bluuebunny/crossref_metadata_2025 huggingface dataset:
The Diversification of the Leguminosae: First Fossil Evidence of the Mimosoideae and Papilionoideae
Authors: Crepet William L. , Taylor D. W.
Published: October 2006

The legumes are an important group of flowering plants with a poorly documented evolutionary history. New fossil evidence provides data on the timing of the origin of the two derived subfamilies of legumes (the Mimosoideae and Papilionoideae). These data strongly suggest the importance of bee pollinators during a major period of angiosperm diversification.
The Detection of Eclipses in the Pluto-Charon System
Authors: Binzel Richard P. , Tholen David J. , Tedesco Edward F. , Buratti Bonnie J. , Nelson Robert M.
Published: October 2006

The first eclipses between Pluto and its satellite ("Charon") were detected in January and February 1985, confirming the satellite's existence. Eclipses lasting a few hours will now occur at 3.2-day intervals for the next 5 to 6 years and then will cease for about 120 years. Careful observations of these eclipses will allow greatly improved determinations to be made of several physical parameters for the Pluto-Charon system: the diameters of the planet and satellite, the surface albedo distribution on one hemisphere of the planet, the orbit of the satellite, and the mass of the planet and hence its density. Knowledge of the density will provide a constraint on models of Pluto's bulk composition.
Mitochondrial DNA Size Variation Within Individual Crickets
Authors: Harrison Richard G. , Rand David M. , Wheeler Ward C.
Published: October 2006

The mitochondrial DNA's of two closely related cricket species (genus
Gryllus
) share a size polymorphism as evidenced by analysis of restriction fragment patterns. Moreover, 12 of 100 field-collected crickets are heteroplasmic, that is these individuals have more than one size class of mitochondrial DNA. No heteroplasmy for restriction site variation is observed. Intraindividual variation in cricket mitochondrial DNA provides a useful marker for studying the transmission genetics of mitochondrial DNA. Available data on patterns of variation in mothers and offspring suggest that random segregation of mitochondrial DNA variants does not occur rapidly in cricket germ-cell lineages.
Brachiopods versus Mussels: Competition, Predation, and Palatability
Authors: Thayer Charles W.
Published: October 2006

Unlike other shell-enclosed marine invertebrates, articulate brachiopods are repellent to predators. Fish, sea stars, snails, and crabs all prefer bivalve molluscs such as mussels to articulates. The mussels tested are mobile and out-compete immobile articulates when space is limited. In subtidal field experiments, mussels alone and predators alone each reduced the survivorship of articulates. However, adding mussels to articulates in the presence of ambient predation increased brachiopod survivorship by diverting predation from the brachiopods to the mussels. Competition from mussels (or mussel-like bivalves) is a plausible cause of the post-Paleozoic decline of articulates.
Generation by Insulin of a Chemical Mediator That Controls Protein Phosphorylation and Dephosphorylation
Authors: Larner J. , Galasko G. , Cheng K. , DePaoli-Roach A. A. , Huang L. , Daggy P. , Kellogg J.
Published: October 2006

Deproteinized skeletal muscle extracts free of major nucleotides from control and insulin-treated rats were fractionated and assayed for inhibition of protein phosphorylation by cyclic adenosine monophosphate (AMP)-dependent and -independent protein kinases. A differential effect of insulin on a particular fraction was observed on cyclic AMP-dependent protein kinase but not on cyclic AMP-independent protein kinases. This fraction that inhibited cyclic AMP-dependent protein kinase also stimulated glycogen synthase phosphoprotein phosphatase. It is proposed that this fraction may contain a mediator substance generateed in the presence of insulin.
Acid Deposition, Smelter Emissions, and the Linearity Issue in the Western United States
Authors: Oppenheimer Michael , Epstein Charles B. , Yuhnke Robert E.
Published: October 2006

The variation in sulfur dioxide emissions from nonferrous metal smelters in the western United States over a 4-year period is compared with the variation in sulfate concentrations in precipitation in the Rocky Mountain states. The data support a linear relation between emissions and sulfate concentration. The geographic separation of emissions sources and precipitation monitors indicates a sulfur transport scale exceeding 1000 kilometers.
Biotechnology in Food Production and Processing
Authors: Knorr Dietrich , Sinskey Anthony J.
Published: October 2006

The food processing industry is the oldest and largest industry using biotechnological processes. Further development of food products and processes based on biotechnology depends upon the improvement of existing processes, such as fermentation, immobilized biocatalyst technology, and production of additives and processing aids, as well as the development of new opportunities for food biotechnology. Improvements are needed in the characterization, safety, and quality control of food materials, in processing methods, in waste conversion and utilization processes, and in currently used food microorganism and tissue culture systems. Also needed are fundamental studies of the structure-function relationship of food materials and of the cell physiology and biochemistry of raw materials.
Mechanism of Insect Resistance to the Microbial Insecticide
Bacillus thuringiensis
Authors: Van Rie J. , McGaughey W. H, , Johnson D. E. , Barnett B. D. , Van Mellaert H.
Published: October 2006

Receptor binding studies show that resistance of a laboratory-selected
Plodia interpunctella
strain to a
Bacillus thuringiensis
insecticidal crystal protein (ICP) is correlated with a 50-fold reduction in affinity of the membrane receptor for this protein. The strain is sensitive to a second type of ICP that apparently recognizes a different receptor. Understanding the mechanism of resistance will provide strategies to prevent or delay resistance and hence prolong the usefulness of
B. thuringiensis
ICPs as environmentally safe insecticides.
An Identified Neuron (CPR) Evokes Neuronal Responses Reflecting Food Arousal in
Aplysia
Authors: Teyke Thomas , Weiss Klaudiusz R. , Kupfermann Irving
Published: October 2006

