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Browsing by Author "Liang, Yan"

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    An Ex Ante Analysis of the Effects of Transgenic Rice on Farm Households’ Nutritional Vulnerability in Bangladesh
    Liang, Yan (Virginia Tech, 2006-05-15)
    Despite concerted efforts at agricultural development over many years, millions of people in developing countries still suffer from poverty and under-nutrition. New crop varieties, such as those released during the green revolution in Asia, increased farmers' income and reduced the level of under-nutrition. In recent years, while the speed of the development of conventional breeding technology has slowed, biotechnology has developed rapidly. In 2005, about 8.5 million farmers in 21 countries grew transgenic crops. Transgenic rice has not been commercially released on a large scale, but progress has been made in developing varieties with potential to increase yield and reduce input costs. In this context, this research aims to provide empirical evidence on the potential effects of introducing transgenic rice on farm households' income and nutritional well-being in Bangladesh, including the impacts on their current nutritional status and nutritional vulnerability over time. To this end, two econometric models are constructed and estimated. A farm household model is employed to project farm households' production and consumption responses to introducing improved rice varieties such as transgenic rice. The model estimates the profit effect of introducing transgenic rice. The influence of the profit effect on farmers' consumption decisions is then considered. Due to the ex ante nature of this research and data limitations, the effects of transgenic rice are assumed to be similar to that of previous high yielding varieties (HYVs), and the impact of transgenic rice on farm household profit is assumed to be similar to the effect of the percentage of rice area in HYVs and the yield effect of transgenic rice is the same as HYVs. On the production side, the supply of three outputs- rice, all other crops and animal products- and demand of labor and fertilizer were estimated. On the consumption side, both poor and non-poor households' demand for rice, wheat/other food, pulse, oil, vegetables/fruits, meat/egg/ milk, fish, and spices were estimated. Based on the parameter estimates, the calorie intake and protein intake elasticities with respect to introducing transgenic rice were computed. The results indicate that the total profit elasticity with respect to the percentage of rice area in HYVs is 0.08. The calorie elasticity with respect to the percentage of rice area in HYVs ranges from 0.062 in non-poor to 0.074 in poor households, and the protein elasticity ranges from 0.075 in non-poor to 0.084 in poor households. The results indicate that transgenic rice is likely to play a positive role in improving farm households' nutritional status in terms of total calorie/protein intake. The magnitude, however, is likely to be moderate, if only the profit effect is considered. A consumption forecasting model is used to examine farmers' nutritional vulnerability a probabilistic concept defined as having a high probability now of suffering a shortfall in the future. It is assumed that when exposed to risk, farmers' consumption decisions have already considered their risk coping strategies. The effect of transgenic rice is reflected by its impact on farm income. Farm households' calorie intake in the future (hunger season) was predicted by a multivariate regression function with the logarithmic daily per resident calorie intake as the dependent variable. The independent variables include variables that represent households' income, flood exposure, assets, and demographic composition. Farm households' nutritional vulnerability profiles, based on the estimation of ex ante mean and variance, indicate that vulnerability exists among surveyed rice farm households. The model also predicts that the income increase induced by introducing transgenic rice will reduce each individual household's probability of suffering a future consumption shortfall and subsequently will reduce its vulnerability. The overall vulnerability profile of farm households improves in Bangladesh.
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    Integrated Frequency-Selective Conduction Transmission-Line EMI Filter
    Liang, Yan (Virginia Tech, 2008-12-08)
    The multi-conductor lossy transmission-line model and finite element simulation tool are used to analyze the high-frequency attenuator and the DM transmission-line EMI filter. The insertion gain, transfer gain, current distribution, and input impedance of the filter under a nominal design are discussed. In order to apply the transmission-line EMI filter to power electronics systems, the performance of the filter under different dimensions, material properties, and source and load impedances must be known. The influences of twelve parameters of the DM transmission-line EMI filter on the cut-off frequency, the roll-off slope, and other characteristics of the insertion gain and transfer gain curves are investigated. The most influential parameters are identified. The current sharing between the copper and nickel conductors under different parameters are investigated. The performance of the transmission-line EMI filter under different source and load impedances is also explored. The measurement setups of the DM transmission-line EMI filter using a network analyzer have been discussed. The network analyzer has a common-ground problem that influences the measured results of the high-frequency attenuator. However, the common-ground problem has a negligible influence on the measured results of the DM transmission-line EMI filter. The connectors and copper strips between the connectors and the filter introduce parasitic inductance to the measurement setup. Both simulated and measured results show that transfer gain curve is very sensitive to the parasitic inductance. However, the insertion gain curve is not sensitive to the parasitic inductance. There are two major methods to reduce the parasitic inductance of the measurement setup: using small connectors and applying a four-terminal measurement setup. The transfer gain curves of three measurement setups are compared: the two-terminal measurement setup with BNC connectors, the two-terminal measurement setup with Sub Miniature version B (SMB) connectors, and the four-terminal measurement setup with SMB connectors. The four-terminal measurement setup with SMB connectors is the most accurate one and is applied for all the transfer gain measurements in this dissertation. This dissertation also focuses on exploring ways to improve the performance of the DM transmission-line EMI filter. Several improved structures of the DM transmission-line EMI filter are investigated. The filter structure without insulation layer can greatly reduce the thickness of the filter without changing its performance. The meander structure can increase the total length of the filter without taking up too much space and results in the cut-off frequency being shifted lower and achieving more attenuation. A prototype of the two-dielectric-layer filter structure is built and measured. The measurement result confirms that a multi-dielectric-layer structure is an effective way to achieve a lower cut-off frequency and more attenuation. This dissertation proposes a broadband DM EMI filter combining the advantages of the discrete reflective LC EMI filter and the transmission-line EMI filter. Two DM absorptive transmission-line EMI filters take the place of the two DM capacitors in the discrete reflective LC EMI filter. The measured insertion gain of the prototype has a large roll-off slope at low frequencies and large attenuation at high frequencies. The dependence of the broadband DM EMI filter on source and load impedances is also investigated. Larger load (source) impedance gives more attenuation no matter it is resistive, inductive or capacitive. The broadband DM EMI filter always has more high-frequency attenuation than the discrete reflective LC EMI filter under different load (source) impedances.