bluuebunny/crossref_metadata_2025 huggingface dataset:
Polyoma Virion and Capsid Crystal Structures
Authors: Adolph K. W. , Caspar D. L. D. , Hollingshead C. J. , Lattman Eaton E. , Phillips W. C. , Murakami W. T.
Published: October 2006

X-ray diffraction shows that complete virus particles and empty capsids crystallize isomorphously. The surface morphology of the protein coat, as revealed by electron microscopy, is the dominant structural feature determining the intensity of x-ray reflections to a resolution of approximately 30 angstroms. The structure and variability of the viral chromatin core can now be analyzed by comparison of electron density maps.
Production of Feedstock Chemicals
Authors: Ng T. K. , Busche R. M. , McDonald C. C. , Hardy R. W. F.
Published: October 2006

Renewable raw materials may be converted by biological means to feedstocks for the chemical industry. Glucose from cornstarch is the current choice as a substrate, although advances may enable the use of less expensive lignocellulosic materials. The production of oxychemicals and their derivatives from renewable resources could amount to about 100 billion pounds annually, or about half of the U.S. production of organic chemicals. Ethanol produced by fermentation is now cost-competitive with industrial ethanol produced from fossil fuel. Biological routes to other oxychemicals exist and are expected to be important in the future. Several product recovery methods may be used, but new energy-conserving methods will be needed to make the engineering-biology combinations economical.
Methane Synthesis on Nickel by a Solid-State Ionic Method
Authors: Gür Turgut M. , Huggins Robert A.
Published: October 2006

The feasibility of electrochemically synthesizing methane by a Fischer-Tropsch type reaction by use of a solid oxide electrolyte has been demonstrated. This solid-state ionic approach provides in situ control of the oxygen activity at the gas-catalyst interface by imposing a suitable voltage drop across an oxygen-conducting solid electrolyte from an external source. Methanation rates for hydrogen-carbon monoxide and hydrogen-carbon dioxide synthesis gas mixtures upon nickel electrodes showed substantial enhancement with the use of this technique, reaching values nearly two orders of magnitude higher than their intrinsic rates.
Hybrid Tree Frogs: Vocalizations of Males and Selective Phonotaxis of Females
Authors: Doherty John A. , Gerhardt H. Carl
Published: October 2006

Male hybrids of reciprocal crosses between gray and pinewoods tree frogs (
Hyla chtysoscelis
×
H. femoralis
) that were raised to sexual maturity in the laboratory produced distinctive vocalizations. Hybrid females preferred the calls of hybrids to calls of gray tree frogs and also chose synthetic calls with a pulse repetition rate typical of the hybrids in preference to calls with a rate typical of pinewoods tree frogs.
Seismic Precursors to the Mount St. Helens Eruptions in 1981 and 1982
Authors: Malone Stephen D. , Boyko Christina , Weaver Craig S.
Published: October 2006

Six categories of seismic events are recognized on the seismograms from stations in the vicinity of Mount St. Helens. Two types of high-frequency earthquakes occur near the volcano and under the volcano at depths of more than 4 kilometers. Medium- and low-frequency earthquakes occur at shallow depths (less than 3 kilometers) within the volcano and increase in number and size before eruptions. Temporal changes in the energy release of the low-frequency earthquakes have been used in predicting all the eruptions since October 1980. During and after eruptions, two types of low-frequency emergent surface events occur, including rockfalls and steam or gas bursts from the lava dome.
Predatory Capture of Toads by Fly Larvae
Authors: Jackman Rodger , Nowicki Stephen , Aneshansley Daniel J. , Eisner Thomas
Published: October 2006

A natural occurrence of predation upon toads (
Scaphiopus multiplicatus
) by fly larvae (
Tabanus punctifer
) is described. The larvae lie buried in mud, seize the toads with hooked mandibles, pull them partly into the mud, and kill them by feeding on their body fluids. The larvae may ordinarily subsist mostly on invertebrates and take Amphibia only opportunistically.
Late Leonardian Plants from West Texas: The Youngest Paleozoic Plant Megafossils in North America
Authors: Mamay Sergius H. , Miller John M. , Rohr David M.
Published: October 2006

Abundant Permian plant megafossils were discovered in the Del Norte Mountains of Brewster County, Trans-Pecos Texas. The flora is dominated by a new and distinctive type of gigantopteroid leaves. Marine invertebrates are closely associated, and this admixture of continental and marine fossils indicates a deltaic depositional setting, probably on the southern margin of the Permian Basin. Conodonts indicate correlation with the uppermost Leonardian Road Canyon Formation in the Glass Mountains. These are the youngest Paleozoic plant megafossils known in North America; they add an important paleontological element to the classic Permian area of this Continent.
Holocene Eruptive Activity of El Chichón Volcano, Chiapas, Mexico
Authors: Tilling Robert I. , Rubin Meyer , Sigurdsson Haraldur , Carey Steven , Duffield Wendell A. , Rose William I.
Published: October 2006

Geologic and radiometric-age data indicate that El Chichón was frequently and violently active during the Holocene, including eruptive episodes about 600, 1250, and 1700 years ago and several undated, older eruptions. These episodes, involving explosive eruptions of sulfur-rich magma and associated dome-growth processes, were apparently separated by intervals of approximately 350 to 650 years. Some of El Chichón's eruptions may correlate with unusual atmospheric phenomena around A.D. 1300 and possibly A.D. 623.
Lead-Iron Phosphate Glass: A Stable Storage Medium for High-Level Nuclear Waste
Authors: Sales B. C. , Boatner L. A.
Published: October 2006

