bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of numerical basis sets to hydrogen bonded systems: A density functional theory study
Authors: Benedek N. A. , Snook I. K. , Latham K. , Yarovsky I.
Published: April 2005

We have investigated and compared the ability of numerical and Gaussian-type basis sets to accurately describe the geometries and binding energies of a selection of hydrogen bonded systems that are well studied theoretically and experimentally. The numerical basis sets produced accurate results for geometric parameters but tended to overestimate binding energies. However, a comparison of the time taken to optimize phosphinic acid dimer, the largest complex considered in this study, shows that calculations using numerical basis sets offer a definitive advantage where geometry optimization of large systems is required.
Current and noise in a model of an alternating current scanning tunneling microscope molecule-metal junction
Authors: Guyon R. , Jonckheere T. , Mujica V. , Crépieux A. , Martin T.
Published: April 2005

The transport properties of a simple model for a finite level structure (a molecule or a dot) connected to metal electrodes in an alternating current scanning tunneling microscope (ac-STM) configuration is studied. The finite level structure is assumed to have strong binding properties with the metallic substrate, and the bias between the STM tip and the hybrid metal-molecule interface has both an ac and a dc component. The finite frequency current response and the zero-frequency photoassisted shot noise are computed using the Keldysh technique, and examples for a single-site molecule (a quantum dot) and for a two-site molecule are examined. The model may be useful for the interpretation of recent experiments using an ac-STM for the study of both conducting and insulating surfaces, where the third harmonic component of the current is measured. The zero-frequency photoassisted shot noise serves as a useful diagnosis for analyzing the energy level structure of the molecule. The present work motivates the need for further analysis of current fluctuations in electronic molecular transport.
Group classification of nonlinear wave equations
Authors: Lahno V. , Zhdanov R.
Published: April 2005

We perform complete group classification of the general class of quasilinear wave equations in two variables. This class may be seen as a generalization of the nonlinear d’Alembert, Liouville, sin∕sinh-Gordon and Tzitzeica equations. We derive a number of new genuinely nonlinear invariant models with high symmetry properties. In particular, we obtain four classes of nonlinear wave equations that admit five-dimensional invariance groups.
High-temperature ferromagnetism in pulsed-laser deposited epitaxial (Zn,Mn)O thin films: Effects of substrate temperature
Authors: Pradhan A. K. , Zhang Kai , Mohanty S. , Dadson J. B. , Hunter D. , Zhang Jun , Sellmyer D. J. , Roy U. N. , Cui Y. , Burger A. , Mathews S. , Joseph B. , Sekhar B. R. , Roul B. K.
Published: April 2005

We report on the observation of remarkable room-temperature ferromagnetism in epitaxial (Zn,Mn)O films grown by a pulsed-laser deposition technique using high-density targets. The optimum growth conditions were demonstrated from x-ray measurements, microstructure, Rutherford backscattering, micro-Raman, and magnetic studies. Superior ferromagnetic properties were observed in (Zn,Mn)O films grown at a substrate temperature of 500°C and with an oxygen partial pressure of 1mTorr. Ferromagnetism becomes weaker with increasing substrate temperature due to the formation of isolated Mn clusters irrespective of higher crystalline quality of the film.
High-efficiency 1.3μmInGaAs∕GaAs quantum-dot microcavity light-emitting diodes grown by metalorganic chemical vapor deposition
Authors: Todaro M. T. , Tasco V. , De Giorgi M. , Martiradonna L. , Rainò G. , De Vittorio M. , Passaseo A. , Cingolani R.
Published: April 2005

We investigate the optical properties of quantum-dot (QD) microcavity light-emitting diodes (MCLED) operating at 1.3μm at room temperature. The active medium consists of a single layer of InGaAs quantum dots, directly grown in a GaAs matrix by metalorganic chemical vapor deposition. Electrical injected QD MCLEDs were fabricated by exploiting a hybrid technology, which employs epitaxial and oxide-based mirrors. Such technology allows us to preserve the QD properties and leads to a wider optical bandwidth of the hybrid top distributed Bragg reflector with respect to the fully epitaxial mirror, resulting in photon recycling of the overall QDs spectrum, thus improving the efficiency of the device. The devices exhibit bright electroluminescence peaked at 1.29μm, with a full width at half maximum of 10 meV. The room-temperature external quantum efficiency of such devices is 0.52%, higher than that reported in the literature for QD MCLEDs operating at 1.3μm at room temperature.
Continuous-wave laser oscillation at 1.3μm in Nd:YAG proton-implanted planar waveguides
Authors: Domenech M. , Vázquez G. V. , Flores-Romero E. , Cantelar E. , Lifante G.
Published: April 2005

This work reports continuous laser oscillation around 1.3μm at room temperature in Nd:YAG planar waveguides fabricated by MeV proton implantation. The performance of the waveguide lasers fabricated with different implantation parameters has been studied in terms of the threshold pump powers and slope efficiencies. These results have been compared with those obtained in Nd:YAG waveguide lasers operating at a wavelength of 1.06μm, taking into account the different emission cross-sectional values of the F3∕24→I11∕24 and F3∕24→I13∕24 transitions.
p
-type conductivity in cubic (Ga,Mn)N thin films
Authors: Edmonds K. W. , Novikov S. V. , Sawicki M. , Campion R. P. , Staddon C. R. , Giddings A. D. , Zhao L. X. , Wang K. Y. , Dietl T. , Foxon C. T. , Gallagher B. L.
Published: April 2005

