bluuebunny/crossref_metadata_2025 huggingface dataset:
A Formation Mechanism for Catalytically Grown Helix-Shaped Graphite Nanotubes
Authors: Amelinckx S. , Zhang X. B. , Bernaerts D. , Zhang X. F. , Ivanov V. , Nagy J. B.
Published: October 2006

The concept of a spatial-velocity hodograph is introduced to describe quantitatively the extrusion of a carbon tubule from a catalytic particle. The conditions under which a continuous tubular surface can be generated are discussed in terms of this hodograph, the shape of which determines the geometry of the initial nanotube. The model is consistent with all observed tubular shapes and explains why the formation process induces stresses that may lead to "spontaneous" plastic deformation of the tubule. This result is due to the violation of the continuity condition, that is, to the mismatch between the extrusion velocity by the catalytic particle, required to generate a continuous tubular surface, and the rate of carbon deposition.
Volume Holographic Storage and Retrieval of Digital Data
Authors: Heanue John F. , Bashaw Matthew C. , Hesselink Lambertus
Published: October 2006

A multiple page fully digital holographic data storage system is demonstrated. This system is used to store and retrieve digital image and compressed video data with a photorefractive crystal. Architecture issues related to spatio-rotational multiplexing and novel error-correcting encoding techniques used to achieve low bit-error rates are discussed.
The Molecular Fossil Record of Oleanane and Its Relation to Angiosperms
Authors: Moldowan J. Michael , Dahl Jeremy , Huizinga Bradley J. , Fago Frederick J. , Hickey Leo J. , Peakman Torren M. , Taylor David Winship
Published: October 2006

Oleanane has been reported in Upper Cretaceous and Tertiary source rocks and their related oils and has been suggested as a marker for flowering plants. Correspondence of oleanane concentrations relative to the ubiquitous microbial marker 17α-hopane with angiosperm diversification (Neocomian to Miocene) suggests that oleanane concentrations in migrated petroleum can be used to identify the maximum age of unknown or unavailable source rock. Rare occurrences of pre-Cretaceous oleanane suggest either that a separate lineage leads to the angiosperms well before the Early Cretaceous or that other plant groups have the rarely expressed ability to synthesize oleanane precursors.
Chemically Anomalous, Preaccretionally Irradiated Grains in Interplanetary Dust from Comets
Authors: Bradley John P.
Published: October 2006

Nonstoichiometric grains with depletions of magnesium and silicon (relative to oxygen) and inclusions of iron-nickel metal and iron-rich sulfides have been identified in interplanetary dust particles from comets. These chemical anomalies accumulate in grains exposed to ionizing radiation. The grains, known as GEMS (glass with embedded metal and sulfides), were irradiated before the accretion of comets, and their inferred exposure ages, submicrometer sizes, and "amorphous" silicate structures are consistent with those of interstellar silicate grains. The measured compositional trends suggest that chemical (as well as isotopic) anomalies can be used to identify presolar interstellar components in primitive meteoritic materials.
Stable High-Order Molecular Sandwiches: Hydrocarbon Polyanion Pairs with Multiple Lithium Ions Inside and Out
Authors: Ayalon Ari , Sygula Andrzej , Cheng Pei-Chao , Rabinovitz Mordecai , Rabideau Peter W. , Scott Lawrence T.
Published: October 2006

Stable ten-component sandwich compounds have been characterized in which four lithium ions reside between two tetraanions derived from corannulene or its alkyl-substituted derivatives and four additional lithium ions decorate the exterior. In tetrahydrofuran solution, the four lithium ions inside the sandwich can exchange environments with the four external lithium atoms, but the two tetraanion decks of the sandwich never separate from one another on the time scale of nuclear magnetic resonance. Theoretical calculations point to a "stacked bowl" conformation and a low energy barrier for synchronous double inversion of the tetraanion bowls in the solvated sandwich compounds.
Electromagnetic Heating in the Early Solar Nebula and the Formation of Chondrules
Authors: Eisenhour Don D. , Daulton Tyrone L. , Buseck Peter R.
Published: October 2006

Certain opaque inclusions within primitive meteorites exhibit textures that suggest chondrules formed during intense, short-duration radiative heating episodes in the early solar system. Experimental support for this interpretation is provided by the textures produced when chondrule-like assemblages are heated with visible laser light. Computer simulations of radiative heating provide additional evidence for the role of electromagnetic energy in heating nebular solids by offering an explanation for the size distributions of chondrules and the presence of dusty chondrule rims. Nebular lightning and magnetic reconnection flares are possible sources of electromagnetic energy for these transient heating events.
The Use of Graft Copolymers to Bind Immiscible Blends
Authors: Gersappe Dilip , Irvine Darrell , Balazs Anna C. , Liu Yun , Sokolov Jon , Rafailovich Miriam , Schwarz Steven , Peiffer Dennis G.
Published: October 2006

Computer simulations and experimental studies were combined to design copolymers that enhance the strength of polymer composites. These copolymers contain side chains that associate across the boundary between phase-separated regions to form a "molecular velcro" that effectively binds the regions together. This behavior significantly improves the structural integrity and mechanical properties of the material. Because the side chains can be fabricated from a large class of compounds, the technique greatly increases the variety of copolymers that can be used in forming high-strength polymer blends.
Climatic Implications of an 8000-Year Hydrogen Isotope Time Series from Bristlecone Pine Trees
Authors: Feng Xiahong , Epstein Samuel
Published: October 2006

