bluuebunny/crossref_metadata_2025 huggingface dataset:
Late Triassic Turtles from South America
Authors: Rougier Guillermo W. , de la Fuente Marcelo S. , Arcucci Andrea B.
Published: October 2006

The discovery of Triassic (Norian) turtles from the northwest part of Argentina extends the South American record of turtles by 60 million years. Two skeletons, one almost complete, represent a new genus and species of a basal turtle,Palaeochersis talampayensis. This turtle is a member of the family Australochelidae that was recently erected forAustralochelys africanusfrom the Lower Jurassic of South Africa. Here, it is proposed that Australochelidae is the sister group ofProterochersisplus Casichelydia, that turtles were diverse by the Late Triassic, and that Casichelydia probably originated during the Jurassic.
Serpentine Stability to Mantle Depths and Subduction-Related Magmatism
Authors: Ulmer Peter , Trommsdorff Volkmar
Published: October 2006

Results of high-pressure experiments on samples of hydrated mantle rocks show that the serpentine mineral antigorite is stable to ∼720°C at 2 gigapascals, to ∼690°C at 3 gigapascals, and to ∼620°C at 5 gigapascals. The breakdown of antigorite to forsterite plus enstatite under these conditions produces 13 percent H
2
O by weight to depths of 150 to 200 kilometers in subduction zones. This H
2
O is in an ideal position for ascent into the hotter, overlying mantle where it can cause partial melting in the source region for calc-alkaline magmas at a depth of 100 to 130 kilometers and a temperature of ∼1300°C. The breakdown of antigorite in hydrated mantle produces an order of magnitude more H
2
O than does the dehydration of altered oceanic crust.
Dinitrogen Cleavage by a Three-Coordinate Molybdenum(III) Complex
Authors: Laplaza Catalina E. , Cummins Christopher C.
Published: October 2006

Cleavage of the relatively inert dinitrogen (N
2
) molecule, with its extremely strong N≡N triple bond, has represented a major challenge to the development of N
2
chemistry. This report describes the reductive cleavage of N
2
to two nitrido (N
3–
) ligands in its reaction with Mo(NRAr)
3
, where R is C(CD
3
)
2
CH
3
and Ar is 3,5-C
6
H
3
(CH
3
)
2
, a synthetic three-coordinate molybdenum(III) complex of known structure. The formation of an intermediate complex was observed spectroscopically, and its conversion (with N≡N bond cleavage) to the nitrido molybdenum(VI) product N≡Mo(NRAr)
3
followed first-order kinetics at 30°C. It is proposed that the cleavage reaction proceeds by way of an intermediate complex in which N
2
bridges two molybdenum centers.
Solar-Like M-Class X-ray Flares on Proxima Centauri Observed by the ASCA Satellite
Authors: Haisch Bernhard , Antunes A. , Schmitt J. H. M. M.
Published: October 2006

Because of instrumental sensitivity limits and stellar distances, the types of x-ray flares observable on stars have been intrinsically much more energetic than those on the sun. Such enormous events are a useful extrapolation of the solar phenomenon if the underlying assumption is correct that they form a continuous sequence involving similar physical processes as on the sun. The Advanced Satellite for Cosmology and Astrophysics (ASCA), with its greater sensitivity and high-energy response, is now able to test this hypothesis. Direct comparison with solar flares measured by the x-ray-monitoring Geostationary Operational Environmental Satellites (GOES) is possible. The detection of flares on Proxima Centauri that correspond to GOES M-class events on the sun are reported.
Head Segmentation in Early Cambrian
Fuxianhuia
: Implications for Arthropod Evolution
Authors: Chen Jun-yuan , Zhou Gui-qing , Edgecombe Gregory D. , Ramsköld Lars
Published: October 2006

The arthropod
Fuxianhuia
from the Chengjiang fauna displays primitive aspects of cephalic segmentation and trunk limb morphology that indicate a basal position within Euarthropoda. The cephalon consists of an eye-bearing sclerite that articulates with a head shield bearing antennules and subchelate appendages. Eye stalks, antennules, and subchelate appendages are proto-, deuto-, and tritocerebral limbs and organs, respectively. The anterior position of the eye-bearing sclerite parallels the embryonic origin of arthropod eye lobes. The head of
Fuxianhuia
includes the acron and one somite and is regarded as a protocephalon. The definitive head of arthropods may have fused separate eye-bearing and appendage-bearing sclerites.
Ordered Metal Nanohole Arrays Made by a Two-Step Replication of Honeycomb Structures of Anodic Alumina
Authors: Masuda Hideki , Fukuda Kenji
Published: October 2006

A highly ordered metal nanohole array (platinum and gold) was fabricated by a two-step replication of the honeycomb structure of anodic porous alumina. Preparation of the negative porous structure of porous alumina followed by the formation of the positive structure with metal resulted in a honeycomb metallic structure. The metal hole array of the film has a uniform, closely packed honeycomb structure approximately 70 nanometers in diameter and from 1 to 3 micrometers thick. Because of its textured surface, the metal hole array of gold showed a notable color change compared with bulk gold.
Scenes From a Marriage—Of Optics and Electronics
Authors: Service Robert F.
Published: October 2006

BALTIMORE—Exploring the common ground between optics and electronics, more than 6800 physicists, spectroscopists, and engineers gathered here from 21 to 26 May at the joint meetings of the Conference on Lasers and Electro-Optics and the Quantum Electronics and Laser Science conference. Participants unveiled new technologies that have sprung up on this common ground, such as an imaging technique that can gauge the chemical composition of materials. They also described ways to broaden that ground, such as a novel approach for integrating lasers and silicon chips—a challenge that has slowed progress toward a new generation of high-speed computers and communications.
Optical Switching and Image Storage by Means of Azobenzene Liquid-Crystal Films
Authors: Ikeda Tomiki , Tsutsumi Osamu
Published: October 2006

