bluuebunny/crossref_metadata_2025 huggingface dataset:
β-Adrenergic-Sensitive Adenylate Cyclase in Secretory Cells of Choroid Plexus
Authors: Nathanson James A.
Published: October 2006

Biochemical evidence supporting the sympathetic control of cerebrospinal fluid production has been obtained through identification of a specific β-adrenergic-sensitive adenylate cyclase in the choroid plexus. The enzyme, which is localized in the secretory epithelium, is activated by low concentrations of isoproterenol and norepinephrine and appears separate from β-adrenergic-sensitive adenylate cyclase present in cerebral blood vessels.
Acid Rain on Acid Soil: A New Perspective
Authors: Krug Edward C. , Frink Charles R.
Published: October 2006

Acid rain is widely believed to be responsible for acidifying soil and water in areas of North America and northern Europe. However, factors commonly considered to make landscapes susceptible to acidification by acid rain are the same factors long known to strongly acidify soils through the natural processes of soil formation. Recovery from extreme and widespread careless land use has also occurred in regions undergoing acidification. There is evidence that acidification by acid rain is superimposed on long-term acidification induced by changes in land use and consequent vegetative succession. Thus, the interactions of acid rain, acid soil, and vegetation need to be carefully examined on a watershed basis in assessing benefits expected from proposed reductions in emissions of oxides of sulfur and nitrogen.
Venus: Identification of Banded Terrain in the Mountains of Ishtar Terra
Authors: Campbell D. B. , Head J. W. , Harmon J. K. , Hine A. A.
Published: October 2006

High resolution images obtained with the Arecibo radar system at a wavelength of 12.6 centimeters reveal numerous parallel 10- to 20-kilometer-wide bands of high radar backscatter situated on and oriented parallel to the major mountain ranges of the Ishtar Terra region of Venus. Geometric and morphological characteristics suggest that the bands represent Earth-like tectonic deformational features, such as folds and faults.
Confirmation of the Carolina Slate Belt as an Exotic Terrane
Authors: Secor Donald T. , Samson Sara L. , Snoke Arthur W. , Palmer Allison R.
Published: October 2006

An assemblage of Middle Cambrian Atlantic faunal province trilobites has been found in the rocks of the Carolina slate belt near Batesburg, South Carolina. Geologic and paleomagnetic data suggest that the Carolina slate belt and the adjacent Charlotte belt constitute an exotic terrane that was accreted to North America in early to middle Paleozoic time.
Low Nitrogen to Phosphorus Ratios Favor Dominance by Blue-Green Algae in Lake Phytoplankton
Authors: Smith Val H.
Published: October 2006

An analysis of growing season data from 17 lakes throughout the world suggests that the relative proportion of blue-green algae (Cyanophyta) in the epilimnetic phytoplankton is dependent on the epilimnetic ratio of total nitrogen to total phosphorus. Blue-green algae tended to be rare when this ratio exceeded 29 to 1 by weight, suggesting that modification of this ratio by control of nutrient additions may provide a means by which lake water quality can be managed.
Peru Coastal Currents During El Niño: 1976 and 1982
Authors: Smith Robert L.
Published: October 2006

Year-long measurements of subsurface current and temperature on Peru's continental shelf included the onset of El Niño in 1976 and 1982. The Peru Coastal Undercurrent more than doubled in speed and advected anomalously warm water poleward. El Niño began in different seasons in 1976 and 1982, but the current and temperature responses were very similar. Acceleration of poleward flow at 10°S occurred several days after sea level rose at the Galápagos Islands in October 1982, suggesting the onset of El Niño propagated as a Kelvin wave.
Mapping the Human Genome: Current Status
Authors: Stephens J. Claiborne , Cavanaugh Mark L. , Gradie Margaret I. , Mador Martin L. , Kidd Kenneth K.
Published: October 2006

The human genome has already been the subject of extensive research activity even though the Human Genome Project is only just officially starting. This review and the accompanying wall chart attempt to provide an integrated, quantitative, and detailed summary of the status of knowledge on the human genome in mid-1990. The analysis has highlighted the rudimentary nature of many of the information links needed for the task. While this overview could not be fully comprehensive and required simplifying assumptions, the results have provided estimates of relative progress on a region-by-region basis throughout the genome.
Mutations Affecting Tea Blockade and Ion Permeation in Voltage-activated K
+
Channels
Authors: MacKinnon Roderick , Yellen Gary
Published: October 2006

Voltage-dependent ion channels are responsible for electrical signaling in neurons and other cells. The main classes of voltage-dependent channels (sodium-, calcium-, and potassium-selective channels) have closely related molecular structures. For one member of this superfamily, the transiently voltage-activated Shaker H4 potassium channel, specific amino acid residues have now been identified that affect channel blockade by the small ion tetraethylammonium, as well as the conduction of ions through the pore. Furthermore, variation at one of these amino acid positions among naturally occurring potassium channels may account for most of their differences in sensitivity to tetraethylammonium.
Oxytocin Receptors: Triggers for Parturition and Lactation?
Authors: Soloff Melvyn S. , Alexandrova Maria , Fernstrom Martha J.
Published: October 2006

