bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase Advance of the Circadian Sleep-Wake Cycle as an Antidepressant
Authors: Wehr Thomas A. , Wirz-Justice Anna , Goodwin Frederick K. , Duncan Wallace , Gillin J. Christian
Published: October 2006

Sleep in depressed patients resembles sleep in normal subjects whose circadian rhythms of temperature and rapid-eye-movement sleep are phase-advanced (shifted earlier) relative to their sleep schedules. If this analogy is relevant to the pathophysiology of depressive illness, advancing the time of sleep and awakening should temporarily compensate for the abnormal timing of depressed patients' circadian rhythms. Four of seven manic-depressive patients studied longitudinally spontaneously advanced their times of awakening (activity onset) as they emerged from the depressive phase of their illness. In a phase-shift experiment, a depressed manic-depressive woman was twice brought out of depression for 2 weeks by advancing her sleep period so that she went to sleep and arose 6 hours earlier than usual. The antidepressant effect of the procedure was temporary and similar in duration to circadian desynchronization induced by jet lag in healthy subjects. This result supports the hypothesis that abnormalities of sleep patterns in some types of depression are due to abnormal internal phase relationships of circadian rhythms.
Genetic Mechanisms of Tumor Suppression by the Human p53 Gene
Authors: Chen Phang-Lang , Chen Yumay , Bookstein Robert , Lee Wen-Hwa
Published: October 2006

Mutations of the gene encoding p53, a 53-kilodalton cellular protein, are found frequently in human tumor cells, suggesting a crucial role for this gene in human oncogenesis. To model the stepwise mutation or loss of both p53 alleles during tumorigenesis, a human osteosarcoma cell line, Saos-2, was used that completely lacked endogenous p53. Single copies of exogenous p53 genes were then introduced by infecting cells with recombinant retroviruses containing either point-mutated or wild-type versions of the p53 cDNA sequence. Expression of wild-type p53 suppressed the neoplastic phenotype of Saos-2 cells, whereas expression of mutated p53 conferred a limited growth advantage to cells in the absence of wild-type p53. Wild-type p53 was phenotypically dominant to mutated p53 in a two-allele configuration. These results suggest that, as with the retinoblastoma gene, mutation of both alleles of the p53 gene is essential for its role in oncogenesis.
Ocelli: A Celestial Compass in the Desert Ant
Cataglyphis
Authors: Fent Karl , Wehner Rüdiger
Published: October 2006

In addition to multifaceted lateral compound eyes, most insects possess three frontal eyes called ocelli. Each ocellus has a single lens, as does the vertebrate eye. The ocelli of some flying insects, locusts and dragonflies, have been shown to function as horizon detectors involved in the visual stabilization of course. In a walking insect, the desert ant
Cataglyphis
, it is now shown that the ocelli can read compass information from the blue sky. When the ant's compound eyes are occluded and both sun and landmarks are obscured, the ocelli, using the pattern of polarized light in the sky as a compass cue, help in guiding the ant back home.
Reciprocal Inhibition and Postinhibitory Rebound Produce Reverberation in a Locomotor Pattern Generator
Authors: Satterlie Richard A.
Published: October 2006

The central pattern generator for swimming in the pteropod mollusk
Clione limacina
consists of at least four pedal interneurons, two each controlling parapodial upstroke and downstroke. The two sets of antagonistic interneurons are linked by reciprocal monosynaptic inhibitory synapses, and all exhibit apparently strong postinhibitory rebound. This simple neuronal network produces reverberating alternate cyclic activity in the absence of tonic drive or apparent feedback modulation.
Polar Motion Measurements: Subdecimeter Accuracy Verified by Intercomparison
Authors: Robertson D. S. , Carter W. E. , Tapley B. D. , Schutz B. E. , Eanes R. J.
Published: October 2006

An important bound on the accuracy of modern techniques for monitoring polar motion is established by intercomparison of measurement series from two different observing techniques, very long baseline interferometry and satellite laser ranging. The root-mean-square differences between the estimates of the pole position from both techniques are shown to be only 2 milliseconds of arc (about 6 centimeters at one Earth radius). In the absence of common systematic errors, these differences bound the total errors in both sets of estimates. An initial investigation did not reveal any clear signature in the pole position that seems to be associated with major earthquakes. Continued measurements at this level of accuracy hold promise for resolving long-standing arguments over such questions as the nature of the excitation mechanism required to maintain the motion of the pole.
Synthesis of Chlorophyllide b from Protochlorophyllide in
Chlamydomonas reinhardtii y-1
Authors: Bednarik Daniel P. , Hoober J. Kenneth
Published: October 2006

In cells of
Chlamydomonas reinhardtii
y-1 kept in the dark, 1,7-phenanthroline stimulated the conversion of protochlorophyllide to chlorophyllide b. A membrane fraction was obtained from degreened cells that was active in this conversion only when phenanthroline was present. Untreated cells excreted protochlorophyllide, which was used as substrate for this in vitro reaction. This system may provide a clue to how chlorophyllide b is synthesized in plant cells.
What Perturbs the γ and δ Rings of Uranus?
Authors: French R. G. , Kangas J. A. , Elliot J. L.
Published: October 2006