Liquid crystals are promising materials for optical switching and image storage because of their high resolution and sensitivity. Azobenzene liquid crystals (LCs) have been developed, in which azobenzene moieties play roles as both mesogens and photosensitive chromophores. Azobenzene LC films showed a nematic phase in trans isomers and no LC phase in cis isomers. Trans-cis photoisomerization of azobenzene with a laser pulse resulted in a nematic-to-isotropic phase transition with a rapid optical response of 200 microseconds.
Managing the Evolution of Insect Resistance to Transgenic Plants
Authors: Alstad D. N. , Andow D. A.
Published: October 2006

The evolution of resistance in pests such as the European corn borer will imperil transgenic maize varieties that express insecticidal crystal proteins ofBacillus thuringiensis. Patchworks of treated and untreated fields can delay the evolution of pesticide resistance, but the untreated refuge fields are likely to sustain heavy damage. A strategy that exploits corn borer preferences and movements can eliminate this problem. Computer simulation indicates that this approach can delay the evolution of resistance and reduce insect damage in the untreated fields of a patchwork planting regime.
Dynamics of Carbonium Ions Solvated by Molecular Hydrogen: CH
5
+
(H
2
)

n

(
n
= 1, 2, 3)
Authors: Boo D. W. , Liu Z. F. , Suits A. G. , Tse J. S. , Lee Y. T.
Published: October 2006

The dynamics of the carbonium ion (CH
5
+
), a highly reactive intermediate with no equilibrium structure, was studied by measuring the infrared spectra for internally cold CH
5
+
(H
2
)

n

(
n
= 1, 2, 3) stored in an ion trap. First-principle molecular dynamics methods were used to directly simulate the internal motion for these ionic complexes. The combined experimental and theoretical efforts substantiated the anticipated scrambling motion in the CH
5
+
core and revealed the effect of the solvent molecular hydrogen in slowing down the scrambling. The results indicate the feasibility of using solvent molecules to stabilize the floppy CH
5
+
ion in order to make it amenable to spectroscopic study.
Ground-Water Radon Anomaly Before the Kobe Earthquake in Japan
Authors: Igarashi G. , Saeki S. , Takahata N. , Sumikawa K. , Tasaka S. , Sasaki Y. , Takahashi M. , Sano Y.
Published: October 2006

Radon concentration in ground water increased for several months before the 1995 southern Hyogo Prefecture (Kobe) earthquake on 17 January 1995. From late October 1994, the beginning of the observation, to the end of December 1994, radon concentration increased about fourfold. On 8 January, 9 days before the earthquake, the radon concentration reached a peak of more than 10 times that at the beginning of the observation, before starting to decrease. These radon changes are likely to be precursory phenomena of the disastrous earthquake.
Atmospheric Trends and Lifetime of CH3CCI3and Global OH Concentrations
Authors: Prinn R. G. , Weiss R. F. , Miller B. R. , Huang J. , Alyea F. N. , Cunnold D. M. , Fraser P. J. , Hartley D. E. , Simmonds P. G.
Published: October 2006

Determination of the atmospheric concentrations and lifetime of trichloroethane (CH3CCl3) is very important in the context of global change. This halocarbon is involved in depletion of ozone, and the hydroxyl radical (OH) concentrations determined from its lifetime provide estimates of the lifetimes of most other hydrogen-containing gases involved in the ozone layer and climate. Global measurements of trichloroethane indicate rising concentrations before and declining concentrations after late 1991. The lifetime of CH3CCl3in the total atmosphere is 4.8 ± 0.3 years, which is substantially lower than previously estimated. The deduced hydroxyl radical concentration, which measures the atmosphere's oxidizing capability, shows little change from 1978 to 1994.
Observation of Bose-Einstein Condensation in a Dilute Atomic Vapor
Authors: Anderson M. H. , Ensher J. R. , Matthews M. R. , Wieman C. E. , Cornell E. A.
Published: October 2006

A Bose-Einstein condensate was produced in a vapor of rubidium-87 atoms that was confined by magnetic fields and evaporatively cooled. The condensate fraction first appeared near a temperature of 170 nanokelvin and a number density of 2.5 × 10
12
per cubic centimeter and could be preserved for more than 15 seconds. Three primary signatures of Bose-Einstein condensation were seen. (i) On top of a broad thermal velocity distribution, a narrow peak appeared that was centered at zero velocity. (ii) The fraction of the atoms that were in this low-velocity peak increased abruptly as the sample temperature was lowered. (iii) The peak exhibited a nonthermal, anisotropic velocity distribution expected of the minimum-energy quantum state of the magnetic trap in contrast to the isotropic, thermal velocity distribution observed in the broad uncondensed fraction.
The Future of Biodiversity
Authors: Pimm Stuart L. , Russell Gareth J. , Gittleman John L. , Brooks Thomas M.
Published: October 2006

Recent extinction rates are 100 to 1000 times their pre-human levels in well-known, but taxonomically diverse groups from widely different environments. If all species currently deemed "threatened" become extinct in the next century, then future extinction rates will be 10 times recent rates. Some threatened species will survive the century, but many species not now threatened will succumb. Regions rich in species found only within them (endemics) dominate the global patterns of extinction. Although new technology provides details of habitat losses, estimates of future extinctions are hampered by our limited knowledge of which areas are rich in endemics.
Restoring Value to the World's Degraded Lands
Authors: Daily Gretchen C.
Published: October 2006