The electrical properties of p-type cubic (Ga,Mn)N films are reported. Hole concentrations above 1018cm−3 at room temperature are observed. Activated behavior is observed down to 150 K, with an acceptor ionization energy of around 45–60 meV. The dependence of hole concentration and ionization energy on Mn concentration indicates that the shallow acceptor level is not simply due to unintentional codoping. Thermopower measurements on freestanding films, capacitance–voltage profilometry, and the dependence of conductivity on thickness and growth temperature, all show that this is not due to diffusion into the substrate. We therefore associate the p-type conductivity with the presence of the Mn in the cubic GaN films.
Triangular lattice of carbon nanotube arrays for negative index of refraction and subwavelength lensing effect
Authors: Wang Y. , Wang X. , Rybczynski J. , Wang D. Z. , Kempa K. , Ren Z. F.
Published: April 2005

Self-assembly of polystyrene microspheres has been utilized in a two-step masking technique to prepare triangular lattices of catalytic nanodots at low cost. Subsequent triangular lattices of aligned carbon nanotubes on a silicon substrate are achieved by plasma-enhanced chemical vapor deposition. Nickel is used both in the nanodots and in the secondary mask. The triangular lattices of carbon nanotube arrays as two-dimensional photonic crystals show higher geometrical symmetry than the hexagonal lattices previously reported, enabling broader applications including negative index of refraction and subwavelength lensing effect.
Shallow trap states in pentacene thin films from molecular sliding
Authors: Kang Joo H. , da Silva Filho Demetrio , Bredas Jean-Luc , Zhu X.-Y.
Published: April 2005

Petacene is one of the most promising organic semiconductors for thin-film transistors. Transport measurements in the past have established the presence of shallow traps but their origins have remained a mystery. Here we show that shallow traps in vapor-deposited crystalline pentacene thin films are due to local defects resulting from the sliding of pentacene molecules along their long molecular axis, while two-dimensional crystalline packing is maintained. Electronic structural calculation confirms that these sliding defects are shallow-charge traps with energies ⩽100meV above (below) the valence band maximum (conduction band minimum).
Effects of AlOx-cap layer on the luminescence and photoconductivity of ZnO thin films
Authors: Hui K. C. , Ong H. C. , Lee P. F. , Dai J. Y.
Published: April 2005

The effects of AlOx-cap layer on the optical and photoelectrical properties of ZnO films have been studied by cathodoluminescence (CL), photoluminescence (PL), and photoconductivity (PC). Both the PL and CL show that the cap layer improves the emission characteristics of ZnO by enhancing the band-edge emission while at the same time reducing the deep-level emissions. To study the origin of improvement, depth-resolved CL has been carried out to map out the emissions at different depths. It shows that the improvement occurs primarily at the film surface, which indicates the cap layer acts as a passivation layer that suppresses the detrimental surface states. The PC measurement on the capped ZnO at room temperature shows a distinctive excitonic feature at 3.29 eV and an overall increment of photoresponse above the band gap. Therefore, our results suggest a higher sensitivity of UV detection can be achieved in ZnO simply be employing a thin AlOx-cap layer.
Localized exciton dynamics in nonpolar (112¯) InxGa1−xN multiple quantum wells grown on GaN templates prepared by lateral epitaxial overgrowth
Authors: Onuma T. , Chakraborty A. , Haskell B. A. , Keller S. , DenBaars S. P. , Speck J. S. , Nakamura S. , Mishra U. K. , Sota T. , Chichibu S. F.
Published: April 2005

Beneficial effects of the localized excitons were confirmed in nonpolar (112¯0) InxGa1−xN multiple quantum wells (QWs) grown on GaN templates prepared by lateral epitaxial overgrowth. Due to the absence of the polarization fields normal to the QW plane, the photoluminescence (PL) peak energy moderately shifted to the higher energy and the radiative lifetime did not change remarkably with the decrease in the well thickness. Similar to the case for polar InGaN QWs, time-resolved PL signals exhibited the nonexponential decay shape, which can be explained by thermalization and subsequent localization of excitons. Although the growth conditions were not fully optimized, values of the PL intensity at 300K divided by that at 8K were 25% and 17% for the peaks at 2.92 and 2.60eV, respectively.
Ab initio study of the effect of hydrogen and point defects on arsenic segregation at Si(100)∕SiO2 interfaces
Authors: Ravichandran Karthik , Windl Wolfgang
Published: April 2005

