bluuebunny/crossref_metadata_2025 huggingface dataset:
The Huastec Region: A Second Locus for the Production of Bronze Alloys in Ancient Mesoamerica
Authors: Hosler Dorothy , Stresser-Pean Guy
Published: October 2006

Chemical analyses of 51 metal artifacts, one ingot, and two pieces of intermediate processed material from two Late Post Classic archeological sites in the Huastec area of Eastern Mesoamerica point to a second production locus for copper-arsenic-tin alloys, copper-arsenic-tin artifacts, and probably copper-tin and copper-arsenic bronze artifacts. Earlier evidence had indicated that these bronze alloys were produced exclusively in West Mexico. West Mexico was the region where metallurgy first developed in Mesoamerica, although major elements of that technology had been introduced from the metallurgies of Central and South America. The bronze working component of Huastec metallurgy was transmitted from the metalworking regions of West Mexico, most likely through market systems that distributed Aztec goods.
Energetic Charged-Particle Phenomena in the Jovian Magnetosphere: First Results from the Ulysses COSPIN Collaboration
Authors: Simpson J. A. , Anglin J. D. , Balogh A. , Burrows J. R. , Cowley S. W. H. , Ferrando P. , Heber B. , Hynds R. J. , Kunow H. , Marsden R. G. , McKibben R. B. , Müller-Mellin R. , Page D. E. , Raviart A. , Sanderson T. R. , Staines K. , Wenzel K. -P. , Wilson Margaret D. , Zhang M.
Published: October 2006

The Ulysses spacecraft made the first exploration of the region of Jupiter's magnetosphere at high Jovigraphic latitudes (∼37° south) on the dusk side and reached higher magnetic latitudes (∼49° north) on the day side than any previous mission to Jupiter. The cosmic and solar particle investigations (COSPIN) instrumentation achieved a remarkably well integrated set of observations of energetic charged particles in the energy ranges of ∼1 to 170 megaelectron volts for electrons and 0.3 to 20 megaelectron volts for protons and heavier nuclei. The new findings include (i) an apparent polar cap region in the northern hemisphere in which energetic charged particles following Jovian magnetic field lines may have direct access to the interplanetary medium, (ii) high-energy electron bursts (rise times ≤ 1 minute and energies extending to > ∼17 megaelectron volts) on the dusk side that are apparently associated with field-aligned currents and radio burst emissions, (iii) persistence of the global 10-hour relativistic electron "clock" phenomenon throughout Jupiter's magnetosphere, (iv) on the basis of charged-particle measurements, apparent dragging of magnetic field lines at large radii in the dusk sector toward the tail, and (v) consistent outflow of megaelectron volt electrons and large-scale departures from corotation for nucleons.
Electrorheological Fluids
Authors: Halsey Thomas C.
Published: October 2006

Suspensions of polarizable particles in nonpolarizable solvents form fibrillated structures in strong electric fields. The resulting increase in viscosity of these "electrorheological" fluids can couple electrical to hydraulic components in a servomechanism. The physical properties of these fluids are unusual owing to the long-range, anisotropic nature of the interparticle forces. Immediately after the electric field is applied, elongated chains or columns of particles form parallel to the field. This structure then coarsens as a result of thermal forces between the columns. In shear flows, fluids show yielding behavior at low stresses followed by shear-thinning behavior at higher stresses.
The Age of Paraná Flood Volcanism, Rifting of Gondwanaland, and the Jurassic-Cretaceous Boundary
Authors: Renne Paul R. , Ernesto Marcia , Pacca Igor G. , Coe Robert S. , Glen Jonathon M. , Prévot Michel , Perrin Mireille
Published: October 2006

The Paraná-Etendeka flood volcanic event produced ∼1.5 × 10
6
cubic kilometers of volcanic rocks, ranging from basalts to rhyolites, before the separation of South America and Africa during the Cretaceous period. New
40
Ar/
39
Ar data combined with earlier paleomagnetic results indicate that Paraná flood volcanism in southern Brazil began at 133 ± 1 million years ago and lasted less than 1 million years. The implied mean eruption rate on the order of 1.5 cubic kilometers per year is consistent with a mantle plume origin for the event and is comparable to eruption rates determined for other well-documented continental flood volcanic events. Paraná flood volcanism occurred before the initiation of sea floor spreading in the South Atlantic and was probably precipitated by uplift and weakening of the lithosphere by the Tristan da Cunha plume. The Parana event postdates most current estimates for the age of the faunal mass extinction associated with the Jurassic-Cretaceous boundary.
The Complete Skull and Skeleton of an Early Dinosaur
Authors: Sereno Paul C. , Novas Fernando E.
Published: October 2006

The unearthing of a complete skull and skeleton of the early dinosaur
Herrerasaurus ischigualastensis
sheds light on the early evolution of dinosaurs. Discovered in the Upper Triassic Ischigualasto Formation of Argentina, the fossils show that
Herrerasaurus
, a primitive theropod, was an agile, bipedal predator with a short forelimb specialized for grasping and raking. The fossils clarify anatomical features of the common ancestor of all dinosaurs.
Herrerasaurus
and younger dinosaurs from Upper Triassic beds in Argentina suggest that the dinosaurian radiation was well under way before dinosaurs dominated terrestrial vertebrate communities in taxonomic diversity and abundance.
An Optimal Transition Path for Controlling Greenhouse Gases
Authors: Nordhaus William D.
Published: October 2006