The γ and δ rings have by far the largest radial perturbations of any of the nine known Uranian rings. These two rings deviate from Keplerian orbits, having typical root-mean-square residuals of about 3 kilometers (compared to a few hundred meters for the other seven known rings). Possible causes for the perturbations include nearby shepherd satellites and Lindblad resonances. If shepherd satellites are responsible, they could be as large as several tens of kilometers in diameter. The perturbation patterns of the γ and δ rings have been examined for evidence of Lindblad resonances of azimuthal wave number
m
= 0, 1, 2, 3, and 4. The δ ring radial residuals are well matched by a 2:1 Lindblad resonance. If this represents a real physical phenomenon and is not an artifact of undersampling, then the most plausible interpretation is that there is an undiscovered satellite orbiting 76,522 ± 8 kilometers from Uranus, with an orbital period of 15.3595 ± 0.0001 hours and a radius of 75 to 100 kilometers. Such a satellite would be easily detected by the Voyager spacecraft when it encounters Uranus. The 2:1 resonance location is 41 ± 9 kilometers inside the δ ring, which makes it unlikely that the resonance is due to a viscous instability within the ring. In contrast, no low-order Lindblad resonance matches the γ ring perturbations, which are probably caused by one or more shepherd satellites large enough to be clearly visible in Voyager images.
Hydrodynamic Measurement of Double-Layer Repulsion Between Colloidal Particle and Flat Plate
Authors: Prieve Dennis C. , Alexander Barbara M.
Published: October 2006

Electrostatic repulsion acting across an electrolyte solution lends stability to paints and printing inks and influences cell adhesion, aggregation, and fusion. A new technique is used to measure this interaction when one of the bodies has colloidal dimensions. The potential energy profile of interactions between a 15-micrometer polystyrene sphere and a glass plate is determined by observing the distribution of separation distances (0.2 to 0.4 micrometer) that the particle samples by Brownian motion. Measurements of the speed with which the sphere is carried by linear shear flow along the wall are used to calculate separation distance. Although evidence for hydrodynamic lift is found, it is not included in the potential profile.
Bacterial Gene Inserted in an Engineered RNA Virus: Efficient Expression in Monocotyledonous Plant Cells
Authors: French Roy , Janda Michael , Ahlquist Paul
Published: October 2006

Brome mosaic virus (BMV) is a plant virus whose genome consists of three RNA components. A previously described viral complementary DNA expression system has been used to express both wild-type and altered genomic RNA's in barley protoplasts. Variants of BMV RNA3 were constructed in which the coat gene had been removed or replaced with sequences encoding chloramphenicol acetyltransferase (CAT). CAT sequences were also inserted near the 5′ end of the intact coat gene. When inoculated on protoplasts together with transcripts of BMV RNA's 1 and 2, all of these RNA3 derivatives were replicated and produced subgenomic RNA's analogous to the normal subgenomic coat protein messenger RNA. RNA3 derivatives in which the CAT coding sequences were oriented with the same polarity as viral genes produced significant CAT activity in protoplasts. CAT expression was improved by inserting the CAT gene in frame with the upstream coat protein initiation codon, and exceeded expression in plant cells transformed with Ti plasmid-based vectors.
Memory Constraints and Flower Choice in
Pieris rapae
Authors: Lewis Alcinda C.
Published: October 2006

Darwin hypothesized that flower constancy in insects that feed on nectar results from the need to learn how to extract nectar from a flower of a given species. In laboratory tests,
Pieris rapae
, the cabbage butterfly, showed flower constancy by continuing to visit flower species with which it had experience. The time required by individuals to find the source of nectar in flowers decreased with successive attempts, the performance following a learning curve. Learning to extract nectar from a second species interfered with the ability to extract nectar from the first. Insects that switch species thus experience a cost in time to learn. These results support recent suggestions on the importance of learning in animal foraging.
Technological Diversification of Japanese Industry
Authors: Kodama Fumio
Published: October 2006

A Japanese database on research and development that disaggregates an industry's intramural expenditure into 31 different product fields is used to measure technological diversification. Sectoral patterns are identified in terms of upstream, downstream, and horizontal diversification—that is, respectively, diversification of an industry's research and development activities into product fields that are industrial inputs of that industry, into those that are outputs, and diversification that is not directed through the path of input-output relations. The pattern of the electronics industry is identified as downstream diversification whereas that of the chemical industry is identified as horizontal. The declining industry is generally making upstream diversification. Japanese corporate and governmental policies, such as trade policy, industrial policy, and the research association scheme, have accelerated technological diversification.
Probing Steric and Hydrophobic Effects on Enzyme-Substrate Interactions by Protein Engineering
Authors: Estell D. A. , Graycar T. P. , Miller J. V. , Powers D. B. , Wells J. A. , Burnier J. P. , Ng P. G.
Published: October 2006

Steric and hydrophobic effects on substrate specificity were probed by protein engineering of subtilisin. Subtilisin has broad peptidase specificity and contains a large hydrophobic substrate binding cleft. A conserved glycine (Gly
166
), located at the bottom of the substrate binding cleft, was replaced by 12 nonionic amino acids by the cassette mutagenesis method. Mutant enzymes showed large changes in specificity toward substrates of increasing size and hydrophobicity. In general, the catalytic efficiency (

k
cat
/K

m
) toward small hydrophobic substrates was increased (up to 16 times) by hydrophobic substitutions at position 166 in the binding cleft. Exceeding the optimal binding volume of the cleft (∼160 Å
3
), by enlarging either the substrate side chain or the side chain at position 166, evoked precipitous drops in catalytic efficiency (

k
cat
/K

m
) (up to 5000 times) as a result of steric hindrance.
Atomic Arrangements at Metal Surfaces
Authors: Noonan J. R. , Davis H. L.
Published: October 2006

