bluuebunny/crossref_metadata_2025 huggingface dataset:
Photometry from Voyager 2: Initial Results from the Neptunian Atmosphere, Satellites, and Rings
Authors: Lane Arthur L. , West Robert A. , Hord Charles W. , Nelson Robert M. , Simmons Karen E. , Pryor Wayne R. , Eposito Larry W. , Horn Linda J. , Wallis Brad D. , Buratti Bonnie J. , Brophy Thomas G. , Yanamandra-Fisher Padma , Colwell Joshua E. , Bliss David A. , Mayo Marvin J. , Smythe William D.
Published: October 2006

The Voyager photopolarimeter successfully accomplished its objectives for the Neptune encounter, performing measurements on the planet, several of its satellites, and its ring system. A photometric map of Neptune at 0.26 micrometer (μm) shows the planet to be bland, with no obvious contrast features. No polar haze was observed. At 0.75 μm, contrast features are observed, with the Great Dark Spot appearing as a low-albedo region and the bright companion as being substantially brighter than its surroundings, implying it to be at a higher altitude than the Great Dark Spot. Triton's linear phase coefficients of 0.011 magnitudes per degree at 0.26 μm and 0.013 magnitudes per degree at 0.75 μm are consistent with a solid-surface object possessing high reflectivity. Preliminary geometric albedos for Triton, Nereid, and 1989N2 were obtained at 0.26 and 0.75 μm. Triton's rotational phase curve shows evidence of two major compositional units on its surface. A single stellar occultation of the Neptune ring system elucidated an internal structure in 1989N1R, in the ∼50-kilometer region of modest optical depth. 1989N2R may have been detected. The deficiency of material in the Neptune ring system, when compared to Uranus', may imply the lack of a "recent" moon-shattering event.
Activation of Developmentally Mutated Human Globin Genes by Cell Fusion
Authors: Papayannopoulou Thalia , Enver Tariq , Takegawa Susumu , Anagnou Nicholas P. , Stamatoyannopoulos George
Published: October 2006

Human fetal globin genes are not expressed in hybrid cells produced by the fusion of normal human lymphocytes with mouse erythroleukemia cells. In contrast, when lymphocytes from persons with globin gene developmental mutations (hereditary persistence of fetal hemoglobin) are used for these fusions, fetal globin is expressed in the hybrid cells. Thus, mutations of developmental origin can be reconstituted in vitro by fusing mutant lymphoid cells with differentiated cell lines of the proper lineage. This system can readily be used for analyses, such as globin gene methylation, that normally require large numbers of pure nucleated erythroid cells, which are difficult to obtain.
Association of Transfer RNA Acceptor Identity with a Helical Irregularity
Authors: McClain William H. , Chen Yong-Min , Foss K. , Schneider Jay
Published: October 2006

The aminoacylation specificity ("acceptor identity") of transfer RNAs (tRNAs) has previously been associated with the position of particular nucleotides, as opposed to distinctive elements of three-dimensional structure. The contribution of a G⋅U wobble pair in the acceptor helix of tRNA
Ala
to acceptor identity was examined with synthetic amber suppressor tRNAs in
Escherichia coli
. The acceptor identity was not affected by replacing the G⋅U wobble pair in tRNA
Ala
with a G⋅A, C⋅A, or U⋅U wobble pair. Furthermore, a tRNA
Ala
acceptor identity was conferred on tRNA
Lys
when the same site in the acceptor helix was replaced with any of several wobble pairs. Additional data with tRNA
Ala
show that a substantial acceptor identity was retained when the G⋅U wobble pair was translocated to another site in the acceptor helix. These results suggest that the G⋅U wobble pair induces an irregularity in the acceptor helix of tRNA
Ala
to match a complementary structure in the aminoacylating enzyme.
Block of Stretch-Activated Ion Channels in
Xenopus
Oocytes by Gadolinium and Calcium Ions
Authors: Yang Xian-Cheng , Sachs Frederick
Published: October 2006

Gadolinium ions produce three distinct kinds of block of the stretch-activated (SA) ion channels in
Xenopus
oocytes: a concentration-dependent reduction in channel open time, a concentration-dependent reduction in open channel current, and a unique, steeply concentration-dependent, reversible inhibition of channel opening. This last effect reduces the probability of a channel being open from about 10
-1
at 5 μ
M
to less than 10
-5
at 10 μ
M
gadolinium. Calcium has effects on open time and current similar to that of gadolinium, but this channel is permeable to calcium and calcium does not completely inhibit channel activity. The availability of a blocker for SA ion channels may help to define their physiological function, and will simplify the use of oocytes as an expression system for ion channels.
Imaging Surface Atomic Structure by Means of Auger Electrons
Authors: Frank Douglas G. , Batina Nikola , Golden Teresa , Lu Frank , Hubbard Arthur T.
Published: October 2006

Measurements of the complete angular distribution of Auger electrons emitted from well-defined platinum[111] single-crystal surfaces have led to the discovery that the distributions are composed of "silhouettes" of surface atoms "back lit" by emission from atoms deeper in the solid. Theoretical simulations of Auger electron angular distributions based upon atomic point emitters and spherical atomic scatterers of uniform cross section are in close agreement with these experimental results, but opposite to previous theoretical predictions. In view of the definitive results obtained and the straightforward agreement between theory and experiment, angular distribution Auger microscopy (ADAM) is useful for direct imaging of interfacial structure and investigation of electron-solid interactions in the physical and biological sciences and engineering. Applicability of ADAM is illustrated by images obtained for monolayers of silver and iodine on platinum[111].
Chemical Bond-Making, Bond-Breaking, and Electron Transfer in Solution
Authors: Arnett Edward M. , Amarnath Kalyani , Harvey Noel G. , Cheng J. P.
Published: October 2006

