction to the surface tension of
a 2+1 dimensional N=1 supersymmetric kink domain wall with chiral domain-wall
fermions.Comment: 23 pages, LATeX; v2: 25 pages, 2 references added, extended
discussion of renormalization schemes which dispels apparent contradiction
with previous result
Multi-wavelength observations of the binary system PSR B1259-63/LS 2883 around the 2010-2011 periastron passage
We report on broad multi-wavelength observations of the 2010-2011 periastron
passage of the gamma-ray loud binary system PSR B1259-63. High resolution
interferometric radio observations establish extended radio emission trailing
the position of the pulsar. Observations with the Fermi Gamma-ray Space
Telescope reveal GeV gamma-ray flaring activity of the system, reaching the
spin-down luminosity of the pulsar, around 30 days after periastron. There are
no clear signatures of variability at radio, X-ray and TeV energies at the time
of the GeV flare. Variability around periastron in the H emission line,
can be interpreted as the gravitational interaction between the pulsar and the
circumstellar disk. The equivalent width of the H grows from a few days
before periastron until a few days later, and decreases again between 18 and 46
days after periastron. In near infrared we observe the similar decrease of the
equivalent width of Br line between the 40th and 117th day after the
periastron. For the idealized disk, the variability of the H line
represents the variability of the mass and size of the disk. We discuss
possible physical relations between the state of the disk and GeV emission
under assumption that GeV flare is directly related to the decrease of the disk
size.Comment: accepted to MNRA
Origin of TeV Galactic Cosmic Rays
We consider a possibility of identification of sources of cosmic rays (CR) of
the energy above 1 TeV via observation of degree-scale extended gamma-ray
emission which traces the locations of recent sources in the Galaxy. Such
emission in the energy band above 100 GeV is produced by CR nuclei and
electrons released by the sources and spreading into the interstellar medium.
We use the data from the Fermi gamma-ray telescope to locate the degree-scale
100 GeV gamma-ray sources. We find that the number of such sources and their
overall power match to those expected when CRs injection events happen every
~100 yr in portions of ~1e50 erg. We find that most of the sources are
associated to pulsars with spin down age less than ~30 kyr and hence to the
recent supernova explosions. This supports the hypothesis of supernova origin
of Galactic CRs. We notice that the degree-scale extended emission does not
surround shell-like supernova remnants without pulsars. Based on this
observation, we argue that the presence of the pulsar is essential for the CR
acceleration process. We expect that a significant fraction of the degree-scale
sources should be detectable as extended sources with km3-scale neutrino
detectors.Comment: 14 pages, 14 figures, accepted for publication in Phys.Rev.
Spin-Vacancy-Induced Long-Range Order in a New Haldane-Gap Antiferromagnet
Magnetic susceptibility, high-field magnetization and inelastic neutron
scattering experiments are used to study the magnetic properties of a new S=1
quasi-1-dimensional antiferromagnet PbNi2V2O8. Inter-chain interactions are
shown to be almost, but not quite, strong enough to destroy the nonmagnetic
singlet ground state and the energy gap in the magnetic excitation spectrum.
Substituting nonmagnetic Mg (S=0) ions for Ni (S=1) induces a
magnetically ordered state at low temperatures. To our knowledge this is the
first observation of doping-induced long-range order in a Haldane-gap system.Comment: 5 pages including 4 figure
Surface states and their possible role in the superconductivity of MgB2
We report layer-Korringa-Kohn-Rostocker calculations for bulk and surface
states as well as the corresponding angle resolved photoemission (ARPES)
intensities of MgB2. Our theoretical results reproduce very well the recent
ARPES data by Uchiyama et al., cond-mat/0111152. At least two surface states
are assigned. Consequences of SFS on the anisotropy of the upper critical
fields and other properties in the superconducting state of small grains in
micropowder samples are briefly discussed.Comment: 4pages, 6figures, corrected typos, references adde
One-Year Risk of Stroke after Transient Ischemic Attack or Minor Stroke
BACKGROUND Previous studies conducted between 1997 and 2003 estimated that the risk of stroke or an acute coronary syndrome was 12 to 20% during the first 3 months after a transient ischemic attack (TIA) or minor stroke. The TIAregistry.org project was designed to describe the contemporary profile, etiologic factors, and outcomes in patients with a TIA or minor ischemic stroke who receive care in health systems that now offer urgent evaluation by stroke specialists.
METHODS We recruited patients who had had a TIA or minor stroke within the previous 7 days. Sites were selected if they had systems dedicated to urgent evaluation of patients with TIA. We estimated the 1-year risk of stroke and of the composite outcome of stroke, an acute coronary syndrome, or death from cardiovascular causes. We also examined the association of the ABCD2 score for the risk of stroke (range, 0 [lowest risk] to 7 [highest risk]), findings on brain imaging, and cause of TIA or minor stroke with the risk of recurrent stroke over a period of 1 year.
RESULTS From 2009 through 2011, we enrolled 4789 patients at 61 sites in 21 countries. A total of 78.4% of the patients were evaluated by stroke specialists within 24 hours after symptom onset. A total of 33.4% of the patients had an acute brain infarction, 23.2% had at least one extracranial or intracranial stenosis of 50% or more, and 10.4% had atrial fibrillation. The Kaplan–Meier estimate of the 1-year event rate of the composite cardiovascular outcome was 6.2% (95% confidence interval, 5.5 to 7.0). Kaplan–Meier estimates of the stroke rate at days 2, 7, 30, 90, and 365 were 1.5%, 2.1%, 2.8%, 3.7%, and 5.1%, respectively. In multivariable analyses, multiple infarctions on brain imaging, large-artery atherosclerosis, and an ABCD2 score of 6 or 7 were each associated with more than a doubling of the risk of stroke.
CONCLUSIONS We observed a lower risk of cardiovascular events after TIA than previously reported. The ABCD2 score, findings on brain imaging, and status with respect to large-artery atherosclerosis helped stratify the risk of recurrent stroke within 1 year after a TIA or minor stroke. (Funded by Sanofi and Bristol-Myers Squibb.)Supported by an unrestricted grant from Sanofi and Bristol-Myers Squibb
- …