bluuebunny/crossref_metadata_2025 huggingface dataset:
Edge Surfaces in Lithographically Textured Molybdenum Disulfide
Authors: Roxlo C. B. , Deckman H. W. , Gland J. , Cameron, S. D. , Chianelli R. R.
Published: October 2006

Lithographic techniques were used to expose edge surfaces in layered molybdenum disulfide single crystals. This microstructuring produced ideal samples for the study of the surface morphology and electronic structure of this catalytically important material. The optical absorption that was measured at mid-gap increased by two orders of magnitude after texturing. This increase resulted from reduced molybdenum at surface defects that are located on edge planes, as shown by photoemission spectroscopy. This information cannot easily be obtained on conventional crystals with predominantly basal plane surfaces.
Superconductivity in Alkaline Earth-Substituted La
2
CuO
4-y
Authors: Bednorz J. Georg , Müller K. Alex , Takashige Masaaki
Published: October 2006

La
2
CuO

4-
y

ceramics containing a few percent of Ca
2+
, Sr
2+
, and Ba
2+
ions have been prepared. Resistivity and susceptibility measurements exhibit superconductive onsets (as in earlier Ba
2+
-containing samples). The onset temperature La
2
CuO

4-
y

with Sr
2+
is higher and its superconductivity-induced diamagnetism larger than that found with Ba
2+
and Ca
2+
. This is proof that the electronic change resulting from alkaline earthdoping, rather than the size effect, is responsible for superconductivity. The ionic radius of Sr
2+
is close to that of La
3+
for which it presumably substitutes.
Physical Properties of Sea Ice Discharged from Fram Strait
Authors: Gow Anthony J. , Tucker Walter B.
Published: October 2006

It is estimated that 84 percent of the ice exiting the Arctic Basin through Fram Strait during June and July 1984 was multiyear ice and that a large percentage of this ice is ridged or otherwise deformed. While freeboard and thickness data, together with salinity measurements on cores, usually sufficed to distinguish between first and multiyear floes, preliminary identification could usually be made on the basis of snow cover measurements with snow cover being much thicker on multiyear ice. Cores from the top half meter of multiyear floes were generally very much harder and more transparent than cores from first-year floes. Age estimates of multiyear floes, based on petrographic and salinity characteristics of cores, did not exceed 4 to 5 years for any of the floes that were observed exiting Fram Strait.
Shocked Quartz in the Cretaceous-Tertiary Boundary Clays: Evidence for a Global Distribution
Authors: Bohor Bruce F. , Modreski Peter J. , Foord Eugene E.
Published: October 2006

Shocked quartz grains displaying planar features were isolated from Cretaceous- Tertiary boundary clays at five sites in Europe, a core from the north-central Pacific Ocean, and a site in New Zealand. At all of these sites, the planar features in the shocked quartz can be indexed to rational crystallographic planes of the quartz lattice. The grains display streaking indicative of shock in x-ray diffraction photographs and also show reduced refractive indices. These characteristic features of shocked quartz at several sites worldwide confirm that an impact event at the Cretaceous-Tertiary boundary distributed ejecta products in an earth-girdling dust cloud, as postulated by the Alvarez impact hypothesis.
Electrophoretic Evidence for Genetic Diploidy in the Bracken Fern (
Pteridium aquilinum
)
Authors: Wolf Paul G. , Haufler Christopher H. , Sheffield Elizabeth
Published: October 2006

Analysis of isozyme variability demonstrates that bracken fern (
Pteridium aquilinum
) has a diploid genetic system and expresses solely disomic inheritance patterns. Electrophoretic data indicate that genetically variable progeny are produced in natural populations after intergametophytic mating rather than by a process involving recombination between duplicated unlinked loci. Although some enzymes are encoded by more than one locus, this has resulted from subcellular compartmentalization of isozymes, and there is no evidence of extensive gene duplication resulting from polyploidy. The conclusions reached in this report differ from those which propose polyploidy as an adaptive mechanism for maintaining genetic variability in
Pteridium
and other homosporous pteridophytes.
Space-Based Radar
Authors: Tsandoulas G. N.
Published: October 2006

The concept of national air defense against aircraft and cruise missiles has been evolving in parallel with the Strategic Defense Initiative and is being referred to as the Air Defense Initiative. One of the most promising sensor concepts for the Air Defense Initiative is space-based radar. Operated at microwave frequencies as an instrument for wide-area surveillance, space-based radar may be useful in mission areas such as fleet defense and battlefield surveillance.
Laser Spectroscopy of Trapped Atomic Ions
Authors: Itano Wayne M. , Bergquist J. C. , Wineland D. J.
Published: October 2006

Recent developments in laser spectroscopy of atomic ions stored in electromagnetic traps are reviewed with emphasis on techniques that appear to hold the greatest promise of attaining extremely high resolution. Among these techniques are laser cooling and the use of single, isolated ions as experimental samples. Doppler shifts and other perturbing influences can be largely eliminated. Atomic resonances with line widths of a few parts in 10
11
have been observed at frequencies ranging from the radio frequency to the ultraviolet. Experimental accuracies of one part in 10
18
appear to be attainable.
Science and Technology Policies and Priorities: A Comparative Analysis
Authors: Lederman Leonard L.
Published: October 2006

