Direct empirical estimation of efficiency in secondary materials markets: The case of steel scrap

The U.S. steel scrap market is used as a test case for a method of directly estimating the efficiency of recycled materials markets. Such markets are examples of commodity markets for which there is no organized futures exchange. If, as widely held, futures markets enhance market efficiency we attempt to answer the question of how recycled commodity markets suffer, if at all, from the lack of a futures exchange. In this paper econometric modeling and time-series methods produce robust estimates of market efficiency as measured by the percent of traders that possess the latest information concerning market disequilibrium. Based on the empirical results it would appear that on a monthly basis the steel scrap industry distributes its commodities in an economically efficient manner and therefore would derive little benefit from an organized futures exchange.     

Sex ratio and optimal harvest of canvasback ducks,A model

The North American population of canvasback ducks (Aythya valisineria) exhibits extreme distortion of the sex ratio in favor of males. This paper describes a model which accounts for this pattern by relatively heavier female mortality in both the breeding and nonbreeding seasons. The density-dependence of winter mortality leads to the conclusion that the observed sex ratio depresses total population numbers. Variation in nesting success is shown to influence sex ratios and strongly depress population numbers. Because a standard harvest scheme can be demonstrated to severely depress the numbers of ducks, an alternative graduated or weighted harvest procedure is recommended.     

TIMBER MANAGEMENT INFLUENCES ON AQUATIC ECOSYSTEMS AND RECOMMENDATIONS FOR FUTURE RESEARCH1

ABSTRACT: Recent watershed research indicates that many timber management practices have profound effects on the water quality of small headwater streams. These streams often support fisheries of high value. Current knowledge seems to indicate that a definite potential exists for a symbiotic relationship between timber and fisheries management. Maximum development of both resources is attainable only if further research efforts recognize the mutually benefiting aspects of these heretofore separate disciplines. Future research should carefully examine the complex interrelationships between small headwater aquatic ecosystems and the riparian forest environment.     

Development of quantitative estimates of uncertainty in environmental risk assessments when the scientific data base is inadequate

The reasons for developing quantitative estimates of uncertainty in environmental risk assessments are discussed along with a method for developing them which involves scientific judgement. In the situation considered here the regulatory needs are ahead of the science, which makes the development of the estimates on uncertainty more difficult, but not impossible. Quantitative estimates for all uncertainties involved in the estimation of risk resulting from exposure to volatile organic compounds (VOCs) in drinking water are developed and tabulated. By far the largest contribution to the uncertainty in the risk estimates for VOCs in drinking water are due to uncertainty in the extrapolation of the dose-response curve to low levels. The uncertainty due to extrapolation is on the order of 10⁴ and 10⁶. Other components of the analysis may contribute uncertainties of a few orders of magnitude. In general the largest uncertainties are in the toxicological data base and the manipulation of it needed to estimate risk. The data base and manipulations needed to estimate exposure due to VOCs in drinking water were at the more an order to magnitudes in uncertainty.     

Sex differences in job attribute preferences

This study investigated the job attribute preferences of male and female MBA candidates. Participants were drawn from 27 different MBA programmes in the United States. Factor analysis of the job attributes questionnaire revealed three primary job attribute dimensions: (1) professional growth; (2) work environment; and (3) salary. Contrary to most previous research, females were found to place a greater emphasis on the professional growth dimension than did males. Males, on the other hand, placed greater emphasis on salary considerations. No sex difference was found in participants' ratings of the work environment job attribute dimension. Consistent with earlier research, women were found to place more importance on the calibre of colleagues than did males. In general, both males and females rated job attributes concerning job content as more important than job attributes concerning job context. These results are discussed with respect to earlier research findings. Finally, the generalizability of these findings to other occupational groups is discussed and managerial implications presented.     

Migration of pollutants in groundwater. III. Numerical dispersion reduction with cartesian coordinates

The partial differential equation governing the movement of a decomposing pollutant undergoing 2-dimensional flow in a saturated aquifer is examined. The analytical solution of the equation is usually not possible, and use of mesh numerical integration techniques causes excessive numerical dispersion to arise from the advection term. We apply two asymmetrical upwind formulas to approximate the advection term. These markedly reduce numerical dispersion without requiring the use of coordinate systems obtained by conformal mapping. Flow within a right angle and flow toward a sink in an otherwise uniform field are analyzed to illustrate the methods.