bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrafast double-pulse ablation of fused silica
Authors: Chowdhury Ihtesham H. , Xu Xianfan , Weiner Andrew M.
Published: April 2005

Ultrafast pump-probe experiments were used to study high-intensity ultrafast pulse-ablation dynamics in fused silica. Two laser pulses with varied time delay and pulse energy were used to irradiate fused silica samples and observe the transient reflectivity and transmissivity of the probe pulse. It was seen that the probe reflectivity initially increased due to the formation of free-electron plasma and then dropped to a low value within a period of about 10ps caused by a rapid structural change at the surface. The time-resolved measurements of reflectivity and transmissivity were also related to atomic force microscopy measurements of the depth of the laser-ablated hole. It was seen that the depth peaked at zero delay between the pulses and decreased within a period of about 1ps as the temporal separation between the pulses was increased caused by the screening by the plasma produced by the first pulse. When the temporal separation is about 100ps or longer, evidence for melting and resolidification during double-pulse ablation was also observed in the form of ridges at the circumference of the ablated holes.
Optical loss and lasing characteristics of high-quality-factor AlGaAs microdisk resonators with embedded quantum dots
Authors: Srinivasan Kartik , Borselli Matthew , Johnson Thomas J. , Barclay Paul E. , Painter Oskar , Stintz Andreas , Krishna Sanjay
Published: April 2005

Optical characterization of AlGaAs microdisk resonant cavities with a quantum dot active region is presented. Direct passive measurement of the optical loss within AlGaAs microdisk resonant structures embedded with InAs∕InGaAs dots-in-a-well (DWELL) is performed using an optical-fiber-based probing technique at a wavelength (λ∼1.4μm) that is red detuned from the dot emission wavelength (λ∼1.2μm). Measurements in the 1.4μm wavelength band on microdisks of diameter D=4.5μm show that these structures support modes with cold-cavity quality factors as high as 3.6×105. DWELL-containing microdisks are then studied through optical pumping at room temperature. Pulsed lasing at λ∼1.2μm is seen for cavities containing a single layer of InAs dots, with threshold values of ∼17μW, approaching the estimated material transparency level. Room-temperature continuous-wave operation is also observed.
Influence of silicon-nanocrystal distribution in SiO2 matrix on charge injection and charge decay
Authors: Ng C. Y. , Chen T. P. , Tse M. S. , Lim V. S. W. , Fung S. , Tseng Ampere A.
Published: April 2005

Influence of distribution of silicon nanocrystals (nc-Si) embedded in SiO2 matrix on charge injection and charge decay of the nc-Si has been investigated with electrostatic force microscopy. For nc-Si distributing in the surface region, the size of charge cloud does not change with decay time, and neighboring charges have no influence on the charge decay. In contrast, for nc-Si distributing away from the surface, the size linearly increases with decay time, and the neighboring charges can either accelerate or resist the charge decay depending on their charge signs. In addition, the characteristic decay time for the first distribution is much shorter than that for the second distribution. These results provide an insight into the dissipation mechanism of the charges stored in the nc-Si.
Production of atmospheric-pressure glow discharge in nitrogen using needle-array electrode
Authors: Takaki K. , Hosokawa M. , Sasaki T. , Mukaigawa S. , Fujiwara T.
Published: April 2005

An atmospheric pressure glow discharge was generated using a needle-array electrode in nitrogen, and the voltage–current characteristics of the glow discharge were obtained in a range from 1 mA to 60 A. A pulsed high voltage with short rise time under 10 ns was employed to generate streamer discharges simultaneously at all needle tips. The large number of streamer discharges prevented the glow-to-arc transition caused by inhomogeneous thermalization. Semiconductor opening switch diodes were employed as an opening switch to shorten the rise time. The glow voltage was almost constant until the discharge current became 0.3 A, whereas the voltage increased with the current higher than 0.3 A. Electron density and temperature in a positive column of the glow discharge at 60 A were obtained to 1.4×1012cm−3 and 1.3 eV from calculation based on nitrogen swarm data.
1.5
μ
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room-temperature emission of square-lattice photonic-crystal waveguide lasers with a single line defect
Authors: Checoury X. , Boucaud P. , Lourtioz J.-M. , Gauthier-Lafaye O. , Bonnefont S. , Mulin D. , Valentin J. , Lozes-Dupuy F. , Pommereau F. , Cuisin C. , Derouin E. , Drisse O. , Legouezigou L. , Lelarge F. , Poingt F. , Duan G. H. , Talneau A.
Published: April 2005

Narrow waveguides consisting of a single defect-line (W1) in a square lattice photonic crystal are fabricated on InP using the substrate approach. A single-mode distributed-feedback laser emission is obtained under optical pumping at room temperature. Lasing occurs at the second folding point of the dispersion curve of the fundamental waveguide mode (wave vector k=0). The emitted wavelength ranges from 1420to1580nm for a lattice period varying from 460to520nm and a constant air filling factor of ∼26%. The highly monomode behavior is explained using two-dimensional plane-wave models. Similar experiments conducted on triangular lattice W1 waveguides do not yield a laser emission. Three-dimensional simulations confirm that triangular lattice W1 waveguides suffer higher losses than their square homologues.
Physical kinetics and thermodynamics of phase transitions probed by dynamic nanocalorimetry
Authors: Château E. , Garden J.-L. , Bourgeois O. , Chaussy J.
Published: April 2005

