Economic analysis of consumer choices based on rice attributes in the food markets of West Africa—the case of Benin

The focus of this study was to investigate consumer preferences for various attributes of rice marketed in Benin. Consumer choice theory postulates that products are consumed not for themselves, but for the characteristics they possess that satisfy consumers’ greater liking of one attribute over another. In the case of rice, quality attributes, as incentives for both producers and consumers, have important price implications. In this study, we empirically analyzed the relationship between the price paid by consumers for their choice of rice and its attributes in the markets of Benin using hedonic pricing and discrete choice models of demand. We used data collected from rice-consuming households in four major provinces of Benin, in both rural and urban areas, during 2006. The results of this econometric estimation indicated that there was considerable variability in consumer preferences for different rice attributes across the regions studied. Nevertheless, consumers paid a premium price for observable attributes, such as grain size and breakage. In addition, both urban and rural consumers preferred imported and parboiled rice to domestic and raw rice. The study results showed that implicit prices paid by consumers for both domestic and imported rice were based on quality attributes. These findings have important implications for future breeding programs aimed at making domestic rice more competitive with imported rice.     

Time‐ and State‐Dependent Input Delay‐Compensated Bang‐Bang Control of a Screw Extruder for 3D Printing

In this paper, a delay‐compensated bang‐bang control design methodology for the control of the nozzle output flow rate of screw extruder‐based three‐dimensional printing processes is developed. A geometrical decomposition of the screw extruder in a partially and a fully filled regions allows to describe the material convection in the extruder chamber by a one‐dimensional hyperbolic partial differential equation (PDE) coupled with an ordinary differential equation. After solving the hyperbolic PDE by the method of characteristics, the coupled PDE–ordinary differential equation's system is transformed into a nonlinear state‐dependent input delay system. The aforementioned delay system is extended to the non‐isothermal case with the consideration of periodic fluctuations acting on the material's convection speed, which represent the process variabilities due to temperature changes in the extruder chamber, resulting to a nonlinear system with an input delay that simultaneously depends on the state and the time variable. Global exponential stability of the nonlinear delay‐free plant is established under a piecewise exponential feedback controller that is designed. By combining the nominal, piecewise exponential feedback controller with nonlinear predictor feedback, the compensation of the time‐dependent and state‐dependent input delay of the extruder model is achieved. Global asymptotic stability of the closed‐loop system under the bang‐bang predictor feedback control law is established when certain conditions related to the extruder design and the material properties, as well as to the magnitude and frequency of the materials transport speed variations, are satisfied. Simulations results are presented to illustrate the effectiveness of the proposed control design. Copyright © 2017 John Wiley & Sons, Ltd.     

Field-dependent abundances of hydride molecular ions in atom probe tomography of III-N semiconductors

We investigate the microscopic behaviour of hydrogen-containing species formed on the surface of III-N semiconductor samples by the residual hydrogen in the analysis chamber in laser-assisted atom probe tomography (APT). We analysed AlGaN/GaN heterostructures containing alternate layers with a thickness of about 20 nm. The formation of H-containing species occurs at field strengths between 22 and 26 V/nm and is independent of the analysed samples. The 3D APT reconstruction makes it possible to map the evolution of the surface behaviour of these species issued by chemical reactions. The results highlight the strong dependence of the relative abundances of hydrides on the surface field during evaporation. The relative abundances of the hydrides decrease when the surface field increases due to the evolution of the tip shape or the different evaporation behaviour of the different layers.