bluuebunny/crossref_metadata_2025 huggingface dataset:
Mantle Phase Changes and Deep-Earthquake Faulting in Subducting Lithosphere
Authors: Kirby Stephen H. , Durham William B. , Stern Laura A.
Published: October 2006

Inclined zones of earthquakes are the primary expression of lithosphere subduction. A distinct deep population of subduction-zone earthquakes occurs at depths of 350 to 690 kilometers. At those depths ordinary brittle fracture and frictional sliding, the faulting processes of shallow earthquakes, are not expected. A fresh understanding of these deep earthquakes comes from developments in several areas of experimental and theoretical geophysics, including the discovery and characterization of transformational faulting, a shear instability connected with localized phase transformations under nonhydrostatic stress. These developments support the hypothesis that deep earthquakes represent transformational faulting in a wedge of olivine-rich peridotite that is likely to persist metastably in coldest plate interiors to depths as great as 690 km. Predictions based on this deep structure of mantle phase changes are consistent with the global depth distribution of deep earthquakes, the maximum depths of earthquakes in individual subductions zones, and key source characteristics of deep events.
Magellan: Mission Summary
Authors: Saunders R. Stephen , Pettengill Gordon H.
Published: October 2006

The Magellan radar mapping mission is in the process of producing a global, high-resolution image and altimetry data set of Venus. Despite initial communications problems, few data gaps have occurred. Analysis of Magellan data is in the initial stages. The radar system data are of high quality, and the planned performance is being achieved in terms of spatial resolution and geometric and radiometric accuracy. Image performance exceeds expectations, and the image quality and mosaickability are extremely good. Future plans for the mission include obtaining gravity data, filling gaps in the initial map, and conducting special studies with the radar.
An Overview of Venus Geology
Authors: Saunders R. Stephen , Arvidson Raymond E. , Head James W. , Schaber Gerald G. , Stofan Ellen R. , Solomon Sean C.
Published: October 2006

The Magellan spacecraft is producing comprehensive image and altimetry data for the planet Venus. Initial geologic mapping of the planet reveals a surface dominated by volcanic plains and characterized by extensive volcanism and tectonic deformation. Geologic and geomorphologic units include plains terrains, tectonic terrains, and surficial material units. Understanding the origin of these units and the relation between them is an ongoing task of the Magellan team.
Epitaxial Cuprate Superconductor/Ferroelectric Heterostructures
Authors: Ramesh R. , Inam A. , Chan W. K. , Wilkens B. , Myers K. , Remschnig K. , Hart D. L. , Tarascon J. M.
Published: October 2006

Thin-film heterostructures of Bi
4
Ti
3
O
12/
Bi
2
Sr
2
CuO

6+
x

have been grown on single crystals of SrTiO
3
, LaAlO
3
, and MgAl
2
O
4
by pulsed laser deposition. X-ray diffraction studies show the presence of
c
-axis orientation only; Rutherford backscattering experiments show the composition to be close to the nominal stoichiometry. The films are ferroelectric and exhibit a symmetric hysteresis loop. The remanent polarization was 1.0 microcoulomb per square centimeter, and the coercive field was 2.0 x 10
5
volts per centimeter. Similar results were obtained with YBa
2
Cu
3
O

7-
x

and Bi
2
Sr
2
CaCu
2
O

8+
x

, and single-crystal Bi
2
Sr
2
CuO

6+
x

as the bottom electrodes. These films look promising for use as novel, lattice-matched, epitaxial ferroelectric film/electrode heterostructures in nonvolatile memory applications.
Samarium-Neodymium Direct Dating of Fluorite Mineralization
Authors: Chesley J. T. , Halliday A. N. , Scrivener R. C.
Published: October 2006

The direct dating of many styles of hydrothermal mineralization has proved difficult, limiting understanding of the geological processes that lead to crustal fluid flow and the formation of major ore deposits. The hydrothermal mineral fluorite (CaF
2
) displays large variations in rare earth element (REE) abundance and samarium/neodymium ratios within a single vein. Samarium-neodymium dating of fluorite from the classic granite-hosted tin deposits of southwest England demonstrates its use as a precise chronometer of mineralization. The concentrations of light rare earth elements (LREEs) in the fluorites are highly variable and suggest the coeval precipitation of an LREE-rich phase as the most likely cause of the extreme variation in samarium/neodymium ratios.
Predictable Upwelling and the Shoreward Transport of Planktonic Larvae by Internal Tidal Bores
Authors: Pineda Jesús
Published: October 2006

Internal tidal bores have a crucial role in the transport of drifting larvae to marine nearshore populations, a key factor in structuring benthic communities. Shoreward transport of larvae and abrupt surface temperature drops lasting days can be explained by invoking the advection of subsurface cold water to the shore by internal tidal bores. This process is predictable within the lunar cycle and brings deep water to the surface (upwelling) in a direction perpendicular to the coastline.
Developments in Automatic Text Retrieval
Authors: Salton Gerard
Published: October 2006

Recent developments in the storage, retrieval, and manipulation of large text files are described. The text analysis problem is examined, and modern approaches leading to the identification and retrieval of selected text items in response to search requests are discussed.
Mid-Ocean Ridges: Discontinuities, Segments and Giant Cracks
Authors: MacDonald Ken C. , Scheirer Daniel S. , Carbotte Suzanne M.
Published: October 2006

