bluuebunny/crossref_metadata_2025 huggingface dataset:
An Antimony Sulfide with a Two-Dimensional, Intersecting System of Channels
Authors: Parise John B.
Published: October 2006

A novel open antimony sulfide framework of composition [Sb
3
S
5
]
-
has been synthesized hydrothermally, in the presence of tetramethyl ammonium ions. Determination of the crystal structure demonstrates that the (Me
4
N)
+
molecules (Me, methyl) occlude a system of intersecting channels at 90° to one another. The three-dimensional framework is assembled from a new building unit, flat s-shaped buckled sheets of edge-linked 4-rings containing Sb
2
S
2
moieties. These are cross-linked in two directions to form the system of channels.
Atomic Force Microscopy of Atomic-Scale Ledges and Etch Pits Formed During Dissolution of Quartz
Authors: Gratz A. J. , Manne S. , Hansma P. K.
Published: October 2006

The processes involved in the dissolution and growth of crystals are closely related. Atomic force microscopy (AFM) of faceted pits (called negative crystals) formed during quartz dissolution reveals subtle details of these underlying physical mechanisms for silicates. In imaging these surfaces, the AFM detected ledges <1 nanometer (nm) high that were spaced 10 to 90 nm apart. A dislocation pit, invisible to optical and scanning electron microscopy measurements and serving as a ledge source, was also imaged. These observations confirm the applicability of ledge-motion models to dissolution and growth of silicates; coupled with measurements of dissolution rate on facets, these methods provide a powerful tool for probing mineral surface kinetics.
A Molecular Genetic Classification of Zooxanthellae and the Evolution of Animal-Algal Symbioses
Authors: Rowan Rob , Powers Dennis A.
Published: October 2006

Zooxanthellae are unicellular algae that occur as endosymbionts in many hundreds of marine invertebrate species. Because zooxanthellae have traditionally been difficult to classify, little is known about the natural history of these symbioses. Zooxanthellae were isolated from 131 individuals in 22 host taxa and characterized by the use of restriction fragment length polymorphisms (RFLPs) in nuclear genes that encode small ribosomal subunit RNA (ssRNA). Six algal RFLPs, distributed host species specifically, were detected. Individual hosts contained one algal RFLP. Zooxanthella phylogenetic relationships were estimated from 22 algal ssRNA sequences—one from each host species. Closely related algae were found in dissimilar hosts, suggesting that animal and algal lineages have maintained a flexible evolutionary relation with each other.
Triton's Global Heat Budget
Authors: Brown R. H. , Johnson T. V. , Goguen J. D. , Schubert G. , Ross M. N.
Published: October 2006

Internal heat flow from radioactive decay in Triton's interior along with absorbed thermal energy from Neptune total 5 to 20 percent of the insolation absorbed by Triton, thus comprising a significant fraction of Triton's surface energy balance. These additional energy inputs can raise Triton's surface temperature between ∼0.5 and 1.5 K above that possible with absorbed sunlight alone, resulting in an increase of about a factor of ∼1.5 to 2.5 in Triton's basal atmospheric pressure. If Triton's internal heat flow is concentrated in some areas, as is likely, local effects such as enhanced sublimation with subsequent modification of albedo could be quite large. Furthermore, indications of recent global albedo change on Triton suggest that Triton's surface temperature and pressure may not now be in steady state, further suggesting that atmospheric pressure on Triton was as much as ten times higher in the recent past.
Breaking the Diffraction Barrier: Optical Microscopy on a Nanometric Scale
Authors: Betzig E. , Trautman J. K. , Harris T. D. , Weiner J. S. , Kostelak R. L.
Published: October 2006

In near-field scanning optical microscopy, a light source or detector with dimensions less than the wavelength (λ) is placed in close proximity (<λ/50) to a sample to generate images with resolution better than the diffraction limit. A near-field probe has been developed that yields a resolution of ∼12 nm (∼λ/43) and signals ∼10
4
- to 10
6
-fold larger than those reported previously. In addition, image contrast is demonstrated to be highly polarization dependent. With these probes, near-field microscopy appears poised to fulfill its promise by combining the power of optical characterization methods with nanometric spatial resolution.
Protein Crystal Growth in Microgravity
Authors: DeLucas Lawrence J. , Smith Craig D. , Smith H. Wilson , Vijay-Kumar Senadhi , Senadhi Shobha E. , Ealick Steven E. , Carter Daniel C. , Snyder Robert S. , Weber Patricia C. , Salemme F. Raymond , Ohlendorf D. H. , Einspahr H. M. , Clancy L. L. , Navia Manuel A. , McKeever Brian M. , Nagabhushan T. L. , Nelson George , McPherson A. , Koszelak S. , Taylor G. , Stammers D. , Powell K. , Darby G. , Bugg Charles E.
Published: October 2006

The crystals of most proteins or other biological macromolecules are poorly ordered and diffract to lower resolutions than those observed for most crystals of simple organic and inorganic compounds. Crystallization in the microgravity environment of space may improve crystal quality by eliminating convection effects near growing crystal surfaces. A series of 11 different protein crystal growth experiments was performed on U.S. space shuttle flight STS-26 in September 1988. The microgravity-grown crystals of γ-interferon D
1
, porcine elastase, and isocitrate lyase are larger, display more uniform morphologies, and yield diffraction data to significantly higher resolutions than the best crystals of these proteins grown on Earth.
Requirement of GTP Hydrolysis for Dissociation of the Signal Recognition Particle from Its Receptor
Authors: Connolly Timothy , Rapiejko Peter J. , Gilmore Reid
Published: October 2006

