bluuebunny/crossref_metadata_2025 huggingface dataset:
Interstellar Polycyclic Aromatic Hydrocarbons and Carbon in Interplanetary Dust Particles and Meteorites
Authors: Allamandola L. J. , Sandford S. A. , Wopenka B.
Published: October 2006

Both interplanetary dust particles (IDPs) and meteorites may contain material that is similar to polycyclic aromatic hydrocarbons (PAHs). The Raman spectra of IDPs and meteorites show features that are similar in position and relative strength to interstellar infrared emission features that have been attributed to vibrational transitions in free, molecular-sized PAHs. The Raman spectra of some IDPs also show red photoluminescence that is similar to the excess red emission seen in some astronomical objects and that has also been attributed to PAHs and hydrogenated amorphous carbon. Moreover, a part of the carbonaceous phase in IDPs and meteorites contains deuterium to hydrogen ratios that are greater than those for terrestrial samples. Deuterium enrichment is expected in small free PAHs that are exposed to ultraviolet radiation in the interstellar medium. Taken together, these observations suggest that some of the carbonaceous material in IDPs and meteorites may have been produced in circumstellar dust shells and only slightly modified in interstellar space.
Disulfate Ion as an Intermediate to Sulfuric Acid in Acid Rain Formation
Authors: Chang S. G. , Littlejohn D. , Hu K. Y.
Published: October 2006

The oxidation of the bisulfite ion by dissolved oxygen to produce sulfate ion involves the formation of a previously undetected intermediate. This intermediate has a fairly strong Raman band at 1090 wave numbers and a weak Raman band at 740 wave numbers, both of which are probably due to sulfur-oxygen stretches. The intermediate is proposed to be the disulfate ion S
2
O
7
2-
, which hydrolyzes into H
+
and either SO
4
2-
or HSO
4
2-
with a half-life of about 52 seconds at 25°C.
Effect of Ship-Stack Effluents on Cloud Reflectivity
Authors: Coakley James A. , Bernstein Robert L. , Durkee Philip A.
Published: October 2006

Under stable meteorological conditions the effect of ship-stack exhaust on overlying clouds was detected in daytime satellite images as an enhancement in cloud reflectivity at 3.7 micrometers. The exhaust is a source of cloud-condensation nuclei that increases the number of cloud droplets while reducing droplet size. This reduction in droplet size causes the reflectivity at 3.7 micrometers to be greater than the levels for nearby noncontaminated clouds of similar physical characteristics. The increase in droplet number causes the reflectivity at 0.63 micrometer to be significantly higher for the contaminated clouds despite the likelihood that the exhaust is a source of particles that absorb at visible wavelengths. The effect of aerosols on cloud reflectivity is expected to have a larger influence on the earth's albedo than that due to the direct scattering and absorption of sunlight by the aerosols alone.
Characterizing Criminal Careers
Authors: Blumstein Alfred , Cohen Jacqueline
Published: October 2006

Most knowledge about crime and criminals derives from cross-sectional analyses that link crime rates in a community with a community's attributes. The criminal-career approach focuses on individual offenders and considers their crime-committing patterns as a longitudinal stochastic process. This approach, which invokes parameters characterizing participation rate, initiation rate, termination rate and the associated career length, and individual offending frequency, offers some important new insights. For example, annual offending frequency appears to be reasonably constant with age for those offenders who stay criminally active, termination rates are relatively low for active offenders in their 30s, and offending frequencies seem to be relatively insensitive to demographic attributes for active offenders. All these observations are opposite to those that would be derived from cross-sectional analysis.
Bat Predation and Its Influence on Calling Behavior in Neotropical Katydids
Authors: Belwood Jacqueline J. , Morris Glenn K.
Published: October 2006

Insectivorous bats have influenced the development of antipredator behavior in moths, green lacewings, crickets, and mantids; until recently, such adaptations were unknown in katydids. Foliage-gleaning bats in Panama can use the female-attracting, airborne calling songs of nocturnal katydids to locate prey. They also feed heavily on these insects. Katydid species sympatric with these bats exhibit markedly reduced calling song duty cycles. Males supplement shortened songs with complex, species-specific tremulations that generate vibrations that are inaudible to bats but reach conspecific females through a shared plant substrate. Female katydids do not call audibly but are also preyed on in large numbers, perhaps as a result of moving toward calling males.
Antarctic Stratospheric Chemistry of Chlorine Nitrate, Hydrogen Chloride, and Ice: Release of Active Chlorine
Authors: Molina Mario J. , Tso Tai-Ly , Molina Luisa T. , Wang Frank C.-Y.
Published: October 2006

The reaction rate between atmospheric hydrogen chloride (HCl) and chlorine nitrate (ClONO
2
) is greatly enhanced in the presence of ice particles; HCl dissolves readily into ice, and the collisional reaction probability for ClONO
2
on the surface of ice with HCl in the mole fraction range from ∼0.003 to 0.010 is in the range from ∼0.05 to 0.1 for temperatures near 200 K. Chlorine (Cl
2
) is released into the gas phase on a time scale of at most a few milliseconds, whereas nitric acid (HNO
3
), the other product, remains in the condensed phase. This reaction could play an important role in explaining the observed depletion of ozone over Antarctica; it releases photolytically active chlorine from its most abundant reservoir species, and it promotes the formation of HNO
3
and thus removes nitrogen dioxide (NO
2
) from the gas phase. Hence it establishes the necessary conditions for the efficient catalytic destruction of ozone by halogenated free radicals. In the absence of HCl, ClONO
2
also reacts irreversibly with ice with a collision efficiency of ∼0.02 at 200 K; the product hypochlorous acid (HOCI) is released to the gas phase on a time scale of minutes.
Sequence-Specific DNA Binding by a Short Peptide Dimer
Authors: Talanian Robert V. , McKnight C. James , Kim Peter S.
Published: October 2006