Geological observations reveal that mid-ocean ridges are segmented by numerous rigid and nonrigid discontinuities. A hierarchy of segmentation, ranging from large, long-lived segments to others that are small, migratory, and transient, determines the pattern and timing of creation of new ocean floor. To the extent that spreading segments behave like giant cracks in a plate, the crack propagation force at segment tips increases with segment length, which may explain why long segments tend to lengthen and prevail over shorter neighboring segments. Partial melting caused by decompression of the upper mantle due to plate separation and changes in the direction of spreading result in the spawning of new short segments so that a balance of long and short segments is maintained.
When Biotas Meet: Understanding Biotic Interchange
Authors: Vermeij Geerat J.
Published: October 2006

When the barrier between biotas with long separate histories breaks down, species invade from one biota to the other. Studies of episodes of marine and terrestrial biotic interchange that have occurred during the last 20 million years show that large-scale extinction of species before the onset of interchange renders biotas especially prone to invasion. As environments and species are being exploited and eliminated on an ever increasing scale in the human-dominated biosphere, the geographical expansion of species from biotas in which evolution of high competitive, defensive, and reproductive abilities has proceeded the furthest will become more frequent. Historical events and interactions are essential ingredients for understanding the current and future structure and composition of the world's biota.
Vapor-Phase Fabrication and Properties of Continuous-Filament Ceramic Composites
Authors: Besmann T. M. , Sheldon B. W. , Lowden R. A. , Stinton D. P.
Published: October 2006

The continuous-filament ceramic composite is becoming recognized as necessary for new, high-temperature structural applications. Yet because of the susceptibility of the filaments to damage from traditional methods for the preparation of ceramics, vapor-phase infiltration has become the fabrication method of choice. The chemical vapor infiltration methods for producing these composites are now being studied in earnest, with the complexity of filament weaves and deposition chemistry being merged with standard heat and mass-transport relationships. Two of the most influential effects on the mechanical properties of these materials are the adhesion and frictional force between the fibers and the matrix, which can be controlled by a tailored interface coating. A variety of materials are available for producing these composites including carbide, nitride, boride, and oxide filaments and matrices. Silicon carbide-based materials are by far the most advanced and are already being used in aerospace applications.
Chemical Imaging of Surfaces with the Scanning Electrochemical Microscope
Authors: Bard Allen J. , Fan Fu-Ren F. , Pierce David T. , Unwin Patrick R. , Wipf David O. , Zhou Feimeng
Published: October 2006

Scanning electrochemical microscopy is a scanning probe technique that is based on faradaic current changes as a small electrode is moved across the surface of a sample. The images obtained depend on the sample topography and surface reactivity. The response of the scanning electrochemical microscope is sensitive to the presence of conducting and electroactive species, which makes it useful for imaging heterogeneous surfaces. The principles and instrumentation used to obtain images and surface reaction-kinetic information are discussed, and examples of applications to the study of electrodes, minerals, and biological samples are given.
Early Cretaceous Uplift in the Ellsworth Mountains of West Antarctica
Authors: Fitzgerald Paul G. , Stump Edmund
Published: October 2006

Apatite fission-track analysis of samples covering a 4.2-kilometer vertical section from the western flank of Vinson Massif, Antarctica's highest mountain, indicates that the Ellsworth Mountains were uplifted by 4 kilometers or more during the Early Cretaceous following the initial separation of East and West Gondwana and accompanying the opening of the Weddell Sea. Relief of at least 1.8 kilometers has persisted in the Ellsworth Mountains since the Early Cretaceous, and a maximum of 3 kilometers of uplift has occurred since that time.
Oxygen Isotope Zoning in Garnet
Authors: Chamberlain C. Page , Conrad Mark E.
Published: October 2006

Oxygen isotope zoning was examined within garnet with the use of the stable isotope laser probe. Four metamorphic garnets from the regional metamorphic terrane in Vermont and the skarn deposit at Carr Fork, Utah, were examined and were found to be concentrically zoned in δ
18
O values. The largest variations in δ
18
O values were observed in the regional metamorphic garnets, where δ
18
O values change by 3 per mil from core to rim. These oxygen isotope zoning profiles reflect the changes in the δ
18
O values of the rocks during garnet growth, which are caused by infiltration of fluids and by dehydration reactions during metamorphism.
Theoretical Fermi-Surface Properties and Superconducting Parameters for K
3
C
60
Authors: Erwin Steven C. , Pickett Warren E.
Published: October 2006

Quantitative theories of superconductivity in alkali-doped C
60
require an accurate and detailed description of the Fermi surface. First-principles calculations of Fermi-surface properties and electronic parameters for K
3
C
60
, the prototype fulleride-superconductor, are reported. The Fermi surface has two sheets; the first is free-electron-like, and the second is multiply-connected, forming two interlocked symmetry-equivalent pieces that never touch. The calculated (clean limit) London penetration depth is λ = 1600 Å. Comparing the Fermi velocity with the experimental coherence length leads to a superconducting pairing strength λ ∼ 5, indicating very strong coupling. Partial nesting in the second Fermi-surface sheet may favor coupling to short-wavelength 〈
q
,0,0〉 optic modes.
Superconductivity in the Fullerenes
Authors: Varma C. M. , Zaanen J. , Raghavachari K.
Published: October 2006

