bluuebunny/crossref_metadata_2025 huggingface dataset:
Deformation Monitoring at Mount St. Helens in 1981 and 1982
Authors: Chadwick W. W. , Swanson D. A. , Iwatsubo E. Y. , Heliker C. C. , Leighley T. A.
Published: October 2006

For several weeks before each eruption of Mount St. Helens in 1981 and 1982, viscous magma rising in the feeder conduit inflated the lava dome and shoved the crater floor laterally against the immobile crater walls, producing ground cracks and thrust faults. The rates of deformation accelerated before eruptions, and thus it was possible to predict eruptions 3 to 19 days in advance. Lack of deformation outside the crater showed that intrusion of magma during 1981 and 1982 was not voluminous.
Cytidine 3′,5′-Monophosphate (Cyclic CMP) Formation in Mammalian Tissues
Authors: Cech Stella Y. , Ignarro Louis J.
Published: October 2006

Mammalian tissues possess the capacity to synthesize cytidine 3′,5′-monophosphate (cyclic CMP) via the enzymatic conversion of cytidine 5′-triphosphate to cyclic CMP by cytidylate cyclase. Cyclic CMP formation occurs best in the presence of manganese or iron, at neutral
p
H, at 37°C, in the absence of detergents, and with whole tissue homogenate fractions. Thus, mammalian tissues are capable of synthesizing not only cyclic AMP and cyclic GMP, but also cyclic CMP.
Different Tumor-Derived p53 Mutants Exhibit Distinct Biological Activities
Authors: Halevy Orna , Michalovitz Dan , Oren Moshe
Published: October 2006

In its wild-type form, the protein p53 can interfere with neoplastic processes. Tumor-derived cells often express mutant p53. Full-length mutant forms of p53 isolated so far from transformed mouse cells exhibit three common properties in vitro: loss of transformation-suppressing activity, gain of pronounced transforming potential, and ability to bind the heat shock protein cognate hsc70. A tumor-derived mouse p53 variant is now described, whose site of mutation corresponds to a hot spot for p53 in human tumors. While absolutely nonsuppressing, it is only weakly transforming and exhibits no detectable hsc70 binding. The data suggest that the ability of a p53 mutant to bind endogenous p53 is not the sole determinant of its oncogenic potential. The data also support the existence of gain-of-function p53 mutants.
Male Esterase 6 Catalyzes the Synthesis of a Sex Pheromone in
Drosophila melanogaster
Females
Authors: Mane Suresh D. , Tompkins Laurie , Richmond Rollin C.
Published: October 2006

Esterase 6, a component of the seminal fluid of
Drosophila melanogaster
males, hydrolyzes
cis
-vaccenyl acetate, a lipid made only by males, to
cis
-vaccenyl alcohol. This reaction occurs in the female reproductive tract and is virtually complete within 6 hours after copulation. Both the alcohol and the acetate decrease the number of matings among pairs of virgin flies in which the female is treated topically with these substances. Although females tested 10 minutes after copulation elicit less courtship than virgin females, females tested 6 hours after copulation stimulate even less courtship if they received active esterase 6 in the seminal fluid of their respective mates. Either the alcohol or a derivative appears to be an antiaphrodisiac that decreases courtship elicited by inseminated females and thus reduces the probability of further mating. Thus the activity of the pheromone depends on a final reaction which occurs in the female, using both substrate and enzyme provided by the male.
Phaeodarian Skeletons: Their Role in Silica Transport to the Deep Sea
Authors: Takahashi Kozo , Hurd David C. , Honjo Susumu
Published: October 2006

The skeletons of phaeodarian Radiolaria transport and redistribute silica to the tropical deep oceans by dissolving in the water column and on the sea floor. The skeletons are initially solid but within a few days to months become progressively more porous while settling through the water column. Phaeodarian Radiolaria are rarely preserved in the bottom sediments; in contrast, polycystine Radiolaria are the dominant Radiolaria preserved in the fossil record. This preservational difference may be due to differences in skeletal constituents.
Global Deforestation: Contribution to Atmospheric Carbon Dioxide
Authors: Woodwell G. M. , Hobbie J. E. , Houghton R. A. , Melillo J. M. , Moore B. , Peterson B. J. , Shaver G. R.
Published: October 2006

A study of effects of terrestrial biota on the amount of carbon dioxide in the atmosphere suggests that the global net release of carbon due to forest clearing between 1860 and 1980 was between 135 × 10
15
and 228 × 10
15
grams. Between 1.8 × 10
15
and 4.7 × 10
15
grams of carbon were released in 1980, of which nearly 80 percent was due to deforestation, principally in the tropics. The annual release of carbon from the biota and soils exceeded the release from fossil fuels until about 1960. Because the biotic release has been and remains much larger than is commonly assumed, the airborne fraction, usually considered to be about 50 percent of the release from fossil fuels, was probably between 22 and 43 percent of the total carbon released in 1980. The increase in carbon dioxide in the atmosphere is thought by some to be increasing the storage of carbon in the earth's remaining forests sufficiently to offset the release from deforestation. The interpretation of the evidence presented here suggests no such effect; deforestation appears to be the dominant biotic effect on atmospheric carbon dioxide. If deforestation increases in proportion to population, the biotic release of carbon will reach 9 × 10
15
grams per year before forests are exhausted early in the next century. The possibilities for limiting the accumulation of carbon dioxide in the atmosphere through reduction in use of fossil fuels and through management of forests may be greater than is commonly assumed.
Biological Consequences of El Niño
Authors: Barber Richard T. , Chavez Francisco P.
Published: October 2006