The transcription factor C/EBP uses a bipartite structural motif to bind DNA. Two protein chains dimerize through a set of amphipathic α helices termed the leucine zipper. Highly basic polypeptide regions emerge from the zipper to form a linked set of DNA contact surfaces. In the recently proposed a "scissors grip" model, the paired set of basic regions begin DNA contact at a central point and track in opposite directions along the major groove, forming a molecular clamp around DNA. This model predicts that C/EBP must undertake significant changes in protein conformation as it binds and releases DNA. The basic region of ligand-free C/EBP is highly sensitive to protease digestion. Pronounced resistance to proteolysis occurred when C/EBP associated with its specific DNA substrate. Sequencing of discrete proteolytic fragments showed that prominent sites for proteolysis occur at two junction points predicted by the "scissors grip" model. One junction corresponds to the cleft where the basic regions emerge from the leucine zipper. The other corresponds to a localized nonhelical segment that has been hypothesized to contain an N-cap and facilitate the sharp angulation necessary for the basic region to track continuously in the major groove of DNA.
Heavy-Electron Metals: New Highly Correlated States of Matter
Authors: Fisk Z. , Hess D. W. , Pethick C. J. , Pines D. , Smith J. L. , Thompson J. D. , Willis J. O.
Published: October 2006

Heavy-electron metals exhibit highly correlated electronic behavior at liquid helium temperatures, with conduction-electron masses some hundred times the free-electron mass. Whether "normal," antiferromagnetic, or superconducting, their electronic behavior differs drastically from their ordinary metallic counterparts. The physical origin of the large mass and unusual superconducting and magnetic properties is the strong coupling between the conduction electrons and the local ƒ-electron moment fluctuations characteristic of these materials.
The Effect of Eurasian Snow Cover on Global Climate
Authors: Barnett T. P. , Dümenil L. , Schlese U. , Roeckner E.
Published: October 2006

Numerical simulations with a global atmospheric circulation model suggest that large-scale variations in the amount of snowfall over Eurasia in the springtime are linked to the subsequent strength of the Asian summer monsoon. Large-scale changes in Eurasian snow cover are coupled to larger scale changes in the global climate system. There is a large, strong teleconnection to the atmospheric field over North America. The model results also show snow cover effects to subsequently alter other climatic fields known to be intimately associated with the El Niño-Southern Oscillation (ENSO) phenomenon. Thus the model results seem to challenge the current dogma that the ENSO phenomenon is solely the result of close coupling between the atmosphere and ocean by suggesting that processes over continental land masses may also have to be considered.
Cooling, Stopping, and Trapping Atoms
Authors: Phillips William D. , Gould Phillip L. , Lett Paul D.
Published: October 2006

Significant advances have been made in the ability to control the motion of neutral atoms. Cooling and trapping atoms present new possibilities for studies of ultracold atoms and atomic interactions. The techniques of laser cooling and deceleration of atomic beams, magnetic and laser trapping of neutral atoms, and a number of recent advances in the use of radiative forces to manipulate atoms are reviewed.
A New High-Temperature Superconductor: Bi
2
Sr
3-x
Ca
x
Cu
2
O
8+y
Authors: Subramanian M. A. , Torardi C. C. , Calabrese J. C. , Gopalakrishnan J. , Morrissey K. J. , Askew T. R. , Flippen R. B. , Chowdhry U. , Sleight A. W.
Published: October 2006

A new superconductor that displays onset behavior near 120 K has been identified as Bi
2
Sr

3-
x

Ca

x

Cu
2
O

8+
y

with
x
ranging from about 0.4 to 0.9. Single crystal x-ray diffraction data were used to determine a pseudo-tetragonal structure based on an A-centered orthorhombic subcell with
a
= 5.399 Å,
b
= 5.414 Å, and
c
= 30.904 Å. The structure contains copper-oxygen sheets as in La
2
CuO
4
and YBa
2
Cu
3
O
7
, but the copper-oxygen chains present in YBa
2
Cu
3
O
7
do not occur in Bi
2
Sr

3-
x

Ca

x

Cu
2
O

8+
y

. The structure is made up of alternating double copper-oxygen sheets and double bismuth-oxygen sheets. There are Ca
2+
and Sr
2+
cations between the adjacent Cu-O sheets; Sr
2+
cations are also found between the Cu-O and Bi-O sheets. Electron microscopy studies show an incommensurate superstructure along the
a
axis that can be approximated by an increase of a factor of 5 over the subcell dimension. This superstructure is also observed by x-ray diffraction on single crystals, but twinning can make it appear that the superstructure is along both
a
and
b
axes. Flux exclusion begins in our samples at about 116 K and is very strong by 95 K. Electrical measurements on a single crystal of Bi
2
Sr