Intramolecular vibrations strongly scatter electrons near the Fermi-surface in doped fullerenes. A simple expression for the electron-phonon coupling parameters for this case is derived and evaluated by quantum-chemical calculations. The observed superconducting transition temperatures and their variation with lattice constants can be understood on this basis. To test the ideas and calculations presented here, we predict that high frequency
H
2
modes acquire a width of about 20% of their frequency in superconductive fullerenes, and soften by about 5% compared to the insulating fullerenes.
Identification of the Molecular Defect in a Family with Spondyloepiphyseal Dysplasia
Authors: Lee Brendan , Vissing Henrik , Ramirez Francesco , Rogers David , Rimoin David
Published: October 2006

Spondyloepiphyseal dysplasias (SED) are a heterogeneous group of inherited disorders characterized by disproportionate short stature and pleiotropic involvement of the skeletal and ocular systems. Evidence has suggested that SED may result from structural defects in type II collagen. To confirm the validity of this hypothesis, the structure of the "candidate" type II collagen gene (COL2A1) has been directly examined in a relatively large SED family. Coarse scanning of the gene by Southern blot hybridization identified an abnormal restriction pattern in one of the affected members of the kindred. Analysis of selected genomic fragments, amplified by the polymerase chain reaction, precisely localized the molecular defect and demonstrated that all affected family members carried the same heterozygous single-exon deletion. As a consequence of the mutation, nearly 90 percent of the assembled type II collagen homotrimers are expected to contain one or more procollagen subunits harboring an interstitial deletion of 36 amino acids in the triple helical domain.
The MHC-Binding and gp120-Binding Functions of CD4 Are Separable
Authors: Lamarre Daniel , Ashkenazi Avi , Fleury Sylvain , Smith Douglas H. , Sekaly Rafick-P. , Capon Daniel J.
Published: October 2006

CD4 is a cell surface glycoprotein that is thought to interact with nonpolymorphic determinants of class II major histocompatibility (MHC) molecules. CD4 is also the receptor for the human immunodeficiency virus (HIV), binding with high affinity to the HIV-1 envelope glycoprotein, gp120. Homolog-scanning mutagenesis was used to identify CD4 regions that are important in class II MHC binding and to determine whether the gp120 and class II MHC binding sites of CD4 are related. Class II MHC binding was abolished by mutations in each of the first three immunoglobulin-like domains of CD4. The gp120 binding could be abolished without affecting class II MHC binding and vice versa, although at least one mutation examined reduced both functions significantly. These findings indicate that, while there may be overlap between the gp120 and class II MHC binding sites of CD4, these sites are distinct and can be separated. Thus it should be possible to design CD4 analogs that can block HIV infectivity but intrinsically lack the ability to affect the normal immune response by binding to class II MHC molecules.
Effects of High Temperature on Silicate Liquid Structure: A Multinuclear NMR Study
Authors: Stebbins J. F. , Farnan Ian
Published: October 2006

The structure of a silicate liquid changes with temperature, and this substantially affects its thermodynamic and transport properties. Models used by geochemists, geophysicists, and glass scientists need to include such effects. In situ, high-temperature nuclear magnetic resonance (NMR) spectroscopy on
23
Na,
27
Al, and
29
Si was used to help determine the time-averaged structure of a series of alkali aluminosilicate liquids at temperatures to 1320°C. Isotropic chemical shifts for
29
Si increase (to higher frequencies) with increasing temperature, probably in response to intermediate-range structural changes such as the expansion of bonds between nonbridging oxygens and alkali cations. In contrast, isotropic chemical shifts for
27
Al decrease with increasing temperature, indicating that more significant short-range structural changes take place for aluminum, such as an increase in mean coordination number. The spectrum of a sodium aluminosilicate glass clearly indicates that at least a few percent of six-coordinated aluminum was present in the liquid at high temperature.
When Do Anomalies Begin?
Authors: Lightman Alan , Gingerich Owen
Published: October 2006

An anomaly in science is an observed fact that is difficult to explain in terms of the existing conceptual framework. Anomalies often point to the inadequacy of the current theory and herald a new one. It is argued here that certain scientific anomalies are recognized as anomalies only after they are given compelling explanations within a new conceptual framework. Before this recognition, the peculiar facts are taken as givens or are ignored in the old framework. Such a "retrorecognition" phenomenon reveals not only a significant feature of the process of scientific discovery but also an important aspect of human psychology.
Molecular Dynamics Simulations of Dimer Opening on a Diamond {001}(2
x
1) Surface
Authors: Garrison Barbara J. , Dawnkaski Eric J. , Srivastava Deepak , Brenner Donald W.
Published: October 2006

Computer simulations of hydrocarbon and related molecules using empirical force fields have become important tools for studying a number of biological and related processes at the atomic scale. Traditional force fields, however, cannot be used to simulate dynamic chemical reactivity that involves changes in atomic hybridization. Application of a many-body potential function allows such reactivity to occur in a computer simulation. Simulations of the reaction of small hydrocarbon molecules adsorbed on a reconstructed diamond {001}(2×1) surface suggest that these hydrocarbons are highly reactive species and that initial stages of diamond growth proceed through a dimer-opening mechanism. Rates estimated from transition state theory of two interconversions between states where the dimer is open and closed are given.
Correlation Between Surface Free Energy and Surface Constitution
Authors: Chaudhury Manoj K. , Whitesides George M.
Published: October 2006

