bluuebunny/crossref_metadata_2025 huggingface dataset:
Solar Nebula Heterogeneity in p-Process Samarium and Neodymium Isotopes
Authors: Andreasen Rasmus , Sharma Mukul
Published: October 2006

Bulk carbonaceous chondrites display a deficit of ∼100 parts per million (ppm) in
144
Sm with respect to other meteorites and terrestrial standards, leading to a decrease in their
142
Nd/
144
Nd ratios by ∼11 ppm. The data require that samarium and neodymium isotopes produced by the p process associated with photodisintegration reactions in supernovae were heterogeneously distributed in the solar nebula. Other samarium and neodymium isotopes produced by rapid neutron capture (r process) in supernovae and by slow neutron capture (s process) in red giants were homogeneously distributed. The supernovae sources supplying the p- and r-process nuclides to the solar nebula were thus disconnected or only weakly connected.
Barium Isotopes in Chondritic Meteorites: Implications for Planetary Reservoir Models
Authors: Ranen Michael C. , Jacobsen Stein B.
Published: October 2006

High-precision barium isotope measurements yielded differences of up to 25 parts per million in the
137
Ba/
136
Ba ratio and 60 parts per million in the
138
Ba/
136
Ba ratio between chondrites and Earth. These differences probably arose from incomplete mixing of nucleosynthetic material in the solar nebula. Chondritic meteorites have a slight excess of supernova-derived material as compared to Earth, demonstrating that the solar nebula was not perfectly homogenized upon formation.
How Does the Brain Deal with the Social World?
Authors: Blakemore Sarah Jayne
Published: October 2006

Social Neuroscience
. People Thinking About Thinking People.
John T. Cacioppo, Penny S. Visser, and Cynthia L. Pickett, Eds.
. MIT Press, Cambridge, MA, 2006. 320 pp. $45, £29.95. ISBN 0-262-03335-6. Social Neuroscience.

Psychologists, psychiatrists, neurologists, radiologists, and neuroscientists discuss the neurobiological foundations of human processing of social information.
Structural Transitions in Amorphous Water Ice and Astrophysical Implications
Authors: Jenniskens Peter , Blake David F.
Published: October 2006

Selected area electron diffraction is used to monitor structural changes of vapor-deposited water ice in vacuum during warm-up from 15 to 188 K. A progression of three amorphous forms of water ice is found with well-defined transitions. The formation of a high-density amorphous form (I
a
h) at 15 K is confirmed, and the transition to the more familiar low-density form (I
a
l) occurs gradually over the range 38 to 68 K. At 131 K, the ice transforms into a third amorphous form (I
a
r), which precedes the crystallization of cubic ice (I
c
) and coexists metastably with I
c
from 148 K until at least 188 K. These structural transformations of amorphous water ice can be used to explain hitherto anomalous properties of astrophysical ices. The structural transition from I
a
h to I
a
l is responsible for the diffusion and recombination of radicals in ultraviolet-photolyzed interstellar ices at low temperatures. The occurrence and persistence of I
a
r explains anomalous gas retention and gas release from water-rich ices at temperatures above 150 K.
Observed Impact of Snow Cover on the Heat Balance and the Rise of Continental Spring Temperatures
Authors: Groisman Pavel Ya. , Karl Thomas R. , Knight Richard W.
Published: October 2006

Analysis of satellite-derived snow cover, radiative balance, and surface air temperature over Northern Hemisphere extratropical land shows that the retreat of the Northern Hemisphere's extent of spring snow cover over the past 20 years parallels a change in the influence of snow cover on the radiative balance and an observed increase of spring temperatures over the same area. These results help explain why the long-term (20th century) increase in surface air temperature over Northern Hemisphere land has been greater in spring than in any other season relative to the interannual variability.
Structure of Solidified Colloidal Array Laser Filters Studied by Cryogenic Transmission Electron Microscopy
Authors: Kamenetzky Eduardo A. , Magliocco Lino G. , Panzer Hans P.
Published: October 2006

Ordered arrays of charged uniform colloidal polystyrene particles in solution form a single-wavelength laser filter that is transparent to other wavelengths. A usable filter was prepared by solidification within an acrylamide—methylene-bisacrylamide gel. The rejection wavelength of the colloidal array filter changes with gel composition. Cryogenic transmission electron microscopy of two gel formulations shows that the colloidal array filter is composed of AAA stacking of close-packed planes. Excellent agreement is found between the layer spacings measured and those predicted from the rejection wavelengths.
Fossil Evidence for the Origin of Aquatic Locomotion in Archaeocete Whales
Authors: Thewissen J. G. M. , Hussain S. T. , Arif M.
Published: October 2006

Recent members of the order Cetacea (whales, dolphins, and porpoises) move in the water by vertical tail beats and cannot locomote on land. Their hindlimbs are not visible externally and the bones are reduced to one or a few splints that commonly lack joints. However, cetaceans originated from four-legged land mammals that used their limbs for locomotion and were probably apt runners. Because there are no relatively complete limbs for archaic archaeocete cetaceans, it is not known how the transition in locomotory organs from land to water occurred. Recovery of a skeleton of an early fossil cetacean from the Kuldana Formation, Pakistan, documents transitional modes of locomotion, and allows hypotheses concerning swimming in early cetaceans to be tested. The fossil indicates that archaic whales swam by undulating their vertebral column, thus forcing their feet up and down in a way similar to modern otters. Their movements on land probably resembled those of sea lions to some degree, and involved protraction and retraction of the abducted limbs.
An Inverted Double Seismic Zone in Chile: Evidence of Phase Transformation in the Subducted Slab
Authors: Comte Diana , Suárez Gerardo
Published: October 2006

