bluuebunny/crossref_metadata_2025 huggingface dataset:
General methods for free-volume theory
Authors: Oversteegen S. M. , Roth R.
Published: May 2005

Free-volume theory for understanding depletion phenomena in mixtures of two species is generally derived using scaled-particle theory for those specific entities. Here we first give a general scaled-particle method for convex bodies in terms of the characteristic geometrical measures of the depletion agent, i.e., its volume, surface area, and integrated mean curvature, in mixtures with hard spheres. Second, we show that similar results can be derived from fundamental-measure theory. This different approach allows us to get a deep insight into the meaning of the various contributions to the theory from a geometrical point of view. From these two methods we arrive at a generalized “recipe” to free-volume theory. This recipe can be based on a desired equation of state for any convex shape of the depletion agents and is also valid for (polydisperse) mixtures of those. This is illustrated by mixtures of spheres with ellipsoids, spheres with several geometries as models for disklike mesogens, e.g., gibbsite, as well as depletion of spheres due to bar-shaped colloids, e.g., goethite.
A model for pore growth in anodically etched gallium phosphide
Authors: Ricci P. C. , Salis M. , Anedda A.
Published: May 2005

The electrochemical etching process of porous gallium phosphide was studied by means of the characteristic current–potential (I–V) curves. Measurements were performed in H2SO4 0.5-M aqueous solution both in the dark and by illuminating the samples with the 351-nm line of an argon laser. Raman spectroscopy was applied to investigate the surface morphology of the samples prepared under different anodizing conditions within the potentiostatic regime. Based on a few reasonable assumptions, a simple model of pore growth is proposed. The enhancing effect in current intensity due to the branching of pores and the opposite effect due to a concomitant decrease in the effective cross area available for carrier transport are accounted for to explain the main features of the recorded I–V curves.
In situ x-ray absorption spectroscopic study of the Li[Ni1∕3Co1∕3Mn1∕3]O2 cathode material
Authors: Deb Aniruddha , Bergmann Uwe , Cramer Stephen P. , Cairns Elton J.
Published: May 2005

The layered LiNi1∕3Co1∕3Mn1∕3O2 system has recently drawn considerable interest for use as a cathode material for rechargeable lithium batteries. In order to investigate the charge-compensation mechanism and structural perturbations occurring in the system during cycling, in situ x-ray absorption spectroscopy (XAS) measurements were performed utilizing a novel electrochemical in situ cell specifically designed for long term x-ray experiments. The cell was cycled at a moderate rate through a typical Li-ion battery operating voltage range (2.9–4.7 V). The electrode contained 2.025 mg of LiNi1∕3Co1∕3Mn1∕3O2 on a 25-μm Al foil and had an area of 0.79cm2. The x-ray absorption spectroscopy (XAS) measurements were performed at the Ni, Co, and the Mn edges at different states of charge (SOC) during cycling, revealing details about the response of the cathode to Li insertion and extraction processes. Changes of bond distance and coordination number of Ni, Co, and Mn absorbers as a function of the state of charge of the material were obtained from the extended x-ray-absorption fine structure (EXAFS) region of the spectra. The x-ray absorption near-edge structure (XANES) region was studied in order to characterize the oxidation states of the 3d transition metals during cycling (Li extraction/insertion). We found that oxidation states of transition metals in LiNi1∕3Co1∕3Mn1∕3O2 are Ni2+, Co3+, and Mn4+, whereas during charging Ni2+ is oxidized to Ni4+ through an intermediate stage of Ni3+,Co3+ is oxidized almost to Co4+ and, utilizing Faraday’s calculation and XAS results, the Co was found to be at Co3.92+ at the end of the charge, while Mn was found to be electrochemically inactive and remains as Mn4+. The EXAFS data that were collected continuously during cycling revealed details about the response of the cathode to Li insertion and extraction. These measurements on the LiNi1∕3Co1∕3Mn1∕3O2 cathode confirmed that the material retains its symmetry and good structural short-range order leading to superior cycling.
Integrated tungsten nanofiber field emission cathodes selectively grown by nanoscale electron beam-induced deposition
Authors: Yang X. , Simpson M. L. , Randolph S. J. , Rack P. D. , Baylor L. R. , Cui H. , Gardner W. L.
Published: May 2005

We report on the fabrication and operation of integrated field emission cathodes containing single tungsten (W) nanofibers selectively grown by nanoscale electron beam induced deposition (EBID). A nonorganometallic precursor, WF6, was used to deposit metallic W fibers. Vacuum electrical testing reveals electrons were successfully extracted from the W nanofiber tip and were collected by a phosphor anode. Direct current versus voltage (I–V) curves exhibited Fowler–Nordheim behavior, indicating the occurrence of cold field emission. Electrical testing of these devices indicated that EBID direct-write is a promising technique for direct production or repair of field emission cathodes.
Alloy destabilization by dislocations
Authors: Léonard François , Haataja Mikko
Published: May 2005

Thermodynamic phase diagrams of alloys are usually computed or experimentally determined under the assumption of perfect crystallinity of the material. Here, we show that dislocations can change the phase stability of alloys and increase the size of the miscibility gap. This dislocation-induced destabilization of the alloy originates from an interaction between the elastic fields of the dislocations and those due to composition variations. We predict that the characteristic time scale for the growth of compositional fluctuations depends inversely on the dislocation mobility.
Green emission from Er-doped GaN powder
Authors: Wu Huaqiang , Poitras Carl B. , Lipson Michal , Spencer Michael G. , Hunting Janet , DiSalvo Francis J.
Published: May 2005

