bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid β-Adrenergic Modulation of Cardiac Calcium Channel Currents by a Fast G Protein Pathway
Authors: Yatani Atsuko , Brown Arthur M.
Published: October 2006

β-Adrenergic agonists activate the G protein, G
s
, which stimulates cardiac calcium currents by both cytoplasmic, indirect and membrane-delimited, direct pathways. To test whether β-adrenergic agonists might use both pathways in the heart, isoproterenol was rapidly applied to cardiac myocytes, resulting in a biphasic increase in cardiac calcium channel currents that had time constants of 150 milliseconds and 36 seconds. β-Adrenergic antagonists of a G protein inhibitor blocked both the fast and slow responses, whereas the adenylyl cyclase activator forskolin produced only the slow response. The presence of a fast pathway in the heart can explain what the slow pathway cannot account for: the ability of cardiac sympathetic nerves to change heart rate within a single beat.
Chemical Signals from Host Plant and Sexual Behavior in a Moth
Authors: Raina Ashok K. , Kingan Timothy G. , Mattoo Autar K.
Published: October 2006

In the phytophagous corn earworm,
Helicoverpa
(
Heliothis
)
zea
, females delay their reproductive behaviors until they find a suitable host on which to deposit their eggs. Perception of volatile chemical signals from corn silk triggers the production of sex pheromone followed by its release, which leads to mating. Several natural corn silk volatiles, including the plant hormone ethylene, induced pheromone production in
H. zea
females. Because
H. zea
larvae feed on the fruiting parts of a wide variety of hosts, ethylene, which is associated with fruit ripening, could act as a common cue.
Deformational Mass Transport and Invasive Processes in Soil Evolution
Authors: Brimhall George H , Chadwick Oliver A. , Lewis Chris J. , Compston William , Williams Ian S. , Danti Kathy J. , Dietrich William E. , Power Mary E. , Hendricks David , Bratt James
Published: October 2006

Soils are differentiated vertically by coupled chemical, mechanical, and biological transport processes. Soil properties vary with depth, depending on the subsurface stresses, the extent of mixing, and the balance between mass removal in solution or suspension and mass accumulation near the surface. Channels left by decayed roots and burrowing animals allow organic and inorganic detritus and precipitates to move through the soil from above. Accumulation occurs at depths where small pores restrict further passage. Consecutive phases of translocation and root growth stir the soil; these processes constitute an invasive dilatational process that leads to positive cumulative strains. In contrast, below the depth of root penetration and mass additions, mineral dissolution by descending organic acids leads to internal collapse under overburden load. This softened and condensed precursor horizon is transformed into soil by biological activity, which stirs and expands the evolving residuum by invasion by roots and macropore networks that allows mixing of materials from above.
Neotropical Mammals and the Myth of Amazonian Biodiversity
Authors: Mares Michael A.
Published: October 2006

Data were compiled on the distribution of mammal taxa (883 species, 242 genera, 45 families, and 10 orders) among South America's six major macrohabitats: lowland Amazon forest, western montane forests, Atlantic rain forest, upland semideciduous forest, southern mesophytic forest, and drylands. The drylands are the richest area in numbers of species supported and are more diverse than the other habitats, including the lowland Amazon rain forest, when endemics are considered. An analysis of number of endemic and nonendemic taxa versus size of area found a simple positive linear relationship: the drylands, almost twice as extensive as the Amazon lowlands, support more endemic taxa. Conservation plans that emphasize the wet tropics and fail to consider the drylands as special repositories of mammal diversity will be unable to preserve a significant number of novel taxa.
A Transient Radio Source near the Center of the Milky Way Galaxy
Authors: Zhao Jun-Hui , Roberts D. A. , Goss W. M. , Frail D. A. , Lo K. Y. , Subrahmanyan R. , Kesteven M. J. , Ekers R. D. , Allen D. A. , Burton M. G. , Spyromilio J.
Published: October 2006

In late December 1990, a new radio source appeared near the center of our galaxy rivaling the intensity of Sgr A
*
(the compact radio source at the galactic center). Following its first detection, the flux density of the galactic center transient (GCT) increased rapidly to a maximum 1 month later, and then declined gradually with a time scale of about 3 months. Surprisingly, the GCT maintained a steep radio spectrum during both its rising and decay phases. The neutral hydrogen (HI) absorption shows similar absorption to that in front of Sgr A
*
; this indicates that the GCT lies near the galactic center. Furthermore, both HI and OH observations show an additional deep absorption at +20 kilometers per second with respect to the local standard of rest. Thus, the GCT is either embedded in or located behind a molecular cloud moving with that velocity. The cloud can be seen on infrared images. Its opacity is shown to be inadequate to conceal a supernova near the galactic center. It is argued that the GCT was probably transient radio emission from synchrotron-radiating plasma associated with an x-ray binary system.
Alternative Forms of Max as Enhancers or Suppressors of Myc-Ras Cotransformation
Authors: Mäkelä Tomi P. , Koskinen Päivi J. , Västrik Imre , Alitalo Kari
Published: October 2006

