Transfer of a supernumerary chromosome between vegetatively incompatible biotypes of the fungus Colletotrichum gloeosporioides

Two biotypes (A and B) of Colletotrichum gloeosporioides infect the tropical legumes Stylosanthes spp. in Australia. These biotypes are asexual and vegetatively incompatible. However, field isolates of biotype B carrying a supernumerary 2-Mb chromosome, thought to originate from biotype A, have been reported previously. We tested the hypothesis that the 2-Mb chromosome could be transferred from biotype A to biotype B under laboratory conditions. Selectable marker genes conferring resistance to hygromycin and phleomycin were introduced into isolates of biotypes A and B, respectively. A transformant of biotype A, with the hygromycin resistance gene integrated on the 2-Mb chromosome, was cocultivated with phleomycin-resistant transformants of biotype B. Double antibiotic-resistant colonies were obtained from conidia of these mixed cultures at a frequency of approximately 10(-7). Molecular analysis using RFLPs, RAPDs, and electrophoretic karyotypes showed that these colonies contained the 2-Mb chromosome in a biotype B genetic background. In contrast, no double antibiotic colonies developed from conidia obtained from mixed cultures of phleomycin-resistant transformants of biotype B with biotype A transformants carrying the hygromycin resistance gene integrated in chromosomes >2 Mb in size. The results demonstrated that the 2-Mb chromosome was selectively transferred from biotype A to biotype B. The horizontal transfer of specific chromosomes across vegetative incompatibility barriers may explain the origin of supernumerary chromosomes in fungi.

Architecture and morphogenesis of grain sorghum, Sorghum bicolor (L.) Moench

Plant architecture has been neglected in most studies of biomass allocation in crops. To help redress this situation for grain sorghum (Sorghum bicolor (L.) Moench), we used a 3D digitiser to measure the dimensions and orientations of vegetative and reproductive structures and derived thermal time-based functions for architectural changes during morphogenesis. Our plants, which were grown in a greenhouse, controlled environment cabinets and the field, covered a large, three-fold, size range when mature. This allowed us to detect some general architectural relationships and to fit morphogenetic functions common across the size range we observed. For example, the relationship between the lengths of successive fully-expanded leaves within a plant was nearly constant for all plants. The lengths of existing leaf blades were accurate predictors of the lengths of up to six subsequently-formed blades in our plants. Similar constant relationships were detected for internode lengths in the panicle and for heights above ground of the collars of successive leaves, even though these traits varied a lot between growth conditions. We suggest that such architectural relationships may be used to link the effect of previous growth conditions to future growth potential, and in that way to predict future partitioning. Our results provide the basis for a preliminary model of sorghum morphogenesis which could eventually become useful in conjunction with crop models by allowing resource acquisition to be related to changes in plant architecture during development. (C) 1999 Elsevier Science B.V. All rights reserved.

The crack tip strain field of AISI 4340 - Part II - Experimental measurements

Crack tip strain maps have been measured for AISI 4340 high strength steel. No significant creep was observed. The measured values of CTOD were greater than expected from the HRR model. Crack tip branching was observed in every experiment. The direction of crack branching was in the same direction as a major ridge'' of epsilon(yy) strain, which in turn was in the same direction as predicted by the HRR model. Furthermore, the measured magnitudes of the epsilon(y)y strain in this same direction were in general greater than the values predicted by the HRR model. This indicates more plasticity in the crack tip region than expected from the HRR model. This greater plasticity could be related to the larger than expected CTOD values. The following discrepancies between the measured strain fields for AISI 4340 and the HRR predictions are noteworthy: (1) The crack branching. (2) Values of CTOD significantly higher than predicted by HRR. (3) The major ridge'' of epsilon(yy) strain an angle of about 60 degrees with the direction of overall propagation of the fatigue precrack, in which the measured magnitudes of the epsilon(yy) strain were greater than the values predicted by the HRR model. (4) Asymmetric shape of the plastic zone as measured by the epsilon(yy) strain. (5) Values of shear strain gamma(xy) significantly higher than predicted by the HRR model. (C) 1999 Kluwer Academic Publishers.

The crack tip strain field of AISI 4340 - Part III - Hydrogen influence

This paper studied the influence of hydrogen and water vapour environments on the plastic behaviour in the vicinity of the crack tip for AISI 4340. Hydrogen and water vapour (at a pressure of 15 Torr) significantly increased the crack tip opening displacement. The crack tip strain distribution in 15 Torr hydrogen was significantly different to that measured in vacuum. In the presence of sufficient hydrogen, the plastic zone was larger, was elongated in the direction of crack propagation and moreover there was significant creep. These observations support the hydrogen enhanced localised plasticity model for hydrogen embrittlement in this steel. The strain distribution in the presence of water vapour also suggests that SCC in AISI 4340 occurs via the hydrogen enhanced localised plasticity mechanism. (C) 1999 Kluwer Academic Publishers.

