排序方式: 共有7条查询结果,搜索用时 15 毫秒
1
1.
2.
M. R. Brozel L. Breivik D. J. Stirland G. M. Williams A. G. Cullis 《Applied Surface Science》1991,50(1-4):475-479
We have investigated the microstructure that occurs both inside and closely associated with dislocation cells in undoped, semi-insulating LEC GaAs. Using A/B etching, we have identified regions containing large volumes of this microstructure for examination by transmission electron microscopy. A precipitate with a possible associated dislocation loop has been observed in such a region. Cathodoluminescence and reverse contrast images show excellent agreement and demonstrate correlation between regions of high precipitate (and dislocation) density and low concentrations of particular unidentified point defects. In-situ, optical scattering imaging by A/B etched surfaces and reverse contrast absorption imaging demonstrate directly the excellent correlation between these techniques for the first time. 相似文献
3.
KA Saeed FO Ayorinde BE Eribo M Gordon L Collier 《Rapid communications in mass spectrometry : RCM》1999,13(19):1951-1957
Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was used for the characterization of a partially transesterified poly(beta-hydroxyalkanoate), PHA, polymer produced by the bacterial strain Alcaligenes eutrophus using saponified vegetable oils as the sole carbon sources. The transesterification was carried out separately under acidic and basic conditions to obtain PHA oligomers weighing less than 10 kDa. The intact oligomers were detected in their cationized [M + Na](+) and [M + K](+) forms by MALDI-TOFMS. A composition analysis, using the MALDI-TOF spectra, indicate that the oligomers obtained via acid catalysis were terminated with a methyl 3-hydroxybutyrate end group, and those obtained by base catalysis had a methyl crotonate (olefinic) termination. In addition to HB (hydroxy butyrate), the oligomers were found to contain a small percentage of HV (hydroxy valerate). This was independently confirmed using gas chromatography/mass spectrometry (GC/MS). In comparison, the analysis of a commercial PHA polymer, transesterified under identical conditions, only showed the presence of HB, i.e. a pure PHB homopolymer. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
4.
5.
FO Ayorinde BE Eribo JH Johnson E Elhilo 《Rapid communications in mass spectrometry : RCM》1999,13(12):1124-1128
Nonylphenol ethoxylates (NPEs) belong to a group of nonionic surfactants that are collectively referred to as alkylphenol ethoxylates (APEs). APEs find widespread use in heavy-duty commercial and household cleaning formulations, shampoos, and industrial processing, i.e. textile manufacture. Their environmental impact depends on the molecular distribution and the extent of their biodegradation in municipal sewage systems, waterways and rivers. We have established two sample preparation methods that have enabled the determination of the molecular distributions of six commercial nonylphenol ethoxylates using matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS). In both methods, alpha-cyano-4-hydroxycinnamic acid, dissolved in acetonitrile/tetrahydrofuran, was used as the matrix. In one set of experiments, the NPEs were dissolved in an acetonitrile/tetrahydrofuran solvent system prior to mixing with the matrix solution, and the resulting MALDI-TOF mass spectra produced mostly sodiated molecules [M + Na](+). The NPEs, all having the formula 4-(C(9)H(19))-C(6)H(4)-(OCH(2)CH(2))(n)-OH, are Surfonic (R)N-95, N-100, N-102, N-120, N-150 and N-300. Surfonic N-95 and N-100 gave n values of 5-20; Surfonic N-102, N-120, N-150, and N-300 gave n values of 5-21, 5-22, 8-25 and 15-40, respectively. In order to develop a sample preparation method that could be used with less polar NPEs, we dissolved the NPEs (except N-300) in pentane prior to mixing with the matrix solution, and found that the MALDI spectral quality was unaffected by the solvent systems. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
6.
7.
K. Alpgård G. Ekspong P.O. Hulth U. Svedin N. Yamdagni F.O. Breivik A.G. Frodesen A. Krogstad V.-M. Hagman V. Karimäki P. Villanen 《Nuclear Physics B》1976,103(2):234-246
Inclusive cross sections are presented for strange-particle production in proton-proton interactions at 19 GeV/c for the pairs and for Λ, Ks0, Σ+, Σ? and Ξ?. The , the KY and the total strange particle cross sections have been found to be 1.40 ± 0.10 mb, 2.69 ± 0.09 mb and 4.23 ± 0.20 mb, respectively. The charged multiplicity distributions for events with Ks0, Λ, or K0 Λ are shown to follow a modified KNO curve, whereas K+ Λ does not. For the inclusive reactions , we find that the average charged multiplicity of the remainder system X++ is the same as when X++ is produced in other reactions with the same system energy and quantum numbers. 相似文献
1