Estimation of Mechanical Parameters in Multicompartment Models Applied to Normal and Obstructed Lungs During Tidal Breathing

A technique is presented which allows quantitative assessment of the use of parallel compartment models for characterizing pulmonary mechanical function during tidal breathing. A model consisting of a conducting airway leading to two parallel parenchymal regions is used. Numerical simulation and sensitivity analysis indicated that a) the compliance of the conducting airway was not significant under the experimental conditions of interest and that b) estimates of the distribution of central and peripheral resistances would not be precise. The techniques were demonstrated using measurements of transpulmonary pressure, flow, and volume changes during tidal breathing obtained from a human subject with normal lungs and a human subject with obstructed lungs. Optimal estimates of the parameters were obtained by minimizing the difference between the model output and experimental data combined from two breathing frequencies. In the estimation procedure, the sum of the peripheral compliances was constrained to equal the independently measured static lung compliance. This constraint was critical for correct evaluation of nonuniform mechanical lung function. From the parameter estimates, the ratio of parenchymal time constants was about five in the subject with normal lungs and 60 in the subject with obstructed lungs. These results suggest that a full study with several normal and obstructed lung subjects is warranted.     

A Physically Based Fluorescent Lamp Model for a SPICE or a Simulink Environment

This paper describes a method of modeling fluorescent lamps. The lamp model can be implemented in all major circuit simulation software packages, an example has been given for SPICE and Simulink. The model is based upon a simplified set of physical equations that gives the model validity over a wider range of operating conditions than current fluorescent lamp SPICE models allow for. The model can be used to model any low-pressure mercury-buffer gas fluorescent lamps by entering key lamp parameters, length, radius, cold-spot temperature, and buffer gas fill pressure. If fill pressure is not known, a default value dependent on lamp radius is used. The model shows good agreement over a wide range of operating frequencies and lamp powers.      

Mathematical modeling of the heart using magnetic resonance imaging

A hybrid three-dimensional solid mathematical model of cardiac ventricular geometry developed using magnetic resonance (MR) images of an in vivo canine heart is discussed. The modeling techniques were validated using MR images of an ex vivo heart and direct measurements of cardiac geometry and mass properties. A spin-echo MR sequence with in-plane resolution of 1.0 mm was used to image the canine heart in eleven short-axis planes at contiguous 5-mm intervals. Contour points on the epicardial, left ventricle (LV), and right ventricle (RV) boundaries were selected manually at each slice level. A boundary representation geometric model was constructed by fitting third-order nonuniform rational B-spline surfaces through each set of surface points. Compared to the anatomic specimen (AS), volume errors of the ex vivo model were 0.3, 1.5, and 5.8% for the LV cavity, RV cavity, and total enclosed volumes, respectively. Comparison of cross-sectional areas of the AS and the model at ten levels demonstrated mean model errors of 4.1, 2.5, and 2.9% for the LV, RV, and epicardial boundaries, respectively     

紫外预电离放电激励XeCl激光器的工作特性

进行了XeCl激光器工作参数优化实验,通过建立和分析XeCl激光器混合气体的动力学方程及模型,模拟计算了不同工作参数条件下,激光输出的瞬态过程,研究讨论了混合气体的配比和压强对准分子激光器的工作特性的影响,模拟分析了激光器最佳的运行参数.根据模拟结果对XeCl激光器的工作参数进行了优化调整实验,气体浓度配比设置为Ne/Xe/HCl=875/15/1,气体总压强设置为3.6×10~5 Pa,获得了单脉冲能量为180 mJ,脉冲宽度为30 ns的308 nm激光输出,脉冲重复频率为20 Hz,脉冲能量不稳定度小于5%.     

A CW CO2 laser with DC-discharge preionization

The application of the plasma-injection technique (involving DC-discharge preionization) to a CW CO₂ laser operating with recirculated gas is described. Measured characteristics of the discharges, the gain, and the output power are presented. An output of 110 W was obtained with a specific efficiency of 1.0 J/l^-1 of flowed gas at a pressure of 10 kPa. A simplified model to calculate a characteristic length of the main discharge, which is useful for design purposes, is developed. This type of laser may be scaled simply to higher output powers, requires a gas mixture with only 20% He, is compact and robust, and yet is simple in its electrical and mechanical requirements     

