bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for Low Temperatures and Biologic Diversity in Cretaceous High Latitudes of Australia
Authors: Rich P. V. , Rich T. H. , Wagstaff B. E. , Mason J. McEwen , Douthitt C. B. , Gregory R. T. , Felton E. A.
Published: October 2006

A diverse terrestrial biota inhabited polar latitudes during the Cretaceous, 105 to 130 Ma (million years ago), along what is now the southeast coast of Australia. This biota, from rocks in the Otway and Strzelecki groups, consisted of more than 150 taxa of vertebrates, invertebrates, and plants. Oxygen isotope ratios in diagenetic calcite suggest that mean annual temperatures were most likely less than 5°C, and rings present in the fossil araucarian-podocarp-ginko woods indicate seasonality. Southeastern Australia, thus, seems to have had a cool, seasonal, nontropical climate. Dinosaurs that have been recovered are up to five species and three genera of hypsilophodontids, all of which were endemic, and three species of theropods. The occurrence of
Allosaurus
sp. and labyrinthodont amphibians, which had become extinct elsewhere in the Jurassic, indicate that isolation may have allowed extended survival of these taxa in Australia. In that dinosaurs coped with high latitudes for at least 65 million years [Valanginian to Albian time in Australia and Campanian to Maastrictian time (80 to 65 Ma) in Alaska] suggests that cold and darkness may not have been prime factors bringing about the extinction of dinosaurs and some other groups at the Cretaceous-Tertiary boundary, unless they were prolonged.
Steroid Hormone Metabolites Are Barbiturate-Like Modulators of the GABA Receptor
Authors: Majewska Maria Dorota , Harrison Neil L. , Schwartz Rochelle D. , Barker Jeffery L. , Paul Steven M.
Published: October 2006

Two metabolites of the steroid hormones progesterone and deoxycorticosterone, 3α-hydroxy-5α-dihydroprogesterone and 3α,5α-tetrahydrodeoxycorticosterone, are potent barbiturate-like ligands of the γ-aminobutyric acid (GABA) receptor-chloride ion channel complex. At concentrations between 10
-7
and 10
-5
M
both steroids inhibited binding of the convulsant t-butylbicyclophosphorothionate to the GABA-receptor complex and increased the binding of the benzodiazepine flunitrazepam; they also stimulated chloride uptake (as measured by uptake of
36
Cl
-
) into isolated brain vesicles, and potentiated the inhibitory actions of GABA in cultured rat hippocampal and spinal cord neurons. These data may explain the ability of certain steroid hormones to rapidly alter neuronal excitability and may provide a mechanism for the anesthetic and hypnotic actions of naturally occurring and synthetic anesthetic steroids.
Macroecology: The Division of Food and Space Among Species on Continents
Authors: Brown James H. , Maurer Brian A.
Published: October 2006

Analyses of statistical distributions of body mass, population density, and size and shape of geographic range offer insights into the empirical patterns and causal mechanisms that characterize the allocation of food and space among the diverse species in continental biotas. These analyses also provide evidence of the processes that couple ecological phenomena that occur on disparate spatial and temporal scales—from the activities of individual organisms within local populations to the dynamics of continent-wide speciation, colonization, and extinction events.
Neocortical Transplants in the Mammalian Brain Lack a Blood-Brain Barrier to Macromolecules
Authors: Rosenstein Jeffrey M.
Published: October 2006

In order to determine whether the blood-brain barrier was present in transplants of central nervous tissue, fetal neocortex, which already possesses blood-brain and blood-cerebrospinal fluid barriers to protein, was grafted into the undamaged fourth ventricle or directly into the neocortex of recipient rats. Horseradish peroxidase or a conjugated human immunoglobulin G-peroxidase molecule was systemically administered into the host. These proteins were detected within the cortical transplants within 2 minutes regardless of the age of the donor or postoperative time. At later times these compounds, which normally do not cross the blood-brain barrier, inundated the grafts and adjacent host brain and also entered the cerebrospinal fluid. Endogenous serum albumin detected immunocytochemically in untreated hosts had a comparable although less extensive distribution. Thus, transplants of fetal central nervous tissue have permanent barrier dysfunction, probably due to microvascular changes, and are not integrated physiologically within the host. Blood-borne compounds, either systemically administered or naturally occurring, which should never contact normal brain tissue, have direct access to these transplants and might affect neuronal function.
Immunological Self, Nonself Discrimination
Authors: Guillet Jean-Gerard , Lai Ming-Zong , Briner Thomas J. , Buus Soren , Sette Alessandro , Grey Howard M. , Smith John A. , Gefter Malcolm L.
Published: October 2006

The ability of immunodominant peptides derived from several antigen systems to compete with each other for T cell activation was studied. Only peptides restricted by a given transplantation antigen are mutually competitive. There is a correlation between haplotype restriction, ability to bind to the appropriate transplantation antigen, and ability to inhibit activation of other T cells restricted by the same transplantation antigen. An exception was noted in that a peptide derived from an antigen, bacteriophage lambda cI repressor, binds to the I-E
d
molecule in a specific way, yet is not I-E
d
-restricted. Comparison of the sequence of the repressor peptide with that of other peptides able to bind to (and be restricted by) I-E
d
and a polymorphic region of the I-E
d
molecule itself revealed a significant degree of homology. Thus, peptides restricted by a given class II molecule appear to be homologous to a portion of the class II molecule itself. The repressor-derived peptide is identical at several polymorphic residues at this site, and this may account for the failure of I-E
d
to act as a restriction element. Comparison of antigenic peptide sequences with transplantation antigen sequences suggests a model that provides a basis for explaining self, nonself discrimination as well as alloreactivity.
A mammalian Mitochondrial RNA Processing Activity Contains Nucleus-Encoded RNA
Authors: Chang David D. , Clayton David A.
Published: October 2006