Designing efficient policies to slow global warming requires an approach that combines economic tools with relations from the natural sciences. The dynamic integrated climate-economy (DICE) model presented here, an intertemporal general-equilibrium model of economic growth and climate change, can be used to investigate alternative approaches to slowing climate change. Evaluation of five policies suggests that a modest carbon tax would be an efficient approach to slow global warming, whereas rigid emissions- or climate-stabilization approaches would impose significant net economic costs.
Linear Metal Nanostructures and Size Effects of Supported Metal Catalysts
Authors: Zuburtikudis loannis , Saltsburg Howard
Published: October 2006

Nickel metal catalysts composed of nanometer by micrometer strips have been produced with solid-state microfabrication techniques. The strips are actually the edges of nickelcatalyst thin films, which are sandwiched between separating support layers, which are also nanometers thick. These linear nanostructures constitute well-defined and well-controlled catalytic entities that reproduce the size of traditional supported metal clusters in one dimension, thus separating size from total number of atoms in the catalyst. Examination of their catalytic activity showed that they duplicate the behavior of conventional supported clusters. A specific rate maximum was observed for the hydrogenolysis of ethane at a nanoscale dimension similar to the cluster size at which the rate is maximum in the case of the supported cluster studies, whereas the hydrogenation of ethylene shows no such size dependency. The results suggest that the surface-to-volume ratio or the number of atoms in the catalytic entity cannot be the source of these size effects and that either support effects or nonequilibrium surface structures are the determining factors.
Tree Ring Correlation Between Prehistoric Landslides and Abrupt Tectonic Events in Seattle, Washington
Authors: Jacoby Gordon C. , Williams Patrick L. , Buckley Brendan M.
Published: October 2006

Radiocarbon ages of submerged trees on landslide deposits in Lake Washington, Seattle, indicate that the most recent slides in three separate areas may have occurred simultaneously about 1000 years ago. Tree ring crossdating shows that seven bark-bearing trees from one of these recent slides and a tree 23 kilometers to the northwest in a probable tsunami deposit on the shore of Puget Sound died in the same season of the same year. The close coincidence among the most recent lake landslides, a probable tsunami, abrupt subsidence, and other possible seismic events gives evidence for a strong prehistoric earthquake in the Seattle region.
Downstream Fining by Selective Deposition in a Laboratory Flume
Authors: Paola Chris , Parker Gary , Seal Rebecca , Sinha Sanjiv K. , Southard John B. , Wilcock Peter R.
Published: October 2006

There has long been debate about the relative importance of abrasion versus selective deposition of the coarsest clasts in causing downstream fining of sediment in river systems. Although high fining rates observed in many natural rivers seem to require strong selective deposition, the ability of selective deposition to produce downstream size sorting has never been measured under controlled conditions. In an experiment using a long flume and a poorly sorted, bimodal gravel feed, downstream fining was produced by a factor of 1.3 in median size and 1.8 in 90th percentile size, over a distance of 21 meters. The experimental conditions rule out abrasion effects. Selective deposition appears to be a natural consequence of the transport and deposition of sufficiently poorly sorted or bimodal gravels and appears to be capable of accounting for fining rates observed in natural gravel rivers.
Dynamics of Soil Carbon During Deglaciation of the Laurentide Ice Sheet
Authors: Harden Jennifer W. , Mark Robert K. , Sundquist Eric T. , Stallard Robert F.
Published: October 2006

Deglaciation of the Laurentide Ice Sheet in North America was accompanied by sequestration of organic carbon in newly exposed soils. The greatest rate of land exposure occurred around 12,000 to 8,000 years ago, and the greatest increase in the rate of carbon sequestration by soils occurred from 8,000 to 4,000 years ago. Sequestration of carbon in deglaciated peat lands continues today, and a steady state has not been reached. The natural rate of carbon sequestration in soils, however, is small relative to the rate of anthropogenic carbon dioxide production.
The Product of the c-
fms
Proto-Oncogene: a Glycoprotein with Associated Tyrosine Kinase Activity
Authors: Rettenmier Carl W. , Chen J. H. , Roussel Martine F. , Sherr Charles J.
Published: October 2006

The c-
fms
proto-oncogene is a member of a gene family that has been implicated in tumorigenesis. Glycoproteins encoded by c-
fms
were identified in cat spleen cells by means of an immune-complex kinase assay performed with monoclonal antibodies to v-
fms
-coded epitopes. The major form of the normal cellular glycoprotein has an apparent molecular weight of 170,000 and, like the product of the viral oncogene, serves as a substrate for an associated tyrosine-specific protein kinase activity in vitro. The results suggest that the transforming glycoprotein specified by v-
fms
is a truncated form of a c-
fms
-coded growth factor receptor.
Why Does the Earth Spin Forward?
Authors: Dones Luke , Tremaine Scott
Published: October 2006

The spins of the terrestrial planets likely arose as the planets formed by the accretion of planetesimals. Depending on the masses of the impactors, the planet's final spin can either be imparted by many small bodies (ordered accretion), in which case the spin is determined by the mean angular momentum of the impactors, or by a few large bodies (stochastic accretion), in which case the spin is a random variable whose distribution is determined by the root-mean-square angular momentum of the impactors. In the case of ordered accretion, the planet's obliquity is expected to be near 0° or 180°, whereas, if accretion is stochastic, there should be a wide range of obliquities. Analytic arguments and extensive orbital integrations are used to calculate the expected distributions of spin rate and obliquity as a function of the planetesimal mass and velocity distributions. The results imply that the spins of the terrestrial planets are determined by stochastic accretion.
Seismic Structure of the Southern East Pacific Rise
Authors: Detrick R. S. , Harding A. J. , Kent G. M. , Orcutt J. A. , Mutter J. C. , Buhl P.
Published: October 2006

