采用高分辨电镜分析Cu掺杂聚-4-甲基-1-戊烯泡沫材料采用高分辨电镜分析Cu掺杂聚-4-甲基-1-戊烯泡沫材料

利用物理掺杂的方法,制备了铜掺杂聚-4-甲基-1-戊烯(PMP)低密度泡沫材料,采用高分辨扫描电子显微镜和透射电子显微镜,分析了泡沫材料的微观结构、成分及微区成分分布。结果表明:与PMP泡沫相比,铜掺杂PMP泡沫的孔洞直径和网络骨架尺寸变大;铜颗粒镶嵌在PMP泡沫的有机骨架上且有团聚现象;泡沫材料中除碳、铜外,还残留有杂质元素氧;铜颗粒被PMP泡沫包裹,与碳网络骨架之间接触紧密。     

计算机控制光学表面成形中大规模驻留时间求解

采用基于稀疏矩阵的大规模非负最小二乘法,对大口径、微浮雕结构光学元件加工中的驻留时间进行了分析与求解,并对该算法开展了正则化研究。仿真结果表明:与传统非负最小二乘法相比,基于稀疏矩阵的大规模非负最小二乘法精度高、效率快。采用该算法仿真加工平均振幅为1.177 6倍波长的大口径、微浮雕结构光学元件,误差面形均方根收敛至0.067倍波长。     

环形电子束积分图像诊断技术

 采用图像诊断方法对高能环形电子束形状及空间尺寸进行了研究,以高能脉冲环形电子束轰击高Z靶材料产生脉冲X射线,X射线经过X射线增感屏转换为可见光,用单次图像采集系统获取可见光的积分图像。为满足诊断所需的空间分辨和系统灵敏度,通过理论计算确立了靶的材料、厚度及X射线增感屏的型号和厚度等参数。根据测试环境,设计了系统的现场安装结构,系统基本满足测试要求。分析从实验中获取的图像,可知环形电子束的内径为36.5 mm,环厚为1 mm,环形不均匀,水平方向电子束强。     

Investigation on the flameholding mechanisms in supersonic flows: backward-facing step and cavity flameholder

Abstract  

As effective devices to extend the fuel residence time in supersonic flow and prolong the duration time for hypersonic vehicles cruising in the near-space with power, the backward-facing step and the cavity are widely employed in hypersonic airbreathing propulsive systems as flameholders. The two-dimensional coupled implicit RANS equations, the standard k-ε turbulence model, and the finite-rate/eddy-dissipation reaction model have been used to generate the flow field structures in the scramjet combustors with the backward-facing step and the cavity flameholders. The flameholding mechanism in the combustor has been investigated by comparing the flow field in the corner region of the backward-facing step with that around the cavity flameholder. The obtained results show that the numerical simulation results are in good agreement with the experimental data, and the different grid scales make only a slight difference to the numerical results. The vortices formed in the corner region of the backward-facing step, in the cavity and upstream of the fuel injector make a large difference to the enhancement of the mixing between the fuel and the free airstream, and they can prolong the residence time of the mixture and improve the combustion efficiency in the supersonic flow. The size of the recirculation zone in the scramjet combustor partially depends on the distance between the injection and the leading edge of the cavity. Further, the shock waves in the scramjet combustor with the cavity flameholder are much stronger than those that occur in the scramjet combustor with the backward-facing step, and this causes a large increase in the static pressure along the walls of the combustor.     

Parallel synthesis of natural product-like polyhydroxylated pyrrolidine and piperidine alkaloids

The preparation of natural product-like polyhydroxylated pyrrolidine and piperidine alkaloids using a combination of solid– and solution-phase organic synthesis is described. The key intermediates, enantiopure five- or six-membered tri-O-benzyl cyclic nitrones, were efficiently prepared on solid support from accessible chiral furanosides and pyranosides, respectively. The substituent diversity was achieved by a diastereoselective addition of a variety of Grignard reagents to the cyclic nitrones in solution-phase synthesis. All reaction steps and work-up procedures were modified to allow the use of automated equipment. A 36-membered demonstration library with three diversity elements (core, configuration, and substituent) was prepared in good yield and purity.     

