bluuebunny/crossref_metadata_2025 huggingface dataset:
Floral Evolution: Attractiveness to Pollinators Increases Male Fitness
Authors: Stanton Maureen L. , Snow Allison A. , Handel Steven N.
Published: October 2006

Because availability of resources often limits seed or fruit set, increased visits by pollinators may not always lead to increases in maternal reproduction. This observation has led evolutionary biologists to hypothesize that a plant's ability to attract pollinators may have its primary impact on male fitness achieved through the fertilization of ovules. This interpretation of angiosperm reproductive ecology is supported by field experiments. Pollinating insects strongly discriminated between two Mendelian petal-color morphs in
Raphanus raphanistrum
, a widespread, self-incompatible crucifer. In experimental populations composed of petal-color homozygotes. color discrimination by naturally occurring pollinators had no statistically significant effect on relative maternal function (fruit and seed production) in the two morphs. In contrast, yellow-flowered individuals were far more successful as fathers (pollen donors) than were the less visited whites. These results suggest that the evolution of floral signals such as petal color may be driven primarily by selection on male function.
The Effect of Electrical Coupling on the Frequency of Model Neuronal Oscillators
Authors: Kepler Thomas B. , Marder Eve , Abbott L. F.
Published: October 2006

Neurons with oscillatory properties are a common feature of the nervous system, but little is known about how neural oscillators shape the behavior of neuronal networks or how network interactions influence the properties of neural oscillators. Mathematical models are used to examine the effect of electrically coupling an oscillatory neuron to a second neuron that is either silent or tonically firing. Models of oscillatory neurons with varying degrees of complexity show that this coupling can either increase or decrease the frequency of an oscillator, depending on its membrane potential wave form, the state of the neuron to which it is coupled, and the strength of the coupling. Thus, electrical coupling provides a flexible mechanism for modifying the behavior of an oscillatory neural network.
Defective Presentation of Endogenous Antigen by a Cell Line Expressing Class I Molecules
Authors: Hosken Nancy A. , Bevan Michael J.
Published: October 2006

Cytotoxic T lymphocytes (CTLs) recognize class I major histocompatibility complex (MHC) molecules associated with antigenic peptides derived from endogenously synthesized proteins. Binding to such peptides is a requirement for class I assembly in the endoplasmic reticulum (ER). A mutant human cell line, T2, assembles and transports to its surface some, but not all, class I MHC molecules. The class I molecules expressed on the surface of T2 do not present peptides derived from cytosolic antigens, although they can present exogenously added peptides to CTL. The transported class I molecules may interact weakly with an unknown retaining factor in the ER such that they can assemble despite the relative shortage of peptides.
First Plasma Wave Observations at Uranus
Authors: Gurnett D. A. , Kurth W. S. , Scarf F. L. , Poynter R. L.
Published: October 2006

Radio emissions from Uranus were detected by the Voyager 2 plasma wave instrument about 5 days before closest approach at frequencies of 31.1 and 56.2 kilohertz. About 10 hours before closest approach the bow shock was identified by an abrupt broadband burst of electrostatic turbulence at a radial distance of 23.5 Uranus radii. Once Voyager was inside the magnetosphere, strong whistler-mode hiss and chorus emissions were observed at radial distances less than about 8 Uranus radii, in the same region where the energetic particle instruments detected intense fluxes of energetic electrons. Various other plasma waves were also observed in this same region. At the ring plane crossing, the plasma wave instrument detected a large number of impulsive events that are interpreted as impacts of micrometer-sized dust particles on the spacecraft. The maximum impact rate was about 30 to 50 impacts per second, and the north-south thickness of the impact region was about 4000 kilometers.
Infrared Observations of the Uranian System
Authors: Hanel R. , Conrath B. , Flasar F. M. , Kunde V. , Maguire W. , Pearl J. , Pirraglia J. , Samuelson R. , Cruikshank D. , Gautier D. , Gierasch P. , Horn L. , Schulte P.
Published: October 2006

The infrared interferometer spectrometer (IRIS) on Voyager 2 recorded thermal emission spectra of Uranus between 200 and 400 cm
-1
and of Miranda and Ariel between 200 and 500 cm
-1
with a spectral resolution of 4.3 cm
-1
. Reflected solar radiation was also measured with a single-channel radiometer sensitive in the visible and near infrared. By combining IRIS spectra with radio science results, a mole fraction for atmospheric helium of 0.15 ± 0.05 (mass fraction, 0.26 ± 0.08) is found. Vertical temperature profiles between 60 and 900 millibars were derived from average polar and equatorial spectra. Temperatures averaged over a layer between 400 to 900 millibars show nearly identical values at the poles and near the equator but are 1 or 2 degrees lower at mid-latitudes in both hemispheres. The cooler zone in the southern hemisphere appears darker in reflected sunlight than the adjacent areas. An upper limit for the effective temperature of Uranus is 59.4 kelvins. Temperatures of Miranda and Ariel at the subsolar point are 86 ± 1 and 84 ± 1 kelvins, respectively, implying Bond albedos of 0.24 ± 0.06 and 0.31 ± 0.06, respectively. Estimates of phase integrals suggest that these satellites have unusual surface microstructure.
The Magnetosphere of Uranus: Hot Plasma and Radiation Environment
Authors: Krimigis S. M. , Armstrong T. P. , Axford W. I. , Cheng A. F. , Gloeckler G. , Hamilton D. C. , Keath E. P. , Lanzerotti L. J. , Mauk B. H.
Published: October 2006