Roughly 43 percent of Earth's terrestrial vegetated surface has diminished capacity to supply benefits to humanity because of recent, direct impacts of land use. This represents an ∼10 percent reduction in potential direct instrumental value (PDIV), defined as the potential to yield direct benefits such as agricultural, forestry, industrial, and medicinal products. If present trends continue, the global loss of PDIV could reach ∼20 percent by 2020. From a biophysical perspective, recovery of ∼5 percent of PDIV is feasible over the next 25 years. Capitalizing on natural recovery mechanisms is urgently needed to prevent further irreversible degradation and to retain the multiple values of productive land.
Luminescence Enhancement by the Introduction of Disorder into Poly(
p
-phenylene vinylene)
Authors: Son S. , Dodabalapur A. , Lovinger A. J. , Galvin M. E.
Published: October 2006

A method is described for increasing luminescence in poly(
p
-phenylene vinylene) (PPV) light-emitting diodes. Cis linkages were engineered into the PPV chain. These linkages interrupt conjugation and interfere with the packing of the polymer chains, which results in the formation of amorphous PPV. Large-area electroluminescent devices were prepared from this polymer. Devices made of an aluminum electrode, PPV as the luminescent layer, and an electron-transporting layer have internal quantum efficiencies of 2 percent, a turn-on voltage of 20 volts, and can carry current densities of 2000 milliamperes per square centimeter. The current density is at least an order of magnitude higher than previously obtained.
Primitive Boron Isotope Composition of the Mantle
Authors: Chaussidon Marc , Marty Bernard
Published: October 2006

Boron isotope ratios are homogeneous in volcanic glasses of oceanic island basalts [–9.9 ± 1.3 per mil, relative to standard NBS 951 (defined by the National Bureau of Standards)], whereas mid-oceanic ridge basalts (MORBs) and back-arc basin basalts (BABBs) show generally higher and more variable ratios. Melts that have assimilated even small amounts of altered basaltic crust show significant variations in the boron isotope ratios. Assimilation may thus account for the higher boron ratios of MORBs and BABBs. A budget of boron between mantle and crust implies that the primitive mantle had a boron isotope ratio of –10 ± 2 per mil and that this ratio was not fractionated significantly during the differentiation of the mantle.
High-
3
He Plume Origin and Temporal-Spatial Evolution of the Siberian Flood Basalts
Authors: Basu Asish R. , Poreda Robert J. , Renne Paul R. , Teichmann Friedrich , Vasiliev Yurii R. , Sobolev Nikolai V. , Turrin Brent D.
Published: October 2006

An olivine nephelinite from the lower part of a thick alkalic ultrabasic and mafic sequence of volcanic rocks of the northeastern part of the Siberian flood basalt province (SFBP) yielded a
40
Ar/
39
Ar plateau age of 253.3 ± 2.6 million years, distinctly older than the main tholeiitic pulse of the SFBP at 250.0 million years. Olivine phenocrysts of this rock showed
3
He/
4
He ratios up to 12.7 times the atmospheric ratio; these values suggest a lower mantle plume origin. The neodymium and strontium isotopes, rare earth element concentration patterns, and cerium/lead ratios of the associated rocks were also consistent with their derivation from a near-chondritic, primitive plume. Geochemical data from the 250-million-year-old volcanic rocks higher up in the sequence indicate interaction of this high-
3
He SFBP plume with a suboceanic-type upper mantle beneath Siberia.
Self-Condensing Vinyl Polymerization: An Approach to Dendritic Materials
Authors: Fréchet Jean M. J. , Henmi Masahiro , Gitsov Ivan , Aoshima Sadahito , Leduc Marc R. , Grubbs R. Bernard
Published: October 2006

Self-condensing vinyl polymerization was used to produce dendritic polymers with both highly branched structures and numerous reactive groups. A vinyl monomer will undergo self-polymerization if it contains a pendant group that can be transformed into an initiating moiety by the action of an external stimulus. The self-polymerization combines features of a classical vinyl polymerization process with those of a polycondensation because growth is accomplished by the coupling of reactive oligomers. Highly branched, irregular dendritic structures with a multiplicity of reactive functionalities are obtained by polymerization of 3-(1-chloroethyl)-ethenylbenzene.
The Effect of Magmatic Activity on Hydrothermal Venting Along the Superfast-Spreading East Pacific Rise
Authors: Urabe T. , Baker E. T. , Ishibashi J. , Feely R. A. , Marumo K. , Massoth G. J. , Maruyama A. , Shitashima K. , Okamura K. , Lupton J. E. , Sonoda A. , Yamazaki T. , Aoki M. , Gendron J. , Greene R. , Kaiho Y. , Kisimoto K. , Lebon G. , Matsumoto T. , Nakamura K. , Nishizawa A. , Okano O. , Paradis G. , Roe K. , Shibata T. , Tennant D. , Vance T. , Walker S. L. , Yabuki T. , Ytow N.
Published: October 2006

A survey of hydrothermal activity along the superfast-spreading (approximately 150 millimeters per year) East Pacific Rise shows that hydrothermal plumes overlay approximately 60 percent of the ridge crest between 13°50′ and 18°40′S, a plume abundance nearly twice that known from any other ridge portion of comparable length. Plumes were most abundant where the axial cross section is inflated and an axial magma chamber is present. Plumes with high ratios of volatile (
3
He, CH
4
, and H
2
S) to nonvolatile (Mn and Fe) species marked where hydrothermal circulation has been perturbed by recent magmatic activity. The high proportion of volatile-rich plumes observed implies that such episodes are more frequent here than on slower spreading ridges.
Catalysis of the Olivine to Spinel Transformation by High Clinoenstatite
Authors: Sharp T. G. , Rubie D. C.
Published: October 2006