Feeding behavior of
Aplysia
is associated with an arousal state characterized by a constellation of maintained behaviors and by a potentiation or depression of responses to specific stimuli. A neuron (the cerebral-pedal regulator or CPR) that has widespread actions on various systems connected with feeding has been identified. CPR excites neurons that modulate or drive (i) body posture, (ii) biting, and (iii) cardiovascular behaviors. CPR also inhibits neurons concerned with defensive responses. Food stimuli, which elicit food arousal in the animal, produce prolonged excitation of the CPR. The results suggest that the CPR may evoke a central motive state representing the neuronal correlate of feeding motivation.
Lattice Images of Solid Xenon Precipitates in Aluminum at Room Temperature
Authors: Donnelly Stephen E. , Rossouw Christopher J.
Published: October 2006

Small solid precipitates (bubbles) of xenon in an aluminum matrix have been formed by ion implantation. Lattice images of this room-temperature inert gas solid were obtained using high-resolution phase-contrast electron microscopy. Many bubbles showed a high degree of crystalline perfection, but regions of defective crystallinity were observed in several cases.
Suppression of HIV Infection in AZT-Treated SCID-hu Mice
Authors: McCune Joseph M. , Namikawa Reiko , Shih Chu-Chih , Rabin Linda , Kaneshima Hideto
Published: October 2006

The SCID-hu mouse, engrafted with human hematolymphoid organs, is permissive for infection with the human immunodeficiency virus (HIV). This mouse model was used to test compounds for antiviral efficacy. Two weeks after infection with HIV, 100 percent (40/40) of SCID-hu mice were positive for HIV by the polymerase chain reaction. When first treated with 3′-azido-3′-deoxythymidine (AZT), none (0/17) were HIV-positive by this assay. However, AZT-treated SCID-hu mice did have a few infected cells; after AZT treatment was stopped, viral spread was detected by polymerase chain reaction in such mice. Thus, the SCID-hu mouse provides a means to directly compare new antiviral compounds with AZT and to further improve antiviral efficacy.
Suppression of Tumorigenicity of Human Prostate Carcinoma Cells by Replacing a Mutated RB Gene
Authors: Bookstein Robert , Shew Jin-Yuh , Chen Phang-Lang , Scully Peter , Lee Wen-Hwa
Published: October 2006

Introduction of a normal retinoblastoma gene (
RB
) into retinoblastoma cells was previously shown to suppress several aspects of their neoplastic phenotype, including tumorigenicity in nude mice, thereby directly demonstrating a cancer suppression function of
RB
. To explore the possibility of a similar activity in a common adult tumor,
RB
expression was examined in three human prostate carcinoma cell lines. One of these, DU145, contained an abnormally small protein translated from an
RB
messenger RNA transcript that lacked 105 nucleotides encoded by exon 21. To assess the functional consequences of this mutation, normal
RB
expression was restored in DU145 cells by retrovirus-mediated gene transfer. Cells that maintained stable exogenous
RB
expression lost their ability to form tumors in nude mice, although their growth rate in culture was apparently unaltered. These results suggest that
RB
inactivation can play a significant role in the genesis of a common adult neoplasm and that restoration of normal
RB
-encoded protein in tumors could have clinical utility.
Electrons in Silicon Microstructures
Authors: Howard R. E. , Jackel L. D. , Mankiewich P. M. , Skocpol W. J.
Published: October 2006

Silicon microstructures only a few hundred atoms wide can be fabricated and used to study electron transport in narrow channels. Spatially localized voltage probes as close together as 0.1 micrometer can be used to investigate a variety of physical phenomena, including velocity saturation due to phonon emission, the local potentials caused by scattering from a single trapped electron, and quantum tunneling or hopping among very few electron states.
Small Shared-Memory Multiprocessors
Authors: Baskett Forest , Hennessy John L.
Published: October 2006

Multiprocessors built from today's microprocessors are economically attractive. Although we can use these multiprocessors for time-sharing applications, it would be preferable to use them as true parallel processors. One key to achieving efficient parallel processing is to match the communications capabilities of the multiprocessor to the communications needs of the problem. The other key is improved parallel programming systems. If these are achieved, then efficient parallel processing can be approached from both ends by providing more communications capability in the hardware and restructuring the problem to reduce the communications requirements.
Determination of Venus Winds by Ground-Based Radio Tracking of the VEGA Balloons
Authors: Preston R. A. , Hildebrand C. E. , Purcell G. H. , Ellis J. , Stelzried C. T. , Finley S. G. , Sagdeev R. Z. , Linkin V. M. , Kerzhanovich V. V. , Altunin V. I. , Kogan L. R. , Kostenko V. I. , Matveenko L. I. , Pogrebenko S. V. , Strukov I. A. , Akim E. L. , Alexandrov Yu. N. , Armand N. A. , Bakitko R. N. , Vyshlov A. S. , Bogomolov A. F. , Gorchankov YU. N. , Selivanov A. S. , Ivanov N. M. , Tichonov V. F. , Blamont J. E. , Boloh L. , Laurans G. , Boischot A. , Biraud F. , Ortega-Molina A. , Rosolen C. , Petit G.
Published: October 2006