The signal recognition particle (SRP) directs signal sequence specific targeting of ribosomes to the rough endoplasmic reticulum. Displacement of the SRP from the signal sequence of a nascent polypeptide is a guanosine triphosphate (GTP)-dependent reaction mediated by the membrane-bound SRP receptor. A nonhydrolyzable GTP analog can replace GTP in the signal sequence displacement reaction, but the SRP then fails to dissociate from the membrane. Complexes of the SRP with its receptor containing the nonhydrolyzable analog are incompetent for subsequent rounds of protein translocation. Thus, vectorial targeting of ribosomes to the endoplasmic reticulum is controlled by a GTP hydrolysis cycle that regulates the affinity between the SRP, signal sequences, and the SRP receptor.
Effect of Wnt-1 and Related Proteins on Gap Junctional Communication in
Xenopus
Embryos
Authors: Olson Daniel J. , Christian Jan L. , Moon Randall T.
Published: October 2006

The proto-oncogene
wnt
-1 (previously referred to as
int
-1) is thought to be important in embryonic pattern formation although its mechanisms of action are unknown. Premature and increased expression of the Wnt-1 protein, achieved by injection of synthetic
wnt
-1 RNA into fertilized
Xenopus
eggs, enhanced gap junctional communication between ventral cells of the developing embryo. This result is consistent with the hypothesis that Wnt proteins activate a receptor-mediated signal transduction pathway and that gap junctional communication can be a target of this pathway. The effects of two Wnt-1-related proteins on gap junctional communication were also investigated: overexpression of Xwnt-8 increased gap junctional coupling in a manner similar to Wnt-1, whereas Xwnt-5A did not. These findings are consistent with the existence of multiple receptors for Wnt proteins.
ROSAT Detection of an X-ray Shadow in the 1/4-keV Diffuse Background in the Draco Nebula
Authors: Snowden S. L. , Mebold U. , Hirth W. , Herbstmeier U. , Schmitt J. H. M. M.
Published: October 2006

The detection by the Roentgen satellite (ROSAT) x-ray telescope of a shadow in the 1/4—kiloelectron volt (C band, 0.1 to 0.284 kiloelectron volt) cosmic diffuse background is reported. The location and morphology of the local minimum in x-rays are in clear agreement with a discrete H I cloud. The shadow is very deep with a minimum level at 50 percent of the surrounding emission; therefore, a minimum of 50 percent of the observed off-cloud flux must originate on the far side of the cloud. The analysis of H I velocity components links the cloud with the Draco nebula (distance ∼600 parsecs); it then follows that there is significant 1/4—kiloelectron volt x-ray emission at a large distance (>400 parsecs) from the galactic plane along this line of sight. The extent of the distant emission region is uncertain, and, if it indicates the existence of a hot galactic corona, it must be patchy in nature.
Localization and Its Absence: A New Metallic State for Conducting Polymers
Authors: Phillips Philip , Wu Hong-Lu
Published: October 2006

A widely held view in solid-state physics is that disorder precludes the presence of long-range transport in one dimension. A series of models has been recently proposed that do not conform to this view. The primary model is the random dimer model, in which the site energies for pairs of lattice sites along a linear chain are assigned one of two values at random. This model has a set of conducting states that ultimately allow an initially localized particle to move through the lattice almost ballistically. This model is applicable to the insulator-metal transition in a wide class of conducting polymers, such as polyaniline and heavily doped polyacetylene. Calculations performed on polyaniline demonstrate explicitly that the conducting states of the random dimer model for polyaniline are coincident with recent calculations of the location of the Fermi level in the metallic regime. A random dimer analysis on polyparaphenylene also indicates the presence of a set of conducting states in the vicinity of the band edge. The implications of this model for the metallic state in other polymers, including heavily doped polyacetylene, are discussed.
Atomic Force Microscope Studies of Fullerene Films: Highly Stable C
60
fcc (311) Free Surfaces
Authors: Snyder Eric J. , Anderson Mark S. , Tong William M. , Williams R. Stanley , Anz Samir J. , Alvarez Marcos M. , Rubin Yves , Diederich François N. , Whetten Robert L.
Published: October 2006

Atomic force microscopy and x-ray diffractometry were used to study 1500 Å-thick films of pure C
60
grown by sublimation in ultrahigh vacuum onto a CaF
2
(111) substrate. Topographs of the films did not reveal the expected close-packed structures, but they showed instead large regions that correspond to a face-centered cubic (311) surface and distortions of this surface. The open (311) structure may have a relatively low free energy because the low packing density contributes to a high entropy of the exposed surface.
Conversion of Ectoderm to Mesoderm by Cytoplasmic Extrusion in Leech Embryos
Authors: Nelson Brad H. , Weisblat David A.
Published: October 2006

The role of cytoplasmic domains in the determination of the fates of ectodermal and mesodermal cells has been investigated in leech embryos. When yolk-deficient cytoplasm (teloplasm) was extruded from the animal pole of the zygote, the ectodermal precursor blastomere was converted to a mesodermal fate. This change of fate can be prevented by replacement of the extruded animal teloplasm with teloplasm from the vegetal pole. The fate of the mesodermal precursor blastomere was unaffected by teloplasm extrusion or rearrangement. These results demonstrate that ectodermal and mesodermal determination of fate involves a binary decision dependent on the position of teloplasm along the animal-vegetal axis.
Ballistic 2-D Imaging Through Scattering Walls Using an Ultrafast Optical Kerr Gate
Authors: Wang L. , Ho P. P. , Liu C. , Zhang G. , Alfano R. R.
Published: October 2006