This article compares the science and technology strategies and priorities of France, Germany, Japan, Sweden, the United Kingdom, and the United States. An analysis is given of similarities and differences, historical settings, research and development allocations, coordinating mechanisms, outputs, dissatisfactions, and recent changes. Also presented are data on performers and funding sources, the character and objectives of work, the industries involved, employment of scientists and engineers, and degrees by field. This comparison provides a way of understanding the advantages and disadvantages of different strategies and an opportunity for one country to learn from the others.
Regulation of Proteolysis at the Neutrophil-Substrate Interface by Secretory Leukoprotease Inhibitor
Authors: Rice William G. , Weiss Stephen J.
Published: October 2006

Human neutrophils can initiate the rapid degradation of extracellular matrix macromolecules by localizing the destructive process to sites of cell-substrate contact. Although plasma and its filtrates contain multiple proteinase inhibitors, these inhibitors did not prevent neutrophils from attacking either underlying fibronectin or elastin. However, subjacent substrates could be protected from neutrophils by recombinant secretory leukoprotease inhibitor, a structurally unique serine proteinase inhibitor whose natural counterpart is normally confined to human mucous secretions. The identification of this extravascular proteinase inhibitor as a potent regulator of subjacent proteolysis could lead to the development of a new class of anti-inflammatory therapeutics.
Sea Surface Temperature, Surface Wind Divergence, and Convection over Tropical Oceans
Authors: Graham N. E. , Barnett T. P.
Published: October 2006

Large-scale convection over the warm tropical oceans provides an important portion of the driving energy for the general circulation of the atmosphere. Analysis of regional associations between ocean temperature, surface wind divergence, and convection produced two important results. First, over broad regions of the Indian and Pacific oceans, sea surface temperatures (SSTs) in excess of 27.5°C are required for large-scale deep convection to occur. However, SSTs above that temperature are not a sufficient condition for convection and further increases in SST appear to have little effect on the intensity of convection. Second, when SSTs are above 27.5°C, surface wind divergence is closely associated with the presence or absence of deep convection. Although this result could have been expected, it was also found that areas of persistent divergent surface flow coincide with regions where convection appears to be consistently suppressed even when SSTs are above 27.5°C. Thus changes in atmospheric stability caused by remotely forced changes in subsidence aloft may play a major role in regulating convection over warm tropical oceans.
Stop-Transfer Regions Do Not Halt Translocation of Proteins into Chloroplasts
Authors: Lubben Thomas H. , Bansberg Joern , Keegstra Kenneth
Published: October 2006

Protein targeting in eukaryotic cells is determined by several topogenic signals. Among these are stop-transfer regions, which halt translocation of proteins across the endoplasmic reticulum membrane. Two different stop-transfer regions were incorporated into precursors for a chloroplast protein, the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase. Both chimeric proteins were imported into chloroplasts and did not accumulate in the envelope membranes. Thus, the stop-transfer signals did not function during chloroplast protein import. These observations support the hypothesis that the mechanism for translocation of proteins across the chloroplast envelope is significantly different from that for translocation across the endoplasmic reticulum membrane.
Ceramics by the Solution-Sol-Gel Route
Authors: Roy Rustum
Published: October 2006

The use of solution mixing followed by gelation to make ultrahomogeneous glasses and ceramics of various oxide compositions for laboratory experimentation, with first organic and later principally colloidal inorganic, precursors was developed over 30 years ago. Major technologies that use the solution-sol-gel route have been developed to make nuclear fuel pellets, ceramic fibers, thin coatings, and abrasive grain. This article reviews the early history and summarizes present research in this field, particularly new processes aimed at achieving xerogel precursors of maximum heterogeneity with respect either to composition or to structure. Such nanocomposites provide major advantages in lowering sintering temperatures, refining microstructure, and controlling morphology and final phase composition.
Direct Cloning of Human Transcripts with HnRNA from Hybrid Cell Lines
Authors: Corbo Laura , Maley Julie A. , Nelson David L. , Caskey C. Thomas
Published: October 2006

A library of human-derived complementary DNA from a human-hamster hybrid cell line containing the Xq24-qter region has been constructed. Complementary DNA synthesis was primed from heterogeneous nuclear (hn) RNA by oligonucleotides derived from conserved regions of human
Alu
repeats. At least 80% of these cloned sequences were of human origin, providing an enrichment of at least two orders of magnitude. Two clones, one containing a fragment of the primary transcript of the human hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene at Xq26 and another recognizing a family of human genes mapping to two regions of Xq24-qter, were characterized. Additional hncDNA clones mapped to a variety of sites in the Xq24-qter region, demonstrating the isolation of many transcriptionally active loci. These clones provide probes for identification of genetic loci on the terminal region of the X chromosome long arm, which is the location of a number of inherited disorders.
A Mechanism for Surface Attachment in Spores of a Plant Pathogenic Fungus
Authors: Hamer John E. , Howard Richard J. , Chumley Forrest G. , Valent Barbara
Published: October 2006

Rice blast disease is caused by a fungus that attacks all above-ground parts of the rice plant. In a study of the means by which the fungus attaches to the hydrophobic rice leaf surface, it was found that spores (conidia) of the rice blast fungus
Magnaporthe grisea
have a mechanism for immediate and persistent attachment to various surfaces, including Teflon. This attachment occurs at the spore apex and is blocked by the addition of the lectin concanavalin A. Microscopy of hydrated conidia shows that a spore tip mucilage that binds concanavalin A is expelled specifically from the conidial apex before germ tube emergence. Ultrastructural analysis of dry conidia shows a large periplasmic deposit, presumably spore tip mucilage, at the apex. The results indicate a novel mechanism for the attachment of phytopathogenic fungal spores to a plant surface.
A Cesium-Selective Ion Sieve Made by Topotactic Leaching of Phlogopite Mica
Authors: Komarneni Sridhar , Roy Rustum
Published: October 2006

