bluuebunny/crossref_metadata_2025 huggingface dataset:
Climate Forcing by Anthropogenic Aerosols
Authors: Charlson R. J. , Schwartz S. E. , Hales J. M. , Cess R. D. , Coakley J. A. , Hansen J. E. , Hofmann D. J.
Published: October 2006

Although long considered to be of marginal importance to global climate change, tropospheric aerosol contributes substantially to radiative forcing, and anthropogenic sulfate aerosol in particular has imposed a major perturbation to this forcing. Both the direct scattering of short-wavelength solar radiation and the modification of the shortwave reflective properties of clouds by sulfate aerosol particles increase planetary albedo, thereby exerting a cooling influence on the planet. Current climate forcing due to anthropogenic sulfate is estimated to be –1 to –2 watts per square meter, globally averaged. This perturbation is comparable in magnitude to current anthropogenic greenhouse gas forcing but opposite in sign. Thus, the aerosol forcing has likely offset global greenhouse warming to a substantial degree. However, differences in geographical and seasonal distributions of these forcings preclude any simple compensation. Aerosol effects must be taken into account in evaluating anthropogenic influences on past, current, and projected future climate and in formulating policy regarding controls on emission of greenhouse gases and sulfur dioxide. Resolution of such policy issues requires integrated research on the magnitude and geographical distribution of aerosol climate forcing and on the controlling chemical and physical processes.
Diffusion Creep in Perovskite: Implications for the Rheology of the Lower Mantle
Authors: Karato Shun-Ichiro , Li Ping
Published: October 2006

High-temperature creep experiments on polycrystalline perovskite (CaTiO
3
), an analog of (Mg,Fe)SiO
3
perovskite of the lower mantle, suggest that (grain size-sensitive) diffusion creep is important in the lower mantle and show that creep rate is enhanced by the transformation from the orthorhombic to the tetragonal structure. These observations suggest that grain-size reduction after a subducting slab passes through the 670-kilometer discontinuity or after a phase transformation from orthorhombic to tetragonal in perovskite will result in rheological softening in the top portions of the lower mantle.
Explosives Detection for Aviation Security
Authors: Fainberg Anthony
Published: October 2006

The threat of terrorism against commercial aviation has received much attention in the past few years. In response, new ways to detect explosives and to combine techniques based on different phenomena into integrated security systems are being developed to improve aviation security. Several leading methods for explosives and weapons detection are presented.
Diamond from the Dabie Shan Metamorphic Rocks and Its Implication for Tectonic Setting
Authors: Shutong Xu , Wen Su , Yican Liu , Laili Jiang , Shouyuan Ji , Okay A. I. , Sengör A. M. C.
Published: October 2006

Diamond occurs in ultrahigh pressure metamorphic rocks from Dabie Shan, Anhui Province, eastern China. Diamond-bearing rocks include eclogite, gamet-pyroxenite, and jadeitite. Diamond occurs in a mineral assemblage with coesite and jadeite. The diamonds and diamondiferous rocks of Dabie Shan are interpreted to be the products of ultrahigh pressure metamorphism in the underthrust basement of the Yangtze continental plate during the early Mesozoic, at greater than 4.0 gigapascals and 900°C. This interpretation is based on the distribution of rock units, the stability field of diamond, and isotopic data indicating a crustal origin for the rocks. Most diamonds occur as euhedral inclusions in garnets and are 10 to 60 micrometers across, although some are up to 700 micrometers across.
Hybridization of Bird Species
Authors: Grant Peter R. , Grant B. Rosemary
Published: October 2006

Hybridization, the interbreeding of species, provides favorable conditions for major and rapid evolution to occur. In birds it is widespread. Approximately one in ten species is known to hybridize, and the true global incidence is likely to be much higher. A longitudinal study of Darwin's finch populations on a Galápagos island shows that hybrids exhibit higher fitness than the parental species over several years. Hybrids may be at an occasional disadvantage for ecological rather than genetic reasons in this climatically fluctuating environment. Hybridization presents challenges to the reconstruction of phylogenies, formulation of biological species concepts and definitions, and the practice of biological conservation.
Recognition of Paleobiochemicals by a Combined Molecular Sulfur and Isotope Geochemical Approach
Authors: Kohnen Math E. L. , Schouten Stefan , Damsté Jaap S. Sinninghe , de Leeuw Jan W. , Merritt Dawn A. , Hayes J. M.
Published: October 2006

Study of organic matter in immature sediments from a Messinian evaporitic basin shows that consideration of structures, modes of occurrence, and carbon isotopic compositions of free and sulfur-bound carbon skeletons allow identification of biochemical precursors. Detailed information concerning biotic communities present during deposition of sediments can be retrieved in this way. Moreover, unprecedented biochemicals were recognized; these extend the horizon of biomarker geochemistry.
Reciprocal Regulation of Adipogenesis by Myc and C/EBPα
Authors: Freytag Svend O. , Geddes Tim J.
Published: October 2006

3T3-L1 adipoblasts that express large amounts of c-Myc cannot terminally differentiate, raising the possibility that Myc inhibits the expression of genes that promote adipogenesis. The CCAAT/enhancer binding protein (C/EBPα) is induced during 3T3-L1 adipogenesis when cells commit to the differentiation pathway. Transfection of 3T3-L1 adipoblasts with the gene that encodes C/EBPα caused overt expression of the adipocyte morphology. Expression of Myc prohibited the normal induction of C/EBPα and prevented adipogenesis. Enforced expression of C/EBPα overcame the Myc-induced block to differentiation. These results provide a molecular basis for the regulation of adipogenesis and implicate Myc and C/EBPα as pivotal controlling elements.
Designed Enediynes: A New Class of DNA-Cleaving Molecules with Potent and Selective Anticancer Activity
Authors: Nicolaou K. C. , Dai W.-M. , Tsay S.-C. , Estevez V. A. , Wrasidlo W.
Published: October 2006

