bluuebunny/crossref_metadata_2025 huggingface dataset:
A 1200-year proxy record of hurricanes and fires from the Gulf of Mexico coast: Testing the hypothesis of hurricane–fire interactions
Authors: Liu Kam-biu , Lu Houyuan , Shen Caiming
Published: December 2007

We present here the first high-resolution pollen record of vegetation response to interactions of hurricane and fire disturbances over the past 1200 yr from a small lake in Alabama on the Gulf of Mexico coast. The paleo tempestological record inferred from the over wash sand layers suggests that the Alabama coast was directly struck by Saffir–Simpson category 4 or 5 hurricanes twice during the last 1200 yr, around 1170 and 860 cal yr BP, suggesting an annual landfall probability of 0.17% for these intense hurricanes. The charcoal data suggest that intense fires occurred after each of these hurricanes. The pollen data suggest that populations of halophytic plants (Chenopodiaceae) and heliophytic shrubs (Myrica) expanded after the hurricane strikes, probably due to saltwater intrusion into the marshes and soil salinization caused by over wash processes. Populations of pines (Pinussp.) decreased significantly after each intense hurricane and the ensuing intense fire, suggesting that repeated hurricane–fire interactions resulted in high tree mortality and probably impeded recruitment and recovery. Our data support the hypothesis that the likelihood and intensity of fire increased significantly after a major hurricane, producing responses by vegetation that are more complex and unpredictable than if the disturbance agents were acting singly and independently.
Tracer interrelationships in the stratosphere
Authors: Plumb R. Alan
Published: December 2007

Relationships between long‐lived stratospheric tracers, manifested in similar spatial structures on scales ranging from a few to several thousand kilometers, are displayed most strikingly if the mixing ratio of one is plotted against another, when the data collapse onto remarkably compact curves. Distinct curves form in the polar vortex, the midlatitude “surf zones”, and the tropics. Theory predicts such relationships for sufficiently rapid mixing along isentropic surfaces. Model results are used to illustrate the formation and seasonal evolution of distinct tracer relationships in the different regions. Using such relationships to associate departures from canonical forms with anomalous chemical or microphysical behavior must be done with care and with full awareness of the meteorological context of the data. Although the theory has been developed in the context of stratospheric tracers, the key requirement is that transport is predominantly two‐dimensional. While the theory is thus inappropriate in the troposphere, it should be applicable to transport in the ocean interior.
Uncertainties of modeling gross primary productivity over Europe: A systematic study on the effects of using different drivers and terrestrial biosphere models
Authors: Jung Martin , Vetter Mona , Herold Martin , Churkina Galina , Reichstein Markus , Zaehle Soenke , Ciais Philippe , Viovy Nicolas , Bondeau Alberte , Chen Youmin , Trusilova Kristina , Feser Frauke , Heimann Martin
Published: December 2007

Continental to global‐scale modeling of the carbon cycle using process‐based models is subject to large uncertainties. These uncertainties originate from the model structure and uncertainty in model forcing fields; however, little is known about their relative importance. A thorough understanding and quantification of uncertainties is necessary to correctly interpret carbon cycle simulations and guide further model developments. This study elucidates the effects of different state‐of‐the‐art land cover and meteorological data set options and biosphere models on simulations of gross primary productivity (GPP) over Europe. The analysis is based on (1) three different process‐oriented terrestrial biosphere models (Biome‐BGC, LPJ, and Orchidee) driven with the same input data and one model (Biome‐BGC) driven with (2) two different meteorological data sets (ECMWF and REMO), (3) three different land cover data sets (GLC2000, MODIS, and SYNMAP), and (4) three different spatial resolutions of the land cover (0.25° fractional, 0.25° dominant, and 0.5° dominant). We systematically investigate effects on the magnitude, spatial pattern, and interannual variation of GPP. While changing the land cover map or the spatial resolution has only little effect on the model outcomes, changing the meteorological drivers and especially the model results in substantial differences. Uncertainties of the meteorological forcings affect particularly strongly interannual variations of simulated GPP. By decomposing modeled GPP into their biophysical and ecophysiological components (absorbed photosynthetic active radiation (APAR) and radiation use efficiency (RUE), respectively) we show that differences of interannual GPP variations among models result primarily from differences of simulating RUE. Major discrepancies appear to be related to the feedback through the carbon‐nitrogen interactions in one model (Biome‐BGC) and water stress effects, besides the modeling of croplands. We suggest clarifying the role of nitrogen dynamics in future studies and revisiting currently applied concepts of carbon‐water cycle interactions regarding the representation of canopy conductance and soil processes.
A phenology‐based reconstruction of interannual changes in past spring seasons
Authors: Rutishauser T. , Luterbacher J. , Jeanneret F. , Pfister C. , Wanner H.
Published: December 2007