A hydrated, sodium phlogopite mica with a
c
-axis spacing [
d
(001)] of 12.23 Å made by careful low-temperature leaching, showed extremely high selectivity for cesium. This newly discovered cesium ion sieve is useful in the decontamination as well as immobilization of cesium at room temperature through chemical bonding and may find applications in nuclear waste disposal and in decontamination of the environment after accidental releases of nuclear materials.
A New Order of Tertiary Zalambdodont Marsupials
Authors: Archer Michael , Hand Suzanne , Godthelp Henk
Published: October 2006

Yalkaparidon coheni
and
Yalkaparidon jonesi
are described here as the first-known members of the marsupial family Yalkaparidontidae and order Yalkaparidontia. Before discovery of these zalambdodont marsupials in unnamed Tertiary sediments from northwestern Queensland, only five orders of australidelphian marsupials were known. Dental and basicranial morphology suggest that notoryctids and yalkaparidontids, which both have highly specialized zalambdodont molars, are dentally convergent. Yalkaparidontids lived in lowland rainforests of northern Australia and appear to have vanished, with the rainforests, sometime in the middle to late Tertiary. Discovery of yalkaparidontids demonstrates a significantly greater breadth of diversity for Australian marsupials.
Presentation of Exogenous Antigen with Class I Major Histocompatibility Complex Molecules
Authors: Rock Kenneth L. , Gamble Sandra , Rothstein Lisa
Published: October 2006

Soluble antigens (Ags) in the extracellular fluids are excluded from the class I major histocompatibility complex (MHC)-restricted pathway of Ag presentation in most cells. However, an exogenous Ag can be internalized, processed, and presented in association with class I MHC molecules on specialized Ag-presenting cells (APCs). These APCs express class II molecules and can simultaneously present exogenous Ags to both class I and class II MHC-restricted T cells. These APCs may be important participants in the regulation of host immune responses. This APC activity may explain several phenomena of cytotoxic T lymphocyte (CTL) priming in vivo and might be exploited for eliciting CTL responses to protein vaccines.
Microemulsions
Authors: Kahlweit Manfred
Published: October 2006

Water and oil can be made completely miscible by adding a sufficient amount of an amphiphilic compound, such as soap or a detergent. For historical reasons, such stable homogeneous solutions are called "microemulsions." In this article the term microemulsion is used in a more restrictive manner; at low concentrations of the amphiphile, mixtures of water, nonpolar solvents, and amphiphiles may separate into three coexisting liquid layers, namely, an aqueous phase, an amphiphile-rich phase, and an oil-rich phase. In the amphiphile-rich phase, which is the microemulsion in the narrower sense, one finds for thermodynamic reasons a maximum of the mutual solubility between water and oil, combined with a minimum of the interfacial tension between the aqueous and the oil-rich phase, properties that are of interest for both theory and application. The present state of art in this rapidly growing field of science is reviewed.
Virus-Like Particles and a Spider Mite Intimately Associated with a New Disease of Barley
Authors: Robertson Nancy L. , Carroll Thomas W.
Published: October 2006

The malting barley—producing regions in Montana and Canada are threatened with a new virus-like barley disease that appears to be etiologically novel. Ultrathin sections of diseased tissue contained enveloped, filamentous virus-like particles that measured 64 nanometers by 126 to 4000 nanometers. These lengths are unique for plant viruses. Unexpectedly, the spider mite,
Petrobia latens
, which has never been reported to be a vector of a pathogen, was found to transmit the causal agent from diseased plants to healthy barley, while noninfective mites failed to do so unless they were allowed prior access to diseased tissue.
Anomalous Upstream Retroflection in the Agulhas Current
Authors: Lutjeharms J. R. E. , van Ballegooyen R. C.
Published: October 2006

The Agulhas current, the major western boundary current of the Southern Hemisphere, plays a crucial role in the water mass balance of the world oceans by controlling the transfer of thermocline water from the Indian to the Atlantic ocean systems. The main mechanism for such transfer is through the shedding of large rings of warm water at the Agulhas retroflection south of Africa. On the basis of satellite imagery and drifter tracks, anomalous reversals of the current are observed to occur far upstream of its characteristic retroflection location. The observations agree with results of an inertial jet model of the current. These anomalous reversals probably cause abrupt and major changes in the fluxes south of Africa and thus in the rate of ring shedding. This unusual flow bimodality in a major component of the global ocean heat transport system could have important climatic implications.
Ultraviolet Radiation Levels During the Antarctic Spring
Authors: Frederick John E. , Snell Hilary E.
Published: October 2006

The decrease in atmospheric ozone over Antarctica during spring implies enhanced levels of ultraviolet (UV) radiation received at the earth's surface. Model calculations show that UV irradiances encountered during the occurrence of an Antarctic "ozone hole" remain less than those typical of a summer solstice at low to middle latitudes. However, the low ozone amounts observed in October 1987 imply biologically effective irradiances for McMurdo Station, Antarctica, that are comparable to or greater than those for the same location at December solstice. Life indigenous to Antarctica thereby experiences a greatly extended period of summerlike UV radiation levels.
The Incommensurate Modulation of the 2212 Bi-Sr-Ca-Cu-O Superconductor
Authors: Gao Yan , Lee Peter , Coppens Philip , Subramania M. A. , Sleight A. W.
Published: October 2006

