bluuebunny/crossref_metadata_2025 huggingface dataset:
The Physics of Organic Superconductors
Authors: Jérome D.
Published: October 2006

The upper temperature for superconductivity in organic conductors has increased from 1 kelvin in 1980, when the phenomenon was discovered in the quasi—one-dimensional cation radical salt tetramethyltetraselenafulvalene phosphorus heptafluoride to 12 kelvin in a new series of organic salts that show nearly two-dimensional electronic properties. These superconductors are attracting interest because of the wide range of new phenomena that they exhibit, including the competition between various ground states, the influence of a magnetic field on a quasi—one-dimensional conductor, the quantization of the Hall effect in a three-dimensional material, the giant magnetoresistance effects related to the two-dimensional nature of the Fermi surface of some materials, and the coherent voltage oscillation of a spin-modulated ground state. Furthermore, there is reason to believe that organic conductors with high superconducting transition temperatures could be produced in the near future. The recent finding of superconductivity in "fullerene" doped with alkali metals supports this optimism.
High-Pressure Chemistry of Hydrogen in Metals: In Situ Study of Iron Hydride
Authors: Badding J. V. , Hemley R. J. , Mao H. K.
Published: October 2006

Optical observations and x-ray diffraction measurements of the reaction between iron and hydrogen at high pressure to form iron hydride are described. The reaction is associated with a sudden pressure-induced expansion at 3.5 gigapascals of iron samples immersed in fluid hydrogen. Synchrotron x-ray diffraction measurements carried out to 62 gigapascals demonstrate that iron hydride has a double hexagonal close-packed structure, a cell volume up to 17% larger than pure iron, and a stoichiometry close to FeH. These results greatly extend the pressure range over which the technologically important iron-hydrogen phase diagram has been characterized and have implications for problems ranging from hydrogen degradation and embrittlement of ferrous metals to the presence of hydrogen in Earth's metallic core.
The Temperature of Cavitation
Authors: Flint Edward B. , Suslick Kenneth S.
Published: October 2006

Ultrasonic irradiation of liquids causes acoustic cavitation: the formation, growth, and implosive collapse of bubbles. Bubble collapse during cavitation generates transient hot spots responsible for high-energy chemistry and emission of light. Determination of the temperatures reached in a cavitating bubble has remained a difficult experimental problem. As a spectroscopic probe of the cavitation event, sonoluminescence provides a solution. Sonoluminescence spectra from silicone oil were reported and analyzed. The observed emission came from excited state C
2
(Swan band transitions,
d
3
II

g

—
a
3
II

u

), which has been modeled with synthetic spectra as a function of rotational and vibrational temperatures. From comparison of synthetic to observed spectra, the effective cavitation temperature was found to be 5075 ± 156 K.
The Role of Magma Overpressure in Suppressing Earthquakes and Topography: Worldwide Examples
Authors: Parsons Tom , Thompson George A.
Published: October 2006

In an extending terrane basaltic magma supplied at a pressure greater than the least principal stress (overpressure) may be capable of suppressing normal faulting and the earthquakes and topographic relief that commonly accompany normal faulting. As vertical dikes intrude, they press against their walls in the direction opposite the least principal stress and increase its magnitude. The emplacement of tabular intrusions causes the internal magma pressure to act selectively in opposition to tectonic stresses. This process tends to equalize the stresses and thus diminishes the deviatoric stress (difference between maximum and minimum stresses) that creates faults and causes earthquakes. Observations of the pattern of seismicity and magmatism worldwide indicate that magmatism commonly supplants large earthquakes as the primary mechanism for accommodating tectonic extension. Recognizing the extent of magmatic stress accommodation is important in assessing seismic and volcanic risks.
Soil Carbon Isotope Evidence for Holocene Habitat Change in the Kenya Rift Valley
Authors: Ambrose Stanley H. , Sikes Nancy E.
Published: October 2006

In eastern Africa the altitude of the boundary between montane forest and lowland savanna grassland changed substantially in response to climate change during the later Holocene, but this is not clearly reflected in regional pollen records. The carbon-13 to carbon-12 ratios of tropical grasses are higher than those of most other plants, and this difference is preserved in soil organic carbon stable isotope ratios. Soil organic matter
13
C/
12
C ratios in profiles along an altitude transect in the central Rift Valley of Kenya suggest that the forest-savanna boundary advanced more than 300 meters in altitude. This could have implications for understanding the effects of climate change on the configuration of floral zones, prehistoric hunter-gatherer land-use patterns, and the timing of the advent of Neolithic food production.
Radar Images of Mars
Authors: Muhleman Duane O. , Butler Bryan J. , Grossman Arie W. , Slade Martin A.
Published: October 2006

Full disk images of Mars have been obtained with the use of the Very Large Array (VLA) to map the radar reflected flux density. The transmitter system was the 70-m antenna of the Deep Space Network at Goldstone, California. The surface of Mars was illuminated with continuous wave radiation at a wavelength of 3,5 cm. The reflected energy was mapped in individual 12-minute snapshots with the VLA in its largest configuration; fringe spacings as small as 67 km were obtained. The images reveal near-surface features including a region in the Tharsis volcano area, over 2000 km in east-west extent, that displayed no echo to the very low level of the radar system noise. The feature, called Stealth, is interpreted as a deposit of dust or ash with a density less than about 0.5 gram per cubic centimeter and free of rocks larger than 1 cm across. The deposit must be several meters thick and may be much deeper. The strongest reflecting geological feature was the south polar ice cap, which was reduced in size to the residual south polar ice cap at the season of observation. The cap image is interpreted as arising from nearly pure CO
2
or H
2
O ice with a small amount of martian dust (less than 2 percent by volume) and a depth greater than 2 to 5 m. Only one anomalous reflecting feature was identified outside of the Tharsis region, although the Elysium region was poorly sampled in this experiment and the north pole was not visible from Earth.
The Mysteries Of Lipoprotein(a)
Authors: Utermann Gerd
Published: October 2006

