Sensorless speed measurement using current harmonic spectralestimation in induction machine drives

This paper proposes a sensorless speed measurement scheme that improves the performance of transducerless induction machine drives, especially for low-frequency operation. Speed-related harmonics that arise from rotor slotting and eccentricity are analyzed using digital signal processing. These current harmonics exist at any nonzero speed and are independent of time-varying parameters, such as stator winding resistance. A spectral estimation technique combines multiple current harmonics to determine the rotor speed with more accuracy and less sensitivity to noise than analog filtering methods or the fast Fourier transform. An on-line initialization routine determines machine-specific parameters required for slot harmonic calculations. This speed detector, which has been verified at frequencies as low as 1 Hz, can provide robust, parameter-independent information for parameter tuning or as an input to a sensorless flux observer for a field-oriented drive. The performance of the algorithm is demonstrated over a wide range of inverter frequencies and load conditions     

Autonomous vehicles

There are various kinds of autonomous vehicles (AV's) which can operate with varying levels of autonomy. This paper is concerned with underwater, ground and aerial vehicles operating in a fully autonomous (nonteleoperated) mode. Further this paper deals with AV's as a special kind of device, rather than full-scale manned vehicles operating unmanned. The distinction is one in which the AV is likely to be designed for autonomous operation rather than being adapted for it as would be the case for manned vehicles. We provide a survey of the technological progress that has been made in AV's, the current research issues and approaches that are continuing that progress, and the applications which motivate this work. It should be noted that issues of control are pervasive regardless of the kind of AV being considered, but that there are special considerations in the design and operation of AV's depending on whether the focus is on vehicles underwater on the ground, or in the air. We have separated the discussion into sections treating each of these categories     

Improved accuracy of burn wound assessment using laser Doppler

The utility of the laser Doppler for determining burn depth has been questioned because of problems with technology and methodology. This study prospectively evaluates the ability of a new laser Doppler technique to predict burn healing time. Using the Periflux System 4000 laser Doppler, readings were taken on 305 burns (147 patients) on postburn day 3 or 4. Sixty-six wounds were used to derive a predictive function (phase I) and 152 wounds were used to test the function (phase II). Blood flow dynamics (flux), microvascular dilation capacity of the wounds to beat stress, and flow motion wave pattern (vasomotion) were studied using the laser Doppler, and seven parameters were evaluated to determine their relative contribution to the prediction of healing time. These parameters are hyperemic flux (flux value after heating to 42 degrees C), average hyperemic wave amplitude (AHWA), number of average flux units >100(F100), number readings with wave amplitude 75 (A5), average flux change (AFC), percentage of average flux increase, and relative flow capacity (RFC = AFC/average hyperemic flux). After readings were made, the wounds were observed and divided into two groups: those that healed in less than 14 days and those that healed or were grafted after 14 days. A step-wise discriminant analysis was used to assess the relative contribution of the Doppler-derived measures to healing time prediction. AHWA, F100, and RFC were included in the final discriminant function explaining 72% of the healing time variance (Wilks' lambda value 0.28; p value <0.0001). Predicted outcome = 0.05(AHWA) + 0.31(F100) + 5.0(RFC) - 2.3. With this derived function, there is 94% accuracy in the prediction of burn wound healing time compared with a physician predictive accuracy of 70%.     

Dependence of attenuation in a vegetation canopy on frequency andplant water content

Theory is presented to provide insight into the observation that attenuation through vegetation is proportional to vegetation water content. In this analysis, the canopy is modeled as a sparse layer of randomly oriented particles (leaves, stalks, etc.) over a flat, homogeneous ground plane (soil) and an expression is obtained for the “optical depth”. The formulas developed by Ulaby and El Rayes are used to relate this expression to the water content of the canopy. In the low frequency extreme (Rayleigh scatterers), the attenuation varies almost linearly with water content and inversely with wavelength. In contrast, in the high frequency limit, the attenuation is independent of both water content and frequency, in between, geometry dependent “resonances” occur even at the low frequency end of the microwave spectrum (e.g. L-band) making the dependence of attenuation on frequency and water content specific to canopy architecture     

WKB近似下的Fourier衍射成象方法

对于介质目标微波衍射成象，本文引入了ＷＫＢ近似来模拟目标内部总场。基于这种近似，我们导出了Ｆｏｕｒｉｅｒ衍射公式，并采用了广义滤波逆传播方法由目标空间谱实现目标特性的重建。计算机模拟结果表明采用ＷＫＢ近似重建目标特性较Ｂｏｒｎ近似有明显改善。     

A preliminary analysis of the biomass energy production potential in Africa in 2025 considering projected land needs for food production

This paper provides a preliminary examination of present and projected land use in Africa to estimate the potential availability of land in 2025 for use in producing biomass energy. Fifty countries are included in the analysis. Future cropland requirements are projected on the basis of average African cereal crop yield improvements since 1972, and minimum nutritional requirements are assumed to be met in 2025 without increasing imports above present absolute levels. Cropland, natural forests and other wilderness areas are excluded from consideration for biomass energy use. Woody biomass energy yields are estimated on the basis of nationally averaged precipitation, using a yield-precipitation correlation for commercial eucalyptus plantations in Brazil. The total African bioenergy production potential in 2025 is estimated to be about 18 EJ per year for a set of baseline assumptions that includes planting only 10% of the available non-crop, non-forest, non-wilderness area with biomass energy crops. A preliminary cost assessment suggests that much of this biomass could be produced for $1–2 GJ⁻¹. A number of uncertainties in the modelling assumptions are examined through a sensitivity analysis. Despite limitations in the model used here, one robust conclusion is that Africa as a whole has a significant biophysical potential for producing biomass energy. This result suggests that more detailed country and sub-country level assessments would be worthwhile to understand better the practical prospects for future biomass energy production in Africa.