Electric-field-induced Mott insulating states in organic field-effect transistors

We consider the possibility that the electrons injected into organic field-effect transistors are strongly correlated. A single layer of acenes can be modeled by a Hubbard Hamiltonian similar to that used for the κ-(BEDT-TTF)2X family of organic superconductors. The injected electrons do not necessarily undergo a transition to a Mott insulator state as they would in bulk crystals when the system is half-filled. We calculate the fillings needed for obtaining insulating states in the framework of the slave-boson theory and in the limit of large Hubbard repulsion U. We also suggest that these Mott states are unstable above some critical interlayer coupling or long-range Coulomb interaction.

On the permutation behaviour of Dickson polynomials of the second kind

The known permutation behaviour of the Dickson polynomials of the second kind in characteristic 3 is expanded and simplified. (C) 2002 Elsevier Science (USA).

On positive solutions of nonlinear elliptic equations involving concave and critical nonlinearities

We study the existence of nonnegative solutions of elliptic equations involving concave and critical Sobolev nonlinearities. Applying various variational principles we obtain the existence of at least two nonnegative solutions.

Geographic variation in the behaviour of the cleaner fish Labroides dimidiatus (Labridae)

Geographical variation in the outcome of interspecific interactions has a range of proximate ecological causes. For instance, cleaning interactions between coral reef fishes can result in benefits for both the cleaner and its clients. However, because both parties can cheat and because the rewards of cheating may depend on the local abundance of ectoparasites on clients, the interaction might range from exploitative to mutualistic. In a comparative analysis of behavioural measures of the association between the cleaner fish Labroides dimidiatus and all its client species, we compared cleaning interactions between two sites on the Great Barrier Reef that differ with respect to mean ectoparasite abundance. At Heron Island, where client fish consistently harbour fewer ectoparasites, client species that tended to pose for cleaners were more likely to receive feeding bites by cleaners than client species that did not pose for cleaners. This was not the case at Lizard Island, where ectoparasites are significantly more abundant. Client fish generally spent more time posing for cleaners at Lizard Island than their conspecifics at Heron Island. However, fish at Heron Island were inspected longer on average by cleaners than conspecifics at Lizard Island, and they incurred more bites and swipes at their sides per unit time from cleaners. These and other differences between the two sites suggest that the local availability of ectoparasites as a food source for cleaners may determine whether clients will seek cleaning, and whether cleaners will feed on parasites or attempt to feed on client mucus. The results suggest that cleaning symbiosis is a mosaic of different outcomes driven by geographical differences in the benefits for both participants.

Optimising cleaning behaviour: minimising the costs and maximising ectoparasite removal

Little is known of how client fish minimise the costs of cleaning behaviour while maximising ectoparasite removal by cleaner fish. Previous studies have found that abundance on fish and infestation behaviour of gnathiid isopods, the main parasite eaten by cleaner fish, varies diurnally. We examined whether reduced foraging is a cost of cleaning behaviour in clients and whether the behaviour of the client fish, the thick-lipped wrasse Hemigymnus melapterus, towards the cleaner fish Labroides dimidiatus varied diurnally to maximise ectoparasite removal, possibly in response to the diurnal changes in the abundance and infestation patterns of gnathiids. We found that during the midday and afternoon, client foraging rates were negatively related to the duration and frequency of inspections, suggesting that cleaning may, at some times of the day, be energetically costly to the client in terms of reduced foraging opportunities. Surprisingly, we found that the duration and frequency of inspections of clients by cleaners did not vary among diel time periods. A model of gnathiid dynamics on individual fish is proposed. It shows that the observed diurnal pattern in gnathiid abundance on fish can be generated with the constant duration and frequency of inspections that was observed in this study. Thus clients would not have more gnathiids removed by modifying their cleaning behaviour.

