490 research outputs found
Network Discovery by Generalized Random Walks
We investigate network exploration by random walks defined via stationary and
adaptive transition probabilities on large graphs. We derive an exact formula
valid for arbitrary graphs and arbitrary walks with stationary transition
probabilities (STP), for the average number of discovered edges as function of
time. We show that for STP walks site and edge exploration obey the same
scaling as function of time . Therefore, edge exploration
on graphs with many loops is always lagging compared to site exploration, the
revealed graph being sparse until almost all nodes have been discovered. We
then introduce the Edge Explorer Model, which presents a novel class of
adaptive walks, that perform faithful network discovery even on dense networks.Comment: 23 pages, 7 figure
Superdeformation in Po
The Yb(Si,5n) reaction at 148 MeV with thin targets was used
to populate high-angular momentum states in Po. Resulting rays
were observed with Gammasphere. A weakly-populated superdeformed band of 10
-ray transitions was found and has been assigned to Po. This is
the first observation of a SD band in the region in a nucleus
with . The of the new band is very similar to those of
the yrast SD bands in Hg and Pb. The intensity profile suggests
that this band is populated through states close to where the SD band crosses
the yrast line and the angular momentum at which the fission process dominates.Comment: 10 pages, revtex, 2 figs. available on request, submitted to Phys.
Rev. C. (Rapid Communications
Mixed axion/neutralino cold dark matter in supersymmetric models
We consider supersymmetric (SUSY) models wherein the strong CP problem is
solved by the Peccei-Quinn (PQ) mechanism with a concommitant axion/axino
supermultiplet. We examine R-parity conserving models where the neutralino is
the lightest SUSY particle, so that a mixture of neutralinos and axions serve
as cold dark matter. The mixed axion/neutralino CDM scenario can match the
measured dark matter abundance for SUSY models which typically give too low a
value of the usual thermal neutralino abundance, such as models with wino-like
or higgsino-like dark matter. The usual thermal neutralino abundance can be
greatly enhanced by the decay of thermally-produced axinos to neutralinos,
followed by neutralino re-annihilation at temperatures much lower than
freeze-out. In this case, the relic density is usually neutralino dominated,
and goes as \sim (f_a/N)/m_{axino}^{3/2}. If axino decay occurs before
neutralino freeze-out, then instead the neutralino abundance can be augmented
by relic axions to match the measured abundance. Entropy production from
late-time axino decays can diminish the axion abundance, but ultimately not the
neutralino abundance. In mixed axion/neutralino CDM models, it may be possible
to detect both a WIMP and an axion as dark matter relics. We also discuss
possible modifications of our results due to production and decay of saxions.
In the appendices, we present expressions for the Hubble expansion rate and the
axion and neutralino relic densities in radiation, matter and decaying-particle
dominated universes.Comment: 31 pages including 21 figure
Repeat prenatal corticosteroid prior to preterm birth: a systematic review and individual participant data meta-analysis for the PRECISE study group (prenatal repeat corticosteroid international IPD study group: assessing the effects using the best level of evidence) - study protocol
Background The aim of this individual participant data (IPD) meta-analysis is to assess whether the effects of repeat prenatal corticosteroid treatment given to women at risk of preterm birth to benefit their babies are modified in a clinically meaningful way by factors related to the women or the trial protocol. Methods/Design The Prenatal Repeat Corticosteroid International IPD Study Group: assessing the effects using the best level of Evidence (PRECISE) Group will conduct an IPD meta-analysis. The PRECISE International Collaborative Group was formed in 2010 and data collection commenced in 2011. Eleven trials with up to 5,000 women and 6,000 infants are eligible for the PRECISE IPD meta-analysis. The primary study outcomes for the infants will be serious neonatal outcome (defined by the PRECISE International IPD Study Group as one of death (foetal, neonatal or infant); severe respiratory disease; severe intraventricular haemorrhage (grade 3 and 4); chronic lung disease; necrotising enterocolitis; serious retinopathy of prematurity; and cystic periventricular leukomalacia); use of respiratory support (defined as mechanical ventilation or continuous positive airways pressure or other respiratory support); and birth weight (Z-scores). For the children, the primary study outcomes will be death or any neurological disability (however defined by trialists at childhood follow up and may include developmental delay or intellectual impairment (developmental quotient or intelligence quotient more than one standard deviation below the mean), cerebral palsy (abnormality of tone with motor dysfunction), blindness (for example, corrected visual acuity worse than 6/60 in the better eye) or deafness (for example, hearing loss requiring amplification or worse)). For the women, the primary outcome will be maternal sepsis (defined as chorioamnionitis; pyrexia after trial entry requiring the use of antibiotics; puerperal sepsis; intrapartum fever requiring the use of antibiotics; or postnatal pyrexia). Discussion Data analyses are expected to commence in 2011 with results publicly available in 2012
Special behavior of alkali beam emission spectroscopy in low-ion-temperature plasma
Beam emission spectroscopy (BES) is a powerful plasma diagnostic method
especially suited for the measurement of plasma density and its fluctuations.
As such, synthetic BES codes are regularly used to aid the design or
utilization of these diagnostic systems. However, synthetic diagnostics can
also be used to study the method in previously not yet explored operational
conditions. This paper presents such an analysis utilizing the RENATE-OD
synthetic diagnostic code for a hypothetical alkali BES system on the HSX
stellarator. HSX is a device featuring an unusual operating regime in the world
of fusion devices due to the low ion temperature and low plasma density. It was
found that BES shows unusual tendencies in these conditions. The relation
between beam energy and plasma penetration in low-ion-temperature plasma,
together with unique emission features facilitated by low-density plasma, and
the underlying reasons behind these features are explored in this paper
Properties of Ellipticity Correlation with Atmospheric Structure from Gemini South
Cosmic shear holds great promise for a precision independent measurement of
, the mass density of the universe relative to the critical
density. The signal is expected to be weak, so a thorough understanding of
systematic effects is crucial. An important systematic effect is the
atmosphere: shear power introduced by the atmosphere is larger than the
expected signal. Algorithms exist to extract the cosmic shear from the
atmospheric component, though a measure of their success applied to a range of
seeing conditions is lacking.
To gain insight into atmospheric shear, Gemini South imaging in conjunction
with ground condition and satellite wind data were obtained. We find that under
good seeing conditions Point-Spread-Function (PSF) correlations persist well
beyond the separation typical of high-latitude stars. Under these conditions,
ellipticity residuals based on a simple PSF interpolation can be reduced to
within a factor of a few of the shot-noise induced ellipticity floor. We also
find that the ellipticity residuals are highly correlated with wind direction.
Finally, we correct stellar shapes using a more sophisticated procedure and
generate shear statistics from stars. Under all seeing conditions in our data
set the residual correlations lie everywhere below the target signal level. For
good seeing we find that the systematic error attributable to atmospheric
turbulence is comparable in magnitude to the statistical error (shape noise)
over angular scales relevant to present lensing surveys.Comment: To appear in ApJ April 10, 2007, 659
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