763 research outputs found
Relaxation and thermalization in the one-dimensional Bose-Hubbard model: A case study for the interaction quantum quench from the atomic limit
Motivated by recent experiments, we study the relaxation dynamics and
thermalization in the one-dimensional Bose-Hubbard model induced by a global
interaction quench. Specifically, we start from an initial state that has
exactly one boson per site and is the ground state of a system with infinitely
strong repulsive interactions at unit filling. Using exact diagonalization and
the density matrix renormalization group method, we compute the time dependence
of such observables as the multiple occupancy and the momentum distribution
function. Typically, the relaxation to stationary values occurs over just a few
tunneling times. The stationary values are identical to the so-called diagonal
ensemble on the system sizes accessible to our numerical methods and we further
observe that the micro-canonical ensemble describes the steady state of many
observables reasonably well for small and intermediate interaction strength.
The expectation values of observables in the canonical ensemble agree
quantitatively with the time averages obtained from the quench at small
interaction strengths, and qualitatively provide a good description of
steady-state values even in parameter regimes where the micro-canonical
ensemble is not applicable due to finite-size effects. We discuss our numerical
results in the framework of the eigenstate thermalization hypothesis. Moreover,
we also observe that the diagonal and the canonical ensemble are practically
identical for our initial conditions already on the level of their respective
energy distributions for small interaction strengths. Finally, we discuss
implications of our results for the interpretation of a recent sudden expansion
experiment [Phys. Rev. Lett. 110, 205301 (2013)], in which the same interaction
quench was realized.Comment: 19 pages, 22 figure
The Underlying Factors of Regional U.S. Hotel Market Resiliency Post 9/11
I was interested in researching the underlying factors that drove resiliency in regional U.S. hotel markets. I did this by conducting an empirical analysis of twenty nine different markets post September 11 and investigating general, leisure and business variables. I concluded that leisure variables were the underlying drivers of resiliency in regional U.S. hotel markets.
I then conducted an event study to try to apply my findings to stock market prices of publicly traded hotel companies. Although it was a challenge to differentiate between companies that depended more on leisure versus business customers due to their asset diversification, I categorized each company into one of the two subsets. If my findings held, I would assume that that the cumulative abnormal returns for the companies that relied on business customers would be more negative than the companies who relied on leisure customers. However, this was not the case, so the findings that leisure variables drive market resiliency were not a good predictor of stock market reaction
Quantum phases and topological properties of interacting fermions in one-dimensional superlattices
The realization of artificial gauge fields in ultracold atomic gases has
opened up a path towards experimental studies of topological insulators and, as
an ultimate goal, topological quantum matter in many-body systems. As an
alternative to the direct implementation of two-dimensional lattice
Hamiltonians that host the quantum Hall effect and its variants, topological
charge-pumping experiments provide an additional avenue towards studying
many-body systems. Here, we consider an interacting two-component gas of
fermions realizing a family of one-dimensional superlattice Hamiltonians with
onsite interactions and a unit cell of three sites, whose groundstates would be
visited in an appropriately defined charge pump. First, we investigate the
grandcanonical quantum phase diagram of individual Hamiltonians, focusing on
insulating phases. For a certain commensurate filling, there is a sequence of
phase transitions from a band insulator to other insulating phases (related to
the physics of ionic Hubbard models) for some members of the manifold of
Hamiltonians. Second, we compute the Chern numbers for the whole manifold in a
many-body formulation and show that, related to the aforementioned quantum
phase transitions, a topological transition results in a change of the value
and sign of the Chern number. We provide both an intuitive and conceptual
explanation and argue that these properties could be observed in quantum-gas
experiments
Inhibition of pancreatic cholesterol esterase reduces cholesterol absorption in the hamster
BACKGROUND: Pancreatic cholesterol esterase has three proposed functions in the intestine: 1) to control the bioavailability of cholesterol from dietary cholesterol esters; 2) to contribute to incorporation of cholesterol into mixed micelles; and 3) to aid in transport of free cholesterol to the enterocyte. Inhibitors of cholesterol esterase are anticipated to limit the absorption of dietary cholesterol. RESULTS: The selective and potent cholesterol esterase inhibitor 6-chloro-3-(1-ethyl-2-cyclohexyl)-2-pyrone (figure 1, structure 1) was administered to hamsters fed a high cholesterol diet supplemented with radiolabeled cholesterol ester. Hamsters were gavage fed (3)H-labeled cholesteryl oleate along with inhibitor 1, 0–200 micromoles. Twenty-four hours later, hepatic and serum radioactive cholesterol levels were determined. The ED(50 )of inhibitor 1 for prevention of the uptake of labeled cholesterol derived from hydrolysis of labeled cholesteryl oleate was 100 micromoles. The toxicity of inhibitor 1 was investigated in a 30 day feeding trial. Inhibitor 1, 100 micromoles or 200 micromoles per day, was added to chow supplemented with 1% cholesterol and 0.5% cholic acid. Clinical chemistry urinalysis and tissue histopathology were obtained. No toxicity differences were noted between control and inhibitor supplemented groups. CONCLUSIONS: Inhibitors of cholesterol esterase may be useful therapeutics for limiting cholesterol absorption
Interaction quantum quenches in the one-dimensional Fermi-Hubbard model with spin imbalance
Using the time-dependent density matrix renormalization group method and
exact diagonalization, we study the non-equilibrium dynamics of the
one-dimensional Fermi-Hubbard model following a quantum quench or a ramp of the
onsite interaction strength. For quenches from the non-interacting to the
attractive regime, we investigate the dynamical emergence of
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) correlations, which at finite spin
polarizations are the dominant two-body correlations in the ground state, and
their signatures in the pair quasi-momentum distribution function. We observe
that the post-quench double occupancy exhibits a maximum as the interaction
strength becomes of the order of the bandwidth. Finally, we study quenches and
ramps from attractive to repulsive interactions, which imprint FFLO
correlations onto repulsively bound pairs. We show that a quite short ramp time
is sufficient to wipe out the characteristic FFLO features in the post-quench
pair momentum distribution functions.Comment: 13 pages, 15 figures, minor revisions, version as publishe
Magnon Heat Transport in doped
We present results of the thermal conductivity of and single-crystals which represent model systems for the
two-dimensional spin-1/2 Heisenberg antiferromagnet on a square lattice. We
find large anisotropies of the thermal conductivity, which are explained in
terms of two-dimensional heat conduction by magnons within the CuO planes.
Non-magnetic Zn substituted for Cu gradually suppresses this magnon thermal
conductivity . A semiclassical analysis of
is shown to yield a magnon mean free path which scales
linearly with the reciprocal concentration of Zn-ions.Comment: 4 pages, 3 figure
Expansion velocity of a one-dimensional, two-component Fermi gas during the sudden expansion in the ballistic regime
We show that in the sudden expansion of a spin-balanced two-component Fermi
gas into an empty optical lattice induced by releasing particles from a trap,
over a wide parameter regime, the radius of the particle cloud grows
linearly in time. This allow us to define the expansion velocity from
. The goal of this work is to clarify the dependence of the
expansion velocity on the initial conditions which we establish from
time-dependent density matrix renormalization group simulations, both for a box
trap and a harmonic trap. As a prominent result, the presence of a
Mott-insulating region leaves clear fingerprints in the expansion velocity. Our
predictions can be verified in experiments with ultra-cold atoms.Comment: 8 pages 10 figures, version as published with minor stylistic change
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