bluuebunny/crossref_metadata_2025 huggingface dataset:
Tropical Temperature Variations Since 20,000 Years Ago: Modulating Interhemispheric Climate Change
Authors: Guilderson Thomas P. , Fairbanks Richard G. , Rubenstone James L.
Published: October 2006

Tropical sea surface temperatures (SSTs), as thermodynamically recorded in Barbados corals, were 5°C colder than present values 19,000 years ago. Variable tropical SSTs may explain the interhemispheric synchroneity of global climate change as recorded in ice cores, snowline reconstructions, and vegetation records. Radiative changes due to cloud type and cloud cover are plausible mechanisms for maintaining cooler tropical SSTs in the past.
Lake-Atmosphere Feedbacks Associated with Paleolakes Bonneville and Lahontan
Authors: Hostetler S. W. , Giorgi F. , Bates G. T. , Bartlein P. J.
Published: October 2006

A high-resolution, regional climate model nested within a general circulation model was used to study the interactions between the atmosphere and the large Pleistocene lakes in the Great Basin of the United States. Simulations for January and July 18,000 years ago indicate that moisture provided by synoptic-scale atmospheric circulation features was the primary component of the hydrologic budgets of Lakes Lahontan and Bonneville. In addition, lake-generated precipitation was a substantial component of the hydrologic budget of Lake Bonneville at that time. This local lake-atmosphere interaction may help explain differences in the relative sizes of these lakes 18,000 years ago.
Theoretical Evidence for a C
60
"Window" Mechanism
Authors: Murry Robert L. , Scuseria Gustavo E.
Published: October 2006

On the basis of semiempirical and high-level ab initio calculations, theoretical evidence is presented of a "window" mechanism operable on the surface of C
60
and other fullerenes. Through this mechanism, large holes may be formed in fullerenes excited to their triplet state, openings through which atoms and small molecules can pass. This work provides a theoretical foundation for experiments that have prepared endohedral noble gas compounds of C
60
under thermal excitation. A method is proposed that could increase the efficiency of the process of noble gas insertion into C
60
and provide a more general means to create endohedral fullerene compounds.
Nanowire Array Composites
Authors: Huber C. A. , Huber T. E. , Sadoqi M. , Lubin J. A. , Manalis S. , Prater C. B.
Published: October 2006

Long, nanometer-size metallic wires can be synthesized by injection of the conducting melt into nanochannel insulating plates. Large-area arrays of parallel wires 200 nanometers in diameter and 50 micrometers long with a packing density of 5 × 10
8
per square centimeter have been fabricated in this way. When charged, the ends of the wires generate strong, short-range electric fields. The nanowire electric fields have been imaged at high spatial resolution with a scanning force microscope.
An Empirical Test of Recruitment Limitation in a Coral Reef Fish
Authors: Doherty Peter , Fowler Tony
Published: October 2006

A long-term, large-scale empirical test of the recruitment limitation hypothesis was done by sampling fish populations from the southern Great Barrier Reef after having monitored their recruitment histories for 9 years. After adjustment for demographic differences, recruitment patterns explained over 90 percent of the spatial variation in abundance of a common damselfish among seven coral reefs. The age structures from individual reefs also preserved major temporal variations in the recruitment signal over at least 10 years. Abundance and demography of this small fish at these spatial and temporal scales can be explained almost entirely as variable recruitment interacting with density-independent mortality.
Crystal Structure, Bonding, and Phase Transition of the Superconducting Na
2
CsC
60
Fulleride
Authors: Prassides Kosmas , Christides Christos , Thomas Ian M. , Mizuki Junichiro , Tanigaki Katsumi , Hirosawa Ichiro , Ebbesen Thomas W.
Published: October 2006

The crystal structure of superconducting Na
2
CsC
60
was studied by high-resolution powder neutron diffraction between 1.6 and 425 K. Contrary to the literature, the structure at low temperatures is primitive cubic (
Pa
3̅), isostructural with pristine C
60
. Anticlockwise rotation of the C
60
units by 98∼ about [111] allows simultaneous optimization of C
60
-C
60
and alkali-fulleride interactions. Optimal Na
+
-C
60
3-
coordination is achieved with each sodium ion located above one hexagon face and three hexagon-hexagon fusions of neighboring fulleride ions (coordination number 12). Reduction of the C
60
molecule lengthens the hexagon-hexagon fusions and shortens the pentagon-hexagon fusions (to ∼1.43 angstroms). On heating, Na
2
CsC
60
undergoes a phase transition to a face-centered-cubic
Fm
3̅
m
phase, best modeled as containing quasi-spherical C
60
3-
ions. The modified structure and intermolecular potential provide an additional dimension to the behavior of superconducting fullerides and should sensitively affect their electronic and conducting properties.
Spatially Resolved Observation of Static Magnetic Flux States in YBa
2
Cu
3
O
7-δ
Grain Boundary Josephson Junctions
Authors: Fischer G. M. , Mayer B. , Gross R. , Nissel T. , Husemann K. -D. , Huebener R. P. , Freltoft T. , Shen Y. , Vase P.
Published: October 2006

With low-temperature scanning electron microscopy, the magnetic flux states in high critical temperature Josephson junctions have been imaged. The experiments were performed with YBa
2
Cu
3
O
7-δ
thin-film grain boundary Josephson junctions fabricated on [001] tilt SrTiO
3
bicrystals. For applied magnetic fields parallel to the grain boundary plane, which correspond to local maxima of the magnetic field dependence of the critical current, the images clearly show the corresponding magnetic flux states in the grain boundary junction. The spatial modulation of the Josephson current density by the external magnetic field is imaged directly with a spatial resolution of about 1 micrometer.
Making Ceramics "Ductile"
Authors: Lawn Brian R. , Padture Nitin P. , Cait Hongda , Guiberteau Fernando
Published: October 2006

