bluuebunny/crossref_metadata_2025 huggingface dataset:
Void Structure in Colloidal Dispersions
Authors: Ito Kensaku , Yoshida Hiroshi , Ise Norio
Published: October 2006

The time evolution of void structures in highly purified polymer latex dispersions was studied with a confocal laser scanning microscope. In such dispersions, which were initially homogeneous, the voids grew with time when the dispersions were kept standing and formed more quickly in the internal material than in material close to the glass-dispersion interface. Void formation is thus not an artifact arising from the presence of the interface. A similar structural inhomogeneity, in apparently homogeneous systems, is discussed for simple ionic solutions, ionic polymer solutions, and Langmuir-Blodgett films.
Synthesis and Characterization of Molybdenum Carbide Clusters Mo

n

C

4
n

, (
n
= 1 to 4)
Authors: Jin Changming , Haufler R. E. , Hettich R. L. , Barshick C. M. , Compton R. N. , Puretzky A. A. , Dem'yanenko A. V. , Tuinman A. A.
Published: October 2006

Laser radiation (XeCl laser, 308-nanometer wavelength) focused into a cell containing Mo(CO)
6
vapor produced ultrafine particles in the extended waist of the laser beam. Negative ion mass spectrometry revealed molybdenum carbide cluster ions with a stoichiometry Mo

n

C

4
n

(
n
= 1 to 4). The Mo

n

C

4
n

–
(
n
= 2 to 4) ions are completely unreactive with NH
3
, H
2
O, and O
2
, suggesting structures in which the molybdenum atoms are unavailable for coordination to additional ligands. Collision-induced dissociation studies of these anions show the loss of MoC
4
units as the main fragmentation pathway. This observation, together with the lack of addition reactions, provides a basis for structures in which a planar cluster of two, three, or four molybdenum atoms is surrounded by, and bonded to, carbon dimers.
Turbulent Mixing Under Drifting Pack Ice in the Weddell Sea
Authors: McPhee Miles G. , Martinson Douglas G.
Published: October 2006

By providing cold, dense water that sinks and mixes to fill the abyssal world ocean, high-latitude air-sea-ice interaction is the main conduit through which the deep ocean communicates with the rest of the climate system. A key element in modeling and predicting oceanic impact on climate is understanding the processes that control the near surface exchange of heat, salt, and momentum. In 1992, the United States—Russian Ice Station Weddell-1 traversed the western Weddell Sea during the onset of winter, providing a platform for direct measurement of turbulent heat flux and Reynolds stress in the upper ocean. Data from a storm early in the drift indicated (i) well-formed Ekman spirals (in both velocity and turbulent stress); (ii) high correlation between mixed layer heat flux and temperature gradients; (iii) that eddy viscosity and eddy thermal diffusivity were similar, about 0.02 square meters per second; and (iv) that the significant turbulent length scale (2 to 3 meters through most of the boundary layer) was proportional to the wavelength at the peak in the weighted vertical velocity spectrum. The measurements were consistent with a simple model in which the bulk eddy viscosity in the neutrally buoyant mixed layer is proportional to kinematic boundary stress divided by the Coriolis parameter.
Detecting Climatic Change Signals: Are There Any "Fingerprints"?
Authors: Schneider Stephen H.
Published: October 2006

Projected changes in the Earth's climate can be driven from a combined set of forcing factors consisting of regionally heterogeneous anthropogenic and natural aerosols and land use changes, as well as global-scale influences from solar variability and transient increases in human-produced greenhouse gases. Thus, validation of climate model projections that are driven only by increases in greenhouse gases can be inconsistent when one attempts the validation by looking for a regional or time-evolving "fingerprint" of such projected changes in real climatic data. Until climate models are driven by time-evolving, combined, multiple, and heterogeneous forcing factors, the best global climatic change "fingerprint" will probably remain a many-decades average of hemispheric- to global-scale trends in surface air temperatures. Century-long global warming (or cooling) trends of 0.5°C appear to have occurred infrequently over the past several thousand years—perhaps only once or twice a millennium, as proxy records suggest. This implies an 80 to 90 percent heuristic likelihood that the 20th-century 0.5 ± 0.2°C warming trend is not a wholly natural climatic fluctuation.
Crystal Structure of the High-Pressure Phase of Solid CO
2
Authors: Aoki K. , Yamawaki H. , Sakashita M. , Gotoh Y. , Takemura K.
Published: October 2006

X-ray diffraction study of solid CO
2
at room temperature has shown that the powder pattern of the high-pressure phase, which supersedes the low-pressure cubic
Pa
3 phase at about 10 gigapascals, is consistently interpreted in terms of an orthorhombic
Cmca
structure. The orthorhombic cell at 11.8 gigapascals has dimensions of 4.330 ± 0.015, 4.657 ± 0.005, 5.963 ± 0.009 angstroms for its
a, b
, and
c
faces, respectively, and a volume of 120.3 ± 0.5 cubic angstroms. Four molecules contained in the unit cell are located at the base-centered positions with their molecular axes inclined at about 52° with respect to the crystallographic
c
axis. The volume change associated with the
Pa
3-
Cmca
transition is close to zero. The structural dimensions obtained for the high-pressure crystalline phase of CO
2
are of great importance for a theoretical understanding of the role of intermolecular interactions, including quadrupole-quadrupole interactions, in molecular condensation.
500,000-Year Stable Carbon Isotopic Record from Devils Hole, Nevada
Authors: Coplen Tyler B. , Winograd Isaac J. , Landwehr Jurate M. , Riggs Alan C.
Published: October 2006