The low-energy charged-particle (LECP) instrument on Voyager 2 measured low-energy electrons and ions near and within the magnetosphere of Uranus. Initial analysis of the LECP measurements has revealed the following. (i) The magnetospheric particle population consists principally of protons and electrons having energies to at least 4 and 1.2 megaelectron volts, respectively, with electron intensities substantially exceeding proton intensities at a given energy. (ii) The intensity profile for both particle species shows evidence that the particles were swept by planetary satellites out to at least the orbit of Titania. (iii) The ion and electron spectra may be described by a Maxwellian core at low energies (less than about 200 kiloelectron volts) and a power law at high energies (greater than about 590 kiloelectron volts; exponent γ, 3 to 10) except inside the orbit of Miranda, where power-law spectra (γ approximately 1.1 and 3.1 for electrons and protons, respectively) are observed. (iv) At ion energies between 0.6 and 1 megaelectron volt per nucleon, the composition is dominated by protons with a minor fraction (about 10
-3
) of molecular hydrogen; the lower limit for the ratio of hydrogen to helium is greater than 10
4
. (v) The proton population is sufficiently intense that fluences greater than 10
16
per square centimeter can accumulate in 10
4
to 10
5
years; such fluences are sufficient to polymerize carbon monoxide and methane ice surfaces. The overall morphology of Uranus' magnetosphere resembles that of Jupiter, as evidenced by the fact that the spacecraft crossed the plasma sheet through the dawn magnetosheath twice per planetary rotation period (17.3 hours). Uranus' magnetosphere differs from that of Jupiter and of Saturn in that the plasma β is at most 0.1 rather than 1. Therefore, little distortion of the field is expected from particle loading at distances less than about 15 Uranus radii.
Will Growth Hormone Swell Milk Surplus?
Authors: Sun Marjorie
Published: October 2006

A debate is raging over whether commercial introduction of bovine growth hormone will exacerbate the financial problems of small dairy farmers
Impact Ejecta Horizon Within Late Precambrian Shales, Adelaide Geosyncline, South Australia
Authors: Gostin Victor A. , Haines Peter W. , Jenkins Richard J. F. , Compston William , Williams Ian S.
Published: October 2006

A solitary layer of shattered crustal rock fragments has been traced over a distance of 260 kilometers within folded 600-million-year-old Precambrian marine shales of the Adelaide Geosyncline, South Australia. The fragments consist entirely of acid to intermediate volcanics (approximately 1575 million years old) displaying shattered mineral grains, shock lamellae in quartz, and small shatter cones. Fragments reach 30 centimeters in diameter and show evidence of vertical fall emplacement. Available evidence points to derivation of the rock fragments from a distant hypervelocity impact into the Gawler Range Volcanics at Lake Acraman, approximately 300 kilometers west of the Adelaide Geosyncline.
The Acraman Impact Structure: Source of Ejecta in Late Precambrian Shales, South Australia
Authors: Williams George E.
Published: October 2006

A major probable impact structure occurs in middle Proterozoic dacitic volcanics in the Gawler Ranges, central South Australia. The structure has an inner depressed area about 30 kilometers in diameter that contains the Lake Acraman salina, an intermediate depression or ring about 90 kilometers in diameter, and a possible outer ring approximately 160 kilometers in diameter. Outcrops of dacite in Lake Acraman are intensely shattered and contain shatter cones and multiple sets of shock lamellae in quartz grains. The Acraman structure is the largest probable impact structure known in Australia and is the likely source of dacitic ejecta found in late Precambrian marine shales some 300 kilometers to the east.
A Fossil Grass (Gramineae: Chloridoideae) from the Miocene with Kranz Anatomy
Authors: Thomasson Joseph R. , Nelson Michael E. , Zakrzewski Richard J.
Published: October 2006

A fossil leaf fragment collected from the Ogallala Formation of northwestern Kansas exhibits features found in taxa of the modern grass subfamily Chloridoideae. These include bullet-shaped, bicellular microhairs, dumbbell-shaped silica bodies, cross-shaped suberin cells, papillae, stomata with low dome- to triangular-shaped subsidiary cells, and Kranz leaf anatomy. The leaf fragment extends the fossil record of plants that show both anatomical and external micromorphological features indicating C
4
photosynthesis back to the Miocene. On the basis of associated mammals, the leaf fragment is assigned a Hemphillian age (7 to 5 million years ago).
Eruption of the Nevado del Ruiz Volcano, Colombia, on 13 November 1985: Gas Flux and Fluid Geochemistry
Authors: Williams Stanley N. , Lowe Donald R. , Stoiber Richard E. , Garcia P. Nestor , Londoño C. Adela , Gemmell J. Bruce , Connor Charles B.
Published: October 2006

