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71.
A series of measurements on the high pressure (up to 18 bar) coaxial e-beam pumped Ar/Xe laser has been made at high power loading (up to 25 MW/cm~2) for various Xe mole fraction in Ar. We found that the optimum laser gas composition in our system was 0.4% Xe in Ar which was independent of the total gas pressure. At the optimum gas composition the output energy increased with increasing total gas pressure up to 16 bar, but the intrinsic efficiency reached a maximum at the total gas pressure of 8 bar. It was also found that at the optimum power deposition for both the 2.63μm and 2.65μm transitions the ratio of the integrated optical energy to that of the 1.73μm transition had a minimum in most cases at the optimum gas mixture for various gas pressures. This ratio increased with increasing gas pressure. The experimental results suggested that besides the 2-body Xe quenching at high Xe fraction and electron collision mixing at high power depositions the heavy particle quenching from Ar at high gas press 相似文献
72.
A complex spectral grating is accumulated by repeated application of a pair of low-power optical programming pulses to a short-term persistent inhomogeneously broadened transition in Tm:YAG at 4.5 K and then probed to investigate the buildup dynamics. The necessary frequency stability is obtained by locking a cw Ti:sapphire laser to a regenerating transient spectral hole in the same transition. Grating accumulation is demonstrated for both a periodic spectral grating, representing a true-time delay, and a complex spectral grating, permitting correlation-based pattern recognition. This work is a step toward demonstrating an optical coherent transient continuously programmed continuous processor. 相似文献
73.
CM Silva MF Duarte ML Mira MH Florêncio K Versluis AJ Heck 《Rapid communications in mass spectrometry : RCM》1999,13(12):1098-1103
Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
74.
75.
Dr. Daniel Brodbeck Dr. Sonia Álvarez-Barcia Dr. Jan Meisner Dr. Florian Broghammer Julian Klepp Dr. Delphine Garnier Dr. Wolfgang Frey Prof. Dr. Johannes Kästner Prof. Dr. René Peters 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(6):1515-1524
Asymmetric 1,2-additions of cyanide yield enantioenriched cyanohydrins as versatile chiral building blocks. Next to HCN, volatile organic cyanide sources are usually used. Among them, cyanoformates are more attractive on technical scale than TMSCN for cost reasons, but catalytic productivity is usually lower. Here, the development of a new strategy for cyanations is described, in which this activity disadvantage is overcome. A Lewis acidic Al center cooperates with an aprotic onium moiety within a remarkably robust bifunctional Al–F–salen complex. This allowed for unprecedented turnover numbers of up to 104. DFT studies suggest an unexpected unique trimolecular pathway in which the ammonium bound cyanide attacks the aldehyde, which itself is activated by the carbonyl group of the cyanoformate binding to the Al center. In addition, a novel practical carboxycyanation method was developed that makes use of KCN as the sole cyanide source. The use of a pyrocarbonate as carboxylating reagent provided the best results. 相似文献
76.
We present a hybridized discontinuous Galerkin (HDG) method for the incompressible Reynolds-averaged Navier-Stokes equations coupled with the Spalart-Allmaras one-equation turbulence model. The method extends upon an HDG method recently introduced by Rhebergen and Wells for the incompressible Navier-Stokes equations. With a special choice of velocity and pressure spaces for both element and trace degrees of freedom (DOFs), the method returns pointwise divergence-free mean velocity fields and properly balances momentum and energy. We further examine the use of different polynomial degrees and meshes to see how the order of the scalar eddy viscosity affects the convergence of the mean velocity and pressure fields, specifically for the method of manufactured solutions. As is standard with HDG methods, static condensation can be employed to remove the element DOFs and thus dramatically reduce the global number of DOFs. Numerical results illustrate the effectiveness of the proposed methodology. 相似文献
77.
Enantiodivergent [4+2] Cycloaddition of Dienolates by Polyfunctional Lewis Acid/Zwitterion Catalysis
M. Sc. Vukoslava Miskov-Pajic M. Sc. Felix Willig M. Sc. Daniel M. Wanner Dr. Wolfgang Frey Prof. Dr. René Peters 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(45):20045-20049
Diels–Alder reactions have become established as one of the most effective ways to prepare stereochemically complex six-membered rings. Different catalysis concepts have been reported, including dienophile activation by Lewis acids or H-bond donors and diene activation by bases. Herein we report a new concept, in which an acidic prodiene is acidified by a Lewis acid to facilitate deprotonation by an imidazolium–aryloxide entity within a polyfunctional catalyst. A metal dienolate is thus formed, while an imidazolium–ArOH moiety probably forms hydrogen bonds with the dienophile. The catalyst type, readily prepared in few steps in high overall yield, was applied to 3-hydroxy-2-pyrone and 3-hydroxy-2-pyridone as well as cyclopentenone prodienes. Maleimide, maleic anhydride, and nitroolefin dienophiles were employed. Kinetic, spectroscopic, and control experiments support a cooperative mode of action. High enantioselectivity was observed even with unprecedented TONs of up to 3680. 相似文献
78.
Khanna Vikram Monroe Jacob I. Doherty Michael F. Peters Baron 《Journal of computer-aided molecular design》2020,34(6):641-646
Journal of Computer-Aided Molecular Design - The decoupling approach to solvation free energy calculations requires scaling the interactions between the solute and the solution with all... 相似文献
79.
Auditory filter shapes were measured for two groups of hearing-impaired subjects, young and elderly, matched for audiometric loss, for center frequencies (fc) of 100, 200, 400, and 800 Hz using a modified notched-noise method [B. R. Glasberg and B. C. J. Moore, Hear. Res. 47, 103-138 (1990)]. Two noise bands, each 0.4fc wide, were used; they were placed both symmetrically and asymmetrically about the signal frequency to allow the measurement of filter asymmetry. The overall noise level was either 77 or 87 dB SPL. Stimuli were delivered monaurally using Sennheiser HD424 earphones. Although auditory filters for the hearing-impaired subjects were generally broader than for normally hearing subjects [Moore et al., J. Acoust. Soc. Am. 87, 132-140 (1990)], some hearing-impaired subjects with mild losses had normal filters. The filters tended to broaden with increasing hearing loss. There were not any clear differences in filter characteristics between young and elderly hearing-impaired subjects. The signal-to-noise ratios at the outputs of the auditory filters required for threshold (K) tended to be lower than normal for the young hearing-impaired subjects, but were not significantly different from normal for the elderly hearing-impaired subjects. The lower K values for the young hearing-impaired subjects may occur because broadened auditory filters reduce the deleterious effects on signal detection of fluctuations in the noise. 相似文献
80.
We study systems with a continuous phase transition that tune their parameters to maximize a quantity that diverges solely at a unique critical point. Varying the size of these systems with dynamically adjusting parameters, the same finite-size scaling is observed as in systems where all relevant parameters are fixed at their critical values. This scheme is studied using a self-tuning variant of the Ising model. It is contrasted with a scheme where systems approach criticality through a target value for the order parameter that vanishes with increasing system size. In the former scheme, the universal exponents are observed in naïve finite-size scaling studies, whereas in the latter they are not. 相似文献