bluuebunny/crossref_metadata_2025 huggingface dataset:
Metal Nanotubule Membranes with Electrochemically Switchable Ion-Transport Selectivity
Authors: Nishizawa Matsuhiko , Menon Vinod P. , Martin Charles R.
Published: October 2006

Membranes containing cylindrical metal nanotubules that span the complete thickness of the membrane are described. The inside radius of the nanotubules can be varied at will; nanotubule radii as small as 0.8 nanometer are reported. These membranes show selective ion transport analogous to that observed in ion-exchange polymers. Ion permselectivity occurs because excess charge density can be present on the inner walls of the metal tubules. The membranes reject ions with the same sign as the excess charge and transport ions of the opposite sign. Because the sign of the excess charge on the tubule can be changed potentiostatically, a metal nanotubule membrane can be either cation selective or anion selective, depending on the potential applied to the membrane.
A Reevaluation of the Ozone Budget with HALOE UARS Data: No Evidence for the Ozone Deficit
Authors: Crutzen P. J. , Grooß J. -U. , Brühl C. , Müller R. , Russell J. M.
Published: October 2006

Recently, additional ozone production mechanisms have been proposed to resolve the ozone deficit problem, which arises from greater ozone destruction than production in several photochemical models of the upper stratosphere and lower mesosphere. A detailed ozone model budget analysis was performed with simultaneous observations of O
3
, HCl, H
2
O, CH
4
, NO, and NO
2
from the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite (UARS) under conditions with the strongest photochemical control of ozone. The results indicate that an ozone deficit may not exist. On the contrary, the use of currently recommended photochemical parameters leads to insufficient ozone destruction in the model.
The Heliospheric Magnetic Field Over the South Polar Region of the Sun
Authors: Balogh A. , Southwood D. J. , Forsyth R. J. , Horbury T. S. , Smith E. J. , Tsurutani B. T.
Published: October 2006

Magnetic field measurements from the Ulysses space mission over the south polar regions of the sun showed that the structure and properties of the three-dimensional heliosphere were determined by the fast solar wind flow and magnetic fields from the large coronal holes in the polar regions of the sun. This conclusion applies at the current, minimum phase of the 11-year solar activity cycle. Unexpectedly, the radial component of the magnetic field was independent of latitude. The high-latitude magnetic field deviated significantly from the expected Parker geometry, probably because of large amplitude transverse fluctuations. Low-frequency fluctuations had a high level of variance. The rate of occurrence of discontinuities also increased significantly at high latitudes.
Cosmic Ray and Solar Particle Investigations Over the South Polar Regions of the Sun
Authors: Simpson J. A. , Connell J. J. , Lopate C. , McKibben R. B. , Zhang M. , Anglin J. D. , Ferrando P. , Rastoin C. , Raviart A. , Heber B. , Müller-Mellin R. , Kunow H. , Sierks H. , Wibberenz G. , Bothmer V. , Marsden R. G. , Sanderson T. R. , Trattner K. J. , Wenzel K. -P. , Paizis C.
Published: October 2006

Observations of galactic cosmic radiation and anomalous component nuclei with charged particle sensors on the Ulysses spacecraft showed that heliospheric magnetic field structure over the south solar pole does not permit substantially more direct access to the local interstellar cosmic ray spectrum than is possible in the equatorial zone. Fluxes of galactic cosmic rays and the anomalous component increased as a result of latitude gradients by less than 50% from the equator to -80°. Thus, the modulated cosmic ray nucleon, electron, and anomalous component fluxes are nearly spherically symmetric in the inner solar system. The cosmic rays and the anomalous nuclear component underwent a continuous, ∼26 day recurrent modulation to -80.2°, whereas all recurring magnetic field compressions and recurring streams in the solar wind disappeared above ∼55°S latitude.
Ulysses Radio and Plasma Wave Observations at High Southern Heliographic Latitudes
Authors: Stone R. G. , MacDowall R. J. , Fainberg J. , Kaiser M. L. , Desch M. D. , Goldstein M. L. , Hoang S. , Bougeret J. L. , Harvey C. C. , Manning R. , Steinberg J. L. , Kellogg P. J. , Lin N. , Goetz K. , Osherovich V. A. , Reiner M. J. , Canu P. , Cornilleau-Wehrlin N. , Lengyel-Frey D. , Thejappa G.
Published: October 2006

Ulysses spacecraft radio and plasma wave observations indicate that some variations in the intensity and occurrence rate of electric and magnetic wave events are functions of heliographic latitude, distance from the sun, and phase of the solar cycle. At high heliographic latitudes, solar type III radio emissions did not descend to the local plasma frequency, in contrast to the emission frequencies of some bursts observed in the ecliptic. Short-duration bursts of electrostatic and electromagnetic waves were often found in association with depressions in magnetic field amplitude, known as magnetic holes. Extensive wave activity observed in magnetic clouds may exist because of unusually large electron-ion temperature ratios. The lower number of intense in situ wave events at high latitudes was likely due to the decreased variability of the high- latitude solar wind.
Abundance and Distribution of Iron on the Moon
Authors: Lucey Paul G. , Taylor G. Jeffrey , Malaret Erick
Published: October 2006

