Are low food prices pro-poor ? net food buyers and sellers in low-income countries

There is a general consensus that most of the poor in developing countries are net food buyers and food price increases are bad for the poor. This could be expected of urban poor, but it is also often attributed to the rural poor. Recent food price increases have increased the importance of this issue, and the possible policy responses to these price increases. This paper examines the characteristics of net food sellers and buyers in nine low-income countries. Although the largest share of poor households are found to be net food buyers, almost 50 percent of net food buyers are marginal net food buyers who would not be significantly affected by food price increases. Only three of the nine countries examined exhibited a substantial proportion of vulnerable households. The average incomes (as measured by expenditure) of net food buyers were found to be higher than net food sellers in eight of the nine countries examined. Thus, food price increases, ceteris paribus, would transfer income from generally higher income net food buyers to poorer net food sellers. The analysis also finds that the occupations and income sources of net sellers and buyers in rural areas are significantly different. In rural areas where food production is the main activity and where there are limited non-food activities, the incomes of net buyers might depend on the incomes and farming activities of net food sellers. These results suggest the need for reevaluation of the consensus on the impact of food prices on food needs. Further work on the regional differences, and more important, on the second order effects, are necessary to answer these questions more precisely. Only on the basis of further analysis can we start generating better policy responses.Food&Beverage Industry,Rural Poverty Reduction,,Poverty Lines

The role of services in rural income : the case of Vietnam

This paper investigates the role of services in the household response to trade reforms in Vietnam. The relative response of the households and income growth after a major trade liberalization in rice are analyzed aiming to answer the following questions: What type of households, in which locations, having access to what type of services, benefited more from the reforms? It focuses on services that have an impact on transaction costs (roads or quality of roads, public transportation, access to credit, extension services, and availability of markets in communication services) because transaction costs are often cited as a barrier to rural households in responding to the price changes and increased incentives offered by trade and other policy reforms. The results suggest that availability of production related services contributes positively to the impact of trade reforms. Although most of the service variables have a positive and significant effect on growth in income, some that are expected to have an impact are not significant. This may be explained by the exceptional coverage of infrastructure services in Vietnam even before the reforms. When service availability is very similar across different localities, household characteristics become more important in determining the response.Transport Economics Policy&Planning,Rural Poverty Reduction,Economic Theory&Research,Housing&Human Habitats

Plane-wave theory of self-doubling optical parametric oscillators

Cataloged from PDF version of article.This paper presents a theoretical analysis of selfdoubling optical parametric oscillators (OPO’s) where a single nonlinear crystal is used for both parametric generation and frequency doubling. In these devices, the parametric generation and frequency-doubling processes are both phase matched for the same direction of propagation inside the crystal. Different polarization geometries for which this simultaneous phasematching condition can potentially be satisfied are identified and categorized. Plane-wave coupled-mode equations are presented for each of these categories. Numerical solutions of these coupledmode equations and calculation of the single-pass saturated signal gain are outlined. Intracavity signal photon flux calculations based on these numerical solutions are presented. The dependence of performance measures such as the photon conversion efficiency on various design parameters are investigated

Trade reforms and welfare : an ex-post decomposition of income in Vietnam

This paper analyzes the impact of trade reforms on household welfare. In particular, it studies the importance of each of the links that together constitute the impact using data from the Vietnamese experience in the 1990s. The implementation of trade reforms in the 1990s, most noteworthy of which was the liberalization of rice, resulted in substantial improvement in welfare as evidenced by the drastic decline in poverty. Using analytical and empirical methods, the author examines the role of each channel (direct versus indirect) in this improvement for different groups of households. Results indicate that the growth has been broad based and pro-poor. Poorer households experienced more growth for each and every group analyzed. And contrary to the standard literature, net buyer households had more growth compared with net sellers, emphasizing the importance of indirect links. Decomposition of the growth shows that for rural households, both the direct effect and the multiplier effect drive growth while the multiplier effect was key in urban areas. The importance of the secondary effects underscores the need for a broader model to estimate the impact of trade reforms fully.Rural Poverty Reduction,Economic Theory&Research,Small Area Estimation Poverty Mapping,Inequality,Consumption

