9,177 research outputs found
Simulation of transition dynamics to high confinement in fusion plasmas
The transition dynamics from the low (L) to the high (H) confinement mode in
magnetically confined plasmas is investigated using a first-principles
four-field fluid model. Numerical results are in close agreement with
measurements from the Experimental Advanced Superconducting Tokamak - EAST.
Particularly, the slow transition with an intermediate dithering phase is well
reproduced by the numerical solutions. Additionally, the model reproduces the
experimentally determined L-H transition power threshold scaling that the ion
power threshold increases with increasing particle density. The results hold
promise for developing predictive models of the transition, essential for
understanding and optimizing future fusion power reactors
Light bullets in quadratic media with normal dispersion at the second harmonic
Stable two- and three-dimensional spatiotemporal solitons (STSs) in
second-harmonic-generating media are found in the case of normal dispersion at
the second harmonic (SH). This result, surprising from the theoretical
viewpoint, opens a way for experimental realization of STSs. An analytical
estimate for the existence of STSs is derived, and full results, including a
complete stability diagram, are obtained in a numerical form. STSs withstand
not only the normal SH dispersion, but also finite walk-off between the
harmonics, and readily self-trap from a Gaussian pulse launched at the
fundamental frequency.Comment: 4 pages, 5 figures, accepted to Phys. Rev. Let
Optimism and Physical Health: A Meta-analytic Review
BackgroundâPrior research links optimism to physical health, but the strength of the association has not been systematically evaluated.
PurposeâThe purpose of this study is to conduct a meta-analytic review to determine the strength of the association between optimism and physical health.
MethodsâThe findings from 83 studies, with 108 effect sizes (ESs), were included in the analyses, using random-effects models.
ResultsâOverall, the mean ES characterizing the relationship between optimism and physical health outcomes was 0.17, p<.001. ESs were larger for studies using subjective (versus objective) measures of physical health. Subsidiary analyses were also conducted grouping studies into those that focused solely on mortality, survival, cardiovascular outcomes, physiological markers (including immune function), immune function only, cancer outcomes, outcomes related to pregnancy, physical symptoms, or pain. In each case, optimism was a significant predictor of health outcomes or markers, all p<.001.
ConclusionsâOptimism is a significant predictor of positive physical health outcomes
Extreme events in discrete nonlinear lattices
We perform statistical analysis on discrete nonlinear waves generated though
modulational instability in the context of the Salerno model that interpolates
between the intergable Ablowitz-Ladik (AL) equation and the nonintegrable
discrete nonlinear Schrodinger (DNLS) equation. We focus on extreme events in
the form of discrete rogue or freak waves that may arise as a result of rapid
coalescence of discrete breathers or other nonlinear interaction processes. We
find power law dependence in the wave amplitude distribution accompanied by an
enhanced probability for freak events close to the integrable limit of the
equation. A characteristic peak in the extreme event probability appears that
is attributed to the onset of interaction of the discrete solitons of the AL
equation and the accompanied transition from the local to the global
stochasticity monitored through the positive Lyapunov exponent of a nonlinear
map.Comment: 5 pages, 4 figures; reference added, figure 2 correcte
Re-evaluation of cosmic ray cutoff terminology
The study of cosmic ray access to locations inside the geomagnetic field has evolved in a manner that has led to some misunderstanding and misapplication of the terminology originally developed to describe particle access. This paper presents what is believed to be a useful set of definitions for cosmic ray cutoff terminology for use in theoretical and experimental cosmic ray studies
Structurally specific thermal fluctuations identify functional sites for DNA transcription
We report results showing that thermally-induced openings of double stranded
DNA coincide with the location of functionally relevant sites for
transcription. Investigating both viral and bacterial DNA gene promoter
segments, we found that the most probable opening occurs at the transcription
start site. Minor openings appear to be related to other regulatory sites. Our
results suggest that coherent thermal fluctuations play an important role in
the initiation of transcription. Essential elements of the dynamics, in
addition to sequence specificity, are nonlinearity and entropy, provided by
local base-pair constraints
Evaluation of ADAS with a supported-driver model for desired allocation of tasks between human and technology performance
Partly automated driving is relevant for solving mobility problems, but also causes concerns with respect to the driverâs reliability in task performance. The supported driver model presented in this paper is therefore intended to answer the question, what type of support and in which circumstances, will enhance the driverâs ability to control the vehicle. It became apparent that prerequisites for performing tasks differ per driving taskâs type and require different support. The possible support for each driving taskâs type, has been combined with support-types to reduce the error causations from each different performance level (i.e. knowledge-based, rule-based and skill-based performance). The allocation of support in relation to performance level and driving taskâs type resulted in a supported driver model and this model relates the requested circumstances to appropriate support types. Among three tested ADAS systems, semi-automated parking showed best allocation of support; converting the demanding parallel parking task into a rather routine-like operation
Evaluation of Load transfer in rigid pavements by Rolling wheel deflectometer and Falling weight deflectometer
Rigid pavements have widespread use, e.g, in motorways and airports, due to their excellent properties such as high bearing capacity and long lifetime. However, when rigid pavements fail it is often due to bad load transfer efficiency (LTE) at its joints. Traditional methods of measuring LTE can be time consuming. Here, we study the possibility of measuring LTE using a moving load with the aim of achieving higher productivity. An experiment simulating Rolling Weight Deflectometer (RWD) measurements on a joint was carried out to gain understanding and confidence that can guide the analysis of real RWD data. Continuous data from measurements across a joint allows for determination of not only the LTE but also additional parameters characterizing the pavement and the joint. A semi-analytical model was implemented for simulating the pavement response next to a joint and used for interpretation and verification of the experimental data. The results show promise for the use of moving loads for rapid evaluation of joints
Discovering Valuable Items from Massive Data
Suppose there is a large collection of items, each with an associated cost
and an inherent utility that is revealed only once we commit to selecting it.
Given a budget on the cumulative cost of the selected items, how can we pick a
subset of maximal value? This task generalizes several important problems such
as multi-arm bandits, active search and the knapsack problem. We present an
algorithm, GP-Select, which utilizes prior knowledge about similarity be- tween
items, expressed as a kernel function. GP-Select uses Gaussian process
prediction to balance exploration (estimating the unknown value of items) and
exploitation (selecting items of high value). We extend GP-Select to be able to
discover sets that simultaneously have high utility and are diverse. Our
preference for diversity can be specified as an arbitrary monotone submodular
function that quantifies the diminishing returns obtained when selecting
similar items. Furthermore, we exploit the structure of the model updates to
achieve an order of magnitude (up to 40X) speedup in our experiments without
resorting to approximations. We provide strong guarantees on the performance of
GP-Select and apply it to three real-world case studies of industrial
relevance: (1) Refreshing a repository of prices in a Global Distribution
System for the travel industry, (2) Identifying diverse, binding-affine
peptides in a vaccine de- sign task and (3) Maximizing clicks in a web-scale
recommender system by recommending items to users
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