Seismic data from the ultrafast-spreading (150 to 162 millimeters per year) southern East Pacific Rise show that the rise axis is underlain by a thin (less than 200 meters thick) extrusive volcanic layer (seismic layer 2A) that thickens rapidly off axis. Also beneath the rise axis is a narrow (less than 1 kilometer wide) melt sill that is in some places less than 1000 meters below the sea floor. The small dimensions of this molten body indicate that magma chamber size does not depend strongly on spreading rate as predicted by many ridge-crest thermal models. However, the shallow depth of this body is consistent with an inverse correlation between magma chamber depth and spreading rate. These observations indicate that the paradigm of ridge crest magma chambers as small, sill-like, midcrustal bodies is applicable to a wide range of intermediate- and fast-spreading ridges.
Magnesium and Calcium Aluminate Liquids: In Situ High-Temperature
27
Al NMR Spectroscopy
Authors: Poe B. T. , McMillan P. F. , Coté B. , Massiot D. , Coutures J. P.
Published: October 2006

The use of high-temperature nuclear magnetic resonance (NMR) spectroscopy provides a means of investigating the structure of refractory aluminate liquids at temperatures up to 2500 K. Time-averaged structural information indicates that the average aluminum coordination for magnesium aluminate (MgAl
2
O
4
) liquid is slightly greater than for calcium aluminate (CaAl
2
O
4
) liquid and that in both liquids it is close to four. Ion dynamics simulations for these liquids suggest the presence of four-, five-, and six-coordinated aluminate species, in agreement with NMR experiments on fast-quenched glasses. These species undergo rapid chemical exchange in the high-temperature liquids, which is evidenced by a single Lorentzian NMR line.
Specific Heat and Thermal Conductivity of Solid Fullerenes
Authors: Olson J. R. , Topp K. A. , Pohl R. O.
Published: October 2006

Evidence is presented that the lattice vibrations of compacted C
60
/C
70
fullerite microcrystals consist predominantly of localized modes. Vibrational motions of the rigid molecules ("buckyballs") have been identified as well as their internal vibrations. Debye waves play only a relatively minor role, except below ∼4 kelvin. By comparison with other crystalline materials, for these materials the Einstein model of the specific heat and thermal conductivity of solids, which is based on the assumption of atoms (in this case, buckyballs) vibrating with random phases, is in much better agreement with the measurements than the Debye model, which is based on collective excitations.
An Inorganic Double Helix: Hydrothermal Synthesis, Structure, and Magnetism of Chiral [(CH
3
)
2
NH
2
]K
4
[V
10
O
10
(H
2
O)
2
(OH)
4
(PO
4
)
7
]·4H
2
O
Authors: Soghomonian Victoria , Chen Qin , Haushalter Robert C. , Zubieta Jon , O'Connor Charles J.
Published: October 2006

Very complicated inorganic solids can be self-assembled from structurally simple precursors as illustrated by the hydrothermal synthesis of the vanadium phosphate, [(CH
3
)
2
NH
2
]K
4
[V
10
O
10
(H
2
O)
2
(OH)
4
(PO
4
)
7
]⋅4H
2
O, 1, which contains chiral double helices formed from interpenetrating spirals of vanadium oxo pentamers bonded together by P
5+
. These double helices are in turn intertwined with each other in a manner that generates unusual tunnels and cavities that are filled with (CH
3
)
2
NH
2
+
and K
+
cations, respectively. The unit cell contents of dark blue phosphate 1, which crystallizes in the enantiomorphic space group
P
4
3
with lattice constants
a
= 12.130 and
c
= 30.555 angstroms, are chiral; only one enantiomorph is present in a given crystal. Magnetization measurements show that 1 is paramagnetic with ten unpaired electrons per formula unit at higher temperatures and that antiferromagnetic interactions develop at lower temperatures.
Fullerenes from a Fulgurite
Authors: Daly Terry K. , Buseck Peter R. , Williams Peter , Lewis Charles F.
Published: October 2006

Peaks at 720 and 840 atomic mass units were identified by mass spectrometry in a sample extracted from a fulgurite, which is a glassy rock that forms where lightning strikes the ground. The peaks are interpreted as arising from C
60
and C
70
and the associated peaks as produced from other fullerenes. The intense conditions generated by the lightning not only melted the rock it struck and fused the associated soil but also allowed fullerenes to form, presumably from the organic debris in the soil.
Formation of Nanometer-Scale Grooves in Silicon with a Scanning Tunneling Microscope
Authors: Kobayashi A. , Grey F. , Williams R. S. , Aono M.
Published: October 2006

Grooves a few nanometers wide can be formed on a Si(111) surface with a scanning tunneling microscope when the tip is above a critical voltage. This may provide a promising approach to nanodevice fabrication. The dependence of the critical voltage on tunneling current, tip polarity, and tip material was studied with silver, gold, platinum, and tungsten tips. The results are consistent with field emission of positive and negative silicon ions. The variation of critical voltage with current is explained quantitatively by a simple tunneling equation that includes the effect of the contact potential between tip and sample.
Strong, Pure, and Uniform Carbon Fibers Obtained Directly from the Vapor Phase
Authors: Wallenberger Frederick T. , Nordine Paul C.
Published: October 2006