3-
x

Ca

x

Cu
2
O

8+
y

show a resistivity drop at about 116 K and apparent zero resistivity at 91 K.
Quantum Mechanics of a Macroscopic Variable: The Phase Difference of a Josephson Junction
Authors: Clarke John , Cleland Andrew N. , Devoret Michel H. , Esteve Daniel , Martinis John M.
Published: October 2006

Experiments to investigate the quantum behavior of a macroscopic degree of freedom, namely the phase difference across a Josephson tunnel junction, are described. The experiments involve measurements of the escape rate of the junction from its zero voltage state. Low temperature measurements of the escape rate for junctions that are either nearly undamped or moderately damped agree very closely with predictions for macroscopic quantum tunneling, with no adjustable parameters. Microwave spectroscopy reveals quantized energy levels in the potential well of the junction in excellent agreement with quantum-mechanical calculations. The system can be regarded as a "macroscopic nucleus with wires."
Localized Dispersal and Recruitment in Great Barrier Reef Corals: The Helix Experiment
Authors: Sammarco Paul W. , Andrews John C.
Published: October 2006

To examine the problem of how far coral larvae disperse from their natal reef, coral recruitment densities were experimentally determined at distances up to 5 kilometers from a small, relatively isolated platform reef, Helix Reef, on the central Great Barrier Reef for 7 months. High concentrations of recruits, accounting for up to 40 percent of all recruitment, were found downstream of the reef in areas of high water residence time, suggesting that near-field (proximal) circulation has a profound influence on dispersal and recruitment of coral larvae. Coral recruitment declined logarithmically with distance from the reef, decreasing by an order of magnitude at radial distances of only 600 to 1200 meters. On an ecological time scale, advective dispersal of semipassive marine larvae with relatively short planktonic lives (minimally days) may be extensive, but success of recruitment is highly limited. Through evolutionary time, sufficient dispersal occurs to ensure gene flow to reef tracts hundreds or possibly thousands of kilometers apart. In the short term, however, coral reefs appear to be primarily self-seeded with respect to coral larvae.
Anaerobic Dormancy Quantified in
Artemia
Embryos: A Calorimetric Test of the Control Mechanism
Authors: Hand Steven C. , Gnaiger Erich
Published: October 2006

Continuous measurement of heat dissipation from brine shrimp embryos during reversible transitions from aerobic development to anaerobic dormancy demonstrates a primary role for intracellular
p
H (
p
H
i
) in this metabolic switching. Artificially elevating the depressed
p
H
i
during anoxia by adding ammonia markedly reactivates metabolism, as judged by increases in heat dissipation, trehalose catabolism, and the ratio of adenosine triphosphate to adenosine diphosphate. Energy flow during anaerobic dormancy is suppressed to 2.4 percent of aerobic values, which is the lowest percentage thus far reported for euryoxic animals. Use of diguanosine tetraphosphate stores cannot account for this observed heat dissipation. Thus, mobilizing trace amounts of trehalose may explain the energy metabolism during quiescence.
Principles of Design of Fluid Transport Systems in Zoology
Authors: LaBarbera Michael
Published: October 2006

Fluid transport systems mediate the transfer of materials both within an organism and between an organism and its environment. The architecture of fluid transport systems is determined by the small distances over which transfer processes are effective and by hydrodynamic and energetic constraints. All fluid transport systems within organisms exhibit one of two geometries, a simple tube interrupted by a planar transfer region or a branched network of vessels linking widely distributed transfer regions; each is determined by different morphogenetic processes. By exploiting the signal inherent in local shear stress on the vessel walls, animals have repeatedly evolved a complex branching hierarchy of vessels approximating a globally optimal system that minimizes the costs of the construction and maintenance of the fluid transport system.
Inclusion of Thermal Motion in Crystallographic Structures by Restrained Molecular Dynamics
Authors: Gros Piet , van Gunsteren Wilfred F. , Hol Wim G. J.
Published: October 2006

A protein crystal structure is usually described by one single structure, which largely omits the dynamical behavior of the molecule. A molecular dynamics method with a time-averaged crystallographic restraint was used to overcome this limitation. This method yields an ensemble of structures in which all possible thermal motions are allowed, that is, in addition to isotropic distributions, anisotropic and anharmonic positional distributions occur as well. In the case of bovine pancreatic phospholipase A
2
, this description markedly improves agreement with the observed x-ray diffraction data compared to the results of the classical one-model structure description. Time-averaged crystallographically restrained molecular dynamics reveals large mobilities in the loops involved in lipid bilayer association.
Studies of Synthetic Polymers by Nonradiative Energy Transfer
Authors: Morawetz Herbert
Published: October 2006

Nonradiative energy transfer between fluorescent labels attached to polymers has been used to characterize polymer miscibility, the interpenetration of chain molecules in solution, micelle formation in graft copolymers, the unfolding of collapsed chain molecules in polymer melts, and the transfer of energy absorbed by a large number of donor labels to a small number of acceptors by an "antenna effect." The change in the emission spectrum after ionomer solutions with different fluorescent counterions were mixed provided rate constants for counterion interchange. The fluorescence behavior of dispersions of donor-labeled polymers stabilized by a graft copolymer with acceptor fluorophores in the solution phase led to inferences about the morphology of the dispersed particles.
Macroevolutionary Interpretations of Symmetry and Synchroneity in the Fossil Record
Authors: Kitchell Jennifer A. , MacLeod Norman
Published: October 2006

