Quadrupole splitting and ground state in FeS and NiS (Fe)

From a Mössbauer study of an oriented single crystal of Ni_0.996S (2% Fe⁵⁷) at 298 K (above the metal-insulator transition at 230 K) the sign of the quadrupole splitting in Fe⁵⁷ is determined to be positive; this contrasts with a negative sign found for FeS and Fe_0.93S. A tentative model is presented that is consistent with these results and with magnetic anisotropy data.     

Pion production via isobar giant resonance formation and decay

A spin, isotopic-spin formalism for the production of pions due to decays of isobar giant resonances formed in peripheral heavy-ion collisions is presented. The projectile nucleus isobar giant resonance state is assumed to coherently form and then incoherently decay to produce the pions. Total spin and isotopic spin for the system are conserved through the concomitant excitation of the target nucleus to an isobaric analog giant resonance state. Comparisons of the predicted total pion cross sections, over a range of energies, are made with heavy-ion pion data.     

Studies of methoxymethyl-directed metalation

To explore the use of methoxymethyl groups to elaborate simple benzenoid precursors to more complex polyketide-derived natural products, the reaction of phenolmetoxymethyl ether $\text{ortho}$-anion was investigated with a number of electrophiles.     

Poincarésupergravity as broken superconformal gravity

We present a locally superconformal invariant theory of supergravity which is gauge equivalent to the usual, Poincaré, supergravity. This is achieved by means of a compensating scalar supermultiplet. This shows that local superconformal symmetry can be made compatible with gravitational phenomenology.     

Accelerating cosmologies from compactification

A solution of the (4+n)-dimensional vacuum Einstein equations is found for which spacetime is compactified on an n-dimensional compact hyperbolic manifold (n> or =2) of time-varying volume to a flat four-dimensional Friedmann-Lemaitre-Robertson-Walker cosmology undergoing a period of accelerated expansion in the Einstein conformal frame. This shows that the "no-go" theorem forbidding acceleration in "standard" (time-independent) compactifications of string or M theory does not apply to "cosmological" (time-dependent) hyperbolic compactifications.     

Catalytic asymmetric cyclopropanation of heteroaryldiazoacetates

Rh(2)(S-DOSP)(4)-catalyzed decomposition of heteroaryldiazoacetates in the presence of styrene results in highly diastereoselective and enantioselective cyclopropanations. Heteroaryldiazoacetates containing both electron-rich and electron-deficient heterocycles, such as thiophene, furan, pyridine, indole, oxazole, isoxazole, and benzoxazole, are effective in this chemistry. These studies broaden the range of diazo compounds containing both electron-withdrawing and electron-donating groups, which undergo highly diastereoselective cyclopropanations.     

Hyper-Kähler manifolds and multiply intersecting branes

Generalized membrane solutions of D = 11 supergravity, for which the transverse space is a toric hyper-Kahler manifold, are shown to have IIB duals representing the intersection of parallel 3-branes with 5-branes whose orientations are determined by their charge vectors. These IIB solutions, which generically preserve 3/16 of the supersymmetry, can be further mapped to solutions of D = 11 supergravity representing the intersection of parallel membranes with any number of fivebranes at arbitrary angles. Alternatively, a subclass (corresponding to non-singular D = 11 solutions) can be mapped to solutions representing the intersection on a string of any number of D-5-branes at arbitrary angles, again preserving 3/16 supersymmetry, as we verify in a special case by a quaternionic extension of the analysis of Berkooz, Douglas and Leigh. We also use similar methods to find new 1/8 supersymmetric solutions of orthogonally intersecting branes.