Self-assembled monolayers (SAMs) of alkylsiloxanes on elastomeric PDMS (polydimethylsiloxane) were used as model systems to study interactions between surfaces. Surface free energies (γsv) of these chemically modified surfaces were estimated by measuring the deformations that resulted from the contact between small semispherical lenses and flat sheets of the elastomer under controlled loads. The measured surface free energies correlated with the surface chemical compositions of the SAMs and were commensurate with the values estimated from the measurements of contact angles. This study provides direct experimental evidence for the validity of estimates of the surface free energies of low-energy solids obtained from contact angles.
Raising Tibet
Authors: Harrison T. Mark , Copeland Peter , Kidd W. S. F. , Yin An
Published: October 2006

Thermochronologic, sedimentologic, oceanographic, and paleoclimatic studies suggest that rapid uplift and unroofing of southern Tibet began about 20 million years ago and that the present elevation of much of the Tibetan plateau was attained by about 8 million years ago. Hypotheses advanced to explain the tectonic evolution of the India-Asia collision, which began about 40 to 50 million years ago, predict the timing and rates of crustal thickening of the southern margin of Asia. However, these models do not predict the prominently enhanced early Miocene denudation and uplift that are manifested in a variety of geological records. A model involving continental extrusion, development of a crustal-scale thrust ramp of the Main Central Thrust beneath the Gangdese belt, and lithospheric delamination provides a history consistent with these observations.
The Fossil Record and Evolution: Comparing Cladistic and Paleontologic Evidence for Vertebrate History
Authors: Norell Mark A. , Novacek Michael J.
Published: October 2006

The fossil record offers the only direct evidence of extinct life and thus has figured prominently in considerations of evolutionary patterns. But the incomplete nature of the fossil record has also been emphasized in arguments that fossils play only a secondary role in the recovery of phylogenetic histories based on extant taxa. Although these criticisms recently have been countered, there is no general understanding of the correspondence between the fossil record and phylogeny. An empirical survey of recently published studies suggests no basis for assuming that the stratigraphic occurrence of fossils always provides a precise reflection of phylogeny. Nevertheless, our survey of a sample of taxa shows a tendency for positive correlation between age and clade rank and, hence, a degree of correspondence between phylogenetic pattern and the paleontologic record.
Chloroplast DNA Evidence on the Ancient Evolutionary Split in Vascular Land Plants
Authors: Raubeson Linda A. , Jansen Robert K.
Published: October 2006

Two groups of extant plants, lycopsids and psilopsids, alternatively have been suggested to be the living representatives of the earliest diverging lineage in vascular plant evolution. The chloroplast DNA (cpDNA) gene order is known to contain an inversion in bryophytes and tracheophytes relative to one another. Characterization of tracheophyte cpDNAs shows that lycopsids share the gene order with bryophytes, whereas all other vascular plants share the inverted gene order. The distribution of this character provides strong support for the fundamental nature of the phylogenetic separation of lycopsids and marks the ancient evolutionary split in early vascular land plants.
Biomass and Carbon Budget of European Forests, 1971 to 1990
Authors: Kauppi Pekka E. , Mielikäinen Kari , Kuusela Kullervo
Published: October 2006

In severely polluted areas, such as locally in Montshegorsk in northwestern Russia, all trees have died. However, measurements from Austria, Finland, France, Germany, Sweden, and Switzerland show a general increase of forest resources. The fertilization effects of pollutants override the adverse effects at least for the time being. Biomass was built up in the 1970s and 1980s in European forests. If there has been similar development in other continents, biomass accumulation in nontropical forests can account for a large proportion of the estimated mismatch between sinks and sources of atmospheric carbon dioxide.
40
Ar/
39
Ar Dating of the Brunhes-Matuyama Geomagnetic Field Reversal
Authors: Baksi A. K. , Hsu V. , McWilliams M. O. , Farrar E.
Published: October 2006

Magnetostratigraphic studies are widely used in conjunction with the geomagnetic polarity time scale (GPTS) to date events in the range 0 to 5 million years ago. A critical tie point on the GPTS is the potassium-argon age of the most recent (Brunhes-Matuyama) geomagnetic field reversal. Astronomical values for the forcing frequencies observed in the oxygen isotope record in Ocean Drilling Project site 677 suggest that the age of this last reversal is 780 ka (thousand years ago), whereas the potassium-argon-based estimate is 730 ka. Results from
40
Ar/
39
Ar incremental heating studies on a series of lavas from Maui that straddle the Brunhes-Matuyama reversal give an age of 783 ± 11 ka, in agreement with the astronomically derived value. The astronomically based technique appears to be a viable tool for dating young sedimentary sequences.
Contact Electrification and Adhesion Between Dissimilar Materials
Authors: Horn Roger G. , Smith Douglas T.
Published: October 2006