An ultrafast optical shutter was used to image ultrasmall objects hidden behind scattering walls by a procedure that selects in time the ballistic component and rejects the scattered diffusive light. Scattering walls used in this experiment included human breast tissue, chicken breast tissue, and a water suspension of polystyrene particles with scattering coefficients up to 21.7. Submillimeter resolution was achieved for two-dimensional ballistic images of a single point, a double-point fluorescence source, and a bar test chart in or behind these different turbid media.
New Approaches to Robotics
Authors: Brooks Rodney A.
Published: October 2006

In order to build autonomous robots that can carry out useful work in unstructured environments new approaches have been developed to building intelligent systems. The relationship to traditional academic robotics and traditional artificial intelligence is examined. In the new approaches a tight coupling of sensing to action produces architectures for intelligence that are networks of simple computational elements which are quite broad, but not very deep. Recent work within this approach has demonstrated the use of representations, expectations, plans, goals, and learning, but without resorting to the traditional uses of central, abstractly manipulable or symbolic representations. Perception within these systems is often an active process, and the dynamics of the interactions with the world are extremely important. The question of how to evaluate and compare the new to traditional work still provokes vigorous discussion.
Gas-Phase Inorganic Chemistry: Monovalent Derivatives of Calcium and Strontium
Authors: Bernath Peter F.
Published: October 2006

The chemistry and spectroscopy of monovalent derivatives of calcium and strontium are described. Laser-driven chemical reactions of calcium and strontium vapors with a variety of small molecules have provided many new free radicals. In general, these species are analogous to the stable molecules obtained in traditional inorganic or organometallic chemistry, but some new families of molecules have been discovered.
Potential Magnitude of Future Vegetation Change in Eastern North America: Comparisons with the Past
Authors: Overpeck Jonathan T. , Bartlein Patrick J. , Webb Thompson
Published: October 2006

Increases in atmospheric trace gas concentrations could warm the global average temperature 1.5° to 4.5°C by the end of the next century. Application of climate-pollen response surfaces to three climate model simulations of doubled preindustrial atmospheric CO
2
levels shows that the change in the equilibrium distribution of natural vegetation over eastern North America over the next 200 to 500 years could be larger than the overall change during the past 7,000 to 10,000 years and equivalent to the change that took place over the 1,000- to 3,000-year period of most rapid deglaciation. Some plant ranges and abundance maxima could shift as much as 500 to 1000 km during the next 200 to 500 years; such changes would have dramatic impacts on silvicultural and natural ecosystems. Although unprecedented vegetation change is likely if climate changes as predicted, forecasting the exact timing and patterns of change will be difficult.
Radical Reactions of C
60
Authors: Krusic P. J. , Wasserman E. , Keizer P. N. , Morton J. R. , Preston K. F.
Published: October 2006

Photochemically generated benzyl radicals react with C
60
producing radical and nonradical adducts R

n

C
60
(R = C
6
H
5
CH
2
) with
n
= 1 to at least 15. The radical adducts with
n
= 3 and 5 are stable above 50°C and have been identified by electron spin resonance (ESR) spectroscopy as the allylic R
3
C
60
.
(3) and cyclopentadienyl R
5
C
60
.
(5) radicals. The unpaired electrons are highly localized on the C
60
surface. The extraordinary stability of these radicals can be attributed to the steric protection of the surface radical sites by the surrounding benzyl substituents. Photochemically generated methyl radicals also add readily to C
60
. Mass spectrometric analyses show the formation of (CH
3
)

n

C
60
with
n
= 1 to at least 34.
Age of Canada Basin Deep Waters: A Way to Estimate Primary Production for the Arctic Ocean
Authors: Macdonald R. W. , Carmack E. C.
Published: October 2006

An empirical model of carbon flux and
14
C-derived ages of the water in the Canada Basin of the Arctic Ocean as a function of depth was used to estimate the long-term rate of primary production within this region. An estimate can be made because the deep waters of the Canadian Basin are isolated from the world oceans by the Lomonosov Ridge (sill depth about 1500 meters). Below the sill, the age of the water correlates with increased nutrients and oxygen utilization and thus provides a way to model the average flux of organic material into the deep basin over a long time period. The
14
C ages of the deep water in the Canada Basin were about 1000 years, the carbon flux across the 1500-meter isobath was 0.3 gram of carbon per square meter per year, and the total production was 9 to 14 grams of carbon per square meter per year. Such estimates provide a baseline for understanding the role of the Arctic Ocean in global carbon cycling.
Morphology and Local Structure in Labyrinthine Stripe Domain Phase
Authors: Seul M. , Monar L. R. , O'Gorman L. , Wolfe R.
Published: October 2006

Analysis of globally disordered, nonequilibrium "labyrinthine" stripe-domain patterns in thin ferrimagnetic garnet films has revealed a well-defined local structure containing an oblong polygonal plaquette as the fundamental motif. Two types of labyrinths were found: one having topological defects, the other composed of a single, unbranched, meandering line. These patterns emerge when the labyrinthine state is approached either by heating at constant magnetic field or by demagnetizing from saturation at constant temperature. Size and aspect ratios of the oblong polygonal plaquettes prove to be independent of the choice of these two mutually orthogonal trajectories within the phase diagram, which is surprising in view of the different mechanisms and concomitant topological constraints governing the evolution of disorder. The significance of this unique local structure is discussed in the general context of defect-mediated melting of two-dimensional stripe phases.
Oscillatory Kinetics and Spatio-Temporal Self-Organization in Reactions at Solid Surfaces
Authors: Ertl Gerhard
Published: October 2006

