bluuebunny/crossref_metadata_2025 huggingface dataset:
Global distribution of agricultural fires in croplands from 3 years of Moderate Resolution Imaging Spectroradiometer (MODIS) data
Authors: Korontzi Stefania , McCarty Jessica , Loboda Tatiana , Kumar Suresh , Justice Chris
Published: June 2006

The Moderate Resolution Imaging Spectroradiometer (MODIS) sensor offers an improved combination of spectral, temporal, and spatial resolution for global fire detection compared to previous sensors. The MODIS Terra active fire product was analyzed to investigate the spatial and temporal occurrence of fires in croplands from 2001 to 2003. Monthly fire counts were analyzed globally, within several regions and for important crop‐producing countries. The annual global total number of fire counts ranged from 1,472,367 to 1,577,952 during the 3 years. Agricultural fires were found to account for 8–11% of the annual global fire activity during the 3 years, but the contribution of agricultural burning was significantly higher on a regional basis. The Russian Federation was the largest contributor to agricultural burning globally during the 3 years, producing 31–36% of all agricultural fires. The global spatial distribution of agricultural fires was fairly similar among the 3 years, but a notable interannual change was observed in the total number of global agricultural fire events. The majority of regions showed similar magnitude and seasonality in their year‐to‐year agricultural fire activity, but in some regions, significant differences were found. At the global scale, agricultural fire activity showed two peaks, the first occurring during April to May, and was associated primarily with burning in the croplands of Eastern Europe and European Russia, and the second in August from burning mainly in the croplands across central Asia and Asiatic Russia. This timing pattern was observed both in 2001 and 2002. The August 2003 fire peak was significantly affected by reduced agricultural fire activity in European Russia. The seasonal and interannual trends in agricultural fire activity are consistent with known national and regional agricultural practices and reported crop production estimates.
Spatial patterns in seasonal and interannual variability of chlorophyll and sea surface temperature in the California Current
Authors: Legaard Kasey R. , Thomas Andrew C.
Published: June 2006

Physical forcing and biological response within the California Current System (CCS) are highly variable over a wide range of scales. Satellite remote sensing offers the only feasible means of quantifying this variability over the full extent of the CCS. Using six years (1997–2003) of daily SST and chlorophyll imagery, we map the spatial dependence of dominant temporal variability at resolutions sufficient to identify recurrent mesoscale circulation and local pattern associated with coastal topography. Here we describe mean seasonal cycles and interannual variation; intraseasonal variability is left to a companion paper (K. R. Legaard and A. C. Thomas, manuscript in preparation, 2006). Coastal upwelling dictates seasonality along north‐central California, where weak cycles of SST fluctuate between spring minima and late summer maxima and chlorophyll peaks in early summer. Off northern California, chlorophyll maxima are bounded offshore by the seasonally recurrent upwelling jet. Seasonal cycles differ across higher latitudes and in the midlatitude Southern California Bight, where upwelling winds are less vigorous and/or persistent. Seasonality along south‐central Baja is strongly affected by processes other than upwelling, despite year‐round upwelling‐favorable winds. Interannual variation is generally dominated by El Niño and La Niña conditions. Interannual SST variance is greatest along south‐central Baja, although interannual variability constitutes a greater fraction of total variance inshore along southern Oregon and much of California. Patterns of interannual chlorophyll variance are consistent with dominant forcing through the widespread depression and elevation of the nutricline during El Niño and La Niña, respectively. Interannual variability constitutes a greater fraction of total chlorophyll variance offshore.
The form of the asymptotic depth‐limited wind wave frequency spectrum
Authors: Young I. R. , Babanin A. V.
Published: June 2006

This paper presents a comprehensive set of field experiments investigating the form of the asymptotic, depth‐limited wind wave frequency spectrum. Such a spectrum represents the upper limit to growth from active wind forcing in finite depth conditions. The data clearly define asymptotic limits for the nondimensional energy and nondimensional wave number as functions of nondimensional water depth. In contrast to deep water spectra, the asymptotic depth‐limited form has a harmonic at a frequency slightly less than twice the spectral peak frequency. A parametric form is proposed for the spectral form, and clear functional relationships are found for all the spectral parameters. These relationships mean that the full asymptotic, depth‐limited spectrum can be determined with knowledge of only the water depth and wind speed.
Modeling the distribution of the volcanic aerosol cloud from the 1783–1784 Laki eruption
Authors: Oman Luke , Robock Alan , Stenchikov Georgiy L. , Thordarson Thorvaldur , Koch Dorothy , Shindell Drew T. , Gao Chaochao
Published: June 2006