The termination of a solid induces changes in the locations of the outermost atoms of the solid. The changes can be minor or as dramatic as the rearrangement of the atoms into a different crystallographic group. Surface crystallography studies have determined that all surfaces are altered by forces induced at the solid-vacuum interface. At the least, the outermost atomic layers are displaced away from positions that they would have had in the bulk environment. Results from experimental and theoretical investigations for the Al(110) surface are discussed to illustrate present understanding of the surface atomic displacements. Some effects that the truncation- induced forces have on the surfaces of binary metal alloys are also discussed.
Localization of PDGF-B Protein in Macrophages in All Phases of Atherogenesis
Authors: Ross Russell , Masuda Junichi , Raines Elaine W. , Gown Allen M. , Katsuda Shogo , Sasahara Masakiyo , Malden L. Trevor , Masuko Hideyuki , Sato Hiroshi
Published: October 2006

Lesions of atherosclerosis occur in the innermost layer of the artery wall and consist primarily of proliferated smooth muscle cells surrounded by large amounts of connective tissue, numerous lipid-laden macrophages, and varying numbers of lymphocytes. Growth-regulatory molecules may be involved in intimal accumulation and proliferation of smooth muscle cells responsible for the occlusive lesions of atherosclerosis. Platelet-derived growth factor (PDGF) B-chain protein was found within macrophages in all stages of lesion development in both human and nonhuman primate atherosclerosis. Thus macrophages may play a critical role in the disease by providing PDGF, a potent chemotactic and growth-stimulatory molecule, to the intimal smooth muscle cells.
Ocean Dynamics and Acoustic Fluctuations in the Fram Strait Marginal Ice Zone
Authors: Dyer Ira , Dahl Peter H. , Baggeroer Arthur B. , Mikhalevsky Peter N.
Published: October 2006

Acoustic waves transmitted over a 100-kilometer path in the Fram Strait marginal ice zone undergo Doppler shifts and fluctuations around these shifts, the former due to quasi-steady motion of both acoustic source and receiver and the latter to unsteady motions of the water column and ice cover. Internal waves and differential Doppler shift usually account for such fluctuations in the deep temperate ocean but only partially explain the results obtained in the marginal ice zone. There the fluctuations are more energetic and may be caused alternatively or additionally by comparably energetic fluctuations in ice-edge eddies or other mesoscale motions.
Observation of Phase Transitions in Spreading Activation Networks
Authors: Shrager Jeff , Hogg Tad , Huberman Bernardo A.
Published: October 2006

Phase transitions, similar to those seen in physical systems, are observed in spreading activation networks. Such networks are used both in theories of cognition and in artificial intelligence applications. This result confirms a predicted abrupt behavioral change as either the topology of the network or the activation parameters are varied across phase boundaries.
Off-Design Performance of Power Plants: An Integrated Gasification Combined-Cycle Example
Authors: Erbes M. R. , Phillips J. N. , Johnson M. S. , Paffenbarger J. , Gluckman M. , Eustis R. H.
Published: October 2006

Fossil-fueled power plants typically operate below their design capacities for a large fraction of their service life. In the United States, increased fuel and capital costs attributable to this off-design operation are considerable. This article describes the reasons for off-design operation and its importance in designing and selecting new power plants. Recent studies of coal gasification combined-cycle power plants show how computer simulations of off-design performance can aid in the design process, and they suggest that such simulations can be useful in reducing the cost of building and operating new power plants.
Calcium-Induced Peptide Association to Form an Intact Protein Domain:
1
H NMR Structural Evidence
Authors: Shaw Gary S. , Hodges Robert S. , Sykes Brian D.
Published: October 2006

The 70-residue carboxyl-terminal domain of the muscle contractile protein troponin-C contains two helix-loop-helix calcium (Ca)-binding sites that are related to each other by approximate twofold rotational symmetry. Hydrophobic residues from the helices and a short three residue β sheet at the interface of the two sites act to stabilize the protein domain in the presence of Ca. A synthetic 34-residue peptide representing one of these sites (site III) has been synthesized and studied by H-1 nuclear magnetic resonance (NMR) spectroscopy. In solution this peptide undergoes a Ca-induced conformational change to form the helix-loop-helix Ca-binding motif. Two-dimensional nuclear Overhauser effect spectra have provided evidence for the formation of a β sheet and interactions between several hydrophobic residues from opposing helices as found in troponin-C. It is proposed that a symmetric two-site dimer similar in tertiary structure to the carboxyl-terminal domain of troponin-C forms from the assembly of two site III peptides in the Ca-bound form.
Climate and Chlorophyll a: Long-Term Trends in the Central North Pacific Ocean
Authors: Venrick E. L. , McGowan J. A. , Cayan D. R. , Hayward T. L.
Published: October 2006

Since 1968 a significant increase in total chlorophyll a in the water column during the summer in the central North Pacific Ocean has been observed. A concomitant increase in winter winds and a decrease in sea surface temperature suggest that long-period fluctuations in atmospheric characteristics have changed the carrying capacity of the central Pacific epipelagic ecosystem.
Icosahedral Solids: A New Phase of Matter?
Authors: Steinhardt Paul J.
Published: October 2006