Max is a basic-helix-loop-helix- leucine zipper protein capable of forming sequence-specific DNA binding complexes with Myc proteins. An alternatively spliced messenger RNA has been identified that encodes a form of Max truncated at the COOH-terminus. This ΔMax protein retained the ability to bind to the CACGTG motif in a complex with c-Myc but lacks the nuclear localization signal and the putative regulatory domain of Max. When tested in a
myc-ras
cotransformation assay in rat embryo fibroblasts, Max suppressed, whereas ΔMax enhanced, transformation. Thus, the
max
gene may encode both a negative and a positive regulator of c-Myc function.
Cell Cycle—Regulated Binding of c-Abl Tyrosine Kinase to DNA
Authors: Kipreos Edward T. , Wang Jean Y. J.
Published: October 2006

The proto-oncogene c-
abl
encodes a protein tyrosine kinase that is localized in the cytoplasm and the nucleus. The large carboxyl-terminal segment of c-Abl was found to contain a DNA-binding domain that was necessary for the association of c-Abl with chromatin. The DNA-binding activity of c-Abl was lost during mitosis when the carboxyl-terminal segment became phosphorylated. In vitro phosphorylation of the DNA-binding domain by cdc2 kinase abolished DNA binding. Homozygous mutant mice expressing a c-Abl tyrosine kinase without the DNA-binding domain have been reported to die of multiple defects at birth. Thus, binding of the c-Abl tyrosine kinase to DNA may be essential to its biological function.
Less Mortality but More Relapses in Experimental Allergic Encephalomyelitis in CD8
-/-
Mice
Authors: Koh Dow-Rhoon , Fung-Leung Wai-Ping , Ho Alexandra , Gray Dawn , Acha-Orbea Hans , Mak Tak-Wah
Published: October 2006

Mice lacking in CD8 were generated from homologous recombination in embryonal stem cells at the CD8 locus and bred with the experimental allergic encephalomyelitis (EAE)susceptible PL/J H-2
u
through four backcross generations to investigate the role of CD8
+
T cells in this model of multiple sclerosis. The disease onset and susceptibility were similar to those of wild-type mice. However, the mutant mice had a milder acute EAE, reflected by fewer deaths, but more chronic EAE, reflected by a higher frequency of relapse. This suggests that CD8
+
T lymphocytes may participate as both effectors and regulators in this animal model.
Soluble Aluminum Silicates: Stoichiometry, Stability, and Implications for Environmental Geochemistry
Authors: Browne B. A. , Driscoll C. T.
Published: October 2006

Soluble aluminum silicate (Al-Si) complexes are critical species for the development and application of geochemical models. A fluorescence probe technique was used to show that Al-Si complexes account for up to 95% of the total inorganic mononuclear Al in natural waters. The presence of these soluble Al-Si species affects the solubility of Al-Si minerals. Soluble Al-Si species may be important intermediates in the weathering reactions of primary Al-Si minerals and should be considered in dissolution models. Soluble Al-Si species may be key components controlling the formation of metastable and new stable minerals during interactions between water and rocks or soils.
Identification of a Zinc Finger Protein That Binds to the Sterol Regulatory Element
Authors: Rajavashisth Tripathi B. , Taylor Annette K. , Andalibi Ali , Svenson Karen L. , Lusis Aldons J.
Published: October 2006

Cholesterol balance in mammalian cells is maintained in part by sterol-mediated repression of gene transcription for the low density lipoprotein receptor and enzymes in the cholesterol biosynthetic pathway. A promoter sequence termed the sterol regulatory element (SRE) is essential for this repression. With the use of an oligonucleotide containing the SRE to screen a human hepatoma complementary DNA expression library, a clone for a DNA binding protein was isolated that binds to the conserved SRE octanucleotide in both a sequence-specific and a single-strand-specific manner. This protein contains seven highly conserved zinc finger repeats that exhibit striking sequence similarity to retroviral nucleic acid binding proteins (NBPs). We have designated the protein "cellular NBP" (CNBP). CNBP is expressed in a wide variety of tissues, is up regulated by sterols, and exhibits binding specificity that correlates with in vivo function. These properties are consistent with a role in sterol-mediated control of transcription.
Evolution of Urea Synthesis in Vertebrates: The Piscine Connection
Authors: Mommsen Thomas P. , Walsh Patrick J.
Published: October 2006

Elasmobranch fishes, the coelacanth, estivating lungfish, amphibians, and mammals synthesize urea by the ornithine-urea cycle; by comparison, urea synthetic activity is generally insignificant in teleostean fishes. It is reported here that isolated liver cells of two teleost toadfishes,
Opsanus beta
and
Opsansus tau
, synthesize urea by the ornithine-urea cycle at substantial rates. Because toadfish excrete ammonia, do not use urea as an osmolyte, and have substantial levels of urease in their digestive systems, urea may serve as a transient nitrogen store, forming the basis of a nitrogen conservation shuttle system between liver and gut as in ruminants and hibernators. Toadfish synthesize urea using enzymes and subcellular distributions similar to those of elasmobranchs: glutamine-dependent carbamoyl phosphate synthethase (CPS III) and mitochondrial arginase. In contrast, mammals have CPS I (ammonia-dependent) and cytosolic arginase. Data on CPS and arginases in other fishes, including lungfishes and the coelacanth, support the hypothesis that the ornithine-urea cycle, a monophyletic trait in the vertebrates, underwent two key changes before the evolution of the extant lungfishes: a switch from CPS III to CPS I and replacement of mitochondrial arginase by a cytosolic equivalent.
Structural Processes at Slow-Spreading Ridges
Authors: Mutter John C. , Karson Jeffrey A.
Published: October 2006