Ribonuclease mitochondrial RNA processing, a site-specific endoribonuclease involved in primer RNA metabolism in mammalian mitochondria, requires an RNA component for its activity. On the basis of copurification and selective inactivation with complementary oligonucleotides, a 135-nucleotide RNA species, not encoded in the mitochondrial genome, is identified as the RNA moiety of the endoribonuclease. This finding implies transport of a nucleus-encoded RNA, essential for organelle DNA replication, to the mitochondrial matrix.
Effect of Water on the Composition of Partial Melts of Greenstone and Amphibolite
Authors: Beard James S. , Lofgren Gary E.
Published: October 2006

Closed-system partial melts of hydrated, metamorphosed arc basalts and andesites (greenstones and amphibolites), where only water structurally bound in metamorphic minerals is available for melting (dehydration melting), are generally water-undersaturated, coexist with plagioclase-rich, anhydrous restites, and have compositions like island arc tonalites. In contrast, water-saturated melting at water pressures of 3 kilobars yields strongly peraluminous, low iron melts that coexist with an amphibolebearing, plagioclase-poor restite. These melt compositions are unlike those of most natural silicic rocks. Thus, dehydration melting over a range of pressures in the crust of island arcs is a plausible mechanism for the petrogenesis of islands arc tonalite, whereas water-saturated melting at pressure of 3 kilobars and above is not.
Long-Range Electronic Perturbations Caused by Defects Using Scanning Tunneling Microscopy
Authors: Mizes H. A. , Foster J. S.
Published: October 2006

Real-space observations of long-range electronic perturbations caused by defects have been made with scanning tunneling microscopy. The defects are isolated adsorbed molecules on the surface of graphite. These defects perturb the charge density, giving periodic oscillations similar to Friedel oscillations. The oscillations have a wavelength √3 times that of the graphite lattice, and the symmetry of the oscillations reflects the nature of the defect.
Hearing in Honey Bees: Detection of Air-Particle Oscillations
Authors: Towne William F. , Kirchner Wolfgang H.
Published: October 2006

Although the airborne sounds produced by dancing honey bees seem essential in the bees' dance communication, attempts to show directly that bees can detect airborne sounds have been unsuccessful. It is shown here that bees can in fact detect airborne sounds and that they do so by detecting air-particle movements. Most vertebrates, by contrast, detect pressure oscillations. Because all traveling sound waves have both components, either can be used in sound detection. The bees' acoustic sense appears to be sensitive enough to allow bees to detect the air-particle movements that occur within several millimeters of a sound-emitting dancer.
Three-Dimensional Spherical Models of Convection in the Earth's Mantle
Authors: Bercovici Dave , Schubert Gerald , Glatzmaier Gary A.
Published: October 2006

Three-dimensional, spherical models of mantle convection in the earth reveal that upwelling cylindrical plumes and downwelling planar sheets are the primary features of mantle circulation. Thus, subduction zones and descending sheetlike slabs in the mantle are fundamental characteristics of thermal convection in a spherical shell and are not merely the consequences of the rigidity of the slabs, which are cooler than the surrounding mantle. Cylindrical mantle plumes that cause hotspots such as Hawaii are probably the only form of active upwelling and are therefore not just secondary convective currents separate from the large-scale mantle circulation. Active sheetlike upwellings that could be associated with mid-ocean ridges did not develop in the model simulations, a result that is in agreement with evidence suggesting that ridges are passive phenomena resulting from the tearing of surface plates by the pull of descending slabs.
U.S. Transit Subsidy Policy: In Need of Reform
Authors: Wachs Martin
Published: October 2006

Public transit in the United States has depended increasingly on public subsidies since the inception of the federal mass transit assistance program in the early 1960s. The subsidies are associated with declining efficiency and labor productivity, as urban transit systems have overcapitalized, simplified fare structures, and extended service into sparse suburban markets. Despite these subsidies, transit has not proved successful in countering the effects on its market of increased automobile ownership and use and of decentralization of residences and places of employment.
Corticotropin-Releasing Factor-Producing Neurons in the Rat Activated by Interleukin-1
Authors: Berkenbosch Frank , van Oers Joep , del Rey Adriana , Tilders Fred , Besedovsky Hugo
Published: October 2006

Intraperitoneal administration of human recombinant interleukin-1 (IL-1) to rats can increase blood levels of corticosterone and adrenocorticotropic hormone (ACTH). The route by which IL-1 affects pituitary-adrenal activity is unknown. That the IL-1-induced pituitary-adrenal activation involves an increased secretion of corticotropin-releasing factor (CRF) is indicated by three lines of evidence. First, immunoneutralization of CRF markedly attenuated the IL-1-induced increase of ACTH blood levels. Second, after blockade of fast axonal transport in hypothalamic neurons by colchicine, IL-1 administration decreased the CRF immunostaining in the median eminence, indicating an enhanced release of CRF in response to IL-1. Third, IL-1 did not stimulate ACTH release from primary cultures of anterior pituitary cells. These data further support the notion of the existence of an immunoregulatory feedback circuit between the immune system and the brain.
Effects of Intracellular Free Magnesium on Calcium Current in Isolated Cardiac Myocytes
Authors: White Richard E. , Hartzell H. Criss
Published: October 2006