A method is described for determining heats of heterolysis, Δ
H
het
, from the heats of reaction of resonancestabilized carbenium ions with carbanions in solution. These results can be converted into heats of homolysis, Δ
H
homo
, for the same bonds by combining Δ
H
het
values with electron transfer energies, Δ
G
ET
(Δ
G
ET
≈ Δ
H
ET
), obtained from redox potentials of the reacting ions. The results provide a comprehensive tabulation of Δ
H
het
, Δ
H
homo
, and Δ
G
ET
values for an extended series of organic compounds and are examined in terms of their interrelationships and a number of related properties of the ions and radicals.
An Aptian Plant with Attached Leaves and Flowers: Implications for Angiosperm Origin
Authors: Taylor David Winship , Hickey Leo J.
Published: October 2006

Recent phylogenetic studies and fossil finds support a new view of the ancestral angiosperm. A diminutive fossil angiosperm from the Aptian of Australia has attached leaves, with intermediate pinnate-palmate, low-rank venation, and lateral axes bearing pistillate organs subtended by bracts and bracteoles that are the oldest direct evidence of flowers. A variety of data suggests a similar morphology for the ancestral angiosperm. This hypothesis explains similarities between rhizomatous to herbaceous Magnoliidae and basal monocots, scarcity of early angiosperm wood, and lack of recognition of earlier remains.
Biological Feedbacks in Global Desertification
Authors: Schlesinger William H. , Reynolds James F. , Cunningham Gary L. , Huenneke Laura F. , Jarrell Wesley M. , Virginia Ross A. , Whitford Walter G.
Published: October 2006

Studies of ecosystem processes on the Jornada Experimental Range in southern New Mexico suggest that long-term grazing of semiarid grasslands leads to an increase in the spatial and temporal heterogeneity of water, nitrogen, and other soil resources. Heterogeneity of soil resources promotes invasion by desert shrubs, which leads to a further localization of soil resources under shrub canopies. In the barren area between shrubs, soil fertility is lost by erosion and gaseous emissions. This positive feedback leads to the desertification of formerly productive land in southern New Mexico and in other regions, such as the Sahel. Future desertification is likely to be exacerbated by global climate warming and to cause significant changes in global biogeochemical cycles.
Purification and Reconstitution of Chloride Channels from Kidney and Trachea
Authors: Landry Donald W. , Akabas Myles H. , Redhead Christopher , Edelman Aleksander , Cragoe Edward J. , Al-Awqati Qais
Published: October 2006

Chloride channels mediate absorption and secretion of fluid in epithelia, and the regulation of these channels is now known to be defective in cystic fibrosis. Indanyl-oxyacetic acid 94 (IAA-94) is a high-affinity ligand for the chloride channel, and an affinity resin based on that structure was developed. Solubilized proteins from kidney and trachea membranes were applied to the affinity matrix, and four proteins with apparent molecular masses of 97, 64, 40, and 27 kilodaltons were eluted from the column by excess IAA-94. A potential-dependent 36Cl- uptake was observed after reconstituting these proteins into liposomes. Three types of chloride channels with single-channel conductances of 26, 100, and 400 picosiemens were observed after fusion of these liposomes with planar lipid bilayers. Similar types of chloride channels have been observed in epithelia.
Specific Expression of Nuclear Proto-Oncogenes Before Entry into Meiotic Prophase of Spermatogenesis
Authors: Wolfes Heiner , Kogawa Katsuhisa , Millette Clarke F. , Cooper Geoffrey M.
Published: October 2006

The expression of proto-oncogenes representative of several functional categories has been investigated during development of mouse male germ cells. The c-
raf
proto-oncogene and three members of the c-
ras
gene family were expressed in mitotically active stem cells, throughout the prophase of meiosis and to varying extents in post-meiotic cell types. In contrast, the nuclear proto-oncogenes c-
fos
, c-
jun
, and c-
myc
were specifically expressed at high levels in type B spermatogonia. High levels of c-
myc
and c-
jun
RNAs were also detected in spermatocytes early in the prophase of meiosis. The type B spermatogonia represent the last mitotic cell division before entry into meiotic prophase; therefore, these nuclear proto-oncogenes may be involved in altering programs of gene expression at this developmental transition.
Dating Pleistocene Archeological Sites by Protein Diagenesis in Ostrich Eggshell
Authors: Brooks A. S. , Hare P. E. , Kokis J. E. , Miller G. H. , Ernst R. D. , Wendorf F.
Published: October 2006

Eggshells of the African ostrich (
Struthio camelus
), ubiquitous in archeological sites in Africa, have been shown by laboratory simulation experiments to retain their indigenous organic matrix residues during diagenesis far better than any other calcified tissue yet studied. The rate of L-isoleucine epimerization to D-alloisoleucine follows reversible first-order kinetics and has been calibrated for local temperature effects and used to estimate the age range of stratified archeological sites. Age estimates are consistent with radiocarbon dates from several stratified archeological sites. With adequate calibration, this technique can provide accurate ages to within 10 to 15 percent for strata deposited within the last 200,000 years in the tropics and the last 1,000,000 years in colder regions such as China.
Twinning in MgSiO
3
Perovskite
Authors: Wang Yanbin , Guyot Francois , Yeganeh-Haeri Amir , Liebermann Robert C.
Published: October 2006

