2,887 research outputs found
Monotonicity and logarithmic convexity relating to the volume of the unit ball
Let stand for the volume of the unit ball in for
. In the present paper, we prove that the sequence
is logarithmically convex and that the sequence
is strictly
decreasing for . In addition, some monotonic and concave properties of
several functions relating to are extended and generalized.Comment: 12 page
Internal Friction of Amorphous Silicon in a Magnetic Field
The internal friction of e-beam amorphous silicon was measured in a magnetic
field between 0 and 6 T, from 1.5-20 K, and was found to be independent of the
field to better than 8%. It is concluded that the low energy excitations
observed in this experiment are predominantly atomic in nature.Comment: 4 pages, 4 figures, REVTe
New times, new politics: history and memory during the final years of the CPGB
This article examines the relationship between collective memory, historical interpretation and political identity. It focuses on the dissolution of the Communist Party of Great Britain (CPGB) as constructed through collective narrative memory, and on Marxist interpretations of history. The divisions within the party and the wider Marxist community, stretching from 1956 until 1991, were often framed around questions of historical interpretation. The events of 1989â1991 created an historical and mnemonic crisis for CPGB members who struggled to reconcile their past identities with their present situation. Unlike the outward-facing revisionism of other political parties, this was an intensely personal affair. The solution for many was to emphasise the need to find new ways to progress socialist aims, without relying on a discredited grand narrative. In contrast, other Communist parties, such as the Communist Party of Britain, which had been established (or âre-establishedâ) in 1988, fared rather better. By adhering to the international party line of renewal and continued struggle, the party was able to hold its narrative together, condemning the excesses of totalitarian regimes, while reaffirming the need for international class struggle
Modulated Amplitude Waves in Bose-Einstein Condensates
We analyze spatio-temporal structures in the Gross-Pitaevskii equation to
study the dynamics of quasi-one-dimensional Bose-Einstein condensates (BECs)
with mean-field interactions. A coherent structure ansatz yields a
parametrically forced nonlinear oscillator, to which we apply Lindstedt's
method and multiple-scale perturbation theory to determine the dependence of
the intensity of periodic orbits (``modulated amplitude waves'') on their wave
number. We explore BEC band structure in detail using Hamiltonian perturbation
theory and supporting numerical simulations.Comment: 5 pages, 4 figs, revtex, final form of paper, to appear in PRE
(forgot to include \bibliography command in last update, so this is a
correction of that; the bibliography is hence present again
Nonequilibrium spectral diffusion due to laser heating in stimulated photon echo spectroscopy of low temperature glasses
A quantitative theory is developed, which accounts for heating artifacts in
three-pulse photon echo (3PE) experiments. The heat diffusion equation is
solved and the average value of the temperature in the focal volume of the
laser is determined as a function of the 3PE waiting time. This temperature is
used in the framework of nonequilibrium spectral diffusion theory to calculate
the effective homogeneous linewidth of an ensemble of probe molecules embedded
in an amorphous host. The theory fits recently observed plateaus and bumps
without introducing a gap in the distribution function of flip rates of the
two-level systems or any other major modification of the standard tunneling
model.Comment: 10 pages, Revtex, 6 eps-figures, accepted for publication in Phys.
Rev.
Evaporative cooling of trapped fermionic atoms
We propose an efficient mechanism for the evaporative cooling of trapped
fermions directly into quantum degeneracy. Our idea is based on an electric
field induced elastic interaction between trapped atoms in spin symmetric
states. We discuss some novel general features of fermionic evaporative cooling
and present numerical studies demonstrating the feasibility for the cooling of
alkali metal fermionic species Li, K, and Rb. We also
discuss the sympathetic cooling of fermionic hyperfine spin mixtures, including
the effects of anisotropic interactions.Comment: to be publishe
Bose-Einstein condensates in standing waves: The cubic nonlinear Schroedinger equation with a periodic potential
We present a new family of stationary solutions to the cubic nonlinear
Schroedinger equation with a Jacobian elliptic function potential. In the limit
of a sinusoidal potential our solutions model a dilute gas Bose-Einstein
condensate trapped in a standing light wave. Provided the ratio of the height
of the variations of the condensate to its DC offset is small enough, both
trivial phase and nontrivial phase solutions are shown to be stable. Numerical
simulations suggest such stationary states are experimentally observable.Comment: 4 pages, 4 figure
Quantum dynamics of evaporatively cooled Bose-Einstein Condensates
We report on dynamical simulations of Bose-Einstein condensation via
evaporative cooling in an atomic trap. The results show evidence for
spontaneous vortex formation and quantum dynamics in small traps.Comment: 4 pages, 3 figure
Whatâs Sex (Composition) Got to Do with It? The Importance of Sex Composition of Gangs for Female and Male Membersâ Offending and Victimization
Sex composition of groups has been theorized in organizational sociology and found in prior work to structure female and male membersâ behaviors and experiences. Peer group and gang literature similarly finds that the sex gap in offending varies across groups of differing sex ratios. Drawing on this and other research linking gang membership, offending, and victimization, we examine whether sex composition of gangs is linked to sex differences in offending in this sample, further assess whether sex composition similarly structures femalesâ and malesâ victimization experiences, and if so, why. Self-report data from gang members in a multi-site, longitudinal study of 3,820 youths are employed. Results support previous findings about variations in member delinquency by both sex and sex composition of the gang and also indicate parallel variations in membersâ victimization. These results are further considered within the context of facilitating effects such as gender dynamics, gang characteristics, and normative orientation
From the superfluid to the Mott regime and back: triggering a non-trivial dynamics in an array of coupled condensates
We consider a system formed by an array of Bose-Einstein condensates trapped
in a harmonic potential with a superimposed periodic optical potential.
Starting from the boson field Hamiltonian, appropriate to describe dilute gas
of bosonic atoms, we reformulate the system dynamics within the Bose-Hubbard
model picture. Then we analyse the effective dynamics of the system when the
optical potential depth is suddenly varied according to a procedure applied in
many of the recent experiments on superfluid-Mott transition in Bose-Einstein
condensates.
Initially the condensates' array generated in a weak optical potential is
assumed to be in the superfluid ground-state which is well described in terms
of coherent states. At a given time, the optical potential depth is suddenly
increased and, after a waiting time, it is quickly decreased so that the
initial depth is restored. We compute the system-state evolution and show that
the potential jump brings on an excitation of the system, incorporated in the
final condensate wave functions, whose effects are analysed in terms of
two-site correlation functions and of on-site population oscillations. Also we
show how a too long waiting time can destroy completely the coherence of the
final state making it unobservable.Comment: 10 pages, 4 figures, to appear on Journal of Physics B (Special
Issue: Levico BEC workshop). Publication status update
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