Thickness Dependence of Photoconductance in Strained BiFeO3 Thin Films With Planar Device Geometry

The recent discovery of efficient charge separation in tetragonal–rhombohedral (T‐R) polymorphic phase boundaries (PPBs) in strained BiFeO₃ (BFO) films is of great interest, and also raised a question of whether the PPBs could enhance the performance of BFO‐based planar photodetectors. To address it, we prepare BFO films with thickness ranging from 8 to 90 nm on the LaAlO₃ substrates, in which the BFO evolves from a pure T phase (without PPBs) to a T‐R mixed phase (with PPBs) due to the strain relaxation. Then, we comparatively investigate the photoconductive properties of these BFO films with the planar device geometry. It is found that the photoconductance first increases and then decreases with increasing film thickness. Particularly, the 50‐nm film containing the pure T phase without any detectable PPBs exhibits the highest photoconductance. This unexpected observation can be understood by analyzing the effects of increasing film thickness and associated phase evolution on the photoconduction‐related parameters.     

铒纤长度对掺铒光源性能影响的实验研究

实验演示了铒纤长度的选择对1550 nm双通后向超荧光掺铒光纤光源(DPB SFS)的平均波长以及谱宽性能的影响,特别是对平均波长稳定性的影响,实验分析了－20℃~60℃之间光源固有平均波长的变化,最终得到了铒纤固有热系数以及整个样机的平均波长稳定性随铒纤长度变化的实验曲线,对超荧光掺铒光纤光源的器件选择和优化设计具有重要参考价值.     

微腔有机电致发光器件角度依赖性的模拟与实验验证

为了分析微腔有机电致发光器件(MOLED)发光的角度依赖性,根据微腔计算公式,采用传输矩阵法进行了模拟计算,并进行了实验验证。所设计器件的结构为Glass/DBR/ITO(58 nm)/NPB(46 nm)/DPVBi(20 nm)/Alq₃(56 nm)/LiF(1 nm )/Al(150 nm)。由实验得到的电致发光(EL)谱可以观察到:随着探测角度的加大,发光峰蓝移、强度减小。与模拟得出的不同观测角度下的反射谱进行比较,发现透射峰值与EL峰值相对应。模拟分析发现,这是由于观测角不同,微腔两个反射镜的S和P偏振的反射率及反射相移不同,同时腔内光学厚度发生变化,即微腔长度变化共同作用所导致。     

三级GEM气体探测器性能的实验研究

GEM探测器是一种新型微型气体探测器(Micro-Pattern Gas Detector), 在粒子物理实验及低能X射线成像系统中有着较大的应用前景. 文章研制了一种适用于低能X射线成像和带电粒子径迹测量的三级GEM气体探测器. 使用放射源⁵⁵Fe对其气体放大特性、电荷传输效率及能量分辨本领等性能进行了实验研究, 重点研究了传输区电场对气体有效增益和能量分辨本领的影响. 实验结果表明, 三级GEM探测器的暗电流和噪声较小, 有效增益能够达到10⁵以上并稳定地工作, 对5.9keV的X射线能量分辨率可达24%, 传输区电场强度大于3000V/(cm.atm)时, 能量分辨率基本稳定在30%左右.     

新型送风末端装置性能的实验研究

对新型送风装置的出风特性进行了实验研究。结果表明 ,该种结构末端装置能产生所要求的动态风 ,其出风速度变化与控制信号变化有很好的一致性 ;当控制信号为模拟自然风时 ,出风速度频谱分析表明 ,在低频段能量较高 ,高频段能量较低 ,变化剧烈 ,与自然风的频谱非常相似 ;而在稳态时 ,频谱变化比较平缓。该送风末端的紊流系数为 0 .0 97;在距离地面 1.1m的高度上 ,速度分布在射流方向速度较高 ,但是覆盖面积较小 ,有待进一步研究改进。     

Numerical Study on the Performance in High-bit-rate Optical Communication Systems

By numerical simulations, we show that picosecond Gaussian optical pulses with a precise optimal frequency chirping can transmit stably in full-dispersion compensation optical fiber links, with not only second- but also third-order dispersion compensation, using dispersion shift fibers with opposite dispersion sign. The optimal pre-chirp is determined principally by the second-order dispersion scheme and scarcely affected by third-order dispersion scheme. It demonstrates that, to a high bit rate transmission system, the pre-chirping technology and higher-order dispersion compensation are two very efficient measures in improving performance of system.     

