Structural relaxation of nanocrystalline PdAu alloy: Mapping pathways through the potential energy landscape

Preparation history and processing have a crucial influence on which configurational state material systems assume. Glasses and nanocrystalline materials usually reside in nonequilibrium states at room temperature, and as a consequence, their thermodynamic, dynamical, and physical properties change with time—even years after manufacture. Such changes, entitled aging or structural relaxation, are all manifestations of paths taken in the underlying potential energy landscape. Since it is highly multidimensional, there is a need to reduce complexity. Here, we demonstrate how to construct a one-dimensional pathway across the energy landscape using strain/volume as an order parameter. On its way to equilibrium, we map the system’s release of energy by calorimetry and the spectrum of barrier heights by dilatometry. The potential energy of the system is reduced by approximately B during relaxation, whereas the crossing of saddle points requires activation energies in the order of 1eV/atom relative to the energy minima. As a consequence, the system behaves as a bad global minimum finder. We also discovered that aging is accompanied by a decrease in the non-ergodicity parameter, suggesting a decline in density fluctuations during aging

A highly virulent variant of HIV-1 circulating in the Netherlands

We discovered a highly virulent variant of subtype-B HIV-1 in the Netherlands. One hundred nine individuals with this variant had a 0.54 to 0.74 log10 increase (i.e., a ~3.5-fold to 5.5-fold increase) in viral load compared with, and exhibited CD4 cell decline twice as fast as, 6604 individuals with other subtype-B strains. Without treatment, advanced HIV-CD4 cell counts below 350 cells per cubic millimeter, with long-term clinical consequences-is expected to be reached, on average, 9 months after diagnosis for individuals in their thirties with this variant. Age, sex, suspected mode of transmission, and place of birth for the aforementioned 109 individuals were typical for HIV-positive people in the Netherlands, which suggests that the increased virulence is attributable to the viral strain. Genetic sequence analysis suggests that this variant arose in the 1990s from de novo mutation, not recombination, with increased transmissibility and an unfamiliar molecular mechanism of virulence