Plant phenological observations are accurately dated information of seasonal vegetation variability in midlatitude climates. In order to extend phenological records into the past and assess climate impacts on vegetation on long timescales, there is a need to make use of historical observations of plant phenology. Here we present a continuous, annually resolved reconstruction of a statistical ‘Spring plant’ defined as the weighted mean for the flowering of cherry and apple tree and budburst beech from plant phenological observations across a range of sites in Switzerland from 1702 to 2005. The reconstruction indicates a statistical reconstruction uncertainty (±3.4 days) at interannual timescale. The earliest and the latest year were observed in 1961 (14 April) and 1879 (13 May), respectively. In the context of the last 300 years, the recent three decades do not show a preponderance of very early years as expected from increased spring temperatures. Most of the years in the period after 1990, however, are earlier than the reconstruction mean (27 April). The 1940s, 1910s, 1890s and the early 18th century are periods with similarly early starts of spring season in comparison with the recent decades. Moving linear trend analysis shows unprecedented agreement towards earlier spring onsets in observed and temperature‐based, reconstructed plant phenological records in the late 20th/early 21st century. Our reconstructed ‘Spring plant’ provides long‐term evidence of vegetation variability for comparisons with temperature measurement and other spring onset indicators such as snow melt. The multicentennial long record offers a high potential for applications in long‐term climate impact studies and vegetation model validations.
Temperature sensitivity of microbial respiration, nitrogen mineralization, and potential soil enzyme activities in organic alpine soils
Authors: Koch Oliver , Tscherko Dagmar , Kandeler Ellen
Published: December 2007

Investigations focusing on the temperature sensitivity of microbial activity and nutrient turnover in soils improve our understanding of potential effects of global warming. This study investigates the temperature sensitivity of C mineralization, N mineralization, and potential enzyme activities involved in the C and N cycle (tyrosine amino‐peptidase, leucine amino‐peptidase, ß‐glucosidase, ß‐xylosidase,N‐acetyl‐ß‐glucosaminidase). Four different study sites in the Austrian alpine zone were selected, and soils were sampled in three seasons (summer, autumn, and winter). A simple first‐order exponential equation was used to calculate constantQ10values for the C and N mineralization over the investigated temperature range (0–30°C). TheQ10values of the C mineralization (average 2.0) for all study sites were significantly higher than for the N mineralization (average 1.7). TheQ10values of both activities were significantly negatively related to a soil organic matter quality index calculated by the ratios of respiration to the organic soil carbon and mineralized N to the total soil nitrogen. The chemical soil properties or microbial biomass did not affect theQ10values of C and N mineralization. Moreover, theQ10values showed no distinct pattern according to sampling date, indicating that the substrate quality and other factors are more important. Using a flexible model function, the analysis of relative temperature sensitivity (RTS) showed that the temperature sensitivity of activities increased with decreasing temperature. The C and N mineralization and potential amino‐peptidase activities (tyrosine and leucine) showed an almost constant temperature dependence over 0–30°C. In contrast, ß‐glucosidase, ß‐xylosidase, andN‐acetyl‐ß‐glucosaminidase showed a distinctive increase in temperature sensitivity with decreasing temperature. Low temperature at the winter sampling date caused a greater increase in theRTSof all microbial activities than for the autumn and summer sampling dates. Our results indicate (1) a disproportion of theRTSfor potential enzyme activities of the C and N cycle and (2) a disproportion of theRTSfor easily degradable C compounds (ß‐glucose, ß‐xylose) compared with the C mineralization of soil organic matter. Thus temperature may play an important role in regulating the decay of different soil organic matter fractions due to differences in the relative temperature sensitivities of enzyme activities.
Toward a Euro Mediterranean tsunami warning system: The case of the February 12, 2007, Ml = 6.1 earthquake
Authors: Olivieri Marco , Scognamiglio Laura
Published: December 2007

UNESCO has made a commitment to the scientific community for the creation of the North East Atlantic and Mediterranean Tsunami Warning System (NEAMTWS). We wonder: “Is the European Seismological community ready to run an Euro Mediterranean tsunami warning system?” In this study we use the February 12, 2007 Ml = 6.1 earthquake, which occurred close to the epicenter of the 1755 Great Lisbon event, as a case study to verify and discuss our actual capability of alerting for a hypothetical tsunami. Starting from the available real‐time data and tools, we emulate an automatic real‐time processing to perform the source analyses needed for discriminating a tsunamigenic earthquake, and subsequently we evaluate the time shift between the release of results and the potential tsunami waterfront reaching the coasts.
Horizontal visibility trends in China 1981–2005
Authors: Che Huizheng , Zhang Xiaoye , Li Yang , Zhou Zijiang , Qu John J.
Published: December 2007

Trends in Chinese horizontal visibility, the frequency of visibility >19 km, and haziness for the period between 1981 and 2005 were evaluated based on data for daily horizontal visibility. Annual means were calculated for each station and for China as a whole. Linear regression analysis was used to characterize long‐term annual trends in these variables. Over the past 25 years, there has been a significant decrease in horizontal visibility (−2.1 km per decade from 1990 to 2005) and the frequency of visibility >19 km (−3.5% per decade) but a significant increase in the 75th percentile annual extinction coefficients (25% per 25 year). According to rapid increase of total energy consumption, the consistent spatial and temporal variations of visibility and haze support the speculation that increased aerosol loadings were responsible for the observed decreases in horizontal visibility over much of East China.
A magnetic anomaly associated with an albedo feature near Airy crater in the lunar nearside highlands
Authors: Blewett D. T. , Hawke B. R. , Richmond N. C. , Hughes C. G.
Published: December 2007

