A nodal Godunov method for Lagrangian shock hydrodynamics on unstructured tetrahedral grids

We present a nodal Godunov method for Lagrangian shock hydrodynamics. The method is designed to operate on three‐dimensional unstructured grids composed of tetrahedral cells. A node‐centered finite element formulation avoids mesh stiffness, and an approximate Riemann solver in the fluid reference frame ensures a stable, upwind formulation. This choice leads to a non‐zero mass flux between control volumes, even though the mesh moves at the fluid velocity, but eliminates volume errors that arise due to the difference between the fluid velocity and the contact wave speed. A monotone piecewise linear reconstruction of primitive variables is used to compute interface unknowns and recover second‐order accuracy. The scheme has been tested on a variety of standard test problems and exhibits first‐order accuracy on shock problems and second‐order accuracy on smooth flows using meshes of up to O(10⁶) tetrahedra. Copyright © 2014 John Wiley & Sons, Ltd.     

High stereocontrol in aldol reaction with ketones: enantioselective synthesis of beta-hydroxy gamma-ketoesters by ester enolate aldol reactions with 2-acyl-2-alkyl-1,3-dithiane 1-oxides

The asymmetric aldol reaction of 1,2-diketones, masked as nonracemic 2-acyl dithiane oxides, with lithium enolates derived from several esters and lactones, proceeds with a high degree of stereocontrol at both carbonyl and enolate prochiral centers, the stereocontrol mainly determined by the configuration of the sulfoxide sulfur atom. The sense of induced stereochemistry observed for ester enolates is different from that seen for lactone enolates. Hydrolysis of the dithiane oxide units of the major diastereoisomerically pure aldol products affords enantiomerically pure tertiary alpha-substituted beta-hydroxy-gamma-ketoesters.     

Performance and scaling effects in a multilayer microfluidic extracorporeal lung oxygenation device

Microfluidic fabrication technologies are emerging as viable platforms for extracorporeal lung assist devices and oxygenators for cardiac surgical support and critical care medicine, based in part on their ability to more closely mimic the architecture of the human vasculature than existing technologies. In comparison with current hollow fiber oxygenator technologies, microfluidic systems have more physiologically-representative blood flow paths, smaller cross section blood conduits and thinner gas transfer membranes. These features can enable smaller device sizes and a reduced blood volume in the oxygenator, enhanced gas transfer efficiencies, and may also reduce the tendency for clotting in the system. Several critical issues need to be addressed in order to advance this technology from its current state and implement it in an organ-scale device for clinical use. Here we report on the design, fabrication and characterization of multilayer microfluidic oxygenators, investigating scaling effects associated with fluid mechanical resistance, oxygen transfer efficiencies, and other parameters in multilayer devices. Important parameters such as the fluidic resistance of interconnects are shown to become more predominant as devices are scaled towards many layers, while other effects such as membrane distensibility become less significant. The present study also probes the relationship between blood channel depth and membrane thickness on oxygen transfer, as well as the rate of oxygen transfer on the number of layers in the device. These results contribute to our understanding of the complexity involved in designing three-dimensional microfluidic oxygenators for clinical applications.     

Solution of the equation of radiative transfer using a Newton–Krylov approach and adaptive mesh refinement

The discrete ordinates method (DOM) and finite-volume method (FVM) are used extensively to solve the radiative transfer equation (RTE) in furnaces and combusting mixtures due to their balance between numerical efficiency and accuracy. These methods produce a system of coupled partial differential equations which are typically solved using space-marching techniques since they converge rapidly for constant coefficient spatial discretization schemes and non-scattering media. However, space-marching methods lose their effectiveness when applied to scattering media because the intensities in different directions become tightly coupled. When these methods are used in combination with high-resolution limited total-variation-diminishing (TVD) schemes, the additional non-linearities introduced by the flux limiting process can result in excessive iterations for most cases or even convergence failure for scattering media. Space-marching techniques may also not be quite as well-suited for the solution of problems involving complex three-dimensional geometries and/or for use in highly-scalable parallel algorithms. A novel pseudo-time marching algorithm is therefore proposed herein to solve the DOM or FVM equations on multi-block body-fitted meshes using a highly scalable parallel-implicit solution approach in conjunction with high-resolution TVD spatial discretization. Adaptive mesh refinement (AMR) is also employed to properly capture disparate solution scales with a reduced number of grid points. The scheme is assessed in terms of discontinuity-capturing capabilities, spatial and angular solution accuracy, scalability, and serial performance through comparisons to other commonly employed solution techniques. The proposed algorithm is shown to possess excellent parallel scaling characteristics and can be readily applied to problems involving complex geometries. In particular, greater than 85% parallel efficiency is demonstrated for a strong scaling problem on up to 256 processors. Furthermore, a speedup of a factor of at least two was observed over a standard space-marching algorithm using a limited scheme for optically thick scattering media. Although the time-marching approach is approximately four times slower for absorbing media, it vastly outperforms standard solvers when parallel speedup is taken into account. The latter is particularly true for geometrically complex computational domains.     

Diels-alder reactions with 2-(Arylsulfinyl)-1,4-benzoquinones: effect of aryl substitution on reactivity, chemoselectivity, and pi-facial diastereoselectivity

Diels-Alder reactions of (SS)-2-(2'-methoxynaphthylsulfinyl)-1, 4-benzoquinone (1b), 2-(p-methoxyphenylsulfinyl)-1,4-benzoquinone (1c), and 2-(p-nitrophenylsulfinyl)-1,4-benzoquinone (1d) with cyclopentadiene are reported. These cycloadditions allowed the highly chemo- and stereoselective formation of both diastereoisomeric endo-adducts resulting from reaction on the unsubstituted double bond C(5)-C(6) of quinones working under thermal and Eu(fod)(3)- or BF(3).OEt(2)-catalyzed conditions. The synthesis of endo-adduct [4aS,5S,8R,8aR,SS]-9d resulting from cycloaddition on the substituted C(2)-C(3) double bond was achieved in a chemo- and diastereoselective way from quinone 1d in the presence of ZnBr(2). The reactivity and selectivity of the process proved to be dependent on the electron density of the arylsulfinyl group.     

Time domain investigation on vibrational dephasing and spectral diffusion in CO-doped solid N2

Infrared picosecond accumulated photon echo experiments have been performed for the first time, using the Orsay Free Electron Laser, on the v = 0-->v = 1 transition of CO in solid nitrogen. The vibrational dephasing time is found to be exceptionally long ( T2>/=120 ns) at low temperature. The analysis of the observed spectral diffusion leads one to assume different energy transfer mechanisms depending on the CO concentration.