Observations of the 1982-1983 El Niño make it possible to relate the anomalous ocean conditions to specific biological responses. In October 1982 upwelling ecosystems in the eastern equatorial Pacific began a series of transitions from the normal highly productive condition to greatly reduced productivity. The highly productive condition had returned by July 1983. Nutrients, phytoplankton biomass, and primary productivity are clearly regulated by the physical changes of El Niño. Evidence from 1982 and 1983 also suggests effects on higher organisms such as fish, seabirds, and marine mammals, but several more years of observation are required to accurately determine the magnitude of the consequences on these higher trophic levels.
Ethane Ocean on Titan
Authors: Lunine Jonathan I. , Stevenson David J. , Yung Yuk L.
Published: October 2006

It is proposed that Saturn's satellite Titan is covered by an ocean one to several kilometers deep consisting mainly of ethane. If the ocean is in thermodynamic equilibrium with an atmosphere of 3 percent (mole fraction) methane, then its composition is roughly 70 percent ethane, 25 percent methane, and 5 percent nitrogen. Photochemical models predict that ethane is the dominant end product of methane photolysis so that the evolving ocean is both the source and sink for continuing photolysis. The coexisting atmosphere is compatible with Voyager data.
Epsilon Carbide: A Low-Temperature Component of Interplanetary Dust Particles
Authors: Christoffersen Roy , Buseck Peter R.
Published: October 2006

Transmission electron microscope study of a chondritic interplanetary dust particle has revealed the presence of epsilon iron-nickel carbide, a low-temperature carbide previously encountered only in metallurgical studies. In these studies ε-carbide was synthesized by carburization of iron or nickel grains in a stream of carbon monoxide or carbon monoxide plus hydrogen. Similar carburization of an iron-nickel metal in situ may have produced ε-carbide during particle heating on atmospheric entry or in solar orbit. Alternatively, the ε-carbide may be a by-product of Fischer-Tropsch reactions in the solar nebula. Such reactions have been proposed as the mechanism of hydrocarbon formation in the early solar system.
Paleoceanographic Model of Neogene Phosphorite Deposition, U.S. Atlantic Continental Margin
Authors: Riggs Stanley R.
Published: October 2006

The Neogene stratigraphic section of the southeastern U.S. continental shelf-coastal plain system is characterized by (i) a series of major regional phosphogenic episodes; (ii) a strong spatial relationship between the structural or topographic framework and phosphate deposition; and (iii) distinct cyclical and regional patterns of deposition of the terrigenous, carbonate, and phosphate lithofacies. The complex depositional patterns are explained by a paleoceanographic model based upon the interaction of glacial eustatic sea-level fluctuations, associated changes in climate, and the dynamics of the Gulf Stream in response to the bathymetric configurations of the continental margin during the past 20 million years.
The Most Luminous Stars
Authors: Humphreys Roberta M. , Davidson Kris
Published: October 2006

Stars with individual luminosities more than a million times that of the sun are now being studied in a variety of contexts. Observational and theoretical ideas about the most luminous stars have changed greatly in the past few years. They can be observed spectroscopically even in nearby galaxies. They are not very stable; some have had violent outbursts in which large amounts of mass were lost. Because of their instabilities, these stars do not evolve to become red supergiants as less luminous stars do. Theoretical scenarios for the evolution of these most massive stars depend on the effects of turbulence and mixing combined with high radiation densities.
Algal Chemical Defense Against Herbivores: Allocation of Phenolic Compounds in the KelpAlaria marginata
Authors: Steinberg Peter D.
Published: October 2006

Higher concentrations of phenolic compounds were found in the reproductive fronds (sporophylls) of the intertidal kelpAlaria marginatathan were found in the vegetative blades. The sporophylls were consumed by herbivorous snails at a lower rate than were the vegetative blades, in both field and laboratory studies. These results indicate that differential internal production of defensive compounds in a marine alga can significantly affect the pattern of herbivory on the plant.
Lignin Signature of Aquatic Humic Substances
Authors: Ertel John R. , Hedges John I. , Perdue Edward M.
Published: October 2006

Lignin-derived phenols dominate the cupric oxide oxidation products of dissolved humic substances from river and lake waters. The relative distributions of these phenols suggest the presence of intact, though oxidized, lignin, which is indicative of the locally dominant vascular plant vegetation. Recognizable lignin is present mostly in humic acid as opposed to fulvic acid fractions. This lignin component represents a source-specific and process-dependent tracer that can uniquely characterize dissolved organic matter.
Subtidal Gastropods Consume Sulfur-Oxidizing Bacteria: Evidence from Coastal Hydrothermal Vents
Authors: Stein Jeffrey L.
Published: October 2006

The black abalone (
Haliotis cracherodii
), a commercially important shallow-water gastropod common off White Point, Southern California, is found frequently at subtidal hydrothermal vents within mats of filamentous sulfur-oxidizing bacteria. Foraging vent abalones actively consume the bacteria and confine their nightly feeding forays to bacterial mats surrounding the vents. The growth of abalones consuming the sulfur bacteria exceeds that of control individuals consuming microalgae and is comparable to reported growth rates of abalones consuming macroalgae. Thus, off White Point, the black abalone may derive a portion of its nutrition from the subsidy of geothermal energy.
Impact Theory of Mass Extinctions and the Invertebrate Fossil Record
Authors: Alvarez Walter , Kauffman Erle G. , Surlyk Finn , Alvarez Luis W. , Asaro Frank , Michel Helen V.
Published: October 2006