Data from two microseismic field experiments in northern Chile revealed an elongated cluster of earthquakes in the subducted Nazca plate at a depth of about 100 kilometers in which down-dip tensional events were consistently shallower than a family of compressional earthquakes. This double seismic zone shows a distribution of stresses of opposite polarity relative to that observed in other double seismic zones in the world. The distribution of stresses in northern Chile supports the notion that at depths of between 90 to 150 kilometers, the basalt to eclogite transformation of the subducting oceanic crust induces tensional deformation in the upper part of the subducted slab and compressional deformation in the underlying mantle.
Modes of Tilting During Extensional Core Complex Development
Authors: Coleman Drew S. , Walker J. Douglas
Published: October 2006

Crustal extension and formation of the Mineral Mountains core complex, Utah, involved tilting of the Mineral Mountains batholith and associated faults during hanging wall and footwall deformation. The batholith was folded in the hanging wall of the Beaver Valley fault between 11 and 9 million years ago yielding about 45° of tilt. Subsequently, the batholith was unroofed along the Cave Canyon detachment fault, and the batholith and fault were tilted approximately 40° during footwall uplift. Recognition of deformed dikes beneath the detachment fault establishes the importance of footwall tilt during formation of extensional core complexes and demonstrates that footwall rebound can be an important process during extension.
Hubble Repair and More Wins Astronomers' Acclaim
Authors: Travis John
Published: October 2006

The repaired Hubble Space Telescope overshadowed everything else at the American Astronomical Society (AAS) Meeting earlier this month in Alexandria, Virginia. The nearly 2000 astronomers who turned out for the society's largest meeting yet provided plenty of "oohs" and "aahs" for every new image. But, in between, some astronomers caught word of a new proposal about how to tell whether the universe is open or closed, more data about mysterious gamma ray bursts, and the crowning of the "Galaxy of the Year."
Decomposition of the Modulated Waves in a Rotating Couette System
Authors: Takeda Yasushi , Fischer Walter E. , Sakakibara Jun
Published: October 2006

The time-dependent velocity field in a rotating Couette system has been decomposed. Successive instantaneous velocity profiles were obtained by an ultrasonic Doppler velocity profile method, and the spatiotemporal velocity field had been analyzed by two-dimensional Fourier transform. The Fourier spectrum is depicted by intrinsic peaks, and the velocity field can be reconstructed with these peak components only, indicating a successful decomposition of the velocity field. This method shows that the so-called broadband component, which is purely spatiotemporal and attributed to chaos, corresponds to a global motion of the wave propagating from roll to roll.
Constraints on Transport and Kinetics in Hydrothermal Systems from Zoned Garnet Crystals
Authors: Jamtveit Bjørn , Hervig Richard L.
Published: October 2006

Zonation of oxygen isotope ratios, fluorine, and rare earth element abundances across garnet crystals from the Permian Oslo Rift reflect temporal variation of the hydrothermal system in which the garnets grew. A sharp rimward decrease in the
18
O/
16
O ratio (of 5 per mil) across the interface between aluminum-rich garnet cores and iron-rich rims indicates influx of meteoric fluids to a system initially dominated by magmatic fluids. This influx may record the transition from ductile to brittle deformation of the hydrothermally altered rocks. In contrast, fluorine and light rare earth element concentrations increase at the core-rim interface. These data may reflect enhanced advective transport and notable kinetic control on trace element uptake by the garnets during brittle deformation.
Large First Hyperpolarizabilities in Push-Pull Polyenes by Tuning of the Bond Length Alternation and Aromaticity
Authors: Marder Seth R. , Cheng Lap-Tak , Tiemann Bruce G. , Friedli Andrienne C. , Blanchard-Desce Mireille , Perry Joseph W. , Skindhøj Jørgen
Published: October 2006

Conjugated organic compounds with 3-phenyl-5-isoxazolone or
N,N
′-diethylthiobarbituric acid acceptors have large first molecular hyperpolarizabilities (β) in comparison with compounds with 4-nitrophenyl acceptors. For example, julolidinyl-(CH=CH)
3
-CH=
N,N
′-diethylthiobarbituric acid, which has 12 atoms between the donor and acceptor, has a β(0) of 911 × 10
-30
electrostatic units, whereas (CH
3
)
2
NC
6
H
4
–(CH=CH)
4
–C
6
H
4
NO
2
, with 16 atoms between its donor and acceptor, has a β(0) of 133 × 10
-30
electrostatic units. The design strategies demonstrated here have resulted in chromophores that when incorporated into poled-polymer electrooptic modulators exhibited significant enhancements in electrooptic coefficients relative to polymers containing the commonly used dye Disperse Red-1. Poled polymer devices based on these or related chromophores may ultimately lead to high-speed electrooptic switching elements with low drive-power requirements, suitable for telecommunications applications.
Math Attendees Find There's Life After Fermat Proof
Authors: Cipra Barry
Published: October 2006

The uncertain status of the recent proof of Fermat's Last Theorem (
Science
, 24 December 1993, p. 1967) was the hot topic in the hallways at the joint meetings of the American Mathematical Society and the Mathematical Association of America, held 12-15 January in Cincinnati. But a few other topics did manage to get discussed. Among them: How gambling pays off in computing the volume of high-dimensional shapes; how a mathematical description of water dripping down a window pane might lead to the design of digital pulses that could race through the optical fibers of the future; and how one can be fooled infinitely often by another theorem of Fermat's.
Stilbazolium-MPS
3
Nanocomposites with Large Second-Order Optical Nonlinearity and Permanent Magnetization
Authors: Lacroix Pascal G. , Clément René , Nakatani Keitaro , Zyss Joseph , Ledoux Isabelle
Published: October 2006

