bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymer-Polymer Phase Behavior
Authors: Bates Frank S.
Published: October 2006

Different polymers can be combined into a single material in many ways, which can lead to a wide range of phase behaviors that directly influence the associated physical properties and ultimate applications. Four factors control polymer-polymer phase behavior: choice of monomers, molecular architecture, composition, and molecular size. Current theories and experiments that deal with the equilibrium thermodynamics and non-equilibrium dynamics of polymer mixtures are described in terms of these experimentally accessible parameters. Two representative molecular architectures, binary linear homopolymer mixtures and diblock copolymers, exhibiting macrophase separation and microphase segregation, respectively, are examined in some detail. Although these model systems are fairly well understood, a myriad of mixing scenarios, with both existing and unrealized materials applications, remain unexplored at a fundamental level.
Free Energy and Temperature Dependence of Electron Transfer at the Metal-Electrolyte Interface
Authors: Chidsey Christopher E. D.
Published: October 2006

The rate constant of the electron-transfer reaction between a gold electrode and an electroactive ferrocene group has been measured at a structurally well-defined metal-electrolyte interface at temperatures from 1° to 47°C and reaction free energies from -1.0 to +0.8 electron volts (eV). The ferrocene group was positioned a fixed distance from the gold surface by the self-assembly of a mixed thiol monolayer of (η
5
C
5
H
5
)Fe(η
5
C
5
H
4
)CO
2
(CH
2
)
16
SH and CH
3
(CH
2
)
15
SH. Rate constants from 1 per second (s
-1
) to 2 × 10
4
s
-1
in 1 molar HClO
4
are reasonably fit with a reorganization energy of 0.85 eV and a prefactor for electron tunneling of 7 × 10
4
s
-1
eV
-1
. Such self-assembled monolayers can be used to systematically probe the dependence of electron-transfer rates on distance, medium, and spacer structure, and to provide an empirical basis for the construction of interfacial devices such as sensors and transducers that utilize macroscopically directional electron-transfer reactions.
Evidence of Strong Earthquake Shaking in the Lower Wabash Valley from Prehistoric Liquefaction Features
Authors: Obermeier S. F. , Bleuer N. R. , Munson C. A. , Munson P. J. , Martin W. S. , McWilliams K. M. , Tabaczynski D. A. , Odum J. K. , Rubin M. , Eggert D. L.
Published: October 2006

Earthquake-induced liquefaction features in Holocene sediments provide evidence of strong prehistoric shaking, magnitude
m
b
6.2 to 6.7, in the Wabash Valley bordering Indiana and Illinois. The source of the one or more earthquakes responsible was almost certainly in or near the Wabash Valley. The largest event is interpreted to have occurred between 7500 and 1500 years ago on the basis of archeological, pedological, and stratigraphic relations.
America's Soaring Prison Population
Authors: Langan Patrick A.
Published: October 2006

Factors widely reported to explain record prison population increases since 1973 were generally not substantiated in national data. No clear evidence was found that prosecutors were increasingly using mandatory prison sentencing laws, that judges were imposing longer prison sentences than previously, or that parole boards were making prisoners serve longer before their first release. Changes since 1973 in population demographics and in police-recorded crime and arrest rates were found to have only a modest impact on prison population growth. The war on drugs was found to have only a small impact despite increased drug arrest and imprisonment rates. One change found to have a major impact was the increased chance of a prison sentence after arrest for nearly every type of crime. This change has helped to drive incarceration rates to their highest levels ever. Accompanying rising incarceration rates have been gradual reductions in U.S. crime rates after 1973, according to annual crime victimization surveys. The possibility that rising incarceration rates are helping to reduce crime must be weighed in debates about America's prisons.
Impact Craters on Venus: Initial Analysis from Magellan
Authors: Phillips Roger J. , Arvidson Raymond E. , Boyce Joseph M. , Campbell Donald B. , Guest John E. , Schaber Gerald G. , Soderblom Laurence A.
Published: October 2006

Magellan radar images of 15 percent of the planet show 135 craters of probable impact origin. Craters more than 15 km across tend to contain central peaks, multiple central peaks, and peak rings. Many craters smaller than 15 km exhibit multiple floors or appear in clusters; these phenomena are attributed to atmospheric breakup of incoming meteoroids. Additionally, the atmosphere appears to have prevented the formation of primary impact craters smaller than about 3 km and produced a deficiency in the number of craters smaller than about 25 km across. Ejecta is found at greater distances than that predicted by simple ballistic emplacement, and the distal ends of some ejecta deposits are lobate. These characteristics may represent surface flows of material initially entrained in the atmosphere. Many craters are surrounded by zones of low radar albedo whose origin may have been deformation of the surface by the shock or pressure wave associated with the incoming meteoroid. Craters are absent from several large areas such as a 5 million square kilometer region around Sappho Patera, where the most likely explanation for the dearth of craters is volcanic resurfacing. There is apparently a spectrum of surface ages on Venus ranging approximately from 0 to 800 million years, and therefore Venus must be a geologically active planet.
Venus Tectonics: Initial Analysis from Magellan
Authors: Solomon Sean C. , Head James W. , Kaula William M. , McKenzie Dan , Parsons Barry , Phillips Roger J. , Schubert Gerald , Talwani Manik
Published: October 2006