The abundance and distribution of iron on the moon is derived from a near-global data set from Clementine. The determined iron content of the lunar highlands crust (∼3 percent iron by weight) supports the hypothesis that much of the lunar crust was derived from a magma ocean. The iron content of lower crustal material exposed by the South Pole-Aitken impact basin on the lunar farside is higher (∼7 to 8 percent by weight) and consistent with a basaltic composition. This composition supports earlier evidence that the lunar crust becomes more mafic with depth. The data also suggest that the bulk composition of the moon differs from that of the Earth's mantle. This difference excludes models for lunar origin that require the Earth and moon to have the same compositions, such as fission and coaccretion, and favors giant impact and capture.
Crack-Like Sources of Dislocation Nucleation and Multiplication in Thin Films
Authors: Jesson D. E. , Chen K. M. , Pennycook S. J. , Thundat T. , Warmack R. J.
Published: October 2006

With the combination of the height sensitivity of atomic force microscopy and the strain sensitivity of transmission electron microscopy, it is shown that near singular stress concentrations can develop naturally in strained epitaxial films. These crack-like instabilities are identified as the sources of dislocation nucleation and multiplication in films of high misfit. This link between morphological instability and dislocation nucleation provides a method for studying the basic micromechanisms that determine the strength and mechanical properties of materials.
Surface Displacement of the 17 May 1993 Eureka Valley, California, Earthquake Observed by SAR Interferometry
Authors: Peltzer Gilles , Rosen Paul
Published: October 2006

Satellite synthetic aperture radar (SAR) interferometry shows that the magnitude 6.1 Eureka Valley earthquake of 17 May 1993 produced an elongated subsidence basin oriented north-northwest, parallel to the trend defined by the aftershock distribution, whereas the source mechanism of the earthquake implies a north-northeast-striking normal fault. The ±3-millimeter accuracy of the radar-observed displacement map over short spatial scales allowed identification of the main surface rupture associated with the event. These observations suggest that the rupture began at depth and propagated diagonally upward and southward on a west-dipping, north-northeast fault plane, reactivating the largest escarpment in the Saline Range.
Single Molecule Electron Paramagnetic Resonance Spectroscopy: Hyperfine Splitting Owing to a Single Nucleus
Authors: Köhler J. , Brouwer A. C. J. , Groenen E. J. J. , Schmidt J.
Published: October 2006

Individual pentacene-
d
14
molecules doped into a
p
-terphenyl-
d
14
host crystal have been studied by optically detected electron paramagnetic resonance spectroscopy. The magnetic resonance transitions between the triplet sublevels of the pentacene molecule and the splitting of the resonance lines for a molecule that contains a carbon-13 nucleus have been observed in an external magnetic field. This splitting is caused by the hyperfine interaction of the triplet electron spin with the single carbon-13 nuclear spin.
Monodisperse Metal Clusters 10 Angstroms in Diameter in a Polymeric Host: The "Monomer as Solvent' Approach
Authors: Golden Josh H. , Deng Haibin , DiSalvoa Francis J. , Fréchet Jean M. J. , Thompson Patrick M.
Published: October 2006

A general methodology is presented for the dispersion of an inorganic compound within an organic polymer host through the use of solubilizing and polymerizable ligands. The dispersion of metal cluster cations 10 angstroms in diameter within a polymer host is achieved by free-radical polymerization of the hexafunctional metal cluster [Mo
6
Cl
8
(NVI)
6
](triflate)
4
with bound polymerizable ligands in
N
-vinylimidazole (NVI) solutions. Copolymerization of the activated cluster-bound ligands with the surrounding medium probably plays a key role in preventing aggregation and produces near monodisperse molecular clusters within the polymer matrix.
Polystyrene-Dendrimer Amphiphilic Block Copolymers with a Generation-Dependent Aggregation
Authors: van Hest J. C. M. , Delnoye D. A. P. , Baars M. W. P. L. , van Genderen M. H. P. , Meijer E. W.
Published: October 2006

A class of amphiphilic macromolecules has been synthesized by combining well-defined polystyrene (PS) with poly(propylene imine) dendrimers. Five different generations, from PS-
dendr
-NH
2
up to PS-
dendr
-(NH
2
)
32
, were prepared in yields of 70 to 90 percent. Dynamic light scattering, conductivity measurements, and transmission electron microscopy show that in aqueous phases, PS-
dendr
-(NH
2
)
32
forms spherical micelles, PS-
dendr
-(NH
2
)
16
forms micellar rods, and PS-
dendr
-(NH
2
)
8
forms vesicular structures. The lower generations of this class of macromolecules show inverted micellar behavior. The observed effect of amphiphile geometry on aggregation behavior is in qualitative agreement with the theory of Israelachvili
et al
. The amphiphiles presented here are similar in shape but different in size as compared with traditional surfactants, whereas they are similar in size but different in shape as compared with traditional block copolymers.
Exceptionally Thermally Stable Polyimides for Second-Order Nonlinear Optical Applications
Authors: Verbiest T. , Burland D. M. , Jurich M. C. , Lee V. Y. , Miller R. D. , Volksen W.
Published: October 2006

The thermal stability of the electric field induced poled order in a new class of second-order optically nonlinear polymers, "donor-imbedded" side-chain polyimides containing no flexible connectors or tethers to the nonlinear optical (NLO) chromophore, is investigated. In these polymers, the electron-donor part of the chromophore is a diaryl-substituted amine that is incorporated as a part of the polymer backbone. The donorimbedded systems used in this study have exceptional chemical stabilities at elevated temperatures (350°C) and impressive poled order stability at extremely high temperatures (300°C). In both respects, they were significantly more stable than a true side-chain polyimide with a similar NLO-active chromophore covalently linked to the polymer backbone by a flexible tether group.
Multiple Morphologies of "Crew-Cut" Aggregates of Polystyrene-
b
-poly(acrylic acid) Block Copolymers
Authors: Zhang Lifeng , Eisenberg Adi
Published: October 2006