We conducted simulations of the atmospheric transformation and transport of the emissions of the 1783–1784 Laki basaltic flood lava eruption (64.10°N, 17.15°W) using the NASA Goddard Institute for Space Studies modelE climate model coupled to a sulfur cycle chemistry model. The model simulations successfully reproduced the aerosol clouds of the 1912 Katmai and 1991 Mount Pinatubo eruptions, giving us confidence in the Laki simulations. Simulations of the Laki eruption produce peak zonal mean sulfate (SO4) concentrations of over 70 ppbv during August and into September 1783 in the upper troposphere and lower stratosphere at high latitudes. While the majority of the sulfate aerosol was removed during the fall and early winter, a significant aerosol perturbation remained into 1784. The peak SO2 gas loading was just over 37 megatons (Mt) in late June with the sulfate loading peaking in late August 1783 at 60 Mt over the average of 3 runs. This yielded a peak sulfate aerosol (75% H2SO4, 25% H2O) loading of over 80 Mt with the total aerosol produced during the entire eruption being about 165 Mt. The resulting sulfate deposition compares well with ice cores taken across Greenland. The top of atmosphere net radiative forcing peaks at −27 W/m2 over the high latitudes during late summer 1783 and produces a global mean forcing of −4 W/m2. The model results confirm that Northern Hemisphere high‐latitude volcanic eruptions produce aerosols that remain mostly confined north of 30°N latitude.
An accelerated time domain finite difference simulation scheme for three‐dimensional transient electromagnetic modeling using geometric multigrid concepts
Authors: Commer Michael , Newman Gregory A.
Published: June 2006

The fact that the transient electromagnetic (TEM) field is smoothed gradually in space with time allows for a reduced spatial sampling rate of the EM field. On the basis of concepts known from multigrid methods, we have developed a restriction operator in order to map the EM field and the material properties from a fine to a coarser finite difference mesh during a forward field simulation with an explicit time‐stepping scheme. Two advantages follow. First, the grid size can be reduced. Field restriction involves reducing the number of grid nodes by a factor of 2 for each Cartesian direction. Second, as can be seen from the Courant‐Friedrichs‐Levy condition, the larger grid spacing allows for proportionally larger time step sizes. After field restriction, a material averaging scheme is employed in order to calculate the underlying effective medium on the coarse simulation grid. Example results show a factor of up to 5 decrease in solution run time, compared to a scheme that uses a constant grid. Key to the accuracy of the approach is knowledge of the proper time range to restrict the fields. An adequate criterion to decide during run time when to restrict involves an error measure for the locations of interest between the fields on the fine mesh and the restricted fields.
Numerical study of dynamic Smagorinsky models in large‐eddy simulation of the atmospheric boundary layer: Validation in stable and unstable conditions
Authors: Kleissl Jan , Kumar Vijayant , Meneveau Charles , Parlange Marc B.
Published: June 2006

Large‐eddy simulation (LES) of atmospheric boundary layer (ABL) flow is performed over a homogeneous surface with different heat flux forcings. The goal is to test the performance of dynamic subgrid‐scale models in a numerical framework and to compare the results with those obtained in a recent field experimental study (HATS (Kleissl et al., 2004)). In the dynamic model the Smagorinsky coefficient cs is obtained from test filtering and analysis of the resolved large scales during the simulation. In the scale‐invariant dynamic model the coefficient is independent of filter scale, and the scale‐dependent model does not require this assumption. Both approaches provide realistic results of mean vertical profiles in an unstable boundary layer. The advantages of the scale‐dependent model become evident in the simulation of a stable boundary layer and in the velocity and temperature spectra of both stable and unstable cases. To compare numerical results with HATS data, a simulation of the evolution of the ABL during a diurnal cycle is performed. The numerical prediction of cs from the scale‐invariant model is too small, whereas the coefficients obtained from the scale‐dependent version of the model are consistent with results from HATS. LES of the ABL using the scale‐dependent dynamic model give reliable results for mean profiles and spectra at stable, neutral, and unstable atmospheric stabilities. However, simulations under strongly stable conditions (horizontal filter size divided by Obukhov length >3.8) display instabilities due to basic flaws in the eddy viscosity closure, no matter how accurately the coefficient is determined.
Using continuous data to estimate clear‐sky errors in inversions of satellite CO2 measurements
Authors: Corbin Katherine D. , Denning A. Scott
Published: June 2006

We used continuous measurements of atmospheric CO2 at two stations to investigate potential errors in inversions of temporal averages of satellite clear‐sky column retrievals. Compared to the complete data sets, the mid‐day CO2 on clear days was systematically lower with a larger winter difference. Net ecosystem exchange (NEE) of CO2 was enhanced on clear vs. all days, the summer boundary layer was deeper, and the CO concentration was systematically lower. During winter these differences cannot account for the CO2 bias, which must be caused by advection. Summertime errors reflect a tradeoff between deeper mixing and enhanced NEE on clear days. If these sites represent mid‐latitude forests and if the CO2 difference is confined to the bottom 15% column mass, then inversions of temporally‐averaged satellite column data products will incur a −0.2 to −0.4 ppm bias. CO2 concentrations must therefore be assimilated at the place and time observed.
Radiogenic isotope fingerprint of Wilkes Land–Adélie Coast Bottom Water in the circum‐Antarctic Ocean
Authors: van de Flierdt Tina , Hemming Sidney R. , Goldstein Steven L. , Abouchami Wafa
Published: June 2006

