Experimental evidence for a dynamical crossover in liquid aluminium

The temperature dependence of the dynamic structure factor at next-neighbour distances has been investigated for liquid aluminium. This correlation function is a sensitive parameter for changes in the local environment and its Fourier transform was measured in a coherent inelastic neutron scattering experiment. The zero frequency amplitude decreases in a nonlinear way and indicates a change in dynamics around 1.4 ∙ Tmelting. From that amplitude a generalized viscosity can be derived which is a measure of local stress correlations on next-neighbour distances. The derived generalized longitudinal viscosity shows a changing slope at the same temperature range. At this temperature the freezing out of degrees of freedom for structural relaxation upon cooling sets in which can be understood as a precursor towards the solid state. That crossover in dynamics of liquid aluminium shows the same signatures as previously observed in liquid rubidium and lead, indicating an universal character.

Anatrichosoma sp. in the footpads of a cat: diagnosis and pathology of Namibian case

Anatrichosoma species are an unusual group of zoonotic trichuroid nematodes. Due to limited knowledge of their life cycle and diagnostic challenges, anatrichosomiasis has been reported only 3 times in domestic animals. A short-haired cat from central Windhoek, Namibia, presented with ulceration, swelling, and sepsis on all four paws, a severe generalized lymphadenopathy and considerable invasive eosinophilia. Histological analysis revealed epidermal hyperplasia, with severe serocellular crusting on the skin surface. One specimen revealed a series of thick-walled eggs within nematode segments with a few sections containing eggs with bioperculate appearance which is compatible with the Aphasmid group of nematodes, more specifically, the genus Anatrichosoma. Ivermectin treatment completely cleared the condition. This is the first report of Anatrichosoma sp. in the Republic of Namibia, identified from a unique location in the capital, Windhoek.

Nonexponential relaxation in a simple liquid metal

A hallmark of the changes in dynamics towards the glass transition is the stretched exponential structural relaxation. Quasielastic neutron scattering results on liquid rubidium demonstrate such a nonexponential relaxation process in a simple liquid metal above the melting point. The nonexponential decay is an indication of non-Markovian dynamics and points to the collective character of the relaxation process. Describing the relaxation dynamics by a two-step process, the long lasting part of the decay process is in remarkable quantitative agreement with predictions from mode coupling theory. The feedback mechanism of the slowing down process in the theoretical description suggests that this contribution is at the origin of the structural arrest. With rising temperature the intermediate scattering function transforms into a simple exponential decay at a temperature range which indicates the end of the highly viscous solidlike behavior in the liquid.

Temperature dependent next-neighbour dynamics of liquid lead

The temperature dependence of the density correlation function at next-neighbour distances has been investigated for the liquid metal lead. This correlation function is a sensitive parameter for changes in the local environment and its Fourier transform was measured in a coherent inelastic neutron scattering experiment. The zero-frequency amplitude related to the long time decay of density fluctuations decreases in a nonlinear way and indicates a change in dynamics above the melting point. The derived generalized longitudinal viscosity shows a decrease near this temperature range. From these observations we suppose that solidification sets in on a microscopic level distinct above the melting point.

Density Dependence of the Interrelation between Single Particle Motion and the Collective Dynamics in Liquid Sodium

Over a wide range of densities we have systematically investigated the single particle motion in liquid sodium in a series of quasielastic neutron scattering experiments. Our experimental results are in excellent agreement with predictions from molecular dynamics simulations and Mode-Coupling-Theory. The results allow to determine the microscopic mechanisms that control the single particle motion on atomic time- and length- scale and to relate these mechanisms to the values of the macroscopic diffusion coefficient at different densities. We can clearly distinguish three different density regimes where respectively three different coupling mechanisms between diffusive motion and collective modes dominate: At high density, particle diffusion is hindered and the main contribution to forward motion of a particle comes from a coupling to longitudinal density modes; however, at slightly reduced density the motion of the particle is coupled to transverse shear modes which cause an enhancement of the diffusive motion and hence of the diffusion coefficient. Only at very low density, the system gradually returns to particle dynamics which is controlled by binary collisions as predicted by simple hard sphere theories.

de Gennes slowing in a liquid metal revisited: a neutron spin-echo study

In liquids the decay of density fluctuations shows a slowing down at the structure factor maximum, which is well known as de Gennes narrowing. Molecular dynamics simulations of the liquid metal rubidium and mode coupling theory suggested that this process can be described by a two-step relaxation function. We have probed these predictions with inelastic neutron scattering using the spin-echo technique to measure the dynamics directly in the time domain. The dynamics of liquid rubidium was investigated near the melting point at times beyond the fast contribution. The resulting intermediate-scattering function is in remarkable agreement with predicted values from the mode coupling calculations.