Results are presented which show that lead-iron phosphate glasses are a promising new waste form for the safe immobilization of both high-level defense and high-level commercial radioactive waste. Relative to the borosilicate nuclear waste glasses that are currently the "reference" waste form for the long-term disposal of nuclear waste, lead-iron phosphate glasses have several distinct advantages: (i) an aqueous corrosion rate that is about 1000 times lower, (ii) a processing temperature that is 100° to 250°C lower, and (iii) a much lower melt viscosity in the temperature range from 800° to 1000°C. Most significantly, the lead-iron phosphate waste form can be processed using a technology similar to that developed for borosilicate nuclear waste glasses.
The East Coast Magnetic Anomaly
Authors: Alsop L. E. , Talwani M.
Published: October 2006

A model is proposed for the East Coast Magnetic Anomaly that, for the first time, incorporates an observed basement feature—a normal fault that consistently lies below the landward flank of the anomaly. The East Coast Magnetic Anomaly is similar to slope anomalies found over passive continental margins in many parts of the world. Thus the proposed model can be used to interpret slope anomalies in general.
Measurements of the Large-Scale Direct-Current Earth Potential and Possible Implications for the Geomagnetic Dynamo
Authors: Lanzerotti L. J. , Medford L. V. , MacLennan C. G. , Thomson D. J. , Meloni A. , Gregori G. P.
Published: October 2006

The magnitude of the large-scale direct-current earth potential was measured on a section of a recently laid transatlantic telecommunications cable. Analysis of the data acquired on the 4476-kilometer cable yielded a mean direct-current potential drop of less than about 0.072 ± 0.050 millivolts per kilometer. Interpreted in terms of a generation of the potential by the earth's geodynamo, such a small value of the mean potential implies that the toroidal and poloidal magnetic fields of the dynamo are approximately equal at the core-mantle boundary.
Invasion and Extinction in the West Indian Ant Fauna: Evidence from the Dominican Amber
Authors: Wilson Edward O.
Published: October 2006

Of 37 genera and well-defined subgenera identified in the amber of the Dominican Republic (late Oligocene or early Miocene), 34 have survived somewhere in the New World tropics to the present, although the species studied thus far are extinct. Of the surviving genera and subgenera, 22 persist on Hispaniola. Fifteen genera and subgenera have colonized the island since amber times, restoring the number of genera and well-defined subgenera now present on Hispaniola to 37. A higher extinction rate has occurred in genera and subgenera that are either highly specialized or possess less colonizing ability, as evidenced by their restriction to the New World.
Paleoseismic Evidence for Recurrence of Earthquakes near Charleston, South Carolina
Authors: Talwani Pradeep , Cox John
Published: October 2006

A destructive earthquake that occurred in 1886 near Charleston, South Carolina, was associated with widespread liquefaction of shallow sand structures and their extravasation to the surface. Several seismically induced paleoliquefaction structures preserved within the shallow sediments in the meizoseismal area of the 1886 event were identified. Field evidence and radiocarbon dates suggest that at least two earthquakes of magnitudes greater than 6.2 preceded the 1886 event in the past 3000 to 3700 years. The evidence yielded an initial estimate of about 1500 to 1800 years for the maximum recurrence of destructive, intraplate earthquakes in the Charleston region.
Evolution of Male Pheromones in Moths: Reproductive Isolation Through Sexual Selection?
Authors: Phelan P. Larry , Baker Thomas C.
Published: October 2006

Central to our understanding of the species concept is knowledge of the nature and evolution of reproductive isolating mechanisms. The once widely accepted model of Dobzhansky, which holds that isolation evolves through selection against hybrids of differentially adapted populations, is now largely rejected. This rejection is due to both theoretical difficulties and a paucity of examples of the predicted pattern of reproductive character displacement. From a survey of five families of Lepidoptera, entailing more than 800 species, evidence is given that male courtship pheromones have evolved within the context of sexual isolation as an adaptive response to mating mistakes between differentially adapted populations; however, distinct from the natural selection model of Dobzhansky, this report suggests the mechanism for change to be sexual selection.
Thunderstorms: An Important Mechanism in the Transport of Air Pollutants
Authors: Dickerson R. R. , Huffman G. J. , Luke W. T. , Nunnermacker L. J. , Pickering K. E. , Leslie A. C. D. , Lindsey C. G. , Slinn W. G. N. , Kelly T. J. , Daum P. H. , Delany A. C. , Greenberg J. P. , Zimmerman P. R. , Boatman J. F. , Ray J. D. , Stedman D. H.
Published: October 2006

Acid deposition and photochemical smog are urban air pollution problems, and they remain localized as long as the sulfur, nitrogen, and hydrocarbon pollutants are confined to the lower troposphere (below about 1-kilometer altitude) where they are short-lived. If, however, the contaminants are rapidly transported to the upper troposphere, then their atmospheric residence times grow and their range of influence expands dramatically. Although this vertical transport ameliorates some of the effects of acid rain by diluting atmospheric acids, it exacerbates global tropospheric ozone production by redistributing the necessary nitrogen catalysts. Results of recent computer simulations suggest that thunderstorms are one means of rapid vertical transport. To test this hypothesis, several research aircraft near a midwestern thunderstorm measured carbon monoxide, hydrocarbons, ozone, and reactive nitrogen compounds. Their concentrations were much greater in the outflow region of the storm, up to 11 kilometers in altitude, than in surrounding air. Trace gas measurements can thus be used to track the motion of air in and around a cloud. Thunderstorms may transform local air pollution problems into regional or global atmospheric chemistry problems.
Ice-Edge Eddies in the Fram Strait Marginal Ice Zone
Authors: Johannessen O. M. , Johannessen J. A. , Svendsen E. , Shuchman R. A. , Campbell W. J. , Josberger E.
Published: October 2006