Tree rings from three dendrochronologically dated bristlecone pines were analyzed for stable hydrogen isotopic composition. These trees give a continuous time series from 8000 years ago to the present that indicates the presence of a postglacial climate optimum 6800 years ago and a continuous cooling since then. The qualitative agreement between this record and records from other sources, such as ice cores, pollen, and treeline fluctuations, indicates that these climate changes were global. This record can serve as a reference for other climate indicators throughout the past 8000 years.
Stream Networks and Long-Term Surface Uplift in the New Madrid Seismic Zone
Authors: Merritts Dorothy , Hesterberg Tim
Published: October 2006

Stream networks are sensitive to low rates of surface uplift and can be used to decipher the history of large earthquakes even where faults do not rupture the surface, as in intraplate seismic zones. Statistical analysis of alluvial network data from topographic maps in the New Madrid seismic zone, in the central United States, shows that stream-segment gradients deviate the most from an estimated natural stream profile where surface uplift is greatest. Evidence of cumulative deformation distilled from stream network patterns represents at least several meters of differential surface uplift during Holocene time, which suggests that more than one cycle of surface deformation occurred.
Ecologists Gather for Mix of Policy, Science in Knoxville
Authors: Culotta Elizabeth
Published: October 2006

Nearly 4000 ecologists and plant biologists gathered in Knoxville, Tennessee, from 7 through 11 August for the joint meeting of the American Institute of Biological Sciences, which was dominated by the 7400-member-strong Ecological Society of America (ESA). In keeping with this year's theme of science and public policy, the meeting featured a hefty dose of applied science as well as plenty of basic research.
The Nature of the Glass Transition in a Silica-Rich Oxide Melt
Authors: Farnan Ian , Stebbins Jonathan F.
Published: October 2006

The atomic-scale dynamics of the glass-to-liquid transition are, in general, poorly understood in inorganic materials. Here, two-dimensional magic angle spinning nuclear magnetic resonance spectra collected just above the glass transition of K
2
Si
4
O
9
at temperatures as high as 583°C are presented. Rates of exchange for silicon among silicate species, which involves Si—O bond breaking, have been measured and are shown to be closely related in time scale to those defined by viscosity. Thus, even at viscosities as high as 10
10
pascal seconds, local bond breaking (in contrast to the cooperative motion of large clusters) is of major importance in the control of macroscopic flow and diffusion.
Molecular Origins of Friction: The Force on Adsorbed Layers
Authors: Cieplak Marek , Smith Elizabeth D. , Robbins Mark O.
Published: October 2006

Simulations and perturbation theory are used to study the molecular origins of friction in an ideal model system, a layer of adsorbed molecules sliding over a substrate. These calculations reproduce several surprising features of experimental results. In most cases, the frictional force on a solid monolayer has a different form from that observed between macroscopic solids. No threshold force or static friction is needed to initiate sliding; instead, the velocity is proportional to the force. As in experiments, incommensurate solid layers actually slide more readily than fluid layers. A comparison of experiment, simulation, and analytic results shows that dissipation arises from anharmonic coupling between phonon modes and substrate-induced deformations in the adsorbate.
Aligned Carbon Nanotube Arrays Formed by Cutting a Polymer Resin—Nanotube Composite
Authors: Ajayan P. M. , Stephan O. , Colliex C. , Trauth D.
Published: October 2006

A simple technique is described here that produces aligned arrays of carbon nanotubes. The alignment method is based on cutting thin slices (50 to 200 nanometers) of a nanotube-polymer composite. With this parallel and well-separated configuration of nanotubes it should be possible to measure individual tube properties and to demonstrate applications. The results demonstrate the nature of rheology, on nanometer scales, in composite media and flow-induced anisotropy produced by the cutting process. The fact that nanotubes do not break and are straightened after the cutting process also suggests that they have excellent mechanical properties.
The Spatial Structure in Liquid Water
Authors: Kusalik Peter G. , Svishchev Igor M.
Published: October 2006

Liquid state structure has traditionally been characterized with the radial distribution functions between atoms. Although these functions are routinely available from x-ray diffraction and neutron scattering experiments or from computer simulations, they cannot be interpreted unambiguously to provide the spatial order in a molecular liquid. A direct approach to determining the spatial structure in the liquid state is demonstrated here. Three-dimensional maps representing the local atomic densities are presented for several water models. These spatial maps provide a picture of the short-range order in liquid water which reveals specific details of its local structure that are important in the understanding of its properties.
Morphology and Ionization of the Interstellar Cloud Surrounding the Solar System
Authors: Frisch Priscilla C.
Published: October 2006

The first encounter between the sun and the surrounding interstellar cloud appears to have occurred 2000 to 8000 years ago. The sun and cloud space motions are nearly perpendicular, an indication that the sun is skimming the cloud surface. The electron density derived for the surrounding cloud from the carbon component of the anomalous cosmic ray population in the solar system and from the interstellar ratio of Mg
+
to Mg
0
toward Sirius support an equilibrium model for cloud ionization (an electron density of 0.22 to 0.44 per cubic centimeter). The upwind magnetic field direction is nearly parallel to the cloud surface. The relative sun-cloud motion indicates that the solar system has a bow shock.
Stress Triggering of the 1994 M = 6.7 Northridge, California, Earthquake by Its Predecessors
Authors: Stein Ross S. , King Geoffrey C. P. , Lin Jian
Published: October 2006