The rational design and biological actions of a new class of DNA-cleaving molecules with potent and selective anticancer activity are reported. These relatively simple enediyne-type compounds were designed from basic chemical principles to mimic the actions of the rather complex naturally occurring enediyne anticancer antibiotics, particularly dynemicin A. Equipped with locking and triggering devices, these compounds damage DNA in vitro and in vivo on activation by chemical or biological means. Their damaging effects are manifested in potent anticancer activity with remarkable selectivities. Their mechanism of action involves intracellular unlocking and triggering of a Bergman reaction, leading to highly reactive benzenoid diradicals that cause severe DNA damage. The results of these studies demonstrate the potential of these de novo designed molecules as biotechnology tools and anticancer agents.
Heteromeric NMDA Receptors: Molecular and Functional Distinction of Subtypes
Authors: Monyer Hannah , Sprengel Rolf , Schoepfer Ralf , Herb Anne , Higuchi Miyoko , Lomeli Hilda , Burnashev Nail , Sakmann Bert , Seeburg Peter H.
Published: October 2006

The
N
-methyl D-aspartate (NMDA) receptor subtype of glutamate-gated ion channels possesses high calcium permeability and unique voltage-dependent sensitivity to magnesium and is modulated by glycine. Molecular cloning identified three complementary DNA species of rat brain, encoding NMDA receptor subunits NMDAR2A (NR2A), NR2B, and NR2C, which are 55 to 70% identical in sequence. These are structurally related, with less than 20% sequence identity, to other excitatory amino acid receptor subunits, including the NMDA receptor subunit NMDAR1 (NR1). Upon expression in cultured cells, the new subunits yielded prominent, typical glutamate- and NMDA-activated currents only when they were in heteromeric configurations with NR1. NR1-NR2A and NR1-NR2C channels differed in gating behavior and magnesium sensitivity. Such heteromeric NMDA receptor subtypes may exist in neurons, since NR1 messenger RNA is synthesized throughout the mature rat brain, while NR2 messenger RNA show a differential distribution.
How to Make Water Run Uphill
Authors: Chaudhury Manoj K. , Whitesides George M.
Published: October 2006

A surface having a spatial gradient in its surface free energy was capable of causing drops of water placed on it to move uphill. This motion was the result of an imbalance in the forces due to surface tension acting on the liquid-solid contact line on the two opposite sides ("uphill" or "downhill") of the drop. The required gradient in surface free energy was generated on the surface of a polished silicon wafer by exposing it to the diffusing front of a vapor of decyltrichlorosilane, Cl
3
Si(CH
2
)
9
CH
3
. The resulting surface displayed a gradient of hydrophobicity (with the contact angle of water changing from 97° to 25°) over a distance of 1 centimeter. When the wafer was tilted from the horizontal plane by 15°, with the hydrophobic end lower than the hydrophilic, and a drop of water (1 to 2 microliters) was placed at the hydrophobic end, the drop moved toward the hydrophilic end with an average velocity of ∼1 to 2 millimeters per second. In order for the drop to move, the hysteresis in contact angle on the surface had to be low (≤10°).
Chaotic Evolution of the Solar System
Authors: Sussman Gerald Jay , Wisdom Jack
Published: October 2006

The evolution of the entire planetary system has been numerically integrated for a time span of nearly 100 million years. This calculation confirms that the evolution of the solar system as a whole is chaotic, with a time scale of exponential divergence of about 4 million years. Additional numerical experiments indicate that the Jovian planet subsystem is chaotic, although some small variations in the model can yield quasiperiodic motion. The motion of Pluto is independently and robustly chaotic.
Induction of Pre-Infection Thread Structures in the Leguminous Host Plant by Mitogenic Lipo-Oligosaccharides of
Rhizobium
Authors: van Brussel Anton A. N. , Bakhuizen Robert , van Spronsen Paulina C. , Spaink Herman P. , Tak Teun , Lugtenberg Ben J. J. , Kijne Jan W.
Published: October 2006

Root nodules of leguminous plants are symbiotic organs in which
Rhizobium
bacteria fix nitrogen. Their formation requires the induction of a nodule meristem and the formation of a tubular structure, the infection thread, through which the rhizobia reach the nodule primordium. In the
Rhizobium
host plants pea and vetch, pre-infection thread structures always preceded the formation of infection threads. These structures consisted of cytoplasmic bridges traversing the central vacuole of outer cortical root cells, aligned in radial rows. In vetch, the site of the infection thread was determined by the plant rather than by the invading rhizobia. Like nodule primordia, pre-infection thread structures could be induced in the absence of rhizobia provided that mitogenic lipo-oligosaccharides produced by
Rhizobium leguminosarum
biovar viciae were added to the plant. In this case, cells in the two outer cortical cell layers containing cytoplasmic bridges may have formed root hairs. A common morphogenetic pathway may be shared in the formation of root hairs and infection threads.
Increasing Rates of Atmospheric Mercury Deposition in Midcontinental North America
Authors: Swain Edward B. , Engstrom Daniel R. , Brigham Mark E. , Henning Thomas A. , Brezonik Patrick L.
Published: October 2006

