泡沫铝在SHPB高温动态下的变形过程研究

利用分离式Hopkinson压杆(SHPB)实验装置研究轻质泡沫铝在动态压缩下的温度相关性,重点设计了一种基于SHPB的可视化高温炉,在此基础上通过高速摄影观测泡沫铝试件在高低温且动态压缩下的变形过程。动态加载下的实验结果表明：常温下,胞壁在变形过程中易于观察到屈曲失稳、撕裂、弯曲等现象,且在压缩的过程中碎片飞溅;高温下材料软化较明显,呈现出更多的塑性弯曲现象,但是屈曲失稳与撕裂的现象并不显著,变形过程中并无碎片产生。     

基于Entropy-Topsis模型的军工企业自主创新能力分析与测评

军工企业要提高自主创新能力、努力增强核心竞争力,必须明确地定位创新型企业的发展目标,转型升级军工企业的科技创新模式。本文基于军工企业的自主创新特征,剖析自主创新能力的影响因素,从研发能力、生产能力、投入能力、成果能力和管理能力等视角设置测评指标,建立Entropy-Topsis评价模型,继而测评25个典型军工企业的自主创新能力,验证测评指标和评价模型的科学性和适用性。     

多晶Si薄膜表面金催化Si纳米线生长

以Au膜作为催化剂和大晶粒多晶Si薄膜为衬底,利用固-液-固生长机制,制备出直径在30～ 100 nm和长度为几百微米的高密度Si纳米线.实验研究了退火温度、生长时间和N2流量对Si纳米线生长的影响.结果表明,随着退火温度的升高,生长时间的延长和N2流量的增加,Si纳米线的长度和密度都显著增加.对不同生长时间下获得的Si纳米线样品进行了X射线衍射测量,结果显示随着生长时间的延长,多晶Si薄膜和表面的Au膜成分都在减少.光致发光谱则显示出弱的蓝光发射和强的红光发射特性,前者应是由非晶SiOx壳层中的氧空位发光中心引起,后者则应归因于Si纳米线芯部与非晶SiOx壳层之间界面区域附近中的Si =O双键态或非桥键氧缺陷中心.     

Synthesis,Crystal Structure and Thermal Behavior of 4,5-Dimethoxy-2-(dinitromethylene)imidazolidine

A new energetic material, 4,5-dimethoxy-2-(dinitromethylene)imidazolidine(DMDNI), was synthesized by the reaction of 4,5-dihydroxyl-2-(dinitromethylene)-imidazolidine(DDNI) and methanol, and structurally characterized by single crystal X-ray diffraction. DMDNI crystallized in triclinic space group P, with crystal data a=0.4324(4) nm, b=1.3599(11) nm, c=1.7503(14) nm, α=77.406(14)°, β=84.494(15)°, γ=87.976(14)°, V=0.9997(14) nm³, Z=4, μ＝0.140 mm^-1, F(000)=488, D_c=1.556 g/cm³, R₁=0.0773 and wR₂=0.1574. Thermal decomposition of DMDNI was studied, and its thermal decomposition process was divided into two stages. The first stage was a mel- ting process and the second stage was an exothermic decomposition process. The enthalpy, apparent activation energy and pre-exponential constant of the exothermic decomposition reaction are -491.5 J/g, 142.3 kJ/mol and 10^14.24 s^-1, respectively. The critical temperature of thermal explosion is 162.47℃. DMDNI has a lower thermal stability than DDNI but it is close to that of 4,5-diacetoxyl-2-(dinitromethylene)-imidazolidine(DADNI).     

Synthesis and Temperature-dependent Electrochemical Properties of Boron-doped Diamond Electrodes on Titanium

On the sand-blasting-treated titanium(Ti) substrate, the boron-doped diamond(BDD) electrodes with a wide potential window were prepared by microwave plasma chemical vapor deposition(MPCVD). The electrochemical oxidation ratios of phenol at BDD/Ti electrodes at elevated temperatures(from 20 ℃ to 80 ℃) were examined by the chemical oxygen demand(COD) of phenol electrolyte during electrolysis. The results show that the COD removal was increased at high temperatures and the optimized temperature for enhancing the electrochemical oxidation ratio of phenol is 60 ℃. The mechanism for the temperature-dependent electrochemical oxidation ratios of phenol at the electrodes was investigated. The study would be favorable for further improving the performance of BDD/Ti electrodes, especially working at high temperatures.     

Dual-band frequency selective surface with large band separation and stable performance

A new technique of designing a dual-band frequency selective surface with large band separation is presented.This technique is based on a delicately designed topology of L-and Ku-band microwave filters.The two band-pass responses are generated by a capacitively-loaded square-loop frequency selective surface and an aperture-coupled frequency selective surface,respectively.A Faraday cage is located between the two frequency selective surface structures to eliminate undesired couplings.Based on this technique,a dual-band frequency selective surface with large band separation is designed,which possesses large band separation,high selectivity,and stable performance under various incident angles and different polarizations.     

Stability of sp carbon (carbyne) chains

An sp carbon chain, which contains only one carbon atom in its cross section, is generally considered unstable. In this Letter, however, the DFT calculations showed that an isolated sp carbon chain is more stable than the smallest armchair (3,0) and zigzag (2,2) single-walled carbon nanotubes (SWCNT). This is consistent with the fact that an isolated sp carbon chain was observed by high-resolution transmission electron microscopy, but isolated (3,0) and (2,2) SWCNTs were never produced. Nevertheless, the sp chain is less stable than lager SWCNTs.     

Novel W-shaped and straight porous ZnO nanobelts

Novel W-shaped porous ZnO nanobelt with the periodical junction angles of about 118° and straight porous ZnO nanobelt have been successfully synthesized. The W-shaped structure growth changes from [0 0 0 1] to periodically. The straight nanobelt grows along [0 0 0 1] direction. Both of the structures have smooth surfaces with high porous density. Based on our X-ray diffraction (XRD), electron microscopy and photoluminescence (PL) spectrum study, the growth mechanism of the special ZnO nanostructures is discussed, emphasizing the effect of alteration of the reactant concentration for two different morphologies.     

间甲基苯甲酸的THz时域光谱

利用THz时域光谱技术测量了间甲基苯甲酸在0.2 ~1.8 THz频率范围内的振动光谱,结合密度泛函理论计算的振动光谱,对观测到的强振动吸收峰进行了指认. 比较不同的芳香化合物的振动光谱,间甲基苯甲酸分子的特征振动峰与其他芳香化合物的振动特征峰在0.2~1.8 THz频率范围内明显不同.