Radar imaging and altimetry data from the Magellan mission have revealed a diversity of deformational features at a variety of spatial scales on the Venus surface. The plains record a superposition of different episodes of deformation and volcanism; strain is both areally distributed and concentrated into zones of extension and shortening. The common coherence of strain patterns over hundreds of kilometers implies that many features in the plains reflect a crustal response to mantle dynamic processes. Ridge belts and mountain belts represent successive degrees of lithospheric shortening and crustal thickening; the mountain belts also show widespread evidence for extension and collapse both during and following crustal compression. Venus displays two geometrical patterns of concentrated lithospheric extension: quasi-circular coronae and broad rises with linear rift zones; both are sites of significant volcanism. No long, large-offset strike-slip faults have been observed, although limited local horizontal shear is accommodated across many zones of crustal shortening. In general, tectonic features on Venus are unlike those in Earth's oceanic regions in that strain typically is distributed across broad zones that are one to a few hundred kilometers wide, and separated by stronger and less deformed blocks hundreds of kilometers in width, as in actively deforming continental regions on Earth.
Multiple Light-Scattering Probes of Foam Structure and Dynamics
Authors: Durian D. J. , Weitz D. A. , Pine D. J.
Published: October 2006

The structure and dynamics of three-dimensional foams are probed quantitatively by exploiting the strong multiple scattering of light that gives foams their familiar white color. Approximating the propagation of light as a diffusion process, transmission measurements provide a direct probe of the average bubble size. A model for dynamic light scattering is developed that can be used to interpret temporal fluctuations in the intensity of multiply scattered light. The results identify previously unrecognized internal dynamics of the foam bubbles. These light-scattering techniques are direct, noninvasive probes of bulk foams and therefore should find wide use in the study of their properties.
Molecular Self-Assembly of Two-Terminal, Voltammetric Microsensors with Internal References
Authors: Hickman James J. , Ofer David , Laibinis Paul E. , Whitesides George M. , Wrighton Mark S.
Published: October 2006

Self-assembly of a ferrocenyl thiol and a quinone thiol onto Au microelectrodes forms the basis for a new microsensor concept: a two-terminal, voltammetric microsensor with reference and sensor functions on the same electrode. The detection is based on measurement of the potential difference of current peaks for oxidation and reduction of the reference (ferrocene) and indicator (quinone) in aqueous electrolyte in a two-terminal, linear sweep voltammogram in which a counterelectrode of relatively large surface area is used. The quinone has a half-wave potential,
E
1/2
, that is pH-sensitive and can be used as a pH indicator; the ferrocene center has an
E
1/2
that is a pH-insensitive reference. The key advantages are that such sensors require no separate reference electrode and function as long as current peaks can be located for reference and indicator molecules.
1990: Annus Mirabilis of Potassium Channels
Authors: Miller Christopher
Published: October 2006

Voltage-gated potassium channels make up a large molecular family of integral membrane proteins that are fundamentally involved in the generation of bioelectric signals such as nerve impulses. These proteins span the cell membrane, forming potassium-selective pores that are rapidly switched open or closed by changes in membrane voltage. After the cloning of the first potassium channel over 3 years ago, recombinant DNA manipulation of potassium channel genes is now leading to a molecular understanding of potassium channel behavior. During the past year, functional domains responsible for channel gating and potassium selectivity have been identified, and detailed structural pictures underlying these functions are beginning to emerge.
Interhemispheric Synchronization of Oscillatory Neuronal Responses in Cat Visual Cortex
Authors: Engel Andreas K. , König Peter , Kreiter Andreas K. , Singer Wolf
Published: October 2006

Neurons in area 17 of cat visual cortex display oscillatory responses that can synchronize across spatially separate columns in a stimulus-specific way. Response synchronization has now been shown to occur also between neurons in area 17 of the right and left cerebral hemispheres. This synchronization was abolished by section of the corpus callosum. Thus, the response synchronization is mediated by corticocortical connections. These data are compatible with the hypothesis that temporal synchrony of neuronal discharges serves to bind features within and between the visual hemifields.
Evidence for Extreme Partitioning of Copper into a Magmatic Vapor Phase
Authors: Lowenstern Jacob B. , Mahood Gail A. , Rivers Mark L. , Sutton Stephen R.
Published: October 2006

The discovery of copper sulfides in carbon dioxide- and chlorine-bearing bubbles in phenocryst-hosted melt inclusions shows that copper resides in a vapor phase in some shallow magma chambers. Copper is several hundred times more concentrated in magmatic vapor than in coexisting pantellerite melt. The volatile behavior of copper should be considered when modeling the volcanogenic contribution of metals to the atmosphere and may be important in the formation of copper porphyry ore deposits.
Photoemission Spectra and Electronic Properties of K

x

C
60
Authors: Wertheim G. K. , Rowe J. E. , Buchanan D. N. E. , Chaban E. E. , Hebard A. F. , Kortan A. R. , Makhija A. V. , Haddon R. C.
Published: October 2006

Photoemission spectra of vacuum deposited layers of C
60
, before and after exposure to K vapor, show that the K donates its conduction electron into the band derived from the lowest unoccupied molecular orbital. A compound with composition of K
3
C
60
, corresponding to the maximum conductivity, has been prepared. In it the potassium atoms presumably occupy both the octahedral and the two tetrahedral interstitial sites of the face-centered-cubic (fcc) C
60
structure.
Impacts, Tsunamis, and the Haitian Cretaceous-Tertiary Boundary Layer
Authors: Maurrasse Florentin J-M. R. , Sen Gautam
Published: October 2006