Mercury contamination of remote lakes has been attributed to increasing deposition of atmospheric mercury, yet historic deposition rates and inputs from terrestrial sources are essentially unknown. Sediments of seven headwater lakes in Minnesota and Wisconsin were used to reconstruct regional modern and preindustrial deposition rates of mercury. Whole-basin mercury fluxes, determined from lake-wide arrays of dated cores, indicate that the annual deposition of atmospheric mercury has increased from 3.7 to 12.5 micrograms per square meter since 1850 and that 25 percent of atmospheric mercury deposition to the terrestrial catchment is exported to the lake. The deposition increase is similar among sites, implying regional or global sources for the mercury entering these lakes.
Synthesis of Fluoropolymers in Supercritical Carbon Dioxide
Authors: DeSimone J. M. , Guan Zihibin , Elsbernd C. S.
Published: October 2006

Fluoropolymers are used in many technologically demanding applications because of their balance of high-performance properties. A significant impediment to the synthesis of variants of commercially available amorphous fluoropolymers is their general insolubility in most solvents except chlorofluorocarbons (CFCs). The environmental concerns about CFCs can be circumvented by preparing these technologically important materials in supercritical fluids. The homogeneous solution polymerization of highly fluorinated acrylic monomers can be achieved in supercritical carbon dioxide by using free radical methods. In addition, detailed decomposition rates and efficiency factors were measured for azobisisobutyronitrile in supercritical carbon dioxide and were compared to those obtained with conventional liquid solvents.
Structure-Based Strategies for Drug Design and Discovery
Authors: Kuntz Irwin D.
Published: October 2006

Most drugs have been discovered in random screens or by exploiting information about macromolecular receptors. One source of this information is in the structures of critical proteins and nucleic acids. The structure-based approach to design couples this information with specialized computer programs to propose novel enzyme inhibitors and other therapeutic agents. Iterated design cycles have produced compounds now in clinical trials. The combination of molecular structure determination and computation is emerging as an important tool for drug development. These ideas will be applied to acquired immunodeficiency syndrome (AIDS) and bacterial drug resistance.
Short-Lived Radioactivity and Magma Genesis
Authors: Gill James , Condomines Michel
Published: October 2006

Short-lived decay products of uranium and thorium have half-lives and chemistries sensitive to the processes and time scales of magma genesis, including partial melting in the mantle and magmatic differentiation in the crust. Radioactive disequilibrium between
238
U,
230
Th, and
226
Ra is widespread in volcanic rocks. These disequilibria and the isotopic composition of thorium depend especially on the extent and rate of melting as well as the presence and composition of vapor during melting. The duration of mantle melting may be several hundred millennia, whereas ascent times are a few decades to thousands of years. Differentiation of most magmas commonly occurs within a few millennia, but felsic ones can be tens of millennia old upon eruption.
Uranium Stabilization of C
28
: A Tetravalent Fullerene
Authors: Guo Ting , Diener M. D. , Chai Yan , Alford M. J. , Haufler R. E. , McClure S. M. , Ohno T. , Weaver J. H. , Scuseria G. E. , Smalley R. E.
Published: October 2006

Laser vaporization experiments with graphite in a supersonic cluster beam apparatus indicate that the smallest fullerene to form in substantial abundance is C
28
. Although ab initio quantum chemical calculations predict that this cluster will favor a tetrahedral cage structure, it is electronically open shell. Further calculations reveal that C
28
in this structure should behave as a sort of hollow superatom with an effective valence of 4. This tetravalence should be exhibited toward chemical bonding both on the outside and on the inside of the cage. Thus, stable closed-shell derivatives of C
28
with large highest occupied molecular orbital—lowest unoccupied molecular orbital gaps should be attainable either by reacting at the four tetrahedral vertices on the outside of the C
28
cage to make, for example, C
28
H
4
, or by trapping a tetravalent atom inside the cage to make endothedral fullerenes such as Ti@C
28
. An example of this second, inside route to C
28
stabilization is reported here: the laser and carbon-arc production of U@C
28
.
Responses to Elevated Carbon Dioxide in Artificial Tropical Ecosystems
Authors: Körner Christian , Arnone John A.
Published: October 2006

Carbon, nutrient, and water balance as well as key plant and soil processes were simultaneously monitored for humid tropical plant communities treated with CO
2
-enriched atmospheres. Despite vigorous growth, no significant differences in stand biomass (of both the understory and overstory), leaf area index, nitrogen or water consumption, or leaf stomatal behavior were detected between ambient and elevated CO
2
treatments. Major responses under elevated CO
2
included massive starch accumulation in the tops of canopies, increased fine-root production, and a doubling of CO
2
evolution from the soil. Stimulated rhizosphere activity was accompanied by increased loss of soil carbon and increased mineral nutrient leaching. This study points at the inadequacy of scaling-up from physiological baselines to ecosystems without accounting for interactions among components, and it emphasizes the urgent need for whole-system experimental approaches in global-change research.
The Present Is Not the Key to the Past: A Polar Forest from the Permian of Antarctica
Authors: Taylor Edith L. , Taylor Thomas N. , Cúneo N. Rubén
Published: October 2006

An in situ Upper Permian fossil forest in the central Transantarctic Mountains near the Beardmore Glacier includes 15 permineralized trunks in growth position; the paleolatitude of the site was approximately 80° to 85° south. Numerous leaves of the seed fern
Glossopteris
are present in the shale in which the trunks are rooted. The trunks are permineralized and tree rings reveal that the forest was a rapidly growing and young forest, persisting in an equable, strongly seasonal climate—a scenario that does not fit with some climate reconstructions for this time period.
Tonic Activation of NMDA Receptors by Ambient Glutamate Enhances Excitability of Neurons
Authors: Sah P. , Hestrin S. , Nicoll R. A.
Published: October 2006

