bluuebunny/crossref_metadata_2025 huggingface dataset:
Research with High-Power Short-Wavelength Lasers
Authors: Holzrichter J. F. , Campbell E. M. , Lindl J. D. , Storm E.
Published: October 2006

Three high-temperature, high-density experiments were conducted recently with the 10-terawatt, short-wavelength Novette laser system at the Lawrence Livermore National Laboratory. The experiments demonstrated successful solutions to problems that arose during previous laser-plasma interaction experiments with long-wavelength (greater than 1 micrometer) lasers: (i) large-scale plasmas, with dimensions approaching those needed for high-gain inertial fusion targets, were produced in which potentially deleterious laser-plasma instabilities were collisionally damped; (ii) deuterium-tritium fuel was imploded to a density of 20 grams per cubic centimeter and a pressure of 10
10
atmospheres under the improved laser conditions, and compression conditions (preheating and pressure) were consistent with code calculations that predict efficient (high-gain) burn of a large thermonuclear fuel mass when driven with a large, short-wavelength laser; and (iii) soft x-rays were amplified by a factor of 700 by stimulated emission at 206 and 209 angstroms (62 electron volts) from selenium ions in a laser-generated plasma. These small, short-pulse x-ray sources are 10
10
to 10
11
times brighter than the most powerful x-ray generators and synchrotron sources available today. The plasma conditions for these experiments were made possible by advances in Nd:glass laser technology, in techniques to generate efficiently its short-wavelength harmonics at 0.53, 0.35, and 0.26 micrometers, and in diagnostic and computational modeling.
Transformation of a Tundra River from Heterotrophy to Autotrophy by Addition of Phosphorus
Authors: Peterson Bruce J. , Hobbie John E. , Hershey Anne E. , Lock Maurice A. , Ford Tim E. , Vestal J. Robie , McKinley Vicky L. , Hullar Meredith A. J. , Miller Michael C. , Ventullo Roy M. , Volk Gregg S.
Published: October 2006

Continuous enrichment of an arctic river with only 10 parts per billion phosphate-phosphorus caused an immediate growth of attached algae for more than 10 kilometers downstream, showing that phosphorus alone limited photosynthesis. As a result of the increased photosynthesis, there was an increase in bacterial activity in films on rocks on the bottom of the stream. The major source of energy became the photosynthetic carbon fixed in the stream rather than the organic material entering from the surrounding tundra, and the overall metabolism of the stream shifted from heterotrophy to autotrophy. An increase in the size and developmental stage of some of the dominant aquatic insects illustrates the food limitation in this nutrient-poor habitat.
Time-Transgressive Late Cenozoic Radiolarian Events of the Equatorial Indo-Pacific
Authors: Johnson David A. , Nigrini Catherine A.
Published: October 2006

A biostratigraphic study of late Cenozoic Radiolaria in the equatorial Indo-Pacific shows an asymmetrical distribution between synchronous and diachronous events. A majority of synchronous events (15 out of 19) are last occurrences; the majority of diachronous events (10 out of 13) are first occurrences. Extinctions may therefore be preferable to first occurrences in the selection of datum levels for the definition of biostratigraphic zonations and for correlation control within global time scales. Diachronous equatorial radiolarian events span 1 to 2 million years, several orders of magnitude longer than the nominal mixing time of the oceans, suggesting that the biological and physical exchange processes associated with speciation events may not follow simple advective mixing models.
A Striking Nitrogen Isotope Anomaly in the Bencubbin and Weatherford Meteorites
Authors: Prombo Carol A. , Clayton Robert N.
Published: October 2006

The stony-iron meteorites Bencubbin and Weatherford contain nitrogen with a ratio of nitrogen-15 to nitrogen-14 larger than normal by as much as a factor of 2. The excess nitrogen-15 may be due either to a nucleosynthetic origin or to extreme isotopic fractionation. In the former case, it may reflect failure to homogenize nitrogen-15 produced in nova explosions. In the latter case, it may reflect chemical processing at temperatures below 40 K in a presolar molecular cloud.
Rationing Health Care: The Choice Before Us
Authors: Aaron Henry , Schwartz William B.
Published: October 2006

Rapid technological advances and upward pressure on wages of hospital personnel are leading to a steady increase in health care spending that is absorbing an ever-larger fraction of gross national product. Eliminating inefficiencies in the system can provide brief fiscal relief, but rationing of beneficial services, even to the well-insured, offers the only prospect for sustained reduction in the growth of health care spending. The United States, which has negligible direct experience with rationing, can learn about choices it will face from the experience of Great Britain where health care has been rationed explicitly for many years.
Myrmecia pilosula
, an Ant with Only One Pair of Chromosomes
Authors: Crosland Michael W. J. , Crozier Ross H.
Published: October 2006

A new sibling species of the primitive Australian ant
Myrmecia pilosula
has a chromosome number of
n
= 1. C-banding techniques confirm that the two chromosomes of workers are homologous. Males are haploid, as in other Hymenoptera, and their somatic cells contain only a single chromosome. This new species is potentially of great importance in both laboratory and field studies on gene organization.
Heliotropism in Modern Stromatolites
Authors: Awramik Stanley M. , Vanyo James P.
Published: October 2006