The marker bed at the Cretaceous-Tertiary boundary of the Beloc Formation (southern Haiti) contains abundant coarse-grained microtektites and minor amounts of shocked quartz grains in the basal part. The upper part is composed of medium-grained marl with amalgamated microtektite lenses and finer-grained marl lenses disseminated throughout. Field and petrographic observations, and the distribution of planktonic foraminifera suggest that the bed formed from a complex sequence of events. A bolide impact nearby produced microtektites that settled to form a nearly pure layer at the base. Vaporized materials with anomalously high extraterrestrial components settled last, along with carbonate sediments. The entire bed became sparsely consolidated. Subsequently, another major disruptive event, perhaps a giant tsunami, partly reworked the initial deposit. Cohesive fragments of the original marker bed mixed with exotic materials were redeposited as lenticular bodies. This process also may have caused further mixing of Cretaceous and Tertiary microfossils, as observed at Beloc and elsewhere.
Expansion and Contraction of the Sahara Desert from 1980 to 1990
Authors: Tucker Compton J. , Dregne Harold E. , Newcomb Wilbur W.
Published: October 2006

Data from polar-orbiting meteorological satellites have been used to determine the extent of the Sahara Desert and to document its interannual variation from 1980 to 1990. The Sahara Desert ranged from 8,633,000 square kilometers in 1980 to 9,982,000 square kilometers in 1984. The greatest annual north-south latitudinal movement of the southern Saharan boundary was 110 kilometers from 1984 to 1985 and resulted in a decrease in desert area of 724,000 square kilometers.
Hybridization Between European and Africanized Honey Bees in the Neotropical Yucatan Peninsula
Authors: Rinderer Thomas E. , Stelzer J. Anthony , Oldroyd Benjamin P. , Buco Steven M. , Rubink William L.
Published: October 2006

A population genetic analysis of honey bees of the Mexican neotropical Yucatan peninsula shows that the range expansion of Africanized bees there has involved extensive introgressive hybridization with European bees. Yucatan honey bee populations now include many colonies with intermediate morphologies. Genotypes of mitochondria have disassociated from historically correlated Africanized or European morphology, producing diverse phenotypic associations. This suggests that the size of resident European populations may be important in explaining previously reported asymmetrical hybridization. Evidence of natural hybridization is encouraging for the use of genetic management to mitigate the effects of Africanized bees in the United States.
Relations Among Fault Behavior, Subsurface Geology, and Three-Dimensional Velocity Models
Authors: Michael Andrew J. , Eberhart-Phillips Donna
Published: October 2006

The development of three-dimensional P-wave velocity models for the regions surrounding five large earthquakes in California has lead to the recognition of relations among fault behavior and the material properties of the rocks that contact the fault at seismogenic depths; regions of high moment release appear to correlate with high seismic velocities whereas rupture initiation or termination may be associated with lower seismic velocities. These relations point toward a physical understanding of why faults are divided into segments that can fail independently, an understanding that could improve our ability to predict earthquakes and strong ground motion.
An Explanation for Neptune's Ring Arcs
Authors: Porco Carolyn C.
Published: October 2006

The Voyager mission revealed a complex system of rings and ring arcs around Neptune and uncovered six new satellites, four of which occupy orbits well inside the ring region. Analysis of Voyager data shows that a radial distortion with an amplitude of approximately 30 kilometers is traveling through the ring arcs, a perturbation attributable to the nearby satellite Galatea. Moreover, the arcs appear to be azimuthally confined by a resonant interaction with the same satellite, yielding a maximum spread in ring particle semimajor axes of 0.6 kilometer and a spread in forced eccentricities large enough to explain the arcs' 15-kilometer radial widths. Additional ring arcs discovered in the course of this study give further support to this model.
Natural Language Processing
Authors: Joshi Aravind K.
Published: October 2006

Natural language processing (NLP) is the study of mathematical and computational modeling of various aspects of language and the development of a wide range of systems. These include spoken language systems that integrate speech and natural language; cooperative interfaces to databases and knowledge bases that model aspects of human-human interaction; multilingual interfaces; machine translation; and message-understanding systems, among others. Research in NLP is highly interdisciplinary, involving concepts in computer science, linguistics, logic, and psychology. NLP has a special role in computer science because many aspects of the field deal with linguistic features of computation and NLP seeks to model language computationally.
Ground-Based Near-Infrared Imaging Observations of Venus During the Galileo Encounter
Authors: Crisp D. , McMuldroch S. , Stephens S. K. , Sinton W. M. , Ragent B. , Hodapp K. -W. , Probst R. G. , Doyle L. R. , Allen D. A. , Elias J.
Published: October 2006

Near-infrared images of Venus, obtained from a global network of ground-based observatories during January and February 1990, document the morphology and motions of the night-side near-infrared markings before, during, and after the Galileo Venus encounter. A dark cloud extended halfway around the planet at low latitudes (>±40°) and persisted throughout the observing program. It had a rotation period of 5.5 ± 0.15 days. The remainder of this latitude band was characterized by small-scale (400 to 1000 kilometers) dark and bright markings with rotation periods of 7.4 ± 1 days. The different rotation periods for the large dark cloud and the smaller markings suggests that they are produced at different altitudes. Mid-latitudes (±40° to 60°) were usually occupied by bright east-west bands. The highest observable latitudes (±60° to 70°) were always dark and featureless, indicating greater cloud opacity. Maps of the water vapor distribution show no evidence for large horizontal gradients in the lower atmosphere of Venus.
Early Cambrian Foraminifera from West Africa
Authors: Culver Stephen J.
Published: October 2006

