几何参数对喷射器性能的影响分析

运用计算流体动力学软件Fluent对喷射器进行数值模拟,研究了工作喷嘴喉部直径、等截面混合室直径和长度等几何参数对喷射器性能的影响,并对数值模拟结果进行了分析。研究表明:在一定的工况下,工作喷嘴及等截面混合室对喷射器性能有极大的影响,存在最佳的喉部和混合室直径使得喷射系数最大;随着混合室长度的增加,喷射器的喷射系数将逐渐降低。     

Degradation and recovery properties of AlGaN/GaN high-electron mobility transistors under direct current reverse step voltage stress

Direct current (DC) reverse step voltage stress is applied on the gate of AlGaN/GaN high-electron mobility transistor (HEMT). Experiments show that parameters degenerate under stress. Large-signal parasitic source/drain resistance (R_S/R_D) and gate-source forward I-V characteristics are recoverable after breakdown of the device under test (DUT). Electrons trapped by both the AlGaN barrier trap and the surface state under stress lead to this phenomenon, and surface state recovery is the major reason for the recovery of device parameters.     

Micromechanism of sulfurizing activated carbon and its ability to adsorb mercury

The effect of ambient environment (dry or wet) and overlapping laser pulses on the laser ablation performance of brass has been investigated. For this purpose, a Q-switched, frequency doubled Nd:YAG laser with a wavelength of 532 nm, pulse energy of 150 mJ, pulse width of 6 ns and repetition rate of 10 Hz is employed. In order to explore the effect of ambient environments, brass targets have been exposed in deionized water, methanol and air. The targets are exposed for 1000, 2000, 3000 and 4000 succeeding pulses in each atmosphere. The surface morphology and chemical composition of ablated targets have been characterized by using Scanning Electron Microscope (SEM), Atomic Force Microscope (AFM) and Attenuated Total Reflection (ATR) techniques. In case of liquid environment, various features like nano- and micro-scale laser-induced periodic surface structures with periodicity 500 nm–1 μm, cavities of size few micrometers with multiple ablative layers and phenomenon of thermal stress cracking are observed. These features are originated by various chemical and thermal phenomena induced by laser heating at the liquid–solid interfaces. The convective bubble motion, explosive boiling, pressure gradients, cluster and colloid formation due to confinement effects of liquids are possible cause for such kind of features. The metal oxides and alcohol formed on irradiated surface are also playing the significant role for the formation of these kinds of structure. In case of air one huge crater is formed along with the redeposition of sputtered material and is ascribed to laser-induced evaporation and oxide formation.     

太赫兹聚合物光子晶体光纤关键制备工艺研究

针对太赫兹聚合物光子晶体光纤的应用需求,对聚合物光纤的制备材料、预制棒制备、拉伸工艺等关键制备工艺进行了研究.分析了聚合物材料的特性,并进行实验验证,结果表明ZEONEX材料的吸收系数低于3cm~(-1),吸水性低于0.01%,玻璃化转变温度和分解温度分别高达136℃和420℃,在太赫兹光纤制备中具有优良性能.预制棒制备和光纤拉伸的工艺方面,在注塑法的基础上改进了模具系统,使用可控的微压拉丝技术,在10200Pa范围内可实现±1.5Pa的微压差精确控制,较大程度上提高了光纤预制棒的成品率和光纤的形变控制,有望制备出高空气填充率的聚合物光子晶体光纤.     

基于腐蚀光纤的温度及葡萄糖溶液浓度传感器

提出并制备了一种基于本征倏逝波原理的温度及葡萄糖溶液浓度传感器.通过研究腐蚀包层厚度与透射光谱之间的关系,确定较为合适的腐蚀厚度.将标准单模光纤包层腐蚀至2.4μm,利用光纤倏逝波对外界介质变化敏感的原理,通过测量输出光功率的变化量实现温度及葡萄糖溶液浓度传感.实验结果表明:传感器在1070℃的温度范围内具有9.58×10~(-3) dBm/℃的灵敏度,线性度达到99.36%;在葡萄糖溶液03%的浓度范围内具有0.126dBm/(g/L)的灵敏度,线性度达到97.95%.该传感器的响应时间小于30s,具有操作简便、测量准确度高、重复性好、适用范围广等优点,具备良好的应用价值.     