Crystals of MgSiO
3
perovskite synthesized at high pressures and temperatures have orthorhombic symmetry under ambient conditions. Examination by transmission electron microscopy shows that the microstructure of crystals synthesized at 26 gigapascals and 1600°C is dominated by a large number of twin domains that are related by reflection operations with respect to {112} and {110} planes. These twins may be associated with the transformations of MgSiO
3
perovskite from the cubic to tetragonal and tetragonal to orthorhombic phases, respectively, upon decreasing pressure and temperature. These observations suggest that under the experimental synthesis conditions, and perhaps in the earth's lower mantle, the stable phase of MgSiO
3
might have the cubic perovskite structure.
Ostwald Ripening of Clays and Metamorphic Minerals
Authors: Eberl Dennis D. , Środoń Jan , Kralik Martin , Taylor Bruce E. , Peterman Zell E.
Published: October 2006

Analyses of particle size distributions indicate that clay minerals and other diagenetic and metamorphic minerals commonly undergo recrystallization by Ostwald ripening. The shapes of their particle size distributions can yield the rate law for this process. One consequence of Ostwald ripening is that a record of the recrystallization process is preserved in the various particle sizes. Therefore, one can determine the detailed geologic history of clays and other recrystallized minerals by separating, from a single sample, the various particle sizes for independent chemical, structural, and isotopic analyses.
Venting of Carbon Dioxide-Rich Fluid and Hydrate Formation in Mid-Okinawa Trough Backarc Basin
Authors: Sakai H. , Gamo T. , Kim E-S. , Tsutsumi M. , Tanaka T. , Ishibashi J. , Wakita H. , Yamano M. , Oomori T.
Published: October 2006

Carbon dioxide-rich fluid bubbles, containing approximately 86 percent CO
2
, 3 percent H
2
S, and 11 percent residual gas (CH
4
+ H
2
), were observed to emerge from the sea floor at 1335- to 1550-m depth in the JADE hydrothermal field, mid-Okinawa Trough. Upon contact with seawater at 3.8°C, gas hydrate immediately formed on the surface of the bubbles and these hydrates coalesced to form pipes standing on the sediments. Chemical composition and carbon, sulfur, and helium isotopic ratios indicate that the CO
2
-rich fluid was derived from the same magmatic source as dissolved gases in 320°C hydrothermal solution emitted from a nearby black smoker chimney. The CO
2
-rich fluid phase may be separated by subsurface boiling of hydrothermal solutions or by leaching of CO
2
-rich fluid inclusion during posteruption interaction between pore water and volcanogenic sediments.
Structural and Electronic Role of Lead in (PbBi)
2
Sr
2
CaCu
2
O
8
Superconductors by STM
Authors: Wu Xian Liang , Zhang Zhe , Wang Yue Li , Lieber Charles M.
Published: October 2006

The structural and electronic effects of lead substitution in the high-temperature superconducting materials Pb

x

Bi

2-
x

Sr
2
CaCu
2
O
8
have been characterized by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Large-area STM images of the Bi(Pb)—O layers show that lead substitution distorts and disorders the one-dimensional superlattice found in these materials. Atomic-resolution images indicate that extra oxygen atoms are present in the Bi(Pb)—O layers. STS data show that the electronic structure of the Bi(Pb)—O layers is insensitive to lead substitution within ±0.5 electron volt of the Fermi level; however, a systematic decrease in the density of states is observed at ≈1 electron volt above the Fermi level. Because the superconducting transition temperatures are independent of
x
(Pb) (
x
≤ 0.7), these microscopic STM and STS data suggest that the lead-induced electronic and structural changes in the Bi(Pb)—O layer do not perturb the electronic states critical to forming the superconducting state in this system.
Synchronous, Alternating, and Phase-Locked Stridulation by a Tropical Katydid
Authors: Sismondo Enrico
Published: October 2006

In the field the chirps of neighboring
Mecopoda
sp. (Orthoptera, Tettigoniidae, and Mecopodinae) males are normally synchronized, but between more distant individuals the chirps are either synchronous or regularly alternating. The phase response to single-stimulus chirps depends on both the phase and the intensity of the stimulus. Iteration of the Poincaré map of the phase response predicts a variety of phase-locked synchronization regimes, including period-doubling bifurcations, in close agreement with experimental observations. The versatile acoustic behavior of
Mecopoda
encompasses most of the phenomena found in other synchronizing insects and thus provides a general model of insect synchronization behavior.
Instrumental Requirements for Global Atmospheric Chemistry
Authors: Albritton D. L. , Fehsenfeld F. C. , Tuck A. F.
Published: October 2006

The field of atmospheric chemistry is data-limited, primarily because of the challenge of measuring the key chemical constituents in the global environment. Several recent advances, however, in rugged, portable, remote-sensing, ground-based instrumentation and accurate, fast-response airborne instrumentation have provided powerful tools for the understanding of stratospheric ozone, particularly in polar regions. Current discoveries of the role of heterogeneous chemical processes point to the need for better techniques for characterization of stratospheric aerosols. In the troposphere, advances in in situ, sensitive methods for detecting reactive nitrogen compounds have demonstrated the role that these compounds have in controlling global oxidation processes, but better measurements of the reservoir species by which the long-ranged transport of pollutant-reactive nitrogen compounds is thought to occur are urgently needed. The role of hydrocarbons, particularly those of natural origin, in ozone formation in rural areas has focused attention on the requirement for better speciation of these ubiquitous compounds. Lastly, rigorous instrument intercomparison experiments have provided unbiased estimates of measurement capabilities.
Energy Sources for Triton's Geyser-Like Plumes
Authors: Brown R. H. , Kirk R. L. , Johnson T. V. , Soderblom L. A.
Published: October 2006

