bluuebunny/crossref_metadata_2025 huggingface dataset:
One Enzyme Makes a Fungal Pathogen, But Not a Saprophyte, Virulent on a New Host Plant
Authors: Schäfer W. , Straney D. , Ciuffetti L. , Van Etten H. D. , Yoder O. C.
Published: October 2006

Certain genes of
Nectria haematococca
, a fungal pathogen of pea (
Pisum sativum
), encode pisatin demethylase (pda), a cytochrome P-450 monoxygenase that detoxifies the phytoalexin pisatin. Because pda is required by
N. haematococca
for pathogenicity on pea, pisatin helps defend pea against
N. haematococca
. The possibility that pisatin is a general defense factor—that is, that pda can confer pathogenicity to fungi not normally pathogenic on pea—was investigated. Genes encoding pda were transformed into and highly expressed in
Cochliobolus heterostrophus
, a fungal pathogen of maize but not of pea, and in
Aspergillus nidulans
, a saprophytic fungus, neither of which produces a significant amount of pda. Transformants contained at least as much pda as did wild-type
N. haematococca
. Recombinant
C. heterostrophus
was normally virulent on maize, but it also caused symptoms on pea, whereas recombinant
A. nidulans
did not affect pea. Thus, phytoalexins can function in nonspecific resistance of plants to microbes; saprophytes appear to lack genes for basic pathogenicity.
Prediction and Theory Evaluation: The Case of Light Bending
Authors: Brush Stephen G.
Published: October 2006

Is a theory that makes successful predictions of new facts better than one that does not? Does a fact provide better evidence for a theory if it was not known before being deduced from the theory? These questions can be answered by analyzing historical cases. Einstein's successful prediction of gravitational light bending from his general theory of relativity has been presented as an important example of how "real" science works (in contrast to alleged pseudosciences like psychoanalysis). But, while this success gained favorable publicity for the theory, most scientists did not give it any more weight than the deduction of the advance of Mercury's perihelion (a phenomenon known for several decades). The fact that scientists often use the word "prediction" to describe the deduction of such previously known facts suggests that novelty may be of little importance in evaluating theories. It may even detract from the evidential value of a fact, until it is clear that competing theories cannot account for the new fact.
The Voyager 2 Encounter with the Neptunian System
Authors: Stone E. C. , Miner E. D.
Published: October 2006

An overview of the Voyager 2 encounter with Neptune is presented, including a brief discussion of the trajectory, the planned observations, and highlights of the results described in the 11 companion papers. Neptune's blue atmosphere has storm systems reminiscent of those in Jupiter's atmosphere. An optically thin methane ice cloud exists near the 1.5-bar pressure level, and an optically thick cloud exists below 3 bars. Neptune's magnetic field is highly tilted and offset from the planet's center; it rotates with a period of 16.11 hours. Two narrow and two broad rings circle the planet; the outermost of these rings has three optically thicker arc segments. Six new moons were discovered in circular prograde orbits, all well inside Triton's retrograde orbit. Triton has a highly reflective and geologically young surface, a thin nitrogen atmosphere, and at least two active geyser-like plumes.
Growth of Greenland Ice Sheet: Interpretation
Authors: Zwally H. Jay
Published: October 2006

An observed 0.23 m/year thickening of the Greenland ice sheet indicates a 25% to 45% excess ice accumulation over the amount required to balance the outward ice flow. The implied global sea-level depletion is 0.2 to 0.4 mm/year, depending on whether the thickening is only recent (5 to 10 years) or longer term (< 100 years). If there is a similar imbalance in the northern 60% of the ice-sheet area, the depletion is 0.35 to 0.7 mm/year. Increasing ice thickness suggests that the precipitation is higher than the long-term average; higher precipitation may be a characteristic of warmer climates in polar regions.
Reverse Transcriptase in a Clinical Strain of
Escherichia coli
: Production of Branched RNA-Linked msDNA
Authors: Lampson Bert C. , Sun Jing , Hsu Mei-Yin , Vallejo-Ramirez Jorge , Inouye Sumiko , Inouye Masayori
Published: October 2006

Branched RNA-linked multicopy single-stranded DNA (msDNA) originally detected in myxobacteria has now been found in a clinical isolate of
Escherichia coli
. Although lacking homology in the primary structure, the
E. coli
msDNA is similar in secondary structure to the myxobacterial msDNA's, including the 2′,5′-phosphodiester linkage between RNA and DNA. A chromosomal DNA fragment responsible for the production of msDNA was cloned in an
E. coli
K12 strain; its DNA sequence revealed an open reading frame (ORF) of 586 amino acid residues. The ORF shows sequence similarity with retroviral reverse transcriptases and ribonuclease H. Disruption of the ORF blocked msDNA production, indicating that this gene is essential for msDNA synthesis.
Phylogenetic Stains: Ribosomal RNA-Based Probes for the Identification of Single Cells
Authors: DeLong Edward F. , Wickham Gene S. , Pace Norman R.
Published: October 2006

