排序方式: 共有17条查询结果,搜索用时 46 毫秒
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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
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van Buuren LD Szczerba D Alarcon R Boersma DJ van den Brand JF Bulten HJ Ent R Ferro-Luzzi M Harvey M Heimberg P Higinbotham DW Klous S Kolster H Lang J Militsyn BL Nikolenko D Norum BE Passchier I Poolman HR Rachek I Simani MC Six E de Vries H Zhou ZL 《Physical review letters》2002,89(1):012001
We report on measurements of the cross section and provide first data on spin correlation parameters A(TT') and A(TL') in inclusive scattering of longitudinally polarized electrons from nuclear-polarized hydrogen. Polarized electrons were injected into an electron storage ring operated at a beam energy of 720 MeV. Polarized hydrogen was produced by an atomic beam source and injected into an open-ended cylindrical cell, located in the electron storage ring. The four-momentum transfer squared ranged from Q2 = 0.2 GeV(2)/c(2) at the elastic scattering peak to Q2 = 0.11 GeV(2)/c(2) at the Delta(1232) resonance. The data provide a stringent test of pion electroproduction models. 相似文献
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Ron G Glister J Lee B Allada K Armstrong W Arrington J Beck A Benmokhtar F Berman BL Boeglin W Brash E Camsonne A Calarco J Chen JP Choi S Chudakov E Coman L Craver B Cusanno F Dumas J Dutta C Feuerbach R Freyberger A Frullani S Garibaldi F Gilman R Hansen O Higinbotham DW Holmstrom T Hyde CE Ibrahim H Ilieva Y de Jager CW Jiang X Jones MK Kang H Kelleher A Khrosinkova E Kuchina E Kumbartzki G LeRose JJ Lindgren R Markowitz P May-Tal Beck S McCullough E Meekins D Meziane M Meziani ZE Michaels R 《Physical review letters》2007,99(20):202002
High-precision measurements of the proton elastic form-factor ratio, mu pG p E/G p M, have been made at four-momentum transfer, Q2, values between 0.2 and 0.5 GeV2. The new data, while consistent with previous results, clearly show a ratio less than unity and significant differences from the central values of several recent phenomenological fits. By combining the new form-factor ratio data with an existing cross-section measurement, one finds that in this Q2 range the deviation from unity is primarily due to G p E being smaller than expected. 相似文献
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Numerous organic and inorganic laboratory standards were gathered from nine European and North American laboratories and were analyzed for their delta(18)O values with a new on-line high temperature pyrolysis system that was calibrated using Vienna standard mean ocean water (VSMOW) and standard light Antartic precipitation (SLAP) internationally distributed reference water samples. Especially for organic materials, discrepancies between reported and measured values were high, ranging up to 2 per thousand. The reasons for these discrepancies are discussed and the need for an exact and reliable calibration of existing reference materials, as well as for the establishment of additional organic and inorganic reference materials is stressed. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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Passchier I van Buuren LD Szczerba D Alarcon R Bauer TS Boersma DJ van Den Brand JF Bulten HJ Ent R Ferro-Luzzi M Harvey M Heimberg P Higinbotham DW Klous S Kolster H Lang J Militsyn BL Nikolenko D Nooren GJ Norum BE Poolman HR Rachek I Simani MC Six E de Vries H Wang K Zhou ZL 《Physical review letters》2002,88(10):102302
The spin-momentum correlation parameter A(V)(ed) was measured for the 2H-->(e-->,e'p)n reaction for missing momenta up to 350 MeV/c at Q2 = 0.21 (GeV/c)(2) for quasielastic scattering of polarized electrons from vector-polarized deuterium. The data give detailed information about the deuteron spin structure and are in good agreement with the results of microscopic calculations based on realistic nucleon-nucleon potentials and including various spin-dependent reaction mechanism effects. The experiment reveals in a most direct manner the effects of the D state in the deuteron ground-state wave function and shows the importance of isobar configurations for this reaction. 相似文献
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We analyze the amplitude for radiative charged pion photoproduction within the framework of heavy baryon chiral perturbation
theory and discuss the best experimental setup for the extraction of the pion polarizabilities from the differential cross
section.
Correspondence: C.-W. Kao, Department of Physics, Chung Yuan Christian University, Chung-Li 320, Taiwan 相似文献
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Wesselmann FR Slifer K Tajima S Aghalaryan A Ahmidouch A Asaturyan R Bloch F Boeglin W Bosted P Carasco C Carlini R Cha J Chen JP Christy ME Cole L Coman L Crabb D Danagoulian S Day D Dunne J Elaasar M Ent R Fenker H Frlez E Gan L Gaskell D Gomez J Hu B Jones MK Jourdan J Keith C Keppel CE Khandaker M Klein A Kramer L Liang Y Lichtenstadt J Lindgren R Mack D McKee P McNulty D Meekins D Mkrtchyan H Nasseripour R Niculescu I Normand K Norum B Pocanic D Prok Y Raue B Reinhold J Roche J Rohe D 《Physical review letters》2007,98(13):132003
We have examined the spin structure of the proton in the region of the nucleon resonances (1.085 GeV相似文献
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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