With laser-assisted chemical vapor deposition, strong and flexible carbon fibers were obtained at high reaction chamber pressures (> 1 bar) with growth rates > 0.3 millimeter per second; their tensile strength (3 gigapascals) approaches that of commercial intermediate modulus carbon fibers made by conventional process routes. With the process described here, carbon fibers can be produced with superior chemical purity and structural uniformity. They may become the material of choice in currently emerging premium end uses, including carbon fiber infrared detection elements.
Bipolar Spin Switch
Authors: Johnson Mark
Published: October 2006

A thin ferromagnetic film can be used to polarize the spin axes of the electrons carrying an electric current in a manner loosely analogous with a light polarizer. When such a film is fabricated on a gold film, a nonequilibrium population of spin-polarized electrons is built up in the gold causing a "spin bottleneck" effect. The addition of a second ferromagnetic film results in a device whose output voltage depends on the orientation of the spins.
Ground-Based Observations of Saturn's North Polar Spot and Hexagon
Authors: Sanchez-Lavega A. , Lecacheux J. , Colas F. , Laques P.
Published: October 2006

Ground-based observations of two conspicuous features near the north pole of Saturn, the polar vortex and the hexagonal wave structure, were made from July 1990 to October 1991, 10 years after their discovery. During this period the polar spot drifted in longitude, relative to system III, by –0.0353° per day on average. Superimposed on this mean motion, the spot also underwent short-term rapid excursions in longitude of up to ∼14° at rates of up to ∼1° per day. The spot also exhibited irregular variations in its latitude location. A combination of these data together with those obtained by Voyager 1 and 2 in 1980 and 1981 shows that the spot drifted –0.0577° per day for the 11-year interval from 1980 to 1991. The large lifetime of both features indicates that they are insensitive to the strong variations in the seasonal heating of the cloud layers in the upper polar atmosphere.
Pattern Recognition in Coupled Chemical Kinetic Systems
Authors: Hjelmfelt A. , Schneider F. W. , Ross J.
Published: October 2006

A network of open, bistable reaction systems coupled by mass transfer is simulated. The mass transfer rates are determined by a Hebb-type rule, and the programmable network can store patterns of high and low concentrations in each bistable system. In a parallel computation, the network recognizes patterns similar, but not necessarily identical, to stored patterns.
A Cold Suboceanic Mantle Belt at the Earth's Equator
Authors: Bonatti Enrico , Seyler Monique , Sushevskaya Nadia
Published: October 2006

An exceptionally low degree of melting of the upper mantle in the equatorial part of the mid-Atlantic Ridge is indicated by the chemical composition of mantle-derived mid-ocean ridge peridotites and basalts. These data imply that mantle temperatures below the equatorial Atlantic are at least ∼150°C cooler than those below the normal mid-Atlantic Ridge, suggesting that isotherms are depressed and the mantle is downwelling in the equatorial Atlantic. An equatorial minimum of the zero-age crustal elevation of the East Pacific Rise suggests a similar situation in the Pacific. If so, an oceanic upper mantle cold equatorial belt separates hotter mantle regimes and perhaps distinct chemical and isotopic domains in the Northern and Southern hemispheres. Gravity data suggest the presence of high density material in the oceanic equatorial upper mantle, which is consistent with its inferred low temperature and undepleted composition. The equatorial distribution of cold, dense upper mantle may be ultimately an effect of the Earth's rotation.
Experimental Realization of the Covalent Solid Carbon Nitride
Authors: Niu Chunming , Lu Yuan Z. , Lieber Charles M.
Published: October 2006

Pulsed laser ablation of graphite targets combined with an intense, atomic nitrogen source has been used to prepare C-N thin film materials. The average nitrogen content in the films was systematically varied by controlling atomic nitrogen flux. Rutherford backscattering measurements show that up to 40 percent nitrogen can be incorporated on average into these solids under the present reaction conditions. Photoelectron spectroscopy further indicates that carbon and nitrogen form an unpolarized covalent bond in these C-N materials. Qualitative tests indicate that the C-N solids are thermally robust and hard. In addition, strong electron diffraction is observed from crystallites within the films. Notably, analysis of these diffraction data show that the only viable structure for the C-N crystallites is that of β-C
3
N
4
, a material predicted theoretically to exhibit superhardness. The experimental synthesis of this new C-N material offers exciting prospects for both basic research and engineering applications.
A Molecular-Based Magnet with a Fully Interlocked Three-Dimensional Structure
Authors: Stumpf Humberto O. , Pei Yu , Kahn Olivier , Ouahab Lahcéne , Grandjean Daniel
Published: October 2006

A compound has been synthesized with the formula (rad)
2
Mn
2
[Cu(opba)]
3
(DMSO)
2
.2H
2
O, where rad
+
is 2-(4-
N
-methylpyridinium)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, opba is orthophenylenebis(oxamato), and DMSO is dimethyl sulfoxide. It consists of two nearly perpendicular graphite-like networks with edge-sharing Mn(II)
6
Cu(II)
6
hexagons. The two networks are fully interlocked with the same topological relationship as that between adjacent rings of a necklace. The compound has three kinds of spin carriers: Mn(II) and Cu(II) ions, antiferromagnetically coupled through oxamato bridges, and rad
+
radical cations, bridging the Cu(II) ions through the nitronyl nitroxide groups and forming Cu-rad chains. The temperature dependence of the magnetization reveals that below 22.5 K, the compound behaves as a magnet.
Spectroscopic Determination of the Phase Composition and Temperature of Nitrogen Ice on Triton
Authors: Tryka Kimberly A. , Brown Robert H. , Anicich Vincent , Cruikshank Dale P. , Owen Tobias C.
Published: October 2006