There is much evidence that the Cretaceous-Tertiary boundary was marked by a massive meteorite impact. Theoretical consideration of the consequences of such an impact predicts sharp extinctions in many groups of animals precisely at the boundary. Paleontological data clearly show gradual declines in diversity over the last 1 to 10 million years in various invertebrate groups. Reexamination of data from careful studies of the best sections shows that, in addition to undergoing the decline, four groups (ammonites, cheilostomate bryozoans, brachiopods, and bivalves) were affected by sudden truncations precisely at the iridium anomaly that marks the boundary. The paleontological record thus bears witness to terminal-Cretaceous extinctions on two time scales: a slow decline unrelated to the impact and a sharp truncation synchronous with and probably caused by the impact.
Rock Avalanches Caused by Earthquakes: Source Characteristics
Authors: Keefer David K.
Published: October 2006

Study of a worldwide sample of historical earthquakes showed that slopes most susceptible to catastrophic rock avalanches were higher than 150 meters and steeper than 25 degrees. The slopes were undercut by fluvial or glacial erosion, were composed of intensely fractured rock, and exhibited at least one other indicator of low strength or potential instability.
Self-Incompatibility: A Self-Recognition System in Plants
Authors: Haring Volker , Gray Julie E. , McClure Bruce A. , Anderson Marilyn A. , Clarke Adrienne E.
Published: October 2006

Self-incompatibility (SI), a genetically controlled mechanism to prevent inbreeding in plants, offers a relatively simple model system for studying the interactions between plant cells or between a plant cell and the secreted product or products of another cell. Examples of two major types of SI, gametophytic and sporophytic, have been studied by cloning cDNAs corresponding to glycoproteins of the female tissues that segregate with particular variants encoded by the putative S locus. These secreted glycoproteins are envisaged to interact with the currently undescribed pollen component to cause arrest of pollen tube growth.
Four Years of Reagan Science Policy: Notable Shifts in Priorities
Authors: Keyworth G. A.
Published: October 2006

Administration priorities for federal support of nondefense research and development emphasize basic research and the concomitant training of students. In 4 years basic research has moved from the smallest to the largest component in nondefense R & D expenditures, and basic research specifically to universities has grown by 26 percent in real terms during that period. New programs for fiscal year 1985 emphasize engineering education and research, as well as improved interactions between universities, federal laboratories, and industry.
High Incidence of "Leapfrog" Pattern of Geographic Variation in Andean Birds: Implications for the Speciation Process
Authors: Remsen J. V.
Published: October 2006

Many species of birds in the humid forests of the Andes show a pattern of geographic variation in color that is virtually unknown in other regions of the world. This pattern, here termed "leapfrog," is one in which two populations very similar in appearance are geographically separated from each other by very different, intervening populations of the same species. Approximately 21 percent of all Andean bird species and superspecies with three or more differentiated populations show the leapfrog pattern, and several of these show multiple cases of leapfrogging color patterns. Lack of concordance in the geographic distribution of taxa showing the leapfrog pattern suggests that there is a strongly random component in phenotypic differentiation with respect to direction, geography, and timing.
Cenozoic High Latitude Heterochroneity of Southern Hemisphere Marine Faunas
Authors: Zinsmeister William J. , Feldmann Rodney M.
Published: October 2006

Discovery of 11 genera, in five classes within the Mollusca, Echinodermata, and Arthropoda in upper Eocene rocks on Seymour Island, Antarctica, previously known only from Late Cenozoic in mid-latitudes, suggests that the high latitude region of the Southern Hemisphere acted as a center of origin and dispersal for a broad spectrum of taxa. Precursors to modern deep- and shallow-water mid-latitude forms evolved and flourished in the high latitudes until conditions in lower latitudes favored their dispersal. These observations of Antarctic marine invertebrates corroborate those recently made about terrestrial mammals and plants in the Arctic.
Analysis of Hydrothermal Vent-Associated Symbionts by Ribosomal RNA Sequences
Authors: Stahl David A. , Lane David J. , Olsen Gary J. , Pace Norman R.
Published: October 2006

Ribosomal RNA (rRNA) sequences were used to establish the phylogenetic affiliations of symbioses in which prokaryotes appear to confer sulfur-based chemoautotrophy on their invertebrate hosts. Two submarine hydrothermal vent animals, the vestimentiferan tube worm
Riftia pachyptila
and the clam
Calyptogena magnifica
, and a tidal-flat bivalve,
Solemya velum
, were inspected. 5S rRNA's were extracted from symbiont-bearing tissues, separated into unique forms, and their nucleotide sequences determined and related to other 5S rRNA's in a phylogenetic tree analysis. The prokaryotic symbionts are related to one another and affiliated with the same narrow phylogenetic grouping as
Escherichia coli
and
Pseudomonas aeruginosa
. The sequence comparisons suggest that
Riftia
is more closely related to the bivalves than their current taxonomic status would suggest.
Phenotypic Variation Within Histocompatibility-Defined Clones of Marine Sponges
Authors: Neigel Joseph E. , Schmahl George P.
Published: October 2006