Computational design and screening of promising energetic materials: Novel azobis(tetrazoles) with ten catenated nitrogen atoms chain

Density functional theory methods were used to study on 2 N10 compounds, 1,1′‐azobis(tetrazole) and 1,1′‐azobis(5‐methyltetrazole). We systematically investigated 10 novel substituted azobis(tetrazoles) with 10 catenated nitrogen atoms and various energetic groups (–CF₃ 1 , –C(NO₂)₃ 3 , –N₃ 5 , –NH₂ 6 , –NHNH₂ 7 , –NHNO₂ 8 , –NO₂ 9 , –OCH₃ 10 , –OH 11 , –ONO₂ 12 ). The optimized geometry, frontier molecular orbitals, electrostatic potential, Infrared and nuclear magnetic resonance spectrum were calculated for inspecting the molecular structure and stability as well as chemical reactivity. The effects of different substituents on the density, enthalpy of formation, heat of explosion, detonation velocity and pressure, and sensitivity of the azobis(tetrazole) derivatives have been investigated. Compound 9 with nitro was found to have remarkable detonation performances (D = 9.61 km/s, P = 42.14 GPa), which are close to the excellent explosive CL‐20. Results show that compounds 1 , 3 , 4 , 7 , 9 , 11, and 12 have high potential to replace RDX. It is surprising that compounds 1 , 3 , 9, and 12 possess better energetic properties than HMX. These novel substituted azobis(tetrazoles) with unique N10 structure may be promising candidates of HEDMs with outstanding performance and acceptable sensitivities.     

Renal Clearable Luminescent WSe2 for Radioprotection of Nontargeted Tissues during Radiotherapy

High‐energy ionizing radiation is widely used in medical diagnosis and cancer radiation therapy. However, high‐energy radiation can also impose significant damages in healthy tissues during medical treatments via direct DNA damages and indirect damages from production of reactive oxygen species (ROS). Therefore, it is urgent to develop highly effective radioprotectants with low toxicities that can meet the increasing needs for alleviating the adverse effects from cancer radiation therapy and nuclear emergency. In this work, strongly catalytic ultrasmall (sub‐5 nm) cysteine‐protected WSe₂ dots are employed to protect healthy tissues against radiation via diminishing radiation‐induced free radicals. The WSe₂ dots with high surface activities can recover radiation‐induced DNA damages and eliminate the excessive ROS generated from radiation. In vivo experiments confirm that the survival rate of mice treated with WSe₂ dots is significantly elevated with radiation damages postponed under exposure to high‐dose ionizing radiation. Furthermore, the free radicals in major organs and hematological system can be appreciably omitted, suggesting their unique role as free radical scavengers. These WSe₂ dots in ultrasmall size show rapid renal clearance of ≈74% injection dose via urine excretion in 24 h and do not cause any apparent toxicity in vivo for up to 30 d.     

负折射指数物质中金属线对电磁波的影响

构造两种结构负折射指数物质(NRM)，利用数值模拟计算两种结构的S参数.由于这种结构尺度比波长小，为精确利用有限积分技术(FIT)进行模拟.通过对这两种结构中金属线位置变化对金属谐振频率影响进行模拟，最后得出由于金属线与谐振环耦合，金属线对称破缺影响谐振环谐振频率和通带，并对等效负折射指数为负的频带产生影响. 关键词： 负折射率 左手物质 通带 金属线对称破缺     

Preparation and characterization of poly(lactic acid)/poly(methyl methacrylate) blend tablets for application in quantitative analysis by micro Raman spectroscopy

Poly(lactic acid) (PLA) is a biodegradable polymer that has a variety of applications, one of which is as biomaterial in surgery or as functional layers on implants, due to its compatibility with living tissue. This paper reports the possibilities of quantification of poly(lactic acid) (PLA) in a polymer matrix such as poly(methyl methacrylate) (PMMA) by micro Raman spectroscopy (MRS). Blends of amorphous poly(DL‐lactic acid) with poly(methyl methacrylate) were prepared by the procedure of dissolution/precipitation. Thermal properties of the blends such as the glass transition temperature (Tg) were characterized by differential scanning calorimetry (DSC). The PLA/PMMA blends exhibited only a single glass transition region, indicating that this system is miscible. The PLA/PMMA system obeys the Gordon–Taylor equation (Tg versus PLA content). Various concentration ratios of PLA blends were prepared to use as a basis for quantitative analysis by MRS. Intensities of the characteristic bands at 813 cm⁻¹ (νCOC of PMMA) and 873 cm⁻¹ (νC―COO of PLA) were used for the calculation. The calibration graph showed a good linear correlation with an R² value of 0.9985. On the basis of the calibration curve obtained, the determined content of several PLA/PMMA blends was in good agreement when compared with nominal contents. The limit of detection (LOD) and quantification (LOQ) were calculated by the calibration data set as signal‐to‐noise method. The relative standard deviation of this method was lower than 10% and the accuracy better than 4%. This study demonstrated that Raman spectroscopy provides an alternative non destructive method for quantitative analysis of PLA in a PMMA matrix. Copyright © 2015 John Wiley & Sons, Ltd.