Magnesium ions play a fundamental role in cellular function, but the effects of changes in the concentration of intracellular ionized magnesium ([Mg
2+
]
i
) on cell physiology have only recently received experimental attention. Increasing [Mg
2+
]
i
from 0.3 to 3.0 m
M
in cardiac cells by internal perfusion has only small effects on the basal voltage-gated calcium current (
I
Ca
) or on
I
Ca
elevated by dihydropyridine calcium channel agonists. In contrast,
I
Ca
elevated by cyclic adenosine monophosphate (cAMP)-dependent phosphorylation decreases by more than 50 percent. The effect of [Mg
2+
]
i
is not due to changes in the concentration of cAMP or in the velocity of phosphorylation but rather appears to be a direct effect on the phosphorylated channel or on channel dephosphorylation.
Temperature Measurements in Carbonatite Lava Lakes and Flows from Oldoinyo Lengai, Tanzania
Authors: Krafft Maurice , Keller Jörg
Published: October 2006

The petrogenesis of carbonatites has important implications for mantle processes and for the magmatic evolution of mantle melts rich in carbon dioxide. Oldoinyo Lengai, Tanzania, is the only active carbonatite volcano on Earth. Its highly alkalic, sodium-rich lava, although different in composition from the more common calcium-rich carbonatites, provides the opportunity for observations of the physical characteristics of carbonatite melts. Temperature measurements on active carbonatitic lava flows and from carbonatitic lava lakes were carried out during a period of effusive activity in June 1988. Temperatures ranged from 491° to 519°C. The highest temperature, measured from a carbonatitic lava lake, was 544°C. These temperatures are several hundred degrees lower than measurements from any silicate lava. At the observed temperatures, the carbonatite melt had lower viscosities than the most fluid basaltic lavas. The unusually low magmatic temperatures were confirmed with 1-atmosphere melting experiments on natural samples.
Disorder-to-Order Transition in Settling Suspensions of Colloidal Silica: X-ray Measurements
Authors: Davis K. E. , Russel W. B. , Glantschnig W. J.
Published: October 2006

Dispersions of colloidal particles exhibit thermodynamic properties similar to those of molecular systems, including a hard sphere disorder-to-order transition. In experiments with organophilic silica in cyclohexane, gravity settling was used to concentrate the particles. With small particles the slow sedimentation permits rearrangement into the iridescent ordered phase, but larger particles form amorphous sediments instead. Scanning electron microscopy of the crystalline sediment indicates hexagonally closepacked layers. X-ray attenuation measurements reveal a discontinuity coincident with the observed boundary between iridescent and opaque regions. Sediments accumulating faster than the maximum rate of crystallization produce a glass, in accord with the classical theory for crystal growth.
Neptune's Wind Speeds Obtained by Tracking Clouds in Voyager Images
Authors: Hammel H. B. , Beebe R. F. , De Jong E. M. , Hansen C. J. , Howell C. D. , Ingersoll A. P. , Johnson T. V. , Limaye S. S. , Magalhães J. A. , Pollack J. B. , Sromovsky L. A. , Suomi V. E. , Swift C. E.
Published: October 2006

Images of Neptune obtained by the narrow-angle camera of the Voyager 2 spacecraft reveal large-scale cloud features that persist for several months or longer. The features' periods of rotation about the planetary axis range from 15.8 to 18.4 hours. The atmosphere equatorward of -53° rotates with periods longer than the 16.05-hour period deduced from Voyager's planetary radio astronomy experiment (presumably the planet's internal rotation period). The wind speeds computed with respect to this radio period range from 20 meters per second eastward to 325 meters per second westward. Thus, the cloud-top wind speeds are roughly the same for all the planets ranging from Venus to Neptune, even though the solar energy inputs to the atmospheres vary by a factor of 1000.
Location and Chemical Synthesis of a Binding Site for HIV-1 on the CD4 Protein
Authors: Jameson Bradford A. , Rao Patricia E. , Kong Lilly I. , Hahn Beatrice H. , Shaw George M. , Hood Leroy E. , Kent Stephen B. H.
Published: October 2006

The human immunodeficiency virus type 1 (HIV-1) uses the CD4 protein as a receptor for infection of susceptible cells. A candidate structure for the HIV-1 binding site on the CD4 protein was identified by epitope mapping with a family of eight functionally distinct CD4-specific monoclonal antibodies in conjunction with a panel of large CD4-derived synthetic peptides. All of the seven epitopes that were located reside within two immunoglobulin-like disulfide loops situated between residues 1 and 168 of the CD4 protein. The CD4-specific monoclonal antibody OKT4A, a potent inhibitor of HIV-1 binding, recognized a site between residues 32 and 47 on the CD4 protein. By analogy to other members of the immunoglobulin superfamily of proteins, this particular region has been predicted to exist as a protruding loop. A synthetic analog of this loop (residues 25 to 58) showed a concentration-dependent inhibition of HIV-1-induced cell fusion. It is proposed that a loop extending from residues 37 to 53 of the CD4 protein is a binding site for the AIDS virus.
Remote Sensing of Ocean Currents
Authors: Goldstein R. M. , Zebker H. A. , Barnett T. P.
Published: October 2006

