228 research outputs found
Beyond Gross-Pitaevskii Mean Field Theory
A large number of effects related to the phenomenon of Bose-Einstein
Condensation (BEC) can be understood in terms of lowest order mean field
theory, whereby the entire system is assumed to be condensed, with thermal and
quantum fluctuations completely ignored. Such a treatment leads to the
Gross-Pitaevskii Equation (GPE) used extensively throughout this book. Although
this theory works remarkably well for a broad range of experimental parameters,
a more complete treatment is required for understanding various experiments,
including experiments with solitons and vortices. Such treatments should
include the dynamical coupling of the condensate to the thermal cloud, the
effect of dimensionality, the role of quantum fluctuations, and should also
describe the critical regime, including the process of condensate formation.
The aim of this Chapter is to give a brief but insightful overview of various
recent theories, which extend beyond the GPE. To keep the discussion brief,
only the main notions and conclusions will be presented. This Chapter
generalizes the presentation of Chapter 1, by explicitly maintaining
fluctuations around the condensate order parameter. While the theoretical
arguments outlined here are generic, the emphasis is on approaches suitable for
describing single weakly-interacting atomic Bose gases in harmonic traps.
Interesting effects arising when condensates are trapped in double-well
potentials and optical lattices, as well as the cases of spinor condensates,
and atomic-molecular coupling, along with the modified or alternative theories
needed to describe them, will not be covered here.Comment: Review Article (19 Pages) - To appear in 'Emergent Nonlinear
Phenomena in Bose-Einstein Condensates: Theory and Experiment', Edited by
P.G. Kevrekidis, D.J. Frantzeskakis and R. Carretero-Gonzalez (Springer
Verlag
Mapping a candidate gene (MdMYB10) for red flesh and foliage colour in apple
<p>Abstract</p> <p>Background</p> <p>Integrating plant genomics and classical breeding is a challenge for both plant breeders and molecular biologists. Marker-assisted selection (MAS) is a tool that can be used to accelerate the development of novel apple varieties such as cultivars that have fruit with anthocyanin through to the core. In addition, determining the inheritance of novel alleles, such as the one responsible for red flesh, adds to our understanding of allelic variation. Our goal was to map candidate anthocyanin biosynthetic and regulatory genes in a population segregating for the red flesh phenotypes.</p> <p>Results</p> <p>We have identified the <it>Rni </it>locus, a major genetic determinant of the red foliage and red colour in the core of apple fruit. In a population segregating for the red flesh and foliage phenotype we have determined the inheritance of the <it>Rni </it>locus and DNA polymorphisms of candidate anthocyanin biosynthetic and regulatory genes. Simple Sequence Repeats (SSRs) and Single Nucleotide Polymorphisms (SNPs) in the candidate genes were also located on an apple genetic map. We have shown that the MdMYB10 gene co-segregates with the <it>Rni </it>locus and is on Linkage Group (LG) 09 of the apple genome.</p> <p>Conclusion</p> <p>We have performed candidate gene mapping in a fruit tree crop and have provided genetic evidence that red colouration in the fruit core as well as red foliage are both controlled by a single locus named <it>Rni</it>. We have shown that the transcription factor MdMYB10 may be the gene underlying <it>Rni </it>as there were no recombinants between the marker for this gene and the red phenotype in a population of 516 individuals. Associating markers derived from candidate genes with a desirable phenotypic trait has demonstrated the application of genomic tools in a breeding programme of a horticultural crop species.</p
Relationship between knee pain and the presence, location, size and phenotype of femorotibial denuded areas of subchondral bone as visualized by MRI
Objective: Conflicting associations between imaging biomarkers and pain in knee osteoarthritis (OA) have been reported. A relation between pain and denuded areas of subchondral bone (dABs) has been suggested and this study explores this relationship further by relating the presence, phenotype, location and size of dABs to different measures of knee pain. Methods: 633 right knees from the Osteoarthritis Initiative (OAI) (250 men, age 61.7 +/- 9.6 yrs, BMI 29.4 +/- 4.7 kg/m(2)) were included. Manual segmentation of the femorotibial cartilage plates was performed on 3 T coronal fast low angle shot with water excitation (FLASHwe) images. dABs were defined as areas where the subchondral bone was uncovered by cartilage. The following measures of pain were used: weightbearing-, non-weightbearing-, moderate-to-severe-, infrequent- and frequent knee pain. Results: Using pain measures from subjects without dABs as a reference, those with at least one dAB had a 1.64-fold higher prevalence ratio [PR, 95% confidence interval (CI) 1.24-2.18] to have frequent and 1.45-fold