Nongenetic phenotypic variation can be identified by its occurrence within genetically uniform clones. A histocompatibility bioassay of clonal identity was used to ascertain the extent of phenotypic variation within natural clones of two species of marine sponges. Multiple morphological forms of the sponge
Aplysina fistularis
were found to occur within single clones, indicating a nongenetic polymorphism. In contrast, a genetic basis is suggested for a polymorphism of
Aplysina cauliformis
; within single clones of this species, individuals were uniform in color and morphology.
Saturn Ring Particles as Dynamic Ephemeral Bodies
Authors: Davis Donald R. , Weidenschilling Stuart J. , Chapman Clark R. , Greenberg Richard
Published: October 2006

Although Saturn's rings are within the Roche zone, the accretion of centimeter-sized particles into large aggregates many meters in diameter occurs readily, on a time scale of weeks. These aggregates are disrupted when tidal stresses exceed their very low strengths; thus most of the mass of the ring system is continually processed through a population of large "dynamic ephemeral bodies," which are continually forming and disintegrating. These large aggregates are not at all like the idealized ice spheres often used in modeling Saturn's ring dynamics. Their coefficient of restitution is low, hence they form a monolayer in the ring plane. The optically observable characteristics of the rings are dominated by the swarm of centimeter-sized particles.
Science and Technology in a World Transformed
Authors: Hamburg David A.
Published: October 2006

In this era of rapid, far-reaching transformation, our way of life is in many respects a novelty for our species. Opportunities arising from profoundly enhanced capabilities in science and technology are felt in every sphere of life from health to communication, yet each advance has side effects that take time to appear. Grave institutional inadequacies are manifested in the prevalence of totalitarian governments, proliferation of devastating weapons, failure of educational institutions to prepare most people for the modern world, failure to use what we know to prevent damage to a large proportion of the world's children; and the weakness of international institutions to deal with global interdependence in the face of persistent ethnocentrism and prejudice. The American scientific community can usefully become more deeply engaged with these great problems.
Time-Domain Reflectometry: Simultaneous Measurement of Soil Water Content and Electrical Conductivity with a Single Probe
Authors: Dalton F. N. , Herkelrath W. N. , Rawlins D. S. , Rhoades J. D.
Published: October 2006

Two parallel metallic rods were used as a wave guide to measure the dielectric constant and electrical conductivity of soils having different electrical conductivities but the same water content. Measurements showed that the two parameters were sufficiently independent to permit simultaneous determinations of water content and bulk electrical conductivity.
The Great Tambora Eruption in 1815 and Its Aftermath
Authors: Stothers Richard B.
Published: October 2006

Quantitative analytical methods are used to reconstruct the course of events during and after the cataclysmic eruption of Mount Tambora, Indonesia, on 10 and 11 April 1815. This was the world's greatest ash eruption (so far as is definitely known) since the end of the last Ice Age. This synthesis is based on data and methods from the fields of volcanology, oceanography, glaciology, meteorology, climatology, astronomy, and history.
A Novel Photosynthetic Purple Bacterium Isolated from a Yellowstone Hot Spring
Authors: Madigan Michael T.
Published: October 2006

A thermophilic photosynthetic purple bacterium was isolated from the waters of a hot spring in Yellowstone National Park, Wyoming. The organism differs from all known purple bacteria in that it grows optimally at a temperature of about 50°C. The isolate contains bacteriochlorophyll a and grows autotrophically, oxidizing sulfide to elemental sulfur which is then stored as globules inside the cell. These properties indicate that the phototroph is a member of the Chromatiaceae (purple sulfur bacteria).
The Eocene/Oligocene Boundary Event in the Deep Sea
Authors: Corliss Bruce H. , Aubry Marie-Pierre , Berggren W. A. , Fenner Juliane M. , Keigwin Lloyd D. , Keller Gerta
Published: October 2006

Analysis of middle Eocene to early, Oligocene calcareous and siliceous microfossils shows gradual biotic changes with no massive extinction event across the Eocene/Oligocene boundary. Biotic changes in the late Paleogene appear to reflect changing paleoclimatic and paleoceanographic conditions and do not support suggestions of a catastrophic biotic event caused by a bolide impact at the Eocenel Oligocene boundary.
Biological Communities at the Florida Escarpment Resemble Hydrothermal Vent Taxa
Authors: Paull C. K. , Hecker B. , Commeau R. , Freeman-Lynde R. P. , Neumann C. , Corso W. P. , Golubic S. , Hook J. E. , Sikes E. , Curray J.
Published: October 2006

Dense biological communities of large epifaunal taxa similar to those found along ridge crest vents at the East Pacific Rise were discovered in the abyssal Gulf of Mexico. These assemblages occur on a passive continental margin at the base of the Florida Escarpment, the interface between the relatively impermeable hemipelagic clays of the distal Mississippi Fan and the jointed Cretaceous limestone of the Florida Platform. The fauna apparently is nourished by sulfide rich hypersaline waters seeping out at near ambient temperatures onto the sea floor.
Trends in Industrial Use of Energy
Authors: Marlay Robert C.
Published: October 2006