The record of carbon-13 (δ
13
C) variations in DH-11 vein calcite core from Devils Hole, Nevada, shows four prominent minima near glacial terminations (glacial-interglacial transitions) V to II. The δ
13
C time series is inversely correlated with the DH-11 oxygen isotope ratio time series and leads it by as much as 7000 years. The δ
13
C variations likely record fluctuations in the δ
13
C of dissolved inorganic carbon of water recharging the aquifer. How such variations are transported 80 kilometers to Devils Hole without obliteration by water-rock reaction remains an enigma. The record may reflect (i) global variations in the δ
13
C of atmospheric CO
2
and, hence, the δ
13
C of continental biomass or (ii) variations in extent and density of vegetation in the southern Great Basin. In the latter case, δ
13
C minima at 414, 334, 246, and 133 thousand years ago mark times of maximum vegetation.
Distinguishing the Direct and Indirect Products of a Gas-Surface Reaction
Authors: Rettner Charles T. , Auerbach Daniel J.
Published: October 2006

It has long been postulated that gas-surface chemical reactions can occur by means of two distinct mechanisms: direct reaction on a single gas-surface encounter or reaction between two adsorbed species. It is shown here that these mechanisms have distinct dynamical signatures, as illustrated by the reaction of hydrogen with chlorine on gold(111). The direct reaction product leaves the surface with a high kinetic energy in a narrow angular distribution that displays a "memory" of the direction and energy of the incident hydrogen atom. The indirect reaction product has a near-thermal energy distribution and an angular distribution that is close to that of a cosine function.
Glacial-Interglacial Changes in Moisture Sources for Greenland: Influences on the Ice Core Record of Climate
Authors: Charles C. D. , Rind D. , Jouzel J. , Koster R. D. , Fairbanks R. G.
Published: October 2006

Large, abrupt shifts in the
18
O/
16
O ratio found in Greenland ice must reflect real features of the climate system variability. These isotopic shifts can be viewed as a result of air temperature fluctuations, but determination of the cause of the changes—the most crucial issue for future climate concerns—requires a detailed understanding of the controls on isotopes in precipitation. Results from general circulation model experiments suggest that the sources of Greenland precipitation varied with different climate states, allowing dynamic atmospheric mechanisms for influencing the ice core isotope shifts.
Paleoindians in Beringia: Evidence from Arctic Alaska
Authors: Kunz Michael L. , Reanier Richard E.
Published: October 2006

Excavations at the Mesa site in arctic Alaska provide evidence for a Paleoindian occupation of Beringia, the region adjacent to the Bering Strait. Eleven carbon-14 dates on hearths associated with Paleoindian projectile points place humans at the site between 9,730 and 11,660 radiocarbon years before present (years B.P.). The presence of Paleoindians in Beringia at these times challenges the notion that Paleoindian cultures arose exclusively in mid-continental North America. The age span of Paleoindians at the Mesa site overlaps with dates from two other cultural complexes in interior Alaska. A hiatus in the record of human occupation occurs between 10,300 and 11,000 years B.P. Late Glacial climatic fluctuations may have made northern Alaska temporarily unfavorable for humans and spurred their southward dispersal.
Destruction Rate of H
3
+
by Low-Energy Electrons Measured in a Storage-Ring Experiment
Authors: Sundström G. , Mowat J. R. , Danared H. , Datz S. , Broström L. , Filevich A. , Källberg A. , Mannervik S. , Rensfelt K. G. , Sigray P. , Ugglas M. af , Larsson M.
Published: October 2006

Knowledge of the abundance of H
3
+
is needed in interstellar and planetary atmospheric chemistry. An important destruction mechanism of H
3
+
is low-energy electron impact followed by dissociation, but estimates of the reaction rate span several orders of magnitude. As an attempt to resolve this uncertainty, the cross section for dissociative recombination of vibrationally cold H
3
+
has been measured with an ion storage ring down to collision energies below 1 millielectron volt. A rate coefficient of 1.15 × 10
-7
cubic centimeters per second at 300 kelvin was deduced. The cross section scaled with collision energy according to
E
–1.15
, giving the rate a temperature dependence of
T
–0.65
.
Hubble Space Telescope Observations of Comet P/Shoemaker-Levy 9 (1993e)
Authors: Weaver H. A. , Feldman P. D. , A'Hearn M. F. , Arpigny C. , Brown R. A. , Helin E. F. , Levy D. H. , Marsden B. G. , Meech K. J. , Larson S. M. , Noll K. S. , Scotti J. V. , Sekanina Z. , Shoemaker C. S. , Shoemaker E. M. , Smith T. E. , Storrs A. D. , Yeomans D. K. , Zellner B.
Published: October 2006

The Hubble Space Telescope observed the fragmented comet P/Shoemaker-Levy 9 (1993e) (P indicates that it is a periodic comet) on 1 July 1993. Approximately 20 individual nuclei and their comae were observed in images taken with the Planetary Camera. After subtraction of the comae light, the 11 brightest nuclei have magnitudes between ∼23.7 and 24.8. Assuming that the geometric albedo is 0.04, these magnitudes imply that the nuclear diameters are in the range ∼2.5 to 4.3 kilometers. If the density of each nucleus is 1 gram per cubic centimeter, the total energy deposited by the impact of these 11 nuclei into Jupiter's atmosphere next July will be ∼4 × 10
30
ergs (∼10
8
megatons of TNT). This latter number should be regarded as an upper limit because the nuclear magnitudes probably contain a small residual coma contribution. The Faint Object Spectrograph was used to search for fluorescence from OH, which is usually an excellent indicator of cometary activity. No OH emission was detected, and this can be translated into an upper limit on the water production rate of ∼2 × 10
27
molecules per second.
Suppression of Rupture in Thin, Nonwetting Liquid Films
Authors: Yerushalmi-Rozen Rachel , Klein Jacob , Fetters Lewis J.
Published: October 2006

