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131.
Marble AE Mastikhin IV MacGregor RP Akl M LaPlante G Colpitts BG Lee-Sullivan P Balcom BJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,168(1):164-174
The results of a magnetic resonance imaging (MRI) investigation concerning the effects of an aluminum honeycomb sandwich panel on the B1 and B0 fields and on subsequent image quality are presented. Although the sandwich panel structure, representative of an aircraft composite material, distorts B0 and attenuates B1, distortion-free imaging is possible using single point (constant time) imaging techniques. A new expression is derived for the error caused by gradient field distortion due to the heterogeneous magnetic susceptibility within a sample and this error is shown not to cause geometric distortion in the image. The origin of the B0 distortion in the sample under investigation was also examined. The graphite-epoxy 'skin' of the panel is the principal source of the B0 distortion. Successful imaging of these structures sets the stage for the development of methods for detecting moisture ingress and degradation within composite sandwich structures. 相似文献
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133.
[structure: see text] Tetrabromobutatriene, C(4)Br(4), can be prepared directly from dibromobutadiyne by reaction with Br(2) at -25 degrees C in concentrated hexanes solution. The cumulene precipitates out of the reaction mixture as a yellow powder. Under palladium-catalyzed coupling conditions, C(4)Br(4) can undergo allylic rearrangement, giving a mixture of products, including some with butenyne backbones. However, in furan solution, C(4)Br(4) reacts cleanly at its central double bond to give the furan Diels-Alder adduct. Under Suzuki conditions, this adduct reacts at the furan double bond rather than at bromide. 相似文献
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135.
The Boson Normal Ordering Problem and Generalized Bell Numbers 总被引:2,自引:0,他引:2
For any function F(x) having a Taylor expansion we solve the boson
normal ordering problem for $F [(a^\dag)^r a^s]$, with r, s positive integers,
$F [(a, a^\dag]=1$, i.e., we provide exact and explicit
expressions for its normal form $\mathcal{N} \{F [(a^\dag)^r a^s]\} = F [(a^\dag)^r a^s]$, where
in $ \mathcal{N} (F) $ all a's are to the
right. The solution involves integer sequences of numbers which, for $ r, s \geq 1 $, are
generalizations of the conventional Bell and Stirling numbers whose values they assume for $ r=s=1 $. A complete
theory of such generalized combinatorial numbers is given including closed-form expressions
(extended Dobinski-type formulas), recursion relations and generating functions. These last are
special expectation values in boson coherent states.AMS Subject Classification: 81R05, 81R15, 81R30, 47N50. 相似文献
136.
Singh JB Sirotenko V Slattery P Smith E Smith RP Snihur R Snow GR Snow J Snyder S Solomon J Sorin V Sosebee M Sotnikova N Soustruznik K Souza M Stanton NR Steinbruck G Stephens RW Stevenson ML Stichelbaut F Stoker D Stolin V Stoyanova DA Strauss M Streets K Strovink M 《Physical review letters》2000,85(24):5068-5073
Bottom-quark production in &pmacr;p collisions at sqrt[s] = 1.8 TeV is studied with 5 pb(-1) of data collected in 1995 by the D0 detector at the Fermilab Tevatron Collider. The differential production cross section for b jets in the central rapidity region ( | y(b)|<1) as a function of jet transverse energy is extracted from a muon-tagged jet sample. Within experimental and theoretical uncertainties, D0 results are found to be higher than, but compatible with, next-to-leading-order QCD predictions. 相似文献
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140.
Stephanie L. Gantt Nancy B. Valentine Adam J. Saenz Mark T. Kingsley Karen L. Wahl 《Journal of the American Society for Mass Spectrometry》1999,10(11):1131-1137
A method to aid in the analysis of bacterial samples of unknown concentration by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is demonstrated. It is shown that in MALDI analysis of bacteria, the intensities of resulting peaks in spectra are sensitive to the microbial concentration. At the high and low ends of the concentration range, no signal can be obtained, leaving very concentrated or very dilute samples indistinguishable. The addition of cytochrome c as an internal control allows the differentiation of these concentrated and dilute samples. The presence of the internal control causes only a 20% to 30% decrease in signal intensity when the bacterial concentration is optimum. However, the signal quality is improved when the internal control is added to some low concentrations of bacteria. 相似文献