切割式双模战斗部毁伤元成型及侵彻钢靶特性研究

 基于60 mm弧锥结合罩爆炸成型弹丸（EFP）装药,设计了一种在药型罩前适当位置安装可抛掷的十字形网栅的切割式双模战斗部结构,其具有生成单个EFP或者多爆炸成型弹丸（MEFP）的功能;根据目标属性,可选择性地改变战斗部的毁伤元成型模式,实施最有效的打击。利用LS-DYNA程序,对两种模式毁伤元成型及侵彻45钢靶过程特性进行了数值模拟,模拟结果与地面静爆实验结果吻合较好。研究表明,该战斗部形成的单个EFP能贯穿25 mm厚45钢靶,可有效打击重装甲目标;经网栅切割后能形成5片具有一定质量和方向性、可贯穿6 mm厚45钢靶的EFP破片,显著提高了对轻装甲目标的毁伤概率。     

微腔有机电致发光器件的角度依赖性

设计并制作了两个器件,一个是微腔有机电致发光器件(MOLED):G/DBR/ITO/NPB(46 nm)/DPVBi(20 nm)/Alq₃(56 nm)/LiF(1 nm)/Al(150 nm);一个是无腔器件(OLED):G/ITO/NPB(46 nm)/DPVBi(20 nm)/Alq₃(56 nm)/LiF(1 nm)/Al(150 nm)。测试并分析了器件性能。OLED在电流密度30 mA/cm²时的电致发光(EL)光谱随观测角度由0°~70°都是一宽谱带,是发光层DPVBi的特征发光谱,峰值都在452 nm处,半峰全宽均为70 nm,色坐标均为(x=0.18,y=0.19),无腔器件没有角度依赖性。相同电流密度下,微腔器件的EL谱随观测角度由0°~70°,发光峰值蓝移,由472 nm逐渐移至428 nm;峰值相对强度渐弱,由0.32变至0.02;半峰全宽由14 nm增加至120 nm;色坐标由(x=0.14,y=0.10)变至(x=0.19,y=0.25),颜色由紫蓝变成蓝白到接近白色。微腔器件具有明显的角度依赖性。     

菲涅耳公式的研究及数值模拟

菲涅耳公式阐述了光在两种不同透明介质的分界面上,发生反射和折射现象时,反射光、折射光的振幅变化规律。本文通过对菲涅尔公式的变形处理,得到了新的表达形式,并且应用Matlab软件进行了数值模拟,使菲涅耳公式的物理意义更清晰明了。     

尾翼型爆炸成型弹丸的数值模拟及实验研究

 在药型罩上粘附铝隔板是一种新的形成尾翼型爆炸成型弹丸（Explosively Formed Projectile,EFP）的实验方法。通过实验和数值模拟对该方法进行了分析,探讨了形成尾翼的机理。利用有限元分析软件LS-DYNA,对大锥角型、球缺型和弧锥结合型3种不同药型罩在采用新方法时形成的尾翼型EFP进行了三维数值模拟分析,并将模拟结果与实验结果进行对比。研究结果表明：3种药型罩均能形成比较明显的尾翼,数值计算结果与实验结果较吻合。该研究为设计尾翼型EFP提供了一种新的参考方法。     

终端设备环境温度检测算法及实验研究

环境温度对于终端电子设备的功耗和温度管理至关重要,而设备内部的温度传感器受内热源影响无法直接检测所在环境的温度。因此,针对含有多个瞬态内热源的终端设备,本文提出基于传热反问题迭代求解的实时环境温度检测算法。通过简化热容热阻网络模型建立系统传热方程,提出双传感器预测偏差修正策略解决由于已知量不足产生的不适定性。此外,基于实际智能手机的实验结果表明算法对实时动态环境温度的检测相对误差在10%以内。     

An Experimental Study on the Performance of a Loop Heat Pipe

Modern electronics require better thermal management technologies to ensure long lifetime stability and reliable working. Aiming to evaluate the feasibility for a loop heat pipe being used for the heat dissipation of electronics, a stainless-steel/water loop heat pipe is design and an experimental system to study its heat transfer performance is set up. Experimental results show that at optimal heat load and with the loop heat pipe being aligned perpendicularly to the horizontal plane, its thermal resistance is lowered to be ～0.27 K/W. The loop heat pipe also shows good startup characteristics and can steadily work as well. All these indicate that the loop heat pipe has the potential to be a good solution for cooling of modern electronics.     