Four geyser-like plumes were discovered near Triton's south pole in areas now in permanent sunlight. Because Triton's southern hemisphere is nearing a maximum summer solstice, insolation as a driver or a trigger for Triton's geyser-like plumes is an attractive hypothesis. Trapping of solar radiation in a translucent, low-conductivity surface layer (in a solid-state greenhouse), which is subsequently released in the form of latent heat of sublimation, could provide the required energy. Both the classical solid-state greenhouse consisting of exponentially absorbed insolation in a gray, translucent layer of solid nitrogen, and the "super" greenhouse consisting of a relatively transparent solid-nitrogen layer over an opaque, absorbing layer are plausible candidates. Geothermal heat may also play a part if assisted by the added energy input of seasonal cycles of insolation.
Hydroxyl Radical Photoproduction in the Sea and Its Potential Impact on Marine Processes
Authors: Mopper Kenneth , Zhou Xianliang
Published: October 2006

Photochemical production rates and steady-state concentrations of hydroxyl radicals (⋅OH) were measured in sunlight-irradiated seawater. Values ranged from 110 nanomolar per hour and 12 × 10
-18
molar in coastal surface water to 10 nanomolar per hour and 1.1 × 10
-18
molar in open ocean surface water. The wavelengths responsible for this production are in the ultraviolet B region (280 to 320 nanometers) of the solar spectrum. Dissolved organic matter (DOM) appears to be the main source for ⋅OH over most of the oceans, but in upwelling areas nitrite and nitrate photolysis may also be important. DOM in the deep sea is degraded more readily by ⋅OH (and its daughter radicals), by a factor of 6 to 15, than is DOM in open-ocean surface water. This finding may in part bear on major discrepancies among current methods for measuring dissolved organic carbon in seawater.
General Relativity at 75: How Right Was Einstein?
Authors: Will Clifford M.
Published: October 2006

The status of experimental tests of general relativity is reviewed on the occasion of its 75th anniversary. Einstein's equivalence principle is well supported by experiments such as the Eötvös experiment, tests of special relativity, and the gravitational redshift experiment. Tests of general relativity have reached high precision, including the light deflection and the perihelion advance of Mercury, proposed by Einstein 75 years ago, and new tests such as the Shapiro time delay and the Nordtvedt effect in lunar motion. Gravitational wave damping has been detected to an accuracy of 1 percent on the basis of measurements of the binary pulsar. The status of the "fifth force" is discussed, along with the frontiers of experimental relativity, including proposals for testing relativistic gravity with advanced technology and spacecraft.
Salicylic Acid: A Likely Endogenous Signal in the Resistance Response of Tobacco to Viral Infection
Authors: Malamy Jocelyn , Carr John P. , Klessig Daniel F. , Raskin Ilya
Published: October 2006

Some cultivars of tobacco are resistant to tobacco mosaic virus (TMV) and synthesize pathogenesis-related (PR) proteins upon infection. In a search for the signal or signals that induce resistance or PR genes, it was found that the endogenous salicylic acid levels in resistant, but not susceptible, cultivars increased at least 20-fold in infected leaves and 5-fold in uninfected leaves after TMV inoculation. Induction of PR1 genes paralleled the rise in salicylic acid levels. Since earlier work has demonstrated that treatment with exogenous salicylic acid induces PR genes and resistance, these findings suggest that salicylic acid functions as the natural transduction signal.
Surface Displacements in the 1906 San Francisco and 1989 Loma Prieta Earthquakes
Authors: Segall Paul , Lisowski Mike
Published: October 2006

The horizontal displacements accompanying the 1906 San Francisco earthquake and the 1989 Loma Prieta earthquake are computed from geodetic survey measurements. The 1906 earthquake displacement field is entirely consistent with right-lateral strike slip on the San Andreas fault. In contrast, the 1989 Loma Prieta earthquake exhibited subequal components of strike slip and reverse faulting. This result, together with other seismic and geologic data, may indicate that the two earthquakes occurred on two different fault planes.
Exploitation of Herbivore-Induced Plant Odors by Host-Seeking Parasitic Wasps
Authors: Turlings T. C. J. , Tumlinson J. H. , Lewis W. J.
Published: October 2006

Corn seedlings release large amounts of terpenoid volatiles after they have been fed upon by caterpillars. Artificially damaged seedlings do not release these volatiles in significant amounts unless oral secretions from the caterpillars are applied to the damaged sites. Undamaged leaves, whether or not they are treated with oral secretions, do not release detectable amounts of the terpenoids. Females of the parasitic wasp
Cotesia marginiventris
(Cresson) learn to take advantage of those plant-produced volatiles to locate hosts when exposed to these volatiles in association with hosts or host by-products. The terpenoids may be produced in defense against herbivores but may also serve a secondary function in attracting the natural enemies of these herbivores.
Astrophysics from the Moon
Authors: Burke Bernard F.
Published: October 2006

The surface of the moon would be an excellent location for astronomical telescopes, and, if a lunar base were to be established, the construction and maintenance of instruments would become feasible. The prospects are reviewed, with particular attention given to large optical aperturesynthesis instruments analogous to the Very Large Array of the National Radio Astronomy Observatory. Typical parameters for a particular system are presented.
Observational Evidence for a Possible New Diffusion Path
Authors: Hacker Bradley R. , Christie John M.
Published: October 2006