Intercalated layered materials comprising an organic dye and inorganic MPS
3
[where M is either the manganese ion (Mn
2+
) or the cadmium ion (Cd
2+
)] phases have been prepared. The intercalation process induces a spontaneous poling, giving rise to an efficiency of 750 times that of urea in second-harmonic generation for the cadmium derivative. In addition, the manganese derivative displays a permanent magnetization below 40 kelvin. Thus, these materials exhibit both a large optical nonlinearity and magnetic ordering.
Shape of Asteroid 4769 Castalia (1989 PB) from Inversion of Radar Images
Authors: Hudson R. Scott , Ostro Steven J.
Published: October 2006

The inversion of previously reported, delay-Doppler images of Castalia yields a 167-parameter, three-dimensional shape model that is bifurcated into two distinct, irregular, kilometer-sized lobes. The crevice that separates the lobes has an average depth of between 100 and 150 meters and is oriented roughly perpendicular to the asteroid's longest dimension. The constrained least-squares reconstruction method introduced here can be used to determine the shape, spin vector, and radar-scattering properties of any asteroid or comet for which delay-Doppler images provide sufficient signal-to-noise ratio, orientational coverage, and spatial resolution.
Double Seismic Zone for Deep Earthquakes in the Izu-Bonin Subduction Zone
Authors: Iidaka Takashi , Furukawa Yoshitsugu
Published: October 2006

A double seismic zone for deep earthquakes was found in the Izu-Bonin region. An analysis of
SP
-converted phases confirms that the deep seismic zone consists of two layers separated by ∼20 kilometers. Numerical modeling of the thermal structure implies that the hypocenters are located along isotherms of 500° to 550°C, which is consistent with the hypothesis that deep earthquakes result from the phase transition of metastable olivine to a high-pressure phase in the subducting slab.
A Molecular Organic Carbon Isotope Record of Miocene Climate Changes
Authors: Schoell M. , Schouten S. , Damsté J. S. Sinninghe , de Leeuw J. W. , Summons R. E.
Published: October 2006

The difference in carbon-13 (
13
C) contents of hopane and sterane biomarkers in the Monterey formation (Naples Beach, California) parallels the Miocene inorganic record of the change in
18
O (δ
18
O), reflecting the Miocene evolution from a well-mixed to a highly stratified photic zone (upper 100 meters) in the Pacific. Steranes (δ
13
C = 25.4 ± 0.7 per mil versus the Pee Dee belemnite standard) from shallow photic-zone organisms do not change isotopically throughout the Miocene. In contrast, sulfur-bound C
35
hopanes (likely derived from bacterial plankton living at the base of the photic zone) have systematically decreasing
13
C concentrations in Middle and Late Miocene samples (δ
13
C = –29.5 to –31.5 per mil), consistent with the Middle Miocene formation of a carbon dioxide—rich cold water mass at the base of the photic zone.
Persistence of Transients in Spatially Structured Ecological Models
Authors: Hastings Alan , Higgins Kevin
Published: October 2006

Simple discrete-time ecological models for a species with alternating reproduction and dispersal are shown to have complex transient dynamics. If the density dependence (nonlinearity) is strong enough, then the time required to reach the final dynamics is usually very long, approaching thousands of generations, and there are typically very sudden changes in the form of the dynamics. Apparent chaos can change to cycles or vice versa. These results are consistent with observed sudden changes in the form of the dynamics of a single species and imply that transient dynamics of ecological models may be more relevant than long-term behavior.
Atomic Force Microscopy of the Electrochemical Nucleation and Growth of Molecular Crystals
Authors: Hillier Andrew C. , Ward Michael D.
Published: October 2006

In situ atomic force microscopy reveals the morphology, surface topography, and growth and dissolution characteristics of microscopic single crystals of the low-dimensional organic conductor (tetrathiafulvalene)Br
0.76
, which are grown by electrocrystallization on a highly oriented pyrolytic graphite electrode in an atomic force microscope liquid cell. The growth modes and the distribution and orientation of topographic features on specific crystal faces, whose identity was determined by "atomic force microscope goniometry," can be correlated with the strength and direction of anisotropic solid-state intermolecular bonding. Growth on the (011) face of (tetrathiafulvalene)Br
0.76
crystals involves the formation of oriented self-similar triangular islands ranging in size from 200 to 5000 angstroms along a side. These nuclei eventually transform into rectangular rafts at larger length scales, where bulk intermolecular bonding interactions and surface energies dominate over nuclei-substrate interactions.
Growth of Diamond from Atomic Hydrogen and a Supersonic Free Jet of Methyl Radicals
Authors: Lee Szetsen Steven , Minsek David W. , Vestyck Daniel J. , Chen Peter
Published: October 2006

The growth of small (∼10-micrometer) diamond particles (on 0.1- or 0.25-micrometer seed crystals) using an effusive glow discharge nozzle for H⋅ and a separate supersonic pyrolysis jet for ⋅CH
3
is reported. Laser micro-Raman, scanning electron microscopy, and x-ray photoelectron spectroscopy data are presented as evidence that well-crystallized diamond is indeed formed. Resonant multiphoton ionization spectroscopy is used as a diagnostic for the gas-phase chemistry indicating that the radical sources are clean and quantitative and that there is no detectable interconversion of ⋅CH
3
to C
2
H
2
under the conditions of the experiment. Diamond growth is found at substrate temperatures greater than or equal to 650°C with no marked increase in the rate of growth up to 850°C. Acetylene does not give good quality diamond under similar conditions.
Adhesion: Molecules and Mechanics
Authors: Kendall Kevin
Published: October 2006

