Quantum stochastic cocycles and completely bounded semigroups on operator spaces

An operator space analysis of quantum stochastic cocycles is undertaken. These are cocycles with respect to an ampliated CCR flow, adapted to the associated filtration of subspaces, or subalgebras. They form a noncommutative analogue of stochastic semigroups in the sense of Skorohod. One-to-one correspondences are established between classes of cocycle of interest and corresponding classes of one-parameter semigroups on associated matrix spaces. Each of these 'global' semigroups may be viewed as the expectation semigroup of an associated quantum stochastic cocycle on the corresponding matrix space. The classes of cocycle covered include completely positive contraction cocycles on an operator system, or C*-algebra; completely contractive cocycles on an operator space; and contraction operator cocycles on a Hilbert space. As indicated by Accardi and Kozyrev, the Schur-action matrix semigroup viewpoint circumvents technical (domain) limitations inherent in the theory of quantum stochastic differential equations. An infinitesimal analysis of quantum stochastic cocycles from the present wider perspective is given in a sister paper.Comment: 32 page

Synthesis and use of a stable aminal derived from TsDPEN in asymmetric organocatalysis

A stable aminal formed stereoselectively from (R,R)-N-tosyl-1,2-diphenyl-1,2-ethylenediamine (TsDPEN) is capable of asymmetric organocatalysis of Diels-Alder and alpha-amination reactions of aldehydes

Studies of the shellside performance of shell-and-tube heat exchangers

Accurate prediction of shellside pressure drop in a baffled shell-and-tube heat exchanger is very difficult because of the complicated shellside geometry. Ideally, all the shellside fluid should be alternately deflected across the tube bundle as it traverses from inlet to outlet. In practice, up to 60% of the shellside fluid may bypass the tube bundle or leak through the baffles. This short-circuiting of the main flow reduces the efficiency of the exchanger. Of the various shellside methods, it is shown that only the multi-stream methods, which attempt to obtain the shellside flow distribution, predict the pressure drop with any degree of accuracy, the various predictions ranging from -30% to +70%, generally overpredicting. It is shown that the inaccuracies are mainly due to the manner in which baffle leakage is modelled. The present multi-stream methods do not allow for interactions of the various flowstreams, and yet it is shown that three main effects are identified, a) there is a strong interaction between the main cross flow and the baffle leakage streams, enhancing the crossflow pressure drop, b) there is a further short-circuit not considered previously i.e. leakage in the window, and c) the crossflow does not penetrate as far, on average, as previously supposed. Models are developed for each of these three effects, along with a new windowflow pressure drop model, and it is shown that the effect of baffle leakage in the window is the most significant. These models developed to allow for various interactions, lead to an improved multi-stream method, named the "STREAM-INTERACTION" method. The overall method is shown to be consistently more accurate than previous methods, with virtually all the available shellside data being predicted to within ±30% and over 60% being within ±20%. The method is, thus, strongly recommended for use as a design method

Ruthenium-catalyzed asymmetric reduction of isoxazolium salts : access to optically active Δ4-isoxazolines

A tethered MsDPEN–ruthenium catalyst reduces a series of isoxazolium salts, affording optically active Δ4-isoxazolines in moderate to good yields and enantioenrichment. The redundancy of heating or high pressures allowed for chemoselective reduction with no subsequent heterocyclic ring opening. Our results reinforce our understanding of the workings of these Noyori-class catalysts

Exploitation of differential electronic densities for the stereoselective reduction of ketones bearing a masked amino surrogate

A tethered ruthenium-TsDPEN catalyst is employed for the facile catalytic asymmetric reduction of α-phthalimyl-α′-ketoethers under mild conditions. Leveraging exclusively on the contrasting electronic densities on the heteroatoms, a series of enantioenriched phthalimyl ether alcohols can be obtained in generally good stereoselectivities from this challenging class of substrate. Subsequent transformation into highly valuable chiral β-amino alcohols is demonstrated to take place without significant losses in yield and optical purity