bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomistic modeling of dopant implantation, diffusion, and activation
Authors: Pelaz L. , Aboy M. , Lopez P. , Marques L. A.
Published: October 2006

Atomistic kinetic Monte Carlo simulations have been performed to illustrate the correlation between the Si interstitial defects generated by ion implantation, and B diffusion and activation in Si. The amount of residual damage is not very affected by moderate dynamic anneal during subamorphizing implants. However, dynamic anneal even at room temperature significantly influences the residual damage in amorphizing implants. The efficiency of the surface as a sink for point defects affects the evolution of Si interstitial defects. They set the Si interstitial supersaturation that is responsible for transient enhanced diffusion of B and also control the formation and dissolution of B–Si interstitial clusters.
Back-gated milliampere-class field emission device based on carbon nanosheets
Authors: Tyler T. , Shenderova O. , Ray M. , Dalton J. , Wang J. , Outlaw R. , Zhu M. , Zhao X. , McGuire G. , Holloway B. C.
Published: October 2006

The fabrication and testing of a back-gated field emission device (bgFED) are reported. The properties of a unique allotrope of carbon, carbon nanosheet (CNS), are exploited for use as a highly effective field emitter material, and CNSs are incorporated into a bgFED capable of producing several milliamperes of emission current. The bgFED is evaluated in terms of triode modulation, high current capability, and short-term stability.
Comparison of different methods to contact to nanowires
Authors: Langford R. M. , Wang T.-X. , Thornton M. , Heidelberg A. , Sheridan J. G. , Blau W. , Leahy R.
Published: October 2006

A comparison of four different methods to make electrical contact to both 100nm gold nanowires and 50nm multiwall carbon nanotubes is given. The techniques are compared in terms of the success yield, contact resistance, complexity of the fabrication steps, and potential for creating novel device structures and architectures. The different methods compared are (i) in situ micromanipulation of wires onto prepatterned electrodes, (ii) ion and electron beam assisted deposition, (iii) electron beam lithography, and (iv) drop casting of wires from solution onto prepatterned electrodes.
Physical and electrical properties of plasma nitrided germanium oxynitride
Authors: Sugawara Takuya , Sreenivasan Raghavasimhan , McIntyre Paul C.
Published: October 2006

The physical and electrical properties of plasma nitrided germanium oxynitride (GeON) and silicon oxynitride (SiON) layers are studied. In this study, two kinds of plasma nitridation process were utilized to form oxynitride layers. High pressure remote inductive coupled plasma and low pressure radial line slot antenna (RLSA) plasma provide radical dominant and ion dominant plasma nitridation processes, respectively. X-ray photoelectron spectroscopy results show different properties of GeON layers based on each plasma nitridation process. The remote (radical) plasma nitridation forms water soluble nitrogen-germanium bonding, and RLSA (ion) plasma nitridation forms water resistant nitrogen-germanium bonding. Although hydrogen containing plasmas or ion dominant plasma process can incorporate high amount of nitrogen into oxynitride layers, such process is accompanied by water insoluble suboxide formation and charging damage. Using p-type metal oxide semiconductor (MOS) capacitors, basic electrical properties of GeON and SiON films were also studied. Approximately four order magnitude higher gate leakage current was observed on GeON MOS capacitor, which results in capacitance reduction and a large dissipation factor at high gate voltage.
Mechanism of germanium plasma nitridation
Authors: Sugawara Takuya , Sreenivasan Raghavasimhan , McIntyre Paul C.
Published: October 2006

The mechanisms of plasma nitridation of germanium (Ge) and silicon (Si) substrates are discussed based on plasma characteristics and oxynitride film properties. Optical emission spectroscopy (OES) study and x-ray photoelectron spectroscopy were utilized to characterize the plasma and film properties, respectively. In this study, high pressure (1.8Torr) remote inductive coupled plasma and low pressure (<50mTorr) radial line slot antenna (RLSA) plasma nitridation processes are utilized to form germanium oxynitride (GeON) and silicon oxynitride (SiON) film. OES results show that high pressure remote plasma nitridation is a radical dominant process. In this process, hydrogen containing neutral radicals (NH* and H*) were important to nitride Ge and Si substrates. This process required high substrate temperature to nitride Ge substrate, whereas Si substrates could be nitrided at low substrate temperature. Low pressure RLSA plasma nitridation is an ion dominant process. In this, N2+ ion species acted as dominant reactive species. Using this process, germanium could be nitrided at low substrate temperature without hydrogen and high nitrogen concentration (∼22at.%) GeON was obtained.
Texture development and grain boundary faceting in an excimer laser-crystallized silicon thin film
Authors: Lee Sung Bo , Moon Jaehyun , Chung Choong-Heui , Kim Yong-Hae , Lee Jin Ho , Choi Duck-Kyun
Published: October 2006

A 50-nm-thick amorphous silicon film on a SiO2 substrate is crystallized by an excimer laser-induced sequential lateral solidification. In the crystallized film, the laser scanning direction has a tendency to generate the ⟨100⟩ texture formation, whereas the surface normal and another in-plane orientation (normal to the scanning direction), designated as rolling direction, do not reveal any distinct texture development. Some grain boundaries are faceted, suggesting having a low trap density. Thus, the presence of the faceted grain boundaries is favorable for polycrystalline silicon electronic devices, such as thin film transistors and solar cells. A further grain boundary faceting might be induced by annealing processes.
Large Punctuational Contribution of Speciation to Evolutionary Divergence at the Molecular Level
Authors: Pagel Mark , Venditti Chris , Meade Andrew
Published: October 2006

