bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma Motions in Planetary Magnetospheres
Authors: Hill T. W. , Dessler A. J.
Published: October 2006

Before direct exploration by spacecraft, Jupiter was the only planet other than Earth that was known to have a magnetic field, as revealed by its nonthermal radio emissions. The term "magnetosphere" did not exist because there was no clear concept of such an entity. The space age provided the opportunity to explore Earth's neighborhood in space and to send instruments to seven of the other eight planets. It was found that interplanetary space is pervaded by a supersonic "solar wind" plasma and that six planets, including Earth, have magnetic fields of sufficient strength to deflect this solar wind and form a comet-shaped cavity called a magnetosphere. Comparative study of these magnetospheres aims to elucidate both the general principles and characteristics that they share in common, and the specific environmental factors that cause the important, and sometimes dramatic, differences in behavior between any two of them. A general understanding of planetary magnetospheres holds the promise of wide applicability in astrophysics, which, for the indefinite future, must rely solely on remote sensing for experimental data.
Atmospheric Lifetime of CHF
2
Br, a Proposed Substitute for Halons
Authors: Talukdar R. , Mellouki A. , Gierczak T. , Burkholder J. B. , McKeen S. A. , Ravishankara A. R.
Published: October 2006

The rate coefficients,
k
1
, for the reaction of OH with CHF
2
Br have been measured using pulsed photolysis and discharge flow techniques at temperatures (
T
) between 233 and 432 K to be
k
1
= (7.4 ± 1.6) × 10
-13
exp[-(1300 ± 100)/
T
] cubic centimeters per molecule per second. The ultraviolet absorption cross sections, σ, of this molecule between 190 and 280 nanometers were measured at 296 K. The
k
1
and σ values were used in a one-dimensional model to obtain an atmospheric lifetime of approximately 7 years for CHF
2
Br. This lifetime is shorter by approximately factors of 10 and 2 than those for CF
3
Br and CF
2
ClBr, respectively. The ozone depletion potentials of the three compounds will reflect these lifetimes.
Satellite Observations of Smoke from Oil Fires in Kuwait
Authors: Limaye S. S. , Suomi V. E. , Velden C. , Tripoli G.
Published: October 2006

Extensive dark smoke clouds associated with burning oil wells in Kuwait have been seen in data from weather satellites since early February 1991. The smoke is dispersed over a wide area. Variable and strong low level winds have held most of the smoke plume below 3 to 5 kilometers within a few hundred kilometers of the source. Thin veils of smoke have been detected in METEOSAT data as far away as 2000 kilometers east of Kuwait, over southwestern Pakistan at heights between 6 and 7 kilometers. The occasional presence of convective clouds over the fires indicates that some scavenging of the smoke is taking place.
Quaternary Raised Coral-Reef Terraces on Sumba Island, Indonesia
Authors: Pirazzoli P. A. , Radtke U. , Hantoro W. S. , Jouannic C. , Hoang C. T. , Causse C. , Best M. Borel
Published: October 2006

A spectacular sequence of coral-reef terraces (six steps broader than 500 meters and many minor substeps) is developed near Cape Laundi, Sumba Island, between an ancient patch reef 475 meters high and sea level. Several raised reefs have been dated with the electron spin resonance and the uranium-series dating methods. The uplift trend deduced from these reefs is 0.5 millimeter per year; most terraces, although polycyclic in origin, appear to correspond to specific interglacial stages, with the oldest terrace formed 1 million years ago. This puts them among the longest and most complete mid-Quaternary terrace sequences.
Early Differentiation of the Earth and the Problem of Mantle Siderophile Elements: A New Approach
Authors: Murthy V. Rama
Published: October 2006

The long-standing problem of the excess abundances of siderophile elements in the mantle can be resolved by considering an equilibrium core-mantle differentiation in the earth at 3000 to 3500 kelvin. This high-temperature differentiation results in mantle siderophile element abundances that closely match the observed values. Some lithophile (light) elements could enter the core in this process as is necessary to account for its low density. The abundances of siderophile elements in the mantle are consistent with the conclusion derived from the recent physical models that the earth was molten during accretion.
Occurrence of Earth-Like Bodies in Planetary Systems
Authors: Wetherill George W.
Published: October 2006

Present theories of terrestrial planet formation predict the rapid "runaway formation'' of planetary embryos. The sizes of the embryos increase with heliocentric distance. These embryos then merge to form planets. In earlier Monte Carlo simulations of the merger of these embryos it was assumed that embryos did not form in the asteroid belt, but this assumption may not be valid. Simulations in which runaways were allowed to form in the asteroid belt show that, although the initial distributions of mass, energy, and angular momentum are different from those observed today, during the growth of the planets these distributions spontaneously evolve toward those observed, simply as a result of known solar system processes. Even when a large planet analogous to "Jupiter'' does not form, an Earth-sized planet is almost always found near Earth's heliocentric distance. These results suggest that occurrence of Earth-like planets may be a common feature of planetary systems.
The Human Papilloma Virus-16 E7 Oncoprotein Is Able to Bind to the Retinoblastoma Gene Product
Authors: Dyson Nicholas , Howley Peter M. , Münger Karl , Harlow Ed
Published: October 2006