The previously suggested segregation model for arsenic at Si∕SiO2 interfaces based on a combined trapping∕pairing model [J. Dabrowski, H.-J. Müssig, V. Zavodinsky, R. Baierle, and M. J. Caldas, Phys. Rev. B 65, 245305 (2002)] requires high binding energies for interface vacancies, which our results of ∼0.2eV cannot confirm. As an alternative explanation, we present ab initio results that show that As and hydrogen bond with an energy gain of 1.5–3 eV with their minimum-energy position at the interface, which creates additional trapping sites for As segregation. The inclusion of hydrogen into the modeling might thus be able to explain the differences between the previous model and experiments.
Origin of the magnetic anisotropy induced by stress annealing in Fe-based nanocrystalline alloy
Authors: Ohnuma M. , Hono K. , Yanai T. , Nakano M. , Fukunaga H. , Yoshizawa Y.
Published: April 2005

The dependence of the structural anisotropy of Fe-Si-B-Nb-Cu alloy on the applied stress during annealing has been studied by transmission x-ray diffraction. After crystallizing under stress, the Fe-Si nanocrystals show anisotropy in the lattice spacing of the (620) planes. Their elongations are proportional to the applied stress and show a linear correlation with the magnetic anisotropy energy, Ku. These results indicate that Ku originates from a magnetoelastic effect due to an elastic elongation of the Fe-Si phase constrained by the surrounding amorphous phase.
High-transmission electrowetting light valves
Authors: Heikenfeld J. , Steckl A. J.
Published: April 2005

High-efficiency spatial light modulation has been demonstrated for transmissive electrowetting (EW) light valves (ELVs). The ELV structure consists of a competitive oil/water-on-dielectric EW cell fabricated on an optically transparent substrate. ELVs are configured as display devices by attaching a diffuse backlight powered by white converted InGaN light emitting diodes. The oil film contains ∼1wt.% nonpolar organic chromophores which absorb with near-neutral optical density across the visible light spectrum. Using the EW effect, spatial light modulation is achieved as the water layer locally displaces the oil film. The transmissivity of the cell can be modulated from ∼5% (zero bias) to >80% (∼30V). ELV switching speed depends on cell size, typically ∼10–100ms for 1 and 3mm2 cells. Additional optical enhancement can decrease the off-state ELV transmissivity to <1%.
Dielectric relaxation and electrical properties of 0.94Pb(Fe1∕2Nb1∕2)O3–0.06PbTiO3 single crystals
Authors: Wang Jie , Tang X. G. , Chan H. L. W. , Choy C. L. , Luo Haosu
Published: April 2005

Dielectric response and electrical conduction properties of 0.94Pb(Fe1∕2Nb1∕2)O3–0.06PbTiO3 single crystals grown by the Bridgman method were studied. It was found that the single crystals did not show any sign of the presence of Curie temperature between room temperature and 300 °C. However, they exhibited very high dielectric constant at a frequency lower than 100 kHz, in the order of 105. Relaxation occurred at higher frequencies with a large decrease in dielectric constant, to about 1500. The thermal activation energy for relaxation was found to be ∼0.17eV, which is quite close to that for ac conductivity. It followed that the relaxation was attributed to the carriers hopping conduction, which is related to the possible jump motion of additional 3d electron between the equivalent positions of Fe ions.
Cavity optimization of optically pumped broad-area microcavity lasers
Authors: Barbay S. , Ménesguen Y. , Sagnes I. , Kuszelewicz R.
Published: April 2005

We demonstrate a cavity optimization method for efficient optical pumping of a semiconductor microcavity. An enhanced pumping efficiency makes it possible to pump broad-area microcavities for, e.g., high-power lasers or parallel optical processing of information. This is especially important in the near-infrared where a pump not absorbed into the active material is absorbed into the substrate and converted into heat. We apply the method to optical pumping of a 80μm diameter laser with a spatially uniform pump profile. This method could also prove useful for the design of vertical external cavity surface emitting lasers.
Evidence of formation of Si–C bonds during growth of Si-doped III–V semiconductor compounds
Authors: Bettini J. , de Carvalho M. M. G
Published: April 2005

In this work, we demonstrate that Si–C bonds are formed in III–V semiconductor compounds grown by chemical beam epitaxy. Our results suggest that the formation of Si–C bonds occurs in III–V epitaxial layers with acceptor Carbon residual concentration and high Si concentrations (>1017cm−3). The main consequence of Si–C bonds is the generation of defects along [111] direction. These defects produce carrier concentration saturation, reduction of electrical mobility, crystal quality degradation, and surface defects.
Glowing Greys and Surface-White: The Photo-Geometric Factors of Luminosity Perception
Authors: Zavagno Daniele , Caputo Giovanni
Published: April 2005

The perception of luminosity is thought to depend upon the intensity of the stimulus: a surface begins to appear self-luminous when it emits or reflects a certain amount of light. This is known as the luminosity threshold. It is a common opinion among vision scientists that such a threshold is correlated to the intensity of a perceptually white surface, in the sense that only an area of the visual field with luminance higher than perceived surface-white will appear luminous. Here we show grey colours that appear luminous in virtue of surrounding luminance ramps. These ramps are intended to mimic halos seen around light sources in natural environments. The results of three experiments indicate that the phenomenon is in direct contradiction to the aforementioned assumptions and suggest the existence of separate perceptual pathways for self-luminosity perception and for surface-colour perception.
Evidence for the Correcting-Mechanism Explanation of the Kanizsa Amodal Shrinkage
Authors: Mitsudo Hiroyuki , Nakamizo Sachio
Published: April 2005