A specific ac nanocalorimeter is presented for the study of kinetics in phase transitions. This apparatus designed by means of microfabrication technologies requires a 50-μm-thick solid or liquid sample. The use of the ac calorimetric method allows an operating frequency range around two decades combined with a very high sensitivity. The ability of this apparatus for thermal spectroscopy is illustrated by measuring the thermal behavior of a homopolymer, the polytetrafluoroethylene, which exhibits two phase transitions at room temperature. The variation of the thermal frequency allows the observation of kinetic effects directly seen on the thermodynamic properties (enthalpy and heat capacity). We demonstrate the possibility of extracting a quantitative value of the kinetic time constant occurring at a first-order phase transition and consequently the capabilities offered by highly sensitive ac calorimetry to investigate direct thermal dynamics in macromolecular samples.
Electrochemical Actuator Devices Based on Polyaniline Yarns and Ionic Liquid Electrolytes
Authors: Lu Wen , Norris Ian D. , Mattes Benjamin R.
Published: April 2005

We report the development of conducting polymer electrochemical linear actuators from ionic liquids (as electrolytes) and polyaniline yarns and hollow fibres (as electrode materials). With a yarn-in-fibre configuration, these actuators were simple to fabricate and allowed two-electrode operation without a reference electrode. Typical electromechanical actuation behavior of expansion, with force decrease, and contraction, with force increase, during charge injection and removal has been realized for these actuators. Stress generation of these actuators was 0.42–0.85 MPa, which exceeds that of skeletal muscle (0.1–0.5 MPa). Practical application of these actuators has been successfully demonstrated by using the electrochemical actuation of a yarn-in-fibre actuator to drive a cantilever object. Importantly, this yarn-in-fibre configuration would allow the combination of an appropriate number of yarns as the actuation electrode to accomplish the mechanical task, depending on the weight of the object.
Electrochemical Detection of Yeast Responses to Catabolizable Molecules
Authors: Baronian Keith H. R. , Gurazada Saroja , Thomas Ancy
Published: April 2005

Cells harvest energy from energy-rich molecules by oxidation of the molecule and the subsequent transfer of electrons to catabolic redox compounds. This transfer can be intercepted by artificial redox compounds (mediators), and the reduction of the mediator can be easily monitored by several electrochemical techniques. This work describes the use of steady-state voltammetry to monitor the catabolic responses of two yeast species to specific molecules.
Fluorescence Microscopy Study of Protein Adsorption at Modified Glassy Carbon Surfaces
Authors: Downard Alison J. , Jackson Sandra L. , Tan Emelyn S. Q.
Published: April 2005

Glassy carbon (GC) surfaces were modified with thin films by means of electrochemically assisted reduction of aryl diazonium salts and oxidation of primary amines. GC plates with modified and unmodified areas were exposed to solutions of fluorescently labelled bovine serum albumin (BSA-FITC). Fluorescence microscopy was found to be a simple and direct method for comparing adsorption of BSA-FITC between the different areas. Modification with methylbenzene, hexylbenzene, poly(ethylene glycol) benzene, and tetraethylene glycol diamine groups increases protein adsorption relative to unmodified GC. Hexylamine and the poly(ethylene glycol) diamine ED-2003 reduce protein adsorption. The results give insight into some factors controlling protein adsorption at these surface films.
Electrochemical Transduction of DNA Hybridization by Long-Range Electron Transfer
Authors: Wong Elicia L. S. , Gooding J. Justin
Published: April 2005

For the detection of DNA hybridization, there are two main challenges that current research aims to overcome: lower detection limits and higher selectivity. We describe here the development of an electrochemical biosensor that used redox-active intercalators to transduce DNA hybridization by long-range electron transfer through DNA duplexes. This study outlines how the sensitivity and selectivity of the biosensor was tuned by careful control of the surface chemistry of the DNA-modified interface. The DNA-modified interface is composed of thiolated DNA and a diluent component, both of which are self-assembled onto a gold electrode. The resultant DNA biosensor has excellent selectivity towards single-base mismatch detection, whilst both the detection limit and sensitivity can easily be adjusted by varying the length of the diluent molecule relative to the length of the thiol linker at the 3´ end of the DNA. The one limitation of such a detection scheme is the slow assay time, which is a consequence of the slow kinetics of intercalation of the redox molecule into the duplexes. Approaches to reducing the assay time to a more commercially viable timescale are outlined.
Redox Coupling to Microbial Respiration: an Evaluation of Secondary Mediators as Binary Mixtures with Ferricyanide
Authors: Pasco Neil , Hay Joanne , Scott Amy , Webber Judith
Published: April 2005

