bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature and Water Viscosity: Physiological Versus Mechanical Effects on Suspension Feeding
Authors: Podolsky Robert D.
Published: October 2006

Water viscosity is inversely related to temperature. This simple physical relation couples two potential influences on organism performance. Seawater viscosity was manipulated, with and without temperature, to distinguish the physiological and mechanical effects of temperature on suspension feeding by ciliated echinoderm larvae. Change in viscosity alone accounted for half of the decline in the feeding rate at lower temperature. High viscosity shifted ingestion toward larger particles, which suggests that viscosity affects particle capture as well as rates of water processing. Temperature-induced change in viscosity, therefore, impacts suspension feeding independently of physiology and has implications for many small-scale biological processes.
Pseudotachylytes Generated During Seismic Faulting and Eclogitization of the Deep Crust
Authors: Austrheim H. , Boundy T. M.
Published: October 2006

Pseudotachylytes are typically interpreted to have formed by frictional melting during coseismic faulting within the upper to middle crust. Pseudotachylytes in the Bergen arcs of western Norway contain microlites including omphacite, garnet, plagioclase, and quartz. This eclogite facies assemblage is stable at temperatures of about 800°C and pressures of 18 to 19 kilobars, corresponding to depths of 60 kilometers or more. The pseudotachylytes are exposed in Grenvillian granulites that locally underwent fluid-induced eclogitization and corresponding volume reduction of approximately 10 percent during the Caledonian continental collision. The pseudotachylytes may have formed as a result of the rapid relaxation of stresses caused by the eclogitization process.
Magnetoreception in Honeybees
Authors: Hsu Chin-Yuan , Li Chia-Wel
Published: October 2006

Magnetoreception by honeybees (
Apis mellifera
) is demonstrated by such activities as comb building and homing orientation, which are affected by the geomagnetic field. In other magnetoreceptive species, iron oxide crystals in the form of magnetite have been shown to be necessary for primary detection of magnetic fields. Here it is shown that trophocytes, which are apparently the only iron granule—containing cells in honeybees, contain super-paramagnetic magnetite. These cells are innervated by the nervous system, which suggests that trophocytes might be primarily responsible for magnetoreception. Electron microscopy also shows cytoskeletal attachments to the iron granule membrane.
Ecosystem Response to Solar Ultraviolet-B Radiation: Influence of Trophic-Level Interactions
Authors: Bothwell Max L. , Sherbot Darren M. J. , Pollock Colleen M.
Published: October 2006

Solar ultraviolet radiation (UVR) can reduce the photosynthesis and growth of benthic diatom communities in shallow freshwater. Nevertheless, greater amounts of algae accumulate in UVR-exposed habitats than in UVR-protected environments. Near-ultraviolet (UVA wavelengths of 320 to 400 nanometers) and mid-ultraviolet (UVB, wavelengths of 280 to 320 nanometers) radiation also inhibit algal consumers (Diptera: Chironomidae). Larval chironomids are more sensitive to UVB than sympatric algae. Differential sensitivity to UVB between algae and herbivores contributes to counterintuitive increases in algae in habitats exposed to UVB. These mesocosm experiments illustrate that predictions of the response of entire ecosystems to elevated UVB cannot be made on single trophic-level assessments.
Surface Pinning as a Determinant of the Bulk Flux-Line Lattice Structure in Copper Oxide Superconductors
Authors: Yoon Seokwon , Dai Hongjie , Liu Jie , Lieber Charles M.
Published: October 2006

Direct knowledge of crystal defects and their perturbation of magnetic flux lines is essential to understanding pinning and to devising approaches that enhance critical currents in superconductors with high critical temperatures (
T
c
). Atomic force microscopy was used to simultaneously characterize crystal defects and the magnetic flux-line lattice in single crystals of Bi
2
Sr
2
CaCu
2
O
8
. Images show that surface defects, which are present on all real samples, pin the flux-line lattice. Above a critical height, the pinning interaction is sufficiently strong to form grain boundaries in the bulk flux-line lattice. These results elucidate the structure of the defects that pin flux lines and demonstrate that surface pinning, through the formation of grain boundaries, can determine the bulk flux-line lattice structure in high-
T
c
materials. The implications of these results to the bulk flux-line lattice structure observed in previous experiments and to enhancing critical currents are discussed.
Thermophysiology of
Tyrannosaurus rex
: Evidence from Oxygen Isotopes
Authors: Barrick Reese E. , Showers William J.
Published: October 2006

The oxygen isotopic composition of vertebrate bone phosphate (δ
p
) is related to ingested water and to the body temperature at which the bone forms. The δ
p
is in equilibrium with the individual's body water, which is at a physiological steady state throughout the body. Therefore, intrabone temperature variation and the mean interbone temperature differences of well-preserved fossil vertebrates can be determined from the δ
p
variation. Values of δ
p
from a well-preserved
Tyrannosaurus rex
suggest that this species maintained homeothermy with less than 4°C of variability in body temperature. Maintenance of homeothermy implies a relatively high metabolic rate that is similar to that of endotherms.
The Role of the Tropical Super Greenhouse Effect in Heating the Ocean Surface
Authors: Lubin Dan
Published: October 2006

