ACFM above a hemispherical pit in an aluminum block

Much of the recent research at the NDE Centre at UCL has revolved round the study of the scattering of thin skin electromagnetic fields by a fatigue crack. The early work concentrated on the perturbations to the surface electric field (ACPD), while the more recent work involved the scattered magnetic field (ACFM). The Centre has recently become involved in a collaborative project, a part of which involves the detection and sizing of pits in mild steels using ACFM and other inspection techniques, and the purpose of this paper is to study the complementary problem of pit detection in non-magnetic conductors. The case of a hemispherical pit was initially chosen on grounds of simplicity, since the modeling work can be done in spherical polar coordinates, whereas the more general case of a spherical cap would require the use of bipolar coordinates. As was the case with most of the fatigue crack modeling, it was assumed initially that the unperturbed magnetic field was uniform

Australasian asphaltite strandings revisited: Their origin and the effects of weathering and biodegradation on their biomarker and isotopic profiles

Reports of bitumen strandings on the coastlines of South Australia, Victoria, Tasmania and Western Australia date from the early 19th Century (Sprigg and Woolley, 1963; Currie et al., 1992; Volkman et al., 1992; McKirdy et al., 1994; Padley, 1995; Edwards et al., 1998 and references therein). The locations of these strandings along Australia’s southern margin (Fig. 1), and their greater frequency in southeastern South Australia, western Victoria and southern Tasmania, fuelled early petroleum exploration in the region on the assumption that they were sourced from local submarine seepages (Sprigg, 1986; Volkman et al., 1992; McKirdy et al., 1994). Accounts describe a variety of oily substances that can be assigned to three categories, each with a different origin: oils (crude and refined), waxy bitumens and asphaltites (McKirdy et al., 1986, 1994; Padley, 1995; Edwards et al., 1998)

Forward and Inverse Processing in Electromagnetic NDE Using Squid

Electromagnetic NDE has been successfully applied to the detection of surface cracks and is routinely used to locate flaws in airframes, pipelines and in steel offshore oil platforms. However, there are still many problems to be solved, particularly in the aviation industry, which require the detection of deeper flaws such as corrosion in multi-layered structures and cracks around rivet holes which are obscured by the head of the rivet. Most systems use coils as detectors (though Hall probes are occasionally used), which have low sensitivity at low frequencies due to the fact that the induced voltage is proportional to the rate of change of magnetic flux through the coil. Unfortunately it is necessary to use low frequencies to detect deep subsurface flaws on account of the skin-depth effect, otherwise the electromagnetic field cannot propagate down to the depth of the flaw. SQUID (Superconducting Quantum Interference Device) sensors are ideally suited to overcome the deficiencies of coils, because they are primarily detectors of magnetic flux which, together with their high sensitivity, makes the detection of deep flaws more likely. SQUIDs have been successfully used for measuring very low magnetic fields, particularly in the field of biomagnetism, and it is hoped to exploit this sensitivity to detect flaws at large stand-off distances for example in pipelines which are surrounded by thick layers of cladding

Petroleum geochemistry of the Amadeus Basin

Amber Jarrett, Dianne Edwards, Chris Boreham and David McKird

Benchmark Problems in Eddy-Current NDE

Inversion of eddy-current data and the reconstruction of flaws is the preeminent problem in electromagnetic nondestructive evaluation (NDE). This places a premium on developing good forward models for computing field-flaw interactions, because all inversion algorithms must, of necessity, rely on such calculations. There has evolved in recent years several sophisticated computational models for the forward problem [1–4], but these models differ significantly in their theoretical and numerical approaches. For example, [1-3] use a volume-integral approach that incorporates fast Fourier transforms with conjugate gradients to solve the resulting linear system of equations, whereas [4] uses finite-elements

Biosecurity risks posed by a large sea-going passenger vessel: Challenges of terrestrial arthropod species detection and eradication