Chemical reactions far from equilibrium on solid surfaces may exhibit typical phenomena of nonlinear dynamics, as exemplified by the catalytic oxidation of carbon monoxide on a platinum(110) single-crystal surface. Depending on the external parameters (temperature and partial pressures of the reactants), the temporal variation of the reaction rate may become oscillatory or even chaotic. In a parallel way, the concentration distributions of the adsorbed species on the surface form spatio-temporal patterns including propagating and standing waves, rotating spirals, as well as irregular and rapidly changing structures denoted "chemical turbulence."
Involvement of a Leukocyte Adhesion Receptor (LFA-1) in HIV-Induced Syncytium Formation
Authors: Hildreth James E. K. , Orentas Rimas J.
Published: October 2006

Cell fusion (syncytium formation) is a major cytopathic effect of infection by human immunodeficiency virus (HIV) and may also represent an important mechanism of CD4
+
T-cell depletion in individuals infected with HIV. Syncytium formation requires the interaction of CD4 on the surface of uninfected cells with HIV envelope glycoprotein gp120 expressed on HIV-infected cells. However, several observations suggest that molecules other than CD4 play a role in HIV-induced cell fusion. The leukocyte adhesion receptor LFA-1 is involved in a broad range of leukocyte interactions mediated by diverse receptor-ligand systems including CD4-class II major histocompatibility complex (MHC) molecules. Possible mimicry of class II MHC molecules by gp120 in its interaction with CD4 prompted an examination of the role of LFA-1 in HIV-induced cell fusion. A monoclonal antibody against LFA-1 completely inhibited HIV-induced syncytium formation. The antibody did not block binding of gp120 to CD4. This demonstrates that a molecule other than CD4 is also involved in cell fusion mediated by HIV.
Two NF1 Translocations Map Within a 600-Kilobase Segment of 17q11.2
Authors: O'Connell Peter , Leach Robin , Cawthon Richard M. , Culver Melanie , Stevens Jeffrey , Viskochil David , Fournier R. E. Keith , Rich Donna C. , Ledbetter David H. , White Ray
Published: October 2006

Balanced translocations, each involving chromosome 17q11.2, have been described in two patients with von Recklinghausen neurofibromatosis (NF1). To better localize the end points of these translocation events, and the NF1 gene (
NF1
) itself, human cosmids were isolated and mapped in the immediate vicinity of
NF1
. One cosmid probe, c11-1F10, demonstrated that both translocation breakpoints, and presumably
NF1
, are contained within a 600-kilobase Nru I fragment.
Monitoring the AIDS Epidemic in the United States: A Network Approach
Authors: Laumann E. O. , Gagnon J. H. , Michaels S. , Michael R. T. , Coleman J. S.
Published: October 2006

Respondents in the 1988 General Social Survey (GSS) were asked to scan their acquaintance networks to identify all those who had been a victim of a homicide or had acquired immunodeficiency syndrome (AIDS). Estimates of the sex, race, age, and regional breakdowns for homicides in the last year and for people with AIDS were compared with official statistics. The GSS estimates for the distribution of homicide victims replicate the official statistics quite well. The GSS estimates for AIDS cases suggest that the data provided to the Centers for Disease Control may underestimate by a substantial margin the prevalence of AIDS in the white population of higher socioeconomic status, overstate the relative prevalence of the disease in the minority populations, underestimate the prevalence of the disease in the Midwest, and overstate it for the East.
Channel Initiation and the Problem of Landscape Scale
Authors: Montgomery David R. , Dietrich William E.
Published: October 2006

Since the 1940s it has been proposed that landscape dissection into distinct valleys is limited by a threshold of channelization that sets a finite scale to the landscape. This threshold is equal to the hillslope length that is just shorter than that necessary to support a channel head. A field study supports this hypothesis by showing that an empirically defined topographic threshold associated with channel head locations also defines the border between essentially smooth, undissected hillslopes and the valley bottoms to which they drain. This finding contradicts assertions that landscapes are scale-independent and suggests that landscape response to changes in climate or land use depends on the corresponding changes in the threshold of channelization.
Dissociation of Individual Molecules with Electrons from the Tip of a Scanning Tunneling Microscope
Authors: Dujardin G. , Walkup R. E. , Avouris PH.
Published: October 2006

The scanning tunneling microscope (STM) can be used to select a particular adsorbed molecule, probe its electronic structure, dissociate the molecule by using electrons from the STM tip, and then examine the dissociation products. These capabilities are demonstrated for decaborane(14) (B
10
H
14
) molecules adsorbed on a silicon(111)-(7 × 7) surface. In addition to basic studies, such selective dissociation processes can be used in a variety of applications to control surface chemistry on the molecular scale.
The Hubble Constant
Authors: Huchra John P.
Published: October 2006