A global array of 20 radio observatories was used to measure the three-dimensional position and velocity of the two meteorological balloons that were injected into the equatorial region of the Venus atmosphere near Venus midnight by the VEGA spacecraft on 11 and 15 June 1985. Initial analysis of only radial velocities indicates that each balloon was blown westward about 11,500 kilometers (8,000 kilometers on the night side) by zonal winds with a mean speed of about 70 meters per second. Excursions of the data from a model of constant zonal velocity were generally less than 3 meters per second; however, a much larger variation was evident near the end of the flight of the second balloon. Consistent systematic trends in the residuals for both balloons indicate the possibility of a solar-fixed atmospheric feature. Rapid variations in balloon velocity were often detected within a single transmission (330 seconds); however, they may represent not only atmospheric motions but also self-induced aerodynamic motions of the balloon.
Thermal Structure of the Venus Atmosphere in the Middle Cloud Layer
Authors: Linkin V. M. , Kerzhanovich V. V. , Lipatov A. N. , Shurupov A. A. , Seiff A. , Ragent B. , Young R. E. , Ingersoll A. P. , Crisp D. , Elson L. S. , Preston R. A. , Blamont J. E.
Published: October 2006

Thermal structure measurements obtained by the two VEGA balloons show the Venus middle cloud layer to be generally adiabatic. Temperatures measured by the two balloons at locations roughly symmetric about the equator differed by about 6.5 kelvins at a given pressure. The VEGA-2 temperatures were about 2.5 kelvins cooler and those of VEGA-1 about 4 kelvins warmer than temperatures measured by the Pioneer Venus Large Probe at these levels. Data taken by the VEGA-2 lander as it passed through the middle cloud agreed with those of the VEGA-2 balloon. Study of individual frames of the balloon data suggests the presence of multiple discrete air masses that are internally adiabatic but lie on slightly different adiabats. These adiabats, for a given balloon, can differ in temperature by as much as 1 kelvin at a given pressure.
Acid Dissolution Experiments: Carbonates and the 6.8-Micrometer Bands in Interplanetary Dust Particles
Authors: Sandford Scott A.
Published: October 2006

A chemical dissolution experiment on an interplanetary dust particle (IDP) showed that carbonates, not acid-insoluble organic compounds, were responsible for virtually all the absorption at 6.8 micrometers seen in the infrared spectra of this particle. The IDP examined had an infrared spectrum characteristic of layer-lattice silicates and belongs to a class of IDP's whose spectra resemble those of protostellar objects like W33 A, which also exhibit a band at 6.8 micrometers.
The Tunneling Microscope: A New Look at the Atomic World
Authors: Golovchenko J. A.
Published: October 2006

A new instrument called the tunneling microscope has recently been developed that is capable of generating real-space images of surfaces showing atomic structure. These images offer a new view of matter on an atomic scale. The current capabilities and limitations and the physics involved in the technique are discussed along with specific results from a study of silicon crystal surfaces.
Geographic Origin of Benthic Foraminiferal Species
Authors: Buzas Martin A. , Culver Stephen J.
Published: October 2006

Museum collections were used to document the worldwide Pliocene and Pleistocene fossil record of 59 species that now occur on the Atlantic continental margin of North America. Tabulation of these data indicates that benthic foraminifera evolve at all latitudes and in all parts of the world ocean rather than from some center or centers of origin. Dispersal in geologic time is very rapid.
Organ-Specific and Light-Induced Expression of Plant Genes
Authors: Fluhr Robert , Kuhlemeier Cris , Nagy Ferenc , Chua Nam-Hai
Published: October 2006

Light plays a pivotal role in the development of plants. The photoregulation of plant genes involves recognition of light quality and quantity by phytochrome and other light receptors. Two gene families,
rbc
S and Cab, which code for abundant proteins active in photosynthesis, the small subunit of ribulose bisphosphate carboxylase and the chlorophyll a/b binding protein, show a 20- to 50-fold increase in transcript abundance in the light. Analyses in calli and transgenic plants of deletions of the
rbc
S gene and of chimeric constructions has allowed localization of two regions involved in light-induced transcription. One element is confined to a 33—base pair region surrounding the TATA box. In addition, an enhancer-like element contained within a 240—base pair fragment can confer phytochrome-induced transcription and organ specificity on nonregulated promoters.
Synthetic Diamond as a Pressure Generator
Authors: Onodera Akifumi , Furuno Katsuhisa , Yazu Shuji
Published: October 2006

Synthetic diamond crystals were used as opposed anvils whose small culet surfaces were driven into contact with each other to generate high static pressures. Pressures in excess of 68 gigapascals (680 kilobars) were achieved, as determined from the fluorescence line of a ruby fragment sandwiched between the diamonds.
HIV-1 Coat Protein Neurotoxicity Prevented by Calcium Channel Antagonists
Authors: Dreyer Evan B. , Kaiser Peter K. , Offermann Jeffrey T. , Lipton Stuart A.
Published: October 2006

