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71.
P. G. Coleman T. C. Griffith G. R. Heyland T. R. Twomey 《Applied Physics A: Materials Science & Processing》1976,11(4):321-325
Total scattering cross-sections for positrons in the rare gases in the energy range of 2–960 eV have been measured using a
time-of-flight system for which the uncertainty arising from forward scattering is substantially lower than in the 1974 experiment
of Canter et al. A comparison of these cross-sections with current theoretical estimates is made. 相似文献
72.
Audouard C Fawcett J Griffith GA Kérourédan E Miah A Percy JM Yang H 《Organic letters》2004,6(23):4269-4272
Direct precursors to analogues of pentopyranoses, 6-deoxyhexoses, and hexoses, in which a CF(2) center replaces the pyranose oxygen, have been synthesized rapidly from trifluoroethanol. A simple scaleable allylation reaction delivers ethers which undergo dehydrofluorination/metalation, followed by addition to either acrolein or cinnamaldehyde, to afford allylic alcohols. Fluorine-assisted [3,3]-rearrangement followed by reduction with sodium borohydride delivers diols, which undergo RCM smoothly to afford cyclohexene diols. 相似文献
73.
Campbell P Thayer HL Billowes J Dendooven P Flanagan KT Forest DH Griffith JA Huikari J Jokinen A Moore R Nieminen A Tungate G Zemlyanoi S Aystö J 《Physical review letters》2002,89(8):082501
The first on-line laser spectroscopy of cooled fission fragments is reported. The r ions, produced in uranium fission, were extracted and separated using an ion guide isotope separator. The ions were cooled and bunched for collinear laser spectroscopy by a gas-filled linear Paul trap. New results for nuclear mean-square charge radii, dipole, and quadrupole moments are reported across the N=60 shape change. The mean-square charge radii are found to be almost identical to those of the Sr isotones and previously offered modeling of the radial changes is critically reviewed. 相似文献
74.
Phillip Griffith 《Transactions of the American Mathematical Society》2001,353(1):77-93
The main result states: if is a module finite extension of excellent local normal domains which is unramified in codimension two and if represents a deformation of the completion of , then there is a corresponding -algebra deformation such that the ring homomorphism represents a deformation of . The main application is to the ascent of the arithmetic Cohen-Macaulay property for an étale map of smooth projective varieties over an algebraically closed field. 相似文献
75.
Martin D. Griffith Justin Leontini Mark C. Thompson Kerry Hourigan 《Journal of Fluids and Structures》2011,27(5-6):855-860
A numerical investigation of the flow past a circular cylinder centred in a two-dimensional channel of varying width is presented. For low Reynolds numbers, the flow is steady. For higher Reynolds numbers, vortices begin to shed periodically from the cylinder. In general, the Strouhal frequency of the shedding vortices increases with blockage ratio. In addition, a two-dimensional instability of the periodic vortex shedding is found, both empirically and by means of a Floquet stability analysis. The instability leads to a beating behaviour in the lift and drag coefficients of the cylinder, which occurs at a Reynolds number higher than the critical Reynolds number for the three-dimensional mode A-type instability, but lower than a Reynolds number for any mode B-type instability. 相似文献
76.
77.
Malgorzata N. Drwal Keli Agama Yves Pommier Renate Griffith 《Journal of computer-aided molecular design》2013,27(12):1037-1049
Purely structure-based pharmacophores (SBPs) are an alternative method to ligand-based approaches and have the advantage of describing the entire interaction capability of a binding pocket. Here, we present the development of SBPs for topoisomerase I, an anticancer target with an unusual ligand binding pocket consisting of protein and DNA atoms. Different approaches to cluster and select pharmacophore features are investigated, including hierarchical clustering and energy calculations. In addition, the performance of SBPs is evaluated retrospectively and compared to the performance of ligand- and complex-based pharmacophores. SBPs emerge as a valid method in virtual screening and a complementary approach to ligand-focussed methods. The study further reveals that the choice of pharmacophore feature clustering and selection methods has a large impact on the virtual screening hit lists. A prospective application of the SBPs in virtual screening reveals that they can be used successfully to identify novel topoisomerase inhibitors. 相似文献
78.