The Hubble constant is the constant of proportionality between recession velocity and distance in the expanding universe. It is a fundamental property of cosmology that sets both the scale and the expansion age of the universe. It is determined by measurement of galaxy radial velocities and distances. Although there has been considerable progress in the development of new techniques for the measurements of galaxy distances, both calibration uncertainties and debates over systematic errors remain. Current determinations still range over nearly a factor of 2; the higher values favored by most local measurements are not consistent with many theories of the origin of large-scale structure and stellar evolution.
Polyhydroxybutyrate, a Biodegradable Thermoplastic, Produced in Transgenic Plants
Authors: Poirier Yves , Dennis Douglas E. , Klomparens Karen , Somerville Chris
Published: October 2006

Polyhydroxybutyrate (PHB), a high molecular weight polyester, is accumulated as a storage carbon in many species of bacteria and is a biodegradable thermoplastic. To produce PHB by genetic engineering in plants, genes from the bacterium
Alcaligenes eutrophus
that encoded the two enzymes required to convert acetoacetyl—coenzyme A to PHB were placed under transcriptional control of the cauliflower mosaic virus 35S promoter and introduced into
Arabidopsis thaliana
. Transgenic plant lines that contained both genes accumulated PHB as electron-lucent granules in the cytoplasm, nucleus, and vacuole; the size and appearance of these granules were similar to the PHB granules that accumulate in bacteria.
Identification of the Ah Receptor Nuclear Translocator Protein (Arnt) as a Component of the DNA Binding Form of the Ah Receptor
Authors: Reyes Herminio , Reisz-Porszasz Suzanne , Hankinson Oliver
Published: October 2006

The Ah (dioxin) receptor binds a number of widely disseminated environmental pollutants, including 2,3,7,8-tetrachlorodibenzo-
p
-dioxin (TCDD) and polycyclic aromatic hydrocarbons, and mediates their carcinogenic effects. The ligand-bound receptor activates
Cyp1a1
gene transcription through interaction with specific DNA sequences, termed xenobiotic responsive elements (XREs). The Ah receptor nuclear translocator protein (Arnt) is required for Ah receptor function. Arnt is now shown to be a structural component of the XRE binding form of the Ah receptor. Furthermore, Arnt and the ligand-binding subunit of the receptor were extracted as a complex from the nuclei of cells treated with ligand. Arnt contains a basic helix-loop-helix motif, which may be responsible for interacting with both the XRE and the ligand-binding subunit.
Rational Design of Potent Antagonists to the Human Growth Hormone Receptor
Authors: Fuh Germaine , Cunningham Brian C. , Fukunaga Rikiro , Nagata Shigekazu , Goeddel David V. , Wells James A.
Published: October 2006

A hybrid receptor was constructed that contained the extracellular binding domain of the human growth hormone (hGH) receptor linked to the transmembrane and intracellular domains of the murine granulocyte colony-stimulating factor receptor. Addition of hGH to a myeloid leukemia cell line (FDC-P1) that expressed the hybrid receptor caused proliferation of these cells. The mechanism for signal transduction of the hybrid receptor required dimerization because monoclonal antibodies to the hGH receptor were agonists whereas their monovalent fragments were not. Receptor dimerization occurs sequentially—a receptor binds to site 1 on hGH, and then a second receptor molecule binds to site 2 on hGH. On the basis of this sequential mechanism, which may occur in many other cytokine receptors, inactive hGH analogs were designed that were potent antagonists to hGH-induced cell proliferation. Such antagonists could be useful for treating clinical conditions of hGH excess, such as acromegaly.
Direct Electrochemical Measurements Inside a 2000 Angstrom Thick Polymer Film by Scanning Electrochemical Microscopy
Authors: Mirkin Michael V. , Fan Fu-Ren F. , Bard Allen J.
Published: October 2006

An extremely small, conically shaped Pt microelectrode tip (with a radius of 30 nanometers) and the precise positioning capabilities of the scanning electrochemical microscope were used to penetrate a thin (200 nanometers) polymer film and obtain directly the standard potential and kinetic parameters of an electrode reaction within the film. The thickness of the film was determined while it was immersed in and swollen by an electrolyte solution. The film studied was the perfluorosulfonate Nafion containing Os(bpy)
3
2+
(bpy, 2,2′-bipyridine) cast on an indium tin oxide surface. The steady-state response at the ultramicroelectrode allowed direct determination of the rate constant for heterogeneous electron transfer
k
° and the diffusion coefficient
D
without complications caused by transport in the liquid phase, charge exchange at the liquid-polymer interface, and resistive drop.
The Origin of Plagues: Old and New
Authors: Krause Richard M.
Published: October 2006

Viruses and bacteria emerge in new and old forms to cause disease epidemics. Some microorganisms recur when changing life-styles (including increased international travel) offer new opportunities; others arise from new genetic variations. These various epidemics connect the future with the past, offering lessons for guarding the health of generations to come—lessons learned from diseases such as tuberculosis, toxic shock syndrome, Lyme disease, streptococcal infection, influenza, and acquired immunodeficiency syndrome (AIDS). The public must be vigilant to the possibility of new epidemics, learn more about the biology and epidemiology of microbes, and strengthen systems of surveillance and detection.
Detection of Hydrothermal Precursors to Large Northern California Earthquakes
Authors: Silver Paul G. , Valette-Silver Nathalie J.
Published: October 2006