Wilkes Land–Adélie Coast Bottom Water encompasses the bottom waters formed around the coast of East Antarctica in the area east of Prydz Bay and west of the Ross Sea (90°E–150°E). Here we show that these bottom waters have not only characteristic physical properties, but also carry a distinct radiogenic isotope signal that traces their dispersal. The Nd, Hf and Pb isotopic compositions of Circum‐Antarctic ferromanganese nodules record the isotopic composition of ambient seawater. Those with the lowest Nd and Hf isotopic ratios and the highest Pb isotopic ratios are from the deep Australian‐Antarctic Basin, and they fingerprint Wilkes Land–Adélie Coast Bottom Water. The data illustrate the potential value of these isotope systems as tracers of present and past deep and bottom waters in the Circum‐Antarctic realm and elsewhere.
Impact of meteorology and emissions on methane trends, 1990–2004
Authors: Fiore Arlene M. , Horowitz Larry W. , Dlugokencky Edward J. , West J. Jason
Published: June 2006

Over the past century, atmospheric methane (CH4) rose dramatically before leveling off in the late 1990s. The processes controlling this trend are poorly understood, limiting confidence in projections of future CH4. The MOZART‐2 global tropospheric chemistry model qualitatively captures the observed CH4 trend (increasing in the early 1990s and then leveling off) with constant emissions. From 1991–1995 to 2000–2004, the CH4 lifetime versus tropospheric OH decreases by 1.6%, reflecting increases in OH and temperature. The rise in OH stems from an increase in lightning NOx as parameterized in the model. A simulation including annually varying anthropogenic and wetland CH4 emissions, as well as the changes in meteorology, best reproduces the observed CH4 distribution, trend, and seasonal cycles. Projections of future CH4 abundances should consider climate‐driven changes in CH4 sources and sinks.
Experimental inflow of groundwater induces a “biogeochemical regime shift” in iron‐rich and acidic sediments
Authors: Blodau Christian , Knorr Klaus‐Holger
Published: June 2006

In acid mine drainage (AMD) polluted lakes, sediments may show a stable iron‐ or sulphate‐reducing regime. We tested the hypothesis that increased inflow of groundwater can trigger a shift between these regimes. Schwertmannite‐bearing sediment, rich in iron (40–43%), sulphur (2.5%), and carbon (4.5%), was sampled from an acidic mine lake, and percolated (0, 5, and 20 L m−2 d−1) with two solutions (1/1 mmol L−1 versus 10/15 mmol L−1 sulphate/ferrous iron, pH 5) in sediment columns. A dissolved organic carbon (DOC) source was added after 46 days (∼2.5 mmol C L−1) to ease the carbon limitation of reductive processes. The sediment remained in an iron‐reducing and acidic regime during percolation without DOC. Percolation at a high rate and addition of DOC raised pH values in schwertmannite‐rich layers from 2.8 to 4.5–5. Schwertmannite transformation to goethite partly accelerated by a factor of >2 but effectively buffered proton consumption only at the low percolation rate. Input of dissolved ferrous iron and sulphate reduced the mobilization of ferrous iron from the sediment. With pH increase, iron reduction slowed relative to CO2 production, sulphate was reduced, and iron sulphides were formed. Input of alkalinity and electron donors by percolation thus shifted the biogeochemical regime from iron to sulphate reduction. Similar regime shifts can be expected for other sediments containing immobile proton or redox buffers when exposed to the advective input of alkalinity and acidity, or electron acceptors and donors.
Long waves in erodible channels and morphodynamic influence
Authors: Lanzoni Stefano , Siviglia Annunziato , Frascati Alessandro , Seminara Giovanni
Published: June 2006

Like most media, open channel flows propagate information through waves. When the channel boundary is fixed, the vectors of information consist typically of surface gravity waves. In the less straightforward case of channels with cohesionless bed and possibly erodible banks, other types of waves arise from the erodible nature of the boundaries and the ability of the stream to transport sediments. In this paper we restrict our attention to the important case of long waves, which can be described by employing the shallow water approximation for the flow field and a quasi‐equilibrium assumption for sediment transport on weakly sloping beds. We focus on a major issue: In which direction is information propagated? This is a problem raised and partially solved by de Vries in the context of one‐dimensional morphological modeling as early as 1965. We review some of the available knowledge on this subject, viewed in a more general context where vectors of information can be a variety of waves: purely longitudinal one‐dimensional sediment waves, two‐dimensional waves driven by large‐scale bed forms (bars), and plan form waves carrying information related to the planform shape of the channel. Both linear and nonlinear, migrating and stationary waves are considered. It turns out that the role played by the Froude number in determining the direction of one‐dimensional perturbations of bed topography is somewhat taken by the aspect ratio of the channel when large‐scale two‐dimensional bed forms as well as planform waves are considered.
Do gravel bed river size distributions record channel network structure?
Authors: Sklar Leonard S. , Dietrich William E. , Foufoula‐Georgiou Efi , Lashermes Bruno , Bellugi Dino
Published: June 2006

