Hemispherical concentrators and spectral filters for planar sensors in diffuse radiation fields

A dielectric hemisphere of refractive index N can act as an N(2) concentrator of isotropic diffuse radiation under appropriate conditions. We give an analytic expression for the gain of a concentrator of arbitrary radius, neglecting surface reflections, and numerical methods for calculating the gain when the surface transmissivity is an arbitrary function of incidence angle. The theory is applied to the design of multilayer spectral filters for hemispherical concentrators. When an appropriate wavelength shift is incorporated into the design process, an 11-layer, coupled-cavity spectral filter on the surface of a hemisphere of index 1.5 shows excellent bandpass performance with a concentrator radius as small as 3 times the sensor radius. This concentrator-filter combination shows a peak response of 97% of the ideal N(2) response at 950 nm, together with a FWHM of 55 nm.     

Measurements of the photocurrent enhancement of reverse-biased silicon photodiodes in the 0.05-1.5-keV photon-energy range

The measured photocurrents from two different p-n-junction silicon photodiodes at 170-? (73-eV) and at 8.34-? (1480-eV) light are presented. One is a standard extreme-UV photodiode fabricated on low resistivity silicon (70-100 Ω cm), and the other is fabricated on high-resistivity silicon (> 2 × 10(4) Ω cm). The photocurrents from the diode on high-resistivity silicon are at least an order of magnitude greater than the photocurrents from the diode on low-resistivity silicon when a reverse bias of 40 V is applied to each. This photocurrent enhancement is 15.4 ± 4 at 8.34 ? and 12.5 ± 2 at 170 ?.     

High-efficiency, argon-laser-pumped Nd:YLF laser system

An Ar-ion laser was used to pump a Nd:YLF laser, in both σ and π polarizations, in a longitudinal scheme. In spite of the small absorption coefficient at the pump (~0.25 cm (-1)), a careful laser design can circumvent this problem, and efficiencies as high as those attained with semiconductor pumping schemes are reported. The laser fundamental parameters were experimentally determined. A double-pass net gain as high as 10(3) was measured, and an output power of 1 W was obtained with a pumping power of 6 W.     

Effects of the handle diameter and tip angle of chopsticks on the food-serving performance of male subjects

The effects of chopsticks handle diameter and tip angle on the food-serving performance of pinching food, pulling food, shearing food and thrusting food, were investigated in this study. A total of 24 male subjects was tested using 12 pairs of experimental chopsticks, consisting of three types of different handle diameters and four types of different tip angles. These results indicated that chopstick handle diameter and tip angle have a significant influence on eating efficiency, and that these two variables have a significant interaction. In addition, chopstick tip diameter also had significant effects on performance at the four tasks and subjective ratings. Generally, according to the results, when the chopsticks design is presented in terms of handle diameter, tip angle and tip diameter, a pair of chopsticks with 6 mm handle diameter × 2 ° tip angle × 4 mm tip diameter would be optimum.     

Perception testing of apparel ease variation

The development of new computer technologies designed to custom-fit apparel has created a need for quantification of apparel fit characteristics. Fit perception and preference data are needed to improve sizing for ready-to-wear and custom-fitted apparel. Tactile responses of subjects to the fit of pants were investigated using an adaptation of an American Society for Testing and Materials (ASTM) sensory perception test. The test was designed to establish thresholds in apparel fit: that is, the smallest difference in garment dimensions that can be consistently perceived and identified. The test samples for the study were a set of 15 pants, which varied in size, made for each participant from precise computer-generated patterns. Four female experts in apparel fit, who comprised the subject panel, each recorded their responses to these pants compared to a control. Control pants were custom-fitted to each panel member; the remaining pants in each set varied from the control by 0.5 to 1.5 cm at a single location (waist, hips, or crotch length). When the pants were presented in a blind test, the panel perceived differences as small as 0.5 cm in pants waist size from the control. Differences of 1.5 cm were perceptible at the hip and crotch. The subject's level of acceptance of the fit variations in the pants was then judged using a preference test. This test revealed differences among individual subjects in the acceptability of fit variations in waist and crotch dimensions; judgements of the acceptability of hip variations were more consistent among the subjects. Judging from the results of this testing, it is concluded that threshold levels at which fit differences can be perceived can be established for different areas of the body, and that perceptible fit variations can be quite small. This testing also showed that individuals vary in their tolerance for fit variations at different locations on the body.     