Stabilization against the rupture and breakup of thin, nonwetting liquid films spread on surfaces is generally sought by modification of equilibrium interfacial properties. A mechanism for suppressing rupture in such films that uses surface-attached polymers together with free chains in the bulk of the film is reported. Films of an oligostyrene liquid, which rupture within several minutes when spread on a silicon wafer, may be stabilized for many months by a polystyrene brush attached to the substrate, together with some free polystyrene in the liquid. The effect may arise from entanglements of the free chains with the immobilized brush.
The Timing of High Sea Levels Over the Past 200,000 Years
Authors: Gallup Christina D. , Edwards R. Lawrence , Johnson Robert G.
Published: October 2006

The230Th ages and234U/238U ratios were determined for Barbados corals that grew during periods of high sea level within the last 200,000 years. The similarity of the initial234U/238U ratios of some of the corals to the modern marine value suggests that these samples are pristine and that the marine234U/238U ratio 83,000 and 200,000 years ago was within 2 per mil of the modern value. The accuracies of the230Th ages are evaluated on the basis of the234U/238U values and a model of the behavior of uranium and thorium isotopes during diagenesis. For the last three interglacial and two intervening interstadial periods, sea level peaked at or after peaks in summer insolation in the Northern Hemisphere. This overall pattern supports the idea that glacial-interglacial cycles are caused by changes in Earth's orbital geometry. The sea-level drop at the end of the penultimate interglacial, the last interglacial, and a subsequent interstadial period lagged behind the decrease in insolation by 5,000 to 10,000 years.
Paleomagnetic Tests of Pacific Plate Reconstructions and Implications for Motion Between Hotspots
Authors: Acton Gary D. , Gordon Richard G.
Published: October 2006

The plate-motion circuit through the South Pacific and Antarctica is shown to fail paleomagnetic tests of consistency. These failures imply that reconstructions of Pacific basin plates relative to surrounding plates inferred from this circuit are systematically in error and that estimates of motion between hotspots inferred from this circuit are probably too large. Therefore, the motions between hotspots remain poorly known and may be much smaller than previously estimated.
Crystal and Molecular Structures of Rhenium Heptafluoride
Authors: Vogt T. , Fitch A. N. , Cockcroft J. K.
Published: October 2006

Rhenium heptafluoride, ReF
7
, is one of only two stable binary compounds MX
7
with a heptacoordinated metal atom M and halide atom X. Its low-temperature crystal structure, as determined by high-resolution powder neutron diffraction, reveals the molecular structure, which has been the subject of speculation and debate for many years. Here it is shown within experimental error that at 1.5 kelvin the lowest energy configuration of ReF
7
has symmetry
C

s

(
m
) and is a distorted pentagonal bipyramid. The deviation of the two axial Re-F bonds from collinear and the puckering of the ring of equatorial fluorine atoms are similar to what has been postulated as one of the conformations of the pseudorotational motion observed at higher temperatures.
Direct Observation of Microscopic Inhomogeneities with Energy-Dispersive Diffraction of Synchrotron-Produced X-rays
Authors: Skelton E. F. , Drews A. R. , Osofsky M. S. , Qadri S. B. , Hu J. Z. , Vanderah T. A. , Peng J. L. , Greene R. L.
Published: October 2006

Evidence of structural inhomogeneities in two high—transition-temperature superconductors, YBa
2
Cu
3
O
7- δ
and Nd

2-
x

Ce

x

CuO

4-
y

, is presented. When samples were illuminated by highly collimated x-rays produced on a synchrotron wiggler, small changes in the lattice were detected over a spatial scale of 10 micrometers. These changes are interpreted as evidence of variations in the oxygen content in one case and in the cerium content in the other; both affect the superconducting properties. The existence of such structural inhomogeneities brings into question whether exotic experimental results obtained from superconducting materials with high transition temperatures actually reflect intrinsic properties.
Cell Fate Determination by the Cell Wall in Early
Fucus
Development
Authors: Berger Frederic , Taylor Alison , Brownlee Colin
Published: October 2006

In multicellular plants, development starts with an asymmetric division of the zygote into two differentiated cells. The nature and distribution of fate-determining factors operating during embryogenesis remain largely obscure. Laser microsurgery was used here to dissect two-celled embryos of the alga
Fucus spiralis
. Removal of protoplasts from the cell wall induced dedifferentiation. However, isolated cells within the walls followed their restricted fate. Moreover, contact of one cell type with the isolated cell wall of the other cell type caused its fate to be switched. The cell wall thus appears to maintain the differentiated state and to direct cell fate in plant development.
From Static to Kinetic Friction in Confined Liquid Films
Authors: Reiter Günter , Demirel A. Levent , Granick Steve
Published: October 2006

The transition from rest to sliding contact of atomically smooth solids separated by molecularly thin liquid films was studied. The films could be deformed nearly reversibly to a large fraction of the film thickness. The modulus of elasticity and yield stress were low, considerably less than for a molecular crystal or glass in the bulk. The transition to dissipative sliding was typically (but not always) discontinuous. The dissipative stress was then nearly velocity-independent. The similar response of monolayers strongly attached to the solid surfaces, presenting a well-defined interface for sliding, suggests that the physical mechanism of sliding may involve wall slip.
The 1990 to 1991 Sudan Earthquake Sequence and the Extent of the East African Rift System
Authors: Girdler R. W. , McConnell D. A.
Published: October 2006