Modern microbial mats and stromatolites exhibiting a preferred orientation toward specular sunlight were found at two sites. In Hamelin Pool of Shark Bay, Western Australia, subtidal decimeter-sized columns and intertidal centimeter-sized tufts were found pointing north. In thermal spring effluents and pools of Yellowstone National Park, mats were found with columnar and conical centimeter-sized structures inclined to the south. These examples of heliotropism in modern stromatolites are each built by a different community of photosynthetic microbes under markedly different environmental conditions. These new observations support the proposal that stromatolites can orient themselves toward the sun.
Cometary Particles: Thin Sectioning and Electron Beam Analysis
Authors: Bradley J. P. , Brownlee D. E.
Published: October 2006

Thin sections (500 to 1000 angstroms thick) of individual micrometeorites (5 to 15 micrometers) have been prepared with an ultramicrotome equipped with a diamond knife. Electron microscopic examination of these sections has revealed the internal structures of chondritic micrometeorites, and a subset of highly porous, fragile particles has been identified. Delicate meteoritic materials such as these are characteristic of debris from cometary meteors.
Inorganic and Organic Sulfur Cycling in Salt-Marsh Pore Waters
Authors: Luther George W. , Church Thomas M. , Scudlark Joseph R. , Cosman Monique
Published: October 2006

Sulfur species in pore waters of the Great Marsh, Delaware, were analyzed seasonally by polarographic methods. The species determined (and their concentrations in micromoles per liter) included inorganic sulfides (≤3360), polysulfides (≤326), thiosulfate (≤104), tetrathionate (≤302), organic thiols (≤2411), and organic disulfides (≤139). Anticipated were bisulfide increases with depth due to sulfate reduction and subsurface sulfate excesses and
p
H minima, the result of a seasonal redox cycle. Unanticipated was the pervasive presence of thiols (for example, glutathione), particularly during periods of biological production. Salt marshes appear to be unique among marine systems in producing high concentrations of thiols. Polysulfides, thiosulfate, and tetrathionate also exhibited seasonal subsurface maxima. These results suggest a dynamic seasonal cycling of sulfur in salt marshes involving abiological and biological reactions and dissolved and solid sulfur species. The chemosynthetic turnover of pyrite to organic sulfur is a likely pathway for this sulfur cycling. Thus, material, chemical, and energy cycles in wetlands appear to be optimally synergistic.
An Industry Picture of U.S. Science Policy
Authors: David Edward E.
Published: October 2006

With regard to promoting the competitiveness of U.S. industry, federal science policy is performing unevenly. Federally supported basic research is not well aligned with industrial needs, although the National Science Foundation's Engineering Research Centers and similar programs are improving matters. Large-scale federal undertakings in science and technology, such as the Apollo program and now the Strategic Defense Initiative, actually tend to divert resources away from commercial research and development. Needed are federal and industrial leaders who will work together to serve the interests of both competitive industry and efficient government in the United States.
Hyperphoretic Dispersal of a
Pyxidiophora
Anamorph
Authors: Blackwell Meredith , Bridges J. Robert , Moser John C. , Perry Thelma J.
Published: October 2006

It has been suggested that
Thaxteriola
species and other minute, nonmycelial fungi associated with arthropods have phylogenetic relationships with the Laboulbeniales. However, direct development of the thallus of
Thaxteriola
from an ascospore of
Pyxidiophora
has now been discovered.
Thaxteriola
is specialized for dispersal by mites carried on pine bark beetles; other fungi dispersed by arthropods in this symbiotic assemblage rely primarily on arthropod specializations.
p
H-Induced Metabolic Transitions in
Artemia
Embryos Mediated by a Novel Hysteretic Trehalase
Authors: Hand Steven C. , Carpenter John F.
Published: October 2006

Gastrula-stage embryos of the brine shrimp
Artemia
undergo reversible transitions between metabolically active and dormant states that are promoted by changes in intracellular
p
H. A macromolecular mechanism for this suppression of energy metabolism that involves regulation of the enzyme trehalase is reported here. Isolated trehalase from these embryos existed in two active forms that interconverted when exposed to physiological transitions in
p
H. This hysteretic interconversion was reversible, required minutes for completion, and involved a change in enzyme polymerization. The two states differed twofold in molecular size and were distinguishable electrophoretically. Compared to the smaller species, the polymerized form was strongly inhibited by acidic
p
H, adenosine 5′-triphosphate, and the substrate trehalose. Thus, the shift in assembly equilibrium toward the aggregated enzyme caused by
p
H values less than or equal to 7.4 may mediate the arrest of trehalose-fueled metabolism and respiration during dormancy in this cryptobiotic organism.
Endogenous Cholecystokinin Reduces Feeding in Young Rats
Authors: Weller Aron , Smith Gerard P. , Gibbs James
Published: October 2006

The hypothesis that endogenous cholecystokinin (CCK) released from the small intestine during feeding causes satiety was tested in rat pups, 9 to 12 days old. Intragastric administration of soybean trypsin inhibitor, a procedure that releases CCK from the small intestine, decreased the subsequent intake of a test meal. This effect was reversed by prior treatment with MK-329, a selective antagonist of CCK at alimentary-type CCK (CCK-A) receptors. Thus, endogenous, small intestinal CCK can cause satiety in the neonatal rat and this effect involves CCK-A receptors.
Electron- and Photon-Stimulated Desorption: Probes of Structure and Bonding at Surfaces
Authors: Madey Theodore E.
Published: October 2006