Deletions or mutations of the retinoblastoma gene, RB1, are common features of many tumors and tumor cell lines. Recently, the RB1 gene product, p105-RB, has been shown to form stable protein/protein complexes with the oncoproteins of two DNA tumor viruses, the adenovirus E1A proteins and the simian virus 40 (SV40) large T antigen. Neither of these viruses is thought to be associated with human cancer, but they can cause tumors in rodents. Binding between the RB anti-oncoprotein and the adenovirus or SV40 oncoprotein can be recapitulated in vitro with coimmunoprecipitation mixing assays. These assays have been used to demonstrate that the E7 oncoprotein of the human papilloma virus type-16 can form similar complexes with p105-RB. Human papilloma virus-16 is found associated with approximately 50 percent of cervical carcinomas. These results suggest that these three DNA viruses may utilize similar mechanisms in transformation and implicate RB binding as a possible step in human papilloma virus-associated carcinogenesis.
Signal Transduction by the Platelet-Derived Growth Factor Receptor
Authors: Williams Lewis T.
Published: October 2006

When platelet-derived growth factor (PDGF) binds to its receptor on a quiescent fibroblast or smooth muscle cell, it stimulates a remarkably diverse group of biochemical responses, including changes in ion fluxes, activation of several kinases, alterations in cell shape, increased transcription of a number of genes, and stimulation of enzymes that regulate phospholipid metabolism. These and other reactions culminate, hours later, in DNA replication and cell division. How does the receptor for PDGF recognize and bind its specific ligand and then transduce this signal across the cell membrane via a single membrane-spanning region? Which of the immediate cellular responses are directly involved in the biochemical pathways that lead to DNA synthesis? How does the PDGF receptor trigger a diverse group of responses? Recent studies of the PDGF receptor have provided insight into these issues.
Visual Observations of the Amorphous-Amorphous Transition in H
2
O Under Pressure
Authors: Mishima Osamu , Takemura K. , Aoki K.
Published: October 2006

The vapor-deposited low-density amorphous phase of H
2
O was directly compressed at 77 kelvin with a diamond-anvil cell, and the boundary between the low-density amorphous phase and the high-density amorphous phase was observed while the sample was warmed under compression. The transition from the low-density amorphous phase to the high-density amorphous phase was distinct and reversible in an apparently narrow pressure range at ∼130 to ∼150 kelvin, which provided experimental evidence for polymorphism in amorphous H
2
O.
U and Sr Isotopes in Ground Water and Calcite, Yucca Mountain, Nevada: Evidence Against Upwelling Water
Authors: Stuckless J. S. , Peterman Z. E. , Muhs D. R.
Published: October 2006

Hydrogenic calcite and opaline silica deposits in fault zones at Yucca Mountain, Nevada, have created considerable public and scientific controversy because of the possible development of a high-level nuclear waste repository at this location. Strontium and uranium isotopic compositions of hydrogenic materials were used to test whether the veins could have formed by upwelling of deep-seated waters. The vein deposits are isotopically distinct from ground water in the two aquifers that underlie Yucca Mountain, indicating that the calcite could not have precipitated from ground water. The data are consistent with a surficial origin for the hydrogenic deposits.
First Fossil Hagfish (Myxinoidea): A Record from the Pennsylvanian of Illinois
Authors: Bardack David
Published: October 2006

A fossil hagfish (Myxinoidea), a new genus from the Pennsylvanian, shows tentacles, structures of the head skeleton and internal organs. No other fossils of this group have been reported. Although this new hagfish differs from living forms in position of the gills, feeding apparatus, and relatively well developed eyes, it is quite similar to its recent relatives. Thus, hagfishes have a long, conservative geological history. Cladograms showing myxinoids as a sister group to the vertebrates are supported.
Reduced Antarctic Ozone Depletions in a Model with Hydrocarbon Injections
Authors: Cicerone R. J. , Elliott Scott , Turco R. P.
Published: October 2006

Motivated by increased losses of Antarctic stratospheric ozone and by improved understanding of the mechanism, a concept is suggested for action to arrest this ozone loss: injecting the alkanes ethane or propane (E or P) into the Antarctic stratosphere. A numerical model of chemical processes was used to explore the concept. The model results suggest that annual injections of about 50,000 tons of E or P could suppress ozone loss, but there are some scenarios where smaller E or P injections could increase ozone depletion. Further, key uncertainties must be resolved, including initial concentrations of nitrogen-oxide species in austral spring, and several poorly defined physical and chemical processes must be quantified. There would also be major difficulties in delivering and distributing the needed alkanes.
Long-Term Mean Vertical Motion over the Tropical Pacific: Wind-Profiling Doppler Radar Measurements
Authors: Gage K. S. , McAfee J. R. , Carter D. A. , Ecklund W. L. , Riddle A. C. , Reid G. C. , Balsley B. B.
Published: October 2006

Measurement from Christmas Island (2°N, 157°W) of long-term mean vertical motions in the tropical atmosphere using very-high-frequency wind-profiling Doppler radar show that there is a transition from downward motion in the free troposphere to upward motion in the upper troposphere and lower stratosphere. The observations in the free troposphere are consistent with a balance between adiabatic and diabatic heating and cooling rates in a clear atmosphere. Comparison of the results at Christmas Island during El Niño and non-El Niño conditions with earlier results obtained for stratiform rain conditions over Pohnpei, Federated States of Micronesia, show that cirrus clouds in the vicinity of the tropopause likely play an important role in determining the sense and magnitude of vertical motions in this region. These results have implications for the exchange of mass between the troposphere and stratosphere over the tropics.
Nutritional Importance of Pyrroloquinoline Quinone
Authors: Killgore John , Smidt Carsten , Duich Lisa , Romero-Chapman Nadia , Tinker Donald , Reiser Karen , Melko Maria , Hyde Dallas , Rucker Robert B.
Published: October 2006