Green light emission has been directly obtained from Er-doped GaN powder. Er is incorporated into GaN powder through the reaction between molten (Ga+Er) and NH3 at 950–1050°C using Bi as a wetting agent. Photoexcitation with an Ar laser results in strong green emissions from two narrow lines at 537 and 558nm, which are identified as Er transitions from the H11∕22 and S3∕24 levels to the I15∕24 ground state. Microprobe analysis reveals that Er atoms are distributed across powder particles.
Suppression of left-handed properties in disordered metamaterials
Authors: Zharov Alexander A. , Shadrivov Ilya V. , Kivshar Yuri S.
Published: May 2005

We show that disorder can modify dramatically the effective magnetic response of a composite metamaterial including its specific property of negative refraction. We demonstrate that a relatively weak disorder in the parameters of the split-ring resonators can reduce and even completely eliminate the finite frequency range where the metamaterial possesses the left-handed properties. This effect is expected to be crucially important for a design of metamaterials operating in the terahertz or visible region of the frequency spectrum.
Determination of the polarization discontinuity at the AlGaN∕GaN interface by electroreflectance spectroscopy
Authors: Winzer A. T. , Goldhahn R. , Gobsch G. , Link A. , Eickhoff M. , Rossow U. , Hangleiter A.
Published: May 2005

The total polarization discontinuity ΔP at an Al0.31Ga0.69N∕GaN heterojunction has been determined by electroreflectance spectroscopy. This technique is based on the analysis of the Franz–Keldysh oscillations observed above the AlGaN band gap, yielding the barrier electric field strength as a function of the applied bias voltage. The threshold field strength, where the two-dimensional electron gas (2DEG) is depleted, corresponds to a ΔP of 1.1×1013e∕cm2 which is only 85% of the theoretical prediction. Applying the same optical method, the 2DEG density at the heterointerface can be accurately determined, as proven by comparison to Shubnikov–de Haas measurements.
Diversity of the magnetic coupling behaviors in the CoFe2∕CoFe2O4 system
Authors: Viart N. , Hassan R. Sayed , Mény C. , Panissod P. , Ulhaq-Bouillet C. , Loison J. L. , Versini G. , Huber F. , Pourroy G.
Published: May 2005

The CoFe2∕CoFe2O4 system has been considered for use as hard electrodes in spin valve devices. In this letter, we focus on the nature and intensity of the magnetic exchange coupling between the two phases. CoFe2∕CoFe2O4 and CoFe2O4∕CoFe2 bilayers were fabricated by pulsed laser deposition from a metallic CoFe2 alloy target in a vacuum and in an O2:N2 oxidizing atmosphere for the metallic and oxide layers, respectively. Depending upon the elaboration conditions, three different coupling behaviors have been observed: Ferromagnetic, biquadratic, and antiferromagnetic. The minor loop shift and the apparent coercive field of the metal observed in the first two cases are of several hundreds of Oe for a metal thickness of 10nm. Those very large loop shifts and coercive fields confirm the potential usefulness of this system in terms of applications.
Permeation and gating in proteins: Kinetic Monte Carlo reaction path following
Authors: Miloshevsky Gennady V. , Jordan Peter C.
Published: May 2005

We present a new Monte Carlo technique, kinetic Monte Carlo reaction path following (kMCRPF), for the computer simulation of permeation and large-scale gating transitions in protein channels. It combines ideas from Metropolis Monte Carlo (MMC) and kinetic Monte Carlo (kMC) algorithms, and is particularly suitable when a reaction coordinate is well defined. Evolution of transition proceeds on the reaction coordinate by small jumps (kMC technique) toward the nearest lowest-energy uphill or downhill states, with the jumps thermally activated (constrained MMC). This approach permits navigation among potential minima on an energy surface, finding the minimum-energy paths and determining their associated free-energy profiles. The methodological and algorithmic strategies underlying the kMCRPF method are described. We have tested it using an analytical model and applied it to study permeation through the curvilinear ClC chloride and aquaporin pores and to gating in the gramicidin A channel. These studies of permeation and gating in real proteins provide extensive procedural tests of the method.
Phase diagram of thin-film relaxor PbMg1∕3Nb2∕3O3
Authors: Tyunina M. , Levoska J.
Published: May 2005

Epitaxial heterostructures of pure perovskite relaxor ferroelectric PbMg1∕3Nb2∕3O3 thin films were grown by pulsed laser ablation varying the temperature of deposition. Dielectric response of the films was studied as a function of frequency, temperature, amplitude of ac electric field, and magnitude of dc electric field. The temperatures of dielectric maxima and the freezing temperatures determined in different regimes were analyzed with respect to the microstructure of the films. Different nonmonotonic tendencies in the behavior of the characteristic temperatures were found. The shift of the electric-field–temperature phase diagram of PbMg1∕3Nb2∕3O3 involving the sequence of transformations between paraelectriclike, glasslike, and ferroelectriclike states was suggested to be responsible for this. The shift of the phase diagram was found to be a monotonic function of the in-plane strain and it was ascribed to the internal electric field.
Four-domain twisted vertically aligned liquid crystal pixels using microrubbing
Authors: Varghese Soney , Crawford Gregory P. , Bastiaansen Cees W. M. , de Boer Dick K. G. , Broer Dirk J.
Published: May 2005