Five prominent ice-edge eddies in Fram Strait on the scale of 30 to 40 kilometers were observed over deep water within 77°N to 79°N and 5°W to 3°E. The use of remote sensing, a satellite-tracked buoy, and in situ oceanographic measurements showed the presence of eddies with orbital speeds of 30 to 40 centimeters per second and lifetimes of at least 20 days. Ice ablation measurements made within one of these ice-ocean eddies indicated that melting, which proceeded at rates of 20 to 40 centimeters per day, is an important process in determining the ice-edge position. These studies give new insight on the formation, propagation, and dissipation of ice-edge eddies.
Remote Sensing of the Fram Strait Marginal Ice Zone
Authors: Shuchman R. A. , Burns B. A. , Johannessen O. M. , Josberger E. G. , Campbell W. J. , Manley T. O. , Lannelongue N.
Published: October 2006

Sequential remote sensing images of the Fram Strait marginal ice zone played a key role in elucidating the complex interactions of the atmosphere, ocean, and sea ice. Analysis of a subset of these images covering a 1-week period provided quantitative data on the mesoscale ice morphology, including ice edge positions, ice concentrations, floe size distribution, and ice kinematics. The analysis showed that, under light to moderate wind conditions, the morphology of the marginal ice zone reflects the underlying ocean circulation. High-resolution radar observations showed the location and size of ocean eddies near the ice edge. Ice kinematics from sequential radar images revealed an ocean eddy beneath the interior pack ice that was verified by in situ oceanographic measurements.
Interocean Differences in Size and Nutrition of Coral Reef Sponge Populations
Authors: Wilkinson Clive R.
Published: October 2006

Sponges consume an order of magnitude more organic matter on Caribbean coral reefs than on the Great Barrier Reef. This rate of consumption is attributed to Caribbean sponge biomass being five to six times greater than that on the Great Barrier Reef, on average, and to the absence in the Caribbean of phototrophic sponges, which are a feature of clean water regions of the Great Barrier Reef. The long temporal and spatial separation of the Atlantic and Pacific oceans has resulted in the evolution of dissimilar sponge faunas, with Caribbean sponges being heterotrophic, whereas many Great Barrier Reef sponges rely on nutritional input from photosynthetic symbionts.
Helium Loss, Tectonics, and the Terrestrial Heat Budget
Authors: Oxburgh E. Ronald , O'Nions R. Keith
Published: October 2006

It has been known for the last decade that primordial helium incorporated in Earth at the time of its formation is still being degassed during the formation of new ocean crust at spreading ocean ridges. It is now clear that somewhat contrary to expectation, substantial degassing is also taking place through the continental crust. In western Europe the escape of mantle volatiles seems to occur largely where the crust is undergoing active extension. Although it is known that melting is the principal process for extracting and concentrating helium from the mantle at ocean ridges, the equivalent subcontinental process remains poorly understood. The same elements that are responsible for most of Earth's radiogenic heating (uranium and thorium) are also responsible for the generation of radiogenic helium. The present rate of mantle heat loss, however, is out of equilibrium with the rate of helium loss—too large by about a factor of 20. Either radiogenic helium is accumulated in the mantle while heat escapes or current models for the bulk chemistry of Earth are in error and much of the terrestrial heat loss is nonradiogenic.
A Weakness in Process Technology
Authors: Thurow Lester C.
Published: October 2006

Although the United States seems to be neither behind when it comes to research and development on new products or the willingness of its consumers to buy new products, the evidence clearly shows that it is behind when it comes to process technologies. Often Americans, even when a correction is made for wage differences, cannot produce goods at the price or quality levels achieved abroad. There is no one overriding reason for this lag in process technologies. An undereducated and trained labor force, too little savings and investment, a failure to see production as a central task, and a number of other factors have all contributed to the problem.
GEOSAT Altimeter Observations of Kelvin Waves and the 1986-87 El Niño
Authors: Miller Laury , Cheney Robert E. , Douglas Bruce C.
Published: October 2006

Two years of GEOSAT altimeter observations are used to investigate the response of sea level to anomalous westerly wind bursts in the tropical Pacific Ocean before and during the 1986-87 El Niño. Sea level time series along the equator show examples of both positive and negative anomalies of 10-centimeter amplitude and 2- to 4-week time scale propagating across the Pacific with phase speeds of 2.4 to 2.8 meters per second, suggesting downwelling and upwelling Kelvin waves, respectively. A comparison of island wind observations with sea level indicates one instance (May 1986) in which a positive sea level anomaly can be related to westerly winds caused by a cross-equatorial cyclone pair in the western Pacific. This episode was followed by additional wind bursts later in the year, and finally by sustained westerlies in the western Pacific during November-December 1986, at the height of El Niño. The GEOSAT observations reveal the sea level response to these meteorological events and provide a synoptic description of the El Niño oceanographic phenomenon.
Seawater Strontium Isotopes, Acid Rain, and the Cretaceous-Tertiary Boundary
Authors: Macdougall J. D.
Published: October 2006