Slow-spreading (<35 millimeters per year) mid-ocean ridges are dominated by segmented, asymmetric, rifted depressions like continental rifts. Fast-spreading ridges display symmetric, elevated volcanic edifices that vary in shape and size along axis. Deep earthquakes, major normal faults, and exposures of lower crustal rocks are common only along slow-spreading ridges. These contrasting features suggest that mechanical deformation is far more important in crustal formation at slow-spreading ridges than at fast-spreading ridges. New seismic images suggest that the nature and scale of segmentation of slow-spreading ridges is integral to the deformational process and not to magmatic processes that may control segmentation on fast-spreading ridges.
Sea-Surface Temperature from Coral Skeletal Strontium/Calcium Ratios
Authors: Beck J. Warren , Edwards R. Lawrence , Ito Emi , Taylor Frederick W. , Recy Jacques , Rougerie Francis , Joannot Pascale , Henin Christian
Published: October 2006

Seasonal records of tropical sea-surface temperature (SST) over the past 10
5
years can be recovered from high-precision measurements of coral strontium/calcium ratios with the use of thermal ionization mass spectrometry. The temperature dependence of these ratios was calibrated with corals collected at SST recording stations and by
18
O/
16
O thermometry. The results suggest that mean monthly SST may be determined with an apparent accuracy of better than 0.5°C. Measurements on a fossil coral indicate that 10,200 years ago mean annual SSTs near Vanuatu in the southwestern Pacific Ocean were about 5°C colder than today and that seasonal variations in SST were larger. These data suggest that tropical climate zones were compressed toward the equator during deglaciation.
Elasticity of α-Cristobalite: A Silicon Dioxide with a Negative Poisson's Ratio
Authors: Yeganeh-Haeri Amir , Weidner Donald J. , Parise John B.
Published: October 2006

Laser Brillouin spectroscopy was used to determine the adiabatic single-crystal elastic stiffness coefficients of silicon dioxide (SiO
2
) in the α-cristobalite structure. This SiO
2
polymorph, unlike other silicas and silicates, exhibits a negative Poisson's ratio; α-cristobalite contracts laterally when compressed and expands laterally when stretched. Tensorial analysis of the elastic coefficients shows that Poisson's ratio reaches a maximum value of –0.5 in some directions, whereas averaged values for the single-phased aggregate yield a Poisson's ratio of –0.16.
Human and
Drosophila
Homeodomain Proteins That Enhance the DNA-Binding Activity of Serum Response Factor
Authors: Grueneberg Dorre A. , Natesan Sridaran , Alexandre Cyrille , Gilman Michael Z.
Published: October 2006

Cells with distinct developmental histories can respond differentially to identical signals, suggesting that signals are interpreted in a fashion that reflects a cell's identity. How this might occur is suggested by the observation that proteins of the homeodomain family, including a newly identified human protein, enhance the DNA-binding activity of serum response factor, a protein required for the induction of genes by growth and differentiation factors. Interaction with proteins of the serum response factor family may allow homeodomain proteins to specify the transcriptional response to inductive signals. Moreover, because the ability to enhance the binding of serum response factor to DNA resides within the homeodomain but is independent of homeodomain DNA-binding activity, this additional activity of the homeodomain may account for some of the specificity of action of homeodomain proteins in development.
Oxygen Isotope Constraints on the Origin of Impact Glasses from the Cretaceous-Tertiary Boundary
Authors: Blum Joel D. , Chamberlain C. Page
Published: October 2006

Laser-extraction oxygen isotope and major element analyses of individual glass spherules from Haitian Cretaceous-Tertiary boundary sediments demonstrate that the glasses fall on a mixing line between an isotopically heavy (δ
18
O = 14 per mil) high-calcium composition and an isotopically light (δ
18
O = 6 per mil) high-silicon composition. This trend can be explained by melting of heterogeneous source rocks during the impact of an asteroid (or comet) ∼65 million years ago. The data indicate that the glasses are a mixture of carbonate and silicate rocks and exclude derivation of the glasses either by volcanic processes or as mixtures of sulfate-rich evaporate and silicate rocks.
Scale and Structure in Natural Food Webs
Authors: Havens Karl
Published: October 2006

The degree to which widely accepted generalizations about food web structure apply to natural communities was determined through examination of 50 pelagic webs sampled consistently with even taxonomic resolution of all trophic levels. The fraction of species in various trophic categories showed no significant overall trends as the number of species varied from 10 to 74. In contrast, the number of links per species increased fourfold over the range of species number, suggesting that the link-species scaling law, defined on the basis of aggregated webs, does not reflect a real ecological trend.
Galileo Encounter with 951 Gaspra: First Pictures of an Asteroid
Authors: Belton M. J. S. , Veverka J. , Thomas P. , Helfenstein P. , Simonelli D. , Chapman C. , Davies M. E. , Greeley R. , Greenberg R. , Head J. , Murchie S. , Klaasen K. , Johnson T. V. , McEwen A. , Morrison D. , Neukum G. , Fanale F. , Anger C. , Carr M. , Pilcher C.
Published: October 2006

Galileo images of Gaspra reveal it to be an irregularly shaped object (19 by 12 by 11 kilometers) that appears to have been created by a catastrophic collisional disruption of a precursor parent body. The cratering age of the surface is about 200 million years. Subtle albedo and color variations appear to correlate with morphological features: Brighter materials are associated with craters especially along the crests of ridges, have a stronger 1-micrometer absorption, and may represent freshly excavated mafic materials; darker materials exhibiting a significantly weaker 1-micrometer absorption appear concentrated in interridge areas. One explanation of these patterns is that Gaspra is covered with a thin regolith and that some of this material has migrated downslope in some areas.
Molecular Structure of the Coalescence of Liquid Interfaces
Authors: Koplik Joel , Banavar Jayanth R.
Published: October 2006