Transmission electron microscopy of experimentally deformed amphibolite suggests that submicroscopic intracrystalline tubes formed around linear defects may be a previously unrecognized kind of diffusion pathway. Deformed and compositionally altered plagioclase and amphibole crystals include moderate densities of linear defects that morphologically resemble unit dislocations but display unusual contrast. During prolonged electron irradiation, the core regions of the defects expand to well-defined tubes that are ∼20 nanometers in diameter. Both observations suggest that the regions about the defect cores are glassy and were filled with silicate-water fluid during the experiments. Intracrystalline transport along these tubes would likely be several orders of magnitude faster than traditionally conceived processes of solid-state volume diffusion, grain-boundary solvent transfer, and ordinary pipe diffusion along dislocation cores.
Local Structure and Chemical Shifts for Six-Coordinated Silicon in High-Pressure Mantle Phases
Authors: Stebbins Jonathan F. , Kanzaki Masami
Published: October 2006

Most of the earth's mantle is made up of high-pressure silicate minerals that contain octahedrally coordinated silicon (Si
VI
), but many thermodynamically important details of cation site ordering remain unknown. Silicon-29 nuclear magnetic resonance (NMR) spectroscopy is potentially very useful for determining short-range structure. A systematic study of silicon-29 chemical shifts for Si
VI
has revealed empirical correlations between shift and structure that are useful in understanding several new calcium silicates. The observed ordering state of a number of high-pressure magnesium silicates is consistent with the results of previous x-ray diffraction studies.
The Spectrum of Comet Austin from 910 to 1180 Å
Authors: Green James C. , Cash Webster , Cook Timothy A. , Stern S. Alan
Published: October 2006

A spectrum of comet Austin (1988 c
1
) has been obtained from 910 to 1180 Å. Three bright emission lines were detected, including a forbidden oxygen line (1128 Å), which are attributable to radiative pumping of neutral oxygen by solar Lyman β. The relative strengths of the observed features should prove to be a useful diagnostic of the physical conditions and radiation fields in cometary comae. In addition, the absence of strong spectral features from highly volatile species such as He, Ar, or N
2
can be used to place constraints on the thermal environment under which the comet was formed and has been processed.
Science, Slogans, and Civic Duty
Authors: Langenberg Donald N.
Published: October 2006

We are beset with slogans for complex and controversial public issues that represent significant bodies of scientific knowledge. Public debate and action on these issues rarely adequately reflect such knowledge and seldom feature scientists playing central roles. Examples are assessment of educational effectiveness through assessment of student learning outcomes and the setting of scientific priorities across the full spectrum of scientific disciplines. It is an unfulfilled civic duty of scientists and engineers to engage themselves more fully and actively in public debate and action on important issues.
Back-Action Evasion as an Alternative to Impedance Matching
Authors: Yurke B.
Published: October 2006

Back-action evasion is a measurement technique originally devised to overcome certain limits imposed by quantum mechanics on the sensitivity of gravitational radiation detectors. The technique is, however, more generally applicable and can be used to improve the sensitivity of instrumentation with noise floors much greater than the quantum noise floor. The principle of back-action evasion is described here by means of a simple example. A comparison of back-action evasion with impedance matching is made to clarify when back-action evasion may be useful. Back-action evasion allows one to achieve a sensitivity comparable to that achieved by impedance matching.
Analysis of the Pioneer-Venus Lyman-α Image of the Hydrogen Coma of Comet P/Halley
Authors: Smyth William H. , Combi Michael R. , Stewart A. I. F.
Published: October 2006

Comet Halley passed within 0.27 astronomical unit of Venus on 4 February 1986, 5 days before perihelion. This provided a unique opportunity to observe the comet's coma with the ultraviolet spectrometer orbiting the planet aboard the Pioneer Venus Orbiter spacecraft when the coma was otherwise obscured from Earth's view by the sun's glare. More than 9000 data points acquired systematically over the 5-day period from 2 to 6 February were combined to construct an excellent Lyman-α image of the hydrogen coma. The Lyman-α image was successfully reproduced with a comprehensive physical model, thereby verifying and documenting the underlying chemical kinetics and dynamics of the hydrogen coma.
Energetic Particles at Venus: Galileo Results
Authors: Williams D. J. , McEntire R. W. , Krimigis S. M. , Roelof E. C. , Jaskulek S. , Tossman B. , Wilken B. , Stüdemann W. , Armstrong T. P. , Fritz T. A. , Lanzerotti L. J. , Roederer J. G.
Published: October 2006

At Venus the Energetic Particles Detector (EPD) on the Galileo spacecraft measured the differential energy spectra and angular distributions of ions ≳ 22 kiloelectron volts (keV) and electrons ≳ 15 keV in energy. The only time particles were observed by EPD was in a series of episodic events [∼0546 to 0638 universal time (UT)] near closest approach (0559:03 UT). Angular distributions were highly anisotropic, ordered by the magnetic field, and showed ions arriving from the hemisphere containing Venus and its bow shock. The spectra showed a power law form with intensities observed into the 120- to 280-keV range. Comparisons with model bow shock calculations show that these energetic ions are associated with the venusian foreshock-bow shock region. Shock-drift acceleration in the venusian bow shock seems the most likely process responsible for the observed ions.
Middle Infrared Thermal Maps of Venus at the Time of the Galileo Encounter
Authors: Orton Glenn S. , Caldwell John , Friedson A. James , Martin Terry Z.
Published: October 2006