Agglutinated foraminifera have been recovered from siltstones in the Walidiala Valley, Taoudeni Basin, West Africa. Associated faunas suggest an Early Cambrian age for these strata. These now earliest known unequivocal foraminifera help constrain hypotheses concerning the origin of skeletalization at the beginning of the Phanerozoic.
Transgenic Plants with Enhanced Resistance to the Fungal Pathogen
Rhizoctonia solani
Authors: Brogue Karen , Chet Ilan , Holliday Mark , Cressman Robert , Biddle Phyllis , Knowlton Susan , Mauvais C. Jeffry , Broglie Richard
Published: October 2006

The production of enzymes capable of degrading the cell walls of invading phytopathogenic fungi is an important component of the defense response of plants. The timing of this natural host defense mechanism was modified to produce fungal-resistant plants. Transgenic tobacco seedlings constitutively expressing a bean chitinase gene under control of the cauliflower mosaic virus 35
S
promoter showed an increased ability to survive in soil infested with the fungal pathogen
Rhizoctonia solani
and delayed development of disease symptoms.
Fullerene Isomerism: Isolation of
C

2
v

,-C
78
and
D
3
-C
78
Authors: Diederich François , Whetten Robert L. , Thilgen Carlo , Ettl Roland , Chao Ito , Alvarez Marcos M.
Published: October 2006

Early reports on the formation of the higher fullerenes C
76
, C
78
, C
84
, C
90
, and C
94
by resistive heating of graphite stimulated theoretical calculations of possible cage structures for these all-carbon molecules. Among the five fullerene structures with isolated pentagons found for C
78
, a closed-shell
D

3
h

-isomer was predicted to form preferentially. Two distinct C
78
-isomers were formed in a ratio of ∼5:1 and could be separated by high-performance liquid chromatography. The carbon-13 nuclear magnetic resonance (NMR) spectrum of the major isomer is uniquely consistent with a
C

2
v

-structure. The NMR data also support a chiral
D
3
-structure for the minor isomer. The isolation of specifically these two isomers of C
78
provides insight into the stability of higher fullerene structures and into the mechanism for fullerene formation in general.
Two Molecular Transitions Influence Cardiac Sodium Channel Gating
Authors: Yue David T. , Lawrence John H. , Marban Eduardo
Published: October 2006

Sodium channels from diverse excitable membranes are very similar in their structure, yet surprisingly heterogeneous in their behavior. The processes that govern the opening and closing of sodium channels have appeared difficult to describe in terms of a single, unifying molecular scheme. Now cardiac sodium channels have been analyzed by high-resolution single-channel recordings over a broad range of potentials. Channels exhibited both complex and simple gating patterns at different voltages. Such behavioral diversity can be explained by the balance between two molecular transitions whereby channels can exit the open state.
DNA Looping Generated by DNA Bending Protein IHF and the Two Domains of Lambda Integrase
Authors: de Vargas Lina Moitoso , Kim Sunghoon , Landy Arthur
Published: October 2006

The multiprotein-DNA complexes that participate in bacteriophage lambda site-specific recombination were used to study the combined effect of protein-induced bending and protein-mediated looping of DNA. The protein integrase (Int) is a monomer with two autonomous DNA binding domains of different sequence specificity. Stimulation of Int binding and cleavage at the low affinity core-type DNA sites required interactions with the high affinity arm-type sites and depended on simultaneous binding of the sequence-specific DNA bending protein IHF (integration host factor). The bivalent DNA binding protein is positioned at high affinity sites and directed, by a DNA bending protein, to interactions with distant lower affinity sites. Assembly of this complex is independent of protein-protein interactions.
Recombinant 47-Kilodalton Cytosol Factor Restores NADPH Oxidase in Chronic Granulomatous Disease
Authors: Lomax Karen J. , Leto Thomas L. , Nunoi Hiroyuki , Gallin John I. , Malech Harry L.
Published: October 2006

A 47-kilodalton neutrophil cytosol factor (NCF-47k), required for activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase superoxide (O
2⋅
-
) production, is absent in most patients with autosomal recessive chronic granulomatous disease (AR-CGD). NCF-47k cDNAs were cloned from an expression library. The largest clone predicted a 41.9-kD protein that contained an arginine and serine-rich COOH-terminal domain with potential protein kinase C phosphorylation sites. A 33-amino acid segment of NCF-47k shared 49% identity with
ras
p21 guanosine triphosphatase activating protein. Recombinant NCF-47k restored O
2⋅
-
-producing activity to AR-CGD neutrophil cytosol in a cell-free assay. Production of active recombinant NCF-47k will enable functional regions of this molecule to be mapped.
Conserved Folding in Retroviral Proteases: Crystal Structure of Synthetic HIV-1 Protease
Authors: Wlodawer Alexander , Miller Maria , Jaskólski Mariusz , Sathyanarayana Bangalore K. , Baldwin Eric , Weber Irene T. , Selk Linda M. , Clawson Leigh , Schneider Jens , Kent Stephen B. H.
Published: October 2006

