27,068 research outputs found
Deformation of a Trapped Fermi Gas with Unequal Spin Populations
The real-space densities of a polarized strongly-interacting two-component
Fermi gas of Li atoms reveal two low temperature regimes, both with a
fully-paired core. At the lowest temperatures, the unpolarized core deforms
with increasing polarization. Sharp boundaries between the core and the excess
unpaired atoms are consistent with a phase separation driven by a first-order
phase transition. In contrast, at higher temperatures the core does not deform
but remains unpolarized up to a critical polarization. The boundaries are not
sharp in this case, indicating a partially-polarized shell between the core and
the unpaired atoms. The temperature dependence is consistent with a tricritical
point in the phase diagram.Comment: Accepted for publication in Physical Review Letter
Coherent storage and phase modulation of single hard x-ray photons using nuclear excitons
Coherent storage and phase modulation of x-ray single-photon wave packets in
resonant scattering of light off nuclei is investigated theoretically. We show
that by switching off and on again the magnetic field in the nuclear sample,
phase-sensitive storage of photons in the keV regime can be achieved.
Corresponding phase modulation of the stored photon can be accomplished
if the retrieving magnetic field is rotated by . The development
of such x-ray single-photon control techniques is a first step towards
forwarding quantum optics and quantum information to shorter wavelengths and
more compact photonic devices.Comment: 12 pages, 6 figures; v2 modified to match the published version,
condensed to 4 figures, results unchange
Low-density series expansions for directed percolation I: A new efficient algorithm with applications to the square lattice
A new algorithm for the derivation of low-density series for percolation on
directed lattices is introduced and applied to the square lattice bond and site
problems. Numerical evidence shows that the computational complexity grows
exponentially, but with a growth factor \lambda < \protect{\sqrt[8]{2}},
which is much smaller than the growth factor \lambda = \protect{\sqrt[4]{2}}
of the previous best algorithm. For bond (site) percolation on the directed
square lattice the series has been extended to order 171 (158). Analysis of the
series yields sharper estimates of the critical points and exponents.Comment: 20 pages, 8 figures (3 of them > 1Mb
On the Connection Between Momentum Cutoff and Operator Cutoff Regularizations
Operator cutoff regularization based on the original Schwinger's proper-time
formalism is examined. By constructing a regulating smearing function for the
proper-time integration, we show how this regularization scheme simulates the
usual momentum cutoff prescription yet preserves gauge symmetry even in the
presence of the cutoff scales. Similarity between the operator cutoff
regularization and the method of higher (covariant) derivatives is also
observed. The invariant nature of the operator cutoff regularization makes it a
promising tool for exploring the renormalization group flow of gauge theories
in the spirit of Wilson-Kadanoff blocking transformation.Comment: 28 pages in plain TeX, no figures. revised and expande
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The cumulative effects of known susceptibility variants to predict primary biliary cirrhosis risk.
Multiple genetic variants influence the risk for development of primary biliary cirrhosis (PBC). To explore the cumulative effects of known susceptibility loci on risk, we utilized a weighted genetic risk score (wGRS) to evaluate whether genetic information can predict susceptibility. The wGRS was created using 26 known susceptibility loci and investigated in 1840 UK PBC and 5164 controls. Our data indicate that the wGRS was significantly different between PBC and controls (P=1.61E-142). Moreover, we assessed predictive performance of wGRS on disease status by calculating the area under the receiver operator characteristic curve. The area under curve for the purely genetic model was 0.72 and for gender plus genetic model was 0.82, with confidence limits substantially above random predictions. The risk of PBC using logistic regression was estimated after dividing individuals into quartiles. Individuals in the highest disclosed risk group demonstrated a substantially increased risk for PBC compared with the lowest risk group (odds ratio: 9.3, P=1.91E-084). Finally, we validated our findings in an analysis of an Italian PBC cohort. Our data suggested that the wGRS, utilizing genetic variants, was significantly associated with increased risk for PBC with consistent discriminant ability. Our study is a first step toward risk prediction for PBC
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