One of the largest earthquakes ever recorded in Africa (surface wave magnitude
M
s
= 7.2) occurred about 50 kilometers east of the Upper River Nile on 20 May 1990. Four days later, two more large earthquakes (
M
s
= 6.4 and 7.0) occurred about 50 kilometers to the northwest in the Nile Valley. In the following months, a further 60 events were recorded by seismic stations worldwide. The earthquakes are associated with two fault systems: one east of the Nile with azimuth southeast and one along the Nile Valley with azimuth north-northeast. The activity alternated between the two fault systems and indicates that the northern extremity of the western branch of the East African Rift System extends at least 350 kilometers north of Lake Albert.
Modulated Magnetic Phases in Rare Earth Metallic Systems
Authors: Chattopadhyay Tapan
Published: October 2006

Neutron scattering has played a key role in the microscopic understanding of the static and dynamic properties of magnetic materials. Modulated magnetic structures first discovered in the late fifties can no longer be referred to as exotic; more than a hundred such phases have already been found in a variety of magnetic systems. Neutron and x-ray magnetic scattering have played a complementary role in the recent discovery and understanding of the modulated magnetic phases in rare earth metallic systems.
Temperatures in Earth's Core Based on Melting and Phase Transformation Experiments on Iron
Authors: Saxena S. K. , Shen G. , Lazor P.
Published: October 2006

Experiments on melting and phase transformations on iron in a laser-heated, diamond-anvil cell to a pressure of 150 gigapascals (approximately 1.5 million atmospheres) show that iron melts at the central core pressure of 363.85 gigapascals at 6350 ± 350 kelvin. The central core temperature corresponding to the upper temperature of iron melting is 6150 kelvin. The pressure dependence of iron melting temperature is such that a simple model can be used to explain the inner solid core and the outer liquid core. The inner core is nearly isothermal (6150 kelvin at the center to 6130 kelvin at the inner core-outer core boundary), is made of hexagonal closest-packed iron, and is about 1 percent solid (MgSiO
3
+ MgO). By the inclusion of less than 2 percent of solid impurities with iron, the outer core densities along a thermal gradient (6130 kelvin at the base of the outer core and 4000 kelvin at the top) can be matched with the average seismic densities of the core.
Origin of Saturn's E Ring: Self-Sustained, Naturally
Authors: Hamilton Douglas P. , Burns Joseph A.
Published: October 2006

Saturn's diffuse E ring spans the region between 3 and 8 saturnian radii (
R
s
), has its peak brightness near the orbit of the satellite Enceladus (3.95
R
s
), and is thought to be composed primarily of icy particles 1.0 ± 0.3 micrometers in radius. Such particles are shown to move periodically along highly elliptical paths that cross the orbits of several saturnian satellites; the resulting energetic collisions of E ring particles with embedded satellites are capable of sustaining the E ring at its current optical depth. With several reasonable assumptions, this model naturally selects Enceladus as the primary source of ring material and may also provide mechanisms that explain the generation of the unusual amount of submicrometer dust in the neighboring F and G rings, the excess of OH molecules observed within the E ring, and the orbital brightness variations of nearby satellites.
Detection of Large Prehistoric Earthquakes in the Pacific Northwest by Microfossil Analysis
Authors: Mathewes Rolf W. , Clague John J.
Published: October 2006

Geologic and palynological evidence for rapid sea level change ∼3400 and ∼2000 carbon-14 years ago (3600 and 1900 calendar years ago) has been found at sites up to 110 kilometers apart in southwestern British Columbia. Submergence on southern Vancouver Island and slight emergence on the mainland during the older event are consistent with a great (magnitude
M
≥ 8) earthquake on the Cascadia subduction zone. The younger event is characterized by submergence throughout the region and may also record a plate-boundary earthquake or a very large crustal or intraplate earthquake. Microfossil analysis can detect small amounts of coseismic uplift and subsidence that leave little or no lithostratigraphic signature.
The Last Deglaciation Event in the Eastern Central Arctic Ocean
Authors: Stein Ruediger , Nam Seung-II , Schubert Carsten , Vogt Christoph , Futterer Dieter , Heinemeier Jan
Published: October 2006

Oxygen isotope records of cores from the central Arctic Ocean yield evidence for a major influx of meltwater at the beginning of the last deglaciation 15.7 thousand years ago (16,650 calendar years B.C.). The almost parallel trends of the isotope records from the Arctic Ocean, the Fram Strait, and the east Greenland continental margin suggest contemporaneous variations of the Eurasian Arctic and Greenland (Laurentide) ice sheets or increased export of low-saline waters from the Arctic within the East Greenland Current during the last deglaciation. On the basis of isotope and carbon data, the modern surface- and deep-water characteristics and seasonally open-ice conditions with increased surface-water productivity were established in the central Arctic at the end of Termination lb (about 7.2 thousand years ago or 6,000 calendar years B.C.).
Seven Million Years of Glaciation in Greenland
Authors: Larsen H. C. , Saunders A. D. , Clift P. D. , Beget J. , Wei W. , Spezzaferri S.
Published: October 2006