We describe a strong crustal magnetic anomaly, recently identified in Lunar Prospector magnetometer data, that is associated with a previously unreported albedo feature near the crater Airy in the lunar nearside highlands. Other workers have demonstrated a correlation between magnetic anomalies and the enigmatic bright markings known as lunar swirls. We have used Earth‐based telescopic spectra and Clementine multispectral images to investigate the compositional and optical maturity characteristics of the Airy swirl. The Airy albedo feature does not exhibit the complex sinuous structure of well‐known swirls such as the Reiner Gamma Formation, but does possess a bright loop and central dark lane. Another strong magnetic anomaly, in the Apollo 16/Descartes region, corresponds to a simple diffuse bright albedo spot. On this basis we suggest that a continuum of swirl morphologies exists on the Moon, with the Airy feature representing an intermediate or incipient swirl form.
Impact of cloud microphysics on hurricane track forecasts
Authors: Fovell Robert G. , Su Hui
Published: December 2007

Simulations of Hurricane Rita (2005) at operational resolutions (30 and 12 km) reveal significant track sensitivity to cloud microphysical details, rivaling variation seen in the National Hurricane Center's multi‐model consensus forecast. Microphysics appears to directly or indirectly modulate vortex characteristics including size and winds at large radius and possibly other factors involved in hurricane motion. Idealized simulations made at higher (3 km) resolution help isolate the microphysical influence.
Spin‐up of South Pacific subtropical gyre freshens and cools the upper layer of the eastern South Pacific Ocean
Authors: Schneider Wolfgang , Fukasawa Masao , Garcés‐Vargas José , Bravo Luis , Uchida Hiroshi , Kawano Takeshi , Fuenzalida Rosalino
Published: December 2007

Temperature and salinity from the upper 200 m of the water column in the South Pacific Ocean were compared basin‐wide along 32°30′S between 1992 and 2003, based on two vertically and horizontally high‐resolution hydrographic repeat‐sections involving 227 station pairs. Additionally, the seasonal cycles of the upper water column temperature and salinity between 90–140°W and 30.5–34.5°S were established utilizing 1540 ARGO profiles from 2003 to 2007; these were related to the hydrographic sections. Furthermore, South Pacific sea surface temperature trends from 1992 to 2003 were addressed. The surface waters (0–200 m) of the eastern South Pacific Ocean, on average and seasonally adjusted, were clearly fresher by 0.1 in 2003. The seasonally adjusted, depth‐integrated temperature was 0.25°C colder in the same region. We relate the observed temperature and salinity changes to a spin‐up of the subtropical gyre circulation caused by intensified wind stress.
Interaction of the bow shock with a tangential discontinuity and solar wind density decrease: Observations of predicted fast mode waves and magnetosheath merging
Authors: Maynard N. C. , Burke W. J. , Ober D. M. , Farrugia C. J. , Kucharek H. , Lester M. , Mozer F. S. , Russell C. T. , Siebert K. D.
Published: December 2007

Shortly after 0600 UT on 7 April 2000 a tangential discontinuity (TD) in the solar wind passed the Advanced Composition Explorer satellite (ACE). It was characterized by a rotation of the interplanetary magnetic field (IMF) by ∼145° and more than a factor‐of‐2 decrease in the plasma density. About 50 min later, Polar encountered more complex manifestations of the discontinuity near noon in the magnetosheath outside the Northern Hemisphere cusp. On the basis of Polar observations, theoretical modeling, and MHD simulations we interpret the event as demonstrating that (1) a fast mode rarefaction wave was generated during the TD‐bow shock interaction, (2) the fast wave carried a significant fraction of the density change to the magnetopause while the remainder stayed with the transmitted discontinuity, and (3) magnetic merging occurred between IMF field lines within the magnetosheath on opposite sides of the discontinuity's surface as it approached the magnetopause. Before the discontinuity passed the spacecraft, Polar detected ions accelerated antiparallel to B in the fast wave and perpendicular to B in a weak slow mode structure located adjacent to and just downstream of the fast wave. The antiparallel accelerated ions in the fast wave had no measurable ion‐velocity dispersion signature, placing their source a few RE equatorward of Polar. Simulation results, a Walén test, detections of wave Poynting flux parallel to B, bidirectional electron heat flux, and ion velocity enhancements all indicate that the three ion bursts associated with the passage of the discontinuity were signatures of time‐dependent, magnetic merging events within the magnetosheath.
Criterion for interchange instability in a plasma connected to a conducting ionosphere
Authors: Xing X. , Wolf R. A.
Published: December 2007

We have combined two empirical numerical models to estimate the entropy parameter PV5/3 in the plasma sheet, where P is the plasma sheet pressure and V = ∫ is the volume of a flux tube containing one unit of magnetic flux. The Tsyganenko and Stern (1996) magnetic field model is used to calculate the flux tube volume, and the Tsyganenko and Mukai (2003) plasma sheet statistical model is used to calculate the plasma sheet pressure. Contour plots for PV5/3 and V in the equatorial plane are presented for various solar wind conditions. These empirical models suggest that, although both PV5/3 and V generally increase tailward, their gradients are generally not parallel or antiparallel to each other, whereas most theoretical discussions of interchange instability assume that the vectors are lined up. The Vasyliunas equation implies that the Birkeland current is proportional to the cross product of ∇PV5/3 and ∇V, so that region 1 and region 2 Birkeland current flow between plasma sheet and ionosphere confirms that the gradients of entropy parameter and flux tube volume are not generally parallel. We present analytical calculations to investigate the criterion for interchange instability in a quasi‐static, low‐β plasma that is connected to a conducting ionosphere and has ∇PV5/3 and ∇V at an arbitrary angle α, which implies shear flows. A boundary layer is assumed to separate two regions with different but uniform PV5/3. The main conclusion is that the system is interchange unstable if α > π/2. The results suggest that the statistical average plasma sheet configuration is interchange stable since the statistical plasma sheet models indicate that α < π/2. Our conclusion is quite different from analyses that neglect shear flow since they imply instability unless ∇PV5/3 and ∇V are exactly parallel.
A single‐column model intercomparison of a heavily drizzling stratocumulus‐topped boundary layer
Authors: Wyant Matthew C. , Bretherton Christopher S. , Chlond Andreas , Griffin Brian M. , Kitagawa Hiroto , Lappen Cara‐Lyn , Larson Vincent E. , Lock Adrian , Park Sungsu , de Roode Stephan R. , Uchida Junya , Zhao Ming , Ackerman Andrew S.
Published: December 2007

