6,334 research outputs found
Interaction ramps in a trapped Bose condensate
Non-adiabatic interaction ramps are considered for trapped Bose-Einstein
condensates. The deviation from adiabaticity is characterized through the
heating or residual energy produced during the ramp. We find that the
dependence of the heat on the ramp time is very sensitive to the ramp protocol.
We explain features of this dependence through a single-parameter effective
description based on the dynamics of the condensate size.Comment: 4 pages, 3 figure
Squeezing in the weakly interacting uniform Bose condensate
We investigate the presence of squeezing in the weakly repulsive uniform Bose
gas, in both the condensate mode and in the nonzero opposite-momenta mode
pairs, using two different variational formulations. We explore the U(1)
symmetry breaking and Goldstone's theorem in the context of a squeezed coherent
variational wavefunction, and present the associated Ward identity. We show
that squeezing of the condensate mode is absent at the mean field
Hartree-Fock-Bogoliubov level and emerges as a result of fluctuations about
mean field as a finite volume effect, which vanishes in the thermodynamic
limit. On the other hand, the squeezing of the excitations about the condensate
survives the thermodynamic limit and is interpreted in terms of density-phase
variables using a number-conserving formulation of the interacting Bose gas.Comment: 8 pages, 3 figures. Version 2 (Sept'06): expanded discussion
Transition Temperature of Dilute, Weakly Repulsive Bose Gas
Within a quasiparticle framework, we reconsider the issue of computing the
Bose-Einstein condensation temperature () in a weakly non-ideal Bose gas.
The main result of this and previous investigations is that increases
with the scattering length , with the leading dependence being either linear
or log-linear in . The calculation of reduces to that of computing the
excitation spectrum near the transition. We report two approaches to
regularizing the infrared divergence at the transition point. One leads to a
-like shift in , and the other allows numerical
calculations for the shift.Comment: 8 pages, 3 figures, revtex
Experimental investigations in epitaxial growth of crystalline layers final report
Epitaxial growth of crystalline layer
Three-loop HTLpt thermodynamics at finite temperature and chemical potential
In this proceedings we present a state-of-the-art method of calculating
thermodynamic potential at finite temperature and finite chemical potential,
using Hard Thermal Loop perturbation theory (HTLpt) up to
next-to-next-leading-order (NNLO). The resulting thermodynamic potential
enables us to evaluate different thermodynamic quantities including pressure
and various quark number susceptibilities (QNS). Comparison between our
analytic results for those thermodynamic quantities with the available lattice
data shows a good agreement.Comment: 5 pages, 6 figures, conference proceedings of XXI DAE-BRNS HEP
Symposium, IIT Guwahati, December 2014; to appear in 'Springer Proceedings in
Physics Series
Efficient GTS Allocation Schemes for IEEE 802.15.4
IEEE 802.15.4 is a standard defined for wireless sensor network applications with limited power and relaxed throughput needs. The devices transmit data during two periods: Contention Access Period (CAP) by accessing the channel using CSMA/CA and Contention Free Period (CFP), which consists of Guaranteed Time Slots (GTS) allocated to individual devices by the network coordinator. The GTS is used by devices for cyclic data transmission and the coordinator can allocate GTS to a maximum of only seven devices. In this work, we have proposed two algorithms for an efficient GTS allocation. The first algorithm is focused on improving the bandwidth utilization of devices, while the second algorithm uses traffic arrival information of devices to allow sharing of GTS slots between more than seven devices. The proposed schemes were tested through simulations and the results show that the new GTS allocation schemes perform better than the original IEEE 802.15.4 standard
Sentence similarity-based source context modelling in PBSMT
Target phrase selection, a crucial component of the state-of-the-art phrase-based statistical machine translation (PBSMT) model, plays a key role in generating accurate translation hypotheses. Inspired by context-rich word-sense disambiguation techniques, machine translation (MT) researchers have successfully integrated various types of source language context into the PBSMT model to improve target phrase selection. Among the various types of lexical and syntactic features, lexical syntactic descriptions in the form of supertags that preserve long-range word-to-word dependencies in a sentence have proven to be effective. These rich contextual features are able to disambiguate a source phrase, on the basis of the local syntactic behaviour of that phrase. In addition to local contextual information, global contextual information such as the grammatical structure of a sentence, sentence length and n-gram word sequences could provide additional important information to enhance this phrase-sense disambiguation. In this work, we explore various sentence similarity features by measuring similarity between a source sentence to be translated with the source-side of the bilingual training sentences and integrate them directly into the PBSMT model. We performed experiments on an English-to-Chinese translation task by applying sentence-similarity features both individually, and collaboratively with supertag-based features. We evaluate the performance of our approach and report a statistically significant relative improvement of 5.25% BLEU score when adding a sentence-similarity feature together with a supertag-based feature
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The impact of fruit flavonoids on memory and cognition
There is intense interest in the studies related to the potential of phytochemical-rich foods to prevent age-related neurodegeneration and cognitive decline. Recent evidence has indicated that a group of plant-derived compounds known as flavonoids may exert particularly powerful actions on mammalian cognition and may reverse age-related declines in memory and learning. In particular, evidence suggests that foods rich in three specific flavonoid sub-groups, the flavanols, anthocyanins and/or flavanones, possess the greatest potential to act on the cognitive processes. This review will highlight the evidence for the actions of such flavonoids, found most commonly in fruits, such as apples, berries and citrus, on cognitive behaviour and the underlying cellular architecture. Although the precise mechanisms by which these flavonoids act within the brain remain unresolved, the present review focuses on their ability to protect vulnerable neurons and enhance the function of existing neuronal structures, two processes known to be influenced by flavonoids and also known to underpin neuro-cognitive function. Most notably, we discuss their selective interactions with protein kinase and lipid kinase signalling cascades (i.e. phosphoinositide-3 kinase/Akt and mitogen-activated protein kinase pathways), which regulate transcription factors and gene expression involved in both synaptic plasticity and cerebrovascular blood flow. Overall, the review attempts to provide an initial insight into the potential impact of regular flavonoid-rich fruit consumption on normal or abnormal deteriorations in cognitive performance
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