Glacial till, glaciomarine diamictites, and ice-rafted detritus found in marine cores collected off the shore of southeast Greenland record multiple Late Cenozoic glaciations beginning in the Late Miocene. Distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast Greenland margin. Glaciers advanced to the sea during several intervals in the Pliocene and Pleistocene. North Atlantic glaciation may have nucleated in southern Greenland rather than further north because of the high mountains and the high levels of precipitation in this region.
Galileo Multispectral Imaging of the North Polar and Eastern Limb Regions of the Moon
Authors: Belton M. J. S. , Greeley R. , Greenberg R. , Geissler P. , McEwen A. , Klaasen K. P. , Heffernan C. , Breneman H. , Johnson T. V. , Head J. W. , Pieters C. , Neukum G. , Chapman C. R. , Anger C. , Carr M. H. , Davies M. E. , Fanale F. P. , Gierasch P. J. , Thompson W. R. , Veverka J. , Sagan C. , Ingersoll A. P. , Pilcher C. B.
Published: October 2006

Multispectral images obtained during the Galileo probe's second encounter with the moon reveal the compositional nature of the north polar regions and the northeastern limb. Mare deposits in these regions are found to be primarily low to medium titanium lavas and, as on the western limb, show only slight spectral heterogeneity. The northern light plains are found to have the spectral characteristics of highlands materials, show little evidence for the presence of cryptomaria, and were most likely emplaced by impact processes regardless of their age.
Simulating the Adsorption of Alkanes in Zeolites
Authors: Smit Berend , Siepmann J. Ilja
Published: October 2006

The configurational-bias Monte Carlo technique is applied to simulate the adsorption of long chain alkanes in zeolites. This simulation technique is several orders of magnitude more efficient than conventional methods that can be used to simulate the adsorption of long chain alkanes. The calculated heats of adsorption are found to be in excellent agreement with experimental data. The results show a surprising chain length dependence of the heats of adsorption. This dependence has a simple molecular explanation in terms of preferential siting of the long chain alkanes.
Orientational Disorder of C
60
in Li
2
CsC
60
Authors: Hirosawa Ichiro , Prassides Kosmas , Mizuki Junichiro , Tanigaki Katsumi , Gevaert Matthew , Lappas Alexandros , Cockcroft Jeremy K.
Published: October 2006

The x-ray diffraction of the nonsuperconducting ternary fulleride Li
2
CsC
60
reveals at room temperature a face-centered-cubic (Fm3̅m) disordered structure that persists to a temperature of 13 Kelvin. The crystal structure is best modeled as containing quasispherical [radius of 3.556(4) angstroms] C
60
3-
ions, in sharp contrast to their orientational state in superconducting face-centered-cubic K
3
C
60
(merohedral disorder) and primitive cubic Na
2
CsC
60
(orientational order). The orientational disorder of the carbon atoms on the C
60
3-
sphere was analyzed with symmetry-adapted spherical-harmonic functions. Excess atomic density is evident in the 〈111〉 directions, indicating strong bonding Li
+
—C interactions, not encountered before in any of the superconducting alkali fullerides. The intercalate-carbon interactions and the orientational state of the fullerenes have evidently affected the superconducting pair-binding mechanism in this material.
Evidence for Monophyly and Arthropod Affinity of Cambrian Giant Predators
Authors: Chen Jun-yuan , Ramsköld Lars , Zhou Gui-qing
Published: October 2006

The Chinese Early Cambrian Chengjiang fauna includes three different anomalocaridids, a globally spread, extinct marine group including the largest known Cambrian animals. Anomalocaridids were active predators, and their presence implies that a complex ecosystem appeared abruptly in the earliest Phanerozoic. Complete specimens display several sets of characters shared only with some other exclusively Cambrian forms. This evidence indicates that anomalocaridids,
Opabinia
, and
Kerygmachela
form a monophyletic clade. Certain features indicate arthropod affinities of the clade, and for this group an unnamed (sub)phylum-level taxon within an arthropod (super)phylum is proposed.
Reconciling Short Recurrence Intervals with Minor Deformation in the New Madrid Seismic Zone
Authors: Schweig Eugene S. , Ellis Michael A.
Published: October 2006

At least three great earthquakes occurred in the New Madrid seismic zone in 1811 and 1812. Estimates of present-day strain rates suggest that such events may have a repeat time of 1000 years or less. Paleoseismological data also indicate that earthquakes large enough to cause soil liquefaction have occurred several times in the past 5000 years. However, pervasive crustal deformation expected from such a high frequency of large earthquakes is not observed. This suggests that the seismic zone is a young feature, possibly as young as several tens of thousands of years old and no more than a few million years old.
Methane to Ethylene with 85 Percent Yield in a Gas Recycle Electrocatalytic Reactor-Separator
Authors: Jiang Y. , Yentekakis I. V. , Vayenas C. G.
Published: October 2006

Methane was oxidatively coupled to ethylene with an ethylene yield up to 85 percent and a total C
2
hydrocarbon yield up to 88 percent in a gas recycle high-temperature (800°C) electrocatalytic or catalytic reactor where the recycled gas passes continuously through a molecular sieve trap in the recycle loop. Oxygen is supplied either electrocatalytically by means of the solid electrolyte support of the silver-based catalyst or in the gas phase. The C
2
products are obtained by subsequent heating of the molecular sieve trap. The selectivity to ethylene is up to 88 percent for methane conversion up to 97 percent.
Role of Deep Cloud Convection in the Ozone Budget of the Troposphere
Authors: Lelieveld Jos , Crutzen Paul J.
Published: October 2006