Simultaneous measurements of surface force and surface charge demonstrate strong attraction due to the spontaneous transfer of electrical charge from one smooth insulator (mica) to another (silica) as a result of simple, nonsliding contact in dry nitrogen. The measured surface charge densities are 5 to 20 millicoulombs per square meter after contact. The work required to separate the charged surfaces is typically 6 to 9 joules per square meter, comparable to the fracture energies of ionic-covalent materials. Observation of partial gas discharges when the surfaces are approximately 1 micrometer apart gives valuable insight into the charge separation processes underlying static electrical phenomena in general.
Appearance of Water Channels in
Xenopus
Oocytes Expressing Red Cell CHIP28 Protein
Authors: Preston Gregory M. , Carroll Tiziana Piazza , Guggino William B. , Agre Peter
Published: October 2006

Water rapidly crosses the plasma membrane of red blood cells (RBCs) and renal tubules through specialized channels. Although selective for water, the molecular structure of these channels is unknown. The CHIP28 protein is an abundant integral membrane protein in mammalian RBCs and renal proximal tubules and belongs to a family of membrane proteins with unknown functions. Oocytes from
Xenopus laevis
microinjected with in vitro-transcribed CHIP28 RNA exhibited increased osmotic water permeability; this was reversibly inhibited by mercuric chloride, a known inhibitor of water channels. Therefore it is likely that CHIP28 is a functional unit of membrane water channels.
Observational Learning in
Octopus vulgaris
Authors: Fiorito Graziano , Scotto Pietro
Published: October 2006

Untrained
Octopus vulgaris
(observers) were allowed to watch conditioned
Octopus
(demonstrators) perform the task of selecting one of two objects that were presented simultaneously and differed only in color. After being placed in isolation, the observers, in a similar test, consistently selected the same object as did the demonstrators. This learning by observation occurred irrespective of the object chosen by the demonstrators as the positive choice and was more rapid than the learning that occurred during the conditioning of animals. The task was performed correctly without significant errors and further conditioning for 5 days. These results show that observational learning can occur in invertebrates.
Colloid Formation During Waste Form Reaction: Implications for Nuclear Waste Disposal
Authors: Bates J. K. , Bradley J. P. , Teetsov A. , Bradley C. R. , ten Brink M. Buchholtz
Published: October 2006

Insoluble plutonium- and americium-bearing colloidal particles formed during simulated weathering of a high-level nuclear waste glass. Nearly 100 percent of the total plutonium and americium in test ground water was concentrated in these submicrometer particles. These results indicate that models of actinide mobility and repository integrity, which assume complete solubility of actinides in ground water, underestimate the potential for radionuclide release into the environment. A colloid-trapping mechanism may be necessary for a waste repository to meet long-term performance specifications.
Natural Versus Anthropogenic Factors Affecting Low-Level Cloud Albedo over the North Atlantic
Authors: Falkowski Paul G. , Kim Yongseung , Kolber Zbigniew , Wilson Cara , Wirick Creighton , Cess Robert
Published: October 2006

Cloud albedo plays a key role in regulating Earth's climate. Cloud albedo depends on column-integrated liquid water content and the density of cloud condensation nuclei, which consists primarily of submicrometer-sized aerosol sulfate particles. A comparison of two independent satellite data sets suggests that, although anthropogenic sulfate emissions may enhance cloud albedo immediately adjacent to the east coast of the United States, over the central North Atlantic Ocean the variability in albedo can be largely accounted for by natural marine and atmospheric processes that probably have remained relatively constant since the beginning of the industrial revolution.
Energetics of Large Fullerenes: Balls, Tubes, and Capsules
Authors: Adams Gary B. , Sankey Otto F. , Page John B. , O'Keeffe Michael , Drabold David A.
Published: October 2006

First-principles calculations were performed to compare the energies of 29 different fullerene structures, with mass number from 60 to 240, and of eight nonhelical graphite tubes of different radii. A quantity called the planarity, which indicates the completeness of the π-bonding, is the single most important parameter determining the energetics of these structures. Empirical equations were constructed for the energies of nonhelical tubes and for those fullerene structures that may be described as balls or capsules. For a given mass number, bail-shaped fullerenes are energetically favored over capsular (tube-like) fullerenes.
Subaqueous Explosive Eruption and Welding of Pyroclastic Deposits
Authors: Kokelaar Peter , Busby Cathy
Published: October 2006

Silicic tuffs infilling an ancient submarine caldera, at Mineral King in California, show microscopic fabrics indicative of welding of glass shards and pumice at temperatures >500°C. The occurrence indicates that subaqueous explosive eruption and emplacement of pyroclastic materials can occur without substantial admixture of the ambient water, which would cause chilling. Intracaldera progressive aggradation of pumice and ash from a thick, fast-moving pyroclastic flow occurred during a short-lived explosive eruption of ∼26 cubic kilometers of magma in water ≥150 meters deep. The thickness, high velocity, and abundant fine material of the erupted gas-solids mixture prevented substantial incorporation of ambient water into the flow. Stripping of pyroclasts from upper surfaces of subaqueous pyroclastic flows in general, both above the vent and along any flow path, may be the main process giving rise to buoyant-convective subaqueous eruption columns and attendant fallout deposits.
Dynamics of Cluster-Surface Collisions
Authors: Cleveland Charles L. , Landman Uzi
Published: October 2006