Measurements made by a Fourier transform infrared (FTIR) spectroradiometer operating in the middle infrared (5 to 20 micrometers, with a spectral resolution of one inverse centimeter) imply that there is an anomalously large greenhouse effect over equatorial oceans that is caused by water vapor. As sea-surface temperature increased from 297 to 303 degrees kelvin, the net infrared cooling at the surface decreased by 30 to 50 watts per square meter. Thus, according to the FTIR data, the super greenhouse effect that had been inferred from satellite measurements contributes directly to radiative heating of the sea surface. The data demonstrate that most of this heating occurs in the middle infrared by means of the continuum emission window of water vapor and that tropical deep convection contributes substantially to this super greenhouse effect.
Alterations of Single Molecule Fluorescence Lifetimes in Near-Field Optical Microscopy
Authors: Ambrose W. Patrick , Goodwin Peter M. , Keller Richard A. , Martin John C.
Published: October 2006

Fluorescence lifetimes of single Rhodamine 6G molecules on silica surfaces were measured with pulsed laser excitation, time-correlated single photon counting, and near-field scanning optical microscopy (NSOM). The fluorescence lifetime varies with the position of a molecule relative to a near-field probe. Qualitative features of lifetime decreases are consistent with molecular excited state quenching effects near metal surfaces. The technique of NSOM provides a means of altering the environment of a single fluorescent molecule and its decay kinetics in a repeatable fashion.
Fine Structure of the Landers Fault Zone: Segmentation and the Rupture Process
Authors: Li Yong-Gang , Aki Keiiti , Vidale John E. , Lee William H. K. , Marone Chris J.
Published: October 2006

Observations and modeling of 3- to 6-hertz seismic shear waves trapped within the fault zone of the 1992 Landers earthquake series allow the fine structure and continuity of the zone to be evaluated. The fault, to a depth of at least 12 kilometers, is marked by a zone 100 to 200 meters wide where shear velocity is reduced by 30 to 50 percent. This zone forms a seismic waveguide that extends along the southern 30 kilometers of the Landers rupture surface and ends at the fault bend about 18 kilometers north of the main shock epicenter. Another fault plane waveguide, disconnected from the first, exists along the northern rupture surface. These observations, in conjunction with surface slip, detailed seismicity patterns, and the progression of rupture along the fault, suggest that several simple rupture planes were involved in the Landers earthquake and that the inferred rupture front hesitated or slowed at the location where the rupture jumped from one to the next plane. Reduction in rupture velocity can tentatively be attributed to fault plane complexity, and variations in moment release can be attributed to variations in available energy.
Stepwise Formation of Multilayered Nanostructural Films from Macromolecular Precursors
Authors: Kleinfeld Elaine R. , Ferguson Gregory S.
Published: October 2006

Sequential adsorption of a cationic polyelectrolyte and individual sheets of the silicate mineral hectorite has allowed controlled, stepwise formation of multilayered films on silicon wafers. Each component adsorbs rapidly by an ion-exchange mechanism, and x-ray diffractometry indicates structural order even in films with thicknesses greater than 0.2 micrometer. The large lateral extent of the silicate sheets (about 25 to 35 nanometers) allows each layer to cover any packing defects in the underlying layer, thus preserving structural order in the growing film. With careful choice of component materials, this method should allow for the preparation of multilayered films with a variety of technologically important properties.
Size Dependence of a First Order Solid-Solid Phase Transition: The Wurtzite to Rock Salt Transformation in CdSe Nanocrystals
Authors: Tolbert S. H. , Alivisatos A. P.
Published: October 2006

Measurements of the size dependence of a solid-solid phase transition are presented. High-pressure x-ray diffraction and optical absorption are used to study the wurtzite to rock salt structural transformation in CdSe nanocrystals. These experiments show that both the thermodynamics and kinetics of this transformation are altered in finite size, as compared to bulk CdSe. An explanation of these results in the context of transformations in bulk systems is presented. Insight into the kinetics of transformations in both bulk and nanocrystal systems can be gained.
First Principles Determination of the Effects of Phosphorus and Boron on Iron Grain Boundary Cohesion
Authors: Wu Ruqian , Freeman A. J. , Olson G. B.
Published: October 2006

Toward an electronic level understanding of intergranular embrittlement and its control in steels, the effects of phosphorus and boron impurities on the energy and electronic properties of both an iron grain boundary and its corresponding intergranular fracture surface are investigated by the local density full potential augmented plane wave method. When structural relaxations are taken into account, the calculated energy difference of phosphorus in the two environments is consistent with its measured embrittlement potency. In contrast to the nonhybridized interaction of iron and phosphorus, iron-boron hybridization permits covalent bonding normal to the boundary contributing to cohesion enhancement. Insights into bonding behavior offer the potential for new directions in alloy composition for improvement of grain boundary-sensitive properties.
Magmatic Vapor Source for Sulfur Dioxide Released During Volcanic Eruptions: Evidence from Mount Pinatubo
Authors: Wallace Paul J. , Gerlach Terrence M.
Published: October 2006

Sulfur dioxide (SO
2
) released by the explosive eruption of Mount Pinatubo on 15 June 1991 had an impact on climate and stratospheric ozone. The total mass of SO
2
released was much greater than the amount dissolved in the magma before the eruption, and thus an additional source for the excess SO
2
is required. Infrared spectroscopic analyses of dissolved water and carbon dioxide in glass inclusions from quartz phenocrysts demonstrate that before eruption the magma contained a separate, SO
2
-bearing vapor phase. Data for gas emissions from other volcanoes in subduction-related arcs suggest that preeruptive magmatic vapor is a major source of the SO
2
that is released during many volcanic eruptions.
A Unified Description of Linear and Nonlinear Polarization in Organic Polymethine Dyes
Authors: Marder Seth R. , Gorman Christopher B. , Meyers Fabienne , Perry Joseph W. , Bourhill Grant , Brédas Jean-Luc , Pierce Brian M.
Published: October 2006