A large bolide impact at the end of the Cretaceous would have produced significant amounts of nitrogen oxides by shock heating of the atmosphere. The resulting acid precipitation would have increased continental weathering greatly and could be an explanation for the observed high ratio of strontium-87 to strontium-86 in seawater at about this time, due to the dissolution of large amounts of strontium from the continental crust. Spikes to high values in the seawater strontium isotope record at other times may reflect similar episodes.
Mussel Growth Supported by Methane as Sole Carbon and Energy Source
Authors: Cary S. Craig , Fisher Charles R. , Felbeck Horst
Published: October 2006

Symbioses between chemoautotrophic bacteria and several specialized marine invertebrates are well documented. However, none of these symbioses have been demonstrated to provide sufficient energy and carbon to the host to enable it to grow. Growth rates of seep mussels collected from hydrocarbon seeps off the coast of Louisiana were measured in a controlled environment where methane was the sole carbon and energy source. The growth rates increased to a maximum of 17.2 micrometers per day in response to methane and approached zero in the absence of methane. These mussels contain methanotrophic symbiotic bacteria in their gills, which suggests that these bacteria provide their hosts with a net carbon flux originating from methane.
Chemical Waves
Authors: Ross John , Müller Stefan C. , Vidal Christian
Published: October 2006

Spatial structures may occur in nonlinear systems far from equilibrium. Chemical waves, which are concentration variations of chemical species propagating in a system, are an example of such structures. A survey is given of some experiments on chemical waves by spectroscopic and microphotographic techniques, arranged according to different types of waves, different geometries, and various properties.
Crystal Structure of Tl
2
Ba
2
Ca
2
Cu
3
O
10
, a 125 K Superconductor
Authors: Torardi C. C. , Subramanian M. A. , Calabrese J. C. , Gopalakrishnan J. , Morrissey K. J. , Askew T. R. , Flippen R. B. , Chowdhry U. , Sleight A. W.
Published: October 2006

There is now a new series of high-temperature superconductors that may be represented as (A
III
O)
2
A
2
II
Ca

n
-1

Cu

n

O

2+2
n

where A
III
is Bi or Tl, A
II
is Ba or Sr, and
n
is the number of Cu-O sheets stacked consecutively. There is a general trend toward higher transition temperatures as
n
increases. The highest
n
value for a bulk phase is three and is found when A
III
is Tl. This compound, Tl
2
Ba
2
Ca
2
Cu
3
O
10
, has the highest transition temperature (∼125 K) of any presently known bulk superconductor. The structure of Tl
2
Ba
2
Ca
2
Cu
3
O
10
has been determined from single-crystal x-ray diffraction data and is tetragonal, with
a
= 3.85 Å and
c
= 35.9 Å. No superstructure is observed, and the material is essentially twin-free. Electron microscopy in the Tl/Ba/Ca/Cu/O system has revealed intergrowths where
n
= 5; such regions may well be responsible for the superconducting onset behavior observed in this system at about 140 K.
A New Speciment of
Archaeopteryx
Authors: Wellnhofer Peter
Published: October 2006

A new specimen of the primordial bird
Archaeopteryx
is reported from the Upper Jurassic Solnhofen Limestone of Bavaria. This "Solnhofen specimen" is the largest of now six skeletal specimens and shows close similarities with the London specimen. It is therefore assigned to
Archaeopteryx lithographica
Meyer. Clear impressions of the feather shafts of the left wing are preserved.
Endothelin: A Novel Peptide in the Posterior Pituitary System
Authors: Yoshizawa Toshihiro , Shinmi Osamu , Giaid Adel , Yanagisawa Masashi , Gibson Sally J. , Kimura Sadao , Uchiyama Yasuo , Polak Julia M. , Masaki Tomoh , Kanazawa Ichiro
Published: October 2006

Endothelin (ET), originally characterized as a 21-residue vasoconstrictor peptide from endothelial cells, is present in the porcine spinal cord and may act as a neuropeptide. Endothelin-like immunoreactivity has now been demonstrated by immunohistochemistry in the paraventricular and supraoptic nuclear neurons and their terminals in the posterior pituitary of the pig and the rat. The presence of ET in the porcine hypothalamus was confirmed by reversed-phase high-pressure liquid chromatography and radioimmunoassay. Moreover, in situ hybridization demonstrated ET messenger RNA in porcine paraventricular nuclear neurons. Endothelin-like immunoreactive products in the posterior pituitary of the rat were depleted by water deprivation, suggesting a release of ET under physiological conditions. These findings indicate that ET is synthesized in the posterior pituitary system and may be involved in neurosecretory functions.
Raoult's Law and the Melting Point Depression in Mesoscopic Systems
Authors: Nimtz Günter , Marquardt Peter D. , Stauffer Dietrich , Weiss Wilfried
Published: October 2006

Data on the melting point depression in small indium or gold particles and in liquid water held between lipid bilayers indicate that these systems obey Raoult's law, with the surface atoms or molecules acting like solute particles in a dilute solution.
Occult
Drosophila
Calcium Channels and Twinning of Calcium and Voltage-Activated Potassium Channels
Authors: Wei Aguan , Salkoff Lawrence
Published: October 2006

In the membrane of the flight muscle cells of developing
Drosophila
a large calcium-sensitive potassium current,
I
Kc
, was found. It was present before the development of voltage-activated potassium channels and seems to be the first potassium current to develop in the membrane. Also present in these early cells were large numbers of occult (hidden) calcium channels, which remained inactive until the end of pupal development. These inactive calcium channels could be made to function by injecting adenosine triphosphate or ethyleneglycol tetraacetic acid into the early cells.
I
Kc
has kinetic properties resembling the later developing voltage-sensitive current
I
Kv
, and is distinct from the fast, transient calcium-dependent outward current
I
Ac
, which appears much later in development.
I
Ac
closely resembles the voltage-sensitive current
I
Av
, also present in these cells. Thus, both of the voltage-sensitive potassium channel types,
I
Av
and
I
Kv
, have similar calcium-sensitive counterparts,
I
Ac
and
I
Kc
, that are present in the same cells.
An Early Event in the Interferon-Induced Transmembrane Signaling Process
Authors: Yap W. H. , Teo T. S. , Tan Y. H.
Published: October 2006