Quantitative analyses of global diversity in the marine fossil record over Phanerozoic time reveal an historically ordered pattern of sequential dominance and increasing diversity. Explanatory models applied to this empirical pattern lead to irreconcilable differences of interpretation. The issue may be resolved by determining the expected distributions and limits of temporal covariation among clades generated by a random branching process. Results also challenge the claim that asymmetries in intra-clade diversity variation provide a directional arrow for the history of life.
Detection of
Borrelia burgdorferi
DNA in Museum Specimens of
Ixodes dammini
Ticks
Authors: Persing David H. , Telford Sam R. , Rys Paul N. , Dodge Deborah E. , White Thomas J. , Malawista Stephen E , Spielman Andrew
Published: October 2006

In order to investigate the potential for
Borrelia burgdorferi
infection before the recognition of Lyme disease as a clinical entity, the polymerase chain reaction (PCR) was used to examine museum specimens of
Ixodes dammini
(deer ticks) for the presence of spirochete-specific DNA sequences. One hundred and thirty-six archival tick specimens were obtained representing various continental U.S. locations; DNA sequences characteristic of modern day isolates of
B. burgdorferi
were detected in 13 1940s specimens from Montauk Point and Hither Hills, Long Island, New York. Five archival specimens of
Dermacentor variabilis
(dog tick) from the same collection and 118
Ixodes
specimens from other endemic and nonendemic sites were negative. These data suggest that the appearance of the Lyme disease spirochete in suitable arthropod vectors preceded, by at least a generation, the formal recognition of this disease as a clinical entity in the United States.
Mental Models in Narrative Comprehension
Authors: Bower Gordon H. , Morrow Daniel G.
Published: October 2006

Readers of stories construct mental models of the situation and characters described. They infer causal connections relating characters' actions to their goals. They also focus attention on characters' movements, thereby activating nearby parts of the mental model. This activation is revealed in readers' faster answering of questions about such parts, with less facilitation the greater their distance from the focus. Recently visited as well as imagined locations are also activated for several seconds. These patterns of temporary activation facilitate comprehension.
New Evidence on the Size and Possible Effects of a Late Pliocene Oceanic Asteroid Impact
Authors: Kyte Frank T. , Zhou Lei , Wasson John T.
Published: October 2006

Debris from a late Pliocene asteroid impact is spread across at least 600 kilometers of the ocean floor in the southeast Pacific. On the basis of iridium concentrations in sediments from six deep-sea cores, the asteroid diameter was at least 0.5 kilometer; the impacting projectile may have been one of the largest in the last few million years. The stratigraphic age of this impact is the same as that inferred for the onset of Northern Hemisphere glaciation.
July Temperatures in Europe from Pollen Data, 6000 Years Before Present
Authors: Huntley Brian , Prentice I. Colin
Published: October 2006

Mean July temperatures across Europe 6000 years before present were reconstructed from palynological data by the transfer function method. Reconstructed summer temperatures were warmer than those at present over most of Europe with the greatest heating, more than 2°C, in the midcontinent and the far north. This pattern is explained by high summer insolation and a weak zonal insolation gradient 6000 years before present and the effective heating of the landmass relative to ocean and coastal areas. A strong land-sea pressure gradient may in turn have increased westerly air flow into southern Europe, which is consistent with cooler reconstructed summer temperatures in the Mediterranean region, and reduced the environmental lapse rate in the central European mountains.
Simulation of Eolian Saltation
Authors: Anderson Robert S. , Haff Peter K.
Published: October 2006

Saltation is important in the transport of sand-sized granular material by wind and in the ejection of dust from the bed both on Earth and on Mars. The evolution of the saltating population and all its characteristic profiles is calculated from inception by pure aerodynamic entrainment through to steady state. Results of numerical simulations of single-grain impacts into granular beds are condensed into analytic expressions for the number and speeds of grains rebounding or ejected (splashed) from the bed. A model is combined with (i) this numerical representation, (ii) an expression for the aerodynamic entrainment rate, and (iii) the modification of the wind velocity profile by saltating grains. Calculated steady state mass fluxes are within the range of mass fluxes measured in wind tunnel experiments; mass flux is nonlinearly dependent on the shear velocity. Aerodynamically entrained grains in the system are primarily seeding agents; at steady state, aerodynamic entrainment is rare. The time for the entire system to reach steady state is roughly 1 second, or several long-trajectory hop times.
Low-Pressure, Metastable Growth of Diamond and "Diamondlike" Phases
Authors: Angus John C. , Hayman Cliff C.
Published: October 2006

Diamond may be grown at low pressures where it is the metastable form of carbon. Recent advances in a wide variety of plasma and electrical discharge methods have led to dramatic increases in growth rates. All of these methods have certain aspects in common, namely, the presence of atomic hydrogen and the production of energetic carbon-containing fragments under conditions that support high mobilities on the diamond surface. Some understanding of the processes taking place during nucleation and growth of diamond has been achieved, but detailed molecular mechanisms are not yet known. Related research has led to the discovery of a new class of materials, the "diamondlike" phases. Vapor-grown diamond and diamondlike materials may have eventual applications in abrasives, tool coatings, bearing surfaces, electronics, optics, tribological surfaces, and corrosion protection.
Chemistry of the Metal-Polymer Interfacial Region
Authors: Leidheiser Henry , Deck Philip D.
Published: October 2006