Techniques for analyzing the structure and composition of solid surfaces with electron and photon beams often cause radiation damage in samples. Damage-producing processes compete with information-producing events during measurements, and beam damage can be a serious perturbation in quantitative surface analysis. There are, however, substantial benefits of electron- and photon-stimulated damage processes for studying molecules adsorbed on surfaces. Direct information about the geometric structure of surface molecules can be obtained from measurements of the angular distributions of ions released by electron- or photon-stimulated desorption. The directions of ion emission are determined by the orientation of the surface bonds that are ruptured by beam irradiation. Moreover, photon-stimulated desorption studies that make use of synchrotron radiation reveal the fundamental electronic excitations that lead to bond-breaking processes at surfaces. These measurements provide new insights into radiation-damage processes in areas as diverse as x-ray optics and semiconductor electronics.
Radar Glory from Buried Craters on Icy Moons
Authors: Eshleman Von R.
Published: October 2006

Three ice-covered moons of Jupiter, in comparison with rocky planets and Earth's moon, produce radar echoes of astounding strengths and bizarre polarizations. Scattering from buried craters can explain these and other anomalous properties of the echoes. The role of such craters is analogous to that of the water droplets that create the apparition known as "the glory," the optically bright region surrounding an observer's shadow on a cloud. Both situations involve the electromagnetic phenomenon of total internal reflection at a dielectric interface, operating in a geometry that strongly favors exact backscattering. Dim surface craters are transformed into bright glory holes by being buried under somewhat denser material, thereby increasing the intensity of their echoes by factors of hundreds. The dielectric interface thus formed at the crater walls nicely accounts for the unusual polarizations of the echoes.
Hydrothermal Plume Measurements: A Regional Perspective
Authors: Baker Edward T. , Massoth Gary J.
Published: October 2006

An extensive deep-tow survey around an active submarine vent field was conducted to map the three-dimensional distribution of hydrothermal emissions and calculate the hydrothermal discharge of heat and manganese. Emissions from the 10-kilometer-long vent field formed a nearly isopycnal plume about 250 meters thick and elongated in the direction of the local net current. Net export of hydrothermal discharge from both point and diffuse sources was estimated from the advective transport of the plume; the heat flux was 5.8 ± 2.9 × 10
8
watts and the dissolved manganese flux was 0.2 ± 0.1 moles per second. Flux measurements of this type could be expanded to encompass entire ridge segments, allowing comparison with theoretical thermal and chemical process models on a common spatial scale.
Early Cretaceous Angiosperm Leaves from Southern South America
Authors: Romero Edgardo J. , Archangelsky Sergio
Published: October 2006

Early angiosperm leaves from the Aptian (113 to 119 million years ago) Baqueró Formation of Patagonia have been found in a fossil flora dominated by more than 100 species of gymnosperms and pteridophytes. They may be the first early Cretaceous angiosperm leaves to be reported from southern South America and one of the few reported in the Southern Hemisphere. The leaves are large, lobate, craspedodromous, and dentate (A-1 teeth) and have ramified tertiary veins and random fourth-order venation. Several of these features have been found in coeval and younger strata elsewhere, but not in the same combination. They were probably a marginal component of the flora.
The Impact of Foreign Graduate Students on Engineering Education in the United States
Authors: Barber Elinor G. , Morgan Robert P.
Published: October 2006

Surveys of chairpersons and faculty members of engineering departments of U.S. universities were conducted in the fall of 1985 to examine the relation between the high proportion of foreign graduate students and the operation and quality of engineering education in the United States. Information was obtained on admissions criteria and policies, financial aid, and the performance of U.S. and foreign students as teaching and research assistants. Overall, the survey respondents believed that foreign students are an asset and that, without them, training and research would suffer. Language and communications were the problems most frequently mentioned as adversely affecting the performance of foreign students.
Design and Synthesis of a Peptide Having Chymotrypsin-Like Esterase Activity
Authors: Hahn Karl W. , Klis Wieslaw A. , Stewart John M.
Published: October 2006

A peptide having enzyme-like catalytic activity has been designed and synthesized. Computer modeling was used to design a bundle of four short parallel amphipathic helical peptides bearing the serine protease catalytic site residues serine, histidine, and aspartic acid at the amino end of the bundle in the same spatial arrangement as in chymotrypsin (ChTr). The necessary "oxyanion hole" and substrate binding pocket for acetyltyrosine ethyl ester, a classical ChTr substrate, were included in the design. The four chains were linked covalently at their carboxyl ends. The peptide has affinity for ChTr ester substrates similar to that of ChTr and hydrolyzes them at rates ∼0.01 that of ChTr; total turnovers > 100 have been observed. The peptide is inhibited by ChTr specific inhibitors and is inactive toward benzoyl arginine ethyl ester, a trypsin substrate. The peptide is inactivated by heating above 60°C, but recovers full catalytic activity upon cooling and lyophilization from acetic acid.
Borehole Measurement of the Newtonian Gravitational Constant
Authors: Hsui Albert T.
Published: October 2006

