bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial and temporal patterns of carbon emissions from forest fires in China from 1950 to 2000
Authors: Lü Aifeng , Tian Hanqin , Liu Mingliang , Liu Jiyuan , Melillo Jerry M.
Published: March 2006

We have estimated the emission of carbon (C) and carbon‐containing trace gases including CO2, CO, CH4, and NMHC (nonmethane hydrocarbons) from forest fires in China for the time period from 1950 to 2000 by using a combination of remote sensing, forest fire inventory, and terrestrial ecosystem modeling. Our results suggest that mean annual carbon emission from forest fires in China is about 11.31 Tg per year, ranging from a minimum level of 8.55 Tg per year to a maximum level of 13.9 Tg per year. This amount of carbon emission is resulted from the atmospheric emissions of four trace gases as follows: (1) 40.66 Tg CO2 with a range from 29.21 to 47.53 Tg, (2) 2.71 Tg CO with a range from 1.48 to 4.30 Tg, (3) 0.112 Tg CH4 with a range from 0.06 to 0.2 Tg, and (4) 0.113 Tg NMHC with a range from 0.05 to 0.19 Tg. Our study indicates that fire‐induced carbon emissions show substantial interannual and decadal variations before 1980 but have remained relatively low and stable since 1980 because of the application of fire suppression. Large spatial variation in fire‐induced carbon emissions exists due to the spatial variability of climate, forest types, and fire regimes.
Correlation of the isotopic composition in precipitation with local conditions in alpine regions
Authors: Liebminger Andreas , Haberhauer Georg , Papesch Wolfgang , Heiss Gerhard
Published: March 2006

Mountains within alpine regions can have a significant influence on the geographic distribution of precipitation and on local‐ to regional‐scale climatic and meteorological conditions. Consequently, the oxygen and hydrogen isotope compositions of precipitation are affected by alpine topography as well. The Austrian Network of Isotopes in Precipitation, one of the oldest and densest networks in the world, is therefore an excellent source of isotope data of the last 30 years for investigating the complex processes governing the isotopic composition of precipitation in alpine regions. Fractionation during phase change processes leads to significant isotopic variation in precipitation. Here we show that the spatial isotopic variability, especially in alpine regions, is to a large extent due to nonequilibrium fractionation. Additionally, we conclude that meteorological conditions prevailing at the sampling site are mainly responsible for the observed seasonal pattern in deuterium excess. These results are validated by stepwise multiple regression as well as by applying an empirical model for deuterium excess, which is an indicator of the differential behavior of D and 18O values in vapor and precipitation. The present results enhance the development of models based on detailed statistical assessment of local climatic conditions to improve the quantitative interpretation of isotope data for paleoclimatology delivered by glacial ice of alpine regions.
Chemical characterization of the ambient organic aerosol soluble in water: 2. Isolation of acid, neutral, and basic fractions by modified size‐exclusion chromatography
Authors: Sullivan Amy P. , Weber Rodney J.
Published: March 2006

A method employing size‐exclusion chromatography (SEC) with Total Organic Carbon detection is developed to isolate and quantify the water‐soluble organic carbon (WSOC) component of ambient aerosol particles by acid, neutral, and basic functional groups. The method provides unique quantitative insights into the characteristics and possible sources of a large fraction of the organic aerosol. The SEC is combined with a XAD‐8 method that separates WSOC into hydrophilic and hydrophobic fractions. Calibrations show the hydrophilic fraction separates into short‐chain aliphatic acids (WSOCxp_a), neutrals (WSOCxp_n, e.g., saccharides, polyols, and short‐chain carbonyls), and organic bases. Recovered hydrophobic fractions are separated into acids (WSOCxrr_a, e.g., aromatic) and neutrals (WSOCxrr_n, e.g., phenols). 13Carbon–nuclear magnetic resonance on ambient samples support the calibration‐based conclusions; however, calibrations only provide a guide to the type of ambient organic compounds expected in each group. Comparisons are made between XAD‐8/SEC results from urban Atlanta summer and winter and biomass burning samples. The largest isolated fraction of Atlanta summer WSOC is WSOCxp_a (29% μg C/μg C), suggesting aliphatic acids of less than C4 or C5 are the dominant secondary organic aerosol product. Combined with WSOCxrr_a, these acid groups are a higher fraction of summer organic carbon (20%) than winter (14%). They are correlated with each other (R2 = 0.74), with WSOCxp_n (R2 = 0.61 and 0.52), and with gaseous 24‐hour averaged volatile organic compounds linked to mobile sources. In biomass burning samples, neutrals (WSOCxp_n and WSOCxrr_n) dominate the WSOC. Atlanta winter samples have characteristics that appear to be a combination of summer and biomass samples.
An assessment of ECMWF analyses and model forecasts over the North Slope of Alaska using observations from the ARM Mixed‐Phase Arctic Cloud Experiment
Authors: Xie Shaocheng , Klein Stephen A. , Yio John J. , Beljaars Anton C. M. , Long Charles N. , Zhang Minghua
Published: March 2006