Incorporating phase retardation effects into radiofrequency resonator models: application to magnetic resonance microscopy

A method is presented for including path propagation effects into models of radiofrequency resonators for use in magnetic resonance imaging. The method is based on the use of Helmholtz retarded potentials and extends our previous work on current density models of resonators based on novel inverse finite Hilbert transform solutions to the requisite integral equations. Radiofrequency phase retardation effects are most pronounced at high field strengths (frequencies) as are static field perturbations due to the magnetic materials in the resonators themselves. Both of these effects are investigated and a novel resonator structure presented for use in magnetic resonance microscopy.

Beach water table fluctuations due to spring-neap tides: moving boundary effects

Tidal water table fluctuations in a coastal aquifer are driven by tides on a moving boundary that varies with the beach slope. One-dimensional models based on the Boussinesq equation are often used to analyse tidal signals in coastal aquifers. The moving boundary condition hinders analytical solutions to even the linearised Boussinesq equation. This paper presents a new perturbation approach to the problem that maintains the simplicity of the linearised one-dimensional Boussinesq model. Our method involves transforming the Boussinesq equation to an ADE (advection-diffusion equation) with an oscillating velocity. The perturbation method is applied to the propagation of spring-neap tides (a bichromatic tidal system with the fundamental frequencies wt and wt) in the aquifer. The results demonstrate analytically, for the first time, that the moving boundary induces interactions between the two primary tidal oscillations, generating a slowly damped water table fluctuation of frequency omega(1) - omega(2), i.e., the spring-neap tidal water table fluctuation. The analytical predictions are found to be consistent with recently published field observations. (C) 2000 Elsevier Science Ltd. All rights reserved.

A two-dimensional analytical solution of groundwater responses to tidal loading in an estuary and ocean

Previous studies on tidal dynamics of coastal aquifers have focussed on the inland propagation of oceanic tides in the cross-shore direction, a configuration that is essentially one-dimensional. Aquifers at natural coasts can also be influenced by tidal waves in nearby estuaries, resulting in a more complex behaviour of head fluctuations in the aquifers. We present an analytical solution to the two-dimensional depth-averaged groundwater flow equation for a semi-infinite aquifer subject to oscillating head conditions at the boundaries. The solution describes the tidal dynamics of a coastal aquifer that is adjacent to a cross-shore estuary. Both the effects of oceanic and estuarine tides on the aquifer are included in the solution. The analytical prediction of the head fluctuations is verified by comparison with numerical solutions computed using a standard finite-difference method. An essential feature of the present analytical solution is the interaction between the cross- and along-shore tidal waves in the aquifer area near the estuary's entry. As the distance from the estuary or coastline increases, the wave interaction is weakened and the aquifer response is reduced, respectively, to the one-dimensional solution for oceanic tides or the solution of Sun (Sun H. A two-dimensional analytical solution of groundwater response to tidal loading in an estuary, Water Resour Res 1997;33:1429-35) for two-dimensional non-interacting tidal waves. (C) 2000 Elsevier Science Ltd. All rights reserved.

Characterisation of Australian isolates of Fusarium oxysporum f. sp cubense by DNA fingerprinting analysis

Genetic variation among Australian isolates of the fungus Fusarium oxysporum f. sp. cubense (Foc), which causes Fusarium wilt in banana, was examined using DNA amplification fingerprinting (DAF). Ninety-four isolates which represented Races 1, 2, 3, and 4, and vegetative compatibility groups (VCGs) 0120, 0124, 0125, 0128, 0129, 01211, 01213/16, and 01220 were analysed. The genetic relatedness among isolates within each VCG, and between the 8 different VCGs of Foc present in Australia was determined. The DNA fingerprint patterns were VCG-specific, with each VCG representing a unique genotype. The genetic similarity among isolates within each VCG ranged from 97% to 100%. Among the different VCGs of Foc, 3 major clusters were distinguished which corresponded with race. All Race 1 and 2 isolates (VCGs 0124, 0125, 0128, and 01220) were closely related and clustered together, the Race 3 isolates from Heliconia clustered separately, and all Race 4 isolates (VCGs 0120, 0129, 01211, and 01213/16) clustered together. Fifteen isolates from Alstonville, NSW, were characterised because although they were classified as Race 2 based on their recovery from cooking banana cultivars, they belonged in VCG 0124, which had previously contained only Race 1 isolates. The occurrence of more than one race within a VCG means that vegetative compatibility grouping cannot be used to assign pathotype to pathogenic race as previously thought. It was possible to distinguish the Race 1 and Race 2 isolates within VCG 0124 using DNA fingerprinting, as each race produced a unique DNA fingerprint pattern. Among the Australian isolates, DNA fingerprinting analysis identified 9 different VCGs and genotypes of Foc.