An object phenomenally shrinks in its horizontal dimension when shown on a 2-D plane as if the central portion of the object were partially occluded by another vertical one in 3-D space (the Kanizsa amodal shrinkage). We examined the predictions of the correcting-mechanism hypothesis proposed by Ohtsuka and Ono (2002, Proceedings of SPIE4864 167 – 174), which states that an inappropriate operation of the mechanism that corrects a phenomenal increase in monocularly visible areas accompanied by a stereoscopic occluder gives rise to the illusion. In this study we measured the perceived width (or height in experiment 3) of a square seen behind a rectangle, while controlling other factors which potentially influence the illusion, such as the division of space or depth stratification. The results of five experiments showed that (a) the perceived width was not influenced when the occluder had a relatively large binocular disparity, but was underestimated when the occluder did not have disparity, and (b) the shrinkage diminished when the foreground rectangle was transparent, was horizontally oriented, or contained no pictorial occlusion cues. These results support the hypothesis that the correcting mechanism, triggered by pictorial occlusion cues, contributes to the Kanizsa shrinkage.
The Influence of Illumination Direction on the Pictorial Reliefs of Lambertian Surfaces
Authors: Nefs Harold T , Koenderink Jan J , Kappers Astrid M L
Published: April 2005

In order to assess the influence of illumination direction on shape constancy, we studied the pictorial relief of computer images of globular 3-D objects. We used two globally convex objects, one with a furrow and one with a dimple. Observers adjusted local surface attitude probes at 200–250 different locations in the image such that they seemed to lie on the pictorial surface. We manipulated the viewing direction and the illumination direction in a 2times2 orthogonal design. Viewing directions were chosen such that the image contained only a few, or no, contour singularities. Changes in the illumination direction were found to induce systematic changes in the settings for both viewing directions. Effects were especially pronounced for images that had no contour singularities. The results showed that a change in the illumination direction can change the local shape of the pictorial relief in addition to the bas-relief ambiguities of scaling and shearing in depth. We found that concavities in the pictorial relief are associated with the darker areas in the image. The deviation from shape constancy cannot be explained by bas-relief ambiguity since the required transformation between the shapes is nonlinear.
Attractiveness of Own-Race, Other-Race, and Mixed-Race Faces
Authors: Rhodes Gillian , Lee Kieran , Palermo Romina , Weiss Mahi , Yoshikawa Sakiko , Clissa Peter , Williams Tamsyn , Peters Marianne , Winkler Chris , Jeffery Linda
Published: April 2005

Averaged face composites, which represent the central tendency of a familiar population of faces, are attractive. If this prototypicality contributes to their appeal, then averaged composites should be more attractive when their component faces come from a familiar, own-race population than when they come from a less familiar, other-race population. We compared the attractiveness of own-race composites, other-race composites, and mixed-race composites (where the component faces were from both races). In experiment 1, Caucasian participants rated own-race composites as more attractive than other-race composites, but only for male faces. However, mixed-race (Caucasian/Japanese) composites were significantly more attractive than own-race composites, particularly for the opposite sex. In experiment 2, Caucasian and Japanese participants living in Australia and Japan, respectively, selected the most attractive face from a continuum with exaggerated Caucasian characteristics at one end and exaggerated Japanese characteristics at the other, with intervening images including a Caucasian averaged composite, a mixed-race averaged composite, and a Japanese averaged composite. The most attractive face was, again, a mixed-race composite, for both Caucasian and Japanese participants. In experiment 3, Caucasian participants rated individual Eurasian faces as significantly more attractive than either Caucasian or Asian faces. Similar results were obtained with composites. Eurasian faces and composites were also rated as healthier than Caucasian or Asian faces and composites, respectively. These results suggest that signs of health may be more important than prototypicality in making average faces attractive.
The influence of the microflora on the physical properties of soils. I. Effects associated with filamentous algae and fungi
Authors: Bond RD , Harris JR
Published: April 2005

Current views that aggregation of soils results from by-products of microbial growth and that filamentous microorganisms contribute very little to physical binding are reviewed. The microscopical examination of soils and aggregates showed fungal mycelium to be persistent in well-aggregated soils, but relatively deficient in soils lacking structure. Cases are cited where physical properties of soils depend upon the presence of filamentous microorganisms: (1) Surface crusts on sands in open plant communities where algae dominate the coenoses with filamentous fungi; (2) the aggregation of deeper horizons of sands by adhesive fungal mycelium; (3) the sand capping to clay subsoils in solonetzic soils bound by abundant fungal mycelium and microbial gums; (4) the water repellence of sandy soils associated with the growth of microorganisms, particularly basidiomycete fungi; (5) the progressive improvement of crumb structure in fine-textured soils associated with increased development of persistent mycelium after several years under pasture.
An examination of the air-pressure infiltration method of measuring hydraulic conductivity of unsaturated porous materials
Authors: Collis-George N , Rosenthal M , Smiles DE
Published: April 2005