Numerous examples of metallic alloys have been discovered, the atomic structures of which display an icosahedral symmetry that is impossible for ordinary periodic crystals. Recent experimental results support the hypothesis that the alloys are examples of a new "quasicrystal" phase of solid matter. Observed deviations from an ideal quasicrystal structure can be explained as "phason strains," a special class of defects predicted to be the dominant type of imperfection formed during solidification.
Voltammetry with Microscopic Electrodes in New Domains
Authors: Wightman R. Mark
Published: October 2006

Voltammetric electrodes of microscopic dimension, termed ultramicroelectrodes, can be used to make measurements that are difficult or impossible with conventional electrochemical techniques. Measurements of chemical concentration can be made with these electrodes on a microsecond time scale and with micrometer spatial resolution. In addition, measurements can be made in highly resistive solutions.
Crystal Structure of Hexaazaoctadecahydrocoronene Dication [HAOC]
2+
, a Singlet Benzene Dication
Authors: Miller Joel S. , Dixon David A. , Calabrese Joseph C.
Published: October 2006

The structures of hexaazaoctadecahydrocoronene, [HAOC]

n

(
n
= 0, + 2), have been determined by single-crystal x-ray diffraction. Although HAOC is aromatic, its dication has a localized structure that is based upon Jahn-Teller-distorted cyanine/
p
-phenylenediammonium fragments. The structure is consistent with the singlet ground state as determined by magnetic susceptibility and contrasts with the simplest Hückel expectation of a triplet ground state.
Pancreatic Secretion by Nonparallel Exocytosis: Potential Resolution of a Long Controversy
Authors: Adelson Joel W. , Miller Paul E
Published: October 2006

The idea that pancreatic digestive enzyme secretion can occur in a nonparallel manner has been controversial because of its presumed incompatibility with the exocytosis secretory mechanism. Correlation and regression analysis of enzyme output by the rabbit pancreas after it is stimulated with cholecystokinin and chymodenin revealed that digestive enzymes are secreted in a highly linked fashion, compatible with exocytosis and with nonparallel secretion. Thus, exocytosis and nonparallel secretion are not contradictory processes, but rather nonparallel secretion is due to exocytosis from heterogeneous sources within the pancreas.
The Relationship Between High-Temperature Superconductivity and the Fractional Quantum Hall Effect
Authors: Laughlin R. B.
Published: October 2006

The case is made that the spin-liquid state of a Mott insulator, hypothesized to exist by Anderson and identified by him as the correct context for discussing high-temperature superconductors, occurs in these materials and exhibits the principles of fractional quantization identified in the fractional quantum Hall effect. The most important of these is that particles carrying a fraction of an elementary quantum number, in this case spin, attract one another by a powerful gauge force, which can lead to a new kind of superconductivity. The temperature scale for the superconductivity is set by an energy gap in the spin-wave spectrum, which is also the fundamental measure of how "liquid" the spins are.
Substance P: Localization in the Central Nervous System and in Some Primary Sensory Neurons
Authors: Hökfelt Tomas , Kellerth Jan Olof , Nilsson Göran , Pernow Bengt
Published: October 2006

Antibodies to substance P with a high titer have been produced and used in immunohistochemical studies on the peripheral and central nervous system of the rat and the cat. Evidence was obtained for the localization of substance P in a certain population of primary sensory neurons, probably small nerve cells with unmyelinated processes. Substance P or a peptide similar to it was also observed in cell bodies in the medial habenula and in probable nerve terminals in many brain areas. The results give morphological support for a transmitter (or modulator) role of substance P in the nervous system.
Levitation in Physics
Authors: Brandt E. H.
Published: October 2006

Several physical effects allow free floatation of solid and even liquid matter. Materials may be levitated by a jet of gas, by intense sound waves, or by beams of laser light. In addition, conductors levitate in strong radio-frequency fields, charged particles in alternating electric fields, and magnets above superconductors or vice versa. Although levitation by means of ferromagnets is unstable, superconductors may be suspended both above and below a magnet as a result of flux pinning. Levitation is used for containerless processing and investigation of materials, for frictionless bearings and high-speed ground transportation, for spectroscopy of single atoms and microparticles, and for demonstrating superconductivity in the new oxide superconductors.
Directed Movement of Latex Particles in the Gynoecia of Three Species of Flowering Plants
Authors: Sanders L. C. , Lord E. M.
Published: October 2006

The secretory matrix of the stylar-transmitting tract of angiosperms has been characterized as a nutrient medium for the growth of pollen tubes, acting to guide tubes to the ovules. When nonliving particles (latex beads) were artificially introduced onto the transmitting tracts of styles of
Hemerocallis flava, Raphanus raphanistrum
, and
Vicia faba
, they were translocated to the ovary at rates similar to those of pollen tubes. Direct observations were made on the movement of individual beads along the secretory epidermis in the style and ovary of
Vicia faba.
The transmitting tract may play an active role in extending tube tips to their destination in the ovary.
Development of Two Types of Calcium Channels in Cultured Mammalian Hippocampal Neurons
Authors: Yaari Yoel , Hamon Brigitte , Lux Hans D.
Published: October 2006