When two bodies of liquid merge, their interfaces must also rupture and rearrange into one. Virtually no information is available concerning the small-scale dynamics of this process. Molecular dynamics simulations of coalescence in systems of about 10,000 Lennard-Jones particles have been performed, arranged so as to mimic laboratory experiments on dense liquids. The coalescence event begins when molecules near the boundary of one liquid body thermally fluctuate into the range of attraction of the other, forming a string of mutually attracting molecules. These molecules gradually thicken into a tendril, which continues to thicken as the bodies smoothly combine in a zipper-like merger.
Rapid Intraplate Strain Accumulation in the New Madrid Seismic Zone
Authors: Liu Lanbo , Zoback Mark D. , Segall Paul
Published: October 2006

Remeasurement of a triangulation network in the southern part of the New Madrid seismic zone with the Global Positioning System has revealed rapid crustal strain accumulation since the 1950s. This area experienced three large (moment magnitudes >8) earthquakes in 1811 to 1812. The orientation and sense of shear is consistent with right-lateral strike slip motion along a northeast-trending fault zone (as indicated by current seismicity). Detection of crustal strain accumulation may be a useful discriminant for identifying areas where potentially damaging intraplate earthquakes may occur despite the absence of large earthquakes during historic time.
Continuous 500,000-Year Climate Record from Vein Calcite in Devils Hole, Nevada
Authors: Winograd Isaac J. , Coplen Tyler B. , Landwehr Jurate M. , Riggs Alan C. , Ludwig Kenneth R. , Szabo Barney J. , Kolesar Peter T. , Revesz Kinga M.
Published: October 2006

Oxygen-18 (δ
18
O) variations in a 36-centimeter-long core (DH-11) of vein calcite from Devils Hole, Nevada, yield an uninterrupted 500,000-year paleotemperature record that closely mimics all major features in the Vostok (Antarctica) paleotemperature and marine δ
18
O ice-volume records. The chronology for this continental record is based on 21 replicated mass-spectrometric uranium-series dates. Between the middle and latest Pleistocene, the duration of the last four glacial cycles recorded in the calcite increased from 80,000 to 130,000 years; this variation suggests that major climate changes were aperiodic. The timing of specific climatic events indicates that orbitally controlled variations in solar insolation were not a major factor in triggering deglaciations. Interglacial climates lasted about 20,000 years. Collectively, these observations are inconsistent with the Milankovitch hypothesis for the origin of the Pleistocene glacial cycles but they are consistent with the thesis that these cycles originated from internal nonlinear feedbacks within the atmosphere-ice sheet-ocean system.
Mass-Spectrometric
230
Th-
234
U-
238
U Dating of the Devils Hole Calcite Vein
Authors: Ludwig Kenneth R. , Simmons Kathleen R. , Szabo Barney J. , Winograd Isaac J. , Landwehr Jurate M. , Riggs Alan C. , Hoffman Ray J.
Published: October 2006

The Devils Hole calcite vein contains a long-term climatic record, but requires accurate chronologic control for its interpretation. Mass-spectrometric U-series ages for samples from core DH-11 yielded
230
Th ages with precisions ranging from less than 1,000 years (2σ) for samples younger than ∼140 ka (thousands of years ago) to less than 50,000 years for the oldest samples (∼566 ka). The
234
U/
238
U ages could be determined to a precision of ∼20,000 years for all ages. Calcite accumulated continuously from 566 ka until ∼60 ka at an average rate of 0.7 millimeter per 10
3
years. The precise agreement between replicate analyses and the concordance of the
230
Th/
238
U and
234
U/
238
U ages for the oldest samples indicate that the DH-11 samples were closed systems and validate the dating technique in general.
Simultaneous Miocene Extension and Shortening in the Himalayan Orogen
Authors: Hodges K. V. , Parrish R. R. , Housh T. B. , Lux D. R. , Burchfiel B. C. , Royden L. H. , Chen Z.
Published: October 2006

The South Tibetan detachment system separates the high-grade metamorphic core of the Himalayan orogen from its weakly metamorphosed suprastructure. It is thought to have developed in response to differences in gravitational potential energy produced by crustal thickening across the mountain front. Geochronologic data from the Rongbuk Valley, north of Qomolangma (Mount Everest) in southern Tibet, demonstrate that at least one segment of the detachment system was active between 19 and 22 million years ago, an interval characterized by large-scale crustal thickening at lower structural levels. These data suggest that decoupling between an extending upper crust and a converging lower crust was an important aspect of Himalayan tectonics in Miocene time.
A Tsunami About 1000 Years Ago in Puget Sound, Washington
Authors: Atwater Brian F. , Moore Andrew L.
Published: October 2006

Water surged from Puget Sound sometime between 1000 and 1100 years ago, overrunning tidal marshes and mantling them with centimeters of sand. One overrun site is 10 kilometers northwest of downtown Seattle; another is on Whidbey Island, some 30 kilometers farther north. Neither site has been widely mantled with sand at any other time in the past 2000 years. Deposition of the sand coincided—to the year or less—with abrupt, probably tectonic subsidence at the Seattle site and with landsliding into nearby Lake Washington. These findings show that a tsunami was generated in Puget Sound, and they tend to confirm that a large shallow earthquake occurred in the Seattle area about 1000 years ago.
Functional Coupling of γ-Aminobutyric Acid Receptors to Chloride Channels in Brain Membranes
Authors: Harris R. Adron , Allan Andrea M.
Published: October 2006