Voltage clamp recordings and noise analysis from pyramidal cells in hippocampal slices indicate that
N
-methyl-D-aspartate (NMDA) receptors are tonically active. On the basis of the known concentration of glutamate in the extracellular fluid, this tonic action is likely caused by the ambient glutamate level. NMDA receptors are voltage-sensitive, thus background activation of these receptors imparts a regenerative electrical property to pyramidal cells, which facilitates the coupling between dendritic excitatory synaptic input and somatic action potential discharge in these neurons.
Neoplastic Transformation of Human Epidermal Keratinocytes by AD12-SV40 and Kirsten Sarcoma Viruses
Authors: Rhim Johng S. , Jay Gilbert , Arnstein Paul , Price Floyd M. , Sanford Katherine K. , Aaronson Stuart A.
Published: October 2006

Recent investigations have begun to dissect the number and nature of genetic alterations associated with cancer cells. In the present study, primary human epidermal keratinocytes acquired indefinite life-span in culture but did not undergo malignant conversion in response to infection with a hybrid of adenovirus 12 and simian virus 40. Addition of Kirsten murine sarcoma virus, which contains a K-
ras
oncogene, to these cells induced morphological alterations associated with the acquisition of neoplastic properties. These findings demonstrate the malignant transformation of human primary epithelial cells in culture and support a multiple-step process for neoplastic conversion.
Seismic Tomogram of the Earth's Mantle: Geodynamic Implications
Authors: Fukao Yoshio
Published: October 2006

Recent seismic tomography of the Earth's mantle has revealed a large-scale pattern of mantle convection comprising upwelling columnar plumes in the Pacific and Africa and downwelling planar sheets along the Circum Pacific. Upwelling and downwelling occur most extensively under the south Pacific and west Pacific, respectively. High-resolution image of plate subduction has been obtained from the dense seismic networks around Japan. Japanese seismologists are in the best position to resolve the internal structure of downwelling current as an integral part of the whole convection system.
Radar Mapping of Mercury: Full-Disk Images and Polar Anomalies
Authors: Harmon J. K. , Slade M. A.
Published: October 2006

A random-code technique has been used at Arecibo to obtain delay-Doppler radar images of the full disk of Mercury. Anomalously bright features were found at the north and south poles. The north polar feature is oblong (4° by 8°) and offset from the pole. The smaller south polar feature is mostly confined to the floor of the crater Chao Meng-Fu. The polar locations and radar properties of these features indicate that they may be produced by volume scattering in ice. The images also reveal a variety of more subdued reflectivity features ranging in size from hundreds to thousands of kilometers; some of these appear to have an impact origin.
Strange Floral Attractors: Pollinator Attraction and the Evolution of Plant Sexual Systems
Authors: Podolsky Robert D.
Published: October 2006

Individual plants of hummingbird-pollinated
Besleria triflora
display two flower morphs: staminate flowers, which have shortened styles and do not produce fruit, and hermaphrodite flowers. Experiments with
B. triflora
indicate that pollinator attraction can drive the evolution of a dimorphic plant sexual system. In field-manipulated plants, visitation increased at large floral displays; however, pollen receipt increased only when staminate flowers were used to enlarge the display. Laboratory experiments showed that staminate flowers do not remove pollen from visiting pollinators, effectively concentrating outcross pollen onto stigmas of fertile flowers. A dimorphic sexual system is favored because the morphology of staminate flowers enhances their role in pollinator attraction.
A Liquid-Solution-Phase Synthesis of Crystalline Silicon
Authors: Heath James R.
Published: October 2006

A liquid-solution-phase technique for preparing submicrometer-sized silicon single crystals is presented. The synthesis is based on the reduction of SiCl
4
and RSiCl
3
(R = H, octyl) by sodium metal in a nonpolar organic solvent at high temperatures (385°C) and high pressures (>100 atmospheres). For R = H, the synthesis produces hexagonal-shaped silicon single crystals ranging from 5 to 3000 nanometers in size. For R = octyl, the synthesis also produces hexagonal-shaped silicon single crystals; however, the size range is controlled to 5.5 ± 2.5 nanometers.
Micropaleontological Evidence for Increased Meridional Heat Transport in the North Atlantic Ocean During the Pliocene
Authors: Dowsett Harry J. , Cronin Thomas M. , Poore Richard Z. , Thompson Robert S. , Whatley Robin C. , Wood Adrian M.
Published: October 2006

The Middle Pliocene (∼3 million years ago) has been identified as the last time the Earth was significantly warmer than it was during the Last Interglacial and Holocene. A quantitative micropaleontological paleotemperature transect from equator to high latitudes in the North Atlantic indicates that Middle Pliocene warmth involved increased meridional oceanic heat transport.
Abrupt Uplift Within the Past 1700 Years at Southern Puget Sound, Washington
Authors: Bucknam Robert C. , Hemphill-Haley Eileen , Leopold Estella B.
Published: October 2006