An internal or external electric field F can drive the chemical structure, bond order alternation, and electronic structure of linear polymethine dyes from a neutral, bond-alternated, polyene-like structure, through a cyanine-like structure, and ultimately to a zwitterionic (charge-separated) bond-alternated structure. As the structure evolves under the influence of F, the linear polarizability α, the first hyperpolarizability β, and the second hyperpolarizability γ are seen to be derivatives, with respect to F, of their next lower order polarization (for α) or polarizability (for β and γ). These derivative relations provide a unified picture of the dependence of the polarizability and hyperpolarizabilities on the structure in linear polymethine dyes. In addition, they allow for predictions of structure-property relations of higher order hyperpolarizabilities.
A Devonian Tetrapod from North America
Authors: Daeschler Edward B. , Shubin Neil H. , Thomson Keith S. , Amaral William W.
Published: October 2006

An early tetrapod fossil from the Upper Devonian of Pennsylvania (Catskill Formation) extends the temporal range of tetrapods in North America and suggests that they attained a virtually global equatorial distribution by the end of the Devonian. Derived features of the shoulder girdle indicate that appendicular mechanisms of support and propulsion were well developed even in the earliest phases of tetrapod history. The specialized morphology of the pectoral skeleton implies that the diversity of early tetrapods was great and is suggestive of innovative locomotor patterns in the first tetrapods.
Fullerenes in the Cretaceous-Tertiary Boundary Layer
Authors: Heymann Dieter , Chibante L. P. Felipe , Brooks Robert R. , Wolbach Wendy S. , Smalley Richard E.
Published: October 2006

High-pressure liquid chromatography with ultraviolet-visible spectral analysis of toluene extracts of samples from two Cretaceous-Tertiary (K-T) boundary sites in New Zealand has revealed the presence of C
60
at concentrations of 0.1 to 0.2 parts per million of the associated soot. This technique verified also that fullerenes are produced in similar amounts in the soots of common flames under ambient atmospheric conditions. Therefore, the C
60
in the K-T boundary layer may have originated in the extensive wildfires that were associated with the cataclysmic impact event that terminated the Mezozoic era about 65 million years ago.
Early Mars: How Warm and How Wet?
Authors: Squyres Steven W. , Kasting James F.
Published: October 2006

Early in its history, Mars underwent fluvial erosion that has been interpreted as evidence for a warmer, wetter climate. However, no atmosphere composed of only CO
2
and H
2
O appears capable of producing mean planetary temperatures even close to 0°C. Rather than by precipitation, aquifer recharge and ground water seepage may have been enabled by hydrothermal convection driven by geothermal heat and heat associated with impacts. Some climatic warming was probably necessary to allow water to flow for long distances across the surface. Modest warming could be provided by even a low-pressure CO
2
atmosphere if it was supplemented with small amounts of CH
4
, NH
3
, or SO
2
. Episodic excursions to high obliquities may also have raised temperatures over some portions of the planet's surface.
Artificial-Life Researchers Try to Create Social Reality
Authors: Flam Faye
Published: October 2006

Some scientists, among them cosmologist Stephen Hawking, argue that computer viruses are alive. A better case might be made for many of the self-replicating silicon-based creatures featured at the fourth Conference on Artificial Life, held on 5 to 8 July in Boston. Researchers from computer science, biology, and other disciplines presented computer programs that, among other things, evolved cooperative strategies in a selfish world and recreated themselves in ever more complex forms.
Impact Crater Densities on Volcanoes and Coronae on Venus: Implications for Volcanic Resurfacing
Authors: Namiki Noriyuki , Solomon Sean C.
Published: October 2006

The density of impact craters on large volcanoes on Venus is half the average crater density for the planet. The crater density on some classes of coronae is not significantly different from the global average density, but coronae with extensive associated volcanic deposits have lower crater densities. These results are inconsistent with both single-age and steady-state models for global resurfacing and suggest that volcanoes and coronae with associated volcanism have been active on Venus over the last 500 million years.
Surface Dating of Dynamic Landforms: Young Boulders on Aging Moraines
Authors: Hallet Bernard , Putkonen Jaakko
Published: October 2006

The dating of landforms is crucial to understanding the evolution, history, and stability of landscapes. Cosmogenic isotope analysis has recently been used to determine quantitative exposure ages for previously undatable landform surfaces. A pioneering application of this technique to date moraines illustrated its considerable potential but suggested a chronology partially inconsistent with existing geological data. Consideration of the dynamic nature of landforms and of the ever-present processes of erosion, deposition, and weathering leads to a resolution of this inconsistency and, more generally, offers guidance for realistic interpretation of exposure ages.
Real-Time Parallel Computation and Visualization of Ultrasonic Pulses in Solids
Authors: Schechter R. S. , Chaskelis H. H. , Mignogna R. B. , Delsanto P. P.
Published: October 2006