The 13 November 1985 eruption of Nevado del Ruiz volcano, in Colombia, released a small volume of pyroclastic material and a disproportionately large volume of volcanic gas. Before the eruption, summit fumarole gases became less water-rich, and the sulfur/chlorine ratio increased. Remote measurements of sulfur dioxide flux after the eruption indicated active degassing at levels associated with eruptive or inter-eruptive stages of other volcanoes. Thermal water analyses revealed increases in magnesium, calcium, and potassium and an increase in the magnesium/chlorine ratio, suggesting that these elements may have been leached from new magma. Ash leachate data showed sulfate and chloride concentrations and ratios that would be expected for the late stages of a major Plinian eruption. Water from the lahar contained high concentrations of sulfate and had a sulfur/chlorine ratio of 4.67, suggesting that water ejected from the crater lake and turbulent mixing of pyroclasts and glacial ice triggered the lahar. Microprobe analyses of pumice from this eruption and the most recent previous event showed similar mixed andesites. The uniform composition of the pumices and the unusually high ratio of gas to magma suggest that, although a new batch of magma triggered this eruption, the pumice that erupted may actually be old. Large volumes of new magma and glacial ice make the volcano dangerous and should stimulate development of an integrated long-term monitoring program to include Tolima volcano, 25 kilometers to the south.
Investigation of Ultrafast Phenomena in the Femtosecond Time Domain
Authors: Shank Charles V.
Published: October 2006

Rapid progress has taken place in the generation and application of femtosecond optical pulses. The impact of these developments is being felt in a broad range of scientific fields, including physics, chemistry, biology, and engineering. These rapidly evolving techniques have been applied to such diverse problems as phase transitions in highly excited semiconductors, molecular photofragment spectroscopy, impulsive phonon generation in solids, and optical radar ranging through biological tissue.
Laboratory Experiments on Planetary and Stellar Convection Performed on Spacelab 3
Authors: Hart J. E. , Toomre J. , Deane A. E. , Hurlburt N. E. , Glatzmaier G. A. , Fichtl G. H. , Leslie F. , Fowlis W. W. , Gilman P. A.
Published: October 2006

Experiments on thermal convection in a rotating, differentially heated hemispherical shell with a radial buoyancy force were conducted in an orbiting microgravity laboratory. A variety of convective structures, or planforms, were observed, depending on the magnitude of the rotation and the nature of the imposed heating distribution. The results are compared with numerical simulations that can be conducted at the more modest heating rates, and suggest possible regimes of motion in rotating planets and stars.
Low-Energy Atom Scattering from Surfaces
Authors: Engel Thomas
Published: October 2006

Experiments in which low-energy atoms are scattered from surfaces represent an important new method for structural analysis of the topmost atomic layers of a surface. The method and its application in a number of areas in surface science, such as detecting surface defects and studying lattice dynamics, are discussed.
Refractory Minerals in Interplanetary Dust
Authors: Christoffersen Roy , Buseck Peter R.
Published: October 2006

A newly studied interplanetary dust particle contains a unique set of minerals that closely resembles assemblages in the refractory, calcium- and aluminum-rich inclusions in carbonaceous chondrite meteorites. The set of minerals includes diopside, magnesium- aluminum spinel, anorthite, perovskite, and fassaite. Only fassaite has previously been identified in interplanetary dust particles. Diopside and spinel occur in complex symplectic intergrowths that may have formed by a reaction between condensed melilite and the solar nebula gas. The particle represents a new link between interplanetary dust particles and carbonaceous chondrites; however, the compositions of its two most abundant refractory phases, diopside and spinel, differ in detail from corresponding minerals in calcium- and aluminum-rich inclusions.
Assessing the Accuracy of Polls and Surveys
Authors: Converse Philip E. , Traugott Michael W.
Published: October 2006

Direct measurements of public opinion about national affairs appear with increasing frequency in all of the mass media. While such survey results are often flagged with statements as to expected error margins, discrepancies between multiple surveys in the news at the same time on what seem to be the same topics may convince casual consumers that such error margins must be considerably understated. A brief review of the several sources of variability and fixed bias in such surveys provides a clearer frame of reference for the evaluation of such data.
Disruption of the Mauna Loa Magma System by the 1868 Hawaiian Earthquake: Geochemical Evidence
Authors: Tilling Robert I. , Rhodes J. Michael , Sparks Joel W. , Lockwood John P. , Lipman Peter W.
Published: October 2006

To test whether a catastrophic earthquake could affect an active magma system, mean abundances (adjusted for "olivine control") of titanium, potassium, phosphorus, strontium, zirconium, and niobium of historic lavas erupted from Mauna Loa Volcano, Hawaii, after 1868 were analyzed and were found to decrease sharply relative to lavas erupted before 1868. This abrupt change in lava chemistry, accompanied by a halved lava-production rate for Mauna Loa after 1877, is interpreted to reflect the disruptive effects of a magnitude 7.5 earthquake in 1868. This interpretation represents a documentable case of changes in magmatic chemical variations initiated or accelerated by a major tectonic event.
Oxygen Supersaturation in the Ocean: Biological Versus Physical Contributions
Authors: Craig H. , Hayward T.
Published: October 2006

A method based on measurements of dissolved molecular nitrogen, molecular oxygen, and argon can distinguish biological from physical contributions to oxygen supersaturation in the ocean. The derived values of biological O
2
production can be used as a check on estimates of total organic productivity measured by instantaneous rates of carbon-14 assimilation. Application to the shallow summer O
2
maxima in the North Pacific gyres shows that about 72% of the O
2
supersaturation maximum at 28°N and about 86% of the maximum at 40°N are due to net photosynthetic production.
Famine: Causes, Prevention, and Relief
Authors: Mellor John W. , Gavian Sarah
Published: October 2006