MICREDOX is a rapid microbial-based assay, which was originally developed at Lincoln Technology to monitor biochemical oxygen demand (BOD).[1] The assay is characterized by high levels of biocatalyst (microorganisms) and redox mediator; these facilitate a fast reaction in which the microbial oxidation of an organic substrate is coupled with the reduction of the mediator. Previous efforts toward optimizing this assay have principally been directed at the selection and performance of different bacterial strains, either singly[2] or as a consortium.[3] Here we report the effect of adding a second mediator to the assay by comparing the coulombic responses and the substrate stoichiometric conversion efficiencies. Escherichia coli and half-strength standard BOD substrate (75 mg glucose L−1, 75 mg glutamic acid L−1; GGA) were incubated for one hour at 37°C in the absence of oxygen with an excess of redox mediator, potassium hexacyanoferrate(iii) (HCF), either individually or as a binary mixture that included a secondary mediator. Secondary redox mediators investigated were p-benzoquinone (BQ), 2,6-dichlorophenolindophenol (DPIP), menadione (MD), neutral red (NR), N,N′-tetramethyl-1,4-phenylenediamine (N-TMPD), phenazine ethosulphate (PES), and 2,3,5,6-tetramethyl-1,4-phenylenediamine (TMPD). When HCF was supplemented with TMPD or PES the stoichiometric conversion efficiency for the oxidation of the GGA by E. coli increased, whereas when supplemented with N-TMPD, MD, DCIP, or BQ the conversion efficiency decreased. No effect was evident when NR was used as the supplement.
Ferricyanide-Mediated Microbial Reactions for Environmental Monitoring
Authors: Morris Kristy , Zhao Huijun , John Richard
Published: April 2005

The ability of microorganisms to use ferricyanide as an alternative electron acceptor for respiratory processes has been known for nearly 100 years. More recently, the use of ferricyanide-mediated bioreactions for environmental monitoring has received much attention. This paper reviews the recent developments of these mediated microbial processes for rapid biochemical oxygen demand analysis and direct toxicity assessment during the past five years. The ability of eukaryotic microorganisms to use ferricyanide as an alternative electron acceptor for a range of applications is also described.
Unsaturated flow properties of soils
Authors: Elrick DE
Published: April 2005

Experiments to determine the unsaturated flow properties of soils are based either on the steady-state Darcy equation or on the transient diffusion equation. An apparatus has been designed to compare the steady-state and transient methods on the same sample. Results indicate that the transient outflow pattern at high moisture contents (using a coarse sand) differs considerably from that predicted by diffusion theory. The extended theory which takes into account the air as well as the water phase also does not agree with the observed transient behaviour at the high moisture contents. At low moisture contents the agreement between the two methods is considerably better. The transient outflow method was found to be inapplicable at the high moisture contents. Much of the difficulty is attributed to the inaccessibility of air to drainable pores under these conditions.
Weathering and soil formation on dolerite in Tasmania with particular reference to several trace elements
Authors: Tiller KG
Published: April 2005

The mineralogy and chemistry of weathering and soil formation have been studied at 17 widely separated sites with contrasting climatic conditions on comparatively uniform dolerite in Tasmania. The clay and fine sand mineralogy of the soils has been related to their degree of weathering. These studies have shown large chemical and mineralogical changes accompanying the initial stages of weathering in some krasnozem soils. The reorganization of cobalt, zirconium, nickel, copper, molybdenum, manganese, and zinc during genesis of four soil groups has been considered in terms of the factors involved. Some of these results indicate that the clay horizon of the podzolic soils has probably been formed by weathering in situ. Seasonal waterlogging in certain horizons has strongly mfluenced the chemistry and mineralogy of weathering in many of these soils. This study has shown that the composition of the parent material has only influenced the geochemistry of trace elements in less weathered soils and that pedogenic factors assumed greater significance as the soils became more strongly weathered. Geomorphic processes had a marked influence on the geochemistry of some soils by the truncation of mature soil profiles.
The swelling of Na-montmorillonite due to water absorption
Authors: Emerson WW
Published: April 2005