Lipoprotein(a) [Lp(a)] is a macromolecular complex found in human plasma that combines structural elements from the lipoprotein and blood clotting systems and that is associated with premature coronary heart disease and stroke. It is assembled from low-density lipoprotein (LDL) and a large hydrophilic glycoprotein called apolipoprotein(a) [apo(a)], which is homologous to the protease zymogen plasminogen. Plasma Lp(a) concentrations vary 1000-fold between individuals and represent a continuous quantitative genetic trait with a skewed distribution in Caucasian populations. Variation in the hypervariable
apo(a)
gene on chromosome 6q2.6-q2.7 and interaction of
apo(a)
alleles with defective LDL-receptor genes explain a large fraction of the variability of plasma Lp(a) concentrations. Though of high theoretical and practical interest, many aspects of the metabolism, function, evolution, and regulation of plasma concentrations of Lp(a) are presently unknown, controversial, or mysterious.
Mechanisms for Regulating Expression of Membrane Isoforms of FcγRIII (CD16)
Authors: Hibbs Margaret L. , Selvaraj Periasamy , Carpén Olli , Springer Timothy A. , Kuster Helmut , Jouvin Marie-Hélène E. , Kinet Jean-Pierre
Published: October 2006

Granulocyte and natural killer (NK) cell Fc receptors for immunoglobulin G (CD16) differ in only a few amino acids, yet have phosphatidylinositol glycan (PIG) or polypeptide membrane anchors, respectively. Mutagenesis shows that anchoring is regulated by a serine residue near the PIG anchor attachment site in the extracellular domain. The NK cell isoform was not expressed on the surface of COS cells unless cotransfected with a subunit that was expressed in NK cells and that was identical to the γ subunit of the high affinity IgE Fc receptor (FcεRI). However, the CD16 sequence and not expression of the γ subunit is dominant in regulating PIG reanchoring.
Repression of the IgH Enhancer in Teratocarcinoma Cells Associated with a Novel Octamer Factor
Authors: Lenardo Michael J. , Staudt Louis , Robbins Paul , Kuang Anna , Mulligan Richard C. , Baltimore David
Published: October 2006

Embryonal carcinoma (EC) cell lines are models for early cells in mouse embryogenesis. A 300-base pair fragment of the heavy chain enhancer was inactive in F9 EC cells, unlike in other nonlymphoid cells where it has significant activity. Alterations of the octamer motif increased enhancer activity. Nuclear extracts from F9 cells contained an octamer binding protein (NF-A3) that was unique to EC cells; the amount of NF-A3 decreased upon differentiation. It is proposed that NF-A3 represses specific regulatory sequences that contain the octamer motif. Thus, the same DNA sequence mediates either negative or positive transcriptional effects, depending on the cell type.
Chemical Microsensors
Authors: Hughes R. C. , Ricco A. J. , Butler M. A. , Martin S. J.
Published: October 2006

Recent developments in the field of chemical microsensors are leading to new applications for which these devices have the potential to supplement or replace traditional analytical chemical instrumentation. The fundamentals of current microelectronic, acoustic wave, optical fiber, and electrochemical microsensors are presented, and a few recent, exciting results in these areas are described. Although future opportunities in the microsensor field are numerous, many significant problems, the majority of them related to the materials utilized for the chemically sensitive layers that are the "front end" of these devices, remain to be explored and solved.
Reactivity of Organic Compounds in Hot Water: Geochemical and Technological Implications
Authors: SISKIN MICHAEL , KATRITZKY ALAN R.
Published: October 2006

Understanding of the reactivity of organic molecules in hot water is developing from studies aimed at explaining how organic matter (kerogen) forms in natural environments and then breaks down into energy source materials. In natural systems where kerogens are depolymerized, hot water is ubiquitous and usually contains salt and minerals. Reactions such as ionic condensation, cleavage, and hydrolysis are facilitated by changes in the chemical and physical properties of water as temperature increases. These changes make the solvent properties of water at high temperature similar to those of polar organic solvents at room temperature, thus facilitating reactions with organic compounds. An understanding of aqueous organic chemistry may lead to potential applications in areas as diverse as the recycling of plastics, the synthesis of chemicals, and coal liquefaction.
Ice Flexure Forced by Internal Wave Packets in the Arctic Ocean
Authors: Czipott Peter V. , Levine Murray D. , Paulson Clayton A. , Menemenlis Dimitris , Farmer David M. , Williams Robin G.
Published: October 2006

Tiltmeters on the Arctic Ocean were used to measure flexure of the ice forced by an energetic packet of internal waves riding the crest of diurnal internal bores emanating from the Yermak Plateau, north of the Svalbard Archipelago. The waves forced an oscillatory excursion of 36 microradians in tilt of the ice, corresponding to an excursion of 16 micrometers per second in vertical velocity at the surface and of 3.5 millimeters in surface displacement. Strainmeters embedded in the ice measured an excursion of 3 × 10
–7
in strain, consistent with ice flexure rather than compression. The measured tilt is consistent with direct measurements of excursions in horizontal current near the surface (12 centimeters per second) and in vertical displacement (36 meters) of the pycnocline 100 meters below the surface.
Phase Transformations in Carbon Fullerenes at High Shock Pressures
Authors: Yoo C. S. , Nellis W. J.
Published: October 2006