Specific binding of tritiated oxytocin to uterine receptors of pregnant rats increases dramatically at term and is maximal during labor. In mammary glands the increase in binding is gradual, reaching a maximum during the lactation period. Concomitant changes in the sensitivity of the uterus and mammary gland to oxytocin indicate that the receptor concentration is of functional significance. Oxytocin receptors, therefore, may regulate the response of the target organs to circulating oxytocin and thereby control the onset of labor and lactation. Ovarian steroids participate in the regulation of oxytocin receptors in a manner as yet unclarified.
Nonimpulse-Mediated Synaptic Transmission During the Generation of a Cyclic Motor Program
Authors: Raper Jonathan A.
Published: October 2006

A small neuronal network in the lobster stomatogastric ganglion, composed of impulse-producing motor neurons, gives rise to cyclic patterned outputs. This network continues to generate its cyclic motor program if impulse production within the ganglion is blocked. Continuously graded, nonimpulse-mediated, chemical synaptic transmission is sufficient to coordinate neuronal activity in a functioning pattern generator.
Catch a Falling Star: Meteorites and Old Ice
Authors: Whillans I. M. , Cassidy W. A.
Published: October 2006

A model for the process of meteorite concentration in blue ice regions of the Antarctic ice sheet is proposed based on data from near the Allan Hills and the assumptions that both meteorite influx and glacial flow have been constant. The meteorite influx is calculated to be 60 × 10
-6
kilogram per square kilometer per year, and the age of the exposed ice to be 0 to 600,000 years, varying with distance from the Allan Hills. These results are in line with other estimates of influx rate and with measurements of the terrestrial ages of the meteorites, providing support for the assumption of steady flow and meteorite influx. This may be the oldest sequence of ice in stratigraphic order yet discovered, and the results imply that this part of the east Antarctic ice sheet has been approximately steady during this time interval.
Nocturnal Aerial Predation of Fireflies by Light-Seeking Fireflies
Authors: Lloyd James E. , Wing Steven R.
Published: October 2006

FemalePhoturisfireflies guided by their prey's luminescence attack flying fireflies at night. They sometimes use this hunting tactic together with prey attraction by mating-signal mimicry. Such predation could have been a major factor in the evolution of signaling behavior of American fireflies. Nocturnal aerial predation by an insect and attack guidance on energy emitted by airborne prey have not previously been reported.
Nuclear Winter: Global Consequences of Multiple Nuclear Explosions
Authors: Turco R. P. , Toon O. B. , Ackerman T. P. , Pollack J. B. , Sagan Carl
Published: October 2006

The potential global atmospheric and climatic consequences of nuclear war are investigated using models previously developed to study the effects of volcanic eruptions. Although the results are necessarily imprecise, due to a wide range of possible scenarios and uncertainty in physical parameters, the most probable first-order effects are serious. Significant hemispherical attenuation of the solar radiation flux and subfreezing land temperatures may be caused by fine dust raised in high-yield nuclear surface bursts and by smoke from city and forest fires ignited by airbursts of all yields. For many simulated exchanges of several thousand megatons, in which dust and smoke are generated and encircle the earth within 1 to 2 weeks, average light levels can be reduced to a few percent of ambient and land temperatures can reach -15° to -25°C. The yield threshold for major optical and climatic consequences may be very low: only about 100 megatons detonated over major urban centers can create average hemispheric smoke optical depths greater than 2 for weeks and, even in summer, subfreezing land temperatures for months. In a 5000-megaton war, at northern mid-latitude sites remote from targets, radioactive fallout on time scales of days to weeks can lead to chronic mean doses of up to 50 rads from external whole-body gamma-ray exposure, with a likely equal or greater internal dose from biologically active radionuclides. Large horizontal and vertical temperature gradients caused by absorption of sunlight in smoke and dust clouds may greatly accelerate transport of particles and radioactivity from the Northern Hemisphere to the Southern Hemisphere. When combined with the prompt destruction from nuclear blast, fires, and fallout and the later enhancement of solar ultraviolet radiation due to ozone depletion, long-term exposure to cold, dark, and radioactivity could pose a serious threat to human survivors and to other species.
Membrane Lipid from Deep-Sea Hydrothermal Vent Methanogen: a New Macrocyclic Glycerol Diether
Authors: Comita Paul B. , Gagosian Robert B.
Published: October 2006

The membrane lipid of a new deep-sea hydrothermal vent methanogen,
Methanococcus jannaschii
, has been structurally characterized. The hydrolyzed polar lipid of this archaebacterium is primarily (95 percent) a macrocyclic glycerol diether, which has not been described previously. The structure was elucidated by a combination of chemical and spectroscopic techniques. An initial survey of selected methanogens failed to indicate the presence of this membrane lipid in any microorganism other than
Methanococcus jannaschii
.
Turbulent Jets and Eddies in the California Current and Inferred Cross-Shore Transports
Authors: Mooers Christopher N. K. , Robinson Allan R.
Published: October 2006