Distributed irreversible deformation in otherwise brittle ceramics (specifically, in silicon carbide and micaceous glass-ceramic) has been observed in Hertzian contacts. The deformation takes the form of an expanding microcrack damage zone below the contact circle, in place of the usual single propagating macrocrack (the Hertzian "cone fracture") outside. An important manifestation of this deformation is an effective "ductility" in the indentation stress-strain response. Control of the associated brittle-ductile transition is readily effected by appropriate design of weak interfaces, large and elongate grains, and high internal stresses in the ceramic microstructure.
Deep, Zonal Subequatorial Currents
Authors: Talley Lynne D. , Johnson Gregory C.
Published: October 2006

Large-scale, westward-extending tongues of warm (Pacific) and cold (Atlantic) water are found between 2000 and 3000 meters both north and south of the equator in the Pacific and Atlantic oceans. They are centered at 5° to 8° north and 10° to 15° south (Pacific) and 5° to 8° north and 15° to 20° south (Atlantic). They are separated in both oceans by a contrasting eastward-extending tongue, centered at about 1° to 2° south, in agreement with previous helium isotope observations (Pacific). Thus, the indicated deep tropical westward flows north and south of the equator and eastward flow near the equator may result from more general forcing than the hydrothermal forcing previously hypothesized.
Retention of Solar Helium and Neon in IDPs in Deep Sea Sediment
Authors: Hiyagon Hajime
Published: October 2006

It was recently proposed that subduction of interplanetary dust particles (IDPs) contained in deep sea sediments could have introduced substantial solar helium and neon to the Earth's mantle. However, it is not certain if IDPs would retain solar noble gases during subduction. A diffusion experiment that examined He and Ne in IDPs in a magnetic separate from Pacific Ocean sediments showed that He and Ne would be lost from IDPs within 3 years at 500°C, and possibly within 10
5
years at 200°C, which suggests that they would be lost from subducting slabs at shallow depths.
Superconducting Mercury-Based Cuprate Films with a Zero-Resistance Transition Temperature of 124 Kelvin
Authors: Tsuei C. C. , Gupta A. , Trafas G. , Mitzi D.
Published: October 2006

The synthesis of high-quality films of the recently discovered mercury-based cuprate films with high transition temperatures has been plagued by problems such as the air sensitivity of the cuprate precursor and the volatility of Hg and HgO. These processing difficulties have been circumvented by a technique of atomic-scale mixing of the HgO and cuprate precursors, use of a protective cap layer, and annealing in an appropriate Hg and O
2
environment. With this procedure, a zero-resistance transition temperature as high as 124 kelvin in
c
axis-oriented epitaxial HgBa
2
CaCu
2
O
6+δ
films has been achieved.
Cytosolic pH Gradients Associated with Tip Growth
Authors: Gibbon Bryan C. , Kropf Darryl L.
Published: October 2006

The presence of a cytosolic pH gradient and its relation to polar tip growth was investigated in rhizoid cells of
Pelvetia
embryos with the use of pH-sensitive microelectrodes and by ratio imaging. Growing rhizoid cells generated a longitudinal pH gradient in which the apical cytosol was 0.3 to 0.5 units more acidic than the cytosol at the base of the cell. Treatment with a membrane-permeant weak acid, propionic acid, dissipated the cytosolic pH gradient and inhibited growth. The magnitude of the pH gradient correlated well with the rate of tip elongation. The pH gradient spatially superimposed on the cytosolic calcium gradient, and inhibition of calcium fluxes by treatment with lanthanum abolished the pH gradient and inhibited growth.
Recent Changes in Atmospheric Carbon Monoxide
Authors: Novelli Paul C. , Masarie Ken A. , Tans Pieter P. , Lang Patricia M.
Published: October 2006

Measurements of carbon monoxide (CO) in air samples collected from 27 locations between 71°N and 41°S show that atmospheric levels of this gas have decreased worldwide over the past 2 to 5 years. During this period, CO decreased at nearly a constant rate in the high northern latitudes. In contrast, in the tropics an abrupt decrease occurred beginning at the end of 1991. In the Northern Hemisphere, CO decreased at a spatially and temporally averaged rate of 7.3 (±0.9) parts per billion per year (6.1 percent per year) from June 1990 to June 1993, whereas in the Southern Hemisphere, CO decreased 4.2 (±0.5) parts per billion per year (7.0 percent per year). This recent change is opposite a long-term trend of a 1 to 2 percent per year increase inferred from measurements made in the Northern Hemisphere during the past 30 years.
Sound Velocities in Dense Hydrogen and the Interior of Jupiter
Authors: Duffy Thomas S. , Vos Willem L. , Zha Chang-sheng , Hemley Russell J. , Mao Ho-kwang
Published: October 2006

Sound velocities in fluid and crystalline hydrogen were measured under pressure to 24 gigapascals by Brillouin spectroscopy in the diamond anvil cell. The results provide constraints on the intermolecular interactions of dense hydrogen and are used to construct an intermolecular potential consistent with all available data. Fluid perturbation theory calculations with the potential indicate that sound velocities in hydrogen at conditions of the molecular layer of the Jovian planets are lower than previously believed. Jovian models consistent with the present results remain discrepant with recent free oscillation spectra of the planet by 15 percent. The effect of changing interior temperatures, the metallic phase transition depth, and the fraction of high atomic number material on Jovian oscillation frequencies is also investigated with the Brillouin equation of state. The present data place strong constraints on sound velocities in the Jovian molecular layer and provide an improved basis for interpreting possible Jovian oscillations.
An in Vitro System for Adhesion and Fusion of Maize Gametes
Authors: Faure J.-E. , Digonnet C. , Dumas C.
Published: October 2006