Convective updrafts in thunderstorms prolong the lifetime of ozone (O
3
) and its anthropogenic precursor NO

x

[nitric oxide (NO) + nitrogen dioxide (NO
2
)] by carrying these gases rapidly upward from the boundary layer into a regime where the O
3
production efficiency is higher, chemical destruction is slower, and surface deposition is absent. On the other hand, the upper troposphere is relatively rich in O
3
and NO

x

from natural sources such as downward transport from the stratosphere and lightning; convective overturning conveys the O
3
and NO

x

toward the Earth's surface where these components are more efficiently removed from the atmosphere. Simulations with a three-dimensional global model suggest that the net result of these counteractive processes is a 20 percent overall reduction in total tropospheric O
3
. However, the net atmospheric oxidation efficiency is enhanced by 10 to 20 percent.
Time-Resolved Imaging of Translucent Droplets in Highly Scattering Turbid Media
Authors: Alfano R. R. , Liang X. , Wang L. , Ho P. P.
Published: October 2006

The spatial distribution of small translucent droplets inside a 50-millimeter-thick Intralipid solution was imaged with a picosecond time and spatial-gated Kerr-Fourier imaging system at a signal level of about 10
–10
of the incident illumination intensity.
Chemical Signature of the Superconducting Phase in the Nd-Ce-Cu-O System
Authors: Nath Amar , Kopelev Nikolai S. , Chechersky Vladimir , Peng Jian-Liang , Greene Richard L. , O Beom-hoan , Larkin Michael I. , Markert John T.
Published: October 2006

The electron-doped material Nd

2–
x

Ce

x

CuO
4
becomes superconducting with a Ce
4+
composition around 0.16, but only after removal of a minuscule amount of extraneous oxygen. This enigmatic behavior was addressed here. A small fraction of copper in the CuO
2
planes of Nd

2–
x

Ce

x

CuO
4
was substituted by cobalt-57, which serves as a microprobe of the chemical environment. Deoxygenation brought about little change in the Mössbauer spectra both above and below the optimal superconducting concentration; however, for
x
= 0.16 a change was observed. In the latter, a major fraction of the magnetically split, five-coordinate species showed itself as a paramagnetically relaxed doublet upon deoxygenation. The abundance of the paramagnetically relaxed species corresponds closely to the diamagnetic volume fraction and thus provides a microscopic signature of the superconducting phase.
Ice Age Paleotopography
Authors: Peltier W. Richard
Published: October 2006

A gravitationally self-consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the Last Glacial Maximum (LGM). The results show that LGM ice volume was approximately 35 percent lower than suggested by the CLIMAP reconstruction and the maximum heights of the main Laurentian and Fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level. Use of these Ice Age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the CLIMAP data set.
Catalytic Activation of Carbon-Fluorine Bonds by a Soluble Transition Metal Complex
Authors: Aizenberg Michael , Milstein David
Published: October 2006

Homogeneous catalytic activation of the strong carbon-fluorine bonds under mild conditions was achieved with the use of rhodium complexes as catalysts. The catalytic reactions between polyfluorobenzenes and hydrosilanes result in substitution of fluorine atoms by hydrogen atoms and are chemo- and regioselective. With individual stoichiometric steps observed and combined, and with intermediates isolated and fully characterized (including crystal structures), these systems demonstrate the effectiveness of a rational approach to catalytic design.
Evidence from Paleosols for the Geological Antiquity of Rain Forest
Authors: Retallack Gregory J. , Germán-Heins Judit
Published: October 2006

Kaolinitic claystones in Paleozoic paleokarst underlying the Middle Pennsylvanian Fort Scott Limestone near Drake, Missouri, contain abundant fossil root traces. These include a surficial root mat as well as stout, woody, deeply penetrating root traces: a rooting pattern similar to that under rain forest. Also similar to soils of rain forest is the deeply weathered clay of the paleosol, in which minimal amounts of nutrient bases remain. Forest communities adapted to oligotrophic clayey substrates in humid climates existed at least 305 million years ago.
Fabrication of Atomic-Scale Structures on Si(001) Surfaces
Authors: Salling C. T. , Lagally M. G.
Published: October 2006

The scanning tunneling microscope has been used to define regular crystalline structures at room temperature by removing atoms from the silicon (001) surface. A single atomic layer can be removed to define features one atom deep and create trenches with ordered floors. Segments of individual dimer rows can be removed to create structures with atomically straight edges and with lateral features as small as one dimer wide. Conditions under which such removal is possible are defined, and a mechanism is proposed.
Direct Spectroscopic Detection of a Zwitterionic Excited State
Authors: Engebretson Daniel S. , Zaleski Jeffrey M. , Leroi George E. , Nocera Daniel G.
Published: October 2006

Two electrons in two weakly coupled orbitals give rise to two states (diradical) with electrons residing in separate orbitals and two states (zwitterionic) with both electrons paired in one orbital or the other. This two-electron, two-orbital state manifold has eluded experimental confirmation because the zwitterionic states have been difficult to locate. Two-photon excitation of fluorescence from Mo
2
CI
4
(PMe
3
)
4
(D

2
d

) has been measured with linearly and circularly polarized light. From the polarization ratio and the energy of the observed transition, the 2
1
A
1
(δ*δ*) excited state has been located and characterized. In conjunction with the one-photon allowed
1
B
2
(δδ*) excited state, the zwitterionic state manifold for the quadruply bonded metal-metal class of compounds is thus established.
Antibody-Mediated Bacteriorhodopsin Orientation for Molecular Device Architectures
Authors: Koyama Koichi , Yamaguchi Naoto , Miyasaka Tsutomu
Published: October 2006