This study presents an intercomparison of single‐column model simulations of a nocturnal heavily drizzling marine stratocumulus‐topped boundary layer. Initial conditions and forcings are based on nocturnal flight observations off the coast of California during the DYCOMS‐II field experiment. Differences in turbulent and microphysical parameterizations between models were isolated by slightly idealizing and standardizing the specification of surface and radiative fluxes. For most participating models, the case was run at both typical operational vertical resolution of about 100 m and also at high vertical resolution of about 10 m. As in prior stratocumulus intercomparisons, the simulations quickly develop considerable scatter in liquid water path (LWP) between models. However, the simulated dependence of cloud base drizzle fluxes on LWP in most models is broadly consistent with recent observations. Sensitivity tests with drizzle turned off show that drizzle substantially decreases LWP for many models. The sensitivity of entrainment rate to drizzle is more muted. Simulated LWP and entrainment are also sensitive to the inclusion of cloud droplet sedimentation. Many models underestimate the fraction of drizzle that evaporates below cloud base, which may distort the simulated feedbacks of drizzle on turbulence, entrainment, and LWP.
Pyrogenic carbon emission from a large wildfire in Oregon, United States
Authors: Campbell John , Donato Dan , Azuma David , Law Beverly
Published: December 2007

We used a ground‐based approach to compute the pyrogenic carbon emissions from the Biscuit Fire, an exceptionally large wildfire, which in 2002 burned over 200,000 ha of mixed conifer forest in southwestern Oregon. A combination of federal inventory data and supplementary ground measurements afforded the estimation of preburn densities for 25 separate carbon pools at 180 independent locations in the burn area. Average combustion factors for each of these pools were then compiled from the postburn assessment of thousands of individual trees, shrubs, and parcels of surface and ground fuel. Combustion factors were highest for litter, duff, and foliage, lowest for live woody pools. Combustion factors also increased with burn severity as independently assessed from remote imagery, endorsing the use of such imagery in scaling emissions to fire area. We estimate the total pyrogenic carbon emissions from the Biscuit Fire to be between 3.5 and 4.4 Tg C (17 and 22 Mg C ha−1) depending on uncertainty in our ability to estimate preburn litter pools and mineral soil combustion with a central estimate of 3.8 Tg C (19 Mg C ha−1). We estimate that this flux is approximately 16 times the annual net ecosystem production of this landscape prior to the wildfire and may have reduced mean net biome production across the state of Oregon by nearly half in the year 2002.
Low-energy electron attachment to SF6. I. Kinetic modeling of nondissociative attachment
Authors: Troe Jürgen , Miller Thomas M. , Viggiano Albert A.
Published: December 2007

Low-energy electron-molecule collisions are analyzed by kinetic modeling within the framework of statistical unimolecular rate theory. Nondissociative electron attachment to SF6 is used to illustrate the approach. An internally consistent representation is provided for attachment cross sections and rate coefficients in relation to detachment lifetimes, and both thermal and specific rate coefficients for detachment. By inspecting experimental data, the contributions of intramolecular vibrational redistribution and vibrationally inelastic collisions can be characterized quantitatively. This allows for a prediction of attachment rate coefficients as a function of electron and gas temperature as well as gas pressure over wide ranges of conditions. The importance of carefully controlling all experimental parameters, including the carrier gas pressure, is illustrated. The kinetic modeling in Part II of this series is extended to dissociative electron attachment to SF6.
Low-energy electron attachment to SF6. II. Temperature and pressure dependences of dissociative attachment
Authors: Troe Jürgen , Miller Thomas M. , Viggiano Albert A.
Published: December 2007

Low-energy electron-molecule collisions, leading to dissociative attachment through metastable anionic states, are kinetically modeled within the framework of statistical unimolecular rate theory. The reaction e−+SF6→SF5−+F is used as an illustrative example. The modeling is applied to new measurements of branching fractions for SF5− formation in the bath gas He between 360 and 670K at 1 and 2Torr, and between 490 and 620K over the range of 0.3–9Torr. The analysis of the data follows the previous kinetic modeling of the nondissociative electron attachment, e−+SF6→SF6−, from Part I of this series. Experimental results from the present work and the literature on branching fractions and total cross sections for anion formation as functions of electron energies, bath gas temperatures and pressures, as well as observation times are analyzed. The assumption of a participation of the electronic ground state of SF6− alone suffices to model the available experimental data. A value of the dissociation energy of SF6− into SF5−+F of E0,dis=1.61(±0.05)eV is determined, which may be compared to the electron affinity of SF6, EA=1.20(±0.05)eV, such as derived in Part III of this series.
Low-energy electron attachment to SF6. III. From thermal detachment to the electron affinity of SF6
Authors: Viggiano Albert A. , Miller Thomas M. , Friedman Jeffrey F. , Troe Jürgen
Published: December 2007