The development of in vitro fertilization systems in flowering plants is important for understanding and controlling the mechanisms of fertilization. Here a method is described in which isolated maize gametes fuse. In a medium containing 5 mM calcium chloride, sperm and egg cells adhere for several minutes and then fuse within 10 seconds. The method is specific to male-female gamete pairs and results in 80 percent fusion, whereas fusions with other combinations of gametic and mesophyllic cells are less frequent. Eggs fertilized in vitro do not fuse with additional male gametes, which suggests that a block to polyspermy exists.
Defects in Carbon Nanostructures
Authors: Zhou O. , Fleming R. M. , Murphy D. W. , Chen C. H. , Haddon R. C. , Ramirez A. P. , Glarum S. H.
Published: October 2006

Previous high-resolution electron microscopy (HREM) observations of the carbon nanotubes have led to a "Russian doll" structural model that is based on hollow concentric cylinders capped at both ends. The structures of the carbon nanotubes and particles were characterized here by bulk physical and chemical property measurements. The individual nanostructure is as compressible as graphite in the
c
axis, and such nanostructures can be intercalated with potassium and rubidium, leading to a saturation composition of "MC
8
." These results are counter to expectations that are based on a Russian doll structure. HREM after intercalation with potassium and deintercalation indicates that individual nanoparticles are a "paper-mache" of smaller graphite layers. Direct current magnetization and electron spin resonance measurements indicate that the electronic properties of the nanostructures are distinctly different from those of graphite. Although the nanostructures have distinct morphologies and electronic properties, they are highly defective and have a local structure similar to turbostratic graphite.
Changes in Atmospheric Circulation and Ocean Ice Cover over the North Atlantic During the Last 41,000 Years
Authors: Mayewski P. A. , Meeker L. D. , Whitlow S. , Twickler M. S. , Morrison M. C. , Bloomfield P. , Bond G. C. , Alley R. B. , Gow A. J. , Meese D. A. , Grootes P. M. , Ram M. , Taylor K. C. , Wumkes W.
Published: October 2006

High-resolution, continuous multivariate chemical records from a central Greenland ice core provide a sensitive measure of climate change and chemical composition of the atmosphere over the last 41,000 years. These chemical series reveal a record of change in the relative size and intensity of the circulation system that transported air masses to Greenland [defined here as the polar circulation index (PCI)] and in the extent of ocean ice cover. Massive iceberg discharge events previously defined from the marine record are correlated with notable expansions of ocean ice cover and increases in PCI. During stadials without discharge events, ocean ice cover appears to reach some common maximum level. The massive aerosol loadings and dramatic variations in ocean ice cover documented in ice cores should be included in climate modeling.
Ceramic Thin-Film Formation on Functionalized Interfaces Through Biomimetic Processing
Authors: Bunker B. C. , Rieke P. C. , Tarasevich B. J. , Campbell A. A. , Fryxell G. E. , Graff G. L. , Song L. , Liu J. , Virden J. W. , McVay G. L.
Published: October 2006

Processing routes have been developed for the production of thin ceramic films through precipitation from aqueous solutions. The techniques are based on crystal nucleation and growth onto functionalized interfaces. Surface functionalization routes have been developed by the mimicking of schemes used by organisms to produce complex ceramic composites such as teeth, bones, and shells. High-quality, dense polycrystalline films of oxides, hydroxides, and sulfides have now been prepared from "biomimetic" synthesis techniques. Ceramic films can be synthesized on plastics and other materials at temperatures below 100°C. As a low-temperature process in which water rather than organic solvents is used, this synthesis is environmentally benign. Nanocrystalline ceramics can be produced, sometimes with preferred crystallite orientation. The direct deposition of high-resolution patterned films has also been demonstrated. The process is well suited to the production of organic-inorganic composites.
Growth of Continental-Scale Metro-Agro-Plexes, Regional Ozone Pollution, and World Food Production
Authors: Chameides W. L. , Kasibhatla P. S. , Yienger J. , Levy H.
Published: October 2006

Three regions of the northern mid-latitudes, the continental-scale metro-agro-plexes, presently dominate global industrial and agricultural productivity. Although these regions cover only 23 percent of the Earth's continents, they account for most of the world's commercial energy consumption, fertilizer use, food-crop production, and food exports. They also account for more than half of the world's atmospheric nitrogen oxide (NO

x

) emissions and, as a result, are prone to ground-level ozone (O
3
) pollution during the summer months. On the basis of a global simulation of atmospheric reactive nitrogen compounds, it is estimated that about 10 to 35 percent of the world's grain production may occur in parts of these regions where ozone pollution may reduce crop yields. Exposure to yield-reducing ozone pollution may triple by 2025 if rising anthropogenic NO

x

emissions are not abated.
Effects of Boundaries on Pattern Formation: Catalytic Oxidation of CO on Platinum
Authors: Graham M. D. , Kevrekidis Ioannis G. , Asakura K. , Lauterbach J. , Krischer K. , Rotermund H.-H. , Ertl G.
Published: October 2006