Rapid phylogenetic identification of single microbial cells was achieved with a new staining method. Formaldehyde-fixed, intact cells were hybridized with fluorescently labeled oligodeoxynucleotides complementary to 16
S
ribosomal RNA (rRNA) and viewed by fluorescence microscopy. Because of the abundance of rRNA in cells, the binding of the fluorescent probes to individual cells is readily visualized. Phylogenetic identification is achieved by the use of oligonucleotides (length 17 to 34 nucleotides) that are complementary to phylogenetic group-specific 16
S
rRNA sequences. Appropriate probes can be composed of oligonucleotide sequences that distinguish between the primary kingdoms (eukaryotes, eubacteria, archaebacteria) and between closely related organisms. The simultaneous use of multiple probes, labeled with different fluorescent dyes, allows the identification of different cell types in the same microscopic field. Quantitative microfluorimetry shows that the amount of an rRNA-specific probe that binds to
Escherichia coli
varies with the ribosome content and therefore reflects growth rate.
Ozone Control and Methanol Fuel Use
Authors: Russell A. G. , St. Pierre D. , Milford J. B.
Published: October 2006

Methanol fuel use in motor vehicles and stationary combustion has the potential to improve air quality. A modeling study of methanol fuel use in Los Angeles, California, shows that the low chemical reactivity of methanol vapor slows ozone formation and would lead to lower ozone concentrations. Predicted peak ozone levels decreased up to 16 percent, and exposure to levels above the federal standard dropped by up to 22 percent, when pure (M100) methanol fuel use was simulated for the year 2000. Similar results were obtained for 2010. Use of a gasoline-methanol blend (M85) resulted in smaller reductions. Predicted formaldehyde levels and exposure were not increased severely, and in some cases declined, in the simulations of methanol use.
Molecular Dynamics in Ordered Structures: Computer Simulation and Experimental Results for Nylon 66 Crystals
Authors: Wendoloski J. J. , Gardner K. H. , Hirschinger J. , Miura H. , English A. D.
Published: October 2006

A detailed comparison between molecular dynamics computer simulations and the experimental characterization of molecular motion through deuterium nuclear magnetic resonance (NMR) spectroscopic methods has been carried out for the crystalline phase of nylon 66 (polyhexamethyleneadipamide) at room temperature and just below the melting point. The computer simulations agree quantitatively with the experimental results at room temperature and qualitatively near the crystalline melting point. Both methods demonstrate that individual methylene groups within the crystals exhibit librational motion, which becomes very large in amplitude near the melting point, rather than undergoing discrete conformational jumps; furthermore, the hydrogen-bonded amides are relatively immobile at all temperatures below 230 degrees Celsius. The simulations are shown to be particularly useful for examining the cooperativity of motion and for providing insight into structural-dynamical correlations. These aspects of the simulations are exemplified by the observation of concerted counterrotation of odd-numbered bonds within the methylene segments and the entropic stabilization of the crystal structure.
Electrodeposited Ceramic Superlattices
Authors: Switzer Jay A. , Shane Michael J. , Phillips Richard J.
Published: October 2006

Ceramic superlattices have been produced by electrodeposition with modulation wavelengths in the range from 5 to 10 nanometers. The Tl
a
Pb
b
O
c
/Tl
d
Pb
e
O
f
superlattices were deposited from a single aqueous solution at room temperature, and the layer thicknesses were galvanostatically controlled. The films showed strong preferred orientation and distinct first-order satellites around the Bragg reflections in the x-ray diffraction pattern. The modulation wavelengths calculated from the satellite spacings were in agreement with those calculated from Faraday's law. Because the modulation wavelengths are of electron mean free path dimensions, this class of degenerate semiconductor metal-oxide superlattices may exhibit thickness-dependent quantum optical, electronic, or optoelectronic effects.
Quantum Confinement and Host/Guest Chemistry: Probing a New Dimension
Authors: Stucky Galen D. , Mac Dougall James E.
Published: October 2006

Nanoparticulate metals and semiconductors that have atomic arrangements at the interface of molecular clusters and "infinite" solid-state arrays of atoms have distinctive properties determined by the extent of confinement of highly delocalized valence electrons. At this interface, the total number of atoms and the geometrical disposition of each atom can be used to significantly modify the electronic and photonic response of the medium. In addition to the novel inherent physical properties of the quantum-confined moieties, their "packaging" into nanocomposite bulk materials can be used to define the confinement surface states and environment, intercluster interactions, the quantum-confinement geometry, and the effective charge-carrier density of the bulk. Current approaches for generating nanostructures of conducting materials are briefly reviewed, especially the use of three-dimensional crystalline superlattices as hosts for quantum-confined semiconductor atom arrays (such as quantum wires and dots) with controlled inter-quantum-structure tunneling.
Double Fertilization in
Ephedra,
a Nonflowering Seed Plant: Its Bearing on the Origin of Angiosperms
Authors: Friedman William E.
Published: October 2006

Double fertilization and the associated formation of endosperm have long been considered unique and defining characters (autapomorphies) of the angiosperms. During normal fertilization in
Ephedra nevadensis,
a nonflowering seed plant, fusion of a second sperm nucleus with the ventral canal nucleus occurs regularly within the egg cytoplasm. The occurrence of double fertilization in
Ephedra
assumes added significance in light of its critical phylogenetic position as a basal member of the most closely related extant group of seed plants (Gnetales) to angiosperms. Thus, double fertilization in angiosperms and
Ephedra
may represent an evolutionary homology.
Fractional Statistics: Quantum Possibilities in Two Dimensions
Authors: Canright G. S. , Girvin S. M.
Published: October 2006

