A 3-D SAR model for current source interstitial hyperthermia

A three-dimensional (3-D) model is presented for the calculation of the specific absorption rate (SAR) in human tissue during current source interstitial hyperthermia. The model is capable of millimeter resolution and can cope with irregular implants in heterogeneous tissue. The SAR distribution is calculated from the electrical potential. The potential distribution is determined by the dielectric properties of the tissue and by the electrode configuration. The dielectric properties and the current injection of the electrodes are represented on a 3-D uniform grid. The calculated potential at an electrode current injection point is not the actual electrode potential at that point. To estimate this potential a grid independent representation of an electrode together with an analytical solution in the neighborhood of the electrode are used. The calculated potential on the electrode surface is used to estimate the electrode impedance. The tissue implementation is validated by comparing calculated distributions with analytical solutions. The electrode implementation is verified by comparing different discretizations of an electrode configuration and by comparing numerically calculated electrode impedances with analytically calculated impedances     

Copolar and cross-polar radiation of Vivaldi antenna on dielectricsubstrate

The copolar and cross-polar radiation patterns of the Vivaldi antenna on a dielectric substrate are calculated and validated by measurements. The method involves a two-step procedure. The electric field distribution across the antenna slot aperture is calculated first. The radiated fields are then calculated, using Green's functions. The continuous exponential tapered shape is approximated by annular linearly tapered sections. The conical transmission-line theory and a variational method yield the electric field in each section. The radiation calculation is based on closed-form expressions for the dyadic Green's function of an elementary electric field source in a conducting half sheet. Both copolar and cross-polar radiation patterns of the Vivaldi antenna are calculated by integrating the Green's functions weighted by the electric field distribution over the antenna aperture. The effect of lateral truncation is taken into account by defining weighting patterns. The method is validated by original measurements and limitations of the model are discussed. Antenna directivity and sensitivity are calculated     

First-Principles Study of Electronic Structure and Thermoelectric Properties of Ge-Doped Tin Clathrates

We calculated the electronic structure and thermoelectric properties of the Ge-doped quaternary clathrate Ba-Ga-Sn-Ge. The electronic structure was calculated by using the WIEN2k code, which is based on the full-potential augmented plane-wave method. Using this method, we calculated the total energies for several Ge configurations to determine the positions of Ge atoms in the unit cell. The calculated Ge positions were in good agreement with the experimental results. Based on the resulting Ge positions, the band structure and thermoelectric properties of the Ba-Ga-Sn-Ge clathrates were calculated.     

Comparison between wurtzite phase and zincblende phase GaN MESFETsusing a full band Monte Carlo simulation

Cutoff frequency, breakdown voltage, and the transconductance of wurtzite and zincblende phase GaN MESFETs have been calculated using a self-consistent, full band Monte Carlo simulation. The effect of interface states on the device performance is modeled by including uniformly depleted regions at the device surface under the passivation layers. It is found that the drain current increases gradually with increasing drain-source voltage at the onset of breakdown for both phases. The calculated breakdown voltage for the wurtzite device is considerably higher than the breakdown voltage calculated for the zincblende device. On the other hand, the zincblende device is calculated to have higher transconductance and cutoff frequency than the wurtzite device. The higher breakdown voltage of the wurtzite phase device is attributed to the higher density of electronic states for this phase compared to the zincblende phase. The higher cutoff frequency and transconductance of the zincblende phase device is apparently due to the greater electron velocity overshoot for this phase compared to that for the wurtzite phase. The maximum cutoff frequency and transconductance of a 0.1 μm gate-length zincblende GaN MESFET are calculated to be 220 GHz and 210 mS/mm, respectively. The corresponding quantities for the wurtzite GaN device are calculated to be 160 GHz and 158 mS/mm     

Two-dimensional numerical analysis of lasing characteristics forself-aligned structure semiconductor lasers

Lasing characteristics in 0.78 μm AlGaAs-GaAs self-aligned structure (SAS) lasers are calculated on the basis of a newly developed two-dimensional analytical method. The calculated results are compared in detail with experimental results for MOVPE (metalorganic vapor phase epitaxial) grown SAS lasers. It is shown that calculated results agree well with experimental results, and that the newly developed two-dimensional simulator is very effective in calculating actual lasing characteristics accurately. The optimum design conditions for AlGaAs-GaAs SAS lasers obtained from experimental and calculated results are discussed     