European Centre for Medium‐Range Weather Forecasts (ECMWF) analysis and model forecast data are evaluated using observations collected during the Atmospheric Radiation Measurement (ARM) October 2004 Mixed‐Phase Arctic Cloud Experiment (M‐PACE) at its North Slope of Alaska (NSA) site. It is shown that the ECMWF analysis reasonably represents the dynamic and thermodynamic structures of the large‐scale systems that affected the NSA during M‐PACE. The model‐analyzed near‐surface horizontal winds, temperature, and relative humidity also agree well with the M‐PACE surface measurements. Given the well‐represented large‐scale fields, the model shows overall good skill in predicting various cloud types observed during M‐PACE; however, the physical properties of single‐layer boundary layer clouds are in substantial error. At these times, the model substantially underestimates the liquid water path in these clouds, with the concomitant result that the model largely underpredicts the downwelling longwave radiation at the surface and overpredicts the outgoing longwave radiation at the top of the atmosphere. The model also overestimates the net surface shortwave radiation, mainly because of the underestimation of the surface albedo. The problem in the surface albedo is primarily associated with errors in the surface snow prediction. Principally because of the underestimation of the surface downwelling longwave radiation at the times of single‐layer boundary layer clouds, the model shows a much larger energy loss (−20.9 W m−2) than the observation (−9.6 W m−2) at the surface during the M‐PACE period.
Second European Space Weather Week
Authors: Simpson Sarah
Published: March 2006

International scientists and applications experts gathered to consider a new generation of space weather activities in Europe.
Herbal remedy magnolol suppresses IL‐6‐induced STAT3 activation and gene expression in endothelial cells
Authors: Chen Shih‐Chung , Chang Ying‐Ling , Wang Danny Ling , Cheng Jing‐Jy
Published: March 2006

Magnolol (Mag), an active constituent isolated from the Chinese herb Hou p'u (Magnolia officinalis) has long been used to suppress inflammatory processes. Chronic inflammation is well known to be involved in vascular injuries such as atherosclerosis in which interleukin (IL)‐6 may participate. Signal transducer and activator of transcription protein 3 (STAT3), a transcription factor involved in inflammation and the cell cycle, is activated by IL‐6. In this study, we evaluated whether Mag can serve as an anti‐inflammatory agent during endothelial injuries. The effects of Mag on IL‐6‐induced STAT3 activation and downstream target gene induction in endothelial cells (ECs) were examined. Pretreatment of ECs with Mag dose dependently inhibited IL‐6‐induced Tyr705 and Ser727 phosphorylation in STAT3 without affecting the phosphorylation of JAK1, JAK2, and ERK1/2. Mag pretreatment of these ECs dose dependently suppressed IL‐6‐induced promoter activity of intracellular cell adhesion molecule (ICAM)‐1 that contains functional IL‐6 response elements (IREs). An electrophoretic mobility shift assay (EMSA) revealed that Mag treatment significantly reduced STAT3 binding to the IRE region. Consistently, Mag treatment markedly inhibited ICAM‐1 expression on the endothelial surface. As a result, reduced monocyte adhesion to IL‐6‐activated ECs was observed. Furthermore, Mag suppressed IL‐6‐induced promoter activity of cyclin D1 and monocyte chemotactic protein (MCP)‐1 for which STAT3 activation plays a role. In conclusion, our results indicate that Mag inhibits IL‐6‐induced STAT3 activation and subsequently results in the suppression of downstream target gene expression in ECs. These results provide a therapeutic basis for the development of Mag as an anti‐inflammatory agent for vascular disorders including atherosclerosis.

British Journal of Pharmacology (2006) 148, 226–232. doi:10.1038/sj.bjp.0706647
Effects of spironolactone on human blood mononuclear cells: mineralocorticoid receptor independent effects on gene expression and late apoptosis induction
Authors: Sønder Søren Ulrik Salling , Mikkelsen Marianne , Rieneck Klaus , Hedegaard Chris Juul , Bendtzen Klaus
Published: March 2006

Spironolactone (SPIR) binds to cytoplasmic mineralocorticoid receptors (MR) and functions as an aldosterone antagonist. Recently, the drug was shown to have an early suppressive effect on several immunoactive and proinflammatory cytokines.

To elucidate the mechanism behind this, the four MR‐binding steroids SPIR, canrenone, 7α‐thiomethyl‐spironolactone and aldosterone (ALDO) were investigated for effects on lipopolysaccharide‐ and phytohemagglutinin‐A‐activated human blood mononuclear cells. Gene expression was examined after 4 h using microarrays, and SPIR affected 1018 transcripts of the (=) 22,000 probed. In contrast, the SPIR‐related steroids affected 17 or fewer transcripts. Combining SPIR and ALDO resulted in 940 affected transcripts, indicating that SPIR has an early gene‐regulatory effect independent of MR.

The affected genes encode a large number of signalling proteins and receptors, including immunoinflammatory response genes and apoptosis and antiapoptosis genes. Apoptosis was evident in CD3‐, CD14‐ and CD19‐positive cells, but only after 18 h of exposure to SPIR.

The transcriptional network involving the differentially regulated genes was examined and the results indicate that SPIR affects genes controlled by the transcription factors NF‐κB, CEBPβ and MYC.

These observations provide new insight into the non‐MR‐mediated effects of SPIR.

British Journal of Pharmacology (2006) 148, 46–53. doi:10.1038/sj.bjp.0706700
Molecular basis of ranolazine block of LQT‐3 mutant sodium channels: evidence for site of action
Authors: Fredj Sandra , Sampson Kevin J , Liu Huajun , Kass Robert S
Published: March 2006

We studied the effects of ranolazine, an antianginal agent with promise as an antiarrhythmic drug, on wild‐type (WT) and long QT syndrome variant 3 (LQT‐3) mutant Na+channels expressed in human embryonic kidney (HEK) 293 cells and knock‐in mouse cardiomyocytes and used site‐directed mutagenesis to probe the site of action of the drug.