Shorelines rose as much as 7 meters along southern Puget Sound and Hood Canal between 500 and 1700 years ago. Evidence for this uplift consists of elevated wave-cut shore platforms near Seattle and emerged, peat-covered tidal flats as much as 60 kilometers to the southwest. The uplift was too rapid for waves to leave intermediate shorelines on even the best preserved platform. The tidal flats also emerged abruptly; they changed into freshwater swamps and meadows without first becoming tidal marshes. Where uplift was greatest, it adjoined an inferred fault that crosses Puget Sound at Seattle and it probably accompanied reverse slip on that fault 1000 to 1100 years ago. The uplift and probable fault slip show that the crust of the North America plate contains potential sources of damaging earthquakes in the Puget Sound region.
Paleoearthquakes in the Puget Sound Region Recorded in Sediments from Lake Washington, U.S.A
Authors: Karlin Robert E. , Abella Sally E. B.
Published: October 2006

Holocene sediments in Lake Washington contain a series of turbidites that were episodically deposited throughout the lake. The magnetic signatures of these terrigenous layers are temporally and areally correlatable. Large earthquakes appear to have triggered slumping on the steep basin walls and landslides in the drainage area, resulting in turbidite deposition. One prominent turbidite appears to have been deposited about 1100 years ago as the result of a large earthquake. Downcore susceptibility patterns suggest that near-simultaneous slumping occurred in at least three separate locations, two of which now contain submerged forests. Several other large earthquakes may have occurred in the last 3000 years.
Purification, Cloning, and Expression of Ciliary Neurotrophic Factor (CNTF)
Authors: Lin Leu-Fen H. , Mismer Drzislav , Lile Jack D. , Armes Lyman G. , Butler Eugene T. , Vannice James L. , Collins Frank
Published: October 2006

Ciliary neurotrophic factor (CNTF) is one of a small number of proteins with neurotrophic activities distinct from nerve growth factor (NGF). CNTF has now been purified and cloned and the primary structure of CNTF from rabbit sciatic nerve has been determined. Biologically active CNTF has been transiently expressed from a rabbit complementary DNA clone. CNTF is a neural effector without significant sequence homologies to any previously reported protein.
Single Crystal Metals Encapsulated in Carbon Nanoparticles
Authors: Ruoff Rodney S. , Lorents Donald C. , Chan Bryan , Malhotra Ripudaman , Subramoney Shekhar
Published: October 2006

Single-domain microcrystals of LaC
2
encapsulated within nanoscale polyhedral carbon particles have been synthesized in a carbon arc. Typical particle sizes are on the order of 20 to 40 nanometers. The stoichiometry and phase of the La-containing crystals have been assigned from characteristic lattice spacings observed by high-resolution transmission electron microscopy and energy dispersive spectroscopy (EDS). EDS spectra show that La and C are the only elements present. Characteristic interatomic distances of 3.39 and 2.78 angstroms identify the compound inside the nanoparticle cavities as α-LaC
2
, the phase of LaC
2
that is stable at room temperature. Bulk α-LaC
2
is metallic and hydrolytic. Observation of crystals of pure encapsulated α-LaC
2
that were exposed to air for several days before analysis indicates that the LaC
2
is protected from degradation by the carbon polyhedral shells of the nanoparticles. A high percentage of the carbon nanoparticles have encapsulated LaC
2
single crystals. These carbon-coated metal crystals form a new class of materials that can be protected in their pure or carbide forms and may have interesting and useful properties.
Evidence from Claw Geometry Indicating Arboreal Habits of
Archaeopteryx
Authors: Feduccia Alan
Published: October 2006

The Late Jurassic
Archaeopteryx
has been thought to have been a feathered predator adapted to running that represented a terrestrial stage in the evolution of true birds from coelurosaurian dinosaurs. Examination of claw geometry, however, shows that (i) modern ground- and tree-dwelling birds can be distinguished on the basis of claw curvature, in that greater claw arcs characterize tree-dwellers and trunk-climbers, and (ii) the claws of the pes (hind foot) and manus (front hand) of
Archaeopteryx
exhibit degrees of curvature typical of perching and trunk-climbing birds, respectively. On this basis,
Archaeopteryx
appears to have been a perching bird, not a cursorial predator.
Molecular Positional Order in Langmuir-Blodgett Films by Atomic Force Microscopy
Authors: Bourdieu L. , Ronsin O. , Chatenay D.
Published: October 2006

Langmuir-Blodgett films of barium arachidate have been studied on both macroscopic and microscopic scales by atomic force microscopy. As prepared, the films exhibit a disordered hexagonal structure; molecularly resolved images in direct space establish a connection between the extent of the positional order and the presence of defects such as dislocations. Upon heating, the films reorganize into a more condensed state with a centered rectangular crystallographic arrangement; in this new state the films exhibit long-range positional order and unusual structural features, such as a height modulation of the arachidic acid molecules.
Evidence for Photochemical Formation of H
2
O
2
and Oxidation of SO
2
in Authentic Fog Water
Authors: Zuo Yuegang , Hoigné Jürg
Published: October 2006

When samples of rain and fog water were exposed to ultraviolet and visible light, reactive transients such as hydrogen peroxide were formed and dissolved organic matter and sulfur dioxide were depleted. These results, in conjunction with those from previous studies, imply that dissolved organic compounds and transition metals such as iron ions are involved in the photochemical formation of hydrogen peroxide and other photooxidants in atmospheric waters.
The Drift of Saturn's North Polar Spot Observed by the Hubble Space Telescope
Authors: Caldwell John , Turgeon Benoit , Hua Xin-Min , Barnet Christopher D. , Westphal James A.
Published: October 2006