Images of the disk of Venus, taken at wavelengths between 8 and 22 micrometers, were obtained a few days after the Galileo spacecraft's closest approach on 8 February 1990; these images show variations in the thickness of the main H
2
SO
4
cloud deck and the overlying temperature structure. Several features are qualitatively similar to those of earlier observations, such as a hot region at the south pole, surrounded by a cold "collar,'' and brightening toward the lower latitudes, where low-contrast banding appears. The collar does have a northern counterpart that is warmer, however. Equatorial limb darkening is quantitatively similar to that of previous observations; fairly constant at wavelengths up to 20 micrometers, where limb darkening increases substantially. In contrast to what was found in previous observations, polar and equatorial limb darkening are nearly the same at most wavelengths. A longitudinal variation is observable that is consistent with a wavenumber-2 behavior and a brightness maximum near local midnight.
Cognate DNA Binding Specificity Retained After Leucine Zipper Exchange Between GCN4 and C/EBP
Authors: Agre Peter , Johnson Peter F. , McKnight Steven L.
Published: October 2006

Both C/EBP and GCN4 are sequence-specific DNA binding proteins that control gene expression. Recent evidence implicates C/EBP as a transcriptional regulator of genes involved in lipid and carbohydrate metabolism. The C/EBP protein binds avidly to the dyad symmetric sequence 5′-ATTGCGCAAT-3′; GCN4 regulates the transcription of genes that control amino acid biosynthesis in yeast, and binds avidly to the dyad symmetric sequence 5′-ATGA(G/C)TCAT-3′. Both C/EBP and GCN4 bind DNA via the same structural motif. This motif has been predicted to be bipartite, consisting of a dimerization interface termed the "leucine zipper" and a DNA contact surface termed the "basic region." Specificity of DNA binding has been predicted to be imparted by the basic region. As a test of this hypothesis, recombinant proteins were created wherein the basic regions and leucine zippers of GCN4 and C/EBP were reciprocally exchanged. In both of the recombinant polypeptides, DNA binding specificity is shown to track with the basic region.
Membrane Anchoring of a Human IgG Fc Receptor (CD16) Determined by a Single Amino Acid
Authors: Lanier Lewis L. , Cwirla Steve , Yu George , Testi Roberto , Phillips Joseph H.
Published: October 2006

CD16 is a low-affinity immunoglobulin G (IgG) Fc receptor that is expressed on natural killer (NK) cells, granulocytes, activated macrophages, and some T lymphocytes. Two similar genes, CD16-I and CD16-II, encode membrane glycoproteins that are anchored by phosphatidylinositol (PI)-glycan and transmembrane polypeptides, respectively. The primary structural requirements for PI-linkage were examined by constructing a series of hybrid cDNA molecules. Although both cDNA's have an identical COOH-terminal hydrophobic segment, CD16-I has Ser
203
whereas CD16-II has Phe
203
. Conversion of Phe to Ser in CD16-II permits expression of a PI-glycan-anchored glycoprotein, whereas conversion of Ser to Phe in CD16-I prevents PI-glycan linkage.
Rapid Formation of Ontong Java Plateau by Aptian Mantle Plume Volcanism
Authors: Tarduno J. A. , Sliter W. V. , Kroenke L. , Leckie M. , Mayer H. , Mahoney J. J. , Musgrave R. , Storey M. , Winterer E. L.
Published: October 2006

The timing of flood basalt volcanism associated with formation of the Ontong Java Plateau (OJP) is estimated from paleomagnetic and paleontologic data. Much of OJP formed rapidly in less than 3 million years during the early Aptian, at the beginning of the Cretaceous Normal Polarity Superchron. Crustal emplacement rates are inferred to have been several times those of the Deccan Traps. These estimates are consistent with an origin of the OJP by impingement at the base of the oceanic lithosphere by the head of a large mantle plume. Formation of the OJP may have led to a rise in sea level that induced global oceanic anoxia. Carbon dioxide emissions likely contributed to the mid-Cretaceous greenhouse climate but did not provoke major biologic extinctions.
Evidence for Multiple Sources of Diamond from Primitive Chondrites
Authors: Russell S. S. , Arden J. W. , Pillinger C. T.
Published: October 2006

Fine-grained diamonds, the most abundant form of circumstellar dust isolated from primitive meteorites, have elemental and isotopic characteristics that are dependent on the host meteorite type. Carbon isotopic compositions vary from –32 to –38 per mil, and nitrogen associated with the diamond changes in overall abundance by over a factor of four from 0.2 to 0.9 weight percent, between ordinary and CM2-type chondrites. Although the ratio of carbon to nitrogen evolves in a distinctive way during combustion of diamond separates, metamorphic degassing of nitrogen is not the main cause of the differences in nitrogen content. The data suggest that intrinsic differences must have been inherited by the diamonds at the time of their formation and that the diamonds were distributed heterogeneously in the solar nebula during condensation. However, the hypothesis that a distinct nitrogen carrier remains hidden within the diamond cannot be ruled out.
Primary Structure of the β Subunit of the DHP-Sensitive Calcium Channel from Skeletal Muscle
Authors: Ruth Peter , Röhrkasten Axel , Biel Martin , Bosse Eva , Regulla Stefan , Meyer Helmut E. , Flockerzi Veit , Hofmann Franz
Published: October 2006

Complementary DNAs for the β subunit of the dihydropyridine-sensitive calcium channel of rabbit skeletal muscle were isolated on the basis of peptide sequences derived from the purified protein. The deduced primary structure is without homology to other known protein sequences and is consistent with the β subunit being a peripheral membrane protein associated with the cytoplasmic aspect of the sarcolemma. The protein contains sites that might be expected to be preferentially phosphorylated by protein kinase C and guanosine 3′,5′-monophosphate-dependent protein kinase. A messenger RNA for this protein appears to be expressed in brain.
Strontium Isotopic Composition of Estuarine Sediments as Paleosalinity-Paleoclimate Indicator
Authors: Ingram B. L. , Sloan D.
Published: October 2006