A long-standing debate in evolutionary biology concerns whether species diverge gradually through time or by punctuational episodes at the time of speciation. We found that approximately 22% of substitutional changes at the DNA level can be attributed to punctuational evolution, and the remainder accumulates from background gradual divergence. Punctuational effects occur at more than twice the rate in plants and fungi than in animals, but the proportion of total divergence attributable to punctuational change does not vary among these groups. Punctuational changes cause departures from a clock-like tempo of evolution, suggesting that they should be accounted for in deriving dates from phylogenies. Punctuational episodes of evolution may play a larger role in promoting evolutionary divergence than has previously been appreciated.
Molecular Loops in the Galactic Center: Evidence for Magnetic Flotation
Authors: Fukui Yasuo , Yamamoto Hiroaki , Fujishita Motosuji , Kudo Natsuko , Torii Kazufumi , Nozawa Satoshi , Takahashi Kunio , Matsumoto Ryoji , Machida Mami , Kawamura Akiko , Yonekura Yoshinori , Mizuno Norikazu , Onishi Toshikazu , Mizuno Akira
Published: October 2006

The central few hundred parsecs of the Milky Way host a massive black hole and exhibit very violent gas motion and high temperatures in molecular gas. The origin of these properties has been a mystery for the past four decades. Wide-field imaging of the
12
CO (rotational quantum number
J
= 1 to 0) 2.6-millimeter spectrum has revealed huge loops of dense molecular gas with strong velocity dispersions in the galactic center. We present a magnetic flotation model to explain that the formation of the loops is due to magnetic buoyancy caused by the Parker instability. The model has the potential to offer a coherent explanation for the origin of the violent motion and extensive heating of the molecular gas in the galactic center.
Patterned Condensation Figures as Optical Diffraction Gratings
Authors: Kumar Amit , Whitesides George M.
Published: October 2006

Heterogeneous, patterned surfaces comprising well-defined hydrophobic and hydrophilic regions and having micrometer-scale periodicities were prepared by patterning the adsorption of ω-functionalized alkanethiolates in self-assembled monolayers (SAMs) on gold. Condensation of water on such surfaces resulted in drops that followed the patterns in the SAMs. These patterned condensation figures (CFs) acted as optical diffraction gratings for reflected (or transmitted) light from a helium-neon laser (wavelength of 632.8 nanometers). Under an atmosphere of constant relative humidity, the development of the condensation figure was monitored quantitatively, as the temperature of the surface was lowered, by following the change in intensity of a first-order diffraction spot. This experimental technique may be useful in the development of new types of optical sensors that respond to their environment by changing the reflectivity of patterned regions and for studying phenomena such as drop nucleation, contact angle hysteresis, and spontaneous dewetting and break-up of thin liquid films.
New Light on the Heart of Darkness of the Solar Chromosphere
Authors: Solanki S. K. , Livingston W. , Ayres T.
Published: October 2006

Solar carbon monoxide spectra indicate the existence of a cool (less than 4000 kelvin) component to the solar chromosphere coexisting with the hot, bright gas at 6000 to 7000 kelvin. However, both the existence and the location of the cool component have been controversial. New high-resolution spectra show that carbon monoxide goes into emission just beyond the limb, allowing it to be probed without photospheric contamination. The cool component has temperatures as low as 3000 to 3500 kelvin and appears to cover 50 to 85 percent of the quiet solar surface. There is a steep temperature rise to normal chromospheric temperatures at a height of 900 to 1100 kilometers. Large horizontal velocities are seen, suggesting that the cool component is maintained by the supersonic adiabatic expansion of upwelling gas in overshooting granules.
Dynamics Affecting the Primary Charge Transfer in Photosynthesis
Authors: Gehlen John N. , Marchi Massimo , Chandler David
Published: October 2006

Analysis of a 60-picosecond molecular dynamics trajectory of the reaction center of
Rhodopseudomonas viridis
provides an understanding of observations concerning vibrational coherence and the nonexponential kinetics of the primary charge transfer in photosynthesis. Complex kinetics arises from energy gap correlations that persist beyond 1 picosecond.
A Magnetohydrodynamic Model of Solar Wind Interaction with Asteroid Gaspra
Authors: Baumgártel Klaus , Sauer Konrad , Bogdanov Alexander
Published: October 2006

The solar wind response to a small-sized magnetized body is modeled on the basis of a two-dimensional magnetohydrodynamic (MHD) plasma description including Hall current corrections (Hall-MHD model). Basic features of the magnetic signatures observed near Galileo's closest approach to asteroid Gaspra are reproduced, assuming Gaspra's magnetic dipole moment to be of the order of 10
14
ampere⋅meters squared and tilted to the solar wind flow direction at an angle of about 45°.
The Cosmological Kibble Mechanism in the Laboratory: String Formation in Liquid Crystals
Authors: Bowick Mark J. , Chandar L. , Schiff E. A. , Srivastava Ajit M.
Published: October 2006

The production of strings (disclination lines and loops) has been observed by means of the Kibble mechanism of domain (bubble) formation in the isotropic-nematic phase transition of the uniaxial nematic liquid crystal 4-cyano-4′-
n
-pentylbiphenyl. The number of strings formed per bubble is about 0.6. This value is in reasonable agreement with a numerical simulation of the experiment in which the Kibble mechanism is used for the order parameter space of a uniaxial nematic liquid crystal.
The Dependence of Electron Transfer Efficiency on the Conformational Order in Organic Monolayers
Authors: Haran Avner , Waldeck David H. , Naaman Ron , Moons Ellen , Cahen David
Published: October 2006