Although enstatite is a major constituent of the Earth's upper mantle and subducting lithosphere, most kinetic studies of olivine phase transformations have typically involved single-phase polycrystalline aggregates. Transmission electron microscopy investigations of olivine to spinel and modified spinel (β phase) reactions in the (Mg, Fe)
2
SiO
4
-(Mg,Fe)SiO
3
system show that transformation of olivine in the stability field of spinel plus β phase begins with coherent nucleation of spinel on high-clinoenstatite grains. These observations demonstrate that high clinoenstatite can catalyze the transformation by enhancing nucleation kinetics and therefore imply that secondary phases can influence reaction kinetics during high-pressure mineral transformations.
Multiscaling Properties of Large-Scale Structure in the Universe
Authors: Martínez V. J. , Paredes S. , Borgani S. , Coles P.
Published: October 2006

The large-scale distribution of galaxies and galaxy clusters in the universe can be described in the mathematical language of multifractal sets. A particularly significant aspect of this description is that it furnishes a natural explanation for the observed differences in clustering properties of objects of different density in terms of multiscaling, the generic consequence of the application of a local density threshold to a multifractal set. The multiscaling hypothesis suggests ways of improving upon the traditional statistical measures of clustering pattern (correlation functions) and exploring further the connection between clustering pattern and dynamics.
Macroscopic Evidence of the Effect of Interfacial Slippage on Adhesion
Authors: Newby Bi-min Zhang , Chaudhury Manoj K. , Brown Hugh R.
Published: October 2006

The adhesion strengths of a viscoelastic adhesive were measured on various substrates that were prepared by grafting silanes bearing organic functional groups to silicon wafers. Conventional theories predict that adhesion should be proportional to the surface free energy of the substrate; but adhesion on a fluorocarbon surface was significantly greater than on some of the hydrocarbon surfaces, although the fluorocarbon surface has the lowest surface free energy. This result could be explained by invoking a model of adhesion based on the slippage of the adhesive at the interface.
Synchrony and Causal Relations Between Permian-Triassic Boundary Crises and Siberian Flood Volcanism
Authors: Renne Paul R. , Black Michael T. , Zichao Zhang , Richards Mark A. , Basu Asish R.
Published: October 2006

The Permian-Triassic boundary records the most severe mass extinctions in Earth's history. Siberian flood volcanism, the most profuse known such subaerial event, produced 2 million to 3 million cubic kilometers of volcanic ejecta in approximately 1 million years or less. Analysis of
40
Ar/
39
Ar data from two tuffs in southern China yielded a date of 250.0 ± 0.2 million years ago for the Permian-Triassic boundary, which is comparable to the inception of main stage Siberian flood volcanism at 250.0 ± 0.3 million years ago. Volcanogenic sulfate aerosols and the dynamic effects of the Siberian plume likely contributed to environmental extrema that led to the mass extinctions.
Organic Heterostructure Field-Effect Transistors
Authors: Dodabalapur A. , Katz H. E. , Torsi L. , Haddon R. C.
Published: October 2006

Organic field-effect transistors have been developed that function as either n-channel or p-channel devices, depending on the gate bias. The two active materials are α-hexathienylene (α-6T) and C
60
. The characteristics of these devices depend mainly on the molecular orbital energy levels and transport properties of α-6T and C
60
. The observed effects are not unique to the two materials chosen and can be quite universal provided certain conditions are met. The device can be used as a building block to form low-cost, low-power complementary integrated circuits.
Observation and Origin of Self-Organized Textures in Agates
Authors: Heaney Peter J. , Davis Andrew M.
Published: October 2006

One of the most impressive manifestations of spontaneous pattern generation in natural materials is iris agate, which contains submicrometer concentric striations that may cycle several thousand times within an individual specimen. Analysis by secondary ion mass spectroscopy and transmission electron microscopy identified the iris texture as alternating layers of fine-grained, highly defective chalcedony and coarse-grained low-defect quartz. This oscillatory zonation in defect concentration may be ascribed to Ostwald-Liesegang crystallization cycles from silica-rich fluids that are variably polymeric and monomeric. Periodic changes in defect concentration and grain size also are observed with wavelengths of hundreds of micrometers and of centimeters, so that agates reveal textural self-similarity over three length scales.
An Improved Procedure for EI Niño Forecasting: Implications for Predictability
Authors: Chen Dake , Zebiak Stephen E. , Busalacchi Antonio J. , Cane Mark A.
Published: October 2006

A coupled ocean-atmosphere data assimilation procedure yields improved forecasts of El Niño for the 1980s compared with previous forecasting procedures. As in earlier forecasts with the same model, no oceanic data were used, and only wind information was assimilated. The improvement is attributed to the explicit consideration of air-sea interaction in the initialization. These results suggest that El Niño is more predictable than previously estimated, but that predictability may vary on decadal or longer time scales. This procedure also eliminates the well-known spring barrier to El Niño prediction, which implies that it may not be intrinsic to the real climate system.
Excitation of Spirals and Chiral Symmetry Breaking in Rayleigh-Bénard Convection
Authors: Ecke Robert E. , Hu Yuchou , Mainieri Ronnie , Ahlers Guenter
Published: October 2006