The incommensurate modulation evident in the diffraction pattern of the superconductor Bi
2
Sr

3-
x

Ca

x

Cu
2
O

8+
y

consists of almost sinusoidally varying displacements of up to 0.4 Å of the Bi and Sr atoms in the
a
- and
c
-directions of the unit cell, and of up to 0.3 Å of the Cu atoms in the
c
direction only. Thus, a newly discovered feature of the Bi
2
Sr

3-
x

Ca

x

Cu
2
O

8+
y

structure is sizable Cu displacement, which is related to static wave formation in the Cu-O sheets. Reported thermal parameters give evidence that similar distortions occur on cooling of the thallium-containing superconductors.
The Challenge of Universal Literacy
Authors: Miller George A.
Published: October 2006

Universal literacy has always been a goal of the United States. But literacy has been a moving target: criteria have risen as technology advanced. Comprehension skills well beyond simple decoding are now required. Research by educators and psychologists has laid a scientific foundation on which new pedagogic methods can be based. But even with better teaching, the hope that all adults can attain the highest levels of literacy skills may be unrealistic.
Middle Archaic Period Domestic Architecture from Southern Peru
Authors: Aldenderfer Mark
Published: October 2006

Domestic or residential structures ranging in age from 6040 to 6850 years old have discovered at the open air site of Asana in the high sierra of southern Peru. These are the earliest domestic structures known from the high elevation zones of the south central Andes, and they are contemporaneous with sites with structures on the north Chilean littoral. Analysis of site structure and content suggests that during the Middle Archaic the site was a logistical camp within a dry
puna
—high sierra settlement system.
Differential Control of U1 Small Nuclear RNA Expression During Mouse Development
Authors: Lund Elsebet , Kahan Brenda , Dahlberg James E.
Published: October 2006

During normal mouse development the relative amounts of two types of U1 small nuclear RNA's (U1 RNA) change significantly. Fetal tissues have comparable levels of the two major types of mouse U1 RNA's, mU1a and mU1b, whereas most differentiated adult tissues contain only mU1a RNA's. Those adult tissues that also accumulate detectable amounts of embryonic (mU1b) RNA's (for example, testis, spleen, and thymus) contain a significant proportion of stem cells capable of further differentiation. Several strains of mice express minor sequence variants of U1 RNA's that are subject to the same developmental controls as the major types of adult and embryonic U1 RNA. The differential accumulation of embryonic U1 RNA's may influence the pattern of gene expression during early development and differentiation.
The Impact of High-Temperature Superconductivity on SQUID Magnetometers
Authors: Clarke John , Koch Roger H.
Published: October 2006

DC and RF Superconducting QUantum Interference Devices (SQUIDs) fabricated from low transition temperature (
T
c
) superconductors and operated at liquid
4
He temperatures are routinely used as ultrasensitive detectors in many applications, for example, as magnetometers, magnetic gradiometers, voltmeters, and motion detectors. SQUIDs fabricated from high
T
c
superconductors such as YBa
2
Cu
3
O
7
and operated in liquid nitrogen at 77 K offer a greater convenience in operation at the expense of a poorer noise performance, particularly at low frequencies. The resolution of SQUID-based magnetometers is compared with that of other types of magnetometers operating at ambient temperatures.
Chemistry of High-Temperature Superconductors
Authors: Sleight A. W.
Published: October 2006

Spectacular advances in superconductors have taken place in the past two years. The upper temperature for superconductivity has risen from 23 K to 122 K, and there is reason to believe that the ascent is still ongoing. The materials causing this excitement are oxides. Those oxides that superconduct at the highest temperatures contain copper-oxygen sheets; however, other elements such as bismuth and thallium play a key role in this new class of superconductors. These superconductors are attracting attention because of the possibility of a wide range of applications and because the science is fascinating. A material that passes an electrical current with virtually no loss is more remarkable when this occurs at 120 K instead of 20 K.
Mapping Epitopes on a Protein Antigen by the Proteolysis of Antigen-Antibody Complexes
Authors: Jemmerson Ronald , Paterson Yvonne
Published: October 2006

A monoclonal antibody bound to a protein antigen decreases the rate of proteolytic cleavage of the antigen, having the greatest effect on those regions involved in antibody contact. Thus, an epitope can be identified by the ability of the antibody to protect one region of the antigen more than others from proteolysis. By means of this approach, two distinct epitopes, both conformationally well-ordered, were characterized on horse cytochrome
c
.
The Role of Chloride Transport in Postsynaptic Inhibition of Hippocampal Neurons
Authors: Misgeld U. , Deisz R. A. , Dodt H. U. , Lux H. D.
Published: October 2006