The observation by transmission electron microscopy of six different stable aggregate morphologies is reported for the same family of highly asymmetric polystyrene-poly-(acrylic acid) block copolymers prepared in a low molecular weight solvent system. Four of the morphologies consist of spheres, rods, lamellae, and vesicles in aqueous solution, whereas the fifth consists of simple reverse micelle-like aggregates. The sixth consists of up to micrometer-size spheres in aqueous solution that have hydrophilic surfaces and are filled with the reverse micelle-like aggregates. In addition, a needle-like solid, which is highly birefringent, is obtained on drying of aqueous solutions of the spherical micelles. This range of morphologies is believed to be unprecedented for a block copolymer system.
A Combinatorial Approach to Materials Discovery
Authors: Xiang X. -D. , Sun Xiaodong , Briceño Gabriel , Lou Yulin , Wang Kai-An , Chang Hauyee , Wallace-Freedman William G. , Chen Sung-Wei , Schultz Peter G.
Published: October 2006

A method that combines thin film deposition and physical masking techniques has been used for the parallel synthesis of spatially addressable libraries of solid-state materials. Arrays containing different combinations, stoichiometries, and deposition sequences of BaCO
3
, Bi
2
O
3
, CaO, CuO, PbO, SrCO
3
, and Y
2
O
3
were generated with a series of binary masks. The arrays were sintered and BiSrCaCuO and YBaCuO superconducting films were identified. Samples as small as 200 micrometers by 200 micrometers in size were generated, corresponding to library densities of 10,000 sites per square inch. The ability to generate and screen combinatorial libraries of solid-state compounds, when coupled with theory and empirical observations, may significantly increase the rate at which novel electronic, magnetic, and optical materials are discovered and theoretical predictions tested.
Astronomers Paint the Big Picture and Fill in the Blanks
Authors: Glanz James
Published: October 2006

PITTSBURGH—Most everything in astronomy is big. But the truly outsized features of the universe—vast filaments of galaxies and its great dark voids—were highlighted when 772 researchers gathered here on 11-15 June for the 186th meeting of the American Astronomical Society. Talks included a new explanation for the large-scale "tapestry" of the universe and a new glimpse of what may fill its voids.
Observation of Individual Chemical Reactions in Solution
Authors: Collinson Maryanne M. , Wightman R. Mark
Published: October 2006

Discrete chemical reaction events occurring in solution have been observed by single photon detection of a bimolecular, chemiluminescent reaction. The reactants were generated from 9,10-diphenylanthracene in acetonitrile with potential pulses applied to an ultramicroelectrode. Electrogenerated radical ions of opposite sign react to yield the excited singlet state of the parent compound. The chemical reactions were restricted to a 20-femtoliter volume adjacent to the electrode by the use of rapid potential pulses. Individual chemical reaction events were stochastic and followed the Poisson distribution, and the interarrival time between successive reaction events was exponentially distributed.
Structure and Density of FeS at High Pressure and High Temperature and the Internal Structure of Mars
Authors: Fei Yingwei , Prewitt Charles T. , Mao Ho-kwang , Bertka Constance M.
Published: October 2006

In situ x-ray diffraction measurements revealed that FeS, a possible core material for the terrestrial planets, transforms to a hexagonal NiAs superstructure with axial ratio (
c/a
) close to the ideal close-packing value of 1.63 at high pressure and high temperature. The high-pressure-temperature phase has shorter Fe-Fe distances than the low-pressure phase. Significant shortening of the Fe-Fe distance would lead to metallization of FeS, resulting in fundamental changes in physical properties of FeS at high pressure and temperature. Calculations using the density of the high-pressure-temperature FeS phase indicate that the martian core-mantle boundary occurs within the silicate perovskite stability field.
Late Glacial Stage and Holocene Tropical Ice Core Records from Huascarán, Peru
Authors: Thompson L. G. , Mosley-Thompson E. , Davis M. E. , Lin P. -N. , Henderson K. A. , Cole-Dai J. , Bolzan J. F. , Liu K. -b.
Published: October 2006

Two ice cores from the col of Huascarán in the north-central Andes of Peru contain a paleoclimatic history extending well into the Wisconsinan (Würm) Glacial Stage and include evidence of the Younger Dryas cool phase. Glacial stage conditions at high elevations in the tropics appear to have been as much as 8° to 12°C cooler than today, the atmosphere contained about 200 times as much dust, and the Amazon Basin forest cover may have been much less extensive. Differences in both the oxygen isotope ratio δ
18
O (8 per mil) and the deuterium excess (4.5 per mil) from the Late Glacial Stage to the Holocene are comparable with polar ice core records. These data imply that the tropical Atlantic was possibly 5° to 6°C cooler during the Late Glacial Stage, that the climate was warmest from 8400 to 5200 years before present, and that it cooled gradually, culminating with the Little Ice Age (200 to 500 years before present). A strong warming has dominated the last two centuries.
Synthesis and Structure of an Iron(III) Sulfide-Ferritin Bioinorganic Nanocomposite
Authors: Douglas Trevor , Dickson Dominic P. E. , Betteridge Steven , Charnock John , Garner C. David , Mann Stephen
Published: October 2006