An air-pressure infiltration method (proposed by Youngs) for determining the hydraulic conductivity of porous material is examined, and a theory for the potential distribution in such a system is proposed. The results of experiments on aluminium oxide powder support the theory. The matric potential during infiltration is not locatable a priori on a predetermined wetting scanning curve of the moisture characteristic, and the implications of this are discussed.
The effect of polyvinyl alcohol on the nitrogen surface area and pore structure of soils
Authors: Williams BG , Greenland DJ , Quirk JP
Published: April 2005

Changes in the specific surface area and pore size distribution due to adsorption of polyvinyl alcohol (PVA) by aggregates of a clay soil have been determined from the desorption isotherms for nitrogen at -195�C. The specific surface area was reduced. The volume of pores less than 30 A wide decreased by an amount considerably in excess of the volume of PVA adsorbed. These results are interpreted in terms of 'peripheral pore occupation' by the polymer, preventing access of nitrogen molecules to pores and surfaces within domains. Adsorption data previously obtained also indicated limited penetration of domains by the polymer.
Calibration and assessment of soil tests for estimating fertilizer requirements. I. Statistical models and tests of significance.
Authors: Colwell JD
Published: April 2005

The calibration of soil tests requires a statistical model to describe the relationship between yield of crop, fertilizer application rate, and soil test. Yield response to fertilizers can be represented by polynomials both in the natural and square-root scales, and these polynomials can be generalized for a given crop and region, using soil test expressions. The generalization can be done using orthogonal polynomials and simultaneous regression equations that relate the coefficients of the polynomials to the soil test variables. This procedure is necessary because of heterogeneity in the residual sum of squares of regressions fitted to the yield data of several fertilizer field experiments within a region. The set of simultaneous regression equations constitutes a direct calibration of the soil test, since it can be used for the estimation of economic fertilizer requirement. Highly significant calibrations are demonstrated for a phosphorus soil test with wheat and a potassium test with potatoes. A nitrogen test gave only non-significant (P > 0.05) relationships.
Influence of evaporation suppressants on water movement in soils
Authors: Kijne JW
Published: April 2005

The soil-water diffusivity was determined as a function of water content for Urrbrae fine sandy loam treated with two fatty alcohols, two amines, Krilium, polyvinyl alcohol, and Carbowax. The fatty alcohols and dodecylamine had the strongest influence on soil-water diffusivity throughout the whole range of soil-water contents. Treatment with these amendments markedly reduced capillary flow of water to the soil surface. Dodecylamine reduced the rate of infiltration into the soil. Heats of wetting of the treated soil samples indicated that penetration rate and diffusivity near saturation were reduced in accordance with the hydrophobic character of the adsorbed compound. Cetyl alcohol was partly desorbed when water permeated through cetyl-alcohol-treated soil, forming a film on the advancing wetting front. This resulted in a slower rate of penetration than would have been expected from the hydrophobic character of the complex.
Nitrification by Aspergillus flavus in sterilized soil
Authors: Doxtader KG , Rovira AD
Published: April 2005

The heterotrophic organism Aspergillus flavus has been shown to produce significant amounts of nitrate in sterile soil supplemented with sucrose and ammonium phosphate. Nitrate was produced in three soils sterilized by steam or by gamma irradiation, but in one soil (Honeoye silt loam, forest sample) considerably more nitrification occurred in the irradiated soil. The amount of nitrate produced by the fungus in soil was much less than that produced in liquid culture medium during the same incubation period, particularly in two of the three soils. Slight inhibition of nitrification occurred when water extracts of two soils were added to the liquid culture medium normally used for studying nitrification by A. flavus. However, the addition of small amounts of sterile soil to this culture medium markedly inhibited nitrification without apparently affecting the growth of the fungus.
The distribution of salt by infiltration of water into dry soil and sand
Authors: Evans GN , Levin I
Published: April 2005

Sulphate and chloride ions (as magnesium salts) were added in solution form, as a slug, to the surface of columns of two air-dry soils and a sand. The soils were pretreated to avoid precipitation of, and exchange effects with, the added salts. Leaching was carried out by ponded fresh water, and the salt and water profiles in the columns determined. In every case the salt was distributed through the column with a pronounced peak nearly halfway between the surface and the wetting front. It is pointed out that existing leaching theories derived for steady-state conditions do not apply to the infiltration case, an extreme example of non-steady-state flow. The differences between the two types of flow, in relation to leaching, and a possible mechanism by which fresh water moved through and advanced ahead of the salt slug during infiltration, are discussed.
Entrapment, stability, and persistence of air bubbles in soil water
Authors: Peck AJ
Published: April 2005