Microrubbing (μ-rubbing) technique is used to create four-domain twisted vertically aligned liquid crystal pixels for wide viewing angle displays. A metallic sphere of 1 mm diameter is used to locally rub a homeotropic polyimide surface to create a four-domain pixel. We use μ-rubbing to accurately control the surface pretilt angle of the liquid crystal from the normal, which directs the liquid crystal molecules to respective direction on applying a voltage. We report on twisted vertically aligned configurations with symmetric isointensity curves, high contrast, and attractive electro-optic performance. The optical simulations of the liquid crystal director orientation, viewing angle characteristics and switching behavior of the four-domain are also presented.
Atomistic mechanisms of strain relaxation due to ductile void growth in ultrathin films of face-centered-cubic metals
Authors: Gungor M. Rauf , Maroudas Dimitrios
Published: May 2005

A comprehensive computational analysis is reported of the atomistic mechanisms of strain relaxation and failure in free-standing Cu thin films under applied biaxial tensile strain for strain levels up to 6%. The analysis focuses on nanometer-scale-thick films with a preexisting void extending across the film thickness and the film plane oriented normal to the [111] crystallographic direction. Our computational study is based on isothermal-isostrain large-scale molecular-dynamics simulations within an embedded-atom-method parametrization for Cu. Our analysis has revealed various regimes in the film’s mechanical response as the applied strain level increases. Within the considered strain range, after an elastic response at a low strain (<2%), void growth is the major strain relaxation mechanism mediated by the emission of perfect screw dislocation pairs from the void surface and subsequent dislocation propagation; as a result, a plastic zone forms around the void. Plastic deformation is accompanied by the glide motion of the dislocations emitted from the void surface, void surface morphological transitions, formation of a step pattern on the film’s surfaces, dislocation jogging, vacancy generation due to gliding jogged dislocations, dislocation-vacancy interactions, vacancy pipe diffusion along dislocation cores, as well as dislocation–dislocation interactions. The increase in film surface roughness with increasing strain eventually leads to nucleation and propagation from the film surfaces of threading dislocation loops, which ultimately break up when they reach the opposite free surface of the thin film.
Thermal decomposition mechanisms of hafnium and zirconium silicates at the atomic scale
Authors: Monaghan S. , Greer J. C. , Elliott S. D.
Published: May 2005

The hafnium and zirconium silicates, (MO2)x(SiO2)1−x, with M=Hf∕Zr, are being considered as high-k gate dielectrics for field-effect transistors as a compromise between high permittivity and thermal stability during processing. Using atomic-scale models of silicates derived from hafnon/zircon, stability before and after simulated thermal annealing is calculated within a density-functional approach. These silicates are found to be thermodynamically unstable with respect to decomposition into SiO2 and MO2 (M=Hf∕Zr). Segregation mechanisms on the atomic scale are studied leading to an insight as to an why SiO2-rich mixtures undergo spinodal decomposition and why, by contrast, MO2-rich phases are metastable, decomposing below typical process temperatures.
Experimental observation of near-heteroclinic cycles in the von Kármán swirling flow
Authors: Nore C. , Moisy F. , Quartier L.
Published: May 2005

The bifurcations and the nonlinear dynamics of the von Kármán swirling flow between exactly counterrotating disks in a stationary cylinder are experimentally investigated by means of visualizations and particle image velocimetry. A regime diagram of the different flow states is determined as a function of the height-to-radius ratio Γ and the Reynolds number Re based on disks rotation speed and cylinder radius. Among the steady and time-dependent states found in the experiment, robust near-heteroclinic cycles, which link two unstable states of azimuthal wavenumber m=2, are observed and characterized in detail for Γ=2. These are compared with the numerical findings of Nore et al. [“The 1:2 mode interaction in exactly counter-rotating von Kármán swirling flow,” J. Fluid Mech 477, 51 (2003)], with a particular emphasis on the influence of the imperfection and the noise of the experimental setup.
Imaging and analysis of subsurface Cu interconnects by detecting backscattered electrons in the scanning electron microscope
Authors: Gignac L. M. , Kawasaki M. , Boettcher S. H. , Wells O. C.
Published: May 2005

Cu – Si O 2 – Si N x interconnects that were located 0.65–2.7-μm below the surface of silicon-integrated circuits were imaged in a scanning electron microscope and a transmission electron microscope with a scanning attachment by detecting backscattered electrons (BSEs) with an incident electron-beam energy (Eo) in the range of 30–400keV. BSE images could be used to detect voids in subsurface Cu interconnects, even in regions covered with upper level Cu lines or vias. As Eo was increased from 30to400keV, structures could be seen as a result of atomic number (Z) contrast farther below the surface while structures closer to the surface had reduced Z contrast. The subsurface beam diameter was measured from BSE images as a function of Eo and depth below the surface. For all Eo, the subsurface beam diameter initially rapidly increased with SiO2 overlayer thickness but, for 150keV, a leveling off in the beam spread was seen for depths >1.7μm. Beam broadening affected whether the TaN∕Ta liners that surrounded the Cu conductors could be seen at the edges of the lines; this contrast was observed only when the subsurface beam diameter was ⩽1.5× the liner thickness. The BSE information depth for imaging 0.2-μm-sized voids in subsurface Cu–SiO2–SiNx interconnect structures at 30 and 150keV was estimated to be 0.65 and 3μm, respectively.
Extreme ultraviolet single-crystal diamond detectors by chemical vapor deposition
Authors: Balducci A. , Marinelli Marco , Milani E. , Morgada M. E. , Tucciarone A. , Verona-Rinati G. , Angelone M. , Pillon M.
Published: May 2005