Amorphous iron sulfide minerals containing either 500 or 3000 iron atoms in each cluster have been synthesized in situ within the nanodimensional cavity of horse spleen ferritin. Iron-57 Mössbauer spectroscopy indicated that most of the iron atoms in the 3000-iron atom cores are trivalent, whereas in the 500-iron atom clusters, approximately 50 percent of the iron atoms are Fe(III), with the remaining atoms having an effective oxidation state of about +2.5. Iron K-edge extended x-ray absorption fine structure data for the 500-iron atom nanocomposite are consistent with a disordered array of edge-shared FeS
4
tetrahedra, connected by Fe(S)
2
Fe bridges with bond lengths similar to those of the cubane-type motif of iron-sulfur clusters. The approach used here for the controlled synthesis of bioinorganic nanocomposites could be useful for the nanoscale engineering of dispersed materials with biocompatible and bioactive properties.
Flotation of Diamond in Mantle Melt at High Pressure
Authors: Suzuki Akio , Ohtani Eiji , Kato Takumi
Published: October 2006

Experiments show that diamond floats in a primitive mantle melt at around 20 gigapascals and 2360°C and in a melt formed by partial melting of the transition zone at about 16 gigapascals and 2270°C. These observations constrain magma densities at high pressure. Diamond precipitated or trapped in a silicate melt at the base of the transition zone or the lower mantle floats and has been accumulating in the transition zone since early in Earth's history. Thus, the transition zone could be a reservoir of diamond.
Ecosystem Experiments
Authors: Carpenter Stephen R. , Chisholm Sallie W. , Krebs Charles J. , Schindler David W. , Wright Richard F.
Published: October 2006

Experimental manipulations of entire ecosystems have been conducted in lakes, catchments, streams, and open terrestrial and marine environments. Experiments have addressed applied problems of ecosystem management and complex responses of communities and ecosystems to perturbations. In the course of some experiments, environmental indicators and models have been developed and tested. Surprising results with implications for ecological understanding and management are common.
Ecology and Climate: Research Strategies and Implications
Authors: Root Terry L. , Schneider Stephen H.
Published: October 2006

Natural and anthropogenic global changes are associated with substantial ecological disturbances. Multiscale interconnections among disciplines studying the biotic and abiotic effects of such disturbances are needed. Three research paradigms traditionally have been used and are reviewed here: scale-up, scale-down, and scale-up with embedded scale-down components. None of these approaches by themselves can provide the most reliable ecological assessments. A fourth research paradigm, called strategic cyclical scaling (SCS), is relatively more effective. SCS involves continuous cycling between large- and small-scale studies, thereby offering improved understanding of the behavior of complex environmental systems and allowing more reliable forecast capabilities for analyzing the ecological consequences of global changes.
International Public Opinion on the Environment
Authors: Bloom David E.
Published: October 2006

This article analyzes public opinion data on environmental issues collected in two major surveys. The data reveal substantial concern about the environment in both developing and industrial countries along with perceptions that the quality of the environment has declined and will continue to decline. Developing country respondents rate their local and national environmental quality lower than do industrial country respondents, whereas both groups rate global environmental quality about the same. The data also reveal considerable willingness among the developing and industrial countries to accept responsibility for the world's environmental problems and recognition of the importance of governments in addressing local and national environmental issues and of strong international agencies in addressing transnational issues.
Environmental Unknowns
Authors: Myers Norman
Published: October 2006

Among the environmental problems ahead, the most important ones could be those that are still unknown to us. This conceptual article explores this prospect on the grounds that it is important not only to supply answers to recognized questions but to raise appropriate new questions.
Quantum Point Contact Switches
Authors: Smith D. P. E.
Published: October 2006

Switching behavior between electron tunneling and ballistic transport states was induced by repeatedly bringing a sharpened nickel wire into contact with a gold surface. The high-conductivity ballistic state had a quantized conductance of 0.977 ± 0.015 (2

e
2
/h

). Switching was accomplished by moving the electrodes with a piezoelectric actuator over a distance of 2 angstroms. The two electrodes and the actuator form a three-terminal device that is demonstrated to be a reliable digital and analog switch; it shows good discrimination between high and low states and possesses the important property of power gain. The conductance channel is most likely only one atom wide and possibly consists of a single atom.
Ferroelectric Field Effect in Epitaxial Thin Film Oxide SrCuO
2
/Pb(Zr
0.52
Ti
0.48
)O
3
Heterostructures
Authors: Ahn C. H. , Triscone J. -M. , Archibald N. , Decroux M. , Hammond R. H. , Geballe T. H. , Fischer Ø. , Beasley M. R.
Published: October 2006

A ferroelectric field effect in epitaxial thin film SrCuO
2
/Pb(Zr
0.52
Ti
0.48
)O
3
heterostructures was observed. A 3.5 percent change in the resistance of a 40 angstrom SrCuO
2
layer (a parent high-temperature superconducting compound) was measured when the polarization field of the Pb(Zr
0.52
Ti
0.48
)O
3
layer was reversed by the application of a pulse of small voltage (<5 volts). This effect, both reversible and nonvolatile, is attributed to the electric field-induced charge at the interface of SrCuO
2
and Pb(Zr
0.52
Ti
0.48
)O
3
. This completely epitaxial thin film approach shows the possibility of making nonvolatile, low-voltage ferroelectric field effect devices for both applications and fundamental studies of field-induced doping in novel compounds like SrCuO
2
.
Female Responses to Ancestral Advertisement Calls in Túngara Frogs
Authors: Ryan Michael J. , Rand A. Stanley
Published: October 2006