Hippocampal inhibitory postsynaptic potentials are depolarizing in granule cells but hyperpolarizing in CA3 neurons because the reversal potentials and membrane potentials of these cells differ. Here the hippocampal slice preparation was used to investigate the role of chloride transport in these inhibitory responses. In both cell types, increasing the intracellular chloride concentration by injection shifted the reversal potential of these responses in a positive direction, and blocking the outward transport of chloride with furosemide slowed their recovery from the injection. In addition, hyperpolarizing and depolarizing inhibitory responses and the hyperpolarizing and depolarizing responses to the inhibitory neurotransmitter γ-aminobutyric acid decreased in the presence of furosemide. These effects of furosemide suggest that the internal chloride activity of an individual hippocampal neuron is regulated by two transport processes, one that accumulates chloride and one that extrudes chloride.
Dynamics of Liquefaction During the 1987 Superstition Hills, California, Earthquake
Authors: Holzer T. L. , Hanks T. C. , Youd T. L.
Published: October 2006

Simultaneous measurements of seismically induced pore-water pressure changes and surface and subsurface accelerations at a site undergoing liquefaction caused by the Superstition Hills, California, earthquake (24 November 1987;
M
= 6.6) reveal that total pore pressures approached lithostatic conditions, but, unexpectedly, after most of the strong motion ceased. Excess pore pressures were generated once horizontal acceleration exceeded a threshold value.
Anomalous Scattering Study of the Bi Distribution in the 2212 Superconductor: Implications for Cu Valency
Authors: Lee P. , Gao Y. , Sheu H. S. , Petricek V. , Restori R. , Coppens P. , Darovskikh A. , Phillips J. C. , Sleight A. W. , Subramanian M. A.
Published: October 2006

The distribution of the bismuth atoms over the cation sites in the 2212 Bi-Sr-Ca-Cu-O superconductor has been determined by anomalous scattering synchrotron crystallography. The analysis of reflection pairs measured at wavelengths of 0.9243 and 0.9600 angstrom shows a delocalization of the bismuth atoms over the calcium and strontium sites. The "mixed" plane between the CuO
2
layers contains 6.0(1.4) percent bismuth (where the number in brackets represents the statistical standard deviation derived from the least-squares refinement of the data), and a much smaller amount of strontium than often assumed. The strontium deficiency is charge-compensated by the creation of electron holes in the CuO
2
layer. The result supports the view that neither extra oxygen nor overlap of the bismuth 6
p
and copper 3
d
bands is needed to account for the holes, which are an essential feature of the superconductivity mechanism.
The Cellular
src
Gene Product Regulates Junctional Cell-to-Cell Communication
Authors: Azarnia R. , Reddy S. , Kmiecik T. E. , Shalloway D. , Loewenstein W. R.
Published: October 2006

Overexpression of the cellular
src
gene in NIH 3T3 cells causes reduction of cell-to-cell transmission of molecules in the 400- to 700-dalton range. This down-regulation of gap junctional communication correlates with the activity of the gene product, the protein tyrosine kinase pp60
c-src
. The down-regulation was enhanced by point mutation of Tyr
527
(a site that is phosphorylated in pp60
c-src
and that inhibits kinase activity) or by substitution of the viral-
src
for the cellular-
src
carboxyl-terminal coding region. Mutation of Tyr
416
(a site phosphorylated upon Tyr
527
mutation) suppresses both the down-regulation of communication by Tyr
527
mutation and that by gene overexpression. The regulation of communication by
src
may be important in the control of embryonic development and cellular growth.
Nuclear Magnetic Resonance Spectroscopy in the Earth Sciences: Structure and Dynamics
Authors: Stebbins Jonathan F. , Farnan Ian
Published: October 2006

Detailed knowledge of the structure and dynamics of the materials that make up the earth is necessary for fundamental understanding of most geological processes. Nuclear magnetic resonance spectroscopy is beginning to play an important role in investigations of inorganic solid materials, as well as of liquids and organic compounds; it has already contributed substantially to our knowledge of minerals and rocks, compositionally simplified analogs of magmas, and the surfaces of silicate crystals. The technique is particularly useful for determining local structure and ordering state in crystals, glasses, and liquids, and is sensitive to atomic motion at the time scales of diffusion and viscosity in silicates. New techniques offer promise for increased resolution for quadrupolar nuclei and for extension of experiments to high temperature and pressure.
Triton: Do We See to the Surface?
Authors: Cruikshank D. P. , Brown R. H. , Giver L. P. , Tokunaga A. T.
Published: October 2006

The quantity and physical state of methane and nitrogen in the atmosphere of Neptune's satellite Triton and on the surface are evaluated by means of new telescopic data and laboratory measurements of these volatiles. Methane ice is seen in some spectral regions, indicating that the atmosphere is sufficiently transparent to permit sunlight penetration to the surface. Some of the molecular nitrogen absorption occurs in the atmosphere, though some must occur in condensed nitrogen (liquid or solid) on Triton's surface, or in a thin cloud of condensed nitrogen. The Voyager spacecraft cameras should see the surface of Triton.
What Has Caused the Secular Increase in Solar Nitrogen-15?
Authors: Kerridge John F.
Published: October 2006

Well-documented variations in the
15
N/
14
N ratio in lunar surface samples apparently result from a secular increase in that ratio in the solar wind during the past few billion years. The cause of this change seems to lie in the solar convective zone but is inexplicable within our present understanding of solar processes. This problem therefore ranks with the solar neutrino deficiency as a major challenge to our solar paradigm.
Airline Deregulation and Public Policy
Authors: Morrison Steven A. , Winston Clifford
Published: October 2006