The strontium isotopic composition of biogenic precipitates that occur in estuarine sediments can be used as proxy indicator of paleosalinity and for assessing precipitation and river discharge rates over thousands of years. In the San Francisco Bay estuary, river water with low
87
Sr/
86
Sr ratio (average, 0.7065) and low Sr concentration (0.13 parts per million) mixes with seawater with a higher
87
Sr/
86
Sr ratio (0.7092) and Sr concentration (7.9 parts per million). The predicted mixing relation between salinity and Sr isotopic composition is confirmed by measurements of modern estuarine surface waters. A paleosalinity record obtained from foraminifera for the ancestral San Francisco Bay during oxygen isotope substage 5e of the last interglacial reflects a global rise and fall of sea level, and short time-scale variations related to fluctuations in discharge rates of the Sacramento and San Joaquin rivers.
Production of Isotopic Variability in Continental Basalts by Cryptic Crustal Contamination
Authors: Glazner Allen F. , Farmer G. Lang
Published: October 2006

Regional variations in the Nd, Sr, and Pb isotopic compositions of Neogene basalts from the western United States are commonly interpreted to originate in the subcontinental mantle. In southern California, isotopic variability is restricted to lavas that lack mantle-derived xenoliths; xenolith-bearing basalts have uniform isotopic compositions similar to those of ocean-island basalts (OIBs). Combined with available geochemical data, these observations suggest that isotopic variability at these volcanoes results from subtle crustal contamination, locally by mafic crust, of primitive OIB-like magma. Recognition of such cryptic contamination may help to reconcile local discrepancies between tectonic and isotopic views of the subcontinental mantle.
Shocked Quartz at the Triassic-Jurassic Boundary in Italy
Authors: Bice D. M. , Newton C. R. , McCauley S. , Reiners P. W. , McRoberts C. A.
Published: October 2006

Quartz grains that appear to have been shock-metamorphosed occur within three closely spaced shale beds from the uppermost Triassic ("Rhaetian") Calcare a Rhaetavicula in the Northern Apennines of Italy. The upper shale coincides with the abrupt termination of the distinctive, uppermost Triassic
Rhaetavicula
fauna and is overlain by the Hettangian (Lower Jurassic) Calcare Massiccio; no extinctions appear to be associated with the two lower layers, which occur 1.2 and 2.4 meters below the boundary shale. Approximately 5 to 10% of the quartz grains within these layers exhibit one or more sets of planar deformational features whose orientations cluster around the rational crystallographic planes (basal, ω, and π) most commonly observed in shocked quartz. Textural and stratigraphic observations support an interpretation of at least three closely spaced impacts at the end of the Triassic.
Rhenium-Osmium Isotope Constraints on the Age of Iron Meteorites
Authors: Horan M. F. , Morgan J. W. , Walker R. J. , Grossman J. N.
Published: October 2006

Rhenium and osmium concentrations and the osmium isotopic compositions of iron meteorites were determined by negative thermal ionization mass spectrometry. Data for the IIA iron meteorites define an isochron with an uncertainty of approximately ±31 million years for meteorites ∼4500 million years old. Although an absolute rheniumosmium closure age for this iron group cannot be as precisely constrained because of uncertainty in the decay constant of
187
Re, an age of 4460 million years ago is the minimum permitted by combined uncertainties. These age constraints imply that the parent body of the IIAB magmatic irons melted and subsequently cooled within 100 million years after the formation of the oldest portions of chondrites. Other iron meteorites plot above the IIA isochron, indicating that the planetary bodies represented by these iron groups may have cooled significantly later than the parent body of the IIA irons.
Rapid Continental Subsidence Following the Initiation and Evolution of Subduction
Authors: Gurnis Michael
Published: October 2006

Dynamic topography resulting from initiation of slab subduction at an ocean-continent margin causes the continental lithosphere to subside rapidly. As subduction continues and the slab shallows, a basin depocenter and forebulge migrate in toward the continental interior. Finally, closure of the ocean basin leads to regional uplift. These active margin processes have commonly been ascribed to supracrustal loading, but numerical modeling shows that dynamic subsidence rates can exceed 100 meters per million years and are similar to rates of sediment accumulation along convergent North American plate margins over the Phanerozoic.
Global Tectonics and Space Geodesy
Authors: Gordon Richard G. , Stein Seth
Published: October 2006

Much of the success of plate tectonics can be attributed to the near rigidity of tectonic plates and the availability of data that describe the rates and directions of motion across narrow plate boundaries ∼1 to 60 kilometers wide. Nonetheless, many plate boundaries in both continental and oceanic lithosphere are not narrow but are hundreds to thousands of kilometers wide. Wide plate boundary zones cover ∼15 percent of Earth's surface area. Space geodesy, which includes very long baseline radio interferometry, satellite laser ranging, and the global positioning system, is providing the accurate long-distance measurements needed to estimate the present motion across and within wide plate boundary zones. Space geodetic data show that plate velocities averaged over years are remarkably similar to velocities averaged over millions of years.
Fractals and Cosmological Large-Scale Structure
Authors: Luo Xiaochun , Schramm David N.
Published: October 2006