Calcium influx through voltage-gated membrane channels plays a crucial role in a variety of neuronal processes, including long-term potentiation and epileptogenesis in the mammalian cortex. Recent studies indicate that calcium channels in some cell types are heterogeneous. This heterogeneity has now been shown for calcium channels in mammalian cortical neurons. When dissociated embryonic hippocampal neurons from rat were grown in culture they first had only low voltage-activated, fully inactivating somatic calcium channels. These channels were metabolically stable and conducted calcium better than barium. Appearing later in conjunction with neurite outgrowth and eventually predominating in the dendrites, were high voltage-activated, slowly inactivating calcium channels. These were metabolically labile and more selective to barium than to calcium. Both types of calcium currents were reduced by classical calcium channel antagonists, but the low voltage-activated channels were more strongly blocked by the anticonvulsant drug phenytoin. These findings demonstrate the development and coexistence of two distinct types of calcium channels in mammalian cortical neurons.
Changing Prospects for Natural Gas in the United States
Authors: Burnet W. M. , Ban S. D
Published: October 2006

Natural gas has emerged as one of the primary options for satisfying the need for environmentally clean energy: the resource base is large, it is the cleanest burning of the fossil fuels, and it can be used efficiently. New engine, combustion, and energy conversion technologies are emerging that will result in use of natural gas in electric generation, emissions reduction, transportation, and residential and commercial cooling.
Glycolysis Preferentially Inhibits ATP-Sensitive K
+
Channels in Isolated Guinea Pig Cardiac Myocytes
Authors: Weiss James N. , Lamp Scott T.
Published: October 2006

In heart, glycolysis may be a preferential source of adenosine triphosphate (ATP) for membrane functions. In this study the patch-clamp technique was used to study potassium channels sensitive to intracellular ATP levels in permeabilized ventricular myocytes. Activation of these K
+
channels has been implicated in marked cellular K
+
loss leading to electrophysiological abnormalities and arrhythmias during myocardial ischemia. The results showed that glycolysis was more effective than oxidative phosphorylation in preventing ATP-sensitive K
+
channels from opening. Experiments in excised inside-out patches suggested that key glycolytic enzymes located in the membrane or adjacent cytoskeleton near the channels may account for their preference for glycolytic ATP.
Identification of an Intracellular Peptide Segment Involved in Sodium Channel Inactivation
Authors: Vassilev Peter M. , Scheuer Todd , Catterall William A.
Published: October 2006

Antibodies directed against a conserved intracellular segment of the sodium channel α subunit slow the inactivation of sodium channels in rat muscle cells. Of four site-directed antibodies tested, only antibodies against the short intracellular segment between homologous transmembrane domains III and IV slowed inactivation, and their effects were blocked by the corresponding peptide antigen. No effects on the voltage dependence of sodium channel activation or of steady-state inactivation were observed, but the rate of onset of the antibody effect and the extent of slowing of inactivation were voltage-dependent. Antibody binding was more rapid at negative potentials, at which sodium channels are not inactivated; antibody-induced slowing of inactivation was greater during depolarizations to more positive membrane potentials. The peptide segment recognized by this antibody appears to participate directly in rapid sodium channel inactivation during large depolarizations and to undergo a conformational change that reduces its accessibility to antibodies as the channel inactivates.
The Chemistry of Solid-State Electronics
Authors: Yablonovitch E.
Published: October 2006

Since the original theoretical insights of Bardeen and Shockley about 40 years ago, the progress of solid-state electronics has been paced by the ability to control chemical bonding structures, particularly at surfaces and interfaces. The functioning of solid-state devices depends on being able to produce interfacial structures with a minimum number of defective chemical bonds. A series of chemical discoveries and insights, on germanium (Ge) and silicon (Si) surfaces and gallium arsenide-aluminum arsenide (GaAs-AlAs) interfaces, has brought the electronics revolution to its present state of development. In most cases, the technological consequences of these accidental discoveries could not be accurately foreseen. With that caution, the technological prognosis for some current research is also reviewed.
Is Soot Composed Predominantly of Carbon Clusters?
Authors: Ebert Lawrence B.
Published: October 2006

Soot generated from diesel fuel in a combustion tube is characterized by microanalysis, x-ray diffraction, chemical reactivity, and nuclear magnetic resonance to address the recent proposal of the significance of carbon clusters in soot. The data support a traditional model of soot as polynuclear aromatic compounds rather than as clusters of carbon atoms with minimal edge site density. The amounts of noncarbon atoms in the soot (hydrogen, oxygen, nitrogen, and sulfur) are commensurate with the edge density of the crystallites (2 by 2 nanometers) inferred from diffraction. The chemistry of soot, in being reduced by potassium metal and alkylated by alkyl iodides, is that known for aromatic compounds and not that anticipated for materials such as graphite, with a small fraction of carbon atoms on edges.
Three-Dimensional Solution Structure of a Single Zinc Finger DNA-Binding Domain
Authors: Lee Min S. , Gippert Garry P. , Soman Kizhake V. , Case David A. , Wright Peter E.
Published: October 2006

The three-dimensional solution structure of a zinc finger nucleic acid binding motif has been determined by nuclear magnetic resonance (NMR) spectroscopy. Spectra of a synthetic peptide corresponding to a single zinc finger from the Xenopus protein Xfin yielded distance and dihedral angle constraints that were used to generate structures from distance geometry and restrained molecular dynamics calculations. The zinc finger is an independently folded domain with a compact globular structure in which the zinc atom is bound by two cysteine and two histidine ligands. The polypeptide backbone fold consists of a well-defined helix, starting as alpha and ending as 3(10) helix, packed against two beta strands that are arranged in a hairpin structure. A high density of basic and polar amino acid side chains on the exposed face of the helix are probably involved in DNA binding.
Regulation of Proenkephalin by Fos and Jun
Authors: Sonnenberg June L. , Rauscher Frank J. , Morgan James I. , Curran Tom
Published: October 2006