Phylogenetic techniques were used to estimate and reconstruct advertisement calls at ancestral nodes. These calls were used to investigate the degree of preference of female túngara frogs (
Physalaemus pustulosus
) for both extant and ancestral calls. Females did not discriminate between calls of males of their own species and calls at their most recent ancestral node. They also recognized calls of three extant species and at four ancestral nodes as the signals of appropriate mates. Both shared ancestral history, and call convergence might differentially influence call preferences.
Force Fluctuations in Bead Packs
Authors: Liu C.-H. , Nagel S. R. , Schecter D. A. , Coppersmith S. N. , Majumdar S. , Narayan O. , Witten T. A.
Published: October 2006

Experimental observations and numerical simulations of the large force inhomogeneities present in stationary bead packs are presented. Forces much larger than the mean occurred but were exponentially rare. An exactly soluble model reproduced many aspects of the experiments and simulations. In this model, the fluctuations in the force distribution arise because of variations in the contact angles and the constraints imposed by the force balance on each bead in the pile.
Total Alignment of Calcite at Acidic Polydiacetylene Films: Cooperativity at the Organic-Inorganic Interface
Authors: Berman Amir , Ahn Dong June , Lio Anna , Salmeron Miquel , Reichert Anke , Charych Deborah
Published: October 2006

Biological matrices can direct the absolute alignment of inorganic crystals such as calcite. Cooperative effects at an organic-inorganic interface resulted in similar co-alignment of calcite at polymeric Langmuir-Schaefer films of 10,12-pentacosadiynoic acid (p-PDA). The films nucleated calcite at the (012) face, and the crystals were co-aligned with respect to the polymer's conjugated backbone. At the same time, the p-PDA alkyl side chains reorganized to optimize the stereochemical fit to the calcite structure, as visualized by changes in the optical spectrum of the polymer. These results indicate the kinds of interactions that may occur in biological systems where large arrays of crystals are co-aligned.
Decadal Trends in the North Atlantic Oscillation: Regional Temperatures and Precipitation
Authors: Hurrell James W.
Published: October 2006

Greenland ice-core data have revealed large decadal climate variations over the North Atlantic that can be related to a major source of low-frequency variability, the North Atlantic Oscillation. Over the past decade, the Oscillation has remained in one extreme phase during the winters, contributing significantly to the recent wintertime warmth across Europe and to cold conditions in the northwest Atlantic. An evaluation of the atmospheric moisture budget reveals coherent large-scale changes since 1980 that are linked to recent dry conditions over southern Europe and the Mediterranean, whereas northern Europe and parts of Scandinavia have generally experienced wetter than normal conditions.
Coordination in Distributed Building
Authors: Theraulaz Guy , Bonabeau Eric
Published: October 2006

A formal model of distributed building is presented that was inspired by the observation of wasp colonies. Algorithms have been obtained that allow a swarm of simple agents, moving randomly on a three-dimensional cubic lattice, to build coherent structures.
Growth of Tobacco Protoplasts Stimulated by Synthetic Lipo-Chitooligosaccharides
Authors: Röhrig Horst , Schmidt Jürgen , Walden Richard , Czaja Inge , Miklaševičs Edvins , Wieneke Ursula , Schell Jeff , John Michael
Published: October 2006

Nodulation (Nod) factors are lipo-chitooligosaccharides (LCOs) secreted by rhizobia to trigger the early steps of nodule organogenesis in leguminous plants. A method to synthesize LCOs in vitro was developed. Synthetic LCOs alleviated the requirement for auxin and cytokinin to sustain growth of cultured tobacco protoplasts. LCOs containing C
18:1
trans
—fatty acyl substituents were more effective than those containing
cis
—fatty acids in promoting cell division as well as in activating an auxin-responsive promoter and the expression of a gene implicated in auxin action. These data indicate that LCOs redirect plant growth also in nonlegumes by activating developmental pathways also targeted by phytohormones.
Dark Auroral Oval on Saturn Discovered in Hubble Space Telescope Ultraviolet Images
Authors: Jaffel Lotfi Ben , Leers Véronique , Sandel Bill R.
Published: October 2006

Hubble Space Telescope ultraviolet images of Saturn obtained with the Faint Object Camera near 220 nanometers reveal a dark oval encircling the north magnetic pole of the planet. The opacity has an equivalent width of ∼11° in latitude and is centered around ∼79° N. The oval shape of the dark structure and its coincidence with the aurora detected by the Voyager Ultraviolet Spectrometer suggest that the aerosol formation is related to the auroral activity.
Homogeneous Catalysis in Supercritical Fluids
Authors: Jessop Philip G. , Ikariya Takao , Noyori Ryoji
Published: October 2006

Supercritical fluids (SCFs), compounds heated and pressurized beyond the critical point, have many unusual properties. Homogeneous molecular catalysts, which have far greater control over selectivity than heterogeneous solid catalysts, are now being tested in SCFs, and early results show that high rates, improved selectivity, and elimination of mass-transfer problems can be achieved. As industry moves away from toxic or environmentally damaging solvents, supercritical carbon dioxide may be an ideal replacement medium for nonpolar or weakly polar chemical processes. More than simply substitutes for nonpolar solvents, SCFs can radically change the observed chemistry. Supercritical carbon dioxide is also an excellent medium for its own fixation, as demonstrated by studies of its hydrogenation.
Polymer Light-Emitting Electrochemical Cells
Authors: Pei Qibing , Yu Gang , Zhang Chi , Yang Yang , Heeger Alan J.
Published: October 2006

