Volume 114, Issue 24, 22 June 2001
Index of content:
114(2001); http://dx.doi.org/10.1063/1.1380233View Description Hide Description
Collisions between neutral K atoms and oriented t-butyl bromide molecules produce the ions and at energies high enough to separate charged particles (≳4 eV). Ions are detected by coincidence tofmass spectrometry for orientation of the t-butyl bromide such that the K atom attacks either the Br end or the t-butyl end of the molecule. At high energies the steric asymmetry factor is larger than that for But at energies near threshold, the steric asymmetry factor reverses sign and attack at the t-butyl end becomes more reactive than attack at the Br end. The electron is apparently transferred into different orbitals at different ends.
114(2001); http://dx.doi.org/10.1063/1.1380693View Description Hide Description
A Flory–Huggins-type lattice model of actin polymerization under equilibrium conditions is employed to analyze new spectroscopic measurements for the extent of actin polymerization as a function of temperature T, salt concentration [KCl], and the initial concentration of actin monomers The theory subsumes existing mechanisms for actin monomer initiation, dimerization, and chain propagation. The extent of polymerization increases with T to an unanticipated maximum, and the calculations explain this unusual effect as arising from a competition between monomer activation, which diminishes upon heating, and propagating chain growth, which increases upon heating. The actin polymerization is described as a rounded phase transition, and the associated polymerization temperature depends strongly, but nearly linearly on and [KCl] over the concentration regimes investigated. Our findings support the suggestion that physicochemical changes can complement regulatory proteins in controlling actin polymerization in living systems.
114(2001); http://dx.doi.org/10.1063/1.1381060View Description Hide Description
We show that a single, reasonable assumption about the probability of rearrangements in a supercooled liquid necessarily implies a direct connection between kinetic and thermodynamic observables in these media. The prediction is tested against available experimental data for supercooled liquids spanning the range of observed kinetics.
114(2001); http://dx.doi.org/10.1063/1.1381009View Description Hide Description
The energies at geometries close to the equilibrium for the and ground states were computed by means of diffusionMonte Carlo simulations. These results allow us to predict the equilibrium geometries and the vibrational frequencies for these exotic systems, and to discuss their stability with respect to the various dissociation channels. Since the adiabatic positron affinities were found to be smaller than the dissociation energies for both complexes, we propose these two molecules as possible candidates in the challenge to produce and detect stable positron–molecule systems. Moreover, low-energy positron scattering on LiF and BeO targets may show vibrational Feshbach resonances as fingerprints of the existence of stable ground states of and