γ-Aminobutyric acid (GABA), the major inhibitory neurotransmitter in mammalian brain, is believed to act by increasing membrane conductance of chloride ions. In this study it was found that GABA agonists increased the uptake of chloride-36 by cell-free membrane preparations from mouse brain. This influx was rapid (less than 5 seconds), and 13 micromolar GABA produced a half-maximal effect. The GABA antagonists (bicuculline and picrotoxin) blocked the effect of GABA, whereas pentobarbital enhanced the action. This may be the first demonstration of functional coupling among GABA and barbiturate receptors and chloride channels in isolated membranes. The technique should facilitate biochemical and pharmacological studies of GABA receptor-effector coupling.
Particles Floating on a Moving Fluid: A Dynamically Comprehensible Physical Fractal
Authors: Sommerer John C. , Ott Edward
Published: October 2006

Measurements of the local dynamics on the surface of a fluid undergoing complicated motion allow prediction of the measured fractal dimension of an aggregate of passive, floating tracers. This realization of a strange attractor in physical space is a rare instance where there is a firm quantitative connection between the dimension of an experimentally observed fractal spatial pattern and the process producing it.
Noble Gas Partitioning Between Metal and Silicate Under High Pressures
Authors: Matsuda J. , Sudo M. , Ozima M. , Ito K. , Ohtaka O. , Ito E.
Published: October 2006

Measurements of noble gas (helium, neon, argon, krypton, and xenon) partitioning between silicate melt and iron melt under pressures up to 100 kilobars indicate that the partition coefficients are much less than unity and that they decrease systematically with increasing pressure. The results suggest that the Earth's core contains only negligible amounts of noble gases if core separation took place under equilibrium conditions.
Mid-Depth Circulation of the Subpolar North Atlantic During the Last Glacial Maximum
Authors: Oppo D. W. , Lehman S. J.
Published: October 2006

Holocene and glacial carbon isotope data of benthic foraminifera from shallow to mid-depth cores from the northeastern subpolar Atlantic show that this region was strongly stratified, with carbon-13—enriched glacial North Atlantic intermediate water (GNAIW) overlying carbon-13—depleted Southern Ocean water (SOW). The data suggest that GNAIW originated north of the polar front and define GNAIW end-member carbon isotope values for studies of water-mass mixing in the open Atlantic. Identical carbon isotope values in the core of GNAIW and below the subtropical thermocline are consistent with rapid cycling of GNAIW through the northern Atlantic. The high carbon isotope values below the thermocline indicate that enhanced nutrient leakage in response to increased ventilation may have extended into intermediate waters. Geochemical box models show that the atmospheric carbon dioxide response to nutrient leakage that results from an increase in ventilation rate may be greater than the response to nutrient redistribution by conversion of North Atlantic deep water into GNAIW. These results underscore the potential rule of Atlantic Ocean circulation changes in influencing past atmospheric carbon dioxide values.
Phosphorus: An Elemental Catalyst for Diamond Synthesis and Growth
Authors: Akaishi Minoru , Kanda Hisao , Yamaoka Shinobu
Published: October 2006

As diamond-producing catalysts, 12 transition metals such as iron, cobalt, and nickel were first reported by General Electric researchers more than 30 years ago. Since then, no additional elemental catalyst has been reported. An investigation of the catalytic action of group V elements is of great interest from the viewpoint of producing an
n
-type semiconducting diamond crystal. In the present study, diamond was synthesized from graphite in the presence of elemental phosphorus at high pressure and temperature (7.7 gigapascals and 1800°C). Furthermore, single-crystal diamond was grown on a diamond seed crystal.
Buckytubes and Derivatives: Their Growth and Implications for Buckyball Formation
Authors: Dravid V. P. , Lin X. , Wang Y. , Wang X. K. , Yee A. , Ketterson J. B. , Chang R. P. H.
Published: October 2006

Transmission electron microscopy (TEM) observations of graphite tubules (buckytubes) and their derivatives have revealed not only the previously reported buckytube geometries but also additional shapes of the buckytube derivatives. Detailed cross-sectional TEM images reveal the cylindrical cross section of buckytubes and the growth pattern of buckytubes as well as their derivatives. These observations of frozen growth stages of buckytubes and derivatives suggest a helical growth mechanism analogous to that of crystal growth via screw dislocations. The helicacy of buckytubes is analyzed by electron diffraction whereas the anisotropy of electronic structure is revealed by momentum transfer resolved electron energy loss spectrometry. Based on the TEM observations, it is proposed that buckytubes act as precursors to closed-shell fullerene (buckyball) formation and the possible steps in buckyball formation are outlined. In arc evaporation experiments in which residue rods (containing various amounts of buckytubes) were used as the starting anode for fullerene production, the amount of buckytubes in the rod was correlated with fullerene yield.
Pressure-Induced Amorphization of
R
-Al
5
Li
3
Cu: A Structural Relation Among Amorphous Metals, Quasi-Crystals, and Curved Space
Authors: Winters Robert R. , Hammack William S.
Published: October 2006