Difference equations associated with fully nonlinear boundary value problems for second order ordinary differential equations

We study the continuous problem y"=f(x,y,y'), xc[0,1], 0=G((y(0),y(1)),(y'(0), y'(1))), and its discrete approximation (y(k+1)-2y(k)+y(k-1))/h(2) =f(t(k), y(k), v(k)), k = 1,..., n-1, 0 = G((y(0), y(n)), (v(1), v(n))), where f and G = (g(0), g(1)) are continuous and fully nonlinear, h = 1/n, v(k) = (y(k) - y(k-1))/h, for k =1,..., n, and t(k) = kh, for k = 0,...,n. We assume there exist strict lower and strict upper solutions and impose additional conditions on f and G which are known to yield a priori bounds on, and to guarantee the existence of solutions of the continuous problem. We show that the discrete approximation also has solutions which approximate solutions of the continuous problem and converge to the solution of the continuous problem when it is unique, as the grid size goes to 0. Homotopy methods can be used to compute the solution of the discrete approximation. Our results were motivated by those of Gaines.

Probing the time course of nonlinear discriminations during human electrodermal conditioning

Animal-based theories of Pavlovian conditioning propose that patterning discriminations are solved using unique cues or immediate configuring. Recent studies with humans, however, provided evidence that in positive and negative patterning two different rules are utilized. The present experiment was designed to provide further support for this proposal by tracking the time course of the allocation of cognitive resources. One group was trained in a positive patterning; schedule (A-, B-, AB+) and a second in a negative patterning schedule (A+, B+, AB-). Electrodermal responses and secondary task probe reaction time were measured. In negative patterning, reaction times were slower during reinforced stimuli than during non-reinforced stimuli at both probe positions while there were no differences in positive patterning. These results support the assumption that negative patterning is solved using a rule that is more complex and requires more resources than does the rule employed to solve positive patterning. (C) 2001 Elsevier Science (USA).

Behaviour of older people admitted for residential respite care

The aim of this pilot study was to determine whether residential respite care is used because of disruptive behaviour displayed by older people. The specific objectives were to 1) characterise older people being admitted for residential respite care, 2) obtain a preliminary estimate of the proportion of older people in residential respite care because of disruptive behaviour, and, 3) examine the relationship between residential respite care and disruptive behaviour. A quantitative approach using a cross-sectional survey was employed. The respite recipients were 35 older people with a mean age of 81.5 years (range 67-96 years). The respite recipients had been admitted for residential respite care to aged care hostels and nursing homes in a provincial city and its surrounding rural area. Nurses rated disruptive behaviour using the Dementia Behavior Disturbance Scale (DBDS). Additional reliability data for the DBDS are provided. The study found that the largest specific group of residential respite care users were widows (31.4%) who lived alone in their own home. The reason for over half (51.4%) of the residential respite admissions was to give a carer a 'break' from the older person. Although a large proportion (80%) of respite recipients were rated as having disruptive behaviour, the proportion of admissions because of disruptive behaviour was much less (28.6%). People with dementia (37.1%) scored significantly higher than people without dementia on the DBDS [F (1,33)=15.57, p

Pea mania: deranged behaviour in cattle grazing a pea crop (Pisum sativum var arvense)

Hypersensitivity to external stimuli, progressing in some animals to manic behaviour, occurred in a cattle herd that grazed a crop of field peas (Pisum sativum var arvense) in the pre-flowering stage. Haematological and biochemical analyses eliminated hypomagnesaemia and ketosis as diagnoses. Other than two steers euthanased due to injuries sustained during manic episodes, all affected animals survived, recovering over 3 days when moved to alternative pasture. No necropsies were conducted. No microbial pathogens or endophytes were found on or in the plants. A previously reported incident in Victoria in 1987 in cattle grazing peas appeared to be of a similar nature. Environmental factors leading to these incidents were not clearly identified.

Behaviour of the black flying fox Pteropus alecto: 1. An ethogram of behaviour, and preliminary characterisation of mother-infant interactions

The black flying fox Pteropus alecto is one of four species of flying fox found on the Australian mainland. Little information exists about the specific behaviour of this species, and no framework for the study of its behaviour has yet been constructed. In the study reported here, two P alecto colonies were observed at two day roosts in South East Queensland, Australia, between 1998-2000. Observations focused on solitary and social actions in general and on mother-infant interactions in some detail and led to the construction of an ethogram that defines each action structurally and functionally, describing accompanying vocalisations where appropriate. Diurnal activity patterns of P. alecto throughout the year consisted predominantly of roosting, grooming and sleeping, and involved little social activity. Social interactions were largely restricted to the seasonal contexts of the birthing/rearing period of October to March and the subsequent courtship/mating season of February to April. In all, 74 behavioural units were defined with the aim of facilitating further research and the implementation of effective conservation strategies for the species.