A standard notion of quantum mechanics is that all particles, elementary or composite, must fall into one of two fundamental categories: fermions or bosons. However, it has recently been discovered that there can be quantum particles which are neither fermions nor bosons. Such particles (anyons) can only occur in two spatial dimensions—yet this does not rule out their existence, for they are found as elementary excitations in confined, quasi—two-dimensional condensed-matter systems and may occur in other systems as well. An overview of the argument for the existence of anyons is presented, along with a discussion of their role in condensed-matter physics.
Femtosecond Pulse Sequences Used for Optical Manipulation of Molecular Motion
Authors: Weiner A. M. , Leaird D. E. , Wiederrecht Gary P. , Nelson Keith A.
Published: October 2006

Optical control over elementary molecular motion is enhanced with timed sequences of femtosecond (10
-15
second) pulses produced by pulse-shaping techniques. Appropriately timed pulse sequences are used to repetitively drive selected vibrations of a crystal lattice, in a manner analogous to repetitively pushing a child on a swing with appropriate timing to build up a large oscillation amplitude. This process corresponds to repetitively "pushing" molecules along selected paths in the lattice. Amplification of selected vibrational modes and discrimination against other modes are demonstrated. Prospects for more extensive manipulation of molecular and collective behavior and structure are clearly indicated.
Observational Contrains on the Global Atmospheric Co
2
Budget
Authors: Tans Pieter P. , Fung Inez Y. , Takahashi Taro
Published: October 2006

Observed atmospheric concentrations of CO
2
and data on the partial pressures of CO
2
in surface ocean waters are combined to identify globally significant sources and sinks of CO
2
. The atmospheric data are compared with boundary layer concentrations calculated with the transport fields generated by a general circulation model (GCM) for specified source-sink distributions. In the model the observed north-south atmospheric concentration gradient can be maintained only if sinks for CO
2
are greater in the Northern than in the Southern Hemisphere. The observed differences between the partial pressure of CO
2
in the surface waters of the Northern Hemisphere and the atmosphere are too small for the oceans to be the major sink of fossil fuel CO
2
. Therefore, a large amount of the CO
2
is apparently absorbed on the continents by terrestrial ecosystems.
Intragranular Diffusion: An Important Mechanism Influencing Solute Transport in Clastic Aquifers?
Authors: Wood Warren W. , Kraemer Thomas F. , Hearn Paul P.
Published: October 2006

Quantification of intragranular porosity in sand-size material from an aquifer on Cape Cod, Massachusetts, by scanning electron microscopy, mercury injection, and epifluorescence techniques shows that there are more reaction sites and that porosity is greater than indicated by standard short-term laboratory tests and measurement techniques. Results from laboratory and field tracer tests show solute nonequilibrium for a reacting ion consistent with a model of diffusion into, and exchange within, grain interiors. These data indicate that a diffusion expression needs to be included in transport codes, particularly for simulation of the transport of radioactive and toxic wastes.
Cl
-
Channels in CF: Lack of Activation by Protein Kinase C and cAMP-Dependent Protein Kinase
Authors: Hwang Tzyh-Chang , Lu Luo , Zeitlin Pamela L. , Gruenert Dieter C. , Huganir Richard , Guggino William B.
Published: October 2006

Secretory chloride channels can be activated by adenosine 3′,5′-monophosphate (cAMP)-dependent protein kinase in normal airway epithelial cells but not in cells from individuals with cystic fibrosis (CF). In excised, inside-out patches of apical membrane of normal human airway cells and airway cells from three patients with CF, the chloride channels exhibited a characteristic outwardly rectifying current-voltage relation and depolarization-induced activation. Channels from normal tissues were activated by both cAMP-dependent protein kinase and protein kinase C. However, chloride channels from CF patients could not be activated by either kinase. Thus, gating of normal epithelial chloride channels is regulated by both cAMP-dependent protein kinase and protein kinase C, and regulation by both kinases is defective in CF.
Mutant Potassium Channels with Altered Binding of Charybdotoxin, a Pore-Blocking Peptide Inhibitor
Authors: MacKinnon Roderick , Miller Christopher
Published: October 2006

The inhibition by charybdotoxin of A-type potassium channels expressed in
Xenopus
oocytes was studied for several splicing variants of the
Drosophila
Shaker
gene and for several site-directed mutants of this channel. Charybdotoxin blocking affinity is lowered by a factor of 3.5 upon replacing glutamate-422 with glutamine, and by a factor of about 12 upon substituting lysine in this position. Replacement of glutamate-422 by aspartate had no effect on toxin affinity. Thus, the glutamate residue at position 422 of this potassium channel is near or in the externally facing mouth of the potassium conduction pathway, and the positively charged toxin is electrostatically focused toward its blocking site by the negative potential set up by glutamate-422.
Multiple Mutations in HIV-1 Reverse Transcriptase Confer High-Level Resistance to Zidovudine (AZT)
Authors: Larder Brendan A. , Kemp Sharon D.
Published: October 2006

Human immunodeficiency virus (HIV) isolates with reduced sensitivity to zidovudine (3′-azido-3′-deoxythymidine, AZT) from individuals with acquired immunodeficiency syndrome (AIDS) or AIDS-related complex were studied to determine the genetic basis of their resistance. Most were sequential isolates obtained at the initiation of and during therapy. Comparative nucleotide sequence analysis of the reverse transcriptase (RT) coding region from five pairs of sensitive and resistant isolates identified three predicted amino acid substitutions common to all the resistant strains (Asp
67
→ Asn, Lys
70
→ Arg, Thr
215
→ Phe or Tyr) plus a fourth in three isolates (Lys
219
→ Gln). Partially resistant isolates had combinations of these four changes. An infectious molecular clone constructed with these four mutations in RT yielded highly resistant HIV after transfection of T cells. The reproducible nature of these mutations should make it possible to develop rapid assays to predict zidovudine resistance by performing polymerase chain reaction amplification of nucleic acid from peripheral blood lymphocytes, thereby circumventing current lengthy HIV isolation and sensitivity testing.
Code of Ant-Plant Mutualism Broken by Parasite
Authors: Letourneau Deborah K.
Published: October 2006