It has been reported that the geophysically determined Newtonian gravitational constant is consistently larger than the laboratory value by 1 to 2% on the basis of gravity measurements in Australian mines. This discrepancy may have strong implications for the physics of gravitation. To test whether similar results can be observed in a different geological environment, gravity measurements in a Michigan borehole have been examined. Although these results cannot be taken as conclusive, owing to the large uncertainties involved in mass determination on a geophysical scale, these measurements are generally consistent with those of the Australian experiment.
Application of Two-Step Laser Mass Spectrometry to Cosmogeochemistry: Direct Analysis of Meteorites
Authors: Hahn Jong Hoon , Zenobi Renato , Bada Jeffrey L. , Zare Richard N.
Published: October 2006

Polycyclic aromatic hydrocarbons in C1, C2, and C3 carbonaceous chondrites and in some ordinary chondrites have been directly analyzed by two-step laser desorption/ laser multiphoton ionization mass spectrometry, a selective and sensitive method requiring only milligram samples. At the ionization wavelength of 266 nanometers, parent ion peaks of polycyclic aromatic hydrocarbons dominate the mass spectra. Quantitative analysis is possible; as an example, the concentration of phenanthrene in the Murchison meteorite was determined to be 5.0 parts per million.
Middle Mississippian Blastoid Extinction Event
Authors: Ausich William I. , Meyer David L. , Waters Johnny A.
Published: October 2006

The Middle Mississippian blastoid (Phylum Echinodermata) extinction event (about 340 million years ago) was a rapid, habitat-specific extinction. Blastoids became rare or absent in shallow-water environments after the extinction, and this change was probably synchronous worldwide. Onshore-offshore habitat shifts have been recognized as an important historical trend among marine benthos. Unlike trends exhibited by other groups, blastoids appear to have repopulated shallow-water habitats after a period of diminished diversity and abundance.
Paleoceanography of Coral Reefs in the Hawaiian-Emperor Chain
Authors: Grigg Richard W.
Published: October 2006

The fossil record of shallow marine organisms in the Hawaiian Archipelago and Emperor seamount chain indicates that reef corals were absent during the first half of the Tertiary. Their appearance during the early Oligocene, 34 million years ago, is associated with several paleoceanographic events that appear to have combined to intensify gradually gyral surface currents in the north Pacific. This association suggests that corals were absent in the early Tertiary because of isolation of the Hawaiian Archipelago from the Indo-West Pacific (IWP), the center of reef coral abundance and diversity in the Pacific. Today, the number of species of reef corals in Hawaii is less than 10 percent of the number of species in the IWP. Since their initial colonization, reef corals have been present continuously in the Hawaiian Archipelago, although not without taxonomic change. Episodes of extinction and recolonization are the most likely cause of change in species composition. Recolonization from the IWP may also explain the low rate of endemism (about 20 percent) in the present-day coral fauna.
Components of Competitiveness
Authors: Klein Lawrence R.
Published: October 2006

There are various ways of looking at economic competitiveness. Some of the popular conceptions of America's relative position are clarified by examining the concept in terms of wage cost, productivity, profit margins, and exchange rates. A quantitative approach is laid out and examined in relation to similar measures for other countries. Also some relationships between competitiveness and the external deficit on current account for the United States are analyzed.
A New Class of Steroids Inhibits Angiogenesis in the Presence of Heparin or a Heparin Fragment
Authors: Crum Rosa , Szabo Sandor , Folkman Judah
Published: October 2006

Steroids that lack glucocorticoid or mineralocorticoid activity were found to inhibit angiogenesis in the presence of heparin or specific heparin fragments. This newly discovered steroid function appears to be governed by distinct structural configurations of the pregnane nucleus. These compounds are here named angiostatic steroids.
Herbicide Resistance in Transgenic Plants Expressing a Bacterial Detoxification Gene
Authors: Stalker David M. , McBride Kevin E. , Malyj Lorraine D.
Published: October 2006

The herbicide bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) is a photosynthetic (photosystem II) inhibitor in plants. A gene,
bxn
, encoding a specific nitrilase that converts bromoxynil to its primary metabolite 3,5-dibromo-4-hydroxybenzoic acid, was cloned from the natural soil bacterium
Klebsiella ozaenae.
For expression in plants, the
bxn
gene was placed under control of a light-regulated tissue-specific promoter, the ribulose bisphosphate carboxylase small subunit. Transfer of this chimeric gene and expression of a bromoxynil-specific nitrilase in leaves of transgenic tobacco plants conferred resistance to high levels of a commercial formulation of bromoxynil. The results presented indicate a successful approach to obtain herbicide resistance by introducing a novel catabolic detoxification gene in plants.
The Isotopic Composition of Methane in Polar Ice Cores
Authors: Craig H. , Chou C. C. , Welhan J. A. , Stevens C. M. , Engelkemeir A.
Published: October 2006

Air bubbles in polar ice cores indicate that about 300 years ago the atmospheric mixing ratio of methane began to increase rapidly. Today the mixing ratio is about 1.7 parts per million by volume, and, having doubled once in the past several hundred years, it will double again in the next 60 years if current rates continue. Carbon isotope ratios in methane up to 350 years in age have been measured with as little as 25 kilograms of polar ice recovered in 4-meter-long ice-core segments. The data show that (i) in situ microbiology or chemistry has not altered the ice-core methane concentrations, and (ii) that the carbon-13 to carbon-12 ratio of atmospheric CH
4
in ice from 100 years and 300 years ago was about 2 per mil lower than at present. Atmospheric methane has a rich spectrum of isotopic sources: the ice-core data indicate that anthropogenic burning of the earth's biomass is the principal cause of the recent
13
CH
4
enrichment, although other factors may also contribute.
Critical Depth for the Survival of Coral Islands: Effects on the Hawaiian Archipelago
Authors: Grigg Richard W. , Epp David
Published: October 2006

