1,696 research outputs found
Instability of (1+1) de sitter space in the presence of interacting fields
Instabilities of two dimensional (1+1) de Sitter space induced by interacting
fields are studied. As for the case of flat Minkowski space, several
interacting fermion models can be translated into free boson ones and vice
versa. It is found that interacting fermion theories do not lead to any
instabilities, while the interacting bosonic sine-Gordon model does lead to a
breakdown of de Sitter symmetry and to the vanishing of the vacuum expectation
value of the S matrix.Comment: 7 page
Leisure Activity, Ethnic Preservation, and Cultural Integration of Older Korean Americans
For immigrant groups, leisure activity has the potential both to increase familiarity with a new culture and to preserve cultural history and identity. Using a qualitative case study design, this research analyzed leisure activities of six older Korean Americans to determine both personal and cultural meanings of leisure. From a personal perspective, leisure was used to create two effects for the older adults: Ki-Bun-Chun-Whan, which is the experience of a shift in emotional atmosphere as a result of engaging in activities; and self-development activities, which provide the older adults with opportunities for learning or growth. Cultural meanings of leisure activities included the re-creation of Koreanness and the reliance on familiar patterns to create a sense of security in a still-strange land. Thus, with the individuals studied in this investigation, leisure activities were used more often for continuity and ethnic preservation than for cultural integration. Social workers can use leisure activities as avenues to increase knowledge and social participation, but they should also take into account the need to preserve cultural and collective identity in older immigrants
Oscillatory relaxation of zonal flows in a multi-species stellarator plasma
The low frequency oscillatory relaxation of zonal potential perturbations is
studied numerically in the TJ-II stellarator (where it was experimentally
detected for the first time). It is studied in full global gyrokinetic
simulations of multi-species plasmas. The oscillation frequency obtained is
compared with predictions based on single-species simulations using simplified
analytical relations. It is shown that the frequency of this oscillation for a
multi-species plasma can be accurately obtained from single-species
calculations using extrapolation formulas. The damping of the oscillation and
the influence of the different inter-species collisions is studied in detail.
It is concluded that taking into account multiple kinetic ions and electrons
with impurity concentrations realistic for TJ-II plasmas allows to account for
the values of frequency and damping rate in zonal flows relaxations observed
experimentally.Comment: 11 figures, 22 page
Bi-log-concave distribution functions
Nonparametric statistics for distribution functions F or densities f=F' under
qualitative shape constraints provides an interesting alternative to classical
parametric or entirely nonparametric approaches. We contribute to this area by
considering a new shape constraint: F is said to be bi-log-concave, if both
log(F) and log(1 - F) are concave. Many commonly considered distributions are
compatible with this constraint. For instance, any c.d.f. F with log-concave
density f = F' is bi-log-concave. But in contrast to the latter constraint,
bi-log-concavity allows for multimodal densities. We provide various
characterizations. It is shown that combining any nonparametric confidence band
for F with the new shape-constraint leads to substantial improvements,
particularly in the tails. To pinpoint this, we show that these confidence
bands imply non-trivial confidence bounds for arbitrary moments and the moment
generating function of F
A finite element based formulation for sensitivity studies of piezoelectric systems
Sensitivity Analysis is a branch of numerical analysis which aims to quantify the affects that variability in the parameters of a numerical model have on the model output. A finite element based sensitivity analysis formulation for piezoelectric media is developed here and implemented to simulate the operational and sensitivity characteristics of a piezoelectric based distributed mode actuator (DMA). The work acts as a starting point for robustness analysis in the DMA technology
Improvements of the particle-in-cell code EUTERPE for petascaling machines
In the present work we report some performance measures and computational improvements recently carried out using the gyrokinetic code EUTERPE (Jost, 2000 [1] and Jost et al., 1999 [2]), which is based on the general particle-in-cell (PIC) method. The scalability of the code has been studied for up to sixty thousand processing elements and some steps towards a complete hybridization of the code were made. As a numerical example, non-linear simulations of Ion Temperature Gradient (ITG) instabilities have been carried out in screw-pinch geometry and the results are compared with earlier works. A parametric study of the influence of variables (step size of the time integrator, number of markers, grid size) on the quality of the simulation is presented.Fil: Sáez, Xavier. Barcelona Supercomputing Center - Centro Nacional de Supercomputacion; EspañaFil: Soba, Alejandro. Barcelona Supercomputing Center - Centro Nacional de Supercomputacion; España. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Sánchez, Edilberto. No especifíca;Fil: Kleiber, Ralf. No especifíca;Fil: Castejón, Francisco. No especifíca;Fil: Cela, José M.. Barcelona Supercomputing Center - Centro Nacional de Supercomputacion; Españ
Can greater muscularity in larger individuals resolve the 3/4 power-law controversy when modelling maximum oxygen uptake?
BACKGROUND: The power function relationship, MR = a.m(b), between metabolic rate (MR) and body mass m has been the source of much controversy amongst biologists for many years. Various studies have reported mass exponents (b) greater than the anticipated 'surface-area' exponent 0.67, often closer to 0.75 originally identified by Kleiber. AIM: The study aimed to provide a biological explanation for these 'inflated' exponents when modelling maximum oxygen uptake (max), based on the observations from this and previous studies that larger individuals develop disproportionately more muscle mass in the arms and legs. RESEARCH DESIGN AND SUBJECTS: A cross-sectional study of 119 professional soccer players from Croatia aged 18-34 was carried out. RESULTS: Here we confirm that the power function relationship between max and body mass of the professional soccer players results in an 'inflated' mass exponent of 0.75 (95% confidence interval from 0.56 to 0.93), but also the larger soccer players have disproportionately greater leg muscle girths. When the analysis was repeated incorporating the calf and thigh muscle girths rather than body mass as predictor variables, the analysis not only explained significantly more of the variance in max, but the sum of the exponents confirmed a surface-area law. CONCLUSIONS: These findings confirm the pitfalls of fitting body-mass power laws and suggest using muscle-girth methodology as a more appropriate way to scale or normalize metabolic variables such as max for individuals of different body sizes
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