Famines are generally caused by decline in food production in successive years brought about by poor weather, war, or both. The consequent complex interactions between prices, employment, and assets impoverish victims and lead to sharply increased mortality. Government policy is a key determinant as to whether or not these conditions mature into widespread famine. India and Bangladesh have succeeded in controlling famines in recent years, but problems in most of Africa remain intractable due to civil unrest and a paucity of resources, including trained people, institutions, and infrastructure. General economic development and political consensus is needed to reduce Africa's vulnerability to famine. In this context, judiciously provided foreign aid can be of immense help.
Recent Mafic Volcanism on Mars
Authors: Lucchitta B. K.
Published: October 2006

The evidence for volcanism on Mars is commonly accepted, but none has been documented in the Valles Marineris equatorial rift system. A recent survey of the troughs in this valley revealed dark patches that are interpreted to be volcanic vents. The configuration and association of these patches with tectonic structures suggest that they are of internal origin; their albedo and color ratios indicate a mafic composition; and their stratigraphic position, crispness of morphologic detail, and low albedo imply that they are young, perhaps even recent.
Foam Structures with a Negative Poisson's Ratio
Authors: Lakes Roderic
Published: October 2006

A novel foam structure is presented, which exhibits a negative Poisson's ratio. Such a material expands laterally when stretched, in contrast to ordinary materials.
Water-Quality Trends in the Nation's Rivers
Authors: Smith Richard A. , Alexander Richard B. , Wolman M. Gordon
Published: October 2006

Water-quality records from two nationwide sampling networks now permit nationally consistent analysis of long-term water-quality trends at more than 300 locations on major U.S. rivers. Observed trends in 24 measures of water quality for the period from 1974 to 1981 provide new insight into changes in stream quality that occurred during a time of major changes in both terrestrial and atmospheric influences on surface waters. Particularly noteworthy are widespread decreases in fecal bacteria and lead concentrations and widespread increases in nitrate, chloride, arsenic, and cadmium concentrations. Recorded increases in municipal waste treatment, use of salt on highways, and nitrogen fertilizer application, along with decreases in leaded gasoline consumption and regionally variable trends in coal production and combustion during the period appear to be reflected in water-quality changes.
Isolation of Extremely Thermophilic Sulfate Reducers: Evidence for a Novel Branch of Archaebacteria
Authors: Stetter Karl O. , Lauerer Gerta , Thomm Michael , Neuner Annemarie
Published: October 2006

Extremely thermophilic archaebacteria are known to be metabolizers of elemental sulfur and the methanogens. A novel group of extremely thermophilic archaebacteria is described, which consists of sulfate-respiring organisms that contain pure factor 420 and that have been isolated from marine hydrothermal systems in Italy. They possess a third type of archaebacterial RNA polymerase structure previously unknown, indicating an exceptional phylogenetic position. Most likely, this group represents a third major branch within the archaebacteria. The existence of sulfate reducers at extremely high temperatures could explain hydrogen sulfide formation in hot sulfate-containing environments, such as submarine hydrothermal systems and deep oil wells.
Asymmetry of Lineages and the Direction of Evolutionary Time
Authors: Gould Stephen Jay , Gilinsky Norman L. , German Rebecca Z.
Published: October 2006

Evolutionary time has a characteristic direction as demonstrated by the asymmetry of clade diversity diagrams in large statistical samples. Evolutionary groups generally concentrate diversity during their early histories, producing a preponderance of bottom-heavy clades among those that arise early in the history of a larger group. This pattern holds across taxonomic levels and across differences in anatomy and ecology (marine invertebrates, terrestrial mammals). The quantitative study of directionality in life's history (replacing vague, untestable, and culturally laden notions of "progress") should receive more attention from paleobiologists.
Pollen and Spores Date Origin of Rift Basins from Texas to Nova Scotia as Early Late Triassic
Authors: Traverse Alfred
Published: October 2006

Palynological studies of the nonmarine Newark Supergroup of eastern North America and of rift basins in the northern Gulf of Mexico facilitate correlation with well-dated marine sections of Europe. New information emphasizes the chronological link between the Newark basins and a Gulf of Mexico basin and their common history in the rifting of North America from Pangea. Shales from the subsurface South Georgia Basin are shown to be of late Karnian age (early Late Triassic). The known time of earliest sedimentation in the Culpeper Basin is extended from Norian (late Late Triassic) to mid-Karnian, and the date of earliest sedimentation in the Richmond and Deep River basins is moved to at least earliest Karnian, perhaps Ladinian. The subsurface Eagle Mills Formation in Texas and Arkansas has been dated palynologically as mid- to late Karnian. The oldest parts of the Newark Supergroup, and the Eagle Mills Formation, mostly began deposition in precursor rift basins that formed in Ladinian to early Karnian time. In the southern Newark basins, sedimentation apparently ceased in late Karnian but continued in the northern basins well into the Jurassic, until genesis of the Atlantic ended basin sedimentation.
Measurement Scales on the Continuum
Authors: Luce R. Duncan , Narens Louis
Published: October 2006

In a seminal article in 1946, S. S. Stevens noted that the numerical measures then in common use exhibited three admissible groups of transformations: similarity, affine, and monotonic. Until recently, it was unclear what other scale types are possible. For situations on the continuum that are homogeneous (that is, objects are not distinguishable by their properties), the possibilities are essentially these three plus another type lying between the first two. These types lead to clearly described classes of structures that can, in principle, be incorporated into the classical structure of physical units. Such results, along with characterizations of important special cases, are potentially useful in the behavioral and social sciences.
Resonant-Mass Detectors of Gravitational Radiation
Authors: Michelson Peter F. , Price John C. , Taber Robert C.
Published: October 2006