A device configuration for light emission from electroactive polymers is described. In these light-emitting electrochemical cells, a
p-n
junction diode is created in situ through simultaneous
p
-type and
n
-type electrochemical doping on opposite sides of a thin film of conjugated polymer that contains added electrolyte to provide the necessary counterions for doping. Light-emitting devices based on conjugated polymers have been fabricated that operate by the proposed electrochemical oxidation-reduction mechanism. Blue, green, and orange emission have been obtained with turn-on voltages close to the band gap of the emissive material.
Energetics, Patterns of Interaction Strengths, and Stability in Real Ecosystems
Authors: de Ruiter Peter C. , Neutel Anje-Margriet , Moore John C.
Published: October 2006

Ecologists have long been studying stability in ecosystems by looking at the structuring and the strengths of trophic interactions in community food webs. In a series of real food webs from native and agricultural soils, the strengths of the interactions were found to be patterned in a way that is important to ecosystem stability. The patterning consisted of the simultaneous occurrence of strong "top down" effects at lower trophic levels and strong "bottom up" effects at higher trophic levels. As the patterning resulted directly from the energetic organization of the food webs, the results show that energetics and community structure govern ecosystem stability by imposing stabilizing patterns of interaction strengths.
Endoreduplication in Maize Endosperm: Involvement of M Phase—Promoting Factor Inhibition and Induction of S Phase—Related Kinases
Authors: Grafi Gideon , Larkins Brian A.
Published: October 2006

Endoreduplication is an endonuclear chromosome duplication that occurs in the absence of mitosis and in
Zea mays
(L.) is required for endosperm development. Induction of DNA synthesis during early stages of endosperm development is maintained by increasing the amount and activity of S phase—related protein kinases, which was demonstrated here by their ability to interact with human E2F or with the adenovirus E1A proteins. In addition it was shown that endoreduplicated endosperm cells contain an inhibitor that suppresses the activity of the M phase—promoting factor (MPF). These results demonstrate that in maize endosperm, endoreduplication proceeds as a result of two events, inhibition of MPF and induction of S phase—related protein kinases.
Keplerian Complexity: Numerical Simulations of Accretion Disk Transport
Authors: Hawley John F.
Published: October 2006

Supercomputer simulations have been used in conjunction with analytic studies to investigate the central issue of astrophysical accretion-disk dynamics: the nature of the angular momentum transport. Simulations provide the means to investigate and experiment with candidate mechanisms, including global hydrodynamic instabilities, spiral shock waves, and local magnetohydrodynamic (MHD) instabilities. Simulations have demonstrated that accretion disks are generally MHD turbulent. These results suggest that the fundamental physical mechanism for angular momentum transport in accretion disks has now been identified.
Numerical Models of Caldera-Scale Volcanic Eruptions on Earth, Venus, and Mars
Authors: Kieffer Susan Werner
Published: October 2006

Volcanic eruptions of gassy magmas on Earth, Venus, and Mars produce plumes with markedly different fluid dynamics regimes. In large part the differences are caused by the differing atmospheric pressures and ratios of volcanic vent pressure to atmospheric pressure. For each of these planets, numerical simulations of an eruption of magma containing 4 weight percent gas were run on a workstation. On Venus the simulated eruption of a pressure-balanced plume formed a dense fountain over the vent and continuous pyroclastic flows. On Earth and Mars, simulated pressure-balanced plumes produced ash columns, ash falls, and possible small pyroclastic flows. An overpressured plume, illustrated for Mars, exhibited a complex supersonic velocity structure and internal shocks.
Short-and Intermediate-Range Structural Ordering in Glassy Boron Oxide
Authors: Youngman R. E. , Haubrich S. T. , Zwanziger J. W. , Janicke M. T. , Chmelka B. F.
Published: October 2006

Ordering at short-length scales is a universal feature of the glassy state. Experiments on boron oxide and other materials indicate that ordering on mesoscopic-length scales may also be universal. The high-resolution nuclear magnetic resonance (NMR) measurements of oxygen in boron oxide glass presented here provide evidence for structural units responsible for ordering on short- and intermediate-length scales. At the molecular level, planar BO
3/2
units accounted for the local ordering. Oxygen-17 NMR spectra resolved detailed features of the inclusion of these units in boroxol rings, oxygen bridging two rings, and oxygen shared between two nonring BO
3/2
units. On the basis of these and corroborative boron-11 NMR and scattering results, boron oxide glass consists of domains that are rich or poor in boroxol rings; these domains are proposed to be the structural basis of intermediate-range order in glassy boron oxide.
Unraveling Nanotubes: Field Emission from an Atomic Wire
Authors: Rinzler A. G. , Hafner J. H. , Nikolaev P. , Nordlander P. , Colbert D. T. , Smalley R. E. , Lou L. , Kim S. G. , Tománek D.
Published: October 2006

Field emission of electrons from individually mounted carbon nanotubes has been found to be dramatically enhanced when the nanotube tips are opened by laser evaporation or oxidative etching. Emission currents of 0.1 to 1 microampere were readily obtained at room temperature with bias voltages of less than 80 volts. The emitting structures are concluded to be linear chains of carbon atoms, C

n

, (
n
= 10 to 100), pulled out from the open edges of the graphene wall layers of the nanotube by the force of the electric field, in a process that resembles unraveling the sleeve of a sweater.
Late Glacial Climate Record of Midwestern United States from the Hydrogen Isotope Ratio of Lake Organic Matter
Authors: Krishnamurthy R. V. , Syrup K. A. , Baskaran M. , Long A.
Published: October 2006

