Perturbation approach to orientational memory functions: Comparison with simulations and experiment

The predictions of a recent theoretical proposal for the calculation of orientational time-correlation functions for low-torque fluids are tested against experiment and computer simulation. In the theory, memory functions are modeled as the product of the free-rotor function multiplied by the perturbation term due to the intermolecular torques. This term is taken to be a Gaussian function of time. The liquids considered include: O₂ (experimental); N₂, F₂, HC?, CC?₄, CH₄ and CBr₄ (all simulated). In most cases agreement with theory was very good, considering that no adjustable parameters were available.     

Supramolecular Recognition: Protonmotive‐Driven Switches or Motors?

A dicationic molecular receptor bearing two cofacially disposed terpyridyl-Pd-Cl units forms stable 1:1 host-guest complexes with planar, neutral platinum(II) complexes. When the guest is modified to incorporate a pyridine group, the now basic guest is protonated by trifluoroacetic acid in acetonitrile solutions. The basic yellow guest forms a stable, deep red 1:1 host-guest complex with the yellow palladium receptor. Addition of trifluoroacetic acid to this host-guest complex leads to the displacement of the guest from the receptor. It is proposed that the dissociation of the guest is caused by electrostatic repulsion between the dicationic receptor and the positively charged protonated guest. Addition of base restores the host-guest complex. This protonmotive translocation of the guest from the host to the solution is discussed in terms of the mechanisms that drive molecular motors, the power stroke and the Brownian ratchet. It is concluded that the system is best described as a molecular switch that operates by the same mechanism as one stroke of a molecular motor     

Radiative electroweak symmetry breaking revisited

In the absence of a tree-level scalar-field mass, renormalization-group methods permit the explicit summation of leading-logarithm contributions to all orders of the perturbative series within the effective potential for SU(2)xU(1) electroweak symmetry. This improvement of the effective potential function is seen to reduce residual dependence on the renormalization mass scale. The all-orders summation of leading-logarithm terms involving the dominant three couplings contributing to radiative corrections is suggestive of a potential characterized by a plausible Higgs boson mass of 216 GeV. However, the tree potential's local minimum at phi=0 is restored if QCD is sufficiently strong.     

Metal-insulator transitions in an expanding metallic fluid: particle formation kinetics

Core-level photoemission spectroscopy provides a local probe of expansion dynamics and associated transient chemical properties as a highly pressurized, metallic fluid expands into vacuum following impulsive heating of a semiconductor by an intense, ultrashort laser pulse. Transient photoemission peak shifts reveal that metal-insulator transitions occur rapidly following laser heating. These experiments probe constituents species and solidification kinetics occurring in the early moments of material ejection and provide insight into how particles arise in the current laser ablation regime.     

Collective behavior of particle-like chemical waves

Stabilized waves in weakly excitable media propagate with constant velocity and can be directionally controlled with applied excitability gradients. Multiple waves with directional control governed by pairwise interaction potentials form cohesive groups. Processional modes arise in collections of waves with random initial conditions, in which spontaneous alignment plays an essential role. Rotational modes occur with special initial conditions, and highly complex orbits are exhibited in larger groups. The ordered behavior is associated with waves following paths of minimum potential.     

Investigation of the electrode/electrolyte interface for the Cu+ ion solid electrolyte N,N′-dimethyl-triethylene diamine-copper(1) bromide

The Cu⁺ ion solid electrolyte 47Cu Br·3(CH₃)₂ C₆H₁₂N₂Br₂ was prepared by hot-pressing and characterised by X-ray analysis and electrical measurements. Novel cell arrangements were used to study the electrochemical behaviour of interfaces between this electrolyte and copper metal and also between this electrolyte and two well known solid solution electrodes (SSEs) for copper, Cu₂Mo₆S_7.59 and Cu_1.8S. The behaviour of the electrolyte/copper interface was correlated with scanning electron microscope (SEM) examinations showing the growth of copper dendrites at the interface. Results from the electrolyte/SSE interfaces showed that there is no interfacial polarisation and that the electrode polarisation is controlled solely by the diffusion of Cu⁺ ions in the SSE. These experiments allowed estimates of the chemical diffusion coefficient for Cu⁺ ions in each material to be made.     

Long unimodal subsequences: a problem of F.R.K. Chung

Let l(n) be the expected length of the longest unimodal subsequence of a random permutation. It is proved here that l(n)?√n converges to 2√2.This settles a conjecture of F.R.K. Chung.