The instantaneous California Current is seen to consist of intense meandering current filaments (jets) intermingled with synoptic-mesoscale eddies. These quasi-geostrophic jets entrain cold, upwelled coastal waters and rapidly advect them far offshore; this behavior accounts for the elongated, cool surface features that are seen extending across the California Current region in satellite infrared imagery. The associated advective mechanism should provide significant cross-shore transports of heat, nutrients, biota, and pollutants. The dynamics of the current system should be crucially influenced by its highly variable structure.
A Search for Iridium Abundance Anomalies at Two Late Cambrian Biomere Boundaries in Western Utah
Authors: Orth Charles J. , Knight Jere D. , Quintana Leonard R. , Gilmore James S. , Palmer Allison R.
Published: October 2006

Iridium concentrations have been measured in samples taken across two Late Cambrian biomere boundaries (crisis zones) in search of evidence for possible elemental abundance anomalies similar to the one observed at the Cretaceous-Tertiary boundary. Sampling was performed in uplifted marine limestone deposits in the House Range of western Utah. Although the two trilobite-brachiopod extinction boundaries could be assigned to ±4 millimeters of vertical section by laboratory examination of the rocks, only background amounts of iridium (2 × 10
-12
to 17 × 10
-12
gram per gram of whole rock) were observed.
Localization, Interactions, and the Metal-Insulator Transition
Authors: Dynes R. C. , Lee P. A.
Published: October 2006

Recent advances in our understanding of electronic conduction have pointed up deficiencies in traditional thinking. For a metal at a sufficiently low temperature, it is known both theoretically and experimentally that the conventional picture in terms of the Boltzmann theory breaks down. Improved understanding of both electron localization and the effects of electron-electron interactions in a disordered medium has led to experimentally verifiable predictions. These effects have an important influence on the nature of the metal-insulator transition.
Methane from Anaerobic Fermentation
Authors: Klass Donald L.
Published: October 2006

Conventional anaerobic digestion is an established technology for wastewater stabilization, but methane production rates and net energy yields are generally too low to make the process competitive as a source of methane. Numerous improvements are being developed to make conversion of plant biomass to methane and simultaneous waste stabilization-methane production practical. Among these improvements are innovative digester designs and process configurations. Efforts to commercialize modern anaerobic digestion technology are progressing.
The End of the Cretaceous: Sharp Boundary or Gradual Transition?
Authors: Alvarez W. , Alvarez L. W. , Asaro F. , Michel H. V.
Published: October 2006

Evidence indicates that the Cretaceous-Tertiary boundary is very sharp, and, within the limits of resolution, it is apparently synchronous at the various boundary localities. Arguments to the contrary, particularly those of Officer and Drake, are shown to be invalid.
Localized All-or-None Calcium Liberation by Inositol Trisphosphate
Authors: Parker Ian , Ivorra Isabel
Published: October 2006

Laser confocal microscopy was used to monitor calcium ion (Ca
2+
) liberation from highly localized (micrometer) regions of intact
Xenopus
oocytes in response to photo-released inositol 1,4,5-trisphosphate (InsP
3
). Local Ca
2+
release varied in an all-or-none manner with increasing amount of InsP
3
, in contrast to signals recorded from larger areas, which grew progressively as the concentration of InsP
3
was raised above a threshold. Liberation of Ca
2+
was restricted to within a few microns of the site of InsP
3
release and, in response to agonist activation, localized regions of the oocyte showed asynchronous oscillations in cytoplasmic Ca
2+
release. Results obtained with this technique provided direct evidence that InsP
3
-induced Ca
2+
liberation was quantized and suggest that the InsP
3
-sensitive Ca
2+
pool may be a collection of independent, localized compartments that release Ca
2+
in an all-or-none manner.
Late Triassic Naticid Drillholes: Carnivorous Gastropods Gain a Major Adaptation but Fail to Radiate
Authors: Fürsich Franz T. , Jablonski David
Published: October 2006

Infaunal and reclining bivalves of the Late Triassic Cassian Formation of northern Italy contain drillholes that closely resemble those produced by modern naticid gastropods. The oldest drillholes previously reported are from the late Early Cretaceous; this suggests that the drilling adaptation was lost soon after its appearance in the Late Triassic and originated independently in another naticid clade 120 million years later. The perceived selective value of such an adaptation may thus not always be a good predictor of its long-term survival, which is ultimately governed by factors that affect the speciation and extinction rates of the clade that carries it.
Solar Photovoltaic Power Systems: An Electric Utility R & D Perspective
Authors: DeMeo Edgar A. , Taylor Roger W.
Published: October 2006

Solar photovoltaic technology is receiving increasing attention as a prospective source of bulk, electric utility power within the next 10 to 20 years. Successful development will require solar energy conversion efficiencies of about 15 percent for photovoltaic flat-plate modules, or about 25 percent for photovoltaic cells using highly concentrated sunlight. Three different cell technologies have a better than even chance of achieving these target efficiencies with costs and operating lifetimes that would allow significant use by electric utilities. The challenge for the next decade is to push photovoltaic technology to its physical limits while expanding markets and user confidence with currently available systems.
Do Bacteria-Sized Marine Eukaryotes Consume Significant Bacterial Production?
Authors: Fuhrman Jed A. , McManus George B.
Published: October 2006