High-quality single-crystal diamond films, homoepitaxially grown by microwave chemical vapor deposition, have been used to produce diamond-based photodetectors. Such devices were tested over a very wide spectral range, from the extreme ultraviolet (UV) (20 nm) up to the near IR region (2400 nm). An optical parametric oscillator tunable laser was used to investigate the 210–2400 nm spectral range in pulse mode. In this region, the spectral response shows a UV to visible contrast of about 6 orders of magnitude. A time response shorter than 5 ns, i.e., the laser pulse duration, was observed. By integrating the pulse shape, a minor slow component was evidenced, which can be explained in terms of trapping–detrapping effects. Extreme UV gas sources and a toroidal grating vacuum monochromator were used to measure the device response down to 20 nm in continuous mode. In particular, the extreme UV He spectrum was measured and the He II m, 30.4 nmand He I 58.4 nm emission lines were clearly detected. The measured time response of 0.2 s is totally due to the instrumental readout time constants. In both experimental setups an extremely good stability and reproducibility of the device response were obtained, whereas no persistent photoconductivity nor undesirable pumping effects were observed.
Long-wave theory of bounded two-layer films with a free liquid–liquid interface: Short- and long-time evolution
Authors: Merkt D. , Pototsky A. , Bestehorn M. , Thiele U.
Published: May 2005

We consider two layers of immiscible liquids confined between an upper and a lower rigid plate. The dynamics of the free liquid–liquid interface is described for arbitrary amplitudes by an evolution equation derived from the basic hydrodynamic equations using long-wave approximation. After giving the evolution equation in a general way, we focus on interface instabilities driven by gravity, thermocapillary and electrostatic fields. First, we study the linear stability discussing especially the conditions for destabilizing the system by heating from above or below. Second, we use a variational formulation of the evolution equation based on an energy functional to predict metastable states and the long-time pattern morphology (holes, drops or maze structures). Finally, fully nonlinear three-dimensional numerical integrations are performed to study the short- and long-time evolution of the evolving patterns. Different coarsening modes are discussed and long-time scaling exponents are extracted.
Synthesis and ethanol sensing properties of ZnSnO3 nanowires
Authors: Xue X. Y. , Chen Y. J. , Wang Y. G. , Wang T. H.
Published: May 2005

ZnSnO 3 nanowires in mass production have been synthesized via thermal evaporation of ZnO, SnO, and graphite mixture powders. X-ray powder diffraction results show that these nanowires are of ZnSnO3 crystal structure. These nanowires have diameters ranging from 20 to 90 nm and lengths of several ten micrometers. Gas sensors fabricated from these ZnSnO3 nanowires show a very high sensitivity to ethanol gas and the sensitivity is up to about 42 against 500 ppm ethanol gas at the operating temperature of 300 °C. Both the response and the recovery time are about 1 s. Mass production and good sensitivities of the nanowires indicate their potential applications in sensor technology at the industry level.
Deconvoluting the influences of heat and plastic deformation on internal strains generated by friction stir processing
Authors: Woo Wanchuck , Choo Hahn , Brown Donald W. , Bourke Mark A. M. , Feng Zhili , David Stan A. , Hubbard Camden R. , Liaw Peter K.
Published: May 2005

Internal-strain profiles in friction-stir processed aluminum-alloy plates were investigated using neutron diffraction. Three different specimens were prepared with a purpose of separating the effects of frictional heating and severe plastic deformation on the internal-strain distribution: (Case 1) a plate processed with both stirring pin and tool shoulder, (Case 2) a plate processed only with the tool shoulder, and (Case 3) a plate processed only with the pin. The comparison between Cases 1 and 2 shows distinctly different strain profiles revealing deconvoluted effects of the different sources (i.e., heat, deformation, or the combination) on the internal strains generated during the friction-stir processing.
Intracellular transport and pathways of carbon flow in plants with crassulacean acid metabolism
Authors: Holtum Joseph A. M. , Smith J. Andrew C. , Neuhaus H. Ekkehard
Published: May 2005

The massive daily reciprocal transfer of carbon between acids and carbohydrates that is unique to crassulacean acid metabolism (CAM) involves extensive and regulated transport of metabolites between chloroplasts, vacuoles, the cytosol and mitochondria. In this review of the CAM pathways of carbon flow and intracellular transport, we highlight what is known and what has been postulated. For three of the four CAM pathway variants currently known (malic enzyme- or PEP carboxykinase-type decarboxylase, and starch- or soluble sugar-type carbohydrate storage), the mechanisms of intracellular transport are still hypothetical and have yet to be demonstrated experimentally. Even in malic enzyme starch-storing species such as Kalanchoë daigremontiana Hamet et Perr. and Mesembryanthemum crystallinum L., the best-described variants of plants with the second-most common mode of photosynthetic carbon metabolism known, no tonoplast or mitochondrial transporter has been functionally described at a molecular level.
Functional leaf anatomy of plants with crassulacean acid metabolism
Authors: Nelson Elizabeth A. , Sage Tammy L. , Sage Rowan F.
Published: May 2005

