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11.
T.?Cs?rg?Email author S.?Hegyi W.?A.?Zajc 《The European Physical Journal C - Particles and Fields》2004,36(1):67-78
The peak of the two-particle Bose-Einstein correlation functions has a very interesting structure. It is often believed to have a multivariate Gaussian form. We show here that for the class of stable distributions, characterized by the index of stability
, the peak has a stretched exponential shape. The Gaussian form corresponds then to the special case of
. We give examples for the Bose-Einstein correlation functions for univariate as well as multivariate stable distributions, and we check the model against two-particle correlation data.Received: 19 November 2003, Revised: 27 April 2004, Published online: 23 June 2004 相似文献
12.
T. Åkesson M.G. Albrow S. Almehed E. Anassontzis R. Batley O. Benary H. Bøggild O. Botner H. Breuker H. Brody V. Burkert B. Callen R. Carosi A.A. Carter J.R. Carter P.C. Cecil V. Chernyatin W.A. Zajc 《Physics letters. [Part B]》1985,158(3):282-288
We have measured the production of direct photons, π0's, and η's in p and pp collisions at √s=53 GeV in the range 2≈pT≈6 GeV/c for the central rapidity region |y| 0.4. No statistically significant difference between pp? and pp interactions is observed. 相似文献
13.
[reaction: see text] General, high-yield tandem electrophilic fluorination and modified Julia olefination for the synthesis of fluoro olefins is reported. A series of alpha-fluoro 1,3-benzothiazol-2-yl sulfone-based synthons were synthesized via deprotonation-fluorination. Of critical importance for high-yield fluorinations were heterogeneous reaction conditions, as under homogeneous conditions only starting sulfones were recovered. The alpha-fluoro 1,3-benzothiazol-2-yl sulfones so obtained were subjected to condensations with a variety of aldehydes and ketones to afford high yields of regiospecifically fluorinated olefins. 相似文献
14.
A Julia–Kocienski approach to trifluoromethyl-substituted alkenes was evaluated in the reactions of 1,3-benzothiazol-2-yl, 1-phenyl-1H-tetrazol-5-yl, and 1-tbutyl-1H-tetrazol-5-yl 2,2,2-trifluoroethyl sulfones with aldehydes. Among the various conditions tested, the best yields were obtained with 1-phenyl-1H-tetrazol-5-yl 2,2,2-trifluoroethyl sulfone, in CsF-mediated, room temperature olefinations in DMSO. Aromatic aldehydes gave (trifluoromethyl)vinyl derivatives in 23–86% yields, with generally moderate stereoselectivity. Straightforward synthesis of the Julia–Kocienski reagent, and conversion to trifluoromethyl-substituted alkenes under mild reaction conditions, are the advantages of this approach. 相似文献
15.
Lakshman MK Keeler JC Ngassa FN Hilmer JH Pradhan P Zajc B Thomasson KA 《Journal of the American Chemical Society》2007,129(1):68-76
A diastereoselective synthesis of the nucleoside adducts corresponding to a cis ring-opening of the carcinogen (+/-)-7 beta, 8 alpha-dihydroxy-9 alpha,10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BaP DE-2) by 2'-deoxyadenosine and 2'-deoxyguanosine is described. The key intermediate (+/-)-10alpha-amino-7beta,8alpha,9alpha-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene was synthesized by a highly diastereoselective dihydroxylation wherein phenylboronic acid was a water surrogate. The resulting boronate ester was converted to a tetraol derivative in which two of the four hydroxyl groups (trans 7, 8) were protected as benzoate esters while the remaining two (cis 9, 10) were free. The cis glycol entity was then subjected to a reaction with 1-chlorocarbonyl-1-methylethylacetate to yield an intermediate chloro monoacetoxy dibenzoate. Displacement of the halide with azide, complete cleavage of the esters, and catalytic reduction of the azide yielded the requisite amino triol. Fluoride displacement from appropriately protected nucleoside derivatives, 6-fluoropurine 2'-deoxyribonucleoside and 2-fluoro-2'-deoxyinosine, by the amino triol then yielded diastereomeric pairs of diol epoxide-adducted 2'-deoxyadenosine (dA) and 2'-deoxyguanosine (dG) nucleosides. Small aliquots of these adducts were separated for characterization purposes. The present approach provides the first diastereoselective synthesis of the cis adducts of BaP DE-2 with 2'-deoxyguanosine as well as the first synthesis of both dA and dG adducts from a common intermediate. An informative analysis of the 1H NMR spectra of the cis adducts synthesized and comparisons to the trans adducts are reported. To gain insight into the diastereoselectivity in the key dihydroxylation step, a computational analysis, including molecular mechanics (MMFF94) and semiempirical AM1 geometry optimizations, yielded results that are in fairly good agreement with the experimental observations. 相似文献
16.
