489 research outputs found
Dynamic Critical Behavior of the Heisenberg Model with Strong Easy Plane Anisotropy
The dynamic critical behavior of the Heisenberg model with a strong
anisotropy of the exchange constant in the z direction is investigated. The
main features of the time evolution of this model are revealed. The static and
dynamic critical behavior of planar magnetic models is shown to be described
well by the Heisenberg model with strong easy plane anisotropy.Comment: 5 pages, 4 figures, 1 tabl
White paper: A plan for cooperation between NASA and DARPA to establish a center for advanced architectures
Large, complex computer systems require many years of development. It is recognized that large scale systems are unlikely to be delivered in useful condition unless users are intimately involved throughout the design process. A mechanism is described that will involve users in the design of advanced computing systems and will accelerate the insertion of new systems into scientific research. This mechanism is embodied in a facility called the Center for Advanced Architectures (CAA). CAA would be a division of RIACS (Research Institute for Advanced Computer Science) and would receive its technical direction from a Scientific Advisory Board established by RIACS. The CAA described here is a possible implementation of a center envisaged in a proposed cooperation between NASA and DARPA
Magnetic excitations of the Cu quantum spin chain in SrCuPtO
We report the magnetic excitation spectrum as measured by inelastic neutron
scattering for a polycrystalline sample of SrCuPtO. Modeling the data
by the 2+4 spinon contributions to the dynamical susceptibility within the
chains, and with interchain coupling treated in the random phase approximation,
accounts for the major features of the powder-averaged structure factor. The
magnetic excitations broaden considerably as temperature is raised, persisting
up to above 100 K and displaying a broad transition as previously seen in the
susceptibility data. No spin gap is observed in the dispersive spin excitations
at low momentum transfer, which is consistent with the gapless spinon continuum
expected from the coordinate Bethe ansatz. However, the temperature dependence
of the excitation spectrum gives evidence of some very weak interchain
coupling.Comment: 9 pages, 5 figure
Исследование характеристик щелевого теплообменника с развитой поверхностью теплообмена
Предложена конструкция водяного многоканального щелевого теплообменника, позволяющего отводить мощность до 750 Вт при температуре имитатора теплового потока 60°С, а также пути повышения технологичности изготовления теплообменника
Frustrated Magnetism in Mott Insulating (VCr)O
V2O3 famously features all four combinations of paramagnetic vs
antiferromagnetic, and metallic vs insulating states of matter in response to
%-level doping, pressure in the GPa range, and temperature below 300 K. Using
time-of-flight neutron spectroscopy combined with density functional theory
calculations of magnetic interactions, we have mapped and analyzed the
inelastic magnetic neutron scattering cross section over a wide range of energy
and momentum transfer in the chromium stabilized antiferromagnetic and
paramagnetic insulating phases (AFI & PI). Our results reveal an important
magnetic frustration and degeneracy of the PI phase which is relieved by the
rhombohedral to monoclinic transition at K due to a significant
magneto-elastic coupling. This leads to the recognition that magnetic
frustration is an inherent property of the paramagnetic phase in and plays a key role in suppressing the magnetic long range
ordering temperature and exposing a large phase space for the paramagnetic Mott
metal-insulator transition to occur.Comment: 16 pages, 11 figure
Four-colour photometry of eclipsing binaries. XLI uvby light curves for AD Bootis, HW Canis Majoris, SW Canis Majoris, V636 Centauri, VZ Hydrae, and WZ Ophiuchi
CONTEXT: Accurate mass, radius, and abundance determinations from binaries
provide important information on stellar evolution, fundamental to central
fields in modern astrophysics and cosmology.
AIMS: Within the long-term Copenhagen Binary Project, we aim to obtain
high-quality light curves and standard photometry for double-lined detached
eclipsing binaries with late A, F, and G type main-sequence components, needed
for the determination of accurate absolute dimensions and abundances, and for
detailed comparisons with results from recent stellar evolutionary models.
METHODS: Between March 1985 and July 2007, we carried out photometric
observations of AD Boo, HW CMA, SW CMa, V636 Cen, VZ Hya, and WZ Oph at the
Str"omgren Automatic Telescope at ESO, La Silla.