There is a difference between adhesion at the molecular level and adhesion in engineering. There is no doubt that molecules of solid materials stick together and can be separated mechanically. The problem is explaining the connection between molecular attractions and mechanical measurements. False ideas such as keying and gluing require critical assessment because they confuse molecules and mechanics. Mechanisms such as adhesive hysteresis, stringing, and clustering deserve evaluation. A rational theory of these phenomena should be based on the theoretical concept of reversible work of adhesion and on the measured quantity of adhesive energy, which includes the extra energy required to restructure the interface as surfaces move.
Gallium Arsenide Transistors: Realization Through a Molecularly Designed Insulator
Authors: Jenkins Phillip P. , MacInnes Andrew N. , Tabib-Azar Massood , Barron Andrew R.
Published: October 2006

A GaAs-based transistor, analogous to commercial silicon devices, has been fabricated with vapor-deposited cubic GaS as the insulator material. The
n
-channel, depletion mode, GaAs field-effect transistor shows, in addition to classical transistor characteristics, a channel mobility of 4665.6 square centimeters per volt per second, an interfacial trap density of 10
11
per electron volt per square centimeter, and a transconductance of 7 millisiemens for a 5-micrometer gate length at a gate voltage of 8 volts. Furthermore, the GaAs transistor shows an on-to-off resistance ratio comparable to that of commercial devices.
El Niño Chaos: Overlapping of Resonances Between the Seasonal Cycle and the Pacific Ocean-Atmosphere Oscillator
Authors: Tziperman Eli , Stone Lewi , Cane Mark A. , Jarosh Hans
Published: October 2006

The El Niño—Southern Oscillation (ENSO) cycle is modeled as a low-order chaotic process driven by the seasonal cycle. A simple model suggests that the equatorial Pacific ocean-atmosphere oscillator can go into nonlinear resonance with the seasonal cycle and that with strong enough coupling between the ocean and the atmosphere, the system may become chaotic as a result of irregular jumping of the ocean-atmosphere system among different nonlinear resonances. An analysis of a time series from an ENSO prediction model is consistent with the low-order chaos mechanism.
In Pittsburgh, Physicists Get Down to the Nitty-Gritty
Authors: Service Robert
Published: October 2006

While some physicists ponder the grand design of the universe, others delve to the atomic scale. That microrealm was the focus of most of the 5300 researchers specializing in biological and condensed-matter physics and in materials science who gathered in Pittsburgh two weeks ago for the annual March meeting of the American Physical Society (APS). Among the more than 5000 papers presented at the meeting were descriptions of building and measuring micromagnets, making atomic movies, and studying sand grains for clues to why some dunes roar.
Antiferromagnetic Ordering and Paramagnetic Behavior of Ferromagnetic Cu
6
and Cu
18
Clusters in BaCuO

2+
x
Authors: Wang Z.-R. , Wang X.-L. , Fernandez-Baca J. A. , Johnston D. C. , Vaknin D.
Published: October 2006

Magnetization and neutron diffraction measurements on polycrystalline BaCuO

2+
x

revealed a combination of magnetic behaviors. The Cu
6
ring clusters and Cu
18
sphere clusters in this compound had ferromagnetic ground states with large spins 3 and 9, respectively. The Cu
6
rings ordered antiferromagnetically below the Néel temperature
T
N
= 15 ± 0.5 kelvin, whereas the Cu
18
spheres remained paramagnetic down to 2 kelvin. The ordered moment below
T
N
was 0.89(5) Bohr magnetons per Cu in the Cu
6
rings, demonstrating that quantum fluctuation effects are small in these atomic clusters. The Cu
18
clusters are predicted to exhibit ferromagnetic intercluster order below about 1 kelvin.
Structure Meets Function at Materials Gathering
Authors: Service Robert F.
Published: October 2006

SAN FRANCISCO—Engineers, physicists, and other scientists interested in material behavior came together at the 1994 spring meeting of the Materials Research Society from 4 to 8 April. Among the 2200 papers given, researchers heard presentations on a variety of functional substances: a semiconductor suitable for a laser that gives off blue light, an improved magnetic refrigerator, and a method of keeping pollutants from forming in engine exhaust.
Confirmation of Earth-Mass Planets Orbiting the Millisecond Pulsar PSR B1257 + 12
Authors: Wolszczan Alexander
Published: October 2006

The discovery of two Earth-mass planets orbiting an old (∼10
9
years), rapidly spinning neutron star, the 6.2-millisecond radio pulsar PSR B1257+12, was announced in early 1992. It was soon pointed out that the approximately 3:2 ratio of the planets' orbital periods should lead to accurately predictable and possibly measurable gravitational perturbations of their orbits. The unambiguous detection of this effect, after 3 years of systematic timing observations of PSR B1257+12 with the 305-meter Arecibo radiotelescope, as well as the discovery of another, moon-mass object in orbit around the pulsar, constitutes irrefutable evidence that the first planetary system around a star other than the sun has been identified.
Strontium Isotopic Composition of Mid-Cretaceous Seawater
Authors: Ingram B. Lynn , Coccioni Rodolfo , Montanari Alessandro , Richter Frank M.
Published: October 2006