Orientated flakes of dry Na-montmorillonite were brought into equilibrium successively with relative vapour pressures of 0.92 and 0.985 and the moisture contents, (001) spacings, and swelling measured, the latter with a travelling microscope. Over saturated water vapour the clay continued to swell with time, in contrast to Ca-montmorillonite. Hysteresis in swelling was only observed at values of p/po > 0.985. The further expansion of flakes when immersed in solutions, N in Na+, of sodium chloride with dilute buffer added (from pH 4.4 to 10) or sodium hydroxide or chloride plus neutral sodium pyrophosphate was determined. The Na+ concentration was then reduced and the corresponding swelling measured, until the flake dispersed. Similar experiments were made on orientated flakes prepared from Na-montmorillonite to which 1.5% cetyltrimethylarnmonium bromide (CTAB) had been added, as well as from Na-montmorillonite which had been washed with lithium chloride and heated before reconversion to the Na form. The expansion of Li-vermiculite crystals in lithium chloride solutions was also determined. In solutions N in Na+ the swelling of Na-montmorillonite flakes was independent of pH, but for Na+ < N/2 the swelling increased sharply above pH 8.0. The swelling of Na-clay + CTAB was much less than untreated clay and was independent of pH. Na-montmorillonite which had been lithium-treated at 95�C gave a swelling pattern at pH 4.4 similar to that of Na-clay + CTAB, whereas in sodium hydroxide the pattern was similar to that of untreated clay. The specific effect of the pyrophosphate anion on the swelling of the CTAB-treated clay was slight. There was marked hysteresis in the swelling of Na-montmorillonite with respect to salt concentration, whereas the swelling of Li-vermiculite was almost reversible. Adding CTAB inhibited the intercrystalline swelling of Na-montmorillonite, the CTA+ ions forming Stern layers on the external surfaces of the crystals. A similar effect was apparently produced in the acetate buffer by aluminium ions released during the lithium treatment. The increase in the swelling of the untreated clay with pH is consistent with the removal of aluminium ions from the external surfaces of the crystals. There must be residual attractive forces between the crystal at high pH to account for the stability of the clay in dilute salt solutions. The edge to face forces linking the silicate sheets together appear to be constant above pH 4.0. Neutral sodium pyrophosphate disperses the clay at Na+ concentrations of < N Na+ by removing aluminium ions and neutralizing positive edge charges. The montmorillonite crystals are considered to be linked mainly edge to edge in a tactoid. The bands observed in thin sections of expanded gels, using polarized light, may be due to a periodicity in the stacking of the silicate sheets forming the crystals.
Trace element contents of some Queensland soils
Authors: Oertel AC , Giles JB
Published: April 2005

The weighted mean concentrations of cobalt, copper, gallium, manganese, molybdenum, nickel, vanadium, zinc, and zirconium (and also of iron) are given for 28 soil profiles from Queensland. The concentrations of the same elements in 118 surface soils are presented as histograms. Soils of any one taxonomic group have characteristic, but not unique, trace element properties. The concentrations in surface soils of most of the elements have well-defined frequency distributions.
Soil history and debris avalanche deposits along the Illawarra scarpland
Authors: Walker PH
Published: April 2005

Two major periods of avalanching have occurred along the Illawarra scarpland. The older, the Scarborough formation, is characterized by a very thick, acid, weathered zone, similar to the lower mottled horizons of laterite profiles. The younger, Keira formation, has relatively shallow red and yellow earth profiles developed in it. Although its profile of deep weathering has some features in common with laterite, the Scarborough formation is not part of the general laterite surface, but represents a separate period of prolonged stability and weathering. The debris-avalanches are thought to have been deposited during excessively wet climatic conditions in the past, and they represent an alternate form of instability compared with the dry phase instability proposed for the K-cycle history of milder hillslope terrain near Nowra.
Soil studies at Swan Hill, Victoria, Australia. IV. Groundsurface history and its expression in the array of soils
Authors: Churchward HM
Published: April 2005

This paper traces the events associated with the development of aeolian and riverine landscapes at Swan Hill. These phenomena are characterized by a sequence of alternations between unstable phases featuring erosion and deposition and stable phases during which soil development occurred. Four groundsurfaces were studied in the aeolian landscape. The unstable phases involved were sufficiently arid to result in a depletion of protective vegetation and allow the destruction of the previous groundsurface by erosion and burial. Inception of more humid conditions allowed the re-establishment of the vegetation. Aridity also extended westward from Swan Hill, but it was probably more severe to the west during the three earlier unstable phases than during the more recent one. Three groundsurfaces on riverine material were studied and it was considered that one of these could be subdivided into two layers. The unstable phases were characterized by deposition resulting in the burial of the previous groundsurface and evidence suggests that it also occurred during the more arid conditions rather than the more humid. There is a waning in magnitudes (as indicated by the degree of profile development) of both the unstable and stable phases from the earlier to the more recent groundsurfaces.
The diffusivity of water in a porous material
Authors: Peck AJ
Published: April 2005

The results of some recent experiments have cast doubt upon the validity of the transient equation for liquid flow in a porous material. Perhaps the most searching trial of the flow equation is to compare diffusivities obtained from transient experiments with those obtained by steady-state methods. Such a trial on one material has indicated that the diffusivities are, in fact, in satisfactory agreement.
A two-well method of determining the hydraulic conductivity of discretelayers in layered saturated soils in the field
Authors: Collis-George N , Evans GN
Published: April 2005

A steady-state method of hydraulic conductivity determination in saturated soils, with particular application to use in discrete soil layers, is presented and discussed. It utilizes two partially lined auger holes with mutually opposite hydraulic conducting surfaces positioned in the desired layer. The use of an electrolytic tank analogue to determine a necessary geometrical factor is described. Some representative field and analogue results are given.
The solubility of potassium from soil illites. I. The dependence of solubility on pH.
Authors: Tucker BM
Published: April 2005

The equilibrium solubility of potassium from the lattice of illites in four soil clays has been measured. This solubility is related to the availability of this potassium and, when account is taken of the fineness of the clay particles, it is found to decrease as the illite structure becomes more degraded by loss of lattice potassium. The solubility depends on the pH of the system in the same way for all the clays, and a minimum value is found near to pH 11. Above this pH, potassium release is due to breakdown of the clay mineral. At lower pH values the release is due either to the instability of the clay mineral structure towards hydrogen ions or to displacement of potassium by other cations acting together with hydrogen ions.
The determination of exchangeable aluminium in soils
Authors: Little I
Published: April 2005