During the period 1973 to 1991 the interval between eruptions from a periodic geyser in Northern California exhibited precursory variations 1 to 3 days before the three largest earthquakes within a 250-kilometer radius of the geyser. These include the magnitude 7.1 Loma Prieta earthquake of 18 October 1989 for which a similar preseismic signal was recorded by a strainmeter located halfway between the geyser and the earthquake. These data show that at least some earthquakes possess observable precursors, one of the prerequisites for successful earthquake prediction. All three earthquakes were further than 130 kilometers from the geyser, suggesting that precursors might be more easily found around rather than within the ultimate rupture zone of large California earthquakes.
Polymerization-Induced Epitaxy: Scanning Tunneling Microscopy of a Hydrogen-Bonded Sheet of Polyamide on Graphite
Authors: Sano Masahito , Sasaki Darryl Y. , Kunitake Toyoki
Published: October 2006

A molecularly thin film of a two-dimensional polymer network formed by hydrogen bonding was synthesized and investigated with scanning tunneling microscopy. Poly(ε-caprolactam) (nylon 6) was epitaxially grown on the basal plane of graphite and an ultrathin film of the polymer was obtained after the bulk materials had been washed away with solvents. The polymer chain has a planar, all-
trans
conformation and adjacent chains run in the antiparallel direction. This produces complete pairing of hydrogen bonding groups, with each amide group lying on a straight line perpendicular to the polymer backbone. This hydrogen-bonded sheet is oriented so that each polymer backbone lies in the (101̅0) direction on the graphite hexagonal lattice, as opposed to the (112̅0) direction taken by other paraffinic molecules studied so far. This experiment shows that hydrogen bonding can be used to control the orientation of macromolecules in two dimensions.
An Accurate Quantum Monte Carlo Calculation of the Barrier Height for the Reaction H + H
2
→ H
2
+ H
Authors: Diedrich Drake L. , Anderson James B.
Published: October 2006

An improved quantum Monte Carlo method has been used to calculate the classical barrier height for the hydrogen exchange reaction H + H
2
→ H
2
+ H with accuracies greater than previously attained. The method is exact in that, except for the easily estimated Monte Carlo statistical or sampling error, it requires no mathematical approximations or physical approximations beyond those of the Schrödinger equation. The minimum in the barrier, occurring for the collinear nuclear configuration with the protons separated by 1.757 bohrs, was found to be 9.61 ± 0.01 kilocalories per mole above H + H
2
.
Silicon Isotopic Composition in Large Meteoritic SiC Particles and
22
Na Origin of
22
Ne
Authors: Brown Lawrence E. , Clayton Donald D.
Published: October 2006

Large silicon carbide (SiC) particles extracted from acid-insoluble residues of carbonaceous chondrites are isotopically anomalous in both silicon and carbon and contain isotopically extreme noble gases. These particles are thought to have originated in mass outflows from red giant stars and to have existed in the interstellar medium at the time the solar system formed from an interstellar cloud. Calculations show that the silicon isotope correlations in those large SiC particles can be generated only in the most massive carbon stars. Consequently, the almost pure neon-22 (
22
Ne) in those particles must be interpreted as the condensation of radioactive sodium-22 (
22
Na) in the particles as they flowed away from the stars. The
22
Na is produced through proton capture by
21
Ne at the base of the surface convection zone. Neon-22 does not exist abundantly in helium shells hot enough to burn magnesium, which is necessary to establish the measured silicon isotopic composition.
Observation of Metastable Structural Excitations and Concerted Atomic Motions on a Crystal Surface
Authors: Hwang Ing-Shouh , Golovchenko Jene
Published: October 2006

The addition of a small number of lead atoms to a germanium(111) surface reduces the energy barrier for activated processes, and with a tunneling microscope it is possible to observe concerted atomic motions and metastable structures on this surface near room temperature. The formation and annihilation of these metastable structural surface excitations is associated with the shift in position of large numbers of germanium surface atoms along a specific row direction like beads on an abacus. The effect provides a mechanism for understanding the transport of atoms on a semiconductor surface.
A High-Resolution Record of Holocene Climate Change in Speleothem Calcite from Cold Water Cave, Northeast Iowa
Authors: Dorale Jeffrey A. , González Luis A. , Reagan Mark K. , Pickett David A. , Murrell Michael T. , Baker Richard G.
Published: October 2006

High-precision uranium-thorium mass spectrometric chronology and
18
O-
13
C isotopic analysis of speleothem calcite from Cold Water Cave in northeast Iowa have been used to chart mid-Holocene climate change. Significant shifts in δ
18
O and δ
13
C isotopic values coincide with well-documented Holocene vegetation changes. Temperature estimates based on
18
O/
16
O ratios suggest that the climate warmed rapidly by about 3δC at 5900 years before present and then cooled by 4δC at 3600 years before present. Initiation of a gradual increase in δ
13
C at 5900 years before present suggests that turnover of the forest soil biomass was slow and that equilibrium with prairie vegetation was not attained by 3600 years before present.
A Vital Stain for the Golgi Apparatus
Authors: Lipsky Naomi Geller , Pagano Richard E.
Published: October 2006

The Golgi complex, a membranous organelle with important functions in membrane traffic and macromolecular synthesis, has been stained in living cells with a fluorescent sphingolipid. Cells were first incubated with liposomes containing
N
-[7-(4-nitrobenzo-2-oxa-1,3-diazole)]-6-aminocaproyl sphingosine (C
6
-NBD-ceramide), or with a bovine serum albumin complex of the fluorescent lipid, and then examined by fluorescence microscopy. An intensely fluorescent perinuclear structure was identified as the Golgi apparatus by its colocalization with known Golgi markers in fixed cells. C
6
-NBD-ceramide was used to observe the morphology of the Golgi apparatus in living cells in the presence or absence of monensin or Colcemid, and during mitosis. In all cases, C
6
-NBD-ceramide revealed a Golgi apparatus in the living cell that was identical to that obtained with conventional procedures that require fixation.
Stress Protection of Transgenic Tobacco by Production of the Osmolyte Mannitol
Authors: Tarczynski Mitchell C. , Jensen Richard G. , Bohnert Hans J.
Published: October 2006

