Mechanical stress and reactivity in organic solids

Organic single crystals provide an ideal model for studying the factors that influence chemical processes in structured media. Reaction trajectories are well defined and reveal the influence of spontaneous mechanical stresses equivalent to tens of thousands of atmospheres. Analysis of molecular and crystal structures helps to explain both local mechanical properties, which influence reactions, and bulk properties such as melting point, compressibility, and surface energy.     

Excitation Gap in the Normal State of Underdoped Bi2Sr2CaCu2O8+delta

Angle-resolved photoemission experiments reveal evidence of an energy gap in the normal state excitation spectrum of the cuprate superconductor Bi2Sr2CaCu2O8+delta. This gap exists only in underdoped samples and closes around the doping level at which the superconducting transition temperature Tc is a maximum. The momentum dependence and magnitude of the gap closely resemble those of the dx2-y2 gap observed in the superconducting state. This observation is consistent with results from several other experimental techniques, which also indicate the presence of a gap in the normal state. Some possible theoretical explanations for this effect are reviewed.     

Aspects of the management of cheetahs, Acinonyx jubatus jubatus, trapped on Namibian farmlands

The Namibian cheetah population has recently undergone serious decline due to human-mediated removals, and investigating the rates and causes of such removals is an important aspect of the future management of cheetah populations outside protected areas. We examined cheetahs that were reported live-trapped or killed on Namibian farmlands between 1991 and 1999. A perceived threat to livestock or game led to the vast majority of live captures and to almost half of the cheetah deaths investigated. Despite this, livestock predation from cheetahs appeared to be minimal, and was usually perpetrated by cheetahs with injuries. Most of the cheetahs were trapped in groups, and cheetahs’ relative sociality leads to the easy removal of entire social units. Long-term monitoring must include detailed consideration of these indiscriminate removals, as they involve many cheetahs, fluctuate between years, often go unreported, and are likely to have a serious impact on cheetah populations outside protected areas.