Laboratory spectra of the first overtone band (2.1480 micrometers, 4655.4 reciprocal centimeters) of solid nitrogen show additional structure at 2.1618 micrometers (4625.8 reciprocal centimeters) over a limited temperature range. The spectrum of Neptune's satellite Triton shows the nitrogen overtone band as well as the temperature-sensitive component. The temperature dependence of this band may be used in conjunction with ground-based observations of Triton as an independent means of determining the temperature of surface deposits of nitrogen ice. The surface temperature of Triton is found to be 38.0
+2.0
–1.0
K, in agreement with previous temperature estimates and measurements. There is no spectral evidence for the presence of α-nitrogen on Triton's surface, indicating that there is less than 10 percent carbon monoxide in solid solution with the nitrogen on the surface.
Labyrinthine Pattern Formation in Magnetic Fluids
Authors: Dickstein Akiva J. , Erramilli Shyamsunder , Goldstein Raymond E. , Jackson David P. , Langer Stephen A.
Published: October 2006

A quasi two-dimensional drop of a magnetic fluid (ferrofluid) in a magnetic field is one example of the many systems, including amphiphilic monolayers, thin magnetic films, and type I superconductors, that form labyrinthine patterns. The formation of the ferrofluid labyrinth was examined both experimentally and theoretically. Labyrinth formation was found to be sensitively dependent on initial conditions, indicative of a space of configurations having a vast number of local energy minima. Certain geometric characteristics of the labyrinths suggest that these multiple minima have nearly equivalent energies. Kinetic effects on pattern selection were found in studies of fingering in the presence of time-dependent magnetic fields. The dynamics of this pattern formation was studied within a simple model that yields shape evolutions in qualitative agreement with experiment.
Giant Magnetoresistance at Low Fields in Discontinuous NiFe-Ag Multilayer Thin Films
Authors: Hylton T. L. , Coffey K. R. , Parker M. A. , Howard J. K.
Published: October 2006

A series of sputtered multilayers of Ni
80
Fe
20
-Ag was prepared to examine the giant magnetoresistance effect before and after annealing. For a wide range of NiFe and Ag thicknesses, no giant magnetoresistance was observed in the unannealed films. After annealing, a large, negative magnetoresistance was observed of order 4 to 6% in applied fields of order 5 to 10 oersteds at room temperature. The appearance of giant magnetoresistance is concurrent with the breakup of the NiFe layers, which is attributable to a magnetostatic interaction that favors local antiparallel alignment of the moments in adjacent layers. These structures may be of significant practical importance as sensors that require large changes in resistance at low fields, such as magnetoresistive heads used in magnetic recording systems.
Chemical Loss of Ozone in the Arctic Polar Vortex in the Winter of 1991-1992
Authors: Salawitch R. J. , Wofsy S. C. , Gottlieb E. W. , Lait L. R. , Newman P. A. , Schoeberl M. R. , Loewenstein M. , Podolske J. R. , Strahan S. E. , Proffitt M. H. , Webster C. R. , May R. D. , Fahey D. W. , Baumgardner D. , Dye J. E. , Wilson J. C. , Kelly K. K. , Elkins J. W. , Chan K. R. , Anderson J. G.
Published: October 2006

In situ measurements of chlorine monoxide, bromine monoxide, and ozone are extrapolated globally, with the use of meteorological tracers, to infer the loss rates for ozone in the Arctic lower stratosphere during the Airborne Arctic Stratospheric Expedition II (AASE II) in the winter of 1991-1992. The analysis indicates removal of 15 to 20 percent of ambient ozone because of elevated concentrations of chlorine monoxide and bromine monoxide. Observations during AASE II define rates of removal of chlorine monoxide attributable to reaction with nitrogen dioxide (produced by photolysis of nitric acid) and to production of hydrochloric acid. Ozone loss ceased in March as concentrations of chlorine monoxide declined. Ozone losses could approach 50 percent if regeneration of nitrogen dioxide were inhibited by irreversible removal of nitrogen oxides (denitrification), as presently observed in the Antarctic, or without denitrification if inorganic chlorine concentrations were to double.
Chemical Modification of the Photoluminescence Quenching of Porous Silicon
Authors: Lauerhaas Jeffrey M. , Sailor Michael J.
Published: October 2006

The photoluminescence of porous silicon can be quenched by adsorbates, and the degree of quenching can be tuned by chemical derivatization of the porous silicon surface. Thus, as-prepared porous silicon has a hydrophobic, hydrogen-terminated surface, and the photoluminescence is strongly quenched by ethanol and weakly quenched by water. Mild chemical oxidation (iodine followed by hydrolysis) produces a hydrophilic porous silicon surface. Photoluminescence from this hydrophilic material is quenched to a lesser extent by ethanol and to a greater extent by water, relative to the original surface. This demonstrates that the visible luminescence from porous silicon is highly surface-sensitive, and the surface interactions can be tuned by specific chemical transformations.
A Potentially Realizable Quantum Computer
Authors: Lloyd Seth
Published: October 2006

Arrays of weakly coupled quantum systems might compute if subjected to a sequence of electromagnetic pulses of well-defined frequency and length. Such pulsed arrays are true quantum computers: Bits can be placed in superpositions of 0 and 1, logical operations take place coherently, and dissipation is required only for error correction. Operated with frequent error correction, such a system functions as a parallel digital computer. Operated in a quantum-mechanically coherent manner, such a device functions as a general-purpose quantum-mechanical micromanipulator, capable of both creating any desired quantum state of the array and transforming that state in any desired way.
The Origin of the Turtle Body Plan: Bridging a Famous Morphological Gap
Authors: Lee Michael S. Y.
Published: October 2006