The
87
Sr/
86
Sr ratio in fish teeth separated from mid-Cretaceous marl and black shale from the northeastern Apennines and Venetian Alps (Italy) define three periods of low
87
Sr/
86
Sr ratio at 121 to 124 million years ago (Ma), 110 to 115 Ma, and 89 to 91 Ma. The
87
Sr/
86
Sr excursions correspond to oceanic anoxic events represented by the Livello Selli, Livello 113, Livello Urbino, and Livello Bonarelli black shale marker beds and probably reflect an increase in the low-
87
Sr/
86
Sr hydrothermal strontium flux associated with the emplacement of the Ontong-Java and Kerguelen plateaus (120 to 110 Ma) and the Caribbean Plateau (89 to 91 Ma). The modeled flux is consistent with the volumes and eruption rates of the oceanic plateaus but is far smaller than expected from the proposed Cretaceous crustal production rates of 50 to 100 percent greater than modern.
Earthquakes with Non—Double-Couple Mechanisms
Authors: Frohlich Cliff
Published: October 2006

Seismological observations confirm that the pattern of seismic waves from some earthquakes cannot be produced by slip along a planar fault surface. More than one physical mechanism is required to explain the observed varieties of these non-double-couple earthquakes. The simplest explanation is that some earthquakes are complex, with stress released on two or more suitably oriented, nonparallel fault surfaces. However, some shallow earthquakes in volcanic and geothermal areas require other explanations. Current research focuses on whether fault complexity explains most observed non-double-couple earthquakes and to what extent ordinary earthquakes have non-double-couple components.
A Crested Theropod Dinosaur from Antarctica
Authors: Hammer William R. , Hickerson William J.
Published: October 2006

Jurassic fossil vertebrates collected from the Falla Formation in the Central Transantarctic Mountains included a partial skull and postcranial elements of a crested theropod,
Cryolophosaurus ellioti
gen. nov. sp. nov. The theropod bears some resemblance to the large tetanurans of the Middle to Late Jurassic but also has primitive ceratosaurian features. Elements from a prosauropod, teeth from scavenging theropods, a pterosaur humerus, and a tritylodont molar were also recovered. The presence of this fauna suggests that a mild climate existed at high paleolatitude in this area of Gondwana during the Early Jurassic.
Terawatt to Petawatt Subpicosecond Lasers
Authors: Perry Michael D. , Mourou Gerard
Published: October 2006

The application of the chirped-pulse amplification technique to solid-state lasers combined with the availability of broad-bandwidth materials has made possible the development of small-scale terawatt and now even petawatt (1000-terawatt) laser systems. The laser technology used to produce these intense pulses and examples of new phenomena resulting from the application of these systems to atomic and plasma physics are described.
Observation of Quantum-Size Effects at Room Temperature on Metal Surfaces With STM
Authors: Avouris Phaedon , Lyo In-Whan
Published: October 2006

Surface steps act as confining barriers for electrons in metal-surface states. Thus, narrow terraces and small single-atom—high metal islands act as low-dimensional, electron-confining structures. In sufficiently small structures, quantum-size effects are observable even at room temperature. Scanning tunneling spectroscopy is used to image the probability amplitude distributions and discrete spectra of the confined states. Examination of the electronic structure of the steps provides evidence for electron-density smoothing and the formation of step-edge states. Estimates of the electron-confining barriers are obtained.
Isotopic Evidence for Neogene Hominid Paleoenvironments in the Kenya Rift Valley
Authors: Kingston John D. , Hill Andrew , Marino Bruno D.
Published: October 2006

Bipedality, the definitive characteristic of the earliest hominids, has been regarded as an adaptive response to a transition from forested to more-open habitats in East Africa sometime between 12 million and 5 million years ago. Analyses of the stable carbon isotopic composition (δ
13
C) of paleosol carbonate and organic matter from the Tugen Hills succession in Kenya indicate that a heterogeneous environment with a mix of C3 and C4 plants has persisted for the last 15.5 million years. Open grasslands at no time dominated this portion of the rift valley. The observed δ
13
C values offer no evidence for a shift from more-closed C3 environments to C4 grassland habitats. If hominids evolved in East Africa during the Late Miocene, they did so in an ecologically diverse setting.
Rechargeable Lithium Batteries with Aqueous Electrolytes
Authors: Li Wu , Dahn J. R. , Wainwright D. S.
Published: October 2006

Rechargeable lithium-ion batteries that use an aqueous electrolyte have been developed. Cells with LiMn
2
O
4
and VO
2
(B) as electrodes and 5 M LiNO
3
in water as the electrolyte provide a fundamentally safe and cost-effective technology that can compete with nickelcadmium and lead-acid batteries on the basis of stored energy per unit of weight.
The Role of Mesoscale Tracer Transports in the Global Ocean Circulation
Authors: Danabasoglu Gokhan , McWilliams James C. , Gent Peter R.
Published: October 2006

Ocean models routinely used in simulations of the Earth's climate do not resolve mesoscale eddies because of the immense computational cost. A new parameterization of the effects of these eddies has been implemented in a widely used model. A comparison of its solution with that of the conventional parameterization shows significant improvements in the global temperature distribution, the poleward and surface heat fluxes, and the locations of deep-water formation.
Langmuir-Blodgett Films of a Functionalized Molecule with Cross-Sectional Mismatch Between Head and Tail
Authors: Garnaes J. , Larsen N. B. , Bjørnholm T. , Jørgensen M. , Kjaer K. , Als-Nielsen J. , Jørgensen J. F. , Zasadzinski J. A.
Published: October 2006

