9,285 research outputs found
The Dynamic Structure Factor of the 1D Bose Gas near the Tonks-Girardeau Limit
While the 1D Bose gas appears to exhibit superfluid response under certain
conditions, it fails the Landau criterion according to the elementary
excitation spectrum calculated by Lieb. The apparent riddle is solved by
calculating the dynamic structure factor of the Lieb-Liniger 1D Bose gas. A
pseudopotential Hamiltonian in the fermionic representation is used to derive a
Hartree-Fock operator, which turns out to be well-behaved and local. The
Random-Phase approximation for the dynamic structure factor based on this
derivation is calculated analytically and is expected to be valid at least up
to first order in , where is the dimensionless interaction
strength of the model. The dynamic structure factor in this approximation
clearly indicates a crossover behavior from the non-superfluid Tonks to the
superfluid weakly-interacting regime, which should be observable by Bragg
scattering in current experiments.Comment: 4 pages, 2 figures misprints in formulas correcte
Phase instabilities in hexagonal patterns
The general form of the amplitude equations for a hexagonal pattern including
spatial terms is discussed. At the lowest order we obtain the phase equation
for such patterns. The general expression of the diffusion coefficients is
given and the contributions of the new spatial terms are analysed in this
paper. From these coefficients the phase stability regions in a hexagonal
pattern are determined. In the case of Benard-Marangoni instability our results
agree qualitatively with numerical simulations performed recently.Comment: 6 pages, 6 figures, to appear in Europhys. Let
Generating ring currents, solitons, and svortices by stirring a Bose-Einstein condensate in a toroidal trap
We propose a simple stirring experiment to generate quantized ring currents
and solitary excitations in Bose-Einstein condensates in a toroidal trap
geometry. Simulations of the 3D Gross-Pitaevskii equation show that pure ring
current states can be generated efficiently by adiabatic manipulation of the
condensate, which can be realized on experimental time scales. This is
illustrated by simulated generation of a ring current with winding number two.
While solitons can be generated in quasi-1D tori, we show the even more robust
generation of hybrid, solitonic vortices (svortices) in a regime of wider
confinement. Svortices are vortices confined to essentially one-dimensional
dynamics, which obey a similar phase-offset--velocity relationship as solitons.
Marking the transition between solitons and vortices, svortices are a distinct
class of symmetry-breaking stationary and uniformly rotating excited solutions
of the 2D and 3D Gross-Pitaevskii equation in a toroidal trapping potential.
Svortices should be observable in dilute-gas experiments.Comment: 8 pages, 4 figures; accepted for publication in J. Phys. B (Letters
Polarizability and dynamic structure factor of the one-dimensional Bose gas near the Tonks-Girardeau limit at finite temperatures
Correlation functions related to the dynamic density response of the
one-dimensional Bose gas in the model of Lieb and Liniger are calculated. An
exact Bose-Fermi mapping is used to work in a fermionic representation with a
pseudopotential Hamiltonian. The Hartree-Fock and generalized random phase
approximations are derived and the dynamic polarizability is calculated. The
results are valid to first order in 1/\gamma where \gamma is Lieb-Liniger
coupling parameter. Approximations for the dynamic and static structure factor
at finite temperature are presented. The results preclude superfluidity at any
finite temperature in the large-\gamma regime due to the Landau criterion. Due
to the exact Bose-Fermi duality, the results apply for spinless fermions with
weak p-wave interactions as well as for strongly interacting bosons.Comment: 13 pages, 5 figures, the journal versio
Convective Nonlinearity in Non-Newtonian Fluids
In the limit of infinite yield time for stresses, the hydrodynamic equations
for viscoelastic, Non-Newtonian liquids such as polymer melts must reduce to
that for solids. This piece of information suffices to uniquely determine the
nonlinear convective derivative, an ongoing point of contention in the rheology
literature.Comment: 4 page
Evidence for virtual Compton scattering from the proton
In virtual Compton scattering an electron is scattered off a nucleon such that the nucleon emits a photon. We show that these events can be selected experimentally, and present the first evidence for virtual Compton scattering from the proton in data obtained at the Stanford Linear Accelerator Center. The angular and energy dependence of the data is well described by a calculation that includes the coherent sum of electron and proton radiation
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The Future of History: Investigating the Preservation of Information in the Digital Age
Abstract This study investigates the challenges of preserving information in the digital age, and explores how this may affect the future of historical knowledge. The study is based on a series of semi-structured interviews with forty-one historians, archivists, librarians, and web researchers. While the results reject the idea of a single ‘digital black hole’ in historical records, they emphasize the importance of the issue for the future of history, and the complexity of the solutions to be adopted. The need for planning, for education, and for cooperation between historians and the information professions is also emphasized
A density-functional approach to fermionization in the 1D Bose gas
A time-dependent Kohn-Sham scheme for 1D bosons with contact interaction is
derived based on a model of spinor fermions. This model is specifically
designed for the study of the strong interaction regime close to the Tonks gas.
It allows us to treat the transition from the strongly-interacting
Tonks-Girardeau to the weakly-interacting quasicondensate regime and provides
an intuitive picture of the extent of fermionization in the system. An
adiabatic local-density approximation is devised for the study of
time-dependent processes. This scheme is shown to yield not only accurate
ground-state properties but also overall features of the elementary excitation
spectrum, which is described exactly in the Tonks-gas limit.Comment: 15 pages, 3 figures, misprints (of published version) correcte
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