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61.
MJ Lazaro AA Herod M Domin Y Zhuo CA Islas R Kandiyoti 《Rapid communications in mass spectrometry : RCM》1999,13(14):1401-1412
Three methods for determining a 'safe' estimate for high-mass limits of MALDI spectra of coal derived liquids were explored, using a sample of coal-tar pitch and its pyridine-insoluble fraction. Co-addition of increasing numbers of single-shot spectra (10, 30, 50 and 100 pulses) showed visually observable reductions in noise levels, consistent with robust and statistically meaningful signals. Three separate types of post-acquisition calculation were used to identify high-mass limits of the spectra. (i) A literature method indicated high-mass limits similar to those observed visually-as a shift from baseline at the highest masses, nearly 350 000 u for the coal tar pitch and about 390 000 u for its pyridine insoluble fraction. (ii) Comparing instrument signal with pre-selected multiples of the standard deviation, upper mass estimates of between 40-60 000 u for the coal-tar pitch and about 95 000 u for its pyridine-insoluble fraction were found. (iii) Calculation of the slope was used to identify 'lift-off' of the spectrum from baseline. The angle between the smoothed spectrum and the baseline was matched to a pre-selected value (e.g. 0.5 degrees and 1 degrees ). However, the arbitrary specification of the key parameter did not establish this last method on a firm basis. The choice of a criterion for estimating high-mass limits of MALDI spectra remains a semi-quantitative procedure; a reasonably conservative high-mass limit may be estimated by comparison of signal with five times the standard deviation. However, evaluation of size exclusion chromatograms of the present samples using polystyrene standards suggests that molecular mass distributions of pitch samples arrived at by MALDI mass spectrometry are, at least partly, determined by the limitations of available instruments. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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Aggarwal MM Ahammed Z Alakhverdyants AV Alekseev I Alford J Anderson BD Anson D Arkhipkin D Averichev GS Balewski J Barnby LS Baumgart S Beavis DR Bellwied R Betancourt MJ Betts RR Bhasin A Bhati AK Bichsel H Bielcik J Bielcikova J Biritz B Bland LC Bonner BE Bouchet J Braidot E Brandin AV Bridgeman A Bruna E Bueltmann S Bunzarov I Burton TP Cai XZ Caines H Calderón de la Barca Sánchez M Catu O Cebra D Cendejas R Cervantes MC Chajecki Z Chaloupka P Chattopadhyay S Chen HF Chen JH Chen JY 《Physical review letters》2010,105(20):202301
The contribution of B meson decays to nonphotonic electrons, which are mainly produced by the semileptonic decays of heavy-flavor mesons, in p + p collisions at √s=200 GeV has been measured using azimuthal correlations between nonphotonic electrons and hadrons. The extracted B decay contribution is approximately 50% at a transverse momentum of pT≥5 GeV/c. These measurements constrain the nuclear modification factor for electrons from B and D meson decays. The result indicates that B meson production in heavy ion collisions is also suppressed at high pT. 相似文献
64.
Van Bael MJ Bekaert J Temst K Van Look L Moshchalkov VV Bruynseraede Y Howells GD Grigorenko AN Bending SJ Borghs G 《Physical review letters》2001,86(1):155-158
A scanning Hall probe microscope is used to study flux pinning in a thin superconducting Pb film covering a square array of single-domain Co dots with in-plane magnetization. We show that single flux quanta of opposite sign thread the superconducting film below T(c) at the opposite poles of these dipoles. Depending on the polarity of the applied field, flux lines are attracted to a specific pole of the dipoles, due to the direct interaction with the vortexlike structures induced by the local stray field. 相似文献
65.
INAA of Minoan ceramics from Kommos,Crete 总被引:1,自引:0,他引:1
R. G. V. Hancock P. P. Betancourt 《Journal of Radioanalytical and Nuclear Chemistry》1987,109(2):393-401
A recent study concerning the deviation of the E–(1+) epithermal neutron flux distribution from the E–1 law, developed by F. DE CORTE et al. is applied to -determination in different channels of the CRN reactor (Strasbourg). It is found that the coefficient is positive inside the reactor core and negative outside. The accuracy of the neutron activation analysis using the corrected resonance integral I() is tested. 相似文献
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Betancourt A Yezza A Halasz A Van Tra H Hawari J 《Journal of chromatography. A》2007,1154(1-2):473-476
In the present study, we used microwave energy instead of conventional heating to transform poly-3-hydroxybutyrate (PHB) into methyl 3-hydroxybutyrate (Me-3HB) in acidified methanol (H2SO4, 10%, v/v) mixture in less than 4 min at 10% microwave power. The microwave assisted method was then applied to analyze PHB produced by Alcaligenes latus. The PHB content in the biomass determined using microwave heating was comparable to the amount found by conventional heating. Moreover, the new esterification method was at least 50 times faster than the conventional method, affording a significant saving of time and energy. 相似文献
69.
Lucas Bacheley Ricardo Molina Betancourt Rathies Ravindra Dr. Gérard Guillamot Dr. Phannarath Phansavath Dr. Virginie Ratovelomanana-Vidal 《European journal of organic chemistry》2023,26(25):e202300383
A straightforward method to access novel families of enantioenriched cis-monofluorinated carbocyclic alcohols has been developed through ATH/DKR in up to 97 % yield, up to 99 : 1 dr and enantioinductions up to 97 % ee. Trans-difluorinated indans, tetrahydronaphthalenes, tetrahydroquinolines and chromans have been synthesized as well by deoxofluorination of the corresponding cis-fluoro alcohols. The reaction was performed on a series of variously substituted 3-fluorochromanols, 3-fluorotetrahydroquinolinols, 2-fluoro inden-1-ols and 2-fluoro 1,2,3,4-tetrahydronaphthalen-1-ols in up to 86 % yields, with diastereoselectivities up to 97 : 3 and enantioselectivities up to >99 % ee. 相似文献
70.
Betancourt JE Subramani C Serrano-Velez JL Rosa-Molinar E Rotello VM Rivera JM 《Chemical communications (Cambridge, England)》2010,46(45):8537-8539
An 8-(phenyl)-2'-deoxyguanosine derivative self-assembles in aqueous media into discrete hexadecamers that further self-assemble above 32 °C into microglobules that encapsulate the drug doxorubicin. 相似文献