C
60
powders were shock-compressed quasi-isentropically and quenched from pressures in the range 10 to 110 GPa (0.1 to 1.1 Mbar). Recovered specimens were analyzed by Raman spectroscopy and optical microscopy. C
60
fullerenes are stable into the 13- to 17-GPa pressure range. The onset of a fast (∼0.5 μs) reconstructive transformation to graphite occurs near 17 GPa. The graphite recovered from 27 GPa and about 600°C is relatively well ordered with crystal planar domain size of about 100 Å. Above 50 GPa a continuous transformation to an amorphous state is observed in recovered specimens. The fast transformation to graphite is proposed to occur by π-electron rehybridization which initiates breakup of the ball structure and formation of the graphite structure at high density.
Perceived Risk, Trust, and the Politics of Nuclear Waste
Authors: Slovic Paul , Flynn James H. , Layman Mark
Published: October 2006

The Department of Energy's program for disposing of high-level radioactive wastes has been impeded by overwhelming political opposition fueled by public perceptions of risk. Analysis of these perceptions shows them to be deeply rooted in images of fear and dread that have been present since the discovery of radioactivity. The development and use of nuclear weapons linked these images to reality and the mishandling of radioactive wastes from the nation's military weapons facilities has contributed toward creating a profound state of distrust that cannot be erased quickly or easily. Postponing the permanent repository and employing dry-cask storage of wastes on site would provide the time necessary for difficult social and political issues to be resolved.
Identification of the Fusion Peptide of Primate Immunodeficiency Viruses
Authors: Bosch Marnix L. , Earl Patricia L. , Fargnoli Kathleen , Picciafuoco Silvia , Giombini Fabrizio , Wong-Staal Flossie , Franchini Genoveffa
Published: October 2006

Membrane fusion induced by the envelope glycoproteins of human and simian immunodeficiency viruses (HIV and SIV
mac
) is a necessary step for the infection of CD4 cells and for the formation of syncytia after infection. Identification of the region in these molecules that mediates the fusion events is important for understanding and possibly interfering with HIV/SIV
mac
infection and pathogenesis. Amino acid substitutions were made in the 15 NH
2
-terminal residues of the SIV
mac
gp32 transmembrane glycoprotein, and the mutants were expressed in recombinant vaccinia viruses, which were then used to infect CD4-expressing T cell lines. Mutations that increased the overall hydrophobicity of the gp32 NH
2
-terminus increased the ability of the viral envelope to induce syncytia formation, whereas introduction of polar or charged amino acids in the same region abolished the fusogenic function of the viral envelope. Hydrophobicity in the NH
2
-terminal region of gp32 may therefore be an important correlate of viral virulence in vivo and could perhaps be exploited to generate a more effective animal model for the study of acquired immunodeficiency syndrome.
Regulation of Calcium Release Is Gated by Calcium Current, Not Gating Charge, in Cardiac Myocytes
Authors: Näbauer Michael , Callewaert Geert , Cleemann Lars , Morad Martin
Published: October 2006

In skeletal muscle, intramembrane charge movement initiates the processes that lead to the release of calcium from the sarcoplasmic reticulum. In cardiac muscle, in contrast, the similarity of the voltage dependence of developed tension and intracellular calcium transients to that of calcium current suggests that the calcium current may gate the release of calcium. Nevertheless, a mechanism similar to that of skeletal muscle continues to be postulated for cardiac muscle. By using rapid exchange (20 to 50 milliseconds) of the extracellular solutions in rat ventricular myocytes in which the intracellular calcium transients or cell shortening were measured, it has now been shown that the influx of calcium through the calcium channel is a mandatory link in the processes that couple membrane depolarization to the release of calcium. Thus, intramembrane charge movement does not contribute to the release of calcium in heart muscle.
Repeat-induced G-C to A-T Mutations in
Neurospora
Authors: Cambareri Edward B. , Jensen Bryan C. , Schabtach Eric , Selker Eric U.
Published: October 2006

In the
Neurospora
genome duplicate sequences are detected and altered in the sexual phase. Both copies of duplicate genes are inactivated at high frequency, whether or not they are linked. Restriction sites change, and affected sequences typically become heavily methylated. To characterize the alterations of the DNA, duplicated sequences were isolated before and after one or more sexual cycles. DNA sequencing and heteroduplex analyses demonstrated that the process (termed RIP) produces exclusively G-C to A-T mutations. Changes occur principally at sites where adenine is 3′ of the changed cytosine. A sequence duplicated at a distant site in the genome lost approximately 10 percent of its G-C pairs in one passage through a cross. A closely linked duplication of the same sequence that was passed twice through a cross lost about half of its G-C pairs. The results suggest a mechanism for the RIP process.
Orientational Ordering of Polymers by Atomic Force Microscope Tip-Surface Interaction
Authors: Leung On Man , Goh M. Cynthia
Published: October 2006

Results of studies on the interaction between the tip of an atomic force microscope and polystyrene molecules in a film spread on a surface are reported. The tip produces a persistent deformation on the film; some of the polymer molecules are eventually pulled up by the tip. Nanometer-size structures are induced, resulting in a pattern that is periodic and is oriented perpendicular to the scan direction.
Paleoceanography of the Tropical Eastern Pacific Ocean
Authors: Grigg Richard W. , Hey Richard
Published: October 2006