A hydrogen isotope time series obtained from an analysis of organic matter extracted from a lake core in Kalamazoo, southwestern Michigan, reveals four distinct isotope stages within the last 12,000 years that can be interpreted in terms of oscillations between cold and warm, dry climates. The most dramatic are a cold phase between 12,000 and 9000 years before present (B.P.), a warm, dry period between 8500 and 2000 years B.P., a cold period between 2000 and 1000 years B.P., and a warming trend since 1000 years B.P. The warming trend of the last 1000 years is comparable in magnitude to the mid-Holocene warm phase.
Laser Separation of Geometrical Isomers of Weakly Bound Molecular Complexes
Authors: Desfrançois Charles , Abdoul-Carime Hassan , Schulz C. P. , Schermann Jean Pierre
Published: October 2006

Molecular assemblies held together by weak intermolecular bonds exhibit a rich variety of geometries. Even a simple complex formed by only two molecules can adopt several conformations corresponding to different geometrical isomers. Isomers of small polar dimers can be isolated nondestructively by taking advantage of a selective and reversible ionization process, with the use of a mass spectrometry method that allows the determination and control of the geometrical configuration of neutral or negatively charged molecular complexes in supersonic beams. Here, the method is applied to isolated nucleic acid base pairs that can be selected in stacked or H-bonded configurations.
Convergent Domestication of Cereal Crops by Independent Mutations at Corresponding Genetic Loci
Authors: Paterson Andrew H. , Lin Yann-Rong , Li Zhikang , Schertz Keith F. , Doebley John F. , Pinson Shannon R. M. , Liu Sin-Chieh , Stansel James W. , Irvine James E.
Published: October 2006

Independent domestication of sorghum, rice, and maize involved convergent selection for large seeds, reduced disarticulation of the mature inflorescence, and daylength-insensitive flowering. These similar phenotypes are largely determined by a small number of quantitative trait loci (QTLs) that correspond closely in the three taxa. The correspondence of these QTLs transcends 65 million years of reproductive isolation. This finding supports models of quantitative inheritance that invoke relatively few genes, obviates difficulties in map-based cloning of QTLs, and impels the comparative mapping of complex phenotypes across large evolutionary distances, such as those that separate humans from rodents and domesticated mammals.
Replicator Neural Networks for Universal Optimal Source Coding
Authors: Hecht-Nielsen Robert
Published: October 2006

Replicator neural networks self-organize by using their inputs as desired outputs; they internally form a compressed representation for the input data. A theorem shows that a class of replicator networks can, through the minimization of mean squared reconstruction error (for instance, by training on raw data examples), carry out optimal data compression for arbitrary data vector sources. Data manifolds, a new general model of data sources, are then introduced and a second theorem shows that, in a practically important limiting case, optimal-compression replicator networks operate by creating an essentially unique natural coordinate system for the manifold.
The Future University: Leaner and Meaner?
Authors: Selvin Paul
Published: October 2006

The U.S. government supports 60% of all university-based research. With budget cuts threatened, schools are trying to streamline and forge new sources of income in ways that will have profound effects on the lives of university researchers.
NRC Pledges Faster Delivery on Reports to Government
Authors: Lawler Andrew
Published: October 2006

Now that Congress has abolished its Office of Technology Assessment, can the National Academy of Sciences fill the gap? Only if it provides more timely reports geared to the needs of Congress and government agencies. It is trying to do just that.
Panel Critiques NASA Science
Authors: Lawler Andrew
Published: October 2006

NASA's $3 billion space science program needs more input from the scientific community, a more powerful voice within NASA. So says a committee of the National Academy of Sciences. NASA says it's already doing what the committee recommends.
Laser Pulses Make Fast Work of an Optical Switch
Authors: Watson Andrew
Published: October 2006

A team of researchers based at Cambridge University has found a way to turn a semiconductor switch on and off with pulses of light, with speeds 10,000 times faster than previous optical switching techniques. The technique may point the way to ultrafast optical computing and communications technologies.
Minimum Population Grows Larger
Authors: Culotta Elizabeth
Published: October 2006

Two new population genetics studies provide sobering news for efforts to protect endangered species. The minimum number of individuals needed to provide a genetically robust population capable of long-term survival may be as high as 10,000. Previous estimates had put the figure at 500, and many endangered species are down to just a few dozen individuals.
Electron Ball Probes "House of Mirrors"
Authors: Glanz James
Published: October 2006

By confining 1000 electrons in a magnetic trap, physicists have found a way to test one of the fundamental theories of physics, quantum electrodynamics, with exquisite precision.
Graduate Education and Research for Economic Growth
Authors: Smith T. P. , Tsang J. C.
Published: October 2006

Industry is the largest consumer for engineering and science doctorates, and doctorate-level training is thus a main link between the U.S. economy and education. Recent pressures on federal research and development funding, and the widening gap between the needs of industry and the expertise of academia, pose several challenges for the nature of graduate training. Fellowships, off-campus research, and opportunities for teaching should be emphasized in graduate schools, versus research assistant support.
PIK-Related Kinases: DNA Repair, Recombination, and Cell Cycle Checkpoints
Authors: Keith Curtis T. , Schreiber Stuart L.
Published: October 2006