A method of remotely measuring near-surface ocean currents with a synthetic aperture radar (SAR) is described. The apparatus consists of a single SAR transmitter and two receiving antennas. The phase difference between SAR image scenes obtained from the antennas forms an interferogram that is directly proportional to the surface current. The first field test of this technique against conventional measurements gives estimates of mean currents accurate to order 20 percent, that is, root-mean-square errors of 5 to 10 centimeters per second in mean flows of 27 to 56 centimeters per second. If the full potential of the method could be realized with spacecraft, then it might be possible to routinely monitor the surface currents of the world's oceans.
Magnitude of Late Quaternary Left-Lateral Displacements Along the North Edge of Tibet
Authors: Peltzer Gilles , Tapponnier Paul , Armijo Rolando
Published: October 2006

Images taken by the earth observation satellite SPOT of the Quaternary morphology at 18 sites on the 2000-kilometer-long Altyn Tagh fault at the north edge of Tibet demonstrate that it is outstandingly active. Long-term, left-lateral strike-slip offsets of stream channels, alluvial terrace edges, and glacial moraines along the fault cluster between 100 and 400 meters. The high elevation of the sites, mostly above 4000 meters in the periglacial zone, suggests that most offsets resulted from slip on the fault since the beginning of the Holocene. These data imply that slip rates are 2 to 3 centimeters per year along much of the fault length and support the hypothesis that the continuing penetration of India into Asia forces Tibet rapidly toward the east.
The Scanning Ion-Conductance Microscope
Authors: Hansma P. K. , Drake B. , Marti O. , Gould S. A. C. , Prater C. B.
Published: October 2006

A scanning ion-conductance microscope (SICM) has been developed that can image the topography of nonconducting surfaces that are covered with electrolytes. The probe of the SICM is an electrolyte-filled micropipette. The flow of ions through the opening of the pipette is blocked at short distances between the probe and the surface, thus limiting the ion conductance. A feedback mechanism can be used to maintain a given conductance and in turn determine the distance to the surface. The SICM can also sample and image the local ion currents above the surfaces. To illustrate its potential for imaging ion currents through channels in membranes, a topographic image of a membrane filter with 0.80-micrometer pores and an image of the ion currents flowing through such pores are presented.
Endothelial Leukocyte Adhesion Molecule 1: an Inducible Receptor for Neutrophils Related to Complement Regulatory Proteins and Lectins
Authors: Bevilacqua Michael P. , Stengelin Siegfried , Gimbrone Michael A. , Seed Brian
Published: October 2006

Focal adhesion of leukocytes to the blood vessel lining is a key step in inflammation and certain vascular disease processes. Endothelial leukocyte adhesion molecule-1 (ELAM-1), a cell surface glycoprotein expressed by cytokine-activated endothelium, mediates the adhesion of blood neutrophils. A full-length complementary DNA (cDNA) for ELAM-1 has now been isolated by transient expression in COS cells. Cells transfected with the ELAM-1 clone express a surface structure recognized by two ELAM-1 specific monoclonal antibodies (H4/18 and H18/7) and support the adhesion of isolated human neutrophils and the promyelocytic cell line HL-60. Expression of ELAM-1 transcripts in cultured human endothelial cells is induced by cytokines, reaching a maximum at 2 to 4 hours and decaying by 24 hours; cell surface expression of ELAM-1 protein parallels that of the mRNA. The primary sequence of ELAM-1 predicts an amino-terminal lectin-like domain, an EGF domain, and six tandem repetitive motifs (about 60 amino acids each) related to those found in complement regulatory proteins. A similar domain structure is also found in the MEL-14 lymphocyte cell surface homing receptor, and in granule-membrane protein 140, a membrane glycoprotein of platelet and endothelial secretory granules that can be rapidly mobilized (<5 minutes) to the cell surface by thrombin and other stimuli. Thus, ELAM-1 may be a member of a nascent gene family of cell surface molecules involved in the regulation of inflammatory and immunological events at the interface of vessel wall and blood.
Far-Red Radiation Reflected from Adjacent Leaves: An Early Signal of Competition in Plant Canopies
Authors: Ballaré Carlos L. , Scopel Ana L. , Sánchez Rodolfo A.
Published: October 2006

When individual seedlings of
Datura ferox
and
Sinapis alba
were transferred to populations formed by plants of similar stature, they responded with an increase in the rate of stem elongation. The reaction was detected within 3 days after transplanting and occurred well before shading among neighbors became important. This rapid response, which may be crucial for success in the competition for light, was reduced or abolished when individual internodes were "blinded" to the far-red radiation scattered by the surrounding seedlings. These results show the operation of a localized, photomorphogenetic control of stem elongation that may play a central role in the plastic adjustment of plants during the early stages of canopy development.
Current Issues and Problems in the Chemical Vapor Deposition of Diamond
Authors: Yarbrough Walter A. , Messier Russell
Published: October 2006