基于波束空间MUSIC的MIMO雷达波达方向估计

在进行波达方向估计时,阵元空间MUSIC方法的计算量通常都比较大。为了解决此问题,采用了波束空间MUSIC的方法,它的计算量较阵元空间MUSIC方法有所下降,将它运用于多输入多输出雷达波达方向的估计问题。计算机仿真实验表明,虽然协方差矩阵特征分解的计算量下降了,但是波束空间MUSIC的性能依然良好。     

薄膜残余应力有限元分析研究

利用有限元软件对薄膜残余应力进行了分析与计算，并与理论计算结果进行对比，说明所建立的模型是合理的。     

掺Yb3+硅酸盐玻璃的制备和光谱特性

为了研究用于高功率激光器的掺Yb3+激光玻璃的制备和光谱特性,采用高温熔融工艺制备了两块碱金属元素含量不同的掺Yb3+硅酸盐激光玻璃,利用相应的光谱仪器测试了两块玻璃样品的吸收光谱和荧光光谱;分析了不同碱金属离子对吸收系数和荧光强度的影响;比较了倒易法和Fuchtbauer-Ladenburg(F-L)法两种不同方法得到的受激发射截面图,得到了Yb3+掺杂玻璃的各个光谱参量和激光参量。结果表明,随着碱金属离子半径的增大,吸收系数和荧光强度减小;样品的吸收截面图与倒易法计算所得的受激发射截面图相似,而与F-L法计算所得的受激发射截面图差别较大,并且倒易法发射截面图中主峰波长较F-L法发射截面图的主峰波长蓝移;最终样品1的增益性能比较好。     

Testing of models used in the theory of mixtures and applied to calculations of the permittivity of moist wood tissue in the microwave range

The calculated complex permittivity of wood tissue calculated from formulas of the mixture theory at microwave frequencies is analyzed. The permittivity is calculated as a function of temperature, moisture content, density, orientation of fibers with respect to the electric-field vector, and wood type. The experimental data for the dielectric properties of tap water with a determined chemical composition that are measured at a frequency of 915 MHz and high temperatures are presented.     

2.5 GHz城市环境电磁态势的计算与补偿

复杂城市空间的电磁态势分布可以通过电磁场数值计算的方法进行预测。文章使用矩量法(MOM)结合一致性几何绕射理论(UTD)的方法对2.5 GHz频率下某小区环境中的电磁态势进行了仿真计算以及实际测量。场景中的树木结构在此频率下显示出比较强烈的波动性,对电磁仿真计算结果产生了不可忽略的影响,文中将其对仿真计算结果的影响进行了单独建模仿真,给出其产生影响的经验值,对仿真结果进行修正。修正结果与测量结果对比证明该经验值在该频率下可以有效补偿计算结果的缺失。     

卫星的红外辐射特征研究

卫星的红外辐射特征对于工作卫星与失效卫星的判别具有重要意义,根据卫星与地球、太阳之间的位置关系,计算了太阳直接辐射角系数,利用随机模拟法计算了地球反照和地球红外辐射角系数,建立了卫星温度控制方程,并利用辐射传递系数的概念和蒙特卡洛方法进行辐射换热的计算,对卫星温度场进行了求解,讨论了卫星红外辐射特征的计算方法,并对其特性进行了分析计算,结果表明：卫星的散热面是区别工作卫星和失效卫星的依据。     

湍流脉动对圆射流红外辐射特性的影响研究

为研究湍流脉动对高温燃气圆射流红外辐射强度的影响,利用大涡模拟方法计算了高温圆射流流场的温度和组分浓度等的瞬时值和平均值,在此基础上分别采用平均温度?辐射法和瞬时温度?辐射法计算了射流场的红外辐射特性。计算结果表明:瞬时温度?辐射法计算的平均光谱辐射强度、平均积分辐射强度和平均辐射亮度均高于平均温度?辐射法计算的结果;湍流脉动越大,掺混区越厚,两种方法的计算结果之间的差值以及射流场红外辐射的脉动幅值均越大,其中射流高温核心区尾缘附近是受湍流影响最强的区域;两种方法计算的平均红外辐射亮度之间的差值沿着径向逐渐降低。对于Re=86 000,环境温度与进口温度之比为0.35的圆射流,在90°探测方向上,瞬时温度?辐射法计算的总的平均积分辐射强度比平均温度?辐射法的计算结果高23.6%左右。     

An efficient method for calculating the d.c. triggering currents in CMOS latch-up

The substrate and well resistances have been calculated from the structure parameters of the fabricated CMOS structures. Based on the ideal diode model and the calculated resistances, the d.c. triggering currents for CMOS latch-up due to the voltage undershoot and overshoot on the parasitic emitters have been calculated. The calculated d.c. triggering currents have been compared with experimental measurements and good agreement has been obtained. Therefore, the proposed method is efficient in calculating the d.c. triggering currents.     