Observations of galaxy-galaxy and cluster-cluster correlations as well as other large-scale structure can be fit with a "limited" fractal with dimension
D
≈ 1.2. This is not a "pure" fractal out to the horizon: the distribution shifts from power law to random behavior at some large scale. If the observed patterns and structures are formed through an aggregation growth process, the fractal dimension
D
can serve as an interesting constraint on the properties of the stochastic motion responsible for limiting the fractal structure. In particular, it is found that the observed fractal should have grown from two-dimensional sheetlike objects such as pancakes, domain walls, or string wakes. This result is generic and does not depend on the details of the growth process.
A Mutant of TTX-Resistant Cardiac Sodium Channels with TTX-Sensitive Properties
Authors: Satin Jonathan , Kyle John W. , Chen Michael , Bell Peter , Cribbs Leanne L. , Fozzard Harry A. , Rogart Richard B.
Published: October 2006

The cardiac sodium channel α subunit (RHI) is less sensitive to tetrodotoxin (TTX) and saxitoxin (STX) and more sensitive to cadmium than brain and skeletal muscle (μl) isoforms. An RHI mutant, with Tyr substituted for Cys at position 374 (as in μl) confers three properties of TTX-sensitive channels: (i) greater sensitivity to TTX (730-fold); (ii) lower sensitivity to cadmium (28-fold); and (iii) altered additional block by toxin upon repetitive stimulation. Thus, the primary determinant of high-affinity TTX-STX binding is a critical aromatic residue at position 374, and the interaction may take place possibly through an ionized hydrogen bond. This finding requires revision of the sodium channel pore structure that has been previously suggested by homology with the potassium channel.
Plate Tectonics and Hotspots: The Third Dimension
Authors: Anderson Don L. , Tanimoto Toshiro , Zhang Yu-shen
Published: October 2006

High-resolution seismic tomographic models of the upper mantle provide powerful new constraints on theories of plate tectonics and hotspots. Midocean ridges have extremely low seismic velocities to a depth of 100 kilometers. These low velocities imply partial melting. At greater depths, low-velocity and high-velocity anomalies record, respectively, previous positions of migrating ridges and trenches. Extensional, rifting, and hotspot regions have deep (> 200 kilometers) low-velocity anomalies. The upper mantle is characterized by vast domains of high temperature rather than small regions surrounding hotspots; the asthenosphere is not homogeneous or isothermal. Extensive magmatism requires a combination of hot upper mantle and suitable lithospheric conditions. High-velocity regions of the upper 200 kilometers of the mantle correlate with Archean cratons.
The Role of Excitatory Amino Acids and NMDA Receptors in Traumatic Brain Injury
Authors: Faden Alan I. , Demediuk Paul , Panter S. Scott , Vink Robert
Published: October 2006

Brain injury induced by fluid percussion in rats caused a marked elevation in extracellular glutamate and aspartate adjacent to the trauma site. This increase in excitatory amino acids was related to the severity of the injury and was associated with a reduction in cellular bioenergetic state and intracellular free magnesium. Treatment with the noncompetitive
N
-methyl-D-aspartate (NMDA) antagonist dextrorphan or the competitive antagonist 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid limited the resultant neurological dysfunction; dextrorphan treatment also improved the bioenergetic state after trauma and increased the intracellular free magnesium. Thus, excitatory amino acids contribute to delayed tissue damage after brain trauma; NMDA antagonists may be of benefit in treating acute head injury.
A High-Pressure Test of Birch's Law
Authors: Campbell A. J. , Heinz D. L.
Published: October 2006

The compressional wave velocities of polycrystalline NaCl and KCl have been measured to over 17 gigapascals, with the use of Brillouin scattering and the diamond anvil cell. This pressure corresponds to 40% compression for NaCl and 60% compression for KCl (including the volume change across the B1-B2 transition). The data obey Birch's Law, which predicts that the velocity of each material is linear with density, except across the B1-B2 phase transition in KCl. This deviation from Birch's Law can be rationalized in terms of an interatomic potential model wherein the vibrational frequencies of the nearest neighbor bonds decrease when going to the eight-coordinated B2 structure from the six-coordinated B1 structure.
Fullerenes from the Geological Environment
Authors: Buseck Peter R. , Tsipursky Semeon J. , Hettich Robert
Published: October 2006

By means of high-resolution transmission electron microscopy, both C
60
and C
70
fullerenes have been found in a carbon-rich Precambrian rock from Russia. The fullerenes were confirmed by Fourier transform mass spectrometry with both laser desorption and thermal desorption/electron-capture methods to verify that the fullerenes were indeed present in the geological sample and were not generated by the laser ionization event. The mass spectra were measured under conditions sufficient to resolve the
13
C/
12
C isotopic ratios for C
60
and C
70
and indicate that these ratios correspond to the normal range of isotopic values.
Kinetics of the OH Reaction with Methyl Chloroform and Its Atmospheric Implications
Authors: Talukdar Ranajit K. , Mellouki Abdelwahid , Schmoltner Anne-Marie , Watson Thomas , Montzka Stephen , Ravishankara A. R.
Published: October 2006

The rate coefficients for the reaction of hydroxyl (OH) radicals with methyl chloroform (CH
3
CCI
3
) were measured between 243 and 379 kelvin with the pulsed photolysis—laserinduced fluorescence method. The measured rate coefficients at 298 and 277 kelvin were ∼20 and ∼15%, respectively, lower than earlier values. These results will increase the tropospheric OH concentrations derived from the CH
3
CCI
3
budget analysis by ∼15%. The predicted atmospheric lifetimes of species whose main loss process is the reaction with OH in the troposphere will be lowered by 15% with consequent changes in their budgets, global warming potentials, and ozone depletion potentials.