Fos and Jun form a heterodimeric complex that associates with the nucleotide sequence motif known as the AP-1 binding site. Although this complex has been proposed to function as a transcriptional regulator in neurons, no specific target gene has yet been identified. Proenkephalin mRNA increased in the hippocampus during seizure just after an increase in c-
fos
and c-
jun
expression was detected. Fos-Jun complexes bound specifically to a regulatory sequence in the 5′ control region of the proenkephalin gene. Furthermore, c-
fos
and c-
jun
stimulated transcription from this control region synergistically in transactivation assays. These data suggest that the proenkephalin gene may be a physiological target for Fos and Jun in the hippocampus and indicate that these proto-oncogene transcription factors may play a role in neuronal responses to stimulation.
A New Mechanism for the Formation of Meteoritic Kerogen-Like Material
Authors: Morgan Windsor A. , Feigelson Eric D. , Wang Hai , Frenklach Michael
Published: October 2006

The carbon in ancient carbonaceous chondritic meteorites is mainly in a hydrocarbon composite similar to terrestrial kerogen, a cross-linked structure of aliphatic and aromatic hydrocarbons. Until recently, the composite has been commonly thought to have been produced in the early solar nebula by a Fischer-Tropsch-type process, involving the catalytic synthesis of hydrocarbons from carbon monoxide and hydrogen on grain surfaces. Instead, the aromatic hydrocarbons may form in gas-phase pyrolysis of simple aliphatics like acetylene and methane by a mechanism developed recently to explain formation of soot in combustion and of aromatic molecules in circumstellar envelopes. Nonequilibrium chemical kinetic calculations indicate that this mechanism can produce meteoritic aromatics if the initial concentration of simple hydrocarbons in the solar nebula was sufficiently but not unreasonably high.
Magellan: Radar Performance and Data Products
Authors: Pettengill Gordon H. , Ford Peter G. , Johnson William T. K. , Raney R. Keith , Soderblom Laurence A.
Published: October 2006

The Magellan Venus orbiter carries only one scientific instrument: a 12.6-centimeter wavelength radar system shared among three data-taking modes. The synthetic-aperture mode images radar echoes from the Venus surface at a resolution of between 120 and 300 meters, depending on spacecraft altitude. In the altimetric mode, relative height measurement accuracies may approach 5 meters, depending on the terrain's roughness, although orbital uncertainties place a floor of about 50 meters on the absolute uncertainty. In areas of extremely rough topography, accuracy is limited by the inherent line-of-sight radar resolution of about 88 meters. The maximum elevation observed to date, corresponding to a planetary radius of 6062 kilometers, lies within Maxwell Mons. When used as a thermal emission radiometer, the system can determine surface emissivities to an absolute accuracy of about 0.02. Mosaicked and archival digital data products will be released in compact disk (CDROM) format.
Osteoclastic Bone Resorption by a Polarized Vacuolar Proton Pump
Authors: Blair Harry C. , Teitelbaum Steven L. , Ghiselli Robert , Gluck Stephen
Published: October 2006

Bone resorption depends on the formation, by osteoclasts, of an acidic extracellular compartment wherein matrix is degraded. The mechanism by which osteoclasts transport protons into that resorptive microenvironment was identified by means of adenosine triphosphate-dependent weak base accumulation in isolated osteoclast membrane vesicles, which exhibited substrate and inhibition properties characteristic of the vacuolar, electrogenic H
+
-transporting adenosine triphosphatase (H
+
-ATPase). Identify of the proton pump was confirmed by immunoblot of osteoclast membrane proteins probed with antibody to vacuolar H
+
-ATPase isolated from bovine kidney. The osteoclast's H
+
-ATPase was immunocytochemically localized to the cell-bone attachment site. Immunoelectron microscopy showed that the H
+
-ATPase was present in the ruffled membrane, the resorptive organ of the cell.
Isolation of a Novel Receptor cDNA Establishes the Existence of Two PDGF Receptor Genes
Authors: Matsui Toshimitsu , Heidaran Mohammad , Miki Toru , Popescu Nicholas , La Rochelle William , Kraus Matthias , Pierce Jacalyn , Aaronson Stuart
Published: October 2006

A genomic sequence and cloned complementary DNA has been identified for a novel receptor-like gene of the PDGF receptor/CSF1 receptor subfamily (platelet-derived growth factor receptor/colony-stimulating factor type 1 receptor). The gene recognized a 6.4-kilobase transcript that was coexpressed in normal human tissues with the 5.3-kilobase PDGF receptor messenger RNA. Introduction of complementary DNA of the novel gene into COS-1 cells led to expression of proteins that were specifically detected with antiserum directed against a predicted peptide. When the new gene was transfected into COS-1 cells, a characteristic pattern of binding of the PDGF isoforms was observed, which was different from the pattern observed with the known PDGF receptor. Tyrosine phosphorylation of the receptor in response to the PDGF isoforms was also different from the known receptor. The new PDGF receptor gene was localized to chromosome 4q11-4q12. The existence of genes encoding two PDGF receptors that interact in a distinct manner with three different PDGF isoforms likely confers considerable regulatory flexibility in the functional responses to PDGF.
Bond Lengths in Free Molecules of Buckminsterfullerene, C
60
, from Gas-Phase Electron Diffraction
Authors: Hedberg Kenneth , Hedberg Lise , Bethune Donald S. , Brown C. A. , Dorn H. C. , Johnson Robert D. , De Vries M.
Published: October 2006