多层压电结构中声表面波特性的计算

The propagation properties of the surface acoustic waves(SAWs) in a ZnO-SiO2-Si multilayered piezoelectric structure are calculated by using the recursive asymptotic method.The phase velocities and the electromechanical coupling coefficients for the Rayleigh wave and the Love wave in the different ZnO-SiO2-Si structures are calculated and analyzed.The Love mode wave is found to be predominantly generated since the c-axis of the ZnO film is generally perpendicular to the substrate.In order to prove the calculated results,a Love mode SAW device based on the ZnO-SiO2-Si multilayered structure is fabricated by micromachining,and its frequency responses are detected.The experimental results are found to be mainly consistent with the calculated ones,except for the slightly larger velocities induced by the residual stresses produced in the fabrication process of the films.The deviation of the experimental results from the calculated ones is reduced by thermal annealing.     

基于层次分析法的引导式电子对抗系统效能评估

文章主要针对引导式电子对抗系统，利用层次分析法计算系统效能。首先，根据其结构组成和干扰过程，建立系统效能评估的层次结构。然后，根据不同的分指标，利用相应的方法计算该指标的值，最后，根据判断矩阵，确定各指标的权重系数，从而计算出引导式电子对抗系统的效能。     

Radiation impedance of a dipole printed on periodic dielectric slabs protruding over a ground plane in an infinite phased array

The radiation impedance of a dipole printed on periodic dielectric slabs standing over a ground plane in an infinite phased array is calculated. The calculation is made by means of modal expansions in terms of longitudinal section electric (LSE) and longitudinal section magnetic (LSM) modes. Derivations of these hybrid space modes and development of the modal expansions are presented first. The impedance of the dipole element is then calculated by a method based on the complex power relations with the aid of Poynting's theorem. The results calculated by the present theory in the limiting case of no dielectric slab loading have been compared with the results calculated by the method of ordinary plane wave expansions. A comparison is also made between results calculated by the theory and the experimental data obtained from waveguide simulators or test array. These results are shown to be in good agreement. An outline of steps to formulate the solution of the current distribution on dipole is also given.     

Calculation of the refractive index of lead-tin-telluride for infrared devices

The refractive indexNof lead-tin-telluride is calculated for frequencies near the fundamental absorption edge. The contribution toNfrom electron states near the band-edges is calculated more exactly than in previous works and a new expression for the contribution from the high frequency region is proposed. Good agreement is obtained between our calculations and experimental results. The change ofNdue to gain in injection laser is also calculated and it is shown that it cannot be neglected.     

安装点数对平板结构热变形的影响

对在轨工作时具有不同的安装点数的平板结构进行了热变形分析计算。对平板结构进行了模型简化并施加了温度载荷和约束条件 ,通过编制的程序 ,计算了平板结构在温度作用和给定约束下的变形、应力和固有频率。通过程序的优选功能 ,获得了满足要求的尽可能少的安装点 ,减重效果明显。文中给出的计算结果 ,对工程设计具有一定的参考意义     

生物组织电导率CMIT平面螺旋激励线圈的分析

计算了平面矩形螺旋线圈的电感值,结果与近似公式计算得出的电感值吻合。另外,通过理论计算发现,矩形平面螺旋线圈产生的磁场具有聚焦的特性,并计算和讨论了分层生物组织的电导率对电感的影响,认为用矩形平面螺旋线圈来做生物组织非接触的电导率成像的激励线圈是可行的。     

Nd:YVO4激光晶体对808nm附近光的吸收特性

研究了Nd:YVO4激光晶体对808nm附近光的吸收。定量给出了不同激活粒子浓度与其吸收808nm光的关系。在测试晶体透过率基础上,通过计算,给出了Nd:YVO4晶体808nm波长光的吸收系数。实验得出了在确定浓度和长度的情况下,晶体对808nm泵浦光吸收系数是一个不与泵浦源功率相关的确定值。计算了п和б两偏振吸收,比较出它们之间的关系。