Highly efficient Raman conversion in O2 pumped by a seeded narrow band second-harmonic Nd:YAG laser

The first-Stokes conversion efficiency for a stimulated Raman scattering (SRS) is usually very low in gaseous oxygen media. In 3.0 Mpa O₂, a single longitudinal mode second harmonic Nd:YAG laser pump source gives a typical vibrational first-Stokes conversion efficiency of only 2.5%, In comparison, the accompanying stimulated Brillouin scattering (SBS) attains a reflectivity of 67%. However, by seeding an OPO beam into the Raman cavity, the first-Stokes photon conversion efficiency now attains a peak value of 54%, while the SBS reflectivity reduces to 5% in a 6.1 Mpa 41:59 O₂/ He mixture. This 54% efficiency was obtained for a seeder laser pulse-width less than one half that of pump laser (6.8 ns). A first-Stokes peak power conversion efficiency as high as 88% has been obtained when the pump and seeder pulse peaks coincide. So, we may expect a higher first-Stokes photon conversion efficiency if the seeder pulse-width can be made equal to or larger than that of the pump pulse. On the other hand, the beam quality of the first-Stokes in an O₂/ He mixture excels that of the pump laser for a seeder energy of 5 mJ and pump energy of 50 mJ. However, at pump energies higher than 105 mJ and a pump laser repetition rate of 10 Hz, the thermal defocusing effect worsens the first-Stokes beam quality. This thermal defocusing effect is a result of the Raman heat release and could be eliminated by fast circulating and cooling the Raman gas medium.     

Structural characteristics of 2024 aluminum alloy plasma-based ion implanted with nitrogen then titanium

As an interlayer in the gradient layers such as AlN/Ti/TiN/DLC prepared by plasma-based ion implantation (PBII) on 2024 aluminum alloy, titanium layer plays an important role in enhancing adhesion, reducing thermal stress, limiting the crack propagation, etc. A series of dual-layers prepared by PBII with nitrogen then titanium at various sputtering currents of titanium target on 2024 aluminum alloy have been reported in this paper. The composition distributions and the chemical states are analyzed using X-ray photoelectron spectroscopy (XPS). The structures are studied with grazing X-ray diffraction (GXRD). The results show that PBII with titanium strongly depends on the sputtering current. It is found that there exists a critical sputtering current corresponding only to a titanium-implanted layer containing TiAl₃. When the sputtering current exceeds the critical value, a titanium-deposited layer rich in -Ti is formed on a titanium-implanted layer. By controlling the sputtering current an appropriate titanium interlayer can be prepared to meet the requirement of forming a proper gradient layer.     

Tunable ultraviolet source from fifth and seventh harmonic generated by mid-infrared pulses filamentation in air

The seventh harmonic generation by tunable mid-infrared femtosecond pulses filamentation in air is observed first time. Pumped by a focused mid-infrared pulses, which pulse duration is ～50 fs and wavelength is tunable from 1300 to 2000 nm, the tunable region of the fifth and seventh harmonic generation can cover the near ultraviolet region from 180 to 400 nm.     

Faddeev–Jackiw canonical path integral quantization for a general scenario,its proper vertices and generating functionals

We generalize the Faddeev–Jackiw canonical path integral quantization for the scenario of a Jacobian with J=1 to that for the general scenario of non-unit Jacobian, give the representation of the quantum transition amplitude with symplectic variables and obtain the generating functionals of the Green function and connected Green function. We deduce the unified expression of the symplectic field variable functions in terms of the Green function or the connected Green function with external sources. Furthermore, we generally get generating functionals of the general proper vertices of any n-points cases under the conditions of considering and not considering Grassmann variables, respectively; they are regular and are the simplest forms relative to the usual field theory.     