Coat protein gp120 from the human immunodeficiency virus type-1 (HIV-1) increased intracellular free calcium and injured rodent retinal ganglion cells and hippocampal neurons in culture. Highly purified recombinant gp120 envelope protein produced these effects in a dose-dependent fashion at picomolar concentrations. Immunoprecipitation with antibody to gp120, but not with control immunoglobulin-containing serum, depleted solutions of the viral envelope protein and also prevented both the rise in intracellular calcium and neuronal toxicity. The gp120-induced increase in intracellular calcium was abrogated by transiently lowering extracellular calcium or by adding the dihydropyridine calcium channel antagonist nimodipine (100 n
M
). Calcium channel antagonists also prevented gp120-induced neuronal injury. In addition, intracellular stores appeared to contribute substantially to the increase in calcium elicited by gp120. Since increases in intracellular calcium have been associated with neurotoxicity, it is possible that an injurious effect of gp120 on neurons might be related to this mechanism and that treatment with calcium channel antagonists may prove useful in mitigating HIV-1-related neuronal injury.
Erythropoietin Retards DNA Breakdown and Prevents Programmed Death in Erythroid Progenitor Cells
Authors: Koury Mark J. , Bondurant Maurice C.
Published: October 2006

The mechanism by which erythropoietin controls mammalian erythrocyte production is unknown. Labeling experiments in vitro with [
3
H]thymidine demonstrated DNA cleavage in erythroid progenitor cells that was accompanied by DNA repair and synthesis. Erythropoietin reduced DNA cleavage by a factor of 2.6. In the absence of erythropoietin, erythroid progenitor cells accumulated DNA cleavage fragments characteristic of those found in programmed cell death (apoptosis) by 2 to 4 hours and began dying by 16 hours. In the presence of erythropoietin, the progenitor cells survived and differentiated into reticulocytes. Thus, apoptosis is a major component of normal erythropoiesis, and erythropoietin controls erythrocyte production by retarding DNA breakdown and preventing apoptosis in erythroid progenitor cells.
Comax: An Expert System for Cotton Crop Management
Authors: Lemmon Hal
Published: October 2006

Expert systems are computer programs that perform at the level of human experts. One expert system, Comax, has been developed that acts as an expert in cotton crop management. The system has a knowledge base consisting of a sophisticated cotton plant simulation computer program, a set of "if-then" rules, and a computer program called an inference engine. Comax determines the best strategy for irrigating, applying fertilizer, and applying defoliants and cotton boll openers. Sensors in the cotton fields automatically report weather conditions to the system, and Comax reevaluates its recommendations daily. Comax was tested on a large farm and demonstrated excellent results in reducing the unit costs of production.
Magnetic Fields at Uranus
Authors: Ness Norman F. , Acuña Mario H. , Behannon Kenneth W. , Burlaga Leonard F. , Connerney John E. P. , Lepping Ronald P. , Neubauer Fritz M.
Published: October 2006

The magnetic field experiment on the Voyager 2 spacecraft revealed a strong planetary magnetic field of Uranus and an associated magnetosphere and fully developed bipolar magnetic tail. The detached bow shock wave in the solar wind supersonic flow was observed upstream at 23.7 Uranus radii (1
R
U
= 25,600 km) and the magnetopause boundary at 18.0
R
U
, near the planet-sun line. A maximum magnetic field of 413 nanotesla was observed at 4.19
R
U
, just before closest approach. Initial analyses reveal that the planetary magnetic field is well represented by that of a dipole offset from the center of the planet by 0.3
R
U
. The angle between Uranus' angular momentum vector and the dipole moment vector has the surprisingly large value of 60 degrees. Thus, in an astrophysical context, the field of Uranus may be described as that of an oblique rotator. The dipole moment of 0.23 gauss
R
3
U
, combined with the large spatial offset, leads to minimum and maximum magnetic fields on the surface of the planet of approximately 0.1 and 1.1 gauss, respectively. The rotation period of the magnetic field and hence that of the interior of the planet is estimated to be 17.29
R
0.10 hours; the magnetotail rotates about the planet-sun line with the same period. The large offset and tilt lead to auroral zones far from the planetary rotation axis poles. The rings and the moons are embedded deep within the magnetosphere, and, because of the large dipole tilt, they will have a profound and diurnally varying influence as absorbers of the trapped radiation belt particles.
Cannibalism in the Neolithic
Authors: Villa Paola , Bouville Claude , Courtin Jean , Helmer Daniel , Mahieu Eric , Shipman Pat , Belluomini Giorgio , Branca Marilí
Published: October 2006

Cannibalism is a provocative interpretation put forth repeatedly for practices at various prehistoric sites, yet it has been so poorly supported by objective evidence that later, more critical reviews almost invariably reject the proposal. The basic data essential to a rigorous assessment of a cannibalism hypothesis include precise contextual information, analysis of postcranial and cranial remains of humans and animals, and detailed bone modification studies. Such data are available from the Neolithic levels of the Fontbrégoua Cave (southeastern France) where several clusters of human and animal bones have been excavated. The analysis of these bones strongly suggests that humans were butchered, processed, and probably eaten in a manner that closely parallels the treatment of wild and domestic animals at Fontbrbégoua.
Interpreting Interpersonal Behavior: The Effects of Expectancies
Authors: Jones Edward E.
Published: October 2006

Attempts to understand the personal characteristics of others, in interactions with them, are complicated by the fact that one tends to find what one expects. This happens not only because processing of information is selective, but also because expectancies cause one to act in ways that elicit behavior interpretable as confirming those expectancies, even when the expectancies might have been mistaken. Studies provide ample evidence of such self-fulfilling prophecies in social interaction and are beginning to spell out the crucial steps in the process for confirming expectancies. Such studies help link the psychology of first impressions to the psychology of long-term relationships by showing how expectancies are sustained or modified through behavioral sequences that are partially determined by initial expectancies.
Quantum States and Atomic Structure of Silicon Surfaces
Authors: Tromp R. M. , Hamers R. J. , Demuth J. E.
Published: October 2006