A model of stress transfer implies that earthquakes in 1933 and 1952 increased the Coulomb stress toward failure at the site of the 1971 San Fernando earthquake. The 1971 earthquake in turn raised stress and produced aftershocks at the site of the 1987 Whittier Narrows and 1994 Northridge ruptures. The Northridge main shock raised stress in areas where its aftershocks and surface faulting occurred. Together, the earthquakes with moment magnitude M ≥ 6 near Los Angeles since 1933 have stressed parts of the Oak Ridge, Sierra Madre, Santa Monica Mountains, Elysian Park, and Newport-Inglewood faults by more than 1 bar. Although too small to cause earthquakes, these stress changes can trigger events if the crust is already near failure or advance future earthquake occurrence if it is not.
Seismic Evidence for a Lower-Crustal Detachment Beneath San Francisco Bay, California
Authors: Brocher Thomas M. , McCarthy Jill , Hart Patrick E. , Holbrook W. Steven , Furlong Kevin P. , McEvilly Thomas V. , Hole John A. , Klemperer Simon L.
Published: October 2006

Results from the San Francisco Bay area seismic imaging experiment (BASIX) reveal the presence of a prominent lower crustal reflector at a depth of ∼15 kilometers beneath San Francisco and San Pablo bays. Velocity analyses indicate that this reflector marks the base of Franciscan assemblage rocks and the top of a mafic lower crust. Because this compositional contrast would imply a strong rheological contrast, this interface may correspond to a lower crustal detachment surface. If so, it may represent a subhorizontal segment of the North America and Pacific plate boundary proposed by earlier thermo-mechanical and geological models.
Astronomers Gossip About The (Cosmic) Neighborhood
Authors: Jayawardhana Ray
Published: October 2006

The Hague, Netherlands, last month welcomed 2000 astronomers from around the world for the 22nd General Assembly of the International Astronomical Union (IAU). From 15 to 27 August, they participated in symposia and discussions on topics ranging from the down-to-Earth issue of light and radio-frequency pollution to the creation of elements at the farthest reaches of time and space, in the big bang. Some of the most striking news, however, came in new findings from our galaxy and its immediate surroundings.
First Images of Asteroid 243 Ida
Authors: Belton M. J. S. , Chapman C. R. , Veverka J. , Klaasen K. P. , Harch A. , Greeley R. , Greenberg R. , Head J. W. , McEwen A. , Morrison D. , Thomas P. C. , Davies M. E. , Carr M. H. , Neukum G. , Fanale F. P. , Davis D. R. , Anger C. , Gierasch P. J. , Ingersoll A. P. , Pilcher C. B.
Published: October 2006

The first images of the asteroid 243 Ida from Galileo show an irregular object measuring 56 kilometers by 24 kilometers by 21 kilometers. Its surface is rich in geologic features, including systems of grooves, blocks, chutes, albedo features, crater chains, and a full range of crater morphologies. The largest blocks may be distributed nonuniformly across the surface; lineaments and dark-floored craters also have preferential locations. Ida is interpreted to have a substantial regolith. The high crater density and size-frequency distribution (–3 differential power-law index) indicate a surface in equilibrium with saturated cratering. A minimum model crater age for Ida—and therefore for the Koronis family to which Ida belongs—is estimated at 1 billion years, older than expected.
Catastrophes, Phase Shifts, and Large-Scale Degradation of a Caribbean Coral Reef
Authors: Hughes Terence P.
Published: October 2006

Many coral reefs have been degraded over the past two to three decades through a combination of human and natural disturbances. In Jamaica, the effects of overfishing, hurricane damage, and disease have combined to destroy most corals, whose abundance has declined from more than 50 percent in the late 1970s to less than 5 percent today. A dramatic phase shift has occurred, producing a system dominated by fleshy macroalgae (more than 90 percent cover). Immediate implementation of management procedures is necessary to avoid further catastrophic damage.
Simultaneous Observation of Columnar Defects and Magnetic Flux Lines in High-Temperature Bi
2
Sr
2
CaCu
2
O
8
Superconductors
Authors: Dai Hongjie , Yoon Seokwon , Liu Jie , Budhani Ramesh C. , Lieber Charles M.
Published: October 2006

Columnar defects generated by heavy-ion irradiation are promising structures for pinning magnetic flux lines and enhancing critical currents in superconductors with high transition temperatures. An approach that combines chemical etching and magnetic decoration was used to highlight simultaneously the distributions of columnar defects and magnetic flux lines in Bi
2
Sr
2
CaCu
2
O
8
superconductors. Analyses of images of the columnar defects and flux-line positions provide insight into flux-line pinning by elucidating (i) the occupancy of columnar defects by flux lines, (ii) the nature of topological defects in the flux-line lattice, and (iii) the translational and orientational order in this lattice.
Grain Size—Dependent Alteration and the Magnetization of Oceanic Basalts
Authors: Kent Dennis V. , Gee Jeff
Published: October 2006

Unblocking temperatures of natural remanent magnetization were found to extend well above the dominant Curie points in samples of oceanic basalts from the axis of the East Pacific Rise. This phenomenon is attributed to the natural presence in the basalts of three related magnetic phases: an abundant fine-grained and preferentially oxidized titanomagnetite that carries most of the natural remanent magnetism, a few coarser and less oxidized grains of titanomagnetite that account for most of the high-field magnetic properties, and a small contribution to both the natural remanent magnetism and high-field magnetic properties from magnetite that may be due to the disproportionation of the oxidized titanomagnetite under sea-floor conditions. This model is consistent with evidence from the Central Anomaly magnetic high that the original magnetization acquired by oceanic basalts upon cooling is rapidly altered and accounts for the lack of sensitivity of bulk rock magnetic parameters to the degree of alteration of the remanence carrier in oceanic basalts.
Rapid Emplacement of Young Oceanic Lithosphere: Argon Geochronology of the Oman Ophiolite
Authors: Hacker Bradley R.
Published: October 2006

