Age determinations and isotopic abundance measurements on lunar samples

A K-Ar age of 2300 x 10(6) years has been determined for a sample of type A crystalline rock (57,34). The presence of an anomalously large quantity of 4 degrees Ar, in a sample of type C breccia (65,35) precluded the calculation of its K-Ar age. Both of the rock types are characterized by low Rb/Sr ratios and consequently low (87)Sr/(86)Sr values. The U-Th-Pb results for a sample of type D fines (84,33) yield a (207)Pb/(206)Pb age of 4760 x 10(6) years, but ages based on U-Pb and Th-Pb ratios are anomalously high. Isotopic compositions of Li, K, Rb, Sr, U, and Th are very close to the accepted values for terrestrial materials.     

Potassium-Argon Ages and Spreading Rates on the Mid-Atlantic Ridge at 45{degrees} North

Potassium-argon dates obtained from extrusives collected on a traverse across the Mid-Atlantic Ridge at 45 degrees N are consistent with the hypothesis of ocean-floor spreading. The dates suggest a spreading rate in the range of 2.6 to 3.2 centimeters per year near the axis of the ridge; the rate agrees with that computed from fission-track dating of basalt glasses. Additional data for a basalt collected 62 kilometers west of the axis gives a spreading rate of 0.8 centimeter per year, which is similar to the rate inferred from magnetic anomaly patterns in the area. Reasons for the difference in calculated spreading rates are discussed.     

Accelerated uplift and magmatic intrusion of the Yellowstone caldera, 2004 to 2006

The Yellowstone caldera began a rapid episode of ground uplift in mid-2004, revealed by Global Positioning System and interferometric synthetic aperture radar measurements, at rates up to 7 centimeters per year, which is over three times faster than previously observed inflation rates. Source modeling of the deformation data suggests an expanding volcanic sill of approximately 1200 square kilometers at a 10-kilometer depth beneath the caldera, coincident with the top of a seismically imaged crustal magma chamber. The modeled rate of source volume increase is 0.1 cubic kilometer per year, similar to the amount of magma intrusion required to supply the observed high heat flow of the caldera. This evidence suggests magma recharge as the main mechanism for the accelerated uplift, although pressurization of magmatic fluids cannot be ruled out.     

Structure of the uncleaved human H1 hemagglutinin from the extinct 1918 influenza virus

The 1918 "Spanish" influenza pandemic represents the largest recorded outbreak of any infectious disease. The crystal structure of the uncleaved precursor of the major surface antigen of the extinct 1918 virus was determined at 3.0 angstrom resolution after reassembly of the hemagglutinin gene from viral RNA fragments preserved in 1918 formalin-fixed lung tissues. A narrow avian-like receptor-binding site, two previously unobserved histidine patches, and a less exposed surface loop at the cleavage site that activates viral membrane fusion reveal structural features primarily found in avian viruses, which may have contributed to the extraordinarily high infectivity and mortality rates observed during 1918.     

Origin and evolution of prebiotic organic matter as inferred from the Tagish Lake meteorite

The complex suite of organic materials in carbonaceous chondrite meteorites probably originally formed in the interstellar medium and/or the solar protoplanetary disk, but was subsequently modified in the meteorites' asteroidal parent bodies. The mechanisms of formation and modification are still very poorly understood. We carried out a systematic study of variations in the mineralogy, petrology, and soluble and insoluble organic matter in distinct fragments of the Tagish Lake meteorite. The variations correlate with indicators of parent body aqueous alteration. At least some molecules of prebiotic importance formed during the alteration.     

Complex multicolor tilings and critical phenomena in tetraphilic liquid crystals

T-shaped molecules with a rod-like aromatic core and a flexible side chain form liquid crystal honeycombs with aromatic cell walls and a cell interior filled with the side chains. Here, we show how the addition of a second chain, incompatible with the first (X-shaped molecules), can form honeycombs with highly complex tiling patterns, with cells of up to five different compositions ("colors") and polygonal shapes. The complexity is caused by the inability of the side chains to separate cleanly because of geometric frustration. Furthermore, a thermoreversible transition was observed between a multicolor (phase-separated) and a single-color (mixed) honeycomb phase. This is analogous to the Curie transition in simple and frustrated ferro- and antiferromagnets; here spin flips are replaced by 180° reorientations of the molecules.