A functionalized surfactant has been investigated as floating monolayers by synchrotron x-ray diffraction and as bilayers transferred to solid supports by the Langmuir-Blodgett technique through atomic force microscopy. The transfer process is accompanied by an increase of the unit cell area (about 17 percent) and by an increase of the average domain diameter of nanometer-scale domains (about three times). The unit cell area of the floating monolayer corresponds to close packing of the head groups and a noncharacteristic packing of the tilted alkyl chains. The larger unit cell area of the bilayer film is consistent with a particular ordered packing of the alkyl chains, leaving free space for the head groups.
Implications for Mantle Dynamics from the High Melting Temperature of Perovskite
Authors: van Keken Peter E. , Yuen David A. , van den Berg Arie P.
Published: October 2006

Recent studies have implied that (Mg,Fe)SiO
3
-perovskite, a likely dominant mineral phase in the lower mantle, may have a high melting temperature. The implications of these findings for the dynamics of the lower mantle were investigated with the use of numerical convection models. The results showed that low homologous temperatures (0.3 to 0.5) would prevail in the modeled lower mantle, regardless of the effective Rayleigh number and internal heating rates. High-temperature ductile creep is possible under relatively cold conditions. In models with low rates of internal heating, local maxima of viscosity developed in the mid-lower mantle that were similar to those obtained from inversion of geoid, topography, and plate velocities.
Species Pool and Dynamics of Marine Paleocommunities
Authors: Buzas Martin A. , Culver Stephen J.
Published: October 2006

Foraminiferal communities in the Cenozoic shelf deposits of the North American Atlantic Coastal Plain exhibit little unity during almost 55 million years of successive transgressions and regressions. Transgression communities are composed of a dynamic mixture of immigrants and newly evolved species. During regressions, species within these communities either became extinct or emigrated. Some emigrants returned during subsequent transgressions, but many did not. The neritic species of the Atlantic and Gulf continental margins constitute a species pool. Immigrants and emigrants transferred into and out of the species pool, while extinctions and originations repeatedly altered its species composition. While the results indicate a lack of local community unity, at the same time they demonstrate the necessity of a species pool to sustain species diversity.
High-Pressure and High-Temperature Experiments on Core-Mantle Segregation in the Accreting Earth
Authors: Hiligren Valerie J. , Drake Michael J. , Rubie David C.
Published: October 2006

The abundances of siderophile elements in the Earth's silicate mantle are too high for the mantle to have been in equilibrium with iron in the core if equilibrium occurred at low pressures and temperatures. It has been proposed that this problem may be solved if equilibrium occurred at high pressures and temperatures. Experimental determination of the distribution of siderophile elements between liquid metal and liquid silicate at 100 kilobar and 2000°C demonstrates that it is unlikely that siderophile element abundances were established by simple metal-silicate equilibrium, which indicates that the segregation of the core from the mantle was a complex process.
Control of Structure and Growth of Polymorphic Crystalline Thin Films of Amphiphilic Molecules on Liquid Surfaces
Authors: Weinbach Susan P. , Kjaer Kristian , Bouwman Wim G. , Grübel Gerhard , Legrand Jean-François , Als-Nielsen Jens , Lahav Meir , Leiserowitz Leslie
Published: October 2006

The spontaneous formation and coexistence of crystalline polymorphic trilayer domains in amphiphilic films at air-liquid interfaces is demonstrated by grazing incidence synchrotron x-ray diffraction. These polymorphic crystallites may serve as models for the early stages of crystal nucleation and growth, helping to elucidate the manner in which additives influence the progress of crystal nucleation, growth, and polymorphism and suggesting ways of selectively generating and controlling multilayers on liquid surfaces. Auxiliary molecules have been designed to selectively inhibit development of the polymorphs, leading primarily to a single phase monolayer.
Crystal Tectonics: Construction of Reticulated Calcium Phosphate Frameworks in Bicontinuous Reverse Microemulsions
Authors: Walsh Dominic , Hopwood Jeremy D. , Mann Stephen
Published: October 2006

The chemical construction of organized architectures is an important aspect of innovative materials synthesis. Bicontinuous water-filled microemulsions can be used as preorganized systems for the fabrication of crystalline calcium phosphate materials with extended reticulated microstructures. These macroporous materials are formed by mineralization reactions located within the interconnecting water channels of the bicontinuous network. The resulting materials represent replicas of the microemulsion architecture, but the pore sizes are incommensurate, suggesting that secondary modifications in the bicontinuous microstructure occur during crystal growth. Synthetic macroporous calcium phosphates could have uses in biomaterial implants.
Shifts in Diversification Rate with the Origin of Angiosperms
Authors: Sanderson Michael J. , Donoghue Michael J.
Published: October 2006

The evolutionary success of flowering plants has been attributed to key innovations that originated at the base of that clade. Maximum likelihood methods were used to assess whether branching rate increases were correlated with the origin of these traits. Four hypotheses for the basal relationships of angiosperms were examined by methods that are robust to uncertainty about the timing of internal branch points. Recent hypotheses based on molecular evidence, or on a combination of molecular and morphological characters, imply that large increases in branching rate did not occur until after the putative key innovations of angiosperms had evolved.
The X-Ray Surface Forces Apparatus: Structure of a Thin Smectic Liquid Crystal Film Under Confinement
Authors: Idziak Stefan H.J. , Safinya Cyrus R. , Hill Robert S. , Kraiser Keith E. , Ruths Marina , Warriner Heidi E. , Steinberg Suzi , Liang Keng S. , Israelachvili Jacob N.
Published: October 2006

