bluuebunny/crossref_metadata_2025 huggingface dataset:
Warm Pool Heat Budget and Shortwave Cloud Forcing: A Missing Physics?
Authors: Ramanathan V. , Subasilar B. , Zhang G. J. , Conant W. , Cess R. D. , Kiehi J. T. , Grassi H. , Shi L.
Published: October 2006

Ship observations and ocean models indicate that heat export from the mixed layer of the western Pacific warm pool is small (<20 watts per square meter). This value was used to deduce the effect of clouds on the net solar radiation at the sea surface. The inferred magnitude of this shortwave cloud forcing was large (≈ – 100 watts per square meter) and exceeded its observed value at the top of the atmosphere by a factor of about 1.5. This result implies that clouds (at least over the warm pool) reduce net solar radiation at the sea surface not only by reflecting a significant amount back to space, but also by trapping a large amount in the cloudy atmosphere, an inference that is at variance with most model results. The excess cloud absorption, if confirmed, has many climatic implications, including a significant reduction in the required tropics to extratropics heat transport in the oceans.
Mechanisms of Magma Generation Beneath Hawaii and Mid-Ocean Ridges: Uranium/Thorium and Samarium/Neodymium Isotopic Evidence
Authors: Sims Kenneth W. W. , DePaolo Donald J. , Murrell Michael T. , Baldridge W. Scott , Goldstein Steven J. , Clague David A.
Published: October 2006

Measurements of uranium/thorium and samarium/neodymium isotopes and concentrations in a suite of Hawaiian basalts show that uranium/thorium fractionation varies systematically with samarium/neodymium fractionation and major-element composition; these correlations can be understood in terms of simple batch melting models with a garnet-bearing peridotite magma source and melt fractions of 0.25 to 6.5 percent. Midocean ridge basalts shows a systematic but much different relation between uranium/thorium fractionation and samarium/neodymium fractionation, which, although broadly consistent with melting of a garnet-bearing peridotite source, requires a more complex melting model.
Ocean Tides for and from TOPEX/POSEIDON
Authors: Le Provost C. , Bennett A. F. , Cartwright D. E.
Published: October 2006

Comparisons of TOPEX/POSEIDON tidal solutions derived from the data of the first year of this altimetric mission with the best previous models and with in situ data show very substantial improvements. Typically, the gain in accuracy for the major lunar tidal component M
2
is 30 percent in root-mean-square differences with reference to a standard ground truth data set from 78 stations distributed over the world ocean. This is a major step, obtained because of the high quality of these altimetric data. The combination of these data with recent numerical models through assimilation methods is pointing toward solutions at the ultimate limits of practical accuracy.
Taboo Search: An Approach to the Multiple Minima Problem
Authors: Cvijović Djurdje , Klinowski Jacek
Published: October 2006

Described here is a method, based on Glover's taboo search for discrete functions, of solving the multiple minima problem for continuous functions. As demonstrated by model calculations, the algorithm avoids entrapment in local minima and continues the search to give a near-optimal final solution. Unlike other methods of global optimization, this procedure is generally applicable, easy to implement, derivative-free, and conceptually simple.
Simulation of Recent Global Temperature Trends
Authors: Graham Nicholas E.
Published: October 2006

Observations show that global average tropospheric temperatures have been rising during the past century, with the most recent portion of record showing a sharp rise since the mid-1970s. This study shows that the most recent portion of the global temperature record (1970 to 1992) can be closely reproduced by atmospheric models forced only with observed ocean surface temperatures. In agreement with a diverse suite of controversial observational evidence from the past 40 years, the upward trend in simulated tropospheric temperatures is caused by an enhancement of the tropical hydrologic cycle driven by increasing tropical ocean temperatures. Although it is possible that the observed behavior is due to natural climate variability, there is disquieting similarity between these model results, observed climate trends in recent decades, and the early expressions of the climatic response to increased atmospheric carbon dioxide in numerical simulations.
Gauging Similarity with
n
-Grams: Language-Independent Categorization of Text
Authors: Damashek Marc
Published: October 2006

A language-independent means of gauging topical similarity in unrestricted text is described. The method combines information derived from
n
-grams (consecutive sequences of
n
characters) with a simple vector-space technique that makes sorting, categorization, and retrieval feasible in a large multilingual collection of documents. No prior information about document content or language is required. Context, as it applies to document similarity, can be accommodated by a well-defined procedure. When an existing document is used as an exemplar, the completeness and accuracy with which topically related documents are retrieved is comparable to that of the best existing systems. The results of a formal evaluation are discussed, and examples are given using documents in English and Japanese.
Timing of Hot Spot—Related Volcanism and the Breakup of Madagascar and India
Authors: Storey Michael , Mahoney John J. , Saunders Andrew D. , Duncan Robert A. , Kelley Simon P. , Coffin Millard F.
Published: October 2006

Widespread basalts and rhyolites were erupted in Madagascar during the Late Cretaceous. These are considered to be related to the Marion hot spot and the breakup of Madagascar and Greater India. Seventeen argon-40/argon-39 age determinations reveal that volcanic rocks and dikes from the 1500-kilometer-long rifted eastern margin of Madagascar were emplaced rapidly (mean age = 87.6 ± 0.6 million years ago) and that the entire duration of Cretaceous volcanism on the island was no more than 6 million years. The evidence suggests that the thick lava pile at Volcan de l'Androy in the south of the island marks the focal point of the Marion hot spot at ∼88 million years ago and that this mantle plume was instrumental in causing continental breakup.
Navigating Complex Labyrinths: Optimal Paths from Chemical Waves
Authors: Steinbock Oliver , Tóth Ágota , Showalter Kenneth
Published: October 2006