Bed load sediment particles supplied to channels by hillslopes are reduced in size by abrasion during downstream transport. The branching structure of the channel network creates a distribution of downstream travel distances to a given reach of river and thus may strongly influence the grain size distribution of the long‐term bed load flux through that reach. Here we investigate this hypothesis, using mass conservation and the Sternberg exponential decay equation for particle abrasion, to predict bed material variability at multiple scales for both natural and artificial drainage networks. We assume that over a sufficiently long timescale, no net deposition occurs and that grains less than 2 mm are swept away in suspension. We find that abrasion during fluvial transport has a surprisingly small effect on the bed load sediment grain size distribution, for the simple case of spatially uniform supply of poorly sorted hillslope sediments. This occurs because at any point in the channel network, local resupply offsets the size reduction of material transported from upstream. Thus river bed material may essentially mirror the coarse component of the size distribution of hillslope sediment supply. Furthermore, there is a predictable distance downstream at which the bed load grain size distribution reaches a steady state. In the absence of net deposition due to selective transport, large‐scale variability in bed material, such as downstream fining, must then be due primarily to spatial gradients in hillslope sediment production and transport characteristics. A second key finding is that average bed load flux will tend to stabilize at a constant value, independent of upstream drainage area, once the rate of silt production by bed load abrasion per unit travel distance is equal to the rate of coarse sediment supply per unit channel length (q). Bed load flux equilibrates over a distance that scales with the inverse of the fining coefficient in the abrasion rate law (α) and can be approximated simply as q/3α. Thus the efficiency of particle abrasion sets a fundamental length scale, shorter for weaker rocks and longer for harder rocks, which controls the expression in the river bed of variability in sediment supply. We explore the role of the abrasion length scale in modulating the influence of sediment supply variability in a number of channel network contexts, including individual tributary junctions, a sequence of tributary inputs along a main stem channel, and variable basin shapes and network architecture as expressed by the width function. These findings highlight the need for both data and theory that can be used to predict the grain size distributions supplied to channels by hillslopes.
Homeostatic regulation of supercoiling sensitivity coordinates transcription of the bacterial genome
Authors: Blot Nicolas , Mavathur Ramesh , Geertz Marcel , Travers Andrew , Muskhelishvili Georgi
Published: June 2006

Regulation of cellular growth implies spatiotemporally coordinated programmes of gene transcription. A central question, therefore, is how global transcription is coordinated in the genome. The growth of the unicellular organism Escherichia coli is associated with changes in both the global superhelicity modulated by cellular topoisomerase activity and the relative proportions of the abundant DNA‐architectural chromatin proteins. Using a DNA‐microarray‐based approach that combines mutations in the genes of two important chromatin proteins with induced changes of DNA superhelicity, we demonstrate that genomic transcription is tightly associated with the spatial distribution of supercoiling sensitivity, which in turn depends on chromatin proteins. We further demonstrate that essential metabolic pathways involved in the maintenance of growth respond distinctly to changes of superhelicity. We infer that a homeostatic mechanism organizing the supercoiling sensitivity is coordinating the growth‐phase‐dependent transcription of the genome.
Sema4D/plexin‐B1 activates GSK‐3β through R‐Ras GAP activity, inducing growth cone collapse
Authors: Ito Yuri , Oinuma Izumi , Katoh Hironori , Kaibuchi Kozo , Negishi Manabu
Published: June 2006

Plexins are receptors for the axonal guidance molecules known as semaphorins, and the semaphorin 4D (Sema4D) receptor plexin‐B1 induces repulsive responses by functioning as an R‐Ras GTPase‐activating protein (GAP). Here we characterized the downstream signalling of plexin‐B1‐mediated R‐Ras GAP activity, inducing growth cone collapse. Sema4D suppressed R‐Ras activity in hippocampal neurons, in parallel with dephosphorylation of Akt and activation of glycogen synthase kinase (GSK)‐3β. Ectopic expression of the constitutively active mutant of Akt or treatment with GSK‐3 inhibitors suppressed the Sema4D‐induced growth cone collapse. Constitutive activation of phosphatidylinositol‐3‐OH kinase (PI(3)K), an upstream kinase of Akt and GSK‐3β, also blocked the growth cone collapse. The R‐Ras GAP activity was necessary for plexin‐B1‐induced dephosphorylation of Akt and activation of GSK‐3β and was also required for phosphorylation of a downstream kinase of GSK‐3β, collapsin response mediator protein‐2. Plexin‐A1 also induced dephosphorylation of Akt and GSK‐3β through its R‐Ras GAP activity. We conclude that plexin‐B1 inactivates PI(3)K and dephosphorylates Akt and GSK‐3β through R‐Ras GAP activity, inducing growth cone collapse.
The effect of delocalization on the exchange energy in meta- and para-linked Pt-containing carbazole polymers and monomers
Authors: Zhang Ning , Hayer Anna , Al-Suti Mohammed K. , Al-Belushi Rayya A. , Khan Muhammad S. , Köhler Anna
Published: June 2006