The rational design of drugs that can inhibit the action of viral proteases depends on obtaining accurate structures of these enzymes. The crystal structure of chemically synthesized HIV-1 protease has been determined at 2.8 angstrom resolution (
R
factor of 0.184) with the use of a model based on the Rous sarcoma virus protease structure. In this enzymatically active protein, the cysteines were replaced by α-amino-
n
-butyric acid, a nongenetically coded amino acid. This structure, in which all 99 amino acids were located, differs in several important details from that reported previously by others. The interface between the identical subunits forming the active protease dimer is composed of four well-ordered β strands from both the amino and carboxyl termini and residues 86 to 94 have a helical conformation. The observed arrangement of the dimer interface suggests possible designs for dimerization inhibitors.
Inhibition of DNA Binding Proteins by Oligonucleotide-Directed Triple Helix Formation
Authors: Maher Louis J. , Wold Barbara , Dervan Peter B.
Published: October 2006

Oligonucleotides that bind to duplex DNA in a sequence-specific manner by triple helix formation offer an approach to the experimental manipulation of sequence-specific protein binding. Micromolar concentrations of pyrimidine oligodeoxyribonucleotides are shown to block recognition of double helical DNA by prokaryotic modifying enzymes and a eukaryotic transcription factor at a homopurine target site. Inhibition is sequence-specific. Oligonucleotides containing 5-methylcytosine provide substantially more efficient inhibition than oligonucleotides containing cytosine. The results have implications for gene-specific repression by oligonucleotides or their analogs.
Luminescent Colloidal Silicon Suspensions from Porous Silicon
Authors: Heinrich Julie L. , Curtis Corrine L. , Credo Grace M. , Sailor Michael J. , Kavanagh Karen L.
Published: October 2006

A procedure for generating colloidal suspensions of Si that exhibit luminescence, attributed to quantum confinement effects, is described. Samples of
n
- or
p
-type Si that have been electrochemically etched to form porous Si can be ultrasonically dispersed into methylene chloride, acetonitrile, methanol, toluene, or water solvents, forming a suspension of fine Si particles that luminesce. Transmission electron microscopy analyses show that the Si particles have irregular shapes, with diameters ranging from many micrometers to nanometers. Luminescent, composite polystyrene/Si films can be made by the addition of polystyrene to a toluene suspension of the Si nanoparticles and casting of the resulting solution onto a glass slide.
Stability of the Astronomical Frequencies Over the Earth's History for Paleoclimate Studies
Authors: Berger A. , Loutre M. F. , Laskar J.
Published: October 2006

The expected changes over the past 500 million years in the principal astronomical frequencies influencing the Earth's climate may be strong enough to be detectable in the geological records, and such effects have been inferred in several cases. Calculations suggest that the shortening of the Earth-moon distance and of the length of the day back in time induced a shortening of the fundamental periods for the obliquity and climatic precession, from 54 to 35, 41 to 29, 23 to 19, and 19 to 16 thousand years over the last half-billion years. At the same time, the precessional constant increased from 50 to 61 arc seconds per year. The changes in the frequencies of the planetary system due to its chaotic motion are much smaller; their influence on the changes of the periods of climatic precession, obliquity, and eccentricity of the Earth's orbit around the sun can be neglected. Eccentricity periods used for Quaternary climate studies may therefore be considered to have been more or less constant for pre-Quaternary times.
Advanced Materials for Aircraft Engine Applications
Authors: Backman Daniel G. , Williams James C.
Published: October 2006

A review of advances for aircraft engine structural materials and processes is presented. Improved materials, such as superalloys, and the processes for making turbine disks and blades have had a major impact on the capability of modern gas turbine engines. New structural materials, notably composites and intermetallic materials, are emerging that will eventually further enhance engine performance, reduce engine weight, and thereby enable new aircraft systems. In the future, successful aerospace manufacturers will combine product design and materials excellence with improved manufacturing methods to increase production efficiency, enhance product quality, and decrease the engine development cycle time.
C
60
Rotation in the Solid State: Dynamics of a Faceted Spherical Top
Authors: Johnson Robert D. , Yannoni Costantino S. , Dorn Harry C. , Salem Jesse R. , Bethune Donald S.
Published: October 2006

The rotational dynamics of C
60
in the solid state have been investigated with carbon-13 nuclear magnetic resonance (
13
C NMR). The relaxation rate due to chemical shift anisotropy (1/
9T
1
CSA
) was precisely measured from the magnetic field dependence of
T
1
, allowing the molecular reorientational correlation time, τ, to be determined. At 283 kelvin, τ = 9.1 picoseconds; with the assumption of diffusional reorientation this implies a rotational diffusion constant
D
= 1.8 × 10
10
per second. This reorientation time is only three times as long as the calculated τ for free rotation and is shorter than the value measured for C
60
in solution (15.5 picoseconds). Below 260 kelvin a second phase with a much longer reorientation time was observed, consistent with recent reports of an orientational phase transition in solid C
60
. In both phases τ showed Arrhenius behavior, with apparent activation energies of 1.4 and 4.2 kilocalories per mole for the high-temperature (rotator) and low-temperature (ratchet) phases, respectively. The results parallel those found for adamantane.
Mechanics of Wind Ripple Stratigraphy
Authors: Forrest Spencer B. , Haff Peter K.
Published: October 2006

Stratigraphic patterns preserved under translating surface undulations or ripples in a depositional eolian environment are computed on a grain by grain basis using physically based cellular automata models. The spontaneous appearance, growth, and motion of the simulated ripples correspond in many respects to the behavior of natural ripples. The simulations show that climbing strata can be produced by impact alone; direct action of fluid shear is unnecessary. The model provides a means for evaluating the connection between mechanical processes occurring in the paleoenvironment during deposition and the resulting stratigraphy preserved in the geologic column: vertical compression of small laminae above a planar surface indicates nascent ripple growth; supercritical laminae are associated with unusually intense deposition episodes; and a plane erosion surface separating sets of well-developed laminae is consistent with continued migration of mature ripples during a hiatus in deposition.
Surface Charge—Induced Ordering of the Au(111) Surface
Authors: Wang Jia , Davenport Alison J. , Isaacs Hugh S. , Ocko B. M.
Published: October 2006