The properties of excitable media are exploited to find minimum-length paths in complex labyrinths. Optimal pathways are experimentally determined by the collection of time-lapse position information on chemical waves propagating through mazes prepared with the Belousov-Zhabotinsky reaction. The corresponding velocity fields provide maps of optimal paths from every point in an image grid to a particular target point. Collisions of waves that were temporarily separated by obstacles mark boundary lines between significantly different paths with the same absolute distance. The pathfinding algorithm is tested in very complex mazes with a simple reaction-diffusion model.
Climatic Warming and the Decline of Zooplankton in the California Current
Authors: Roemmich Dean , McGowan John
Published: October 2006

Since 1951, the biomass of macrozooplankton in waters off southern California has decreased by 80 percent. During the same period, the surface layer warmed—by more than 1.5°C in some places—and the temperature difference across the thermocline increased. Increased stratification resulted in less lifting of the thermocline by wind-driven upwelling. A shallower source of upwelled waters provided less inorganic nutrient for new biological production and hence supported a smaller zooplankton population. Continued warming could lead to further decline of zooplankton.
Impact of CLOD Pathogen on Pacific Coral Reefs
Authors: Littler Mark M. , Littler Diane S.
Published: October 2006

A bacterial pathogen of coralline algae was initially observed during June 1993 and now occurs in South Pacific reefs that span a geographic range of at least 6000 kilometers. The occurrence of the coralline algal pathogen at Great Astrolabe Reef sites (Fiji) increased from zero percent in 1992 to 100 percent in 1993, which indicates that the pathogen may be in an early stage of virulence and dispersal. Because of the important role played by coralline algae in reef building, this pathogen, designated coralline lethal orange disease (CLOD), has the potential to greatly influence coral reef ecology and reef-building processes.
A "Double-Diamond Superlattice" Built Up of Cd
17
S
4
(SCH
2
CH
2
OH)
26
Clusters
Authors: Vossmeyer T. , Reck G. , Katsikas L. , Haupt E. T. K. , Schulz B. , Weller H.
Published: October 2006

A simple preparation of Cd
17
S
4
(SCH
2
CH
2
OH)
26
clusters in aqueous solution leads to the formation of colorless blocky crystals. X-ray structure determinations revealed a superlattice framework built up of covalently linked clusters. This superlattice is best described as two enlarged and interlaced diamond or zinc blende lattices. Because both the superlattice and the clusters display the same structural features, the crystal structure resembles the self-similarities known from fractal geometry. The optical spectrum of the cluster solution displays a sharp transition around 290 nanometers with a large absorption coefficient (∼84,000 per molar per centimeter).
Conformation of Macromolecules in the Gas Phase: Use of Matrix-Assisted Laser Desorption Methods in Ion Chromatography
Authors: von Helden Gert , Wyttenbach Thomas , Bowers Michael T.
Published: October 2006

Conformational data for macromolecules in the gas phase have been obtained by the coupling of a matrix-assisted laser desorption ion source to an ion chromatograph. A series of polyethylene glycol (PEG) polymers "cationized" (converted to a cation) by sodium ions (Na
+
PEG9 to Na
+
PEG19) and a protonated neurotransmitter protein, bradykinin, were studied. Mobilities of Na
+
PEG9 to Na
+
PEG19 are reported. Detailed modeling of Na
+
PEG9 with molecular mechanics methods indicates that the lowest energy structure has the Na
+
ion "solvated" by the polymer chain with seven oxygen atoms as nearest neighbors. The agreement between the model and experiment is within 1 percent for Na
+
PEG9, Na
+
PEG13, and Na
+
PEG17, giving strong support to both the method and the deduced structures. Similar agreement was obtained in initial studies that modeled experimental data for arginine-protonated bradykinin.
Self-Assembled Metal Colloid Monolayers: An Approach to SERS Substrates
Authors: Freeman R. Griffith , Grabar Katherine C. , Allison Keith J. , Bright Robin M. , Davis Jennifer A. , Guthrie Andrea P. , Hommer Michael B. , Jackson Michael A. , Smith Patrick C. , Walter Daniel G. , Natan Michael J.
Published: October 2006

The self-assembly of monodisperse gold and silver colloid particles into monolayers on polymer-coated substrates yields macroscopic surfaces that are highly active for surface-enhanced Raman scattering (SERS). Particles are bound to the substrate through multiple bonds between the colloidal metal and functional groups on the polymer such as cyanide (CN), amine (NH
2
), and thiol (SH). Surface evolution, which can be followed in real time by ultraviolet-visible spectroscopy and SERS, can be controlled to yield high reproducibility on both the nanometer and the centimeter scales. On conducting substrates, colloid monolayers are electrochemically addressable and behave like a collection of closely spaced microelectrodes. These favorable properties and the ease of monolayer construction suggest a widespread use for metal colloid-based substrates.
Granular Convection Observed by Magnetic Resonance Imaging
Authors: Ehrichs E. E. , Jaeger H. M. , Karczmar Greg S. , Knight James B. , Kuperman Vadim Yu. , Nagel Sidney R.
Published: October 2006