Crassulacean acid metabolism (CAM) has evolved independently on dozens of occasions and is now found in over 7% of plant species. In this study, the leaf structure of a phylogenetically diverse assemblage of 18 CAM plants was compared with six C3 plants and four C4 plants to assess whether consistent anatomical patterns that may reflect functional constraints are present. CAM plants exhibited increased cell size and increased leaf and mesophyll thickness relative to C3 and C4 species. CAM species also exhibited reduced intercellular air space (IAS) and reduced length of mesophyll surface exposed to IAS per unit area (Lmes / area). The low volume of IAS and low exposure of mesophyll surface to IAS likely increases internal resistance to CO2 in CAM tissues. While this diffusional barrier may limit uptake of CO2 during Phases II and IV, carbon economy could be enhanced through the reduced loss of internal CO2 during all four phases of CAM.
Research note: Large gene family of phosphoenolpyruvate carboxylase in the crassulacean acid metabolism plant Kalanchoe pinnata (Crassulaceae) characterised by partial cDNA sequence analysis
Authors: Gehrig Hans H. , Wood Joshua A. , Cushman Mary Ann , Virgo Aurelio , Cushman John C. , Winter Klaus
Published: May 2005

Clones coding for a 1100-bp cDNA sequence of phosphoenolpyruvate carboxylase (PEPC) of the constitutive crassulacean acid metabolism (CAM) plant Kalanchoe pinnata (Lam.) Pers., were isolated by reverse transcription-polymerase chain reaction (RT–PCR) and characterised by restriction fragment length polymorphism analysis and DNA sequencing. Seven distinct PEPC isogenes were recovered, four in leaves and three in roots (EMBL accession numbers: AJ344052–AJ344058). Sequence similarity comparisons and distance neighbour-joining calculations separate the seven PEPC isoforms into two clades, one of which contains the three PEPCs found in roots. The second clade contains the four isoforms found in leaves and is divided into two branches, one of which contains two PEPCs most similar with described previously CAM isoforms. Of these two isoforms, however, only one exhibited abundant expression in CAM-performing leaves, but not in very young leaves, which do not exhibit CAM, suggesting this isoform encodes a CAM-specific PEPC. Protein sequence calculations suggest that all isogenes are likely derived from a common ancestor gene, presumably by serial gene duplication events. To our knowledge, this is the most comprehensive identification of a PEPC gene family from a CAM plant, and the greatest number of PEPC isogenes reported for any vascular plant to date.
Temporal dynamics of water repellency and soil moisture in eucalypt plantations, Portugal
Authors: Leighton-Boyce Gemma , Doerr Stefan H. , Shakesby Richard A. , Walsh Rory P. D. , Ferreira António J. D. , Boulet Anne-Karine , Coelho Celeste O. A.
Published: May 2005

This paper investigates water repellency and soil moisture under 4 different Eucalyptus globulus plantations in Portugal. On 8 occasions over a 16-month period, measurements were made at 3 depths (surface, 0.10 and 0.20 m) at 60 points on four 10 by 18 m grids. The main results are: (i) at all sites and depths, spatial frequency of repellency (defined as percentage of repellent grid points) followed a moisture-related seasonal cycle, its amplitude being greatest for the longest established site, where surface repellency was contiguous in dry late-summer conditions, but was entirely absent after wet winter conditions; (ii) at a few points at 2 sites, repellency persisted during winter; (iii) repellency severity was dichotomously distributed regardless of season (i.e. soils were generally either wettable or highly repellent); and (iv) at the longest established site, when soil moisture was <14% soils were repellent, and when soil moisture was >27% soils were wettable. This may either support the existence of a ‘transition zone’, or be an artefact of the different scales of repellency and soil moisture assessments. Reasons for the observed changes in repellency and their relationship with soil moisture and antecedent rainfall are explored and soil hydrological implications discussed.
The impact of soil water repellency on soil hydrological and erosional processes under Eucalyptus and evergreen Quercus forests in the Western Mediterranean
Authors: Coelho C. O. A. , Laouina A. , Regaya K. , Ferreira A. J. D. , Carvalho T. M. M. , Chaker M. , Naafa R. , Naciri R. , Boulet A. K. , Keizer J. J.
Published: May 2005

Forest areas of the Mediterranean regions of Portugal, Morocco, and Tunisia are suffering major land use changes, with the replacement of traditional evergreen Quercus species (i.e. Quercus suber and Quercus ilex) by fast-growing Eucalyptus species.
Since Eucalyptus species are amongst those with a higher impact on soil water repellency, this study examined the effect of the replacement on soil properties, water repellency, and on soil hydrological processes and erosion rates. Measurements were performed in areas that correspond to the climatic distribution of evergreen Quercus suber: at Mação and Portel in Portugal; Ben Slimane in Morocco; and Cap Bon, Sousse, and Ain Snoussi in Tunisia.
Soil superficial characteristics, including vegetation and litter cover, organic matter content, soil compaction and shear strength, and water repellency were measured for evergreen oak and Eucalyptus stands and related to soil erosion rates and soil hydrological processes.
The data are based on the spatial distribution of properties assessed through the use of intensive spatial sampling and on rainfall simulations to address soil hydrological and erosional processes. The results show very different wetting patterns for some of the Eucalyptus stands during dry and moist periods, as a result of strong hydrophobic characteristics following dry spells. Nevertheless, the Eucalyptus stands in semi-arid climate show no sign of water repellency, which contradicts the theory that water repellency is purely a result of dry conditions. The experiments show no significant increases on overland flow amounts and erosion rates as direct result of soil water repellence (hydrophobicity) characteristics.
Water repellency under natural conditions in sandy soils of southern Spain
Authors: Garcíía Francisco J. Moral , Dekker Louis W. , Oostindie Klaas , Ritsema Coen J.
Published: May 2005