The effect of boundaries on pattern formation was studied for the catalytic oxidation of carbon monoxide on platinum surfaces. Photolithography was used to create microscopic reacting domains on polycrystalline foils and single-crystal platinum (110) surfaces with inert titanium overlayers. Certain domain geometries give rise to patterns that have not been observed on the untreated catalyst and bring to light surface mechanisms that have no analog in homogeneous reaction-diffusion systems.
Trends in Stomatal Density and
13
C/
12
C Ratios of
Pinus flexilis
Needles During Last Glacial-Interglacial Cycle
Authors: Van de Water P. K. , Leavitt S. W. , Betancourt J. L.
Published: October 2006

Measurements of stomatal density and δ
13
C of limber pine (
Pinus flexilis
) needles (leaves) preserved in pack rat middens from the Great Basin reveal shifts in plant physiology and leaf morphology during the last 30,000 years. Sites were selected so as to offset glacial to Holocene climatic differences and thus to isolate the effects of changing atmospheric CO
2
levels. Stomatal density decreased ∼17 percent and δ
13
C decreased ∼1.5 per mil during deglaciation from 15,000 to 12,000 years ago, concomitant with a 30 percent increase in atmospheric CO
2
. Water-use efficiency increased ∼15 percent during deglaciation, if temperature and humidity were held constant and the proxy values for CO
2
and δ
13
C of past atmospheres are accurate. The δ
13
C variations may help constrain hypotheses about the redistribution of carbon between the atmosphere and biosphere during the last glacial-interglacial cycle.
Quantifying Global Warming from the Retreat of Glaciers
Authors: Oerlemans Johannes
Published: October 2006

Records of glacier fluctuations compiled by the World Glacier Monitoring Service can be used to derive an independent estimate of global warming during the last 100 years. Records of different glaciers are made comparable by a two-step scaling procedure: one allowing for differences in glacier geometry, the other for differences in climate sensitivity. The retreat of glaciers during the last 100 years appears to be coherent over the globe. On the basis of modeling of the climate sensitivity of glaciers, the observed glacier retreat can be explained by a linear warming trend of 0.66 kelvin per century.
New Instruments Shed Light On Astronomy's Future
Authors: Travis John
Published: October 2006

KONA, HAWAII-The snowy 14,000-foot summit of Mauna Kea, with its bevy of powerful telescopes including the just-completed Keck, provided an appropriate backdrop for a recent ocean-side gathering of astronomers and engineers to discuss "Astronomical Telescopes and Instrumentation for the 21st Century." Last month's meeting was organized by the Society of Photo-Optical Instrumentation Engineers, and included a status report on liquid mirror telescopes, discussion of a space observatory that may make optical and x-ray astronomers best friends, and a modest proposal to cover the globe with a network of small, automated telescopes.
Topographic Forcing of the Atmosphere and a Rapid Change in the Length of Day
Authors: Salstein David A. , Rosen Richard D.
Published: October 2006

During June to September 1992, a special campaign was held to measure rapid changes in Earth's rotation rate and to relate these measurements to variations in the atmosphere's angular momentum, due principally to changes in zonal winds. A strong rise in both length of day and atmospheric momentum during a particular 6-day subperiod is documented, and this example of a short-period perturbation is identified with a specific regional coupling mechanism. Mountain torques within the southern tropics appear to account for most of the rapid momentum transfer between the solid Earth and atmosphere, with those across South America especially important.
Anisotropy and Coherent Vortex Structures in Planetary Turbulence
Authors: McWilliams James C. , Weiss Jeffrey B. , Yavneh Irad
Published: October 2006

High-resolution numerical simulations were made of unforced, planetary-scale fluid dynamics. In particular, the simulation was based on the quasi-geostrophic equations for a Boussinesq fluid in a uniformly rotating and stably stratified environment, which is an idealization for large regions of either the atmosphere or ocean. The solutions show significant discrepancies from the long-standing theoretical prediction of isotropy. The discrepancies are associated with the self-organization of the flow into a large population of coherent vortices. Their chaotic interactions govern the subsequent evolution of the flow toward a final configuration that is nonturbulent.
Thousandfold Change in Resistivity in Magnetoresistive La-Ca-Mn-O Films
Authors: Jin S. , Tiefel T. H. , McCormack M. , Fastnacht R. A. , Ramesh R. , Chen L. H.
Published: October 2006

A negative isotropic magnetoresistance effect more than three orders of magnitude larger than the typical giant magnetoresistance of some superlattice films has been observed in thin oxide films of perovskite-like La
0.67
Ca
0.33
MnO

x

. Epitaxial films that are grown on LaAIO
3
substrates by laser ablation and suitably heat treated exhibit magnetoresistance values as high as 127,000 percent near 77 kelvin and ∼1300 percent near room temperature. Such a phenomenon could be useful for various magnetic and electric device applications if the observed effects of material processing are optimized. Possible mechanisms for the observed effect are discussed.
Stomatal Size in Fossil Plants: Evidence for Polyploidy in Majority of Angiosperms
Authors: Masterson Jane
Published: October 2006

Three published estimates of the frequency of polyploidy in angiosperms (30 to 35 percent, 47 percent, and 70 to 80 percent) were tested by estimating the genome size of extinct woody angiosperms with the use of fossil guard cell size as a proxy for cellular DNA content. The inferred chromosome numbers of these extinct species suggest that seven to nine is the primitive haploid chromosome number of angiosperms and that most angiosperms (approximately 70 percent) have polyploidy in their history.
Antarctic Total Ozone in 1958
Authors: Newman Paul A.
Published: October 2006