含铝炸药水下爆炸性能的实验研究

对RS211、HL-1、HL-2这3种含铝炸药和TNT炸药进行了水下爆炸实验,测量了4种炸药水下爆炸冲击波压力剖面和气泡脉动周期,获得了4种炸药水下爆炸冲击波的峰值超压、冲量、能量和气泡能。实验结果表明,在所研究的范围内,与TNT炸药相比,含铝炸药的冲击波能量有明显增加,约为TNT炸药的1.20～1.35倍,气泡能有显著增加,约为TNT炸药的1.50～2.30倍,表明在炸药中加入铝粉对于提高炸药水中爆炸威力是有益的。     

FAE装置参数对燃料抛撒与爆炸威力影响的实验研究

 采用高速运动分析系统对FAE实验装置爆炸抛撒过程进行观测,描述了燃料抛撒过程的不同阶段,实验研究了比药量、长径比、壳体材质等装置参数对燃料抛撒与爆炸威力的影响。结果表明,燃料抛撒过程可分为射流形成与扩散运动阶段、燃料两向膨胀运动阶段和气液融合运动阶段。不同阶段对应不同的流体动力学特征,对云团形成的贡献不同。在实验装置总体优化条件下,适当增大比药量可提高云团覆盖面积与体积;在实验范围内长径比不是影响云团状态的显著因素,但长径比较大时可使燃料抛撒均匀性更好;采用钢质壳体时云雾抛撒状态明显优于铝质壳体。实验证明,采用碳钢壳体、比药量3%左右、长径比为3~5且装置参数良好匹配时,可获得理想的云团状态和高威力爆炸波毁伤效应。     

Experimental and Numerical Study of Aerosol Coagulation by Gravitation

The behaviors of aerosols having particle diameters of 1–5 μm were studied experimentally and the results were compared with numerical calculations. For the experimental study, a specially designed coagulation cylinder was developed and the moment method was used in the numerical predictions. The experimental results were characterized by the size parameters including the geometric mean diameter (GMD), the geometric standard deviation (GSD) and the particle number concentration (N). Particle distributions in the cylinder were measured at certain time intervals. In a closed cylinder, the mechanism governing aerosol behavior appeared to be gravitational coagulation. Separately, the numerical calculations were carried out using the moment method. The experimental results and the numerical predictions were in reasonable agreement. It is believed that the present work represents the first experimental study on gravitational coagulation.     

Numerical and Experimental Study of an Optimized p-SOS Diode

Technical Physics - We report on the results of experimental investigation and numerical simulation of switching of SOS diode with p+P0n+ structure and with reduced thickness of P0-base. The...     

Experimental and Numerical Study of Free Convection on an Isothermal Downward Cone

Abstract

The laminar free-convection heat transfer from an isothermal downward cone in air is investigated experimentally and numerically. The experimental investigation is carried out by Mach-Zehnder interferometery technique and the numerical simulation was done by Fluent. The cone tip angle has been kept constant to 45° and it was suspended from its base throughout the experiment. This article focuses on the effect of Rayleigh number variation on the local and average free-convection heat transfer coefficient over the conical surface. The local and average Nusselt numbers were determined for the Rayleigh number range of 4.9×10⁵ to 1.1×10⁶. Also, the experiment and the numerical simulation were carried out on a vertical isothermal cylinder of circular cross section in order to compare results with other researchers for the verification of our experimental and numerical results. The significant influence of the upper end surface of the cone, both in the experimental and numerical studies, indicated a recirculation region above the upper end surface which affects the local convection heat transfer at the slant trailing edge and causes it to increase. Also, a correlation for the calculation of the local Nusselt number over the cone is proposed.     

Numerical Study on the Performance in High bit rate Optical Communication Systems

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结霜工况下的冷风机传热性能试验研究

文中对冷风机在结霜工况下的传热性能进行了试验研究 ,简述了结霜工况下传热系数测试的原理、方法和主要过程。根据实验结果对影响冷风机传热性能的主要因素进行了分析 ,并得出了一些有益的结论