A series of novel platinum-containing carbazole monomers and polymers was synthesized and fully characterized by UV-VIS absorption, luminescence, and photoinduced absorption studies. In these compounds, a carbazole unit is incorporated into the main chain via either a para- or a meta-linkage. We discuss the effects of linkage and polymerization on the energy levels of S1, T1, and Tn. The S1-T1 splitting observed for the meta-linked monomer (0.4eV) is only half of that in the para-linked monomer (0.8eV). Upon polymerization, the exchange energy in the para-linked compound reduces, yet still remains larger than in the meta-linked polymer. We attribute the difference in exchange energy to the difference in wave function overlap between electron and hole in these compounds.
Confined crystallization of cylindrical diblock copolymers studied by dynamic Monte Carlo simulations
Authors: Wang Maoxiang , Hu Wenbing , Ma Yu , Ma Yu-Qiang
Published: June 2006

We report dynamic Monte Carlo simulations of polymer crystallization confined in the cylindrical microdomains of diblock copolymers. The microdomains were prepared via spontaneous microphase separation from homogeneous melt, and the major component was then frozen in a vitreous amorphous state to make a hard confinement to the crystallization of the minor component. We found that during the isothermal crystallization at high temperatures, crystal orientations are dominantly perpendicular to the cylinder axis at the early stage of crystal nucleation and remain to the final state; while if the block junctions are broken before crystallization, crystal orientations are dominantly parallel at the early stage of crystal nucleation, and eventually other orientations take the place of parallel preferences. Analysis of bond orientations in the heterogeneous melts demonstrates the microscopic origin of oriented crystal nucleation.
Periodic forcing of scroll rings and control of Winfree turbulence in excitable media
Authors: Alonso S. , Sagués F. , Mikhailov A. S.
Published: June 2006

By simulations of the Barkley model, action of uniform periodic nonresonant forcing on scroll rings and wave turbulence in three-dimensional excitable media is investigated. Sufficiently strong rapid forcing converts expanding scroll rings into the collapsing ones and suppresses the Winfree turbulence caused by the negative tension of wave filaments. Slow strong forcing has an opposite effect, leading to expansion of scroll rings and induction of the turbulence. These effects are explained in the framework of the phenomenological kinematic theory of scroll waves.
Vacuum heating in the interaction of ultrashort, relativistically strong laser pulses with solid targets
Authors: Cai Hong-bo , Yu Wei , Zhu Shao-ping , Zheng Chun-yang , Cao Li-hua , Pei Wen-bing
Published: June 2006

An analytical fluid model for vacuum heating during the oblique incidence by an ultrashort ultraintense p-polarized laser on a solid-density plasma is proposed. The steepening of an originally smooth electron density profile as the electrons are pushed inward by the laser is included self-consistently. It is shown that the electrons being pulled out and then returned to the plasma at the interface layer by the wave field can lead to a phenomenon like wave breaking since the front part of the returning electrons always move slower than the trailing part. This can lead to heating of the plasma at the expense of the wave energy. An estimate for the efficiency of laser energy absorption by the vacuum heating is given. It is also found that for the incident laser intensity parameter, aL>0.5, the absorption rate peaks at an incident angle 45°−52° and it reaches a maximum of 30% at aL≈1.5.
Femtosecond laser induced associative desorption of H2 from Ru(0001): Comparison of “first principles” theory with experiment
Authors: Luntz A. C. , Persson M. , Wagner S. , Frischkorn C. , Wolf M.
Published: June 2006

A three dimensional model based on molecular dynamics with electronic frictions is developed to describe the femtosecond laser induced associative desorption of H2 from Ru(0001)(1×1)H. Two molecular coordinates (internuclear separation d and center of mass distance to surface z) and a single phonon coordinate are included in the dynamics. Both the potential energy surface and the electronic friction tensor are calculated by density functional theory so that there are no adjustable parameters in the comparison of this model with the wide range of experiments available for this system. This “first principles” dynamic model gives results in semiquantitative agreement with all experimental results; nonlinear fluence dependence of the yield, isotope effect, two pulse correlation, and energy partitioning. The good agreement of theory with experiment supports a description of this surface femtochemistry in terms of thermalized hot electron induced chemistry with coupling to nuclear coordinates through electronic frictions. By comparing the dynamics with the analytical one dimensional frictional model used previously to fit the experiments for this system, we show that the success of the one dimensional model is based on the rapid intermixing of the z and d coordinates as the H–H climbs out of the adsorption well. However, projecting the three dimensional dynamics onto one dimension introduces a fluence (adsorbate temperature) dependent “entropic” barrier in addition to the potential barrier for the chemistry. This implies that some caution must be used in interpreting activation energies obtained in fitting experiments to the one dimensional model.
Numerical modeling of diffusive heat transport across magnetic islands and local stochastic field
Authors: Yu Q.
Published: June 2006

The heat diffusion across magnetic islands is studied numerically and compared with analytical results. For a single island, the enhanced radial heat diffusivity, χr, due to the parallel transport along the field lines is increased over a region of about the island width w. The maximum enhanced heat conductivity at the rational surface is proportional to w2(χ‖χ⊥)1∕2 for sufficiently high values of χ‖∕χ⊥, where χ‖∕χ⊥ is the ratio between the parallel and the perpendicular heat diffusivity. For low ratios of χ‖∕χ⊥, however, the maximum value of χr is proportional to w4χ‖. In a locally stochastic magnetic field, χr is again proportional to w4χ‖ for low χ‖∕χ⊥, which is in agreement with the analytical results. With increasing χ‖∕χ⊥,χr is dominated first by the additive effect of individual islands and then by the field ergodicity.
Energy flow of moving dissipative topological solitons
Authors: Gorbach A. V. , Denisov S. , Flach S.
Published: June 2006

