FREQ: A computational package for multivariable system loop-shaping procedures

Many approaches in the field of linear, multivariable time-invariant systems analysis and controller synthesis employ loop-sharing procedures wherein design parameters are chosen to shape frequency-response singular value plots of selected transfer matrices. A software package, FREQ, is documented for computing within on unified framework many of the most used multivariable transfer matrices for both continuous and discrete systems. The matrices are evaluated at user-selected frequency-response values, and singular values against frequency. Example computations are presented to demonstrate the use of the FREQ code

IMPACTS OF INCOME CHANGES AND MODEL SPECIFICATION ON FOOD DEMAND IN URBAN CHINA

Functional form specification is a crucial task in demand analysis. Four food demand systems for 12 aggregated food items in urban China are estimated and compared using province level data for the period 1992-1999. The results show the expenditure elasticities especially for grain are different based on the functional form selection. According to the measures of forecasting accuracy, we conclude the following: for ex post simulation, the simpler the models, the better the performances, whereas for ex ante forecasting, the more complicated the model, the better the predictions. We further conclude that the LES and QES outperform the LA/AIDS and AIDS. Therefore, model selection should depend on the study purpose. In addition, as urban Chinese household income increases, they will consume more aquatic products, poultry and milk than other foods. This potential trend will certainly benefit the fishery and livestock industries as well as feed grain producers in China or other countries such as Taiwan. However, high own-price elasticities of these three food groups suggest that the profitability of suppliers and traders is very sensitive to price changes.Demand and Price Analysis,

FOOD DEMAND IN URBAN CHINA: AN APPLICATION OF A MULTI-STAGE CENSORED DEMAND SYSTEM

Since its economic reform, China has changed significantly as it makes its transition from a centrally-planned to a consumer-oriented economy and thus has gradually increased household income and changed consumption patterns in urban China. This study attempts to provide an in-depth understanding of heterogeneous consumer patterns in urban China by developing a multi-stage censored demand system using household data. Specifically, this study develops an economic model considering heterogeneous consumption patterns across households and commodity groupings and estimates econometric models of a Quadratic Almost Ideal Demand System (QAIDS) using household data. Three methodologies are integrated including constructing a multi-stage demand system, incorporating demographic variables using the 'ordinary budget share scaling and translation' (OBSSAT), and employing a two-step estimator to deal with zero consumption problems. This study covers three provinces in China, Shandong, Jiangsu, and Guangdong, and uses household data from 1998 provided by the National Bureau of Statistics (NBS). Based on the Chinese food guide pyramid, a three-level utility tree is constructed dividing 18 food items into five subgroups. An empirical analysis is conducted by estimating econometric models to examine the impact of the potential factors, e.g., income and demographic variables, on food demand. The results show the uniqueness of this study in three dimensions. First, using the OBSSAT helps answer the question of "how to break down the heterogeneous consumption patterns in urban China?" In addition, our findings also show that China should be treated as several markets instead of one. Second, the QAIDS has not previously been applied to the study of food demand in urban China. Our results show that the QAIDS is superior to the AIDS; however, the degree of importance for the quadratic term decreases as demographic and censoring effects are considered in a demand system. Finally, 18 food items are broken down into five food subgroups and are estimated by a multi-stage censored QAIDS. Including this large food bundle in a demand system provides us detailed information of the relationship among food items.Demand and Price Analysis,

Computer-aided design and distributed system technology development for large space structures

Proposed large space structures have many characteristics that make them difficult to analyze and control. They are highly flexible, with components mathematically modeled by partial differential equations or very large systems of ordinary differential equations. They have many resonant frequencies, typically low and closely spaced. Natural damping may be low and/or improperly modeled. Coupled with stringent operational requirements of orientation, shape control, and vibration suppression, and the inability to perform adequate ground testing, these characteristics present an unconventional identification and control design problem to the systems theorist. Some of the research underway within Langley's Spacecraft Control Branch, Guidance and Control Division aimed at developing theory and algorithms to treat large space structures systems identification and control problems is described. The research areas to be considered are computer-aided design algorithms, and systems identification and control of distributed systems

Energy-Efficient Power Allocation in OFDM Systems with Wireless Information and Power Transfer

This paper considers an orthogonal frequency division multiplexing (OFDM) downlink point-to-point system with simultaneous wireless information and power transfer. It is assumed that the receiver is able to harvest energy from noise, interference, and the desired signals. We study the design of power allocation algorithms maximizing the energy efficiency of data transmission (bit/Joule delivered to the receiver). In particular, the algorithm design is formulated as a high-dimensional non-convex optimization problem which takes into account the circuit power consumption, the minimum required data rate, and a constraint on the minimum power delivered to the receiver. Subsequently, by exploiting the properties of nonlinear fractional programming, the considered non-convex optimization problem, whose objective function is in fractional form, is transformed into an equivalent optimization problem having an objective function in subtractive form, which enables the derivation of an efficient iterative power allocation algorithm. In each iteration, the optimal power allocation solution is derived based on dual decomposition and a one-dimensional search. Simulation results illustrate that the proposed iterative power allocation algorithm converges to the optimal solution, and unveil the trade-off between energy efficiency, system capacity, and wireless power transfer: (1) In the low transmit power regime, maximizing the system capacity may maximize the energy efficiency. (2) Wireless power transfer can enhance the energy efficiency, especially in the interference limited regime.Comment: 6 pages, Accepted for presentation at the IEEE International Conference on Communications (ICC) 201