The structure, energetics, and dynamics of shock conditions generated in a nano-cluster upon impact on a crystalline surface are investigated with molecular-dynamics simulations for a 561-atom argon cluster incident with a velocity of 3 kilometers per second onto a sodium chloride surface. The "piling-up" shock phenomenon occurring upon impact, coupled with cascades of energy and momentum transfer processes and inertial confinement of material in the interior of the cluster, creates a transient medium lasting for about a picosecond and characterized by extreme local density, pressure, and kinetic temperature. The nano-shock conditions and impulsive nature of interactions in the newly formed compressed nonequilibrium environment open avenues for studying chemical reactivity and dynamics catalyzed via cluster impact.
Current Issues and Problems in Welding Science
Authors: David S. A. , DebRoy T.
Published: October 2006

Losses of life and property due to catastrophic failure of structures are often traced to defective welds. However, major advances have taken place in welding science and technology in the last few decades. With the development of new methodologies at the crossroad of basic and applied sciences, the promise of science-based tailoring of composition, structure, and properties of the weldments may be fulfilled. This will require resolution of several contemporary issues and problems concerning the structure and properties of the weldments as well as intelligent control and automation of the welding processes.
Thermoelasticity of Silicate Perovskite and Magnesiowüstite and Stratification of the Earth's Mantle
Authors: Stixrude Lars , Hemley R. J. , Fei Y. , Mao H. K.
Published: October 2006

Analyses of x-ray-diffraction measurements on (Mg,Fe)SiO
3
perovskite and (Mg,Fe)O magnesiowüstite at simultaneous high temperature and pressure are used to determine pressure-volume-temperature equations of state and thermoelastic properties of these lower mantle minerals. Detailed comparison with the seismically observed density and bulk sound velocity profiles of the lower mantle does not support models of this region that assume compositions identical to that of the upper mantle. The data are consistent with lower mantle compositions consisting of nearly pure perovskite (>85 percent), which would indicate that the Earth's mantle is compositionally, and by implication, dynamically stratified.
Plasma Composition in Jupiter's Magnetosphere: Initial Results from the Solar Wind Ion Composition Spectrometer
Authors: Geiss J. , Gloeckler G. , Balsiger H. , Fisk L. A. , Galvin A. B. , Gliem F. , Hamilton D. C. , Ipavich F. M. , Livi S. , Mall U. , Ogilvie K. W. , von Steiger R. , Wilken B.
Published: October 2006

The ion composition in the Jovian environment was investigated with the Solar Wind Ion Composition Spectrometer on board Ulysses. A hot tenuous plasma was observed throughout the outer and middle magnetosphere. In some regions two thermally different components were identified. Oxygen and sulfur ions with several different charge states, from the volcanic satellite Io, make the largest contribution to the mass density of the hot plasma, even at high latitude. Solar wind particles were observed in all regions investigated. Ions from Jupiter's ionosphere were abundant in the middle magnetosphere, particularly in the high-latitude region on the dusk side, which was traversed for the first time.
Mechanism of Membrane Anchoring Affects Polarized Expression of Two Proteins in MDCK Cells
Authors: Brown Deborah A. , Crise Bruce , Rose John K.
Published: October 2006

The signals that direct membrane proteins to the apical or basolateral plasma membrane domains of polarized epithelial cells are not known. Several of the class of proteins anchored in the membrane by glycosyl-phosphatidylinositol (GPI) are expressed on the apical surface of such cells. However, it is not known whether the mechanism of membrane anchorage or the polypeptide sequence provides the sorting information. The conversion of the normally basolateral vesicular stomatitis virus glycoprotein (VSV G) to a GPI-anchored protein led to its apical expression. Conversely, replacement of the GPI anchor of placental alkaline phosphatase with the transmembrane and cytoplasmic domains of VSV G shifted its expression from the apical to the basolateral surface. Thus, the mechanism of membrane anchorage can determine the sorting of proteins to the apical or basolateral surface, and the GPI anchor itself may provide an apical transport signal.
Macroscopic Quantum Effects in Nanometer-Scale Magnets
Authors: Awschalom David D. , DiVincenzo David P. , Smyth Joseph F.
Published: October 2006

Quantum tunneling, the passage of a microscopic system from one state to another by way of a classically forbidden path, is theoretically possible in the macroscopic world. One can now make direct observations of such macroscopic quantum tunneling in very small magnetic structures. This is possible because of significant advances both in the ability to obtain magnetic systems of almost any desirable size, shape, and composition and in the development of superconducting instrumentation for the detection of extremely weak magnetic signals. As an example, measurements on magnetic horse spleen ferritin proteins with the predictions of quantum tunneling theory are discussed and shown.
Bacterial Sulfate Reduction Above 100°C in Deep-Sea Hydrothermal Vent Sediments
Authors: Jørgensen Bo Barker , Isaksen Mai F. , Jannasch Holger W.
Published: October 2006

