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1.
We present optimal estimates for the asymptotic behavior of
strongly continuous semigroups in terms of growth abscissas of the resolvent function of the generator . In particular we give Ljapunov's classical stability condition a definite form for (infinite dimensional) abstract Cauchy problems: The abscissa of boundedness of equals the growth bound of the classical solutions of .
strongly continuous semigroups in terms of growth abscissas of the resolvent function of the generator . In particular we give Ljapunov's classical stability condition a definite form for (infinite dimensional) abstract Cauchy problems: The abscissa of boundedness of equals the growth bound of the classical solutions of .
2.
Identification of selenium species in urine by ion-pairing HPLC–ICP–MS using laboratory-synthesized standards 总被引:1,自引:0,他引:1
Wrobel K Wrobel K Kannamkumarath SS Caruso JA 《Analytical and bioanalytical chemistry》2003,377(4):670-674
This study focused on the detection/identification of possible selenium metabolites in human urine. Organoselenium compounds not commercially unavailable were synthesized and characterized by electrospray mass spectrometry. Separation of selenomethionine, methylselenomethionine, trimethylselonium, selenoethionine, and selenoadenosylmethionine was achieved by ion-pairing HPLC with a mobile phase of 2 mmol L–1 hexanesulfonic acid, 0.4% acetic acid, 0.2% triethanolamine (pH 2.5), and 5% methanol. The column effluent was introduced on-line to inductively coupled plasma–mass spectrometry for selenium-specific detection (77Se and 78Se). For selenium speciation in urine, solid-phase extraction was carried out using C18 cartridges modified with hexanesulfonic acid. Selective retention of cationic species was observed from acidified urine (perchloric acid, pH 2.0). After elution with methanol, evaporation, and dissolution in the mobile phase, the sample was introduced to the HPLC–ICP–MS system and the chromatographic peaks were assigned by adding standards. The species identified in urine were selenomethionine, trimethylselonium ion, and selenoadenosylmethionine. The last species was detected for the first time and our results suggest that selenomethionine might enter the metabolic pathway of its sulfur analog in the activated methylation cycle.Kazimierz Wrobel and Katarzyna Wrobel are on the leave from the Institute of Scientific Research, University of Guanajuato, L. de Retana No. 5, 36000 Guanajuato, Gto., Mexico 相似文献
3.
Simple tandemly organized (GTG)n/(CAC)n sequences are spread throughout the human chromosomes. The most informative DNA fingerprints for the testing of pedigrees and/or paternity were obtained with the simple triplet repeat probe (GTG)5 or its complement (CAC)5. These hypervariable simple-repeat fragments are stably inherited in a Mendelian fashion. Using these highly discriminating probes, all human individuals could, theoretically, be differentiated, except for genetically identical monozygotic twins. Examples from actual case work are reported and pertinent advantages of this methodology are discussed. 相似文献
4.
A. M. Wrobel B. Lamontagne M. R. Wertheimer 《Plasma Chemistry and Plasma Processing》1988,8(3):315-329
We have investigated O2/CF4 plasma etching of five commercial polymers: polyimide, polyamide, polyethylene terephthalate, polycarbonate and cured epoxy resin. A new large-area microwave plasma apparatus has been used in this work, but the same apparatus can also be used as a capacitively coupled radiofrequency (13.56 MHz) discharge reactor. The effect of operating parameters such as pressure, etchant gas composition, excitation frequency and sample temperature upon etch kinetics has been examined. We have observed distinct maxima in the etch rate as functions of pressure and CF4 concentration. Activation, energies evaluated from the Arrhenius plots fall in the range 0.04-0.2 eV, in agreement with data in the literature. Dry etch susceptibility of a given polymer correlates strongly with the degree of unsaturation in the polymer's structure 相似文献
5.
6s–9s electronic Raman scattering in caesium vapour is used to generate tunable 16m radiation. Output energies in excess of 8 J were obtained, with peak powers in the kilowatt range. 相似文献
6.
7.
The scope and limitations of the 7-hydroxy-2-ethylbenzisoxazolium salt method of forming amide bonds are outlined through the synthesis of a variety of simple peptide derivatives containing all of the common amino acids with the exceptions of arginine and histidine. The 3-acyloxy-2-hydroxy-N-ethylbenzamides derived from C-terminal serine or threonine containing peptides are found to react with amines at anomalously slow rates and with the formation of transesterified byproducts; a mechanistic explanation is offered. The utility of the method for the synthesis of medium sized peptides is examined by synthesis of oligomers of Gly-L-Leu-Gly. 相似文献
8.
Baunack S Plotnikov A Wrobel R Vogt C Wetzig K 《Analytical and bioanalytical chemistry》2002,374(4):681-684
The suitability of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for precise analysis of YNi(2)B(2)C has been investigated. The intensity ratios B/Y and Ni/Y were found to vary during ablation as a function of the ablation conditions. This could be because of fractionation, owing to incongruent ablation or transport and plasma effects. The bottoms and surroundings of the craters were investigated by scanning Auger electron spectrometry. The bottoms of the craters produced by ablation are covered with a thin oxide comparable with that on the polished crystal surface.The craters are surrounded by an oxide layer the dimensions and thickness of which depend on the laser conditions. The formation of this oxide can be assumed to be a result of partial oxidation of sample material during the ablation process; the oxide is then redeposited around the laser crater. 相似文献
9.
Ultrashort-pulse laser ablation of indium phosphide in air 总被引:4,自引:0,他引:4
J. Bonse J.M. Wrobel J. Krüger W. Kautek 《Applied Physics A: Materials Science & Processing》2001,72(1):89-94
Ablation of indium phosphide wafers in air was performed with low repetition rate ultrashort laser pulses (130 fs, 10 Hz)
of 800 nm wavelength. The relationships between the dimensions of the craters and the ablation parameters were analyzed. The
ablation threshold fluence depends on the number of pulses applied to the same spot. The single-pulse ablation threshold value
was estimated to be φth(1)=0.16 J/cm2. The dependence of the threshold fluence on the number of laser pulses indicates an incubation effect. Morphological and
chemical changes of the ablated regions were characterized by means of scanning electron microscopy and Auger electron spectroscopy.
Received: 30 May 2000 / Accepted: 31 May 2000 / Published online: 23 August 2000 相似文献
10.
The low-temperature single-crystal spectrum of TMCBD has revealed a low-lying triplet state at 25 718 cm-1 (72·5 kcal/mol). The observed band is ascribed to a 3 Au (3 A 2) ← 1 Ag nπ* transition on the basis of its small singlet-triplet splitting, its polarization behaviour, and its vibrational structure. The 3 Au state is first-order spin-orbit coupled to either or both of the 1 B 2u or 1 B 3u states. No evidence for two or more nπ* transitions was found. Several multi-membered progressions in the carbonyl wagging mode indicate the presence of a distorted excited state, in which the carbonyl carbons attain a pyramidal conformation. Analysis of the site symmetry shows that TMCBD is distorted to a boat-shaped C 2v structure in its triplet nπ* state. 相似文献