Coral islands drown when sea level rise exceeds the maximum potential of coral reefs to grow upward (about 10 millimeters per year). During the Holocene transgression (18,000 years ago to present) sea levels rose at rates of up to 10 to 20 millimeters per year, and most coral island reefs situated deeper than a critical depth of 30 to 40 meters below present day sea level drowned. Coral islands that did not drown during the Holocene transgression apparently all developed on antecedent foundations shallower than critical depth. During low stands in sea level during the Pleistocene, these islands were elevated and subject to subaerial erosion. Today, in the Hawaiian Archipelago, the depth of drowned banks is inversely related to summit area; smaller banks are progressively deeper, evidently because of erosional truncation during low sea level stands. Bank summit area may therefore be an important factor determining the failure or success of coral islands.
A Dwarf Mutant of
Arabidopsis
Generated by T-DNA Insertion Mutagenesis
Authors: Feldmann Kenneth A. , Marks M. David , Christianson Michael L. , Quatrano Ralph S.
Published: October 2006

Most plant genes that control complex traits of tissues, organs, and whole plants are uncharacterized. Plant height, structure of reproductive organs, seed development and germination, for example, are traits of great agronomic importance. However, in the absence of knowledge of the gene products, current molecular approaches to isolate these important genes are limited. Infection of germinating seeds of
Arabidopsis thaliana
with
Agrobacterium
results in transformed lines in which the integrated T-DNA from
Agrobacterium
and its associated kanamycin-resistance trait cosegregate with stable, phenotypic alterations. A survey of 136 transformed lines produced plants segregating in a manner consistent with Mendelian predictions for phenotypes altered in height, flower structure, trichomes, gametogenesis, embryogenesis, and seedling development. This report is the characterization of a dwarf mutant in which the phenotype is inherited as a single recessive nuclear mutation that cosegregates with both the kanamycin-resistance trait and the T-DNA insert.
Improving the Efficiency of Electricity Use in Manufacturing
Authors: Ross Marc
Published: October 2006

Largely in response to the energy shocks of the 1970s, U.S. manufacturers reduced their real fossil fuel intensity (the weighted-average ratio of energy use to production in each subsector) by 50% and achieved zero growth in real electricity intensity. In the future, adoption of new technologies for increasing the efficiency of electricity use is likely to continue to be as important as new modes of electrification, implying that the real electricity intensity will be stable; but the outcome depends on electricity pricing and other policies, public and private.
Man-Made Transients Observed by the Gamma-Ray Spectrometer on the Solar Maximum Mission Satellite
Authors: Rieger Erich , Kanbach Gottfried , Reppin Claus , Vestrand W. Thomas , Forrest David J. , Chupp Edward L.
Published: October 2006

Since launch in early 1980 the Gamma-Ray Spectrometer (GRS) onboard the Solar Maximum Mission (SMM) satellite has monitored the sun at gamma-ray energies. In addition to observations of solar flares, cosmic gamma-ray bursts, and precipitating radiation belt electrons, the instrument has detected a new class of high-energy transient events that cannot be attributed to any of these phenomena. The duration of these transients can range from 1 second to more than 10 minutes. The average event rate between 1980 and 1986 was about five per month. However, in February 1987 this rate increased by more than a factor of 25 and continued at this high level until June 1988. These transients can be subdivided into three classes: (i) 0.511-megaelectron volt annihilation line events, (ii) particle events, and (iii) broad-band photon continuum—like events. Evidence is presented that these transients are not of natural origin. It is found that the most likely sources of these events are reactors in earth orbiting satellites. Apart from the threat these reactors pose upon accidental reentry, the reactor-generated transients may have a deleterious effect on cosmic observations obtained with gamma-ray detectors in low earth orbit.
Rhenium-Osmium and Samarium-Neodymium Isotopic Systematics of the Stillwater Complex
Authors: Lambert David D. , Morgan John W. , Walker Richard J. , Shirey Steven B. , Carlson Richard W. , Zientek Michael L. , Koski Michael S.
Published: October 2006

Isotopic data for the Stillwater Complex, Montana, which formed about 2700 Ma (million years ago), were obtained to evaluate the role of magma mixing in the formation of strategic platinum-group element (PGE) ore deposits. Neodymium and osmium isotopic data indicate that the intrusion formed from at least two geochemically distinct magmas. Ultramafic affinity (U-type) magmas had initial ε
Nd
of -0.8 to -3.2 and a chondritic initial
187
Os/
186
Os ratio of ∼0.88, whereas anorthositic affinity (A-type) magmas had ε
Nd
of -0.7 to +1.7 and an initial
187
Os/
186
Os ratio of ∼1.13. These data suggest that U-type magmas were derived from a lithospheric mantle source containing recycled crustal materials whereas A-type magmas originated either by crustal contamination of basaltic magmas or by partial melting of basalt in the lower crust. The Nd and Os isotopic data also suggest that Os, and probably the other PGEs in ore horizons such as the J-M Reef, was derived from A-type magmas. The Nd and Os isotopic heterogeneity observed in rocks below the J-M Reef also suggests that A-type magmas were injected into the Stillwater U-type magma chamber at several stages during the development of the Ultramafic series.
Origins and Movement of Fluids During Deformation and Metamorphism in the Canadian Cordillera
Authors: Nesbitt Bruce E. , Muehlenbachs Karlis
Published: October 2006