The electron transfer through an organized organic monolayer of alkyl chains adsorbed on a silicon wafer has been studied. The silicon was used as an electrode in a three-electrode electrochemical cell, and the current versus voltage response was measured. The results show that when the chains in the monolayer are in the "all trans" configuration, the charge transfer efficiency is higher than when the chains have a "gauche" configuration. A mechanism rationalizing all the observations is suggested.
Increasing Turnover Through Time in Tropical Forests
Authors: Phillips O. L. , Gentry A. H.
Published: October 2006

Tree turnover rates were assessed at 40 tropical forest sites. Averaged across inventoried forests, turnover, as measured by tree mortality and recruitment, has increased since the 1950s, with an apparent pantropical acceleration since 1980. Among 22 mature forest sites with two or more inventory periods, forest turnover also increased. The trend in forest dynamics may have profound effects on biological diversity.
Chain Pullout and Mobility Effects in Friction and Lubrication
Authors: Brown H. R.
Published: October 2006

The interfacial shear stress that occurs when a network of a polymer that is highly mobile at the segment level (an elastomer) is slid over a smooth surface of an immobile (glassy) polymer has been measured. The glassy material is covered by a thin layer of end-attached chains of the mobile material. The experiment was designed so that there were no free chains at the interface; the slip occurred between network chains on the one side and rigid material plus end-attached mobile chains on the other side. Two main results were obtained. (i) The interfacial shear stress is strongly affected by the segment mobility of the materials on both sides of the slip plane, and considerably lower stress is observed when the materials on both sides of the interface are highly mobile. (ii) Very thin layers of tethered chains can increase the interfacial friction. Both results are relevant to the understanding of a number of practical situations that range from the operation of thin layers of lubricants, such as those found in magnetic storage devices, to the problem of wall slip and melt fracture in polymer processing.
Why Snakes Have Forked Tongues
Authors: Schwenk Kurt
Published: October 2006

The serpent's forked tongue has intrigued humankind for millennia, but its function has remained obscure. Theory, anatomy, neural circuitry, function, and behavior now support a hypothesis of the forked tongue as a chemosensory edge detector used to follow pheromone trails of prey and conspecifics. The ability to sample simultaneously two points along a chemical gradient provides the basis for instantaneous assessment of trail location. Forked tongues have evolved at least twice, possibly four times, among squamate reptiles, and at higher taxonomic levels, forked tongues are always associated with a wide searching mode of foraging. The evolutionary success of advanced snakes might be due, in part, to perfection of this mechanism and its role in reproduction.
5-Coordinate Si Compounds as Intermediates in the Synthesis of Silicates in Nonaqueous Media
Authors: Herreros Bruno , Carr Stuart W. , Klinowski Jacek
Published: October 2006

Sodium silicoglycolate, an organosilicon compound in which silicon is in 5-coordination with respect to oxygen, is shown to be a reaction intermediate in the synthesis of a purely siliceous sodalite with ethylene glycol as solvent. The presence of silicon-29 nuclear magnetic resonances at –105.5 ± 0.3 parts per million in solution and –102.7 parts per million in the solid state as well as x-ray powder diffraction patterns demonstrate that 5-coordinate silicon is intimately involved in the synthesis. Silicon compounds of the 5-coordinate type are highly reactive and are promising starting materials for the synthesis of novel silicone polymers, molecular sieves, glasses, semiconductors, and ceramics. We have used sodium silicoglycolate to prepare the molecular sieve silicalite as well as sodalites of different compositions.
Short-Lived Chemical Heterogeneities in the Archean Mantle with Implications for Mantle Convection
Authors: Blichert-Toft Janne , Albarede Francis
Published: October 2006

The neodymium isotope and samarium-neodymium systematics of 2.7-billion-year-old mantle-derived magmas indicate that the lifetime of chemical heterogeneities was much shorter in the Archean mantle than in the modern mantle. Isotopic evidence is compatible with a Rayleigh number 100 times larger and convection 10 times faster in the Late Archean compared with the present-day mantle. Modern plate tectonics thus may be an improbable analog for the Archean. Chemical heterogeneities in the mantle may originate upon magma migration and mineralogical phase changes rather than by recycling of oceanic and continental crust.
Following Ion Diffusion in Solution
Authors: Rondot S. , Cazaux J. , Aaboubi O. , Chopart J. P. , Olivier A.
Published: October 2006

An x-ray projection microscope equipped with a charge-coupled device camera allows direct observation of zinc (Zn
2+
) ions diffusing in aqueous hydrochloric acid solution during the corrosion of zinc foil and pellets. Time series of microradiographic images with a lateral resolution on the order of 10 micrometers allow observation of the time and spatial evolution of the colorless Zn
2+
ions in solution without any previous treatment. The concentration distribution of the ions can be quantified from these images. This technique should find applications in the biology, chemistry, and electrochemistry of aqueous solutions, allowing direct observation of the behavior and concentration fluctuations of medium or heavy ions moving in a weakly absorbing medium.
Diamond Coating of Titanium Alloys
Authors: Drory M. D. , Hutchinson J. W.
Published: October 2006