As掺杂碲镉汞富碲液相外延材料特性的研究

对富碲液相外延As掺杂碲镉汞(HgCdTe)材料的研究发现,其电学性能存在着不稳定性,材料霍尔参数的实验数据与均匀材料的理论计算结果也不能很好的吻合.通过采用剥层变温霍尔测量和二次离子质谱(SIMS)测试对材料纵向均匀性进行检测的结果显示,外延材料中的As在高温富汞激活退火过程中具有向材料表面扩散的效应,导致在表面形成了高于主体层浓度1～2个量级的高浓度表面层,并导致了AsTe受主的浓度在HgCdTe薄膜中呈非均匀分布.考虑这一效应并采用双层模型的霍尔参数计算方法后,As掺杂HgCdTe液相外延材料的电学行为得到了较好的解释,并较为准确地获得了退火后材料表面层与主体层的受主浓度及受主能级等电学参数.     

固液混合火箭发动机尾焰的红外特性研究

针对固液混合火箭发动机中Al2O3颗粒运动的影响,对喷管的内流场和外流场进行了一体化数值仿真,得到了温度、压力、组分浓度以及粒子浓度等参数的分布。利用以最新的分子光谱数据库HITRAN和HITEMP为基础编写的逐线积分法计算了气体光谱吸收系数,采用米氏散射模型计算了固体粒子的辐射特性参数。利用基于有限体积法离散辐射传输方程的模型计算出了尾焰的红外辐射亮度。通过进一步求解,得到了特定波段的光谱辐射强度。在8—14岬波段,利用红外热像仪进行了试验,并将试验结果与数值计算结果进行了比较。结果表明,该计算模型和方法能较好地模拟固液混合火箭发动机尾焰的红外辐射特性。     

基于多项式插值的小波变换预滤波器设计

该文提出了基于多项式插值的预滤波器设计方法, 这种方法从分析尺度函数出发设计预滤波器。信号均匀采样时, 预滤波器是时不变滤波器, 其系数是分析尺度函数各阶矩的线性组合。预滤波器的逼近阶取决于分析尺度函数的支撑集长度而不是正则阶。该设计方法有两个突出的优点：可以设计比传统预滤波器更高逼近阶的预滤波器,如综合尺度函数整数点的值构成的特殊预滤波器和由预尺度函数法产生的预滤波器等,可以很自然地推广到信号非均匀采样的情况, 相应的预滤波器是时变滤波器, 逼近阶依赖于分析尺度函数的支撑集长度和采样点的分布。数值结果表明, 利用基于多项式插值的小波变换预滤波器可以得到逼近效果更好的初始尺度系数。     

Operating characteristics of TE copper bromide lasers

Detailed operating characteristics of transversely excited (TE) double-pulse copper bromide lasers employing discharge stabilization techniques are reported. With careful optimization of operating temperature, buffer gas pressure, dissociation and excitation energies, and pulse delay times, specific output energies up to 35μJ/cm³have been obtained for a device of active volume 150 cm³. The nature of the dominant processes influencing ground state and metastable copper atom densities in the interpulse region are discussed in terms of the observed effects of temperature and gas pressure on the characteristic delay times.     

Quantification of electromagnetic absorption in humans from body-mounted communication transceivers

The internal electric (E) field and energy deposition in a full-size adult male mannequin in the immediate vicinity of 1.5 W body-mounted communication transceivers have been measured. Transceivers operating at the four frequencies 50, 150, 450, and 800 MHz, and placed at various locations vis-à-vis the body were used. The mannequin was filled with two-thirds muscle-simulant biological phantom mixtures at each of the four frequencies. The complex permittivities (ε^*) of these mixtures were confirmed by measurement. The internal E-field distribution was measured by three-dimensional implantable E-field probes. Relatively superficial energy depositions were obtained at points close to the location of the transceiver antenna for the two higher frequencies with energy depositions typically less than 1-2 W/kg. Considerably reduced energy depositions were measured at the two lower frequencies on account of in-depth and wider dissemination of the absorbed energy and the relatively high ε^*of the tissues which results in an increased shielding of the body.     

Integrated electro-thermomechanical analysis of nonuniformly chip-powered microelectronic system

An integrated electrical, fluid flow and thermomechanical analysis is presented to study a product reliability and thermal management solution in an actual or nonuniform chip power distribution of an integrated circuit device in a realistic system application environment. This study aims to improve the existing limitations both on electrothermal analysis where simplified thermal boundary conditions is mostly used and on the current thermal and fluid flow analysis where uniform chip power is widely used to calculate the temperature. In this approach, the localized on-chip power distribution is obtained by using a transistor-level circuit model for simulating the interaction between the macro and functional blocks. A computational fluid dynamics analysis is used to calculate the fluid flow and heat transfer solution with a realistic thermal boundary conditions. To address the ultimate thermal induced mechanical stress and reliability effects on the chip-packaged assembly due to the nonuniform chip power distribution, finite element model is employed for the sequential steady-state heat transfer and mechanical analysis. The results are then discussed and specifically compared with the solutions based on the uniform chip power conditions.     

