Catalytic, asymmetric transannular aldolizations: total synthesis of (+)-hirsutene

We report an asymmetric, catalytic transannular aldolization that provides polycyclic products useful for natural product synthesis. We found that a proline-derivative catalyzes the transannular aldol reaction of 1,4-cyclooctanediones to the corresponding cyclic beta-hydroxy ketones in good yields and with high enantioselectivities. The utility of our reaction has been demonstrated in a total synthesis of (+)-hirustene.     

Theoretical studies of five-membered ring ketene acetals

Cyclic ketene acetals are a class of organic molecules characterized by a nucleophilic exo-methylene carbon attached to a carbon with two adjacent O, N, or S atoms. We have carried out a systematic computational study of a series of five-membered cyclic acetals like 2-methylene-1,3-dioxolane and its OS, SS, NO, NS, and NN analogs as well as all the protonated species. The calculations were performed at the MP2 level using a triple zeta plus polarization basis set. The nucleophilicity was discussed in terms of geometrical factors, calculated atomic charges, calculated chemical shifts, and proton affinities. All the six neutral species were strong nucleophiles. The NN analog was predicted to be the strongest and the SS analog the weakest nucleophile.     

Constrained dynamics of localized excitations causes a non-equilibrium phase transition in an atomistic model of glass formers

Recent progress has demonstrated that trajectory space for both kinetically constrained lattice models and atomistic models can be partitioned into a liquid-like and an inactive basin with a non-equilibrium phase transition separating these behaviors. Recent work has also established that excitations in atomistic models have statistics and dynamics like those in a specific class of kinetically constrained models. But it has not been known whether the non-equilibrium phase transitions occurring in the two classes of models have similar origins. Here, we show that the origin is indeed similar. In particular, we show that the number of excitations identified in an atomistic model serves as the order parameter for the inactive-active phase transition for that model. In this way, we show that the mechanism by which excitations are correlated in an atomistic model - by dynamical facilitation - is the mechanism from which the active-inactive phase transition emerges. We study properties of the inactive phase and show that it is amorphous lacking long-range order. We also discuss the choice of dynamical order parameters.     

Dual-etalon frequency-comb cavity ringdown spectrometer

We have demonstrated a spectroscopic technique for simultaneously obtaining broad spectral bandwidth and high frequency resolution absorption measurements, with 5 μs temporal resolution, continuously for tens of microseconds in an apparatus with no active stabilization. The technique utilizes two passive air-gap etalons to imprint two frequency comb patterns onto a single pulsed light source. The air-gap etalons also serve as cavity ringdown cells increasing the sensitivity of the absorption spectroscopy by increasing the interrogation path length. Here, we demonstrate the operation of the spectrometer utilizing a ~0.15 cm(-1) bandwidth pulsed dye laser and two nearly identical 300 MHz free-spectral range confocal air-gap etalons each with a finesse of ~1 × 10(5), to investigate the (1,1,3) overtone of water and the R(7) transition of the O(2) b(1)Σ(g)(+)←X(3)Σ(g)(-) (2,0) band with high spectral resolution.     

Basis for Breakup States of Three Identical Particles

 A new basis for expanding three-body momentum-space states for three identical particles is studied. The basis states are simultaneously eigenstates of the total angular momentum and the total antisymmetrization operator. The total kinetic energy and two Dalitz-Fabri variables are chosen as the remaining three continuous variables. Zernike polynomials are used as a basis set for a generalized Fourier expansion in the Dalitz-Fabri variables. Born approximations to the nucleon-deuteron breakup amplitude (zero total orbital angular momentum) are calculated for Malfliet-Tjon I–III potentials and displayed in a Dalitz plot that shows the global structures of the reaction probabilities. Numerical results are presented, which indicate favorable convergence properties of the generalized Fourier expansion. These results suggest that the new basis set may be attractive in more realistic calculations. Received July 28, 2000; accepted in final form January 29, 2001     

More Operator Versions of the Schwarz Inequality

Some new operator versions of the Schwarz inequality are obtained. One of them is a counterpart of the variance-covariance inequality in the context of noncommutative probability. Received: 14 April 2000 / Accepted: 10 May 2000     

-Body Quantum Scattering Theory in Two Hilbert Spaces: -Body Integral Equations

Scattering for a nonrelativistic system of distinguishable and spinless particles interacting via short-range pair potentials is considered. Half-on-shell integral equations (the CG equations) are proposed, the solutions of which determine approximate scattering amplitudes that converge to the exact scattering amplitude. It is proved, under mild H?lder integrability assumptions, that these apparently singular equations actually have a compact kernel for real energies and, consequently, a unique solution. The CG equations have a structure that is much simpler than the Yakubovskii equations and similar to that of coupled-reaction-channel equations. The driving terms look like distorted-wave Born integrals and nonorthogonality integrals. However, there is no restriction to channels with only two asymptotic bound clusters and for all channels, no matter how many bound clusters, appropriate boundary conditions are exactly satisfied. This work completes the establishment of a rigorous mathematical link between the solutions of the half-on-shell CG equations and the on-shell transition operators defined in time-dependent multichannel scattering theory, and it provides for the first time a rigorous theoretical basis for practical calculations of scattering amplitudes for certain problems with . Received October 27, 1997; accepted for publication December 29, 1997     

Wire number doubling in high-wire-number regime increasesZ-accelerator X-ray power

Doubling the number of tungsten wires from 120 to 240, keeping the mass fixed, increased the radiated X-ray power relative to the electrical power at the insulator stack of the Z accelerator by (35±15)% for 8.75- and 20-mm radii Z-pinch wire arrays. One-dimensional radiation magneto hydrodynamic calculations suggest that the arrays were operating in a quasi “plasma-shed” regime, where the plasma generated by the individual wires partially merge prior to the inward implosion of the entire array