Polar projections of 50 images of Saturn at 889 nanometers and 25 images at 718 nanometers taken by the Hubble Space Telescope in November 1990, as well as 3 images at each wavelength taken in June 1991, have been examined. Among them, 31 show the north polar spot, which is associated with Saturn's polar hexagon, in locations suitable for measurement. In each image, planetocentric coordinates of the polar spot were determined, and the movement of the spot with respect to Saturn's system III rotation rate was studied. During the period of observation, the polar spot had first a short-term westward movement and then a long-term eastward drift. The rate of the long-term drift was –0.060 ± 0.008 degrees per day with respect to system III, approximately 50 percent greater than previously determined from Voyager. The original 1980 and 1981 Voyager data were combined with the new Hubble images to form an 11-year base line. The eastward drift over the longer period was –0.0569 degrees per day. The long-term drift could be due to uncertainty in the standard value of the internal rotation period, which is 810.7939 ± 0.148 degrees per 24-hour day. The short-term movement in November 1990 has a rate that is greater in magnitude but opposite in sign and probably represents a real, transient motion of the spot relative to the internal rotation system.
Removal of Contaminants from Soils by Electric Fields
Authors: Probstein Ronald F. , Hicks R. Edwin
Published: October 2006

Application of a direct-current electric field in soils that contain contaminated liquids is expected to produce an important in situ means of environmental restoration. The electric field induces a motion of the liquid and dissolved ions that transports the contaminants to wells for removal. Electrode chemistry plays an important role, and reagents can be introduced at the electrodes to enhance contaminant removal rates. Experiments and modeling demonstrate high degrees of contaminant removal, propagation of sharp acid and base wave fronts from the electrodes, and a "focusing" effect by which metals accumulate in regions of the soil.
Manganese Oxide Octahedral Molecular Sieves: Preparation, Characterization, and Applications
Authors: Shen Y. F. , Zerger R. P. , DeGuzman R. N. , Suib S. L. , McCurdy L. , Potter D. I. , O'Young C. L.
Published: October 2006

A thermally stable 3 × 3 octahedral molecular sieve corresponding to natural todorokite (OMS-1) has been synthesized by autoclaving layer-structure manganese oxides, which are prepared by reactions of MnO
4
-
and Mn
2+
under markedly alkaline conditions. The nature and thermal stability of products depend strongly on preparation parameters, such as the MnO
4
-
/Mn
2+
ratio, pH, aging, and autoclave conditions. The purest and the most thermally stable todorokite is obtained at a ratio of 0.30 to 0.40. Autoclave treatments at about 150° to 180°C for more than 2 days yield OMS-1, which is as thermally stable (500°C) as natural todorokite minerals. Adsorption data give a tunnel size of 6.9 angstroms and an increase of cyclohexane or carbon tetrachloride uptake with dehydration temperature up to 500°C. At 600°C, the tunnel structure collapses. Both Lewis and Brönsted acid sites have been observed in OMS-1. Particular applications of these materials include adsorption, electrochemical sensors, and oxidation catalysis.
The Relation Between Biological Activity of the Rain Forest and Mineral Composition of Soils
Authors: Lucas Y. , Luizao F. J. , Chauvel A. , Rouiller J. , Nahon D.
Published: October 2006

In most soils of the humid tropics, kaolinitic topsoil horizons overlie more gibbsitic horizons. This arrangement cannot be produced simply by leaching. Quantitative measurement of the turnover of chemical elements in the litterfall in an Amazonian ecosystem indicates that the forest cycles a significant amount of elements, particularly silicon. As a result, fluids that percolate through topsoil horizons already contain dissolved silicon. This effect keeps silicon from being leached down and may account for the stability of kaolinite in the soil upper horizons. The soil mineral composition is thus maintained by biological activity.
Tectonics and Volcanism of Eastern Aphrodite Terra, Venus: No Subduction, No Spreading
Authors: Hansen Vicki L. , Phillips Roger J.
Published: October 2006

Eastern Aphrodite Terra, a deformed region with high topographic relief on Venus, has been interpreted as analogous to a terrestrial extensional or convergent plate boundary. However, analysis of geological and structural relations indicates that the tectonics of eastern Aphrodite Terra is dominated by blistering of the crust by magma diapirs. The findings imply that, within this region, vertical tectonism dominates over horizontal tectonism and, consequently, that this region is neither a divergent nor a convergent plate boundary.
Van der Waals Epitaxial Growth of α-Alumina Nanocrystals on Mica
Authors: Steinberg S. , Ducker W. , Vigil G. , Hyukjin C. , Frank C. , Tseng M. Z. , Clarke D. R. , Israelachvili J. N.
Published: October 2006

Lattice mismatch stresses, which severely restrict heteroepitaxial growth, are greatly minimized when thin alumina films are grown by means of van der Waals forces on inert mica substrates. A 10-nanometer-thick epitaxial film exhibits crystallographic sixfold symmetry, a lattice constant close to that of the basal plane [0001] of α-alumina (sapphire), and an aluminum:oxygen atomic ratio of 1:1.51 ± 0.02 (measured by x-ray photoelectron spectroscopy), again the same as for bulk sapphire. The film is free of steps and grain boundaries over large areas and appears to be an ideal model system for studying adhesion, tribology, and other surface phenomena at atomic scales.
A Large Drop in Atmospheric
14
C/
12
C and Reduced Melting in the Younger Dryas, Documented with
230
Th Ages of Corals
Authors: Edwards R. Lawrence , Beck J. Warren , Burr G. S. , Donahue D. J. , Chappell J. M. A. , Bloom A. L. , Druffel E. R. M. , Taylor F. W.
Published: October 2006