A restudy of pareiasaurs reveals that these primitive reptiles are the nearest relatives of turtles. The two groups share numerous derived characters, such as a reduced presacral count, an acromion process, and a trochanter major, which are absent in other basal amniotes. Many traits long thought specific to chelonians also occur in pareiasaurs and must have evolved before the distinctive turtle shell appeared. Evidence uniting captorhinid or procolophonoids with turtles is shown to be weak. The phylogeny proposed here also suggests that certain features of the earliest turtle (
Proganochelys
) that have been interpreted as specializations, such as the large supratemporal and robust metacarpals, are primitive for turtles. In pareiasaurs, the osteoderms represent the precursors of the chelonian shell and the morphology of the anterior region is consistent with the idea that the shoulder girdle in turtles has migrated posteriorly into the rib cage.
Pressure-Induced Enhancement of
T
c
Above 150 K in Hg-1223
Authors: Nuñez-Regueiro M. , Tholence J. -L. , Antipov E. V. , Capponi J. -J. , Marezio M.
Published: October 2006

The recently discovered homologous series HgBa
2
Ca

n
-1

Cu

n

O

2
n
+2+δ

possesses remarkable properties. A superconducting transition temperature,
T
c
, as high as 133 kelvin has been measured in a multiphase Hg-Ba-Ca-Cu-O sample and found to be attributable to the Hg-1223 compound. Temperature-dependent electrical resistivity measurements under pressure on a (> 95%) pure Hg-1223 phase are reported. These data show that
T
c
increases steadily with pressure at a rate of about 1 kelvin per gigapascal up to 15 gigapascals, then more slowly and reaches a
T
c
= 150 kelvin, with the onset of the transition at 157 kelvin, for 23.5 gigapascals. This large pressure variation (as compared to the small effects observed in similar compounds with the optimal
T
c
) strongly suggests that higher critical temperatures could be obtained at atmospheric pressure.
Confinement of Electrons to Quantum Corrals on a Metal Surface
Authors: Crommie M. F. , Lutz C. P. , Eigler D. M.
Published: October 2006

A method for confining electrons to artificial structures at the nanometer lengthscale is presented. Surface state electrons on a copper(111) surface were confined to closed structures (corrals) defined by barriers built from iron adatoms. The barriers were assembled by individually positioning iron adatoms with the tip of a 4-kelvin scanning tunneling microscope (STM). A circular corral of radius 71.3 Å was constructed in this way out of 48 iron adatoms. Tunneling spectroscopy performed inside of the corral revealed a series of discrete resonances, providing evidence for size quantization. STM images show that the corral's interior local density of states is dominated by the eigenstate density expected for an electron trapped in a round two-dimensional box.
Ultrafast Optical Kerr Effect in Liquids and Solids
Authors: Righini Roberto
Published: October 2006

In the optical Kerr effect, the electric field of light incident on a transparent sample induces an anisotropic refractive index, which is measured by its effect on the passage of a second light beam. The advent of lasers powerful enough to generate a measurable effect, and which can be pulsed on femtosecond time scales, has made the optical Kerr effect into a practical technology for investigating the molecular structure and interactions of condensed systems such as pure liquids, liquid solutions, and plastic crystals.
The Transition State of the F + H
2
Reaction
Authors: Manolopoulos David E. , Stark Klaus , Werner Hans-Joachim , Arnold Don W. , Bradforth Stephen E. , Neumark Daniel M.
Published: October 2006

The transition state region of the F + H
2
reaction has been studied by photoelectron spectroscopy of FH
2
–
. New para and
normal
FH
2
–
photoelectron spectra have been measured in refined experiments and are compared here with exact three-dimensional quantum reactive scattering simulations that use an accurate new ab initio potential energy surface for F + H
2
. The detailed agreement that is obtained between this fully ab initio theory and experiment is unprecedented for the F + H
2
reaction and suggests that the transition state region of the F + H
2
potential energy surface has finally been understood quantitatively.
Functions of Sphingolipids and Sphingolipid Breakdown Products in Cellular Regulation
Authors: Hannun Yusuf A. , Bell Robert M.
Published: October 2006

The discovery that breakdown products of cellular sphingolipids are biologically active has generated interest in the role of these molecules in cell physiology and pathology. Sphingolipid breakdown products, sphingosine and lysosphingolipids, inhibit protein kinase C, a pivotal enzyme in cell regulation and signal transduction. Sphingolipids and lysosphingolipids affect significant cellular responses and exhibit antitumor promoter activities in various mammalian cells. These molecules may function as endogenous modulators of cell function and possibly as second messengers.
High Rate of HTLV-II Infection in Seropositive IV Drug Abusers in New Orleans
Authors: Lee Helen , Swanson Priscilla , Shorty Vernon S. , Zack Jerome A. , Rosenblatt Joseph D. , Chen Irvin S. Y.
Published: October 2006