Electron diffraction patterns of the fullerene C
60
in the gaseous state have been obtained by volatilizing it from a newly designed oven-nozzle at 730°C. The many peaks of the experimental radial distribution curve calculated from the scattered intensity are completely consistent with icosahedral symmetry for the free molecule. On the basis of this symmetry assumption, least-squares refinement of a model incorporating all possible interatomic distances led to the values
r
g
(C
1
-C
2
) = 1.458(6) angstroms (Å) for the thermal average bond length within the five-member ring (that is, for the bond fusing five- and six-member rings) and
r
g
(C
1
-C
6
) = 1.401(10) Å for that connecting five-member rings (the bond fusing six-member rings). The weighted average of the two bond lengths and the difference between them are the values 1.439(2) Å and 0.057(6) Å, respectively. The diameter of the icosahedral sphere is 7.113(10) Å. The uncertainties in parentheses are estimated 2σ values.
Tunneling Spectroscopy of M
3
C
60
Superconductors: The Energy Gap, Strong Coupling, and Superconductivity
Authors: Zhang Zhe , Chen Chia-Chun , Lieber Charles M.
Published: October 2006

Tunneling spectroscopy has been used to characterize the magnitude and temperature dependence of the superconducting energy gap (Δ) for K
3
C
60
and Rb
3
C
60
. At low temperature the reduced energy gap, 2Δ/
k
T
c
(where
T
c
is the transition temperature) has a value of 5.3 ± 0.2 and 5.2 ± 0.3 for K
3
C
60
and Rb
3
C
60
, respectively. The magnitude of the reduced gap for these materials is significantly larger than the value of 3.53 predicted by Bardeen-Cooper-Schrieffer theory. Hence, these results show that the pair-coupling interaction is strong in the M
3
C
60
superconductors. In addition, measurements of Δ(
T
) for both K
3
C
60
and Rb
3
C
60
exhibit a similar mean-field temperature dependence. The characterization of Δ and Δ(
T
) for K
3
C
60
and Rb
3
C
60
provides essential constraints for theories evolving to describe superconductivity in the M
3
C
60
materials.
Natural Vegetation as a Source or Sink for Atmospheric Ammonia: A Case Study
Authors: Langford A. O. , Fehsenfeld F. C.
Published: October 2006

Measurements of gaseous ammonia above a montane-subalpine forest in the Colorado mountains show that the role of the forest as a source or sink depends on the atmospheric concentrations. The canopy appeared to be an ammonia source when exposed to air containing low concentrations, but a sink when exposed to air enriched by nearby agricultural sources. The forest-averaged compensation point was 0.8 part per billion by volume at 20°C. The net burden of ammonia and other nitrogen species of anthropogenic origin at this site was much less than at forest sites in the eastern United States and Europe and may provide a valuable resource for this nitrogen-limited ecosystem.
NMR Diffraction and Spatial Statistics of Stationary Systems
Authors: Barrall G. A. , Frydman L. , Chingas G. C.
Published: October 2006

Nuclear magnetic resonance (NMR) spatial imaging data may be acquired, processed, and interpreted in ways that provide information directly analogous to diffraction experiments, with length scales determined by gradient strengths rather than radiation wavelengths. This approach, originally considered by Mansfield nearly two decades ago, provides access to autocorrelations of sample density that statistically characterize small-scale density variations. These NMR "Patterson functions" can be acquired orders of magnitude more rapidly than comparably resolved NMR images and are suitable for spatial characterization of small features in bulk samples, such as morphology in structural materials. Unlike hindered diffusion approaches, neither mobility, penetrants, nor transport time are required for examining granularity and porosity.
Photon Number Squeezed States in Semiconductor Lasers
Authors: Yamamoto Yoshihisa , Machida Susumu , Richardson Wayne H.
Published: October 2006

Electromagnetic fields, with the noise on one quadrature component reduced to below the quantum mechanical zero-point fluctuation level and the noise on the other quadrature component enhanced to above it, are currently of great interest in quantum optics because of their potential applications to various precision measurements. Such squeezed states of light are usually produced by imposing nonlinear unitary evolution on coherent (or vacuum) states. On the other hand, squeezed states with reduced photon number noise and enhanced phase noise are generated directly by a constant current-driven semiconductor laser. This is the simplest scheme for the generation of nonclassical light, and so far it has yielded the largest quantum noise reduction. The mutual coupling between a lasing junction and an external electrical circuit provides opportunities for exploring the macroscopic and microscopic quantum effects in open systems.
Direct Observation of Chemical Bond Dynamics on Surfaces
Authors: Yates J. T. , Alvey M. D. , Dresser M. J. , Henderson M. A. , Kiskinova M. , Ramsier R. D. , Szabó A.
Published: October 2006

The dynamics of chemisorbed species as they swing to-and-fro on their adsorption sites may be directly observed with electron-stimulated desorption. The observation of the thermal disorder in adsorbate chemical bond directions, through studies of the thermal excitation of librational modes, allows one to visualize the potential energy surfaces controlling the structure and dynamics of adsorbates on single crystal metal and semiconductor surfaces. This information may be useful in understanding surface diffusion as well as the spatial aspects of surface chemical reactions.
Neurotransmitter Release from Synaptotagmin-Deficient Clonal Variants of PC 12 Cells
Authors: Shoji-Kasai Yoko , Yoshida Akira , Sato Kazuki , Hoshino Toshimitsu , Ogura Akihiko , Kondo Shunzo , Fujimoto Yoshiko , Kuwahara Reiko , Kato Rika , Takahashi Masami
Published: October 2006