Up to 60 percent of the total marine primary production (or about one-fourth of the total global carbon dioxide fixation) passes through the free-living bacterioplankton. Grazing by bacteriovores is probably the predominant fate of the bacteria, although data are scarce. Evidence is presented that previously uncharacterized, small eukaryotes that are able to pass even 0.6-micrometer filters may be responsible for a large fraction (more than 50 percent) of the total grazing in coastal waters. These organisms have not yet been observed microscopically.
Wolves, Moose, and the Allometry of Population Cycles
Authors: Peterson R. O. , Page R. E. , Dodge K. M.
Published: October 2006

After a decade of dramatic population fluctuations, protected populations of wolves and moose in Isle Royale National Park in Lake Superior returned in 1983 to the levels observed in the 1950's. Inherent lags in this predator-prey system and the strong recovery of the moose population following a wolf population crash suggest that these populations may continue to cycle with a period length of about 38 (95 percent confidence interval, ±13) years. Such a long-term cycle is consistent with the proposal that period length of herbivore population cycles will characteristically scale according to the fourth root of body mass, a basic allometric relation linking physiological cycles to population processes.
X-Ray Gas Scintillation Spectrometer Experiment
Authors: Andresen R. D. , Boella G. , Falconi B. , Lamb P. , Manzo G. , Raymont J. , Re S. , Sims M. R. , Villa G.
Published: October 2006

The payload complement on Spacelab 1 included a spectrometer for observations of the brighter cosmic x-ray sources. The primary scientific objective was to study the detailed spectral features of cosmic x-ray sources and their associated temporal variations over a wide energy range from about 2 to 80 kiloelectron volts. The instrument, based on the gas scintillation proportional counter, had a geometrical area of some 180 square centimeters with an energy resolution of about 9 percent at 7 kiloelectron volts. The results presented here show new results from two galactic binary x-ray sources, Cygnus X-3 and Centaurus X-3, and from the Perseus cluster of galaxies. The excellent energy resolution of the instrument permits line features to be identified in these sources with unprecedented quality.
Energy and the U.S. Economy: A Biophysical Perspective
Authors: Cleveland Cutler J. , Costanza Robert , Hall Charles A. S. , Kaufmann Robert
Published: October 2006

A series of hypotheses is presented about the relation of national energy use to national economic activity (both time series and cross-sectional) which offer a different perspective from standard economics for the assessment of historical and current economic events. The analysis incorporates nearly 100 years of time series data and 3 years of cross-sectional data on 87 sectors of the United States economy. Gross national product, labor productivity, and price levels are all correlated closely with various aspects of energy use, and these correlations are improved when corrections are made for energy quality. A large portion of the apparent increase in U.S. energy efficiency has been due to our ability to expand the relative use of high-quality fuels such as petroleum and electricity, and also to relative shifts in fuel use between sectors of the economy. The concept of energy return on investment is introduced as a major driving force in our economy, and data are provided which show a marked decline in energy return on investment for all our principal fuels in recent decades. Future economic growth will depend largely on the net energy yield of alternative fuel sources, and some standard economic models may need to be modified to account for the biophysical constraints on human economic activity.
Ground Water Redox Reactions: An Analysis of Equilibrium State Applied to Eh Measurements and Geochemical Modeling
Authors: Lindberg Ralph D. , Runnells Donald D.
Published: October 2006

Computer modeling of 611 high-quality analyses of normal ground waters from diverse geographic areas reveals that aqueous oxidation-reduction reactions are generally not at equilibrium. Multiple redox couples present in individual samples yield computed Nernstian Eh (redox potential) values spanning as much as 1000 millivolts. The computed Eh values do not agree with each other, nor do they agree with the single "master" value measured in the field with a platinum electrode. Because of internal disequilibrium, the use of any measured Eh value as input to equilibrium hydrogeochemical computer models will generally yield misleading results for normal ground waters.
Remote Acoustic Imaging of the Plume from a Submarine Spring in an Arctic Fjord
Authors: Hay Alex E.
Published: October 2006

Acoustic backscatter observations at 200 kilohertz were made of the buoyant plume from a submarine spring at a depth of 47 meters in Cambridge Fiord, Baffin Island. Vertical velocities of up to 37 centimeters per second are inferred from the ascent rates of discrete scattering structures in the plume.
Biology Contravenes Taxonomy in the Myxozoa: New Discoveries Show Alternation of Invertebrate and Vertebrate Hosts
Authors: Wolf Ken , Markiw Maria E.
Published: October 2006

For 80 years the infectivity of salmonid whirling disease has eluded discovery. New findings now show that this myxosporean disease of fish is initiated by what is regarded as an actinosporean produced in a tubificid oligochaete. Experimental results provide evidence that, instead of being considered as representatives of separate classes in the phylum Myxozoa, the myxosporean and actinosporean are alternating life forms of a single organism.
Sequence-Specific DNA Binding by the c-Myc Protein
Authors: Blackwell T. Keith , Kretzner Leo , Blackwood Elizabeth M. , Eisenman Robert N. , Weintraub Harold
Published: October 2006