Mice fed a chemically defined diet devoid of pyrroloquinoline quinone (PQQ) grew poorly, failed to reproduce, and became osteolathyritic. Moreover, severely affected mice had friable skin, skin collagen that was readily extractable into neutral salt solutions, and decreased lysyl oxidase. The identification of functional defects in connective tissue and the growth retardation associated with PQQ deprivation suggest that PQQ plays a fundamental role as a growth factor or vitamin.
Rational Design and Synthesis of New Polymeric Material
Authors: Allcock Harry R.
Published: October 2006

Polymers constitute one of the four main areas of materials science. Modern research in polymers focuses on the ways in which tailored macromolecules organize themselves in the solid state and on materials design and synthesis at the interface between polymer science and the fields of ceramics, metals, and electroactive or electrooptical materials.
Water in Earth's Mantle: The Role of Nominally Anhydrous Minerals
Authors: Bell David R. , Rossman George R.
Published: October 2006

Most minerals of Earth's upper mantle contain small amounts of hydrogen, structurally bound as hydroxyl (OH). The OH concentration in each mineral species is variable, in some cases reflecting the geological environment of mineral formation. Of the major mantle minerals, pyroxenes are the most hydrous, typically containing ∼200 to 500 parts per million H
2
O by weight, and probably dominate the water budget and hydrogen geochemistry of mantle rocks that do not contain a hydrous phase. Garnets and olivines commonly contain ∼1 to 50 parts per million. Nominally anhydrous minerals constitute a significant reservoir for mantle hydrogen, possibly accommodating all water in the depleted mantle and providing a possible mechanism to recycle water from Earth's surface into the deep mantle.
Percolation Theory, Thermoelasticity, and Discrete Hydrothermal Venting in the Earth's Crust
Authors: Germanovich L. N. , Lowell Robert P.
Published: October 2006

As hydrothermal fluid ascends through a network of cracks into cooler crust, heat is transferred from the fluid to the adjacent rock. The thermal stresses caused by this heating close cracks that are more or less vertical. This heating may affect network connections and destroy the permeable crack network. Thermoelastic stresses caused by a temperature difference of ∼100°C can decrease the interconnectivity of a crack network to the percolation threshold. If the temperature is slightly less, thermoelastic stresses may focus the discharge in hydrothermal systems into discrete vents.
Lectins as Cell Recognition Molecules
Authors: Sharon Nathan , Lis Halina
Published: October 2006

Lectins on cell surfaces mediate cell-cell interactions by combining with complementary carbohydrates on apposing cells. They play a key role in the control of various normal and pathological processes in living organisms.
Inhibition of Antigen-Induced Lymphocyte Proliferation by Tat Protein from HIV-1
Authors: Viscidi Raphael P. , Mayur Kumudini , Lederman Howard M. , Frankel Alan D.
Published: October 2006

The purified human immunodeficiency virus type-1 (HIV-1) Tat protein inhibited lymphocyte proliferation induced by tetanus toxoid or Candida antigens by 66 to 97% at nanomolar concentrations of Tat. In contrast, Tat did not cause a significant reduction of lymphocyte proliferation in response to mitogens such as phytohemagglutinin or pokeweed mitogen. Inhibition was blocked by oxidation of the cysteine-rich region of Tat or by incubation with an antibody to Tat before the assay. A synthetic Tat peptide (residues 1 to 58) also inhibited antigen-stimulated proliferation. Experiments with H9 and U937 cell lines showed that Tat can easily enter both lymphocytes and monocytes. The specific inhibition of antigen-induced lymphocyte proliferation by Tat mimics the effect seen with lymphocytes from HIV-infected individuals and suggests that Tat might directly contribute to the immunosuppression associated with HIV infection.
UV Spectrum and Proposed Role of Diethylberyllium in a
7
Li-
7
Be Solar Neutrino Experiment
Authors: Dyer P.
Published: October 2006

Although measurement of the solar neutrino flux via the
7
Li(
v
e
,e
–
)
7
Be reaction was proposed many years ago, no experiment has been implemented since it has been difficult to identify a sensitive
7
Be detection technique. Here it is proposed that the
7
Be atom be incorporated into a volatile molecule, placed in a buffer-gas-filled cell, and then extracted by photodissociation; after excitation by a tunable laser, bursts of photons would be detected. The absorption spectrum of the molecular candidate diethylberyllium has been measured between 186 and 270 nanometers in a spectrophotometer to determine the required photodissociation laser wavelength and intensity.
Isotope Effect in Superconducting Fullerenes
Authors: Chakravarty Sudip , Kivelson Steven A. , Salkola Markku I. , Tewari Shubha
Published: October 2006

The effect of isotopic substitution on the superconducting transition temperature,
T
c
, in alkali-doped C
60
has been examined. Paradoxically, it is found that a substantial decrease in
T
c
with the increasing isotopic mass is possible even when the attractive interaction is not mediated by phonons but is instead of purely electronic origin. In particular, it is shown that the experimentally measured isotopic shifts are consistent with a recently proposed electronic mechanism. Further predictions are presented that can be tested by experiment.
Crust Formation and Plate Motion in the Early Archean
Authors: Kröner A. , Layer P. W.
Published: October 2006

