Ion-implanted target for soft x-ray laser investigations

Ion-implantation has been used to make a target suitable for the investigation of soft X-ray laser action via resonant photo-pumping. Neon was implanted on one side of a thin aluminum foil and sodium fluoride was coated on the other side. A 100 picosecond laser pulse at 2 × 10¹⁴ W cm^-2was used to irradiate the neon side, and 330 ps later the sodium fluoride side was irradiated with a similar pulse. X-ray spectroscopy was used to measure the state of ionisation of the neon, and the inferred electron temperature was compared with a one-dimensional computer simulation. The spectral brightness of the pumping radiation was also estimated.     

An EPR study of optical absorption of the oxygen-vacancy pair in electron-irradiated silicon

The negative charge state of the vacancy-oxygen pair (Si-B1) in irradiated silicon was populated by illumination with polarized light, from which the direction of the electric dipole moment was determined to be near 〈110〉 perpendicular to the (Si-O-Si) bond axis. Energy dependence of the alignment suggests the presence of an optical absorption band at λ = 1.30 μm.     

Hydrogen complexes and their vibrations in undoped crystalline silicon

Geometry, relative stability, and vibration frequencies of hydrogen complexes — with and without the presence of vacancies and self-interstitials — are calculated. Assignments proposed by various experimental investigators for hydrogen related vibrational bands are discussed based on the relation between Si-H bond-character and stretching mode frequency.     

The effect of spatial correlations on steady-state nucleation kinetics in dense fluid systems

A widely used expression for the steady-state nucleation rate is determined, in part, by the concentration of critical nuclei in a constrained equilibrium state of the system under consideration. We show that when a dense solvent is present, the values of the constrained equilibrium concentrations reflect the spatial correlations that arise from reactant-solvent molecule collisions. We evaluate the effect of such correlations for a simple, model fluid in terms of measurable reaction rate constants; our analysis shows that correlations influence each step in the multistep process of cluster formation and that the overall impact on the nucleation rate is cumulative. We argue that the very low, homogeneous nucleation rates observed in certain miscibility gap experiments are easily understood in the context of our analysis.Supported in part by a grant from the Research Corporation of the Cottrell Foundation.John Simon Guggenheim Memorial Fellow.     

Structure elucidation and synthesis of (2s)-4-oxo-1-azabicyclo[3.3.0]octa-5,7-diehe-2-carboxylic acid,a new metabolite isolated ercm stheptomyces oliyacbjs

The structure of a new metabolite isolated from $\text{Streptomyces}$$\text{olivaceus}$ has been shown to be (2S)-4-oxo-1-azabicyclo[3.3.0]octa-5,7-diene-2-carboxylic acid by means of its spectroscopic properties and total synthesis.     

叶轮机械设计自变数在内外环壁面上的限制条件及轴流式叶轮机械S1流面的翘曲

本文利用中心流面法的概念,指出叶轮机械的设计白变数在内、外环壁面上应有附加的限制条件,并导得其具体简明方程。同时,还定性地分析了S₁流面的翘曲情况。     

超导临界温度理论(Ⅰ)

本文求出了Eliashberg方程在T=T_c时的解,得到了下面的临界温度级数表示式: 其中α₀(μ^*),α₁(μ^*)等系数是μ^*的函数.此式表明,T_c不仅依赖于λ,〈ω²〉和μ^*,而且依赖于有效声子谱α²F(ω)的各级矩〈ω²n〉.这是区别于前人的T_c公式最重要的一点。这说明像McMillan以及Allen和Dynes的T_c公式不仅是近似的,而主要是他们没有能正确地概括出α²F(ω)对T_c的影响.     

Size-specific reactions of copper cluster ions with a methanol molecule

Chemisorption of a methanol molecule onto a size-selected copper cluster ion, Cu(n)+ (n = 2-10), and subsequent reactions were investigated in a gas-beam geometry at a collision energy less than 2 eV in an apparatus based on a tandem-type mass spectrometer. Mass spectra of the product ions show that the following two reactions occur after chemisorption: dominant formation of Cu(n-1)+(H)(OH) (H(OH) formation) in the size range of 4-5 and that of Cu(n)O+ (demethanation) in the size range of 6-8 in addition to only chemisorption in the size range larger than 9. Absolute cross sections for the chemisorption, the H(OH) formation, and the demethanation processes were measured as functions of cluster size and collision energy. Optimized structures of bare copper cluster ions, reaction intermediates, and products were calculated by use of a hybrid method (B3LYP) consisting of the molecular orbital and the density functional methods. The origin of the size-dependent reactivity was explained as the structural change of cluster, two-dimensional to three-dimensional structures.