The thermal attachment of electrons to SF6 is measured in a flowing-afterglow Langmuir-probe apparatus monitoring electron concentrations versus axial position in the flow tube. Temperatures between 300 and 670K and pressures of the bath gas He in the range of 0.3–9Torr are employed. Monitoring the concentrations of SF6− and SF5−, the latter of which does not detach electrons under the applied conditions, an onset of thermal detachment and dissociation of SF6 at temperatures above about 530K is observed. Analysis of the mechanism allows one to deduce thermal detachment rate coefficients. Thermal dissociation rate coefficients for the reaction SF6−→SF5−+F can only be estimated by unimolecular rate theory based on the results from Part I and II of this series. Under the applied conditions they are found to be smaller than detachment rate coefficients. Combining thermal attachment and detachment rates in a third-law analysis, employing calculated vibrational frequencies of SF6 and SF6−, leads to the electron affinity (EA) of SF6−. The new value of EA=1.20(±0.05)eV is significantly higher than previous recommendations which were based on less direct methods.
Interactions of transition metal atoms in high-spin states: Cr2, Sc–Cr, and Sc–Kr
Authors: Rajchel Łukasz , Żuchowski Piotr S. , Kłos Jacek , Szczȩśniak Małgorzata M. , Chałasiński Grzegorz
Published: December 2007

The high-spin van der Waals states are examined for the following dimers: Cr2 (Σg+13), Sc–Cr (Σ+8, Π8, Δ8), and Sc–Kr (Σ+2, Π2, Δ2). These three systems offer a wide range of van der Waals interactions: anomalously strong, intermediate, and typically weak. The single-reference [coupled cluster with single, double, and noniterative triple excitations, RCCSD(T)] method is used in the calculations for all three systems. In addition, a range of configuration-interaction based methods is applied in Cr2 and Sc–Cr. The three dimers are shown to be bound by the dispersion interaction of varying strength. In a related effort, the dispersion energy and its exchange counterpart are calculated using the newly developed open-shell variant of the symmetry-adapted perturbation theory (SAPT). The restricted open-shell time-dependent Hartree-Fock linear response function is used in the calculations of the dispersion energy in Sc–Cr and Sc–Kr calculations, while the restricted open-shell time-dependent density functional linear response function is used for Cr2. A hybrid method combining the repulsive restricted open-shell Hartree-Fock (or complete active space self-consistent field) interaction energy with the dispersion and exchange-dispersion terms is tested against the RCCSD(T) results for the three complexes. The Cr2 (Σg+13) complex has the well depth of 807.8cm−1 at the equilibrium distance of 6.18a0 and the dissociation energy of 776.8cm−1. The octet-state Sc–Cr is about four times more strongly bound with the order of well depths of Δ8>Π8>Σ+8 and a considerable anisotropy. The enhanced bonding is attributed to the unusually strong dispersion interaction. Sc–Kr (Σ+2, Π2, Δ2) is a typical van der Waals dimer with well depths in the range of 81cm−1 (Δ2), 84cm−1 (Σ+2), and 86cm−1 (Π2). The hybrid model based on SAPT leads to results which are in excellent qualitative agreement with RCCSD(T) for all three interactions.
Efficient knot group identification as a tool for studying entanglements of polymers
Authors: Mansfield Marc L.
Published: December 2007

A technique is presented for the identification of the knot group of knots, links, and other embedded graphs as a tool in numerical studies of entanglements of polymers. With this technique, the knot group is simultaneously more discriminating and easier to calculate than the knot invariants that have been used in such studies in the past. It can be applied even in cases of very complex knot projections with hundreds of crossings. Starting from an arbitrary projection of an embedded graph, we generate a sequence of representations, any one of which is a full and complete representation of the knot group. Any two knot groups are isomorphic if they have identical representations. Therefore, we compare the sequence of representations of any given knot or link against a previously determined lookup table, and if the group of the knot or link is represented in this table we eventually find a match and identify the knot group.
Development of knotting during the collapse transition of polymers
Authors: Mansfield Marc L.
Published: December 2007

A dynamic Monte Carlo simulation of the collapse transition of polymer chains is presented. The chains are represented as self-avoiding walks on the simple cubic lattice with a nearest-neighbor contact potential to model the effect of solvent quality. The knot state of the chains is determined using the knot group procedure presented in the accompanying paper. The equilibrium knot spectrum and the equilibrium rms radius of gyration as functions of the chain length and the contact potential are reported. The collapse transition was studied following quenches from good-to poor-solvent conditions. Our results confirm the prediction that the newly formed globule is not yet at equilibrium, since it has not yet achieved its equilibrium knot spectrum. For our model system, the relaxation of the knot spectrum is about an order of magnitude slower than that of the radius of gyration. The collapse transition is also studied for a model in which both ends of the chain remain in good-solvent conditions. Over the time scale of these simulations, knot formation is frustrated in this inhomogeneous model, verifying that the mechanism of knotting is the tunneling of chain ends in and out of the globule.
Formation of nonextinct ring-banded textures and multistacked lamella of tetra-aniline-block-poly(L-lactide) rod-coil diblock oligomer films induced by solvent vapor treatment
Authors: Luo Chunxia , Huang Weihuan , Wang Hanfu , Han Yanchun
Published: December 2007

