A High-Pressure Test of Birch's Law

The compressional wave velocities of polycrystalline NaCl and KCl have been measured to over 17 gigapascals, with the use of Brillouin scattering and the diamond anvil cell. This pressure corresponds to 40% compression for NaCl and 60% compression for KCl (including the volume change across the B1-B2 transition). The data obey Birch's Law, which predicts that the velocity of each material is linear with density, except across the B1-B2 phase transition in KCl. This deviation from Birch's Law can be rationalized in terms of an interatomic potential model wherein the vibrational frequencies of the nearest neighbor bonds decrease when going to the eight-coordinated B2 structure from the six-coordinated B1 structure.     

Environmental beliefs and farm practices of New Zealand farmers Contrasting pathways to sustainability

Sustainable farming, and waysto achieve it, are important issues foragricultural policy. New Zealand provides aninteresting case for examining sustainableagriculture options because gene technologieshave not been commercially released and thereis a small but rapidly expanding organicsector. There is no strong governmentsubsidization of agriculture, so while policiesseem to favor both options to some degree,neither has been directly supported. Resultsfrom a survey of 656 farmers are used to revealthe intentions, environmental values, andfarming practices for organic, conventional,and GE intending farmers. The results show thatorganic and conventional farmers are relativelysimilar but contrast to GE intending farmers,especially with respect to perceivedconsequences of each technology. While 75%of farmers have not yet made a commitmentto either technology, one fifth were GEintending and one quarter may become organic.Organic farmers have different attitudes tonature, matched in part by conventionalfarmers. In terms of policy for sustainableagriculture, the results suggest that organicand conventional farmers are incrementallymoving towards agroecological sustainabilitywhile GE intending farmers are committed tointensive production methods of which GEproducts are potentially important. GEintending farmers reject incrementalism infavor of a revolutionary technological fix forsustainability concerns in agriculture.Overall, the results show that there areclearly two different paradigms ofsustainability among farmers. Policies that areseeking to achieve sustainable agriculture needto address the tensions that span the differentparadigms.     

Tomatine and parasitic wasps: potential incompatibility of plant antibiosis with biological control

alpha-Tomatine, an alkaloid in tomato plants, is toxic to an endoparasite of a major lepidopterous pest of tomatoes. The parasite acquires the alkaloid from its host after the host ingests the alkaloid. This form of interaction creates a potential dilemma to controlling herbivorous pests through chemical antibiosis in plants.     

Solution of a protein crystal structure with a model obtained from NMR interproton distance restraints

Model calculations were performed to test the possibility of solving crystal structures of proteins by Patterson search techniques with three-dimensional structures obtained from nuclear magnetic resonance (NMR) interproton distance restraints. Structures for crambin obtained from simulated NMR data were used as the test system; the root-mean-square deviations of the NMR structures from the x-ray structure were 1.5 to 2.2 A for backbone atoms and 2.0 to 2.8 A for side-chain atoms. Patterson searches were made to determine the orientation and position of the NMR structures in the unit cell. The correct solution was obtained by comparing the rotation function results of several of the NMR structures and the average structure derived from them. Conventional refinement techniques reduced the R factor from 0.43 at 4 A resolution to 0.27 at 2 A resolution without inclusion of water molecules. The partially refined structure has root-mean-square backbone and side-chain atom deviations from the x-ray structure of 0.5 and 1.3 A, respectively.