40
Ar/
39
Ar dates of emplacement-related metamorphic rocks beneath the Samail ophiolite in Oman show that cooling to <525°C occurred within ∼1 million years of igneous crystallization of the ophiolite. This unexpectedly short time span and rapid cooling means that old, cold continental or oceanic lithosphere must have been adjacent to the ophiolite during spreading and then been thrust beneath the ophiolite almost immediately afterward.
Kinematics of the Asal Rift (Djibouti) Determined from the Deformation of Fieale Volcano
Authors: De Chabalier Jean-Bernard , Avouac Jean-Philippe
Published: October 2006

Because of its subaerial exposure the Asal rift segment provides an exceptional opportunity to quantify the deformation field of an active rift and assess the contribution of tectonics and volcanism to rifting processes. The present topography of the Asal rift results from the tectonic dismemberment during the last 100,000 years of a large central volcanic edifice that formed astride the rift zone 300,000 to 100,000 years ago. Three-dimensional deformation of this volcano has been quantified from the combined analysis of the topography and geology. The analysis indicates that spreading at 17 to 29 millimeters per year in a N40° ± 5°E direction accounts for most of the separation between Arabia and Somalia. The small topographic subsidence relative to extension suggests that tectonic thinning of the crust has been balanced by injection and underplating of magmatic material of near crustal density. The methodology developed in this study could also be applied to quantify deformation in relatively inaccessible areas where the main available information is topography or bathymetry.
All-Polymer Field-Effect Transistor Realized by Printing Techniques
Authors: Garnier Francis , Hajlaoui Ryad , Yassar Abderrahim , Srivastava Pratima
Published: October 2006

A field-effect transistor has been fabricated from polymer materials by printing techniques. The device characteristics, which show high current output, are insensitive to mechanical treatments such as bending or twisting. This all-organic flexible device, realized with mild techniques, opens the way for large-area, low-cost plastic electronics.
Stabilization of Atomic Hydrogen in Both Solution and Crystal at Room Temperature
Authors: Sasamori Riichi , Okaue Yoshihiro , Isobe Toshiyuki , Matsuda Yoshihisa
Published: October 2006

Atomic hydrogen has been stably encapsulated in both solution and crystal at room temperature. Upon γ-ray irradiation of [(CH
3
)
3
Si]
8
Si
8
O
20
, which is the trimethylsilylated derivative of the silicate anion with a double four-ring (D4R) cage, electron spin resonance (ESR) spectra revealed that a single hydrogen atom is encapsulated in the center of the D4R cage and is stable for periods of many months. Attack by chemically reactive species such as oxygen was prevented by the D4R cage, but the ESR signal of the hydrogen atom was sensitive to the magnetic interaction caused by the presence of the O
2
molecule near the cage.
Vertical Aluminophosphate Molecular Sieve Crystals Grown at Inorganic-Organic Interfaces
Authors: Feng Sue , Bein Thomas
Published: October 2006

Tubular aluminophosphate molecular sieve crystals were grown at an organic interface with their channels (7 angstroms in cross section) vertical to the substrate. To induce surface nucleation and oriented growth of AIPO
4
-5 crystals, organophosphonate layers cross-linked with Zr(IV) were assembled on a gold substrate and the modified substrate was immersed in a hydrothermal bath containing reagents for the synthesis of the molecular sieve. Reflection-absorption infrared studies demonstrated the stability of the phosphonate layers under these conditions. Drastic changes in the morphology of the surface-grown crystals from spherical agglomerates to vertical needles to thin tilted needles could be achieved by adjusting the water content of the synthesis bath. Nitrogen sorption in these structures on a piezoelectric device confirmed the presence of zeolitic microporosity.
Functional Group Imaging by Chemical Force Microscopy
Authors: Frisbie C. Daniel , Rozsnyai Lawrence F. , Noy Aleksandr , Wrighton Mark S. , Lieber Charles M.
Published: October 2006

Mapping the spatial arrangement of chemical functional groups and their interactions is of significant importance to problems ranging from lubrication and adhesion to recognition in biological systems. A force microscope has been used to measure the adhesive and friction forces between molecularly modified probe tips and organic monolayers terminating in a lithographically defined pattern of distinct functional groups. The adhesive interactions between simple CH
3
/CH
3
, CH
3
/COOH, and COOH/COOH functional groups correlate directly with friction images of sample surfaces patterned with these groups. Thus, by monitoring the friction between a specifically functionalized tip and sample, one can produce friction images that display predictable contrast and correspond to the spatial distribution of functional groups on the sample surface. Applications of this chemically sensitive imaging technique are discussed.
Superconductivity in SrCuO
2
-BaCuO
2
Superlattices: Formation of Artificially Layered Superconducting Materials
Authors: Norton D. P. , Chakoumakos B. C. , Budai J. D. , Lowndes D. H. , Sales B. C. , Thompson J. R. , Christen D. K.
Published: October 2006