An x-ray surface forces apparatus for simultaneously measuring forces and structures of confined complex fluids under static and flow conditions is described. This apparatus, combined with an intense synchrotron x-ray source, allows investigation of molecular orientations within a thin liquid crystal film confined between two shearing mica surfaces 3900 angstroms apart. The layer-forming smectic liquid crystal 8CB (4-cyano-4′-octylbiphenyl) adopted a series of distinct planar layer orientations, including the bulk flow-forbidden
b
orientation.
Deep Seismic Expression of an Ancient Plate Boundary in Europe
Authors: Zielhuis Alet , Nolet Guust
Published: October 2006

Seismological results on the structure of the upper mantle below Europe reveal a marked contrast in seismic properties between Precambrian and younger parts of Europe. The Precambrian craton in eastern Europe is characterized by high shear-wave velocities, which can be explained by low temperatures. The transition to low seismic velocities below Phanerozoic Europe coincides with the crustal boundary zone of the craton and exists to depths of at least 140 kilometers. Despite the long and complex tectonic history of the plate boundary zone, the transition is remarkably sharp, which rules out any significant lateral transport of asthenospheric material across the suture zone.
Magnetic Susceptibility of Molecular Carbon: Nanotubes and Fullerite
Authors: Ramirez A. P. , Haddon R. C. , Zhou O. , Fleming R. M. , Zhang J. , McClure S. M. , Smalley R. E.
Published: October 2006

Elemental carbon can be synthesized in a variety of geometrical forms, from three-dimensional extended structures (diamond) to finite molecules (C
60
fullerite). Results are presented here on the magnetic susceptibility of the least well-understood members of this family, nanotubes and C
60
fullerite. (i) Nanotubes represent the cylindrical form of carbon, intermediate between graphite and fullerite. They are found to have significantly larger orientation-averaged susceptibility, on a per carbon basis, than any other form of elemental carbon. This susceptibility implies an average band structure among nanotubes similar to that of graphite. (ii) High-resolution magnetic susceptibility data on C
60
fullerite near the molecular orientational-ordering transition at 259 K show a sharp jump corresponding to 2.5 centimeter-gram-second parts per million per mole of C
60
. This jump directly demonstrates the effect of an intermolecular cooperative transition on an intramolecular electronic property, where the susceptibility jump may be ascribed to a change in the shape of the molecule due to lattice forces.
Water on Mars: Clues from Deuterium/Hydrogen and Water Contents of Hydrous Phases in SNC Meteorites
Authors: Watson Laurie Leshin , Hutcheon Ian D. , Epstein Samuel , Stolper Edward M.
Published: October 2006

Ion microprobe studies of hydrous amphibole, biotite, and apatite in shergottite-nakhlite-chassignite (SNC) meteorites, probable igneous rocks from Mars, indicate high deuterium/hydrogen (D/H) ratios relative to terrestrial values. The amphiboles contain roughly one-tentn as much water as expected, suggesting that SNC magmas were less hydrous than previously proposed. The high but variable D/H values of these minerals are best explained by postcrystallization D enrichment of initially D-poor phases by martian crustal fluids with near atmospheric D/H (about five times the terrestrial value). These igneous phases do not directly reflect the D/H ratios of martian "magmatic" water but provide evidence for a D-enriched martian crustal water reservoir.
Protonated Ozone: Experimental Detection of O
3
H
+
and Evaluation of the Proton Affinity of Ozone
Authors: Cacace Fulvio , Speranza Maurizio
Published: October 2006

The elusive protonated ozone ion (O
3
H
+
) has been long postulated as a reactive intermediate but never experimentally observed. This ion has been detected here in mass spectrometric experiments with the use of Fourier transform ion cyclotron resonance. In these experiments, ozone (O
3
) was protonated by strong acids—for example, H
3
+
, KrH
+
, XeH
+
, and CH
5
+
. The hitherto experimentally unknown proton affinity of O
3
was evaluated by a "bracketing" technique and determined to be 148 ± 3 kilocalories mole
-1
at 298 kelvin, in excellent agreement with a value determined in a recent theoretical study of the O
3
/O
3
H
+
system, which was 148 kilocalories mole
-1
at zero temperature (∼149.5 kilocalories mole
-1
at 298 kelvin).
A Cascade of Structure in a Drop Falling from a Faucet
Authors: Shi X. D. , Brenner Michael P. , Nagel Sidney R.
Published: October 2006

A drop falling from a faucet is a common example of a mass fissioning into two or more pieces. The shape of the liquid in this situation has been investigated by both experiment and computer simulation. As the viscosity of the liquid is varied, the shape of the drop changes dramatically. Near the point of breakup, viscous drops develop long necks that then spawn a series of smaller necks with ever thinner diameters. Simulations indicate that this repeated formation of necks can proceed ad infinitum whenever a small but finite amount of noise is present in the experiment. In this situation, the dynamical singularity occurring when a drop fissions is characterized by a rough interface.
Worldwide Initiation of Holocene Marine Deltas by Deceleration of Sea-Level Rise
Authors: Stanley Daniel Jean , Warne Andrew G.
Published: October 2006

Radiocarbon-dated deltaic sequences of Holocene age from different parts of the world began to accumulate within a restricted time range, from about 8500 to 6500 years ago. Evaluation of major delta processes indicates that deceleration in sea-level rise was the key factor in Holocene delta formation. Within many deltas, there is as much as a 2000-year age range between basal deposits in seaward and landward cores. This age difference records the progressive landward migration of near mean sea-level depositional environments during the lower to mid-Holocene. Establishment of a chronostratigraphic framework for Holocene delta development provides a fundamental global baseline for distinguishing sea-level change from vertical land motion by tectonism and isostasy, and for evaluating rates of future marine incursion into low-lying deltas.
"Molecule Corrals" for Studies of Monolayer Organic Films
Authors: Patrick David L. , Cee Victor J. , Beebe Thomas P.
Published: October 2006