Mounting evidence for voluminous continental crust formation in the early Archean involving intracrustal melting and selective preservation of granitoid rocks suggests that initial crust formation and growth were predominantly by magmatic underplating in plumegenerated Iceland-type settings. Collision of these early islands to give rise to larger blocks is suggested by extensive horizontal shortening in both supracrustal and granitoid assemblages. Preservation of early Archean high-grade gneisses that were once at depths of 20 to 30 kilometers implies that these blocks developed thick, subcrustal roots despite high mantle heat flow. Rigid continental plates must have existed since at least 3.5 billion years ago, and greenstone belts (composed of mixed metavolcanic and metasedimentary sequences intruded by granitoid plutons) probably developed on or near these microcontinents. Paleomagnetic data with good age control from at least one ancient craton suggest that plate motion was at normal minimum average velocities of about 17 millimeters per year with respect to the poles during the period 3.5 billion to 2.4 billion years ago. If this is true on a global scale, Archean plate motion was not faster than in later geologic times.
Defensive Behaviors in Infant Rhesus Monkeys: Environmental Cues and Neurochemical Regulation
Authors: Kalin Ned H. , Shelton Steven E.
Published: October 2006

To survive, primates must detect danger in time to activate appropriate defensive behaviors. In this study, the defensive behaviors of infant rhesus monkeys exposed to humans were characterized. It was observed that the direction of the human's gaze is a potent cue for the infant. Infants separated from their mothers were active and emitted frequent distress vocalizations. When a human entered the room but did not look at the infant, it became silent and froze in one position. If the human stared at the infant, it responded with aggressive barking. Alterations of the opiate system affected the frequency of the infant's distress calls without affecting barking and freezing, whereas benzodiazepine administration selectively reduced barking and freezing. This suggests that opiate and benzodiazepine systems regulate specific defensive behaviors in primates and that these systems work together to mediate behavioral responses important for survival.
Physicists Rock the Standard Model in Dallas
Authors: Flam Faye
Published: October 2006

The 1400 physicists who converged on Dallas 2 weeks ago for the International High Energy Physics meeting came from all over. Ask them about the state of their field, however, and you'll find a common dream—to go beyond the standard model of particles and forces. For physicists "searching for chinks in the model's armor," as several put it, the elusive, unobtrusive neutrino is a promising object of study. And while the meeting saw the possibility of a superheavy "17-keV" neutrino fade, cosmic ray-produced neutrinos gave new hints of physics in that over-the-rainbow region beyond the standard model.
Microtektites and Mass Extinctions: Evidence for a Late Devonian Asteroid Impact
Authors: Claeys Philippe , Casier Jean-Georges , Margolis Stanley V.
Published: October 2006

Glass spherules, similar to microtektites, have been found near the Frasnian-Famennian boundary (F/F) (Upper Devonian) at Senzeilles, Belgium, contemporaneous with one of the largest marine mass extinctions of the Phanerozoic. These spherules exhibit a wide range of compositions and display teardrop, dumbbell, and compound morphologies analogous to microtektites. In addition, they lack crystallites, have few or no vesicles, and have a low content of volatile material. These characteristics are supportive of an impact origin. The Siljan Ring (Sweden) and Charlevoix structure (Quebec, Canada) are candidate craters of this age. The presence of microtektites near the F/F boundary supports the hypothesis that an impact caused the Upper Devonian worldwide benthic mass extinctions.
Mechanisms of Porphyroblast Crystallization: Results from High-Resolution Computed X-ray Tomography
Authors: Carlson William D. , Denison Cambria
Published: October 2006

Quantitative three-dimensional analysis of rock textures is now possible with the use of high-resolution computed x-ray tomography. When applied to metamorphic rocks, this technique provides data on the sizes and positions of minerals that allow mechanisms of porphyroblast crystallization to be identified. Statistical analysis of the sizes and spatial disposition of thousands of garnet crystals in three regionally metamorphosed rocks with diverse mineralogies, in conjunction with simple numerical models for crystallization, reveals in all cases the dominance of crystallization mechanisms whose kinetics are governed by rates of intergranular diffusion of nutrients.
Ulysses at Jupiter: An Overview of the Encounter
Authors: Smith E. J. , Wenzel K. -P. , Page D. E.
Published: October 2006

In February 1992, the Ulysses spacecraft flew through the giant magnetosphere of Jupiter. The primary objective of the encounter was to use the gravity field of Jupiter to redirect the spacecraft to the sun's polar regions, which will now be traversed in 1994 and 1995. However, the Ulysses scientific investigations were well suited to observations of the Jovian magnetosphere, and the encounter has resulted in a major contribution to our understanding of this complex and dynamic plasma environment. Among the more exciting results are (i) possible entry into the polar cap, (ii) the identification of magnetospheric ions originating from Jupiter's ionosphere, Io, and the solar wind, (iii) observation of longitudinal asymmetries in density and discrete wave-emitting regions of the Io plasma torus, (iv) the presence of counter-streaming ions and electrons, field-aligned currents, and energetic electron and radio bursts in the dusk sector on high-latitude magnetic field lines, and (v) the identification of the direction of the magnetic field in the dusk sector, which is indicative of tailward convection. This overview serves as an introduction to the accompanying reports that present the preliminary scientific findings. Aspects of the encounter that are common to all of the investigations, such as spacecraft capabilities, the flight path past Jupiter, and unique aspects of the encounter, are presented herein.
Comet Yanaka (1988r): A New Class of Carbon-Poor Comet
Authors: Fink Uwe
Published: October 2006