In many polymer-metal systems, chemical bonds are formed that involve metal-oxygen-carbon complexes. Infrared and Mössbauer spectroscopic studies indicate that carboxylate groups play an important role in some systems. The oxygen sources may be the polymer, the oxygen present in the oxide on the metal surface, or atmospheric oxygen. Diffusion of metal ions from the substrate into the polymer interphase may occur in some systems that are cured at elevated temperatures. It is unclear whether a similar, less extensive diffusion occurs over long time periods in systems maintained at room temperature. The interfacial region is dynamic, and chemical changes occur with aging at room temperature. Positron annihilation spectroscopy may have application to characterizing the voids at the metal-polymer interface.
Femtosecond Clocking of the Chemical Bond
Authors: Rosker Mark J. , Dantus Marcos , Zewail Ahmed H.
Published: October 2006

When a chemical bond is broken in a direct dissociation reaction, the process is so rapid that it has generally been considered instantaneous and thus unmeasurable. However, the bond does persist for times on the order of 10
-13
seconds after the photon has been absorbed. Femtosecond (10
-15
second) laser techniques can be used to directly clock this process, which describes the dynamics of the chemical bond. The time required to break the chemical bond in an elementary reaction has been measured and the characteristic repulsion length for the potential governing fragment separation has been obtained.
The Ecological Context of Life History Evolution
Authors: Partridge Linda , Harvey Paul H.
Published: October 2006

There is now a good theoretical understanding of life history evolution, and detailed explicit optimality models have been constructed. These present a challenge for empirical work examining some of the assumptions, such as the extent and mechanisms of the costs of growth and reproduction. In addition, there is an obvious need for comparative tests of the models. These tests, properly applied, may be particularly informative because they can deal with multiple independent variables, including ecological variables, and can reveal broad trends against a background of constraints on optima and the rate of evolutionary approach to them.

Life histories are the probabilities of survival and the rates of reproduction at each age in the life-span. Reproduction is costly, so that fertility at all ages cannot simultaneously be maximized by natural selection. Allocation of reproductive effort has evolved in response to the demographic impact of different environments but is constrained by genetic variance and evolutionary history.
Plasticity of the Differentiated State
Authors: Blau Helen M. , Pavlath Grace K. , Hardeman Edna C. , Chiu Choy-Pik , Silberstein Laura , Webster Steven G. , Miller Steven C. , Webster Cecelia
Published: October 2006

Heterokaryons provide a model system in which to examine how tissue-specific phenotypes arise and are maintained. When muscle cells are fused with nonmuscle cells, muscle gene expression is activated in the nonmuscle cell type. Gene expression was studied either at a single cell level with monoclonal antibodies or in mass cultures at a biochemical and molecular level. In all of the nonmuscle cell types tested, including representatives of different embryonic lineages, phenotypes, and developmental stages, muscle gene expression was induced. Differences among cell types in the kinetics, frequency, and gene dosage requirements for gene expression provide clues to the underlying regulatory mechanisms. These results show that the expression of genes in the nuclei of differentiated cells is remarkably plastic and susceptible to modulation by the cytoplasm. The isolation of the genes encoding the tissue-specific
trans
-acting regulators responsible for muscle gene activation should now be possible.
Protein-Tyrosine Kinase Activity in
Saccharomyces cerevisiae
Authors: Schieven Gary , Thorner Jeremy , Martin G. Steven
Published: October 2006

Saccharomyces cerevisiae
was examined for tyrosine kinase activity in vitro because this organism offers molecular and genetic approaches for analyzing the role of tyrosine phosphorylation in cellular growth control that are unavailable in higher eukaryotes. Yeast extracts phosphorylated a random copolymer (glutamic acid:tyrosine, 80:20) at tyrosine in a reaction that was linear with respect to time and protein concentration. In the absence of added copolymer, phosphotyrosine was 0.1 percent of the total phosphoamino acids labeled with [γ-
32
P]adenosine triphosphate in endogenous yeast proteins. However, specific activities of these reactions were low (approximately 1 percent of those in extracts of chick embryo fibroblasts). Lack of significant incorporation of label from [α-
32
P]adenosine triphosphate into the copolymer or endogenous yeast proteins demonstrated that nucleotide interconversion, adenylylation, and subsequent hydrolysis could not account for the generation of phosphotyrosine observed.
Capillary Electrophoresis
Authors: Gordon Manuel J. , Huang Xiaohua , Pentoney Stephen L. , Zare Richard N.
Published: October 2006

Electrophoretic separations carried out in capillary tubes offer the possibilities of rapid and automated analyses of small volumes of complex mixtures with unprecedented resolution and sensitivity. Some emerging developments of this new instrumentation are reviewed.
Rapid Growth of Magnesium-Carbonate Weathering Products in a Stony Meteorite from Antarctica
Authors: Jull A. J. T. , Cheng S. , Gooding J. L. , Velbel M. A.
Published: October 2006