Stable isotope data from quartz veins in the Canadian Cordillera indicate that crustal fluids were heterogeneous in terms of sources and flow paths during Mesozoic-Cenozoic metamorphism and deformation. In regions of strike-slip and extensional faulting, the fluid regime to depths of at least 15 kilometers was dominated by convected, chemically evolved meteoric water. In contrast, in thrust faulted regions, the fluid regime was dominated by fluids derived from metamorphic devolatilization reactions. Deep convection of meteoric water implies that fluid pressures are hydrostatic in such systems not lithostatic, as had been commonly assumed. The occurrence of significantly lower fluid pressures would necessitate reevaluation of the manner in which metamorphic phase equilibria and stress relations in the crust are modeled. In addition, this study indicates that mesothermal gold deposits in the Canadian Cordillera are a product of the meteoric water convection process.
Orthogonal Self-Assembled Monolayers: Alkanethiols on Gold and Alkane Carboxylic Acids on Alumina
Authors: Laibinis Paul E. , Hickman James J. , Wrighton Mark S. , Whitesides George M.
Published: October 2006

This work demonstrates the practicality of forming two self-assembled monolayers (SAMs), independently but simultaneously, by adsorption of two different adsorbates from a common solution onto a substrate exposing two different materials at its surface. The experimental procedure and the degree of independence achieved in the resulting SAMs are illustrated by examination of monolayers obtained by adsorption of alkanethiols on gold and alkane carboxylic acids on alumina. This procedure provides a method for modifying the surface characteristics of microlithographically generated patterns and offers a versatile technique for controlling solid-vapor and solid-liquid interfacial properties in systems having patterns with dimensions of the order of 1 micrometer.
Chemotransduction in the Carotid Body: K
+
Current Modulated by
P
O
2
In Type I Chemoreceptor Cells
Authors: López-Barneo José , López-López José R. , Ureña Juán , Gonzalez Constancio
Published: October 2006

The ionic currents of carotid body type I cells and their possible involvement in the detection of oxygen tension (
P
O
2
) in arterial blood are unknown. The electrical properties of these cells were studied with the whole-cell patch clamp technique, and the hypothesis that ionic conductances can be altered by changes in
P
O
2
was tested. The results show that type I cells have voltage-dependent sodium, calcium, and potassium channels. Sodium and calcium currents were unaffected by a decrease in
P
O
2
from 150 to 10 millimeters of mercury, whereas, with the same experimental protocol, potassium currents were reversibly reduced by 25 to 50 percent. The effect of hypoxia was independent of internal adenosine triphosphate and calcium. Thus, ionic conductances, and particularly the O
2
-sensitive potassium current, play a key role in the transduction mechanism of arterial chemoreceptors.
Heterologous Expression of Excitability Proteins: Route to More Specific Drugs?
Authors: Lester Henry A.
Published: October 2006

Many clinically important drugs act on the intrinsic membrane proteins (ion channels, receptors, and ion pumps) that control cell excitability. A major goal of pharmacology has been to develop drugs that are more specific for a particular subtype of excitability molecule. DNA cloning has revealed that many excitability proteins are encoded by multigene families and that the diversity of previously recognized pharmacological subtypes is matched, and probably surpassed, by the diversity of messenger RNAs that encode excitability molecules. In general, the diverse subtypes retain their properties when the excitability proteins are expressed in foreign cells such as oocytes and mammalian cell lines. Such heterologous expression may therefore become a tool for testing drugs against specific subtypes. In a systematic research program to exploit this possibility, major considerations include alternative processing of messenger RNA for excitability proteins, coupling to second-messenger systems, and expression of enough protein to provide material for structural studies.
Quisqualate Activates a Rapidly Inactivating High Conductance Ionic Channel in Hippocampal Neurons
Authors: Tang Cha-Min , Dichter Marc , Morad Martin
Published: October 2006

Glutamate activates a number of different receptor-channel complexes, each of which may contribute to generation of excitatory postsynaptic potentials in the mammalian central nervous system. The rapid application of the selective glutamate agonist, quisqualate, activates a large rapidly inactivating current (3 to 8 milliseconds), which is mediated by a neuronal ionic channel with high unitary conductance (35 picosiemens). The current through this channel shows pharmacologic characteristics similar to those observed for the fast excitatory postsynaptic current (EPSC); it reverses near 0 millivolts and shows no significant voltage dependence. The amplitude of the current through this channel is many times larger than that through the other non-NMDA (
N
-methyl-D-aspartate) channels. These results suggest that this high-conductance quisqualate-activated channel may mediate the fast EPSC in the mammalian central nervous system.
Electrides: Ionic Salts with Electrons as the Anions
Authors: Dye James L.
Published: October 2006

Electrides are ionic compounds that have alkali metal cations complexed by a crown ether or cryptand, with trapped electrons as counterions. The crystal structures and properties of two electrides illustrate the diversity that is encountered. One, Cs
+
(18-crown-6)
z
e
-
, has relatively isolated, trapped electrons apparently centered at each anionic site. It has a low conductivity consistent with electron localization, with an activation energy for conductivity of at least 0.45 electron volt. The other, K
+
(cryptand[2.2.2])e
-
, has electron pairs trapped in an elongated cavity in a singlet ground state, but there is also a thermally accessible paramagnetic state available. This electride is much more conducting, with an activation energy of only 0.02 electron volt.
Structure of
E. coli
Glutaminyl-tRNA Synthetase Complexed with tRNA
Gln
and ATP at 2.8 Å Resolution
Authors: Rould Mark A. , Perona John J. , Söll Dieter , Steitz Thomas A.
Published: October 2006