The accumulation of sugar alcohols and other low molecular weight metabolites such as proline and glycine-betaine is a widespread response that may protect against environmental stress that occurs in a diverse range of organisms. Transgenic tobacco plants that synthesize and accumulate the sugar alcohol mannitol were engineered by introduction of a bacterial gene that encodes mannitol 1-phosphate dehydrogenase. Growth of plants from control and mannitol-containing lines in the absence and presence of added sodium chloride was analyzed. Plants containing mannitol had an increased ability to tolerate high salinity.
Dynamics of Elliptical Galaxies
Authors: Merritt David
Published: October 2006

Elliptical galaxies were once thought to be similar in their structure and dynamics to rotationally flattened bodies like stars. The discovery that elliptical galaxies rotate much more slowly than a fluid body with the same shape has led to a qualitative change in our understanding of the dynamics of these systems. It is now believed that elliptical galaxies are fully triaxial in shape. Self-consistent triaxial equilibria have been constructed and appear to be long-lived; they are made possible by the existence of conserved quantities, or integrals of motion, for galactic potentials without rotational symmetry. Many self-consistent equilibria are unstable; the nonexistence of elliptical galaxies with axis ratios more extreme than 3:1 is probably the result of such an instability. There is evidence for strong central mass concentrations, perhaps massive black holes, at the centers of some nearby galaxies. Recent observations suggest that many elliptical galaxies formed through the merger of two or more spiral galaxies.
A Model of Human Acute Lymphoblastic Leukemia in Immune-Deficient SCID Mice
Authors: Kamel-Reid Suzanne , Letarte Michelle , Sirard Christian , Doedens Monica , Grunberger Tom , Fulop Gabrielle , Freedman Melvin H. , Phillips Robert A. , Dick John E.
Published: October 2006

A human acute lymphoblastic leukemia (ALL) cell line that was transplanted into immune-deficient SCID mice proliferated in the hematopoietic tissues, invaded various organs, and led to the death of the mice. The distribution of leukemic cells in SCID mice was similar to the course of the disease in children. A-1 cells marked with a retrovirus vector showed clonal evolution after the transplant. SCID mice that were injected with bone marrow from three patients with non-T ALL had leukemic cells in their bone marrow and spleen. This in vivo model of human leukemia is an approach to understanding leukemic growth and progression and is a novel system for testing new treatment strategies.
Condensed Matter Physicists Shrink Their Horizons
Authors: Flam Faye
Published: October 2006

In the world of the condensed matter physicist, a micron is a chasm and a millimeter an ocean. At the March American Physical Society meeting in Seattle, some of the 4500 physicists probed the hazards of the micro world, where weird quantum effects can scramble information. Others outlined its opportunities: Molecular engineering that is leading to new information storage materials, and minute structures that could form tethers and containers in some future nanotechnology.
The Stalemate in Food and Agricultural Research, Teaching, and Extension
Authors: Meyer James H.
Published: October 2006

The development of leaders and colleges with the vision and ability to create an environment for both short- and long-term responses to societal concerns will be critical for the survival of these LGCAs. They will need help in escaping from old ideas, which means escaping from old organizations built on the past. A new sponsoring organization is needed to aid in this effort. With a new intellectual foundation, and the future firmly in mind, then and only then should a new national organization be instituted.
Large Odd-Numbered Carbon Clusters from Fullerene-Ozone Reactions
Authors: McElvany Stephen W. , Callahan John H. , Ross Mark M. , Lamb Lowell D. , Huffman Donald R.
Published: October 2006

The odd-numbered carbon clusters C
119
, C
129
, and C
139
have been observed in the mass spectra of toluene extracts of fullerene soots and of the products of ozone-fullerene reactions. Specifically, ozone-C
60
reactions yield C
119
, ozone-C
70
reactions yield C
139
, and ozone-(C
60
/C
70
) reactions produce C
119
, C
129
, and C
139
. These unexpected species correspond to dimers of C
60
, C
60
/C
70
, and C
70
, respectively, less one carbon atom, and are stable gas-phase ions with behavior similar to that of fullerenes. The results suggest a new route to functionalization and derivatization of fullerenes through controlled ozone-catalyzed cage-opening reactions.
A Bimetallic Hydroformylation Catalyst: High Regioselectivity and Reactivity Through Homobimetallic Cooperativity
Authors: Broussard Melanie E. , Juma Booker , Train Spencer G. , Peng Wei-Jun , Laneman Scott A. , Stanley George G.
Published: October 2006

The
racemic
and
meso
diastereomers of an electron-rich binucleating tetraphosphine ligand have been used to prepare homobimetallic rhodium norbornadiene complexes. The
racemic
bimetallic Rh complex is an excellent hydroformylation catalyst for 1-alkenes, giving both a high rate of reaction and high regioselectivity for linear aldehydes, whereas the
meso
complex is considerably slower and less selective. A mechanism involving bimetallic cooperativity between the two rhodium centers in the form of an intramolecular hydride transfer is proposed. Mono- and bimetallic model complexes in which the possibility for bimetallic cooperativity has been reduced or eliminated are very poor catalysts.
Tropical Deforestation and Habitat Fragmentation in the Amazon: Satellite Data from 1978 to 1988
Authors: Skole David , Tucker Compton
Published: October 2006