Current issues and problems in the chemical vapor deposition (CVD) of diamond are those which relate to its characterization, its nucleation on foreign surfaces, the question of its formation in preference to the other phases of solid carbon (for example, graphite, chaoite, or lonsdaleite), why different morphologies and crystallographic orientations (textures) are seen in different experiments or with different parameters in the same experiment, and finally whether well-crystallized metastable phases can be obtained by CVD in other material systems or are only a peculiarity of carbon chemistry. Whether a given carbon coating is justly described as diamond has been such an issue, and coatings should clearly show evidence for diamond by x-ray diffraction and Raman spectroscopy before the claim of diamond is made. Experimental results have not been consistent in many cases, and much work remains to be done before an accurate assessment can be made of the technological impact of the development.
The Framework Topology of ZSM-18, a Novel Zeolite Containing Rings of Three (Si,Al)-O Species
Authors: Lawton Stephen L. , Rohrbaugh Wayne J.
Published: October 2006

ZSM-18 is the first known aluminosilicate zeolite to contain rings of three (Si,Al)-O species (3-rings). Its framework topology has been determined by hypothetical model building, subsequent constrained distance and angle least-squares refinements of atomic coordinates, and x-ray powder diffraction pattern simulations. Its channel structure is characterized by a linear unidimensional 12-ring channel, with an approximate pore opening of 7.0 angstroms. In addition, the channels are lined with pockets that are capped by 7-rings with dimensions of 2.8 angstroms by 3.5 angstroms. An intraframework packing model of the organic moiety used in the synthesis suggests that a strong templating effect may be responsible for the formation of this unusual zeolite structure.
Fossil Soils and Grasses of a Middle Miocene East African Grassland
Authors: Retallack Gregory J. , Dugas D. P. , Bestland E. A.
Published: October 2006

Fossil soils and grasses from the well-known Miocene mammal locality of Fort Ternan, southwestern Kenya, are evidence of a mosaic of grassy woodland and wooded grassland some 14 million years ago. This most ancient wooded grassland yet known on the African continent supported more abundant and diverse antelopes than known earlier in Africa. Ape fossils at Fort Ternan, including
Kenyapithecus wickeri,
were associated with woodland parts of the vegetation mosaic revealed by paleosols. Grassland habitats were available in East Africa long before the evolutionary divergence of apes and humans some 5 to 10 million years ago.
Brefeldin A Specifically Inhibits Presentation of Protein Antigens to Cytotoxic T Lymphocytes
Authors: Yewdell Jonthan W. , Bennink Jack R.
Published: October 2006

Cytotoxic T lymphocytes (CTLs) recognize foreign antigens, including viral proteins, in association with major histocompatibility complex (MHC) class I molecules. Brefeldin A, a specific inhibitor of exocytosis, completely and reversibly inhibited the presentation of viral proteins, but not exogenous peptides, to MHC class I-restricted CTLs directed against influenza virus antigens. The effect of brefeldin A on antigen presentation correlated with its inhibition of intracellular transport of newly synthesized class I molecules. Brefeldin A is thus a specific inhibitor of antigen processing for class I-restricted T cell recognition. Its effect on antigen presentation supports the idea that exogenous peptide antigens associate with cell surface class I molecules, whereas protein antigens processed via the cytosolic route associate with nascent class I molecules before they leave the trans-Golgi complex.
Fluid Processes in Subduction Zones
Authors: Peacock Simon M.
Published: October 2006

Fluids play a critical role in subduction zones and arc magmatism. At shallow levels in subduction zones (<40 kilometers depth), expulsion of large volumes of pore waters and CH
4
-H
2
O fluids produced by diagenetic and low-grade metamorphic reactions affect the thermal and rheological evolution of the accretionary prism and provide nutrients for deep-sea biological communities. At greater depths, H
2
O and CO
2
released by metamorphic reactions in the subducting oceanic crust may alter the bulk composition in the overlying mantle wedge and trigger partial melting reactions. The location and conse-quences of fluid production in subduction zones can be constrained by consideration of phase diagrams for relevant bulk compositions in conjunction with fluid and rock pressure-temperature-time paths predicted by numerical heat-transfer models. Partial melting of subducting, amphibole-bearing oceanic crust is predicted only within several tens of million years of the initiation of subduction in young oceanic lithosphere. In cooler subduction zones, partial melting appears to occur primarily in the overlying mantle wedge as a result of fluid infiltration.
Numerical Transforms
Authors: Bracewell R. N.
Published: October 2006

Numerical computation of transforms is now widely practiced in science and industry and has been revolutionized by the development of fast transforms that make feasible computing projects that once could not be contemplated. The article discusses the significance of transforms in numerical work, defines the modern forms of several common transforms and their inverses, gives examples, and describes and gives references to methods of numerical evaluation.
A Comparison of the Contribution of Various Gases to the Greenhouse Effect
Authors: Rodhe Henning
Published: October 2006

The current concern about an anthropogenic impact on global climate has made it of interest to compare the potential effect of various human activities. A case in point is the comparison between the emission of greenhouse gases from the use of natural gas and that from other fossil fuels. This comparison requires an evaluation of the effect of methane emissions relative to that of carbon dioxide emissions. A rough analysis based on the use of currently accepted values shows that natural gas is preferable to other fossil fuels in consideration of the greenhouse effect as long as its leakage can be limited to 3 to 6 percent.
The CFC-Ozone Issue: Progress on the Development of Alternatives to CFCs
Authors: Manzer L. E.
Published: October 2006