Newly discovered
Phyllobaenus
beetles are parasites of a mutualism.
Piper
ant-plants in tropical forests provide lipid and protein-rich food cells and shelter for
Pheidle bicornis
ants while the ants remove small herbivores and vines from the foliage. In contrast to all other ant-plants,
Piper
ant-plants produce food bodies only when
Pheidole bicornis
is present in the plant. However,
Phyllobaenus
beetles can stimulate the plants to produce food bodies as if ants were present. The beetles then inhabit the plant, exploiting nest sites and food produced by the plants for ants. These beetles may also prey on ant brood, depriving the plants of resources and services provided by the ants.
The Underclass: Definition and Measurement
Authors: Mincy Ronald B. , Sawhill Isabel V. , Wolf Douglas A.
Published: October 2006

The term "underclass" has been widely used by journalists and by some social scientists but, until recently, has not been clearly defined or quantified. Most of the recent quantitatively oriented literature on the topic has used a definition that emphasizes either the persistence of poverty or the number of people living in neighborhoods where the incidence of poverty or dysfunctional behavior is high. Conclusions about the size and growth of the underclass are sensitive to the definition chosen, but most available evidence suggests that it is small but growing.
Identification of the Products from the Reaction of Chlorine with the Silicon(111)-(7×7) Surface
Authors: Boland John J. , Villarrubia J. S.
Published: October 2006

The various products from the reaction of chlorine (Cl) with the adatom layer of the Si(111)-(7×7) surface have been identified with scanning tunneling microscopy (STM). Initially, a single Cl atom reacts with the adatom dangling bond. At higher surface coverage, additional Cl atoms insert themselves into the Si-Si backbonds between the adatom and rest-atom layers, producing adatoms that have reacted with two or three Cl atoms. These products are characterized by different registries with respect to the underlying rest layer and appear in STM images as adatoms of different sizes, consistent with the breaking of Si-Si backbonds and the formation of new Si-Cl bonds.
Coincidence Counting in Time-of-Flight Mass Spectrometry: A Test for Chemical Microhomogeneity
Authors: Park M. A. , Gibson K. A. , Quinones K. , Schweikert M. A.
Published: October 2006

Coincidence counting techniques have been combined with time-of-flight mass spectrometry in the examination of surfaces for chemical microhomogeneity. A mathematical formalism was developed to describe the principles underlying this coincidence counting technique and was used to produce a quantitative method for handling the data obtained. This technique of testing for chemical homogeneity has been demonstrated with a sample that consists of a physical mixture of polystyrene and crystals of NaF which were tenths of micrometers in diameter. Ultimately this approach is expected to be useful for the routine testing of surfaces for chemical homogeneity at the level of tens of nanometers.
Enhancement of Symbioses Between Butterfly Caterpillars and Ants by Vibrational Communication
Authors: DeVries P. J.
Published: October 2006

Butterfly caterpillars produce calls that appear to play a role in maintaining symbiotic associations with ants. A survey of butterfly species from South and Central America, North America, Europe, Thailand, and Australia suggests that the ability for caterpillars to call has evolved independently at least three times, and that calling may be ubiquitous among ant-associated species. Because ants use substrate-borne sound in their communication systems, this study points to the possibility that the calls of one insect species have evolved to attract other, unrelated species.
The Energetic Cost of Limbless Locomotion
Authors: Walton Michael , Jayne Bruce C. , Bennet Albert F.
Published: October 2006

The net energetic cost of terrestrial locomotion by the snake
Coluber constrictor
, moving by lateral undulation, is equivalent to the net energetic cost of running by limbed animals (arthropods, lizards, birds, and mammals) of similar size. In contrast to lateral undulation and limbed locomotion, concertina locomotion by
Coluber
is more energetically expensive. The findings do not support the widely held notion that the energetic cost of terrestrial locomotion by limbless animals is less than that of limbed animals.
Ice: A New Dosage Form of an Old Drug
Authors: Cho Arthur K.
Published: October 2006

Ice, which has been described as the drug of the 1990s, is a pure form of (+)methamphetamine hydrochloride; it is more dangerous because of its purity and because it can be inhaled. Taken by this route, the drug causes an effect similar to that from an intravenous dose, and much more intense than that from ingestion. The detailed mechanism of action differs from that of cocaine, but the overall stimulant effect of methamphetamine is similar. Methamphetamine effects, however, persist for hours, whereas cocaine effects are over in minutes. Ice is, therefore, just another agent for abuse by those seeking psychostimulation and, as with cocaine, compulsive abusers of amphetamines consume the drug repeatedly and continuously. Unlike cocaine, methamphetamine is a synthetic compound and is manufactured in illicit laboratories within the United States.
Possible Early Pennsylvanian Ancestor of the Cycadales
Authors: Leary Richard L.
Published: October 2006