A rational method for constructing highly oriented films of purple membrane (PM) has been established by using two kinds of bispecific antibodies with different antigen-binding sites, one binding to a specific side of bacteriorhodopsin and the other to a phospholipid hapten. A hapten monolayer deposited on a metal electrode was treated with a bispecific antibody solution and incubated with a PM suspension to produce a highly oriented PM film, as confirmed by electron microscopy in which an immunogold labeling technique was used. This antibody-mediated PM monolayer was then used in the construction of a light-sensing photoelectric device. A comparison of the two incorporated PM monolayers showed that highly efficient photocurrents were produced by the PM monolayer whose unidirectionally oriented cytoplasmic surface faces the electrode.
Excimers and Exciplexes of Conjugated Polymers
Authors: Jenekhe Samson A. , Osaheni John A.
Published: October 2006

Observations of intermolecular excimers in several π-conjugated polymers and exciplexes of these polymers with tris(
p
-tolyl)amine are reported. It is shown that the luminescence of conjugated polymer thin films originates from excimer emission and that the generally low quantum yield is the result of self-quenching. Thus, in sufficiently dilute solution, the "single-chain" emission has a quantum yield of unity. Exciplex luminescence and exciplex-mediated charge photogeneration have much higher quantum yields than the excimer-mediated photophysical processes. These results provide a basis for understanding and controlling the photophysics of conjugated polymers in terms of supramolecular structure and morphology.
The Temporal Distribution of Seismic Radiation During Deep Earthquake Rupture
Authors: Houston Heidi , Vidale John E.
Published: October 2006

The time history of energy release during earthquakes illuminates the process of failure, which remains enigmatic for events deeper than about 100 kilometers. Stacks of teleseismic records from regional arrays for 122 intermediate (depths of 100 to 350 kilometers) and deep (depths of 350 to 700 kilometers) earthquakes show that the temporal pattern of short-period seismic radiation has a systematic variation with depth. On average, for intermediate depth events more radiation is released toward the beginning of the rupture than near the end, whereas for deep events radiation is released symmetrically over the duration of the event, with an abrupt beginning and end of rupture. These findings suggest a variation in the style of rupture related to decreasing fault heterogeneity with depth.
NCSA Mosaic and the World Wide Web: Global Hypermedia Protocols for the Internet
Authors: Schatz Bruce R. , Hardin Joseph B.
Published: October 2006

Network information systems reached the public consciousness this year as a result of the phenomenal growth in the use of the Internet. In particular, the software constituting NCSA (National Center for Supercomputing Applications) Mosaic and the World Wide Web have made global hypermedia a widespread reality for the first time. The technology underlying this software is described to explain the protocols behind information spaces. These include the historical predecessors, the current protocols with examples, future directions for the software, and discussion of research systems with different architectures. Reasons for its popularity are given, with the goal of illuminating successful services for the National Information Infrastructure.
Mercury-Based Cuprate High-Transition Temperature Grain-Boundary Junctions and SQUIDs Operating Above 110 Kelvin
Authors: Gupta A. , Sun J. Z. , Tsuei C. C.
Published: October 2006

The superconducting transport characteristics of HgBa
2
CaCu
2
O
6+δ
(Hg-1212) films and grain-boundary junctions grown on (100)-oriented SrTiO
3
bicrystal substrates have been investigated. The films exhibit a zero-resistance temperature of ∼120 kelvin and sustain large critical current densities, with values as high as 10
6
amperes per square centimeter at around 100 kelvin. On the other hand, the grain boundaries behave as weak links, with substantially lower critical currents, as is observed for other cuprate superconductors. A reduction of three orders of magnitude in critical current was observed for transport across a 36.8° grain boundary. The current-voltage characteristics of bridges across such a grain boundary show weak-link behavior qualitatively resembling that of a resistively shunted junction. Single-level direct-current superconducting quantum interference devices (SQUIDs) have been fabricated with such bicrystal junctions. These SQUIDs show clear periodic voltage modulations when subjected to applied magnetic fields. The SQUIDs operate at temperatures as high as 111.8 kelvin, which makes them attractive for operation in portable sensors and devices that utilize nonconventional cooling methods.
Single-Crystalline (KC
60
)

n

: A Conducting Linear Alkali Fulleride Polymer
Authors: Pekker S. , Jánossy A. , Mihaly L. , Chauvet O. , Carrard M. , Forró L.
Published: October 2006

Single crystals of a linear cycloadduct conducting polymer, (KC
60
)

n

, have been grown that are a few tenths of a millimeter in length. Partial oxidation under toluene transformed these crystals into bundles of fibers. The degree of polymerization exceeded 100,000.
Newtonian Dislocation Creep in Quartzites: Implications for the Rheology of the Lower Crust
Authors: Wang J. N. , Hobbs B. E. , Ord A. , Shimamoto T. , Toriumi M.
Published: October 2006

Mechanical and microstructural evidence indicates that a natural and a synthetic quartzite deformed by Newtonian dislocation (Harper-Dorn) creep at temperatures higher than 1073 K and stresses lower than 300 megapascals. The observation of this creep in these materials suggests that the lower crust may flow like a Newtonian viscous fluid by a dislocation mechanism at stresses much smaller than those previously postulated.
Molecular Recognition by Self-Assembled Monolayers of Cavitand Receptors
Authors: Schierbaum K. D. , Weiss T. , van Veizen E. U. Thoden , Engbersen J. F. J. , Reinhoudt D. N. , Göpel W.
Published: October 2006