Spiral-defect populations in low-Prandtl number Rayleigh-Bénard convection with slow rotation about a vertical axis were measured in carbon dioxide at high pressure. The results indicate that spirals act like "thermally excited" defects and that the winding direction of a spiral is analogous to a magnetic spin. Rotation about a vertical axis, the spiral analog of the magnetic field, breaks the zero-rotation chiral symmetry between clockwise and counterclockwise spiral defects. Many properties of spiral-defect statistics are well described by an effective statistical-mechanical model.
Is It Time to Begin Ph.D. Population Control?
Authors: Holden Constance
Published: October 2006

Scientists—and some scientific societies, such as the American Chemical Society—are beginning to call for Ph.D. “birth control.” But the establishment—that is, scientists representing the National Science Foundation and the National Academy of Sciences—has been resisting these calls, arguing instead that with broader training, Ph.D.s will be able to find rewarding jobs. A sidebar examines the impact of non-U.S. Ph.D.s on the science job market.
Plio-Pleistocene African Climate
Authors: deMenocal Peter B.
Published: October 2006

Marine records of African climate variability document a shift toward more arid conditions after 2.8 million years ago (Ma), evidently resulting from remote forcing by cold North Atlantic sea-surface temperatures associated with the onset of Northern Hemisphere glacial cycles. African climate before 2.8 Ma was regulated by low-latitude insolation forcing of monsoonal climate due to Earth orbital precession. Major steps in the evolution of African hominids and other vertebrates are coincident with shifts to more arid, open conditions near 2.8 Ma, 1.7 Ma, and 1.0 Ma, suggesting that some Pliocene (Plio)-Pleistocene speciation events may have been climatically mediated.
Emission Measurements of the Concorde Supersonic Aircraft in the Lower Stratosphere
Authors: Fahey D. W. , Keim E. R. , Boering K. A. , Brock C. A. , Wilson J. C. , Jonsson H. H. , Anthony S. , Hanisco T. F. , Wennberg P. O. , Miake-Lye R. C. , Salawitch R. J. , Louisnard N. , Woodbridge E. L. , Gao R. S. , Donnelly S. G. , Wamsley R. C. , Del Negro L. A. , Solomon S. , Daube B. C. , Wofsy S. C. , Webster C. R. , May R. D. , Kelly K. K. , Loewenstein M. , Podolske J. R. , Chan K. R.
Published: October 2006

Emission indices of reactive gases and particles were determined from measurements in the exhaust plume of a Concorde aircraft cruising at supersonic speeds in the stratosphere. Values for NO
x
(sum of NO and NO
2
) agree well with ground-based estimates. Measurements of NO
x
and HO
x
indicate a limited role for nitric acid in the plume. The large number of submicrometer particles measured implies efficient conversion of fuel sulfur to sulfuric acid in the engine or at emission. A new fleet of supersonic aircraft with similar particle emissions would significantly increase stratospheric aerosol surface areas and may increase ozone loss above that expected for NO
x
emissions alone.
P′P′ Precursors Under Africa: Evidence for Mid-Mantle Reflectors
Authors: LeStunff Yves , Wicks Charles W. , Romanowicz Barbara
Published: October 2006

Observations of precursors to P′P′ from a recent exceptionally large deep earthquake in the Fiji Islands (moment magnitude = 7.6) at an array of broadband stations in California revealed mid-mantle reflectors near depths of 785 kilometers and 1200 kilometers under the southern African rift. Such observations, previously reported primarily in subduction zones, suggest that these reflectors may have a global character. Our analysis, which also indicated a sharp, uplifted 670-kilometer discontinuity, demonstrates the power of sparse regional broadband arrays for the study of weak, frequency-dependent features in deep-Earth structure.
Radar Images of Asteroid 4179 Toutatis
Authors: Ostro Steven J. , Hudson R. Scott , Jurgens Raymond F. , Rosema Keith D. , Campbell Donald B. , Yeomans Donald K. , Chandler John F. , Giorgini Jon D. , Winkler Ron , Rose Randy , Howard S. Denise , Slade Martin A. , Perillat Phil , Shapiro Irwin I.
Published: October 2006

Delay-Doppler images of the Earth-crossing asteroid 4179 Toutatis achieve resolutions as fine as 125 nanoseconds (19 meters in range) and 8.3 millihertz (0.15 millimeter per second in radial velocity) and place hundreds to thousands of pixels on the asteroid, which appears to be several kilometers long, topographically bifurcated, and heavily cratered. The image sequence reveals Toutatis to be in an extremely slow, non-principal axis rotation state.
Geomorphically Driven Late Cenozoic Rock Uplift in the Sierra Nevada, California
Authors: Small Eric E. , Anderson Robert S.
Published: October 2006

Geologists have long accepted that the Sierra Nevada, California, experienced significant late Cenozoic tectonically induced uplift. A flexural-isostatic model presented here shows, however, that a large fraction of the primary evidence for uplift could be generated by the lithospheric response to coupled erosion of the Sierra Nevada and deposition in the adjacent Central Valley and therefore requires less tectonic forcing than previously believed. The sum of range-wide erosion and the resultant isostatic rock uplift would have lowered Sierra mean elevation by 200 to 1000 meters since 10 million years ago and could also have increased summit elevations during the current period of relief production.
Quantitative Monitoring of Gene Expression Patterns with a Complementary DNA Microarray
Authors: Schena Mark , Shalon Dari , Davis Ronald W. , Brown Patrick O.
Published: October 2006

