1,499 research outputs found
Quantum dynamical correlations: Effective potential analytic continuation approach
We propose a new quantum dynamics method called the effective potential
analytic continuation (EPAC) to calculate the real time quantum correlation
functions at finite temperature. The method is based on the effective action
formalism which includes the standard effective potential. The basic notions of
the EPAC are presented for a one-dimensional double well system in comparison
with the centroid molecular dynamics (CMD) and the exact real time quantum
correlation function. It is shown that both the EPAC and the CMD well reproduce
the exact short time behavior, while at longer time their results deviate from
the exact one. The CMD correlation function damps rapidly with time because of
ensemble dephasing. The EPAC correlation function, however, can reproduce the
long time oscillation inherent in the quantum double well systems. It is also
shown that the EPAC correlation function can be improved toward the exact
correlation function by means of the higher order derivative expansion of the
effective action.Comment: RevTeX4, 20 pages, 6 eps figure
Increasing the coherence time of Bose-Einstein-condensate interferometers with optical control of dynamics
Atom interferometers using Bose-Einstein condensate that is confined in a
waveguide and manipulated by optical pulses have been limited by their short
coherence times. We present a theoretical model that offers a physically simple
explanation for the loss of contrast and propose the method for increasing the
fringe contrast by recombining the atoms at a different time. A simple,
quantitatively accurate, analytical expression for the optimized recombination
time is presented and used to place limits on the physical parameters for which
the contrast may be recovered.Comment: 34 Pages, 8 Figure
Critical Temperature and Condensate Fraction of a Fermion Pair Condensate
We report on measurements of the critical temperature and the temperature
dependence of the condensate fraction for a fermion pair condensate of 6Li
atoms. The Bragg spectroscopy is employed to determine the critical temperature
and the condensate fraction after a fast magnetic field ramp to the molecular
side of the Feshbach resonance. Our measurements reveal the level-off of the
critical temperature and the limiting behavior of condensate fraction near the
unitarity limit
Flow Equation for Supersymmetric Quantum Mechanics
We study supersymmetric quantum mechanics with the functional RG formulated
in terms of an exact and manifestly off-shell supersymmetric flow equation for
the effective action. We solve the flow equation nonperturbatively in a
systematic super-covariant derivative expansion and concentrate on systems with
unbroken supersymmetry. Already at next-to-leading order, the energy of the
first excited state for convex potentials is accurately determined within a 1%
error for a wide range of couplings including deeply nonperturbative regimes.Comment: 24 pages, 8 figures, references added, typos correcte
Revealing the Superfluid Lambda Transition in the Universal Thermodynamics of a Unitary Fermi Gas
We have observed the superfluid phase transition in a strongly interacting
Fermi gas via high-precision measurements of the local compressibility, density
and pressure down to near-zero entropy. Our data completely determine the
universal thermodynamics of strongly interacting fermions without any fit or
external thermometer. The onset of superfluidity is observed in the
compressibility, the chemical potential, the entropy, and the heat capacity. In
particular, the heat capacity displays a characteristic lambda-like feature at
the critical temperature of . This is the first clear
thermodynamic signature of the superfluid transition in a spin-balanced atomic
Fermi gas. Our measurements provide a benchmark for many-body theories on
strongly interacting fermions, relevant for problems ranging from
high-temperature superconductivity to the equation of state of neutron stars.Comment: 11 pages, 8 figure
Physical modelling of backward erosion piping in foundation beneath levee
Centrifuge model tests are performed to observe piping progression in foundation beneath levee and to examine influence of repeated seepage and thickness of foundation ground on piping progression. Once the pipe is formed beneath the levee, hydraulic gradient upstream of the pipe tip becomes larger while that along the pipe becomes rather small. Shift of this large hydraulic gradient position to the upstream with rise of the flood water level leads to the large subsidence of the slope in the protected side and marked increase in flow rate. Repeated seepage and thickness of the permeable foundation layer have influence on stability of levee against piping. Repeated seepage makes the piping progression faster and levee vulnerable to the piping formation. With the thinner permeable foundation layer beneath the levee, the levee is at higher risk to cause brittle failure while the required hydraulic gradient to cause piping is larger
Anomalous Stability of nu=1 Bilayer Quantum Hall State
We have studied the fractional and integer quantum Hall (QH) effects in a
high-mobility double-layer two-dimensional electron system. We have compared
the "stability" of the QH state in balanced and unbalanced double quantum
wells. The behavior of the n=1 QH state is found to be strikingly different
from all others. It is anomalously stable, though all other states decay, as
the electron density is made unbalanced between the two quantum wells. We
interpret the peculiar features of the nu=1 state as the consequences of the
interlayer quantum coherence developed spontaneously on the basis of the
composite-boson picture.Comment: 5 pages, 6 figure
Phase II study of S-1, a novel oral fluoropyrimidine derivative, in patients with metastatic colorectal carcinoma
This study set out to evaluate, in patients with metastatic colorectal carcinoma, the efficacy and toxicity of S-1, which contains tegafur, 5-chloro-2,4-dihydroxypyridine (CDHP) and potassium oxonate, based on a biochemical modulation of 5-fluorouracil (5-FU) targeted at inhibition of dihydropyrimidine dehydrogenase (DPD). Sixty-three patients with measurable metastatic colorectal carcinoma were enrolled into the study. None of the patients had received prior chemotherapy except for adjuvant setting. S-1 was administered orally twice daily at a standard dose of 80 mg m–2day–1for 28 days followed by a 14-day rest. This agent is continued until disease progression, unaccepted toxicity, or patient refusal. Twenty-two (35%) of the 62 eligible patients achieved PR with a 95% confidence interval of 25–48%. Five of the 10 patients with a history of adjuvant chemotherapy achieved partial remission. The median survival time was 12 months. Major adverse reactions included myelosuppressive and gastrointestinal toxicities, though their incidence of grade 3 or 4 being 13% in neutropenia and less than 10% in the others. None of the 53 patients treated as outpatients required hospitalization due to adverse reactions: These results suggest that S-1 achieves similar responses to those of infusional 5-FU plus leucovorin and shows the potential of another biochemical modulation with easily manageable toxicity. © 2000 Cancer Research Campaig
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