Human interferon stimulates a transient two- to threefold increase in the concentration of diacylglycerol and inositol tris-phosphate within 15 to 30 seconds of cell exposure to interferon. Antibodies to interferon inhibit this effect. The stimulation was measurable in isolated cell membranes exposed to interferon. Human α and β, but not γ, interferon stimulate this increase in cells containing the appropriate interferon receptor. The effect was proportional to the number of interferon receptors. Both the diacylglycerol increase and antiviral effects induced by interferon could be correlated in terms of dose dependence. Thus, a transient diacylglycerol increase is an early event in the interferon-induced transmembrane signaling process.
The Chemistry of Self-Splicing RNA and RNA Enzymes
Authors: Cech Thomas R.
Published: October 2006

Proteins are not the only catalysts of cellular reactions; there is a growing list of RNA molecules that catalyze RNA cleavage and joining reactions. The chemical mechanisms of RNA-catalyzed reactions are discussed with emphasis on the self-splicing ribosomal RNA precursor of
Tetrahymena
and the enzymatic activities of its intervening sequence RNA. Wherever appropriate, catalysis by RNA is compared to catalysis by protein enzymes.
Three-Dimensional Structure of an Oncogene Protein: Catalytic Domain of Human c-H-
ras
P21
Authors: de Vos Abraham M. , Tong Lung , Milburn Michael V. , Matias Pedro M. , Jancarik Jarmila , Noguchi Shigeru , Nishimura Susumu , Miura Kazunobu , Ohtsuka Eiko , Kim Sung-Hou
Published: October 2006

The crystal structure at 2.7 Å resolution of the normal human c-H-
ras
oncogene protein lacking a flexible carboxyl-terminal 18 residue reveals that the protein consists of a six-stranded β sheet, four α helices, and nine connecting loops. Four loops are involved in interactions with bound guanosine diphosphate: one with the phosphates, another with the ribose, and two with the guanine base. Most of the transforming proteins (in vivo and in vitro) have single amino acid substitutions at one of a few key positions in three of these four loops plus one additional loop. The biological functions of the remaining five loops and other exposed regions are at present unknown. However, one loop corresponds to the binding site for a neutralizing monoclonal antibody and another to a putative "effector region"; mutations in the latter region do not alter guanine nucleotide binding or guanosine triphosphatase activity but they do reduce the transforming activity of activated proteins. The data provide a structural basis for understanding the known biochemical properties of normal as well as activated
ras
oncogene proteins and indicate additional regions in the molecule that may possibly participate in other cellular functions.
An Empirical Model for Predicting Diffusion Coefficients in Silicate Minerals
Authors: Fortier Steven M. , Giletti Bruno J.
Published: October 2006

An empirical model describing the diffusion kinetics of oxygen in silicate minerals under hydrothermal conditions has been established for temperatures between 773 and 1073 Kelvin at 100 megapascals of water pressure. The equation, log
D
= α + (β/
T
) + [(γ + (δ/
T
))
Z
], where
D
is the diffusion coefficient, α, β, γ, and δ are constants,
T
is the Kelvin temperature, and
Z
is the total ionic porosity, may be used to predict diffusion coefficients, in most cases to within the reported experimental reproducibility of a factor of 2. For oxygen diffusion, α = -2, β = -3.4 × 10
4
K, γ = -0.13, and δ = 6.4 × 10
2
K, for
D
in square centimeters per second. Limited data for the diffusion of argon in silicates suggest that the model describes this system as well.
Amazon River Discharge and Climate Variability: 1903 to 1985
Authors: Richey Jeffrey E. , Nobre Carlos , Deser Clara
Published: October 2006

Reconstruction of an 83-year record (1903 to 1985) of the discharge of the Amazon River shows that there has been no statistically significant change in discharge over the period of record and that the predominant interannual variability occurs on the 2- to 3-year time scale. Oscillations of river discharge predate significant human influences in the Amazon basin and reflect both extrabasinal and local factors. Cross-spectrum analyses of Amazon flow anomalies with indicators of the El Niño-Southern Oscillation phenomenon suggest that the oscillations in the hydrograph are coupled to the tropical Pacific climate cycle.
Energetic Charged Particles in the Magnetosphere of Neptune
Authors: Stone E. C. , Cummings A. C. , Loooper M. D. , Selesnick R. S. , Lal N. , McDonald F. B. , Trainor J. H. , Chenette D. L.
Published: October 2006

The Voyager 2 cosmic ray system (CRS) measured significant fluxes of energetic [≳ 1 megaelectron volt (MeV)] trapped electrons and protons in the magnetosphere of Neptune. The intensities are maximum near a magnetic
L
shell of 7, decreasing closer to the planet because of absorption by satellites and rings. In the region of the inner satellites of Neptune, the radiation belts have a complicated structure, which provides some constraints on the magnetic field geometry of the inner magnetosphere. Electron phase-space densities have a positive radial gradient, indicating that they diffuse inward from a source in the outer magnetosphere. Electron spectra from 1 to 5 MeV are generally well represented by power laws with indices near 6, which harden in the region of peak flux to power law indices of 4 to 5. Protons have significantly lower fluxes than electrons throughout the magnetosphere, with large anisotropies due to radial intensity gradients. The radiation belts resemble those of Uranus to the extent allowed by the different locations of the satellites, which limit the flux at each planet.
Gamma Rays and Neutrinos as Clues to the Origin of High Energy Cosmic Rays
Authors: Gaisser Thomas K.
Published: October 2006