Pulsed-laser deposition was used to synthesize artificially layered high-temperature superconductors. Thin-film compounds were formed when the constraint of epitaxy was used to stabilize SrCuO
2
-BaCuO
2
superlattices in the infinite layer structure. Using this approach, two new structural families, Ba
2
Sr

n
–1

,Cu

n
+1

O

2
n
+2+δ

and Ba
4
Sr

n
–1

Cu

n
+3

O

2
n
+6+δ

, have been synthesized; these families superconduct at temperatures as high as 70 kelvin.
Facile Catalyst Separation Without Water: Fluorous Biphase Hydroformylation of Olefins
Authors: Horváth István T. , Rábai József
Published: October 2006

A novel concept for performing stoichiometric and catalytic chemical transformations has been developed that is based on the limited miscibility of partially or fully fluorinated compounds with nonfluorinated compounds. A fluorous biphase system (FBS) consists of a fluorous phase containing a dissolved reagent or catalyst and another phase, which could be any common organic or nonorganic solvent with limited or no solubility in the fluorous phase. The fluorous phase is defined as the fluorocarbon (mostly perfluorinated alkanes, ethers, and tertiary amines)—rich phase of a biphase system. An FBS compatible reagent or catalyst contains enough fluorous moieties that it will be soluble only or preferentially in the fluorous phase. The most effective fluorous moieties are linear or branched perfluoroalkyl chains with high carbon number; they may also contain heteroatoms. The chemical transformation may occur either in the fluorous phase or at the interface of the two phases. The application of FBS has been demonstrated for the extraction of rhodium from toluene and for the hydroformylation of olefins. The ability to separate a catalyst or a reagent from the products completely at mild conditions could lead to industrial application of homogeneous catalysts or reagents and to the development of more environmentally benign processes.
Partial Control of an Ion-Molecule Reaction by Selection of the Internal Motion of the Polyatomic Reagent Ion
Authors: Guettler Robert D. , Jones Glenn C. , Posey Lynmarie A. , Zare Richard N.
Published: October 2006

The ion-molecule reaction NH
3
+
+ ND
3
has been studied at various collision energies (1 to 5 electron volts in the center of mass) with preparation of the NH
3
+
reagent in two nearly isoenergetic vibrational states. One state corresponds to pure out-of-plane bending of the planar NH
3
+
ion (0.60 electron volts), whereas the other state is a combination of in-plane and out-of-plane motion (0.63 electron volts). The product branching ratios differ markedly for these two vibrational-state preparations. The differences in reactivity suggest that the in-plane totally symmetric stretching mode is essentially inactive in controlling the branching ratio of this reaction.
Early Cretaceous Dinosaurs from the Sahara
Authors: Sereno Paul C. , Wilson Jeffrey A. , Larsson Hans C. E. , Dutheil Didier B. , Sues Hans-Dieter
Published: October 2006

A major question in Mesozoic biogeography is how the land-based dinosaurian radiation responded to fragmentation of Pangaea. A rich fossil record has been uncovered on northern continents that spans the Cretaceous, when continental isolation reached its peak. In contrast, dinosaur remains on southern continents are scarce. The discovery of dinosaurian skeletons from Lower Cretaceous beds in the southern Sahara shows that several lineages of tetanuran theropods and broad-toothed sauropods had a cosmopolitan distribution across Pangaea before the onset of continental fragmentation. The distinct dinosaurian faunas of Africa, South America, and Asiamerica arose during the Cretaceous by differential survival of once widespread lineages on land masses that were becoming increasingly isolated from one another.
Low-Temperature Relaxation and Entropic Barriers in Supercooled Liquids
Authors: Mohanty Udayan , Oppenheim Irwin , Taubes Clifford H.
Published: October 2006

The low-temperature relaxation dynamics of supercooled liquids are a long-standing theoretical problem of considerable interest. The vast amount of experimental data on such liquids indicates that viscosity and diffusion in supercooled liquids are non-Arrhenius over a wide range of temperatures. The non-Arrhenius temperature dependence of the relaxation time of the slow modes in glass-forming liquids is investigated in connection with the topology of the potential energy landscape in configuration space. An analogy is made between the derived dynamical equations and Cooper's formulation of the pair equation in superconductivity.
Middle Cambrian Arthropod Embryos with Blastomeres
Authors: Zhang Xi-guang , Pratt Brian R.
Published: October 2006

A phosphatized Middle Cambrian (∼510 million years ago) fauna from Duyun, southern China, has yielded fossil embryos that may be of arthropod affinity and could belong to the co-occurring eodiscid trilobite
Pagetia
sp. The shell was most likely flexible and possessed at least two thin layers. Four embryos reveal blastomeres, and two embryonic stages are represented. These embryos demonstrate that the basic paradigm for the growth of the invertebrate embryo has not changed in more than half a billion years.
Fragmentation and Flow Regulation of River Systems in the Northern Third of the World
Authors: Dynesius Mats , Nilsson Christer
Published: October 2006

Seventy-seven percent of the total water discharge of the 139 largest river systems in North America north of Mexico, in Europe, and in the republics of the former Soviet Union is strongly or moderately affected by fragmentation of the river channels by dams and by water regulation resulting from reservoir operation, interbasin diversion, and irrigation. The remaining free-flowing large river systems are relatively small and nearly all situated in the far north, as are the 59 medium-sized river systems of Norway, Sweden, Finland, and Denmark. These conditions indicate that many types of river ecosystems have been lost and that the populations of many riverine species have become highly fragmented. To improve the conservation of biodiversity and the sustainable use of biological resources, immediate action is called for to create an international preservation network of free-flowing river systems and to rehabilitate exploited rivers in areas that lack unaffected watercourses.
Autumn Bloom of Antarctic Pack-Ice Algae
Authors: Fritsen C. H. , Lytle V. I. , Ackley S. F. , Sullivan C. W.
Published: October 2006