A titanium alloy was coated with a thin layer of synthetic diamond by chemical vapor deposition methods, achieving exceptional adhesion. Scientific and technological opportunities exist for the development of diamond-coated metal alloys and for a better understanding of adhesion mechanisms of hard, brittle coatings. An indentation method of wide applicability for measuring the adhesion of such coatings is discussed.
El Niño on the Devil's Staircase: Annual Subharmonic Steps to Chaos
Authors: Jin Fei-Fei , Neelin J. David , Ghil Michael
Published: October 2006

The source of irregularity in El Niño, the large interannual climate variation of the Pacific ocean-atmosphere system, has remained elusive. Results from an El Niño model exhibit transition to chaos through a series of frequency-locked steps created by nonlinear resonance with the Earth's annual cycle. The overlapping of these resonances leads to the chaotic behavior. This transition scenario explains a number of climate model results and produces spectral characteristics consistent with currently available data.
Unexpected Square Symmetry Seen by Atomic Force Microscopy in Bilayer Films of Disk-Like Molecules
Authors: Maliszewskyj Nicholas C. , Heiney Paul A. , Josefowicz Jack Y. , McCauley John P. , Smith Amos B.
Published: October 2006

Thin films of disk-shaped molecules are expected to display anisotropic optical and transport properties, leading to applications in optical display or sensor technologies. Bilayer Langmuir-Blodgett films of monomeric triphenylene mesogens have been studied by atomic force microscopy. The triphenylene cores of the constituent molecules tend to promote the formation of columnar structures in the plane of the substrate and along the direction of deposition of the film. Atomic force microscopy images of bilayer Langmuir-Blodgett films revealed two types of structure, one corresponding to an aligned columnar structure and the other to an unusual square lattice, which may result from the superposition of columnar structures in adjacent layers that intersect at near right angles. Annealing such bilayers near the melting point of the bulk compound improved the structural ordering by reducing the angular spread of orientations associated with the well-developed columnar structure in some areas and by producing a more distinct square lattice in other areas of the sample.
Stellar Luminosity Variations and Global Warming
Authors: Foukal Peter
Published: October 2006

Recent studies indicate that variation in the sun's luminosity is less than that observed in many other stars of similar magnetic activity. Current findings also indicate that in more active stars, the attenuation by faculae of sunspot luminosity modulation is less effective than in the sun at present. The sun could thus become photometrically more variable (and dimmer) if its magnetic activity exceeded present levels. But the levels of solar activity required for this to occur are not observed in carbon-14 and beryllium-10 records over the past several millennia, which indicates that such an increase in amplitude of surface magnetism-driven variations in solar luminosity is unlikely in the present epoch.
Molecular Nanotube Aggregates of β- and γ-Cyclodextrins Linked by Diphenylhexatrienes
Authors: Li Guang , McGown Linda B.
Published: October 2006

Linked by strings of diphenylhexatriene (DPH) molecules, β- and γ-cyclodextrins (CDs) can form nanotube aggregates that contain as many as ∼20 βCDs (20 nanometers long) or ∼20 to 35 γCDs (20 to 35 nanometers long). Nanotube formation was indicated in solution, by fluorescence anisotropy and light scattering results, and on graphite surfaces, by scanning tunneling microscopy. Tubes were not observed for the smaller αCDs. Molecular modeling shows that CD cavity size and the rodlike DPH structure are key factors in nanotube formation. Spectra generated by proton nuclear magnetic resonance indicate the inclusion of DPH in the interior of the CDs and formation of nanotubes in βCDs and γCDs only. The photophysical properties of DPH are affected by its arrangement into a one-dimensional array within the CD nanotube, possibly because of exciton formation.
A Catastrophic Death Assemblage and Paleoclimatic Implications of Pliocene Seabirds of Florida
Authors: Emslie Steven D. , Morgan Gary S.
Published: October 2006

A deposit of fossil seabirds from the late Pliocene of Florida includes more than 130 skeletons of an extinct cormorant that is related phylogenetically to Recent species currently restricted to the eastern north Pacific. Evidence suggests the birds died in a single catastrophic event, perhaps a red tide. The fossil cormorant, along with other extinct seabirds and marine mammals, supports molluscan evidence for cold-water upwelling along the Florida Gulf Coast during the Pliocene. A decline in species richness of marine vertebrates throughout the Pliocene of Florida coincides with cessation of upwelling after emergences of the Panamanian Land Bridge.
Dielectric Asymmetry in the Photosynthetic Reaction Center
Authors: Steffen Martin A. , Lao Kaiqin , Boxer Steven G.
Published: October 2006

Although the three-dimensional structure of the bacterial photosynthetic reaction center (RC) reveals a high level of structural symmetry, with two nearly equivalent potential electron transfer pathways, the RC is functionally asymmetric: Electron transfer occurs along only one of the two possible pathways. In order to determine the origins of this symmetry breaking, the internal electric field present in the RC when charge is separated onto structurally characterized sites was probed by using absorption band shifts of the chromophores within the RC. The sensitivity of each probe chromophore to an electric field was calibrated by measuring the Stark effect spectrum, the change in absorption due to an externally applied electric field. A quantitative comparison of the observed absorption band shifts and those predicted from vacuum electrostatics gives information on the effective dielectric constant of the protein complex. These results reveal a significant asymmetry in the effective dielectric strength of the protein complex along the two potential electron transfer pathways, with a substantially higher dielectric strength along the functional pathway. This dielectric asymmetry could be a dominant factor in determining the functional asymmetry of electron transfer in the RC.
Diacetylenic Lipid Tubules: Experimental Evidence for a Chiral Molecular Architecture
Authors: Schnur J. M. , Ratna B. R. , Selinger J. V. , Singh A. , Jyothi G. , Easwaran K. R. K.
Published: October 2006

