The cyclodimerisation of 3-methyl-2-butenenitrile

3-Methyl-2-butenenitrile (1) cyclodimerised on treatment with lithium diisopropylamide in dimethoxyethane at temperatures between ?78°C and 0°C to 3-amino-4-cyano-1,5,5-trimethyl-1,3-cyclohexadiene (2) the structure of which was established by acid hydrolysis to the known 4-cyano-1,5,5-trimethyl-1-cyclohexene-3-one (3).     

Conical parametric scattering of a single extraordinary beam in BaTiO3 crystal

In this paper, the parametric scattering of a single extraordinary polarized beam of laser in BaTiO₃ photorefractive crystal has been investigated experimentally and theoretically. The resulting pattern consists of beam fanning, isotropic ring, and anisotropic one. Among all parts of scattering pattern, isotropic ring has not been studied as much as beam fanning and anisotropic ring, and there still are some differences in reports about it. Therefore, the study has mainly focused on this part. In this experimental configuration, isotropic ring is just visible in positive angles although the other parts of parametric scattering pattern can be visible from behind and in front of the crystal. In addition to steady state pattern in forward and backward directions, its transient behavior with the rotation of crystal has been studied. The results of experiments have been analyzed carefully, and their theoretical explanations have been presented based on the standard theory of parametric scattering in photorefractive crystals. It has been shown that this configuration corresponds to the so called parametric B-process scattering.     

Correlation between the superconducting and normal state properties of amorphous molybdenum - silicon alloys

Measurements on amorphous Mo_1?xSi_x (0.27 ≤ × ≤ 0.77) show that with increasing x the superconducting transition temperature, T_c, decreases linearly with x for x ≤ x₀ ≡ 0.63 ± 0.05. The superconducting transition width and normal state resistivity increase rapidly with increasing x as x approaches x₀. For x > x₀, T_c drops below 1.5K. Transmission electron diffraction measurements (0.65 ≤ × ≤ 0.75) detect the presence of a second amorphous phase which resembles a-Si only for samples with x ? 0.75. The behavior near x₀ could be attributed to the onset of an electronic transition involving the conversion of metallically bonded Si to covalently bonded Si.     

Observation of rf-induced dc voltages in sputtered binary superconducting films

We have observed that an rf current of frequency 1–5 MHz, passing through a sputtered binary superconducting film, can induce a dc voltage as large as 1 mV across the film for temperatures near the critical temperature T_C. The largest induced voltage has been observed in films which are microscopically inhomogeneous, such as Mo₆₃C₃₇ films which exhibit columnar microstructure. We suggest that the effect may be due to an inverse ac Josephson effect in a randomly connected series array of many microscopic superconducting weak links that are expected to exist close to T_C.     

Self-chemical ionization of diethylzinc

The self-chemical ionization of diethylzinc is examined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and semiempirical molecular orbital calculations. Electron impact of diethylzinc neutral produces the radical cation, C(4)H(15)Zn(+) (m/z x 122), which reacts further with the neutral (C(2)H(5))(2)Zn to give the following product ions: Zn(+) (m/z x 64), C(2)H(5)Zn(+) (m/z x 93), C(4)H(9)Zn(+) (m/z x 121), C(4)H(11)Zn(2)(+) (m/z x 187), and C(6)H(15)Zn(2)(+) (m/z x 215). To determine the structure and pathways for production of these ions, monoisotopic (12)C(4)H(15)(64)Zn(+), (64)Zn(+) and (12)C(2)H(5)(64)Zn(+) were individually isolated and reacted with the neutral background. We also performed semiempirical molecular orbital calculations (ZINDO/1). The molecular orbital calculations and experimental data are consistent in predicting that the ethyl group on the diethylzinc cation carries the positive charge. Copyright 1999 John Wiley & Sons, Ltd.     

Electroreflectance and Raman scattering investigation of glow-discharge amorphous Si:F:H

The electroreflectance and Raman scattering spectra of several samples of glow-discharge amorphous Si:F:H films have been investigated. We have observed for the first time modulated optical spectroscopy structure above the absorption edge for a disordered semiconductor. The energy positions of these structures, at 3.4 and 4.5 eV, correspond to peaks seen in crystalline silicon. In particular, the latter feature can be related to the degree of disorder in the material. Also we have seen for the first time in disordered silicon (except for ion-damaged, laser annealed samples) peaks in the Raman spectra intermediate between amorphous (465 cm^-1) and crystalline materials (522 cm^-1). These experimental results provide strong evidence that a-Si:F:H possesses “microcrystalline” or some other intermediate range order (i.e., an improved connectivity between the elements of the random network.)     

Development of high catalytic activity disordered hydrogen-storage alloys for electrochemical application in nickel–metal hydride batterie

Multi-element, multiphase disordered metal hydride alloys have enabled the widespread commercialization of nickel–metal hydride (NiMH) batteries by allowing high capacity and good kinetics while overcoming the crucial barrier of unstable oxidation/corrosion behavior to obtain long cycle life. Alloy-formula optimization and advanced materials processing have been used to promote a high concentration of active hydrogen-storage sites vital for raising NiMH specific energy. New commercial applications demand fundamentally higher specific power and discharge-rate kinetics. Disorder at the metal/electrolyte interface has enabled a surface oxide with less than 70 ? metallic nickel alloy inclusions suspended within the oxide, which provide exceptional catalytic activity to the metal hydride electrode surface. Received: 14 August 2000 / Accepted: 6 November 2000 / Published online: 9 February 2001     

怀孕期头发中一些元素含量的变化趋势

用同步辐射激发X射线荧光分析,对11个产妇怀孕期间头发内一些元素含量的变化趋势进行了测量,在各自对比的基础上,得到了一些结果。     

Chemical bond approach to the structures of chalcogenide glasses with reversible switching properties

The structures of some chalcogenide glasses of interest due to their reversible threshold swithching (Si₁₈Ge₇As₃₅Te₄₀) and memory switching (Ge₁₅Te₈₁Sb₂S₂ and Ge₂₄Te₇₂Sb₂S₂) properties have been examined in terms of the chemical bonds expected to be present in these materials. Using simple considerations based on coordination numbers and bond energies, the average number of near neighbors of each type expected to surround a given central atom has been estimated. These average numbers of bonds have been used to estimate the cohesive energies of these glasses, assuming simple additivity of bond energies. The results of these calculations can be used to rationalize the observed switching properties of these materials, as well as to suggest criteria for selecting other materials with desirable properties.