Nesquehonite, a hydrous magnesium carbonate, occurs as a weathering product on the surface of the Antarctic meteorite LEW 85320 (H5 chondrite). Antarctic meteorites have resided on the earth for periods of 10
4
to 10
6
years, but the time needed for weathering products to form has been uncertain. Isotopic measurements of δ
13
C and δ
18
O indicate that the nesquehonite formed at near freezing temperatures by reaction of meteoritic minerals with terrestrial water and carbon dioxide. Results from carbon-14 dating suggest that, although the meteorite has been in Antarctica for at least 3.2 × 10
4
to 3.3 × 10
4
years, the nesquehonite formed after A.D. 1950.
Space, Stars, C
60
, and Soot
Authors: Kroto Harold
Published: October 2006

Although carbon has been subjected to far more study than all other elements put together, the buckminsterfullerene hollow-cage structure, recently proposed to account for the exceptional stability of the C
60
cluster, has shed a totally new and revealing light on several important aspects of carbon's chemical and physical properties that were quite unsuspected and others that were not previously well understood. Most significant is the discovery that C
60
appears to form spontaneously, and this has particularly important implications for particle formation in combustion and in space as well as for the chemistry of polyaromatic compounds. The intriguing revelation that 12 pentagonal "defects" convert a planar hexagonal array of any size into a quasi-icosahedral cage explains why some intrinsically planar materials form quasi-crystalline particles, as appears to occur in the case of soot. Although the novel structural proposal has still to be unequivocally confirmed, this article pays particular attention to the way in which it provides convincing explanations of puzzling observations in several fields, so lending credence to the structure proposed for C
60
.
A 250,000-Year Climatic Record from Great Basin Vein Calcite: Implications for Milankovitch Theory
Authors: Winograd Isaac J. , Coplen Tyler B. , Szabo Barney J. , Riggs Alan C.
Published: October 2006

A continuous record of oxygen-18 (δ
18
O) variations in the continental hydrosphere during the middle-to-late Pleistocene has been obtained from a uranium-series dated calcitic vein in the southern Great Basin. The vein was deposited from ground water that moved through Devils Hole—an open fault zone at Ash Meadows, Nevada—between 50 and 310 ka (thousand years ago). The configuration of the δ
18
O versus time curve closely resembles the marine and Antarctic ice core (Vostok) δ
18
O curves; however, the U-Th dates indicate that the last interglacial stage (marine oxygen isotope stage 5) began before 147 ± 3 ka, at least 17,000 years earlier than indicated by the marine δ
18
O record and 7,000 years earlier than indicated by the less well dated Antarctic δ
18
O record. This discrepancy and other differences in the timing of key climatic events suggest that the indirectly dated marine δ
18
O chronology may need revision and that orbital forcing may not be the principal cause of the Pleistocene ice ages.
The Origin of the Superstructure in Bi
2
Sr
2
CaCu
2
O
8+δ
as Revealed by Scanning Tunneling Microscopy
Authors: Kirk M. D. , Nogami J. , Baski A. A. , Mitzi D. B. , Kapitulnik A. , Geballe T. H. , Quate C. F.
Published: October 2006

Real-space images with atomic resolution of the BiO plane of Bi
2
Sr
2
CaCu
2
O
8+δ
were obtained with a scanning tunneling microscope. Single-crystal samples were cleaved and imaged under ultrahigh vacuum conditions at room temperature. The images clearly show the one-dimensional incommensurate superstructure along the
b
-axis that is common to this phase. High-resolution images show the position of the Bi atoms, revealing the structural nature of the superlattice. A missing row of Bi atoms occurs either every nine or ten atomic sites in both 〈110〉 directions, accounting for the measured incommensurate periodicity of the superstructure. A model is proposed that includes missing rows of atoms, as well as displacements of the atomic positions along both the
a
- and
c
-axis directions.
Potential Metal-Binding Domains in Nucleic Acid Binding Proteins
Authors: Berg Jeremy M.
Published: October 2006

A systematic search for sequences that potentially could form metal-binding domains in proteins has been performed. Five classes of proteins involved in nucleic acid binding or gene regulation were found to contain such sequences. These observations suggest numerous experiments aimed at determining whether metal-binding domains are present in these proteins and, if present, what roles such domains play in the processes of nucleic acid binding and gene regulation.
Molecular Genetic Relationships of the Extinct Dusky Seaside Sparrow
Authors: Avise John C. , Nelson William S.
Published: October 2006

Mitochondrial DNA from the extinct dusky seaside sparrow (
Ammodramus maritimus nigrescens
) was compared in terms of nucleotide sequence divergence to mitochondrial DNAs from extant populations of seaside sparrows. Analyses of restriction sites revealed a close phylogenetic affinity of
A. m. nigrescens
to other sparrow populations along the Atlantic coast of the United States but considerable genetic distance from Gulf coast birds. Concerns and applied management strategies for the seaside sparrow have been based on a morphological taxonomy that does not adequately reflect evolutionary relationships within the complex.
Urban Air Pollution: State of the Science
Authors: Seinfeld John H.
Published: October 2006

Urban air pollution is comprised of a highly complex mixture of gaseous and particulate components. Much progress has been made in our understanding of the detailed chemistry and physics of air pollution, but important areas of uncertainty still remain.
Uranium-Series Dated Authigenic Carbonates and Acheulian Sites in Southern Egypt
Authors: Szabo B. J. , McHugh W. P. , Schaber G. G. , Haynes C. V. , Breed C. S.
Published: October 2006