A leaching procedure employing 1N potassium chloride was found to yield satisfactory estimates of exchangeable aluminium in subsoil samples. The use of 1N ammonium acetate solutions as extractants was not recommended. When buffered at pH 4.8 these solutions gave low results, whereas at pH 4.0 there was some attack on hydroxy-aluminium polymers, which led to erroneous results, particularly in sesquioxidic soils. Satisfactory estimates of exchangeable aluminium in subsoils were obtained by potentiometric titration of soil suspensions in 1N potassium chloride with 0.1N sodium hydroxide, provided allowance was made for the contribution of pH-dependent charge between pH 4.0 and 5.5. This procedure gave values consistently lower than those obtained by leaching with 1N potassium chloride, and of the order of 81 % of these. This was consistent with the formation of an aluminium compound with the formula Ak6(OH)153+ whose existence has been postulated by other workers.
Reactions between boron and clays
Authors: Hingston FJ
Published: April 2005

Sorption of boron by Kent sand kaolinite, WilIalooka illite, and Marchagee montmorillonite in 0.01M CaCl2 is consistent with a mechanism described by the Langmuir equation, except that deviations occur at solution concentrations greater than about 10 �g B/ml. The quantity of boron adsorbed increases markedly with pH, and is rapid, reversible, and unaffected by the concentration of calcium chloride present. Complete desorption of surface boron, without significant solution of lattice boron, is achieved with 0.01M mannitol solution. Comparing the three clays at pH 7.5 on a surface area basis, the illite is most reactive (1.18 �g B/m2), followed by the kaolinite (0.28 �g B/m2) and the montmorillonite (0.02 �g B/m2). For illite, which is the most reactive of the three minerals, the magnitude of the above values emphasizes the small proportion (less than 1.4%) of the total surface area occupied by boron. Consideration of the reaction between boron and clays suggests that either boric acid molecules or borate ions could be the adsorbed species. Increasing sorption with pH could be explained either by the increasing proportion of borate ions to boric acid with pH or by a greater number of sites on the clay surface at higher pH values.
A study of the relationships between the yield of irrigated lucerne and the properties of some grey and brown soils of heavy texture in south-west New South Wales
Authors: Loveday J
Published: April 2005

Correlations between the yield of irrigated lucerne and specific properties of a sequence of grey and brown soils of heavy texture have been investigated under conditions of high superphosphate application and the normal watering regime of the district. Yield is strongly correlated with increment in available water per irrigation, which appears to be largely dependent on degree of cracking as controlled by clay content. A significant evaluation of differences in the chosen range of soils, therefore, would seem to be the status of accession of available water, but its measurement is long and tedious. Significant correlations between yield and more easily measured properties have been sought and found. The properties correlating with yield are clay, fine sand, apparent density, total exchangeable metal cations, exchangeable calcium, exchangeable potassium, and exchangeable sodium of the 1-4 in, layer and chloride and exchangeable potassium of the 8-12 in. layer. Because of a high degree of association between a number of these, the best yield prediction equation involves two only, viz. exchangeable calcium at 1-4 in. (XI as m-equiv./100 g) and chloride at 8-12 in. (X2 as %). The regression equation is Y = 85.1 + 28.3 X1 - 330.6 X2, accounting for 66% of the variability in yield. In the absence of data on exchangeable calcium, other properties closely correlated with it would have predictive value, e.g. clay content at 1-4 in. (X3 as %), the regression becoming Y = 98.5 - 266.1 X2 - 3.6 X3. The technique of seeking soil-plant relationships by direct experimentation is discussed briefly.
A field method for measurement of gas diffusion into soils
Authors: McIntyre DS , Philip JR
Published: April 2005

A transient method for field measurement of gas diffusion into soil is presented. The theory of the method and the results of preliminary tests are given. Diffusion takes place from a reservoir mounted on a tube driven into the soil. The theoretical analysis is used in the design of the experimental method, the relative importance of the various parameters involved in apparatus design and in measurement being evaluated. The apparatus is described and sample calculations of parameters given. When porosity is uniform with depth, diffusion coefficients obtained in the field agree well with results of diffusion measurements of other workers made under better controlled (laboratory) conditions.
A study of some brigalow soils based on trace-element profiles
Authors: Oertel AC , Giles JB
Published: April 2005