Air bubbles in soil water affect both hydraulic conductivity and moisture content at a given capillary potential. Consequently changes in the volume of entrapped air, which are not included in the specification of relationships between hydraulic conductivity, moisture content, and capillary potential, will affect all soil-water interactions. Current understanding of the process of air bubble entrapment during infiltration suggests that, in nature, significant air entrapment will often occur. It is shown that infiltrating water can dissolve only a very small volume of air, much less than the amount usually entrapped. Air bubbles in saturated soils are unstable since their pressure must exceed atmospheric, resulting in a diffusive flux of dissolved air from bubbles to menisci contacting the external atmosphere. However, stable bubbles are possible in unsaturated soils. Bubbles which are constrained by pore architecture to non-spherical shapes are usually stable, and spherical bubbles can be stable when the magnitude of the capillary potential exceeds about 3 bars. An approximate analysis of the characteristic time of bubble equilibration indicates that, in an example, it is of order 104 sec, but it may be greater or less by at least a factor 10. Since the equilibration time will be often at least as large as the period of significant soil temperature changes, it cannot be assumed that the entrapped air in a field soil is in an equilibrium state. In such circumstances unstable bubbles may be quasi-permanent. It is suggested that the slow growth of entrapped bubbles may account for the anomalously slow release of water observed in some outflow experiments. Changes of entrapped air volume may also account for the reported dependence of soil-water characteristics on the magnitude of the steps of capillary potential.
Effects of soil composition on the relationships between soil test values for phosphorus fertilizer requirements
Authors: Colwell JD , Donnelly JD
Published: April 2005

The correlations between the P test values obtained by a series of standard procedures were found to be improved by allowing for the effects of soil composition, particularly with respect to reactive iron, aluminium, magnesium, and calcium. The high correlations thus obtained suggest that most of the P test procedures will be of about equal value for estimating P fertilizer requirements if allowance is made for the effects of variations in soil composition. They also suggest that P test calibration equations should include variables representing soil Fe, Al, Mg, or Ca, as well as the actual P test.
Flooded rice soils of Northern Australia. II. Chemical profiles
Authors: Williams BG
Published: April 2005

Changes in chemical and electrochemical properties of a flooded calcareous soil sown to rice were monitored during the season of flooding. Considerable variations in specific conductivity, individual cation concentrations, bicarbonate concentration, and carbon dioxide pressures were observed within the soil profile to depths of 30 cm. Redox potential and pH tended to be uniform within a profile except when CaSO4 or H2SO4 were added to the surface soil. Both field and pot experiments showed profile variations in soil properties and the significance of this is discussed in terms of the root distribution of rice.
Studies on soil potassium. I. A theoretical model of the Q/I relationship
Authors: Ross PJ , Fergus IF , Martin AE
Published: April 2005

To describe the Q/I isotherm for labile soil potassium, Beckett (1964a) has proposed a theoretical niodel which assumes two types of exchange site and characterizes the isotherm by four parameters. This paper discusses the model and shows how it can be fitted to data by least squares so that tests of hypotheses concerning the parameters can be carried out. The usefulness of this approach was tested on published data and on new experimental data for 10 soils (nine from Queensland, one from South Australia) subjected to a range of cropping and storage treatments. In all cases the model described the data adequately, although this was to be expected since it contains four adjustable parameters. Statistical tests on some of the published data showed that graphical estimates of parameters, and conclusions based on such estimates, are unreliable. Tests of significance suggested that exhaustive cropping changed the form of the Q/I isotherm for only three of the 10 Australian soils. These three soils all contained illite, and yielded more non-exchangeable potassium to plants than the other seven. It is suggested that the changes were due to increases in the interlamellar surface areas accessible to exchange, and that some of the newly exposed exchange sites were highly specific for potassium. If this is so, the simple two-site model is theoretically inadequate for these soils at least, since after cropping it appears to group together, as non-specific, sites with a wide range of specificities.
The effect of height of sample and confinement on the moisture characteristic of an aggregated swelling clay soil
Authors: Collis-George N , Bridge BJ
Published: April 2005

The pore pressure/moisture content relationship of 0.5-1.0 mm aggregates of Narrabri soil, initially 1.66 cm high, was examined at 1/3 cm height intervals by means of dual source gamma ray scanning, for confined and unconfined conditions. In the unconfined sample, absorption and desorption of water to or from the interaggregate pore space occurred at less negative pore water pressures than in the confined sample. In the latter, the swelling aggregates deformed into the inter-aggregate pore space during absorption and reduced the size of the pores. In the unconfined sample, absorption into the inter-aggregate pore space occurred at less negative water pressures with increasing height in the sample. During absorption, bulk density decreased with height in the sample, and bulk density at all points within the sample decreased until pore water pressures were between -20 to - 10 cmH2O. At pore water pressures closer to zero, bulk density increased as the sample compacted under its own weight. During desorption, bulk density increased at all heights as the pore water pressures decreased from zero to - 8 cmH2O, because of isotropic stress imparted by the hanging water column. During this phase normal shrinkage occurred, therefore overburden potentials, and hence moisture potentials, could be calculated. Between - 10 and - 50 cmH2O, the inter-aggregate pore space drained rapidly, and no further increase in bulk density was detectable and hence moisture potential equates to manometric pressure. It was found that the derived moisture characteristics (� versus �) are different for different heights in the aggregate mass. This result is of consequence to the theory of hydrostatics in swelling media. In the unconfined sample, no differences in the pore water pressure/moisture content relationships occurred with height during absorption or desorption, and bulk density remained constant throughout. The application of these results to the behaviour of swelling soils in the field is briefly discussed. The use of dual source gamma ray scanning seems an essential tool for further investigations.
Sorption and precipitation of iron on kaolinite. IV. Further characteristics of sorption From 0.15 M solutions
Authors: Fordham AW
Published: April 2005