A central question in the study of amorphous materials is the extent to which they are ordered. When the crystalline intermetallic
R
-Al
5
Li
3
Cu is compressed to 23.2 gigapascals at ambient temperature, an amorphous phase is produced whose order can be described as defects in a curved-space crystal. This result supports a structural relation between quasi-crystals and amorphous metals based on icosahedral ordering. This result also shows that a metallic crystal can be made amorphous by compression.
Soil Quality and Financial Performance of Biodynamic and Conventional Farms in New Zealand
Authors: Reganold John P. , Palmer Alan S. , Lockhart James C. , Macgregor A. Neil
Published: October 2006

Biodynamic farming practices and systems show promise in mitigating some of the detrimental effects of chemical-dependent, conventional agriculture on the environment. The physical, biological, and chemical soil properties and economic profitability of adjacent, commercial biodynamic and conventional farms (16 total) in New Zealand were compared. The biodynamic farms in the study had better soil quality than the neighboring conventional farms and were just as financially viable on a per hectare basis.
Computer-Simulation Methods in the Study of Noncrystalline Materials
Authors: Yonezawa Fumiko
Published: October 2006

Computer-assisted physics can be considered the third approach besides experimental and theoretical physics. Numerical simulations are especially useful in the study of noncrystalline materials such as liquids, glasses, amorphous solids, and liquid crystals. Some applications of computer simulations to these materials are discussed.
A Laccase Associated with Lignification in Loblolly Pine Xylem
Authors: Bao Wuli , O'Malley David M. , Whetten Ross , Sederoff Ronald R.
Published: October 2006

Peroxidase has been thought to be the only enzyme that oxidizes monolignol precursors to initiate lignin formation in plants. A laccase was purified from cell walls of differentiating xylem of loblolly pine and shown to coincide in time and place with lignin formation and to oxidize monolignols to dehydrogenation products in vitro. These results suggest that laccase participates in lignin biosynthesis and therefore could be an important target for genetic engineering to modify wood properties or to improve the digestibility of forage crops.
Slow Magnetic Relaxation in Iron: A Ferromagnetic Liquid
Authors: Chamberlin R. V. , Scheinfein M. R.
Published: October 2006

The remanent magnetization of single-crystal iron whiskers has been measured from 10
-5
to 10
4
seconds after the removal of an applied field. The observed response is accurately modeled by localized magnon relaxation on a Gaussian size distribution of dynamically correlated domains, virtually identical to the distribution of excitations in glass-forming liquids. When fields of less than 1 oersted are removed, some relaxation occurs before 10
-5
second has elapsed; but when larger fields are removed, essentially all of the response can be accounted for by magnon relaxation over the available time window. The model provides a physical picture for the mechanism and observed distribution of Landau-Lifshitz damping parameters.
Phenotypic Basis of Reproductive Success in a Social Insect: Genetic and Social Determinants
Authors: Keller Laurent , Ross Kenneth G.
Published: October 2006

Social insects live in societies that include both reproductive and nonreproductive adults. Understanding the factors that determine which individuals become successful reproductives is necessary to explain the evolution of these societies. The phenotypic effects of the gene
Pgm-3
(or a closely linked gene) that may cause workers of the fire ant
Solenopsis invicta
to selectively execute all queens of a specific genotype were investigated. These effects, which involve differences in queen reproductive development, are expressed only in colonies exhibiting a particular type of social organization (multiple-queen colonies), and it is only in such colonies that selective execution on the basis of genotype occurs. This is an unusual example of genotype-environment interaction in gene expression in which the environmental component is the social environment. The queens executed are, surprisingly, those with the greatest reproductive development. Thus, there is a counterintuitive relation between the potential and realized reproductive success of queens in multiple-queen societies of this ant.
Polycrystalline CVD Diamond Films with High Electrical Mobility
Authors: Plano M. A. , Landstrass M. I. , Pan L. S. , Han S. , Kania D. R. , McWilliams S. , Ager J. W.
Published: October 2006

Advances in the deposition process have led to dramatic improvements in the electronic properties of polycrystalline diamond films produced by chemical vapor deposition (CVD). It is now possible to produce CVD diamond with properties approaching those of IIa natural diamonds. The combined electron-hole mobility, as measured by transient photoconductivity at low carrier density, is 4000 square centimeters per volt per second at an electric field of 200 volts per centimeter and is comparable to that of the best single-crystal IIa natural diamonds. Carrier lifetimes measured under the same conditions are 150 picoseconds for the CVD diamond and 300 picoseconds for single-crystal diamond. The collection distance at a field of 10 kilovolts per centimeter is 15 micrometers for the CVD diamond as compared to 30 micrometers for natural diamonds. The electrical qualities appear to correlate with the width of the diamond Raman peak. Also, although the collection distance at the highest fields in the films nearly equals the average grain size, there is no evidence of deleterious grain boundary effects.
Crystal Structure of a Silyl Cation with No Coordination to Anion and Distant Coordination to Solvent
Authors: Lambert Joseph B. , Zhang Shizhong , Stern Charlotte L. , Huffman John C.
Published: October 2006

The crystal structure of a stable silyl cation, triethylsilylium, in the form of its tetrakis(pentafluorophenyl)borate salt [Et
3
Si
+
(C
6
F
5
)
4
B
-
] (Et, ethyl) shows no coordination between cation and anion. The closest silicon-fluorine distance is greater than 4 angstroms. A toluene solvent molecule is close enough to cause some deviations from planarity at the silicon, but the silicon-toluene distance is well beyond the sum of the silicon and carbon covalent radii. The toluene molecule is essentially planar and undistorted, as expected if little or no positive charge has been transferred from silicon to toluene.
Evidence from Western North America for Rapid Shifts in Climate During the Last Glacial Maximum
Authors: Allen Bruce D. , Anderson Roger Y.
Published: October 2006