While it has been known for some time that the c-Myc protein binds to random DNA sequences, no sequence-specific binding activity has been detected. At its carboxyl terminus, c-Myc contains a basic—helix-loop-helix (bHLH) motif, which is important for dimerization and specific DNA binding, as demonstrated for other bHLH protein family members. Of those studied, most bHLH proteins bind to sites that contain a CA- -TG consensus. In this study, the technique of selected and amplified binding-sequence (SAAB) imprinting was used to identify a DNA sequence that was recognized by c-Myc. A purified carboxyl-terminal fragment of human c-Myc that contained the bHLH domain bound in vitro in a sequence-specific manner to the sequence, CACGTG. These results suggest that some of the biological functions of Myc family proteins are accomplished by sequence-specific DNA binding that is mediated by the carboxyl-terminal region of the protein.
Calmodulin Activation of Adenylate Cyclase in Pancreatic Islets
Authors: Valverde Isabel , Vandermeers André , Anjaneyulu Renu , Malaisse Willy J.
Published: October 2006

Pancreatic islets contain calmodulin. The protein binds to a particulate fraction derived from the islets and stimulates adenylate cyclase activity in this subcellular fraction, both phenomena being activated by ionized calcium. A calcium-dependent stimulation of adenylate cyclase by endogenous calmodulin may contribute to the accumulation of adenosine 3′,5′-monophosphate evoked by insulin releasing agents in the islet cells.
Venus: Volcanism and Rift Formation in Beta Regio
Authors: Campbell D. B. , Head J. W. , Harmon J. K. , Hine A. A.
Published: October 2006

A new high-resolution radar image of Beta Regio, a Venus highland area, confirms the presence of a major tectonic rift system and associated volcanic activity. The lack of identifiable impact craters, together with the apparent superposition of the Theia Mons volcanic structure on the rift system, suggest that at least some of the volcanic activity occurred in relatively recent geologic time. The presence of topographically similar highland areas elsewhere on Venus (Aphrodite Terra, Dali Chasma, and Diana Chasma) suggests that rifting and volcanism are significant processes on Venus.
Increased Stratospheric Hydrogen Chloride in the El Chichón Cloud
Authors: Mankin William G. , Coffey M. T.
Published: October 2006

Spectroscopic observations of the total column amount of hydrogen chloride above an altitude of 12 kilometers in the latitude range 20° to 40°N have been made both before and 3 to 6 months after the eruptions of El Chichón Volcano in March and April 1982. In the region of the cloud of volcanic aerosols, the hydrogen chloride total column after the eruptions increased by approximately 40 percent, even after allowance is made for the global secular increase in hydrogen chloride of 5 percent per year. The column amounts of hydrogen fluoride show no such increase.
Chemical Sensing in Process Analysis
Authors: Hirschfeld T. , Callis J. B. , Kowalski B. R.
Published: October 2006

Improvements in process control, which determine production efficiency and product quality, are critically dependent upon on-line process analysis. The technology of the required instrumentation will be substantially expanded by advances in sensing devices. In the future, the hardware will consist of sensor arrays and miniaturized instruments fabricated by microlithography and silicon micromachining. Chemometrics will be extensively used in software to provide error detection, self-calibration, and correction as well as multivariate data analysis for the determination of anticipated and unanticipated species. A number of examples of monolithically fabricated sensors now exist and more will be forthcoming as the new paradigms and new tools are widely adopted. A trend toward not only on-line but even in-product sensors is becoming discernible.
Trapped Ions, Laser Cooling, and Better Clocks
Authors: Wineland D. J.
Published: October 2006

Ions that are stored in electromagnetic "traps" provide the basis for extremely high resolution spectroscopy. By using lasers, the kinetic energy of the ions can be cooled to millikelvin temperatures, thereby suppressing Doppler frequency shifts. Potential accuracies of frequency standards and clocks based on such experiments are anticipated to be better than one part in 10
15
.
Energy Conservation Through More Efficient Lighting
Authors: Maya J. , Grossman M. W. , Lagushenko R. , Waymouth J. F.
Published: October 2006

The efficiency of a mercury-rare gas electrical discharge, which forms the basis of a fluorescent lamp, can be increased about 5 percent simply by increasing the concentration of mercury-196 from 0.146 percent (natural) to about 3 percent. These findings can be implemented immediately without any significant change in the process of manufacturing of this widely used source of illumination, provided that mercury-196 can be obtained economically. The potential energy savings for the United States are estimated to be worth in excess of $200 million per year.
Iridium Anomaly in the Upper Devonian of the Canning Basin, Western Australia
Authors: Playford Phillip E. , McLaren Digby J. , Orth Charles J. , Gilmore James S. , Goodfellow Wayne D.
Published: October 2006

A moderate iridium anomaly, about 20 times the local background, has been found in Upper Devonian rocks in the Canning Basin. It occurs at or near the Frasnian-Famennian boundary, which is known to be associated with a major mass-extinction event of global extent. The anomaly occurs in an extremely condensed limestone sequence laid down under quiet deepwater conditions. Its occurrence suggests a causal link with some form of meteoroid impact. Moreover, carbon isotope data indicate that a large reduction in biomass could have occurred at this level. However, the anomaly coincides with a stromatolite bed containing the fossil cyanobacterium
Frutexites
; iridium, platinum, iron, manganese, cobalt, arsenic, antimony, and cerium are preferentially concentrated in filaments of this organism, with concentrations ranging from two to five times that of the matrix. It is possible that
Frutexites
extracted these elements directly from seawater, without the need for their derivation from an extraterrestrial source.
Leaf Herbivores Decrease Fitness of a Tropical Plant
Authors: Marquis Robert J.
Published: October 2006