A network of second-generation low-temperature gravitational radiation detectors is nearing completion. These detectors, sensitive to mechanical strains of order 10
-18
, are possible because of a variety of technical innovations that have been made in cryogenics, low-noise superconducting instrumentation, and vibration isolation techniques. Another five orders of magnitude improvement in energy sensitivity of resonant-mass detectors is possible before the linear amplifier quantum limit is encountered.
A Reassessment of
Astraspis desiderata
, the Oldest North American Vertebrate
Authors: Elliott David K.
Published: October 2006

The fossil evidence for the early evolution of vertebrates consists of the remains of agnathans, jawless vertebrates, from the Ordovician of Australia, North America, and Bolivia. Because of the fragmentary nature of the material, it has not been possible to reconstruct these animals sufficiently well to understand their relation to each other and to later vertebrates. Though two genera have been known from the Harding Sandstone of North America since 1892, there are still only three articulated specimens known, two of
Astraspis desiderata
and one of
Eriptychius americanus.
The most recently found specimen of
Astraspis
was reexamined and found to show the orbit, a series of eight branchial openings and a complete tail, structures hitherto undescribed in any Ordovician vertebrate. A reconstruction of Astraspis shows, on the basis of the series of branchial openings, that it is a primitive craniate and not a heterostracan as previously thought.
An Upper Eocene Frog from the Dominican Republic and Its Implication for Caribbean Biogeography
Authors: Poinar George O. , Cannatella David C.
Published: October 2006

A frog of the leptodactylid genus
Eleutherodactylus
is reported from Eocene amber found in the Dominican Republic. It is the first described amphibian fossil in amber, and the oldest complete lissamphibian fossil from Mesoamerica (Central America and Mexico). Dating of the amber matrix indicates that by the end of the Eocene a diverse fauna was present in the Antilles, much earlier than has generally been proposed. The presence of this and other amber fossils from this same age suggests that Tertiary patterns of landmass movements were significant in determining the present distribution of species.
Reports Refractory Interplanetary Dust Particles
Authors: Zolensky Michael E.
Published: October 2006

Criteria are described by which refractory interplanetary dust particles (IDPs) can be differentiated from the products of spacecraft debris. These criteria have been used to discover and characterize IDPs that are composed predominantly of refractory phases. Two of these particles contain hibonite, perovskite, spinel, refractory glass, and a melilite; only hibonite was identified within a third. The grain size for all particles ranges from 0.05 to 1 micrometer, so that they are much finer grained than the refractory calcium- and aluminum-rich inclusions in meteorites. The glass-containing refractory IDPs may be primitive nebular condensates that never completely crystallized and thus have been preserved extant.
Methyl Chloride Transferase: a Carbocation Route for Biosynthesis of Halometabolites
Authors: Wuosmaa Anne Marie , Hager Lowell P.
Published: October 2006

Enzymatic synthesis of methyl halides through an
S
-adenosyl methionine transfer mechanism has been detected in cell extracts of
Phellinus promaceus
(a white rot fungus),
Endocladia muricata
(a marine red algae), and
Mesembryanthemum crystallium
(ice plant). This mechanism represents a novel pathway for the formation of halometabolites. The Michaelis constants for chloride and bromide ion and for
S
-adenosyl methionine in the reaction have been determined for the enzyme from
E. muricata
. A recent survey of marine algae indicates that there may be a broad distribution of this enzyme among marine algae.
The Structure of a Complex of Recombinant Hirudin and Human α-Thrombin
Authors: Rydel Timothy J. , Ravichandran K. G. , Tulinsky A. , Bode Wolfram , Huber Robert , Roitsch Carolyn , Fenton John W.
Published: October 2006

The crystallographic structure of a recombinant hirudin-thrombin complex has been solved at 2.3 angstrom (Å) resolution. Hirudin consists of an NH
2
-terminal globular domain and a long (39 Å) COOH-terminal extended domain. Residues Ile
1
to Tyr
3
of hirudin form a parallel β-strand with Ser
214
to Glu
217
of thrombin with the nitrogen atom of Ile
1
making a hydrogen bond with Ser
195
Oγ atom of the catalytic site, but the specificity pocket of thrombin is not involved in the interaction. The COOH-terminal segment makes numerous electrostatic interactions with an anion-binding exosite of thrombin, whereas the last five residues are in a helical loop that forms many hydrophobic contacts. In all, 27 of the 65 residues of hirudin have contacts less than 4.0 Å with thrombin (10 ion pairs and 23 hydrogen bonds). Such abundant interactions may account for the high affinity and specificity of hirudin.
Polarity and Velocity of Sliding Filaments: Control of Direction by Actin and of Speed by Myosin
Authors: Sellers James R. , Kachar Bechara
Published: October 2006

Myosin filaments, which are responsible for a large repertoire of motile activities in muscle and nonmuscle cells, can translocate actin filaments both toward and away from their central bare zone. This bidirectional movement suggests that there is enough flexibility in the head portion of the tightly packed myosin molecules in the native myosin filaments to move actin filaments not only in the expected direction, but also in the direction opposite to that predicted by the regular structure of muscle—away from the center of the myosin filament.
Four-Dimensional Heteronuclear Triple-Resonance NMR Spectroscopy of Interleukin-1β in Solution
Authors: Kay Lewis E. , Clore G. Marius , Bax Ad , Gronenborn Angela M.
Published: October 2006