We study the energy flow due to the motion of topological solitons in nonlinear extended systems in the presence of damping and driving. The total field momentum contribution to the energy flux, which reduces the soliton motion to that of a point particle, is insufficient. We identify an additional exchange energy flux channel mediated by the spatial and temporal inhomogeneity of the system state. In the well-known case of a dc external force the corresponding exchange current is shown to be small but nonzero. For the case of ac driving forces, which lead to a soliton ratchet, the exchange energy flux mediates the complete energy flow of the system. We also consider the case of combination of ac and dc external forces, as well as spatial discretization effects.
Effect of resonant-frequency mismatch on attractors
Authors: Wang Xingang , Lai Ying-Cheng , Lai Choy Heng
Published: June 2006

Resonant perturbations are effective for harnessing nonlinear oscillators for various applications such as controlling chaos and inducing chaos. Of physical interest is the effect of small frequency mismatch on the attractors of the underlying dynamical systems. By utilizing a prototype of nonlinear oscillators, the periodically forced Duffing oscillator and its variant, we find a phenomenon: resonant-frequency mismatch can result in attractors that are nonchaotic but are apparently strange in the sense that they possess a negative Lyapunov exponent but its information dimension measured using finite numerics assumes a fractional value. We call such attractors pseudo-strange. The transition to pesudo-strange attractors as a system parameter changes can be understood analytically by regarding the system as nonstationary and using the Melnikov function. Our results imply that pseudo-strange attractors are common in nonstationary dynamical systems.
Simple adaptive synchronization of chaotic systems with random components
Authors: Chen Yen-Sheng , Chang Chien-Cheng
Published: June 2006

Practical systems usually possess random components. Random components often affect the robustness of synchronism and must be taken into consideration in the design of synchronization. In the present study, we assume that the system satisfies the Lipschitz condition, and the random component is uniformly bounded. By the partial stability theory, we are able to prove that two simple adaptive variable structure controllers achieve synchronization of chaotic systems. Moreover, we discuss how the controllers can be modified to eliminate the undesired phenomenon of chattering. The Duffing two-well system and the Chua circuit system are simulated to illustrate the theoretical analysis.
Infrared absorption of CH3SO2 detected with time-resolved Fourier-transform spectroscopy
Authors: Chu Li-Kang , Lee Yuan-Pern
Published: June 2006

A step-scan Fourier-transform spectrometer coupled with a 6.4m multipass absorption cell was employed to detect time-resolved infrared absorption spectra of the reaction intermediate CH3SO2 radical, produced upon irradiation of a flowing gaseous mixture of CH3I and SO2 in CO2 at 248nm. Two transient bands with origins at 1280 and 1076cm−1 were observed and are assigned to the SO2-antisymmetric and SO2-symmetric stretching modes of CH3SO2, respectively. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predicted the geometry, vibrational, and rotational parameters of CH3SO2 and CH3OSO. Based on predicted rotational parameters, the simulated absorption band of the SO2-antisymmetric stretching mode that is dominated by the b-type rotational structure agrees satisfactorily with experimental results. In addition, a band near 1159cm−1 observed at a later period is tentatively attributed to CH3SO2I. The reaction kinetics of CH3+SO2→CH3SO2 and CH3SO2+I→CH3SO2I based on the rise and decay of absorption bands of CH3SO2 and CH3SO2I agree satisfactorily with previous reports.
Forced Hall magnetic reconnection: Parametric variation of the “Newton Challenge”
Authors: Huba J. D.
Published: June 2006

A parametric study of forced magnetic reconnection using a 2D Hall magnetohydrodynamic (MHD) code based on the “Newton Challenge” is presented. The “Newton Challenge” defined a magnetic reconnection problem in which reconnection was initiated by a spatially and temporally dependent inflow velocity on the upstream boundary. In this study the magnitude and time dependence of the inflow velocity are varied, as well as the length of the system and the boundary conditions. The general conclusion is that reconnection occurs sooner and faster for stronger impulsive drives (e.g., larger inflow velocities and longer time scales). The results are fairly insensitive to system length. Finally, the Hall MHD results are compared to results from a particle-in-cell simulation study.
Cardiac glycosides provide neuroprotection against ischemic stroke: Discovery by a brain slice-based compound screening platform
Authors: Wang James K. T. , Portbury Stuart , Thomas Mary Beth , Barney Shawn , Ricca Daniel J. , Morris Dexter L. , Warner David S. , Lo Donald C.
Published: June 2006