A high-capacity system was developed to monitor the expression of many genes in parallel. Microarrays prepared by high-speed robotic printing of complementary DNAs on glass were used for quantitative expression measurements of the corresponding genes. Because of the small format and high density of the arrays, hybridization volumes of 2 microliters could be used that enabled detection of rare transcripts in probe mixtures derived from 2 micrograms of total cellular messenger RNA. Differential expression measurements of 45
Arabidopsis
genes were made by means of simultaneous, two-color fluorescence hybridization.
Galileo Lives With Balky Tape Recorder
Authors: Kerr Richard A.
Published: October 2006

The trouble-plagued Galileo spacecraft, due to reach Jupiter in December, hit another glitch when a data-storage tape stuck. Engineers have managed to free it, and they hope they can prevent a recurrence. If not, the spacecraft may not be able to store and transmit important data, including some images of the planet and its moons.
Radio Tags Speed Compound Synthesis
Authors: Service Robert F.
Published: October 2006

A new process promises to speed up the already rapid technology called combinatorial chemistry. The new technique uses microchips to keep track of the way chemical building blocks are assembled in potentially millions of individual combinations.
Reverse Weathering, Clay Mineral Formation, and Oceanic Element Cycles
Authors: Mackenzie Fred T. , Kump Lee R.
Published: October 2006

Reverse weathering is a process by which new clays are formed by chemical combination of elemental material from oceans and marine sediments. Mackenzie and Kump review the history of research into this process and comment on the research report by Michalopoulos and Aller (
p. 614
), which has “reopened the Pandora's box of reverse weathering in sediments.”
Neurotrophins and Neuronal Plasticity
Authors: Thoenen Hans
Published: October 2006

There is increasing evidence that neurotrophins (NTs) are involved in processes of neuronal plasticity besides their well-established actions in regulating the survival, differentiation, and maintenance of functions of specific populations of neurons. Nerve growth factor, brain-derived neurotrophic factor, NT-4/5, and corresponding antibodies dramatically modify the development of the visual cortex. Although the neuronal elements involved have not yet been identified, complementary studies of other systems have demonstrated that NT synthesis is rapidly regulated by neuronal activity and that NTs are released in an activity-dependent manner from neuronal dendrites. These data, together with the observation that NTs enhance transmitter release from neurons that express the corresponding signal-transducing Trk receptors, suggest a role for NTs as selective retrograde messengers that regulate synaptic efficacy.
Influence of Sulfide Inhibition of Nitrification on Nitrogen Regeneration in Sediments
Authors: Joye Samantha B. , Hollibaugh James T.
Published: October 2006

Nitrification, a central process in the nitrogen cycle, converts ammonium to nitrite or nitrate. In experiments with estuarine sediment, addition of 60 and 100 μM hydrogen sulfide (HS
−
) reduced nitrification by 50 and 100 percent, respectively. Aerobic incubation of ammonium-enriched sediment slurries showed that previous HS
−
exposure reduced nitrification for at least 24 hours; nitrification rates recovered slowly after one-time HS
−
exposure. Sulfide inhibition of nitrification could limit nitrogen loss through coupled nitrification-denitrification and may contribute to the previously observed difference in net nitrogen cycling between freshwater and marine sediments. This interaction could also exacerbate eutrophication in coastal environments.
Relaxation of Arterial Smooth Muscle by Calcium Sparks
Authors: Nelson M. T. , Cheng H. , Rubart M. , Santana L. F. , Bonev A. D. , Knot H. J. , Lederer W. J.
Published: October 2006

Local increases in intracellular calcium ion concentration ([Ca
2+
]
i
) resulting from activation of the ryanodine-sensitive calcium-release channel in the sarcoplasmic reticulum (SR) of smooth muscle cause arterial dilation. Ryanodine-sensitive, spontaneous local increases in [Ca
2+
]
i
(Ca
2+
sparks) from the SR were observed just under the surface membrane of single smooth muscle cells from myogenic cerebral arteries. Ryanodine and thapsigargin inhibited Ca
2+
sparks and Ca
2+
-dependent potassium (K
Ca
) currents, suggesting that Ca
2+
sparks activate K
Ca
channels. Furthermore, K
Ca
channels activated by Ca
2+
sparks appeared to hyperpolarize and dilate pressurized myogenic arteries because ryanodine and thapsigargin depolarized and constricted these arteries to an extent similar to that produced by blockers of K
Ca
channels. Ca
2+
sparks indirectly cause vasodilation through activation of K
Ca
channels, but have little direct effect on spatially averaged [Ca
2+
]
i
, which regulates contraction.
Antibiotics That Resist Resistance
Authors: Service Robert F.
Published: October 2006

Drug-resistant bacteria have been on the offensive for years, with few new compounds available for a counterattack. But at a recent meeting, pharmaceutical companies introduced a promising crop of new antibiotics, with a variety of ways to beat back resistance. Whether companies have enough incentives to develop the most effective anti-resistance strategies—narrow-spectrum antibiotics—remains an open question. See sidebar (p. 725).
Tracking the Fingerprints of Drug Resistance
Authors: Service Robert F.
Published: October 2006

Drug-resistant bacteria are hard to classify and track with traditional methods, so researchers are using DNA fingerprinting techniques to identify and follow new and dangerous strains. See main story (
p. 724
).
Sea-Floor Data Flow From Postwar Era
Authors: Lawler Andrew
Published: October 2006

The maps that came in from the cold: Researchers have used data collected by U.S. Navy spy satellites to produce finely detailed topographical maps of the features that lie beneath the world's oceans. They are the first major fruits of an effort to declassify scientific data collected during the Cold War, and more releases are on the way.
Satellite Offers a View of the Coolest Objects in the Cosmos
Authors: Hellemans Alexander
Published: October 2006