Landsat satellite imagery covering the entire forested portion of the Brazilian Amazon Basin was used to measure, for 1978 and 1988, deforestation, fragmented forest, defined as areas less than 100 square kilometers surrounded by deforestation, and edge effects of 1 kilometer into forest from adjacent areas of deforestation. Tropical deforestation increased from 78,000 square kilometers in 1978 to 230,000 square kilometers in 1988 while tropical forest habitat, severely affected with respect to biological diversity, increased from 208,000 to 588,000 square kilometers. Although this rate of deforestation is lower than previous estimates, the effect on biological diversity is greater.
Quantification of the Influence of Surface Structure on C—H Bond Activation by Iridium and Platinum
Authors: Johnson Dale F. , Weinberg W. Henry
Published: October 2006

The trapping-mediated dissociative chemisorption of ethane on the closest packed Ir(111) surface has been investigated, and the activation energy and preexponential factor of the surface reaction rate coefficient have been measured. These results are compared to those of ethane activation on Pt(111) and on the missing row reconstructed Ir(110)-(1×2) and Pt(110)-(1×2) surfaces, allowing a quantitative determination of the effect surface structure has on the catalytic activation of C—H bonds. In the order Pt(111), Pt(110)-(1×2), Ir(111), and Ir(110)-(1×2), the activation energies for the dissociative chemisorption of ethane are 16.6, 10.5, 10.3, and 5.5 kilocalories per mole, demonstrating that the electronic and geometric effects are of approximately equal importance for ethane activation on these catalysts.
Magnetic Field Signatures Near Galileo's Closest Approach to Gaspra
Authors: Kivelson M. G. , Bargatze L. F. , Khurana K. K. , Southwood D. J. , Walker R. J. , Coleman P. J.
Published: October 2006

Two large magnetic field rotations were recorded by the spacecraft Galileo 1 minute before and 2 minutes after its closest approach to the asteroid Gaspra. The timing and the geometry of the field changes suggest a connection with Gaspra, and the events can be interpreted as the result of the draping of the solar wind field around a magnetospheric obstacle. Gaspra's surface field is inferred to be within an order of magnitude of Earth's surface field, and its magnetic moment per unit mass is in the range observed for iron meteorites and highly magnetized chondrites. The location of the magnetic signatures suggests that perturbations are carried by waves in the magnetosonic-whistler mode with wavelengths between electron and ion gyro radii.
Structure of Membrane Surfactant and Liquid Crystalline Smectic Lamellar Phases Under Flow
Authors: Safinya Cyrus R. , Sirota Eric B. , Bruinsma Robijn F. , Jeppesen Claus , Plano Robert J. , Wenzel Lawrence J.
Published: October 2006

Synchrotron x-ray scattering studies were performed to probe the nonequilibrium structures of two layered systems at high shear rates: the smectic-A phase of the thermotropic liquid crystal 4-cyano-4′-octylbiphenyl (8CB) and the lamellar L
α
phases of surfactant membranes composed of sodium dodecyl sulfate and pentanol. Whereas the lamellar surfactant phases oriented primarily with their layers parallel to the shearing plates, as expected intuitively, in the corresponding high shear regime, the smectic-A liquid crystalline material oriented with the layers perpendicular to the shearing plates. A careful numerical study revealed that this surprising layer orientation results from nonlinear dynamics of the liquid crystal director and is caused by the flow distortion of thermal fluctuations.
Microprocessors: From Desktops to Supercomputers
Authors: Baskett Forest , Hennessy John L.
Published: October 2006

Continuing improvements in integrated circuit technology and computer architecture have driven microprocessors to performance levels that rival those of supercomputers—at a fraction of the price. The use of sophisticated memory hierarchies enables microprocessor-based machines to have very large memories built from commodity dynamic random access memory while retaining the high bandwidth and low access time needed in a high-performance machine. Parallel processors composed of these high-performance microprocessors are becoming the supercomputing technology of choice for scientific and engineering applications. The challenges for these new supercomputers have been in developing multiprocessor architectures that are easy to program and that deliver high performance without extraordinary programming efforts by users. Recent progress in multiprocessor architecture has led to ways to meet these challenges.
Reversible Rotation of Antimony Dimers on the Silicon (001) Surface with a Scanning Tunneling Microscope
Authors: Mo Y. W.
Published: October 2006

The scanning tunneling microscope (STM) was used to control the configuration of antimony clusters on the (001) surface of silicon. In particular, the STM tip induced a reversible rotation between two orthogonal orientations of individual antimony dimers on the surface. This simple rotation can be explained by an atomic-scale torque exerted on the antimony dimers by the STM tip. The reversibility of this process could provide a basis for making atomic-scale memory cells.
A Two-Tiered Approach to Long-Range Climate Forecasting
Authors: Bengtsson L. , Schlese U. , Roeckner E. , Latif M. , Barnett T. P. , Graham N.
Published: October 2006

Long-range global climate forecasts were made by use of a model for predicting a tropical Pacific sea-surface temperature (SST) in tandem with an atmospheric general circulation model. The SST is predicted first at long lead times into the future. These ocean forecasts are then used to force the atmospheric model and so produce climate forecasts at lead times of the SST forecasts. Prediction of seven large climatic events of the 1970s to 1990s by this technique are in good agreement with observations over many regions of the globe.