Molecular self-assembly is of key importance for the rational design of advanced materials. To investigate the causal relation between molecular structure and the consequent self-assembled microstructure, self-assembled tubules of diacetylenic lipids were studied. Circular-dichroism studies give experimental evidence that the formation of tubules is driven by chiral molecular packing, in agreement with recent theories of tubules. On the basis of these results, a molecular mechanism for the formation of tubules is proposed.
High-Resolution Nuclear Magnetic Resonance Spectroscopy in a Circularly Polarized Laser Beam
Authors: Buckingham A. D. , Parlett L. C.
Published: October 2006

Nuclei in a fluid subjected to a continuous wave circularly polarized light beam are predicted to experience a static magnetic field proportional to E
±
× E
±
, where E
±
is the electric vector of the right or left circularly polarized wave and the dot denotes a time derivative. The field strongly depends on the local electronic structure and is present in all atoms. For an intensity of 10 watts per square centimeter propagating in the direction of the field of a magnetic resonance spectrometer, the general theory presented here predicts shifts of ± 4 × 10
-8
hertz for protons and ± 10
-5
hertz for fluorine-19. Larger shifts are predicted if the laser frequency is near an optical absorption.
Examining Nanoenvironments in Solids on the Scale of a Single, Isolated Impurity Molecule
Authors: Moerner W. E.
Published: October 2006

Optical spectroscopy of single impurity molecules in solids can be used as an exquisitely sensitive probe of the structure and dynamics of the specific local environment around the single molecule (the "nanoenvironment"). Recently observed effects such as spectral diffusion, perturbations by external fields, changes in molecular photophysics, shifts in vibrational modes, optical modification of the absorption spectrum, dynamics due to amorphous system physics, and magnetic resonance of a single molecular spin attest to the vitality of and growing interest in this new field, which may lead to optical storage on the single-molecule level.
Size-Specific Infrared Spectra of Benzene-(H
2
O)

n

Clusters (
n
= 1 through 7): Evidence for Noncyclic (H
2
O)

n

Structures
Authors: Pribble R. Nathaniel , Zwier Timothy S.
Published: October 2006

Resonant ion-dip infrared spectroscopy has been used to record size-specific infrared spectra of C
6
H
6
-(H
2
O)

n

clusters with
n
= 1 through 7 in the O—H stretch region. The O—H stretch spectra show a dramatic dependence on cluster size. For the
n
= 3 to 5 clusters, the transitions can be divided into three types—attributable to free, π hydrogen-bonded, and single donor water-water O—H stretches—consistent with a C
6
H
6
-(H
2
O)

n

structure in which benzene is on the surface of a cyclic (H
2
O)

n

cluster. In
n
= 6 and 7 clusters, the spectra show distinct new transitions in the 3500 to 3600 wave number region. After comparison of these results with the predictions of ab initio calculations on (H
2
O)

n

clusters, these new transitions have been assigned to double donor O—H stretches associated with the formation of a more compact, noncyclic structure beginning with (H
2
O)
6
. This is the same size cluster for which ab initio calculations predict that a changeover to noncyclic (H
2
O)

n

structures will occur.
The Abundance of Heavy Elements in Interstellar Gas
Authors: Cardelli Jason A.
Published: October 2006

The Goddard high-resolution spectrograph aboard the Hubble Space Telescope has been used to produce interstellar abundance measures of gallium, germanium, arsenic, krypton, tin, thallium, and lead, the heaviest elements detected in interstellar gas. These heavy elements arise from stellar nuclear processes (slow- and rapid-process neutron capture) that are different from those that produce zinc and the lighter elements previously observed. These data allow investigators to study how the heavy elements chemically interact with interstellar dust and to compare interstellar heavy element abundances in the current galactic epoch to those present at the time of the formation of the solar system. For example, the data indicate that the abundance of atoms in interstellar dust cannot be explained by simple condensation models alone and must be heavily influenced by chemistry in the interstellar medium. Also, the data for some elements suggest that their true galactic cosmic abundances may be different from the "fossil" abundances incorporated into the solar system 4.6 billion years ago.
Prehistoric Cultural Ecology in Southern Jordan
Authors: Henry Donald O.
Published: October 2006

Research in the mountains of southern Jordan resulted in the discovery of 109 archaeological sites that are from the Lower Paleolithic to the Chalcolithic period [150 to 6 thousand years ago (ka)]. Beginning with the Middle Paleolithic (70 ka) two site types (long-term and ephemeral camps) are recognized. Long-term sites have larger areas, thicker deposits, higher artifact densities, and more abundant archaeological features than ephemeral sites. Their natural settings (elevation and exposure) and associated seasonal evidence (phytolith and cementum increment data) indicate that long-term sites were occupied during the winter, wet season and ephemeral sites during the warm, dry season. These differences in site use and seasonality likely reflect an adaptive strategy of transhumance that persisted to modern Bedouin times. At the end of the Pleistocene, the onset of warmer, drier conditions induced a shift of the long-term winter camps from relatively low (800 to 1000 meters above sea level) to high (1000 to 1250 meters above sea level) elevations and largely reversed the earlier transhumant pattern.
Dispersion Polymerizations in Supercritical Carbon Dioxide
Authors: DeSimone J. M. , Maury E. E. , Menceloglu Y. Z. , McClain J. B. , Romack T. J. , Combes J. R.
Published: October 2006