Methoxycarbonyl-terminated hyperbranched poly(amine-ester) as templates for synthesis of silver nanoparticles

Highly stable and spherical silver nanoparticles, stabilized by methoxycarbonyl-terminated hyperbranched poly(amine-ester) (HPAE-COOCH₃), were synthesized in water with reducing AgNO₃/HPAE-COOCH₃ using two methods, viz. NaBH₄ and ultraviolet irradiation. HPAE-COOCH₃ was found to play a key role in the formation of nanoparticles. UV–visible absorption, Transmission electron microscopic (TEM), and Fourier transform infrared spectroscopy (FT-IR) had been used to study the structure and characterization of the silver nanoparticles. The absorption peaks of the silver nanoparticles appear at ~420 nm in UV–visible absorption spectra; average particle size reduced by NaBH₄ is ~30 nm, which is ~10 and ~15 nm, respectively, when ultraviolet irradiation time is 12 and 24 h. FT-IR spectra confirm that there is strong interaction between silver nanoparticles and HPAE-COOCH₃. And silver nanoparticles/HPAE-COOCH₃ aqueous solution can keep stable for more than 3 months.     

Leading-order actions of Goldstino fields

This paper starts with a self-contained discussion of the so-called Akulov–Volkov action S_AV\mathcal{S}_{\mathrm{AV}}, which is traditionally taken to be the leading-order action of the Goldstino field. Explicit expressions for S_AV\mathcal{S}_{\mathrm{AV}} and its chiral version S_AV^ch\mathcal{S}_{\mathrm{AV}}^{\mathrm{ch}} are presented. We then turn to the issue on how these actions are related to the leading-order action S_NL\mathcal{S}_{\mathrm{NL}} proposed in the newly proposed constrained superfield formalism. We show that S_NL\mathcal{S}_{\mathrm{NL}} may yield S_AV/S_AV^ch\mathcal{S}_{\mathrm {AV}}/\mathcal{S}_{\mathrm{AV}}^{\mathrm{ch}} or a totally different action S_KS\mathcal{S}_{\mathrm{KS}}, depending on how the auxiliary field in the former is integrated out. However, S_KS\mathcal{S}_{\mathrm{KS}} and S_AV/S_AV^ch\mathcal{S}_{\mathrm {AV}}/\mathcal{S}_{\mathrm{AV}}^{\mathrm{ch}} always yield the same S-matrix elements, as one would have expected from general considerations in quantum field theory.     

Geometries and electronic properties of NbnV(0, ±1) (n = 1−6) clusters studied by density-functional theory

Using density functional theory (DFT) with valence basis set LANL2TZ to study the relative stabilities and electronic properties of the most stable structures of Nb _n V^(0,?±1) (n = 1?6) clusters. The ground state structures of Nb _n V ^(0,?±1) keep the similar geometric structure as the host Nb _n clusters. The doping of vanadium atom enhances the chemical activities of Nb _n clusters. The Nb₃V and Nb₆V are more stable than other clusters. The average binding energy of charged systems (Nb _n V⁺ and Nb _n V^? clusters) are generally larger than neutral Nb _n V clusters natural population analysis shows that there are charge transfers from niobium to vanadium atoms in the small Nb_1?4V, however, for larger clusters (Nb₅V and Nb₆V), the charge transfers are from vanadium to niobium atoms. The vertical and adiabatic ionization potentials (VIP and AIP) are estimated and the vertical one is more close to experimental results.     

A secure quantum key distribution scheme based on variable quantum encoding algorithms

The security of the quantum secret key plays a critical role in quantum communications.Thus far,one problem that still exists in existing protocols is the leakage of the length of the secret key.In this letter,based on variable quantum encoding algorithms,we propose a secure quantum key distribution scheme,which can overcome the security problem involving the leakage of the secret key.Security analysis shows that the proposed scheme is both secure and effective.