Industry's use of energy, accounting for approximately 40 percent of U.S. consumption, changed significantly after 1973. In 1982 industry consumed one-third less energy than trends established before 1973 would have predicted. Part of this reduction resulted from improvements in the efficiency of industrial process technologies. Most is attributed, however, to slower growth in industrial economic activity and unprecedented changes in the composition of industrial output away from industries that consume large amounts of energy.
Auditory Illusions Demonstrating That Tones Are Assimilated to an Internalized Musical Scale
Authors: Shepard Roger N. , Jordan Daniel S.
Published: October 2006

Judgments of relations between tones in a sequence derived from the major diatonic scale (do, re, mi, . . .) by systematic distortions (either equalization or stretching of intervals) reveal that Western listeners interpret the tones relative to that musical scale even when they try to judge the purely physical relations between the tones.
A Circumstellar Disk Around β Pictoris
Authors: Smith Bradford A. , Terrile Richard J.
Published: October 2006

A circumstellar disk has been observed optically around the fourth-magnitude star β Pictoris. First detected in the infrared by the Infrared Astronomy Satellite last year, the disk is seen to extend to more than 400 astronomical units from the star, or more than twice the distance measured in the infrared by the Infrared Astronomy Satellite. The β Pictoris disk is presented to Earth almost edge-on and is composed of solid particles in nearly coplanar orbits. The observed change in surface brightness with distance from the star implies that the mass density of the disk falls off with approximately the third power of the radius. Because the circumstellar material is in the form of a highly flattened disk rather than a spherical shell, it is presumed to be associated with planet formation. It seems likely that the system is relatively young and that planet formation either is occurring now around β Pictoris or has recently been completed.
Different Red Light Requirements for Phytochrome-Induced Accumulation of
cab
RNA and
rbcS
RNA
Authors: Kaufman Lon S. , Thompson William F. , Briggs Winslow R.
Published: October 2006

For several species of plants the abundance of those transcripts encoding the chlorophyll a/b binding protein (
cab
RNA) and the small subunit of ribulose-1,5-biphosphate carboxylase-oxygenase (
rbcS
RNA) has been established as being under the control of phytochrome. However, this conclusion does not take into account the various types of phytochrome control based on both the fluence of red light necessary to induce the response and the ability of far red light either to induce or to reverse the response. The fluence of red light necessary to induce the accumulation of
rbcS
RNA was found to be 10,000 times greater than that necessary to induce the accumulation of
cab
RNA. Furthermore, far red light alone was capable of inducing the accumulation of
cab
RNA. It is possible, therefore, that developing pea buds accumulate
cab
RNA before
rbcS
and that
cab
RNA is not subject to the normal end-of-day signals affecting many phytochrome responses.
A Simple and General Method for Transferring Genes into Plants
Authors: Horsch R. B. , Fry J. E. , Hoffmann N. L. , Wallroth M. , Eichholtz D. , Rogers S. G. , Fraley R. T.
Published: October 2006

Transformed petunia, tobacco, and tomato plants have been produced by means of a novel leaf disk transformation-regeneration method. Surface-sterilized leaf disks were inoculated with an
Agrobacterium tumefaciens
strain containing a modified tumor-inducing plasmid (in which the phytohormone biosynthetic genes from transferred DNA had been deleted and replaced with a chimeric gene for kanamycin resistance) and cultured for 2 days. The leaf disks were then transferred to selective medium containing kanamycin. Shoot regeneration occurred within 2 to 4 weeks, and transformants were confirmed by their ability to form roots in medium containing kanamycin. This method for producing transformed plants combines gene transfer, plant regeneration, and effective selection for transformants into a single process and should be applicable to plant species that can be infected by
Agrobacterium
and regenerated from leaf explants.
Interfacial Catalysis: the Mechanism of Phospholipase A
2
Authors: Scott David L. , White Steven P. , Otwinowski Zbyszek , Yuan Wei , Gelb Michael H. , Sigler Paul B.
Published: October 2006

A chemical description of the action of phospholipase A
2
(PLA
2
) can now be inferred with confidence from three high-resolution x-ray crystal structures. The first is the structure of the PLA
2
from the venom of the Chinese cobra (
Naja naja atra
) in a complex with a phosphonate transition-state analogue. This enzyme is typical of a large, well-studied homologous family of PLA
2
s. The second is a similar complex with the evolutionarily distant bee-venom PLA
2
. The third structure is the uninhibited PLA
2
from Chinese cobra venom. Despite the different molecular architectures of the cobra and bee-venom PLA
2
s, the transition-state analogue interacts in a nearly identical way with the catalytic machinery of both enzymes. The disposition of the fatty-acid side chains suggests a common access route of the substrate from its position in the lipid aggregate to its productive interaction with the active site. Comparison of the cobra-venom complex with the uninhibited enzyme indicates that optimal binding and catalysis at the lipid-water interface is due to facilitated substrate diffusion from the interfacial binding surface to the catalytic site rather than an allosteric change in the enzyme's structure. However, a second bound calcium ion changes its position upon the binding of the transition-state analogue, suggesting a mechanism for augmenting the critical electrophile.
New Approaches in Economic Analysis
Authors: Leontief Wassily , Duchin Faye , Szyld Daniel B.
Published: October 2006

