Non-equilibrium effects in steady relativistic e+e−γe^+e^-\gamma winds

We consider an ultra-relativistic wind consisting of electron-positron pairs and photons with the principal goal of finding the asymptotic Lorentz factor $\gamma_{\infty}$ for zero baryon number. The wind is assumed to originate at radius $r_i$ where it has a Lorentz factor $\gamma_i$ and a temperature $T_i$ sufficiently high to maintain pair equilibrium. As $r$ increases, $T$ decreases and becomes less than the temperature corresponding to the electron mass $m_e$, after which non-equilibrium effects become important. Further out in the flow the optical depth $\tau$ drops below one, but the pairs may still be accelerated by the photons until $\tau$ falls below $\sim 2\times10^{-5} \gamma_{i}^{3/4}$. Radiative transfer calculations show that only at this point do the radiation flux and pressure start to deviate significantly from their blackbody values. The acceleration of the pairs increases $\gamma$ by a factor $\sim 45$ as compared to its value at the photosphere; it is shown to approach \gamma_{\infty} \sim 1.4\times 10^3 (r_i/10^6\mbox{cm})^{1/4} \gamma_{i}^{3/4} T_i/m_e.Comment: 41 pages, 9 figures. Submitted to MNRA

Productivity Puzzles - should employee participation be an issue?

In this paper we review econometric efforts aiming to identify whether employee participation adds to productivity growth. The overall picture is mixed. Participation may lead to significant but not substantial higher productivity. The theoretical predictions, pointing to the importance of institutional setting and a need to establish quality cooperation and long-term commitment from both management and workers, seem to be supported by the empirical results. An emerging hypothesis is that both the intensity of involvement and a combination of involvement, economic rewards and participation in decisions significantly influence productivity.productivity, cooperation, participation

MARKET SEGMENTATION WITHIN CONTINGENT VALUATION

A finite probability mixture model is combined with a contingent valuation model to analyze the existence of differential market segments in a hypothetical market. The approach has at least two principle benefits. First, the model is capable of identifying market segments within the hypothetical market. Second, the model can be used to estimate WTP/WTA within each segment. The model is illustrated using a data set collected on consumer response to genetically modified foods in Norway.Agribusiness,

OPTIMAL CONTROL OF PEST RESISTANCE TO TRANSGENIC CROP VARIETIES

Transgenic corn varieties entered the market in 1996. These plant varieties carry a gene from the soil bacterium Bacillus thuringiensis kurstaki, Bt, that makes the plant produce a toxin deadly to the pest insect European Corn Borer (ECB) Ostrinia nubilalis (Hübner). Since ECB may build up genetic resistance to this toxin, the growers of transgenic corn varieties are required to plant a portion of their field (refuge) with regular corn. This requirement is expected to prolong the efficiency of Bt corn in combating the ECB because some non-resistant pests can survive in the refuge, and thereby dilute the build-up of resistance in the overall pest population. A fixed refuge size of 20 percent is the currently recommended "rule-of-thumb" by the Environmental Protection Agency (EPA). Past work has searched for an economically-optimal refuge size utilizing discrete-time simulation approaches in which refuge size is treated as an exogenous parameter whose optimal value is found through numerical iteration. The objective of this work is to fine-tune parametric refuge specifications by formulating a bioeconomic model capable of endogenously determining the optimal trajectory of refuge sizes over time via an analytical optimal-control rule. The model will provide novel comparative statics/dynamics results demonstrating the sensitivity of the optimal trajectory to important economic and biological parameters.Crop Production/Industries,

EMPIRICAL TAXONOMY OF ENVIRONMENTAL ETHICAL ARCHETYPES

Economists usually assume that the private ethical system of individuals is Utilitarian. However, one finds a much broader range of ethical positions in the environmental ethics literature. Moreover, environmental policy debates seem to elicit alternative ethical systems. It would therefore seem prudent to increase our understanding of the role played by alternative environmental ethical systems. In this study we follow some descriptive ethical studies in examining the empirical ethical position of people based on a broad cross section of the American public. We review some taxonomic literature in environmental ethics and develop a conceptual model of the formation of environmental values. We then use canonical correlation to investigate the existence of environmental values and their relationship to childhood experiences. We find four ethical systems linked to four different "types" of people. One of the ethical systems is decidedly spiritual and one seems rather ill-defined or indifferent towards nature. The other two systems show anthropocentric values, one more conservation minded, one more use minded.Environmental Economics and Policy,

Hypertension and common mental disorders in a nationally-representative sample of South African adults

Includes bibliographical references (leaves 96-98).This thesis examines the associations between self-reported hypertension diagnosis and Diagnostic and Statistical Manual of Mental Disorders 4th edition (DSM-IV) defined a) anxiety disorders b) depressive disorders and c) comorbid anxiety-depression, both lifetime and 12-month, adjusting for potential confounding variables

A Mixture Model of Consumers' Intended Purchase Decisions for Genetically Modified Foods

A finite probability mixture model is used to analyze the existence of multiple market segments for a pre-market good. The approach has at least two principal benefits. First, the model is capable of identifying likely market segments and their differentiating characteristics. Second, the model can be used to estimate the discount different consumer groups require to purchase the good. The model is illustrated using stated preference survey data collected on consumer responses to the potential introduction in Norway of bread made with genetically modified wheat.