We find preferential ranolazine block of sustained vs peak Na+channel current for LQT‐3 mutant (ΔKPQ and Y1795C) channels (IC50=15 vs 135 μM) with similar results obtained in HEK 293 cells and knock‐in myocytes.

Ranolazine block of both peak and sustained Na+channel current is significantly reduced by mutation (F1760A) of a single residue previously shown to contribute critically to the binding site for local anesthetic (LA) molecules in the Na+channel.

Ranolazine significantly decreases action potential duration (APD) at 50 and 90% repolarization by 23±5 and 27±3%, respectively, in ΔKPQ mouse ventricular myocytes but has little effect on APD of WT myocytes.

Computational modeling of human cardiac myocyte electrical activity that incorporates our voltage‐clamp data predicts marked ranolazine‐induced APD shortening in cells expressing LQT‐3 mutant channels.

Our results demonstrate for the first time the utility of ranolazine as a blocker of sustained Na+channel activity induced by inherited mutations that cause human disease and further, that these effects are very likely due to interactions of ranolazine with the receptor site for LA molecules in the sodium channel.

British Journal of Pharmacology(2006)148, 16–24. doi:10.1038/sj.bjp.0706709
Biological properties of a specific Gαq/11 inhibitor, YM‐254890, on platelet functions and thrombus formation under high‐shear stress
Authors: Uemura Toshio , Kawasaki Tomihisa , Taniguchi Masatoshi , Moritani Yumiko , Hayashi Kazumi , Saito Tetsu , Takasaki Jun , Uchida Wataru , Miyata Keiji
Published: March 2006

The effects of YM‐254890, a specific Gαq/11 inhibitor, on platelet functions, thrombus formation under high‐shear rate condition and femoral artery thrombosis in cynomolgus monkeys were investigated.

YM‐254890 concentration dependently inhibited ADP‐induced intracellular Ca2+ elevation, with an IC50 value of 0.92±0.28 μM.

P‐selectin expression induced by ADP or thrombin receptor agonist peptide (TRAP) was strongly inhibited by YM‐254890, with IC50 values of 0.51±0.02 and 0.16±0.08 μM, respectively.

YM‐254890 had no effect on the binding of fibrinogen to purified GPIIb/IIIa, but strongly inhibited binding to TRAP‐stimulated washed platelets.

YM‐254890 completely inhibited platelet shape change induced by ADP, but not that induced by collagen, TRAP, arachidonic acid, U46619 or A23187.

YM‐254890 attenuated ADP‐, collagen‐, TRAP‐, arachidonic acid‐ and U46619‐induced platelet aggregation with IC50 values of <1 μM, whereas it had no effect on phorbol 12‐myristate 13‐acetate‐, ristocetin‐, thapsigargin‐ or A23187‐induced platelet aggregation.

High‐shear stress‐induced platelet aggregation and platelet‐rich thrombus formation on a collagen surface under high‐shear flow conditions were concentration dependently inhibited by YM‐254890.

The antithrombotic effect of YM‐254890 was evaluated in a model of cyclic flow reductions in the femoral artery of cynomolgus monkeys. The intravenous bolus injection of YM‐254890 dose dependently inhibited recurrent thrombosis without affecting systemic blood pressure or prolonging template bleeding time.

YM‐254890 is a useful tool for investigating Gαq/11‐coupled receptor signaling and the physiological roles of Gαq/11.

British Journal of Pharmacology (2006) 148, 61–69. doi:10.1038/sj.bjp.0706711
Anti‐inflammatory effect of buddlejasaponin IV through the inhibition of iNOS and COX‐2 expression in RAW 264.7 macrophages via the NF‐κB inactivation
Authors: Won Jong‐Heon , Im Ho‐Taek , Kim Yang‐Hee , Yun Kyung‐Jin , Park Hee‐Juhn , Choi Jong‐Won , Lee Kyung‐Tae
Published: March 2006

Buddlejasaponin IV isolated from Pleurospermum kamtschatidum is an anti‐inflammatory compound that inhibits NO, PGE2 and TNF‐α production. Here, we studied the mode of action of this compound.

Buddlejasaponin IV (2.5–10 μM) reduced lipopolysaccaride (LPS (1 μg ml−1))‐induced levels of iNOS and COX‐2 at the protein levels, and iNOS, COX‐2, TNF‐α, interleukin (IL)‐1β and IL‐6 mRNA expression in RAW 264.7 macrophages in a concentration‐dependent manner, as determined by Western blotting and RT–PCR, respectively.

Buddlejasaponin IV inhibited the LPS‐induced activation of nuclear factor‐κB (NF‐κB), a transcription factor necessary for proinflammatory mediators, iNOS, COX‐2, TNF‐α, IL‐1β and IL‐6 expression. This effect was accompanied by a parallel reduction in IκB‐α degradation and phosphorylation, and by the nuclear translocation of the NF‐κB p65 subunit.

The effects of buddlejasaponin IV on acute phase inflammation were studied on serotonin‐ and carrageenan–induced paw edema. The antiedematous effect of buddlejasaponin IV was compared with 10 mg kg−1 of indomethacin p.o. Maximum inhibitions of 26 and 41% were noted at a dose of 20 mg kg−1 for serotonin‐ and carrageenan‐induced paw edema, respectively.

The analgesic effect of buddlejasaponin IV was evaluated using acetic acid‐induced writhing and hot‐plate tests. Buddlejasaponin IV (10 and 20 mg kg−1, p.o.) was found to have a marked analgesic effect in both models.