The East Pacific Barrier (EPB) is the most effective marine barrier to dispersal of tropical shallow-water fauna in the world today. The fossil record of corals in the eastern Pacific suggests this has been true throughout the Cenozoic. In the Cretaceous, the EPB was apparently less effective in limiting dispersal. Equatorial circulation in the Pacific then appears to have been primarily east to west and the existence of oceanic atolls (now drowned guyots) in the eastern Pacific probably aided dispersal. Similarly, in the middle and early Mesozoic and late Paleozoic, terranes in the central tropical Pacific likely served as stepping stones to dispersal of tropical shelf faunas, reducing the isolating effect of an otherwise wider Pacific Ocean (Panthalassa).
Modeling 100,000-Year Climate Fluctuations in Pre-Pleistocene Time Series
Authors: Crowley Thomas J. , Kim Kwang-Yul , Mengel John G. , Short David A.
Published: October 2006

A number of pre-Pleistocene climate records exhibit significant fluctuations at the 100,000-year (100-ky) eccentricity period, before the time of such fluctuations in global ice volume. The origin of these fluctuations has been obscure. Results reported here from a modeling study suggest that such a response can occur over low-latitude land areas involved in monsoon fluctuations. The twice yearly passage of the sun across the equator and the seasonal timing of perihelion interact to increase both 100-ky and 400-ky power in the modeled temperature field. The magnitude of the temperature response is sufficiently large to leave an imprint on the geologic record, and simulated fluctuations resemble those found in records of Triassic lake levels.
Thermal Conductivity of Monolithic Organic Aerogels
Authors: Lu X. , Arduini-Schuster M. C. , Kuhn J. , Nilsson O. , Fricke J. , Pekala R. W.
Published: October 2006

The total thermal conductivity λ of resorcinol-formaldehyde aerogel monoliths has been measured as a function of density ρ in the range from ρ = 80 to 300 kilograms per cubic meter. A record-low conductivity value in air at 300 K of λ ≈ 0.012 watt per meter per kelvin was found for ρ ≈ 157 kilograms per cubic meter. Caloric measurements under variation of gas pressure as well as spectral infrared transmission measurements allowed the determination of solid conductivity, gaseous conductivity, and radiative conductivity as a function of density. The development of such low conductivity materials is of great interest with respect to the substitution of environmentally harmful insulating foams made from chlorofluorocarbons.
Epitaxial Growth and the Art of Computer Simulations
Authors: Metiu Horia , Lu Yan-Ten , Zhang Zhenyu
Published: October 2006

The results of kinetic simulations of the aggregates formed during the deposition of atoms on a semiconductor surface are reviewed. Because the kinetic parameters are poorly known and the accuracy of the existing interatomic potentials has not been sufficiently tested, the goal has been to reach a qualitative understanding of the formation of unusual patterns during growth, such as the segregation of aluminum during the growth of aluminum-gallium-arsenide (AlGaAs) coherent tilted superlattices and the formation of thin, long, and parallel islands during the deposition of Si on an Si(100) surface. Kinetic mechanisms for these phenomena are proposed.
Evidence for Ammonium-Bearing Minerals on Ceres
Authors: King Trude V. V. , Clark R. N. , Calvin W. M. , Sherman D. M. , Brown R. H.
Published: October 2006

Spectra obtained from recent telescopic observation of 1-Ceres and laboratory measurements and theoretical calculations of three component mixtures of Ceres analog material suggest that an ammoniated phyllosilicate is present on the surface of the asteroid, rather than H
2
O frost as had been previously reported. The presence of an ammoniated phyllosilicate, most likely ammoniated saponite, on the surface of Ceres implies that secondary temperatures could not have exceeded 400 kelvin.
Bulk Chemical Characteristics of Dissolved Organic Matter in the Ocean
Authors: Benner Ronald , Pakulski J. Dean , McCarthy Matthew , Hedges John I. , Hatcher Patrick G.
Published: October 2006

Dissolved organic matter (DOM) is the largest reservoir of reduced carbon in the oceans. The nature of DOM is poorly understood, in part, because it has been difficult to isolate sufficient amounts of representative material for analysis. Tangential-flow ultrafiltration was shown to recover milligram amounts of >1000 daltons of DOM from seawater collected at three depths in the North Pacific Ocean. These isolates represented 22 to 33 percent of the total DOM and included essentially all colloidal material. The elemental, carbohydrate, and carbon-type (by
13
C nuclear magnetic resonance) compositions of the isolates indicated that the relative abundance of polysaccharides was high (∼50 percent) in surface water and decreased to ∼25 percent in deeper samples. Polysaccharides thus appear to be more abundant and reactive components of seawater DOM than has been recognized.
Transformation by v-
sis
Occurs by an Internal Autoactivation Mechanism
Authors: Bejcek Bruce E. , Li Dean Y. , Deuel Thomas F.
Published: October 2006

