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

De Finetti's construction as a categorical limit

This paper reformulates a classical result in probability theory from the 1930s in modern categorical terms: de Finetti's representation theorem is redescribed as limit statement for a chain of finite spaces in the Kleisli category of the Giry monad. This new limit is used to identify among exchangeable coalgebras the final one.Comment: In proceedings of CMCS 202

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