Vibrations in a granular material can spontaneously produce convection rolls reminiscent of those seen in fluids. Magnetic resonance imaging provides a sensitive and noninvasive probe for the detection of these convection currents, which have otherwise been difficult to observe. A magnetic resonance imaging study of convection in a column of poppy seeds yielded data about the detailed shape of the convection rolls and the depth dependence of the convection velocity. The velocity was found to decrease exponentially with depth; a simple model for this behavior is presented here.
Effect of Predators and Area on Invasion: An Experiment with Island Spiders
Authors: Schoener Thomas W. , Spiller David A.
Published: October 2006

To assay the effect of area and predators on invasion success, spiders were introduced onto islands that were large, with lizard predators; large, without lizard predators; or small, without lizard predators. Short-term survival was greater on islands without than with predators; area had no effect. Spiders initially increased substantially on both groups of islands without lizards, but after 5 years they nearly died off on small islands while persisting on most large islands; populations in the presence of predators never increased above initial sizes. Results show how predators as well as area are important in determining invasion success.
The Microscopic Basis of the Glass Transition in Polymers from Neutron Scattering Studies
Authors: Frick B. , Richter D.
Published: October 2006

Recent neutron scattering experiments on the microscopic dynamics of polymers below and above the glass transition temperature
T
g
are reviewed. The results presented cover different dynamic processes appearing in glasses: local motions, vibrations, and different relaxation processes such as α- and β-relaxation. For the α-relaxation, which occurs above
T
g
, it is possible to extend the time-temperature superposition principle, which is valid for polymers on a macroscopic scale, to the microscopic time scale. However, this principle is not applicable for temperatures approaching
T
g
. Below
T
g
, an inelastic excitation at a frequency of some hundred gigahertz (on the order of several wave numbers), the "boson peak," survives from a quasi-elastic overdamped scattering law at high temperatures. The connection between this boson peak and the fast dynamic process appearing near
T
g
is discussed.
High-Pressure Elasticity of Iron and Anisotropy of Earth's Inner Core
Authors: Stixrude Lars , Cohen R. E.
Published: October 2006

A first principles theoretical approach shows that, at the density of the inner core, both hexagonal [hexagonal close-packed (hcp)] and cubic [face-centered-cubic (fcc)] phases of iron are substantially elastically anisotropic. A forward model of the inner core based on the predicted elastic constants and the assumption that the inner core consists of a nearly perfectly aligned aggregate of hcp crystals shows good agreement with seismic travel time anomalies that have been attributed to inner core anisotropy. A cylindrically averaged aggregate of fcc crystals disagrees with the seismic observations.
Regional Forest Fragmentation and the Nesting Success of Migratory Birds
Authors: Robinson Scott K. , Thompson Frank R. , Donovan Therese M. , Whitehead Donald R. , Faaborg John
Published: October 2006

Forest fragmentation, the disruption in the continuity of forest habitat, is hypothesized to be a major cause of population decline for some species of forest birds because fragmentation reduces nesting (reproductive) success. Nest predation and parasitism by cowbirds increased with forest fragmentation in nine midwestern (United States) landscapes that varied from 6 to 95 percent forest cover within a 10-kilometer radius of the study areas. Observed reproductive rates were low enough for some species in the most fragmented landscapes to suggest that their populations are sinks that depend for perpetuation on immigration from reproductive source populations in landscapes with more extensive forest cover. Conservation strategies should consider preservation and restoration of large, unfragmented "core" areas in each region.
Rupture Characteristics of the Deep Bolivian Earthquake of 9 June 1994 and the Mechanism of Deep-Focus Earthquakes
Authors: Silver Paul G. , Beck Susan L. , Wallace Terry C. , Meade Charles , Myers Stephen C. , James David E. , Kuehnel Randy
Published: October 2006

The

M
w

= 8.3 deep (636 kilometers) Bolivian earthquake of 9 June 1994 was the largest deep-focus earthquake ever recorded. Seismic data from permanent stations plus portable instruments in South America show that rupture occurred on a horizontal plane and extended at least 30 by 50 kilometers. Rupture proceeded at 1 to 3 kilometers per second along the down-dip azimuth of the slab and penetrated through more than a third of the slab thickness. This extent is more than three times that expected for a metastable wedge of olivine at the core of the slab, and thus appears to be incompatible with an origin by transformational faulting. These large events may instead represent slip on preserved zones of weakness established in oceanic lithosphere at the Earth's surface.
The Effect of H
2
O on the 410-Kilometer Seismic Discontinuity
Authors: Wood B. J.
Published: October 2006

The 410-kilometer seismic discontinuity is generally considered to be caused by a phase transformation of the main constituent of the upper mantle, olivine, α-(Mg,Fe)
2
SiO
4
, to β-(Mg,Fe)
2
SiO
4
. Recent data show that H
2
O dissolves in olivine and other nominally anhydrous mantle minerals and that the partitioning of H
2
O between olivine and β-(Mg,Fe)
2
SiO
4
is about 1:10. Such behavior strongly affects the region over which the α to β phase transformation occurs and hence the seismic discontinuity that results. The observed width of the discontinuity constrains the maximum H
2
O content of upper mantle olivine to about 200 parts per million by weight.
Cosuppression, Flower Color Patterns, and Metastable Gene Expression States
Authors: Jorgensen Richard A.
Published: October 2006