The Antarctic ozone hole results from catalytic destruction of ozone by chlorine radicals. The hole develops in August, reaches its full depth in early October, and is gone by early December of each year. Extremely low total ozone measurements were made at the Antarctic Dumont d'Urville station in 1958. These measurements were derived from spectrographic plates of the blue sky, the moon, and two stars. These Dumont plate data are inconsistent with 1958 Dobson spectrophotometer ozone measurements, inconsistent with present-day Antarctic observations, and inconsistent with meteorological and theoretical information. There is no credible evidence for an ozone hole in 1958.
Quantum Cascade Laser
Authors: Faist Jerome , Capasso Federico , Sivco Deborah L. , Sirtori Carlo , Hutchinson Albert L. , Cho Alfred Y.
Published: October 2006

A semiconductor injection laser that differs in a fundamental way from diode lasers has been demonstrated. It is built out of quantum semiconductor structures that were grown by molecular beam epitaxy and designed by band structure engineering. Electrons streaming down a potential staircase sequentially emit photons at the steps. The steps consist of coupled quantum wells in which population inversion between discrete conduction band excited states is achieved by control of tunneling. A strong narrowing of the emission spectrum, above threshold, provides direct evidence of laser action at a wavelength of 4.2 micrometers with peak powers in excess of 8 milliwatts in pulsed operation. In quantum cascade lasers, the wavelength, entirely determined by quantum confinement, can be tailored from the mid-infrared to the submillimeter wave region in the same heterostructure material.
A Mechanism of Lithium Storage in Disordered Carbons
Authors: Sato Kenji , Noguchi Minoru , Demachi Atsushi , Oki Naohiko , Endo Morinobu
Published: October 2006

High-resolution electron microscopy and lithium-7 nuclear magnetic resonance measurements were carried out for a disordered carbon material, prepared by heat treatment of polyphenylene, in which lithium was stored electrochemically. The nuclear magnetic resonance spectrum suggests the existence of Li
2
covalent molecules in the carbon material. This extra covalent site of lithium storage promises extraordinarily high energy density for secondary batteries.
A Putative Role of the Xanthophyll, Zeaxanthin, in Blue Light Photoreception of Corn Coleoptiles
Authors: Quiñones Miguel A. , Zeiger Eduardo
Published: October 2006

Both flavins and carotenoids have some of the attributes expected for a photoreceptor mediating blue light-induced phototropism in plants. Besides the classical photoreceptor candidate, β-carotene, coleoptiles contain many other carotenoids, including the main components of the xanthophyll cycle, violaxanthin and zeaxanthin. Here, dark-grown coleoptiles accumulated violaxanthin, but lacked zeaxanthin. Coleoptiles devoid of zeaxanthin did not bend in response to a blue light pulse. Coleoptile tips converted violaxanthin into zeaxanthin in the light. Manipulation of coleoptile zeaxanthin content by red light, red light plus darkness, or incubation with the inhibitor of zeaxanthin formation, dithiothreitol, resulted in a blue light-induced bending that was proportional to zeaxanthin content. These data indicate that zeaxanthin may be a blue light photoreceptor in corn coleoptiles.
A Seismotectonic Model for the 300-Kilometer-Long Eastern Tennessee Seismic Zone
Authors: Powell Christine A. , Bollinger G. A. , Chapman Martin C. , Sibol Matthew S. , Johnston Arch C. , Wheeler Russell L.
Published: October 2006

Ten years of monitoring microearthquakes with a regional seismic network has revealed the presence of a well-defined, linear zone of seismic activity in eastern Tennessee. This zone produced the second highest release of seismic strain energy in the United States east of the Rocky Mountains during the last decade, when normalized by crustal area. The data indicate that seismicity produced by regional, intraplate stresses is now concentrating near the boundary between relatively strong and weak basement crustal blocks.
Effects of Manipulated Diet on Size and Performance of Brachyuran Crab Claws
Authors: Smith L. David , Palmer A. Richard
Published: October 2006

Crabs grown experimentally on fully shelled prey developed larger and stronger claws than those raised on nutritionally equivalent unshelled prey. When one claw was immobilized, claws also became asymmetrical. These use-induced changes differ from skeletal remodelling in vertebrates and many invertebrates because changes in the rigid exoskeleton can occur only after molting, and claw muscle mass must be reduced substantially before the molt. Such short-term adaptive responses to environmental stimuli, if heritable, could yield long-term evolutionary changes in claw size and, if combined with behavioral biases toward one side (handedness), could also promote the evolution of claw dimorphism.
Global Variations in the Geoid/Topography Admittance of Venus
Authors: Simons Mark , Hager Bradford H. , Solomon Sean C.
Published: October 2006

Global representations of geoid height and topography are used to map variations in the geoid/topography ratio (admittance) of Venus. The admittance values are permissive of two mutually exclusive models for convection-driven topography. In the first, compressive highland plateaus are expressions of present mantle downwelling, broad volcanic rises are expressions of mantle upwelling, and lowlands overlie regions with no substantial vertical motion in the mantle. In the second, compressive highland plateaus are remnants of an earlier regime of high crustal strain, and most other long-wavelength topographic variations arise from normal convective tractions at the base of the lithosphere.
Surface Vibrational Spectroscopic Studies of Hydrogen Bonding and Hydrophobicity
Authors: Du Quan , Freysz Eric , Shen Y. Ron
Published: October 2006