Transformation by the v-
sis
oncogene appears to require an interaction of its protein product, p28

v-
sis

, with the receptor for the platelet-derived growth factor (PDGF). However, this interaction may not occur at the cell surface as predicted by the autocrine hypothesis because phenotypic transformation was not reversed by incubation of SSV-NRK cells with antisera to PDGF and because morphological transformation did not occur when nontransformed NRK cells were cultured continuously with p28

v-
sis

. A mutant of the wild-type v-
sis
gene was constructed that encodes a v-
sis
protein targeted for retention within the endoplasmic reticulum and Golgi. NRK cells expressing the mutant v-
sis
gene did not secrete any detectable v-
sis
protein but were as fully transformed as wild-type v-
sis
transfectants. The results support a mechanism of transformation by v-
sis
in which internal activation of the PDGF receptor occurs before expression of either p28

v-
sis

or the PDGF receptor at the cell surface.
A New Type of Meteoritic Diamond in the Enstatite Chondrite Abee
Authors: Russell S. S. , Pillinger C. T. , Arden J. W. , Lee M. R. , Ott U.
Published: October 2006

Diamonds with δ
13
C values of –2 per mil and less than 50 parts per million (by mass) nitrogen have been isolated from the Abee enstatite chondrite by the same procedure used for concentrating Cδ, the putative interstellar diamond found ubiquitously in primitive meteorites and characterized by δ
13
C values of –32 to –38 per mil, nitrogen concentrations of 2,000 to 12,500 parts per million, and δ
15
N values of –340 per mil. Because the Abee diamonds have typical solar system isotopic compositions for carbon, nitrogen, and xenon, they are presumably nebular in origin rather than presolar. Their discovery in an unshocked meteorite eliminates the possibility of origins normally invoked to account for diamonds in ureilites and iron meteorites and suggests a low-pressure synthesis. The diamond crystals are ∼100 nanometers in size, are of an unusual lath shape, and represent ∼100 parts per million of Abee by mass.
Mantle Plumes and Entrainment: Isotopic Evidence
Authors: Hart S. R. , Hauri E. H. , Oschmann L. A. , Whitehead J. A.
Published: October 2006

Many oceanic island basalts show sublinear subparallel arrays in Sr-Nd-Pb isotopic space. The depleted upper mantle is rarely a mixing end-member of these arrays, as would be expected if mantle plumes originated at a 670-kilometer boundary layer and entrained upper mantle during ascent. Instead, the arrays are fan-shaped and appear to converge on a volume in isotopic space characterized by low
87
Sr/
86
Sr and high
143
Nd/
144
Nd,
206
Pb/
204
Pb, and
3
He/
4
He ratios. This new isotopic component may be the lower mantle, entrained into plumes originating from the core-mantle boundary layer.
A Global Traveling Wave on Venus
Authors: Smith Michael D. , Gierasch Peter J. , Schinder Paul J.
Published: October 2006

The dominant large-scale pattern in the clouds of Venus has been described as a "Y" or "ψ" and tentatively identified by earlier workers as a Kelvin wave. A detailed calculation of linear wave modes in the Venus atmosphere verifies this identification. Cloud feedback by infrared heating fluctuations is a plausible excitation mechanism. Modulation of the large-scale pattern by the wave is a possible explanation for the Y. Momentum transfer by the wave could contribute to sustaining the general circulation.
Paleotemperatures in the Southwestern United States Derived from Noble Gases in Ground Water
Authors: Stute M. , Schlosser P. , Clark J. F. , Broecker W. S.
Published: October 2006

A paleotemperature record based on measurements of atmospheric noble gases dissolved in ground water of the Carrizo aquifer (Texas) shows that the annual mean temperature in the southwestern United States during the last glacial maximum was about 5°C lower than the present-day value. In combination with evidence for fluctuations in mountain snow lines, this cooling indicates that the glacial lapse rate was approximately the same as it is today. In contrast, measurements on deep-sea sediments indicate that surface temperatures in the ocean basins adjacent to our study area decreased by only about 2°C. This difference between continental and oceanic records poses questions concerning our current understanding of paleoclimate and climate-controlling processes.
Electron-Tunneling Pathways in Cytochrome c
Authors: Wuttke Deborah S. , Bjerrum Morten J. , Winkler Jay R. , Gray Harry B.
Published: October 2006

Distant Fe
2+
-Ru
3+
electronic couplings have been extracted from intramolecular electrontransfer rates in Ru(histidine
x
) (where X = 33, 39, 62, and 72) derivatives of cytochrome c. The couplings increase according to 62 (0.0060) < 72 (0.057) < 33 (0.097) < 39 (0.11 per wave numbers); however, this order is out of line with the histidine to heme edge-edge distances [62 (14.8) > 39 (12.3) > 33 (11.1) > 72 (8.4 angstroms)]. The rates (and the couplings) correlate with the lengths of σ-tunneling pathways comprised of covalent bonds, hydrogen bonds, and through-space jumps from the histidines to the heme group. Space jumps greatly decrease couplings: One from Pro
71
to Met
80
extends the σ-tunneling length of the His
72
pathway by roughly 10 covalent-bond units.
High-Resolution Imaging by Fourier Transform X-ray Holography
Authors: McNulty Ian , Kirz Janos , Jacobsen Chris , Anderson Erik H. , Howells Malcolm R. , Kern Dieter P.
Published: October 2006

Fourier transform x-ray holography has been used to image gold test objects with submicrometer structure, resolving features as small as 60 nanometers. The hologram-recording instrument uses coherent 3.4-nanometer radiation from the soft x-ray undulator beamline X1A at the National Synchrotron Light Source. The specimen to be imaged is placed near the first-order focal spot produced by a Fresnel zone plate; the other orders, chiefly the zeroth, illuminate the specimen. The wave scattered by the specimen interferes with the spherical reference wave from the focal spot, forming a hologram with fringes of low spatial frequency. The hologram is recorded in digital form by a charge-coupled device camera, and the specimen image is obtained by numerical reconstruction.
Airborne Studies of the Smoke from the Kuwait Oil Fires
Authors: Hobbs Peter V. , Radke Lawrence F.
Published: October 2006