An assessment of the effects of airline deregulation on travelers and carriers indicates that deregulation has provided travelers and carriers with $14.9 billion of annual benefits (1988 dollars). Airport congestion, airline safety, airline bankruptcy, and mergers are also analyzed and found in most cases to have reduced benefits. But, these costs should not be attributed to deregulation per se, but to failures by the government to pursue appropriate policies in these areas. Pursuit of policies that promote airline competition and efficient use of airport capacity would significantly increase the benefits from deregulation and would provide valuable guidance for other industries undergoing the transition to deregulation.
Spatially Resolved Observation of Supercurrents Across Grain Boundaries in YBaCuO Films
Authors: Mannhart J. , Gross R. , Hipler K. , Huebener R. P. , Tsuei C. C. , Dimos D. , Chaudhari P.
Published: October 2006

Spatially resolved resistivity measurements of current transport across individual grain boundaries have been made on superconducting YBa
2
Cu
3
O
7
. These experiments were done by low-temperature scanning electron microscopy with a resolution of 1 to 2 micrometers, and they show directly the limitation of the critical current density caused by grain boundaries in YBa
2
Cu
3
O
7
. Furthermore, complex spatial patterns of the current transport across grain boundaries were observed. These patterns reflect self-excited resonances of the grain boundaries and are closely correlated to the unexplained "sub-gap structure" in the current-voltage characteristics of polycrystalline YBa
2
Cu
3
O
7
.
cAMP Evokes Long-Term Facilitation in
Aplysia
Sensory Neurons That Requires New Protein Synthesis
Authors: Schacher S. , Castellucci V. F. , Kandel E. R.
Published: October 2006

Behavioral sensitization leads to both short- and long-term enhancement of synaptic transmission between the sensory and motor neurons of the gill-withdrawal reflex in
Aplysia
. Serotonin (5-HT), a transmitter important for short-term sensitization, can evoke long-term enhancement of synaptic strength detected 1 day later. Because 5-HT mediates short-term facilitation through adenosine 3′,5′-monophosphate (cAMP)-dependent protein phosphorylation, the role of cAMP in the long-term modulation of this identified synapse was examined. Like 5-HT, cAMP can also evoke long-term facilitation lasting 24 hours. Unlike the short-term change, the long-lasting change is blocked by anisomycin, a reversible inhibitor of protein synthesis, and therefore must involve the synthesis of gene products not required for the short-term change.
Conversion of Normal Behavior to Shiverer by Myelin Basic Protein Antisense cDNA in Transgenic Mice
Authors: Katsuki Motoya , Sato Masahiro , Kimura Minoru , Yokoyama Minesuke , Kobayashi Kimio , Nomura Tatsuji
Published: October 2006

Myelin basic proteins (MBPs) are coded by the single gene necessary for myelin formation in the central nervous system of the mouse. An antisense MBP mini-gene was constructed and used to determine the function of antisense DNA in transgenic mice. Several transgenic offspring of a founder transgenic mouse, AS100, were converted from the normal to mutant shiverer phenotype. Antisense MBP messenger RNA was expressed in these mice, and the endogenous MBP messenger RNA, the MBP, and the myelination in the central nervous system were reduced.
Magnetic Fields at Neptune
Authors: Ness Norman F. , Acuña Mario H. , Burlaga Leonard F. , Connerney John E. P. , Lepping Ronald P. , Neubauer Fritz M.
Published: October 2006

The National Aeronautics and Space Administration Goddard Space Flight Center-University of Delaware Bartol Research Institute magnetic field experiment on the Voyager 2 spacecraft discovered a strong and complex intrinsic magnetic field of Neptune and an associated magnetosphere and magnetic tail. The detached bow shock wave in the supersonic solar wind flow was detected upstream at 34.9 Neptune radii (
R
N
), and the magnetopause boundary was tentatively identified at 26.5
R
N
near the planet-sun line (1
R
N
= 24,765 kilometers). A maximum magnetic field of nearly 10,000 nanoteslas (1 nanotesla = 10
-5
gauss) was observed near closest approach, at a distance of 1.18
R
N
. The planetary magnetic field between 4 and 15
R
N
can be well represented by an offset tilted magnetic dipole (OTD), displaced from the center of Neptune by the surprisingly large amount of 0.55
R
N
and inclined by 47° with respect to the rotation axis. The OTD dipole moment is 0.133 gauss-
R
N
3
. Within 4
R
N
, the magnetic field representation must include localized sources or higher order magnetic multipoles, or both, which are not yet well determined. The obliquity of Neptune and the phase of its rotation at encounter combined serendipitously so that the spacecraft entered the magnetosphere at a time when the polar cusp region was directed almost precisely sunward. As the spacecraft exited the magnetosphere, the magnetic tail appeared to be monopolar, and no crossings of an imbedded magnetic field reversal or plasma neutral sheet were observed. The auroral zones are most likely located far from the rotation poles and may have a complicated geometry. The rings and all the known moons of Neptune are imbedded deep inside the magnetosphere, except for Nereid, which is outside when sunward of the planet. The radiation belts will have a complex structure owing to the absorption of energetic particles by the moons and rings of Neptune and losses associated with the significant changes in the diurnally varying magnetosphere configuration. In an astrophysical context, the magnetic field of Neptune, like that of Uranus, may be described as that of an "oblique" rotator.
A Light Source Smaller Than the Optical Wavelength
Authors: Lieberman K. , Harush S. , Lewis A. , Kopelman R.
Published: October 2006