考虑有功协调优化的配电网动态电压控制

配电网电压动态变化特征日益凸显,对配电网动态优化控制提出了新的要求。除此之外,配电网有功与无功的耦合特性也使得仅基于无功/电压的控制方法效果降低。因此,提出了一种考虑有功/无功快速协调优化的配电网动态电压控制方法,实现在秒级时间尺度内关键节点的电压恢复。首先建立配电网有功/无功控制设备动态模型,并基于模型预测控制理论建立了动态电压控制系统预测模型。设计了面向配电网电压协调控制的多目标自适应优化策略,基于配电网同步相量测量单元动态测量数据实现有功/无功控制设备出力的动态协调。仿真结果表明,该方法能够实现配电网电压波动的秒级抑制,并将目标节点电压快速无差地恢复至扰动前水平。     

具有主动故障穿越能力的光伏逆变器自治控制方法研究北大核心CSCD

文中设计了一种具有主动故障穿越能力的自治智能光伏(photovoltaic,PV)逆变器,所提逆变器具有有功功率和无功功率的解耦控制特性,它可以根据电网状态或电网运行员命令在预期的运行模式之间无缝切换。智能逆变器根据电网状态自动调整其有功和无功功率设定值,在正常电网和故障电网条件模式下分别以最大功率点跟踪(maximum power point tracking,MPPT)和低电压穿越(low voltage ride through,LVRT)模式运行。此外,文中还提出了一种新型自治模型预测控制(autonomous model predictive control,AMPC)方法,以提高智能PV逆变器的运行效率。AMPC包括在线权重因子自动调整和控制目标归一化,以消除传统模型预测控制中所需的试错权重因子设计阶段。最后,通过实验,验证基于AMPC并网智能PV逆变器的性能,实验结果表明,所提基于MPC的智能PV逆变器具有故障穿越、有功和无功功率设定值的自治调整、运行模式之间的无缝转换等优点。     

静电喷印技术在太赫兹超表面制备中的应用

近年来,太赫兹技术快速发展,基于超表面的太赫兹器件受到广泛关注,并已应用于太赫兹成像、光谱和生物传感等诸多领域。但太赫兹超表面器件的制备复杂且成本高,而静电喷印技术无需掩模版,成本低、精度高且易于在异形曲面上制作。基于静电喷印技术设计和制备了太赫兹吸波器,并利用太赫兹时域光谱系统（THz-TDS）对样品进行了性能测试,实验与仿真结果基本相符,在0.098~0.353 THz频段内吸收大于90%。此外,还设计了太赫兹线极化转换器,在0.167~0.355 THz频段内的极化转换大于95%,相对带宽约72%,并分析了所设计样品的制备工艺条件,验证了静电喷印技术对于制备太赫兹极化转换器的可行性。研究成果表明,静电喷印技术在太赫兹超表面器件的制备中具有广泛的应用前景。     

Liquid chromatography combined with tandem mass spectrometry for the confirmation of sarafloxacin in catfish tissue

A specific chromatographic LC/MS/MS assay is described for the confirmatory identification of residues of sarafloxacin, an arylfluoroquinolone antibacterial agent, in catfish tissue. This confirmatory method takes advantage of the specificity provided by sample preparation, liquid chromatography, and tandem mass spectrometry. This kind of multidimensional analysis is commonly used in environmental, pharmacokinetic, residue, and other studies. However, we demonstrate the addition of a previously unreported criterion, the use of ion ratio ranges from the tandem mass spectrometry (MS/MS) experiment as an aid in confirmation. Using the described method, we were able to achieve MS/MS product ion ratios with <7% variation during 1 day of analysis for over 25 injections. We believe the addition of this criterion will increase the scientific certainty of the confirmatory method.     

Motion processing using asymmetric shunting lateral inhibitory networks

Asymmetrically connected inhibitory shunting networks are believed to occur in many areas of the brain, including the visual system; they can explain many peripheral visual phenomena. This paper illustrates their usefulness in motion detection, and compares details of their performance with experimental results. Two stimuli are considered: drifting gratings and jumping bars. An elementary motion detector (EMD) is defined, consisting of a pair of opposite-directed asymmetric inhibitory networks. A frequency-space expansion (equivalent to a Volterra-Wiener expansion) is used to examine the EMD's response to a drifting grating. The EMD can be tuned to independent spatial and temporal frequencies: by summing the outputs of a number of EMDs, a velocity-tuned network is obtained. This velocity-tuned network is very well suited to certain field effect transistor (FET) implementations. Since the network is nonlinear, the response to a drifting grating does not fully characterize its behaviour. The response to a jumping bar stimulus is also examined. Two animals are considered: *Cats: the work of Emerson et al on the response of directionally selective (DS) complex cells in cat visual cortex to a white noise signal. *Flies: the work of Franceschini et al on the response of the fly H1 cell to stimulation of two neighbouring receptor cells, and that of Horridge and Marcelja on the fly H1 response to various jumping bar and edge stimuli. Agreement with all three of these experiments cannot be expected, because the results for the two animals are not consistent. There are two main differences: *Time development of the velocity-tuned signal: for the fly H1 cell this generally consists of two sharp (ON and OFF) responses to the second presentation of the bar signal, while for the cat DS cell a more slowly varying signal is observed. *Response to two presentations of the bar signal in the same position (i.e., a 'jumping bar' that jumps zero distance): for the fly H1 cell there is generally no response, while the cat DS cell responds significantly. The velocity-tuned network agrees well with the results for the cat DS cells.