As part of a program to determine the chemical composition of a sample population of comets, a very unusual comet, Yanaka (1988r), was observed in January 1989. Although the comet showed the usual emissions of OI and NH
2
, it did not display any hint of C
2
or CN emission. The comet is depleted in C
2
by at least a factor of 100 and in CN by a factor of 25 relative to typical comets. If comets originate from interstellar clouds, Yanaka (1988r) could be an interloper from a cloud of different composition. If Yanaka (1988r) was formed within our solar system, the solar nebula was less uniform than assumed by most present models of formation.
Fluorogenic Substrate Detection of Viable Intracellular and Extracellular Pathogenic Protozoa
Authors: Jackson Peter R. , Pappas Michael G. , Hansen Brian D.
Published: October 2006

Viable
Leishmania
promastigotes and amastigotes were detected by epifluorescence microscopy with fluorescein diacetate being used to mark living parasites and the nucleic acid-binding compound ethidium bromide to stain dead cells. This procedure is superior to other assays because it is faster and detects viable intracellular as well as extracellular
Leishmania
. Furthermore, destruction of intracellular pathogens by macrophages is more accurately determined with fluorescein diacetate than with other stains. The procedure may have applications in programs to develop drugs and vaccines against protozoa responsible for human and animal disease.
Time and Metamorphic Petrology: Calcite to Aragonite Experiments
Authors: Hacker B. R. , Kirby S. H. , Bohlen S. R.
Published: October 2006

Although the equilibrium phase relations of many mineral systems are generally well established, the rates of transformations, particularly in polycrystalline rocks, are not. The results of experiments on the calcite to aragonite transformation in polycrystalline marble are different from those for earlier experiments on powdered and single-crystal calcite. The transformation in the polycrystalline samples occurs by different mechanisms, with a different temperature dependence, and at a markedly slower rate. This work demonstrates the importance of kinetic studies on fully dense polycrystalline aggregates for understanding mineralogic phase changes in nature. Extrapolation of these results to geological time scales suggests that transformation of calcite to aragonite does not occur in the absence of volatiles at temperatures below 200°C. Kinetic hindrance is likely to extend to higher temperatures in more complex transformations.
Biological Weighting Function for the Inhibition of Phytoplankton Photosynthesis by Ultraviolet Radiation
Authors: Cullen John J. , Neale Patrick J. , Lesser Michael P.
Published: October 2006

Severe reduction of stratospheric ozone over Antarctica has focused increasing concern on the biological effects of ultraviolet-B (UVB) radiation (280 to 320 nanometers). Measurements of photosynthesis from an experimental system, in which phytoplankton are exposed to a broad range of irradiance treatments, are fit to an analytical model to provide the spectral biological weighting function that can be used to predict the short-term effects of ozone depletion on aquatic photosynthesis. Results show that UVA (320 to 400 nanometers) significantly inhibits the photosynthesis of a marine diatom and a dinoflagellate, and that the effects of UVB are even more severe. Application of the model suggests that the Antarctic ozone hole might reduce near-surface photosynthesis by 12 to 15 percent, but less so at depth. The experimental system makes possible routine estimation of spectral weightings for natural phytoplankton.
Direct Observation of ClO from Chlorine Nitrate Photolysis
Authors: Minton Timothy K. , Nelson Christine M. , Moore Teresa A. , Okumura Mitchio
Published: October 2006

Chlorine nitrate photolysis has been investigated with the use of a molecular beam technique. Excitation at both 248 and 193 nanometers led to photodissociation by two pathways, ClONO
2
→ ClO + NO
2
and ClONO
2
→ Cl + NO
3
, with comparable yields. This experiment provides a direct measurement of the ClO product channel and consequently raises the possibility of an analogous channel in ClO dimer photolysis. Photodissociation of the ClO dimer is a critical step in the catalytic cycle that is presumed to dominate polar stratospheric ozone destruction. A substantial yield of ClO would reduce the efficiency of this cycle.
Brain Dopamine and Serotonin Receptor Sites Revealed by Digital Subtraction Autoradiography
Authors: Altar C. Anthony , O'Neil Stephen , Walter Robert J. , Marshall John F.
Published: October 2006

Autoradiography combined with image analysis permitted quantitative visualization of dopamine (D
2
) and serotonin (S
2
) binding sites in rat brain. Forebrain sections were incubated with tritiated spiroperidol alone or with tritiated spiroperidol plus unlabeled compounds that saturated the D
2
or S
2
sites. By subtracting the digitized image of an autoradiograph derived from the latter sections from that of the former, the D
2
or S
2
sites were specifically revealed. The resulting quantitative images demonstrate the differing anatomical distributions of these sites. The D
2
site is largely restricted to the striatal complex (caudate-putamen, nucleus accumbens septi, and olfactory tubercle), whereas the S
2
site is enriched in layer 5 of motor cortex, the perirhinal and cingulate cortices, and the claustrum.
An Inducible Endothelial Cell Surface Glycoprotein Mediates Melanoma Adhesion
Authors: Rice G. Edgar , Bevilacqua Michael P.
Published: October 2006