Airborne studies of smoke from the Kuwait oil fires were carried out in the spring of 1991 when ∼4.6 million barrels of oil were burning per day. Emissions of sulfur dioxide were ∼57% of that from electric utilities in the United States; emissions of carbon dioxide were ∼2% of global emissions; emissions of soot were ∼3400 metric tons per day. The smoke absorbed ∼75 to 80% of the sun's radiation in regions of the Persian Gulf. However, the smoke probably had insignificant global effects because (i) particle emissions were less than expected, (ii) the smoke was not as black as expected, (iii) the smoke was not carried high in the atmosphere, and (iv) the smoke had a short atmospheric residence time.
Pressure-Induced Coordination Changes in Alkali-Germanate Melts: An in Situ Spectroscopic Investigation
Authors: Farber Daniel L. , Williams Quentin
Published: October 2006

The structure of liquid Na2Ge2O5⋅H2O, a silicate melt analog, has been studied with Raman spectroscopy to pressures of 2.2 gigapascals. Upon compression, a peak near ∼240 wavenumbers associated with octahedral GeO6groups grows relative to a peak near ∼500 wavenumbers associated with tetrahedral GeO4groups. This change corresponds to an increase in octahedral germanium in the liquid from near 0% at ambient pressures to >50% at a pressure of 2.2 gigapascals. Silicate liquids plausibly undergo similar coordination changes at depth in the Earth. Such structural changes may generate decreases in the fusion slopes of silicates at high pressures as well as neutrally buoyant magmas within the transition zone of the Earth's mantle.
Effects of Aerosol from Biomass Burning on the Global Radiation Budget
Authors: Penner Joyce E. , Dickinson Robert E. , O'Neill Christine A.
Published: October 2006

An analysis is made of the likely contribution of smoke particles from biomass burning to the global radiation balance. These particles act to reflect solar radiation directly; they also can act as cloud condensation nuclei, increasing the reflectivity of clouds. Together these effects, although uncertain, may add up globally to a cooling effect as large as 2 watts per square meter, comparable to the estimated contribution of sulfate aerosols. Anthropogenic increases of smoke emission thus may have helped weaken the net greenhouse warming from anthropogenic trace gases.
Slow Crack Growth in Single-Crystal Silicon
Authors: Connally J. A. , Brown S. B.
Published: October 2006

Time-dependent crack growth has been measured on a precracked, single-crystal silicon cantilever beam 75 micrometers long that was excited at resonance. Growth of the precrack changes the resonant frequency of the beam, which is correlated to crack length. The measured steady-state crack growth rate was as slow as 2.9 × 10
–13
meter per second, although the apparatus can measure crack growth rates as low as 10
–15
meter per second. It is postulated that static fatigue of the native surface silica layer is the mechanism for crack growth. These experiments demonstrate the possibility of rate-dependent failure of silicon devices and the applicability of linear elastic fracture mechanics to small-scale micromechanical devices. The results indicate that slow crack growth must therefore be considered when evaluating the reliability of thin-film silicon structures.
Glassy Microspherules (Microtektites) from an Upper Devonian Limestone
Authors: Wang Kun
Published: October 2006

The properties of microspherules recovered from an Upper Devonian marine limestone immediately overlain by a geochemical anomaly of siderophile and chalcophile elements are similar to those of impact-derived microtektites. These microspherules are glass, have splash-form shapes, contain spherical vesicles and lechatelierite inclusions, and show oxide compositional variations similar to those in known microtektites. These characteristics suggest that these Upper Devonian microspherules have an impact origin. A bolide impact may have occurred about 365 million years ago on the South China Plate and caused a faunal extinction on eastern Gondwana.
Morphological Disparity in the Cambrian
Authors: Briggs Derek E. G. , Fortey Richard A. , Wills Matthew A.
Published: October 2006

An analysis of the range of morphology among arthropods demonstrates that disparity among living arthropods is similar to that in Cambrian arthropods. The range of morphological design resulting from the Cambrian "explosion" has been overestimated, reflecting a tendency to separate as "problematic" taxa that cannot be accommodated in the classification on the basis of the living biota. Problematic taxa are largely an artifact of an inadequate taxonomy. Special evolutionary processes may not be necessary to explain the early radiation of the metazoans.
Three-Dimensional Solution Structure of Human Interleukin-4 by Multidimensional Heteronuclear Magnetic Resonance Spectroscopy
Authors: Powers Robert , Garrett Daniel S. , March Carl J. , Frieden Eric A. , Gronenborn Angela M. , Clore G. Marius
Published: October 2006

The three-dimensional solution structure of recombinant human interleukin-4, a protein of 133 residues and 15.4 kilodaltons that plays a key role in the immune and inflammatory systems, has been solved by multidimensional heteronuclear magnetic resonance spectroscopy. The structure is dominated by a left-handed four-helix bundle with an unusual topology comprising two overhand connections. The linker elements between the helices are formed by either long loops, small helical turns, or short strands. The overall topology is remarkably similar to that of growth hormone and granulocyte-macrophage colony stimulating factor, despite the absence of any sequence homology, and substantial differences in the relative lengths of the helices, the length and nature of the various connecting elements, and the pattern of disulfide bridges. These three proteins, however, bind to cell surface receptors belonging to the same hematopoietic superfamily, which suggests that interleukin-4 may interact with its receptor in an analogous manner to that observed in the crystal structure of the growth hormone-extracellular receptor complex.
Role for Excitatory Amino Acids in Methamphetamine-Induced Nigrostriatal Dopaminergic Toxicity
Authors: Sonsalla Patricia K. , Nicklas William J. , Heikkila Richard E.
Published: October 2006