The crystal structure of
Escherichia coli
glutaminyl-tRNA synthetase (GlnRS) complexed with its cognate glutaminyl transfer RNA (tRNA
Gln
) and adenosine triphosphate (ATP) has been derived from a 2.8 angstrom resolution electron density map and the known protein and tRNA sequences. The 63.4-kilodalton monomeric enzyme consists of four domains arranged to give an elongated molecule with an axial ratio greater than 3 to 1. Its interactions with the tRNA extend from the anticodon to the acceptor stem along the entire inside of the L of the tRNA. The complexed tRNA retains the overall conformation of the yeast phenylalanine tRNA (tRNA
Phe
) with two major differences: the 3′ acceptor strand of tRNA
Gln
makes a hairpin turn toward the inside of the L, with the disruption of the final base pair of the acceptor stem, and the anticodon loop adopts a conformation not seen in any of the previously determined tRNA structures. Specific recognition elements identified so far include (i) enzyme contacts with the 2-amino groups of guanine via the tRNA minor groove in the acceptor stem at G2 and G3; (ii) interactions between the enzyme and the anticodon nucleotides; and (iii) the ability of the nucleotides G73 and U1 ⋅ A72 of the cognate tRNA to assume a conformation stabilized by the protein at a lower free energy cost than noncognate sequences. The central domain of this synthetase binds ATP, glutamine, and the acceptor end of the tRNA as well as making specific interactions with the acceptor stem. It is structurally similar to the dinucleotide binding motifs of the tyrosyl- and methionyl- tRNA synthetases, suggesting that all synthetases may have evolved from a common domain that can recognize the acceptor stem of the cognate tRNA.
Efficient Multistep Photoinitiated Electron Transfer in a Molecular Pentad
Authors: Gust Devens , Moore Thomas A. , Moore Ana L. , Lee Seung-Joo , Bittersmann Edith , Luttrull David K. , Rehms Aden A. , DeGraziano Janice M. , Ma Xiaochun C. , Gao Feng , Belford Robert E. , Trier Todd T.
Published: October 2006

A synthetic five-part molecular device has been prepared that uses a multistep electron transfer strategy similar to that of photosynthetic organisms to capture light energy and convert it to chemical potential in the form of long-lived charge separation. It consists of two covalently linked porphyrin moieties, one containing a zinc ion (P
Zn
) and the other present as the free base (P). The metallated porphyrin bears a carotenoid polyene (C) and the other a diquinone species (Q
A
-Q
B
). Excitation of the free-base porphyrin in a chloroform solution of the pentad yields an initial charge-separated state, C-P
Zn
-P
⋅+
-Q
A
⋅-
-Q
B
, with a quantum yield of 0.85. Subsequent electron transfer steps lead to a final charge-separated state, C
⋅+
-P
Zn
-P-Q
A
-Q
B
⋅-
, which is formed with an overall quantum yield of 0.83 and has a lifetime of 55 microseconds. Irradiation of the free-base form of the pentad, C-P-P-Q
A
-Q
B
, gives a similar charge-separated state with a lower quantum yield (0.15 in dichloromethane), although the lifetime is increased to ∼340 microseconds. The artificial photosynthetic system preserves a significant fraction (∼1.0 electron volt) of the initial excitation energy (1.9 electron volts) in the long-lived, charge-separated state.
Holocene Mean Uplift Rates Across an Active Plate-Collision Boundary in Taiwan
Authors: Wang Chung-Ho , Burnett William C.
Published: October 2006

Samples of Holocene fossil coral from uplifted reefs of three tectonically distinct, yet geographically proximal regions of Taiwan have been dated by uranium-series and
14
C isotopes. Applying corrections for altitude change caused by sea level fluctuations enables evaluation of long-term average Holocene uplift rates for three areas across an active convergent margin: (i) the Hengchun Peninsula of the Eurasian tectonic plate; (ii) the Eastern Coastal Range of Taiwan, a plate boundary; and (iii) two offshore islands, Lanyu and Lutao, both situated on the leading edge of the adjoining Philippine Plate. The data indicate that while all three areas have experienced uplift through the Holocene, plate collision has caused significantly higher uplift rates in the region directly along the plate boundary.
The Superswell and Mantle Dynamics Beneath the South Pacific
Authors: McNutt Marcia K. , Judge Anne V.
Published: October 2006

The region of sea floor beneath French Polynesia (the "Superswell") is anomalous in that its depth is too shallow, flexural strength too weak, seismic velocity too slow, and geoid anomaly too negative for its lithospheric age as determined from magnetic isochrons. These features evidently are the effect of excess heat and extremely low viscosity in the upper mantle that maintain a thin lithospheric plate so easily penetrated by volcanism that 30 percent of the heat flux from all hot spots is liberated in this region, which constitutes only 3 percent of the earth's surface. The low-viscosity zone may facilitate rapid plate motion and the development of small-scale convection. A possible heat supply for the Superswell is a mantle reservoir enriched in radioactive isotopes as suggested by the geochemical signature of lavas from Superswell volcanoes.
Switch Protein Alters Specificity of RNA Polymerase Containing a Compartment-Specific Sigma Factor
Authors: Kroos Lee , Kunkel Barbara , Losick Richard
Published: October 2006

