Host selection in phytophagous insects: a new explanation for learning in adults

Insect learning can change the preferences an egg laying female displays towards different host plant species. Current hypotheses propose that learning may be advantageous in adult host selection behaviour through improved recognition, accuracy or selectivity in foraging. In this paper, we present a hypothesis for when learning can be advantageous without such improvements in adult host foraging. Specifically, that learning can be an advantageous strategy for egg laying females when larvae must feed on more than one plant in order to complete development, if the fitness of larvae is reduced when they switch to a different host species. Here, larvae benefit from developing on the most abundant host species, which is the most likely choice of host for an adult insect which increases its preference for a host species through learning. The hypothesis is formalised with a mathematical model and we provide evidence from studies on the behavioural ecology, of a number of insect species which demonstrate that the assumptions of this hypothesis may frequently be fulfilled in nature. We discuss how multiple mechanisms may convey advantages in insect learning and that benefits to larval development, which have so far been overlooked, should be considered in explanations for the widespread occurrence of learning.

A new diffusion and flow theory for activated carbon from low pressure to capillary condensation range

In this paper, we develop a theory for diffusion and flow of pure sub-critical adsorbates in microporous activated carbon over a wide range of pressure, ranging from very low to high pressure, where capillary condensation is occurring. This theory does not require any fitting parameter. The only information needed for the prediction is the complete pore size distribution of activated carbon. The various interesting behaviors of permeability versus loading are observed such as the maximum permeability at high loading (occurred at about 0.8-0.9 relative pressure). The theory is tested with diffusion and flow of benzene through a commercial activated carbon, and the agreement is found to be very good in the light that there is no fitting parameter in the model. (C) 2001 Elsevier Science B.V. All rights reserved.

Biostatistics in Australia: Directions in the new millennium

The Biostatistics Collaboration of Australia (BCA) was formed in response to a shortage of statisticians seeking careers in the medical and health professions. The Collaboration has been successful in developing postgraduate courses (Graduate Certificate, Graduate Diploma and Masters) offered by a consortium of seven Australian Universities. These courses are available through a distance learning medium. The BCA was successful in securing funding from the Federal government to launch these courses, which commenced in March 2001. Two traineeships by the NSW Department of Health have also been awarded and a third is currently advertised. There has been close collaboration with governments, the pharmaceutical industry and research organisations to ensure that course content reflects practical problems and addresses industry needs. A second objective of the BCA is to provide ongoing workshops for practising biostatisticians to enhance professional development. These workshops serve to ring together biostatisticians from both within Australia and the Asia-Pacific region, providing a forum for discussion of current statistical thinking. (author abstract)

New methods for the assessment of in vitro and in vivo stress cracking in biomedical polyurethanes

This article describes a new test method for the assessment of the severity of environmental stress cracking of biomedical polyurethanes in a manner that minimizes the degree of subjectivity involved. The effect of applied strain and acetone pre-treatment on degradation of Pellethane 2363 80A and Pellethane 2363 55D polyurethanes under in vitro and in vivo conditions is studied. The results are presented using a magnification-weighted image rating system that allows the semi-quantitative rating of degradation based on distribution and severity of surface damage. Devices for applying controlled strain to both flat sheet and tubing samples are described. The new rating system consistently discriminated between. the effects of acetone pre-treatments, strain and exposure times in both in vitro and in vivo experiments. As expected, P80A underwent considerable stress cracking compared with P55D. P80A produced similar stress crack ratings in both in vivo and in vitro experiments, however P55D performed worse under in vitro conditions compared with in vivo. This result indicated that care must be taken when interpreting in vitro results in the absence of in vivo data. (C) 2001 Elsevier Science Ltd. All rights reserved.

Can long-distance dispersal be inferred from the New Zealand plant fossil record?

New Zealand is generally thought to have been physically isolated from the rest of the world for over 60 million years. But physical isolation may not mean biotic isolation, at least on the time scale of millions of years. Are New Zealand's present complement of plants the direct descendants of what originally rafted from Gondwana? Or has there been total extinction of this initial flora with replacement through long-distance dispersal (a complete biotic turnover)? These are two possible extremes which have come under recent discussion. Can the fossil record be used to decide the relative importance of the two endpoints, or is it simply too incomplete and too dependent on factors of chance? This paper suggests two approaches to the problem-the use of statistics to apply levels of confidence to first appearances in the fossil record and the analysis of trends based on the entire palynorecord. Statistics can suggest that the first appearance of a taxon was after New Zealand broke away from Gondwana-as long as the first appearance in the record was not due to an increase in biomass from an initially rare state. Two observations can be drawn from the overall palynorecord that are independent of changes in biomass: (1) The first appearance of palynotaxa common to both Australia and New Zealand is decidedly non-random. Most taxa occur first in Australia. This suggests a bias in air or water transport from west to east. (2) The percentage of endemic palynospecies in New Zealand shows no simple correlation with the time New Zealand drifted into isolation. The conifer macrorecord also hints at complete turnover since the Cretaceous.

Repeated flood events and fossil forests at Curio Bay (Middle Jurassic), New Zealand

During the Middle Jurassic, the regional environment of Curio Bay, southeast South Island, New Zealand, was a fluvial plain marginal to volcanic uplands. Intermittent flashy, poorly-confined flood events buried successive conifer forests. With the termination of each flood, soils developed and vegetation was reestablished. In most cases, this developed into coniferous forest. In approximately 40 m of vertical section, 10 fossil forest horizons can be distinguished, highlighting a type of fluvial architecture which is poorly documented. Flood-basin material is minimal, but a short-Lived floodbasin lake is inferred to have developed within the interval of study. Paleocurrent indicators suggest enclosure of the basin on more than one side. Sedimentation style suggests a relatively dry (less than humid but not arid) climate with seasonal rainfall. (C) 2001 Elsevier Science B.V. All rights reserved.

Cultural frictions: John Romeril's The 'Floating World'

Hailed as an 'unruly masterpiece', John Romeril's The Floating World is one of the few 'new wave' Australian plays representing Australians and their Asian 'others' to be restaged periodically since its premiere in 1974. Paying particular attention to production of the play that have used Japanese theatre forms such as kabuki and bunraku, this article focuses primarily on the ways in which the significations of race have been interpreted by the critical establishment. The fascinating stage history of The Floating World is treated as a barometer of Australian theatre's response to the challenge of representing cultural conflict, during a period marked by public debate about the desirability, and inevitability, of Australia's political, economic and cultural 'enmeshment' with Asia.

A new method of threshold voltage extraction via MOSFET gate-to-substrate capacitance measurement

A new method to extract MOSFET's threshold voltage VT by measurement of the gate-to-substrate capacitance C-gb of the transistor is presented. Unlike existing extraction methods based on I-V data, the measurement of C-gb does not require de drain current to now between drain and source thus eliminating the effects of source and drain series resistance R-S/D, and at the same time, retains a symmetrical potential profile across the channel. Experimental and simulation results on devices with different sizes are presented to justify the proposed method.