The systemic administration of either methamphetamine or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to experimental animals produces degenerative changes in nigrostriatal dopaminergic neurons or their axon terminals. This study was conducted to determine if excitatory amino acids, which appear to be involved in various neurodegenerative disorders, might also contribute to the dopaminergic neurotoxicity produced in mice by either methamphetamine or MPTP. MK-801, phencyclidine, and ketamine, noncompetitive antagonists of one subtype of excitatory amino acid receptor, the N-methyl-D-aspartate receptor, provided substantial protection against neurotoxicity produced by methamphetamine but not that produced by MPTP. These findings indicate that excitatory amino acids play an important role in the nigrostriatal dopaminergic damage induced by methamphetamine.
Commitment of Neural Crest Cells to the Sensory Neuron Lineage
Authors: Sieber-Blum Maya
Published: October 2006

Clonal cultures and monoclonal antibodies against a lineage-specific epitope, stage-specific embryonic antigen-1 (SSEA-1) were used to analyze the commitment of quail neural crest cells to the sensory neuron pathway. There were two distinct populations of sensory cells at the time of gangliogenesis. Postmitotic neuroblasts that remained in close association with the neural tube coexisted with a large number of pluripotent cells that formed the leading edge of the emigrating cells and gave rise to sensory and autonomic neuroblasts and to melanocytes. The data suggest a dual origin of spinal sensory neuroblasts and a predominantly late divergence of the autonomic and sensory lineages.
Genetic and Pharmacological Suppression of Oncogenic Mutations in
RAS
Genes of Yeast and Humans
Authors: Schafer William R. , Kim Rosalind , Sterne Rachel , Thorner Jeremy , Kim Sung-Hou , Rine Jasper
Published: October 2006

The activity of an oncoprotein and the secretion of a pheromone can be affected by an unusual protein modification. Specifically, posttranslational modification of yeast a-factor and Ras protein requires an intermediate of the cholesterol biosynthetic pathway. This modification is apparently essential for biological activity. Studies of yeast mutants blocked in sterol biosynthesis demonstrated that the membrane association and biological activation of the yeast Ras2 protein require mevalonate, a precursor of sterols and other isoprenes such as farnesyl pyrophosphate. Furthermore, drugs that inhibit mevalonate biosynthesis blocked the in vivo action of oncogenic derivatives of human Ras protein in the
Xenopus
oocyte assay. The same drugs and mutations also prevented the posttranslational processing and secretion of yeast a-factor, a peptide that is farnesylated. Thus, the mevalonate requirement for Ras activation may indicate that attachment of a mevalonate-derived (isoprenoid) moiety to Ras proteins is necessary for membrane association and biological function. These observations establish a connection between the cholesterol biosynthetic pathway and transformation by the
ras
oncogene and offer a novel pharmacological approach to investigating, and possibly controlling,
ras
-mediated malignant transformations.
A Novel mRNA of the A4 Amyloid Precursor Gene Coding for a Possibly Secreted Protein
Authors: de Sauvage Frédéric , Octave Jean-Noël
Published: October 2006

The gene, encoding the A4 peptide found in the amyloid core of senile plaques isolated from the cerebral cortex of patients with Alzheimer's disease, produces at least three precursors that resemble cell surface receptors. A clone isolated from a human brain complementary DNA library contained the structural sequence for an A4 amyloid peptide precursor with a serine protease inhibitor domain in which 208 amino acids at the carboxyl terminal are replaced by 20 amino acids derived from nucleotide sequences with homology to the Alu repeat family. This protein devoid of the transmembrane domain most likely represents a secreted form of the A4 amyloid peptide precursor.
Machining Oxide Thin Films with an Atomic Force Microscope: Pattern and Object Formation on the Nanometer Scale
Authors: Kim Yun , Lieber Charles M.
Published: October 2006

An atomic force microscope (AFM) has been used to machine complex patterns and to form free structural objects in thin layers of MoO
3
grown on the surface of MoS
2
. The AFM tip can pattern lines with ≤10-nanometer resolution and then image the resulting structure without perturbation by controlling the applied load. Distinct MoO
3
structures can also be defined by AFM machining, and furthermore these objects can be manipulated on the MoS
2
substrate surface with the AFM tip. These results suggest application to nanometer-scale diffraction gratings, high-resolution lithography masks, and possibly the assembly of nanostructures with novel properties.
Maintenance of Strong Rotational Winds in Venus' Middle Atmosphere by Thermal Tides
Authors: Newman Matthew , Leovy Conway
Published: October 2006

The cloud-level atmosphere of Venus takes little more than 4 days to complete one rotation, whereas the solid planet below has a 243-day period. Computer simulations of the circulation of the Venus middle atmosphere between 40 and 85 kilometers, as driven by solar radiation absorbed in the clouds, reproduce (i) the observed cloud-level rotation rate, (ii) strong vertical shears above and below the cloud tops, and (iii) midlatitude jets and strong poleward flow on the day side. Simulated circulations converge to yield nearly the same zonal winds when initialized with both stronger or weaker rotation rates. These results support the hypothesis that the observed cloud-top rotation rate is maintained by statistical balance between fluxes of momentum by thermal tides and momentum advection by mean meridional circulation.
Benzene Forms Hydrogen Bonds with Water
Authors: Suzuki Sakae , Green Peter G. , Bumgarner Roger E. , Dasgupta Siddharth , Goddard William A. , Blake Geoffrey A.
Published: October 2006