A method has been developed for the efficient emission of light from subwavelength dimensions. It is based on packaging photons as molecular excitons, effectively reducing the volume of the light beam by 10
9
and making possible propagation through dimensions of 1 nanometer. Molecular microcrystals are grown in the tips of micropipettes that have inner diameters of 100 nanometers or less. Measurements are presented that demonstrate this improvement in transmission for pipettes of various diameters. The ultrasmall dimensions of these light sources, the wavelength range (ultraviolet to red) of their emission, their ease of production, and their expected unique abilities for high efficiency excitation-imaging of surfaces portend significant applications for this methodology.
Global Climate Change and Intensification of Coastal Ocean Upwelling
Authors: Bakun Andrew
Published: October 2006

A mechanism exists whereby global greenhouse warming could, by intensifying the alongshore wind stress on the ocean surface, lead to acceleration of coastal upwelling. Evidence from several different regions suggests that the major coastal upwelling systems of the world have been growing in upwelling intensity as greenhouse gases have accumulated in the earth's atmosphere. Thus the cool foggy summer conditions that typify the coastlands of northern California and other similar upwelling regions might, under global warming, become even more pronounced. Effects of enhanced upwelling on the marine ecosystem are uncertain but potentially dramatic.
Gaussian Free-Energy Dependence of Electron-Transfer Rates in Iridium Complexes
Authors: Fox Lucius S. , Kozik Mariusz , Winkler Jay R. , Gray Harry B.
Published: October 2006

The kinetics of photoinduced electron-transfer (ET) reactions have been measured in a series of synthetic donor-acceptor complexes. The electron donors are singlet or triplet excited iridium(I) dimers (Ir
2
), and the acceptors are
N
-alkylpyridinium groups covalently bound to phosphinite ligands on the Ir
2
core. Rate constants for excited-state ET range from 3.5 × 10
6
to 1.1 × 10
11
per second, and thermal back ET (pyridinium radical to Ir
2
+
) rates vary from 2.0 × 10
10
to 6.7 × 10
7
per second. The variation of these rates with driving force is in remarkably good agreement with the Marcus theory prediction of a Gaussian free-energy dependence.
Antigen-Specific Helper Function of Cell-Free T Cell Products Bearing TCR V
β
8 Determinants
Authors: Guy Rina , Ullrich Stephen J. , Foo-Philips Michele , Hathcock Karen S. , Appella Ettore , Hodes Richard J.
Published: October 2006

Although the T cell receptor (TCR) αβ heterodimer and its encoding genes have been characterized, a cell-free form of this receptor, which is needed for the study of functional or ligand-binding properties of the receptor, has not previously been isolated. When the cell-free supernatant products of activated cloned T helper (T
H
) cells were found to mediate helper activity with antigen specificity identical to that of intact T cells, experiments were carried out to determine whether this functional activity was mediated by a cell-free form of TCR-related material. A disulfide-linked dimer indistinguishable from the T cell surface αβ heterodimer was precipitated from cell-free supernatants of cloned T
H
cells with F23.1, a monoclonal antibody specific for a TCR V
β
8 determinant. Moreover, when cell-free T
H
products were bound to and eluted from immobilized F23.1, these affinity-purified materials had antigen-specific and major histocompatibility complex-restricted helper activity that synergized with recombinant lymphokines in the generation of B cell antibody responses. These findings suggest that the factor isolated from T cell supernatants is a cell-free form of the TCRαβ dimer.
The Design and Catalytic Properties of a Simplified Ribonuclease P RNA
Authors: Waugh David S. , Green Christopher J. , Pace Norman R.
Published: October 2006

Ribonuclease P (RNase P) RNA is the catalytic moiety of the ribonucleoprotein enzyme that removes precursor sequences from the 5′ ends of pre-transfer RNAs in eubacteria. Phylogenetic variation according to recently proposed secondary structure models was used to identify structural elements of the RNase P RNA that are dispensable for catalysis. A simplified RNase P RNA that consists only of evolutionarily conserved features was designed, synthesized, and characterized. Although the simplified RNA (
Min
1 RNA) is only 263 nucleotides in length, in contrast to the 354 to 417 nucleotides of naturally occurring RNase P RNAs, its specificity of pre-tRNA cleavage is identical to that of the native enzymes. Moreover, the catalytic efficiencies of the
Min
1 RNA and the native RNA enzymes are similar. These results focus the search for the catalytic elements of RNase P RNAs to their conserved structure.
Cumulate Xenolith in Oahu, Hawaii: Implications for Deep Magma Chambers and Hawaiian Volcanism
Authors: Sen Gautam , Jones Robert E.
Published: October 2006

The maximum depth at which large (>1000 km
3
) terrestrial mafic magma chambers can form has generally been thought to be the Moho, which occurs at a mean depth of about 35 kilometers beneath the continents and 8 kilometers beneath ocean basins. However, the presence of layers of cumulus magnesium-rich spinel and olivine and intercumulus garnet in an unusual mantle xenolith from Oahu, Hawaii, suggests that this rock is a fragment of a large magma chamber that formed at a depth of about 90 kilometers; Hawaiian shield-building magmas may pond and fractionate in such magma chambers before continuing their ascent. This depth is at or near the base of the 90-million-year-old lithosphere beneath Oahu; thus, rejuvenated stage alkalic magmas containing mantle xenoliths evidently also originate below the lithosphere.
Crystal Versus Solution Structures of Enzymes: NMR Spectroscopy of a Crystalline Serine Protease
Authors: Smith Steven O. , Farr-Jones Shauna , Griffin Robert G. , Bachovchin William W.
Published: October 2006

