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ToddCOCHRANE ChunLeiLIU ZhiYongZHENG 《数学学报(英文版)》2003,19(2):327-338
We obtain formulac and estimates for character sums of the type S(x,f,p^m)=∑x=1^p^mx(f(f)),where p^m is a prime power with m≥2,x is a multiplicative character(mod p^m),and f=f1/f2 is a rational function over Z.In particular,if p is odd,d=deg(f1) deg(f2) and d^*=max(deg(f1),deg(f2)) then we obtain |S(x,f,p^m)|≤(d-1)p^m(1-1/d^*) for any non-constant f (mod p) and primitive character x.For p=2 an extra factor of 2√2 is needed. 相似文献
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Karol Al Ayed Ross D. Ballantine Michael Hoekstra Samantha J. Bann Charlotte M. J. Wesseling Alexander T. Bakker Zheng Zhong Yong-Xin Li Nora C. Brüchle Mario van der Stelt Stephen A. Cochrane Nathaniel I. Martin 《Chemical science》2022,13(12):3563
Brevicidine and laterocidine are two recently discovered lipopeptide antibiotics with promising antibacterial activity. Possessing a macrocyclic core, multiple positive charges, and a lipidated N-terminus, these lipopeptides exhibit potent and selective activity against Gram-negative pathogens, including polymyxin-resistant isolates. Given the low amounts of brevicidine and laterocidine accessible by fermentation of the producing microorganisms, synthetic routes to these lipopeptides present an attractive alternative. We here report the convenient solid-phase syntheses of both brevicidine and laterocidine and confirm their potent anti-Gram-negative activities. The synthetic routes developed also provide convenient access to novel structural analogues of both brevicidine and laterocidine that display improved hydrolytic stability while maintaining potent antibacterial activity in both in vitro assays and in vivo infection models.Convenient solid-phase approaches are described for the synthesis of brevicidine and laterocidine. Also reported are novel analogues including a laterocidine variant with enhanced hydrolytic stability and potent in vivo antibacterial activity. 相似文献
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Terence Davis Matthew C Dix Michal J Rokicki Amy JC Brook Caroline S Widdowson David Kipling Mark C Bagley 《Chemistry Central journal》2011,5(1):1-5
To develop more potent small molecules with enhanced free radical scavenger properties, a series of N-substituted isatin derivatives was synthesized, and the cytoprotective effect on the apoptosis of PC12 cells induced by H2O2 was screened. All these compounds were found to be active, and N-ethyl isatin was found with the most potent activity of 69.7% protective effect on PC12 cells. Structure-activity relationship analyses showed the bioactivity of N-alkyl isatins decline as the increasing of the chain of the alkyl group, furthermore odd-even effect was found in the activity, which is interesting for further investigation. 相似文献
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In a recent paper we used a phase-field model of solidification in deeply undercooled pure melts to show that a kinetic instability could result in dendrite tip splitting, and we speculated that such tip splitting could give rise to the phenomenon of spontaneous grain refinement. Here we present evidence, from the as-solidified microstructure of deeply undercooled ultrahigh purity Cu, of what appears to be dendrite tip splitting during recalescence. The significance of this finding in a nongrain refined sample is discussed in terms of the current theories for spontaneous grain refinement. 相似文献
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The relative rates of H-transfer between partners in ion-neutral complexes were compared with those in intramolecular rearrangements using results of first differential photoionization mass spectrometry measurements. Complex-mediated H-transfers are inferred to have rates of the same order as those for intramolecular hydrogen rearrangements, suggesting a similar range of motion of the reactive sites in both types of reactions. It is also concluded that at their fastest H-transfers take place between the partners in ion-neutral complexes within at most the time of several rotations of the partners in the complexes. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
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P. Campbell J. Billowes E.C.A. Cochrane P. Dendooven D.E. Evans J.A.R. Griffith J. Huikari A. Jokinen I.D. Moore A. Nieminen K. Peräjärvi G. Tungate G. Yeandle J. Äystö 《Hyperfine Interactions》2000,131(1-4):83-90
Magnetic interactions and microstructure in the amorphous and nanocrystalline Fe90Zr7Cu1B2 alloy were investigated. These studies were carried out in the temperature range from 140 up to 380 K, using a Mössbauer spectrometer and completely automated set-up for measurements of magnetic properties. It has been found that the Curie temperature and quadrupole splitting decrease after annealing the sample at 573 K for 1 h (invar effect). However, this behaviour is not observed in nanocrystalline samples. In the early stages of crystallization (the volume fraction of the crystalline phase equal to about 0.06) α-Fe grains above the Curie temperature of amorphous matrix may be treated as non-interacting particles. The particle size estimated by Mössbauer spectra and magnetization curve analysis is equal to about 4 nm. 相似文献