MEMS-based gas flow sensors

Micro-electro-mechanical system (MEMS) devices integrate various mechanical elements, sensors, actuators, and electronics on a single silicon substrate in order to accomplish a multitude of different tasks in a diverse range of fields. The potential for device miniaturization made possible by MEMS micro-fabrication techniques has facilitated the development of many new applications, such as highly compact, non-invasive pressure sensors, accelerometers, gas sensors, etc. Besides their small physical footprint, such devices possess many other advantages compared to their macro-scale counterparts, including greater precision, lower power consumption, more rapid response, and the potential for low-cost batch production. One area in which MEMS technology has attracted particular attention is that of flow measurement. Broadly speaking, existing micro-flow sensors can be categorized as either thermal or non-thermal, depending upon their mode of operation. This paper commences by providing a high level overview of the MEMS field and then describes some of the fundamental thermal and non-thermal micro-flow sensors presented in the literature over the past 30 years or so.     

Experimental and numerical investigation into the joule heating effect for electrokinetically driven microfluidic chips utilizing total internal reflection fluorescence microscopy

This paper presents a detection scheme for analyzing the temperature distribution nearby the channel wall in a microfluidic chip utilizing a temperature-dependent fluorescence dye. An advanced optical microscope system—total internal reflection fluorescence microscope (TIRFM) is used for measuring the temperature distribution on the channel wall at the point of electroosmotic flow in an electrokinetically driven microfluidic chip. In order to meet the short working distance of the objective type TIRFM scheme, microscope cover glass slits are used to fabricate the microfluidic chips. The short fluorescence excitation depth from a TIRFM system makes the intensity information obtained using TIRFM is not sensitive to the channel depth variation which ususally biases the measured results while using a conventional Epi-fluorescence microscope (EPI-FM). Therefore, a TIRFM can precisely describe the temperature profile of the distance within 100 nm of the channel wall where consists of the Stern layer and the diffusion layer for an electrokinetic microfluidic system. Results indicate the proposed TIRFM provides higher measurement sensitivity over the EPI-FM. Significant temperature gradient along the channel depth is experimentally observed. In addition, the measured wall temperature distributions can be the boundary conditions for numerical investigation into the joule heating effect. The proposed method gives a precise temperature profile of microfluidic channels and shows the substantial impact on developing a numerical simulation model for precisely predicting the joule heating effect in microfluidic chips.     

Logistic混沌网络会议加密系统的设计

文章采用Logistic混沌序列对实时视频传输系统进行数据的分块加／解密,并从算法的安全性、效率等方面进行了性能分析,该算法具有良好的实时性、快速性和易实施性,可以有效地防止敏感信息被轻易的窃取、篡改和传播,有效保障网络视频传输的流畅性及安全性。     

决策支持系统在跨部门电子政务工程中的实现

决策支持系统合理应用到跨部门电子政务工程中不但可以降低大量的人力和财力成本,还会为电子政务中半结构化或非结构化问题提供重要的决策支持。文章提供了一种跨部门电子政务工程中决策支持系统技术架构的设计,为决策支持系统在跨部门电子政务工程中的实现提供了一种方法。     

Combining the Hanning windowed interpolated FFT in both directions

The interpolated fast Fourier transform (IFFT) has been proposed as a way to eliminate the picket fence effect (PFE) of the fast Fourier transform. The modulus based IFFT, cited in most relevant references, makes use of only the 1st and 2nd highest spectral lines. An approach using three principal spectral lines is proposed. This new approach combines both directions of the complex spectrum based IFFT with the Hanning window. The optimal weight to minimize the estimation variance is established on the first order Taylor series expansion of noise interference. A numerical simulation is carried out, and the results are compared with the Cramer-Rao bound. It is demonstrated that the proposed approach has a lower estimation variance than the two-spectral-line approach. The improvement depends on the extent of sampling deviating from the coherent condition, and the best is decreasing variance by 2/7. However, it is also shown that the estimation variance of the windowed IFFT with the Hanning is significantly higher than that of without windowing.     