The level of detail of economic models has until recently been limited by the availability of computational capability. At present, the constraint is the systematic compilation of detailed and comprehensive economic and technical data and the ability to manipulate them. The effective use of enhanced data processing capabilities will have to proceed hand in hand with a concerted effort to develop the economic database and with the shift from analytic approaches based on aggregative data to those that can take advantage of detailed information.
Recurring Origins of Allopolyploid Species in
Asplenium
Authors: Werth Charles R. , Guttman Sheldon I. , Eshbaugh W. Hardy
Published: October 2006

A large proportion of plant species has originated through allopolyploidy: interspecific hybridization followed by chromosome doubling. Heterozygosity remains fixed in allopolyploids because of nonsegregation of parental chromosomes. Two allotetraploid species of the fern genus
Asplenium
show allozyme polymorphisms at loci that are polymorphic in their diploid progenitors, indicating that each has originated more than once and implicating continued gene flow from diploids to tetraploids.
Authigenic Potassium Feldspar in Cambrian Carbonates: Evidence of Alleghanian Brine Migration
Authors: Hearn Paul P. , Sutter John F.
Published: October 2006

The shallow-water limestones and dolostones of the Conococheague Limestone (Upper Cambrian) of western Maryland contain large amounts of authigenic potassium feldspar. The presence of halite daughter crystals in breached fluid inclusions, low whole-rock ratios of chlorine to bromine, and thermochemical data suggest that the potassium feldspar formed at low temperature by the reaction of connate brines with intercalated siliciclastic debris. Analyses of argon age spectra indicate that the authigenic feldspar probably formed during Late Pennsylvanian to Early Permian time. These results may indicate mobilization and migration of connate brines brought about by Alleghanian folding. The widespread occurrence of authigenic potassium feldspar in Cambrian and Ordovician carbonate rocks throughout the Appalachians suggests that this may have occurred throughout the entire basin.
Wallace H. Carothers and Fundamental Research at Du Pont
Authors: Smith John K. , Hounshell David A.
Published: October 2006

In the Depression decade, the research group headed by Wallace H. Carothers made two discoveries—neoprene and nylon—that have had an enormous impact on E. I. du Pont de Nemours and industrial research generally. At the same time, Carothers's many publications helped establish the foundations of polymer science. A theoretical organic chemist, he left Harvard University to take part in Du Pont's new fundamental research program. Although founded on the academic model, it soon began to reflect its industrial setting. Some surprising experimental results, the research philosophy of a new research director, and the economic realities of the Great Depression pushed Du Pont's pure scientists toward more practical or mission-oriented goals. Nylon and neoprene emerged from this creative tension between chemists interested in science and management committed to innovation.
Killing of Fibroblasts by Dexamethasone or Dibutyryl Adenosine 3′,5′-Monophosphate Is Not a Valid Test for Cystic Fibrosis
Authors: Kurz James B. , Perkins John P. , Buchwald Manuel
Published: October 2006

Assays based on the counting of total cells and of colony-forming cells were used to demonstrate that neither dexamethasone nor dibutyryl adenosine 3′,5′-monophosphate (cyclic AMP) kills human fibroblasts under a variety of conditions. These results contradict those of previous studies showing that dexamethasone and dibutyryl cyclic AMP kill a higher percentage of fibroblasts from normal humans than from individuals with cystic fibrosis.
A Dominant Mutation That Predisposes to Multiple Intestinal Neoplasia in the Mouse
Authors: Moser Amy Rapaich , Pitot Henry C. , Dove William F.
Published: October 2006

In a pedigree derived from a mouse treated with the mutagen ethylnitrosourea, a mutation has been identified that predisposes to spontaneous intestinal cancer. The mutant gene was found to be dominantly expressed and fully penetrant. Affected mice developed multiple adenomas throughout the entire intestinal tract at an early age.
Cretaceous Extinctions: Evidence for Wildfires and Search for Meteoritic Material
Authors: Wolbach Wendy S. , Lewis Roy S. , Anders Edward
Published: October 2006

Clay samples from three Cretaceous-Tertiary boundary sites contain 0.36 to 0.58 percent graphitic carbon, mainly as fluffy aggregates of 0.1 to 0.5 micrometers—apparently a worldwide layer of soot. It may have been produced by wildfires triggered by a giant meteorite. This carbon, corresponding to a global abundance of 0.021 ± 0.006 gram per square centimeter, could have greatly enhanced the darkening and cooling of the earth by rock dust, which has been suggested as a cause of the extinctions. The surprisingly large amount of soot (10 percent of the present biomass of the earth) implies either that much of the earth's vegetation burned down or that substantial amounts of fossil fuels were ignited also. The particle-size distribution of the soot is similar to that assumed for the smoke cloud of "nuclear winter," but the global distribution is more uniform and the amounts are much greater, suggesting that soot production by large wildfires is about 10 times more efficient that has been assumed for a nuclear winter. Thus cooling would be more pervasive and lasting. No trace of meteoritic noble gases and no meteoritic spinel were found in these carbon fractions. Accordingly, limits can be set on the mass fraction of the meteorite that escaped degassing (≤3 × 10
-5
) or vaporization (≤0.04). Thus it seems unlikely that comets contributed significant amounts of prebiotic organic matter to the primitive earth.
Ambient Levels of Ozone Reduce Net Photosynthesis in Tree and Crop Species
Authors: Reich Peter B. , Amundson Robert G.
Published: October 2006