An autumn bloom of sea-ice algae was observed from February to June of 1992 within the upper 0.4 meter of multiyear ice in the Western Weddell Sea, Antarctica. The bloom was reliant on the freezing of porous areas within the ice that initiated a vertical exchange of nutrient-depleted brine with nutrient-rich seawater. This replenishment of nutrients to the algal community allowed the net production of 1760 milligrams of carbon and 200 milligrams of nitrogen per square meter of ice. The location of this autumn bloom is unlike that of spring blooms previously observed in both polar regions.
Precipitation Hardening in the First Aerospace Aluminum Alloy: The Wright
Flyer
Crankcase
Authors: Gayle Frank W. , Goodway Martha
Published: October 2006

Aluminum has had an essential part in aerospace history from its very inception: An aluminum copper alloy (with a copper composition of 8 percent by weight) was used in the engine that powered the historic first flight of the Wright brothers in 1903. Examination of this alloy shows that it is precipitation-hardened by Guinier-Preston zones in a bimodal distribution, with larger zones (10 to 22 nanometers) originating in the casting practice and finer ones (3 nanometers) resulting from ambient aging over the last 90 years. The precipitation hardening in the Wright
Flyer
crankcase occurred earlier than the experiments of Wilm in 1909, when such hardening was first discovered, and predates the accepted first aerospace application of precipitation-hardened aluminum in 1910.
Ultrahigh-Resolution X-ray Tomography
Authors: Haddad W. S. , McNulty I. , Trebes J. E. , Anderson E. H. , Levesque R. A. , Yang L.
Published: October 2006

Ultrahigh-resolution three-dimensional images of a microscopic test object were made with soft x-rays collected with a scanning transmission x-ray microscope. The test object consisted of two different patterns of gold bars on silicon nitride windows that were separated by ∼5 micrometers. Depth resolution comparable to the transverse resolution was achieved by recording nine two-dimensional images of the object at angles between –50 and +55 degrees with respect to the beam axis. The projections were then combined tomographically to form a three-dimensional image by means of an algorithm using an algebraic reconstruction technique. A transverse resolution of ∼1000 angstroms was observed. Artifacts in the reconstruction limited the overall depth resolution to ∼6000 angstroms; however, some features were clearly reconstructed with a depth resolution of ∼1000 angstroms.
A Central Role of Salicylic Acid in Plant Disease Resistance
Authors: Delaney Terrence P. , Uknes Scott , Vernooij Bernard , Friedrich Leslie , Weymann Kris , Negrotto David , Gaffney Thomas , Gut-Rella Manuela , Kessmann Helmut , Ward Eric , Ryals John
Published: October 2006

Transgenic tobacco and
Arabidopsis thaliana
expressing the bacterial enzyme salicylate hydroxylase cannot accumulate salicylic acid (SA). This defect not only makes the plants unable to induce systemic acquired resistance, but also leads to increased susceptibility to viral, fungal, and bacterial pathogens. The enhanced susceptibility extends even to host-pathogen combinations that would normally result in genetic resistance. Therefore, SA accumulation is essential for expression of multiple modes of plant disease resistance.
Calcium-Calmodulin Modulation of the Olfactory Cyclic Nucleotide-Gated Cation Channel
Authors: Liu Mingyao , Chen Tsung-Yu , Ahamed Basheer , Li Jess , Yau King-Wai
Published: October 2006

Although several ion channels have been reported to be directly modulated by calcium-calmodulin, they have not been conclusively shown to bind calmodulin, nor are the modulatory mechanisms understood. Study of the olfactory cyclic nucleotide-activated cation channel, which is modulated by calcium-calmodulin, indicates that calcium-calmodulin directly binds to a specific domain on the amino terminus of the channel. This binding reduces the effective affinity of the channel for cyclic nucleotides, apparently by acting on channel gating, which is tightly coupled to ligand binding. The data reveal a control mechanism that resembles those underlying the regulation of enzymes by calmodulin. The results also point to the amino-terminal part of the olfactory channel as an element for gating, which may have general significance in the operation of ion channels with similar overall structures.
The Validity of the "Diradical" Hypothesis: Direct Femtoscond Studies of the Transition-State Structures
Authors: Pedersen S. , Herek J. L. , Zewail A. H.
Published: October 2006

Direct studies of diradicals, the molecular species hypothesized to be archetypal of chemical bond transformations in many classes of reactions, have been made using femtosecond laser techniques with mass spectrometry in a molecular beam. These studies are aimed at "freezing" the diradicals in time and in the course of the reaction. The passage of these species through the transition-state region was observed and the effect of total energy and alkyl substitution on the rates of bond closure and cleavage was examined. The results establish the nature of these intermediates and define their existence during reactions.
Long-Term Behavioral Recovery in Parkinsonian Rats by an HSV Vector Expressing Tyrosine Hydroxylase
Authors: During Matthew J. , Naegele Janice R. , O'Malley Karen L. , Geller Alfred I.
Published: October 2006