The occurrence and consequences of fire-induced water repellency have been studied in several regions of Spain since 1989. The occurrence of water repellency formed under natural conditions, however, has only been described for a few areas in Spain since 1998. The purpose of the present study was to investigate the severity of naturally occurring water repellency in the sandy soils of the Natural Park of Doñana in southern Spain. The persistence and degree of soil water repellency were measured on field-moist and dried sandy soil samples taken beneath Pinus pinea trees. Around 50% of the field-moist soil samples taken at 0–0.10 m depths exhibited (actual) water repellency. Potential water repellency, measured after drying the samples at 60°C, showed for 68% of the samples slight to extreme water repellency. The organic matter content was found to be positively correlated with persistence and with degree of potential water repellency.
Soil water repellency under dry and wet antecedent weather conditions for selected land-cover types in the coastal zone of central Portugal
Authors: Keizer J. J. , Coelho C. O. A. , Matias M. J. S. , Domingues C. S. P. , Ferreira A. J. D.
Published: May 2005

This paper reports on the first systematic inventory of soil water repellency in Portuguese coastal dune sand areas. Since water repellency is widely associated with certain vegetation types or individual plant species, this inventory concerned arable land as well as 6 natural and semi-natural land-cover types representative for the vegetation zonation in the study area. Since water repellency further is a feature that commonly varies through time, disappearing when soils become wet, initial sampling was carried out during late summer 2000 and later repeated, at 1 of the 2 sites per land-cover type, during early spring 2001. Water repellency was principally measured in the field using the Molarity of an Ethanol Droplet (MED) test.
Under the dry summer conditions, water repellency was a widespread phenomenon at and immediately below, the soil surface and numerous significant differences in ethanol classes existed between the land-cover types. The transient nature of water repellency was confirmed by many instances of significantly lower spring than summer ethanol classes. These significant differences were in general accompanied by a significant negative correlation of the summer and spring ethanol classes with volumetric soil moisture content. The sites’ overall repellency levels under dry antecedent weather conditions were significantly correlated with their overall levels of soil organic matter.
The role of tree stem proximity in the spatial variability of soil water repellency in a eucalypt plantation in coastal Portugal
Authors: Keizer J. J. , Ferreira A. J. D. , Coelho C. O. A. , Doerr S. H. , Malvar M. C. , Domingues C. S. P. , Perez I. M. B. , Ruiz C. , Ferrari K.
Published: May 2005

Certain organic compounds derived from living organisms or their decaying parts are generally accepted to induce soil water repellency. Water repellency may therefore be expected to increase with proximity to organisms releasing hydrophobic compounds. This hypothesis is tested here for Eucalyptus globulus trees, since eucalypt species are frequently associated with elevated repellency levels. In a young, first-rotation plantation on coastal dune sands in central Portugal, repeat measurements of water repellency using the ‘Molarity of an Ethanol Droplet’ (MED) test were carried out in situ between April 2001 and May 2002. On 25 dates, repellency was measured at initially 2 and later 3 distances on 2 sides of 8–11 randomly selected trees. On 15 occasions, additional repellency measurements were performed within small grids aside 3 of the selected trees.
The postulated decrease in topsoil water repellency with increased distance from eucalypt tree stems was found to apply on several individual measurement dates, as well as, more unexpectedly since repellency usually is a transient phenomenon, for the study period as a whole. The results confirm the general association of eucalypt trees with water repellency, and indicate that tree stem proximity is an important but not sufficient factor to explain repellency distribution in topsoil.
Spatial and temporal variability of soil water repellency of Amazonian pastures
Authors: Johnson Mark S. , Lehmann Johannes , Steenhuis Tammo S. , Vargem de Oliveira Luciélio , Fernandes Erick C. M.
Published: May 2005

Fire is commonly used to establish and maintain pastures in the Amazon. Fire is also known to induce soil water repellency but few published data exist for the humid tropics. The objectives of this study were to characterise the intensity and spatial variability of water repellency on previously burned pasture soils in the Amazon, and its effect on the nutrient status of the forage grass Brachiaria brizantha (Hochst.) Stapf. Surface soils of pastures and forests in north-western Mato Grosso, Brazil, were found to exhibit soil water repellency using MED and WDPT tests. Soil water repellency was found only within 0–0.01 m of the mineral soil surface, with soil below 0.01 m found to be hydrophilic in all cases.
Spatial variability of repellency was high for both pasture and forest soils. For pasture soils, soil water repellency was strongest on recently burned pastures, which exhibited some extremely high values (MED > 8 m). Repellency decreased rapidly with time following burning. Increasing soil water repellency was associated with decreasing N: P ratios of B. brizantha above-ground biomass (r2 = 0.66, P = 0.004). These findings indicate that soil water repellency and pasture productivity are inversely related. Since pasture abandonment fuels continued deforestation, disrupting the processes causing pasture degradation may lead to more sustainable land use in the Amazon.
Exponential increase of publications related to soil water repellency
Authors: Dekker Louis W. , Oostindie Klaas , Ritsema Coen J.
Published: May 2005