In plants, transgenes often induce rapid turnover of homologous endogenous transcripts. This "cosuppression" of homologous genes is an extremely nonlinear response to small increases in gene expression or dosage, inversely amplifying them into dramatic phenotypic alterations. Pigment transgenes elicit metastable cosuppression patterns organized by flower morphology. Pattern organization and metastability reflect regulatory states (probably transgene transcription states) that respond to morphological features and are labile to physiology and development. Shifts between regulatory states can be highly ordered; for example, a shift may be imposed on a population of cells defining a meristem, which then stably maintains and transmits the new state throughout growth.
Interannual and Interdecadal Variability in 335 Years of Central England Temperatures
Authors: Plaut G. , Ghil M. , Vautard R.
Published: October 2006

Understanding the natural variability of climate is important for predicting its near-term evolution. Models of the oceans' thermohaline and wind-driven circulation show low-frequency oscillations. Long instrumental records can help validate the oscillatory behavior of these models. Singular spectrum analysis applied to the 335-year-long central England temperature (CET) record has identified climate oscillations with interannual (7- to 8-year) and interdecadal (15- and 25-year) periods, probably related to the North Atlantic's wind-driven and thermohaline circulation, respectively. Statistical prediction of oscillatory variability shows CETs decreasing toward the end of this decade and rising again into the middle of the next.
Aligned Carbon Nanotube Films: Production and Optical and Electronic Properties
Authors: de Heer Walt A. , Bacsa W. S. , Châtelain A. , Gerfin T. , Humphrey-Baker R. , Forro L. , Ugarte D.
Published: October 2006

Carbon nanotube material can now be produced in macroscopic quantities. However, the raw material has a disordered structure, which restricts investigations of both the properties and applications of the nanotubes. A method has been developed to produce thin films of aligned carbon nanotubes. The tubes can be aligned either parallel or perpendicular to the surface, as verified by scanning electron microscopy. The parallel aligned surfaces are birefringent, reflecting differences in the dielectric function along and normal to the tubes. The electrical resistivities are anisotropic as well, being smaller along the tubes than perpendicular to them, because of corresponding differences in the electronic transport properties.
Phonons Localized at Step Edges: A Route to Understanding Forces at Extended Surface Defects
Authors: Niu L. , Gaspar D. J. , Sibener S. J.
Published: October 2006

Inelastic helium atom scattering has been used to measure the phonons on a stepped metallic crystalline surface, Ni(977). When the scattering plane is oriented parallel to the step edges and perpendicular to the terraces, two branches of step-induced phonons are observed. These branches are identified as transversely polarized, step-localized modes that propagate along the step edge. Analysis reveals significant anisotropy in the force field near the step edge, with all forces near the step edge being substantially smaller than in the bulk. Such measurements provide valuable information on metallic bonding and interface stability near extended surface defects.
Corotating Variations of Cosmic Rays Near the South Heliospheric Pole
Authors: Kóta J. , Jokipii J. R.
Published: October 2006

Three-dimensional simulations of the heliospheric modulation of galactic cosmic ray protons show that corotating variations in the intensity can persist to quite high heliographic latitudes. Variations are seen at latitudes considerably higher than the maximum latitude extension of the heliographic current sheet, in regions where the solar wind velocity and magnetic field show no significant variation. Similar conclusions may apply also to lower energy particles, which may be accelerated at lower latitudes. Cosmic ray variations caused by corotating interaction regions present at low heliographic latitudes can propagate to significantly higher latitudes.
Ulysses Solar Wind Plasma Observations at High Southerly Latitudes
Authors: Phillips J. L. , Bame S. J. , Feldman W. C. , Gosling J. T. , Hammond C. M. , McComas D. J. , Goldstein B. E. , Neugebauer M. , Scime E. E. , Suess S. T.
Published: October 2006

Solar wind plasma observations made by the Ulysses spacecraft through –80.2° solar latitude and continuing equatorward to –40.1° are summarized. Recurrent high-speed streams and corotating interaction regions dominated at middle latitudes. The speed of the solar wind was typically 700 to 800 kilometers per second poleward of –35°. Corotating reverse shocks persisted farther south than did forward shocks because of the tilt of the heliomagnetic streamer belt. Sporadic coronal mass ejections were seen as far south as –60.5°. Proton temperature was higher and the electron strahl was broader at higher latitudes. The high-latitude wind contained compressional, pressure-balanced, and Alfvénic structures.
Mineral Resources, Environmental Issues, and Land Use
Authors: Hodges Carroll Ann
Published: October 2006

Contrary to predictions from the 1950s through the mid-1980s, persistent shortages of nonfuel minerals have not occurred, despite prodigious consumption, and world reserves have increased. Global availability of raw materials is relevant to policy decisions regarding mineral development and land use. Justification for environmental protection may exceed that for mining a specific ore body. Demand for environmental accountability is rising worldwide, and new technologies are enabling internalization of costs. Mineral-rich developing nations plagued by inefficient state-owned mining enterprises, high population growth rates, and environmental degradation could realize substantial benefit by reforming government policies to encourage foreign investment in resources and by appropriate allocation of mineral rents.
Mesostructure Design with Gemini Surfactants: Supercage Formation in a Three-Dimensional Hexagonal Array
Authors: Huo Qisheng , Leon Rosa , Petroff Pierre M. , Stucky Galen D.
Published: October 2006

