3,386 research outputs found
TDRSS/user satellite timing study
A timing analysis for data readout through the Tracking and Data Relay Satellite System (TDRSS) was presented. Various time tagging approaches were considered and the resulting accuracies delineated. The TDRSS was also defined and described in detail
Large-N estimates of universal amplitudes of the CP^{N-1} theory and comparison with the JQ model
We present computations of certain finite-size scaling functions and
universal amplitude ratios in the large-N limit of the CP^{N-1} field theory.
We pay particular attention to the uniform susceptibility, the spin stiffness
and the specific heat. Field theoretic arguments have shown that the
long-wavelength description of the phase transition between the Neel and
valence bond solid states in square lattice S=1/2 anti-ferromagnets is expected
to be the non-compact CP^1 field theory. We provide a detailed comparison
between our field theoretic calculations and quantum Monte Carlo data close to
the Neel -VBS transition on a S=1/2 square-lattice model with competing
four-spin interactions (the JQ model).Comment: 15 page
Quantum criticality of U(1) gauge theories with fermionic and bosonic matter in two spatial dimensions
We consider relativistic U(1) gauge theories in 2+1 dimensions, with N_b
species of complex bosons and N_f species of Dirac fermions at finite
temperature. The quantum phase transition between the Higgs and Coulomb phases
is described by a conformal field theory (CFT). At large N_b and N_f, but for
arbitrary values of the ratio N_b/N_f, we present computations of various
critical exponents and universal amplitudes for these CFTs. We make contact
with the different spin-liquids, charge-liquids and deconfined critical points
of quantum magnets that these field theories describe. We compute physical
observables that may be measured in experiments or numerical simulations of
insulating and doped quantum magnets.Comment: 30 pages, 8 figure
Spin fluctuations with two-dimensional XY behavior in a frustrated S = 1/2 square-lattice ferromagnet
The spin dynamics of the layered square-lattice vanadate Pb2VO(PO4)2 is
investigated by electron spin resonance at various magnetic fields and at
temperatures above magnetic ordering. The linewidth divergence towards low
temperatures seems to agree with isotropic Heisenberg-type spin exchange
suggesting that the spin relaxation in this quasi-two dimensional compound is
governed by low-dimensional quantum fluctuations. However, a weak easy- plane
anisotropy of the g factor points to the presence of a planar XY type of
exchange. Indeed, we found that the linewidth divergence is described best by
XY-like spin fluctuations which requires a single parameter only. Therefore,
ESR-probed spin dynamics could establish Pb2VO(PO4)2 as the first frustrated
square lattice system with XY-inherent spin topological fluctuations.Comment: 5 pages, 3 figure
Clinical and economic outcomes in thrombolytic treatment of peripheral arterial occlusive disease and deep venous thrombosis
PurposeOver the past 2 decades the use of thrombolytic therapy in the management of peripheral occlusive diseases, most notably peripheral arterial occlusion (PAO) and deep venous thrombosis (DVT), has become an accepted and potentially preferable alternative to surgery. We examined the period when urokinase was in short supply and subsequently unavailable, to explore potential differences in clinical outcome and economic effect between urokinase and recombinant tissue plasminogen activator (rt-PA).Material and methodsData were obtained from the Premier Perspective Database, a broad clinical database that contains information on inpatient medical practices and resource use. The study population included all patients hospitalized in 1999 and 2000 with a primary or secondary diagnosis of PAO or DVT. Incidence was calculated for common adverse events, including bleeding complications, intracranial hemorrhage, amputation, and death. Cost data were also abstracted from the database, and are expressed as mean ± SD.ResultsDemographic variables were similar in the urokinase and rt-PA groups. The rate of bleeding complications was similar in the urokinase and rt-PA groups. There were no intracranial hemorrhages in the urokinase group, compared with a rate of 1.5% in the rt-PA PAO group (P = .087) and 1.9% in the rt-PA DVT group (P = .175). The in-hospital mortality rate was lower in the urokinase-treated PAO subgroup (3.6% vs 8.5%; P = .026), but a similar finding in the DVT subgroup did not achieve statistical significance (4% vs 9.8%; P = .069). While pharmacy costs were greater in the urokinase-treated group (5579 vs 6009, P < .001; PAO subgroup, 15,409 vs 12,398, P = .003), overall hospital costs did not differ significantly between the 2 groups. This finding appears to be explained by a shorter hospital stay and reduced room and board costs in the urokinase-treated group.ConclusionThere were significant differences in outcome in patients with PAO and DVT who received treatment with urokinase and rt-PA. While pharmacy costs were significantly greater when urokinase was used, reduction in length of stay accounted for similar total hospital costs compared with rt-PA. These findings must be considered in the context of the retrospective nature of the analysis and the potential to use dosing regimens that differ from those in this study
Evolution of Magnetism in Single-Crystal Honeycomb Iridates
We report the successful synthesis of single-crystals of the layered iridate,
(NaLi)IrO, , and a thorough study of
its structural, magnetic, thermal and transport properties. The new compound
allows a controlled interpolation between NaIrO and LiIrO,
while maintaing the novel quantum magnetism of the honeycomb Ir planes.
The measured phase diagram demonstrates a dramatic suppression of the N\'eel
temperature, , at intermediate suggesting that the magnetic order in
NaIrO and LiIrO are distinct, and that at , the
compound is close to a magnetically disordered phase that has been sought after
in NaIrO and LiIrO. By analyzing our magnetic data with a
simple theoretical model we also show that the trigonal splitting, on the
Ir ions changes sign from NaIrO and LiIrO, and the
honeycomb iridates are in the strong spin-orbit coupling regime, controlled by
\jeff=1/2 moments.Comment: updated version with more dat
Quantum Aspects of Black Hole Entropy
This survey intends to cover recent approaches to black hole entropy which
attempt to go beyond the standard semiclassical perspective. Quantum
corrections to the semiclassical Bekenstein-Hawking area law for black hole
entropy, obtained within the quantum geometry framework, are treated in some
detail. Their ramification for the holographic entropy bound for bounded
stationary spacetimes is discussed. Four dimensional supersymmetric extremal
black holes in string-based N=2 supergravity are also discussed, albeit more
briefly.Comment: 13 Pages Revtex with 3 eps figures; based on plenary talk given at
the International Conference on Gravitation and Cosmology, Kharagpur, India,
January, 2000 One reference adde
Observation of Spin-glass-like Behavior in SrRuO3 Epitaxial Thin Films
We report the observation of spin-glass-like behavior and strong magnetic
anisotropy in extremely smooth (~1-3 \AA) roughness) epitaxial (110) and (010)
SrRuO3 thin films. The easy axis of magnetization is always perpendicular to
the plane of the film (unidirectional) irrespective of crystallographic
orientation. An attempt has been made to understand the nature and origin of
spin-glass behavior, which fits well with Heisenberg model.Comment: 5 pages, 5 Figure
Evidence for an unconventional magnetic instability in the spin-tetrahedra system Cu_2Te_2O_5Br_2
Thermodynamic experiments as well as Raman scattering have been used to study
the magnetic instabilities in the spin-tetrahedra systems Cu_2Te_2O_5X_2, X=Cl
and Br. While the phase transition observed in the Cl system at T_o=18.2 K is
consistent with 3D AF ordering, the phase transition at T_o=11.3 K in the Br
system has several unusual features. We propose an explanation in terms of
weakly coupled tetrahedra with a singlet-triplet gap and low lying singlets.Comment: 4 pages, 4 figure
- …