Automated estimation of rock fragment distributions using computer vision and its application in mining

Size distribution of rock fragments obtained from blasting and crushing in the mining industry has to be monitored for optimal control of a variety of processes before reaching the final grinding, milling and the froth flotation processes. Whenever feasible, mechanical sieving is the routine procedure to determine the cumulative rock weight distribution on conveyor belts or free falling off the end of transfer chutes. This process is tedious and very time consuming, even more so if a complete set of sieving meshes is used. A computer vision technique is proposed based on a series of segmentation, filtering and morphological operations specially designed to determine rock fragment sizes from digital images. The final step uses an area-based approach to estimate rock volumes. This segmentation technique was implemented and results of cumulative rock volume distributions obtained from this approach were compared to the mechanical fragment distributions. The technique yielded rock distribution curves which represents an alternative to the mechanical sieving distributions.     

Optimal selection of frequencies for estimating parameters fromrespiratory impedance data

The goal of this study was to evaluate whether optimal selection of a reduced number of frequency points would still result in statistically reliable parameter estimates. A direct-search technique is described which optimally places a small number of frequencies so that the volume of the parameter joint confidence region is minimized. The accuracy of the parameters estimated from a full data set (50 evenly spaced points) is compared to that achievable with optimal designs using 20, 10, or 5 frequency points. The techniques were applied to parameters obtained from healthy dogs and humans. Results indicated that with ten optimally chosen frequencies most parameter uncertainties are only slightly higher than that achievable with 50 frequencies while parameter uncertainties increase greatly when only five optimal points are used. This suggests that the technique of forced oscillation permits identification of the distribution of respiratory system properties without the need for extensive data acquisition     

Hepatic bipolar radio-frequency ablation between separated multiprong electrodes

Radio-frequency (RF) ablation has become an important means of treatment of nonresectable primary and metastatic liver tumors. Major limitations are small lesion size, which make multiple applications necessary, and incomplete killing of tumor cells, resulting in high recurrence rates. We examined a new bipolar RF ablation method incorporating two probes with hooked electrodes (RITA model 30). We performed monopolar and bipolar in vivo experiments on three pigs. The electrodes were 2.5 cm apart and rotated 45 degrees relative to each other. We used temperature-controlled mode at 95 degrees C. Lesion volumes were 3.9+/-1.8 cm3 (n=7) for the monopolar case and 12.2 +/- 3 cm3 (n=10) for the bipolar case. We generated finite-element models (FEMs) of monopolar and bipolar configurations. We analyzed the distribution of temperature and electric field of the finite element model. The lesion volumes for the FEM are 7.95 cm3 for the monopolar and 18.79 cm3 for the bipolar case. The new bipolar method creates larger lesions and is less dependent on local inhomogenities in liver tissue-such as blood perfusion-compared with monopolar RF ablation. A limitation of the new method is that the power dissipation of the two probes cannot be controlled independently in response to different conditions in the vicinity of each probe. This may result in nonuniform lesions and decreased lesion size.     

Nonuniform sampling techniques for antenna applications

Recent investigations have demonstrated that uniform sampling techniques can be effectively applied for construction of far-field patterns of antennas. There are, however, many circumstances for which it may not be practical to directly utilize uniform sampling techniques. A two-dimensional sampling technique which can employ irregularly (nonuniformly) spaced samples (amplitude and phase) in order to generate the complete far-field patterns is presented. The technique implements a matrix inversion algorithm which depends only on the nonuniform sampled data point locations and with no dependence on the actual field values at these points. A powerful simulation algorithm is presented to allow a real-life simulation of many reflector/feed configurations and to determine the usefulness of the nonuniform sampling technique for the co-polar and cross-polar patterns. Additionally, an overlapped window concept and a generalized error simulation model are discussed to identify the stability of the technique for recovering the field data among the nonuniform sampled data. Numerical results are tailored for the pattern reconstruction of a 20-m offset reflector antenna operating atL-band. This reflector is planned to be used in a proposed measurement concept of large antennas aboard the space shuttle, whereby it would be almost impractical to accurately control the movement of the shuttle with respect to the radio frequency (RF) source in prescribed directions in order to generate uniform (u, v) sampled points. Also, application of the nonuniform sampling technique to patterns obtained using near-field measured data is demonstrated. Finally, results of an actual far-field measurement are presented for the construction of patterns of a reflector antenna from a set of nonuniformly distributed measured amplitude and phase data.     

