16,962 research outputs found
Monte Carlo simulation by computer for life-cycle costing
Prediction of behavior and support requirements during the entire life cycle of a system enables accurate cost estimates by using the Monte Carlo simulation by computer. The system reduces the ultimate cost to the procuring agency because it takes into consideration the costs of initial procurement, operation, and maintenance
Validity of adiabaticity in Cavity QED
This paper deals with the concept of adiabaticity for fully quantum
mechanically cavity QED models. The physically interesting cases of Gaussian
and standing wave shapes of the cavity mode are considered. An analytical
approximate measure for adiabaticity is given and compared with numerical wave
packet simulations. Good agreement is obtained where the approximations are
expected to be valid. Usually for cavity QED systems, the large atom-field
detuning case is considered as the adiabatic limit. We, however, show that
adiabaticity is also valid, for the Gaussian mode shape, in the opposite limit.
Effective semiclassical time dependent models, which do not take into account
the shape of the wave packet, are derived. Corrections to such an effective
theory, which are purely quantum mechanical, are discussed. It is shown that
many of the results presented can be applied to time dependent two-level
systems.Comment: 10 pages, 9 figure
Impurity in a bosonic Josephson junction: swallowtail loops, chaos, self-trapping and the poor man's Dicke model
We study a model describing identical bosonic atoms trapped in a
double-well potential together with a single impurity atom, comparing and
contrasting it throughout with the Dicke model. As the boson-impurity coupling
strength is varied, there is a symmetry-breaking pitchfork bifurcation which is
analogous to the quantum phase transition occurring in the Dicke model. Through
stability analysis around the bifurcation point, we show that the critical
value of the coupling strength has the same dependence on the parameters as the
critical coupling value in the Dicke model. We also show that, like the Dicke
model, the mean-field dynamics go from being regular to chaotic above the
bifurcation and macroscopic excitations of the bosons are observed. Overall,
the boson-impurity system behaves like a poor man's version of the Dicke model.Comment: 17 pages, 16 figure
Dicke-type phase transition in a multimode optomechanical system
We consider the "membrane in the middle" optomechanical model consisting of a
laser pumped cavity which is divided in two by a flexible membrane that is
partially transmissive to light and subject to radiation pressure. Steady state
solutions at the mean-field level reveal that there is a critical strength of
the light-membrane coupling above which there is a symmetry breaking
bifurcation where the membrane spontaneously acquires a displacement either to
the left or the right. This bifurcation bears many of the signatures of a
second order phase transition and we compare and contrast it with that found in
the Dicke model. In particular, by studying limiting cases and deriving
dynamical critical exponents using the fidelity susceptibility method, we argue
that the two models share very similar critical behaviour. For example, the
obtained critical exponents indicate that they fall within the same
universality class. Away from the critical regime we identify, however, some
discrepancies between the two models. Our results are discussed in terms of
experimentally relevant parameters and we evaluate the prospects for realizing
Dicke-type physics in these systems.Comment: 14 pages, 6 figure
Research study on materials processing in space experiment number M512: Nickel - 12 wt percent tin alloy evaluation
Nickel-tin (12 wt percent tin) samples were processed in the sphere forming experiment on Skylab 2. The results were characterized for sphericity, density, microhardness, porosity, surface morphology, segregation, chemical composition, Curie point, and crystallography. These results are discussed along with conclusions and recommendations
Informed consent comprehension in African research settings
ObjectivePrevious reviews on participants' comprehension of informed consent information have focused on developed countries. Experience has shown that ethical standards developed on Western values may not be appropriate for African settings where research concepts are unfamiliar. We undertook this review to describe how informed consent comprehension is defined and measured in African research settings.MethodsWe conducted a comprehensive search involving five electronic databases: Medline, Embase, Global Health, EthxWeb and Bioethics Literature Database (BELIT). We also examined African Index Medicus and Google Scholar for relevant publications on informed consent comprehension in clinical studies conducted in sub-Saharan Africa. 29 studies satisfied the inclusion criteria; meta-analysis was possible in 21 studies. We further conducted a direct comparison of participants' comprehension on domains of informed consent in all eligible studies.ResultsComprehension of key concepts of informed consent varies considerably from country to country and depends on the nature and complexity of the study. Meta-analysis showed that 47% of a total of 1633 participants across four studies demonstrated comprehension about randomisation (95% CI 13.9–80.9%). Similarly, 48% of 3946 participants in six studies had understanding about placebo (95% CI 19.0–77.5%), while only 30% of 753 participants in five studies understood the concept of therapeutic misconception (95% CI 4.6–66.7%). Measurement tools for informed consent comprehension were developed with little or no validation. Assessment of comprehension was carried out at variable times after disclosure of study information. No uniform definition of informed consent comprehension exists to form the basis for development of an appropriate tool to measure comprehension in African participants.ConclusionsComprehension of key concepts of informed consent is poor among study participants across Africa. There