These results suggest that the inhibitions of the expressions of iNOS, COX‐2, TNF‐α, IL‐1β and IL‐6 by blocking NF‐κB activation, are responsible for the anti‐inflammatory effects of buddlejasaponin IV isolated from P. kamtschatidum.

British Journal of Pharmacology (2006) 148, 216–225. doi:10.1038/sj.bjp.0706718
Compilation of Wavelengths, Energy Levels, and Transition Probabilities for W I and W II
Authors: Kramida A. E. , Shirai T.
Published: March 2006

Energy levels, wavelengths, and transition probabilities of the first and second spectra of tungsten, W I and W II, have been compiled. Wavelengths of observed transitions and energy levels derived from those wavelengths have been obtained from a critical evaluation of the available literature. Measured transition probabilities for some of the observed transitions have been compiled from the published literature.
A Reference Equation of State for the Thermodynamic Properties of Ethane for Temperatures from the Melting Line to 675 K and Pressures up to 900 MPa
Authors: Bücker D. , Wagner W.
Published: March 2006

A new formulation for the thermodynamic properties of the fluid phase of ethane in the form of a fundamental equation explicit in the Helmholtz energy is presented. The functional form of the residual part was developed using state-of-the-art linear and nonlinear optimization algorithms. It contains 44 coefficients which were fitted to selected data for the thermal and caloric properties of ethane both in the single-phase region and on the liquid–vapor phase boundary. This work provides information on the available experimental data for the thermodynamic properties of ethane and presents all details of the new formulation. The new equation of state describes the pρT surface of ethane with an uncertainty in density of less than 0.02%–0.03% (coverage factor k=2 corresponding to a level of confidence of about 95%) from the melting line up to temperatures of 520 K and pressures of 30 MPa. In the gaseous and supercritical region, high precision speed of sound data are represented generally within less than 0.015%. Other reliable data sets are represented within their experimental uncertainties. The primary data, to which the equation was fitted, cover the fluid region from the melting line to temperatures of 675 K and pressures of 900 MPa. Beyond this range the equation shows reasonable extrapolation behavior up to very high temperatures and pressures. In addition to the equation of state, independent equations for the vapor pressure, the saturated-liquid and saturated-vapor densities, and the melting pressure are given. Tables of thermodynamic properties calculated from the new formulation are listed in the Appendix.
The Ionization Constant of Water over Wide Ranges of Temperature and Density
Authors: Bandura Andrei V. , Lvov Serguei N.
Published: March 2006

A semitheoretical approach for the ionization constant of water, KW, is used to fit the available experimental data over wide ranges of density and temperature. Statistical thermodynamics is employed to formulate a number of contributions to the standard state chemical potential of the ionic hydration process. A sorption model is developed for calculating the inner-shell term, which accounts for the ion–water interactions in the immediate ion vicinity. A new analytical expression is derived using the Bragg–Williams approximation that reproduces the dependence of a mean ion solvation number on the solvent chemical potential. The proposed model was found to be correct at the zero-density limit. The final formulation has a simple analytical form, includes seven adjustable parameters, and provides good fitting of the collected KW data, within experimental uncertainties, for a temperature range of 0–800 °C and densities of 0–1.2 g cm−3.
Standard Reference Data for the Viscosity of Toluene
Authors: Santos Fernando J. V. , Nieto de Castro Carlos A. , Dymond John H. , Dalaouti Natassa K. , Assael Marc J. , Nagashima Akira
Published: March 2006

Viscosity is an important transport property for the optimum design of a chemical process plant and for the development of molecular theories of the liquid state. A large amount of experimental viscosity data has been produced for all types of liquids, from alternative refrigerants to molten salts and molten metals. The accuracy of these data is related to the operating conditions of the instrument and, for this purpose as well as for the calibration of relative instruments, standard reference data for viscosity are necessary over a wide range of temperatures. New experimental data on the viscosity of liquid toluene along the saturation line have been obtained recently, mostly at low temperatures. The quality of the data is such that recommended values can be proposed with uncertainties of 0.5% (95% confidence level) for 260 K⩽T⩽370 K and 2% for 210 K⩽T<260 K and 370 K<T⩽400 K. A discussion about the uncertainties in the measurements and about the purity of the samples is made. The proposed value for the viscosity of liquid toluene at 298.15 K and 0.1 MPa is η=554.2±3.3 μPa s.
Estimation of Closed Cup Flash Points of Combustible Solvent Blends
Authors: Catoire Laurent , Paulmier Stéphanie , Naudet Valérie
Published: March 2006

A simple formulation is developed for the accurate estimation of flash points of miscible combustible solvent mixtures. It consists of an equation, which was previously validated for pure compounds. It is shown that this procedure allows accurate estimations for ideal and nonideal binary and ternary mixtures. This method does not need prerequisites such as the lower flammability limits of pure components and the use of the Le Chatelier law.
Cross Sections for Electron Collisions with Nitrogen Molecules
Authors: Itikawa Yukikazu
Published: March 2006

Cross section data have been compiled for electron collisions with nitrogen molecules, based on 104 references. Cross sections are collected and reviewed for: total scattering, elastic scattering, momentum transfer, excitations of rotational, vibrational, and electronic states, dissociation, ionization, and emission of radiation. For each process, the recommended values of the cross section are presented for use. The literature has been surveyed through the end of 2003.
Solubility of Structurally Complicated Materials: I. Wood
Authors: Horvath Ari L.
Published: March 2006