The self-assembly processes of the rod-coil diblock oligomer thin film of tetra-aniline (TANI)-block-poly(L-lactide) (PLLA) with different film thicknesses induced in the coil-selective solvent of acetone vapor at room temperature were studied. The morphologies of the oligomer films were determined by the film thickness. For the thicker film (232nm), the nonextinct concentric ring-banded textures could form. While for the thinner and appropriate film (about 6nm), multistacked diamond-shaped appearances with the periodic thickness being about 8.5nm(6-nm-thick extended PLLA chain and 2.5-nm-thick p-π conjugating TANI bimolecular layer) formed. The possible formation models of those two regular morphologies were presented in detail.
Mechanical properties of carbon nanocones
Authors: Wei J. X. , Liew K. M. , He X. Q.
Published: December 2007

In this paper, the elastic and plastic properties of single-walled carbon nanocones (CNCs) under tension are investigated employing molecular dynamics simulation. The force-deformation responses of CNCs are obtained and compared with those of carbon nanotubes (CNTs). CNCs with a larger apex angle present a larger failure strength but a smaller maximum strain under tension. Following this law, CNTs exhibit the smallest failure strength but greatest maximum strain due to their zero conical angles. The mechanical properties such as Young’s modulus, elastic strain limit, and ultimate force are determined and discussed.
Self-catalytic solution for single-crystal nanowire and nanotube growth
Authors: Noor Mohammad S.
Published: December 2007

Vast majority of nanowires is grown by the chemical vapor deposition (CVD), molecular beam epitaxy (MBE), metal-organic CVD (MOCVD), or the laser ablation method via the vapor-liquid-solid (VLS) route. Others are grown via the oxide-assisted route. In this investigation a self-catalytic synthesis route based on VLS formalism and suitable for the CVD, MBE, MOCVD, or the laser ablation method has been described. Various issues pertaining to growth kinetics, nanowire alignment, diameter distribution, and nanotube formation have been addressed. The strength of the self-catalytic route has been highlighted. As this route does not make use of foreign element catalytic agents to mediate the synthesis, it suffers from difficulties. Attempts have been made to elucidate means to overcome these difficulties. Attempts have also been made to explain the means to separate the nanowires thus produced from the substrate/scaffold, and to control their physicochemical characteristics.
Tuning the crystal structure and magnetic properties of Fe doped In2O3 nanocrystals
Authors: Chu Dewei , Zeng Yu-Ping , Jiang Dongliang , Ren Zhongming
Published: December 2007

Fe doped In2O3 nanocrystals were synthesized by a coprecipitation method under external magnetic fields. X-ray diffraction data and high-resolution transmission electron microscopy analyses indicated the formation of single phase without any parasitic phases. The crystal structure of the nanocrystals is tuned by changing Fe concentrations and intensities of magnetic fields. Room temperature ferromagnetism in Fe doped In2O3 nanocrystals can be activated by suitable magnetic fields.
Low volume fraction rimming flow in a rotating horizontal cylinder
Authors: Chen Po-Ju , Tsai Yu-Te , Liu Ta-Jo , Wu Ping-Yao
Published: December 2007

An experimental study was carried out to examine how uniform rimming flow is established for a very small volume fraction of aqueous Newtonian solutions in a partially filled rotating horizontal cylinder. There exists a certain critical volume fraction (Vc) for each solution, where the rotational speed required to achieve uniform rimming flow takes a minimum value. Counterintuitively, it takes greater rotation speeds for both larger and smaller volume fractions than this. Axial instabilities are observed for liquid volume fractions above or below this critical value. For V>Vc the defects are mainly of shark-teeth and turbulent types, while for VVc, but has very little effect for V<Vc. The lowest volume fraction for rimming flow found in the present study is 0.25%. The dimensionless minimum rotational speed Ω to achieve rimming flow is presented as a function of the dimensionless liquid volume fraction ϕ. The competing effects of fluid inertia and viscous force on rimming flow are demonstrated from a dimensionless plot of Ω versus ϕ.
Cavity ring-down spectroscopy of jet-cooled silane isotopologues in the Si–H stretch overtone region
Authors: Bisson R. , Dang T. T. , Sacchi M. , Beck R. D.
Published: December 2007

Absorption spectra of silane in the region of the first overtone of the Si–H stretch vibration have been recorded in a seeded supersonic jet expansion by cavity ring-down spectroscopy as well as in a static gas cell at room temperature by photoacoustic spectroscopy. Spectral simplification due to strong rotational cooling in the jet expansion enables us to clearly resolve and assign the rovibrational transitions of the (2000) and (1100) bands of the three isotopologues, Si28H4, Si29H4, and Si30H4, in their natural isotopic abundance. Interconversion between different nuclear spin species of SiH4 is found to be absent during the jet expansion. Isotope shifts for Si29H4 and Si30H4 relative to Si28H4 are measured and found to be suitable for selective vibrational excitation of any of three silane isotopologues by pulsed laser excitation in a jet expansion.
Formation of supercooled liquid solutions from nanoscale amorphous solid films of methanol and ethanol
Authors: Smith R. Scott , Ayotte Patrick , Kay Bruce D.
Published: December 2007

