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1.
Deerenberg S Schrekker HS van Strijdonck GP Kamer PC van Leeuwen PW Fraanje J Goubitz K 《The Journal of organic chemistry》2000,65(16):4810-4817
A series of chiral phosphine-phosphite ligands 1-6 have been synthesized and used in the enantioselective palladium-catalyzed reaction of rac-1,3-diphenyl-2-propenyl acetate with dimethyl malonate as nucleophile. Ligands 1a, 2, 3, 5a, 6a, and 6b have been synthesized starting from racemic tert-butylphenylphosphinoborane. The use of dynamically resolved Li phosphide (-)-sparteine provided the optically pure ligands. Crystals of the allylpalladium (6a) complex were obtained, suitable for X-ray crystal structure determination. The X-ray crystal structure of the allylpalladium (6a) complex revealed a longer palladium-carbon bond distance trans to the phosphine moiety indicating that the attack of the nucleophile takes place at the carbon trans to the phosphine moiety. This was confirmed by the fact that the phosphine moiety did not affect the enantioselectivity directly. Under mild reaction conditions, enantioselectivities up to 83% were obtained (25 degrees C) with ligand 1e. Systematic variation of the ligand bridge and the phosphite moiety showed that the configuration of the product is controlled by the atropisomerism of the biphenyl substituent at the phosphite moiety. The conformation of the biphenyl group, in turn, is controlled by the substituent at the chiral carbon in the bridge. Ligands with large bite angles yielded higher enantioselectivities. 相似文献
2.
Petra DG Kamer PC Spek AL Schoemaker HE van Leeuwen PW 《The Journal of organic chemistry》2000,65(10):3010-3017
A new class of efficient catalysts was developed for the asymmetric transfer hydrogenation of unsymmetrical ketones. A series of chiral N,S-chelates (6-22) was synthesized to serve as ligands in the iridium(I)-catalyzed reduction of ketones. Both formic acid and 2-propanol proved to be suitable as hydrogen donors. Sulfoxidation of an (R)-cysteine-based aminosulfide provided a diastereomeric ligand family containing a chiral sulfur atom. The two chiral centers of these ligands showed a clear effect of chiral cooperativity. In addition, aminosulfides containing two asymmetric carbon atoms in the backbone were synthesized. Both the sulfoxide-containing beta-amino alcohols and the aminosulfides derived from 1,2-disubstituted amino alcohols gave rise to high reaction rates and moderate to excellent enantioselectivities in the reduction of various ketones. The enantioselective outcome of the reaction was favorably affected by selecting the most appropriate hydrogen donor. Enantioselectivities of up to 97% were reached in the reduction of aryl-alkyl ketones. 相似文献
3.
Li CK Séguin FH Frenje JA Petrasso RD Delettrez JA McKenty PW Sangster TC Keck RL Soures JM Marshall FJ Meyerhofer DD Goncharov VN Knauer JP Radha PB Regan SP Seka W 《Physical review letters》2004,92(20):205001
Target areal density (rhoR) asymmetries in OMEGA direct-drive spherical implosions are studied. The rms variation / for low-mode-number structure is approximately proportional to the rms variation of on-target laser intensity / with an amplification factor of approximately 1/2(C(r)-1), where C(r) is the capsule convergence ratio. This result has critical implications for future work on the National Ignition Facility as well as OMEGA. 相似文献
4.
Progress in direct-drive inertial confinement fusion research at the
laboratory for laser energetics
R. L. McCrory D. D. Meyerhofer S. J. Loucks S. Skupsky R. Betti T. R. Boehly T. J.B. Collins R. S. Craxton J. A. Delettrez D. H. Edgell R. Epstein K. A. Fletcher C. Freeman J. A. Frenje V. Yu. Glebov V. N. Goncharov D. R. Harding I. V. Igumenshchev R. L. Keck J. D. Kilkenny J. P. Knauer C. K. Li J. Marciante J. A. Marozas F. J. Marshall A. V. Maximov P. W. McKenty S. F.B. Morse J. Myatt S. Padalino R. D. Petrasso P. B. Radha S. P. Regan T. C. Sangster F. H. Séguin W. Seka V. A. Smalyuk J. M. Soures C. Stoeckl B. Yaakobi J. D. Zuegel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(2):233-238
Direct-drive inertial confinement fusion (ICF) is
expected to demonstrate high gain on the National Ignition Facility (NIF) in
the next decade and is a leading candidate for inertial fusion energy
production. The demonstration of high areal densities in hydrodynamically
scaled cryogenic DT or D2 implosions with neutron yields that are a
significant fraction of the “clean” 1-D predictions will validate the
ignition-equivalent direct-drive target performance on the OMEGA laser at
the Laboratory for Laser Energetics (LLE). This paper highlights the
recent experimental and theoretical progress leading toward achieving this
validation in the next few years.
