近高超声速高温蓝宝石窗口下中波红外成像退化分析仿真与性能测试实验

本文基于高温红外窗口热辐射红外成像探测器干扰机理,开展高温红外窗口成像分析、仿真与实验验证研究工作. 根据流体仿真计算获得的高温窗口温度及实验测得的窗口发射率、吸收率等参数,开展窗口热辐射计算;建立了光学窗口介质内部辐射传输路径和强度计算模型,并给出了窗口辐射出射模型以及相应红外成像模型;基于光学追迹方法,把窗口热辐射成像的计算问题转换成了光学计算问题;设计了一种基于高温蓝宝石红外窗口的加热实验,对红外成像仿真结果进行了检验. 通过仿真结果与窗口加热实验结果对照,将基于模型分析获取图像与实验结果图像作差,得到的平均每个像素误差值为0.45;实验发现在窗口约773 K条件下,设计的中波红外成像系统的信噪比、对比度分别降低到原来三分之一左右,而整个红外成像系统NETD值由原来的约52 mK上升到了954 mK. 本文提出的窗口热辐射分析方法可以有效估计窗口热辐射对中波红外成像的影响,设计的实验对成像系统的指标验证有较好的用途,同时对红外成像系统波段细化优选和成像参数调整,降低图像退化程度,都有着重要的指导意义. 关键词： 近高超声速 高温蓝宝石窗口 气动效应 仿真与实验     

Effect of annealing on the structure of quenched isotactic polypropylene

Smectic isotactic polypropylene films were annealed at different temperatures for different times. Density, wide-angle x-ray scattering (WAXS), differential scanning calorimetry, and the transport properties of methylene chloride vapor were used to follow the transformation of the smectic phase into the monoclinic phase. The results of WAXS diffractograms indicate different saturation levels of crystallization with the maximum order attained progressively more quickly at higher temperatures. Density measurements, however, show that, after a first saturation level, a further increase of this parameter occurs after long annealing times; and this second step is lower, the higher the temperature. Sorption and diffusion, analyzed to investigate the amorphous component, show that annealing the smectic phase at 50°C results in a decrease of amorphous fraction without transformation of the smectic phase. The transition from smectic to monoclinic phase occurs at temperatures higher than 60°C. During the annealing at 80°C there is first a decrease of amorphous fraction corresponding to the first saturation level of the density, and then a further decrease of amorphouse phase corresponding to the final increase of density after 24 hr of annealing.     

Optimal laser heating of plasmas with constant density

The laser heating of a plasma with constant density is analyzed using optimal control theory. Heating strategies that minimize the total energy spent, the heating time, or a linear combination of the two, for several values of weighting coefficients, are obtained by determining the optimal laser intensity associated with each point of the phase plane. A numerical example is used to illustrate the application of the theory. In this particular example, savings in the energy spent up to 75%, compared with the energy required using a constant laser pulse, are obtained when minimum energy trajectories are implemented. Strategies that minimize the heating time, however, did not yield a significant reduction in the heating time. Numerical results may depend strongly on the initial state of the system as well as on the final ion temperature of the plasma.Based on a thesis submitted as partial fulfillment for a Ph.D. degree at the University of Michigan. Financial support, provided to the first author by Consejo Nacional de Ciencia y Tecnología, Universidad Nacional Autónoma de México, by the National Science Foundation, and by the Michigan Memorial Phoenix Project, is deeply appreciated.     

感应加热在铁路工务部门的应用

本文介绍了用涡流加热的方法更换铁路隧道螺旋道钉的技术 .该方法较好地解决了目前我国铁路部门螺旋道钉难以更换的问题 .     

Maxwell’s Equations in Two-Phase Systems I: Local Electrodynamic Equilibrium

The method of volume averaging is used to examine the form of Maxwell's equations in two-phase systems. The volume averaged equations for the individual phases are developed and used to identify the condition of local electrodynamic equilibrium. When this condition is satisfied, the electric and magnetic fields in the two phases are close enough so that single equations can be used to describe these fields. The one-equation model for the electric and magnetic fields is obtained without the need for closure problems; however, the constraints associated with the principle of local electrodynamic equilibrium are very severe and are not satisfied for many processes.     

Nonlinear conduction of irradiation‐crosslinked high‐density polyethylene/acetylene carbon black composites at the electric–thermal equilibrium state

At the electric–thermal equilibrium state, the nonlinear conduction behaviors of high‐density polyethylene/acetylene carbon black composites crosslinked with electron‐beam irradiation have been studied in wide ranges of electric field and ambient temperature. Critical electric field E_0.5 at the global electrical breakdown and the corresponding apparent resistivity are related to the intrinsic resistivity at given ambient temperatures. The relationship between the nonlinear conduction and the intrinsic positive temperature coefficient effect of resistivity is established by a discussion of E_0.5 as a function of the macroscopic resistivity temperature coefficient. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1979–1984, 2006     

Reduced self-heating by strained silicon substrate engineering

Substrate engineering innovations such as SOI and the use of Si/SiGe virtual substrates become necessary in order to maintain performance leverage of integrated circuits with continued scaling. The relevance of thermal effects in device design increases since the thermal conductivity of these new materials is poor. The electrical performance of devices fabricated on thin virtual substrates grown by two different techniques is presented. It is found that self-heating is reduced and that thermal resistance measurements agree with modelling predictions. The reduction in performance enhancement seen in many strained Si MOSFETs is found here to be largely due to self-heating effects, rather than parasitics or the loss of strain.     

自制加热元件及湿度测量控制器的应用

介绍利用电阻加热丝、印制基板材料设计制做的加热元件和用晶体管作温度传感器设计制做温度测量控制器的电路工作原理及其在物理实验中的应用。     

Quasi-isothermal measurement of frequency dependent heat capacity of semicrystalline polyethylene at the melting temperature using light heating modulated temperature DSC

Frequency dependence of the heat capacity of semicrystalline polyethylene was measured using light heating modulated temperature DSC (LMDSC). The quasi-isothermal measurement was carried out in the melting temperature range of the crystal. Two decades of the frequency, from 0.01 to 1 Hz, was covered by the LMDSC instrument constructed in the author's laboratory. It was found that in the melting temperature range polyethylene exhibited Debye relaxation with the relaxation time of 14 s and had excess heat capacity independent of the kinetics. The excess heat capacity and the relaxation strength could be attributed to the disordered crystals generated during rapid cooling from the molten state and/or its surrounding amorphous region instead of the stable crystals reorganized during the quasi-isothermal measurement.     

Heat Capacity of Titanium in the Temperature Range 1500 to 1900 K Measured by a Millisecond Pulse-heating Technique

Heat capacity of titanium in the temperature range 1500 to 1900 K was measured by a pulse-heating system, operating in the millisecond time regime. The measurement technique is based on selfheating of a tube-shaped specimen from room temperature to melting in approximately 500 ms and measuring current through the specimen, voltage drop along a defined portion of the specimen, and temperature of the specimen every 0.5 ms. A total of 12 measurements on 3 tube-shaped specimens was made. The reproducibility between individual measurements was 0.4%, between different specimens 0.7%. The extended measurement uncertainty (at a confidence level of 95%) is estimated to be 3%. This revised version was published online in July 2006 with corrections to the Cover Date.