21,556 research outputs found

    Savings and technology choice for risk averse farmers

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    Farmers in developing countries have limited opportunities for borrowing to even out variability associated with risky farm income, but they can save. A dynamic programming model of savings is presented in the current paper which examines optimal savings strategies for farmers, using a case study of integrated rice-shrimp farms in Vietnam. It is shown that when savings are accounted for, the expected utility ranking of different risky farm choices may not differ that much between farmers with different levels of risk aversion.Farm Management, Risk and Uncertainty,

    The economics of land degradation and technological change: a case study in Vietnam

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    This paper explores the economics of land degradation in the rice-shrimp system in the Mekong Delta of Vietnam. A bioeconomic NPV model was developed to evaluate and compare the long-term benefits of alternative production choices and farm technologies. There is an alternative rice-shrimp technology emerging in Vietnam that does not have the same land degrading impacts as the 'traditional' system, however the high capital outlay and risk associated with such technology presents its own problems. In the paper the economic incentives for adoption of the non-land degrading rice-shrimp technology are explored. Conclusions are drawn with regard to the opportunity cost of land degradation and technological change. Some conclusions are also provided on the policy implications arising from the results presented.land degradation, technological change, Vietnam, Environmental Economics and Policy,

    Theoretical and material studies on thin-film electroluminescent devices

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    A theoretical study of resonant tunneling in multilayered heterostructures is presented based on an exact solution of the Schroedinger equation under the application of a constant electric field. By use of the transfer matrix approach, the transmissivity of the structure is determined as a function of the incident electron energy. The approach presented is easily extended to many layer structures where it is more accurate than other existing transfer matrix or WKB models. The transmission resonances are compared to the bound state energies calculated for a finite square well under bias using either an asymmetric square well model or the exact solution of an infinite square well under the application of an electric field. The results show good agreement with other existing models as well as with the bound state energies. The calculations were then applied to a new superlattice structure, the variablly spaced superlattice energy filter, (VSSEP) which is designed such that under bias the spatial quantization levels fully align. Based on these calculations, a new class of resonant tunneling superlattice devices can be designed

    Cavitation Scaling Experiments With Headforms: Bubble Acoustics

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    Recently Ceccio and Brennen [1][2][3] have examined the interaction between individual traveling cavitation bubbles and the structure of the boundary layer and flow field in which the bubble is growing and collapsing. They were able to show that individual bubbles are often fissioned by the fluid shear and that this process can significantly effect the acoustic signal produced by the collapse. Furthermore they were able to demonstrate a relationship between the number of cavitation events and the nuclei number distribution measured by holographic methods in the upstream flow. Kumar and Brennen [4][5] have further examined the statistical properties of the acoustical signals from individual cavitation bubbles on two different headforms in order to learn more about the bubble/flow interactions. All of these experiments were, however, conducted in the same facility with the same size of headform (5.08cm in diameter) and over a fairly narrow range of flow velocities (around 9m/s). Clearly this raises the issue of how the phenomena identified change with speed, scale and facility. The present paper will describe further results from experiments conducted in order to try to answer some of these important questions regarding the scaling of the cavitation phenomena. These experiments (see also Kuhn de Chizelle et al. [6][7]) were conducted in the Large Cavitation Channel of the David Taylor Research Center in Memphis Tennessee, on similar Schiebe headforms which are 5.08, 25.4 and 50.8cm in diameter for speeds ranging up to 15m/s and for a range of cavitation numbers

    Development of Si3N4 and SiC of improved toughness

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    The application of energy absorbing surface layers to Si3N4 and SiC was investigated. Among the layers studied were microcracked materials such as iron titanate and a silica-zircon mixture and porous materials such as reaction sintered Si3N4. Energy absorption due to microcrack extension upon impact was found not to be an important mechanism. Instead, the fivefold improvement in Charpy and ballistic impact at elevated temperature (1250 C and 1370 C) found for Fe2TiO5 was due to plastic deformation while similar improvement found for silica-zircon mixtures at RT was due to crushing of the porous material. Due to thermal expansion mismatch, these two materials could not withstand thermal cycling when used as energy absorbing surface layers on Si3N4. Reaction sintered Si3N4 layers on dense Si3N4 were found to give up to a sevenfold increase in ballistic impact resistance due to crushing of the layer upon impact. High porosity (45%), large particle size R.S. Si3N4 layers fabricated from -100, +200 mesh Si powder gave better impact improvement than less porous (30%), small particle size layers fabricated from -325 mesh Si powder

    Search, Moral Hazard, and Price Dispersion

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    We study the effects of insurance coverage on consumer search behavior and the pricing of services covered by insurance, constructing a general equilibrium model of moral hazard in search with an endogenous price distribution. When an insured event occurs, households request quotes from firms, who offer a homogenous service at various prices. We show that lower coinsurance rates reduce the amount of search by households, allowing firms to increase their prices. Hence, moral hazard in search is far more costly than shown in previous models, which ignored equilibrium firm response to changes in consumer search behavior.

    Civil helicopter wire strike assessment study. Volume 1: Findings and recommendations

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    Approximately 208 civil helicopter wire strike accidents for a ten year period 1970 to 1979 are analyzed. It is found that 83% of the wire strikes occurred during bright clear weather. Analysis of the accidents is organized under pilot, environment, and machine factors. Methods to reduce the wire strike accident rate are discussed, including detection/warning devices, identification of wire locations prior to flight, wire cutting devices, and implementation of training programs. The benefits to be gained by implementing accident avoidance methods are estimated to be fully justified by reduction in injury and death and reduction of aircraft damage and loss

    The Design of an Uncertainty Model For The Tidal Constituent and Residual Interpolation (TCARI) Method for Tidal Correction of Bathymetric Data

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    Recent advances in processing multibeam sonar data brought about by the Combined Uncertainty and Bathymetric Estimator (CUBE) [1] have demonstrated the value of identifying and tracking survey uncertainties. Most of these uncertainties were outlined in Hare, Godin, and Mayer uncertainty model developed in 1995 [2]. That report identified the uncertainties in the various electronic systems used to acquire the bathymetric data. However, one of the largest contributors to the overall error budge t in a near coastal hydrographic survey is that contributed by water level uncertainty. As the ocean mapping industry pushes for ever finer spatial details in its data, the traditional method of discrete tide zoning [3] must be abandoned for a more robust method that can match the requirements of the data. The method currently under investigation by the National Oceanic and Atmospheric Administration is the Tidal Constituent And Residual Interpolation (TCARI) method [4]. TCARI has the ability to interpolate the water level at a vessel’s position for any location and instance in time. It can also produce a gridded water level surface of the entire survey area. While the potential of this method is encouraging, a rigorous investigation of the uncertainties associated with it has yet to be completed. This research seeks to close that gap by examining the uncertainties in this method, using both observed water level information from around the country as well as data acquired during the original 1995 NOS Kinematic GPS experiment in Galveston Bay, Texas [5]
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