Evidence indicative of layering in the original parent material of a soil can be obtained from trace-element profiles. Some of the layers detected by this means in the parent materials of the brigalow soils examined were not apparent in the field. Trace element profiles also provided confirmatory evidence for the occurrence of a buried soil. The present alkaline-acid boundary of brigalow soils with acid substrata frequently did not coincide with a layer interface, and two distinct levels of concentration of pH-sensitive trace elements were found in the alkaline layer of some of these soils. These observations are compatible with movement of the alkaline-acid boundary during pedogenesis. Of the elements boron, cobalt, copper, gallium, manganese, molybdenum, nickel, lead, vanadium, and zirconium, all but cobalt, manganese, and nickel, which were pH-sensitive, had profiles that were typical of grey and brown soils of heavy texture. In addition, the average silt-plus-clay profile of the brigalow soils examined was almost identical with that of typical soils of this taxonomic group. These results support the conclusion from field observations that, apart from reaction, brigalow soils are mostly typical grey or brown soils of heavy texture.
The mineralogy and chemistry of manganese in some Australian soils
Authors: Taylor RM , McKenzie RM , Norrish K
Published: April 2005

The mineralogical and chemical compositions of 28 manganese nodules from Australian soils were studied. Specific manganese minerals were identified in 26 of these after extraction and concentration from the associated soil minerals; 10 were lithiophorite Li2A18 (Mn2+, Co, Ni)2, Mn4+10O35.14H2O; 10 were birnessite, (Ca, Mg, Na2, K2)x Mn4+Mn2+(O, OH)2; 3 were hollandite, Ba(Mn4+, Fe3+)8O16; 1 was todorokite (Mn2+, Mg, Ca)Mn4+6O13.3-4H2O; 1 was pyrolusite MnO2; 1 contained both lithiophorite and hollandite. With the possible exception of pyrolusite, all samples were found to contain varying amounts of Ni, Co, Mg, Ba, Al, K, Na, Fe, and Ca. Although there was overlap in the chemistry of the birnessite and lithiophorite groups, the mean concentrations of aluminium, iron, and lithium were lower and the mean concentration of calcium and magnesium higher in the former group. Pure manganese oxides and hydroxides appear to be quite rare as secondary soil minerals. Lithiophorite occurred mainly in neutral to acid subsurface soils, whereas birnessite, although found in both acid and alkaline soils, was more common in alkaline surface horizons. The average crystallite size of the manganese mineral aggregates was quite small, being of the order of 0.02 �m for birnessites and 0.1 �m for the lithiophorites.
The impedance of soil seals and the forces of emerging seedlings
Authors: Arndt W
Published: April 2005

Surface seals were produced on field plots of Tippera sandy clay by simulated rainfall and natural drying. The impedance was determined by recording the force required to bring about the emergence of mechanical probes buried prior to seal formation. In comparison with the impedance of loose dry soil, wetting and draining to field capacity caused a two- to threefold increase in impedance. On drying to 6% water content the impedance increased to a maximum of four to nine times the initial dry soil value. On further drying to 2% water content the impedance decreased to about two-thirds of the maximum value. Axial seedling forces calculated for a range of stem diameters and assumed turgor pressures were matched with the seal impedance data to produce a model which provides a quantitative assessment of the mechanical impedance met by seedlings.
The drainage component of the water balance equation
Authors: Rose CW , Stern WR
Published: April 2005

A method is presented for determining the drainage term in the water balance equation, which may then be used to solve for evaporation from field crops. Questions concerning accuracy in determination of the drainage term are considered. Two special problems that arise in this context with swelling clay soils are discussed, namely, the variation of bulk density with water content, and the inference of in situ soil water suction from volumetric water content measurement.
Resistance to penetration of fine probes in compressible soil
Authors: Farrell DA , Greacen EL
Published: April 2005

Fine metal probes are being used to simulate the penetration of plant roots into soil. Existing soil mechanics theories on the bearing capacity of piles were used to estimate the point resistance of these probes but were found to be unsatisfactory. It is considered that this was due to the fact that sufficient emphasis is not given to soil compression by these theories. A new theory is proposed that is based on the model of an expanding sphere in a plastic-elastic medium at the point of the probe. Compression of the soil to accommodate the volume of the probe is assumed to occur in two main zones, a zone of compression with plastic failure surrounding the probe and, outside this, a zone of elastic compression. In estimating the point resistance to the penetrometer, the mean contact pressure on the conical surface of the point has been assumed to be equal to the pressure required to form a cavity large enough to take the probe. For three soils ranging from a loam (12% clay) to a clay soil (48% clay) at three bulk densities and two water contents the calculated point resistances were on the average within 10% of the values determined by experiment.
Emergence response of subterranean clover to dissolved gypsum in relation to soil properties and evaporative conditions
Authors: Loveday J , Scotter DR
Published: April 2005

Using small plots set in the earthen floor of an open glasshouse, the emergence response of subterranean clover to dissolved gypsum has been determined on 10 soils covering a range of clay and exchangeable sodium levels. The response on a loam soil of low exchangeable sodium percentage (E.S.P.) has been examined at three times of differing evaporative potential. For loams and clay loams, the appearance of a response depends on the severity of evaporative conditions as well as on the E.S.P. On clay soils not naturally self mulching, some response is probably always obtained but, in general, the higher the clay content and the higher the E.S.P. and evaporative potential, the more likely is an emergence response to dissolved gypsum. Emergence was found to be highly correlated with the matric potential of the surface 1/2 in. at the time emergence began. From a consideration of the relationships between emergence and moisture status, the most significant effect of the gypsum treatment seems to be the delay of several days it causes in the air drying of the surface soil, probably because of improved transmission of moisture from beneath. Parallel effects on surface soil temperature to those on moisture can be explained in terms of differences in amount of evaporative cooling. Relationships found between emergence and emergence response to gypsum on the one hand and clay content and E.S.P. on the other are presumably a reflection of the relationship of these soil properties to porosity and moisture transmission.
Physical changes in seedbed material resulting from the application of dissolved gypsum
Authors: Scotter DR , Loveday J
Published: April 2005