Synchrotron surface x-ray scattering (SXS) studies have been carried out at the Au(111)/electrolyte interface to determine the influence of surface charge on the microscopic arrangement of gold surface atoms. At the electrochemical interface, the surface charge density can be continuously varied by controlling the applied potential. The top layer of gold atoms undergoes a reversible phase transition between the (1 × 1) bulk termination and a (23 × √3) reconstructed phase on changing the electrode potential. In order to differentiate the respective roles of surface charge and adsorbates, studies were carried out in 0.1 M NaF, NaCl, and NaBr solutions. The phase transition occurs at an induced surface charge density of 0.07 ± 0.02 electron per atom in all three solutions.
Voltage-Dependent Calcium Channels in Plant Vacuoles
Authors: Pantoja Omar , Gelli Angie , Blumwald Eduardo
Published: October 2006

Free calcium (Ca
2+
) in the cytoplasm of plant cells is important for the regulation of many cellular processes and the transduction of stimuli. Control of cytoplasmic Ca
2+
involves the activity of pumps, carriers, and possibly ion channels. The patch-clamp technique was used to study Ca
2+
channels in the vacuole of sugar beet cells. Vacuolar currents showed inward rectification at negative potentials, with a single-channel conductance of 40 picosiemens and an open probability dependent on potential. Channels were inhibited by verapamil and lanthanum. These channels could participate in the regulation of cytoplasmic Ca
2+
by sequestering Ca
2+
inside the vacuole.
Long-Term Potentiation in the Motor Cortex
Authors: Iriki Atsushi , Pavlides Constantine , Keller Asaf , Asanuma Hiroshi
Published: October 2006

Long-term potentiation (LTP) is a model for learning and memory processes. Tetanic stimulation of the sensory cortex produces LTP in motor cortical neurons, whereas tetanization of the ventrolateral nucleus of the thalamus, which also projects to the motor cortex, does not. However, after simultaneous high-frequency stimulation of both the sensory cortex and the ventrolateral nucleus of the thalamus, LTP of thalamic input to motor cortical neurons is induced. This associative LTP occurs only in neurons in the superficial layers of the motor cortex that receive monosynaptic input from both the sensory cortex and the ventrolateral nucleus of the thalamus. Associative LTP in the motor cortex may constitute a basis for the retention of motor skills.
Type I and Type II GABA
A
-Benzodiazepine Receptors Produced in Transfected Cells
Authors: Pritchett Dolan B. , Lüddens Hartmut , Seeburg Peter H.
Published: October 2006

GABA
A
(γ-aminobutyric acid A)-benzodiazepine receptors expressed in mammalian cells and assembled from one of three different α subunit variants (α
1
, α
2
, or α
3
) in combination with a β
1
and a γ
2
subunit display the pharmacological properties of either type I or type II receptor subtypes. These receptors contain high-affinity binding sites for benzodiazepines. However, CL 218 872, 2-oxoquazepam, and methyl β-carboline-3-carboxylate (β-CCM) show a temperature-modulated selectivity for α
1
subunit-containing receptors. There were no significant differences in the binding of clonazepam, diazepam, Ro 15-1788, or dimethoxy-4-ethyl-β-carboline-3-carboxylate (DMCM) to all three recombinant receptors. Receptors containing the α
3
subunit show greater GABA potentiation of benzodiazepine binding than receptors containing the α
1
or α
2
subunit, indicating that there are subtypes within the type II class. Thus, diversity in benzodiazepine pharmacology is generated by heterogeneity of the α subunit of the GABA
A
receptor.
p53: A Frequent Target for Genetic Abnormalities in Lung Cancer
Authors: Takahashi Takashi , Nau Marion M. , Chiba Itsuo , Birrer Michael J. , Rosenberg Richard K. , Vinocour Michelle , Levitt Mark , Pass Harvey , Gazdar Adi F. , Minna John D.
Published: October 2006

Allele loss is a hallmark of chromosome regions harboring recessive oncogenes. Lung cancer frequently demonstrates loss of heterozygosity on 17p. Recent evidence suggests that the p53 gene located on 17p13 has many features of such an antioncogene. The p53 gene was frequently mutated or inactivated in all types of human lung cancer. The genetic abnormalities of p53 include gross changes such as homozygous deletions and abnormally sized messenger RNAs along with a variety of point or small mutations, which map to the p53 open reading frame and change amino acid sequence in a region highly conserved between mouse and man. In addition, very low or absent expression of p53 messenger RNA in lung cancer cell lines compared to normal lung was seen. These findings, coupled with the previous demonstration of 17p allele loss in lung cancer, strongly implicate p53 as an anti-oncogene whose disruption is involved in the pathogenesis of human lung cancer.
A Formalin-Inactivated Whole SIV Vaccine Confers Protection in Macaques
Authors: Murphey-Corb Michael , Martin Louis N. , Davison-Fairburn Billie , Montelaro Ronald C. , Miller Mark , West Melanie , Ohkawa Susumu , Baskin Gary B. , Zhang Jing-Yu , Putney Scott D. , Allison Anthony C. , Eppstein Deborah A.
Published: October 2006