Soil water repellency is much more wide-spread than formerly thought. During the last decades, it has been a topic of study for soil scientists and hydrologists in at least 21 States of the USA, in Canada, Australia, New Zealand, Mexico, Colombia, Chile, Congo, Nepal, India, Hong Kong, Taiwan, China, Ecuador, Venezuela, Brazil, Mali, Japan, Israel, Turkey, Egypt, South Africa, Germany, The Netherlands, Spain, Portugal, United Kingdom, Denmark, Sweden, Finland, Poland, Slovakia, Russia, France, Italy, and Greece. Although, water repellent soils already have been indicated at the end of the nineteenth century, they have been discovered and studied in most countries in the last decades. Water repellency is most common in sandy soils with grass cover and in nature reserves, but has also been observed in loam, heavy clay, peat, and volcanic ash soils. From 1940 to 1970 research was focussed on identifying vegetation types responsible for inducing water repellency and on developing techniques to quantify the degree of water repellency. Of special interest has been the effects of wildfire on the development of soil water repellency and its consequences for soil erosion. Due to increasing concern over the threat to surface and groundwater posed by the use of agrichemicals and organic fertilisers, studies on water repellent soils have also been focused on its typical flow behavior with runoff and the existence of preferential flow paths. Since the end of the 1950s, wetting agents and clay amendments have been studied to ameliorate water repellent soils. Since 1883, more than 1200 articles related to soil water repellency have been published in journals, reports, and theses. An exponential increase in number of publications started in 1960, resulting in an average of 200 publications per 5 years.
Electrostatic mechanism of nucleosomal array folding revealed by computer simulation
Authors: Sun Jian , Zhang Qing , Schlick Tamar
Published: May 2005

Although numerous experiments indicate that the chromatin fiber displays salt-dependent conformations, the associated molecular mechanism remains unclear. Here, we apply an irregular Discrete Surface Charge Optimization (DiSCO) model of the nucleosome with all histone tails incorporated to describe by Monte Carlo simulations salt-dependent rearrangements of a nucleosomal array with 12 nucleosomes. The ensemble of nucleosomal array conformations display salt-dependent condensation in good agreement with hydrodynamic measurements and suggest that the array adopts highly irregular 3D zig-zag conformations at high (physiological) salt concentrations and transitions into the extended “beads-on-a-string” conformation at low salt. Energy analyses indicate that the repulsion among linker DNA leads to this extended form, whereas internucleosome attraction drives the folding at high salt. The balance between these two contributions determines the salt-dependent condensation. Importantly, the internucleosome and linker DNA–nucleosome attractions require histone tails; we find that the H3 tails, in particular, are crucial for stabilizing the moderately folded fiber at physiological monovalent salt.
A major role for proteolytic activity and proteinase-activated receptor-2 in the pathogenesis of infectious colitis
Authors: Hansen Kristina K. , Sherman Philip M. , Cellars Laurie , Andrade-Gordon Patricia , Pan Zhengying , Baruch Amos , Wallace John L. , Hollenberg Morley D. , Vergnolle Nathalie
Published: May 2005

Citrobacter rodentium
is a bacterial pathogen that causes a murine infectious colitis equivalent to enterohemorrhagic
Escherichia coli
infection in humans. Colonic luminal fluid from
C. rodentium
-infected mice, but not from sham-infected mice, contains active serine proteinases that can activate proteinase-activated receptor-2 (PAR
2
). We have identified granzyme A and murine trypsins to be present in
C. rodentium
-infected luminal fluid, as determined by mass spectrometry and Western blot analysis. Inflammatory indices (colonic mucosa macroscopic damage score, increased intestinal wall thickness, granulocyte infiltration, and bacterial translocation from the colonic lumen to peritoneal organs) were all increased in
C. rodentium
-infected mice, compared with sham-infected mice. Soybean trypsin inhibitor-treated wild-type mice and untreated PAR
2
-deficient (PAR
2
-/-
) mice (compared with their wild-type littermates) both had substantially reduced levels of
C. rodentium
-induced inflammation. These data point to an important role for both pathogen-induced host serine proteinases and PAR
2
in the setting of infectious colitis.
Climate change threats to plant diversity in Europe
Authors: Thuiller Wilfried , Lavorel Sandra , Araújo Miguel B. , Sykes Martin T. , Prentice I. Colin
Published: May 2005

Climate change has already triggered species distribution shifts in many parts of the world. Increasing impacts are expected for the future, yet few studies have aimed for a general understanding of the regional basis for species vulnerability. We projected late 21st century distributions for 1,350 European plants species under seven climate change scenarios. Application of the International Union for Conservation of Nature and Natural Resources Red List criteria to our projections shows that many European plant species could become severely threatened. More than half of the species we studied could be vulnerable or threatened by 2080. Expected species loss and turnover per pixel proved to be highly variable across scenarios (27-42% and 45-63% respectively, averaged over Europe) and across regions (2.5-86% and 17-86%, averaged over scenarios). Modeled species loss and turnover were found to depend strongly on the degree of change in just two climate variables describing temperature and moisture conditions. Despite the coarse scale of the analysis, species from mountains could be seen to be disproportionably sensitive to climate change (≈60% species loss). The boreal region was projected to lose few species, although gaining many others from immigration. The greatest changes are expected in the transition between the Mediterranean and Euro-Siberian regions. We found that risks of extinction for European plants may be large, even in moderate scenarios of climate change and despite inter-model variability.
Cardiac implications of increased arterial entry and reversible 24-h central and peripheral norepinephrine levels in melancholia
Authors: Gold Philip W. , Wong Ma-Li , Goldstein David S. , Gold Herman K. , Ronsaville Donna S. , Esler Murray , Alesci Salvatore , Masood Anwar , Licinio Julio , Geracioti Thomas D. , Perini Giulia , DeBellis Michael D. , Holmes Courtney , Vgontzas Alexandros N. , Charney Dennis S. , Chrousos George P. , McCann Samuel M. , Kling Mitchel A.
Published: May 2005