Growth and compaction behaviour of copper concentrate granules in a rotating drum

In order to understand the growth and compaction behaviour of chalcopyrite (copper concentrate), batch granulation tests were carried out using a rotating drum. The granule growth exhibited induction-type behaviour, as defined by Iveson and Litster [AIChE J. 44 (1998) 15 10]. There were two consecutive stages during granulation: the induction stage, during which the granules are gradually being compacted and little or no growth occurs, and the rapid growth stage, which starts when the granules have become surface wet and are rapidly growing. In agreement with earlier findings. an increased amount of binder liquid shortened the induction time. The compaction behaviour was also investigated. A displaced volume method was adopted to determine the porosity of the granules. It was shown that this technique had a limitation as it was unable to detect the reduction of the volumes of the granule pores after the granules had become surface wet. Due to this, some of the measurements were not suited for fitting a three-parameter empirical model. Attempts were made to determine whether the rapid growth stage started with the pore saturation exceeding a certain critical value, but due to the scatter in the porosity measurements and the fact that some of the measurements could not be used, it was not possible to determine a critical pore saturation, However, the porosity measurements clearly demonstrated that the porosity of the granules decreased during the induction stage of an experiment and that when rapid growth occurred, the granules had a pore saturation was around 0.85. This value was slightly lower than unity, which is most likely due to trapped air bubbles. (C) 2002 Published by Elsevier Science B.V.

Extra-pair paternity and mate-guarding behaviour in the brown thornbill

We used multilocus DNA fingerprinting to assess parentage in the brown thornbill, Acanthiza pusilla, a socially monogamous Australian passerine. Extra-pair paternity was uncommon (6.2% of 178 offspring; 11.9% of 67 broods) and there was no evidence of intra-specific brood parasitism. Extra-pair paternity was limited because pairs spent more time together when females were fertile and males were able to evict intruding males before they could approach the female. Males were responsible for the close proximity of partners during the fertile period. Mate guarding therefore appears to be a male tactic aimed at preventing female infidelity rather than a cooperative behaviour of the pair aimed at preventing extra-pair copulations and/or female harassment. Females did not attempt to escape male guarding and were rarely observed to solicit copulations from intruding males. Nevertheless, females paired to smaller and younger males were more likely to cuckold their mates than females paired to larger and older males. This suggests that females may be more likely to seek or accept extra-pair matings when paired to small, young males or that old, large males are better at preventing their mates from engaging in extra-pair copulations. We found that male age but not male size influences mate-guarding behaviour. Older males tended to respond more aggressively to intruders. We therefore speculate that the relationship between male size/age and extra-pair paternity in brown thornbills may arise because female thornbills prefer large males as mates but are unable to express this preference as easily when paired to older males.

Behaviour of the black flying fox Pteropus alecto: 2. Territoriality and courtship

Flying foxes are commonly thought of as highly social mammals, yet little is known about the dynamics of their social interactions at a day roost. The aim of the present study was to examine the nature of the seasonal activities of territoriality and courtship amongst wild flying foxes in Australia. Focal observations were conducted at two permanent roosts of black flying foxes Pteropus alecto during periods of peak social interaction in the summers of 1999 and 2000 in urban Brisbane, Queensland. Observations of male territoriality were conducted at dawn and began eight weeks prior to the commencement of mating. The majority of defense bouts (87%) consisted of ritualised pursuit, while 13% of bouts involved physical contact expressed as either wrestling or hooking. One male with an unusually large territory took significantly longer to defend it than other males with less territory to defend. Observations of courtship revealed repetitive courtship sequences, including pre-copulatory approaches by the males, copulation attempts and grooming/resting periods. Thirty-four complete courtship sequences incorporating 135 copulation attempts were recorded over two seasons. Females actively resisted courtship approaches by males, forcing males to display a continuous determination to mate over time where determination can be considered an indicator of 'fitness'. The courtship bout length of females with suckling young was significantly longer ((x) over bar +/- SE; 230.9 +/- 22.16 s) than that of females unencumbered by large pups (158.5 +/- 9.69 s), although the length of copulations within those courtships was not (45.6 +/- 5.19 versus 36.2 +/- 3.43 s).