Plane-wave theory of single-crystal upconversion optical parametric oscillators

Ankara : Department of Electrical and Electronics Engineering and Institute of Engineering and Sciences, Bilkent Univ., 1998.Thesis (Master's) -- Bilkent University, 1998.Includes bibliographical references leaves 62-66.'rhis thesis pi'('s('nts a theoi'etical analysis of single-crystal upconversion optical parametric oscillators (OPO’s) where a single nonlinear crystal is used for both the OPO and sum-frequency generation (SPG) or second-harmonic generation (SHG). In these devices, the OPO and SFG/SHG processes are both phase matched for the same direction of propagation inside the crystal. Different polarization geometries for which this simultaneous phase matching condition can potentially be satisfied are identified and categorized, for both biréfringent. a.nd quasi-phcise matching methods. This categorization results in four classes of sumfrequency generating OPO’s (SF-OPO’s) and three classes of self-doubling OPO’s (SD-OPO’s). Plane-wa.ve coupled mode equations a.re presented for each of these seven classes. Solutions of these coupled mode equations, and calculation of the single-pass saturated signal gain are outlined. The dependence of the photon conversion efficiency on various design parameters are investigated. .Λ pulsed plane-wave model that takes into account the temporal profiles of the fields and the group velocity mismatch between pulses is constructed. This model is in good qualitative agreement with experimental measurements of a class-G SF-OPO.Dikmelik, YamaçM.S

Single-crystal sum-frequency-generating optical parametric oscillator

Cataloged from PDF version of article.We report a synchronously pumped optical parametric oscillator that generates the sum frequency of the pump and the signal wavelengths. A single KTiOPO4 (KTP) crystal is used for both parametric generation and sum-frequency generation in which these two processes are simultaneously phase matched for the same direction of propagation. The parametric oscillator, pumped by a femtosecond Ti:sapphire laser at a wavelength of 827 nm, generates a blue output beam at 487 nm with 43% power-conversion efficiency. The polarization geometry of simultaneous phase matching requires rotation of the pump polarization before the cavity. Adjusting the group delay between the two orthogonally polarized pump components to compensate for the group-velocity mismatch in the KTP crystal increases the photon-conversion efficiency more than threefold. Angle tuning in conjunction with pump wavelength tuning provides output: tunability in the 484-512-nm range. A planewave model that takes group-velocity mismatch into account is in good agreement with our experimental results. (C) 1999 Optical Society of America [S0740-3224(99)01309-0]

Plane-wave dynamics of optical parametric oscillation with simultaneous sum-frequency generation

The plane wave dynamics of a single-crystal upconversion optical parametric oscillators (OPO) with simultaneous sum-frequency generation (SFG) was studied. It was presumed that simultaneous phase-matching of the SFG and OPO processes were achieved by utilizing birefringent phase matching (BPM). Potential polarization geometries for collinear BPM led to four different sets of coupled mode equations depending on which field components were common to the two processes. The sets were designated as classes A through D. Classes A and D were efficient frequency upconverters. The performance of class A OPO's was limited by crystal properties whereas classes C and D was optimized by adjusting the polarization rotation angle

Plane-wave dynamics of optical parametric oscillation with simultaneous sum-frequency generation

This paper presents a theoretical analysis of sum-frequency generating optical parametric oscillators where a single nonlinear crystal is used for both parametric generation and sum-frequency generation. In these devices, the parametric and sum-frequency generation processes are both phase matched for the same direction of propagation inside the crystal. Different polarization geometries for which this simultaneous phase-matching condition can potentially be satisfied are identified and categorized, for both birefringent and quasi-phase-matching methods. Plane-wave coupled-mode equations are presented for each of these categories. Solutions of these coupled mode equations and calculation of the single-pass saturated signal gain are outlined. Intracavity signal photon flux density calculations based on these solutions lead to stable steady-state upconversion, multistability, and chaos. The dependence of the photon conversion efficiency on various design parameters are investigated

Advances in femtosecond single-crystal sum-frequency generating optical parametric oscillators

The effect of compensating the group velocity mismatch between the orthogonal pump components on the conversion efficiency of the optical parametric oscillators (OPOs) was investigated. A femtosecond single-crystal sum-frequency generating optical parametric oscillators (OPO) based on a Ti:sapphire laser pumped KTiOPO4 crystal was used. presented. The crystal was phase matched for a specific signal wavelength corresponding to the operational wavelength of the laser. The crystal was also phase-matched for the sum-frequency generations (SFG) of the pump and the signal beams yielded a blue output beam. The conversion efficiency of the OPOs increased by compensating the group velocity mismatch