Compact regions in the Milky Way, such as accreting degenerate binary stars, may be sites of acceleration of particles with energies far greater than produced at any man-made accelerator, present or proposed. If so, they would emit characteristic neutral radiation of ultra-high energy, which might be strong enough to be detectable at Earth. The quest for these faint but energetic signals is the focus of more than 50 large, ground-based experiments that are looking for high energy photons or neutrinos from point sources in our galaxy and beyond. Several sources have been claimed, but the signals appear to have unexpected and puzzling features that must be clarified before the field can settle into a routine phase of systematic investigation. In the meantime, the potentially profound implications for particle physics, as well as astrophysics, make this field one of intense activity.
Physical Conditions at the Base of a Fast Moving Antarctic Ice Stream
Authors: Engelhardt Hermann , Humphrey Neil , Kamb Barclay , Fahnestock Mark
Published: October 2006

Boreholes drilled to the bottom of ice stream B in the West Antarctic Ice Sheet reveal that the base of the ice stream is at the melting point and the basal water pressure is within about 1.6 bars of the ice overburden pressure. These conditions allow the rapid ice streaming motion to occur by basal sliding or by shear deformation of unconsolidated sediments that underlie the ice in a layer at least 2 meters thick. The mechanics of ice streaming plays a role in the response of the ice sheet to climatic change.
Evolutionary Significance of Morphospecies: A Test with Cheilostome Bryozoa
Authors: Jackson Jeremy B. C. , Cheetham Alan H.
Published: October 2006

Much of the controversy concerning the theory of punctuated equilibrium stems from skepticism about the biologic validity of fossil morphospecies, particularly for supposedly simple invertebrate taxa like cheilostome Bryozoa that form the bulk of the fossil record. However, evidence from breeding experiments and protein electrophoresis shows that morphospecific identity of cheilostomes is heritable and that morphospecies are genetically distinct with no indication of morphologically cryptic species. Thus paleontologists can study cheilostome evolution at the species level, and previously demonstrated patterns suggesting punctuated speciation in cheilostomes should be taken at face value.
Radar Reflectivity of Titan
Authors: Muhleman Duane O. , Grossman Arie W. , Butler Bryan J. , Slade Martin A.
Published: October 2006

The present understanding of the atmosphere and surface conditions on Saturn's largest moon, Titan, including the stability of methane, and an application of thermodynamics leads to a strong prediction of liquid hydrocarbons in an ethane-methane mixture on the surface. Such a surface would have nearly unique microwave reflection properties due to the low dielectric constant. Attempts were made to obtain reflections at a wavelength of 3.5 centimeters by means of a 70-meter antenna in California as the transmitter and the Very Large Array in New Mexico as the receiving instrument. Statistically significant echoes were obtained that show Titan is not covered with a deep, global ocean of ethane, as previously thought. The experiment yielded radar cross sections normalized by the Titan disk of 0.38 ± 0.15, 0.78 ± 0.15, and 0.25 ± 0.15 on three consecutive nights during which the sub-Earth longitude on Titan moved 50 degrees. The result for the combined data for the entire experiment is 0.35 ± 0.08. The cross sections are very high, most consistent with those of the Galilean satellites; no evidence of the putative liquid ethane was seen in the reflection data. A global ocean as shallow as about 200 meters would have exhibited reflectivities smaller by an order of magnitude, and below the detection limit of the experiment. The measured emissivity at similar wavelengths of about 0.9 is somewhat inconsistent with the high reflectivity.
Caloris Basin: An Enhanced Source for Potassium in Mercury's Atmosphere
Authors: Sprague Ann L. , Kozlowski Richard W. H. , Hunten Donald M.
Published: October 2006

Enhanced abundances of neutral potassium (K) in the atmosphere of Mercury have been found above the longitude range containing Caloris Basin. Results of a large data set including six elongations of the planet between June 1986 and January 1988 show typical K column abundances of ∼5.4 × 10
8
K atoms/cm
2
. During the observing period in October 1987, when Caloris Basin was in view, the typical K column was ∼2.7 × 10
9
K atoms/cm
2
. Another large value (2.1 × 10
9
K atoms/cm
2
) was seen over the Caloris antipode in January 1988. This enhancement is consistent with an increased source of K from the well-fractured crust and regolith associated with this large impact basin. The phenomenon is localized because at most solar angles, thermal alkali atoms cannot move more than a few hundred kilometers from their source before being lost to ionization by solar ultraviolet radiation.
Neutron and Gamma Ray Scattering Measurements for Subsurface Geochemistry
Authors: Ellis Darwin V.
Published: October 2006

Developed for the oil industry, well logging instrumentation based on electrical, acoustic, and nuclear measurements has been providing information about the localization and evaluation of hydrocarbon-bearing strata for petroleum geologists and engineers since 1927. This method of exploring properties of the earth's crust without taking physical samples is attracting a growing audience of geologists and geophysicists because of recent developments that permit nondestructive measurements of subsurface geochemistry. A combination of nuclear measurement techniques, which use gamma ray and neutron sources, can provide detailed information on rock composition of interest to both industry and academia.
Scatterers in Triton's Atmosphere: Implications for the Seasonal Volatile Cycle
Authors: Pollack James B. , Schwartz Joel M. , Rages Kathy
Published: October 2006