A straightforward access to protected 8-fluoro nucleosides via metalation-electrophilic fluorination under heterogeneous reaction conditions is reported. This is the first synthesis of 8-fluoro-2'-deoxyribonucleoside derivatives. Phenylsulfonyl substituted nucleosides are accompanying byproducts, possibly indicating a competing radical process. Higher yields of 8-fluoro derivatives were obtained with 2'-deoxyribonucleosides, as compared to ribonucleosides. Deprotection of the hydroxyl groups leading to 8-fluoro-2'-deoxyadenosine using TASF in methylene chloride demonstrates the compatibility of desilylation with 8-fluoro substituted nucleosides. NMR data indicate a syn conformation of the 8-fluoro derivatives. 相似文献
17.
The phase diagrams of nifedipine-polyethylene glycol (PEG) 4000 and nifedipine-mannitol systems have been determined. Heating
experiments on thermodynamically equilibrated co-melts revealed eutectic behaviour for nifedipine-PEG 4000 mixtures, with
the composition of the eutectic point between 40 and 45%w/w of nifedipine. These observations were supported by optical and hot stage microscopy. Nifedipine and mannitol were negligibly
miscible in the solid-state, behaving as a binary system with monotectic characteristics. Application of phase diagrams to
the production of solid dispersions is shown to be rational, since they provide valuable information on the state of the binary
systems under preparation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
Abbott T Akiba Y Beavis D Bloomer MA Bond PD Chasman C Chen Z Chu YY Cole BA Costales JB Crawford HJ Cumming JB Debbe R Duek E Engelage J Fung SY Gushue S Hamagaki H Hansen O Hayano RS Hayashi S Haustein PE Homma S Huang HZ Ikeda Y Juricic I Kang J Katcoff S Kaufman S Kimura K Kitamura K Kurita K Ledoux RJ LeVine MJ Miake Y Morse RJ Moskowitz B Nagamiya S Olness J Parsons CG Remsberg LP Sakurai H Sarabura M Stankus P Steadman SG Stephans GS Sugitate T Tannenbaum MJ van Dijk JH Videbaek F 《Physical review letters》1993,70(10):1393-1396
19.
Synthesis of a novel, stable reagent (1,3-benzothiazol-2-ylsulfonyl)fluoroacetonitrile from readily synthesized ethyl alpha-(1,3-benzothiazol-2-ylsulfanyl)-alpha-fluoroacetate is reported. Aldehydes undergo condensations with (1,3-benzothiazol-2-ylsulfonyl)fluoroacetonitrile in the presence of DBU leading to alpha-fluoro acrylonitriles in high yields and with good Z-stereoselectivity. Lowering of reaction temperature increases the Z selectivity. 相似文献
20.
A mild and efficient synthesis of 1-aryl-1-fluoroethenes from benzothiazolyl (aryl)fluoromethyl sulfones and paraformaldehyde, under DBU- or Cs(2)CO(3)-mediated conditions at room temperature, is described. A comparable diethyl fluoro(naphthalen-2-yl)methylphosphonate reagent does not react with paraformaldehyde under these mild conditions. The utility of the methodology for synthesis of terminal α-fluoroalkenes bearing electron-withdrawing functionalities is also shown. 相似文献