Molecular beam techniques are used to create layered nanoscale composite films of amorphous methanol and ethanol at 20K. The films are then heated, and temperature programed desorption and infrared spectroscopy are used to observe the mixing, desorption, and crystallization behavior from the initially unmixed amorphous layers. We find that the initially unmixed amorphous layers completely intermix to form a deeply supercooled liquid solution after heating above Tg. Modeling of the desorption kinetics shows that the supercooled liquid films behave as ideal solutions. The desorption rates from the supercooled and crystalline phases are then used to derive the binary solid-liquid phase diagram. Deviations from ideal solution desorption behavior are observed when the metastable supercooled solution remains for longer times in regions of the phase diagram when thermodynamically favored crystallization occurs. In those cases, the finite lifetime of the metastable solutions results in the precipitation of crystalline solids. Finally, in very thick films at temperatures and compositions where a stable liquid should exist, we unexpectedly observe deviations from ideal solution behavior. Visual inspection of the sample indicates that these apparent departures from ideality arise from dewetting of the liquid film from the substrate. We conclude that compositionally tailored nanoscale amorphous films provide a useful means for preparing and examining deeply supercooled solutions in metastable regions of the phase diagram.
Superlens-cloaking of small dielectric bodies in the quasistatic regime
Authors: Bruno Oscar P. , Lintner Stéphane
Published: December 2007

It has been conjectured that, in the quasistatic regime, dielectric bodies of finite size could be perfectly cloaked by certain cylindrical arrangements of materials of positive and negative permittivities known as superlenses. We show that, although they do not cloak perfectly dielectrics objects of any size, cylindrical superlenses do cloak, to a significant extent, dielectric bodies of small size.
Determination of neutral carbon concentration in electron cyclotron resonance generated plasma discharges
Authors: Ene A. B. , Lindner P. , Stirn R. , Schumacher U.
Published: December 2007

Carbon containing plasmas play an important role not only in plasma technology but also in thermonuclear fusion research. In order to understand and control the processes taking place in the plasma, the knowledge of the carbon ground state density is of major importance. It can be determined by absorption and emission spectroscopy. Detailed measurements were performed in the past to determine the silicon ground state density by means of spectroscopy of the self-absorbed spectral lines of the silicon ground state multiplet at 251nm. The same procedure was applied for the determination of the carbon concentration, for which the carbon multiplet at 165nm was analyzed and compared to a simulated spectrum. The ground state density was determined by two independent methods.
Evaluation of a multimode fiber optic low coherence interferometer for path length resolved Doppler measurements of diffuse light
Authors: Varghese Babu , Rajan Vinayakrishnan , Van Leeuwen Ton G. , Steenbergen Wiendelt
Published: December 2007

The performance of a graded index multimode fiber optic low coherence Mach-Zehnder interferometer with phase modulation is analyzed. Investigated aspects were its ability to measure path length distributions and to perform path length resolved Doppler measurements of multiple scattered photons in a turbid suspension of particles undergoing Brownian and translational motion. The path length resolution of this instrument is compared with a system using single mode fibers for illumination and detection. The optical path lengths are determined from the zero order moment of the phase modulation peak in the power spectrum. The weighted first moment, which is equal to the average Doppler shift, shows a linear response for different mean flow velocities within the physiological range.
Neutron production from feedback controlled thermal cycling of a pyroelectric crystal
Authors: Tang V. , Meyer G. , Morse J. , Schmid G. , Spadaccini C. , Kerr P. , Rusnak B. , Sampayan S. , Naranjo B. , Putterman S.
Published: December 2007

The LLNL Crystal Driven Neutron Source is operational and has produced record ion currents of ∼10nA and neutron output of 1.9(±0.3)×105 per thermal cycle using a crystal heating rate of 0.2°C∕s from 10to110°C. A 3cm diameter by 1cm thick LiTaO3 crystal with a socket secured field emitter tip is thermally cycled with feedback control for ionization and acceleration of deuterons onto a deuterated target to produce D–D fusion neutrons. The entire crystal and temperature system is mounted on a bellows which allows movement of the crystal along the beam axis and is completely contained on a single small vacuum flange. The modular crystal assembly permitted experimental flexibility. Operationally, flashover breakdowns along the side of the crystal and poor emitter tip characteristics can limit the neutron source. The experimental neutron results extend earlier published work by increasing the ion current and pulse length significantly to achieve a factor-of-two higher neutron output per thermal cycle. These findings are reviewed along with details of the instrument.
Size dependence of the electronic structures and electron-phonon coupling in ZnO quantum dots
Authors: Ray S. C. , Low Y. , Tsai H. M. , Pao C. W. , Chiou J. W. , Yang S. C. , Chien F. Z. , Pong W. F. , Tsai M.-H. , Lin K. F. , Cheng H. M. , Hsieh W. F. , Lee J. F.
Published: December 2007