Sorption and desorption of small amounts of iron(III) on kaolinite suspended in 0.15M sodium perchlorate solutions was measured at various times over a range of pH values and temperatures. In addition, the effects of transferring these systems from one temperature to another was investigated. The results showed that some of the sorbed iron was strongly bound to the clay, whilst the remainder re-equilibrated relatively rapidly following changes of solution concentration or temperature. The reactions could be regarded as consecutive, the amount of iron sorbed during the first (reversible) stage being one of the factors controlling the amount of strongly bound iron. The extent of both reactions was increased by increasing temperature. The effects of various competing ions introduced at the same time as iron confirmed that the reversible reaction was not a simple electrostatic process but rather specific sorption of hydrolysed ionic species. Extraction of sorbed iron by several reagents endorsed the strong affinity between some of the sorbed iron and the clay. Attempts to define the location of sorbed iron by the use of reagents capable of reacting with either the basal surfaces or the edges of kaolinite particles failed to give conclusive results because of unavoidable secondary reactions.
Arylsulphatase clay interactions. I. Adsorption of arylsulphatase by kaolinite and montmorillonite
Authors: Simpson GH , Hughes JD
Published: April 2005

The extent of arylsulphatase adsorption by both montmorillonite and kaolinite was determined using 0.1-1.0 �m fraction of sodium-clay freed from organic material, and a commercially purified arylsulphatase. Kaolinite-arylsulphatase affinity decreased with increasing solution enzyme concentration, but montmorillonitearylsulphatase affinity increased up to a solution enzyme concentration of approximately 15 mg/100 mg of clay, and decreased at higher enzyme concentrations. X-ray diffraction of the montmorillonite-arylsulphatase complex provided evidence of intercalation of the enzyme in the 2:1 lattice structure, as well as destruction of secondary and tertiary structures of the enzyme following adsorption on the interlattice surfaces.
Modelling aquifer recharge and water use in the Koo-Wee-Rup basin
Authors: Longley TS , Turner AK , Lawson JD
Published: April 2005

Overpumping for irrigation has caused a general lowering of the piezometric surface in a multilayered aquifer in the Westernport Bay area of Victoria. This lowering effectively increases costs for agricultural production because of the higher pumping lifts now needed, and sets a limit to further development for irrigation in this vegetable-growing locality. In addition, there is now some seawater intrusion into the aquifer. A finite-difference model had been developed by the Department of Minerals and Energy of Victoria for the prediction of piezometric surfaces associated with steady-state pumping rates. This model was altered so that the influence of various possible recharge sources on the piezometric surface could be predicted. The recharge sources were infiltration from rainfall in localities where there are outcrops of the aquifer formation, beds of rivers passing over the general area, and rainfall infiltration in the surrounding hill country. Correspondence between the results of the model and the field behaviour as recorded in a dense grid of bores, was adequate in that it confirmed the existence and relative importance of the postulated recharge sources. Recommendations are made as to the limited advisability of artificial recharge of the aquifer from surface sources.
Preferential solute movement through larger soil voids. Ii. Experiments with saturated soil
Authors: Kanchanasut P , Scotter DR , Tillman RW
Published: April 2005

Miscible displacement experiments, with chloride and phosphate ions in the displacing solution, were conducted on soil material manipulated to contain different void geometries. In packed 50 mm long columns of 0.2-0.5 mm aggregates the displacing solution moved fairly uniformly through the soil, with the relative chloride concentration in the effluent reaching 0.5 approximately 8 min after chloride was applied to the surface. The relative phosphate concentration reached 0.5 after approximately 7 h. In 50 mm long cast-columns of the same soil material containing a single cylindrical channel 0.5 mm in diameter, or a slit 12 mm by 0.2 mm, both chloride and phosphate moved almost instantaneously through the columns, reaching a relative concentration of 0.5 in less than a minute. The cast columns and packed aggregate columns all had similar hydraulic conductivities. These results are in general agreement with a previously developed theoretical model. An 'undisturbed' core of the same soil showed similar pronounced preferential movement of chloride and phosphate, indicating the presence of a continuous void greater than the critical minimum size. However, in contrast a duplicate core gave results more like those found for the columns of aggregates. Soil water retentivity curves are shown to be of very limited value for predicting preferential solute movement.
Relationships between particle size, fabric and other factors in some Australian soils
Authors: Brewer R
Published: April 2005

Soil fabrics at the level of related distribution of f-matrix (usually finer material) to f-members (usually coarser units) are considered in relation to particle size distribution for a number of randomly selected Australian profiles. Three major fabric continua are recognized: the chlamydic iunctic and matrigranic sequences. The majority of samples in the first two sequences have ratios of clay to silt greater and less than one, respectively, and successive stages correlate with increasing proportions of silt plus clay; fabrics of samples that fall out of sequence in relation to percentage of silt plus clay are explained on the basis of composition and/or specific processes, especially fine-grained carbonates, organic matter, faunal activity, and illuviation. The matrigranic sequence does not correlate with particle size distribution, but seems to be related to composition and/or specific processes such as faunal activity. The usefulness of the results lies in the possibility of using the conclusions to reduce the number of thin sections required to characterize areas of soil, particularly within restricted areas.
The nature and possible origins of soluble salts in deeply weathered landscapes of eastern Australia
Authors: Gunn RH , Richardson DP
Published: April 2005