One therapeutic approach to treating Parkinson's disease is to convert endogenous striatal cells into levo-3,4-dihydroxyphenylalanine (L-dopa)-producing cells. A defective herpes simplex virus type 1 vector expressing human tyrosine hydroxylase was delivered into the partially denervated striatum of 6-hydroxydopamine-lesioned rats, used as a model of Parkinson's disease. Efficient behavioral and biochemical recovery was maintained for 1 year after gene transfer. Biochemical recovery included increases in both striatal tyrosine hydroxylase enzyme activity and in extracellular dopamine concentrations. Persistence of human tyrosine hydroxylase was revealed by expression of RNA and immunoreactivity.
Meltwater Input to the Southern Ocean During the Last Glacial Maximum
Authors: Shemesh Aldo , Burckle Lloyd H. , Hays James D.
Published: October 2006

Three records of oxygen isotopes in biogenic silica from deep-sea sediment cores from the Atlantic and Indian sectors of the Southern Ocean reveal the presence of isotopically depleted diatomaceous opal in sediment from the last glacial maximum. This depletion is attributed to the presence of lids of meltwater that mixed with surface water along certain trajectories in the Southern Ocean. An increase in the drainage from Antarctica or extensive northward transport of icebergs are among the main mechanisms that could have produced the increase in meltwater input to the glacial Southern Ocean. Similar isotopic trends were observed in older climatic cycles at the same cores.
Exsolution in Ferromagnesian Olivine of the Divnoe Meteorite
Authors: Petaev Michail I. , Brearley Adrian J.
Published: October 2006

Ferromagnesian olivine, one of the most common minerals in the solar system, has been widely regarded as a continuous solid solution, although several thermodynamic analyses have suggested the possibility of a miscibility gap at low temperatures. Natural ferromagnesian olivine from the Divnoe meteorite contains compositionally different exsolution lamellae, providing direct evidence for the existence of a miscibility gap in iron-magnesium olivine solid solutions.
Teleseismic Search for Slow Precursors to Large Earthquakes
Authors: Ihmlé Pierre F. , Jordan Thomas H.
Published: October 2006

Some large earthquakes display low-frequency seismic anomalies that are best explained by episodes of slow, smooth deformation immediately before their high-frequency origin times. Analysis of the low-frequency spectra of 107 shallow-focus earthquakes revealed 20 events that had slow precursors (95 percent confidence level); 19 were slow earthquakes associated with the ocean ridge-transform system, and 1 was a slow earthquake on an intracontinental transform fault in the East African Rift system. These anomalous earthquakes appear to be compound events, each comprising one or more ordinary (fast) ruptures in the shallow seismogenic zone initiated by a precursory slow event in the adjacent or subjacent lithosphere.
Nanoscale Imaging of Molecular Adsorption
Authors: Cai Heng , Hillier Andrew C. , Franklin Kevin R. , Nunn C. Craig , Ward Michael D.
Published: October 2006

In situ atomic force microscope observations were made of the adsorption of anions (1– or 2–) of the organic diacid 5-benzoyl-4-hydroxy-2-methoxybenzenesulfonic acid from aqueous solution onto the (0001) surface of hydrotalcite (HT), a layered clay. This adsorption process is believed to mimic the ion-exchange reactions that occur within the layers of HT and other layered clays. Atomic force microscope images of the (0001) surfaces of HT, acquired in aqueous solutions, reveal an ordered structure with respect to magnesium and aluminum atoms. In the presence of the anions, atomic force microscopy indicates pH-dependent adsorption onto the formally cationic HT surface. The anion coverage is governed by electroneutrality and steric interactions between the bulky anions within the adsorbed layer, whereas the orientation of the anions with respect to the HT surface is dictated by coulombic interactions and hydrogen bonding between the anion's sulfonate moiety and clay hydroxyl triads. These observations reveal that the reversible adsorption of molecular species can be examined directly by in situ atomic force microscopy, providing details of surface stoichiometry and adlayer symmetry on the local, molecular level.
A Remarkable Auroral Event on Jupiter Observed in the Ultraviolet with the Hubble Space Telescope
Authors: Gérard J. C. , Grodent D. , Dols V. , Prangé R. , Waite J. H. , Gladstone G. R. , Franke K. A. , Paresce F. , Storrs A. , Jaffel L. Ben
Published: October 2006

Two sets of ultraviolet images of the Jovian north aurora were obtained with the Faint Object Camera on board the Hubble Space Telescope. The first series shows an intense discrete arc in near corotation with the planet. The maximum apparent molecular hydrogen emission rate corresponds to an electron precipitation of ∼1 watt per square meter, which is about 30,000 times larger than the solar heating by extreme ultraviolet radiation. Such a particle heating rate of the auroral upper atmosphere of Jupiter should cause a large transient temperature increase and generate strong thermospheric winds. Twenty hours after initial observation, the discrete arc had decreased in brightness by more than one order of magnitude. The time scale and magnitude of the change in the ultraviolet aurora leads us to suggest that the discrete Jovian auroral precipitation is related to large-scale variations in the current system, as is the case for Earth's discrete aurorae.
A Sharper View of Impact Craters from Clementine Data
Authors: Pieters C. M. , Staid M. I. , Fischer E. M. , Tompkins S. , He G.
Published: October 2006