Parallel processing has changed the way much computational physics is done. Areas such as condensed matter physics, fluid dynamics, and other fields are making use of massively parallel computers to solve immense and important problems in new ways. Simulating wave propagation is another area that has benefited through the use of parallel processing. This is graphically illustrated in this article by various numerical simulations of ultrasonic pulses propagating through solids carried out on a massively parallel computer. These computations are accompanied by visualizations of the resulting wavefield. The calculations and visualizations, together, can be completed in only seconds to several minutes and compare well with experimental data. The computations and parallel processing techniques described should be important in related fields, such as geophysics, acoustics, and mechanics.
The Phase Boundary Between α- and β-Mg
2
SiO
4
Determined by in Situ X-ray Observation
Authors: Morishima H. , Kato T. , Suto M. , Ohtani E. , Urakawa S. , Utsumi W. , Shimomura O. , Kikegawa T.
Published: October 2006

The stability of Mg
2
SiO
4
, a major constituent in the Earth's mantle, has been investigated experimentally by in situ observation with synchrotron radiation. A cubic-type high-pressure apparatus equipped with sintered diamond anvils has been used over pressures of 11 to 15 gigapascals and temperatures of 800° to 1600°C. The phase stability of α-Mg
2
SiO
4
and β-Mg
2
SiO
4
was determined by taking account of the kinetic behavior of transition. The phase boundary between α-Mg
2
SiO
4
and β-Mg
2
SiO
4
is approximated by the linear expression
P
= (9.3 ± 0.1) + (0.0036 ± 0.0002)
T
where
P
is pressure in gigapascals and
T
is temperature in degrees Celsius.
A 160-Femtosecond Optical Image Processor Based on a Conjugated Polymer
Authors: Halvorson Craig , Hays Andrew , Kraabel Brett , Wu Rulian , Wudl Fred , Heeger Alan J.
Published: October 2006

Degenerate ground-state conjugated polymers exhibit large third-order nonlinear optical susceptibilities, including substantial two-photon absorption. With the use of a machine architecture suited to these material properties, ultrafast optical processors are possible. A four-wave mixing optical correlator was built with an air-stable, processable, degenerate ground-state conjugated polymer, poly(1,6-heptadiester). The continuously updatable processor correlates two 5000-pixel images in less than 160 femtoseconds, achieving peak processing rates of 3 × 10
16
operations per second.
Mechanism of the Selective Catalytic Reduction of Nitric Oxide by Ammonia Elucidated by in Situ On-Line Fourier Transform Infrared Spectroscopy
Authors: Topsøe Nan-Yu
Published: October 2006

The selective catalytic reduction reaction of nitric oxide by ammonia over vanadia-titania catalysts is one of the methods of removing NO

x

pollution. In the present study, it has been possible to identify the reaction mechanism and the nature of the active sites in these catalysts by combining transient or steady-state in situ (Fourier transform infrared spectroscopy) experiments directly with on-line activity studies. The results suggest a catalytic cycle that consists of both acid and redox reactions and involves both surface V—OH (Brønsted acid sites) and V=O species. A fundamental microkinetic model is proposed, which accounts for the observed industrial kinetics performance.
A Redox Fuel Cell That Operates with Methane as Fuel at 120°C
Authors: Bergens Steven H. , Gorman Christopher B. , Palmore G. Tayhas R. , Whitesides George M.
Published: October 2006

Platinum black efficiently catalyzes the oxidation of methane by iron(III) to generate carbon dioxide and eight equivalents of iron(II) in solutions of sulfuric acid in water. The rate of oxidation increases over 4 hours to reach ∼4.83 × 10
-2
moles of iron(II) per gram atom of surface platinum per second. A redox fuel cell was assembled that used this reaction in a liquid reformer to generate soluble reducing equivalents of iron(II) from methane, which was electrochemically oxidized to iron(III) in the cell. A vanadium(V)-(IV)—nitric acid-O
2
redox system catalyzed the electrochemical reduction of O
2
. The open-circuit voltage of the cell was 0.48 volt, and the maximum power output of the cell was 8.1 milliwatts per cubic centimeter of graphite felt electrode.
A Spectroscopic Measurement of the Coronal Density of Procyon
Authors: Schmitt J. H. M. M. , Haisch B. M. , Drake J. J.
Published: October 2006

One of the open key issues in the astrophysics of stellar coronae is the determination of their spatial structure and density. From almost all previous measurements, one can infer merely the presence of a corona, which for the most energetic stellar coronae may exceed the solar x-ray output by as much as five orders of magnitude, but no information can be obtained on the densities and hence volumes and sizes of the hot x-ray emitting material. A direct spectroscopic measurement of the coronal density was obtained for the star Procyon with the spectrometer on board the Extreme Ultraviolet Explorer satellite; the ratio of two Fe XIV lines at 211.32 and 264.79 angstroms was used to determine a density of ∼4 × 10
9
to 7 × 10
9
electrons per cubic centimeter, which is a factor of 2 to 3 higher than typical solar active region densities. From this value, we estimate that ∼6 percent of the stellar surface is covered with ∼7 × 10
4
coronal loops.
Carbon Dioxide Supersaturation in the Surface Waters of Lakes
Authors: Cole Jonathan J. , Caraco Nina F. , Kling George W. , Kratz Timothy K.
Published: October 2006