Experiments were conducted to measure the photosynthetic response of three crop and four tree species to realistic concentrations of ozone and (for tree species only) simulated acidic rain. The ozone concentrations were representative of those found in clean ambient air, in mildly to moderately polluted air such as occurs in much of the United States during the summer, and in more heavily polluted air. However, the highest concentrations of ozone used were lower than those found regularly in the Los Angeles area. The mean
p
H of the simulated acid rain treatments ranged from more alkaline to much more acidic than the mean
p
H of precipitation in the United States. Exposure to any increase in ozone reduced net photosynthesis in all species tested. In contrast, acidic rain had no negative effect on photosynthesis in tree species, and no interaction between ozone and acidic rain was observed. Ozone-induced reductions in photosynthesis were related to declines in growth or yield. Species with higher stomatal conductances and thus higher potential for pollutant uptake exhibited greater negative responses to similar ozone treatments. Since exposure to ozone concentrations typical of levels of the pollutant observed in the eastern half of the United States reduced the rates of net photosynthesis of all species tested, reductions in net photosynthesis may be occurring over much of the eastern United States.
Energy Extraction and Use in a Nomadic Pastoral Ecosystem
Authors: Coughenour M. B. , Ellis J. E. , Swift D. M. , Coppock D. L. , Galvin K. , McCabe J. T. , Hart T. C.
Published: October 2006

An analysis of annual energy flows in an arid tropical ecosystem inhabited by nomadic pastoralists provides insight into a subsistence life-style that has persisted in droughted environments for hundreds to thousands of years. Although a large fraction of the total energy consumed by the Ngisonyoka of Kenya followed a single pathway from plant to animal to human, they also harvested solar energy from a relatively diverse assemblage of energy flow channels. Energy utilization and conversion efficiencies were generally low, as the system is maintenance- rather than production-oriented. Energy flow to maintenance must be relatively high to support biotic responses that enable tolerance of abiotic variability and to stabilize energy flow under the stress of severe droughts. Energy utilization by the Ngisonyoka is therefore consistent with ecological patterns that promote rather than diminish ecological stability under stress.
Conservation Tillage
Authors: Gebhardt Maurice R. , Daniel Tommy C. , Schweizer Edward E. , Allmaras Raymond R.
Published: October 2006

Conservation production systems combine tillage and planting practices to reduce soil erosion and loss of water from farmland. Successful conservation tillage practices depend on the ability of farm managers to integrate sound crop production practices with effective pest management systems. More scientific information is needed to determine the relations between tillage practices and physical, chemical, and biological soil factors that affect plant and pest ecology. There is a need to devise improved pest management strategies for conservation tillage and to better understand the impact of conservation tillage on water quality, especially as it is related to use of agricultural chemicals. While savings in fuel, labor, and soil have induced many farmers to adopt conservation tillage, improved methods and equipment should increase adoption even more.
Infanticide in Prairie Dogs: Lactating Females Kill Offspring of Close Kin
Authors: Hoogland John L.
Published: October 2006

Infanticide, although common in a wide range of species including humans and other primates, is poorly understood. A 7-year study under natural conditions reveals that infanticide within colonies of black-tailed prairie dogs (
Cynomys ludovicianus
) is striking for three reasons. It is the major source of juvenile mortality, accounting for the total or partial demise of 51 percent of all litters born. The most common killers are resident lactating females. The most common victims are the offspring of close kin.
Kinetics of Energy Flow in the Phycobilisome Core
Authors: Glazer A. N. , Chan C. , Williams R. C. , Yeh Sheila W. , Clark J. H.
Published: October 2006

Light energy absorbed by the 576 bilin chromophores in the six rods of the phycobilisome of the cyanobacterium
Synechocystis
6701 is funneled into a 1.5 × 10
6
dalton core. The 72 bilins of the core function as a single unit with respect to the rate-limiting processes for energy flow within these particles.
The Costs of the Soviet Empire
Authors: Wolf Charles
Published: October 2006

A comprehensive framework is developed and applied to estimate the economic costs incurred by the Soviet Union in acquiring, maintaining, and expanding its empire. The terms "empire" and "costs" are explicitly defined. Between 1971 and 1980, the average ratio between empire costs and Soviet gross national product was about 3.5 percent; as a ratio to Soviet military spending, empire costs averaged about 28 percent. The burden imposed on Soviet economic growth by empire costs is also considered, as well as rates of change in these costs, and the important political, military, and strategic benefits associated by the Soviet leadership with maintenance and expansion of the empire. Prospective empire costs and changes in Soviet economic constraints resulting from the declining performance of the domestic economy are also considered.
Influence of Scene-Based Properties on Visual Search
Authors: Enns James T. , Rensink Ronald A.
Published: October 2006

The task of visual search is to determine as rapidly as possible whether a target item is present or absent in a display. Rapidly detected items are thought to contain features that correspond to primitive elements in the human visual system. In previous theories, it has been assumed that visual search is based on simple two-dimensional features in the image. However, visual search also has access to another level of representation, one that describes properties in the corresponding three-dimensional scene. Among these properties are three dimensionality and the direction of lighting, but not viewing direction. These findings imply that the parallel processes of early vision are much more sophisticated than previously assumed.
Optical Activity and Ferroelectricity in Liquid Crystals
Authors: Goodby J. W.
Published: October 2006