Paired carbon-14 (
14
C) and thorium-230(
230
Th) ages were determined on fossil corals from the Huon Peninsula, Papua New Guinea. The ages were used to calibrate part of the
14
C time scale and to estimate rates of sea-level rise during the last deglaciation. An abrupt offset between the
14
C and
230
Th ages suggests that the atmospheric
14
C/
12
C ratio dropped by 15 percent during the latter part of and after the Younger Dryas (YD). This prominent drop coincides with greatly reduced rates of sea-level rise. Reduction of melting because of cooler conditions during the YD may have caused an increase in the rate of ocean ventilation, which caused the atmospheric
14
C/
12
C ratio to fall. The record of sea-level rise also shows that globally averaged rates of melting were relatively high at the beginning of the YD. Thus, these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the Mississippi to the St. Lawrence River triggered the YD event.
Deceleration of Interstellar Hydrogen at the Heliospheric Interface
Authors: Lallement Rosine , Bertaux Jean-Loup , Clarke John T.
Published: October 2006

High-resolution spectra of nearby stars show absorption lines due to material in the local interstellar cloud. This cloud is deduced to be moving at 26 kilometers per second with respect to the sun, and in the same direction as the "interstellar wind" flowing through the solar system. Measurements by the Ulysses spacecraft show that neutral helium is drifting through the solar system at the same velocity, but neutral hydrogen appears to be moving at only 20 kilometers per second, a result confirmed by new measurements of the hydrogen emission line taken by the High-Resolution Spectrograph on the Hubble Space Telescope. These results indicate that neutral hydrogen atoms from the local interstellar cloud are preferentially decelerated at the heliospheric interface, most likely by charge-exchange with interstellar protons, while neutral helium is unaffected by the plasma. The magnitude of the observed deceleration implies an interstellar plasma density of 0.06 to 0.10 per cubic centimeter, which in turn implies that the heliospheric shock should be less than 100 astronomical units from the sun.
A 3620-Year Temperature Record from
Fitzroya cupressoides
Tree Rings in Southern South America
Authors: Lara Antonio , Villalba Ricardo
Published: October 2006

A tree-ring width chronology of alerce trees (
Fitzroya cupressoides
) from southern Chile was used to produce an annually resolved 3622-year reconstruction of departures from mean summer temperatures (December to March) for southern South America. The longest interval with above-average temperatures was from 80 B.C. to A.D. 160. Long intervals with below-average temperatures were recorded from A.D. 300 to 470 and from A.D. 1490 to 1700. Neither this proxy temperature record nor instrumental data for southern South America for latitudes between 35° and 44°S provide evidence of a warming trend during the last decades of this century that could be related to anthropogenic causes. The data also indicate that alerce is the second longest living tree after the bristlecone pine (
Pinus longaeva
).
Helium-3 from the Mantle: Primordial Signal or Cosmic Dust?
Authors: Anderson Don L.
Published: October 2006

Helium-3 in hotspot magmas has been used as unambiguous evidence for the existence of a primordial, undegassed reservoir deep in the Earth's mantle. However, a large amount of helium-3 is delivered to the Earth's surface by interplanetary dust particles (IDPs). Recycling of deep-sea sediments containing these particles to the mantle, and eventual incorporation in magma, can explain the high helium-3/helium-4 ratios of hotspot magmas. Basalts with high helium-3/helium-4 ratios may represent degassing of helium introduced by ancient (probably 1.5 to 2.0 billion years old) pelagic sediments rather than degassing of primordial lower mantle material brought to the surface in plumes. Influx of IDPs can also explain the neon and siderophile compositions of mantle samples.
Evidence of Thermal Metamorphism on the C, G, B, and F Asteroids
Authors: Hiroi Takahiro , Pieters Carlé M. , Zolensky Michael E. , Lipschutz Michael E.
Published: October 2006

Reflectance spectra (0.3 to 2.6 micrometers) of 14 C, G, B, and F asteroids and 21 carbonaceous chondrite powders are compared in detail. Only three thermally metamorphosed CM-Cl chondrites that have a weak ultraviolet absorption are shown to have close counterparts among those asteroids. Reflectance spectra of heated Murchison CM2 chondrite are compared with the average C and G type asteroid spectra. Murchison heated at 600° to 1000°C exhibits a similar weak ultraviolet absorption and provides the best analog for those spectra. Comparison of ultraviolet absorption strengths between 160 C, G, B, and F asteroids and carbonaceous chondrites suggests that surface minerals of most of those asteroids are thermally metamorphosed at temperatures around 600° to 1000°C.
Crystallization at Inorganic-organic Interfaces: Biominerals and Biomimetic Synthesis
Authors: Mann Stephen , Archibald Douglas D. , Didymus Jon M. , Douglas Trevor , Heywood Brigid R. , Meldrum Fiona C. , Reeves Nicholas J.
Published: October 2006

Crystallization is an important process in a wide range of scientific disciplines including chemistry, physics, biology, geology, and materials science. Recent investigations of biomineralization indicate that specific molecular interactions at inorganic-organic interfaces can result in the controlled nucleation and growth of inorganic crystals. Synthetic systems have highlighted the importance of electrostatic binding or association, geometric matching (epitaxis), and stereochemical correspondence in these recognition processes. Similarly, organic molecules in solution can influence the morphology of inorganic crystals if there is molecular complementarity at the crystal-additive interface. A biomimetic approach based on these principles could lead to the development of new strategies in the controlled synthesis of inorganic nanophases, the crystal engineering of bulk solids, and the assembly of organized composite and ceramic materials.
Comparisons Between Seismic Earth Structures and Mantle Flow Models Based on Radial Correlation Functions
Authors: Jordan Thomas H. , Puster Peter , Glatzmaier Gary A. , Tackley Paul J.
Published: October 2006