Damage by insect herbivores to neighboring individuals of the shrub
Piper arieianum
in a neotropical wet forest varies greatly. This differential damage has a genetic basis and results in a 2-year decrease in growth, seed production, and seed viability, with larger plants recovering before smaller plants. The results provide evidence that leaf herbivores represent a potentially strong selective force for the evolution of plant defenses.
Disk-to-Disk Transfer as the Rate-Limiting Step for Energy Flow in Phycobilisomes
Authors: Glazer A. N. , Yeh Sheila W. , Webb S. P. , Clark J. H.
Published: October 2006

A broadly tunable picosecond laser source and an ultrafast streak camera were used to measure temporally and spectrally resolved emission from intact phycobilisomes and from individual phycobiliproteins as a function of excitation wavelength. Both wild-type and mutant phycobilisomes of the unicellular cyanobacteriumSynechocystis6701 were examined, as well as two biliproteins, R-phycoerythrin (240 kilodaltons, 34 bilins) and allophycocyanin (100 kilodaltons, 6 bilins). Measurements of intact phycobilisomes with known structural differences showed that the addition of an average of 1.6 phycoerythrin disks in the phycobilisome rod increased the overall energy transfer time by 30 ± 5 picoseconds. In the isolated phycobiliproteins the onset of emission was as prompt as that of a solution of rhodamine B laser dye and was independent of excitation wavelength. This imposes an upper limit of 8 picoseconds (instrument-limited) on the transfer time from "sensitizing" to "fluorescing" chromophores in these biliproteins. These results indicate that disk-to-disk transfer is the slowest energy transfer process in phycobilisomes and, in combination with previous structural analyses, show that with respect to energy transfer the lattice of approximately 625 light-harvesting chromophores in theSynechocystis6701 wild-type phycobilisome functions as a linear five-point array.
Galileo, Planetary Atmospheres, and Prograde Revolution
Authors: Parker G. D.
Published: October 2006

Early in March 1610 Galileo was preoccupied with curious brightness variations of the newly discovered satellites of Jupiter. In formulating an incorrect explanation he advanced important generalizations about the existence of planetary atmospheres and counterclockwise circulation within the solar system.
Gas Exchange-Wind Speed Relation Measured with Sulfur Hexafluoride on a Lake
Authors: Wanninkhof Rik , Ledwell James R. , Broecker Wallace S.
Published: October 2006

Gas-exchange processes control the uptake and release of various gases in natural systems such as oceans, rivers, and lakes. Not much is known about the effect of wind speed on gas exchange in such systems. In the experiment described here, sulfur hexafluoride was dissolved in lake water, and the rate of escape of the gas with wind speed (at wind speeds up to 6 meters per second) was determined over a 1-month period. A sharp change in the wind speed dependence of the gas-exchange coefficient was found at wind speeds of about 2.4 meters per second, in agreement with the results of wind-tunnel studies. However, the gas-exchange coefficients at wind speeds above 3 meters per second were smaller than those observed in wind tunnels and are in agreement with earlier lake and ocean results.
Rheology of Glacier Ice
Authors: Jezek Kenneth C. , Alley Richard B. , Thomas Robert H.
Published: October 2006

A new method for calculating the stress field in bounded ice shelves is used to compare strain rate and deviatoric stress on the Ross Ice Shelf, Antarctica. The analysis shows that strain rate (per second) increases as the third power of deviatoric stress (in newtons per square meter), with a constant of proportionality equal to 2.3 x 10
-25
.
A view of Interphase Chromosomes
Authors: Manuelidis Laura
Published: October 2006

Metaphase chromosomes are dynamically modified in interphase. This review focuses on how these structures can be modified, and explores the functional mechanisms and significance of these changes. Current analyses of genes often focus on relatively short stretches of DNA and consider chromatin conformations that incorporate only a few kilobases of DNA. In interphase nuclei, however, orderly transcription and replication can involve highly folded chromosomal domains containing hundreds of kilobases of DNA. Specific "junk" DNA sequences within selected chromosome domains may participate in more complex levels of chromosome folding, and may index different genetic compartments for orderly transcription and replication. Three-dimensional chromosome positions within the nucleus may also contribute to phenotypic expression. Entire chromosomes are maintained as discrete, reasonably compact entities in the nucleus, and heterochromatic coiled domains of several thousand kilobases can acquire unique three-dimensional positions in differentiated cell types. Some aspects of neoplasia may relate to alterations in chromosome structure at several higher levels of organization.
Genetics of Growth Predict Patterns of Brain-Size Evolution
Authors: Riska Bruce , Atchley William R.
Published: October 2006