The Estancia basin in southwestern United States contains evidence for strong and rapid pulsations in the supply of moisture brought into the region during the last ice age. The pulses were recorded during episodes of stream discharge that spread plumes of fresh water laden with quartz sand over the saline lake. The largest pulses in stream discharge lasted only a few decades, were organized into cycles that were spaced approximately 200 to 250 and 2000 years apart, and were of sufficient magnitude to freshen and maintain the lake at its maximum recorded elevation.
Detection of Interstellar Pick-Up Hydrogen in the Solar System
Authors: Gloeckler G. , Galvin A. B. , Ipavich F. M. , Geiss J. , Balsiger H. , von Steiger R. , Fisk L. A. , Ogilvie K. W. , Wilken B.
Published: October 2006

Interstellar hydrogen ionized primarily by the solar wind has been detected by the SWICS instrument on the Ulysses spacecraft at a distance of 4.8 astronomical units from the sun. This "pick-up" hydrogen is identified by its distinct velocity distribution function, which drops abruptly at twice the local solar wind speed. From the measured fluxes of pick-up protons and singly charged helium, the number densities of neutral hydrogen and helium in the distant regions of the solar system are estimated to be 0.077 ± 0.015 and 0.013 ± 0.003 per cubic centimeter, respectively.
Teleseismic Detection of a Slow Precursor to the Great 1989 Macquarie Ridge Earthquake
Authors: Ihmlé Pierre F. , Harabaglia Paolo , Jordan Thomas H.
Published: October 2006

Low-frequency spectra for the 1989 Macquarie Ridge earthquake (magnitude 8.2) show an amplitude increase and a phase-delay decrease below 6 millihertz that require a short-term slow precursor. This earthquake can be modeled as a compound event in which a fast-rupturing, ordinary earthquake was initiated by an episode of slow, smooth deformation that began more than 100 seconds before the main shock. The moment released in the slow precursor was large, about 3 × 10
20
newton-meters, equivalent to an event of magnitude 7.6. The data are consistent with the precursor being generated in a region of the oceanic upper mantle below the main rupture.
The Atmosphere During the Younger Dryas
Authors: Mayewski P. A. , Meeker L. D. , Whitlow S. , Twickler M. S. , Morrison M. C. , Alley R. B. , Bloomfield P. , Taylor K.
Published: October 2006

One of the most dramatic climate change events observed in marine and ice core records is the Younger Dryas, a return to near-glacial conditions that punctuated the last deglaciation. High-resolution, continuous glaciochemical records, newly retrieved from central Greenland, record the chemical composition of the arctic atmosphere at this time. This record shows that both the onset and the termination of the Younger Dryas occurred within 10 to 20 years and that massive, frequent, and short-term (decadal or less) changes in atmospheric composition occurred throughout this event. Changes in atmospheric composition are attributable to changes in the size of the polar atmospheric cell and resultant changes in source regions and to the growth and decay of continental biogenic source regions.
The Nature of the Landers-Mojave Earthquake Line
Authors: Nur Amos , Ron Hagai , Beroza Gregory C.
Published: October 2006

The Landers, California, earthquake of 28 June 1992 (magnitude = 7.3) is the latest of six significant earthquakes in the past 60 years whose epicenters and slip directions define a 100-kilometer alignment running approximately N15°W across the central Mojave region. This pattern may indicate a geologically young throughgoing fault that replaces numerous older strike-slip faults by obliquely cutting across them. These older faults, and perhaps also the bend in the San Andreas fault, may be losing their ability to accommodate upper crustal deformation because they have become unfavorably oriented with respect to the regional stress field.
Relation of Major Volcanic Center Concentration on Venus to Global Tectonic Patterns
Authors: Crumpler L. S. , Head James W. , Aubele Jayne C.
Published: October 2006

Global analysis of NASA Magellan image data indicates that a major concentration of volcanic centers covering ∼40 percent of the surface of Venus occurs between the Beta, Atla, and Themis regiones. Associated with this enhanced concentration are geological characteristics commonly interpreted as rifting and mantle upwelling. Interconnected low plains in an annulus around this concentration are characterized by crustal shortening and infrequent volcanic centers that may represent sites of mantle return flow and net downwelling. Together, these observations suggest the existence of relatively simple, large-scale patterns of mantle circulation similar to those associated with concentrations of intraplate volcanism on Earth.
Requirement of Salicylic Acid for the Induction of Systemic Acquired Resistance
Authors: Gaffney Thomas , Friedrich Leslie , Vernooij Bernard , Negrotto David , Nye Gordon , Uknes Scott , Ward Eric , Kessmann Helmut , Ryals John
Published: October 2006

It has been proposed that salicylic acid acts as an endogenous signal responsible for inducing systemic acquired resistance in plants. The contribution of salicylic acid to systemic acquired resistance was investigated in transgenic tobacco plants harboring a bacterial gene encoding salicylate hydroxylase, which converts salicylic acid to catechol. Transgenic plants that express salicylate hydroxylase accumulated little or no salicylic acid and were defective in their ability to induce acquired resistance against tobacco mosaic virus. Thus, salicylic acid is essential for the development of systemic acquired resistance in tobacco.
Multiple Ion Association in Supercritical Aqueous Solutions of Single Electrolytes
Authors: Oelkers Eric H. , Helgeson Harold C.
Published: October 2006