Three-dimensional numerical simulations were conducted of mantle convection in which flow through the transition zone is impeded by either a strong chemical change or an endothermic phase change. The temperature fields obtained from these models display a well-defined minimum in the vertical correlation length at or near the radius where the barrier is imposed, even when the fields were filtered to low angular and radial resolutions. However, evidence for such a feature is lacking in the shear-velocity models derived by seismic tomography. This comparison suggests that any stratification induced by phase or chemical changes across the mid-mantle transition zone has a relatively small effect on the large-scale circulation of mantle material.
Chemistry of the Fullerenes: The Manifestation of Strain in a Class of Continuous Aromatic Molecules
Authors: Haddon R. C.
Published: October 2006

Within the π-orbital axis vector theory, the total rehybridization required for closure of the fullerenes is approximately conserved. This result allows the development of a structure-based index of strain in the fullerenes, and it is estimated that about 80 percent of the heat of formation of the carbon atoms in C
60
may be attributed to a combination of σ strain and steric inhibition of resonance. Application of this analysis to the geometries of structurally characterized organometallic derivatives of C
60
and C
70
shows that the reactivity exhibited by the fullerenes may be attributed to the relief of a combination of local and global strain energy. C
60
is of ambiguous aromatic character with anomalous magnetic properties but with the reactivity of a continuous aromatic molecule, moderated only by the tremendous strain inherent in the spheroidal structure.
Chicxulub Multiring Impact Basin: Size and Other Characteristics Derived from Gravity Analysis
Authors: Sharpton Virgil L. , Burke Kevin , Camargo-Zanoguera Antonio , Hall Stuart A. , Lee D. Scott , Marín Luis E. , Suáarez-Reynoso Gerardo , Quezada-Muñeton Juan Manuel , Spudis Paul D. , Urrutia-Fucugauchi Jaime
Published: October 2006

The buried Chicxulub impact structure in Mexico, which is linked to the Cretaceous- Tertiary (K-T) boundary layer, may be significantly larger than previously suspected. Reprocessed gravity data over Northern Yucatan reveal three major rings and parts of a fourth ring, spaced similarly to those observed at multiring impact basins on other planets. The outer ring, probably corresponding to the basin's topographic rim, is almost 300 kilometers in diameter, indicating that Chicxulub may be one of the largest impact structures produced in the inner solar system since the period of early bombardment ended nearly 4 billion years ago.
High-
T
c
Molecular-Based Magnets: Ferrimagnetic Mixed-Valence Chromium(III)-Chromium(II) Cyanides with
T
c
at 240 and 190 Kelvin
Authors: Mallah T. , Thiébaut S. , Verdaguer M. , Veillet P.
Published: October 2006

Molecular-based magnets with high magnetic-ordering temperatures,
T
c
, can be obtained by mild chemistry methods by focusing on the bimetallic and mixed-valence transition metal μ-cyanide of the Prussian blue family. A simple orbital model was used to predict the electronic structure of the metal ions required to achieve a high ordering temperature. The synthesis and magnetic properties of two compounds, [Cr
5
(CN)
12
]⋅10H
2
O and Cs
0.75
[Cr
2.125
(CN)
6
]⋅5H
2
O, which exhibited magnetic-ordering temperatures of 240 and 190 kelvin, respectively, are reported, together with the strategy for further work.
A Simple Kinetic Model of Polymer Adsorption and Desorption
Authors: Douglas Jack F. , Johnson Harry E. , Granick Steve
Published: October 2006

A model of the desorption and adsorption of a polymer layer at a planar surface indicates a transition from exponential kinetics at high temperatures to nonexponential kinetics (stretched exponential with index one-half) at lower temperatures where these processes are diffusion-limited. Measurements of polystyrene desorption through polyisoprene overlayers show this predicted transition. Corroborative results are obtained for polystyrene desorption through polymethylmethacrylate overlayers. This identification of two distinct kinetic regimes suggests a unifying perspective from which to analyze polymer and biopolymer mobility at surfaces.
Trench-Parallel Flow Beneath the Nazca Plate from Seismic Anisotropy
Authors: Russo R. M. , Silver P. G.
Published: October 2006

Shear-wave splitting of
S
and
SKS
phases reveals the anisotropy and strain field of the mantle beneath the subducting Nazca plate, Cocos plate, and the Caribbean region. These observations can be used to test models of mantle flow. Two-dimensional entrained mantle flow beneath the subducting Nazca slab is not consistent with the data. Rather, there is evidence for horizontal trench-parallel flow in the mantle beneath the Nazca plate along much of the Andean subduction zone. Trench-parallel flow is attributable to retrograde motion of the slab, the decoupling of the slab and underlying mantle, and a partial barrier to flow at depth, resulting in lateral mantle flow beneath the slab. Such flow facilitates the transfer of material from the shrinking mantle reservoir beneath the Pacific basin to the growing mantle reservoir beneath the Atlantic basin. Trench-parallel flow may explain the eastward motions of the Caribbean and Scotia sea plates, the anomalously shallow bathymetry of the eastern Nazca plate, the long-wavelength geoid high over western South America, and it may contribute to the high elevation and intense deformation of the central Andes.