Experimental evidence is presented supporting a developmental model that explains the genetic basis for brain and body size associations. Evolutionary change in body size causes correlated change in brain size because some genes affect both traits. The commonly observed correlation between brain and body size results from genetic variation in growth determinants affecting both traits simultaneously during fetal and early postnatal growth. Later growth reduces brain-body correlation because of changes in the underlying causal components of growth in each trait. Brain-body size evolution shows a different pattern at higher taxonomic levels from that seen within and between closely related species because body-size evolution among higher taxa occurs primarily by change in early portions of growth, which share more genetic growth determinants with brain size.
Arabidopsis thaliana
and Plant Molecular Genetics
Authors: Meyerowitz Elliot M. , Pruitt Robert E.
Published: October 2006

Arabidopsis thaliana
is a small flowering plant with various properties that make it an excellent organism for experiments in molecular genetics. These properties include having a small nuclear genome, a near absence of dispersed repetitive DNA, and a generation time of 4 to 5 weeks. In addition, mutations that affect hormone synthesis and response, many different enzyme activities, and numerous developmental processes have been identified and characterized.
Phosphorylated Proteins as Physiological Effectors
Authors: Greengard Paul
Published: October 2006

A variety of neurotransmitters, hormones, and other regulatory agents affect the phosphorylation of specific proteins in their target tissues. The types of stimuli that share this common effect on protein phosphorylation include numerous substances that do not act through cyclic AMP. These and other observations suggest that many different classes of regulatory substances achieve certain of their biological effects by altering the phosphorylation of specific proteins.
The Health Sector's Share of the Gross National Product
Authors: Fuchs Victor R.
Published: October 2006

Between 1947 and 1987 expenditures for health care in the United States grew 2.5 percent per annum faster than expenditures for other goods and services. The health sector's share of the gross national product rose from well under 5 percent in the late 1940s to more than 11 percent in the late 1980s. The expenditures gap has two components: health care prices rose 1.6 percent per annum more rapidly than other prices, while the quantity of health care grew 0.9 percent per annum faster than other quantities. Many factors, including wages, productivity, technology, and insurance contributed to these trends. No single explanation suffices, and no simple solution is apparent.
A Voltage-Dependent Chloride Current Linked to the Cell Cycle in Ascidian Embryos
Authors: Block Melodye L. , Moody William J.
Published: October 2006

A voltage-dependent chloride current has been found in early ascidian embryos that is a minor conductance in the oocyte and in interphase blastomeres but that increases transiently in amplitude by more than tenfold during each cell division. Repeated cycles in the density of this chloride current could be recorded for up to 6 hours (four cycles) in cleavage-arrested embryos, whether they were activated by sperm or calcium ionophore. These data suggest that there is a direct link between the cell cycle clock and the properties of this channel, a link that results in pronounced cyclical changes in the electrical properties of early blastomeres.
Identification of Hydroxymethanesulfonate in Fog Water
Authors: Munger J. William , Tiller Christine , Hoffmann Michael R.
Published: October 2006

Previous studies have suggested that hydroxymethanesulfonate ion (HMSA) can be an important species in fog and cloud water. Formation of HMSA explains observed excesses of sulfur in the S(IV) state (+4 oxidation state) and formaldehyde (CH
2
O) in fogs and clouds. HMSA was determined in fog water by a novel ion-pairing chromatographic technique. Concentrations in samples collected in Bakersfield, California, within 5 kilometers of major sources of sulfur dioxide (SO
2
), were as high as 300 micromoles per liter. Total CH
2
O and S(IV) concentrations, which were measured independently, ranged from 10 to 200 and 5 to more than 300 micromoles per liter, respectively. Concentrations of CH
2
O, S(IV), and HMSA at Buttonwillow, California, which is 15 kilometers from the nearest source of SO
2
, were less than those at Bakersfield but not absent. These data confirm that HMSA forms in atmospheric water droplets and can reach appreciable concentrations. HMSA represents an important source of acidity for water droplets and may also play a role in long-distance transport and transformation of SO
2
.
Terrestrial Observations from NOAA Operational Satellites
Authors: Yates H. , Strong A. , McGinnis D. , Tarpley D.
Published: October 2006

Important applications to oceanography, hydrology, and agriculture have been developed from operational satellites of the National Oceanic and Atmospheric Administration and are currently expanding rapidly. Areas of interest involving the oceans include sea surface temperature, ocean currents, and ocean color. Satellites can monitor various changing hydrological phenomena, including regional and global snow cover, river and sea ice extent, and areas of global inundation. Agriculturally important quantities derived from operational satellite observations include precipitation, daily temperature extremes, canopy temperatures, insolation, and snow cover. This overview describes the current status of each area.
Model for the Intrusion of Batholiths Associated with the Eruption of Large-Volume Ash-Flow Tuffs
Authors: Whitney James A. , Stormer John C.
Published: October 2006