Surface vibrational spectroscopy by sum-frequency generation was used to study hydrophobicity at the molecular level at various interfaces: water—surfactant-coated quartz, water-hexane, and water-air. In all cases, hydrophobicity was characterized by the appearance of dangling hydroxyl bonds on 25 percent of the surface water molecules. At the water-quartz interface, packing restrictions force the water surface layer to have a more ordered, ice-like structure. A partly wettable water-quartz interface was also studied.
Diurnal and Semidiurnal Variations in the Earth's Rotation Rate Induced by Oceanic Tides
Authors: Ray R. D. , Steinberg D. J. , Chao B. F. , Cartwright D. E.
Published: October 2006

Recent space-geodetic observations have revealed daily and subdaily variations in the Earth's rotation rate. Although spectral analysis suggests that the variations are primarily of tidal origin, comparisons to previous theoretical predictions based on various ocean models have been less than satisfactory. This disagreement is partly caused by deficiencies in physical modeling. Rotation predictions based on a reliable tidal-height model, with corresponding tidal currents inferred from a modified form of Laplace's momentum equations, yield predictions of tidal variations in Universal Time that agree with very long baseline interferometer observations to 2 microseconds. This agreement resolves a major discrepancy between theory and observation and establishes the dominant role of oceanic tides for inducing variation in the Earth's rotation at these frequencies.
Record of Volcanism Since 7000 B.C. from the GISP2 Greenland Ice Core and Implications for the Volcano-Climate System
Authors: Zielinski G. A. , Mayewski P. A. , Meeker L. D. , Whitlow S. , Twickler M. S. , Morrison M. , Meese D. A. , Gow A. J. , Alley R. B.
Published: October 2006

Sulfate concentrations from continuous biyearly sampling of the GISP2 Greenland ice core provide a record of potential climate-forcing volcanism since 7000 B.C. Although 85 percent of the events recorded over the last 2000 years were matched to documented volcanic eruptions, only about 30 percent of the events from 1 to 7000 B.C. were matched to such events. Several historic eruptions may have been greater sulfur producers than previously thought. There are three times as many events from 5000 to 7000 B.C. as over the last two millennia with sulfate deposition equal to or up to five times that of the largest known historical eruptions. This increased volcanism in the early Holocene may have contributed to climatic cooling.
Estimates of Diapycnal Mixing in the Abyssal Ocean
Authors: Toole John M. , Schmitt Raymond W. , Polzin Kurt L.
Published: October 2006

Profiles of diapycnal eddy diffusivity to a maximum depth of 4000 meters were derived from ocean velocity and temperature microstructure data obtained in conjunction with separate experiments in the Northeast Pacific and Northeast Atlantic oceans. These profiles indicate that in the ocean interior where the internal wave field is at background intensity, the diapycnal eddy diffusivity is small (on the order of 0.1 × 10–4meters squared per second) and independent of depth, in apparent contradiction with large-scale budget studies. Enhanced dissipation is observed in regions of elevated internal wave energy, particularly near steeply sloping boundaries (where the eddy diffusivity estimates exceed 1 × 10–4meters squared per second). These results suggest that basin-averaged mixing rates may be dominated by processes occurring near the ocean boundaries.
A New Look at Proton Transfer Dynamics Along the Hydrogen Bonds in Amides and Peptides
Authors: Kearley G. J. , Fillaux F. , Baron M.-H. , Bennington S. , Tomkinson J.
Published: October 2006

Vibrational spectroscopy with inelastic neutron scattering can provide spectra that are more detailed and easier to interpret than optical spectra. The spectral intensity depends on energy transfer and kinetic momentum transfer, allowing determination of the potential function. Experiments reveal that the proton involved in intermolecular hydrogen bonding in
N
-methylacetamide and polyglycine I vibrates almost independently. An ionic representation (N
δ-
⋅⋅⋅H
+
⋅⋅⋅O
δ-
) of the hydrogen bond is more realistic than the normally accepted covalent model (NH⋅⋅⋅O). For polyglycine I, the proton experiences a local, symmetric double-minimum potential arising from dynamic exchange between the amide-like (CONH) and imidol-like (HOCN) forms of the peptide unit.
Critical Behavior in the Satisfiability of Random Boolean Expressions
Authors: Kirkpatrick Scott , Selman Bart
Published: October 2006

Determining the satisfiability of randomly generated Boolean expressions with
k
variables per clause is a popular test for the performance of search algorithms in artificial intelligence and computer science. It is known that for
k
= 2, formulas are almost always satisfiable when the ratio of clauses to variables is less than 1; for ratios larger than 1, the formulas are almost never satisfiable. Similar sharp threshold behavior is observed for higher values of
k
. Finite-size scaling, a method from statistical physics, can be used to characterize size-dependent effects near the threshold. A relationship can be drawn between thresholds and computational complexity.
Discovery of Intense Gamma-Ray Flashes of Atmospheric Origin
Authors: Fishman G. J. , Bhat P. N. , Mallozzi R. , Horack J. M. , Koshut T. , Kouveliotou C. , Pendleton G. N. , Meegan C. A. , Wilson R. B. , Paciesas W. S. , Goodman S. J. , Christian H. J.
Published: October 2006

Detectors aboard the Compton Gamma Ray Observatory have observed an unexplained terrestrial phenomenon: brief, intense flashes of gamma rays. These flashes must originate in the atmosphere at altitudes above at least 30 kilometers in order to escape atmospheric absorption and reach the orbiting detectors. At least a dozen such events have been detected over the past 2 years. The photon spectra from the events are very hard (peaking in the high-energy portion of the spectrum) and are consistent with bremsstrahlung emission from energetic (million—electron volt) electrons. The most likely origin of these high-energy electrons, although speculative at this time, is a rare type of high-altitude electrical discharge above thunderstorm regions.
Automatic Analysis, Theme Generation, and Summarization of Machine-Readable Texts
Authors: Salton Gerard , Allan James , Buckley Chris , Singhal Amit
Published: October 2006