higher for moderate-to-severe knee pain (95% CI 1.13-1.85). Subjects with dABs in central subregions had a 1.53-fold increased prevalence of having weightbearing pain (95% Cl 1.20-1.97), especially when the central subregion was moderately (>10%) denuded (PR 1.81, 95% CI 135-2.42). Individuals with cartilage-loss-type dABs had a slightly higher prevalence (PR 1.13, 95% CI 1.00-1.27) of having frequent knee pain compared to individuals with intra-chondral-osteophyte-type dABs. Conclusion: This study supports a positive relation between femorotibial dABs and knee pain, especially when the dABs are located centrally (i.e., in weightbearing regions) or when the respective central subregion is moderately denuded. (C) 2013 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved
Entropy production from stochastic dynamics in discrete full phase space
The stochastic entropy generated during the evolution of a system interacting
with an environment may be separated into three components, but only two of
these have a non-negative mean. The third component of entropy production is
associated with the relaxation of the system probability distribution towards a
stationary state and with nonequilibrium constraints within the dynamics that
break detailed balance. It exists when at least some of the coordinates of the
system phase space change sign under time reversal, and when the stationary
state is asymmetric in these coordinates. We illustrate the various components
of entropy production, both in detail for particular trajectories and in the
mean, using simple systems defined on a discrete phase space of spatial and
velocity coordinates. These models capture features of the drift and diffusion
of a particle in a physical system, including the processes of injection and
removal and the effect of a temperature gradient. The examples demonstrate how
entropy production in stochastic thermodynamics depends on the detail that is
included in a model of the dynamics of a process. Entropy production from such
a perspective is a measure of the failure of such models to meet Loschmidt's
expectation of dynamic reversibility
A Randomised Controlled Trial of Extended Anticoagulation Treatment Versus Standard Treatment for the Prevention of Recurrent VTE and Post-thrombotic Syndrome in Patients Being Treated for a First Episode of Unprovoked VTE (The ExACT Study)
Venous thromboembolism (VTE) is prevalent and impactful, with a risk of death, morbidity and recurrence. Postâthrombotic syndrome (PTS) is a common consequence and associated with impaired quality of life (QoL). The ExACT study was a nonâblinded, prospective, multicentred randomised controlled trial comparing extended versus limited duration anticoagulation following a first unprovoked VTE (proximal deep vein thrombosis or pulmonary embolism). Adults were eligible if they had completed â„3 months anticoagulation (remaining anticoagulated). The primary outcome was time to first recurrent VTE from randomisation. The secondary outcomes included PTS severity, bleeding, QoL and Dâdimers. Twoâhundred and eightyâone patients were recruited, randomised and followed up for 24 months (mean age 63, male:female 2:1). There was a significant reduction in recurrent VTE for patients receiving extended anticoagulation [2·75 vs. 13·54 events/100 patient years, adjusted hazard ratio (aHR) 0·20 (95% confidence interval (CI): 0·09 to 0·46, P < 0·001)] with a nonâsignificant increase in major bleeding [3·54 vs. 1·18 events/100 patient years, aHR 2·99 (95% CI: 0·81â11·05, P = 0·10)]. Outcomes of PTS and QoL were no different between groups. Dâdimer results (on anticoagulation) did not predict VTE recurrence. In conclusion, extended anticoagulation reduced VTE recurrence but did not reduce PTS or improve QoL and was associated with a nonâsignificant increase in bleeding. Results also suggest very limited clinical utility of Dâdimer testing on anticoagulated patients
To Act and Learn: A Bakhtinian Exploration of Action Learning
This paper considers the work of the Russian social philosopher and cultural theorist, Mikhail Mikhailovich Bakhtin as a source of understanding for those involved in action learning. Drawing upon data gathered over two years during the evaluation of 20 action learning sets in the north of England, we will seek to work with the ideas of Bakhtin to consider their value for those involved in action learning. We consider key Bakhtin features such as Making Meaning, Participative Thinking, Theoreticism and Presence, Others and Outsideness, Voices and Carnival to highlight how Bakhtin's can enhance our understanding of the nature of action and learning
How limit cycles and quasi-cycles are related in systems with intrinsic noise
Fluctuations and noise may alter the behavior of dynamical systems
considerably. For example, oscillations may be sustained by demographic
fluctuations in biological systems where a stable fixed point is found in the
absence of noise. We here extend the theoretical analysis of such stochastic
effects to models which have a limit cycle for some range of the model