RESULTS: We obtained complete uvby light curves, ephemerides, and standard
uvby\beta indices for all six systems.For V636 Cen and HW CMa, we present the
first modern light curves, whereas for AD Boo, SW CMa, VZ Hya, and WZ Oph, they
are both more accurate and more complete than earlier data. Due to a high
orbital eccentricity (e = 0.50), combined with a low orbital inclination (i =
84.7), only one eclipse, close to periastron, occurs for HW CMa. For the two
other eccentric systems, V636 Cen (e = 0.134) and SW CMa (e = 0.316), apsidal
motion has been detected with periods of 5270 +/- 335 and 14900 +/- 3600 years,
respectively.Comment: Only change is: Bottom lines (hopefully) not truncated anymore.
Accepted for publication in Astonomy & Astrophysic
Cardiac lipid content is unresponsive to a physical activity training intervention in type 2 diabetic patients, despite improved ejection fraction
Background: Increased cardiac lipid content has been associated with diabetic cardiomyopathy. We recently showed that cardiac lipid content is reduced after 12 weeks of physical activity training in healthy overweight subjects. The beneficial effect of exercise training on cardiovascular risk is well established and the decrease in cardiac lipid content with exercise training in healthy overweight subjects was accompanied by improved ejection fraction. It is yet unclear whether diabetic patients respond similarly to physical activity training and whether a lowered lipid content in the heart is necessary for improvements in cardiac function. Here, we investigated whether exercise training is able to lower cardiac lipid content and improve cardiac function in type 2 diabetic patients. Methods: Eleven overweight-to-obese male patients with type 2 diabetes mellitus (age: 58.4 +/- 0.9 years, BMI: 29.9 +/- 0.01 kg/m(2)) followed a 12-week training program (combination endurance/strength training, three sessions/week). Before and after training, maximal whole body oxygen uptake (VO2max) and insulin sensitivity (by hyperinsulinemic, euglycemic clamp) was determined. Systolic function was determined under resting conditions by CINE-MRI and cardiac lipid content in the septum of the heart by Proton Magnetic Resonance Spectroscopy. Results: VO2max increased (from 27.1 +/- 1.5 to 30.1 +/- 1.6 ml/min/kg, p = 0.001) and insulin sensitivity improved upon training (insulin stimulated glucose disposal (delta Rd of glucose) improved from 5.8 +/- 1.9 to 10.3 +/- 2.0 mu mol/kg/min, p = 0.02. Left-ventricular ejection fraction improved after training (from 50.5 +/- 2.0 to 55.6 +/- 1.5%, p = 0.01) as well as cardiac index and cardiac output. Unexpectedly, cardiac lipid content in the septum remained unchanged (from 0.80 +/- 0.22% to 0.95 +/- 0.21%, p = 0.15). Conclusions: Twelve weeks of progressive endurance/strength training was effective in improving VO(2)max, insulin sensitivity and cardiac function in patients with type 2 diabetes mellitus. However, cardiac lipid content remained unchanged. These data suggest that a decrease in cardiac lipid content in type 2 diabetic patients is not a prerequisite for improvements in cardiac function.Cardiovascular Aspects of Radiolog
All-sky search for periodic gravitational waves in LIGO S4 data
We report on an all-sky search with the LIGO detectors for periodic
gravitational waves in the frequency range 50-1000 Hz and with the frequency's
time derivative in the range -1.0E-8 Hz/s to zero. Data from the fourth LIGO
science run (S4) have been used in this search. Three different semi-coherent
methods of transforming and summing strain power from Short Fourier Transforms
(SFTs) of the calibrated data have been used. The first, known as "StackSlide",
averages normalized power from each SFT. A "weighted Hough" scheme is also
developed and used, and which also allows for a multi-interferometer search.
The third method, known as "PowerFlux", is a variant of the StackSlide method
in which the power is weighted before summing. In both the weighted Hough and
PowerFlux methods, the weights are chosen according to the noise and detector
antenna-pattern to maximize the signal-to-noise ratio. The respective
advantages and disadvantages of these methods are discussed. Observing no
evidence of periodic gravitational radiation, we report upper limits; we
interpret these as limits on this radiation from isolated rotating neutron
stars. The best population-based upper limit with 95% confidence on the
gravitational-wave strain amplitude, found for simulated sources distributed
isotropically across the sky and with isotropically distributed spin-axes, is
4.28E-24 (near 140 Hz). Strict upper limits are also obtained for small patches
on the sky for best-case and worst-case inclinations of the spin axes.Comment: 39 pages, 41 figures An error was found in the computation of the C
parameter defined in equation 44 which led to its overestimate by 2^(1/4).
The correct values for the multi-interferometer, H1 and L1 analyses are 9.2,
9.7, and 9.3, respectively. Figure 32 has been updated accordingly. None of
the upper limits presented in the paper were affecte
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