A new equation of state for helium nanobubbles embedded in UO2 matrix calculated via molecular dynamics simulations

International audienceMolecular dynamics simulations have been carried out to determine the equation of state of helium inside nanobubbles embedded into UO2 matrix.The parameters of this equation of state are fitted with the Brearley and MacInnes hard-sphere model based on the formalism of Carnahan-Starling used in fuel performance codes.This new equation of state takes into account the interactions between the surrounding UO2 matrix and the helium atoms. Four nanobubble sizes of diameters 1, 2, 5, and 10 nm have been investigated over four temperatures 300, 500, 700, and 900 K and for initial helium concentration inside the bubble ranging from 0.33x10^5 to 3.9x10^5 mol.m^-3 (corresponding to helium-to-vacancy ratio of 0.3 to 3.3, respectively).We observe that helium atoms are inhomogeneously distributed inside the bubble.A boundary layer of 1 nm thickness appears at the bubble surface in which helium atoms are more concentrated and diffuse into the UO2 matrix. We also observe a saturation of the helium atoms that can be incorporated into the bubble.This concentration limit is equal to 1.6 helium atom per vacancy in UO2.It corresponds to an atomic volume of 7.8x10^-30 m^3, which is almost half of the value proposed with the original Brearley and MacInnes model (13x10^-30 m^3).For this threshold concentration and for bubble of diameter higher than 5~nm, micro-cracks and dislocations appear at the bubble surface.We calculated the critical pressures inside the bubble that yields to this onset of crack in UO2.These critical pressures are in good agreement with those calculated with the Griffith criterion for brittle fracture

Comorbidities and Race/Ethnicity Among Adults with Stimulant Use Disorders in Residential Treatment

Comorbid physical and mental health problems are associated with poorer substance abuse treatment outcomes; however, little is known about these conditions among stimulant abusers at treatment entry. This study compared racial and ethnic groups on baseline measures of drug use patterns, comorbid physical and mental health disorders, quality of life, and daily functioning among cocaine and stimulant abusing/dependent patients. Baseline data from a multi-site randomized clinical trial of vigorous exercise as a treatment strategy for a diverse population of stimulant abusers (N = 290) were analyzed. Significant differences between groups were found on drug use characteristics, stimulant use disorders, and comorbid mental and physical health conditions. Findings highlight the importance of integrating health and mental health services into substance abuse treatment and could help identify potential areas for intervention to improve treatment outcomes for racial and ethnic minority groups

Men and women from the STRIDE clinical trial: An assessment of stimulant abstinence symptom severity at residential treatment entry

Background and Objectives Gender‐specific factors associated with stimulant abstinence severity were examined in a stimulant abusing or dependent residential treatment sample (N = 302). Method Bivariate statistics tested gender differences in stimulant abstinence symptoms, measured by participant‐reported experiences of early withdrawal. Multivariate linear regression examined gender and other predictors of stimulant abstinence symptom severity. Results Women compared to men reported greater stimulant abstinence symptom severity. Anxiety disorders and individual anxiety‐related abstinence symptoms accounted for this difference. African American race/ethnicity was predictive of lower stimulant abstinence severity. Discussion and Conclusions Women were more sensitive to anxiety‐related stimulant withdrawal symptoms. Scientific Significance Clinics that address anxiety‐related abstinence symptoms, which more commonly occur in women, may improve treatment outcome. (Am J Addict 2015;XX:XX –XX

Neutron Transfer Studied with a Radioactive beam of 24Ne, using TIARA at SPIRAL

A general experimental technique for high resolution studies of nucleon transfer reactions using radioactive beams is briefly described, together with the first new physics results that have been obtained with the new TIARA array. These first results from TIARA are for the reaction 24Ne(d,p)25Ne, studied in inverse kinematics with a pure radioactive beam of 100,000 pps from the SPIRAL facility at GANIL. The reaction probes the energies of neutron orbitals relevant to very neutron rich nuclei in this mass region and the results highlight the emergence of the N=16 magic number for neutrons and the associated disappearance of the N=20 neutron magic number for the very neutron rich neon isotopes.Comment: Proceedings of the Carpathian Summer School of Physics, Mamaia-Constanta, Romania, 13-24 June 200

Gender Presentation and Membership Bias in Greek Organizations

The study objective was to explore the possibility of discrimination and bias based on perceived gender presentation. In this study, subjects were female and male undergraduate students of both Greek and non-Greek affiliations at a University in the Southeastern United States. Subjects were asked to rate the probability of extending group membership to others based on perceived visual gender appearance. In the pilot study, 150 University of Central Florida students were polled to assess three categories of visual gender presentation in pictures: average gender presentation (typical female or male), extreme gender presentation (extremely feminine or extremely masculine) and non-traditional gender presentation (masculine females or effeminate males). Three pictures of each gender presentation category were then chosen for the final study. In both studies, The Crowne-Marlowe (1964) Social Desirability Scale (CMDS) was administered. Results indicated no difference in the ratings between Greek and non-Greek participants. However, the results did show a statistically significant bias against individuals of average and non-traditional gender presentation versus individuals who represented extreme gender presentation. Hence, subjects were more likely to extend membership to individuals who appeared to be extremely feminine or extremely masculine. There was also a statistically significant bias favoring average over non-traditional gender presentation individuals. Additionally, social desirability bias played a significant role in how subjects made their selection. The study not only shows significant relationships between gender presentation and discrimination, but also provides evidence that male students prefer hyper-masculine males and female students prefer hyper-feminine females

Backward error analysis and the substitution law for Lie group integrators

Butcher series are combinatorial devices used in the study of numerical methods for differential equations evolving on vector spaces. More precisely, they are formal series developments of differential operators indexed over rooted trees, and can be used to represent a large class of numerical methods. The theory of backward error analysis for differential equations has a particularly nice description when applied to methods represented by Butcher series. For the study of differential equations evolving on more general manifolds, a generalization of Butcher series has been introduced, called Lie--Butcher series. This paper presents the theory of backward error analysis for methods based on Lie--Butcher series.Comment: Minor corrections and additions. Final versio

On phenomenon of scattering on resonances associated with discretisation of systems with fast rotating phase

Numerical integration of ODEs by standard numerical methods reduces a continuous time problems to discrete time problems. Discrete time problems have intrinsic properties that are absent in continuous time problems. As a result, numerical solution of an ODE may demonstrate dynamical phenomena that are absent in the original ODE. We show that numerical integration of system with one fast rotating phase lead to a situation of such kind: numerical solution demonstrate phenomenon of scattering on resonances that is absent in the original system.Comment: 10 pages, 5 figure

A micropillar for cavity optomechanics

We present a new micromechanical resonator designed for cavity optomechanics. We have used a micropillar geometry to obtain a high-frequency mechanical resonance with a low effective mass and a very high quality factor. We have coated a 60-$\mu$m diameter low-loss dielectric mirror on top of the pillar and are planning to use this micromirror as part of a high-finesse Fabry-Perot cavity, to laser cool the resonator down to its quantum ground state and to monitor its quantum position fluctuations by quantum-limited optical interferometry