The electronic structures and optical properties of various sizes of ZnO quantum dots (QDs) were studied using x-ray absorption, photoluminescence, and Raman spectroscopy. The increase in the intensity ratio of the second-order Raman spectra of longitudinal optical mode and its fundamental mode, which is related to the strength of the electron-phonon coupling (EPC), is found to increase with the size of QD. The trend of EPC also correlates with the increase of the intensity ratio of the O 2pπ (Iπ) and 2pσ (Iσ) orbital features in the O K-edge x-ray absorption near-edge structure (XANES) as the size of QD increases. The EPC and XANES results suggest that the crystal orientations of ZnO QDs are approximately aligned with the c axis parallel with the polarization of x-ray photons.
Decomposition driven interface evolution for layers of binary mixtures. I. Model derivation and stratified base states
Authors: Thiele Uwe , Madruga Santiago , Frastia Lubor
Published: December 2007

A dynamical model is proposed to describe the coupled decomposition and profile evolution of a free surface film of a binary mixture. An example is a thin film of a polymer blend on a solid substrate undergoing simultaneous phase separation and dewetting. The model is based on model-H describing the coupled transport of the mass of one component (convective Cahn-Hilliard equation) and momentum (Navier-Stokes-Korteweg equations) supplemented by appropriate boundary conditions at the solid substrate and the free surface. General transport equations are derived using phenomenological nonequilibrium thermodynamics for a general nonisothermal setting taking into account Soret and Dufour effects and interfacial viscosity for the internal diffuse interface between the two components. Focusing on an isothermal setting the resulting model is compared to literature results and its base states corresponding to homogeneous or vertically stratified flat layers are analyzed.
Improvement in electric and dielectric properties of nanoferrite synthesized via reverse micelle technique
Authors: Thakur Sangeeta , Katyal S. C. , Singh M.
Published: December 2007

Nano nickel zinc ferrite (Ni0.58Zn0.42Fe2O4) with fascinating dielectric properties which reveal a direction for application was synthesized by reverse micelle technique. Dielectric constant and dielectric losses are controlled up to a measurement temperature of around 473K at higher frequency range of 9–19MHz. The dielectric loss of the sample investigated at room temperature is only 0.003 at 19MHz. The presently studied nanoferrite also exhibits a high value of dc resistivity, 108Ωcm. High resistivity and low dielectric constant and loss can be corelated to small grain size and better compositional stoichiometry obtained as a result of processing via reverse micelle technique at low sintering temperature (773K).
Pockels response in calcium barium niobate thin films
Authors: Helsten R. , Razzari L. , Ferrera M. , Ndione P. F. , Gaidi M. , Durand C. , Chaker M. , Morandotti R.
Published: December 2007

The electro-optical response of calcium barium niobate ferroelectric thin films is characterized using a single beam setup in reflection geometry. Clear evidence of a Pockels response together with an r33 coefficient as high as 130pm∕V is found. This large value and the high Curie temperature of the material under study (>250°C) can be considered as a promising feature for the fabrication of hybrid, integrated electro-optical modulators working at a high repetition rate.
Confocal microscope photoluminescence and electrical characteristics of single poly(3-hexylthiophene) nanowire strand
Authors: Lee Seok Ho , Park Dong Hyuk , Kim Kihyun , Joo Jinsoo , Kim Dae-Chul , Kim Hyun-Jun , Kim Jeongyong
Published: December 2007

The photoluminescence (PL) spectra and images of a single strand of poly(3-hexylthiophene) (P3HT) nanowires with different doping states were compared by means of a laser confocal microscope with a high spatial resolution. The P3HT nanowires were electrochemically synthesized by using an ionic liquid as a dopant. From the ultraviolet and visible absorption spectra, the doping and dedoping effects of the P3HT nanowires through the treatment of organic solvent were investigated. The electrical conductivity of the single strand of the lightly doped P3HT nanowires was estimated to be ∼3.5×10−3S∕cm, which was higher than that (∼5.4×10−5S∕cm) of the dedoped one. From the laser confocal microscope PL experiments, we quantitatively observed more homogeneous and three to eight times brighter light emission from the single strand of the dedoped P3HT nanowires.
Thickness dependence of the electronic properties in V2O3 thin films
Authors: Grygiel C. , Simon Ch. , Mercey B. , Prellier W. , Frésard R. , Limelette P.
Published: December 2007

High quality vanadium sesquioxide V2O3 films (170–1100Å) were grown using the pulsed laser deposition technique on (0001)-oriented sapphire substrates, and the effects of film thickness on the lattice strain and electronic properties were examined. X-ray diffraction indicates that there is an in-plane compressive lattice parameter (a), close to −3.5% with respect to the substrate and an out-of-plane tensile lattice parameter (c). The thin film samples display metallic character between 2 and 300K, and no metal-to-insulator transition is observed. At low temperature, the V2O3 films behave as a strongly correlated metal, and the resistivity (ρ) follows the equation ρ=ρ0+AT2, where A is the transport coefficient in a Fermi liquid. Typical values of A have been calculated to be 0.14μΩcmK−2, which is in agreement with the coefficient reported for V2O3 single crystals under high pressure. Moreover, a strong temperature dependence of the Hall resistance confirms the electronic correlations of these V2O3 thin film samples.
Suppression of the turbulent decay of an afterspark channel with residual current
Authors: Leonov Sergey V. , Isaenkov Yuri I. , Shneider Mikhail N.
Published: December 2007

This paper presents the results of an experimental study of a pulse discharge in air at atmospheric pressure and the post-discharge channel decay. It is shown for the first time that a relatively small residual current suppresses the development of gas-dynamic instability and stabilizes the channel. The results of the experiments are compared with predictions of our previously developed theoretical model.