The effect of an initial irrigation of gypsum solution, as compared with water, on water retention and transmission in a seedbed loam and clay and the subsequent changes in porosity during drying have been studied. A marked increase in hydraulic conductivity, particularly in the clay soil, and concomitant increases in total and air-filled porosity at all matric potentials, from near saturation to oven dry, were measured. The data provide an explanation of the earlier observation that improved emergence resulting from gypsum treatment was associated with the maintenance of higher matric potentials in the surface 4 in. of soil for longer periods after irrigation.
Studies on the Phosphate Potentials of Soils IV The mechanism of the 'soil/solution ratio effect'
Authors: White R.E
Published: April 2005

The equilibrium phosphate potentialSP and the slope of the quantity/intensity (Q/I) relation of three contrasted soils increased as the soil/solution ratio was decreased from 115 to 1/50. On allowing the soil phosphate to achieve equilibrium by prolonged storage under constant environmental conditions, the equilibrium potentialSP and the slope dQ/dI remained constant and independent of the soil/solution ratio. The 'soil/solution ratio effect' is interpreted in terms of phosphate disequilibrium, a condition common in soils in situ, which can be due to either non-uniform removal of phosphate or to non-uniform distribution of soluble phosphate recently added to the soil. The two kinds of disequilibrium cannot be distinguished by their observed soil/solution ratio effects, but may be identified by the direction of change of the potentialsp on the attainment of equilibrium in the soil. PotentialSP values measured in initially phosphate-free solutions are discussed with reference to their dependence on the soil/solution ratio. Aslyng's method of extrapolating to 'zero dilution' gives a reasonably accurate measure of the true potentialSP of an 'equilibrium' soil, but is in error for a 'disequilibrium' soil. It is suggested that the equilibrium potentialSP determined at a 1/50 (or smaller) soil/solution ratio will provide an adequate measure of the mean potentialSP of a disequilibrium soil.
Characterizing soil aeration with a platinum microelectrode. II. Response under controlled soil physical conditions
Authors: McIntyre DS
Published: April 2005

Platinum microelectrode currents were measured in glass beads and two soils each at two different moisture contents. Diffusivity was kept constant for each soil at each moisture content but oxygen content was varied by changing the composition of the aerating gas. Results showed that current was strongly dependent on voltage; no plateau appeared in the current-voltage curves, but when comparison was made at constant effective voltage, rather than at constant applied voltage, a linear relation existed between current and oxygen concentration up to 21%. Electrical resistance of the soil was measured to allow comparison at constant effective voltage. Oxygen flux calculated at constant effective voltage, unlike that at constant applied voltage, is characteristic of soil aeration conditions irrespective of other physical properties, provided the moisture content of the soil is sufficiently high for satisfactory operation of the method.
Germination of seeds as influenced by matric potential and by area of contact between seed and soil water
Authors: Collis-George N , Hector JB
Published: April 2005

Experiments with Medicago tribuloides and Lactuca sativa confirm Sedgley's conclusion that the wetted area of contact is a factor controlling germination of the seed. The evidence suggests that this is of consequence at matric potentials near that of free water and is most important for germination of the last seeds in each population. Matric potential is shown to be an important factor in seed germination over and above its effect in controlling the wetted contact area of seed and medium. Prewetting the seed at matric potentials near that of free water for a few minutes increases the germination rate markedly and minimizes the normal effect of matric potential. The results and experimental conclusions are discussed and are shown to indicate the need for further investigation. They show that it is practicable to design experiments to distinguish the effects of the various facets of soil water energy on seed germination behaviour.
Proposed outflow method for the determination of the hydraulic conductivity of unsaturated porous materials
Authors: Collis-George N , Rosenthal MJ
Published: April 2005

Examination of the existing outflow methods reveals that none of the available methods consider membrane impedance without simultaneously involving subjective curve matching. A method is proposed that meets both these requirements and also allows determination of hydraulic conductivity after only small changes of moisture content; the results are therefore easier to interpret. A comparison is made between results obtained from the proposed method and from published outflow methods, as well as from the horizontal infiltration and 'air-pressure' methods. The results obtained exhibit hysteresis for both diffusivity and hydraulic conductivity as functions of moisture content. An hypothesis explaining occurrence of hysteresis in hydraulic conductivity at low moisture contents is presented. It is concluded that the proposed outflow method is experimentally suited to the dry end of the moisture content range, because of the restriction imposed at high moisture contents by the membrane impedance being large relative to the sample impedance. A simple criterion to determine the range of validity of the method is proposed.
Sorption and infiltration in heterogeneous media
Authors: Philip JR
Published: April 2005