The ultraviolet-visible camera on the Clementine spacecraft obtained high-spatial resolution images of the moon in five spectral channels. Impact craters mapped with these multispectral images show a scale of lithologic diversity that varies with crater size and target stratigraphy. Prominent lithologic variations (feldspathic versus basaltic) occur within the south wall of Copernicus (93 kilometers in diameter) on the scale of 1 to 2 kilometers. Lithologic diversity at Tycho (85 kilometers in diameter) is less apparent at this scale, although the impact melt of these two large craters is remarkably similar in this spectral range. The lunar surface within and around the smaller crater Giordano Bruno (22 kilometers in diameter) is largely dominated by the mixing of freshly excavated material with surrounding older soils derived from a generally similar feldspathic lithology.
The South Pole Region of the Moon as Seen by Clementine
Authors: Shoemaker E. M. , Robinson M. S. , Eliason E. M.
Published: October 2006

The Clementine mission has provided the first comprehensive set of high-resolution images of the south pole region of the moon. Within 5° of latitude of the pole, an area of an estimated 30,000 square kilometers remained in shadow during a full lunar rotation and is a promising target for future exploration for ice deposits. The Schrödinger Basin (320 kilometers in diameter), centered at 75°S, is one of the two youngest, least modified, great multiring impact basins on the moon. A large maar-type volcano localized along a graben within the Schrödinger Basin probably erupted between 1 and 2 billion years ago.
Topographic-Compositional Units on the Moon and the Early Evolution of the Lunar Crust
Authors: Lucey Paul G. , Spudis Paul D. , Zuber Maria , Smith David , Malaret Erick
Published: October 2006

The distribution of elevations on the moon determined by Clementine deviates strongly from a normal distribution, suggesting that several geologic processes have influenced the topography. The hypsograms for the near side and far side of the moon are distinctly different, and these differences correlate with differences in composition as determined by Apollo orbital geochemistry, Clementine global multispectral imaging, and ground-based spectroscopy. The hypsograms and compositional data indicate the presence of at least five compositional-altimetric units. The lack of fill of the South Pole—Aitken Basin by mare basalts suggests poor production efficiency of mare basalt in the mantle of this area of the moon.
Clementine Observations of the Aristarchus Region of the Moon
Authors: McEwen Alfred S. , Robinson Mark S. , Eliason Eric M. , Lucey Paul G. , Duxbury Tom C. , Spudis Paul D.
Published: October 2006

Multispectral and topographic data acquired by the Clementine spacecraft provide information on the composition and geologic history of the Aristarchus region of the moon. Altimetry profiles show the Aristarchus plateau dipping about 1° to the north-northwest and rising about 2 kilometers above the surrounding lavas of Oceanus Procellarum to the south. Dark, reddish pyroclastic glass covers the plateau to average depths of 10 to 30 meters, as determined from the estimated excavation depths of 100- to 1000-meter-diameter craters that have exposed materials below the pyroclastics. These craters and the walls of sinuous rilles also show that mare basalts underlie the pyroclastics across much of the plateau. Near-infrared images of Aristarchus crater reveal olivine-rich materials and two kilometer-sized outcrops of anorthosite in the central peaks. The anorthosite could be either a derivative of local magnesium-suite magmatism or a remnant of the ferroan anorthosite crust that formed over the primordial magma ocean.
The Transfer RNA Identity Problem: a Search for Rules
Authors: Saks Margaret E. , Sampson Jeffrey R. , Abelson John N.
Published: October 2006

Correct recognition of transfer RNAs (tRNAs) by aminoacyl-tRNA synthetases is central to the maintenance of translational fidelity. The hypothesis that synthetases recognize anticodon nucleotides was proposed in 1964 and had considerable experimental support by the mid-1970s. Nevertheless, the idea was not widely accepted until relatively recently in part because the methodologies initially available for examining tRNA recognition proved hampering for adequately testing alternative hypotheses. Implementation of new technologies has led to a reasonably complete picture of how tRNAs are recognized. The anticodon is indeed important for 17 of the 20
Escherichia coli
isoaccepting groups. For many of the isoaccepting groups, the acceptor stem or position 73 (or both) is important as well.
Magnetic Resonance Microscopy of Embryonic Cell Lineages and Movements
Authors: Jacobs Russell E. , Fraser Scott E.
Published: October 2006

Key events in vertebrate embryogenesis are difficult to observe in many species. High-resolution magnetic resonance imaging was used to follow cell movements and lineages in developing frog embryos. A single cell was injected at the 16-cell stage with a contrast agent, based on the gadolinium chelate gadolinium-diethylenetriamine pentaacetic acid-dextran. The labeled progeny cells could be followed uniquely in three-dimensional magnetic resonance images, acquired from the embryo over several days. The results show that external ectodermal and internal mesodermal tissues extend at different rates during amphibian gastrulation and neurulation.
Requirement for Transcription Factor IRF-1 in NO Synthase Induction in Macrophages
Authors: Kamijo R. , Harada H. , Matsuyama T. , Bosland M. , Gerecitano J. , Shapiro D. , Le J. , Koh S. I. , Kimura T. , Green S. J. , Mak T. W. , Taniguchi T. , Vilček J.
Published: October 2006

Production of nitric oxide (NO) by macrophages is important for the killing of intracellular infectious agents. Interferon (IFN)- γ and lipopolysaccharide stimulate NO production by transcriptionally up-regulating the inducible NO synthase (iNOS). Macrophages from mice with a targeted disruption of the IFN regulatory factor-1 (IRF-1) gene (IRF-1
-/-
mice) produced little or no NO and synthesized barely detectable iNOS messenger RNA in response to stimulation. Two adjacent IRF-1 response elements were identified in the iNOS promoter. Infection with
Mycobacterium bovis
(BCG) was more severe in IRF-1
-/-
mice than in wild-type mice. Thus, IRF-1 is essential for iNOS activation in murine macrophages.