Data on the partial pressure of carbon dioxide (CO
2
) in the surface waters from a large number of lakes (1835) with a worldwide distribution show that only a small proportion of the 4665 samples analyzed (less than 10 percent) were within ±20 percent of equilibrium with the atmosphere and that most samples (87 percent) were supersaturated. The mean partial pressure of CO
2
averaged 1036 microatmospheres, about three times the value in the overlying atmosphere, indicating that lakes are sources rather than sinks of atmospheric CO
2
. On a global scale, the potential efflux of CO
2
from lakes (about 0.14 × 10
15
grams of carbon per year) is about half as large as riverine transport of organic plus inorganic carbon to the ocean. Lakes are a small but potentially important conduit for carbon from terrestrial sources to the atmospheric sink.
Magnetism from the Atom to the Bulk in Iron, Cobalt, and Nickel Clusters
Authors: Billas Isabelle M.L. , Châtelain A. , de Heer Walt A.
Published: October 2006

Molecular beam deflection measurements of small iron, cobalt, and nickel clusters show how magnetism develops as the cluster size is increased from several tens to several hundreds of atoms for temperatures between 80 and 1000 K. Ferromagnetism occurs even for the smallest sizes: for clusters with fewer than about 30 atoms the magnetic moments are atomlike; as the size is increased up to 700 atoms, the magnetic moments approach the bulk limit, with oscillations probably caused by surface-induced spin-density waves. The trends are explained in a magnetic shell model. A crystallographic phase transition from high moment to low moment in iron clusters has also been identified.
X-ray Variability in the Hot Supergiant ζ Orionis
Authors: Berghöfer Thomas W. , Schmitt Jürgen H. M. M.
Published: October 2006

Hot massive stars represent only a small fraction of the stellar population of the galaxy, but their enormous luminosities make them visible over large distances. Therefore, they are ideal standard candles, used to determine distances of near galaxies. Their mass loss due to supersonic winds driven by radiation pressure contributes significantly to the interstellar medium and thus to the chemical evolution of galaxies. All hot stars are soft x-ray sources; in contrast to the sun with its highly variable x-ray flux, long time scale x-ray variability is not common among hot stars. An analysis is presented here of an unusual increase in x-ray flux observed with the roentgen observatory satellite during a period of 2 days for the hot supergiant ζ Orionis, the only episode of x-ray variability that has been found in a hot star. These observations provide the most direct evidence so far for the scenario of shock-heated gas in the winds of hot stars.
Negative Absolute Temperatures: "Hot" Spins in Spontaneous Magnetic Order
Authors: Hakonen Pertti , Lounasmaa Olli V.
Published: October 2006

Depending on the sign of the spin temperature in the picokelvin range, antiferromagnetic nuclear and ferromagnetic nuclear orders in silver are caused by the same interactions. In rhodium, the antiferromagnetic state is preferred both at temperatures greater than and temperatures less than zero. The lowest and "highest" temperatures ever produced on this scale and measured, 280 and –750 picokelvin, respectively, have been reached in the course of these experiments. The results on silver, in particular, show that negative temperatures are real, not fictitious, quantities.
Greenland Ice Evidence of Hemispheric Lead Pollution Two Millennia Ago by Greek and Roman Civilizations
Authors: Hong Sungmin , Candelone Jean-Pierre , Patterson Clair C. , Boutron Claude F.
Published: October 2006

Analysis of the Greenland ice core covering the period from 3000 to 500 years ago—the Greek, Roman, Medieval and Renaissance times—shows that lead is present at concentrations four times as great as natural values from about 2500 to 1700 years ago (500 B.C. to 300 A.D.). These results show that Greek and Roman lead and silver mining and smelting activities polluted the middle troposphere of the Northern Hemisphere on a hemispheric scale two millennia ago, long before the Industrial Revolution. Cumulative lead fallout to the Greenland Ice Sheet during these eight centuries was as high as 15 percent of that caused by the massive use of lead alkyl additives in gasoline since the 1930s. Pronounced lead pollution is also observed during Medieval and Renaissance times.
Nitrogen Uptake, Dissolved Organic Nitrogen Release, and New Production
Authors: Bronk Deborah A. , Glibert Patricia M. , Ward Bess B.
Published: October 2006

In oceanic, coastal, and estuarine environments, an average of 25 to 41 percent of the dissolved inorganic nitrogen (NH
4
+
and NO
3
–
) taken up by phytoplankton is released as dissolved organic nitrogen (DON). Release rates for DON in oceanic systems range from 4 to 26 nanogram-atoms of nitrogen per liter per hour. Failure to account for the production of DON during nitrogen-15 uptake experiments results in an underestimate of gross nitrogen uptake rates and thus an underestimate of new and regenerated production. In these studies, traditional nitrogen-15 techniques were found to underestimate new and regenerated production by up to 74 and 50 percent, respectively. Total DON turnover times, estimated from DON release resulting from both NH
4
+
and NO
3
–
uptake, were 10 ± 1, 18 ± 14, and 4 days for oceanic, coastal, and estuarine sites, respectively.
Capillarity and Wetting of Carbon Nanotubes
Authors: Dujardin E. , Ebbesen T. W. , Hiura H. , Tanigaki K.
Published: October 2006

The wetting and capillarity of carbon nanotubes were studied in detail here. Nanotubes are not "super-straws," although they can be wet and filled by substances having low surface tension, such as sulfur, selenium, and cesium, with an upper limit to this tension less than 200 millinewtons per meter. This limit implies that typical pure metals will not be drawn into the inner cavity of nanotubes through capillarity, whereas water and organic solvents will. These results have important implications for the further use of carbon nanotubes in experiments on a nanometer scale.
Direct Determination of Grain Boundary Atomic Structure in SrTiO
3
Authors: McGibbon M. M. , Browning N. D. , Chisholm M. F. , McGibbon A. J. , Pennycook S. J. , Ravikumar V. , Dravid V. P.
Published: October 2006