吉林省农田黑土肥力变化趋势及评价

通过吉林省3个典型黑土实验点(15年玉米和水稻连作)的长期测定,对土壤养分变化进行了分析,并采用数值化的方法对其综合肥力进行了评价.研究结果表明,土壤有机质含量3个实验点均呈增加趋势;土壤全氮、碱解氮和速效钾含量平原玉米地呈下降趋势,而坡地玉米地和平原水稻田呈上升趋势;近年来,速效磷含量3个实验点均下降明显.肥力综合评价表明,平原玉米地的综合肥力略呈下降趋势,而坡地玉米地和平原水稻田的综合肥力呈现上升趋势,总体反映出在常规管理条件下,典型地块肥力15年来没有严重的退化现象.     

基于延迟合并嵌入的带障碍的时钟树布线算法

提出一种在带障碍情况下,基于延迟合并嵌入方法的时钟树构建算法,并在时钟树构造过程中引入了轨迹图以保证布线可以绕过障碍．该算法以已知障碍为布线约束,首先自底向上计算时钟树内部节点的可能位置,然后自顶向下确定每个节点的确切位置．实验结果表明,该算法能够正确、有效地实现有障碍存在时的时钟树布线,线长优化率超过7％．     

Measurement of birefringence for optical recording of disk substrates

We experimentally investigate the birefringence of bare and coated substrates for magneto-optical recording, using ellipsometry at wavelengths of 632.8 and 780 nm. The polarization rotation and ellipticity of reflected or transmitted light are measured for different incident angles and for different orientations of the incident linear polarization. The measured data are then fitted by the MULTILAYER computer program, which solves the Maxwell equations for a plane wave propagating in a multilayer structure. This approach makes it possible to determine, with high accuracy, the orientations of the principal axes of the substrate and the corresponding refractive indices. The results show that one of the principal axes is always along the substrate's normal direction, but the orientations of the in-plane principal axes can be much different from the radial and track directions. A special feature of the ellipsometers that were used is that a glass hemisphere is placed in contact with the substrate to eliminate refraction of the incident beam. This enables a maximum propagation angle of 70° (with respect to the normal) in the substrate and hence increases the measurement sensitivity. Certain anomalies have been observed, which we believe are associated with the variation of birefringence properties along the thickness direction.     

Piecewise straight-line correlation algorithm for navigation of autonomous systems with robotics applications

Autonomous moving systems, such as free moving robots and ‘nursing’ robots, accumulate errors during path tracking. While moving, correlation between measurement of the pattern characterizing the path and a previously recorded pattern stored in the computer of the tracking system can be found. Based on this correlation, it is possible to evaluate the system deviations from the desired path and calculate the required action to correct the movement of the vehicle. For certain applications the path characterizing pattern can be based on piecewice sections of nonparallel straight lines. The pattern can be obtained by filtering the straight lines from a picture of the path vicinity. To perform the required correlation between the actual measurement and this pattern a novel correlation algorithm, based on MSD (Mean Square Difference), is derived. MSD has an advantage over other methods for path pattern correlation, when there are no scaling errors between the measurement and the pattern in memory. Moreover, MSD converges to ML (Maximum Likelihood) for errors which are small with respect to the pattern measurement. Two main issues in implementing the new correlation process are discussed:

1. The near optimum performance of the new correlation algorithm, along with its simplicity, and the way in which it ‘handles’ real-time calculations with minimum computational effort.
2. The evaluation of the performance bound for the correlation process.

It is shown that, with the proposed method, deterministic errors in measuring the distances to these lines do not affect the correlation in the longitudinal (x) direction. Thus, only random measurement errors among the lines will cause correlation errors in x. In the lateral (y) direction, however, the obtained error is identical in size to the bias error.     

Retroreflecting ellipsometer for measuring the birefringence of optical disk substrates

A retroreflecting ellipsometer has been constructed for measuring the birefringence of optical disk substrates. In contrast to conventional ellipsometers with two mechanical arms, this system has only one arm along which both the incident and reflected beams travel. This construction eliminates the mechanical limitations of conventional ellipsometers, thereby permitting normal incidence on the sample. In addition, the single arm is adjustable in two dimensions, with the polar incident angle, θ(inc), varying from 0° to 70°, and the azimuthal incident angle, Φ(inc), varying from 0° to 360°. The condition of normal incidence permits accurate measurement of in-plane birefringence. The adjustability of both θ(inc) and Φ(inc) is necessary for the measurement of possible tilts of the index ellipsoid, and also for the variation of birefringence through the substrate thickness. Measurement results showing the useful features of the equipment are presented. The optics of the hemispherical assembly used for retroreflection as well as for the elimination of undesirable refractions are also studied by use of the ZEMAX lens design program.