Conventional heterogeneous dispersion polymerizations of unsaturated monomers are performed in either aqueous or organic dispersing media with the addition of interfacially active agents to stabilize the colloidal dispersion that forms. Successful stabilization of the polymer colloid during polymerization results in the formation of high molar mass polymers with high rates of polymerization. An environmentally responsible alternative to aqueous and organic dispersing media for heterogeneous dispersion polymerizations is described in which supercritical carbon dioxide (CO
2
) is used in conjunction with molecularly engineered free radical initiators and amphipathic molecules that are specifically designed to be interfacially active in CO
2
. Conventional lipophilic monomers, exemplified by methyl methacrylate, can be quantitatively (>90 percent) polymerized heterogeneously to very high degrees of polymerization (>3000) in supercritical CO
2
in the presence of an added stabilizer to form kinetically stable dispersions that result in micrometer-sized particles with a narrow size distribution.
Synthesis and Properties of a Cuprate Superconductor Containing Double Mercury-Oxygen Layers
Authors: Radaelli P. G. , Perroux M. , Marezio M. , de Brion S. , Tholence J. L. , Huang Q. , Santoro A.
Published: October 2006

A cuprate superconductor containing double mercury layers was synthesized with a high-pressure, high-temperature technique. The compound, with chemical formula Hg
2
Ba
2
-Y

1-
x

Ca

x

Cu
2
O
8-δ
, contains a double HgO layer with structure similar to that of rock salt. The prototype compound Hg
2
Ba
2
YCu
2
O
8-δ
is an insulator. Superconductivity is induced in the system by partially replacing yttrium with calcium.
Fibrous Mini-Collagens in
Hydra
Nematocysts
Authors: Holstein T. W. , Benoit M. , Herder G. v. , David C. N. , Wanner G. , Gaub H. E.
Published: October 2006

Nematocysts (cnidocysts) are exocytotic organelles found in all cnidarians. Here, atomic force microscopy and field emission scanning electron microscopy reveal the structure of the nematocyst capsule wall. The outer wall consists of globular proteins of unknown function. The inner wall consists of bundles of collagen-like fibrils having a spacing of 50 to 100 nanometers and cross-striations at intervals of 32 nanometers. The fibrils consist of polymers of "mini-collagens," which are abundant in the nematocysts of
Hydra
. The distinct pattern of mini-collagen fibers in the inner wall can provide the tensile strength necessary to withstand the high osmotic pressure (15 megapascals) in the capsules.
Spatial Organization and Time Dependence of Jupiter's Tropospheric Temperatures, 1980-1993
Authors: Orton Glenn S. , Friedson A. James , Yanamandra-Fisher Padmavati A. , Caldwell John , Hammel Heidi B. , Baines Kevin H. , Bergstralh Jay T. , Martin Terry Z. , West Robert A. , Veeder Glenn J. , Lynch David K. , Russell Ray , Malcom Michael E. , Golisch William F. , Griep David M. , Kaminski Charles D. , Tokunaga Alan T. , Herbst Thomas , Shure Mark
Published: October 2006

The spatial organization and time dependence of Jupiter's temperatures near 250-millibar pressure were measured through a jovian year by imaging thermal emission at 18 micrometers. The temperature field is influenced by seasonal radiative forcing, and its banded organization is closely correlated with the visible cloud field. Evidence was found for a quasi-periodic oscillation of temperatures in the Equatorial Zone, a correlation between tropospheric and stratospheric waves in the North Equatorial Belt, and slowly moving thermal features in the North and South Equatorial Belts. There appears to be no common relation between temporal changes of temperature and changes in the visual albedo of the various axisymmetric bands.
Fast Algorithms for Classical Physics
Authors: Greengard Leslie
Published: October 2006

Some of the recently developed fast summation methods that have arisen in scientific computing are described. These methods require an amount of work proportional to
N
or
N
log
N
to evaluate all pairwise interactions in an ensemble of
N
particles. Traditional methods, by contrast, require an amount of work proportional to

N
2

. As a result, large-scale simulations can be carried out using only modest computer resources. In combination with supercomputers, it is possible to address questions that were previously out of reach. Problems from diffusion, gravitation, and wave propagation are considered.
Discovery of Microwave Emission from Four Nearby Solar-Type G Stars
Authors: Güdel Manuel , Schmitt Jürgen H. M. M. , Benz Arnold O.
Published: October 2006

Radio waves from the sun were detected 50 years ago, but the microwave detection of other single solar-type stars has remained a challenge. Here, the discovery of four solar-type radio stars is reported. These "solar twin" G stars are radio sources up to 3000 times stronger than the quiet sun. The microwaves most likely originate from a large number of relativistic electrons, possibly produced along with coronal heating, a process that is not understood. Two of the stars are younger than the sun and rotate more rapidly; the dynamo process in the stellar interior is therefore presumably more vigorous, resulting in enhanced coronal activity. One of the detections, however, is an old, metal-deficient G dwarf.
Large Clusters of Metal Ions: The Transition from Molecular to Bulk Magnets
Authors: Gatteschi Dante , Caneschi Andrea , Pardi Luca , Sessoli Roberta
Published: October 2006

