固态热容激光器3维瞬态热畸变模拟分析

 根据固态热容激光器的动态工作特性,考虑热力学参数与温度的关系,采用3维有限差分方法模拟分析了薄片热容激光器的3维温度和热应力分布随时间的变化关系。计算了热容激光器的热畸变和退偏损耗随时间的动态变化规律,并与采用连续水冷却方式工作的圆棒激光器的热畸变特性做了比较。模拟结果显示,形变是引起波前相位畸变的主要因素,退偏损耗随泵浦时间增加和泵浦功率增大而非线性增大。     

子束排列方式对固体激光器光束合成特性的影响

 建立了固体激光器矩形光斑光束合成的理论模型,对诺·格公司给出的2束、4束、8束合成实验结果进行分析,并通过数值模拟,得到了不同子束排列方式下合成光斑的远场图形。通过仿真模拟可以得出:排列结构影响远场光斑的形状;子束间距决定了合成光束远场光斑的衍射旁瓣的大小和多少。采用环围能量进行分析,研究了远场光斑中主瓣能量随激光阵列占空比的变化。结果显示,远场光束环围功率随子束间距的增大而逐渐下降,而且参与相干合成子束越多,下降越大。     

平面飞片下气体绝热压缩后的聚能效应——两次不寻常的爆炸实验结果

揭示了可以展现垂直高速飞行的飞片在碰撞目的物的瞬间会产生极高速气流的聚能效应现象.在一般的爆炸压实实验中,飞片下的空间都是大气状态下的空气,空气量都很少,不会超过1 g,但在飞片高速飞行状态下,大多数气体很难向四周排出,最后形成绝热压缩气体,气流以万米/秒以上高速向四周喷射在出能量可切断很厚的钢板.这是从未被注意过的、...     

重载操作机钳臂结构多工况拓扑优化设计

钳臂是重载操作机夹持机构的重要组成部分,其力学性能和疲劳性能直接影响着操作机的正常使用功能.本文针对重载锻压操作机钳臂结构进行了典型工况下的力学性能分析,在此基础上对钳臂结构进行了多工况拓扑优化,给出了材料布局以及力的最优传递路径,并进一步进行尺寸优化.结果表明,优化后的钳臂结构在保持良好力学性能的同时,减少了材料用量...     

The effect of a HfO2 insulator on the improvement of breakdown voltage in field-plated GaN-based HEMT

A GaN/Al_0.3Ga_0.7N/AlN/GaN high-electron mobility transistor utilizing a field plate (with a 0.3 μm overhang towards the drain and a 0.2 μm overhang towards the source) over a 165-nm sputtered HfO₂ insulator (HfO₂-FP-HEMT) is fabricated on a sapphire substrate. Compared with the conventional field-plated HEMT, which has the same geometric structure but uses a 60-nm SiN insulator beneath the field plate (SiN-FP-HEMT), the HfO₂-FP-HEMT exhibits a significant improvement of the breakdown voltage (up to 181 V) as well as a record field-plate efficiency (up to 276 V/μm). This is because the HfO₂ insulator can further improve the modulation of the field plate on the electric field distribution in the device channel, which is proved by the numerical simulation results. Based on the simulation results, a novel approach named the proportional design is proposed to predict the optimal dielectric thickness beneath the field plate. It can simplify the field-plated HEMT design significantly.     

1-3型压电复合材料宽带水声换能器研究

1-3型压电复合材料换能器具有重量轻、声阻抗率低等优点,复合材料换能器带宽的拓展一般采用匹配层的方法.采用厚度振动模态理论、横向模态理论和有限元方法对1-3型压电复合材料换能器进行研究,应用ANSYS软件建立换能器的有限元模型,然后进行结构优化,最终制作了一个利用厚度振动模态和一阶横向模态的1-3型压电复合材料宽带换能...     

CoFe2O4纳米晶与牛血清白蛋白和牛血红蛋白的相互作用：吸附、纳米晶的团聚及蛋白构象的变化

水热制备了约10nm的CoFe₂O₄纳米晶,通过Zeta电势、动态光散射（Dynamic Light Scattering,DLS）和傅立叶变换红外光谱（FTIR）技术研究了纳米晶与牛血清白蛋白（Bovine Serum Albumin,BSA）和牛血红蛋白（Hemoglobin）的相互作用。纳米晶对BSA和血红蛋白都有很强的吸附,其中对血红蛋白的吸附符合静电吸附的规律,而对BSA的吸附则不符合静电吸附的规律。在pH=5.5和7.0时纳米晶对BSA和血红蛋白的吸附容量分别达到237.9mg·g^-1和256.9mg·g^-1。DLS结果表明蛋白质能够导致纳米晶团聚。吸附BSA或血红蛋白后,纳米晶的DLS粒径由51nm分别增大到472nm和114nm。CoFe₂O₄纳米晶还导致了蛋白质FTIR谱发生明显变化。BSA和血红蛋白的酰胺I带由于纳米晶的作用分别减少了4cm^-1和6cm^-1。     

生物过滤器中非均匀性流动的数值研究

生物过滤技术因其具有有效性、低成本和环境友好等优点引起了人们的广泛关注.该技术主要通过生物过滤器去除含有H2S等废气的有毒有害气体.运用格子Boltzmann方法对三种生物过滤器模型中多孔介质的非均匀性流动进行了数值模拟.数值模拟结果表明,多孔介质的性质和进口流动条件对临界Rayleigh数有显著影响,临界Rayleigh数随着多孔介质的孔隙度和Darcy数的增大而逐渐变小,并随着进口Reynolds数的增大而逐渐变大.所得结果可望为生物过滤器的优化设计提供一个合理的理论依据.     

DEIReconstructor:a software for diffraction enhanced imaging processing and tomography reconstruction

Diffraction enhanced imaging (DEI) has been widely applied in many fields, especially when imaging low-Z samples or when the difference in the attenuation coefficient between different regions in the sample is too small to be detected. Recent developments of this technique have presented a need for a new software package for data analysis. Here, the Diffraction Enhanced Image Reconstructor (DEIReconstructor), developed in Matlab, is presented. DEIReconstructor has a user-friendly graphical user interface and runs under any of the 32-bit or 64-bit Microsoft Windows operating systems including XP and Win7. Many of its features are integrated to support imaging preprocessing, extract absorption, refractive and scattering information of diffraction enhanced imaging and allow for parallel-beam tomography reconstruction for DEI-CT. Furthermore, many other useful functions are also implemented in order to simplify the data analysis and the presentation of results. The compiled software package is freely available.     

High-efficiency S-band harmonic tuning GaN amplifier

In this paper, we present a high-efficiency S-band gallium nitride （GaN） power amplifier （PA）. This amplifier is fabri- cated based on a self-developed GaN high-electron-mobility transistor （HEMT） with 10 mm gate width on SiC substrate. Harmonic manipulation circuits are presented in the amplifier. The matching networks consist of microstrip lines and discrete components. Open-circuited stub lines in both input and output are used to tune the 2rid harmonic wave and match the GaN HEMT to the highest efficiency condition. The developed amplifier delivers an output power of 48.5 dBm （70 W） with a power-added efficiency （PAE） of 72.2% at 2 GHz in pulse condition. When operating at 1.8-2.2 GHz （20% relative bandwidth）, the amplifier provides an output power higher than 48 dBm （,-~ 65 W）, with a PAE over 70% and a power gain above 15 dB. When operating in continuous-wave （CW） operating conditions, the amplifier gives an output power over 46 dBm （40 W） with PAE beyond 60% over the whole operation frequency range.