Field investigations in southern Egypt have yielded Acheulian artifacts in situ in authigenic carbonate deposits (CaCO3-cemented alluvium) along the edges of now-aggraded paleovalleys (Wadi Arid and Wadi Safsaf). Uranium-series dating of 25 carbonate samples from various localities as far apart as 70 kilometers indicates that widespread carbonate deposition occurred about 45, 141 and 212 ka (thousand years ago). Most of the carbonate appears to have been precipitated from groundwater, which suggests that these three episodes of deposition may be related to late Pleistocene humid climates that facilitated human settlement in this now hyperarid region. Carbonate cements from sediments containing Acheulian artifacts provide a minimum age of 212 ka for early occupation of the paleovalleys.
Time and Spatial Dependence of the Concentration of Less Than 10
5
Microelectrode-Generated Molecules
Authors: Licht Stuart , Cammarata Vince , Wrighton Mark S.
Published: October 2006

The time and spatial dependence of the concentration of as few as 40,000 electrogenerated, redox-active molecules has been determined. The distance between generator and detector microelectrodes in an array used in the study could be varied from 0.8 to 28 micrometers. Measurements of a sufficiently small ensemble of molecules allowed the experimental results to be compared with a quantitative simulation of the random movement of each member of the ensemble. The transit time of an electrogenerated species from the generator to a collector microelectrode was measured as a function of viscosity, diffusivity, and distance.
Heat Flow and Hydrothermal Circulation in the Cascade Range, North-Central Oregon
Authors: Ingebritsen S. E. , Sherrod D. R. , Mariner R. H.
Published: October 2006

In north-central Oregon a large area of near-zero near-surface conductive heat flow occurs in young volcanic rocks of the Cascade Range. Recent advective heat flux measurements and a heat-budget analysis suggest that ground-water circulation sweeps sufficient heat out of areas where rocks younger than 6 Ma (million years ago) are exposed to account for the anomalously high advective and conductive heat discharge measured in older rocks at lower elevations. Earlier workers have proposed that an extensive midcrustal magmatic heat source is responsible for this anomalously high heat flow. Instead, high heat flow in the older rocks may be a relatively shallow phenomenon caused by regional ground-water flow. Any deeper anomaly may be relatively narrow, spatially variable, and essentially confined to the Quaternary (less than 2 Ma) arc. Magmatic intrusion at a rate of 9 to 33 cubic kilometers per kilometer of arc length per million years can account for the total heat flow anomaly. Deep drilling in the areas of high heat flow in the older rocks could indicate which model is more appropriate for the near-surface heat flow data.
Identification of an Allatotropin from Adult
Manduca Sexta
Authors: Kataoka Hiroshi , Toschi Anne , Li Jorge P. , Carney Robert L. , Schooley David A. , Kramer Steven J.
Published: October 2006

A peptide that strongly stimulates the secretion of juvenile hormone from corpora allata in vitro (allatotropin) has been purified from extracts of heads of pharate adult
Manduca sexta
. The primary structure of this 13-residue peptide has been determined: H-Gly-Phe-Lys-Asn-Val-Glu-Met-Met-Thr-Ala-Arg-Gly-Phe-NH
2
. This neurohormone has no sequence similarity with any known neuropeptide from other organisms. Synthetic allatotropin, as well as truncation fragments, including one with the five amino terminal residues deleted, showed in vitro activity indistinguishable from that of native allatotropin.
Efficient Trans-Splicing of a Yeast Mitochondrial RNA Group II Intron Implicates a Strong 5′ Exon-Intron Interaction
Authors: Jacquier Alain , Rosbash Michaek
Published: October 2006

The reaction mechanism for self-splicing introns requires the existence of a 5′ exon binding site on the intron. Experimental evidence is now presented consistent with the existence of such a binding site by demonstrating efficient and accurate trans-self-splicing of a yeast mitochondrial group II intron. Partial and complete trans-splicing reactions take place in the absence of branch formation, part of the usual pathway of nuclear splicing and group II self-splicing. In addition to indicating the existence of a 5′ exon binding site on the intron, the results have mechanistic implications for group II self-splicing and perhaps for nuclear splicing as well.
Macrophage Cytotoxicity: Role for L-Arginine Deiminase and Imino Nitrogen Oxidation to Nitrite
Authors: Hibbs John B. , Taintor Read R. , Vavrin Zdenek
Published: October 2006

Previous studies have shown that cytotoxic activated macrophages cause inhibition of DNA synthesis, of mitochondrial respiration, and of aconitase activity in tumor target cells. An L-arginine-dependent biochemical pathway synthesizing L-citrulline and nitrite, coupled to an effector mechanism, is now shown to cause this pattern of metabolic inhibition. Murine cytotoxic activated macrophages synthesize L-citrulline and nitrite in the presence of L-arginine but not D-arginine. L-Citrulline and nitrite biosynthesis by cytotoxic activated macrophages is inhibited by
N
G
-monomethyl-L-arginine, which also inhibits this cytotoxic effector mechanism. This activated macrophage cytotoxic effector system is associated with L-arginine deiminase activity, and the imino nitrogen removed from the guanido group of L-arginine by the deiminase reaction subsequently undergoes oxidation to nitrite. L-Homoarginine, an alternative substrate for this deiminase, is converted to L-homocitrulline with concurrent nitrite synthesis and similar biologic effects.
RNA Complementary to a Herpesvirus α Gene mRNA Is Prominent in Latently Infected Neurons
Authors: Stevens J. G. , Wagner E. K. , Devi-Rao G. B. , Cook M. L. , Feldman L. T.
Published: October 2006