At low temperatures, liquid crystal-like arrays made up of inorganic-cluster and organic molecular units readily undergo reversible lyotropic transformations. Gemini surfactants, with two quaternary ammonium head groups separated by a methylene chain of variable length and with each head group attached to a hydrophobic tail, can be used to control organic charge sitting relative to the bivariable hydrophobic tail configurations. This approach has led to the synthesis of a mesophase (SBA-2) that has three-dimensional hexagonal (
P
6
3
/
mmc
) symmetry, regular supercages that can be dimensionally tailored, and a large inner surface area. This mesostructure analog of a zeolite cage structure does not appear to have a lyotropic surfactant or lipid liquid crystal mesophase counterpart. Through the modification of gemini charge separation and each of the two organic tails, these syntheses can be used to optimize templating effects, including the synthesis of MCM-48 at room temperature.
Beryllium-10 Dating of the Duration and Retreat of the Last Pinedale Glacial Sequence
Authors: Gosse J. C. , Klein J. , Lawn B. , Middleton R. , Evenson E. B.
Published: October 2006

Accurate terrestrial glacial chronologies are needed for comparison with the marine record to establish the dynamics of global climate change during transitions from glacial to interglacial regimes. Cosmogenic beryllium-10 measurements in the Wind River Range indicate that the last glacial maximum (marine oxygen isotope stage 2) was achieved there by 21,700 ± 700 beryllium-10 years and lasted 5900 years. Ages of a sequence of recessional moraines and striated bedrock surfaces show that the initial deglaciation was rapid and that the entire glacial system retreated 33 kilometers to the cirque basin by 12,100 ± 500 beryllium-10 years.
Lehmann Discontinuity as the Base of an Anisotropic Layer Beneath Continents
Authors: Gaherty James B. , Jordan Thomas H.
Published: October 2006

Long-period surface-wave (
R
1
,
G
1
), body-wave (
S, SS, SSS
), and
ScS
-reverberation data have been inverted to obtain anisotropic structures along seismic corridors that sample Australia and the western Pacific. These models support the proposal that the Lehmann discontinuity beneath stable continents represents a transition from an anisotropic lithosphere to a more isotropic material in the lower part of the continental tectosphere.
Atomic-Scale Desorption Through Electronic and Vibrational Excitation Mechanisms
Authors: Shen T. -C. , Wang C. , Abeln G. C. , Tucker J. R. , Lyding J. W. , Avouris Ph. , Walkup R. E.
Published: October 2006

The scanning tunneling microscope has been used to desorb hydrogen from hydrogen-terminated silicon (100) surfaces. As a result of control of the dose of incident electrons, a countable number of desorption sites can be created and the yield and cross section are thereby obtained. Two distinct desorption mechanisms are observed: (i) direct electronic excitation of the Si-H bond by field-emitted electrons and (ii) an atomic resolution mechanism that involves multiple-vibrational excitation by tunneling electrons at low applied voltages. This vibrational heating effect offers significant potential for controlling surface reactions involving adsorbed individual atoms and molecules.
EUVE Observations of Jupiter During the Impact of Comet Shoemaker-Levy 9
Authors: Gladstone G. Randall , Hall Doyle T. , Waite J. Hunter
Published: October 2006

The Extreme Ultraviolet Explorer (EUVE) satellite conducted extensive observations of the jovian system before, during, and after the impact of the fragments of comet Shoemaker-Levy 9 in July 1994. About 2 to 4 hours after the impacts of several of the larger fragments, the brightness of the neutral helium (He I) resonance line at 58.4 nanometers temporarily increased by a factor of about 10. The transient 58.4-nanometer brightenings are most simply explained by resonant scattering of sunlight from the widespread high-altitude remnants of the larger impact plumes. Other possible sources of emission, such as electron impact excitation of He or radiative recombination of He
+
, may contribute to the observed signal.
ROSAT Observations of X-ray Emissions from Jupiter During the Impact of Comet Shoemaker-Levy 9
Authors: Waite J. H. , Gladstone G. R. , Franke K. , Lewis W. S. , Fabian A. C. , Brandt W. N. , Na C. , Haberl F. , Clarke J. T. , Hurley K. C. , Sommer M. , Bolton S.
Published: October 2006

Röntgensatellit (ROSAT) observations made shortly before and during the collision of comet Shoemaker-Levy 9 with Jupiter show enhanced x-ray emissions from the planet's northern high latitudes. These emissions, which occur at System III longitudes where intensity enhancements have previously been observed in Jupiter's ultraviolet aurora, appear to be associated with the comet fragment impacts in Jupiter's southern hemisphere and may represent brightenings of the jovian x-ray aurora caused either by the fragment impacts themselves or by the passage of the fragments and associated dust clouds through Jupiter's inner magnetosphere.
Microchronology and Demographic Evidence Relating to the Size of Pre-Columbian North American Indian Populations
Authors: Snow Dean R.
Published: October 2006

Recent estimates for the size of the aggregate North American Indian population in A.D. 1492 vary from about 18 million to less than 2 million. The unusually favorable archaeological characteristics of Mohawk Iroquois sites in eastern New York have allowed a detailed demographic reconstruction of one case for the period A.D. 1400 to 1776. The case indicates that exogenous epidemics did not reach the region until the 17th century and supports arguments favoring the lower populations estimates for North America as a whole.
Controlled Folding of Micrometer-Size Structures
Authors: Smela Elisabeth , Inganäs Olle , Lundström Ingemar
Published: October 2006