An atomic structure model for a 25° [001] symmetric tilt grain boundary in SrTiO
3
has been determined directly from experimental data with the use of high-resolution
Z
-contrast imaging coupled with electron energy loss spectroscopy. The derived model of the grain boundary was refined by bond-valence sum calculations and reveals candidate sites for dopant atoms in the boundary plane. These results show how the combined techniques can be used to deduce the atomic structure of defects and interfaces without recourse to preconceived structural models or image simulations.
Physical and Biological Controls on Carbon Cycling in the Equatorial Pacific
Authors: Murray James W. , Barber Richard T. , Roman Michael R. , Bacon Michael P. , Feely Richard A.
Published: October 2006

The equatorial Pacific is the largest oceanic source of carbon dioxide to the atmosphere and has been proposed to be a major site of organic carbon export to the deep sea. Study of the chemistry and biology of this area from 170° to 95°W suggests that variability of remote winds in the western Pacific and tropical instability waves are the major factors controlling chemical and biological variability. The reason is that most of the biological production is based on recycled nutrients; only a few of the nutrients transported to the surface by upwelling are taken up by photosynthesis. Biological cycling within the euphotic zone is efficient, and the export of carbon fixed by photosynthesis is small. The fluxes of carbon dioxide to the atmosphere and particulate organic carbon to the deep sea were about 0.3 gigatons per year, and the production of dissolved organic carbon was about three times as large. The data establish El Niño events as the main source of interannual variability.
Atomic-Scale Dynamics of a Two-Dimensional Gas-Solid Interface
Authors: Stranick S. J. , Kamna M. M. , Weiss P. S.
Published: October 2006

The interface between a two-dimensional (2D) molecular gas and a 2D molecular solid has been imaged with a low-temperature, ultrahigh-vacuum scanning tunneling microscope. The solid consists of benzene molecules strongly bound to step edges on a Cu{111} surface. Benzene molecules on the Cu{111} terraces move freely as a 2D gas at 77 kelvin. Benzene molecules transiently occupy well-defined adsorption sites at the 1D edge of the 2D solid. Diffusion of molecules between these sites and exchange between the two phases at the interface are observed. On raised terraces of the copper surface, the 2D gas is held in a cage of the solid as in a 2D nanometer-scale gas bulb.
Electronic Coherence and Nonlinear Susceptibilities of Conjugated Polyenes
Authors: Mukamel Shaul , Takahashi Akira , Wang Hong Xiang , Chen Guanhua
Published: October 2006

A dynamic theory that connects electronic motions and the nonlinear optical response of conjugated polyenes is developed by introducing the concept of electronic normal modes. A useful picture for the mechanism of optical nonlinearities is obtained by identifying the few dominant modes. This quasi-particle electron-hole representation establishes a close analogy with small semiconductor particles (quantum dots) and is very different from the traditional approach based on electronic eigenstates. The effective conjugation length (coherence size), which controls the scaling and saturation of the static third-order susceptibility χ
(3)
with the number of double bonds, is related to the coherence of the relative motion of electron-hole pairs created upon optical excitation.
Removal of Stratospheric O
3
by Radicals: In Situ Measurements of OH, HO
2
, NO, NO
2
, ClO, and BrO
Authors: Wennberg P. O. , Cohen R. C. , Stimpfle R. M. , Koplow J. P. , Anderson J. G. , Salawitch R. J. , Fahey D. W. , Woodbridge E. L. , Keim E. R. , Gao R. S. , Webster C. R. , May R. D. , Toohey D. W. , Avallone L. M. , Proffitt M. H. , Loewenstein M. , Podolske J. R. , Chan K. R. , Wofsy S. C.
Published: October 2006

Simultaneous in situ measurements of the concentrations of OH, HO
2
, ClO, BrO, NO, and NO
2
demonstrate the predominance of odd-hydrogen and halogen free-radical catalysis in determining the rate of removal of ozone in the lower stratosphere during May 1993. A single catalytic cycle, in which the rate-limiting step is the reaction of HO
2
with ozone, accounted for nearly one-half of the total O
3
removal in this region of the atmosphere. Halogen-radical chemistry was responsible for approximately one-third of the photochemical removal of O
3
; reactions involving BrO account for one-half of this loss. Catalytic destruction by NO
2
, which for two decades was considered to be the predominant loss process, accounted for less than 20 percent of the O
3
removal. The measurements demonstrate quantitatively the coupling that exists between the radical families. The concentrations of HO
2
and ClO are inversely correlated with those of NO and NO
2
. The direct determination of the relative importance of the catalytic loss processes, combined with a demonstration of the reactions linking the hydrogen, halogen, and nitrogen radical concentrations, shows that in the air sampled the rate of O
3
removal was inversely correlated with total NO

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Paleomagnetic Record of a Geomagnetic Field Reversal from Late Miocene Mafic Intrusions, Southern Nevada
Authors: Ratcliff Catherine D. , Geissman John W. , Perry Frank V. , Crowe Bruce M. , Zeitler Peter K.
Published: October 2006