In initial attempts to define the molecular events responsible for the latent state of herpes simplex virus, in situ hybridization was utilized to search for virally encoded RNA transcripts in latently infected sensory neurons. The use of cloned probes representing the entire viral genome indicated that transcripts encoded within terminal repeats were present. When the α genes encoding ICP-0, ICP-4, and ICP-27 and the γ
1
gene encoding VP-5 were employed, only RNA transcripts hybridizing to the ICP-0 probe were detected. In latently infected cells, the ICP-0—related transcripts were localized principally in the nucleus; this was not the case in acutely (productively) infected neurons or in neurons probed for RNA transcripts coding for actin. In Northern blotting experiments, an RNA of 2.6 kilobases was detected with the ICP-0 probe. When single-stranded DNAs from the ICP-0 region were used as probes, RNA from the strand complementary to that encoding ICP-0 messenger RNA (mRNA) was the major species detected. This RNA species may play a significant role in maintaining the latent infection.
Mitogens and Oncogenes Can Block the Induction of Specific Voltage-Gated Ion Channels
Authors: Caffrey John M. , Brown Arthur M. , Schneider Michael D.
Published: October 2006

The mechanisms underlying the ontogeny of voltage-gated ion channels in muscle are unknown. Whether expression of voltage-gated channels is dependent on mitogen withdrawal and growth arrest, as is generally true for the induction of muscle-specific gene products, was investigated in the BC
3
H1 muscle cell line by patch-clamp techniques. Differentiated BC
3
H1 myocytes expressed functional Ca2
+
and Na
+
channels that corresponded to those found in T tubules of skeletal muscle. However, Ca2
+
and Na
+
channels were first detected after about 5 days of mitogen withdrawal. In order to test whether cellular oncogenes, as surrogates for exogenous growth factors, could prevent the expression of ion channels whose induction was contingent on mitogen withdrawal, BC
3
H1 cells were modified by stable transfection with oncogene expression vectors. Expression vectors containing v-
erb
B, or c-
myc
under the control of the SV40 promoter, delayed but did not prevent the appearance of functional Ca2
+
and Na
+
channels. In contrast, transfection with a Val
12
c-H-
ras
vector, or cotransfection of c-
myc
together with v-
erb
B, suppressed the formation of functional Ca2
+
and Na
+
channels for ≥4 weeks. Potassium channels were affected neither by mitogenic medium nor by transfected oncogenes. Thus, the selective effects of certain oncogenes on ion channel induction corresponded to the suppressive effects of mitogenic medium.
Mimicking Photosynthesis
Authors: Gust Devens , Moore Thomas A.
Published: October 2006

Although the concept of an artificial photosynthetic reaction center that mimics natural electron- and energy-transfer processes is an old one, in recent years major advances have occurred. In this review, some relatively simple molecular dyads that mimic certain aspects of photosynthetic electron transfer and singlet or triplet energy transfer are described. Dyads of this type have proven to be extremely useful for elucidating basic photochemical principles. In addition, their limitations, particularly in the area of temporal stabilization of electronic charge separation, have inspired the development of much more complex multicomponent molecular devices. The use of the basic principles of photoinitiated electron transfer to engineer desirable properties into the more complex species is exemplified. The multiple electrontransfer pathways available with these molecules make it possible to fine-tune the systems in ways that are impossible with simpler molecules. The study of these devices not only contributes to our understanding of natural photosynthesis, but also aids in the design of artificial solar energy harvesting systems and provides an entry into the nascent field of molecular electronics.
Photovoltaics Today and Tomorrow
Authors: Hubbard H. M.
Published: October 2006

In the next several decades it is expected that the United States and the rest of the nations of the world will greatly expand their consumption of electricity. But many questions will accompany this expansion: Can we build enough generating capacity? Do we have enough energy resources? Can we accommodate centralized and dispersed needs, large and small applications, and the diverse requirements of all sections of the world? And can we increase consumption without increasing environmental degradation? Photovoltaics, which by means of solid-state technology turn photon energy into electricity, can make a substantial contribution toward fulfilling these energy needs. Historically, the drawbacks to photovoltaics have been cost and technological maturity. But more than a decade of research has greatly advanced the technology and has brought it to the point of entering large electricity markets. Advances in the next two decades should make it possible for photovoltaics to become one of the world's preferred technologies for generating electrical energy.
Model Simulation of the Cretaceous Ocean Circulation
Authors: Barron Eric J. , Peterson William H.
Published: October 2006

Three-dimensional numerical ocean circulation model experiments that were designed to evaluate the circulation characteristics for the mid-Cretaceous (∼100 million years ago) show that the primary direction of flow through the Tethys Ocean was eastward; in contrast, a westward flowing circumglobal Tethys current has been a consistent feature of earlier reconstructions of Cretaceous ocean circulation. The model studies demonstrate that (i) ocean circulation is sufficiently sensitive to the role of continental positions, sea level, and climate to limit the application of modern analogs to past circulations, and (ii) reconstructions based on limited biogeographic data may not provide unique surface circulation patterns.