Chlorofluorocarbons (CFCs) are now believed to be major contributors to the seasonal ozone depletion over the Antarctic continent. However, because they are so important to many aspects of modern society, it would be irresponsible to immediately cease their production. The identification of suitable substitutes is difficult when issues such as toxicity, flammability, cost, environmental impact, and physical properties are considered. Several candidates that meet these criteria have been selected by the industry and significant research and development programs are under way to commercialize them. Unlike the simple, fully halogenated CFCs, which can only be made in the single step, there are many potentially viable routes to the alternatives, but these will require significant improvements in catalysis. Many other important issues such as materials compatibility, energy efficiency, the needs of developing countries, and the product life cycle of the alternatives need to be resolved before a timely transition to substitutes can be accomplished.
New Mechanisms for Chemistry at Surfaces
Authors: Ceyer Sylvia T.
Published: October 2006

It is becoming increasingly apparent that chemistry at surfaces, whether it be heterogeneous catalysis, semiconductor etching, or chemical vapor deposition, is controlled by much more than the nature and structure of the surface. Recent experiments that principally make use of molecular beam techniques have revealed that the energy at which an incident molecule collides with a surface can be the key factor in determining its reactivity with or on the surface. In addition, the collision energy of an incident particle has proven essential to the finding of new mechanisms for reaction or desorption of molecules at surfaces, collision-induced activation and collision-induced desorption. These phenomena are often responsible for the different surface chemistry observed under conditions of high reactant pressure, such as those present during a heterogeneous catalytic reaction, and of low pressure of reactants (< 10
-4
torr), such as those present in an ultrahigh vacuum surface science experiment. This knowledge of the microscopic origins of the effect of pressure on the chemistry at surfaces has allowed the development of a scheme to bypass the high-pressure requirement. Reactions that are normally observed only at high reactant pressures, and which are the ones most often of practical importance, can now be carried out in low-pressure, ultrahigh vacuum environments.
Diffraction from Polymerized Membranes
Authors: Abraham Farid F. , Nelson David R.
Published: October 2006

Flexible polymerized membranes in a good solvent are expected to exhibit a remarkable low-temperature flat phase, characterized by a diverging bending rigidity, vanishing elastic constants, and large fluctuations both parallel and perpendicular to the surface. A theory of the equilibrium structure factor provides a good fit to extensive molecular dynamics simulations of simplified "tethered surface" models of these materials. These results show how information about the size, thickness, and internal structure of polymerized membranes can be extracted from diffraction experiments.
Water and Solutions at Negative Pressure: Raman Spectroscopic Study to -80 Megapascals
Authors: Green J. L. , Durben D. J. , Wolf G. H. , Angell C. A.
Published: October 2006

Microscopic inclusions of aqueous fluids trapped in interstices in quartz and other crystals provide novel systems for the deliberate study of liquids under tension. Liquids under tension should differ in interesting ways from those at ambient pressure or compressed liquids because attractive, rather than repulsive, forces should dominate their behavior. Static tensions in excess of 100 megapascals (∼1000 atmospheres) have been obtained reproducibly. Video-recorded observations of the final liquid rupture process, coupled with extrapolations of data at positive pressure, suggest that the homogeneous vapor nucleation point was reached in two of the cases studied. Raman spectra of the fluids at -80 megapascals show that an isothermal volume stretch of ∼5 percent by volume has only a weak effect on the spectral features and is similar to the effect of isobaric heating.
Rapid, Sensitive Bioluminescent Reporter Technology for Naphthalene Exposure and Biodegradation
Authors: King J. M. H. , DiGrazia P. M. , Applegate B. , Burlage R. , Sanseverino J. , Dunbar P. , Larimer F. , Sayler G. S.
Published: October 2006

A bioluminescent reporter plasmid for naphthalene catabolism (pUTK21) was developed by transposon (Tn4431) insertion of the
lux
gene cassette from
Vibrio fischeri
into a naphthalene catabolic plasmid in
Pseudomonas fluorescens
. The insertion site of the
lux
transposon was the
nahG
gene encoding for salicylate hydroxylase. Luciferase-mediated light production from
P. fluorescens
strains harboring this plasmid was induced on exposure to naphthalene or the regulatory inducer metabolite, salicylate. In continuous culture, light induction was rapid (15 minutes) and was highly responsive to dynamic changes in naphthalene exposure. Strains harboring pUTK21 were responsive to aromatic hydrocarbon contamination in Manufactured Gas Plant soils and produced sufficient light to serve as biosensors of naphthalene exposure and reporters of naphthalene biodegradative activity. The robust and sensitive nature of the bioluminescent reporter technology suggests that new sensing methods can be developed for on-line process monitoring and control in complex environmental matrices.
Mouse Embryonic Stem Cells and Reporter Constructs to Detect Developmentally Regulated Genes
Authors: Gossler Achim , Joyner Alexandra L. , Rossant Janet , Skarnes William C.
Published: October 2006

A strategy was devised for identifying regions of the mouse genome that are transcriptionally active in a temporally and spatially restricted manner during development. The approach is based on the introduction into embryonic stem cells of two types of
lacZ
reporter constructs that can be activated by flanking mouse genomic sequences. Embryonic stem cells containing the
lacZ
constructs were used to produce chimaeric mice. Developmental regulation of
lacZ
expression occurred at a high frequency. Molecular cloning of the flanking endogenous genes and introduction of these potential insertional mutations into the mouse germ line should provide an efficient means of identifying and mutating novel genes important for the control of mammalian development.
Genetic Engineering of Livestock
Authors: Pursel Vernon G. , Pinkert Carl A. , Miller Kurt F. , Bolt Douglas J. , Campbell Roger G. , Palmiter Richard D. , Brinster Ralph L. , Hammer Robert E.
Published: October 2006