柔性支承柱面气膜密封CFD数值分析

针对柔性气膜密封技术在航空发动机中的应用需求,使用CFD数值分析技术分析柔性支承柱面气膜的密封性能。首先在Proe中建立柱面气膜的密封参数化模型,并分析了气膜密封原理;然后基于有限元分析的Linear Soid划分方法,使用ANSA网格划分软件来划分网格,得到柔性支承柱面的静压、速度和剪应力分布等数据,并分析柱面结构参数与操作参数对柔性支承柱面气膜密封性能的影响。实验结果表明,粘度、压差和转速等操作参数能明显影响柔性支承柱面气膜的密封性能。     

螺旋槽位置特征对气膜密封性能影响的仿真研究

为了更有效地进行螺旋槽位置选取及确定气膜密封性能的影响因素,文中对螺旋槽位置特征对气膜密封的性能影响进行仿真研究。通过理论分析以及ANSYS建模软件定义,对两种状态下的压力场模型以及静环开槽和动环开槽两种气膜结构模型进行了建模。在此基础上,利用FLUENT软件仿真研究了静环开槽和动环开槽结构下的静压分布与剪切应力分布情况,并进一步分析了不同操作参数对柱面气膜密封性能的影响。通过仿真结果可以说明,静环开槽的气膜模型要略优于动环开槽的气膜模型,且压差和空气黏度对气膜密封性影响显著。     

Contamination control for gas delivery from a liquid source insemiconductor manufacturing

Gas delivery from a liquid source, common in semiconductor manufacturing, raises contamination control concerns not only due to impurity levels in the source. In addition, the lower vapor pressure of impurity species compared to that of the host (source) species causes impurity concentrations in delivered gas to increase as the source is used up. A physics-based dynamic simulator to describe the time-dependent variation of impurity level in such a gas delivery system has been developed and applied to the important case of CHClF₂ impurities in host CHF₃ liquid, as routinely used for dry etching processes. The time-dependence of CHClF ₂ impurity concentration is also dependent on the operating temperature of the liquid source: for higher temperatures, the fast rise in impurity concentration and the liquid-dry point occur earlier, while the final impurity level after this point is lower. The dynamic simulator represents a useful tool for avoiding contamination problems with liquid delivery systems and for optimizing materials usage (for cost and environmental benefits) by structuring source usage procedures consistent with contamination-sensitivity of the process. The results also suggest benefits in materials usage if specific source temperatures (different from room temperature) were imposed. The physical basis of the dynamic simulator allows more general application to other systems     

LSA operation of large volume bulk GaAs samples

Peak pulse powers of 350 watts, with 3 percent efficiency at X-band frequencies, were obtained from large volume GaAs devices operating in the LSA mode. Experimental dependence of the LSA mode on circuit loading, applied voltage, and the ratio of carrier concentration to frequency are reported. The results are shown to be in excellent agreement with Copeland's theoretical calculations. The high-current state frequently observed in GaAs samples is shown to result from impact ionization in the high-field portion of dipole domains. A simple expression is derived relating the sample length and carrier concentration to the voltage at which switching to the high-current state occurs. The prevention of high-field domains to permit LSA operation of long samples at high voltages is briefly discussed.     

A bond graph model-based evaluation of a control scheme to improve the dynamic performance of a solid oxide fuel cell

A control strategy for a solid oxide fuel cell (SOFC) is developed in this paper to maintain required cell operating conditions while ensuring good fuel efficiency and satisfying the constraints on the transient performance. To verify the controller performance, a zero-dimensional true bond graph model of an SOFC system is developed which makes use of a C-field for two gas species in order to model the cathode and anode channel gases. Moreover, an existing R-field model has been extended for modeling of forced convection of a mixture of two gas species. The coupling between the chemical, thermal, mechanical and the hydraulic domains, which is encountered in a fuel cell system, is represented in a unified manner by using true bond graphs. The fuel utilization (FU) and the air utilization (AU) are interpreted in terms of the partial pressures of the gases. The static characteristics of the fuel cell obtained are in good agreement with the data from the literature. The dynamic response of the fuel cell to step changes in load current is obtained. From the simulations it is shown that all the control objectives are achieved by the proposed control system.