A specimen of
Lesleya
, previously known only as isolated sterile foliage, has been found with two rows of ovule-bearing receptacles on opposite sides of the petiole. This specimen is from the Lower Pennsylvanian (Namurian B or C) of western Illinois. The fertile portion of this specimen is similar to
Phasmatocycas kansana
Mamay from the Lower Permian of Kansas and Texas, which Mamay interpreted as an ancestral form to cycads.
Phasmatocycas
was found attached to the base of
Taeniopteris
by Gillespie and Pfefferkorn. The foliar portions,
Lesleya
and
Taeniopteris
, have many features in common; the major morphologic difference is curvature of the veins.
Lesleya
and its attached fertile petiole are proposed as ancestors of
Taeniopteris
and
Phasmatocycas
, and ultimately, the ancestors of modern cycads. This extends the age of known precursors of cycads back from the Early Permian to Early Pennsylvanian (about 320 million years ago), approximately 35 million years earlier.
Ubiquitous Expression of
sevenless
: Position-Dependent Specification of Cell Fate
Authors: Basler Konrad , Hafen Ernst
Published: October 2006

Specification of cell fate in the compound eye of
Drosophila
appears to be controlled entirely by cell interactions. The
sevenless
gene is required for the correct determination of one of the eight photoreceptor cells (R7) in each ommatidium. It encodes a transmembrane protein with a tyrosine kinase domain and is expressed transiently on a subpopulation of ommatidial precursor cells including the R7 precursors. It is shown here that heat shock-induced indiscriminate expression of a
sevenless
complementary DNA throughout development can correctly specify R7 cell identity without affecting the development of other cells. Furthermore, discontinuous supply of
sevenless
protein during eye development leads to the formation of mosaic eyes containing stripes of
sevenless
+
and
sevenless
-
ommatidia, suggesting that R7 cell fate can be specified only within a relatively short period during ommatidial assembly. These results support the hypothesis that the specification of cell fate by position depends on the interaction of a localized signal with a receptor present on many undifferentiated cells, and that the mere presence of the receptor alone is not sufficient to specify cell fate.
Parallel Association of Fos and Jun Leucine Zippers Juxtaposes DNA Binding Domains
Authors: Gentz Reiner , Rauscher Frank J. , Abate Cory , Curran Tom
Published: October 2006

The protein products of the
fos
and
jun
proto-oncogenes form a heterodimeric complex that participates in a stable high affinity interaction with DNA elements containing AP-1 binding sites. The effects of deletions and point mutations in Fos and Jun on protein complex formation and DNA binding have been examined. The data suggest that Fos and Jun dimerize via a parallel interaction of helical domains containing a heptad repeat of leucine residues (the leucine zipper). Dimerization is required for DNA binding and results in the appropriate juxtaposition of basic amino acid regions from Fos and Jun, both of which are required for association with DNA.
Photoacoustic "Signatures" of Particulate Matter: Optical Production of Acoustic Monopole Radiation
Authors: Diebold G. J. , Khan M. I. , Park S. M.
Published: October 2006

Absorption of pulsed laser radiation by a single particle generates a photoacoustic wave whose time profile can be measured with a wideband pressure transducer. Solution of the wave equation for pressure in one, two, and three dimensions shows that the photoacoustic wave is determined by the geometry and dimensions of the particle, and by its sound speed and density relative to the fluid that surrounds it. Photoacoustic waves, referred to here as signatures, are reported in experiments in which fluid droplets, cylinders, and layers are irradiated with 10-nanosecond laser pulses.
Hematite Nanospheres of Possible Colloidal Origin from a Precambrian Banded Iron Formation
Authors: Ahn Jung Ho , Buseck Peter R.
Published: October 2006

Exceptionally small spheres (nanospheres) of hematite (diameters between 120 and 200 nanometers) occur in the Marra Mamba Iron Formation of the Hamersley Basin, Australia. The nanospheres are clustered into small aggregates and may have formed by structural ordering and dehydration of colloidal iron hydroxide particles. Individual spheres consist of numerous thin, curved hematite platelets surrounding a central void that is approximately half the diameter of the sphere; this texture suggests that they formed by a volume reduction of the original colloidal particles by ∼12.5%. The occurrence of hematite nanospheres supports the hypothesis that some of the iron was deposited colloidally during the development of banded iron formations, approximately 2.5 billion years ago.
Surface and Airborne Evidence for Plumes and Winds on Triton
Authors: Hansen C. J. , McEwen A. S. , Ingersoll A. P. , Terrile R. J.
Published: October 2006

Aeolian features on Triton that were imaged during the Voyager Mission have been grouped. The term "aeolian feature" is broadly defined as features produced by or blown by the wind, including surface and airborne materials. Observations of the latitudinal distributions of the features probably associated with current activity (known plumes, crescent streaks, fixed terminator clouds, and limb haze with overshoot) all occur from latitude -37° to latitude -62°. Likely indicators of previous activity (dark surface streaks) occur from latitude -5° to -70°, but are most abundant from -15° to -45°, generally north of currently active features. Those indicators which give information on wind direction and speed have been measured. Wind direction is a function of altitude. The predominant direction of the surface wind streaks is found to be between 40° and 80° measured clockwise from north. The average orientation of streaks in the northeast quadrant is 59°. Winds at 1- to 3-kilometer altitude are eastward, while those at >8 kilometers blow west.
Triton's Plumes: The Dust Devil Hypothesis
Authors: Ingersoll Andrew P. , Tryka Kimberly A.
Published: October 2006