Confirmed infection with HTLV-II (human T cell leukemia virus type II) has been described only in rare cases. The major limitation to serological diagnosis of HTLV-II has been the difficulty of distinguishing HTLV-II from HTLV-I (human T cell leukemia virus type I) infection, because of substantial cross-reactivity between the viruses. A sensitive modification of the polymerase chain reaction method was used to provide unambiguous molecular evidence that a significant proportion of intravenous drug abusers are infected with HTLV, and the majority of these individuals are infected with HTLV-II rather than HTLV-I. Of 23 individuals confirmed by polymerase chain reaction analysis to be infected with HTLV, 21 were identified to be infected with HTLV-II, and 2 were infected with HTLV-I. Molecular identification of an HTLV-II—infected population provides an opportunity to investigate the pathogenicity of HTLV-II in humans.
Complementary DNA Coding Click Beetle Luciferases Can Elicit Bioluminescence of Different Colors
Authors: Wood Keith V. , Lam Y. Amy , Seliger Howard H. , McElroy William D.
Published: October 2006

Eleven complementary DNA (cDNA) clones were generated from messenger RNA isolated from abdominal light organs of the bioluminescent click beetle,
Pyrophorus plagiophthalamus
. When expressed in
Escherichia coli
, these clones can elicit bioluminescence that is readily visible. The clones code for luciferases of four types, distinguished by the colors of bioluminescence they catalyze: green (546 nanometers), yellow-green (560 nanometers), yellow (578 nanometers), and orange (593 nanometers). The amino acid sequences of the different luciferases are 95 to 99 percent identical with each other, but are only 48 percent identical with the sequence of firefly luciferase (
Photinus pyralis
). Because of the different colors, these clones may be useful in experiments in which multiple reporter genes are needed.
Molecular Recognition and Metal Ion Template Synthesis
Authors: McMurry Thomas J. , Raymond Kenneth N. , Smith Paul H.
Published: October 2006

Methods for the design and synthesis of ligands intended to be specific for a metal ion have been a recent chemical development. This article describes how this process can be inverted so that the specifics of the coordination environment around the metal ion can be used as a template in large-scale ligand synthesis. The synthesis of macrobicyclic ligands for ferric ion has been accomplished by using active esters of catechol ligands in which catecholate coordination to iron is a prelude to the organic chemical reactions that link the coordination subunits together into one ligand system surrounding a central metal ion coordination site. The lanthanide(III) ions, which are among the most labile metal ions known, have coordination numbers of 8 or higher, and thus their encapsulation into a macrobicyclic structure is a challenging problem. Lanthanide amine complexes have been used as metal templates in the synthesis of such macrobicyclic lanthanide complexes. There is evidence that such a complex is inert to exchange in aqueous solution.
The Neuronal Growth-Associated Protein GAP-43 Induces Filopodia in Non-Neuronal Cells
Authors: Zuber Mauricio X. , Goodman Daniel W. , Karns Larry R. , Fishman Mark C.
Published: October 2006

The neuron-specific protein GAP-43 is associated with the membrane of the nerve growth cone and thus may be important to the activity of this distinctive neuronal structure. Transient transfection of COS and NIH 3T3 cells with appropriate vectors resulted in expression of GAP-43 in these non-neuronal cells; as in neurons, transfected GAP-43 associated with the membrane. In addition, many long fine filopodial processes extended from the periphery of such transfected cells. Stable CHO cell lines expressing GAP-43 also exhibited processes that were more numerous, far longer, and more complex than those of CHO cell lines not transfected or transfected with control plasmids. Thus GAP-43 may directly contribute to growth cone activity by regulating cell membrane structure and enhancing extension of filopodial processes.
Clathrin: A Role in the Intracellular Retention of a Golgi Membrane Protein
Authors: Payne Gregory S. , Schekman Randy
Published: October 2006

Yeast mutants deficient in the clathrin heavy chain secrete a precursor form of the α-factor, a peptide-mating pheromone. Analysis of this defect indicates that the endoprotease Kex2p, which is responsible for initiating proteolytic maturation of the α-factor precursor in the Golgi apparatus, is unexpectedly present at the plasma membrane in mutant cells. This result suggests that clathrin is required for the retention of Kex2p in the Golgi apparatus.
Intracellular Targeting and Structural Conservation of a Prohormone-Processing Endoprotease
Authors: Fuller Robert S. , Brake Anthony J. , Thorner Jeremy
Published: October 2006

The prohormone-processing endoprotease (
KEX2
gene product) of the yeast
Saccharomyces cerevisiae
is a membrane-bound, 135,000-dalton glycoprotein, which contains both asparagine-linked and serine- and threonine-linked oligosaccharide and resides in a secretory compartment. Analysis of mutant
kex2
genes truncated at their 3′ end indicates that carboxyl terminal domains of the enzyme are required for its proper localization within the cell. A human gene product, "furin," shares 50% identity with the catalytic domain of Kex2 protease and is, therefore, a candidate for a human prohormone-processing enzyme.
Sodium Channel Inactivation in Squid Axon Is Removed by High Internal
p
H or Tyrosine-Specific Reagents
Authors: Brodwick Malcolm S. , Eaton Douglas C.
Published: October 2006

In squid axon, internal alkalinization from
p
H 7.1 to
p
H 10.2 results in a reversible decrease of the maximum inward current and the steady state sodium channel inactivation. Similar effects were observed after treatment of the axon with tetranitromethane or after iodination with lactoperoxidase. These results suggest that a tyrosine residue is an essential component of the inactivation process in this nerve.
Regulation of Calcium Concentration in Voltage-Clamped Smooth Muscle Cells
Authors: Becker Peter L. , Singer Joshua J. , Walsh John V. , Fay Frederic S.
Published: October 2006