Hematogenous metastasis requires the arrest and extravasation of blood-borne tumor cells, possibly involving direct adhesive interactions with vascular endothelium. Cytokine activation of cultured human endothelium increases adhesion of melanoma and carcinoma cell lines. An inducible 110-kD endothelial cell surface glycoprotein, designated INCAM-110, appears to mediate adhesion of melanoma cells. In addition, an inducible endothelial receptor for neutrophils, ELAM-1, supports the adhesion of a human colon carcinoma cell line. Thus, activation of vascular endothelium in vivo that results in increased expression of INCAM-110 and ELAM-1 may promote tumor cell adhesion and affect the incidence and distribution of metastases.
The Colonization of Beringia and the Peopling of the New World
Authors: Hoffecker John F. , Powers W. Roger , Goebel Ted
Published: October 2006

The colonization of Beringia appears closely linked to the arrival of the oldest firmly documented archeological tradition in mid-latitude North America (Paleoindian). The discovery of a Paleoindian complex in central Alaska, combined with the recent redating of the Bering Land Bridge and key archeological sites, suggests that Beringia was settled during the final Pleistocene interstadial (12,000 to 11,000 years before present). Its population expanded rapidly into other parts of the New World. Beringia probably was colonized in response to changes in climate and vegetation that occurred during this interstadial. Access to the Americas was controlled by Beringian environments and not by changing sea levels or continental ice masses.
Ancient and Modern, Rock and Fluid Meet in San Francisco
Authors: Kerr Richard A.
Published: October 2006

With 6000 attendees and 4700 presentations, the annual fall meeting of the American Geophysical Union (AGU) in San Francisco last month was the biggest yet. And that made room for even more diversity than usual. Only the AGU could accommodate news of asteroid impacts and extinctions one-third of a billion years ago and a progress report on the first direct measurements of centimeter-scale ocean mixing, an ongoing study in the Atlantic.
A 100-Year Average Recurrence Interval for the San Andreas Fault at Wrightwood, California
Authors: Fumal Thomas E. , Schwartz David P. , Pezzopane Silvio K. , Weldon Ray J.
Published: October 2006

Evidence for five large earthquakes during the past five centuries along the San Andreas fault zone 70 kilometers northeast of Los Angeles, California, indicates that the average recurrence interval and the temporal variability are significantly smaller than previously thought. Rapid sedimentation during the past 5000 years in a 150-meter-wide structural depression has produced a greater than 21-meter-thick sequence of debris flow and stream deposits interbedded with more than 50 datable peat layers. Fault scarps, colluvial wedges, fissure infills, upward termination of ruptures, and tilted and folded deposits above listric faults provide evidence for large earthquakes that occurred in A.D. 1857, 1812, and about 1700, 1610, and 1470.
Far-Ultraviolet Astronomy on the Astro-1 Space Shuttle Mission
Authors: Davidsen Arthur F.
Published: October 2006

The Astro-1 mission obtained observations related to a wide variety of current problems in astronomy during a 9-day flight of the space shuttle Columbia. Early results from one of the instruments, the Hopkins Ultraviolet Telescope, are reviewed here. Among these are new insights concerning the origin of the ultraviolet light from the old stellar population in elliptical galaxies, new evidence for a hot, gaseous corona surrounding the Milky Way, improved views of the physical conditions in active galactic nuclei, and a measurement of the ionization state of the local interstellar medium.
A 2000-Year Tree Ring Record of Annual Temperatures in the Sierra Nevada Mountains
Authors: Scuderi Louis A.
Published: October 2006

Tree ring data have been used to reconstruct the mean late-season (June through January) temperature at a timberline site in the Sierra Nevada, California, for each of the past 2000 years. Long-term trends in the temperature reconstruction are indicative of a 125-year periodicity that may be linked to solar activity as reflected in radiocarbon and auroral records. The results indicate that both the warm intervals during the Medieval Warm Epoch (∼A.D. 800 to 1200) and the cold intervals during the Little Ice Age (∼A.D. 1200 to 1900) are closely associated with the 125-year period. Significant changes in the phase of the 125-year temperature variation occur at the onset and termination of the most recent radiocarbon triplet and may indicate chaotic solar behavior.
Volatilization of High Molecular Weight DNA by Pulsed Laser Ablation of Frozen Aqueous Solutions
Authors: Nelson Randall W. , Rainbow Matthew J. , Lohr Dennis E. , Williams Peter
Published: October 2006

DNA has been volatilized by pulsed laser ablation of a thin film of a frozen aqueous DNA solution. The target film was irradiated in vacuum by a pulsed laser at power densities sufficient to ablate the ice matrix. The expanding ablated water vapor entrained embedded DNA molecules and expelled them into the gas phase. Ejection of DNA molecules as large as 410 kilodaltons was verified by collection of the ablation products and subsequent mass analysis by polyacrylamide gel electrophoresis with autoradiographic detection.
Chemists Gather in Denver to Get the Big Picture
Authors: Amato Ivan
Published: October 2006

The Rockies were hidden by clouds, but "Welcome ACS" signs were visible all over the Mile High City from 28 March to 2 April. No wonder the city's boosters were cheering: More than 10,000 scientists, purveyors of laboratory equipment, and other chemophiles had flooded into Denver to take in a vision of chemistry's intellectual scope that was wide enough to compensate for the missing scenic grandeur. In just a tiny sampling of the roughly 4800 presentations, chemistry appears in guises ranging from the most basic molecule making, through cleanup strategies for major environmental challenges, to forensic methods for unraveling a historical mystery.
Vapor-Condensation Generation and STM Analysis of Fullerene Tubes
Authors: Ge Maohui , Sattler Klaus
Published: October 2006

