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61.
The aza-Darzens (‘ADZ’) reactions of N-diphenylphosphinyl (‘N-Dpp’) imines with chiral enolates derived from N-bromoacetyl 2S-2,10-camphorsultam proceed in generally good yield to give N-diphenylphosphinyl aziridinoyl sultams. However, the stereoselectivity of the reaction is dependent upon the structure of the imine substituent: when the chiral enolate was reacted with arylimines substituted in the ortho-position, mixtures of cis- and trans-2′R,3′R-aziridines were obtained, often with a complete selectivity in favour of the trans-isomer. 相似文献
62.
The structural and electronic transport properties of La1−x
Ce
x
MnO3 (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with
Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration
up to 50% doping. The system La0.5Ce0.5MnO3 also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition. 相似文献
63.
In order to understand the origin of the Hofmeister series, a statistical-mechanical analysis, based upon the Kirkwood-Buff (KB) theory, has been performed to extract information regarding protein hydration and water-mediated protein-salt interactions from published experimental data-preferential hydration and volumetric data for bovine serum albumin in the presence of a wide range of salts. The analysis showed a linear correlation between the preferential hydration parameter and the protein-cosolvent KB parameter. The same linear correlation holds even when nonelectrolyte cosolvents, such as polyethelene glycol, have been incorporated. These results suggest that the Hofmeister series is due to a wide variation of the water-mediated protein-cosolvent interaction (but not the change of protein hydration) and that this mechanism is a special case of a more general scenario common even to the macromolecular crowding. 相似文献
64.
Michael Tan Paul Rosenberg Jong Souk Yeo Moray McLaren Sagi Mathai Terry Morris Huei Pei Kuo Joseph Straznicky Norman P. Jouppi Shih-Yuan Wang 《Applied Physics A: Materials Science & Processing》2009,95(4):945-953
Buses have historically provided a flexible communications structure in computer systems. However, signal integrity constraints
of high-speed electronics have made multi-drop electrical buses infeasible. Instead, we propose an optical data bus for computer
interconnections. It has two sets of optical waveguides, one as a fan-out and the other as a fan-in, that are used to interconnect
different modules attached to the bus. A master module transmits optical signals which are received by all the slave modules
attached to the bus. Each slave module in turn sends data back on the bus to the master module. Arrays of lasers, photodetectors,
waveguides, microlenses, beamsplitters, and Tx/Rx integrated circuits are used to realize the optical data bus. With 1 mW
of laser power, we are able to interconnect eight different modules at 10 Gb/s per channel. An aggregate bandwidth of over
25 GB/s is achievable with 10-bit wide signaling paths. 相似文献
65.
We present an efficient method to accurately calculate the reconstruction properties of a Bessel-Gauss beam after an arbitrary obstruction. Our method makes use of the well-known conical wave features of Bessel-Gauss beams, by considering the projection of the obstacle in space as a result of the travelling conical waves that produce the Bessel-Gauss beams. This approach, of projecting the obstacle boundaries rather than propagating the field itself, results in fast and accurate predictions of the field after any obstacle. We successfully predict the reconstruction properties of a Bessel-Gauss beam after three complex obstacles by calculating the boundaries of the various projected regions. This method has no restrictions regarding the geometry of the obstacle or its placement in the Bessel-Gauss field. 相似文献
66.
Focsa C Poclet A Pinchemel B Le Roy RJ Bernath PF 《Journal of Molecular Spectroscopy》2000,203(2):330-338
The A'(1)Pi-X(1)Sigma(+) near-infrared system of CaO was observed for the first time at high resolution using a Fourier transform spectrometer. The A'(1)Pi-X(1)Sigma(+) chemiluminescence was excited in a Ca + N(2)O flame produced in a Broida-type oven. More than 3000 rotational lines, classified into 19 bands involving the A'(1)Pi 0 = v' = 3 and the X(1)Sigma(+) 1 = v" = 7 vibrational levels were measured in the 4000-10 000 cm(-1) region with a precision of 0.005 cm(-1). The X(1)Sigma(+) (v = 0, 1) millimeter-wave and X(1)Sigma(+) (v = 0-3) infrared data available in the literature were merged with our new electronic data in order to obtain improved Dunham constants for the ground state of CaO. Very peculiar perturbations are observed in the higher vibrational levels of the A'(1)Pi state, so the upper levels of transitions with v' = 2 and 3 were represented by term values in our least-squares analysis. The interaction of the A'(1)Pi (v >/= 2) levels with the nearby b(3)Sigma(+) (v-2) levels has been detected. An extended set of A'(1)Pi (v = 0-3) data has been obtained which is suitable for use in a future multistate deperturbation analysis of the a(3)Pi approximately A'(1)Pi approximately b(3)Sigma(+) approximately A(1)Sigma(+) complex of excited states. The new near-infrared spectra of the A'(1)Pi-X(1)Sigma(+) transition of CaO also permits the first direct high-resolution linkage between the orange and green systems and the near-infrared bands. Copyright 2000 Academic Press. 相似文献
67.
Wong KL Chu MS Luce TC Petty CC Politzer PA Prater R Chen L Harvey RW Austin ME Johnson LC La Haye RJ Snider RT 《Physical review letters》2000,85(5):996-999
Experimental evidence is reported of an internal kink instability driven by a new mechanism: barely trapped suprathermal electrons produced by off-axis electron cyclotron heating on the DIII-D tokamak. It occurs in plasmas with an evolving safety factor profile q(r) when q(min) approaches 1. This instability is most active when ECCD is applied on the high field side of the flux surface. It has a bursting behavior with poloidal/toroidal mode number = m/n = 1/1. In positive magnetic shear plasmas, this mode becomes the fishbone instability. This observation can be qualitatively explained by the drift reversal of the barely trapped suprathermal electrons. 相似文献
68.
LeClair P Swagten HJ Kohlhepp JT van De Veerdonk RJ de Jonge WJ 《Physical review letters》2000,84(13):2933-2936
Co/Al2O3/Co magnetic tunnel junctions with an interfacial Cu layer have been investigated with in situ growth characterization and ex situ magnetotransport measurements. Cu interlayers grown on Co give an approximately exponential decay of the tunneling magnetoresistance with xi approximately 0.26 nm while those grown on Al2O3 have a decay length of 0.70 nm. The difference in decay lengths can be explained by different growth morphologies, and in this way clarifies a present disagreement in the literature. For monolayer coverage of Cu, we show that the tunneling spin polarization is suppressed by at least a factor of 2 compared to Co and beyond approximately 5 ML it becomes vanishingly small. 相似文献
69.
By combining a measure of activity in transform-coded image blocks with frequency sensitivity data, suitable psychovisual coefficient quantisation step sizes can be calculated. A number of possible definitions for an activity function A/sub F/ are proposed. The most suitable of these is determined by comparing results on a subjective basis.<> 相似文献
70.