The electronic and geometric structures of surfaces are closely related to each other. Conventional surface science techniques can study one or the other, but not both at the same time. Recent developments in scanning tunneling microscopy have made it possible to study simultaneously the electronic and geometric structure of Si(111) and Si(001) surfaces. Surface states can be atomically resolved in space and energy; thus the electronic structure of single atoms on surfaces can be studied in detail. The various surface states observed on silicon surfaces are found to derive from different atomic-scale features in the surface geometric structure. Scanning tunneling microscopy has now bridged the gap between electronic and geometric structure, providing a unique opportunity to obtain a better understanding of many surface processes at the atomic level.
The Color of the Surface of Venus
Authors: Pieters C. M. , Head J. W. , Pratt S. , Patterson W. , Garvin J. , Barsukov V. L. , Basilevsky A. T. , Khodakovsky I. L. , Selivanov A. S. , Panfilov A. S. , Gektin Yu. M. , Narayeva Y. M.
Published: October 2006

Multispectral images of the basaltic surface of Venus obtained by Venera 13 were processed to remove the effects of orange-colored incident radiation resulting from interactions with the thick Venusian atmosphere. At visible wavelengths the surface of Venus appears dark and without significant color. High-temperature laboratory reflectance spectra of basaltic materials indicate that these results are consistent with mineral assemblages bearing either ferric or ferrous iron. A high reflectance in the near-infrared region observed at neighboring Venera 9 and 10 sites, however, suggests that the basaltic surface material contains ferric minerals and thus may be relatively oxidized.
Laser Remote Sensing of the Atmosphere
Authors: Killinger Dennis K. , Menyuk Norman
Published: October 2006

Laser beams can be used as long-range spectroscopic probes of the chemical composition and physical state of the atmosphere. The spectroscopic, optical, and laser requirements for atmospheric laser remote sensing are reviewed, and the sensitivity and limitations of the technique are described. A sampling of recent measurements includes the detection of urban air pollution and toxic chemicals in the atmosphere, the measurement of global circulation of volcanic ash in the upper atmosphere, and the observation of wind shear near airports.
Trace Fossil Evidence for Late Ordovician Animals on Land
Authors: Retallack Gregory J. , Feakes Carolyn R.
Published: October 2006

Fossil burrows within newly recognized buried soils in the Late Ordovician Juniata Formation, near Potters Mills in central Pennsylvania, represent the oldest reported nonmarine trace fossils. They are thought to have been an original part of the soil because their greater density toward the top of the paleosols corresponds with mineralogical, microstructural, and chemical changes attributed to ancient weathering and because about half the burrows are encrusted with nodular carbonate, interpreted as caliche. Associated fossil caliche, the size distribution of the burrows, and their W-shaped backfills are evidence that the burrows may have been excavated by bilaterally symmetrical organisms that grew in well-defined growth increments and were able to withstand desiccation. Among well-known soil organisms, millipedes are burrowing animals that satisfy these requirements, but have a fossil record not quite this old. This trace fossil evidence for animals on land, together with recent palynological evidence for land plants of a bryophytic grade of evolution during Late Ordovician time, are indications of terrestrial ecosystems of slightly greater antiquity and complexity than hitherto suspected.
Verification and Arms Control
Authors: Eimer Manfred , Drell Sidney
Published: October 2006

Verification of arms control agreements has become a matter of widespread interest in the scientific community; the methods used by signatories to ensure compliance and the past record of compliance by the United States and the Soviet Union are being vigorously debated.
Science
has asked two experts in arms control, Manfred Eimer and Sidney Drell, to respond to questions about the means of verification, the current verifiability of agreements, and the future outlook.
Site-Specific Nick in the T-DNA Border Sequence as a Result of
Agrobacterium vir
Gene Expression
Authors: Wang Kan , Stachel Scott E. , Timmerman Benedikt , Van Montagu Marc , Zambryski Patricia C.
Published: October 2006

The T-DNA transfer process of
Agrobacterium tumefaciens
is activated by the induction of the expression of the Ti plasmid virulence (
vir
) loci by plant signal molecules such as acetosyringone. The
vir
gene products act in trans to mobilize the T-DNA element from the bacterial Ti plasmid. The T-DNA is bounded by 25—base pair direct repeat sequences, which are the only sequences on the element essential for transfer. Thus, specific reactions must occur at the border sites to generate a transferable T-DNA copy. The T-DNA border sequences were shown in this study to be specifically nicked after
vir
gene activation. Border nicks were detected on the bottom strand just after the third or fourth base (± one or two nucleotides) of the 25—base pair transfer-promoting sequence. Naturally occurring and base-substituted derivatives of the 25—base pair sequences are effective substrates for acetosyringone-induced border cleavage, whereas derivatives carrying only the first 15 or last 19 base pairs of the 25—base pair sequence are not. Site-specific border cleavages occur within 12 hours after acetosyringone induction and probably represent an early step in the T-DNA transfer process.
Electronic Theory for Materials Science
Authors: Ehrenreich Henry
Published: October 2006