During sporulation in
Bacillus subtilis
, expression of developmental genes
spoIVCB
and
cotD
is induced in the mother cell compartment of the sporangium at morphological stages IV and V, respectively. A 27-kilodalton RNA polymerase sigma factor called σ
K
(or σ
27
) has been found that causes weak transcription of
spoIVCB
and strong transcription of
cotD
. A 14-kD protein was also discovered that changes the specificity of σ
K
-containing RNA polymerase, greatly stimulating
spoIVCB
transcription and markedly repressing
cotD
transcription. Both σ
K
and the 14-kD protein are products of genes known to be required for expression of specific genes in the mother cell. Thus, σ
K
directs gene expression in the mother cell and it is proposed that inactivation or sequestering of the 14-kD protein switches the temporal pattern of gene expression during the transition from stages IV to V of development.
An Organ-Specific Differentiation Gene,
pha-1
, from
Caenorhabditis elegans
Authors: Schnabel Heinke , Schnabel Ralf
Published: October 2006

Embryonic lethal mutations in the nematode
Caenorhabditis elegans
were generated and screened for phenotypes that suggest regulatory functions in order to identify genes involved in the control ofearly development. In embryos homozygous for mutations in one such gene,
pha-1
, the pharynx fails to undergo late differentiation and morphogenesis. Early pharynx development is not affected; thus,
pha-1
controls the latter stages of this developmental process. All markers specific for differentiation in various pharyngeal cell types tested are affected, suggesting that
pha-1
acts in an organ-specific, rather than cell type-specific, manner. The temperature-sensitive phases of both temperature-sensitive mutations indicate that
pha-1
function is required solely during midembryogenesis, shortly before the onset of morphogenesis.
Ridge Spreading, Subduction, and Sea Level Fluctuations
Authors: Gurnis Michael
Published: October 2006

A numerical model of mantle convection shows that sea level fluctuations are not simply associated with temporal changes in ocean c plate spreading. In the dynamic model, sea level rises rapidly and then falls toward a steady value (but one still higher than the initial) following increased ridge spreading; this time dependence results from profound changes in the deep thermal structure under ocean and continent. The use of past variations in oceanic spreading to infer sea level fluctuations is called into question. With more realistic models and better continental stratigraphy, constraints may be placed on the viscosity structure of the mantle.
Organizational Aspects of Engineering System Safety: The Case of Offshore Platforms
Authors: Paté-Cornell M. Elisabeth
Published: October 2006

Organizational errors are often at the root of failures of critical engineering systems. Yet, when searching for risk management strategies, engineers tend to focus on technical solutions, in part because of the way risks and failures are analyzed. Probabilistic risk analysis allows assessment of the safety of a complex system by relating its failure probability to the performance of its components and operators. In this article, some organizational aspects are introduced to this analysis in an effort to describe the link between the probability of component failures and relevant features of the organization. Probabilities are used to analyze occurrences of organizational errors and their effects on system safety. Coarse estimates of the benefits of certain organizational improvements can then be derived. For jacket-type offshore platforms, improving the design review can provide substantial reliability gains, and the corresponding expense is about two orders of magnitude below the cost of achieving the same result by adding steel to structures.
New Fossil Evidence on the Sister-Group of Mammals and Early Mesozoic Faunal Distributions
Authors: Shubin Neil H. , Crompton A. W. , Sues Hans-Dieter , Olsen Paul E.
Published: October 2006

Newly discovered remains of highly advanced mammal-like reptiles (Cynodontia: Tritheledontidae) from the Early Jurassic of Nova Scotia, Canada, have revealed that aspects of the characteristic mammalian occlusal pattern are primitive. Mammals and tritheledontids share an homologous pattern of occlusion that is not seen in other cynodonts. The new tritheledontids represent the first definite record of this family from North America. The extreme similarity of North American and African tritheledontids supports the hypothesis that the global distribution of terrestrial tetrapods was homogeneous in the Early Jurassic. This Early Jurassic cosmopolitanism represents the continuation of a trend toward increased global homogeneity among terrestrial tetrapod communities that began in the late Paleozoic.
Manipulation of Adsorbed Atoms and Creation of New Structures on Room-Temperature Surfaces with a Scanning Tunneling Microscope
Authors: Whitman L. J. , Stroscio Joseph A. , Dragoset R. A. , Celotta R. J.
Published: October 2006

A general method of manipulating adsorbed atoms and molecules on room-temperature surfaces with the use of a scanning tunneling microscope is described. By applying an appropriate voltage pulse between the sample and probe tip, adsorbed atoms can be induced to diffuse into the region beneath the tip. The field-induced diffusion occurs preferentially toward the tip during the voltage pulse because of the local potential energy gradient arising from the interaction of the adsorbate dipole moment with the electric field gradient at the surface. Depending upon the surface and pulse parameters, cesium (Cs) structures from one nanometer to a few tens of nanometers across have been created in this way on the (110) surfaces of gallium arsenide (GaAs) and indium antimonide (InSb), including structures that do not naturally occur.