Vast amounts of text material are now available in machine-readable form for automatic processing. Here, approaches are outlined for manipulating and accessing texts in arbitrary subject areas in accordance with user needs. In particular, methods are given for determining text themes, traversing texts selectively, and extracting summary statements that reflect text content.
Younger Dryas Age Advance of Franz Josef Glacier in the Southern Alps of New Zealand
Authors: Denton G. H. , Hendy C. H.
Published: October 2006

A corrected radiocarbon age of 11,050 ± 14 years before present for an advance of the Franz Josef Glacier to the Waiho Loop terminal moraine on the western flank of New Zealand's Southern Alps shows that glacier advance on a South Pacific island was synchronous with initiation of the Younger Dryas in the North Atlantic region. Hence, cooling at the beginning of the Younger Dryas probably reflects global rather than regional forcing. The source for Younger Dryas climatic cooling may thus lie in the atmosphere rather than in a North Atlantic thermohaline switch.
Phase Transitions Between β and γ (Mg, Fe)
2
SiO
4
in the Earth's Mantle: Mechanisms and Rheological Implications
Authors: Rubie D. C. , Brearley A. J.
Published: October 2006

The mechanisms of the phase transformations between the spinel (γ) and modified spinel (β) polymorphs of Mg
2
SiO
4
have been studied experimentally between 15 and 20 gigapascals and 800° to 950°C. The γ to β transformation occurs by a shear mechanism, whereas the β to γ transformation involves grain-boundary nucleation and interface-controlled growth. These contrasting mechanisms are a consequence of the number of independent slip systems that are available in the respective crystal structures. This result leads to the prediction that in subduction zones and perhaps also rising plumes in the Earth's mantle, the γ to β transformation should be accompanied by a transient reduction in strength.
Synchrotron Infrared Absorbance Measurements of Hydrogen in MgSiO
3
Perovskite
Authors: Meade Charles , Reffner John A. , Ito Eiji
Published: October 2006

Micro-infrared spectroscopic measurements on single crystals of MgSiO
3
perovskite document two pleochroic hydroxyl absorbance peaks at 3483 and 3423 centimeter
–1
. These measurements were obtained with the use of a synchrotron infrared source for spectroscopy. These data are consistent with a trace hydrogen content of 700 ± 170 hydrogen atoms per 10
6
silicon atoms in the nominally anhydrous MgSiO
3
perovskite. When integrated over the volume of the lower mantle, this concentration is comparable to 12 percent of the mass of hydrogen in the Earth's hydrosphere.
Force Detection of Nuclear Magnetic Resonance
Authors: Rugar D. , Züger O. , Hoen S. , Yannoni C. S. , Vieth H.-M. , Kendrick R. D.
Published: October 2006

Micromechanical sensing of magnetic force was used to detect nuclear magnetic resonance with exceptional sensitivity and spatial resolution. With a 900 angstrom thick silicon nitride cantilever capable of detecting subfemtonewton forces, a single shot sensitivity of 1.6 × 10
13
protons was achieved for an ammonium nitrate sample mounted on the cantilever. A nearby millimeter-size iron particle produced a 600 tesla per meter magnetic field gradient, resulting in a spatial resolution of 2.6 micrometers in one dimension. These results suggest that magnetic force sensing is a viable approach for enhancing the sensitivity and spatial resolution of nuclear magnetic resonance microimaging.
New Phases of C
60
Synthesized at High Pressure
Authors: Iwasa Y. , Arima T. , Fleming R. M. , Siegrist T. , Zhou O. , Haddon R. C. , Rothberg L. J. , Lyons K. B. , Carter H. L. , Hebard A. F. , Tycko R. , Dabbagh G. , Krajewski J. J. , Thomas G. A. , Yagi T.
Published: October 2006

The fullerene C
60
can be converted into two different structures by high pressure and temperature. They are metastable and revert to pristine C
60
on reheating to 300°C at ambient pressure. For synthesis temperatures between 300° and 400°C and pressures of 5 gigapascals, a nominal face-centered-cubic structure is produced with a lattice parameter
a
o
= 13.6 angstroms. When treated at 500° to 800°C at the same pressure, C
60
transforms into a rhombohedral structure with hexagonal lattice parameters of
a
o
= 9.22 angstroms and
c
o
= 24.6 angstroms. The intermolecular distance is small enough that a chemical bond can form, in accord with the reduced solubility of the pressure-induced phases. Infrared, Raman, and nuclear magnetic resonance studies show a drastic reduction of icosahedral symmetry, as might occur if the C
60
molecules are linked.
Electrodeposited Defect Chemistry Superlattices
Authors: Switzer Jay A. , Hung Chen-Jen , Breyfogle Bryan E. , Shumsky Mark G. , Van Leeuwen Robert , Golden Teresa D.
Published: October 2006

Nanometer-scale layered structures based on thallium(III) oxide were electrodeposited in a beaker at room temperature by pulsing the applied potential during deposition. The conducting metal oxide samples were superlattices, with layers as thin as 6.7 nanometers. The defect chemistry was a function of the applied overpotential: High overpotentials favored oxygen vacancies, whereas low overpotentials favored cation interstitials. The transition from one defect chemistry to another in this nonequilibrium process occurred in the same potential range (100 to 120 millivolts) in which the rate of the back electron transfer reaction became significant. The epitaxial structures have the high carrier density and low electronic dimensionality of high transition temperature superconductors.
Habitat Fragmentation, Species Loss, and Biological Control
Authors: Kruess Andreas , Tscharntke Teja
Published: October 2006

