431 research outputs found
Measuring the equation of state of trapped ultracold bosonic systems in an optical lattice with in-situ density imaging
We analyze quantitatively how imaging techniques with single-site resolution
allow to measure thermodynamical properties that cannot be inferred from
time-of-light images for the trapped Bose-Hubbard model. If the normal state
extends over a sufficiently large range, the chemical potential and the
temperature can be extracted from a single shot, provided the sample is in
thermodynamic equilibrium. When the normal state is too narrow, temperature is
low but can still be extracted using the fluctuation-dissipation theorem over
the entire trap range as long as the local density approximation remains valid,
as was recently suggested by Qi Zhou and Tin-Lun Ho [arXiv:0908.3015]. However,
for typical present-day experiments, the number of samples needed is of the
order of 1000 in order to get the temperature at least accurate, but it
is possible to reduce the variance by 2 orders of magnitude if the
density-density correlation length is short, which is the case for the
Bose-Hubbard model. Our results provide further evidence that cold gases in an
optical lattices can be viewed as quantum analog computers.Comment: 8 pages, 10 figure
Influence of the trap shape on the superfluid-Mott transition in ultracold atomic gases
The coexistence of superfluid and Mott insulator, due to the quadratic
confinement potential in current optical lattice experiments, makes the
accurate detection of the superfluid-Mott transition difficult. Studying
alternative trapping potentials which are experimentally realizable and have a
flatter center, we find that the transition can be better resolved, but at the
cost of a more difficult tuning of the particle filling. When mapping out the
phase diagram using local probes and the local density approximation we find
that the smoother gradient of the parabolic trap is advantageous.Comment: 5 pages, 6 figure
US Presidential election 2012 prediction using census corrected Twitter model
Unpublished Reports</p
Study of the and capture reactions using the shell model embedded in the continuum
We apply the realistic shell model which includes the coupling between
many-particle (quasi-)bound states and the continuum of one-particle scattering
states to the spectroscopy of mirror nuclei: B and Li, as well as to
the description of low energy cross sections (the astrophysical S factors) in
the capture reactions: and .Comment: 36 pages, 10 figure
Childhood socioeconomic position and objectively measured physical capability levels in adulthood: a systematic review and meta-analysis
<p><b>Background:</b> Grip strength, walking speed, chair rising and standing balance time are objective measures of physical capability that characterise current health and predict survival in older populations. Socioeconomic position (SEP) in childhood may influence the peak level of physical capability achieved in early adulthood, thereby affecting levels in later adulthood. We have undertaken a systematic review with meta-analyses to test the hypothesis that adverse childhood SEP is associated with lower levels of objectively measured physical capability in adulthood.</p>
<p><b>Methods and Findings:</b> Relevant studies published by May 2010 were identified through literature searches using EMBASE and MEDLINE. Unpublished results were obtained from study investigators. Results were provided by all study investigators in a standard format and pooled using random-effects meta-analyses. 19 studies were included in the review. Total sample sizes in meta-analyses ranged from N = 17,215 for chair rise time to N = 1,061,855 for grip strength. Although heterogeneity was detected, there was consistent evidence in age adjusted models that lower childhood SEP was associated with modest reductions in physical capability levels in adulthood: comparing the lowest with the highest childhood SEP there was a reduction in grip strength of 0.13 standard deviations (95% CI: 0.06, 0.21), a reduction in mean walking speed of 0.07 m/s (0.05, 0.10), an increase in mean chair rise time of 6% (4%, 8%) and an odds ratio of an inability to balance for 5s of 1.26 (1.02, 1.55). Adjustment for the potential mediating factors, adult SEP and body size attenuated associations greatly. However, despite this attenuation, for walking speed and chair rise time, there was still evidence of moderate associations.</p>
<p><b>Conclusions:</b> Policies targeting socioeconomic inequalities in childhood may have additional benefits in promoting the maintenance of independence in later life.</p>
Spin Correlation in tt-bar Production from pp-bar Collisions at sqrt(s)=1.8 TeV
The D0 collaboration has performed a study of spin correlation in tt-bar
production for the process tt-bar to bb-bar W^+W^-, where the W bosons decay to
e-nu or mu-nu. A sample of six events was collected during an exposure of the
D0 detector to an integrated luminosity of approximately 125 pb^-1 of
sqrt{s}=1.8 TeV pp-bar collisions. The standard model (SM) predicts that the
short lifetime of the top quark ensures the transmission of any spin
information at production to the tt-bar decay products.
The degree of spin correlation is characterized by a correlation coefficient
k. We find that k>-0.25 at the 68% confidence level, in agreement with the SM
prediction of k=0.88.Comment: Submitted to PRL, Added references, minor changes to tex
A measurement of the W boson mass using large rapidity electrons
We present a measurement of the W boson mass using data collected by the D0
experiment at the Fermilab Tevatron during 1994--1995. We identify W bosons by
their decays to e-nu final states where the electron is detected in a forward
calorimeter. We extract the W boson mass, Mw, by fitting the transverse mass
and transverse electron and neutrino momentum spectra from a sample of 11,089 W
-> e nu decay candidates. We use a sample of 1,687 dielectron events, mostly
due to Z -> ee decays, to constrain our model of the detector response. Using
the forward calorimeter data, we measure Mw = 80.691 +- 0.227 GeV. Combining
the forward calorimeter measurements with our previously published central
calorimeter results, we obtain Mw = 80.482 +- 0.091 GeV
Search for R-parity Violating Supersymmetry in Dimuon and Four-Jets Channel
We present results of a search for R-parity-violating decay of the neutralino
chi_1^0, taken to be the Lightest Supersymmetric Particle. It is assumed that
this decay proceeds through one of the lepton-number violating couplings
lambda-prime_2jk (j=1,2; k=1,2,3). This search is based on 77.5 pb-1 of data,
collected by the D0 experiment at the Fermilab Tevatron in ppbar collisions at
a center of mass energy of 1.8 TeV in 1992-1995.Comment: 10 pages, 3 figure
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