We report here the results of a chemical genetic screen using small molecules with known pharmacologies coupled with a cortical brain slice-based model for ischemic stroke. We identified a small-molecule compound not previously appreciated to have neuroprotective action in ischemic stroke, the cardiac glycoside neriifolin, and demonstrated that its properties in the brain slice assay included delayed therapeutic potential exceeding 6 h. Neriifolin is structurally related to the digitalis class of cardiac glycosides, and its putative target is the Na
+
/K
+
-ATPase. Other cardiac glycoside compounds tested also showed neuroprotective activity, although with lower apparent potencies. In subsequent whole-animal studies, we found that neriifolin provided significant neuroprotection in a neonatal model of hypoxia/ischemia and in a middle cerebral artery occlusion model of transient focal ischemia. The neuroprotective potential of Na
+
/K
+
-ATPase is of particular interest because of its known “druggability”; indeed, Food and Drug Administration-approved, small-molecule compounds such as digitoxin and digoxin have been in clinical usage for congestive heart failure and arrhythmias for several decades. Thus, an existing cardiac glycoside or closely related compound could provide an accelerated path toward clinical trial testing for ischemic stroke. Our findings underscore the important role that hypothesis-neutral, high-content, tissue-based screens can play in the identification of new candidate drugs and drug targets for the treatment of diseases for which validated therapeutic pathways are not currently available.
Nutrient additions to a tropical rain forest drive substantial soil carbon dioxide losses to the atmosphere
Authors: Cleveland Cory C. , Townsend Alan R.
Published: June 2006

Terrestrial biosphere–atmosphere carbon dioxide (CO
2
) exchange is dominated by tropical forests, where photosynthetic carbon (C) uptake is thought to be phosphorus (P)-limited. In P-poor tropical forests, P may also limit organic matter decomposition and soil C losses. We conducted a field-fertilization experiment to show that P fertilization stimulates soil respiration in a lowland tropical rain forest in Costa Rica. In the early wet season, when soluble organic matter inputs to soil are high, P fertilization drove large increases in soil respiration. Although the P-stimulated increase in soil respiration was largely confined to the dry-to-wet season transition, the seasonal increase was sufficient to drive an 18% annual increase in CO
2
efflux from the P-fertilized plots. Nitrogen (N) fertilization caused similar responses, and the net increases in soil respiration in response to the additions of N and P approached annual soil C fluxes in mid-latitude forests. Human activities are altering natural patterns of tropical soil N and P availability by land conversion and enhanced atmospheric deposition. Although our data suggest that the mechanisms driving the observed respiratory responses to increased N and P may be different, the large CO
2
losses stimulated by N and P fertilization suggest that knowledge of such patterns and their effects on soil CO
2
efflux is critical for understanding the role of tropical forests in a rapidly changing global C cycle.
Attentional modulation of sensorimotor processes in the absence of perceptual awareness
Authors: Sumner Petroc , Tsai Pei-Chun , Yu Kenny , Nachev Parashkev
Published: June 2006

Attention modulates visual perception and is generally considered inextricably linked with conscious awareness: we become aware of stimuli as we attend to them, and we attend to stimuli as we become aware of them. Recent evidence suggests that attention can also modulate the effects of stimuli that remain invisible, and a natural explanation is that attention enhances weak perceptual representations, bringing them closer to conscious threshold even if they do not reach that threshold. However, there is also the possibility that attention may modulate neural processes that are entirely separate from those supporting conscious perception: sensorimotor mechanisms that do not create awareness however much they are enhanced. Here we provide evidence in support of this second hypothesis by showing that attentional cueing can modulate the behavioral response to invisible stimuli in a way that is distinct from enhancing their visibility. We used a masked-prime paradigm that produces a negative or positive compatibility effect depending on the perceptual strength (duration or brightness) of the prime. We found that attention enhanced the effect of both visible and invisible primes and also increased the likelihood of detecting the prime (i.e., boosted perceptual strength). Crucially, the pattern of attentional influence on priming could not be explained by attentional modulation of the prime’s perceptual strength but was predicted by a direct attentional influence on the nonconscious priming process itself. Therefore, in addition to regulating what we perceive, attention seems to influence our behavior through sensorimotor processes that are not involved in conscious awareness.
Identification of aHoxc8-regulated transcriptional network in mouse embryo fibroblast cells
Authors: Lei Haiyan , Juan Aster H. , Kim Moo-Sang , Ruddle Frank H.
Published: June 2006

The transcription factor,Hoxc8, is a member of the homeobox gene family that is vital for growth and differentiation. Previously, we identified 34 genes whose expression levels were changed at least 2-fold by forced expression ofHoxc8in C57BL/6J mouse embryo fibroblast cells using a mouse 16,463-gene oligonucleotide microarray. In the present study, we used the combined power of microarray profiling, global Hoxc8 DNA-binding site analysis, and high-throughput chromatin immunoprecipitation assays to identify direct and biologically relevant targets ofHoxc8 in vivo. Here we show that 19 of the 34 responsive genes contain Hoxc8 consensus DNA-binding sequence(s) in their regulatory regions. Chromatin immunoprecipitation analysis indicated that Hoxc8-DNA interaction was detected in five of the 19 candidate genes. All of these five target genes have been implicated in oncogenesis, cell adhesion, proliferation, and apoptosis. Overall, the genes described here should aid in the understanding of global regulatory networks ofHoxgenes and to provide valuable insight into the molecular basis ofHoxc8in development and carcinogenesis.
Spatial differences in breeding success in the pied avocet Recurvirostra avosetta: effects of habitat on hatching success and chick survival
Authors: Lengyel Szabolcs
Published: June 2006