Scanning tunneling microscopy (STM) studies have demonstrated that monolayer-deep, flat-bottomed, circular etch pits can be grown on highly ordered pyrolytic graphite by high-temperature etching in the presence of oxygen. In this work, these graphite etch pits are used as "molecule corrals" to isolate ensembles of molecules for study by STM. The nucleation of self-assembled molecular films in the corrals took place by nucleation events separate from those leading to self-assembly on the surrounding terrace and allowed the measurement of the nucleation rate constant in the corrals. The dependence of the nucleation rate for self-assembly on pit size shows that nucleation occurs at open terrace sites and that step edges (that is, the corral's perimeter) and confinement inhibit film growth.
Probing Single Molecule Dynamics
Authors: Xie X. Sunney , Dunn Robert C.
Published: October 2006

The room temperature dynamics of single sulforhodamine 101 molecules dispersed on a glass surface are investigated on two different time scales with near-field optics. On the 10
-2
- to 10
2
-second time scale, intensity fluctuations in the emission from single molecules are examined with polarization measurements, providing insight into their spectroscopic properties. On the nanosecond time scale, the fluorescence lifetimes of single molecules are measured, and their excited-state energy transfer to the aluminum coating of the near-field probe is characterized. A movie of the time-resolved emission demonstrates the feasibility of fluorescence lifetime imaging with single molecule sensitivity, picosecond temporal resolution, and a spatial resolving power beyond the diffraction limit.
Lunar Laser Ranging: A Continuing Legacy of the Apollo Program
Authors: Dickey J. O. , Bender P. L. , Faller J. E. , Newhall X X , Ricklefs R. L. , Ries J. G. , Shelus P. J. , Veillet C. , Whipple A. L. , Wiant J. R. , Williams J. G. , Yoder C. F.
Published: October 2006

On 21 July 1969, during the first manned lunar mission, Apollo 11, the first retroreflector array was placed on the moon, enabling highly accurate measurements of the Earthmoon separation by means of laser ranging. Lunar laser ranging (LLR) turns the Earthmoon system into a laboratory for a broad range of investigations, including astronomy, lunar science, gravitational physics, geodesy, and geodynamics. Contributions from LLR include the three-orders-of-magnitude improvement in accuracy in the lunar ephemeris, a several-orders-of-magnitude improvement in the measurement of the variations in the moon's rotation, and the verification of the principle of equivalence for massive bodies with unprecedented accuracy. Lunar laser ranging analysis has provided measurements of the Earth's precession, the moon's tidal acceleration, and lunar rotational dissipation. These scientific results, current technological developments, and prospects for the future are discussed here.
Creation of Liquid Crystal Waveguides with Scanning Force Microscopy
Authors: Rüetschi M. , Grütter P. , Fünfschilling J. , Güntherodt H.-J.
Published: October 2006

The rubbing of a polymer layer, a commonly applied process, leads to an anisotropic surface morphology, aligning liquid crystal molecules. Scanning force microscopy can be used to intentionally create areas with a similar anisotropy by operating the instrument at loads in the range of 10
-7
to 10
-5
newtons. These areas have an orientation effect on liquid crystals indistinguishable from the rubbing process, which allows a systematic investigation of the orientation properties of an alignment layer as a function of its nanometer-scale morphology. Refractive index patterns can be tailored with this method by scratching a suitable area, as demonstrated by fabrication of an optical waveguide 6 micrometers wide and 5 millimeters long.
Measurement of Laser-Plasma Electron Density with a Soft X-ray Laser Deflectometer
Authors: Ress D. , DaSilva L. B. , London R. A. , Trebes J. E. , Mrowka S. , Procassini R. J. , Barbee T. W. , Lehr D. E.
Published: October 2006

A soft x-ray laser (wavelength λ = 15.5 nanometers) was used to create a moiré deflectogram of a high-density, laser-produced plasma. The use of deflectometry at this short wavelength permits measurement of the density spatial profile in a long-scalelength (3 millimeters), high-density plasma. A peak density of 3.2 × 10
21
per cubic centimeter was recorded.
Arctic Ocean Gravity Field Derived From ERS-1 Satellite Altimetry
Authors: Laxon Seymour , McAdoo David
Published: October 2006

The derivation of a marine gravity field from satellite altimetry over permanently ice-covered regions of the Arctic Ocean provides much new geophysical information about the structure and development of the Arctic sea floor. The Arctic Ocean, because of its remote location and perpetual ice cover, remains from a tectonic point of view the most poorly understood ocean basin on Earth. A gravity field has been derived with data from the ERS-1 radar altimeter, including permanently ice-covered regions. The gravity field described here clearly delineates sections of the Arctic Basin margin along with the tips of the Lomonosov and Arctic mid-ocean ridges. Several important tectonic features of the Amerasia Basin are clearly expressed in this gravity field. These include the Mendeleev Ridge; the Northwind Ridge; details of the Chukchi Borderland; and a north-south trending, linear feature in the middle of the Canada Basin that apparently represents an extinct spreading center that "died" in the Mesozoic. Some tectonic models of the Canada Basin have proposed such a failed spreading center, but its actual existence and location were heretofore unknown.