A method is presented that dramatically improves the resolution of protein nuclear magnetic resonance (NMR) spectra by increasing their dimensionality to four. The power of this technique is demonstrated by the application of four-dimensional carbon-13—nitrogen-15 (
13
C-
15
N)—edited nuclear Overhauser effect (NOE) spectroscopy to interleukin-1β, a protein of 153 residues. The NOEs between NH and aliphatic protons are first spread out into a third dimension by the
15
N chemical shift of the amide
15
N atom and subsequently into a fourth dimension by the
13
C chemical shift of the directly bonded
13
C atoms. By this means ambiguities in the assignment of NOEs between NH and aliphatic protons that are still present in the three-dimensional
15
N-edited NOE spectrum due to extensive chemical shift overlap and degeneracy of aliphatic resonances are completely removed. Consequently, many more approximate interproton distance restraints can be obtained from the NOE data than was heretofore possible, thereby expanding the horizons of three-dimensional structure determination by NMR to larger proteins.
High-Temperature Cubic Boron Nitride P-N Junction Diode Made at High Pressure
Authors: Mishima Osamu , Tanaka Junzo , Yamaoka Shinobu , Fukunaga Osamu
Published: October 2006

A p-n junction diode of cubic boron nitride was made by growing an n-type crystal epitaxially on a p-type seed crystal at a pressure of 55 kilobars and a temperature of about 1700°C. A temperature-difference solvent method was used for the crystal growth, and beryllium and silicon were doped as acceptors and donors, respectively. Formation of the p-n junction was clearly confirmed at 1 bar by rectification characteristics and by existence of a space charge layer of the junction as observed by electron beam induced current measurement. This diode operated at 530°C.
New Evidence on the State of Stress of the San Andreas Fault System
Authors: Zoback Mark D. , Zoback Mary Lou , Mount Van S. , Suppe John , Eaton Jerry P. , Healy John H. , Oppenheimer David , Reasenberg Paul , Jones Lucile , Raleigh C. Barry , Wong Ivan G. , Scotti Oona , Wentworth Carl
Published: October 2006

Contemporary in situ tectonic stress indicators along the San Andreas fault system in central California show northeast-directed horizontal compression that is nearly perpendicular to the strike of the fault. Such compression explains recent uplift of the Coast Ranges and the numerous active reverse faults and folds that trend nearly parallel to the San Andreas and that are otherwise unexplainable in terms of strike-slip deformation. Fault-normal crustal compression in central California is proposed to result from the extremely low shear strength of the San Andreas and the slightly convergent relative motion between the Pacific and North American plates. Preliminary in situ stress data from the Cajon Pass scientific drill hole (located 3.6 kilometers northeast of the San Andreas in southern California near San Bernardino, California) are also consistent with a weak fault, as they show no right-lateral shear stress at ∼2-kilometer depth on planes parallel to the San Andreas fault.
Reaction of Chlorine Nitrate with Hydrogen Chloride and Water at Antarctic Stratospheric Temperatures
Authors: Tolbert Margaret A. , Rossi Michel J. , Malhotra Ripudaman , Golden David M.
Published: October 2006

Laboratory studies of heterogeneous reactions important for ozone depletion over Antarctica are reported. The reaction of chlorine nitrate (ClONO
2
) with H
2
O and hydrogen chloride (HCl) on surfaces that simulate polar stratospheric clouds [ice and nitric acid (HNO
3
)—ice and sulfuric acid] are studied at temperatures relevant to the Antarctic stratosphere. The reaction of ClONO
2
on ice and certain mixtures of HNO
3
and ice proceeded readily. The sticking coefficient of ClONO
2
on ice of 0.009 ± 0.002 was observed. A reaction produced gas-phase hypochlorous acid (HOCl) and condensed-phase HNO
3
; HOCl underwent a secondary reaction on ice producing dichlorine monoxide (Cl
2
O). In addition to the reaction with H
2
O, ClONO
2
reacted with HCl on ice to form gas-phase chlorine (Cl
2
) and condensed-phase HNO
3.
Essentially all of the HCl in the bulk of the ice can react with ClONO
2
on the ice surface. The gaseous products of the above reactions, HOCl, Cl
2
O, and Cl
2
, could readily photolyze in the Antarctic spring to produce active chlorine for ozone depletion. Furthermore, the formation of condensed-phase HNO
3
could serve as a sink for odd nitrogen species that would otherwise scavenge the active chlorine.
Does Ammonia Hydrogen Bond?
Authors: Nelson David D. , Fraser Gerald T. , Klemperer William
Published: October 2006

Spectroscopic characterizations of the stereochemistry of complexes of ammonia (NH
3
) have strongly confirmed some long-held ideas about the weak interactions of NH
3
while casting doubt on others. As expected, NH
3
is observed to be a nearly universal proton acceptor, accepting hydrogen bonds from even some of the weakest proton donors. Surprisingly, no evidence has been found to support the view that NH
3
acts as a proton donor through hydrogen bonding. A critical evaluation of the work that has been done to gather such evidence, as well as of earlier work involving condensed-phase observations, suggests that NH
3
might well be best described as a powerful hydrogen-bond acceptor with little propensity to donate hydrogen bonds.
Effects of Acid Rain on Freshwater Ecosystems
Authors: Schindler D. W.
Published: October 2006