Late Miocene (about 8.65 million years ago) mafic intrusions and lava flows along with remagnetized host rocks from Paiute Ridge, southern Nevada, provide a high-quality paleomagnetic record of a geomagnetic field reversal. These rocks yield thermoremanent magnetizations with declinations of 227° to 310° and inclinations of –7° to 49°, defining a reasonably continuous virtual geomagnetic pole path over west-central Pacific longitudes. Conductive cooling estimates for the intrusions suggest that this field transition, and mafic magmatism, lasted only a few hundred years. Because this record comes principally from intrusive rocks, rather than sediments or lavas, it is important in demonstrating the longitudinal confinement of the geomagnetic field during a reversal.
Strength of Diamond
Authors: Weidner Donald J. , Wang Yanbin , Vaughan Michael T.
Published: October 2006

The yield strength of diamond is measured under a pressure of 10 gigapascals at temperatures up to 1550°C by the analysis of x-ray peak shapes on diamond diffraction lines in a powdered sample as a function of pressure and temperature. At room temperature, the diamond crystals exhibit elastic behavior with increasing pressure. Significant ductile deformation is observed only at temperatures above 1000°C at this pressure. The differential yield strength of diamond decreases with temperature from 16 gigapascals at 1100°C to 4 gigapascals at 1550°C. Transmission electron microscopy observations on the recovered sample indicate that the dominant deformation mechanism under high pressure and temperature is crystal plasticity.
Surface-Skimming Stoneflies: A Possible Intermediate Stage in Insect Flight Evolution
Authors: Marden James H. , Kramer Melissa G.
Published: October 2006

Insect wings appear to have evolved from gills used by aquatic forms for ventilation and swimming, yet the nature of intermediate stages remains a mystery. Here a form of nonflying aerodynamic locomotion used by aquatic insects is described, called surface skimming, in which thrust is provided by wing flapping while continuous contact with the water removes the need for total aerodynamic weight support. Stoneflies surface skim with wing areas and muscle power output severely reduced, which indicates that surface skimming could have been an effective form of locomotion for ancestral aquatic insects with small protowings and low muscle power output.
Plant Embryogenesis: Zygote to Seed
Authors: Goldberg Robert B. , de Paiva Genaro , Yadegari Ramin
Published: October 2006

Most differentiation events in higher plants occur continuously in the postembryonic adult phase of the life cycle. Embryogenesis in plants, therefore, is concerned primarily with establishing the basic shoot-root body pattern of the plant and accumulating food reserves that will be used by the germinating seedling after a period of embryonic dormancy within the seed. Recent genetics studies in
Arabidopsis
have identified genes that provide new insight into how embryos form during plant development. These studies, and others using molecular approaches, are beginning to reveal the underlying processes that control plant embryogenesis.
Simulations of Atmospheric Variability Induced by Sea Surface Temperatures and Implications for Global Warming
Authors: Kumar Arun , Leetmaa Ants , Ji Ming
Published: October 2006

An atmospheric general circulation model was forced with observed interannual changes in the global sea surface temperatures (SSTs) for the period 1982 to 1993. The simulated seasonal surface air temperature patterns over land areas closely resemble the observed. Over most of the globe, the patterns also resemble those associated with El Niño events and are also reproduced in simulations with weak warm tropical SSTs near the date line. An exception is northern Asia, where the mechanisms for the observed warming are unclear. The results suggest that enhanced air-sea interactions resulting from recent, more persistent warm oceanic conditions in the tropics contributed to the observed global warming trend during this period.
Use of Taylor-Aris Dispersion for Measurement of a Solute Diffusion Coefficient in Thin Capillaries
Authors: Bello Michael S. , Rezzonico Roberta , Righetti Pier Giorgio
Published: October 2006

A method for the fast measurement of the diffusion coefficients of both small and large molecules in thin capillaries is reported. The method relies on Taylor-Aris dispersion theory and uses standard instrumentation for capillary zone electrophoresis. With this equipment, which consists of thin capillaries (50 to 100 micrometers in inner diameter), an injection system, detector ports, and computer data acquisition, a sample plug is pumped through the capillary at known velocity and the peak dispersion coefficient (
D
*
) is measured. With the experimentally measured values of
D
*
and flow velocity, and knowledge of the inner diameter of the capillary, the molecular diffusion coefficient (
D
) can be rapidly derived. For example, for ovalbumin a
D
value of 0.759 × 10
-6
square centimeter per second is found versus a tabulated value of 0.776 × 10
-6
square centimeter per second (error, 2 percent). For hemoglobin a
D
value of 0.676 × 10
-6
square centimeter per second is obtained versus a literature value of 0.690 × 10
-6
square centimeter per second (error, 1.5 percent).
Experimental Evidence That Competition Promotes Divergence in Adaptive Radiation
Authors: Schluter Dolph
Published: October 2006

Interspecific competition driving divergence in adaptive radiation has not previously been tested experimentally. Natural selection on a morphologically variable species of stickleback fish was contrasted in the presence and absence of a close relative. Selection was nondirectional when the target species was alone, whereas addition of the second species favored individuals most different from it morphologically and ecologically. Disproportionately severe competition between similar phenotypes indicates frequency-dependent selection, verifying a crucial element of theory of competition and character divergence. The findings help resolve outstanding debates on the ecological causes of diversification and the evolutionary consequences of competitive interactions.
Isolation of Virus Capable of Lysing the Brown Tide Microalga,
Aureococcus anophagefferens
Authors: Milligan K. L. Drewes , Cosper Elizabeth M.
Published: October 2006