Some of the important ingredients used in theoretical investigations of the electronic properties of materials are delineated by means of examples. The importance of examining the physical behavior of related materials is emphasized as a means of establishing the credibility of theoretical explanations. Since the ability to deal realistically with complex technologically important materials is limited by analytic and computational capabilities, theories for materials science must aim at the development of comprehensive and predictive models based on physically motivated approximations. The emergence of such models and their ability to describe a broad range of properties foreshadows an increasingly important role of theoretical analysis in the future development of the field.
Solution of a Protein Crystal Structure with a Model Obtained from NMR Interproton Distance Restraints
Authors: Brünger Axel T. , Campbell Robert L. , Clore G. Marius , Gronenborn Angela M. , Karplus Martin , Petsko Gregory A. , Teeter Martha M.
Published: October 2006

Model calculations were performed to test the possibility of solving crystal structures of proteins by Patterson search techniques with three-dimensional structures obtained from nuclear magnetic resonance (NMR) interproton distance restraints. Structures for crambin obtained from simulated NMR data were used as the test system; the root-mean-square deviations of the NMR structures from the x-ray structure were 1.5 to 2.2 Å for backbone atoms and 2.0 to 2.8 Å for side-chain atoms. Patterson searches were made to determine the orientation and position of the NMR structures in the unit cell. The correct solution was obtained by comparing the rotation function results of several of the NMR structures and the average structure derived from them. Conventional refinement techniques reduced the
R
factor from 0.43 at 4 Å resolution to 0.27 at 2 Å resolution without inclusion of water molecules. The partially refined structure has root-mean-square backbone and side-chain atom deviations from the x-ray structure of 0.5 and 1.3 Å, respectively.
Chemical Reactions on Clays
Authors: Laszlo Pierre
Published: October 2006

Layer aluminosilicates catalyze reactions in numerous ways. They stabilize high-energy intermediates. They can store energy in their lattice structures and can release it in the form of chemical energy. They can catalyze redox reactions and can serve as photocatalytic devices. They often exhibit high surface acidity. Organic reactions that are catalyzed by the agency of clays are reviewed. The role of clays in prebiotic chemistry is also examined.
Avascular Necrosis: Occurrence in Diving Cretaceous Mosasaurs
Authors: Rothschild Bruce , Martin Larry D.
Published: October 2006

A study of vertebrae of extinct giant marine lizards showed the presence of avascular necrosis in two of the three most common genera of these mosasaurs,
Platecarpus
and
Tylosaurus.
This bone disease was invariably present (involving 5 to 66% of vertebrae) in these genera, but absent in a third genus
Clidastes.
Differential occurrence of avascular necrosis may be related to decompression syndrome, suggesting different habitat and diving habits of the respective genera.
Accelerator Mass Spectrometry for Measurement of Long-Lived Radioisotopes
Authors: Elmore David , Phillips Fred M.
Published: October 2006

Particle accelerators, such as those built for research in nuclear physics, can also be used together with magnetic and electrostatic mass analyzers to measure rare isotopes at very low abundance ratios. All molecular ions can be eliminated when accelerated to energies of millions of electron volts. Some atomic isobars can be eliminated with the use of negative ions; others can be separated at high energies by measuring their rate of energy loss in a detector. The long-lived radioisotopes
10
Be,
14
C,
26
Al,
36
Cl, and
129
I can now be measured in small natural samples having isotopic abundances in the range 10
-12
to 10
-15
and as few as 10
5
atoms. In the past few years, research applications of accelerator mass spectrometry have been concentrated in the earth sciences (climatology, cosmochemistry, environmental chemistry, geochronology, glaciology, hydrology, igneous petrogenesis, minerals exploration, sedimentology, and volcanology), in anthropology and archeology (radiocarbon dating), and in physics (searches for exotic particles and measurement of half-lives). In addition, accelerator mass spectrometry may become an important tool for the materials and biological sciences.
Polychlorinated Biphenyl Dechlorination in Aquatic Sediments
Authors: Brown John F. , Bedard Donna L. , Brennan Michael J. , Carnahan James C. , Feng Helen , Wagner Robert E.
Published: October 2006

The polychlorinated biphenyl (PCB) residues in the aquatic sediments from six PCB spill sites showed changes in PCB isomer and homolog (congener) distribution that indicated the occurrence of reductive dechlorination. The PCB dechlorinations exhibited several distinct congener selection patterns that indicated mediation by several different localized populations of anaerobic microorganisms. The higher (more heavily chlorinated) PCB congeners that were preferentially attacked by the observed dechlorination processes included all those that are either pharmacologically active or persistent in higher animals. All the lower (less heavily chlorinated) PCB congeners formed by the dechlorinations were species that are known to be oxidatively biodegradable by the bacteria of aerobic environments.
Effect of Lizards on Spider Populations: Manipulative Reconstruction of a Natural Experiment
Authors: Schoener Thomas W. , Spiller David A.
Published: October 2006

Which species affect one another, how intensely, and the mechanisms of those effects are crucial data for understanding how ecological communities work. Tropical islands without lizards, the major top predators, have about ten times as dense web spider populations as those with lizards; processes responsible for this effect were experimentally simulated by removing lizards from randomly selected mainland plots. Spider densities in removal plots averaged 2.5 times as high as controls. Spider survival, prey abundance, and prey consumption were all negatively affected by lizards. Contrary to most studies, predator removal caused an increase in the number of spider species.
A New Method for Analyzing Powder Diffraction Patterns: Confirmation of a Predicted Phase of SF
6
Authors: Bartell Lawrence S. , Caillat Jacques C. , Powell Brian M.
Published: October 2006