The NIF will initially be configured for X-ray drive and with no beams
placed at the target equator to provide a symmetric irradiation of a
direct-drive capsule. LLE is developing the “polar-direct-drive” (PDD)
approach that repoints beams toward the target equator. Initial 2-D
simulations have shown ignition. A unique “Saturn-like” plastic ring
around the equator refracts the laser light incident near the equator toward
the target, improving the drive uniformity.
LLE is currently constructing the multibeam, 2.6-kJ/beam, petawatt laser
system OMEGA EP. Integrated fast-ignition experiments, combining the OMEGA
EP and OMEGA Laser Systems, will begin in FY08. 相似文献
5.
This paper presents an anisotropic mesh adaptation method applied to industrial combustion problems. The method is based on a measure of the distance between two Riemannian metrics called metric non‐conformity. This measure, which can be used to build a cost function to adapt meshes comprising several types of mesh elements, provides the basis for a generic mesh adaptation approach applicable to various types of physical problems governed by partial differential equations. The approach is shown to be applicable to industrial combustion problems, through the specification of a target metric computed as the intersection of several Hessian matrices reconstructed from the main variables of the governing equations. Numerical results show that the approach is cost effective in that it can drastically improve the prediction of temperature and species distributions in the flame region of a combustor while reducing computational cost. The results can be used as a basis for pollutant prediction models. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
6.
Sandee AJ van Der Veen LA Reek JN Kamer PC Lutz M Spek AL van Leeuwen PW 《Angewandte Chemie (International ed. in English)》1999,38(21):3231-3235
By a sol-gel process a rhodium complex containing a diphosphane with a large natural P-Rh-P bite angle is covalently anchored in a silica matrix (see picture). The immobilized catalyst is a very selective hydroformylation catalyst that is completely and conveniently separated from the product and can be reused in numerous cycles. 相似文献
7.
Sangster TC Goncharov VN Radha PB Smalyuk VA Betti R Craxton RS Delettrez JA Edgell DH Glebov VY Harding DR Jacobs-Perkins D Knauer JP Marshall FJ McCrory RL McKenty PW Meyerhofer DD Regan SP Seka W Short RW Skupsky S Soures JM Stoeckl C Yaakobi B Shvarts D Frenje JA Li CK Petrasso RD Séguin FH 《Physical review letters》2008,100(18):185006
The first observation of ignition-relevant areal-density deuterium from implosions of capsules with cryogenic fuel layers at ignition-relevant adiabats is reported. The experiments were performed on the 60-beam, 30-kJUV OMEGA Laser System [T. R. Boehly, Opt. Commun. 133, 495 (1997)10.1016/S0030-4018(96)00325-2]. Neutron-averaged areal densities of 202+/-7 mg/cm2 and 182+/-7 mg/cm2 (corresponding to estimated peak fuel densities in excess of 100 g/cm3) were inferred using an 18-kJ direct-drive pulse designed to put the converging fuel on an adiabat of 2.5. These areal densities are in good agreement with the predictions of hydrodynamic simulations indicating that the fuel adiabat can be accurately controlled under ignition-relevant conditions. 相似文献
8.
The purpose of this work is to introduce and validate a new staggered control volume method for the simulation of 2D/axisymmetric incompressible flows. The present study introduces a numerical procedure for solving the Navier–Stokes equations using the primitive variable formulation. The proposed method is an extension of the staggered grid methodology to unstructured triangular meshes for a control volume approach which features ease of handling of irregularly shaped domains. Two alternative elements are studied: transported scalars are stored either at the sides of an element or at its vertices, while the pressure is always stored at the centre of an element. Two interpolation functions were investigated for the integration of the momentum equations: a skewed mass-weighted upwind function and a flow-oriented exponential shape function. The momentum equations are solved over the covolume of a side or of a vertex and the pressure–velocity coupling makes use of a localized linear reconstruction of the discontinuous pressure field surrounding an element in order to obtain the pressure gradient terms. The pressure equation is obtained through a discretization of the continuity equation which uses the triangular element itself as the control volume. The method is applied to the simulation of the following test cases: backward-facing step flow, flow over a two-dimensional obstacle and flow in a pipe with sudden contraction of cross-sectional area. All numerical investigations are compared with experimental data from the literature. A grid convergence and error analysis study is also carried out for flow in a driven cavity. Results compared favourably with experimental data and so the new control volume scheme is deemed well suited for the prediction of incompressible flows in complex geometries. © 1997 John Wiley & Sons, Ltd. 相似文献
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