Triton's plumes are narrow columns 10 kilometers in height, with tails extending horizontally for distances over 100 kilometers. This structure suggests that the plumes are an atmospheric rather than a surface phenomenon. The closest terrestrial analogs may be dust devils, which are atmospheric vortices originating in the unstable layer close to the ground. Since Triton has such a low surface pressure, extremely unstable layers could develop during the day. Patches of unfrosted ground near the subsolar point could act as sites for dust devil formation because they heat up relative to the surrounding nitrogen frost. The resulting convection would warm the atmosphere to temperatures of 48 kelvin or higher, as observed by the Voyager radio science team. Assuming that velocity scales as the square root of temperature difference times the height of the mixed layer, a velocity of 20 meters per second is derived for the strongest dust devils on Triton. Winds of this speed could raise particles provided they are a factor of 10
3
to 10
4
less cohesive than those on Earth.
Pressure Dependence of Elastic Wave Velocity for β-Mg
2
SiO
4
and the Composition of the Earth's Mantle
Authors: Gwanmesia Gabriel D. , Rigden Sally , Jackson Ian , Liebermann Robert C.
Published: October 2006

The pressure dependence of the elastic wave velocities for hot-pressed, elastically isotropic polycrystals of the β (modified spinel) phase of magnesium orthosilicate (Mg
2
SiO
4
) has been determined at room temperature to 3 gigapascals (GPa) by ultrasonic pulse interferometry. Pressure derivatives of the bulk (
dK/dP
= 4.8) and shear (
dG/dP
= 1.7) moduli derived from the travel times of the compressional (P) and shear (S) waves clearly demonstrate that the velocity contrast between the olivine and β phases of Mg
2
SiO
4
decreases with increasing pressure. When combined with plausible values for the (as yet unmeasured) temperature derivatives, these new data can be used to calculate the contrast in P and S wave velocities across an olivine-β phase transformation occurring at pressure-temperature conditions corresponding to about 400 kilometers depth in the earth. The seismologically observed contrasts Δ
V
in both P and S wave velocities constrain the percentage of orthosilicate in a model mantle of uniform chemical composition for appropriate relative magnitudes of the temperature (
T
) derivatives of the bulk and shear moduli for the β phase. Allowed combinations of orthosilicate content (percent),
dK/dT
, and
dG/dT
(both in gigapascals per Kelvin) for a pair of recent seismological models with Δ
V
p
= Δ
V
s
= 4.6% include (65, -0.018, -0.020), (55, -0.015, -0.018), and (45, -0.012, -0.016).
Fabrication and Use of Nanometer-Sized Electrodes in Electrochemistry
Authors: Penner Reginald M. , Heben Michael J. , Longin Teresa L. , Lewis Nathan S.
Published: October 2006

Electrodes with electrochemical dimensions as small as 10 angstroms have been fabricated and used for electrochemical studies. These nanometer-scale electrodes have enabled the measurement of electron-transfer rate constants,
k
het
, that are two orders of magnitude faster than
k
het
values accessible with any other electrochemical method.
El Niño-Southern Oscillation Displacements of the Western Equatorial Pacific Warm Pool
Authors: McPhaden M. J. , Picaut J.
Published: October 2006

The western equatorial Pacific warm pool (sea-surface temperatures >29°C) was observed to migrate eastward across the date line during the 1986-1987 El Niño-Southern Oscillation event. Direct velocity measurements made in the upper ocean from 1986 to 1988 indicate that this migration was associated with a prolonged reversal in the South Equatorial Current forced by a large-scale relaxation of the trade winds. The data suggest that wind-forced zonal advection plays an important role in the thermodynamics of the western Pacific warm pool on interannual time scales.
Control of a Desert-Grassland Transition by a Keystone Rodent Guild
Authors: Brown James H. , Heske Edward J.
Published: October 2006

Twelve years after three species of kangaroo rats (
Dipodomys
spp.) were removed from plots of Chihuahuan Desert shrub habitat, density of tall perennial and annual grasses had increased approximately threefold and rodent species typical of arid grassland had colonized. These were just the most recent and dramatic in a series of changes in plants and animals caused by experimental exclusion of
Dipodomys
. In this ecosystem kangaroo rats are a keystone guild: through seed predation and soil disturbance they have major effects on biological diversity and biogeochemical processes.
Lutropin-Choriogonadotropin Receptor: An Unusual Member of the G Protein-Coupled Receptor Family
Authors: McFarland K. C. , Sprengel Rolf , Phillips Heidi S. , Köhler Martin , Rosemblit Nora , Nikolics Karoly , Segaloff Deborah L. , Seeburg Peter H.
Published: October 2006

A complementary DNA (cDNA) for the rat luteal lutropin-choriogonadotropin receptor (LH-CG-R) was isolated with the use of a DNA probe generated in a polymerase chain reaction with oligonucleotide primers based on peptide sequences of purified receptor protein. As would be predicted from the cDNA sequence, the LH-CG-R consists of a 26-residue signal peptide, a 341-residue extracellular domain displaying an internal repeat structure characteristic of members of the leucine-rich glycoprotein (LRG) family, and a 333-residue region containing seven transmembrane segments. This membrane-spanning region displays sequence similarity with all members of the G protein-coupled receptor family. Hence, the LH-CG-R gene may have evolved by recombination of LRG and G protein-coupled receptor genes. Cells engineered to express LH-CG-R cDNA bind human choriogonadotropin with high affinity and show an increase in cyclic adenosine monophosphate when exposed to hormone. As revealed by RNA blot analysis and in situ hybridization, the 4.4-kilobase cognate messenger RNA is prominently localized in the rat ovary.
The Effect of Deprenyl (Selegiline) on the Natural History of Parkinson's Disease
Authors: Tetrud James W. , Langston J. William
Published: October 2006