Clusters of metal ions are a class of compounds actively investigated for their magnetic properties, which should gradually change from those of simple paramagnets to those of bulk magnets. However, their interest lies in a number of different disciplines: chemistry, which seeks new synthetic strategies to make larger and larger clusters in a controlled manner; physics, which can test the validity of quantum mechanical approaches at the nanometer scale; and biology, which can use them as models of biomineralization of magnetic particles.
Saturation of Cubic Optical Nonlinearity in Long-Chain Polyene Oligomers
Authors: Samuel Ifor D. W. , Ledoux Isabelle , Dhenaut Christophe , Zyss Joseph , Fox Harold H. , Schrock Richard R. , Silbey Robert J.
Published: October 2006

The scaling of the cubic nonlinearity γ with chain length in polyenic molecules has received considerable theoretical attention. Earlier experimental investigations have been restricted to oligomers with fewer than 20 double bonds because of problems associated with the synthesis and solubility of conjugated molecules. These synthetic difficulties have been overcome in the present study by the use of modern living polymerization techniques. Solution measurements of γ as a function of chain length in long-chain (up to 240 double bonds) model polyene oligomers are reported. A saturation of the increase of γ with chain length is observed, and the onset of this saturation occurs for chain lengths considerably longer than predicted from theory.
Virulence and Local Adaptation of a Horizontally Transmitted Parasite
Authors: Ebert Dieter
Published: October 2006

Parasites are thought to maximize the number of successfully transmitted offspring by trading off propagule production against host survival. In a horizontally transmitted microparasitic disease in
Daphnia
, a planktonic crustacean, increasing geographic distance between host and parasite origin was found to be correlated with a decrease in spore production and virulence. This finding indicates local adaptation of the parasite, but contradicts the hypothesis that long-standing coevolved parasites are less virulent than novel parasites. Virulence can be explained as the consequence of balancing the positive genetic correlation between host mortality and strain-specific spore production.
Nanocatalysis by the Tip of a Scanning Tunneling Microscope Operating Inside a Reactor Cell
Authors: McIntyre B. J. , Salmeron M. , Somorjai G. A.
Published: October 2006

The platinum-rhodium tip of a scanning tunneling microscope that operates inside of an atmospheric-pressure chemical reactor cell has been used to locally rehydrogenate carbonaceous fragments deposited on the (111) surface of platinum. The carbon fragments were produced by partial dehydrogenation of propylene. The reactant gas environment inside the cell consisted of pure H
2
or a 1:9 mixture of CH
3
CHCH
2
and H
2
at 300 kelvin. The platinum-rhodium tip acted as a catalyst after activation by short voltage pulses. In this active state, the clusters in the area scanned by the tip were reacted away with very high spatial resolution.
Milankovitch Forcing of the Last Interglacial Sea Level
Authors: Crowley Thomas J. , Kim Kwang-Yul
Published: October 2006

During the last interglacial, sea level was as high as present, 4000 to 6000 years before peak Northern Hemisphere insolation receipt 126,000 years ago. The sea-level results are shown to be consistent with climate models, which simulate a 3° to 4°C July temperature increase from 140,000 to 130,000 years ago in high latitudes, with all Northern Hemisphere land areas being warmer than present by 130,000 years ago. The early warming occurs because obliquity peaked earlier than precession and because precession values were greater than present before peak precessional forcing occurred. These results indicate that a fuller understanding of the Milankovitch-climate connection requires consideration of fields other than just insolation forcing at 65°N.
Origin and Metamorphic Redistribution of Silicon, Chromium, and Phosphorus in the Metal of Chondrites
Authors: Zanda Brigitte , Bourot-Denise Michéle , Perron Claude , Hewins Roger H.
Published: October 2006

Chromium, silicon, and phosphorus concentrations of 0.1 to 1 percent by weight are common in metal grains in the least metamorphosed ordinary and carbonaceous chondrites. These concentrations are fairly uniform within single chondrules (but different from chondrule to chondrule) and are inversely correlated with the fayalite concentrations of the chondrule olivines. This relation shows that these chromium, silicon, and phosphorus concentrations could not have been established by condensation or equilibration in the solar nebula but are the result of metal-silicate equilibration within chondrules. Two generations of inclusions made by the exsolution of those elements have been identified: One formed during chondrule cooling and the other formed during metamorphism. The distribution and composition of the latter in type 3 to type 5 chondrites are consistent with increasing metamorphism relative to type 2 and type 3.0 material.
Interannual Variability of Temperature at a Depth of 125 Meters in the North Atlantic Ocean
Authors: Levitus Sydney , Antonov John I. , Boyer Timothy P.
Published: October 2006

Analyses of historical ocean temperature data at a depth of 125 meters in the North Atlantic Ocean indicate that from 1950 to 1990 the subtropical and subarctic gyres exhibited linear trends that were opposite in phase. In addition, multivariate analyses of yearly mean temperature anomaly fields between 20°N and 70°N in the North Atlantic show a characteristic space-time temperature oscillation from 1947 to 1990. A quasidecadal oscillation, first identified at Ocean Weather Station C, is part of a basin-wide feature. Gyre and basin-scale variations such as these provide the observational basis for climate diagnostic and modeling studies.
Spring Phytoplankton Production in the Western Ross Sea
Authors: Arrigo Kevin R. , McClain Charles R.
Published: October 2006