Dynamics of trapped Bose-Einstein condensates: Beyond the mean-field

Since dilute Bose gas condensates were first experimentally produced, the Gross-Pitaevskii equation has been successfully used as a descriptive tool. As a mean-field equation, it cannot by definition predict anything about the many-body quantum statistics of condensate. We show here that there are a class of dynamical systems where it cannot even make successful predictions about the mean-field behavior, starting with the process of evaporative cooling by which condensates are formed. Among others are parametric processes, such as photoassociation and dissociation of atomic and molecular condensates.

Ultrasound evaluation of polymer gel dosimeters

A new method for the evaluation of radiotherapy 3D polymer gel dosimeters has been developed using ultrasound to assess the significant structural changes that occur following irradiation of the dosimeters. The ultrasonic parameters of acoustic speed of propagation, attenuation and transmitted signal intensity were measured as a function of absorbed radiation dose. The dose sensitivities for each parameter were determined as 1.8 x 10(-4) s m(-1) Gy(-1), 3.9 dB m(-1) Gy(-1) and 3.2 V-1 Gy(-1) respectively. All parameters displayed a strong variation with absorbed dose that continued beyond absorbed doses of 15 Gy. The ultrasonic measurements demonstrated a significantly larger dynamic range in dose response curves than that achieved with previously published magnetic resonance imaging (MRI) dose response data. It is concluded that ultrasound shows great potential as a technique for the evaluation of polymer gel dosimeters.

Tidal fluctuations in a leaky confined aquifer: localised effects of an overlying phreatic aquifer

Damping of tidal head fluctuations in a leaky confined coastal aquifer is enhanced by leakage into an overlying phreatic aquifer. We show that the phreatic aquifer is, however, resistant to the leakage flow and in particular, a deep phreatic aquifer can reduce the leakage effects significantly. An analytical solution, based on a vertical flow model for the phreatic aquifer, is derived for quantifying the role of this upper free water body in tidal propagation in the lower semi-confined aquifer. (C) 2002 Elsevier Science B.V. All rights reserved.

Review of stress corrosion cracking of pipeline steels in "low" and "high" pH solutions

This paper reviews the current understanding of the mechanisms of stress corrosion cracking of pipeline steels. The similarities, the differences and the influencing factors are considered for the high pH stress corrosion cracking caused by a concentrated bicarbonate-carbonate solution, and for the low pH stress corrosion cracking due to a diluter solution. For high pH stress corrosion cracking, it is well accepted that the mechanism involves anodic dissolution for crack initiation and propagation. In contrast, it has been suggested that the low pH stress corrosion cracking is associated with the dissolution of the crack tip and sides, accompanied by the ingress of hydrogen into the pipeline steel. But the precise influence of hydrogen on the mechanism needs to be further studied. (C) 2003 Kluwer Academic Publishers.

Visualization of learning in multilayer perceptron networks using principal component analysis

This paper is concerned with the use of scientific visualization methods for the analysis of feedforward neural networks (NNs). Inevitably, the kinds of data associated with the design and implementation of neural networks are of very high dimensionality, presenting a major challenge for visualization. A method is described using the well-known statistical technique of principal component analysis (PCA). This is found to be an effective and useful method of visualizing the learning trajectories of many learning algorithms such as back-propagation and can also be used to provide insight into the learning process and the nature of the error surface.

An equivalent algorithm for simulating thermal effects of magma intrusion problems in porous rocks

An equivalent algorithm is proposed to simulate thermal effects of the magma intrusion in geological systems, which are composed of porous rocks. Based on the physical and mathematical equivalence, the original magma solidification problem with a moving boundary between the rock and intruded magma is transformed into a new problem without the moving boundary but with a physically equivalent heat source. From the analysis of an ideal solidification model, the physically equivalent heat source has been determined in this paper. The major advantage in using the proposed equivalent algorithm is that the fixed finite element mesh with a variable integration time step can be employed to simulate the thermal effect of the intruded magma solidification using the conventional finite element method. The related numerical results have demonstrated the correctness and usefulness of the proposed equivalent algorithm for simulating the thermal effect of the intruded magma solidification in geological systems. (C) 2003 Elsevier B.V. All rights reserved.

Apparent strain localization and shear wave dispersion in elastic fault gouge with microrotations

Shear deformation of fault gouge or other particulate materials often results in observed strain localization, or more precisely, the localization of measured deformation gradients. In conventional elastic materials the strain localization cannot take place therefore this phenomenon is attributed to special types of non-elastic constitutive behaviour. For particulate materials however the Cosserat continuum which takes care of microrotations independent of displacements is a more appropriate model. In elastic Cosserat continuum the localization in displacement gradients is possible under some combinations of the generalized Cosserat elastic moduli. The same combinations of parameters also correspond to a considerable dispersion in shear wave propagation which can be used for independent experimental verification of the proposed mechanism of apparent strain localization in fault gouge.