A vaccine against human immunodeficiency virus (HIV) would be highly effective in stopping the acquired immunodeficiency syndrome (AIDS) epidemic. A comprehensive evaluation of potential vaccine methodologies can be made by means of the simian model for AIDS, which takes advantage of the similarities in viral composition and disease potential between simian immunodeficiency virus (SIV) infection of rhesus macaques and HIV infection in humans. Immunization with a formalin-inactivated whole SIV vaccine potentiated with either alum and the Syntex adjuvant threonyl muramyl dipeptide (MDP) or MDP alone resulted in the protection of eight of nine rhesus monkeys challenged with ten animal-infectious doses of pathogenic virus. These results demonstrate that a whole virus vaccine is highly effective in inducing immune responses that can protect against lentivirus infection and AIDS-like disease.
Allosteric Effects of Nucleotide Cofactors on
Escherichia coli
Rep Helicase&DNA Binding
Authors: Wong Isaac , Lohman Timothy M.
Published: October 2006

The
Escherichia coli
Rep helicase unwinds duplex DNA during replication. The functional helicase appears to be a dimer that forms only on binding DNA. Both protomers of the dimer can bind either single-stranded or duplex DNA. Because binding and hydrolysis of adenosine triphosphate (ATP) are essential for helicase function, the energetics of DNA binding and DNA-induced Rep dimerization were studied quantitatively in the presence of the nucleotide cofactors adenosine diphosphate (ADP) and the nonhydrolyzable ATP analog AMPP(NH)P. Large allosteric effects of nucleotide cofactors on DNA binding to Rep were observed. Binding of ADP favored Rep dimers in which both protomers bound single-stranded DNA, whereas binding of AMPP(NH)P favored simultaneous binding of both single-stranded and duplex DNA to the Rep dimer. A rolling model for the active unwinding of duplex DNA by the dimeric Rep helicase is proposed that explains vectorial unwinding and predicts that helicase translocation along DNA is coupled to ATP binding, whereas ATP hydrolysis drives unwinding of multiple DNA base pairs for each catalytic event.
Metallo-Carbohedrenes [M
8
C
12
+
(M = V, Zr, Hf, and Ti)]: A Class of Stable Molecular Cluster Ions
Authors: Guo B. C. , Wei S. , Purnell J. , Buzza S. , Castleman A. W.
Published: October 2006

Findings of magic peaks corresponding to M
8
C
12
+
(M = V, Zr, and Hf) formed from reactions of the respective metals with various small hydrocarbons, in conjunction with recent findings for the titanium system, establish metallo-carbohedrenes as a stable general class of molecular cluster ions. A dodecahedral structure of
T
h
point symmetry accounts for the stability of these ionic clusters.
Vibrational Modes and the Dynamic Solvent Effect in Electron and Proton Transfer
Authors: Barbara Paul F. , Walker Gilbert C. , Smith Terrance P.
Published: October 2006

This article primarily reviews recent work on ultrafast experiments on excited state intramolecular electron and proton transfer, with an emphasis on experiments on chemical systems that have been analyzed theoretically. In particular, those systems that have been quantitatively characterized by static spectroscopy, which provides detailed information about the reaction potential energy surface and about other parameters that are necessary to make a direct comparison to theoretical predictions, are described.
The Schumann Resonance: A Global Tropical Thermometer
Authors: Williams Earle R.
Published: October 2006

The Schumann resonance, a global electromagnetic phenomenon, is shown to be a sensitive measure of temperature fluctuations in the tropical atmosphere. The link between Schumann resonance and temperature is lightning flash rate, which increases nonlinearly with temperature in the interaction between deep convection and ice microphysics.
Oxygen Isotopes in Biogenic Silica: Global Changes in Ocean Temperature and Isotopic Composition
Authors: Shemesh A. , Charles C. D. , Fairbanks R. G.
Published: October 2006

A record of oxygen isotopes in biogenic silica from a deep-sea sediment core from the Southern Ocean reveals that marine diatoms retain their primary isotopic composition after burial. As a result, the marine diatom record can be combined with data on coexisting planktonic foraminifera to monitor past surface temperature and isotopic composition of seawater. The coupling of these two records allows the solution of two paleotemperature equations for each core interval. Data from a South Atlantic core show that the average δ
18
O during the glacial period at this site was higher by about 1.3 per mil than average Holocene values, and that average glacial-age temperatures were not significantly different from average Holocene values.
Paleoclimatic Signature in Terrestrial Flood Deposits
Authors: Koltermann Christine E. , Gorelick Steven M.
Published: October 2006

Large-scale process simulation was used to reconstruct the geologic evolution during the past 600,000 years of an alluvial fan in northern California. In order to reproduce the sedimentary record, the simulation accounted for the dynamics of river flooding, sedimentation, subsidence, land movement that resulted from faulting, and sea level changes. Paleoclimatic trends induced fluctuations in stream flows and dominated the development of the sedimentary deposits. The process simulation approach serves as a quantitative means to explore the genesis of sedimentary architecture and its link to past climatic conditions and fault motion.
Access to a Messenger RNA Sequence or Its Protein Product Is Not Limited by Tissue or Species Specificity
Authors: Sarkar Gobinda , Sommer Steve S.
Published: October 2006