The regulation of intracellular calcium concentration in single smooth muscle cells was investigated by simultaneously monitoring electrical events at the surface membrane and calcium concentration in the cytosol. Cytosolic calcium concentration rose rapidly during an action potential or during a voltage-clamp pulse that elicited calcium current; a train of voltage-clamp pulses caused further increases in the calcium concentration up to a limit of approximately 1 μM. The decline of the calcium concentration back to resting levels occurred at rates that varied with the calcium concentration in an apparently saturable manner. Moreover, the rate of decline at any given calcium concentration was enhanced after a higher, more prolonged increase of calcium. The process responsible for this enhancement persisted for many seconds after the calcium concentration returned to resting levels. Thus, the magnitude and duration of a calcium transient appear to regulate the subsequent calcium removal.
Synthesis of Functional Human Hemoglobin in Transgenic Mice
Authors: Behringer Richard R. , Ryan Thomas M. , Reilly Michael P. , Asakura Toshio , Palmiter Richard D. , Brinster Ralph L. , Townes Tim M.
Published: October 2006

Human α- and β-globin genes were separately fused downstream of two erythroid-specific deoxyribonuclease (DNase) I super-hypersensitive sites that are normally located 50 kilobases upstream of the human β-globin gene. These two constructs were coinjected into fertilized mouse eggs, and expression was analyzed in transgenic animals that developed. Mice that had intact copies of the transgenes expressed high levels of correctly initiated human α- and β-globin messenger RNA specifically in erythroid tissue. An authentic human hemoglobin was formed in adult erythrocytes that when purified had an oxygen equilibrium curve identical to the curve of native human hemoglobin A (Hb A). Thus, functional human hemoglobin can be synthesized in transgenic mice. This provides a foundation for production of mouse models of human hemoglobinopathies such as sickle cell disease.
Factors That Predict Individual Vulnerability to Amphetamine Self-Administration
Authors: Piazza Pier Vincenzo. , Deminière Jean-Marie. , Le Moal Michel. , Simon Hervé.
Published: October 2006

Clinical observations show that there is considerable individual variability in the response to the addictive properties of drugs. This individual variability needs to be taken into account in animal models of addiction. Like humans, only some rats readily self-administer low doses of psychostimulants. The individual animals at risk can be identified on the basis of their response to environmental or pharmacological challenges. This predisposition to develop self-administration can be induced by repeated treatment with amphetamine. These results may help elucidate the neurobiological basis of addiction liability observed in both rats and humans.
Symbiotic Marine Bacteria Chemically Defend Crustacean Embryos from a Pathogenic Fungus
Authors: Gil-Turnes M, Sofia , Hay Mark E. , Fenical William
Published: October 2006

Embryos of the shrimp
Palaemon macrodactylus
are remarkably resistant to infection by the fungus
Lagenidium callinectes
, a recognized pathogen of many crustaceans. An
Alteromonas
sp. bacterial strain consistently isolated from the surface of the embryos, produces 2,3-indolinedione (isatin), a compound that inhibits the pathogenic fungus. If exposed to the fungus, bacteria-free embryos quickly die, whereas similar embryos reinoculated with the bacteria or treated only with 2,3-indolinedione live well. The commensal
Alteromonas
sp. bacteria protect shrimp embryos from fungal infection by producing and liberating the antifungal metabolite 2,3-indolinedione.
Human Cells Lacking mtDNA: Repopulation with Exogenous Mitochondria by Complementation
Authors: King Michael P. , Attardi Giuseppe
Published: October 2006

Two human cell lines (termed ρ
0
), which had been completely depleted of mitochondrial DNA (mtDNA) by long-term exposure to ethidium bromide, were found to be dependent on uridine and pyruvate for growth because of the absence of a functional respiratory chain. Loss of either of these two metabolic requirements was used as a selectable marker for the repopulation of ρ
0
cells with exogenous mitochondria by complementation. Transformants obtained with various mitochondrial donors exhibited a respiratory phenotype that was in most cases distinct from that of the ρ
0
parent or the donor, indicating that the genotypes of the mitochondrial and nuclear genomes as well as their specific interactions play a role in the respiratory competence of a cell.
Interleukin-1 Stimulates the Secretion of Hypothalamic Corticotropin-Releasing Factor
Authors: Sapolsky Robert , Rivier Catherine , Yamamoto Gayle , Plotsky Paul , Vale Wylie
Published: October 2006

There is now evidence that the immune system, during times of infectious challenge, can stimulate the secretion of glucocorticoids, the adrenal steroids that mediate important aspects of the response to stress. Specifically, secretion of interleukin-1 (IL-1), a monocyte lymphokine secreted after infection, appears at least in part responsible for this effect. Glucocorticoids are secreted in response to a neuroendocrine cascade involving, first, the brain, then the pituitary, and finally the adrenal gland. In this report, human IL-1 is shown to activate the adrenocortical axis at the level of the brain, stimulating the release of the controlling hormone corticotropin-releasing factor (CRF) from the hypothalamus. Infusion of IL-1 induced a significant secretion of CRF into the circulation exiting the hypothalamus, whereas immunoneutralization of CRF blocked the stimulatory effect of IL-1 on glucocorticoid secretion. IL-1 appeared to have no acute direct stimulatory effects on the pituitary or adrenal components of this system. Furthermore, IL-1 did not cause a nonspecific release of other hypothalamic hormones. Thus, the lymphokine acts in a specific manner to activate the adrenocortical axis at the level of the brain; this effect appears to be unrelated to the known pyrogenic effects of IL-1 within the hypothalamus.