The effects of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), a neurotoxin that produces the symptoms of Parkinson's disease, can be fully prevented in experimental animals by inhibiting monoamine oxidase B. On the basis of this observation, a double-blind, placebo-controlled study in patients with early Parkinson's disease was initiated to determine whether deprenyl (a selective monoamine oxidase B inhibitor) would delay the need for L-dopa therapy by slowing the progression of the disease. Fifty-four patients were randomly assigned to deprenyl (10 mg/day) or placebo treatment groups and followed until L-dopa therapy was indicated or until the patient had been in the study for 3 years. Analysis of Kaplan-Meier survival curves for each group showed that deprenyl delayed the need for L-dopa therapy; the average time until L-dopa was needed was 312.1 days for patients in the placebo group and 548.9 days for patients in the deprenyl group. Disease progression, as monitored by five different assessment scales, was slowed (by 40 to 83% per year) in the deprenyl group compared to placebo. Therefore, early deprenyl therapy delays the requirement for antiparkinsonian medication, possibly by slowing progression of the disease.
Protection of Dentate Hilar Cells from Prolonged Stimulation by Intracellular Calcium Chelation
Authors: Scharfman Helen E. , Schwartzkroin Philip A.
Published: October 2006

Prolonged afferent stimulation of the rat dentate gyrus in vivo leads to degeneration only of those cells that lack immunoreactivity for the calcium binding proteins parvalbumin and calbindin. In order to test the hypothesis that calcium binding proteins protect against the effects of prolonged stimulation, intracellular recordings were made in hippocampal slices from cells that lack immunoreactivity for calcium binding proteins. Calcium binding protein-negative cells showed electrophysiological signs of deterioration during prolonged stimulation; cells containing calcium binding protein did not. When neurons without calcium binding proteins were impaled with microelectrodes containing the calcium chelator BAPTA, and BAPTA was allowed to diffuse into the cells, these cells showed no deterioration. These results indicate that, in a complex tissue of the central nervous system, an activity-induced increase in intracellular calcium can trigger processes leading to cell deterioration, and that increasing the calcium binding capacity of a cell decreases its vulnerability to damage.
A Water Storage Adaptation in the Maya Lowlands
Authors: Scarborough Vernon L. , Gallopin Gary G.
Published: October 2006

Prehispanic water management in the Maya Lowlands emphasized collection and storage rather than the canalization and diversion accentuated in highland Mexico. Reexamination of site maps of the ancient Maya city of Tikal, Guatemala, has revealed an important, overlooked factor in Maya centralization and urban settlement organization. In a geographical zone affected by an extended dry season and away from permanent water sources, large, well-planned reservoirs provided resource control as well as political leverage.
Salicornia bigelovii
Torr.: An Oilseed Halophyte for Seawater Irrigation
Authors: Glenn Edward P. , O'Leary James W. , Watson M. Carolyn , Thompson T. Lewis , Kuehl Robert O.
Published: October 2006

The terrestrial halophyte,
Salicornia bigelovii
Torr., was evaluated as an oilseed crop for direct seawater irrigation during 6 years of field trials in an extreme coastal desert environment. Yields of seed and biomass equaled or exceeded freshwater oilseed crops such as soybean and sunflower. The seed contained 26 to 33 percent oil, 31 percent protein, and was low in fiber and ash (5 to 7 percent). The oil and meal were extracted by normal milling equipment, and the oil was high in linoleic acid (73 to 75 percent) and could replace soybean oil in chicken diets. The meal had antigrowth factors, attributed to saponins, but could replace soybean meal in chicken diets amended with the saponin antagonist, cholesterol.
Salicornia bigelovii
appears to be a potentially valuable new oilseed crop for subtropical coastal deserts.
San Andreas Fault Zone Head Waves Near Parkfield, California
Authors: Ben-Zion Yehuda , Malin Peter
Published: October 2006

Microearthquake seismograms from the borehole seismic network on the San Andreas fault near Parkfield, California, provide three lines of evidence that first
P
arrivals are "head" waves refracted along the cross-fault material contrast. First, the travel time difference between these arrivals and secondary phases identified as direct
P
waves scales linearly with the source-receiver distance. Second, these arrivals have the emergent wave character associated in theory and practice with refracted head waves instead of the sharp first breaks associated with direct
P
arrivals. Third, the first motion polarities of the emergent arrivals are reversed from those of the direct
P
waves as predicted by the theory of fault zone head waves for slip on the San Andreas fault. The presence of fault zone head waves in local seismic network data may help account for scatter in earthquake locations and source mechanisms. The fault zone head waves indicate that the velocity contrast across the San Andreas fault near Parkfield is approximately 4 percent. Further studies of these waves may provide a way of assessing changes in the physical state of the fault system.
Satellite-Image-Derived Velocity Field of an Antarctic Ice Stream
Authors: Bindschadler R. A. , Scambos T. A.
Published: October 2006