Nitrogen and methane ices on the surface of Triton, Neptune's largest satellite, are exchanged between the summer and winter hemispheres on a seasonal time scale. Images of the satellite's sky obtained by the Voyager 2 spacecraft show the presence of several types of scattering materials that provide insights into this seasonal cycle of volatiles. Discrete clouds, probably composed of N
2
ice particles, arise in regions of active sublimation. They are found chiefly poleward of 30°S in the southern, summer hemisphere. Haze particles, probably made of hydrocarbon ices, are present above most, but not all places. Recent snowfall may have occurred at low southern latitudes in places where they are absent. The latent heat released in the formation of the discrete clouds may have a major impact on the thermal balance of the lower atmosphere. Triton may have been less red at the time of the Voyager flyby than 12 years earlier due to recent N
2
snowfall at a wide range of latitudes.
Initiation by Yeast RNA Polymerase II at the Adenoviral Major Late Promoter in Vitro
Authors: Lue Neal F. , Flanagan Peter M. , Sugimoto Katsunori , Kornberg Roger D.
Published: October 2006

Transcription of the yeast
CYC1
promoter fused to a sequence lacking guanosine residues provided a rapid, sensitive assay of initiation by RNA polymerase II in yeast extracts. Initiation was enhanced by yeast and mammalian activator proteins. The adenoviral major late promoter fused to the G-minus sequence was transcribed in yeast extracts with an efficiency comparable to that observed in HeLa extracts, showing that promoters as well as transcription factors are functionally interchangeable across species. Initiation occurred at different sites, approximately 30 and 63 to 69 base pairs downstream of the TATA element of the adenoviral promoter in HeLa and yeast extracts, respectively, distances characteristic of initiation in the two systems in vivo. A component of the transcription system and not the promoter sequence determines the distance to the initiation site.
Calcic Micas in the Allende Meteorite: Evidence for Hydration Reactions in the Early Solar Nebula
Authors: Keller Lindsay P. , Buseck Peter R.
Published: October 2006

Two calcic micas, clintonite and margarite, have been identified in alteration products in a calcium- and aluminum-rich inclusion (CAI) in the Allende meteorite. Clintonite replaces grossular in alteration veins, and margarite occurs as lamellae in anorthite. Their occurrence suggests that, in addition to undergoing high-temperature alteration by a volatile and iron-rich vapor that produced the grossular and anorthite, some CAIs underwent alteration at moderate temperatures (≤400 kelvin). Petrographic evidence suggests that the calcic micas formed before accretion but after the formation of the layered rim sequences that surround the CAI. These calcic micas provide strong evidence that, contrary to theoretical calculations, some hydration reactions occurred in the early solar nebula.
Synchrotron X-Ray Diffraction from a Microscopic Single Crystal Under Pressure
Authors: Skelton E. F. , Ayers J. D. , Qadri S. B. , Moulton N. E. , Cooper K. P. , Finger L. W. , Mao H. K. , Hu Z.
Published: October 2006

Metallic filaments with submicrometer diameters have been fabricated. Standard diffraction techniques with conventional x-ray sources were unsuccessful in identifying the structure of these materials. However, with the use of synchrotron radiation produced on a wiggler beam line, diffraction data were obtained in measurement periods as short as 10 milliseconds. Two cylindrical single crystals of bismuth were studied, each with a diameter of 0.22 ± 0.02 micrometer. The volume of sample illuminated for these measurements was 0.38 cubic micrometer, less than 0.5 femtoliter. The crystals are grown in glass capillaries, and, because bismuth expands on solidification, they are under a residual hoop stress. The crystallographic data indicate the presence of a linear compressive strain of about 2 percent, which is assumed to be the result of a residual stress of about 2 gigapascals.
The Galileo Venus Encounter
Authors: Johnson Torrence V. , Yeates Clayne M. , Young Richard , Dunne James
Published: October 2006

The Galileo spacecraft passed Venus on its way to Jupiter on 10 February 1990, less than 4 months after launch from Earth aboard the shuttle Atlantis. Because Galileo's instruments were selected for broad-based planetary exploration, the spacecraft was able to obtain a wide range of measurements during the Venus encounter. Together with ground-based observations conducted during the encounter, these observations have yielded more accurate information about the planet's plasma environment, cloud patterns, and the possible existence of lightning.
Galileo Ultraviolet Spectrometer Experiment: Initial Venus and Interplanetary Cruise Results
Authors: Hord C. W. , Barth C. A. , Esposito L. W. , McClintock W. E. , Pryor W. R. , Simmons K. E. , Stewart A. I. F. , Thomas G. E. , Ajello J. M. , Lane A. L. , West R. W. , Sandel B. R. , Broadfoot A. L. , Hunten D. M. , Shemansky D. E.
Published: October 2006

The Galileo Extreme Ultraviolet Spectrometer obtained a spectrum of Venus atmospheric emissions in the 55.0- to 125.0-nanometer (nm) wavelength region. Emissions of helium (58.4 nm), ionized atomic oxygen (83.4 nm), and atomic hydrogen (121.6 nm), as well as a blended spectral feature of atomic hydrogen (Lyman-β) and atomic oxygen (102.5 nm), were observed at 3.5-nm resolution. During the Galileo spacecraft cruise from Venus to Earth, Lyman-α emission from solar system atomic hydrogen (121.6 nm) was measured. The dominant source of the Lyman-α emission is atomic hydrogen from the interstellar medium. A model of Galileo observations at solar maximum indicates a decrease in the solar Lyman-α flux near the solar poles. A strong day-to-day variation also occurs with the 27-day periodicity of the rotation of the sun.
Activation-Driven Programmed Cell Death and T Cell Receptor ζη Expression
Authors: Merćep Mladen , Weissman Allan M. , Frank Stuart J. , Klausner Richard D. , Ashwell Jonathan D.
Published: October 2006

