Chemical reaction fronts in ordered and disordered cellular flows with opposing winds

We present experiments on the motion of chemical fronts in ordered and disordered vortex flows with imposed uniform winds. Fronts in a chain of alternating vortices are found to freeze (pin to the separatrix) for a wide range of opposing winds that grows nonlinearly with the characteristic strength of the underlying vorticity. Experiments in spatially disordered flows demonstrate that freezing of fronts is common to cellular flows; furthermore, it is not dependent on boundary conditions. We therefore anticipate similar pinning in a wide range of 2D cellular flows and front-producing systems.     

Efficient optimisation of per-channel pre-compensation in WDM 20-Gbit/s RZ-DPSK transmission in non-slope matched submarine links

We propose a computationally efficient method to the per-channel dispersion optimisation applied to 50 GHz-spaced N × 20-Gbit/s wavelength division multiplexing return-to-zero differential phase shift keying transmission in non-zero dispersion-shifted fibre based submarine systems.     

Analytic solution for the nondegenerate quantum control problem

We present an analytic solution for the nondegenerate quantum control problem, i.e., the transfer of a deliberate amount of population, 0%-100%, between arbitrary initial Psi(t)> and final Psi'(t)> states, which can be expanded in terms of nondegenerate energy eigenstates k>. The solution constitutes a robust two-photon multicomponent adiabatic passage, via an intermediate eigenstate 0>, which relies on three types of "null states."     

Pressure induced metallization of the antiferromagnetic-insulator CoI

Abstract

High pressure electrical measurements were conducted in the antiferromagnetic insulator CoI, using a miniature Diamond Anvil Cell (DAC). The existence of a Mott Transition predicted from high pressure ¹²⁹I Mgssbauer Spectroscopy (MS)¹ has been verified. At about 8 GPa the system becomes metal1ic as evidenced by the temperature behavior of the conductivity. The conductivity at room temperature, however, still increases with increasing pressure, leveling off at 11 GPa. The metallic behavior in the 8 -11 GPa is explained by coexistence of metallic and insulating clusters via a percolating process. Above 11 GPa the material is completely metallic. This mechanism is consistent with the MS findings.     

Rare-earth valence-state studies of the series RIn3 and RSn3 derived from quadrupole coupling constants

Time-differential perturbed angular correlation was applied to measure the quadrupole coupling constants of¹¹¹Cd (247 keV) at the In and Sn sites for rare-earth compounds of the series RIn₃ and RSn₃ that have the AuCu₃ structure. Definitive evidence was found for Yb and Eu having lower valence states relative to the assumed value of +3 for the other rare earths. Measurements at liquid helium temperatures and pressures to 18.5 kbar indicate that the room temperature valencies of CeSn₃, YbSn₃, and YbIn₃ have not changed.Work done under the auspices of the US Energy Research and Development Administration     

The electronic structure of non-dilute alloys

Recent developments in the multiple scattering theory of disordered substitutional alloys are reviewed. In view of experimental advances in alloy spectroscopy, the approaches involving the most realistic single particle Hamiltonians are emphasized. Specifically, we focus on the application of the average t-matrix approximation to the muffin tin model of the alloy. It is shown that the electronic structures of α phase CuZn and paramagnetic CuNi alloys can be characterized in terms of their respective complex energy bands. The interpretations of several experiments, bearing on the real as well as the imaginary parts of the complex bands, are discussed.