Functional Methods and Effective Potentials for Nonlinear Composites

A formulation of variational principles in terms of functional integrals is proposed for any type of local plastic potentials. The minimization problem is reduced to the computation of a path integral. This integral can be used as a starting point for different approximations. As a first application, it is shown how to compute to second-order the weak-disorder perturbative expansion of the effective potentials in random composite. The three-dimensional results of Suquet and Ponte-Casta\~neda (1993) for the plastic dissipation potential with uniform applied tractions are retrieved and extended to any space dimension, taking correlations into account. In addition, the viscoplastic potential is also computed for uniform strain rates.Comment: 20 pages, accepted for publication in JMP

The Children's Revised Impact of Event Scale (CRIES):Validity as a screening instrument for PTSD

The Children's Revised Impact of Event Scale (CRIES) is a brief child-friendly measure designed to screen children at risk for Posttraumatic Stress Disorder (PTSD). It has good face and construct validity, a stable factor structure, correlates well with other indices of distress, and has been used to screen very large samples of at-risk-children following a wide range of traumatic events. However, few studies have examined the scale's validity against a structured diagnostic interview based on the DSM-IV criteria for PTSD. In the present study, the CRIES and the PTSD section of the Anxiety Disorders Interview Schedule-Child and Parent Version (ADIS-CP) were administered to a sample of children and adolescents (n=63) recruited from hospital accident and emergency rooms and the validity of the CRIES as a screening tool evaluated. Cutoff scores were chosen from this sample with a low base-rate of PTSD (11.1%) to maximize sensitivity and minimize the likelihood that children with a diagnosis of PTSD would fail to be identified. Cutoff scores were then cross-validated in a sample of 52 clinically referred children who had a high base-rate of PTSD (67.3%). A cutoff score of 30 on the CRIES-13 and a cutoff score of 17 on the CRIES-8 maximized sensitivity and specificity, minimized the rate of false negatives, and correctly classified 75-83% of the children in the two samples. The CRIES-8 (which lacks any arousal items) worked as efficiently as the CRIES-13 (which includes arousal items) in correctly classifying children with and without PTSD. Results are discussed in light of the current literature and of the need for further development of effective screens for children at-risk of developing PTSD

Environmentally Adjusted Agricultural Productivity in the Great Plains

This study adjusts 1960-1996 agricultural productivity gains in a panel of Great Plains states to account for the discharge of pesticide and nitrogen effluents into the environment. The agricultural-environmental technology is approximated with translog distance functions that allow us to contrast traditional versus environmentally adjusted productivity gains. Findings indicate technical change has been increasingly biased toward environmentally friendly production. While the environmental adjustment reduced overall productivity gains during the sample period, in recent years adjusted productivity outpaced the traditional measure, reflecting the pro-environment bias in technical change.agricultural productivity, distance function, environmental externalities, nitrogen, pesticides, technical change bias, Environmental Economics and Policy, Productivity Analysis,

Optical properties of irregular interstellar grains

In order to study the interaction of light with interstellar grains, the authors represent an irregular particle by a network of interacting dipoles whose polarizability is determined in a first approach by the Clausius-Mossoti relationship. Typically, 10,000 dipoles are considered. In the case of spherical particles, the results from Mie theory are fully recovered. The main interest of this method is to study with good accuracy the implications of surface roughness and/or inhomogeneities on optical properties in the infrared spectral range, particularly of the silicate emission features

Simulation study of copper(I) and copper(II) species in ZSM-5 zeolite

Low energy configurations of CuI and CuII species in the ZSM-5 zeolite, probed by energy minimisation techniques, are found to be bound strongly to framework aluminium or copper species

Pupil remapping for high contrast astronomy: results from an optical testbed

The direct imaging and characterization of Earth-like planets is among the most sought-after prizes in contemporary astrophysics, however current optical instrumentation delivers insufficient dynamic range to overcome the vast contrast differential between the planet and its host star. New opportunities are offered by coherent single mode fibers, whose technological development has been motivated by the needs of the telecom industry in the near infrared. This paper presents a new vision for an instrument using coherent waveguides to remap the pupil geometry of the telescope. It would (i) inject the full pupil of the telescope into an array of single mode fibers, (ii) rearrange the pupil so fringes can be accurately measured, and (iii) permit image reconstruction so that atmospheric blurring can be totally removed. Here we present a laboratory experiment whose goal was to validate the theoretical concepts underpinning our proposed method. We successfully confirmed that we can retrieve the image of a simulated astrophysical object (in this case a binary star) though a pupil remapping instrument using single mode fibers.Comment: Accepted in Optics Expres

Efficiency of New Ethanol Plants in the U.S. North-Central Region

Replaced with revised version of paper 07/29/09.Ethanol, Efficiency, DEA, Production Economics, Resource /Energy Economics and Policy,