I studied the breeding biology of pied avocets Recurvirostra avosetta in natural habitats (alkaline lakes), and in semi‐natural sites (dry fishpond, reconstructed wetlands) in Hungary to relate habitat selection patterns to spatial and temporal variation in breeding success. Colonies were initiated earlier in semi‐natural sites than in natural habitats, and earlier on islands than on the mainland. Hatching success was higher on islands than on the mainland, in semi‐natural sites than in natural habitats, in colonies of at least 15 pairs than in smaller colonies, and for nests initiated earlier than later within a colony. Fledging success was higher in the wet years (1999–2000) than in the dry year (1998), decreased strongly by season in both habitats and increased with average daily temperature in the first week post‐hatch in 1999–2000. Most pairs hatching young in semi‐natural sites attempted to lead their chicks to feeding areas in natural habitats, whereas no such movement occurred in the opposite direction. Chick mortality due to predation was high during brood movements and only 23% of the pairs moving their young produced fledglings, compared to 43% for pairs remaining in semi‐natural sites and 68% for pairs hatching and rearing young in natural habitats (total n=192 broods). These results suggest that semi‐natural sites were more suitable for nesting, whereas natural habitats were more suitable for chick‐rearing. The opposing trends in habitat‐related breeding success between nesting and chick‐rearing suggest sub‐optimal habitat selection by Pied Avocets due to an incorrect assessment of the potential for successful reproduction of semi‐natural sites, which may thus function as ecological traps.
Review article: renal circulatory changes in cirrhosis‐‐pathogenesis and therapeutic prospects.
Authors: Forrest EH , Jalan R , Hayes PC
Published: June 2006

Renal dysfunction in cirrhosis describes a spectrum of abnormalities which lead to the clinical manifestations of ascites, peripheral oedema and hepato‐renal failure. This article reviews the processes underlying this dysfunction with particular regard to the disturbance in the renal circulation. Renal haemodynamic changes occur early in cirrhosis prior to the development of ascites. However, as the liver disease progresses these changes become more profound and lead ultimately to severe cortical hypoperfusion. Renal blood flow and glomerular filtration rate do not appear to correlate well with the presence of ascites, and a separate defect in tubular sodium handling is likely to be present. The development of portal hypertension is a possible trigger of increased renal vascular resistance, whereas a deterioration in liver function may relate to the impaired tubular handling of sodium. The peripheral vasodilatation hypothesis seeks to relate these renal changes to the activation of vasopressor systems after the development of arteriolar vasodilatation. Correlations between systemic vascular resistance and renal blood flow have been difficult to establish. A variety of substances may mediate the renal circulatory changes. The likelihood is that the increase in systemic vasoconstrictors is compensatory, and that it is the locally active vasoactive substances, particularly those derived from the endothelium, which play a major role in the development of renal vasoconstriction. The management of ascites is fraught with complications, and the treatment of hepato‐renal syndrome inadequate. Liver transplantation is currently the only therapy which gives any hope of long‐term response and survival. Methods of improving the renal circulation by mechanically lowering portal pressure or by antagonizing locally active renal vasoconstrictors may be beneficial.
Ranitidine bismuth citrate: a novel anti‐ulcer agent with different physico‐chemical characteristics and improved biological activity to a bismuth citrate‐ranitidine admixture.
Authors: McColm AA , McLaren A , Klinkert G , Francis MR , Connolly PC , Grinham CJ , Campbell CJ , Selway S , Williamson R
Published: June 2006

BACKGROUND: Ranitidine bismuth citrate (RBC) is a new chemical entity for the treatment of peptic ulcer disease. RESULTS: RBC is freely soluble in water (more than 600 mg/mL at pH 4.6), whereas an equimolar admixture of its component molecules, bismuth citrate and ranitidine, formed an almost totally insoluble suspension. Even at very low pH values (around 2.0), the solubility of bismuth in ranitidine bismuth citrate was at least two‐fold better than in the admixture. Comparison of several physico‐chemical characteristics indicated that RBC possessed significantly different melting point properties, X‐ray powder diffraction patterns, infra‐red spectra and 13C‐NMR solid‐state spectra to the admixture. Ranitidine bismuth citrate inhibited human pepsin isoenzymes 1, 2, 3 and 5 but the admixture was inactive. RBC showed approximately two‐fold greater anti‐Helicobacter pylori activity in vitro than the admixture (geometric mean minimum inhibitory concentrations of 12.5 and 25.7 mg/L, respectively) and was more rapidly bactericidal. In a mouse model of gastric H. pylori colonization, 200 mg/kg of bismuth, given as RBC, eradicated the organism from all mice while only 10% of infections were eradicated by equivalent levels of bismuth in admixture form. CONCLUSION: It is believed that the significantly greater solubility of RBC, especially at lower pH values, is highly relevant to its better antipepsin and anti‐H. pylori action compared to the insoluble admixture of bismuth citrate and ranitidine.