Fullerene tubular structures can be generated by vapor condensation of carbon on an atomically flat graphite surface. Scanning tunneling microscope (STM) images revealed the presence of tubes with extremely small diameters (from 10 to 70 angstroms), most of which are terminated by hemispherical caps. Atomic resolution images of such structures showed that the tubes have a helical graphitic nature. The formation of the tubes under the quasi-free conditions suggests that the growth to tubular rather than spherical configurations is preferred for "giant fullerenes."
Microfossils of the Early Archean Apex Chert: New Evidence of the Antiquity of Life
Authors: Schopf J. William
Published: October 2006

Eleven taxa (including eight heretofore undescribed species) of cellularly preserved filamentous microbes, among the oldest fossils known, have been discovered in a bedded chert unit of the Early Archean Apex Basalt of northwestern Western Australia. This prokaryotic assemblage establishes that trichomic cyanobacterium-like microorganisms were extant and morphologically diverse at least as early as ∼3465 million years ago and suggests that oxygen-producing photoautotrophy may have already evolved by this early stage in biotic history.
Pliocene Paleoclimate and East Antarctic Ice-Sheet History from Surficial Ash Deposits
Authors: Marchant David R. , Swisher Carl C. , Lux Daniel R. , West David P. , Denton George H.
Published: October 2006

The preservation, age, and stratigraphic relation of an in situ ashfall layer with an underlying desert pavement in Arena Valley, southern Victoria Land, indicate that a cold-desert climate has persisted in Arena Valley during the past 4.3 million years. These data indicate that the present East Antarctic Ice Sheet has endured for this time and that average temperatures during the Pliocene in Arena Valley were no greater than 3°C above present values. One implication is that the collapse of the East Antarctic Ice Sheet due to greenhouse warming is unlikely, even if global atmospheric temperatures rise to levels last experienced during mid-Pliocene times.
High-Resolution and Analytical Transmission Electron Microscopy of Mineral Disorder and Reactions
Authors: Veblen David R. , Banfield Jillian F. , Guthrie George D. , Heaney Peter J. , Ilton Eugene S. , Livi Kenneth J. T. , Smelik Eugene A.
Published: October 2006

Crystal defects and chemical reactions occurring at scales beyond the resolution of light microscopes have major effects on the chemical and physical properties of rocks and minerals. High-resolution imaging, diffraction, and chemical analysis in the transmission electron microscope have become important methods for exploring mineral defect structures and reaction mechanisms and for studying the distribution of phases resulting from reactions. These techniques have shown that structural disorder is common in some rock-forming minerals but rare in others. They have also established mechanisms by which many reactions occur at the atomic cluster scale. These data thus provide an atomistic basis for understanding the kinetics of geological reactions. Furthermore, apparent major-element, minor-element, and trace-element chemistry of minerals can be influenced by submicroscopic inclusions or intergrowths, which commonly form as products of solid-state reactions.
Recent Variability in the Southern Oscillation: Isotopic Results from a Tarawa Atoll Coral
Authors: Cole Julia E. , Fairbanks Richard G. , Shen Glen T.
Published: October 2006

In the western tropical Pacific, the interannual migration of the Indonesian Low convective system causes changes in rainfall that dominate the regional signature of the El Niño—Southern Oscillation (ENSO) system. A 96-year oxygen isotope record from a Tarawa Atoll coral (1°N, 172°E) reflects regional convective activity through rainfall-induced salinity changes. This monthly resolution record spans twice the length of the local climatological record and provides a history of ENSO variability comparable in quality with those derived from instrumental climate data. Comparison of this coral record with a historical chronology of EI Niño events indicates that climate anomalies in coastal South America are occasionally decoupled from Pacific-wide ENSO extremes. Spectral analysis suggests that the distribution of variance in this record has shifted among annual to interannual periods during the present century, concurrent with observed changes in the strength of the Southern Oscillation.
Spatiotemporal Patterns in the Energy Release of Great Earthquakes
Authors: Romanowicz Barbara
Published: October 2006

For the past 80 years, the energy released in great strike-slip and thrust earthquakes has occurred in alternating cycles of 20 to 30 years. This pattern suggests that a global transfer mechanism from poloidal to toroidal components of tectonic plate motions is operating on time scales of several decades. The increase in seismic activity in California in recent years may be related to an acceleration of global strike-slip moment release, as regions of shear deformation mature after being reached by stresses that have propagated away from regions of great subduction decoupling earthquakes in the 1960s.
Complex Patterns in a Simple System
Authors: Pearson John E.
Published: October 2006

Numerical simulations of a simple reaction-diffusion model reveal a surprising variety of irregular spatiotemporal patterns. These patterns arise in response to finite-amplitude perturbations. Some of them resemble the steady irregular patterns recently observed in thin gel reactor experiments. Others consist of spots that grow until they reach a critical size, at which time they divide in two. If in some region the spots become overcrowded, all of the spots in that region decay into the uniform background.
Small-Scale Convective Instability and Upper Mantle Viscosity Under California
Authors: Zandt George , Carrigan Charles R.
Published: October 2006