Activation of spontaneously dividing T cell hybridomas induces interleukin-2 (IL-2) production, a cell cycle block, and programmed cell death. T cell hybridomas that express the T cell antigen receptor (TCR) ζ homodimer (ζ
2
), but not the TCR ζη heterodimer, were studied. The ζη
-
cells produced little or no inositol phosphates (IP) when stimulated with antigen. In most cases the hydrolysis of phosphoinositides was also impaired after stimulation with antibody to CD3, although one ζη
-
cell produced normal concentrations of IP. The ζη
-
cells slowed their growth and secreted IL-2 in response to both stimuli. However, the ζη
-
cells did not die after activation with antigen. Since activated thymocytes also undergo programmed cell death, these results may have important implications for the role of the ζη TCR in negative selection.
Indole-3-Acetic Acid Biosynthesis in the Mutant Maize
orange pericarp
, a Tryptophan Auxotroph
Authors: Wright Allen D. , Sampson Michael B. , Neuffer M. Gerald , Michalczuk Lech , Slovin Janet Pernise , Cohen Jerry D.
Published: October 2006

The maize mutant
orange pericarp
is a tryptophan auxotroph, which results from mutation of two unlinked loci of tryptophan synthase B. This mutant was used to test the hypothesis that tryptophan is the precursor to the plant hormone indole-3-acetic acid (IAA). Total IAA in aseptically grown mutant seedlings was 50 times greater than in normal seedlings. In mutant seedlings grown on media containing stable isotope-labeled precursors, IAA was more enriched than was tryptophan. No incorporation of label into IAA from tryptophan could be detected. These results establish that IAA can be produced de novo without tryptophan as an intermediate.
Eighth Millennium Pottery from a Prehistoric Shell Midden in the Brazilian Amazon
Authors: Roosevelt A. C. , Housley R. A. , Imazio da Silveira M. , Maranca S. , Johnson R.
Published: October 2006

The earliest pottery yet found in the Western Hemisphere has been excavated from a prehistoric shell midden near Santarém in the lower Amazon, Brazil. Calibrated accelerator radiocarbon dates on charcoal, shell, and pottery and a thermoluminescence date on pottery from the site fall from about 8000 to 7000 years before the present. The early fishing village is part of a long prehistoric trajectory that contradicts theories that resource poverty limited cultural evolution in the tropics.
Effects of Buried Ionizable Amino Acids on the Reduction Potential of Recombinant Myoglobin
Authors: Varadarajan Raghavan , Zewert Thomas E. , Gray Harry B. , Boxer Steven G.
Published: October 2006

The temperature dependences of the reduction potentials (
E
°′) of wild-type human myoglobin (Mb) and three site-directed mutants have been measured by the use of thin-layer spectroelectrochemistry. Residue Val
68
, which is in van der Waals contact with the heme in Mb, has been replaced by Glu, Asp, and Asn. The changes in
E
°′ and the standard entropy (Δ
S
°′) and enthalpy (Δ
H
°′) of reduction in the mutant proteins were determined relative to values for wild type; the change in
E
°′ at 25°C was about -200 millivolts for the Glu and Asp mutants, and about -80 millivolts for the Asn mutant. At
p
H 7.0, reduction of Fe(III) to Fe(II) in the Glu and Asp mutants is accompanied by uptake of a proton by the protein. These studies demonstrate that Mb can tolerate substitution of a buried hydrophobic group by potentially charged and polar residues and that such amino acid replacements can lead to substantial changes in the redox thermodynamics of the protein.
Transfer RNA Genes: Landmarks for Integration of Mobile Genetic Elements in
Dictyostelium discoideum
Authors: Marschalek Rolf , Brechner Thomas , Amon-Böhm Elfi , Dingermann Theodor
Published: October 2006

In prokaryotes and eukaryotes mobile genetic elements frequently disrupt the highly conservative structures of chromosomes, which are responsible for storage of genetic information. The factors determining the site for integration of such elements are still unknown. Transfer RNA (tRNA) genes are associated in a highly significant manner with different putative mobile genetic elements in the cellular slime mold
Dictyostelium discoideum
. These results suggest that tRNA genes in
D. discoideum
, and probably tRNA genes generally in lower eukaryotes, may function as genomic landmarks for the integration of different transposable elements in a strictly position-specific manner.
Origins for the Near-Earth Asteroids
Authors: Binzel Richard P. , Xu Shui , Bus Schelte J. , Bowell Edward
Published: October 2006

Because of their short dynamical lifetimes, the population of near-Earth asteroids (NEAs) must be resupplied. Two sources have been hypothesized: main-belt asteroids and extinct comet nuclei. The difficulty of making physical measurements for similar sized (diameter
D
less than 5 kilometers) main-belt asteroids and comet nuclei has limited comparative tests for distinguishing between these alternatives. A new survey of physical properties for
D
< 5 kilometers main-belt asteroids reveals that their spin rate and shape distributions are similar to those of NEAs, as is fully consistent with a main-belt origin for most NEAs. Physical data on comet nuclei are limited. If the existing sample is representative of the comet population, analysis of the asteroid and comet samples constrains the fraction of comet nuclei to between 0 and 40 percent of the total NEA population.