The mortality of chronic heart failure (CHF) doubles either when CHF patients are depressed or when their plasma norepinephrine (NE) level exceeds those of controls by ≈40%. We hypothesized that patients with major depression had centrally driven, sustained, stress-related, and treatment-reversible increases in plasma NE capable of increasing mortality in CHF patients with depression. We studied 23 controls and 22 medication-free patients with melancholic depression. In severely depressed patients before and after electroconvulsive therapy (ECT), we measured cerebrospinal fluid (CSF) NE, plasma NE, plasma epinephrine (EPI), and plasma cortisol hourly for 30 h. In mildly-to-moderately depressed melancholic patients, we assessed basal and stress-mediated arterial NE appearance. Severely depressed patients had significant increases in mean around-the-clock levels of CSF NE (
P
< 0.02), plasma NE (
P
< 0.02), plasma EPI (
P
< 0.02), and plasma cortisol (
P
< 0.02). CSF NE, plasma NE, and cortisol all rose together throughout the night and peaked in the morning. Each fell to control values after ECT. Mildly-to-moderately melancholic patients also had increased basal (
P
< 0.05) and stress-related (
P
< 0.03) arterial NE-appearance rates. Severely melancholic depressed, medication-free patients had around-the-clock increases in plasma NE levels capable of increasing mortality in CHF. Twenty-four-hour indices of central noradrenergic, adrenomedullary, and adrenocortical secretion were also elevated. Concurrent diurnal rhythms of these secretions could potentiate their cardiotoxicity. Even mildly-to-moderately depressed melancholic patients had clinically relevant increases in the arterial NE-appearance rate. These findings will not apply to all clinical subtypes of major depression.
Transgenic human C-reactive protein is not proatherogenic in apolipoprotein E-deficient mice
Authors: Hirschfield Gideon M. , Gallimore J. Ruth , Kahan Melvyn C. , Hutchinson Winston L. , Sabin Caroline A. , Benson G. Martin , Dhillon Amar P. , Tennent Glenys A. , Pepys Mark B.
Published: May 2005

The association between circulating concentrations of C-reactive protein (CRP) and future atherothrombotic events has provoked speculation about a possible pathogenetic role of CRP. However, we show here that transgenic expression of human CRP had no effect on development, progression, or severity of spontaneous atherosclerosis, or on morbidity or mortality, in male apolipoprotein E (apoE)-deficient C57BL/6 mice up to 56 weeks, despite deposition of human CRP and mouse complement component 3 in the plaques. Although female apoE knockouts develop atherosclerosis more rapidly than males, the human CRP transgene is under sex hormone control and is expressed at human levels only in males. We therefore studied only male mice. The concentration of mouse serum amyloid P component, an extremely sensitive systemic marker of inflammation, remained normal throughout except for transient spikes in response to fighting in a few animals, indicating that atherogenesis in this model is not associated with an acute-phase response. However, among human CRP transgenic mice, the circulating CRP concentration was higher in apoE knockouts than in wild-type controls. The higher CRP values were associated with substantially lower estradiol concentrations in the apoE-deficient animals. Human CRP transgene expression is thus up-regulated in apoE-deficient mice, apparently reflecting altered estrogen levels, despite the absence of other systemic signs of inflammation. Extrapolation to human pathology from this xenogeneic combination of human CRP with apoE deficiency-mediated mouse atherosclerosis must be guarded. Nevertheless, the present results do not suggest that human CRP is either proatherogenic or atheroprotectivein vivo.
Essential role for Gα
13
in endothelial cells during embryonic development
Authors: Ruppel Kathleen M. , Willison David , Kataoka Hiroshi , Wang Alice , Zheng Yao-Wu , Cornelissen Ivo , Yin Liya , Xu Shan Mei , Coughlin Shaun R.
Published: May 2005

Toward identifying the roles of protease-activated receptor-1 (PAR1) and other G protein-coupled receptors important for vascular development, we investigated the role of Gα
13
in endothelial cells in the mouse embryo. LacZ inserted into
G
α

13

exon 1 was highly expressed in endothelial cells at midgestation. Endothelial-specific
G
α

13

knockout embryos died at embryonic days 9.5–11.5 and resembled the PAR1 knockout. Restoration of Gα
13
expression in endothelial cells by use of a Tie2 promoter-driven Gα
13
transgene rescued development of endothelial-specific
G
α

13

knockout embryos as well the embryonic day 9.5 vascular phenotype in
G
α

13

conventional knockouts; transgene-positive
G
α

13

-/-
embryos developed for several days beyond their transgene-negative
G
α

13

-/-
littermates and then manifested a previously uncharacterized phenotype that included intracranial bleeding and exencephaly. Taken together, our results suggest a critical role for Gα
13
in endothelial cells during vascular development, place Gα
13
as a candidate mediator of PAR1 signaling in this process, and reveal roles for Gα
13
in other cell types in the mammalian embryo.