The surface velocity of a rapidly moving ice stream has been determined to high accuracy and spatial density with the use of sequential satellite imagery. Variations of ice velocity are spatially related to surface undulations, and transverse velocity variations of up to 30 percent occur. Such large variations negate the concept of plug flow and call into question earlier mass-balance calculations for this and other ice streams where sparse velocity data were used. The coregistration of images with the use of the topographic undulations of the ice stream and the measurement of feature displacement with cross-correlation of image windows provide significant improvements in the use of satellite imagery for ice-flow determination.
Venus Volcanism: Initial Analysis from Magellan Data
Authors: Head James W. , Campbell Donald B. , Elachi Charles , Guest John E. , McKenzie Dan P. , Saunders R. Stephen , Schaber Gerald G. , Schubert Gerald
Published: October 2006

Magellan images confirm that volcanism is widespread and has been fundamentally important in the formation and evolution of the crust of Venus. High-resolution imaging data reveal evidence for intrusion (dike formation and cryptodomes) and extrusion (a wide range of lava flows). Also observed are thousands of small shield volcanoes, larger edifices up to several hundred kilometers in diameter, massive outpourings of lavas, and local pyroclastic deposits. Although most features are consistent with basaltic compositions, a number of large pancake-like domes are morphologically similar to rhyolite-dacite domes on Earth. Flows and sinuous channels with lengths of many hundreds of kilometers suggest that extremely high effusion rates or very fluid magmas (perhaps komatiites) may be present. Volcanism is evident in various tectonic settings (coronae, linear extensional and compressional zones, mountain belts, upland rises, highland plateaus, and tesserae). Volcanic resurfacing rates appear to be low (less than 2 km
3
/yr) but the significance of dike formation and intrusions, and the mode of crustal formation and loss remain to be established.
Interstellar Shock Waves
Authors: McKee Christopher F. , Draine Bruce T.
Published: October 2006

An understanding of interstellar shock waves is crucial in determining the structure of the interstellar medium. By causing the gas to radiate, interstellar shocks provide astronomers with valuable diagnostics on both the physical conditions in the interstellar medium and the energy source that produced the shock. The complexity of the interstellar plasma—its degree of ionization, its molecular content, the presence of small dust grains and cosmic rays, and the magnetic field—leads to a rich variety of structures for interstellar shocks, which are being actively investigated both observationally and theoretically.
Ordered Overlayers of C
60
on GaAs(110) Studied with Scanning Tunneling Microscopy
Authors: Li Y. Z. , Patrin J. C. , Chander M. , Weaver J. H. , Chibante L. P. F. , Smalley R. E.
Published: October 2006

Studies of C
60
overlayer growth on GaAs(110) with scanning tunneling microscopy show large first monolayer islands that are locally well ordered, structurally stable, and commensurate with the GaAs surface owing to molecule-substrate interactions. Within the distorted close-packed structure, two distinct adsorption sites were identified, one of them being elevated because of stress in the C
60
monolayer.
Self-Assembled Organic Monolayers: Model Systems for Studying Adsorption of Proteins at Aurfaces
Authors: Prime Kevin L. , Whitesides George M.
Published: October 2006

Self-assembled monolayers (SAMs) of ω-functionalized long-chain alkanethiolates on gold films are excellent model systems with which to study the interactions of proteins with organic surfaces. Monolayers containing mixtures of hydrophobic (methyl-terminated) and hydrophilic [hydroxyl-, maltose-, and hexa(ethylene glycol)-terminated] alkanethiols can be tailored to select specific degrees of adsorption: the amount of protein adsorbed varies monotonically with the composition of the monolayer. The hexa(ethylene glycol)-terminated SAMs are the most effective in resisting protein adsorption. The ability to create interfaces with similar structures and well-defined compositions should make it possible to test hypotheses concerning protein adsorption.
Proximate Constraints on the Evolution of Egg Size, Number, and Total Clutch Mass in Lizards
Authors: Sinervo Barry , Licht Paul
Published: October 2006

Proximate constraints on egg size, number, and total clutch mass in side-blotched lizards were examined by experimentally reducing average clutch size from 4.6 eggs to one, two, and three eggs. Eggs from experimentally altered clutches were larger than those from controls, reflecting the trade-off between egg size and number. Moreover, the increased frequency of females with oviducally bound eggs or eggs that burst at oviposition suggests that egg size in clutches with very few eggs are at a functional upper size limit. These proximate constraints may also limit evolution of egg size in another group of lizards (
Anolis
) that only produces one-egged clutches.
Conjugated Polymer Films for Gas Separations
Authors: Anderson Mark R. , Mattes Benjamin R. , Reiss Howard , Kaner Richard B.
Published: October 2006

Permeabilities for a series of gases through free-standing films of the conjugated polymer polyaniline are reported. A remarkable selectivity has been achieved for important gas pairs including hydrogen-nitrogen, oxygen-nitrogen, and carbon dioxide-methane. The selectivity values of 3590 for H
2
/N
2
, 30 for O
2
/N
2
, and 336 for CO
2
/CH
4
surpass the highest previously reported values of 313, 16, and 60 for the nonconjugated polymers poly(trifluorochloroethylene), cellulose nitrate, and a fluorinated polyimide, respectively. The process for tailoring gas selectivity of a polyaniline membrane involves first enhancing the permeabilities of gases with small diameters [<3.5 angstroms (Å)] by doping and undoping the polymer film with counterions of an appropriate size. High selectivities are then achieved by decreasing the permeabilities of larger gases (>3.5 Å diameter) through controlled redoping of the polymer. The permanent morphological changes induced in this conjugated polymer system and others indicate the potential for development of universal membranes for gas separations.