Wood is a complex and nonuniform material. Its overall solubility is a combination of the individual components’ ability to come into contact with the specified solvent (e.g., acetone) or blend. The components extracted from wood with a specified solvent represent the solubility of wood in that solvent at the condition described. Some wood compounds are soluble in water and organic solvents but the integral part of the cellular structure cannot be removed by common solvents at ambient temperature. High severities are needed for increased solubility/liquefaction due to temperature, time, and catalytic effects.
Wavelengths, Transition Probabilities, and Energy Levels for the Spectra of Rubidium (Rb I through Rb XXXVII)
Authors: Sansonetti J. E.
Published: March 2006

Energy levels, with designations and uncertainties, have been compiled for the spectra of the neutral atom and all positive ions of rubidium (Z=37). Wavelengths with classifications, intensities, and transition probabilities are also tabulated. In addition, ground states and ionization energies are listed. For most ionization stages experimental data are available; however for ionization stages where only theoretical calculations or fitted values exist, these are reported. There are a few ionization stages for which only a calculated ionization potential is available.
Rotationally selected product pair correlation: F+CD4→DF(ν′)+CD3(ν2=and2,N)
Authors: Zhou Jingang , Shiu Weicheng , Lin Jim J. , Liu Kopin
Published: March 2006

The product pair correlation of the title reaction was measured with rotational selection for both the vibrationally ground CD3(ν=0) and umbrella-excited CD3(ν2=2) products. A striking linear relationship was found between the rotational energy of the selected CD3 product and the correlated kinetic energy release (or the average vibrational energy of the DF coproduct). Such a linearly correlated (or anticorrelated) dependence appears to be stronger for CD3(ν2=2,N) than for CD3(ν=0,N). The mechanistic implication of the observation is that the rotational motion N of the CD3 product tends to lie antiparallel to the orbital angular momentum l′ of the two departing products. The dependency on the K quantum number—the projection of N on the top axis—is, on the other hand, less significant yet noticeable.
Implementation and synchronization of 3×3 grid scroll chaotic circuits with analog programmable devices
Authors: Hulub Marian , Frasca Mattia , Fortuna Luigi , Arena Paolo
Published: March 2006

The implementation of circuits with complex dynamics is a very challenging problem. In this paper we present a new chaotic circuit based on the dynamical equations introduced in IEEE Trans. Circuits Syst., I: Fundam. Theory Appl. 51, 2476–2490 (2004). This circuit has been realized by using programmable analog devices, and, in particular, field programmable analog arrays have been used to implement a two-dimensional 3×3 grid scroll chaotic attractor. The implementation of complex dynamics with low cost circuits is very appealing; moreover, the implementation of the chaotic attractor discussed in this paper is not present in the literature. The experimental results including the synchronization between two chaotic circuits show complete agreement with the simulation results reported in IEEE Trans. Circuits Syst., I: Fundam. Theory Appl. 51, 2476–2490 (2004).
Controlling chaos in spatially extended beam-plasma system by the continuous delayed feedback
Authors: Hramov Alexander E. , Koronovskii Alexey A. , Rempen Irene S.
Published: March 2006

In this paper we discuss the control of complex spatio-temporal dynamics in a spatially extended nonlinear system (fluid model of Pierce diode) based on the concepts of controlling chaos in the systems with few degrees of freedom. A presented method is connected with stabilization of unstable homogeneous equilibrium state and the unstable spatio-temporal periodical states analogous to unstable periodic orbits of chaotic dynamics of the systems with few degrees of freedom. We show that this method is effective and allows to achieve desired regular dynamics chosen from a number of possible in the considered system.
Geometric diagnostics of complex patterns: Spiral defect chaos
Authors: Riecke Hermann , Madruga Santiago
Published: March 2006

Motivated by the observation of spiral patterns in a wide range of physical, chemical, and biological systems, we present an automated approach that aims at characterizing quantitatively spiral-like elements in complex stripelike patterns. The approach provides the location of the spiral tip and the size of the spiral arms in terms of their arc length and their winding number. In addition, it yields the number of pattern components (Betti number of order 1), as well as their size and certain aspects of their shape. We apply the method to spiral defect chaos in thermally driven Rayleigh-Bénard convection and find that the arc length of spirals decreases monotonically with decreasing Prandtl number of the fluid and increasing heating. By contrast, the winding number of the spirals is nonmonotonic in the heating. The distribution function for the number of spirals is significantly narrower than a Poisson distribution. The distribution function for the winding number shows approximately an exponential decay. It depends only weakly on the heating, but strongly on the Prandtl number. Large spirals arise only for larger Prandtl numbers (Pr≳1). In this regime the joint distribution for the spiral length and the winding number exhibits a three-peak structure, indicating the dominance of Archimedean spirals of opposite sign and relatively straight sections. For small Prandtl numbers the distribution function reveals a large number of small compact pattern components.
Configurational constant pressure molecular dynamics
Authors: Braga Carlos , Travis Karl P.
Published: March 2006

