Beta decay of neutron-rich 118Rh and the lowest excited states in 118Pd

Beta decay of a refractory isotope ¹¹⁸Rh produced in symmetric fission and mass separated by the ion guide technique has been applied for the study of low-lying excited states of ¹¹⁸Pd. The yrast band in ¹¹⁸Pd has been observed up to a 6⁺ state and the lowest states of the asymmetric γ-band have been identified. The measured half-life of ¹¹⁸Rh is (300±60)ms. The systematics of the excited states in neutron-rich Pd-isotopes implies the saturation towards an O(6) symmetry at N = 70. Received: 19 June 2000 / Accepted: 1 August 2000     

Production of neutron-rich isotopes in fission of uranium induced by neutrons of 20 MeV average energy

In the context of a parameter study conducted by several laboratories for future European radioactive beam facilities based on fast-neutron induced fission, in particular for the SPIRAL-II project at GANIL, we have measured the yields of neutron-rich isotopes in the mass range of 88 to 144. These nuclei were obtained as fission products of natural uranium bombarded by neutrons of 20 MeV average energy emitted by a thick carbon target irradiated by 50 MeV deuterons. Yields have been measured using on-line mass separation with the ion-guide method. Compared with proton-induced fission at 25 MeV the magnitude of cross-sections, except for the symmetric region, is similar. Z-distributions of isobars have the same width, 0.7 charge units, but their maxima are shifted by about 0.8 charge units, favouring production of the neutron-richer isobars. Our data allow calculations of absolute cross-sections for fission of natural uranium induced by neutrons of about 20 MeV. Received: 10 July 2000 / Accepted: 27 October 2000     

Nonstatistical dynamics in deep potential wells: a quasiclassical trajectory study of methyl loss from the acetone radical cation

The loss of methyl radical from the acetone radical cation, following its formation from the enol isomer, has been found to be nonergodic. The origins of this behavior are probed computationally by a quasiclassical trajectory simulation on an AM1-SRP potential energy surface. Experimental reaction outcomes are qualitatively reproduced, and evidence is presented that coherent excitation of the CCO angle bending during isomerization is a significant factor in the nonstatistical behavior.     

Algebraic cohomology of compact monoids

We outline the development of a cohomology theory for compact monoids which extends the existing theory for finite monoids. This research was inspired by the work of K. H. Hofmann and P. S. Mostert [2], which defines the cohomology of a compact group in terms of the Čech cohomology of its classifying space. We use the classifying space construction of A. Dold and R. Lashof [1]. These results are contained in the author’s doctoral dissertation, submitted to Tulane University and written under the direction of Professor K. H. Hofmann. This research was partially supported by a National Aeronautics and Space Administration Graduate Traineeship.     

Uniform free topological groups and Samuel compactifications

The uniform free topological group over a uniform space μX is embedded in the uniform free topological group over the Samuel compactification of μX if and only if μX is pseudocompact. Several consequences of this result are explored.     

Entropy-energy decomposition from nonequilibrium work trajectories

We derive expressions for the equilibrium entropy and energy changes in the context of the Jarzynski equality relating nonequilibrium work to equilibrium free energy. The derivation is based on a stochastic path integral technique that reweights paths at different temperatures. Stochastic dynamics generated by either a Langevin equation or a Metropolis Monte Carlo scheme are treated. The approach enables the entropy-energy decomposition from trajectories evolving at a single-temperature and does not require simulations or measurements at two or more temperatures. Both finite difference and analytical formulae are derived. Testing is performed on a prototypical model system and the method is compared with existing thermodynamic integration and thermodynamic perturbation approaches for entropy-energy decomposition. The new formulae are also put in the context of more general, dynamics-independent expressions that derive from either a fluctuation theorem or the Feynman-Kac theorem.     

High-frequency hearing in phocid and otariid pinnipeds: an interpretation based on inertial and cochlear constraints (L)

Audiograms in air and underwater, determined by previous workers for four pinniped species, two eared seals (Otariidae) and two phocids (Phocidae), are supplemented here by measurements on their middle ear ossicular mass, enabling mechanistic interpretations of high-frequency hearing and audiogram differences. Otariid hearing is not largely affected by the medium (air/water). This indicates that cochlear constraints limit high-frequency hearing in otariids. Phocids, however, have massive middle ear ossicles, and underwater hearing has radically shifted towards higher frequencies. This suggests that the high-frequency hearing of phocids in air is constrained by ossicle inertia.