Tony Ngo Timothy J. Nicholas Junli Chen Angela M. Finch Renate Griffith 《Journal of computer-aided molecular design》2013,27(4):305-319
The α1-adrenoceptors (α1-ARs), in particular the α1A-AR subtype, are current therapeutic targets of choice for the treatment of urogenital conditions, such as benign prostatic hyperplasia (BPH). Due to the similarity between the transmembrane domains of the α1-AR subtypes, and the serotonin receptor subtype 1A (5-HT1A-R), currently used α1-AR subtype-selective drugs to treat BPH display considerable off-target affinity for the 5-HT1A-R, leading to side effects. We describe the construction and validation of pharmacophores for 5-HT1A-R agonists and antagonists. Through the structural diversity of the training sets used in their development, these pharmacophores define the properties of a compound needed to bind to 5-HT1A receptors. Using these and previously published pharmacophores in virtual screening and profiling, we have identified unique chemical compounds (hits) that fit the requirements to bind to our target, the α1A-AR, selectively over the off-target, the 5-HT1A-R. Selected hits have been obtained and their affinities for α1A-AR, α1B-AR and 5-HT1A-R determined in radioligand binding assays, using membrane preparations which contain human receptors expressed individually. Three of the tested hits demonstrate statistically significant selectivity for α1A-AR over 5-HT1A-R. All seven tested hits bind to α1A-AR, with two compounds displaying K i values below 1 μM, and a further two K i values of around 10 μM. The insights and knowledge gained through the development of the new 5-HT1A-R pharmacophores will greatly aid in the design and synthesis of derivatives of our lead compound, and allow the generation of more efficacious and selective ligands. 相似文献
79.
Basran J Efimov I Chauhan N Thackray SJ Krupa JL Eaton G Griffith GA Mowat CG Handa S Raven EL 《Journal of the American Chemical Society》2011,133(40):16251-16257
Heme dioxygenases catalyze the oxidation of L-tryptophan to N-formylkynurenine (NFK), the first and rate-limiting step in tryptophan catabolism. Although recent progress has been made on early stages in the mechanism, there is currently no experimental data on the mechanism of product (NFK) formation. In this work, we have used mass spectrometry to examine product formation in a number of dioxygenases. In addition to NFK formation (m/z = 237), the data identify a species (m/z = 221) that is consistent with insertion of a single atom of oxygen into the substrate during O(2)-driven turnover. The fragmentation pattern for this m/z = 221 species is consistent with a cyclic amino acetal structure; independent chemical synthesis of the 3a-hydroxypyrroloindole-2-carboxylic acid compound is in agreement with this assignment. Labeling experiments with (18)O(2) confirm the origin of the oxygen atom as arising from O(2)-dependent turnover. These data suggest that the dioxygenases use a ring-opening mechanism during NFK formation, rather than Criegee or dioxetane mechanisms as previously proposed. 相似文献
80.
Stereoselective Fluorination Alters the Geometry of a Cyclic Peptide: Exploration of Backbone‐Fluorinated Analogues of Unguisin A
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Dr. Xiang‐Guo Hu Dr. Donald S. Thomas Prof. Renate Griffith Dr. Luke Hunter 《Angewandte Chemie (International ed. in English)》2014,53(24):6176-6179
New methods for enhancing the efficiency of peptide cyclization, and for fine‐tuning the conformations of cyclic peptides, are valuable from a drug development perspective. Herein stereoselective fluorination is investigated as a new strategy for achieving these goals. Four vicinal difluorinated analogues of the natural cyclic heptapeptide unguisin A have been efficiently synthesized. The analogues are found to adopt dramatically different secondary structures, controlled by the fluorine stereochemistry. 相似文献