We propose two new algorithms for generating isothermal-isobaric molecular dynamics. The algorithms are based on an extended phase space dynamics where two extra degrees of freedom, representing the thermostat and the barostat, are included. These new methods adopt a totally different approach towards molecular dynamics simulation in the isothermal-isobaric ensemble. They are fully configurational in the sense that only the particle positions are required in the control of the system temperature and pressure. Following on from the works of Delhommelle and Evans [Mol. Phys., 99, 1825 (2001)] and of Braga and Travis [J. Chem. Phys., 123, 134101 (2005)] concerning configurational canonical dynamics, these new algorithms can be seen as a natural extension to the isothermal-isobaric ensemble. We have validated both of our new configurational isothermal-isobaric schemes by conducting molecular dynamics simulations of a Lennard-Jones fluid and comparing the static and dynamic properties for a single state point. We find that both schemes generate similar results compared with schemes which use kinetic temperature and pressure control. We have also monitored the response of the system to a series of isothermal compressions and isobaric quenches. We find that the configurational schemes performed at least as well as the kinetic based scheme in bringing the system temperature and pressure into line with the set point values of these variables. These new methods will potentially play a significant role in simulations where the calculation of the kinetic temperature and pressure can be problematic. A well known example resides in the field of nonequilibrium simulations where the kinetic temperature and pressure require a knowledge of the streaming velocity of the fluid in order to calculate the true peculiar velocities (or momenta) that enter into their definitions. These are completely avoided by using our configurational thermostats and barostats, since these are independent of momenta. By extending the analysis of Kusnezov et al. [Ann. Phys., 204, 155 (1990)] in order to derive a set of generalized Nosé-Hoover equations of motion which can generate isothermal-isobaric dynamics in a number of different ways, we are able to show that both of our new configurational barostats and Hoover’s kinetic isothermal-isobaric scheme are special cases of this more general set of equations. This generalization can be very powerful in generating constant pressure dynamics for a variety of systems.
Synchronization of electronic genetic networks
Authors: Wagemakers Alexandre , Buldú Javier M. , García-Ojalvo Jordi , Sanjuán Miguel A. F.
Published: March 2006

We describe a simple analog electronic circuit that mimics the behavior of a well-known synthetic gene oscillator, the repressilator, which represents a set of three genes repressing one another. Synchronization of a population of such units is thoroughly studied, with the aim to compare the role of global coupling with that of global forcing on the population. Our results show that coupling is much more efficient than forcing in leading the gene population to synchronized oscillations. Furthermore, a modification of the proposed analog circuit leads to a simple electronic version of a genetic toggle switch, which is a simple network of two mutual repressor genes, where control by external forcing is also analyzed.
Towards a force field based on density fitting
Authors: Piquemal Jean-Philip , Cisneros G. Andrés , Reinhardt Peter , Gresh Nohad , Darden Thomas A.
Published: March 2006

Total intermolecular interaction energies are determined with a first version of the Gaussian electrostatic model (GEM-0), a force field based on a density fitting approach using s-type Gaussian functions. The total interaction energy is computed in the spirit of the sum of interacting fragment ab initio (SIBFA) force field by separately evaluating each one of its components: electrostatic (Coulomb), exchange repulsion, polarization, and charge transfer intermolecular interaction energies, in order to reproduce reference constrained space orbital variation (CSOV) energy decomposition calculations at the B3LYP/aug-cc-pVTZ level. The use of an auxiliary basis set restricted to spherical Gaussian functions facilitates the rotation of the fitted densities of rigid fragments and enables a fast and accurate density fitting evaluation of Coulomb and exchange-repulsion energy, the latter using the overlap model introduced by Wheatley and Price [Mol. Phys. 69, 50718 (1990)]. The SIBFA energy scheme for polarization and charge transfer has been implemented using the electric fields and electrostatic potentials generated by the fitted densities. GEM-0 has been tested on ten stationary points of the water dimer potential energy surface and on three water clusters (n=16,20,64). The results show very good agreement with density functional theory calculations, reproducing the individual CSOV energy contributions for a given interaction as well as the B3LYP total interaction energies with errors below kBT at room temperature. Preliminary results for Coulomb and exchange-repulsion energies of metal cation complexes and coupled cluster singles doubles electron densities are discussed.
Sojourn time for rank one perturbations
Authors: Asch J. , Astaburuaga M. A. , Briet P. , Cortés V. H. , Duclos P. , Fernández C.
Published: March 2006

We consider a self-adjoint, purely absolutely continuous operator M. Let P be a rank one operator Pu=⟨φ,u⟩φ such that for β0 Hβ0≔M+β0P has a simple eigenvalue E0 embedded in its absolutely continuous spectrum, with corresponding eigenvector ψ. Let Hω be a rank one perturbation of the operator Hβ0, namely, Hω=M+(β0+ω)P. Under suitable conditions, the operator Hω has no point spectrum in a neighborhood of E0, for ω small. Here, we study the evolution of the state ψ under the Hamiltonian Hω, in particular, we obtain explicit estimates for its sojourn time τω(ψ)=∫−∞∞∣⟨ψ,e−iHωtψ⟩∣2dt. By perturbation theory, we prove that τω(ψ) is finite for ω≠0, and that for ω small it is of order ω−2. Finally, by using an analytic deformation technique, we estimate the sojourn time for the Friedrichs model in Rn.
Exact and quasiexact solvability of second-order superintegrable quantum systems: I. Euclidean space preliminaries
Authors: Kalnins E. G. , Miller W. , Pogosyan G. S.
Published: March 2006

