X-ray diffraction of metastable structures from supercooled liquid hydrogen.

We report time resolved observations of the crystallization from liquid hydrogen, supercooled to temperatures below the melting point, using 11.2 keV X-ray diffraction from the Linac Coherent Light Source (LCLS). Changes to the metastable solid and liquid structure factors have been dynamically measured. This allows for a direct determination of the lowest energy crystal polymorphs, the stacking probabilities, as well as the liquid and solid densities and temperatures. Such measurements provide experimental evidence of an Arrhenius-like growth kinetics along the stacking direction during supercooling.

Building global environmental health capacity through international scientific cooperation and partnerships.

Sponsored by the Fogarty International Center, the NIEHS, and NIOSH, the International Training and Research Program in Environmental and Occupational Health (ITREOH) supports training of health professionals worldwide. The program grants awards to U.S. academic institutions, which partner with institutions in low- and middle-income countries to address health threats of regional importance.

Environmental health moves into the 21st century.

Over the past half century, environmental health research has branched from a descriptive, observational process into one of hypothesis driven and mechanistically based science. Nevertheless, the meaning of observed effects of exposures in experimental systems to human public health remains elusive. Recent advances in genetics and "omics" hold great promise to further our abilities to assess potential human health effects and to manage exposures properly. But the comfort of 100% certainty will not be available in the foreseeable future, leaving us with the challenge of designing relevant experiments and test systems upon which to base "logical" policy in risk management.