Extensive areas of salt-affected soils in eastern Australia occur on the exposed lower zones of lateritic profiles or in derived materials. Analyses of 96 samples of mottled and pallid zones collected in this study show that they generally contain appreciable soluble salts, predominantly sodium chloride, particularly where they developed in argillaceous sedimentary rocks which underlie about two-thirds of the area, and in some granitic rocks. Analyses of 96 samples of unweathered rocks indicate that some contain moderate to appreciable quantities of sodium and chloride, and it is suggested that these and other soluble ions accumulated in the lower zones as a result of deep weathering in the Mid-Tertiary. Atmospheric accessions of sea salts in rain or dry fallout at present rates account partly for the occurrence of salt-affected soil landscapes in some coastal areas but are unlikely sources of salts far inland. Soils formed in situ on weathered basalt, argillaceous sedimentary and granitic rocks which have been exposed at the surface since the Late Tertiary are not salt-affected, because climatic, topographic and hydrologic conditions are different from those of the Mid-Tertiary and only small volumes of rock are involved.
A synoptic approach for crop loss assessment used to study wheat. II. Relationships between soil properties and traditional soil classifications
Authors: Veitch LG , Stynes BA
Published: April 2005

Study of the relationship between soil properties and traditional soil classifications, using the canonical analysis procedure, showed that both a highly significant and a substantial relationship exists. Classification data on average accounts for about 35% of the total variation of the soil variable data, individual values ranging from about 8% for average log salinity to 74% for the -0.1 bar water content of the soil. The analysis showed that classification data in five soil groups could be substantially retained in two dimensions. The soil variables most involved in the first dimension were per cent clay and the -0.1 bar water content of the soil, and in the second dimension, the available water content of the subsoil (30-100 cm), average pH and average log salinity. These results should be useful in other studies where it is desired to incorporate soil information in a model designed to account for variation in one or more measures of interest.
The development of a red-brown earth. I. A reinterpretation of published data
Authors: Chittleborough DJ , Oades JM
Published: April 2005

Previously published chemical and physical data for the Urrbrae loam, and the conclusions drawn from these data concerning profile development, have been appraised. Translocation of clay seems likely to have played a significant role in the development of the Urrbrat: loam, a red-brown earth (calcic rhodoxeralf). Both A and B horizons apparently did not originate as distinct sedimentary deposits nor was much additional clay formed in position. Further experimental evidence is required to substantiate the clay illuviation hypothesis.
Estimation of river channel volume using water chemistry
Authors: Allison GB , Leaney FW
Published: April 2005

Changes in concentration of chloride and sodium have been used to estimate the volume of water stored in an 84 km length of the River Murray. A value of 44 x 106 m3 was obtained, compared with a value of 59 x 106 m3 obtained by survey. Sources of error in our estimates are discussed as are possible explanations for the differences between the two values.
A model for prediction of calcium-sodium exchange reactions in sodic soils
Authors: Arora Y , Singh NT
Published: April 2005

The material balance equation that describes the miscible displacement involving cation exchange was solved numerically for prediction of calcium-sodium exchange during reclamation of sodic soils. This exchange process was studied for Fatehpur loamy sand and Bhabiana loam. Four columns of each soil were packed and saturated with sodium by leaching with 0.1 M sodium chloride solution. The adsorbed sodium was displaced by 0.50 M calcium nitrate solution. Different volumes of calcium nitrate solution were passed to cause differential removal of exchangeable sodium. Nonlinear exchange isotherms were developed for the soils and incorporated in the convective-dispersive transport equation, which was solved by finite difference technique. Good agreement between the computed and experimental profiles of soluble and exchangeable calcium following input of different volumes of calcium nitrate solution was obtained. Last traces of exchangeable sodium which were difficult to remove from Bhabiana loam were not predicted by the model. Reasons for this discrepancy are enumerated.
Estimation of the plant available water capacity of a soil profile
Authors: Mullins JA
Published: April 2005

The plant available water capacity (PAWC) was measured for a range of soils (black earths, grey, brown and red clays, krainozems, yellow earths and solodized solonetz/solodics) used for dryland agriculture in the uplands of th,- eastern Darling Downs of Queensland. Using these data, two one-parameter models - one based on the electrical conductivity profile and the other on observable profile features - were derived for estimating the PAWC of the soil profile. The electrical conductivity profile model reliably estimated the PAWC for black earths and grey, brown and red clays. In the case of the deep, black earths, it accounted for 90% of the variation. The observable profile feature model reliably estimated the PAWC for black earths and grey, brown and red clays and in the case of the grey, brown and red clays accounted for 88% of the variation. The models for the solodized solonetz/solodics were not significant. In addition the profile feature model provided estimates of PAWC for the krasnozems (grouped with black earths) and for the yellow earths and solodized solonetz/solodics as a group. An alternative technique for the estimation of PAWC for krasnozems and yellow earths is also presented. The techniques will provide a rapid first appraisal of the PAWC of a soil profile.