Acid-vulnerable areas are more numerous and widespread than believed 7 years ago. Lakes and streams in acid-vulnerable areas of northeastern North America have suffered substantial declines in acid-neutralizing capacity, the worst cases resulting in biological damage. Many invertebrates are very sensitive to acidification, with some disappearing at
p
H values as high as 6.0. However, the recent rate of acidification of lakes is slower than once predicted, in part the result of decreases in sulfur oxide emissions. A discussion of some of the processes that have contributed to the acidification of lakes as well as those that have protected acid-sensitive freshwaters is presented.
Supercomputer Analysis of Sedimentary Basins
Authors: Bethke Craig M. , Altaner Stephen P. , Harrison Wendy J. , Upson Craig
Published: October 2006

Geological processes of fluid transport and chemical reaction in sedimentary basins have formed many of the earth's energy and mineral resources. These processes can be analyzed on natural time and distance scales with the use of supercomputers. Numerical experiments are presented that give insights to the factors controlling subsurface pressures, temperatures, and reactions; the origin of ores; and the distribution and quality of hydrocarbon reservoirs. The results show that numerical analysis combined with stratigraphic, sea level, and plate tectonic histories provides a powerful tool for studying the evolution of sedimentary basins over geologic time.
Heterogeneous and Epitaxial Nucleation of Protein Crystals on Mineral Surfaces
Authors: McPherson Alexander , Shlichta Paul
Published: October 2006

Fifty different mineral samples were tested as potential heterogeneous or epitaxial nucleants for four commonly crystallized proteins. It was found, by conventional protein crystallization techniques, that for each protein there was a set of mineral substrates that promoted nucleation of crystals at lower critical levels of supersaturation than required for spontaneous growth. Numerous examples, involving all four proteins, were observed of modification of crystal habit and, in some cases, unit cell properties promoted by the presence of the mineral nucleants. In at least one case, the growth of lysozyme on the mineral apophyllite, it was shown by lattice analysis and x-ray diffraction that the nucleation and growth of the protein crystal on the mineral was likely to involve a direct lattice match.
Spongivory in Hawksbill Turtles: A Diet of Glass
Authors: Meylan Anne
Published: October 2006

The hawksbill (
Eretmochelys imbricata
), an endangered marine turtle associated with coral reefs throughout the tropics, feeds almost exclusively on sponges in the Caribbean, and possibly throughout its range. It is one of fewer than a dozen vertebrates that are known to specialize on this widely distributed but well-defended food resource. The diet is taxonomically narrow and highly uniform geographically, includes sponges that are toxic to other vertebrates, and contains more silica than that of other vertebrates. By affecting space competition, spongivory by hawksbills may influence succession and diversity of reef communities.
Manufacturing Innovation and American Industrial Competitiveness
Authors: Cohen Stephen S. , Zysman John
Published: October 2006

An erosion of manufacturing capacities has contributed substantially to America's trade problems. The difficulty lies not in U.S. machines and technology, but in U.S. strategies for automation and the goals American firms seek to achieve through production innovation. Mass production and administrative hierarchies created the basis for American industrial preeminence in the years after World War II. There is substantial evidence that American firms have been unable to adopt or adapt to the production innovations emerging abroad. A sustained weakness in manufacturing capabilities could endanger the technology base of the country.
Tryptophan-Requiring Mutants of the Plant
Arabidopsis thaliana
Authors: Last Robert L. , Fink Gerald R.
Published: October 2006

Although amino acid auxotrophs are among the most frequently isolated mutations in microorganisms, no mutants that require amino acids have been isolated at the whole plant level. Tryptophan-requiring mutants of the cruciferous plant
Arabidopsis thaliana
have now been isolated by selecting for resistance to 5-methylanthranilic acid. The tryptophan requirement of one mutant,
trp1-1
, results from a defect in the second step of the tryptophan pathway catalyzed by anthranilate phosphoribosyl transferase. Mutant
trp1-1
plants are highly fluorescent and aromatic because they accumulate anthranilic acid and anthranilate β-glucoside. Plants homozygous for the
trp1-1
mutation exhibit a syndrome of morphological defects suggestive of a defect in the biosynthesis, metabolism, or localization of a tryptophan derivative such as auxin. All of these morphological phenotypes cosegregate with the tryptophan requirement as a simple Mendelian recessive trait.
Intramolecular Long-Distance Electron Transfer in Organic Molecules
Authors: Closs Gerhard L. , Miller John R.
Published: October 2006

Intramolecular long-distance electron transfer (ET) has been actively studied in recent years in order to test existing theories in a quantitative way and to provide the necessary constants for predicting ET rates from simple structural parameters. Theoretical predictions of an "inverted region," where increasing the driving force of the reaction will decrease its rate, have begun to be experimentally confirmed. A predicted nonlinear dependence of ET rates on the polarity of the solvent has also been confirmed. This work has implications for the design of efficient photochemical charge-separation devices. Other studies have been directed toward determining the distance dependence of ET reactions. Model studies on different series of compounds give similar distance dependences. When different stereochemical structures are compared, it becomes apparent that geometrical factors must be taken into account. Finally, the mechanism of coupling between donor and acceptor in weakly interacting systems has become of major importance. The theoretical and experimental evidence favors a model in which coupling is provided by the interaction with the orbitals of the intervening molecular fragments, although more experimental evidence is needed.
The Science of Patterns
Authors: Steen Lynn Arthur
Published: October 2006