A recent computer simulation reproduced all of the solid-state transitions known for sulfur hexafluoride and predicted the unknown structure of its coldest phase. Subsequent neutron diffraction experiments that were performed to establish the structure of this phase could not be interpreted by conventional procedures. A method for analyzing Debye-Scherrer diffraction patterns was designed to avoid the many false minima that are encountered in standard analyses of low-symmetry phases. The structure found with this method confirmed the previous theoretical prediction.
Monitoring Earth and Sun by Satellite
Authors: Kerr Richard A.
Published: October 2006

Researchers attending the spring meeting of the American Geophysical Union held 18 to 21 May in Baltimore have grown familiar with doing geophysical studies by satellite. Here are three current examples discussed at the meeting: gauging the output of the sun, measuring crustal movement, and deciphering the mineral composition of surface rocks.
A Major Food Web Component in the Orinoco River Channel: Evidence from Planktivorous Electric Fishes
Authors: Lundberg John G. , Lewis William M. , Saunders James F. , Mago-Leccia Francisco
Published: October 2006

Deep-water sampling of the Orinoco River main channel resulted in the collection of an unexpectedly high abundance and diversity of specialized fishes. Twenty-eight of the more than 60 species collected belong to the Gymnotiformes (New World electric or knife fishes). One of the more numerous of these, a recently described species of the genus
Rhabdolichops
, consumes large numbers of very small planktonic Crustacea and insect larvae. These items are captured in the very swift, turbid, and deep waters of the Orinoco. Although the strong dependence of the river food web on terrestrial and floodplain food sources is well known, the specialized capabilities of
Rhabdolichops
and of other fishes that occur with it indicate a significant extension of the river food web into the main channel.
Artificial Intelligence and Natural Resource Management
Authors: Coulson Robert N. , Folse L. Joseph , Loh Douglas K.
Published: October 2006

The use of artificial intelligence (AI) in natural resource management began with the development of expert systems for problem-solving and decision-making. The use of expert systems in turn led to the development of other AI procedures pertinent to natural resource management. Of particular significance are (i) integrated expert systems, which link management models with natural resource models; (ii) intelligent geographic information systems, which permit interpretation of relations within and among landscape data themes; and (iii) AI modeling of animal behavior and interaction with the environment. These procedures provide new ways to view classic problems in systems analysis.
Biogenic Sulfur and the Acidity of Rainfall in Remote Areas of Canada
Authors: Nriagu Jerome O. , Holdway Douglas A. , Coker Robert D.
Published: October 2006

Sulfur released from any given natural or anthropogenic source carries an isotopic signature that can be used to trace its flow through the environment. Measurements of the concentration and isotopic composition of sulfur in weekly bulk precipitation samples collected over a 4-year period at a remote location in northern Ontario were recorded. The long-term isotopic data and the measurement on the production and release of dimethyl sulfide from boreal wetlands show that biogenic sources can account for up to 30 percent of the acidifying sulfur burden in the atmosphere in remote areas of Canada. The data suggest that significant biological reemission of anthropogenic sulfur is occurring. The role of this process in the continuing acidification of the environment for years to come must be a matter of concern.
Monitoring Biosynthesis of Wheat Cell-Wall Phenylpropanoids in Situ
Authors: Lewis N. G. , Yamamoto E. , Wooten J. B. , Just G. , Ohashi H. , Towers G. H. N.
Published: October 2006

Lignins and suberins are complex plant cell-wall macromolecules that are composed mainly of phenylpropanoid residues derived from L-phenylalanine. Lignins and suberins are considered to be covalently linked to carbohydrates and to lipids, respectively. The bonding of these important structural materials within cell walls has never been established. By feeding specifically labeled [
13
C]ferulic acid over extended durations to seedlings of
Triticum aestivum
L. and by using solid-state carbon-13 nuclear magnetic resonance techniques, the major resonances due to specific carbons in the propanoid side chains of these cell-wall polymers have been identified in situ. The signals were found to differ significantly from those of synthetic lignins, which have usually been considered to be good approximations of natural lignin structure.
The Federal Deficit: How Does It Matter?
Authors: Eisner Robert
Published: October 2006

Government deficits and debt are surpluses and assets of the private sector of the economy that stimulate private spending. Official measures of deficits are misleading, however, for failing to distinguish public investment from current spending and for failing to adjust for inflation. Correctly measured real deficits have contributed to the growth of gross national product, consumption, and imports, and to investment as well. Optimal policy consistent with balanced growth calls not for elimination of the nominal deficit but rather for prudent deficit reduction accompanied by and stemming at least partly from sufficient monetary stimulus to achieve and sustain relatively full employment.
Multidimensional Analysis of an Evolving Lineage
Authors: Wake David B. , Larson Allan
Published: October 2006

To identify the forces directing organismal evolution, a general analytical system is developed to synthesize structuralist and Darwinian traditions in an explicitly historical framework. Morphological features of lungless salamanders are examined to identify hierarchical systems of developmental and functional constraint on evolution and their interactions with processes at the genic and populational levels. Characteristic patterns of change occur repeatedly in the evolutionary history of this group.
Rotation and Solvation of Ammonium Ion
Authors: Perrin Charles L. , Gipe Robert K.
Published: October 2006