We show that second-order superintegrable systems in two-dimensional and three-dimensional Euclidean space generate both exactly solvable (ES) and quasiexactly solvable (QES) problems in quantum mechanics via separation of variables, and demonstrate the increased insight into the structure of such problems provided by superintegrability. A principal advantage of our analysis using nondegenerate superintegrable systems is that they are multiseparable. Most past separation of variables treatments of QES problems via partial differential equations have only incorporated separability, not multiseparability. Also, we propose another definition of ES and QES. The quantum mechanical problem is called ES if the solution of Schrödinger equation can be expressed in terms of hypergeometric functions Fnm and is QES if the Schrödinger equation admits polynomial solutions with coefficients necessarily satisfying a three-term or higher order of recurrence relations. In three dimensions we give an example of a system that is QES in one set of separable coordinates, but is not ES in any other separable coordinates. This example encompasses Ushveridze’s tenth-order polynomial QES problem in one set of separable coordinates and also leads to a fourth-order polynomial QES problem in another separable coordinate set.
Temperature dependence of magnetocrystalline anisotropy constants in the single variant state of L1-type FePt bulk single crystal
Authors: Inoue K. , Shima H. , Fujita A. , Ishida K. , Oikawa K. , Fukamichi K.
Published: March 2006

The temperature dependence of magnetocrystalline anisotropy constants and the saturation magnetization in a single variant state have been investigated for L10-type Fe60Pt40 bulk single crystal prepared under compressive stress. The uniaxial magnetocrystalline anisotropy constant Ku evaluated from the magnetization curve is 6.9×107ergcm−3 at 5K. The values of the second- and fourth-order magnetocrystalline anisotropy constants K1 and K2 at 5K determined by the Sucksmith–Thompson method are 7.4 and 0.13×107ergcm−3, respectively. Both the values of Ku and K1 decrease with increasing temperature T, while K2 is almost independent of T. The difference between the power law of the Callen and Callen model is described by the dimensionality and the thermal variation of the axial ratio c∕a due to the thermal expansion.
Magnetocapacitance without magnetoelectric coupling
Authors: Catalan G.
Published: March 2006

The existence of a magnetodielectric (magnetocapacitance) effect is often used as a test for multiferroic behavior in new material systems. However, strong magnetodielectric effects can also be achieved through a combination of magnetoresistance and the Maxwell-Wagner effect, unrelated to true magnetoelectric coupling. The fact that this resistive magnetocapacitance does not require multiferroic materials may be advantageous for practical applications. Conversely, however, it also implies that magnetocapacitance per se is not sufficient to establish that a material is multiferroic.
Probing anisotropic interaction potentials of unsaturated hydrocarbons with He*(2S3) metastable atom: Attractive-site preference of σ-direction in C2H2 and π-direction in C2H4
Authors: Horio Takuya , Hatamoto Takuro , Maeda Satoshi , Kishimoto Naoki , Ohno Koichi
Published: March 2006

State-resolved collision energy dependence of Penning ionization cross sections of acetylene (C2H2) and ethylene (C2H4) with He*(2S3) metastable atoms was observed in a wide collision energy range from 20to350meV. A recently developed discharge nozzle source with a liquid N2 circulator was employed for the measurements in the low-energy range from 20to80meV. Based on classical trajectory calculations for the energy dependence of the partial ionization cross sections, anisotropic potential energy surfaces for the present systems were obtained by optimizing ab initio model potentials for the chemically related systems Li+C2H2 and C2H4. In the case of C2H2, the global minimum was found to be located around the H atom along the molecular axis with a well depth of 48meV (ca. 1.1kcal∕mol). On the other hand, a dominant attractive well with a depth of 62meV (ca. 1.4kcal∕mol) was found in the πCC electron region of C2H4. These findings were discussed in connection with orbital interactions between molecular orbitals of the target molecules and atomic orbitals of the metastable atom. It is concluded that σ-type unoccupied molecular orbitals of C2H2 and a πCC-type highest occupied molecular orbital of C2H4 play a significant role for the attractive-site preference of σ direction in C2H2 and π direction in C2H4, respectively.
Arrays of microdots of gold nanoparticles immobilized above gold surface probed by optical second-harmonic microscopy
Authors: Tsuboi Kazuma , Kajikawa Kotaro
Published: March 2006

Gold nanoparticle arrays are fabricated on a planar gold surface obtained from UV-photopatterned self-assembled monolayer (SAM) films. The arrays are composed of microdots in which spherical gold nanoparticles are immobilized above a gold surface with a gap distance of a few nanometers supported by SAM films used as a spacer. Two kinds of preparation methods were examined: (1) to pattern a spacer SAM film that makes cross-linkage between the gold surface and the gold nanoparticles, and (2) to form ordered microholes in a SAM film, followed by deposition of the spacer SAM film that makes the cross-linkage in the microholes. Both methods provide us with the ordered microdots of gold nanoparticles on a gold surface. The formation of the microdot arrays were probed by optical second-harmonic microscopy.
Design and control of spin gates in two quantum-dot arrays
Authors: Usaj Gonzalo , Balseiro C. A.
Published: March 2006

We study the spin-spin interaction between quantum dots coupled through a two-dimensional electron gas with spin-orbit interaction. We show that the interplay between transverse electron focusing and spin-orbit coupling allows to dynamically change the symmetry of the effective spin-spin Hamiltonian. That is, the interaction can be changed from Ising-like to Heisenberg-like and vice versa. The sign and magnitude of the coupling constant can also be tuned.
Morphological instability of failure fronts
Authors: Grinfeld M. A. , Schoenfeld S. E. , Wright T. W.
Published: March 2006

There are various observations and experiments showing that, in addition to standard shock-wave fronts, which propagate with high trans-sonic velocities, some other much slower wave fronts can propagate within substance undergoing intensive damage. These moving fronts propagate within intact substance leaving behind them intensively damaged substance. These fronts were coined as failure waves. The failure waves can be modeled differently—in this letter they are modeled as sharp interfaces separating two states: the intact and comminuted states. Several penetration experiments with transparent glasses and ceramics have shown that failure fronts have an extremely rough morphology. We suggest a simple thermodynamic theory which allows interpreting appearance of the roughness as a manifestation of morphological instability of failure fronts. For the case of isotropic phases the instability criterion is presented in explicit form.
Piezoelectric strain in AlGaN∕GaN heterostructure field-effect transistors under bias
Authors: Sarua A. , Ji Hangfeng , Kuball M. , Uren M. J. , Martin T. , Nash K. J. , Hilton K. P. , Balmer R. S.
Published: March 2006

