23,174 research outputs found
Small-Scale Variations of HI Spectra from Interstellar Scintillatio
I suggest that radio-wave scattering by the interstellar plasma, in
combination with subsonic gradients in the Doppler velocity of interstellar HI,
is responsible for the observed small-scale variation in HI absorption spectra
of pulsars. Velocity gradients on the order of 0.05 to 0.3 km/s across 1 AU can
produce the observed variations. I suggest observational tests to distinguish
between this model and the traditional picture of small-scale opacity
variations from cloudlets.Comment: 24 pages, 2 figures, Latex, uses AASTe
Fluctuation and dissipation dynamics in fusion reactions from stochastic mean-field approach
By projecting the stochastic mean-field dynamics on a suitable collective
path during the entrance channel of heavy-ion collisions, expressions for
transport coefficients associated with relative distance are extracted. These
transport coefficients, which have similar forms to those familiar from nucleon
exchange model, are evaluated by carrying out TDHF simulations. The
calculations provide an accurate description of the magnitude and form factor
of transport coefficients associated with one-body dissipation and fluctuation
mechanism.Comment: 9 pages, 5 figure
The Dual Formulation of Cosmic Strings and Vortices
We study four dimensional systems of global, axionic and local strings. By
using the path integral formalism, we derive the dual formulation of these
systems, where Goldstone bosons, axions and missive vector bosons are described
by antisymmetric tensor fields, and strings appear as a source for these tensor
fields. We show also how magnetic monopoles attached to local strings are
described in the dual formulation. We conclude with some remarks.Comment: 18 pages, CU-TP-588 and CERN-TH.6780/9
Combinatorial Assortment Optimization
Assortment optimization refers to the problem of designing a slate of
products to offer potential customers, such as stocking the shelves in a
convenience store. The price of each product is fixed in advance, and a
probabilistic choice function describes which product a customer will choose
from any given subset. We introduce the combinatorial assortment problem, where
each customer may select a bundle of products. We consider a model of consumer
choice where the relative value of different bundles is described by a
valuation function, while individual customers may differ in their absolute
willingness to pay, and study the complexity of the resulting optimization
problem. We show that any sub-polynomial approximation to the problem requires
exponentially many demand queries when the valuation function is XOS, and that
no FPTAS exists even for succinctly-representable submodular valuations. On the
positive side, we show how to obtain constant approximations under a
"well-priced" condition, where each product's price is sufficiently high. We
also provide an exact algorithm for -additive valuations, and show how to
extend our results to a learning setting where the seller must infer the
customers' preferences from their purchasing behavior
The Galam Model of Minority Opinion Spreading and the Marriage Gap
In 2002, Serge Galam designed a model of a minority opinion spreading. The
effect is expected to lead a conservative minority to prevail if the issue is
discussed long enough. Here we analyze the marriage gap, i.e. the difference in
voting for Bush and Kerry in 2004 between married and unmarried people. It
seems possible to interpret this marriage gap in terms of the Galam model.Comment: 6 page
The Surface of a Bose-Einstein Condensed Atomic Cloud
We investigate the structure and collective modes of a planar surface of a
trapped Bose-Einstein condensed gas at zero temperature. In the long-wavelength
limit we find a mode similar to the gravity wave on the surface of a fluid with
the frequency and the wavenumber related by . Here
is the force due to the confining potential at the surface and is the
particle mass. At shorter wavelengths we use a variational approach and find
corrections to of order . We demonstrate the usefulness
of the concept of an effective surface tension for describing both static and
dynamic properties of condensed atomic clouds.Comment: 8 pages, REVTEX, submitted to Phys. Rev.
Specific heat of the Kelvin modes in low temperature superfluid turbulence
It is pointed out that the specific heat of helical vortex line excitations,
in low temperature superfluid turbulence experiments carried out in helium II,
can be of the same order as the specific heat of the phononic quasiparticles.
The ratio of Kelvin mode and phonon specific heats scales with L_0 T^{-5/2},
where L_0 represents the smoothed line length per volume within the vortex
tangle, such that the contribution of the vortex mode specific heat should be
observable for L_0 = 10^6-10^8 cm^{-2}, and at temperatures which are of order
1-10 mK.Comment: 3 pages, 1 figur
Quantized Roentgen Effect in Bose-Einstein Condensates
A classical dielectric moving in a charged capacitor can create a magnetic
field (Roentgen effect). A quantum dielectric, however, will not produce a
magnetization, except at vortices. The magnetic field outside the quantum
dielectric appears as the field of quantized monopoles
Additional outcomes and subgroup analyses of NXY-059 for acute ischemic stroke in the SAINT I trial
<p><b>Background and Purpose:</b> NXY-059 is a free radical-trapping neuroprotectant demonstrated to reduce disability from ischemic stroke. We conducted analyses on additional end points and sensitivity analyses to confirm our findings.</p>
<p><b>Methods:</b> We randomized 1722 patients with acute ischemic stroke to a 72-hour infusion of placebo or intravenous NXY-059 within 6 hours of stroke onset. The primary outcome was disability at 90 days, as measured by the modified Rankin Scale (mRS), a 6-point scale ranging from 0 (no residual symptoms) to 5 (bed-bound, requiring constant care). Additional and exploratory analyses included mRS at 7 and 30 days; subgroup interactions with final mRS; assessments of activities of daily living by Barthel index; and National Institutes of Health Stroke Scale (NIHSS) neurological scores at 7 and 90 days.</p>
<p><b>Results:</b> NXY-059 significantly improved the distribution of the mRS disability score compared with placebo at 7, 30, and 90 days (Cochran-Mantel-Haenszel test P=0.002, 0.004, 0.038, respectively; 90-day common odds ratio 1.20; 95% CI, 1.01 to 1.42). The benefit was not attributable to any specific baseline characteristic, stratification variable or subgroup interaction. Neurological scores were improved at 7 days (odds ratio [OR], 1.46; 95% CI, 1.13, 1.89; P=0.003) and the Barthel index was improved at 7 and 30 days (OR, 1.55; 95% CI, 1.22, 1.98; P<0.0001; OR, 1.27; 95% CI, 1.01, 1.59; P=0.02).</p>
<p><b>Conclusions:</b> NXY-059 within 6 hours of acute ischemic stroke significantly reduced disability. Benefit on neurological scores and activities of daily living was detectable early but not significant at 90 days; however, our trial was underpowered to measure effects on the neurological examination. The benefit on disability is not confounded by interactions and is supported by other outcome measures.</p>
An intelligent assistant for exploratory data analysis
In this paper we present an account of the main features of SNOUT, an intelligent assistant for exploratory data analysis (EDA) of social science survey data that incorporates a range of data mining techniques. EDA has much in common with existing data mining techniques: its main objective is to help an investigator reach an understanding of the important relationships ina data set rather than simply develop predictive models for selectd variables. Brief descriptions of a number of novel techniques developed for use in SNOUT are presented. These include heuristic variable level inference and classification, automatic category formation, the use of similarity trees to identify groups of related variables, interactive decision tree construction and model selection using a genetic algorithm
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