Several types of microactuators have been fabricated, from simple paddles to self-assembling and -disassembling cubes. Conducting bilayers made of a layer of polymer and a layer of gold were used as hinges to connect rigid plates to each other and to a silicon substrate. The bending of the hinges was electrically controlled and reversible, allowing precise three-dimensional positioning of the plates. The structures were released from the substrate with a technique based on differential adhesion. This method, which avoids the use of a sacrificial layer and allows the actuators to pull themselves off the surface, may have general applications in micromachining. Possibilities include the manufacture of surfaces whose light reflection or chemical properties can be switched.
A Scattered-Wave Image of Subduction Beneath the Transverse Ranges
Authors: Revenaugh J.
Published: October 2006

Over 5600 short-period recordings of teleseismic events were used to create deterministic maps of
P
-wave scatterers in the upper mantle beneath Southern California. Between depths of 50 and 200 kilometers, the southern flank of the slab subducting beneath the Transverse Ranges is marked by strong scattering. The marked scattering indicates that the edge of the slab is a sharp thermal boundary. Such a boundary could be produced by slab shearing or small-scale convection in the surrounding mantle. The northern limb of the slab is not a strong scatterer, consistent with thicker lithosphere north of the Transverse Ranges.
Evidence for Mate Fidelity in the Gray Seal
Authors: Amos Bill , Twiss Sean , Pomeroy Paddy , Anderson Sheila
Published: October 2006

Colonially breeding gray seals are polygynous. Males are larger than females, compete with each other for position among aggregated females, and contribute no parental care. Genetic analysis of pups born on the island of North Rona, Scotland, reveals large numbers of full siblings, although dominant males father disproportionately few of these. This result cannot be explained by mating patterns based solely on male dominance and the spatio-temporal organization of the breeding colony. Instead, many full siblings must result from choices favoring previous parental combinations. Thus, polygyny and partner fidelity appear to operate simultaneously in this breeding colony.
Precursory Chemical Changes in Ground Water: Kobe Earthquake, Japan
Authors: Tsunogai Urumu , Wakita Hiroshi
Published: October 2006

Chloride (Cl
–
) and sulfate (SO
4
2–
) ion concentrations of ground water issuing from two wells located near the epicenter of the Kobe earthquake in Japan fluctuated before the disastrous magnitude 7.2 event on 17 January 1995. The samples measured were pumped ground water packed in bottles and distributed in the domestic market as drinking water from 1993 to April 1995. Analytical results demonstrate that Cl
–
and SO
4
2–
concentrations increased steadily from August 1994 to just before the earthquake. Water sampled after the earthquake showed much higher Cl
–
and SO
4
2–
concentrations. The precursory changes in chemical composition may reflect the preparation stage of a large earthquake.
Landscape Ecology: Spatial Heterogeneity in Ecological Systems
Authors: Pickett S. T. A. , Cadenasso M. L.
Published: October 2006

Many ecological phenomena are sensitive to spatial heterogeneity and fluxes within spatial mosaics. Landscape ecology, which concerns spatial dynamics (including fluxes of organisms, materials, and energy) and the ways in which fluxes are controlled within heterogeneous matrices, has provided new ways to explore aspects of spatial heterogeneity and to discover how spatial pattern controls ecological processes.
Cooling of Tropical Brazil (5°C) During the Last Glacial Maximum
Authors: Stute M. , Forster M. , Frischkorn H. , Serejo A. , Clark J. F. , Schlosser P. , Broecker W. S. , Bonani G.
Published: October 2006

A 30,000-year paleotemperature record derived from noble gases dissolved in carbon-14-dated ground water indicates that the climate in lowland Brazil (Piaui Province, 7°S, 41.5°W; altitude, 400 meters) was 5.4° ± 0.6°C cooler during the last glacial maximum than today. This result suggests a rather uniform cooling of the Americas between 40°S and 40°N. A 5.4°C cooling of tropical South America is consistent with pollen records, snow line reconstructions, and strontium/calcium ratios and δ
18
O coral records but is inconsistent with the sea-surface temperature reconstruction of CLIMAP (Climate: Long-Range Investigation, Mapping and Prediction). On the basis of these results, it appears that the tropical Americas are characterized by a temperature sensitivity comparable to that found in higher latitudes.
Observation of Stable Shapes and Conformal Diffusion in Genus 2 Vesicles
Authors: Michalet Xavier , Bensimon David
Published: October 2006

The observed equilibrium shapes of phospholipid vesicles of topological genus 2 (shapes with two holes) are found to be in agreement with theoretical predictions on the basis of a minimization of the elastic curvature energy for fluid membranes under the constraints of constant area, volume, and area difference (between the inner and outer layers of the membrane). For some particular geometrical characteristics, the shapes of the vesicles change continuously and randomly on a slow time scale (tens of seconds) and thus exhibit conformal diffusion. This phenomenon is a reflection of the conformal degeneracy of the elastic curvature energy. Its observation sets a limit (three constraints) on the number of physical constraints relevant to the determination of the shapes of vesicles.
Confinement-Induced Phase Transitions in Simple Liquids
Authors: Klein Jacob , Kumacheva Eugenia
Published: October 2006

The liquid-to-solid transition of a simple model liquid confined between two surfaces was studied as a function of surface separation. From large surface separations (more than 1000 angstroms) down to a separation corresponding to seven molecular layers, the confined films displayed a liquid-like shear viscosity. When the surface separation was further decreased by a single molecular spacing, the films underwent an abrupt, reversible transition to a solid. At the transition, the rigidity of the confined films (quantified in terms of an "effective viscosity") increased reversibly by at least seven orders of magnitude.
Osmium-187 Enrichment in Some Plumes: Evidence for Core-Mantle Interaction?
Authors: Walker Richard J. , Morgan John W. , Horan Mary F.
Published: October 2006