Some liquid-crystalline phases of optically active materials are themselves optically active and have dissymmetric structures. The cholesteric phase and smectics C*, I*, and F* have a helical order of their molecules. Plane-polarized light is rotated by the helix, and when the pitch of the helix is comparable to the wavelength of visible light, these phases will reflect irridescent light of a single color. The smectics phases can exhibit ferroelectricity and have been utilized recently in fast-switching light valves. A relation between the microscopic property of molecular configuration and the macroscopic properties of ferroelectricity and the rotation of plane-polarized light is developed.
Synthesis of Todorokite
Authors: Golden D. C. , Chen C. C. , Dixon J. B.
Published: October 2006

Todorokite of chemical composition (Mg
0.77
Na
0.03
)(Mg
0.18
Mn
2+
0.60
Mn
4+
5.22
) O
12
⋅ 3.07 H
2
O was synthesized by a two-step procedure. First, sodium birnessite was synthesized and magnesium was exchanged for sodium to form magnesium birnessite, which was autoclaved under a saturated steam pressure at 155°C for 8 hours to form well-crystallized todorokite. Synthesized todorokite particles consisted of fibers extending from a central plate. The plate itself was made of twinned fibers forming a trilling pattern. The infrared spectra and x-ray diffraction patterns were similar to those of natural todorokite samples. Calcium birnessite and nickel birnessite, when autoclaved under conditions similar to those for magnesium birnessite, yielded a todorokite structure. However, the formation of todorokite from calcium and nickel birnessite was less extensive.
High-Resolution Climatic Analysis and Southwest Biogeography
Authors: Neilson Ronald P.
Published: October 2006

Meteorologists and climatologists have produced significant new data on the fluid dynamics of the atmosphere, thus allowing biologists to examine more closely the cause-effect relation between the large-scale structure of the atmosphere and the dominant patterns of global biogeography. The inability to characterize the high-frequency variability of the weather has constrained such efforts. A method that allows year-to-year patterns of weather variability to be characterized in the contexts of global warming and cooling trends is applied in a combined analysis of long-term monthly weather records and data from an ecological monitoring project in southern New Mexico. The analysis suggests a cause-effect hypothesis of recent desertification in the North American Southwest. The links between the atmosphere and the biosphere are based on the fundamentally different responses to specific weather regimes of semidesert grasses with a C
4
photosynthetic pathway and desert shrubs with a C
3
photosynthetic pathway. The hypothesis appears to be of sufficient generality to explain the complex, but well-documented, floristic changes that have occurred in the same region since the last glacial maximum.
Nitrogen Fixation by
Azotobacter vinelandii
Strains Having Deletions in Structural Genes for Nitrogenase
Authors: Bishop Paul E. , Premakumar R. , Dean Dennis R. , Jacobson Marty R. , Chisnell John R. , Rizzo Thomas M. , Kopczynski Jennifer
Published: October 2006

Phenotypic reversal of Nif
-
mutant strains to Nif
+
under molybdenum-deficient conditions has been cited as evidence that
Azotobacter vinelandii
possesses two nitrogen fixation systems: the conventional molybdenum-enzyme system and an alternative nitrogen-fixation system. Since explanations other than the existence of an alternative system were possible, deletion strains of
A. vinelandii
lacking the structural genes for conventional nitrogenase (nifHDK) were constructed. These strains were found to grow in molybdenum-deficient nitrogen-free media, reduce acetylene (at low rates), and incorporate molecular nitrogen labeled with nitrogen-15. Thus it can be concluded that the phenotypic reversal phenomenon cannot be due to altered phenotypic expression of
nif
mutations under molybdenum-deficient conditions, but is due to the existence of an alternative nitrogen-fixation system in
A. vinelandii
as originally proposed.
Sexual Dimorphism in
Catasetum
Orchids: Forcible Pollen Emplacement and Male Flower Competition
Authors: Romero Gustavo A. , Nelson Craig E.
Published: October 2006

Orchids of the Neotropical genus
Catasetum
have sexually dimorphic flowers; that is, male and female flowers are distinctly different in shape and color. Male flowers forcibly attach a large pollinarium onto euglossine bees.
Euglossa
bees leave the male flower in response to pollinarium emplacement by
Catasetum ochraceum
and subsequently avoid male but not female flowers. This evidence suggests that sexual dimorphism promotes pollination. The aversion of the bee to pollinarium attachment and its avoidance of male flowers thereafter apparently reflect competition among male flowers that probably evolved concurrently with sexual dimorphism. Among
Catasetum
species, the extent of dimorphism is correlated with the degree of apparent aversion caused by the male flower (weight of the pollinarium). Thus, aversive pollinarium emplacement can account for widespread sexual dimorphism in
Catasetum
and for interspecific variations in its expression.
Tenuous Structures from Disorderly Growth Processes
Authors: Witten T. A. , Cates M. E.
Published: October 2006

Colloidal aggregation and other random growth processes produce structures that behave differently from ordinary bulk matter. Much of this behavior can be described in terms of the invariance of the aggregates under changes of spatial length scale: they appear to be fractals. There are two types of basic mechanisms for producing fractal aggregates. Those in which aggregation proceeds cluster by cluster can be understood qualitatively in terms of a solvable schematic model. The diffusion-limited aggregation or deposition of individual particles to make a large cluster is not as well understood. It is closely related to several irreversible processes in other areas of physics, such as two-fluid displacement in porous materials and the dielectric breakdown of insulators. More generally, disorderly growth mechanisms provide structures having unique properties, many of which can be understood by using simple statistical principles.