It is shown by angle-resolved x-ray photoelectron spectroscopy that cavitands derived from resorcin[4]arenes provided with four dialkylsulfide chains form stable monolayers on gold surfaces that are well organized by self-assembly. The cavitand headgroups at the surface of the resorcin[4]arene monolayer act as molecular recognition sites for small organic molecules with remarkable selectivity for perchloroethylene (C
2
Cl
4
). Comparative thermal desorption experiments indicate binding sites with high interaction energies of C
2
Cl
4
at the surface of the resorcin[4]arene monolayers. Fast and reversible "host-guest" interactions were found by the monitoring of extremely small mass changes (in the nanogram range) with a quartz microbalance oscillator provided with gold electrodes coated by resorcin[4]arene monolayers.
Encoding of Olfactory Information with Oscillating Neural Assemblies
Authors: Laurent Gilles , Davidowitz Hananel
Published: October 2006

In the brain, fast oscillations of local field potentials, which are thought to arise from the coherent and rhythmic activity of large numbers of neurons, were observed first in the olfactory system and have since been described in many neocortical areas. The importance of these oscillations in information coding, however, is controversial. Here, local field potential and intracellular recordings were obtained from the antennal lobe and mushroom body of the locust
Schistocerca americana.
Different odors evoked coherent oscillations in different, but usually overlapping, ensembles of neurons. The phase of firing of individual neurons relative to the population was not dependent on the odor. The components of a coherently oscillating ensemble of neurons changed over the duration of a single exposure to an odor. It is thus proposed that odors are encoded by specific but dynamic assemblies of coherently oscillating neurons. Such distributed and temporal representation of complex sensory signals may facilitate combinatorial coding and associative learning in these, and possibly other, sensory networks.
Thorium-230 Ages of Corals and Duration of the Last Interglacial Sea-Level High Stand on Oahu, Hawaii
Authors: Szabo Barney J. , Ludwig Kenneth R. , Muhs Daniel R. , Simmons Kathleen R.
Published: October 2006

Thorium-230 ages of emergent marine deposits on Oahu, Hawaii, have a uniform distribution of ages from ∼114,000 to ∼131,000 years, indicating a duration for the last interglacial sea-level high stand of ∼17,000 years, in contrast to a duration of ∼8000 years inferred from the orbitally tuned marine oxygen isotope record. Sea level on Oahu rose to ≥1 to 2 meters higher than present by 131,000 years ago or ∼6000 years earlier than inferred from the marine record. Although the latter record suggests a shift back to glacial conditions beginning at ∼119,000 years ago, the Oahu coral ages indicate a near present sea level until ∼114,000 years ago.
Crustal Architecture of the Cascadia Forearc
Authors: Trehu A. M. , Asudeh I. , Brocher T. M. , Luetgert J. H. , Mooney W. D. , Nabelek J. L. , Nakamura Y.
Published: October 2006

Seismic profiling data indicate that the thickness of an accreted oceanic terrane of Paleocene and early Eocene age, which forms the basement of much of the forearc beneath western Oregon and Washington, varies by approximately a factor of 4 along the strike of the Cascadia subduction zone. Beneath the Oregon Coast Range, the accreted terrane is 25 to 35 kilometers thick, whereas offshore Vancouver Island it is about 6 kilometers thick. These variations are correlated with variations in arc magmatism, forearc seismicity, and long-term forearc deformation. It is suggested that the strength of the forearc crust increases as the thickness of the accreted terrane increases and that the geometry of the seaward edge of this terrane influences deformation within the subduction complex and controls the amount of sediment that is deeply subducted.
Simulating the Self-Assembly of Gemini (Dimeric) Surfactants
Authors: Karaborni S. , Esselink K. , Hilbers P. A. J. , Smit B. , Karthauser J. , van Os N. M. , Zana R.
Published: October 2006

The morphologies and dynamics of aggregates formed by surfactant molecules are known to influence strongly performance properties spanning biology, household cleaning, and soil cleanup. Molecular dynamics simulations were used to investigate the morphology and dynamics of a class of surfactants, the gemini or dimeric surfactants, that are of potential importance in several industrial applications. Simulation results show that these surfactants form structures and have dynamic properties that are drastically different from those of single-chain surfactants. At the same weight fraction, single-chain surfactants form spherical micelles whereas gemini surfactants, whose two head groups are coupled by a short hydrophobic spacer, form thread-like micelles. Simulations at different surfactant concentrations indicate the formation of various structures, suggesting an alternative explanation for the unexpected viscosity behavior of gemini surfactants.
The Magnitude 6.7 Northridge, California, Earthquake of 17 January 1994
Authors:   Scientists of the U.S. Geological Survey and the Southern California Earthquake Center
Published: October 2006

The most costly American earthquake since 1906 struck Los Angeles on 17 January 1994. The magnitude 6.7 Northridge earthquake resulted from more than 3 meters of reverse slip on a 15-kilometer-long south-dipping thrust fault that raised the Santa Susana mountains by as much as 70 centimeters. The fault appears to be truncated by the fault that broke in the 1971 San Fernando earthquake at a depth of 8 kilometers. Of these two events, the Northridge earthquake caused many times more damage, primarily because its causative fault is directly under the city. Many types of structures were damaged, but the fracture of welds in steel-frame buildings was the greatest surprise. The Northridge earthquake emphasizes the hazard posed to Los Angeles by concealed thrust faults and the potential for strong ground shaking in moderate earthquakes.