Problems of unsteady water transfer in unsaturated heterogeneous media are mathematically very complicated, and, in general, each problem for each medium requires its own ad hoc solution (e.g, by high speed computer). The approach is necessarily a piecemeal one and does not lead readily to generalizations. This paper reports a first attempt at an alternative method of attack, in which we identify and explore subclasses of problems that are amenable to quasi-analytical methods of analysis. The work deals, specifically, with problems of absorption and desorption in one-dimensional heterogeneous media. The extension to one-dimensional infiltration is also indicated. We consider 'scale-heterogeneous' media, i.e, media in which the internal geometry is everywhere geometrically similar but in which the characteristic internal length scale is free to vary spatially. The spatial variation of the hydraulic conductivity function and of the capillary potential function are thus connected. It is shown that, if the conductivity and potential functions are of certain simple forms (which are reasonable approximations to those found for soils, at least over certain ranges of potential), the flow equation, with potential as a variable, may be solved readily by established methods. The potential profiles preserve similarity, but the moisture profiles (which are found by a simple supplementary calculation) do not. Examples are given of absorption and desorption in five scale-heterogeneous media. The examples are for �0/�1 = 100 (absorption) and 0.01 (desorption), where �0 is the initial potential and �1 is the potential at which water is supplied to, or removed from, the surface. The solutions may be adapted very simply to apply to any other scale-heterogeneous medium of this class. They can also be extended readily to embrace other values of �0/�1, by reference to solutions in the literature, or by use of a rapid and accurate numerical method. Solutions of the corresponding one-dimensional infiltration problem may be found by similar means, use being made of quasi-analytical methods previously established in the analysis of infiltration in homogeneous media.
A classification of soil aggregates based on their coherence in water
Authors: Emerson WW
Published: April 2005

Soil aggregates have been divided into seven classes by observing the coherence of the clay fraction after reacting aggregates with water. The reactions used were: immersion of dry aggregates in water, immersion of wet remoulded aggregates in water, and suspension of aggregates in water. One further class was distinguished by the presence of carbonate. Illite and montmorillonite clays were modified so as to exhibit the physical properties of some of the aggregate classes. The results with the clays were then used to explain the characteristic properties of aggregates derived from a wide variety of soils in the various classes. For example, class 2 aggregates show partial dispersion when placed, dry, in water. The minimum percentage of exchangeable sodium present in aggregates of this class was equal to that required for dispersion of the dry Na/Ca-clays immersed in water. Examples are given of where the detection of dispersion from aggregates can be useful in the field. As only simple tests are used, the proposed method of classification can be easily carried out under field conditions.
Phosphate sorbing sites in acid soils. I. An examination of the use of ammonium fluoride as a selective extractant for aluminium-bound phosphate in phosphated soils
Authors: Bromfield SM
Published: April 2005

Soils, aluminium oxides, and iron oxides were phosphated with 1M ammonium phosphate at pH 4.0. These and crystalline iron and aluminium phosphates were extracted at pH 7 and pH 8.5 with ammonium chloride and ammonium fluoride both at 1:300 and 1:2000 sample/extractant ratios. Crystalline iron phosphate was readily distinguished from crystalline aluminium phosphate due to the much lower solubility of the iron phosphate in ammonium fluoride. On the other hand, phosphated iron oxides, especially phosphated haematites, released much of their phosphate to ammonium fluoride and thus could be confused with crystalline aluminium phosphate and phosphated aluminium oxides. The discrimination between phosphated oxides of iron and aluminium although poor was better at the narrower sample/extractant ratio of 1:300, the pH of the extractant being relatively unimportant. Under these conditions, phosphated soils released a larger proportion of their phosphate than did phosphated hydrated iron oxides. This suggests that hydrated iron oxides do not dominate sorption in these soils. X-ray data were consistent with this view. The relative importance of iron and aluminium in phosphated soils containing appreciable amounts of gibbsite, kaolin, and haematite could not be assessed using ammonium fluoride extractions. Since ammonium fluoride does not readily discriminate between phosphated oxides of iron and aluminium, it is unwise to assume that this reagent dissolves mainly aluminium-bound phosphate from soils fertilized with phosphate.
Carbohydrates in some Australian soils
Authors: Oades JM
Published: April 2005

Carbohydrate contents of soils and soil fractions were determined by acid hydrolysis, clarification of the hydrolysate with charcoal, and the use of anthrone for the colorimetric determination of monosaccharides. Between 4 and 14% of the soil organic carbon was present as carbohydrate. During the growth of a pasture there is an accumulation of carbohydrate materials in partly decomposed plant remains in the soil. When such materials are removed, the proportion of the remainder of the soil organic matter in the form of carbohydrate is not changed by different cropping practices, in spite of large changes in the absolute amounts of carbohydrates present. Neither total organic matter nor total carbohydrate content is very closely correlated with aggregate stability. The differences in aggregate stability brought about by changes in seasons and cropping practices, and indicated by the periodate technique to be associated with polysaccharides, are most likely a result of qualitative changes within the soil carbohydrate fraction.