Groningen, the Netherlands—An infrared astronomy satellite to be launched this month by the European Space Agency will offer unprecedented views of cool objects, such as gas clouds that form the birthplaces of stars, comets in the outer reaches of the solar system, and the dusty disks that may spawn planets.
Cracking the Neuronal Code
Authors: Ferster David , Spruston Nelson
Published: October 2006

How does the brain code information? Ferster and Spruston weigh the evidence in favor of a rate code (that the rate of action-potential firing carries the key information) and a temporal code (in which the pattern of firing is crucial, not just the rate).
Thailand Weighs AIDS Vaccine Tests
Authors: Cohen Jon
Published: October 2006

San Patong, Thailand—The first large-scale tests to determine the effectiveness of the current generation of AIDS vaccines could begin in Thailand next year. The U.S. National Institutes of Health last year declined to test the same vaccines in the United States because they showed too little promise, but different cost-benefit calculations may apply in Thailand.
Science
interviewed leading researchers in Thailand and the West to take the pulse of the debate as Thai officials weigh whether the tests should go ahead.
Tamoxifen's Trials and Tribulations
Authors: Marshall Eliot
Published: October 2006

A controversial clinical trial to determine whether the drug tamoxifen can protect healthy women against breast cancer has run into a new obstacle. The National Heart, Lung, and Blood Institute, which was providing some funding, is reducing its commitment because it believes that the data will not shed light on tamoxifen's cardiovascular effects, as previously hoped.
'Eraser' Rubs Out Information to Reveal Light's Dual Nature
Authors: Watson Andrew
Published: October 2006

Cambridge, U.K.—A team of physicists in Austria has provided new experimental confirmation for one of the more bizarre predictions of quantum mechanics: The behavior of one photon in a pair can appear to affect the properties of its sibling instantaneously, even if they are widely separated in space.
Monoclonal Antibodies at Age 20: Promise at Last?
Authors: Hall Stephen S.
Published: October 2006

When they were first produced 2 decades ago, monoclonal antibodies were enthusiastically touted as “magic bullets” that would find wide application in medical therapeutics and diagnostics. But a variety of problems including severe immune reactions prevented them from living up to the early hype. A recent conference on monoclonals and cancer therapy suggests, however, that some of the difficulties are slowly being overcome.
New Clues Found to How Some People Live With HIV
Authors: Cohen Jon
Published: October 2006

Nearly 15 years ago, before tests for HIV had been developed, an infected man donated blood in Sydney, Australia, and seven people received transfusions of his contaminated blood. So far, however, neither the donor nor the recipients have shown any harmful effects. The reason, as a team of researchers reports in this issue of
Science
(
p. 988
), appears to be that the virus is missing parts of a gene called
nef.
This may explain why some people infected with HIV survive for long periods without developing AIDS, and a few researchers are arguing that it may point the way to a vaccine made from an attenuated virus.
Asian Anthropoids Strike Back
Authors: Culotta Elizabeth
Published: October 2006

A new fossil find from China, unveiled last week at the Society of Vertebrate Paleontology meeting, suggests that a tiny creature called
Eosimias
is the oldest known anthropoid, the group of higher primates that includes humans as well as monkeys and apes. The fossil, a complete jaw, has been dated to 40 million years ago. Some question whether
Eosimias
is a true anthropoid, but if the claim holds up, it would mean that the anthropoids' family tree took root in Asia, rather than Africa.
Remembering X-rays
Authors: Kirz Janos
Published: October 2006

November 1995 is the centenary of the discovery of x-rays by Wilhelm Conrad Röntgen. In his Perspective, Kirz recounts the events surrounding this important discovery.
Protein Design: A Hierarchic Approach
Authors: Bryson James W. , Betz Stephen F. , Lu Helen S. , Suich Daniel J. , Zhou Hongxing X. , O'Neil Karyn T. , DeGrado William F.
Published: October 2006

The de novo design of peptides and proteins has recently emerged as an approach for investigating protein structure and function. Designed, helical peptides provide model systems for dissecting and quantifying the multiple interactions that stabilize secondary structure formation. De novo design is also useful for exploring the features that specify the stoichiometry and stability of α-helical coiled coils and for defining the requirements for folding into structures that resemble native, functional proteins. The design process often occurs in a series of discrete steps. Such steps reflect the hierarchy of forces required for stabilizing tertiary structures, beginning with hydrophobic forces and adding more specific interactions as required to achieve a unique, functional protein.
Geophysics of the Pitman Fracture Zone and Pacific-Antarctic Plate Motions During the Cenozoic
Authors: Cande Steven C. , Raymond Carol A. , Stock Joann , Haxby William F.
Published: October 2006

Multibeam bathymetry and magnetometer data from the Pitman fracture zone (FZ) permit construction of a plate motion history for the South Pacific over the past 65 million years. Reconstructions show that motion between the Antarctic and Bellingshausen plates was smaller than previously hypothesized and ended earlier, at chron C27 (61 million years ago). The fixed hot-spot hypothesis and published paleomagnetic data require additional motion elsewhere during the early Tertiary, either between East Antarctica and West Antarctica or between the North and South Pacific. A plate reorganization at chron C27 initiated the Pitman FZ and may have been responsible for the other right-stepping fracture zones along the ridge. An abrupt (8°) clockwise rotation in the abyssal hill fabric along the Pitman flowline near the young end of chron C3a (5.9 million years ago) dates the major change in Pacific-Antarctic relative motion in the late Neogene.
NASA Urged to Rethink Plan for Institutes
Authors: Lawler Andrew
Published: October 2006