The phosphatidylinositol kinase-related (PIK-related) kinases form a new subgroup within the protein kinase family of enzymes. Although the substrates of these kinases are not yet known, recent reports show that they participate in recombination processes, chromosome maintenance, and the cell cycle.
Exciting Resonances
Authors: Voss David
Published: October 2006

Excitons are electron-hole pairs that can transport energy while remaining charge neutral. A group at Stanford has recently found a way to create excitons directly in a quantum well device, which may permit future studies of fundamental quantum physics.
Nanochannel Glass Replica Membranes
Authors: Pearson D. H. , Tonucci R. J.
Published: October 2006

The preparation of thin metallic membranes containing uniform, patterned voids with diameters as small as 40 nanometers and packing densities greater than 3 × 10
9
voids per square centimeter is described. These membranes, made of platinum, gold, tungsten, and molybdenum, have been fabricated by thin-film deposition with nanochannel glass wafers as substrates. The membranes are well suited for use as masks in substrate patterning applications such as ion implantation, reactive ion etching, and materials deposition. Results are presented on their use in the parallel patterning of silicon by direct materials deposition with features in the 100-nanometer size regime.
Shape and Non-Principal Axis Spin State of Asteroid 4179 Toutatis
Authors: Hudson R. Scott , Ostro Steven J.
Published: October 2006

Radar observations of Toutatis placed hundreds to thousands of pixels per image on the asteroid and revealed it to be a non-principal axis rotator. The radar data are used to calculate Toutatis's three-dimensional shape, spin state, and the ratios of the principal moments of inertia. Toutatis is rotating in a long-axis mode characterized by periods of 5.41 days (rotation about the long axis) and 7.35 days (average for long-axis precession), and its dimensions along the principal axes are 1.92, 2.40, and 4.60 kilometers. To within the model's uncertainties, Toutatis's density is homogeneous, or its inhomogeneities mimic the inertia tensor of a homogeneous body.
Myt1: A Membrane-Associated Inhibitory Kinase That Phosphorylates Cdc2 on Both Threonine-14 and Tyrosine-15
Authors: Mueller Paul R. , Coleman Thomas R. , Kumagai Akiko , Dunphy William G.
Published: October 2006

Cdc2 is the cyclin-dependent kinase that controls entry of cells into mitosis. Phosphorylation of Cdc2 on threonine-14 and tyrosine-15 inhibits the activity of the enzyme and prevents premature initiation of mitosis. Although Wee1 has been identified as the kinase that phosphorylates tyrosine-15 in various organisms, the threonine-14-specific kinase has not been isolated. A complementary DNA was cloned from
Xenopus
that encodes Myt1, a member of the Wee1 family that was discovered to phosphorylate Cdc2 efficiently on both threonine-14 and tyrosine-15. Myt1 is a membrane-associated protein that contains a putative transmembrane segment. Immunodepletion studies suggested that Myt1 is the predominant threonine-14-specific kinase in
Xenopus
egg extracts. Myt1 activity is highly regulated during the cell cycle, suggesting that this relative of Wee1 plays a role in mitotic control.
Dissociation of Synchronization and Excitability in Furosemide Blockade of Epileptiform Activity
Authors: Hochman Daryl W. , Baraban Scott C. , Owens James W. M. , Schwartzkroin Philip A.
Published: October 2006

Furosemide, a chloride cotransport inhibitor, reversibly blocked synchronized burst discharges in hippocampal slices without reducing the pyramidal cell response to single electrical stimuli. Images of the intrinsic optical signal acquired during these slice experiments indicated that furosemide coincidentally blocked changes in extracellular space. In urethane-anesthetized rats, systemically injected furosemide blocked kainic acid-induced electrical discharges recorded from cortex. These results suggest that (i) neuronal synchronization involved in epileptiform activity can be dissociated from synaptic excitability; (ii) nonsynaptic mechanisms, possibly associated with furosemide-sensitive cell volume regulation, may be critical for synchronization of neuronal activity; and (iii) agents that affect extracellular volume may have clinical utility as antiepileptic drugs.
Europeans Clash Over Space Station
Authors: Clery Daniel
Published: October 2006

On the eve of a key meeting of the European Space Agency's(ESA's) governing council, European governments are sharply divided over their contributions to the U.S.–led international space station. Unless a deal can be struck, Europe's contribution to the project may be in jeopardy—and ESA itself could be severely damaged. A sidebar examines similar disagreements over ESA's space science budget, with the United Kingdomand Germany pressing for cuts in the science budget
Designer Tissues Take Hold
Authors: Service Robert F.
Published: October 2006

By engineering polymers that attract and bind liver, nerve, and other cells, scientists are beginning to create artificial organs that are biologically “real” and may one day be used to supplement or replace damaged body parts. A sidebar looks at efforts, such as growing artificial skin on collagen matrices, that are close to clinical use.
New Ways to Avoid Organ Rejection Buoy Hopes
Authors: Roush Wade
Published: October 2006

Boston—Researchers reported at a meeting in Boston two promising strategies for preventing the body from rejecting tissue transplanted from another species. One involves treating the transplanted tissue with anti-oxidant drugs to prevent host blood that rushes into the transplant from damaging a key enzyme. The other, more controversial, strategy involves genetically engineering the donor animal to express human immune regulators in its tissues. In theory, tissue from such animals should itself suppress an acute rejection response when it is transplanted into humans.