is a vital need to develop a uniform definition for informed consent comprehension in low literacy research settings in Africa. This will be an essential step towards developing appropriate tools that can adequately measure informed consent comprehension. This may consequently suggest adequate measures to improve the informed consent procedure.ObjectifLes normes éthiques élaborées selon les valeurs occidentales ne sont peut-être pas appropriées au contexte africain où les concepts de recherche ne sont pas familiers. Cette revue décrit comment la compréhension du consentement éclairé est définie et mesurée dans les cadres de recherche africains.MéthodesDes recherches ont été effectuées sur Medline, Embase, Global Health, EthxWeb, base de données de la Bioéthique Littérature, Index Medicus African et Google Scholar pour des publications pertinentes sur la compréhension du consentement éclairé dans les études cliniques menées en Afrique sub-saharienne. 29 études répondaient aux critères d'inclusion; une méta-analyse a été possible pour 21 études. La compréhension des participants sur les domaines du consentement éclairé dans toutes les études admissibles a été comparée directement.RésultatsLa compréhension des concepts clés du consentement éclairé varie considérablement selon les pays et dépend de la nature et de la complexité de l’étude. La méta-analyse a montré que 47% des participants ont compris la randomisation (IC95%: 13,9 - 80,9%), 48% ont compris le placebo (IC95%: 19,0 - 77,5%), 30% ont compris le concept de méprise thérapeutique (IC95%: 4,6 - 66,7%). Les outils de mesure de la compréhension du consentement éclairé étaient développés avec peu ou pas de validation.ConclusionsLa compréhension des concepts clés du consentement éclairé est faible en Afrique. Il y a une nécessité vitale d’élaborer une définition uniforme pour la compréhension du consentement éclairé dans les cadres de recherche avec un faible niveau d'alphabétisation en Afrique.ObjetivoLos estándares éticos desarrollados basándose en valores occidentales podrían no ser apropiados para emplazamientos Africanos en donde los conceptos de investigación no son familiares. En esta revisión se describe como la comprensión del consentimiento informado se define y mide en un centro de investigación Africano.MétodosSe buscaron publicaciones relevantes sobre la comprensión del consentimiento informado en estudios clínicos en África subsahariana en Medline, Embase, Global Health, EthxWeb, Bioethics Literature Database, African Index Medicus y Google Scholar. 29 estudios satisfacían los criterios de inclusión y el metaanálisis era posible para 21. La comprensión del consentimiento informado por parte de los participantes se comparó directamente en todos los estudios elegibles.ResultadosLa comprensión de conceptos claves del consentimiento informado varió de forma considerable entre países, y dependía de la naturaleza y de la complejidad del estudio. El meta-análisis mostró que un 47% entendía la aleatorización (IC 95% 13.9-80.9%); un 48% entendía el placebo (IC 95% 19.0-77.5%); y un 30% entendió el concepto terapéutico errado (IC 95% 4.6-66.7%). Las herramientas para medir la comprensión del consentimiento informado se desarrollaron con poca o ninguna validación.ConclusionesEn África, la comprensión de conceptos claves del consentimiento informado es pobre. Existe una necesidad vital de desarrollar una definición uniforme para la comprensión del consentimiento informado en lugares con bajos niveles de alfabetización en África
A method for the estimation of p-mode parameters from averaged solar oscillation power spectra
A new fitting methodology is presented which is equally well suited for the
estimation of low-, medium-, and high-degree mode parameters from -averaged
solar oscillation power spectra of widely differing spectral resolution. This
method, which we call the "Windowed, MuLTiple-Peak, averaged spectrum", or
WMLTP Method, constructs a theoretical profile by convolving the weighted sum
of the profiles of the modes appearing in the fitting box with the power
spectrum of the window function of the observing run using weights from a
leakage matrix that takes into account both observational and physical effects,
such as the distortion of modes by solar latitudinal differential rotation. We
demonstrate that the WMLTP Method makes substantial improvements in the
inferences of the properties of the solar oscillations in comparison with a
previous method that employed a single profile to represent each spectral peak.
We also present an inversion for the internal solar structure which is based
upon 6,366 modes that we have computed using the WMLTP method on the 66-day
long 2010 SOHO/MDI Dynamics Run. To improve both the numerical stability and
reliability of the inversion we developed a new procedure for the
identification and correction of outliers in a frequency data set. We present
evidence for a pronounced departure of the sound speed in the outer half of the
solar convection zone and in the subsurface shear layer from the radial sound
speed profile contained in Model~S of Christensen-Dalsgaard and his
collaborators that existed in the rising phase of Solar Cycle~24 during
mid-2010
Dilute gas of ultracold two-level atoms inside a cavity; generalized Dicke model
We consider a gas of ultracold two-level atoms confined in a cavity, taking
into account for atomic center-of-mass motion and cavity mode variations. We
use the generalized Dicke model, and analyze separately the cases of a
Gaussian, and a standing wave mode shape. Owing to the interplay between
external motional energies of the atoms and internal atomic and field energies,
the phase-diagrams exhibit novel features not encountered in the standard Dicke
model, such as the existence of first and second order phase transitions
between normal and superradiant phases. Due to the quantum description of
atomic motion, internal and external atomic degrees of freedom are highly
correlated leading to modified normal and superradiant phases.Comment: 10 pages, 7 figure
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