Genetic engineering of livestock is expected to have a major effect on the agricultural industry. However, accurate assessment of the consequences of transgene expression is impossible without multigenerational studies. A systematic study of the beneficial and adverse consequences of long-term elevations in the plasma levels of bovine growth hormone (bGH) was conducted on two lines of transgenic pigs. Two successive generations of pigs expressing the bGH gene showed significant improvements in both daily weight gain and feed efficiency and exhibited changes in carcass composition that included a marked reduction in subcutaneous fat. However, long-term elevation of bGH was generally detrimental to health: the pigs had a high incidence of gastric ulcers, arthritis, cardiomegaly, dermatitis, and renal disease. The ability to produce pigs exhibiting only the beneficial, growth-promoting effects of growth hormone by a transgenic approach may require better control of transgene expression, a different genetic background, or a modified husbandry regimen.
Not So Hot "Hot Spots" in the Oceanic Mantle
Authors: Bonath Enrico
Published: October 2006

Excess volcanism and crustal swelling associated with hot spots are generally attributed to thermal plumes upwelling from the mantle. This concept has been tested in the portion of the Mid-Atlantic Ridge between 34° and 45° (Azores hot spot). Peridotite and basalt data indicate that the upper mantle in the hot spot has undergone a high degree of melting relative to the mantle elsewhere in the North Atlantic. However, application of various geothermometers suggests that the temperature of equilibration of peridotites in the mantle was lower, or at least not higher, in the hot spot than elsewhere. The presence of H
2
O-rich metasomatized mantle domains, inferred from peridotite and basalt data, would lower the melting temperature of the hot spot mantle and thereby reconcile its high degree of melting with the lack of a mantle temperature anomaly. Thus, some so-called hot spots might be melting anomalies unrelated to abnormally high mantle temperature or thermal plumes.
The Flight from the Arts and Sciences: Trends in Degrees Conferred
Authors: Turner Sarah E. , Bowen William G.
Published: October 2006

After rising steadily between 1954 and 1968, the percentage of all bachelor's degrees awarded in the arts and sciences declined dramatically. These swings cannot be explained by demographic variables; however, they have been affected by changes in the academic profiles of educational institutions that were in turn related to trends in enrollment. Even more important have been the changing choices of fields of study made by men and women (particularly in the case of the humanities), in part as a consequence of widening opportunities for women. The flight from the arts and sciences now appears to be over, and in the future gender-related variables can be expected to have less impact on the distribution of degrees conferred.
Heat-Producing Elements and the Thermal and Baric Patterns of Metamorphic Belts
Authors: Chamberlain C. Page , Sonder Leslie J.
Published: October 2006

The character of sedimentary basins, before they are deformed and metamorphosed, may strongly influence the thermal and baric patterns of metamorphic belts. Crustal thickening of anoxic sedimentary basins and subsequent thermal reequilibration may produce large areas of high-grade metamorphic rocks and granites because the concentrations of the heat-producing elements are high in such basins. In New England there is a spatial association among granites and high-grade metasedimentary rocks rich in U and Th that now form the Central Maine terrane. The high content of heat-producing elements in these rocks is attributed to fixing of U and Th in highly reduced sediments that were deposited in an anoxic basin that formed in the Silurian. When the basin was thickened during the Devonian Acadian orogeny, the thermal energy generated by the U- and Th-rich sediments produced the observed broad zone of high-grade rocks and anatectic granites. This hypothesis was tested with thermal calculations that reproduce most of the first-order thermal and baric patterns of the Acadian Appalachians, if pretectonic lateral variations in heat production are assumed.
Cloning and Sequencing of Porcine LH-hCG Receptor cDNA: Variants Lacking Transmembrane Domain
Authors: Loosfelt Hugues , Misrahi Micheline , Atger Michel , Salesse Roland , Vu Hai-Luu Thi Mai Tu , Jolivet André , Guiochon-Mantel Anne , Sar Sokhavuth , Jallal Bahija , Garnier Jean , Milgrom Edwin
Published: October 2006

Complementary DNA clones, encoding the LH-hCG (luteinizing hormone-human choriogonadotropic hormone) receptor were isolated by screening a λgt11 library with monoclonal antibodies. The primary structure of the protein was deduced from the DNA sequence analysis; the protein contains 696 amino acids with a putative signal peptide of 27 amino acids. Hydropathy analysis suggests the existence of seven transmembrane domains that show homology with the corresponding regions of other G protein-coupled receptors. Three other types of clones corresponding to shorter proteins were observed, in which the putative transmembrane domain was absent. These probably arose through alternative splicing. RNA blot analysis showed similar patterns in testis and ovary with a major RNA of 4700 nucleotides and several minor species. The messenger RNA was expressed in COS-7 cells, yielding a protein that bound hCG with the same affinity as the testicular receptor.
Thermodynamics of Surface Morphology
Authors: Williams Ellen D. , Bartelt N. C.
Published: October 2006