Large sea-going passenger vessels can pose a high biosecurity risk. The risk posed by marine species is well documented, but rarely the risk posed by terrestrial arthropods. We conducted the longest running, most extensive monitoring program of terrestrial arthropods undertaken on board a passenger vessel. Surveillance was conducted over a 19-month period on a large passenger (cruise) vessel that originated in the Baltic Sea (Estonia). The vessel was used as an accommodation facility to house workers at Barrow Island (Australia) for 15 months, during which 73,061 terrestrial arthropods (222 species - four non-indigenous (NIS) to Australia) were collected and identified on board. Detection of Tribolium destructor Uytt., a high-risk NIS to Australia, triggered an eradication effort on the vessel. This effort totalled more than 13,700 human hours and included strict biosecurity protocols to ensure that this and other non-indigenous species (NIS) were not spread from the vessel to Barrow Island or mainland Australia. Our data demonstrate that despite the difficulties of biosecurity on large vessels, stringent protocols can stop NIS spreading from vessels, even where vessel-wide eradication is not possible. We highlight the difficulties associated with detecting and eradicating NIS on large vessels and provide the first detailed list of species that inhabit a vessel of this kind

Experimental summary 1988

1. Disease complexes in wheat field screening trials. 2. Glasshouse screening for wheat leaf disease resistance. 3. Effect of phosphate, stand density and Rovral on Pleiochaeta setosa in lupins. 4. Genotype and rvral for Pleichaeta setosa in lupins. 5. Control of Septoria in early sown wheat. 6. Controlling Pyrenophora graminea leaf stripe in barley. 7. Effect of environment on leaf stripe in barley. 8. Unusual seed quality problems

Organic facies of the Frome Embayment and Callabonna Sub-basin: what and where are the uranium reductants?

Bernd H Michaelsen, Adrian J Fabris, John L Keeling, David M McKirdy, Laszlo F Katona and Les R Tucke

A common neural system mediating two different forms of social judgement

Background: A wide range of neuropsychiatric conditions, including schizophrenia and autistic spectrum disorder (ASD), are associated with impairments in social function. Previous studies have shown that individuals with schizophrenia and ASD have deficits in making a wide range of social judgements from faces, including decisions related to threat (such as judgements of approachability) and decisions not related to physical threat (such as judgements of intelligence). We have investigated healthy control participants to see whether there is a common neural system activated during such social decisions, on the basis that deficits in this system may contribute to the impairments seen in these disorders. Method: We investigated the neural basis of social decision making during judgements of approachability and intelligence from faces in 24 healthy participants using functional magnetic resonance imaging (fMRI). We used conjunction analysis to identify common brain regions activated during both tasks. Results: Activation of the amygdala, medial prefrontal cortex, inferior prefrontal cortex and cerebellum was seen during performance of both social tasks, compared to simple gender judgements from the same stimuli. Task-specific activations were present in the dorsolateral prefrontal cortex in the intelligence task and in the inferior and middle temporal cortex in the approachability task. Conclusions: The present study identified a common network of brain regions activated during the performance of two different forms of social judgement from faces. Dysfunction of this network is likely to contribute to the broad-ranging deficits in social function seen in psychiatric disorders such as schizophrenia and ASD

Virus diseases of annual medics.

Trial 87A19, 87MT50 Persistence of AMV in annual medic swards. In 1990, the fourth year of this trial, although the medic plants were numerous the burr medic swards at Avondale grew poorly and weeds were widespread in the plots, especially long storkbill, flatweed and grasses. Poor growth was due to nodulation failure caused by low soil pH (5.3 in water). Hardly any medic plants were left in the Zodiac medic plot at Avondale while a few remained at Mt. Barker. Location: Avondale and Mt. Barker. Trial 88A21 Effect of AMV on the productivity of burr medic swards after cropping, regeneration and grazing. Location: Avondale 88A21 was allowed to regenerate in 1990 following cropping with barley in 1989. It was hard grazed in summer and autumn (first germination was in February following summer rains). Then, at the beginning of June sheep were excluded and the buffers resown with oats. It was subsequently grazed again from mid-August to early-September (3 weeks) but as grazing was uneven all plots were mown (4 cm cutting height) at the end of this period to even them up. Trial 90A5 Effect of AMV on the productivity of newly sown burr medic swards. Location: Avondale 90A5 was sown in early June and grazed portions of plots were grazed from August 15 - September 7. There were major differences in the plots due to seed source. With all three cultivars the infected seed stocks produced more vigorous growth. This was visible from July to September in ungrazed portions of plots but was largely removed by grazing. When the phosphorus content of the seed stocks sown was determined it was higher in infected than healthy seed. Seed phosphorus seemed the most likely cause of better growth of infected seed