Thermal calculations and convection analysis, constrained by seismic tomography results, suggest that a small-scale convective instability developed in the upper 200 kilometers of the mantle under California after the upwelling and cooling of asthenosphere into the slab window associated with the formation of the San Andreas transform boundary. The upper bound for the upper mantle viscosity in the slab window, 5 × 10
19
pascal seconds, is similar to independent estimates for the asthenosphere beneath young oceanic and tectonically active continental regions. These model calculations suggest that many tectonically active continental regions characterized by low upper mantle seismic velocities may be affected by time-dependent small-scale convection that can generate localized areas of uplift and subsidence.
Molecular Dynamics of Adsorption and Segregation from an Alkane Mixture
Authors: Xia T. K. , Landman Uzi
Published: October 2006

Adsorption and segregation of
n
-hexadecane molecules from an equal by weight mixture of
n
-hexadecane and
n
-hexane to an Au(001) surface at 315 kelvin are studied with the use of molecular dynamics simulations. Preferential adsorption of
n
-hexadecane at the solid-to-liquid interface together with subsequent layer-by-layer growth of an ordered, wetting interface were observed. The long chains penetrate and adsorb at the interfacial layer by means of a sequential segmental mechanism involving end-segment anchoring and displacive desorption of preadsorbed
n
-hexane molecules.
Refuge Theory and Biological Control
Authors: Hawkins Bradford A. , Thomas Matthew B. , Hochberg Michael E.
Published: October 2006

An important question in ecology is the extent to which populations and communities are governed by general rules. Recent developments in population dynamics theory have shown that hosts' refuges from their insect parasitoids predict parasitoid community richness patterns. Here, the refuge theory is extended to biological control, in which parasitoids are imported for the control of insect pests. Theory predicts, and data confirm, that the success of biological control is inversely related to the proportion of insects protected from parasitoid attack. Refuges therefore provide a general mechanism for interpreting ecological patterns at both the community level (their species diversity) and population level (their dynamics).
Construction of Large DNA Segments in
Escherichia coli
Authors: O'Connor Michael , Peifer Mark , Bender Welcome
Published: October 2006

Recombinant DNA clones containing large pieces of DNA are useful in the study of large genetic units, but these are difficult to make in most bacterial cloning vectors. A strategy is described that uses general and site-specific recombination to construct large pieces of eukaryotic DNA from smaller cloned segments. The large clones are propagated on F factor-based plasmids in
Escherichia coli
. They can be easily modified to introduce mutations or rearrangements. These techniques were applied to the construction of large DNA segments from the bithorax complex of
Drosophila
.
Protection Against Streptococcal Pharyngeal Colonization with a Vaccinia: M Protein Recombinant
Authors: Fischetti Vincent A. , Hodges Walter M. , Hruby Dennis E.
Published: October 2006

Phagocytosis of group A streptococci requires type-specific antibodies directed against the variable determinants of the bacterial surface M protein molecule. As a step toward developing a broadly protective anti-streptococcal vaccine, a vaccinia virus (VV) recombinant was constructed that expresses the conserved region of the structural gene encoding the M6 molecule (VV:M6′). Mice immunized intranasally with the VV:M6′ virus showed markedly reduced pharyngeal colonization by streptococci after intranasal and oral challenge with these bacteria. M protein-specific serum immunoglobulin G was significantly elevated in vaccinated animals and absent in controls. A similar approach may prove useful for the identification of protective determinants present on other bacterial and viral pathogens.
Stabilization of Z DNA in Vivo by Localized Supercoiling
Authors: Rahmouni A. Rachid , Wells Robert D.
Published: October 2006

Biological processes such as transcription may generate domains of supercoiling on a circular DNA. The existence of these domains in
Escherichia coli
was investigated by the ability of different lengths of (CG) tracts, cloned upstream or downstream from the tetracycline resistance gene (
tet
) of pBR322, to adopt the Z structure in vivo. Segments as short as 12 base pairs adopt the Z form when cloned upstream from the
tet
gene (Eco RI site), whereas no Z DNA was detected when this sequence was cloned downstream (Sty I site), even with a 74-base pair (CG) tract that requires less supercoiling than shorter tracts for the B-Z transition. Hence the localized supercoil density in pBR322 can be as high as -0.038 and as low as -0.021 at different loci. These data demonstrate the existence of the Z structure for commonly found natural sequences and support the notion of domains of negative supercoiling in vivo.
Thymotaxin, a Chemotactic Protein, Is Identical to β
2
-Microglobulin
Authors: Dargemont Catherine , Dunon Dominique , Deugnier Marie-Ange , Denoyelle Monique , Girault Jeanne-Marie , Lederer Florence , Lê Kim Ho Diep , Godeau François , Thiery Jean Paul , Imhof Beat A.
Published: October 2006

Thymotaxin, an 11-kilodalton protein chemotactic for rat bone marrow hematopoietic precursors, was purified from media conditioned by a rat thymic epithelial cell line. The NH2-terminal sequence of thymotaxin was identical to that of rat β
2
-microglobulin (β2m). Antibodies to β2m removed thymotaxin activity from the fraction containing the 11-kilodalton protein. Chemotactic activity was observed with rat plasma β2m, human β2m, and mouse recombinant β2m, further supporting the identity of thymotaxin with β2m. The directional migration, as opposed to random movement, of the cells was also confirmed. The only rat bone marrow cells that migrated toward β2m were Thy1
+
immature lymphoid cells devoid of T cell, B cell, and myeloid cell differentiation markers.