Synaptotagmin (p65) is an abundant synaptic vesicle protein of neurons and contains regions similar to the regulatory domain of protein kinase C. These domains are thought to be involved in calcium-dependent interaction with membrane phospholipids during exocytosis. To assess the functional role of synaptotagmin, synaptotagmin-deficient clonal variants of PC12 cells were isolated. All of the variant cells released catecholamine and adenosine triphosphate in response to elevated intracellular concentrations of calcium, which suggests that synaptotagmin is not essential for secretion of catecholamine and adenosine triphosphate from PC12 cells.
Brain Region and Gene Specificity of Neuropeptide Gene Expression in Cultured Astrocytes
Authors: Shinoda Hisaharu , Marini Ann M. , Cosi Cristina , Schwartz Joan P.
Published: October 2006

Astrocytes have many neuronal characteristics, such as neurotransmitter receptors, ion channels, and neurotransmitter uptake systems. Cultured astrocytes were shown to express certain neuropeptide genes, with specificity for both the gene expressed and the brain region from which the cells were prepared. Somatostatin messenger RNA and peptides were detected only in cerebellar astrocytes, whereas proenkephalin messenger RNA and enkephalin peptides were present in astrocytes of cortex, cerebellum, and striatum. Cholecystokinin was not expressed in any of the cells. These results support the hypothesis that peptides synthesized in astrocytes may play a role in the development of the central nervous system.
Electron Photodetachment Cross Sections of Small Carbon Clusters: Evidence for Nonlinear Isomers
Authors: Zajfman D. , Feldman H. , Heber O. , Kella D. , Majer D. , Vager Z. , Naaman R.
Published: October 2006

Absolute cross sections for photodetachment of negative carbon clusters are reported for C

n

-
(
n
= 3, ..., 8). The results indicate that various neutral isomers exist, some with electron affinities as low as 1 electron volt. The method of production plays an important role in the characteristics of carbon clusters.
Temperature and Size Variabilities of the Western Pacific Warm Pool
Authors: Yan Xiao-Hai , Ho Chung-Ru , Zheng Quanan , Klemas Vic
Published: October 2006

Variabilities in sea-surface temperature and size of the Western Pacific Warm Pool were tracked with 10 years of satellite multichannel sea-surface temperature observations from 1982 to 1991. The results show that both annual mean sea-surface temperature and the size of the warm pool increased from 1983 to 1987 and fluctuated after 1987. Possible causes of these variations include solar irradiance variabilities, El Niño—Southern Oscillation events, volcanic activities, and global warming.
Lidar Observations of the Meteoric Deposition of Mesospheric Metals
Authors: Kane Timothy J. , Gardner Chester S.
Published: October 2006

The mesospheric sodium and iron layers at an altitude between about 80 and 110 kilometers are routinely monitored by atmospheric physicists using resonance fluorescence lidar techniques because these constituents are excellent tracers of mesopause chemistry and dynamics. The mesospheric metals are the products of meteoric ablation. Existing ablation profiles are model calculations based in part on radar observations of the ionized background atmosphere left in the wake of high-speed (> 20 kilometers per second) meteoroids. Thin trails of neutral metal atoms, ablated from individual meteoroids, are occasionally observed with high-power lidars. The vertical distribution of 101 sodium and 5 iron meteor trails observed during the past 4 years at Urbana, Illinois; Arecibo, Puerto Rico; and near Hawaii is approximately Gaussian in shape with a centroid height of 89.0 (± 0.3) kilometers and a root-mean-square width of 3.3 (± 0.2) kilometers. This directly measured ablation profile is nearly the same as the mean iron layer profile but is considerably different from existing models and the distribution of ionized meteor trails observed by radars. A lower limit on the influx to the mesopause region from the lidar meteors is approximately 1.6 × 10
3
sodium and 2.7 × 10
4
iron atoms per second per square centimeter, which corresponds to an annual flux of meteoric debris into the mesosphere of about 2.0 (± 0.6) gigagrams. Because the lidars can detect only the ablation trails left by the larger meteors, the observations suggest that the actual meteoric influx may be larger than the more recently reported values, which range between 16 and 78 gigagrams per year.
Annealing C
60
+
: Synthesis of Fullerenes and Large Carbon Rings
Authors: Hunter Joanna , Fye James , Jarrold Martin F.
Published: October 2006

Laser vaporization of graphite generates C
60
+
cluster ions that are fullerenes and a mixture of roughly planar polycyclic polyyne ring isomers. Experimental studies of the annealing of the non-fullerene C
60
+
ions indicate that they can be converted (in the gas phase) into the fullerene and an isomer that appears to be a large monocyclic ring. Some fragmentation is associated with conversion to the fullerene geometry, but the majority of the non-fullerene C
60
+
isomers are cleanly converted into an intact fullerene. The emergence of the monocyclic ring (as the clusters are annealed) suggests that this is a relatively stable non-spheroidal form of these all carbon molecules. The estimated activation energies for the observed structural interconversions are relatively low, suggesting that these processes may play an important role in the synthesis of spheroidal fullerenes.