Coastal zone color scanner (CZCS) imagery of the western Ross Sea revealed the presence of an intense phytoplankton bloom covering >106,000 square kilometers in early December 1978. This bloom developed inside the Ross Sea polynya, within 2 weeks of initial polynya formation in late November. Primary productivity calculated from December imagery (3.9 grams of carbon per square meter per day) was up to four times the values measured during in situ studies in mid-January to February 1979. Inclusion of this early season production yields a spring-to-summer estimate of 141 to 171 grams of carbon per square meter, three to four times the values previously reported for the western Ross Sea.
Coupled Land-Ocean-Atmosphere Processes and South Asian Monsoon Variability
Authors: Meehl Gerald A.
Published: October 2006

Results from a global coupled ocean-atmosphere climate model and a model with specified tropical convective heating anomalies show that the South Asian monsoon was an active part of the tropical biennial oscillation (TBO). Convective heating anomalies over Africa and the western Pacific Ocean associated with the TBO altered the simulated pattern of atmospheric circulation for the Northern Hemisphere winter mid-latitude over Asia. This alteration in the mid-latitude circulation maintained temperature anomalies over South Asia through winter and helped set up the land-sea temperature contrast for subsequent monsoon development. South Asian snow cover contributed to monsoon strength but was symptomatic of the larger scale alteration in the mid-latitude atmospheric circulation pattern.
Temporally Unstable Recurrence of Earthquakes Due to Breaks in Fractal Scaling
Authors: McCloskey John , Bean C. J.
Published: October 2006

Observed sequences of large earthquakes are not consistent in either recurrence time or energy release; long-term prediction has been impossible even in areas, such as Parkfield, with well-defined recurrence intervals. The seismic gap hypothesis, which predicts characteristic earthquakes in areas of the circum-Pacific belt that have not produced recent great earthquakes, has also failed to predict the observed clustering of high-energy events. Models in which fractal scaling is broken at high magnitude predict that characteristic events and recurrence behavior will be unstable in time. The central predictions of these models are supported by recent observations at Landers and Big Bear in California.
Nature of Stress on the Atomic Level in Dense Polymer Systems
Authors: Gao Jianping , Weiner Jerome H.
Published: October 2006

Stress in dense polymer systems is classically viewed as being molecular in character and is based on the entropic spring concept. A description on the atomic level has been developed on the basis of extensive computer simulations. An important new concept is the intrinsic monomer stress (IMS), the individual monomer contribution to the macroscopic stress referred to a local moving coordinate system in which the backbone bonds attached to that monomer are fixed. The IMS is time-independent and, for a given polymer system at fixed density, has the same value in the equilibrium melt, with the melt undergoing stress relaxation, and in the deformed cross-linked system.
A Theropod Dinosaur Embryo and the Affinities of the Flaming Cliffs Dinosaur Eggs
Authors: Norell Mark A. , Clark James M. , Demberelyin Dashzeveg , Rhinchen Barsbold , Chiappe Luis M. , Davidson Amy R. , McKenna Malcolm C. , Altangerel Perle , Novacek Michael J.
Published: October 2006

An embryonic skeleton of a nonavian theropod dinosaur was found preserved in an egg from Upper Cretaceous rocks in the Gobi Desert of Mongolia. Cranial features identify the embryo as a member of Oviraptoridae. Two embryo-sized skulls of dromaeosaurids, similar to that of
Velociraptor
, were also recovered in the nest. The eggshell microstructure is similar to that of ratite birds and is of a type common in the Djadokhta Formation at the Flaming Cliffs (Bayn Dzak). Discovery of a nest of such eggs at the Flaming Cliffs in 1923, beneath the
Oviraptor philoceratops
holotype, suggests that this dinosaur may have been a brooding adult.
Self-Assembly of
n
-Alkyl Thiols as Disulfides on Au(111)
Authors: Fenter P. , Eberhardt A. , Eisenberger P.
Published: October 2006

A grazing incidence x-ray diffraction study of CH
3
(CH
2
)
9
SH self-assembled on the (111) surface of gold revealed a disulfide head group structure, which provides a context in which to understand the structure and self-assembly process of this widely studied system. The structure consists of a nearly hexagonal two-dimensional arrangement of the hydrocarbon chains with a dimerization of the sulfur head groups (accommodated through a gauche bond), resulting in a S-S spacing of 2.2 angstroms. These results demonstrate the importance of internal molecular degrees of freedom in the templating of "soft" organic materials on inorganic substrates.
Atomic Control of the SrTiO
3
Crystal Surface
Authors: Kawasaki Masashi , Takahashi Kazuhiro , Maeda Tatsuro , Tsuchiya Ryuta , Shinohara Makoto , Ishiyama Osamu , Yonezawa Takuzo , Yoshimoto Mamoru , Koinuma Hideomi
Published: October 2006

The atomically smooth SrTiO
3
(100) with steps one unit cell in height was obtained by treating the crystal surface with a pH-controlled NH
4
F-HF solution. The homoepitaxy of SrTiO
3
film on the crystal surface proceeds in a perfect layer-by-layer mode as verified by reflection high-energy electron diffraction and atomic force microscopy. Ion scattering spectroscopy revealed that the TiO
2
atomic plane terminated the as-treated clean surface and that the terminating atomic layer could be tuned to the SrO atomic plane by homoepitaxial growth. This technology provides a well-defined substrate surface for atomically regulated epitaxial growth of such perovskite oxide films as YBa
2
Cu
3
O
7-δ
.