Classical thermodynamic descriptions of surfaces treat surface orientation as a thermodynamic degree of freedom and thus allow for the possibility of reversible changes in surface morphology as a function of temperature or impurity concentration. The existence of these transitions has been confirmed experimentally. Advances in surface diffraction and imaging techniques now make it possible to characterize such transitions quantitatively in terms of the atomic structure, and particularly in terms of the behavior of steps on surfaces. Statistical mechanical models can be used to analyze the observations to determine the fundamental energetic parameters governing the observed thermodynamic behavior.
Phase Transition and Thermal Expansion of MgSiO
3
Perovskite
Authors: Wang Yanbin , Weidner Donald J. , Liebermann Robert C. , Liu Xing , Ko Jaidong , Vaughan Michael T. , Zhao Yusheng , Yeganeh-Haeri Amir , Pacalo Rosemary E. G.
Published: October 2006

Results from in situ x-ray diffraction experiments with a DIA-type cubic anvil apparatus (SAM 85) reveal that MgSiO
3
perovskite transforms from the orthorhombic
Pbnm
symmetry to another perovskite-type structure above 600 kelvin (K) at pressures of 7.3 gigapascals; the apparent volume increase across the transition is 0.7%. Unit-cell volume increased linearly with temperature, both below (1.44 × 10
-5
K
-1
) and above (1.55 × 10
-5
K
-1
) the transition. These results indicate that the physical properties measured on the
Pbnm
phase should be used with great caution because they may not be applicable to the earth's lower mantle. A density analysis based on the new data yields an iron content of 10.4 weight percent for a pyrolite composition under conditions corresponding to the lower mantle. All current equation-of-state data are compatible with constant chemical composition in the upper and lower mantle; thus, these data imply that a chemically layered mantle is unnecessary, and whole-mantle convection is possible.
Polymer Brushes
Authors: Milner S. T.
Published: October 2006

Polymers attached by one end to an interface at relatively high coverage stretch away from the interface to avoid overlapping, forming a polymer "brush." This simple picture may serve as the basis for models in diverse interfacial systems in polymer science, such as polymeric surfactants, stabilized suspensions of colloidal particles, and structures formed by block copolymers. The structure and dynamics of polymer brushes have been the subject of considerable theoretical and experimental activity in recent years. An account is given of recent advances in theoretical understanding of stretched polymers at interfaces, and the diverse experimental probes of systems modeled by brushes are briefly reviewed.
Physics in Strong Magnetic Fields Near Neutron Stars
Authors: Harding Alice K.
Published: October 2006

Electromagnetic phenomena occurring in the strong magnetic fields of neutron stars are currently of great interest in high-energy astrophysics. Observations of rotation rate changes and cyclotron lines in pulsars and γ-ray bursts indicate that surface magnetic fields of neutron stars often exceed 10
12
gauss. In fields this strong, where electrons behave much as if they were in bound atomic states, familiar processes undergo profound changes, and exotic processes become important. Strong magnetic fields affect the physics in several fundamental ways: Energies perpendicular to the field are quantized, transverse momentum is not conserved, and electron-positron spin is important. Neutron stars therefore provide a unique laboratory for the study of physics in extremely high fields that cannot be generated on Earth.
Evidence for a Phytotoxic Hydroxy-Aluminum Polymer in Organic Soil Horizons
Authors: Hunter Douglas , Ross Donald S.
Published: October 2006

The toxicity of Al that has been mobilized in soil, streams, and lakes through acid deposition primarily has been attributed to mononuclear Al species. Polynuclear Al species are more toxic than mononuclear species, but they have not been considered to be significant in the environment. Aluminum-27 nuclear magnetic resonance (NMR) spectra of forested spodosol soil horizon samples show the presence of polynuclear AlO
4
Al
12
(OH)
24
(H
2
O)
12
7+
. The AlO
4
Al
12
(OH)
24
(H
2
O)
12
7+
species accounted for 30 percent of the aqueous Al observable by NMR, and this could make a significant contribution to the toxicity of the Al in these soils.
Earth's Core-Mantle Boundary: Results of Experiments at High Pressures and Temperatures
Authors: Knittle Elise , Jeanloz Raymond
Published: October 2006

Laboratory experiments document that liquid iron reacts chemically with silicates at high pressures (≥2.4 × 10
10
Pascals) and temperatures. In particular, (Mg,Fe)SiO
3
perovskite, the most abundant mineral of Earth's lower mantle, is expected to react with liquid iron to produce metallic alloys (FeO and FeSi) and nonmetallic silicates (SiO
2
stishovite and MgSiO
3
perovskite) at the pressures of the core-mantle boundary, 14 × 10
10
Pascals. The experimental observations, in conjunction with seismological data, suggest that the lowermost 200 to 300 kilometers of Earth's mantle, the D′′ layer, may be an extremely heterogeneous region as a result of chemical reactions between the silicate mantle and the liquid iron alloy of Earth's core. The combined thermal-chemical-electrical boundary layer resulting from such reactions offers a plausible explanation for the complex behavior of seismic waves near the core-mantle boundary and could influence Earth's magnetic field observed at the surface.
Microtektites, Microkrystites, and Spinels from a Late Pliocene Asteroid Impact in the Southern Ocean
Authors: Margolis Stanley V. , Claeys Philippe , Kyte Frank T.
Published: October 2006

The properties of glassy spherules found in sedimentary deposits of a late Pliocene asteroid impact into the southeast Pacific are similar to those of both microtektites and microkrystites. These spherules probably formed from molten silicate droplets that condensed from an impact-generated vapor cloud. The spherules contain inclusions of magnesioferrite spinels similar to those in spherules found at the Cretaceous-Tertiary boundary, indicating that both sets of spherules are impact debris formed under similar physical and chemical conditions.