Mountain View, California—NASA wants to shift its in-house research, now carried out at a dozen centers across the country, to the private sector. However, universities may not be interested in buying what NASA is selling.
Security Schemes Aspire to No-Fuss System Protection
Authors: Mann Charles C.
Published: October 2006

Baltimore—Protecting computer systems from intruders often means trading away convenience for security. But two approaches described last month at the National Information Systems Security Conference in Baltimore could boost security without hampering users. One would rely on swarms of autonomous programs to monitor a system for intruders. The other, called “software forensics,” would examine hacker programs for stylistic clues that could help investigators track down the few “hacker kingpins” thought to be responsible for most malign programs. Details of both projects can be found at
http://www.cs.purdue.edu/coast/coast.html.
Do Kenya Tools Root Birth of Modern Thought in Africa?
Authors: Gutin JoAnn
Published: October 2006

Mastery of abstract concepts is supposedly signaled by sophisticated tools that suddenly appear in the archaeological record about 50,000 years ago in Europe. But new finds of carefully shaped stone tools in Africa, from a 250,000-year-old site, indicate that modern thought may have taken form much earlier
National Monitoring Network Does Science--and a Lot More
Authors: Plafker Ted
Published: October 2006

Beijing—A new environmental research network has been given the challenging job of monitoring current conditions and providing workable solutions to the country's serious environmental problems. However, it faces a tough task in overcoming bureaucratic rivalries and a tradition of limited access to such data.
Reconstitution of
I
KATP
: An Inward Rectifier Subunit Plus the Sulfonylurea Receptor
Authors: Inagaki Nobuya , Gonoi Tohru , Clement John P. , Namba Noriyuki , Inazawa Johji , Gonzalez Gabriela , Aguilar-Bryan Lydia , Seino Susumu , Bryan Joseph
Published: October 2006

A member of the inwardly rectifying potassium channel family was cloned here. The channel, called BIR (Kir6.2), was expressed in large amounts in rat pancreatic islets and glucose-responsive insulin-secreting cell lines. Coexpression with the sulfonylurea receptor SUR reconstituted an inwardly rectifying potassium conductance of 76 picosiemens that was sensitive to adenosine triphosphate (ATP) (
I
KATP
) and was inhibited by sulfonylureas and activated by diazoxide. The data indicate that these pancreatic β cell potassium channels are a complex composed of at least two subunits-BIR, a member of the inward rectifier potassium channel family, and SUR, a member of the ATP-binding cassette superfamily. Gene mapping data show that these two potassium channel subunit genes are clustered on human chromosome 11 at position 11p15.1.
Real-Space Structure of Colloidal Hard-Sphere Glasses
Authors: van Blaaderen Alfons , Wiltzius Pierre
Published: October 2006

The real-space structure of hard-sphere glasses quenched from colloidal liquids in thermodynamic equilibrium has been determined. Particle coordinates were obtained by combining the optical sectioning capability of confocal fluorescence microscopy with the structure of specially prepared fluorescent silica colloids. Both the average structure and the local structure of glasses, with volume fractions ranging from 0.60 to 0.64, were in good agreement with glasses and random close packings generated by computer simulations. No evidence of a divergent correlation length was found. The method used to obtain the three-dimensional particle coordinates is directly applicable to other colloidal structures, such as crystals, gels, and flocs.
Synthesis of Crystalline Superlattices by Controlled Crystallization of Modulated Reactants
Authors: Noh Myungkeun , Thiel James , Johnson David C.
Published: October 2006

A series of crystalline superlattice compounds containing an integral number of intergrown transition metal-dichalcogenide layers was prepared through controlled crystallization of Ti/Se/Nb/Se superlattice reactants rather than through epitaxial growth. The component elemental-layer thicknesses and annealing sequence were chosen to favor interfacial nucleation of the component binary compounds. The layered reactants contracted in the
c
-axis direction during an initial low-temperature anneal as NbSe
2
and TiSe
2
crystallites nucleated and grew along the interfaces, kinetically trapping the desired superlattice structure. The
c
-axis domain size increased gradually as a function of annealing time and temperature, yielding high-quality
c
-axis-oriented TiSe
2
/NbSe
2
crystalline superlattices after annealing at 500°C. The large number of observed 00ℓ diffraction orders permitted the average crystal structure of the superlattice in the direction of the
c
axis to be determined through a Rietveld analysis.
Solution Structure of a Bovine Immunodeficiency Virus Tat-TAR Peptide-RNA Complex
Authors: Puglisi Joseph D. , Chen Lily , Blanchard Scott , Frankel Alan D.
Published: October 2006

The Tat protein of bovine immunodeficiency virus (BIV) binds to its target RNA, TAR, and activates transcription. A 14-amino acid arginine-rich peptide corresponding to the RNA-binding domain of BIV Tat binds specifically to BIV TAR, and biochemical and in vivo experiments have identified the amino acids and nucleotides required for binding. The solution structure of the RNA-peptide complex has now been determined by nuclear magnetic resonance spectroscopy. TAR forms a virtually continuous A-form helix with two unstacked bulged nucleotides. The peptide adopts a β-turn conformation and sits in the major groove of the RNA. Specific contacts are apparent between critical amino acids in the peptide and bases and phosphates in the RNA. The structure is consistent with all biochemical data and demonstrates ways in which proteins can recognize the major groove of RNA.