Viruses have been hypothesized to control blooms of
Aureococcus anophagefferens
gen. et sp. nov. (Chrysophyceae), a marine phytoplankton that since 1985 has caused devastating summer blooms called "brown tide." By means of ultrafiltration methods, viruses specific to this alga were isolated from both the Great South Bay and Peconic Bay systems of Long Island, New York, during the summer bloom period of 1992. Cell lysis of healthy algal cultures was demonstrated, as well as continuing reinfection with serial transfers of cultures. Electron microscope surveys yielded images of phage-like virus particles with tails that could attach to
A. anophagefferens
cells within minutes of exposure. The isolation and cultivation of this virus highlights the need for further study of viral infection of eukaryotic algae and the potential for a better understanding of algal bloom control by viral infection.
Conducting Carbon Wires in Ordered, Nanometer-Sized Channels
Authors: Wu Chun-Guey , Bein Thomas
Published: October 2006

The encapsulation of graphite-type carbon wires in the regular, 3-nanometer-wide hexagonal channels of the mesoporous host MCM-41 is reported. Acrylonitrile monomers are introduced through vapor or solution transfer and polymerized in the channels with external radical initiators. Pyrolysis of the intrachannel polyacrylonitrile results in filaments whose microwave conductivity is about 10 times that of bulk carbonized polyacrylonitrile. The MCM host plays a key role in ordering the carbon structure, most likely through the parallel alignment of the precursor polymer chains in the channels. The fabrication of stable carbon filaments in ordered, nanometer-sized channels represents an important step toward the development of nanometer electronics.
Simulations of Gas-Phase Chemical Reactions: Applications to S
N
2 Nucleophilic Substitution
Authors: Hase William L.
Published: October 2006

Computer simulations and animations of the motion of atoms as a chemical reaction proceeds give a detailed picture of how the reaction occurs at a microscopic level. This information is particularly useful for testing the accuracy of statistical models, which are used to calculate various attributes of chemical reactions. Such simulations and animations, in concert with experimental and ab initio studies, have begun to provide a microscopic picture of the intimate details of a particular class of gas-phase ion-molecule bimolecular reactions known as S
N
2 nucleophilic substitution. In these reactions, a nucleophile is displaced from a molecule by another nucleophile. The dynamical model of S
N
2 reactions that emerges from the computer studies, and its relation to statistical theories, is discussed here.
Growth and Sintering of Fullerene Nanotubes
Authors: Colbert D. T. , Zhang J. , McClure S. M. , Nikolaev P. , Chen Z. , Hafner J. H. , Owens D. W. , Kotula P. G. , Carter C. B. , Weaver J. H. , Rinzler A. G. , Smalley R. E.
Published: October 2006

Carbon nanotubes produced in arcs have been found to have the form of multiwalled fullerenes, at least over short lengths. Sintering of the tubes to each other is the predominant source of defects that limit the utility of these otherwise perfect fullerene structures. The use of a water-cooled copper cathode minimized such defects, permitting nanotubes longer than 40 micrometers to be attached to macroscopic electrodes and extracted from the bulk deposit. A detailed mechanism that features the high electric field at (and field-emission from) open nanotube tips exposed to the arc plasma, and consequent positive feedback effects from the neutral gas and plasma, is proposed for tube growth in such arcs.
A Double Mass Extinction at the End of the Paleozoic Era
Authors: Stanley S. M. , Yang X.
Published: October 2006

Three tests based on fossil data indicate that high rates of extinction recorded in the penultimate (Guadalupian) stage of the Paleozoic era are not artifacts of a poor fossil record. Instead, they represent an abrupt mass extinction that was one of the largest to occur in the past half billion years. The final mass extinction of the era, which took place about 5 million years after the Guadalupian event, remains the most severe biotic crisis of all time. Taxonomic losses in the Late Permian were partitioned among the two crises and the intervening interval, however, and the terminal Permian crisis eliminated only about 80 percent of marine species, not 95 or 96 percent as earlier estimates have suggested.
Nickel Oxide Interstratified α-Zirconium Phosphate, a Composite Exhibiting Ferromagnetic Behavior
Authors: Shpeizer Boris , Poojary Damodara M. , Ahn Kyungsoo , Runyan Charles E. , Clearfield Abraham
Published: October 2006

As part of an ongoing research program to synthesize novel pillared layered materials, nickel and cobalt hydroxyacetates were inserted between the layers of amine intercalates of α-zirconium phosphate. The structure of the resultant nickel composite, derived from x-ray powder data, was found to consist of a three-tiered layer of nickel atoms bridged by hydroxo and acetato groups. Heating to 420°C converted the hydroxyacetate layers to oxide and imparted ordered magnetic domains to the composite. The phosphate layers appear to act as a template directing the growth of the inserted layers in this class of composite materials.
Double Flood Basalts and Plume Head Separation at the 660-Kilometer Discontinuity
Authors: Bercovici David , Mahoney John
Published: October 2006

Several of the world's flood basalt provinces display two distinct times of major eruptions separated by between 20 million and 90 million years. These double flood basalts may occur because a starting mantle plume head can separate from its trailing conduit upon passing the interface between the upper mantle and the lower mantle. This detached plume head eventually triggers the first flood basalt event. The remaining conduit forms a new plume head, which causes the second eruptive event. The second plume head is predicted to arrive at the lithosphere at least 10 million years after the first plume head, in general agreement with observations regarding double flood basalts.