The currently known upper temperature limit for growth of organisms, shared by a number of archaebacteria, is 110°C. However, among the sulfate-reducing bacteria, growth temperatures of greater than 100°C have not been found. A search for high-temperature activity of sulfate-reducing bacteria was done in hot deep-sea sediments at the hydrothermal vents of the Guaymas Basin tectonic spreading center in the Gulf of California. Radiotracer studies revealed that sulfate reduction can occur at temperatures up to 110°C, with an optimum rate at 103° to 106°C. This observation expands the upper temperature limit of this process in deep-ocean sediments by 20°C and indicates the existence of an unknown group of hyperthermophilic bacteria with a potential importance for the biogeochemistry of sulfur above 100°C.
Verification of the Onsager Reciprocal Relations in a Molten Silicate Solution
Authors: Spera Frank J. , Trial Alain F.
Published: October 2006

A key hypothesis in the generalized theory of nonequilibrium thermodynamics is the principle of microscopic time invariance as enunciated by Onsager in the 1930s. At the macroscopic level, Onsager's hypothesis is represented by a set of relations known as the Onsager reciprocal relations, which, when applied to isothermal, multicomponent diffusion, demand the symmetry of the phenomenological matrix that connects mass fluxes to chemical potential gradients. On the basis of experimentally determined diffusion coefficients and thermochemical data for the molten system CaO-Al
2
O
3
-SiO
2
, the Onsager phenomenological coefficients have been computed, including an analysis of error. Within experimental uncertainty, the Onsager matrix is indeed symmetric.
Identification of a Second Dynamic State During Stick-Slip Motion
Authors: Yoshizawa Hisae , McGuiggan Patricia , Israelachvili Jacob
Published: October 2006

Stick-slip, or interrupted, motion rather than smooth uninterrupted motion occurs in many different phenomena such as friction, fluid flow, material fracture and wear, sound generation, and sensory "texture." During stick-slip, a system is believed to undergo transitions between a static (solid-like) state and a kinetic (liquid-like) state. The stick-slip motion between various types of pretreated surfaces was measured, and a second, much more kinetic state that exhibits ultra-low friction was found. Transitions to and from this super-kinetic state also give rise to stick-slip motion but are fundamentally different from conventional static-kinetic transitions. The results here suggest practical conditions for the control of unwanted stick-slip and the attainment of ultra-low friction.
The
18
O/
16
O Ratio of 2-Billion-Year-Old Seawater Inferred from Ancient Oceanic Crust
Authors: Holmden C. , Muehlenbachs K.
Published: October 2006

An oxygen isotope profile of the 2-billion-year-old Purtuniq ophiolite overlaps with similar profiles of younger ophiolites and the modern oceanic crust. This overlap implies (i) that there was a similar style of seawater—ocean crust interaction during the past 2 billion years; (ii) that the oxygen isotope composition of early Proterozoic seawater was similar to the modern value; (iii) that early Proterozoic sea-floor spreading rates were similar to, or greater than, average modern rates; and (iv) that early Proterozoic carbonate rocks and cherts with low
18
O/
16
O ratios do not reflect global-scale
18
O depletion of early Proterozoic oceans.
Outgassed Water on Mars: Constraints from Melt Inclusions in SNC Meteorites
Authors: McSween Harry Y. , Harvey Ralph P.
Published: October 2006

The SNC (shergottite-nakhlite-chassignite) meteorites, thought to be igneous rocks from Mars, contain melt inclusions trapped at depth in early-formed crystals. Determination of the pre-eruptive water contents of SNC parental magmas from calculations of the solidification histories of these amphibole-bearing inclusions indicates that martian magmas commonly contained 1.4 percent water by weight. When combined with an estimate of the volume of igneous materials on Mars, this information suggests that the total amount of water outgassed since 3.9 billion years ago corresponds to global depths on the order of 200 meters. This value is significantly higher than previous geochemical estimates but lower than estimates based on erosion by floods. These results imply a wetter Mars interior than has been previously thought and support suggestions of significant outgassing before formation of a stable crust or heterogeneous accretion of a veneer of cometary matter.
Velocity Structure of a Gas Hydrate Reflector
Authors: Singh Satish C. , Minshull Timothy A. , Spence George D.
Published: October 2006

Seismic reflection profiles across many continental margins have imaged bottom-simulating reflectors (BSRs) parallel to the seabed; these are often interpreted as the base of a zone in which methane hydrate "ice" is stable. Waveform inversion of seismic reflection data can be used to estimate from seismic data worldwide the velocity structure of a BSR and its thickness. A test of this method at a drill site of the Ocean Drilling Program predicts that sediment pores beneath the BSR contain free methane for approximately 30 meters. The hydrate and underlying gas represent a large global reservoir of methane, which may have economic importance and may influence global climate.
The Relative Roles of Sulfate Aerosols and Greenhouse Gases in Climate Forcing
Authors: Kiehl J. T. , Briegleb B. P.
Published: October 2006

Calculations of the effects of both natural and anthropogenic tropospheric sulfate aerosols indicate that the aerosol climate forcing is sufficiently large in a number of regions of the Northern Hemisphere to reduce significantly the positive forcing from increased greenhouse gases. Summer sulfate aerosol forcing in the Northern Hemisphere completely offsets the greenhouse forcing over the eastern United States and central Europe. Anthropogenic sulfate aerosols contribute a globally averaged annual forcing of –0.3 watt per square meter as compared with +2.1 watts per square meter for greenhouse gases. Sources of the difference in magnitude with the previous estimate of Charlson
et al
. are discussed.
The Opposition Effect of the Moon: The Contribution of Coherent Backscatter
Authors: Hapke Bruce W. , Nelson Robert M. , Smythe William D.
Published: October 2006