Fully rotationally resolved spectra of three isotopic species of 1:1 clusters of benzene with water (H
2
O, D
2
O, and HDO) were fit to yield moments of inertia that demonstrate unambiguously that water is positioned above the benzene plane in nearly free internal rotation with both hydrogen atoms pointing toward the π cloud. Ab initio calculations (MP2 level of electron correlation and 6-31 G
**
basis set with basis set superposition error corrections) predict a binding energy
D
e
≳ 1.78 kilocalories per mole. In both the experimental and theoretical structures, water is situated nearly 1 angstrom within the van der Waals contacts of the monomers, a clear manifestation of hydrogen bond formation in this simple model of aqueous-π electron interactions.
Genesis of Acetate and Methane by Gut Bacteria of Nutritionally Diverse Termites
Authors: Brauman Alain , Kane Matthew D. , Labat Marc , Breznak John A.
Published: October 2006

The evolution of different feeding guilds in termites is paralleled by differences in the activity of their gut microbiota. In wood-feeding termites, carbon dioxide—reducing acetogenic bacteria were found to generally outprocess carbon dioxide—reducing methanogenic bacteria for reductant (presumably hydrogen) generated during microbial fermentation in the hindgut. By contrast, acetogenesis from hydrogen and carbon dioxide was of little significance in fungus-growing and soil-feeding termites, which evolved more methane than their wood- and grass-feeding counterparts. Given the large biomass of termites on the earth and especially in the tropics, these findings should help refine global estimates of carbon dioxide reduction in anoxic habitats and the contribution of termite emissions to atmospheric methane concentrations.
Identification of the Cystic Fibrosis Gene: Genetic Analysis
Authors: Kerem Bat-Sheva , Rommens Johanna M. , Buchanan Janet A. , Markiewicz Danuta , Cox Tara K. , Chakravarti Aravinda , Buchwald Manuel , Tsui Lap-Chee
Published: October 2006

Approximately 70 percent of the mutations in cystic fibrosis patients correspond to a specific deletion of three base pairs, which results in the loss of a phenylalanine residue at amino acid position 508 of the putative product of the cystic fibrosis gene. Extended haplotype data based on DNA markers closely linked to the putative disease gene locus suggest that the remainder of the cystic fibrosis mutant gene pool consists of multiple, different mutations. A small set of these latter mutant alleles (about 8 percent) may confer residual pancreatic exocrine function in a subgroup of patients who are pancreatic sufficient. The ability to detect mutations in the cystic fibrosis gene at the DNA level has important implications for genetic diagnosis.
Synergism Between HIV gp120 and gp120-Specific Antibody in Blocking Human T Cell Activation
Authors: Mittler Robert S. , Hoffmann Michael K.
Published: October 2006

The human immunodeficiency virus (HIV) binds to CD4-positive cells through interaction of its envelope glycoprotein (gp120) with the CD4 molecule. CD4 is a prominent immunoregulatory molecule, and chronic exposure to antibody against CD4 (anti-CD4) has been shown to cause immunodeficiency in mice. T cell-dependent in vitro immune responses can also be inhibited by anti-CD4. Experimental findings reported here indicate that CD4-bound gp120 attracts gp120-specific antibodies derived from the blood of HIV-seropositive individuals to form a trimolecular complex with itself and CD4. Thus targeted to CD4, the gp120-specific antibody functions as an antibody to CD4; it cross-links and modulates the CD4 molecules and suppresses the activation of T cells as measured by mobilization of intracellular calcium (Ca
i
2+
). The synergism between gp120 and anti-gp120 in blocking T cell activation occurs at low concentrations of both components. Neither gp120 nor anti-gp120 inhibits T cell activation by itself in the concentrations tested.
A Biochemical Correlate of the Critical Period for Synaptic Modification in the Visual Cortex
Authors: Dudek Serena M. , Bear Mark F.
Published: October 2006

Stimulation of phosphoinositide hydrolysis by excitatory amino acids was studied in synaptoneurosomes of kitten striate cortex at several postnatal ages. Ibotenate and glutamate stimulated phosphoinositide turnover during the second and third postnatal months;
N
-methyl-D-aspartate and DL-α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) were without effect. The developmental profile of ibotenate-stimulated phosphoinositide turnover parallels the postnatal changes in cortical susceptibility to visual deprivation. The transient increase in ibotenate-stimulated phosphoinositide turnover does not occur in visual cortex of kittens reared in complete darkness.
Hypomethylation of DNA from Benign and Malignant Human Colon Neoplasms
Authors: Goelz Susan E. , Vogelstein Bert , Hamilton Stanley R. , Feinberg Andrew P.
Published: October 2006

The methylation state of DNA from human colon tissue displaying neoplastic growth was determined by means of restriction endonuclease analysis. When compared to DNA from adjacent normal tissue, DNA from both benign colon polyps and malignant carcinomas was substantially hypomethylated. With the use of probes for growth hormone, γ-globin, α-chorionic gonadotropin, and γ-crystallin, methylation changes were detected in all 23 neoplastic growths examined. Benign polyps were hypomethylated to a degree similar to that in malignant tissue. These results indicate that hypomethylation is a consistent biochemical characteristic of human colonic tumors and is an alteration in the DNA that precedes malignancy.