The hydrogen-bonding status of His
57
in the catalytic triad (Asp-His-Ser) of serine proteases has important mechanistic implications for this class of enzymes. Recent nitrogen-15 nuclear magnetic resonance (NMR) studies of α-lytic protease find His
57
and Ser
195
to be strongly hydrogen-bonded, a result that conflicts with the corresponding crystallographic studies, thereby suggesting that the crystal and solution structures may differ. This discrepancy is addressed and resolved in a nitrogen-15 NMR study of the enzyme in the crystalline state. The results show that the His-Ser and Asp-His interactions are identical in crystals and solutions, but that in crystals His
57
titrates with a
pK
a
of 7.9, nearly one
pK
a
unit higher than in solution. This elevated
pK
a
accounts for the absence of the His-Ser hydrogen bond in previous x-ray studies.
The Impact Cratering Record on Triton
Authors: Strom Robert G. , Croft Steven K. , Boyce Joseph M.
Published: October 2006

Impact craters on Triton are scarce owing to the relatively recent resurfacing by icy
melts. The most heavily cratered surface has a crater density about the same as the lunar
maria. The transition diameter from simple to complex craters occurs at a diameter of
about 11 kilometers, and the depth-diameter relationship is similar to that of other icy
satellites when gravity is taken into account. The crater size-frequency distribution has
a differential -3 slope (cumulative -2 slope) and is the same as that for the fresh crater
population on Miranda. The most heavily cratered region is on the leading hemisphere in
Triton's orbit. Triton may have a leading-trailing asymmetry in its crater population.
Based primarily on the similarity of size distributions on Triton and Miranda and the
relatively young surface on Triton, the source of Triton's craters is probably comets. The
very peculiar size distribution of sharp craters on the "cantaloupe" terrain and other
evidence suggests they are volcanic explosion craters.
Highly Parallel Computation
Authors: Denning Peter J. , Tichy Walter F.
Published: October 2006

Highly parallel computing architectures are the only means to achieve the computational rates demanded by advanced scientific problems. A decade of research has demonstrated the feasibility of such machines, and current research focuses on which architectures are best suited for particular classes of problems. The architectures designated as MIMD and SIMD have produced the best results to date; neither shows a decisive advantage for most near-homogeneous scientific problems. For scientific problems with many dissimilar parts, more speculative architectures such as neural networks or data flow may be needed.
Putative Skeletal Neural Crest Cells in Early Late Ordovician Vertebrates from Colorado
Authors: Smith Moya Meredith
Published: October 2006

Two vertebrates from the Colorado Formation are known to have acellular bone and dentine, tissues found in heterostracan fishes and proposed as the primitive exoskeleton. High-resolution optical microscopy and scanning electron microscopy indicate that a third vertebrate is represented by a quite distinct exoskeleton of denticles, with many cell and cell process spaces throughout, tissue that resembles that of osteostracans more than heterostracans. Cellular bone coexists with cellular dentine in this Ordovician vertebrate, demonstrating that these skeletal tissues are as old as acellular bone. Both are proposed to come from neural crest because denticles are considered homologous with teeth.
Field-Based Evidence for Devolatilization in Subduction Zones: Implications for Arc Magmatism
Authors: Bebout Gray E.
Published: October 2006

Metamorphic rocks on Santa Catalina Island, California, afford examination of fluid-related processes at depths of 15 to 45 kilometers in an Early Cretaceous subduction zone. A combination of field, stable isotope, and volatile content data for the Catalina Schist indicates kilometer-scale transport of large amounts of water-rich fluid with uniform oxygen and hydrogen isotope compositions. The fluids were liberated in devolatilizing, relatively low-temperature (400° to 600°C) parts of the subduction zone, primarily by chlorite-breakdown reactions. An evaluation of pertinent phase equilibria indicates that chlorite in mafic and sedimentary rocks and melange may stabilize a large volatile component to great depths (perhaps >100 kilometers), depending on the thermal structure of the subduction zone. This evidence for deep volatile subduction and large-scale flow of slab-derived, water-rich fluids lends credence to models that invoke fluid addition to sites of arc magma genesis.
The Search for Evidence of Large Prehistoric Earthquakes Along the Atlantic Seaboard
Authors: Amick David , Gelinas Robert
Published: October 2006

The spacial distribution of seismically induced liquefaction features discovered along the Atlantic seaboard suggests that during the last 2000 to 5000 years, large earthquakes (body wave magnitude,
m
b
≥ 5.8 ± 0.4) in this region may have been restricted exclusively to South Carolina. Paleoliquefaction evidence for six large prehistoric earthquakes was discovered there. At least five of these past events originated in the Charleston, South Carolina, area, the locale of a magnitude 7+ event in 1886. During the past two millennia, large events may have occurred about every 500 to 600 years.
The Quasi-Stationary and Transient States of the Solar Wind
Authors: Neugebauer M.
Published: October 2006

There are two states of the solar wind: quasi-stationary and transient. After 30 years of measurements by interplanetary spacecraft, the differences in the physical properties of the two types of wind are fairly well determined, but the physical processes involved in their accelerations are not yet understood in detail. The solar wind exists in part because the upper solar atmosphere, called the corona, is very hot, but the heating mechanisms are also not well understood. Recent research suggests a link between the heating and acceleration mechanisms.