From nitrogen-15 spin-lattice relaxation times and nuclear Overhauser enhancements, the rotational correlation time τ
c
for
15
NH
4
+
was determined in a series of solvents. Values of τ
c
range from 0.46 to 20 picoseconds. The solvent dependence of τ
c
cannot be explained in terms of solvent polarity, molecular dipole moment, solvent basicity, solvent dielectric relaxation, or solvent viscosity. The rapid rotation and the variation with solvent can be accounted for by a model that involves hydrogen bonding of an NH proton to more than one solvent molecule in a disordered solvation environment.
Oxygen Isotope Effect in High-Temperature Oxide Superconductors
Authors: zur Loye Hans-Conrad , Leary Kevin J. , Keller Steven W. , Ham William K. , Faltens Tanya A. , Michaels James N. , Stacy Angelica M.
Published: October 2006

The effect of oxygen isotope substitution on the superconducting transition temperature,
T
c
, has been measured for BaBi
0.25
Pb
0.75
O
3
(
T
c
≈ 11 K) and La
1.85
Ca
0.15
CuO
4
(
T
c
≈ 20 K), and is compared to the shifts observed for La
1.85
Sr
0.15
CuO
4
(
T
c
≈ 37 K) and YBa
2
Cu
3
O
7
(
T
c
≈ 92 K). For all four materials, the transition temperature is shifted to lower temperature upon substitution of oxygen-18 for oxygen-16. The observed shifts demonstrate that phonons are involved in the electron-pairing mechanism in these oxide superconductors.
Chaos Versus Noisy Periodicity: Alternative Hypotheses for Childhood Epidemics
Authors: Olsen L. F. , Schaffer W. M.
Published: October 2006

Whereas case rates for some childhood diseases (chickenpox) often vary according to an almost regular annual cycle, the incidence of more efficiently transmitted infections such as measles is more variable. Three hypotheses have been proposed to account for such fluctuations. (i) Irregular dynamics result from random shocks to systems with stable equilibria. (ii) The intrinsic dynamics correspond to biennial cycles that are subject to stochastic forcing. (iii) Aperiodic fluctuations are intrinsic to the epidemiology. Comparison of real world data and epidemiological models suggests that measles epidemics are inherently chaotic. Conversely, the extent to which chickenpox outbreaks approximate a yearly cycle depends inversely on the population size.
Regional Variation of Extracellular Space in the Hippocampus
Authors: McBain Chris J. , Traynelis Stephen F. , Dingledine Raymond
Published: October 2006

The factors responsible for the unusual susceptibility of the hippocampus to seizures and ischemic cell damage are not well understood. The CA1 pyramidal subfield of the hippocampus is particularly vulnerable to seizure activity and damage after ischemia. The possibility was examined that regional differences exist in extracellular volume, which might influence neuronal excitability and response to injury in the hippocampus. CA1 stratum pyramidale exhibited an exceptionally low extracellular volume fraction (EVF) of 0.12, whereas the EVFs of CA3 and dentate were considerably higher—0.18 and 0.15, respectively. The EVF of CA1 stratum pyramidale was reversibly reduced by 30 percent when the extracellular potassium concentration was raised from 3.5 to 8.5 mM, a procedure that induced spontaneous electrographic seizures in CA1. Thus there are regional variations in the properties of the extracellular space in the hippocampus that might underlie the propensity of the CA1 region to develop seizures and to suffer damage after ischemia.
Possible Evidence for Superconducting Layers in Single Crystal YBa
2
Cu
3
O
7-x
by Field Ion Microscopy
Authors: Melmed A. J. , Shull R. D. , Chiang C. K. , Fowler H. A.
Published: October 2006

The high-transition-temperature superconducting ceramic material YBa
2
Cu
3
O

7-
x

(0<
x
< 0.5) has been examined by field ion microscopy. Specimens from nominally superconducting and nonsuperconducting samples (determined by magnetic susceptibility measurements) were studied by field ion microscopy and significant differences were found. Preferential imaging of atomic or molecular layers, due to preferential field evaporation, field ionization, or both, was found in the superconducting phase below the transition temperature and is interpreted as possible evidence for the occurrence of relatively highly conducting layers in the YBa
2
Cu
3
O

7-
x

unit cell perpendicular to the orthorhombic
c
-axis. Similar results were obtained for YbBa
2
Cu
3
O

7-
x

.
Free-Electron Lasers
Authors: Brau Charles A.
Published: October 2006

Free-electron lasers are tunable, potentially powerful sources of coherent radiation over a broad range of wavelengths from the far-infrared to the far-ultraviolet regions of the spectrum. These unique capabilities make them suitable for a broad variety of applications from medicine to strategic defense.
Template Supercoiling by a Chimera of Yeast
GAL4
Protein and Phage T7 RNA Polymerase
Authors: Ostrander Elaine A. , Benedetti Piero , Wang James C.
Published: October 2006

Fusion of the DNA-binding domain of yeast
GAL4
protein to the amino terminus of bacteriophage T7 RNA polymerase yields a chimera that retains the characteristics of its components. The presence of the
GAL4
peptide allows the chimeric enzyme to anchor itself on the DNA template, and this anchoring in turn drives the formation of a supercoiled DNA loop, in linear or circular templates, when RNA synthesis at the polymerase site forces a translocation of the DNA relative to the site. Nonspecific interaction between the chimeric enzyme and DNA appears to be sufficient to effect supercoiling during transcription. Transcription by the chimeric polymerase is strictly dependent on the presence of a T7 promoter; thus it provides a tool in vitro and in vivo for specifically supercoiling DNA segments containing T7 promoter sequences.