RNA amplification with transcript sequencing (RAWTS) is a rapid and sensitive method of direct sequencing that involves complementary DNA synthesis, polymerase chain reaction (PCR) with a primer or primers containing a phage promoter, transcription from the phage promoter, and reverse transcriptase-mediated sequencing. By means of RAWTS, it was possible to sequence each of four tissue-specific human messenger RNAs (blue pigment, factor IX, phenylalanine hydroxylase, and tyrosine hydroxylase) in four cell types examined (white blood cells, liver, K562 erythroleukemia cells, and chorionic villus cells). These results indicate that there is a basal rate of transcription, splicing, and polyadenylation of tissue-specific mRNAs in adult and embryonic tissues. In addition to revealing sequence information, it is possible to generate a desired in vitro translation product by incorporating a translation initiation signal into the appropriate PCR primer. RAWTS can be used to obtain novel mRNA sequence information from other species as illustrated with a segment of the catalytic domain of factor IX. In general, the ability to obtain mRNA sequences rapidly across species boundaries should aid both the study of protein evolution and the identification of sequences crucial for protein structure and function.
Drugs from Emasculated Hormones: The Principle of Syntopic Antagonism
Authors: Black James
Published: October 2006

This lecture illustrates the early stages in the planning and discovery of propranolol, an adrenaline β-adrenergic receptor antagonist, and cimetidine, a histamine H
2
-receptor antagonist—the first examples of clinically useful drugs from each of these classes. The significance of selective agonists, partial agonists, and syntopic antagonists and the importance of the bioassay and the use of molar models in the drug discovery process are discussed. For the future, an outline of potential developments in hormone-receptor concepts is offered leading to the conclusion that progress may depend on improvements in bioassays and related molar modeling.
The Chemistry of Bulk Hydrogen: Reaction of Hydrogen Embedded in Nickel with Adsorbed CH
3
Authors: Johnson A. D. , Daley S. P. , Utz A. L. , Ceyer S. T.
Published: October 2006

Studies in heterogeneous catalysis have long speculated on or have provided indirect evidence for the role of hydrogen embedded in the catalyst bulk as a primary reactant. This report describes experiments carried out under single-collision conditions that document the distinctive reactivity of hydrogen embedded in the bulk of the metal catalyst. Specifically, the bulk H atom is shown to be the reactive species in the hydrogenation of CH
3
adsorbed on Ni(111) to form CH
4
, while the H atoms bound to the surface were unreactive. These results unambiguously demonstrate the importance of bulk species to heterogeneous catalytic chemistry.
Surface Order and Stability of Langmuir-Blodgett Films
Authors: Schwartz D. K. , Garnaes J. , Viswanathan R. , Zasadzinski J. A. N.
Published: October 2006

Angstrom-resolution atomic force microscope images of Langmuir-Blodgett monolayers and multilayers of cadmium arachidate in air and under water show a dramatic change from a disordered arrangement to a crystalline lattice by the addition or removal of a single layer of molecules. The disordered surface is less stable than the ordered one to mechanical stresses such as atomic force microscopy tip forces or at the air-water contact line during contact angle measurements. The difference in the degree of order in the alkyl chains is attributed to the strong attractive interaction between headgroups in the presence of the divalent cation.
Existence of an Orientational Electric Dipolar Response in C
60
Single Crystals
Authors: Alers G. B. , Golding Brage , Kortan A. R. , Haddon R. C. , Theil F. A.
Published: October 2006

The dielectric constant ε and conductivity σ of undoped C
60
single crystals have been measured as a function of temperature, 10 K <
T
< 330 K, and frequency, 0.2 kilohertz <
f
< 100 kilohertz. On cooling below the first-order structural phase transition at 260 K, a Debye-like relaxational contribution to the dielectric response is observed, which requires the presence of permanent electric dipoles. The relaxation rate is thermally activated with a broad distribution of energies centered at 270 millielectron volts. The existence of a dipole moment in C
60
is unexpected, because it is precluded by symmetry for the pure ordered cubic phase. These data suggest that the high degree of frozen-in orientational disorder of the C
60
molecules is responsible for the existence of electric dipolar activity.
Evidence for Liquid-Phase Cirrus Cloud Formation from Volcanic Aerosols: Climatic Implications
Authors: Sassen Kenneth
Published: October 2006

Supercooled droplets in cirrus uncinus cell heads between -40° and -50°C are identified from Project FIRE [First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment] polarization lidar measurements. Although short-lived, complexes of these small liquid cells seem to have contributed importantly to the formation of the cirrus. Freezing-point depression effects in solution droplets, apparently resulting from relatively large cloud condensation nuclei of volcanic origin, can be used to explain this rare phenomenon. An unrecognized volcano-cirrus cloud climate feedback mechanism is implied by these findings.
Diverse and Contrasting Effects of Habitat Fragmentation
Authors: Robinson George R. , Holt Robert D. , Gaines Michael S. , Hamburg Steven P. , Johnson Michael L. , Fitch Henry S. , Martinko Edward A.
Published: October 2006

Different components of an ecosystem can respond in very different ways to habitat fragmentation. An archipelago of patches, representing different levels of fragmentation, was arrayed within a successional field and studied over a period of 6 years. Ecosystem processes (soil mineralization and plant succession) did not vary with the degree of subdivision, nor did most measures of plant and animal community diversity. However, fragmentation affected vertebrate population dynamics and distributional patterns as well as the population persistence of clonal plant species. The results highlight the dangers of relying on broad community measures in lieu of detailed population analyses in studies of fragmented habitats.