The opposition effect, the sharp surge in brightness of an astronomical object observed near zero phase angle, which has been known for more than a century, has generally been explained by shadow hiding. The reflectances of several Apollo lunar soil samples have been measured as a function of phase angle in linearly and circularly polarized light. All samples exhibited a decrease in the linear polarization ratio and an increase in the circular polarization ratio in the opposition peak. This provides unequivocal proof that most of the lunar opposition effect is caused by coherent backscatter, not shadow hiding. This result has major implications for the interpretation of photometric observations of bodies in the solar system, including the Earth.
Water Sources for Subduction Zone Volcanism: New Experimental Constraints
Authors: Pawley Alison R. , Holloway John R.
Published: October 2006

Despite its acknowledged importance, the role of water in the genesis of subduction zone volcanism is poorly understood. Amphibole dehydration in subducting oceanic crust at a single pressure is assumed to generate the water required for melting, but experimental constraints on the reaction are limited, and little attention has been paid to reactions involving other hydrous minerals. Experiments on an oceanic basalt at pressure-temperature conditions relevant to subducting slabs demonstrate that amphibole dehydration is spread over a depth interval of at least 20 kilometers. Reactions involving other hydrous minerals, including mica, epidote, chloritoid, and lawsonite, also release water over a wide depth interval, and in some subduction zones these phases may transport water to deep levels in the mantle.
Rheology of the Upper Mantle: A Synthesis
Authors: Karato Shun-ichiro , Wu Patrick
Published: October 2006

Rheological properties of the upper mantle of the Earth play an important role in the dynamics of the lithosphere and asthenosphere. However, such fundamental issues as the dominant mechanisms of flow have not been well resolved. A synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the Earth's upper mantle. The hot and shallow upper mantle flows by dislocation creep, whereas cold and shallow or deep upper mantle may flow by diffusion creep. When the stress increases, grain size is reduced and the upper mantle near the transition between these two regimes is weakened. Consequently, deformation is localized and the upper mantle is decoupled mechanically near these depths.
The Ischigualasto Tetrapod Assemblage (Late Triassic, Argentina) and
40
Ar/
39
Ar Dating of Dinosaur Origins
Authors: Rogers Raymond R. , Swisher Carl C. , Sereno Paul C. , Monetta Alfredo M. , Forster Catherine A. , Martínez Ricardo N.
Published: October 2006

40
Ar/
39
Ar dating of sanidine from a bentonite interbedded in the Ischigualasto Formation of northwestern Argentina yielded a plateau age of 227.8 ± 0.3 million years ago. This middle Carnian age is a direct calibration of the Ischigualasto tetrapod assemblage, which includes some of the best known early dinosaurs. This age shifts last appearances of Ischigualasto taxa back into the middle Carnian, diminishing the magnitude of the proposed late Carnian tetrapod extinction event. By 228 million years ago, the major dinosaurian lineages were established, and theropods were already important constituents of the carnivorous tetrapod guild in the Ischigualasto—Villa Unión Basin. Dinosaurs as a whole remained minor components of tetrapod faunas for at least another 10 million years.
Net Exchange of CO
2
in a Mid-Latitude Forest
Authors: Wofsy S. C. , Goulden M. L. , Munger J. W. , Fan S.-M. , Bakwin P. S. , Daube B. C. , Bassow S. L. , Bazzaz F. A.
Published: October 2006

The eddy correlation method was used to measure the net ecosystem exchange of carbon dioxide continuously from April 1990 to December 1991 in a deciduous forest in central Massachusetts. The annual net uptake was 3.7 ± 0.7 metric tons of carbon per hectare per year. Ecosystem respiration, calculated from the relation between nighttime exchange and soil temperature, was 7.4 metric tons of carbon per hectare per year, implying gross ecosystem production of 11.1 metric tons of carbon per hectare per year. The observed rate of accumulation of carbon reflects recovery from agricultural development in the 1800s. Carbon uptake rates were notably larger than those assumed for temperate forests in global carbon studies. Carbon storage in temperate forests can play an important role in determining future concentrations of atmospheric carbon dioxide.
Reaction Product Imaging: The H + D
2
Reaction
Authors: Kitsopoulos Theofanis N. , Buntine Mark A. , Baldwin David P. , Zare Richard N. , Chandler David W.
Published: October 2006

The differential cross section for the H + D
2
→ HD + D reaction has been measured using a technique called reaction product imaging. In this experiment, a photolytically produced beam of hydrogen (H) atoms crossed a beam of cold deuterium (D
2
) molecules. Product D atoms were ionized at the intersection of the two particle beams and accelerated toward a position-sensitive detector. The ion images appearing on the detector are two-dimensional projections of the three-dimensional velocity distribution of the D atom products. The reaction was studied at nominal center-of-mass collision energies of 0.54 and 1.29 electron volts. At the lower collision energy, the measured differential cross section for D atom production, summed over all final states of the HD(
v,J
) product, is in good agreement with recent quasi-classical trajectory calculations. At the higher collision energy, the agreement between the theoretical predictions and experimental results is less favorable.