Pyroclastic eruption and the intrusion of batholiths associated with large-volume ash-flow tuffs may be driven by a decrease in reservoir pressure caused by the low density of the magma column due to vesiculation. Batholithic intrusion would then be accomplished by the subsidence and settling of kilometer-sized crustal blocks through the magma chamber, resulting in eventual collapse to form large caldera structures at the surface. Such a model does not require the formation of a large, laterally extensive, shallow magma chamber before the onset of large-volume ash-flow eruptions. Eruption could commence directly from a deeper reservoir, with only a small channelway being opened to the surface before the onset of catastrophic ash-flow eruptions of the scale of Yellowstone or Long Valley. Such a model has wide-ranging implications, and explains many of the problems inherent in the simple collapse model involving shallow magma chambers as well as the process and timing of batholith intrusion in such cases.
Quantum Monte Carlo
Authors: Ceperley David , Alder Berni
Published: October 2006

An outline of a random walk computational method for solving the Schrödinger equation for many interacting particles is given, together with a survey of results achieved so far and of applications that remain to be explored. Monte Carlo simulations can be used to calculate accurately the bulk properties of the light elements hydrogen, helium, and lithium as well as the properties of the isolated atoms and of molecules made up from these elements. It is now possible to make reliable predictions of the behavior of these substances under experimentally difficult conditions, such as high pressure, and of properties that are difficult to measure experimentally, such as the momentum distribution in superfluid helium. For chemical systems, the stochastic method has a number of advantages over the widely used variational approach to determine ground-state properties, namely fast convergence to the exact result within objectively established error bounds.
Perspectives on Artificial Intelligence Programming
Authors: Bobrow Daniel G. , Stefik Mark J.
Published: October 2006

Programs are judged not only by whether they faithfully carry out the intended processing but also by whether they are understandable and easily changed. Programming systems for artificial intelligence applications use specialized languages, environments, and knowledge-based tools to reduce the complexity of the programming task. Language styles based on procedures, objects, logic, rules, and constraints reflect different models for organizing programs and facilitate program evolution and understandability. To make programming easier, multiple styles can be integrated as sublanguages in a programming environment. Programming environments provide tools that analyze programs and create informative displays of their structure. Programs can be modified by direct interaction with these displays. These tools and languages are helping computer scientists to regain a sense of control over systems that have become increasingly complex.
A Carbonate-Rich, Hydrated, Interplanetary Dust Particle: Possible Residue from Protostellar Clouds
Authors: Tomeoka Kazushige , Buseck Peter R.
Published: October 2006

Transmission electron microscopy of a hydrated interplanetary dust particle (IDP) indicates that it contains abundant magnesium-iron carbonates, primarily breunnerite and magnesian siderite. This IDP displays a strong absorption band at 6.8 micrometers in its infrared spectrum, similar to that in certain protostellar spectra. The carbonates probably account for the 6.8-micrometer band in the IDP spectrum, suggesting that carbonate also may occur in interstellar dust and be the source of the controversial 6.8-micrometer feature from the protostellar spectra.
Conserved Residues Make Similar Contacts in Two Repressor-Operator Complexes
Authors: Pabo Carl O. , Aggarwal Aneel K. , Jordan Steven R. , Beamer Lesa J. , Obeysekare Upul R. , Harrison Stephen C.
Published: October 2006

Comparison of a λ repressor-operator complex and a 434 repressor-operator complex reveals that three conserved residues in the helix-turn-helix (HTH) region make similar contacts in each of the crystallographically determined structures. These conserved residues and their interactions with phosphodiester oxygens help establish a frame of reference within which other HTH residues make contacts that are critical for site-specific recognition. Such "positioning contacts" may be important conserved features within families of HTH proteins. In contrast, the structural comparisons appear to rule out any simple "recognition code" at the level of detailed side chain-base pair interactions.
Diamonds and the African Lithosphere
Authors: Boyd F. R. , Gurney John J.
Published: October 2006

Data and inferences drawn from studies of diamond inclusions, xenocrysts, and xenoliths in the kimberlites of southern Africa are combined to characterize the structure of that portion of the Kaapvaal craton that lies within the mantle. The craton has a root composed in large part of peridotites that are strongly depleted in basaltic components. The asthenosphere boundary shelves from depths of 170 to 190 kilometers beneath the craton to approximately 140 kilometers beneath the mobile belts bordering the craton on the south and west. The root formed earlier than 3 billion years ago, and at that time ambient temperatures in it were 900° to 1200°C; these temperatures are near those estimated from data for xenoliths erupted in the Late Cretaceous or from present-day heat-flow measurements. Many of the diamonds in southern Africa are believed to have crystallized in this root in Archean time and were xenocrysts in the kimberlites that brought them to the surface.
Marine Cobalt Resources
Authors: Manheim F. T.
Published: October 2006

Ferromanganese oxides in the open oceans are more enriched in cobalt than any other widely distributed sediments or rocks. Concentrations of cobalt exceed 1 percent in ferromanganese crusts on seamounts, ocean ridges, and other raised areas of the ocean. The cobalt-rich crusts may be the slowest growing of any earth material, accumulating one molecular layer every 1 to 3 months. Attention has been drawn to crusts as potential resources because they contain cobalt, manganese, and platinum, three of the four priority strategic metals for the United States. Moreover, unlike abyssal nodules, whose recovery is complicated by their dominant location in international waters, some of the most cobalt-rich crusts occur within the exclusive economic zone of the United States and other nations. Environmental impact statements for crust exploitation are under current development by the Department of the Interior.