Optical experiments and weak interactions

Recent optical experiments have demonstrated cases in which mirror symmetry in stable atoms is broken during absorption of light. These results, which are in contradiction with quantum electrodynamics, support the theory of unification of the electromagnetic and weak forces. The interpretation of these experimental results is based on exchanges of weak neutral Z(0) bosons between the electrons and the nucleus of the atom. The information obtained from low-energy experiments is different from, but complementary to, the results of high-energy experiments. Sensitive measurements in a simple, reliably computable atom are in quantitative agreement with the standard electroweak theory and put stringent constraints on alternative models. Attaining sufficient accuracy in the experiments and the computations for the electroweak radiative corrections to manifest themselves is now the challenge for experimenters and theorists.     

Changing climate: geothermal evidence from permafrost in the alaskan arctic

Temperature profiles measured in permafrost in northernmost Alaska usually have anomalous curvature in the upper 100 meters or so. When analyzed by heat-conduction theory, the profiles indicate a variable but widespread secular warming of the permafrost surface, generally in the range of 2 to 4 Celsius degrees during the last few decades to a century. Although details of the climatic change cannot be resolved with existing data, there is little doubt of its general magnitude and timing; alternative explanations are limited by the fact that heat transfer in cold permafrost is exclusively by conduction. Since models of greenhouse warming predict climatic change will be greatest in the Arctic and might already be in progress, it is prudent to attempt to understand the rapidly changing thermal regime in this region.     

Cliff swallow colonies as information centers

Colonies of cliff swallows (Aves: Hirundo pyrrhonota) appear to be information centers in which colony residents acquire information on the location of food sources. Individuals that have been unsuccessful on a foraging trip return to the colony, locate a successful forager, and follow that individual to a food source. Individuals often follow, and are followed by, their neighbors within the colony, possibly because neighbors can observe foraging success through food brought back to nestlings. All individuals are equally likely to follow others or be followed, and thus all individuals benefit from opportunities to receive information.