parameters. We formulate a description of fluctuations about the periodic orbit
which allows the relation between the stochastic oscillations in the fixed
point phase and the oscillations in the limit cycle phase to be elucidated. In
the case of the limit cycle, a suitable transformation into a co-moving frame
allow fluctuations transverse and longitudinal with respect to the limit cycle
to be effectively decoupled. While longitudinal fluctuations are of a diffusive
nature, those in the transverse direction follow a stochastic path more akin to
an Ornstein-Uhlenbeck process. Their power spectrum is computed analytically
within a van Kampen expansion in the inverse system size. This is carried out
in two different ways, and the subsequent comparison with numerical simulations
illustrates the effects that can occur due to diffusion in the longitudinal
direction.Comment: 15 pages, 14 figure
Probing quantum and thermal noise in an interacting many-body system
The probabilistic character of the measurement process is one of the most
puzzling and fascinating aspects of quantum mechanics. In many-body systems
quantum mechanical noise reveals non-local correlations of the underlying
many-body states. Here, we provide a complete experimental analysis of the
shot-to-shot variations of interference fringe contrast for pairs of
independently created one-dimensional Bose condensates. Analyzing different
system sizes we observe the crossover from thermal to quantum noise, reflected
in a characteristic change in the distribution functions from Poissonian to
Gumbel-type, in excellent agreement with theoretical predictions based on the
Luttinger liquid formalism. We present the first experimental observation of
quasi long-range order in one-dimensional atomic condensates, which is a
hallmark of quantum fluctuations in one-dimensional systems. Furthermore, our
experiments constitute the first analysis of the full distribution of quantum
noise in an interacting many-body system
Intelligent OS X malware threat detection with code inspection
With the increasing market share of Mac OS X operating system, there is a corresponding increase in the number of malicious programs (malware) designed to exploit vulnerabilities on Mac OS X platforms. However, existing manual and heuristic OS X malware detection techniques are not capable of coping with such a high rate of malware. While machine learning techniques offer promising results in automated detection of Windows and Android malware, there have been limited efforts in extending them to OS X malware detection. In this paper, we propose a supervised machine learning model. The model applies kernel base Support Vector Machine (SVM) and a novel weighting measure based on application library calls to detect OS X malware. For training and evaluating the model, a dataset with a combination of 152 malware and 450 benign were is created. Using common supervised Machine Learning algorithm on the dataset, we obtain over 91% detection accuracy with 3.9% false alarm rate. We also utilize Synthetic Minority Over-sampling Technique (SMOTE) to create three synthetic datasets with different distributions based on the refined version of collected dataset to investigate impact of different sample sizes on accuracy of malware detection. Using SMOTE datasets we could achieve over 96% detection accuracy and false alarm of less than 4%. All malware classification experiments are tested using cross validation technique. Our results reflect that increasing sample size in synthetic datasets has direct positive effect on detection accuracy while increases false alarm rate in compare to the original dataset
Predicting Progressive Glaucomatous Optic Neuropathy Using Baseline Standard Automated Perimetry Data
PURPOSE. To test the hypothesis that specific locations and patterns of threshold findings within the visual field have predictive value for progressive glaucomatous optic neuropathy (pGON). METHODS. Age-adjusted standard automated perimetry thresholds, along with other clinical variables gathered at the initial examination of 168 individuals with high-risk ocular hypertension or early glaucoma, were used as predictors in a classification tree model. The classification variable was a determination of pGON, based on longitudinally gathered stereo optic nerve head photographs. Only data for the worse eye of each individual were included. Data from 100 normal subjects were used to test the specificity of the models. RESULTS. Classification tree models suggest that patterns of baseline visual field findings are predictive of pGON with sensitivity 65% and specificity 87% on average. Average specificity when data from normal subjects were run on the models was 69%. CONCLUSIONS. Classification trees can be used to determine which visual field locations are most predictive of poorer prognosis for pGON. Spatial patterns within the visual field convey useable predictive information, in most cases when thresholds are still well within the classically defined normal range. (Invest Ophthalmol Vis Sci. 2009;50:674 -680
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