Solute speciation in supercritical aqueous alkali metal halide solutions plays an important role in various industrial and natural processes, for example, corrosion of metals, solvent extraction, crystal growth, metamorphism, and the formation of hydrothermal ore deposits. To better characterize such speciation, degrees of formation of polyatomic clusters of sodium and chlorine ions have been computed with the aid of dissociation constants generated from Monte Carlo calculations which are consistent with both supercritical conductance measurements and electrostatic theory. The calculations indicate that the solute in alkali-halide solutions is successively dominated by increasingly complex polyatomic clusters as the solute molality increases at pressures and temperatures where the dielectric constant of water is ≲ 15.
Altered Growth and Cell Walls in a Fucose-Deficient Mutant of
Arabidopsis
Authors: Reiter Wolf-Dieter , Chapple Clint C. S. , Somerville Chris R.
Published: October 2006

A biochemical screening procedure was developed to identify mutants of
Arabidopsis thaliana
in which the polysaccharide composition of the cell wall was altered. Over 5000 ethyl methanesulfonate—mutagenized plants were analyzed by this method, leading to the identification of 38 mutant lines. One complementation group of mutants was completely deficient in L-fucose, a constituent of pectic and hemicellulosic polysaccharides. These mutant plants were dwarfed in growth habit, and their cell walls were considerably more fragile than normal.
In Situ Observations of Aerosol and Chlorine Monoxide After the 1991 Eruption of Mount Pinatubo: Effect of Reactions on Sulfate Aerosol
Authors: Wilson J. C. , Jonsson H. H. , Brock C. A. , Toohey D. W. , Avallone L. M. , Baumgardner D. , Dye J. E. , Poole L. R. , Woods D. C. , DeCoursey R. J. , Osborn M. , Pitts M. C. , Kelly K. K. , Chan K. R. , Ferry G. V. , Loewenstein M. , Podolske J. R. , Weaver A.
Published: October 2006

Highly resolved aerosol size distributions measured from high-altitude aircraft can be used to describe the effect of the 1991 eruption of Mount Pinatubo on the stratospheric aerosol. In some air masses, aerosol mass mixing ratios increased by factors exceeding 100 and aerosol surface area concentrations increased by factors of 30 or more. Increases in aerosol surface area concentration were accompanied by increases in chlorine monoxide at mid-latitudes when confounding factors were controlled. This observation supports the assertion that reactions occurring on the aerosol can increase the fraction of stratospheric chlorine that occurs in ozone-destroying forms.
Unusual Radar Echoes from the Greenland Ice Sheet
Authors: Rignot E. J. , Ostro S. J. , van Zyl J. J. , Jezek K. C.
Published: October 2006

Airborne radar images of part of the Greenland ice sheet reveal icy terrain whose radar properties are unique among radar-studied terrestrial surfaces but resemble those of Jupiter's icy Galilean satellites. The 5.6- and 24-centimeter-wavelength echoes from the Greenland percolation zone, like the 3.5- and 13-centimeter-wavelength echoes from the icy satellites, are extremely intense and have anomalous circular and linear polarization ratios. However, the detailed subsurface configurations of the Galilean satellite regoliths, where heterogeneities are the product of prolonged meteoroid bombardment, are unlikely to resemble that within the Greenland percolation zone, where heterogeneities are the product of seasonal melting and refreezing.
Why Is the Temperature of the Universe 2.726 Kelvin?
Authors: Turner Michael S.
Published: October 2006

The Cosmic Background Explorer satellite has recently made the most accurate measurement of the temperature of the universe, determining it to be 2.726 ± 0.01 kelvin. In trying to understand why the temperature has this value, one is led to discover the most fundamental features of the universe—an early, radiation-dominated epoch, enormous entropy per nucleon, synthesis of the light elements around 3 minutes after the bang, and a small excess of matter over antimatter—as well as some of the most pressing issues in cosmology today—the development of structure in the universe and the identification of the nature of the ubiquitous dark matter.
Atomic Stabilization by Super-Intense Lasers
Authors: Eberly J. H. , Kulander K. C.
Published: October 2006

Supercomputer simulations predict the creation of an unexpectedly stable form of atomic matter when ordinary atoms are irradiated by very intense, high-frequency laser pulses. In the rising edge of a very intense pulse of ionizing radiation, the atom's wave function distorts adiabatically into a distribution with two well-separated peaks. As the intensity increases, the peak spacing increases so that the atomic electron spends more time far from the nucleus and the ionization rate decreases. This leads to the surprising and counter-intuitive result that the atom becomes more stable as the ionizing radiation gets stronger.
Inner Core Anisotropy Due to the Magnetic Field—induced Preferred Orientation of Iron
Authors: Karato Shun-ichiro
Published: October 2006

Anisotropy of the inner core of the Earth is proposed to result from the lattice preferred orientation of anisotropic iron crystals during their solidification in the presence of a magnetic field. The resultant seismic anisotropy is related to the geometry of the magnetic field in the core. This hypothesis implies that the observed anisotropy (fast velocity along the rotation axis) indicates a strong toroidal field in the core, which supports a strong field model for the geodynamo if the inner core is made of hexagonal close-packed iron.