38 research outputs found
A forced thermal ratchet in a memory heat bath
The present work studies a non-Markovian forced thermal ratchet model on an
asymmetric periodic potential. The Brownian dynamics is described by a
generalized Langevin equation with an Ornstein-Uhlenbeck-type friction memory
kernel. We show that for the case of a time-dependent driving force, also in
the form of an Ornstein-Uhlenbeck-like process, an exact expression of the
probability current can be derived. We also obtain the behavior of the
particle's average rate of flow as a function of the external amplitude force
and of the bath temperature when the driving force behaves as a square wave
modulation. All our results are compared with those obtained in the Markovian
case and we find, fairly remarkably, that in some cases a friction memory
kernel results in an enhancement of the curren
Brownian motion of a charged particle driven internally by correlated noise
We give an exact solution to the generalized Langevin equation of motion of a
charged Brownian particle in a uniform magnetic field that is driven internally
by an exponentially-correlated stochastic force. A strong dissipation regime is
described in which the ensemble-averaged fluctuations of the velocity exhibit
transient oscillations that arise from memory effects. Also, we calculate
generalized diffusion coefficients describing the transport of these particles
and briefly discuss how they are affected by the magnetic field strength and
correlation time. Our asymptotic results are extended to the general case of
internal driving by correlated Gaussian stochastic forces with finite
autocorrelation times.Comment: 10 pages, 4 figures with subfigures, RevTeX, v2: revise
Carnot, Stirling, Ericsson stochastic heat engines: Efficiency at maximum power
This work obtains the efficiency at maximum power for a stochastic heat
engine performing Carnot-like, Stirling-like and Ericsson-like cycles. For the
mesoscopic engine a Brownian particle trapped by an optical tweezers is
considered. The dynamics of this stochastic engine is described as an
overdamped Langevin equation with a harmonic potential, whereas is in contact
with two thermal baths at different temperatures, namely, hot () and cold
(). The harmonic oscillator Langevin equation is transformed into a
macroscopic equation associated with the mean value
using the original Langevin approach. At equilibrium stationary state this
quantity satisfies a state-like equation from which the thermodynamic
properties are calculated. To obtained the efficiency at maximum power it is
considered the finite-time cycle processes under the framework of low
dissipation approach.Comment: 2 3pages, 5 figure
Electronic plasma diffusion with radiation reaction force and time-dependent electric field
In this work the explicit solution of the electronic plasma diffusion with
radiation reaction force, under the action of an exponential decay external
electric field is given. The electron dynamics is described by a classical
generalized Langevin equation characterized by an Ornstein-Uhlenbeck-type
friction memory kernel, with an effective memory time which accounts for the
effective thermal interaction between the electron and its surroundings
(thermal collisions between electrons + radiation reaction force). The incident
electric field exerts an electric force on the electron, which in turn can
induce an additional damping to the braking radiation force, allowing a delay
in the electron characteristic time. This fact allows that the effective memory
time be finite and positive, and as a consequence, obtaining physically
admissible solutions of the stochastic Abraham-Lorentz-like equation. It is
shown that the diffusion process is quasi-Markovian which includes the
radiation effects.Comment: 16 pages, 8 figure
A Spanish-language patient safety questionnaire to measure medical and nursing students' attitudes and knowledge
Objective. To design and validate a questionnaire for assessing attitudes and knowledge about patient safety using a sample of medical and nursing students undergoing clinical training in Spain and four countries in Latin America. Methods. In this cross-sectional study, a literature review was carried out and total of 786 medical and nursing students were surveyed at eight universities from five countries (Chile, Colombia, El Salvador, Guatemala, and Spain) to develop and refine a Spanish-language questionnaire on knowledge and attitudes about patient safety. The scope of the questionnaire was based on five dimensions (factors) presented in studies related to patient safety culture found in PubMed and Scopus. Based on the five factors, 25 reactive items were developed. Composite reliability indexes and Cronbach''s alpha statistics were estimated for each factor, and confirmatory factor analysis was conducted to assess validity. After a pilot test, the questionnaire was refined using confirmatory models, maximum-likelihood estimation, and the variance-covariance matrix (as input). Multiple linear regression models were used to confirm external validity, considering variables related to patient safety culture as dependent variables and the five factors as independent variables. Results. The final instrument was a structured five-point Likert self-administered survey (the "Latino Student Patient Safety Questionnaire") consisting of 21 items grouped into five factors. Compound reliability indexes (Cronbach''s alpha statistic) calculated for the five factors were about 0.7 or higher. The results of the multiple linear regression analyses indicated good model fit (goodness-of-fit index: 0.9). Item-total correlations were higher than 0.3 in all cases. The convergent-discriminant validity was adequate. Conclusions. The questionnaire designed and validated in this study assesses nursing and medical students'' attitudes and knowledge about patient safety. This instrument could be used to indirectly evaluate whether or not students in health disciplines are acquiring and thus likely to put into practice the professional skills currently considered most appropriate for patient safety
Severe Pneumonia Associated with Pandemic (H1N1) 2009 Outbreak, San Luis Potosí, Mexico
Severe pneumonia developed in young adults who had no identifiable risk factors
Search for W W/W Z resonance production in ℓνqq final states in pp collisions at √s=13 TeV with the ATLAS detector
A search is conducted for new resonances decaying into a W W or W Z boson pair, where one W boson decays leptonically and the other W or Z boson decays hadronically. It is based on proton-proton collision data with an integrated luminosity of 36.1 fb −1 collected with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of s=13 TeV in 2015 and 2016. The search is sensitive to diboson resonance production via vector-boson fusion as well as quark-antiquark annihilation and gluon-gluon fusion mechanisms. No significant excess of events is observed with respect to the Standard Model backgrounds. Several benchmark models are used to interpret the results. Limits on the production cross section are set for a new narrow scalar resonance, a new heavy vector-boson and a spin-2 Kaluza-Klein graviton.[Figure not available: see fulltext.]
Whole-genome sequencing reveals host factors underlying critical COVID-19
Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease
The nonlinear relaxation time and quasideterministic-theory approaches to characterize the decay of unestable states
We present the relationship between nonlinear-relaxation-time (NLRT) and quasideterministic approaches to characterize the decay of an unstable state. The universal character of the NLRT is established. The theoretical results are applied to study the dynamical relaxation of the Landau model in one and n variables and also a laser model