Micro-Raman spectroscopy was used to study piezoelectric strain in AlGaN∕GaN heterostructure field-effect transistors under bias. The measurements were made through the transparent SiC substrate. Strain in the GaN layer varied over the device area and was dependent on bias voltage, and affected, in particular, the gate-drain gap and area underneath the drain contact. The observed strain in GaN was shown to be related to the electric field component normal to the surface. Finite element simulations of electric field distribution show good qualitative agreement with the experimental data. Effects of strain on Raman temperature measurements in transistors are also discussed.
Self-organization of nanoneedles in Fe∕GaAs (001) epitaxial thin film
Authors: Huang Y. Z. , Wang S. G. , Wang C. , Xie Z. B. , Cockayne D. J. H. , Ward R. C. C.
Published: March 2006

Well-aligned nanoneedles are found to form in a Fe∕GaAs (001) epitaxial thin film when irradiated with a Ga+ ion beam normal to the sample surface at an ion dose of 3×1017∕cm2 in a focused ion beam. These nanoneedles, with their axes perpendicular to the original sample surface, are composed of GaAs nanorods with Fe nanoislands situated at the top. The GaAs nanorods, formed from the GaAs substrate, are crystalline and in the same crystal orientation as the GaAs substrate. The crystalline nature of the Fe thin film is disrupted by the ion sputtering, becoming nanocrystalline Fe islands. It is the thin Fe layer that is responsible for the formation of the nanoneedles. The ion sputtering of the Fe layer roughens the sample surface due to the uneven sputtering rate of the Fe layer. The removal of the Fe layer exposes the substrate to the incident ions, which then sputter the substrate leading to the formation of the nanoneedles.
X-ray generation using carbon-nanofiber-based flexible field emitters
Authors: Tan T. T. , Sim H. S. , Lau S. P. , Yang H. Y. , Tanemura M. , Tanaka J.
Published: March 2006

Carbon nanofibers were grown on flexible polyimide substrates using an ion-beam sputtering technique. Field emission measurement showed a fairly low threshold voltage of 1.5V∕μm with a current density of 1μA∕cm2. The field enhancement factor was determined to be 4400. The emitter showed resilience when exploited as a high voltage electron source for x-ray generation. The x-ray generated by the flexible emitter is capable of delivering fine images of biological samples with superior sharpness, resolution, and contrast.
Electrical activation and electron spin coherence of ultralow dose antimony implants in silicon
Authors: Schenkel T. , Liddle J. A. , Persaud A. , Tyryshkin A. M. , Lyon S. A. , de Sousa R. , Whaley K. B. , Bokor J. , Shangkuan J. , Chakarov I.
Published: March 2006

We implanted ultralow doses (2×1011cm−2) of antimony ions (Sb121) into isotopically enriched silicon (Si28) and find high degrees of electrical activation and low levels of dopant diffusion after rapid thermal annealing. Pulsed electron spin resonance shows that spin echo decay is sensitive to the dopant depths, and the interface quality. At 5.2K, a spin decoherence time, T2, of 0.3ms is found for profiles peaking 50nm below a Si∕SiO2 interface, increasing to 0.75ms when the surface is passivated with hydrogen. These measurements provide benchmark data for the development of devices in which quantum information is encoded in donor electron spins.
Metal–polymer composite with nanostructured filler particles and amplified physical properties
Authors: Bloor D. , Graham A. , Williams E. J. , Laughlin P. J. , Lussey D.
Published: March 2006

The limits of conductivity of a novel elastomeric matrix–nanostructured nickel powder composite are reported. The conductivity falls by a factor of ⩾2×1014 for compression and by a similar amount in extension. Uncompressed and highly compressed composite displays ohmic behavior but between these limits the current-voltage characteristics are highly nonlinear. The matrix intimately coats the filler so that even above the expected percolation threshold the composite has a very low conductivity. The conductivity of the composite is increased under all mechanical deformations. These and other unusual properties are amplified versions of smaller effects seen in composites containing less highly structured fillers.
Electric field enhancement by a nanometer-scaled conical metal tip in the context of scattering-type near-field optical microscopy
Authors: Goncharenko A. V. , Dvoynenko M. M. , Chang Hung-Chih , Wang Juen-Kai
Published: March 2006

We present a numerical study of the electric field enhancement in the immediate vicinity of the apex of a conical silver tip and show that an optimal cone angle exists, allowing one to maximize the electric field. This angle depends on the tip length, the wavelength, as well as on the distance from the apex to the observation point. So both the angle and length of the tip can be considered as parameters to adjust the peak enhancement resonant position for a laser source wavelength. At the same time, reducing the cone angle does not ensure a concurrent increase in the electric field enhancement. A simple qualitative interpretation is proposed to explain this phenomenon based on competition of two mechanisms affecting the electric field near the tip apex. The results obtained show that the point-like dipole approximation is invalid for description of the field enhancement of a finite-size metal tip in the case of scattering-type near-field optical microscopy. One more conclusion is that the model of a sharp semi-infinite perfectly conducting tip is also not adequate in our case.