多层媒质中声聚焦控制及其用于热疗的分析

基于伪逆算法提出了一种可对多层生物组织中的肿瘤进行声聚焦控制的方法.对一10×10个正方形阵元的相控阵在肿瘤位于不同深度处时产生的声场进行了仿真,同时计算了生物组织内不同时刻的温度分布,并对不同声辐射功率下加热到相同热剂量时的温度分布进行比较.研究结果表明,该方法能快速有效地对不同深度不同尺寸的肿瘤进行准确地声能聚焦控制;声辐射功率越大时,治疗区域中相同等温曲线所围区域较窄;激发频率、声辐射功率及照射时间均相同时,肿瘤在深度较浅位置时治疗区域温度要高,且此区域较粗短,而在较深位置时治疗区域温度相对较低,且此区域变得狭长.     

铌酸锂电光调制器的温度特性研究

采用折射率椭球基本理论和数值计算方法,分析了纵向和横向调制下,出射光光强随温度的变化趋势,以及在这过程中与晶体折射率、晶体热膨胀系数及晶体尺寸间的关系,并进行了相应的数值模拟。结果表明,纵向调制下出射光光强随温度的变化趋势只跟晶体折射率的变化有关;横向调制下出射光光强随温度的变化趋势不仅要受到晶体折射率的影响,还要受到晶体尺寸及其膨胀系数的影响,因此可以利用特殊尺寸的晶体来提高电光调制器的温度稳定性。     

热处理对SiO2薄膜折射率和吸收特性的影响分析

采用离子束溅射技术,在熔融石英基底上制备了SiO2薄膜,并通过椭偏光谱法和表面热透镜技术研究了热处理对其光学特性的影响。热处理对离子束溅射SiO2薄膜折射率影响较大,随着热处理温度增加,SiO2薄膜折射率先减小后增大,当热处理温度为550 ℃时,折射率达到最小。经过热处理后,SiO2薄膜的弱吸收均得到了降低,在2 ppm(1 ppm=10-6)左右,当热处理温度为550 ℃时,获得的SiO2薄膜弱吸收最小仅为1.1 ppm。实验结果表明:采用合适的热处理温度,能大大改善离子束溅射SiO2薄膜的折射率和吸收特性。     

提高系统容错性的软件技术

计算机在现代军事装备中的作用日益重要,他在装备研制中所占工作量的比例越来越大。由于军用计算机的工作环境一般较恶劣,常容易引起计算机电源不稳定等问题,因此,如何保证计算机系统的可靠性已成为影响装备质量的关键因素。本文综合分析嵌入式系统中提高计算机容错性的常用技术,并给出采用软件恢复块实现掉电恢复的实例。     

退火对射频磁控溅射氧化锌薄膜性能的影响

采用射频磁控溅射技术在SiO2/Si上淀积高c轴取向的ZnO薄膜,在氧气和氩气的混合气氛、不同温度(400~900℃)下进行快速热退火处理。利用X-射线衍射(XRD)、原子力显微镜(AFM)、扫描电镜(SEM)和透射电镜(TEM)对薄膜结构、形貌与界面状态性能进行了分析。研究结果表明,ZnO薄膜的晶粒尺寸随着退火温度的升高而增大,衍射峰强度增强,峰位随之偏移;SEM分析显示薄膜呈柱状生长,表现出较好的c轴取向性;TEM分析表明ZnO与下电极Pt是呈共格生长,晶格匹配很好。     

Functionalized Asymmetric Linear Acenes for High‐Performance Organic Semiconductors

A series of compounds from the tetraceno[2,3‐b]thiophene and the anthra[2,3‐b]thiophene family of semiconducting molecules has been made. Specifically, synthetic routes to functionalize the parent molecules with bromo and then hexyl groups are shown. The bromo‐ and hexyl‐functionalized tetraceno[2,3‐b]thiophene and anthra[2,3‐b]thiophene were characterized in the top‐contact thin‐film transistor (TFT) geometry. They give high mobilities, ranging from 0.12 cm² V^?1 s^?1 for α‐n‐hexylanthra[2,3‐ b]thiophene to as high as 0.85 cm² V^?1 s^?1 for α‐bromotetraceno[2,3‐b]thiophene. Notably, grain size increases, going from the shorter anthra[2,3‐b]thiophene core to the longer tetraceno[2,3‐b]thiophene core, with a corresponding increase in mobility. The transition from undesirable 3D to desirable 2D thin‐film growth is explained by the increase in length of the molecule, in this case by one benzene ring, which results in an increase in intralayer interactions relative to interlayer interactions.     

Relevance of Thermal Mismatch in Large-Area Composite Substrates for HgCdTe Heteroepitaxy

It is well known that the large lattice mismatch (>14%) associated with CdTe/Si, CdTe/Ge, and CdTe/GaAs composite substrates, is a great contributor to large dislocation densities and other defects that limit the performance of HgCdTe-based infrared detectors. Though thermal expansion mismatch is another possible contributor to material defects, little work has been done towards documenting and understanding its effects in these systems. Here, we perform studies to determine the relative contributions of lattice and thermal mismatch to CdTe film characteristics, including dislocation density and residual stress. Unannealed and thermally cycled films are characterized using x-ray diffraction, defect decoration, and Nomarski and transmission electron microscopy. For CdTe/Si, the residual stress is consistently observed to be tensile, while for CdTe/Ge and CdTe/GaAs, a compressive residual film stress is measured. We show based on theoretically predicted stress levels that the experimental measurements imply the dominance of thermal mismatch in the residual stress characteristics.     

LCOS显示芯片像素单元热分析

热分析技术是LCoS芯片可靠性设计的关键所在,通过使用有限元分析软件ANSYS建立了LCoS芯片像素单元的有限元模型,严格模拟了LCoS显示芯片工作时像素单元内部的热场分布情况,实验结果为LCoS芯片及其应用系统的热设计提供了重要的数值依据.     

镁锌铁氧体磁芯的工艺研究

针对镁锌铁氧体与镍锌铁氧体磁芯在高频性能和机械强度方面存在的差异,对材料配方,烧结工艺,制料工艺等方面进行了调整。结果表明:起始磁导率μi为50~2000时,镁锌铁氧体磁芯完全可替代镍锌铁氧体磁芯,从而大幅降低原材料成本。     

片式电阻混合焊点热循环负载可靠性研究

对在不同工艺参数下形成的、并且经过不同周数热循环负载的片式电阻混合焊点、有铅焊点和无铅焊点进行了外观检测和剪切测试。结果显示,在不同工艺参数下形成的混合焊点的剪切力,随热循环周数的变化趋势有所不同,但是在保证片式电阻焊端和焊料充分熔融的情况下,部分混合焊点的平均剪切力比有铅焊点高,热循环1 000周后,为9.1～11.1 N。