Calculations with data for asteroidal cores indicate that Earth's outer core may have a rhenium/osmium ratio at least 20 percent greater than that of the chondritic upper mantle, potentially leading to an outer core with an osmium-187/osmium-188 ratio at least 8 percent greater than that of chondrites. Because of the much greater abundance of osmium in the outer core relative to the mantle, even a small addition of metal to a plume ascending from the D" layer would transfer the enriched isotopic signature to the mixture. Sources of certain plume-derived systems seem to have osmium-187/osmium-188 ratios 5 to 20 percent greater than that for chondrites, consistent with the ascent of a plume from the core-mantle boundary.
Emplacement of Cretaceous-Tertiary Boundary Shocked Quartz from Chicxulub Crater
Authors: Alvarez Walter , Claeys Philippe , Kieffer Susan W.
Published: October 2006

Observations on shocked quartz in Cretaceous-Tertiary (K-T) boundary sediments compellingly tied to Chicxulub crater raise three problems. First, in North America shocked quartz occurs above the main K-T ejecta layer. Second, shocked quartz is more abundant west than east of Chicxulub. Third, shocked quartz reached distances requiring initial velocities up to 8 kilometers per second, corresponding to shock pressures that would produce melt, not the moderate-pressure shock lamellae observed. Shock devolatilization and the expansion of carbon dioxide and water from impacted wet carbonate, producing a warm, accelerating fireball after the initial hot fireball of silicate vapor, may explain all three problems.
Urban Leakage of Liquefied Petroleum Gas and Its Impact on Mexico City Air Quality
Authors: Blake Donald R. , Rowland F. Sherwood
Published: October 2006

Alkane hydrocarbons (propane, isobutane, and
n
-butane) from liquefied petroleum gas (LPG) are present in major quantities throughout Mexico City air because of leakage of the unburned gas from numerous urban sources. These hydrocarbons, together with olefinic minor LPG components, furnish substantial amounts of hydroxyl radical reactivity, a major precursor to formation of the ozone component of urban smog. The combined processes of unburned leakage and incomplete combustion of LPG play a significant role in causing the excessive ozone characteristic of Mexico City. Reductions in ozone levels should be possible through changes in LPG composition and lowered rates of leakage.
Boron Nitride Nanotubes
Authors: Chopra Nasreen G. , Luyken R. J. , Cherrey K. , Crespi Vincent H. , Cohen Marvin L. , Louie Steven G. , Zettl A.
Published: October 2006

The successful synthesis of pure boron nitride (BN) nanotubes is reported here. Multi-walled tubes with inner diameters on the order of 1 to 3 nanometers and with lengths up to 200 nanometers were produced in a carbon-free plasma discharge between a BN-packed tungsten rod and a cooled copper electrode. Electron energy-loss spectroscopy on individual tubes yielded B:N ratios of approximately 1, which is consistent with theoretical predictions of stable BN tube structures.
Sprites, ELF Transients, and Positive Ground Strokes
Authors: Boccippio Dennis J. , Williams Earle R. , Heckman Stan J. , Lyons Walter A. , Baker Ian T. , Boldi Robert
Published: October 2006

In two summertime mesoscale convective systems (MCSs), mesospheric optical sprite phenomena were often coincident with both large-amplitude positive cloud-to-ground lightning and transient Schumann resonance excitations of the entire Earth-ionosphere cavity. These observations, together with earlier studies of MCS electrification, suggest that sprites are triggered when the rapid removal of large quantities of positive charge from an areally extensive charge layer stresses the mesosphere to dielectric breakdown.
A Large Northern Hemisphere Terrestrial CO
2
Sink Indicated by the
13
C/
12
C Ratio of Atmospheric CO
2
Authors: Ciais P. , Tans P. P. , Trolier M. , White J. W. C. , Francey R. J.
Published: October 2006

Measurements of the concentrations and carbon-13/carbon-12 isotope ratios of atmospheric carbon dioxide can be used to quantify the net removal of carbon dioxide from the atmosphere by the oceans and terrestrial plants. A study of weekly samples from a global network of 43 sites defined the latitudinal and temporal patterns of the two carbon sinks. A strong terrestrial biospheric sink was found in the temperate latitudes of the Northern Hemisphere in 1992 and 1993, the magnitude of which is roughly half that of the global fossil fuel burning emissions for those years. The challenge now is to identify those processes that would cause the terrestrial biosphere to absorb carbon dioxide in such large quantities.
Impact of Food and Predation on the Snowshoe Hare Cycle
Authors: Krebs Charles J. , Boutin Stan , Boonstra Rudy , Sinclair A. R. E. , Smith J. N. M. , Dale Mark R. T. , Martin K. , Turkington R.
Published: October 2006

Snowshoe hare populations in the boreal forests of North America go through 10-year cycles. Supplemental food and mammalian predator abundance were manipulated in a factorial design on 1-square-kilometer areas for 8 years in the Yukon. Two blocks of forest were fertilized to test for nutrient effects. Predator exclosure doubled and food addition tripled hare density during the cyclic peak and decline. Predator exclosure combined with food addition increased density 11-fold. Added nutrients increased plant growth but not hare density. Food and predation together had a more than additive effect, which suggests that a three-trophic-level interaction generates hare cycles.
Templating of Mesoporous Molecular Sieves by Nonionic Polyethylene Oxide Surfactants
Authors: Bagshaw Stephen A. , Prouzet Eric , Pinnavaia Thomas J.
Published: October 2006