The rapid growth of computing and applications has helped cross-fertilize the mathematical sciences, yielding an unprecedented abundance of new methods, theories, and models. Examples from statistical science, core mathematics, and applied mathematics illustrate these changes, which have both broadened and enriched the relation between mathematics and science. No longer just the study of number and space, mathematical science has become the science of patterns, with theory built on relations among patterns and on applications derived from the fit between pattern and observation.
Iron Photoreduction and Oxidation in an Acidic Mountain Stream
Authors: McKnight D. M. , Kimball B. A. , Bencala K. E.
Published: October 2006

In a small mountain stream in Colorado that receives acidic mine drainage, photoreduction of ferric iron results in a well-defined increase in dissolved ferrous iron during the day. To quantify this process, an instream injection of a conservative tracer was used to measure discharge at the time that each sample was collected. Daytime production of ferrous iron by photoreduction was almost four times as great as nighttime oxidation of ferrous iron. The photoreduction process probably involves dissolved or colloidal ferric iron species and limited interaction with organic species because concentrations of organic carbon are low in this stream.
Global Sea Level and Earth Rotation
Authors: Peltier W. R.
Published: October 2006

Recent analyses of long time scale secular variations of sea level, based on tide gauge observations, have established that sea level is apparently rising at a globally averaged rate somewhat in excess of 1 millimeter per year. It has been suggested that the nonsteric component of this secular rate might be explicable in terms of ongoing mass loss from the small ice sheets and glaciers of the world. Satellite laser ranging and very long baseline interferometry data may be used to deliver strong constraints on this important scenario because of the information that these systems provide on variations of the length of day and of the position of the rotation pole with respect to the earth's surface geography. These data demonstrate that the hypothesis of mass loss is plausible if the Barents Sea was covered by a substantial ice sheet at the last maximum of the current ice age 18,000 years ago.
Aluminum-Induced Calcium Deficiency Syndrome in Declining Red Spruce
Authors: Shortle Walter C. , Smith Kevin T.
Published: October 2006

Prolonged suppression of cambial growth has apparently caused a decline in radial growth in many mature red spruce,Picea rubens.Surveys indicate that this decline occurs in trees throughout the natural range of red spruce and is independent of elevation, tree size, and age class. In addition, crowns of mature red spruce at high elevations across the northeastern United States have been dying back. Understanding the physiological basis for the growth decline is essential for the judicious management of the red spruce resource. A sequence of events is inferred through which an imbalance of aluminum and calcium in the fine root environment reduces the rate of wood formation, decreases the amount of functional sapwood and live crown, and leaves large trees more vulnerable to extant secondary diseases and insect pests.
Structure and Function of Lipopolysaccharide Binding Protein
Authors: Schumann Ralf R. , Leong Steven R. , Flaggs Gail W. , Gray Patrick W. , Wright Samuel D. , Mathison John C. , Tobias Peter S. , Ulevitch Richard J.
Published: October 2006

The primary structure of lipopolysaccharide binding protein (LBP), a trace plasma protein that binds to the lipid A moiety of bacterial lipopolysaccharides (LPSs), was deduced by sequencing cloned complementary DNA. LBP shares sequence identity with another LPS binding protein found in granulocytes, bactericidal/permeability-increasing protein, and with cholesterol ester transport protein of the plasma. LBP may control the response to LPS under physiologic conditions by forming high-affinity complexes with LPS that bind to monocytes and macrophages, which then secrete tumor necrosis factor. The identification of this pathway for LPS-induced monocyte stimulation may aid in the development of treatments for diseases in which Gram-negative sepsis or endotoxemia are involved.
Cloning of an Interleukin-3 Receptor Gene: a Member of a Distinct Receptor Gene Family
Authors: Itoh Naoto , Yonehara Shin , Schreurs Jolanda , Gorman Daniel M , Maruyama Kazuo , Ishii Ai , Yahara Ichiro , Arai Ken-Ichi , Miyajima Atsushi
Published: October 2006

Interleukin-3 (IL-3) binds to its receptor with high and low affinities, induces tyrosine phosphorylation, an d promotes the proliferation and differentiation of hematopoietic cells. A binding component of the IL-3 receptor was cloned. Fibroblasts transfected with the complementary DNA bound IL-3 with a low affinity [dissociation constant (
K
d
) of 17.9 ± 3.6 n
M
]. No consensus sequence for a tyrosine kinase was present in the cytoplasmic domain. Thus, additional components are required for a functional high affinity IL-3 receptor. A sequence comparison of the IL-3 receptor with other cytokine receptors (erythropoietin, IL-4, IL-6, and the β chain IL-2 receptor) revealed a common motif of a distinct receptor gene family.
A Catalytic RNA and Its Gene from
Salmonella typhimurium
Authors: Baer Madeline , Altman Sidney
Published: October 2006

The gene for the RNA subunit (M1 RNA) of ribonuclease P from
Salmonella typhimurium
directs the synthesis of an RNA that can cleave transfer RNA precursor molecules. The mature M1 RNA coded for by
Salmonella typhimurium
is 375 nucleotides long and has six nucleotide changes in comparison to M1 RNA from Escherichia coli. The regions for promotion and termination of transcription are closely conserved, but adjacent regions of nucleotide sequences show considerable drift.