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21.
Kickham JE Guérin F Stewart JC Stephan DW 《Angewandte Chemie (International ed. in English)》2000,39(18):3263-3266
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Stewart D. Johnson 《Communications in Mathematical Physics》1987,110(2):185-190
For the transformationT:[0,1][0,1] defined byT(x)=x(1–x) with 04, a is shown to exist for whichT has no restrictive intervals, hence is sensitive to initial conditions, but for which no finite absolutely continuous invariant measure exists forT.Supported by the U.S. Army Research Office through the Mathematical Sciences Institute of Cornell University 相似文献
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25.
Thaler F Valsasina B Baldi R Xie J Stewart A Isacchi A Kalisz HM Rusconi L 《Analytical and bioanalytical chemistry》2003,376(3):366-373
beta-Elimination of the phosphate group on phosphoserine and phosphothreonine residues and addition of an alkyldithiol is a useful tool for analysis of the phosphorylation states of proteins and peptides. We have explored the influence of several conditions on the efficiency of this PO(4)(3-) elimination reaction upon addition of propanedithiol. In addition to the described influence of different bases, the solvent composition was also found to have a major effect on the yield of the reaction. In particular, an increase in the percentage of DMSO enhances the conversion rate, whereas a higher amount of protic polar solvents, such as water or isopropanol, induces the opposite effect. We have also developed a protocol for enrichment of the modified peptides, which is based on solid-phase covalent capture/release with a dithiopyridino-resin. The procedure for beta-elimination and isolation of phosphorylated peptides by solid-phase capture/release was developed with commercially available alpha-casein. Enriched peptide fragments were characterized by MALDI-TOF mass spectrometric analysis before and after alkylation with iodoacetamide, which allowed rapid confirmation of the purposely introduced thiol moiety. Sensitivity studies, carried out in order to determine the detection limit, demonstrated that samples could be detected even in the low picomolar range by mass spectrometry. The developed solid-phase enrichment procedure based on reversible covalent binding of the modified peptides is more effective and significantly simpler than methods based on the interaction between biotin and avidin, which require additional steps such as tagging the modified peptides and work-up of the samples prior to the affinity capture step. 相似文献
26.
Mark Strobel Stewart Corn Christopher S. Lyons Gary A. Korba 《Journal of polymer science. Part A, Polymer chemistry》1987,25(5):1295-1307
ESCA and contact angle measurements were used to characterize the surfaces of Polyethylene and polypropylene films exposed to SF6, CF4, and C2F6 plasmas. None of these gases polymerized in the plasma. However, all plasma treatments grafted fluorinated functionalities directly to the polymer surfaces. SF6 plasmas graft fluorine atoms to a polyolefin surface. CF4 plasmas also react by a mechanism dominated by fluorine atoms, but with some contribution from CFx-radical reactions. Although C2F6 does not polymerize, the mechanism of grafting is still dominated by the reactions of CFx radicals. For all gases studied, the lack of polymerization is attributed to competitive ablation and polymerization reactions occurring under conditions of ion bombardment. 相似文献
27.
Ondansetron and its hydroxylated metabolites were determined in human serum using solid-phase extraction (SPE) and liquid chromatography/positive ion electrospray tandem mass spectrometry. Pyrimethamine was used as the internal standard. The analytes were eluted from the SPE cartridge using 2 x 1 ml of methanol containing 0.5% triethylamine, evaporated under vacuum and the residue was reconstituted in the mobile phase. The liquid chromatographic separation was achieved on a silica column using a mobile phase of aqueous 20 mM ammonium acetate (pH 4.7)-acetonitrile (85 : 15, v/v) at a flow-rate of 0.4 ml min(-1). The method was linear over the range 1-500 ng ml(-1) for ondansetron and each of the metabolites in human serum. The intra-day accuracy was better than 9.1% and the precision was <10.3%; the inter-day accuracy was better than 9.5% and the precision was <12.6%. The limit of detection was 250 pg ml(-1) based on a signal-to-noise ratio of 3. The absolute recovery from serum for all analytes was >90%. 相似文献
28.
Most quantum chemists regard semiempirical methods as ephemeral and computationally cost efficient. For this reason, an article dealing with computational efficiency of semiempirical methods is probably very unfashionable. However, experience at a big computer installation, shared by ab-initio and semiempirical quantum chemists shows that the second group actually consumes more computer time than the first. Obviously, the greater size of the molecules in semiempirical calculations outweighs the inherent efficiency of these methods. The present article describes a simple method for accelerating SCF -type semiempirical methods. 相似文献
29.
Juliet D Risner Thomas P Nolan James Bentley Erol Girt Samuel D Harkness Robert Sinclair 《Microscopy and microanalysis》2007,13(2):70-79
For this analytical TEM study, nonmagnetic oxygen-rich boundaries were introduced into Co-Pt-alloy perpendicular recording media by cosputtering Co and Pt with TiO2. Increasing the TiO2 content resulted in changes to the microstructure and elemental distribution within grains and boundaries in these films. EFTEM imaging was used to generate composition maps spanning many tens of grains, thereby giving an overall depiction of the changes in elemental distribution occurring with increasing TiO2 content. Comparing EFTEM with spectrum-imaging maps created by high-resolution STEM with EDXS and EELS enabled both corroboration of EFTEM results and quantification of the chemical composition within individual grain boundary areas. The difficulty of interpreting data from EDXS for these extremely thin films is discussed. Increasing the TiO2 content of the media was found to create more uniformly wide Ti- and O-rich grain boundaries as well as Ti- and O-rich regions within grains. 相似文献
30.
Christophe Bongars Peter Bougeard Adrian Bury Christopher J. Cooksey Michael D. Johnson Stewart Mitchell Paul A. Owens Famida Rajah 《Journal of organometallic chemistry》1985,289(1):163-171
5-Methylhex-5-enylcobaloxime reacts with carbon tetrachloride and with fluorotrichloromethane at 80–100°C to give substantially pure 1-methyl-1-(β,β,β-trichloroethyl)- and 1-methyl-1-β-fluoro-β,β-dichloroethyl)-cyclopentane. Hex-5-enylco-baloxime also gives trichloroethylcyclopentane from carbon tetrachloride, but the yield is dependent on the concentration of carbon tetrachloride. Similar cyclisation to give trichloroethyl- or fluorodichloroethyltetrahydrofuran is observed in the reactions of hex-3-oxo-5-enylcobaloxime with carbon tetrachloride and fluorotrichloromethane. However, no cyclisation was observed in the reactions of the ester, hex-2-one-3-oxo-5-enylcobaloxime, with carbon tetrachloride. These reactions are believed to take place by attack of a polyhalogenomethyl radical at the terminal unsaturated carbon of the organic ligand, followed either by an intramolecular homolytic displacement in which the carbon radical at position-5 attacks carbon-1 with displacement of cobaloxime(II), or by a halogen atom abstraction. 相似文献