Mesoporous silica molecular sieves have been prepared by the hydrolysis of tetraethylorthosilicate in the presence of low-cost, nontoxic, and biodegradable polyethylene oxide (PEO) surfactants, which act as the structure-directing (templating) agents. This nonionic, surfactant-neutral, inorganic-precursor templating pathway to mesostructures uses hydrogen bonding interactions between the hydrophilic surfaces of flexible rod- or worm-like micelles and Si(OC
2
H
5
)
4-x
(OH)
x
hydrolysis products to assemble an inorganic oxide framework. Disordered channel structures with uniform diameters ranging from 2.0 to 5.8 nanometers have been obtained by varying the size and structure of the surfactant molecules. Metal-substituted silica and pure alumina mesostructures have also been prepared by the hydrolysis of the corresponding alkoxides in the presence of PEO surfactants. These results suggest that nonionic templating may provide a general pathway for the preparation of mesoporous oxides.
Turbulent Dynamics in the Solar Convection Zone
Authors: Brummell Nicholas , Toomre Juri , Cattaneo Fausto
Published: October 2006

Observations of the sun reveal highly complex flows and magnetic structures that must result from turbulent convection in the solar envelope. A remarkable degree of large-scale coherence emerges from the small-scale turbulent dynamics, as seen in the cycles of magnetic activity and in the differential rotation profile of this star. High-performance computing now permits numerical simulations of compressible turbulence and magnetohydrodynamics with sufficient resolution to show that compact structures of vorticity and magnetic fields can coexist with larger scales. Such structured turbulence is yielding transport properties for heat and angular momentum at considerable variance with earlier models. These simulations are elucidating the coupling of turbulent fluid motions with rotation and magnetic fields, which must control the interlinked differential rotation and magnetic dynamo action.
Branched Threadlike Micelles in an Aqueous Solution of a Trimeric Surfactant
Authors: Danino Dganit , Talmon Yeshayahu , Levy Hélène , Beinert Gerard , Zana Raoul
Published: October 2006

Very long threadlike micelles observed in aqueous solutions of some surfactants have attracted much attention because of the peculiar rheological properties of these systems. Molecular dynamics simulations have suggested that branched threadlike micelles should exist in concentrated solutions of dimeric surfactants. Here experimental evidence, obtained from transmission electron microscopy at cryogenic temperature, is presented of branched threadlike micelles in aqueous solutions of a triquaternary ammonium (trimeric) surfactant made up of three amphiphilic moieties connected at the level of the head-groups by two propanediyl spacers.
Interhemispheric Correlation of Late Pleistocene Glacial Events
Authors: Lowell T. V. , Heusser C. J. , Andersen B. G. , Moreno P. I. , Hauser A. , Heusser L. E. , Schlüchter C. , Marchant D. R. , Denton G. H.
Published: October 2006

A radiocarbon chronology shows that piedmont glacier lobes in the Chilean Andes achieved maxima during the last glaciation at 13,900 to 14,890, 21,000, 23,060, 26,940, 29,600, and ≥33,500 carbon-14 years before present (
14
C yr B.P.) in a cold and wet Subantarctic Parkland environment. The last glaciation ended with massive collapse of ice lobes close to 14,000
14
C yr B.P., accompanied by an influx of North Patagonian Rain Forest species. In the Southern Alps of New Zealand, additional glacial maxima are registered at 17,720
14
C yr B.P., and at the beginning of the Younger Dryas at 11,050
14
C yr B. P. These glacial maxima in mid-latitude mountains rimming the South Pacific were coeval with ice-rafting pulses in the North Atlantic Ocean. Furthermore, the last termination began suddenly and simultaneously in both polar hemispheres before the resumption of the modern mode of deep-water production in the Nordic Seas. Such interhemispheric coupling implies a global atmospheric signal rather than regional climatic changes caused by North Atlantic thermohaline switches or Laurentide ice surges.
Isolation of the Heterofullerene C
59
N as Its Dimer (C
59
N)
2
Authors: Hummelen Jan C. , Knight Brian , Pavlovich James , González Rosario , Wudl Fred
Published: October 2006

The heterofullerene ion C
59
N
+
is formed efficiently in the gas phase during fast atom bombardment mass spectroscopy of a cluster-opened N-MEM (
N
-methoxyethoxy methyl) ketolactam. This transformation is shown to occur also in solution in the presence of strong acid, affording biazafullerenyl (C
59
N)
2
in good yield. It is proposed that the azafullerene dimer is formed upon in situ reduction of the highly reactive azafulleronium ion. The isolation and characterization of biazafullerenyl opens a viable route for the preparation of other heterofullerenes in solution.
A Stable High-Index Surface of Silicon: Si(5 5 12)
Authors: Baski A. A. , Whitman L. J. , Erwin S. C.
Published: October 2006

A stable high-index surface of silicon, Si(5 5 12), is described. This surface forms a 2 × 1 reconstruction with one of the largest unit cells ever observed, 7.7 angstroms by 53.5 angstroms. Scanning tunneling microscopy (STM) reveals that the 68 surface atoms per 2 × 1 unit cell are reconstructed only on a local scale. A complete structural model for the surface is proposed, incorporating a variety of features known to exist on other stable silicon surfaces. Simulated STM images based on this model have been computed by first-principles electronic-structure methods and show excellent agreement with experiment.