Fragmentation of habitats in the agricultural landscape is a major threat to biological diversity, which is greatly determined by insects. Isolation of habitat fragments resulted in decreased numbers of species as well as reduced effects of natural enemies. Manually established islands of red clover were colonized by most available herbivore species but few parasitoid species. Thus, herbivores were greatly released from parasitism, experiencing only 19 to 60 percent of the parasitism of nonisolated populations. Species failing to successfully colonize isolated islands were characterized by small and highly variable populations. Accordingly, lack of habitat connectivity released insects from predator control.
Geophysicists Celebrate Two Satellites, Mourn a Third
Authors: Kerr Richard A.
Published: October 2006

Searching for a common theme in a gathering as diverse as the spring meeting of the American Geophysical Union (AGU) in Baltimore last month might seem futile. But satellites, both natural and artificial, provided some of the meeting's high points. Researchers reported on the first science results from the Clementine spacecraft's 2-month sojourn orbiting the moon, the revealing color of the small moon that accompanies the asteroid Ida, and the planned termination of the Magellan spacecraft orbiting Venus.
Near-Field Spectroscopy of the Quantum Constituents of a Luminescent System
Authors: Hess H. F. , Betzig E. , Harris T. D. , Pfeiffer L. N. , West K. W.
Published: October 2006

Luminescent centers with sharp (<0.07 millielectron volt), spectrally distinct emission lines were imaged in a GaAs/AlGaAs quantum well by means of low-temperature near-field scanning optical microscopy. Temperature, magnetic field, and linewidth measurements establish that these centers arise from excitons laterally localized at interface fluctuations. For sufficiently narrow wells, virtually all emission originates from such centers. Near-field microscopy/spectroscopy provides a means to access energies and homogeneous line widths for the individual eigenstates of these centers, and thus opens a rich area of physics involving quantum resolved systems.
Rotating Spiral Waves Created by Geometry
Authors: Agladze Konstantin , Keener James P. , Müller Stefan C. , Panfilov Alexander
Published: October 2006

The Belousov-Zhabotinsky reagent and numerical simulations were used to show that under high-frequency stimuli, rotating spiral waves can be initiated in a homogeneous excitable medium in the vicinity of domain boundaries or inexcitable barriers with sharp corners.
Multiplex Spectroscopy: Determining the Transition Moments and Absolute Concentrations of Molecular Species
Authors: Germann Geoffrey J. , Rakestraw David J.
Published: October 2006

A procedure is described that uses two spectroscopic techniques, absorption and infrared degenerate four-wave mixing, in tandem (multiplex) to measure the transition dipole moments and absolute concentrations of molecular species in situ. The method is demonstrated by the measurement of the relative transition moments and concentrations of two dissimilar sample gas components, hydrogen chloride and nitrogen dioxide, but is applicable to a wide variety of molecules and, thus, can provide new information for transient molecular species. Further, difficulties in obtaining quantitative information through techniques such as laser-induced fluorescence, coherent anti-Stokes Raman scattering, and degenerate four-wave mixing spectroscopies can be overcome when a multiplex approach is used.
Conducting Polyaniline Filaments in a Mesoporous Channel Host
Authors: Wu Chun-Guey , Bein Thomas
Published: October 2006

Conducting filaments of polyaniline have been prepared in the 3-nanometer-wide hexagonal channel system of the aluminosilicate MCM-41. Adsorption of aniline vapor into the dehydrated host, followed by reaction with peroxydisulfate, leads to encapsulated polyaniline filaments. Spectroscopic data show that the filaments are in the protonated emeraldine salt form, and chromatography indicates chain lengths of several hundred aniline rings. The filaments have significant conductivity while encapsulated in the channels, as measured by microwave absorption at 2.6 gigahertz. This demonstration of conjugated polymers with mobile charge carriers in nanometer channels represents a step toward the design of nanometer electronic devices.
Asymmetric Phase Effects and Mantle Convection Patterns
Authors: Liu Mian
Published: October 2006

Recent high-pressure experiments and thermodynamic calculations have shown that the Clapeyron slope of the spinel-perovskite phase transition at a depth of 660 kilometers in the Earth's mantle changes from negative to positive at temperatures above 1700° to 2000°C. In numerical experiments that account for this phase behavior, cold downwelling flows were impeded at the phase boundary, but hot plumes ascended to the upper mantle with ease. The resultant mantle convection was partially layered and strongly time-dependent. Mantle layering was weaker when the mantle was hotter and when the Rayleigh number was larger.
MCM-22: A Molecular Sieve with Two Independent Multidimensional Channel Systems
Authors: Leonowicz Michael E. , Lawton Jeffrey A. , Lawton Stephen L. , Rubin Mae K.
Published: October 2006

The molecular sieve MCM-22 contains structural features previously unobserved in this class of materials. Its framework topology, derived from high-resolution electron micrographs and refined with synchrotron x-ray diffraction powder data, contains two independent pore systems, both of which are accessed through rings composed of ten tetrahedral (T) atoms (such as Si, Al, and B). One of these pore systems is defined by two-dimensional, sinusoidal channels. The other consists of large supercages whose inner free diameter, 7.1 angstroms, is defined by 12 T—O species (12-rings) and whose inner height is 18.2 angstroms. These coexisting pore systems may provide opportunities for a wide variety of catalytic applications in the petrochemical and refining industries. Another structural feature is an unusual -T-O-T- chain that passes through the center of a modified dodecasil-1H [435663] cage.