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排序方式: 共有556条查询结果,搜索用时 31 毫秒
31.
Kylstra NJ Worthington RA Patel A Knight PL Vazquez De Aldana JR Roso L 《Physical review letters》2000,85(9):1835-1838
An analysis of the influence of the magnetic field of an intense, high-frequency laser pulse on the stabilization of an atomic system is presented. We demonstrate that at relatively modest intensities the magnetic field can significantly alter the dynamics of the system. In particular, a breakdown of stabilization occurs, thereby restricting the intensity regime in which the atom is relatively stable against ionization. Counterpropagating pulses do not negate the detrimental effects of the magnetic field. We compare our quantum mechanical results with classical Monte Carlo simulations. 相似文献
32.
We describe the use of tapered hollow-core photonic crystal fibres for delivery and compression of ultrashort optical pulses. We demonstrate delivery of transform-limited pulses with less than 100 fs pulse length and above 50 nJ energy through 8 m of fibre, in a single transverse mode. 相似文献
33.
Jonathan Levine Michael R. Savina Thomas Stephan Nicolas Dauphas Andrew M. Davis Kim B. Knight Michael J. Pellin 《International journal of mass spectrometry》2009,288(1-3):36-43
Resonance ionization mass spectrometry offers extremely high sensitivity and elemental selectivity in microanalysis, but the isotopic precision attainable by this technique has been limited. Measured isotope ratios are sensitive to small fluctuations in the pointing, pulse timing, and wavelength of the resonance lasers. We show that, by minimizing these fluctuations using feedback controls and by power-broadening the optical transitions, we are able to measure chromium isotope ratios with statistics-limited precision better than 1%. Small additional improvements in reproducibility come from careful shaping of the electric field in the region where atoms are photoionized and from minimizing pulse-to-pulse variations in the time-of-flight mass spectrometer through which the photoions travel. The increased reproducibility of isotopic measurements on standard materials has enabled us to detect anomalous chromium isotopic abundances in presolar SiC grains extracted from primitive meteorites. 相似文献
34.
Keith Knight 《Applications of Mathematics》2008,53(3):223-234
We consider the asymptotic distribution of covariate values in the quantile regression basic solution under weak assumptions.
A diagnostic procedure for assessing homogeneity of the conditional densities is also proposed.
The research for this paper was supported by a grant from the Natural Sciences and Engineering Research Council of Canada. 相似文献
35.
We demonstrate the importance of collective behaviour in two identical two-level atoms. When the atoms become very close together a cascade three-level atom analysis can be adopted to show the increasing possibility of simultaneous jumps. Due to the dipole-dipole interaction the intermediate one-atom excited state is detuned by a large amount when the atoms are close together but leaving the upper two-atom excited state in two-photon resonance. The relative importance of multiple jumps compared with stepwise independent jumps is then changed dramatically. 相似文献
36.
T. Pavolini J. Callaway Th. N. Bennett N. L. Knight N. E. Seligson und E. S. Boldyrewa 《Fresenius' Journal of Analytical Chemistry》1934,97(1-2):53-54
Ohne Zusammenfassung 相似文献
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39.
Silvin P. Knight Louise Newman John D. OConnor James Davis Rose Anne Kenny Roman Romero-Ortuno 《Entropy (Basel, Switzerland)》2021,23(1)
In this cross-sectional study, the relationship between noninvasively measured neurocardiovascular signal entropy and physical frailty was explored in a sample of community-dwelling older adults from The Irish Longitudinal Study on Ageing (TILDA). The hypothesis under investigation was that dysfunction in the neurovascular and cardiovascular systems, as quantified by short-length signal complexity during a lying-to-stand test (active stand), could provide a marker for frailty. Frailty status (i.e., “non-frail”, “pre-frail”, and “frail”) was based on Fried’s criteria (i.e., exhaustion, unexplained weight loss, weakness, slowness, and low physical activity). Approximate entropy (ApEn) and sample entropy (SampEn) were calculated during resting (lying down), active standing, and recovery phases. There was continuously measured blood pressure/heart rate data from 2645 individuals (53.0% female) and frontal lobe tissue oxygenation data from 2225 participants (52.3% female); both samples had a mean (SD) age of 64.3 (7.7) years. Results revealed statistically significant associations between neurocardiovascular signal entropy and frailty status. Entropy differences between non-frail and pre-frail/frail were greater during resting state compared with standing and recovery phases. Compared with ApEn, SampEn seemed to have better discriminating power between non-frail and pre-frail/frail individuals. The quantification of entropy in short length neurocardiovascular signals could provide a clinically useful marker of the multiple physiological dysregulations that underlie physical frailty. 相似文献
40.
Muhammad NajeebUllah David W. Knight Munawar Ali Munawar Fusillo Vincenzo 《Tetrahedron》2010,66(34):6761-2710
A convenient and efficient method for the synthesis of triphenodioxazines [TPDOs] 1 by oxidative cyclisation of 2,5-bis-(arylamino)-3,6-dichlorocyclohexa-2,5-diene-1,4-diones 6 using potassium persulfate as the oxidising agent in 95?97% sulfuric acid triggered by microwave irradiation is described. 相似文献