原子吸收法测定脑活素类药物中十种金属元素含量

利用火焰原子吸收分光光度法直接测定八种不同品牌的脑活素类生物制剂中镁、钾、钙、铬、锰、铁、钴、镍、铜、锌的含量。统计学处理分析结果表明：七种国产品牌制剂与奥地利脑活素的金属元素比较,存在不同程度的差异。探讨了药效与金属元素的相关性,分析了微量元素在脑活素类物生制剂中所起的作用,为临床合理选用药物提供了有用数据。     

Anomalous elasticity of an ordered lamellar liquid foam

We investigate experimentally the linear viscoelastic properties of a lamellar liquid foam as a function of the cell size and spatial organisation. The system consists of multilamellar vesicles generated by a simple shear flow on a lyotropic lamellar phase. The vesicles can be prepared either in an amorphous or a spatially ordered state. Their size is easily tunable in the range R = 0.5-15 μm. Whereas the shear modulus of the amorphous lamellar foam is alike that of usual liquid foams or concentrated emulsions and scales linearly with 1/R, the elastic modulus of the ordered foam is almost independent of the cell size. This result --probably the first describing the elasticity of an ordered foam-like system-- remains unexplained. Received 7 August 2000     

掺钴氧化钛电极的制备、表征及其光电性能

采用溶胶-凝胶法在纯钛片上制备了掺Co氧化钛薄膜光电极,运用扫描电子显微镜(SEM)、 X射线衍射(XRD)等分析手段对其进行表征,并对其结构和性能的相互关系进行了研究.结果表明,掺5%Co, 500℃热处理的TiO2电极具有最大的可见光响应.过量的Co掺入将析出新相CoTiO3,并促使TiO2由锐钛矿型转变为金红石型,使电极光电效应减低.而高温处理的掺钴TiO2也将析出CoTiO3,对电极光电性能有阻碍作用.     

纤维型人工肌肉的研究进展

近年来,随着人工智能领域的不断发展,柔性机器人开始兴起.为了满足人们对人机交互和环境适应性的新要求,柔性驱动器作为柔性机器人的关键部件受到了广泛的关注.人工肌肉作为最常见的柔性驱动器之一,它对外界刺激反应迅速,并且能够响应刺激产生旋转,收缩和伸长等运动.在各种人工肌肉中,纤维型人工肌肉以其优异的驱动性能和广阔的应用前景...     

The generation of ground-state structures and electronic properties of ternary AlkTilNim clusters (k + l + m = 4) from a two-stage density functional theory global searching approach

Structural and electronic properties of ternary clusters Al_kTi_lNi_m, where k, l, and m are integers and k + l + m = 4 , are investigated. These clusters are generated and studied by performing a two-stage density functional theory (DFT) calculations using the Slater, Vosko, Wilks, and Nusair (SVWN) and Becke three-parameter, Lee-Yang-Parr (B3LYP) functional exchange correlations. In the first stage, an unbiased global search algorithm coupled with a DFT code with a light exchange-correlation and smaller basis sets are used to generate the lowest energy cluster structures. It is then followed by further optimization using another round of DFT calculation with heavy exchanged correlations and large basis set. Electronic properties of the structures obtained via the two-stage procedure are then studied via DFT calculations. The results are illustrated in the form of ternary diagram. Our DFT calculations find that the stability of the cluster increases with the increase in the number of nickel atoms inside the clusters. Our findings provide new insight into the ternary metallic cluster through the structure, stability, chemical order, and electronic properties studies.     

A Key Intermediate in Copper‐Mediated Arene Trifluoromethylation, [nBu4N][Cu(Ar)(CF3)3]: Synthesis,Characterization, and C(sp2)−CF3 Reductive Elimination

The synthesis, characterization, and C(sp²)?CF₃ reductive elimination of stable aryl[tris(trifluoromethyl)]cuprate(III) complexes [nBu₄N][Cu(Ar)(CF₃)₃] are described. Mechanistic investigations, including kinetic studies, studies of the effect of temperature, solvent, and the para substituent of the aryl group, as well as DFT calculations, suggest that the C(sp²)?CF₃ reductive elimination proceeds through a concerted carbon–carbon bond‐forming pathway.