Path integrals for continuous-time Markov chains

This note presents a method of evaluating the distribution of a path integral for Markov chains on a countable state space.

A real-time PCR assay for the detection of Neisseria gonorrhoeae by LightCycler

The detection of Neisseria gonorrhoeae by the polymerase chain reaction (PCR) is now recognized as a sensitive and specific method of diagnosing infection by the organism. In this Study 152 urine specimens were examined for N. gonorrhoeae by a real-time PCR method using the LightCycler platform and results were compared to an in-house PCR assay using an ELISA-based detection method. N. gonorrhoeae DNA was detected in 29 (19%) specimens by LightCycler PCR (LC-PCR) and in 31 (20%) specimens by the in house PCR method. The LightCycler assay proved to be specific and 94% sensitive when compared to the in house PCR method. These features combined with the rapid turn-around time for results makes the LC-PCR particularly suitable for the detection of N. gonorrhoeae in a routine clinical laboratory. (C) 2002 Elsevier Science Inc. All rights reserved.

Reasoning about real-time repetitions: terminating and nonterminating

It is common for a real-time system to contain a nonterminating process monitoring an input and controlling an output. Hence, a real-time program development method needs to support nonterminating repetitions. In this paper we develop a general proof rule for reasoning about possibly nonterminating repetitions. The rule makes use of a Floyd-Hoare-style loop invariant that is maintained by each iteration of the repetition, a Jones-style relation between the pre- and post-states on each iteration, and a deadline specifying an upper bound on the starting time of each iteration. The general rule is proved correct with respect to a predicative semantics. In the case of a terminating repetition the rule reduces to the standard rule extended to handle real time. Other special cases include repetitions whose bodies are guaranteed to terminate, nonterminating repetitions with the constant true as a guard, and repetitions whose termination is guaranteed by the inclusion of a fixed deadline. (C) 2002 Elsevier Science B.V. All rights reserved.

Saving, productivity and national income: a discrete-time geometric framework

This paper proposes an alternative geometric framework for analysing the inter-relationship between domestic saving, productivity and income determination in discrete time. The framework provides a means of understanding how low saving economies like the United States sustained high growth rates in the 1990s whereas high saving Japan did not. It also illustrates how the causality between saving and economic activity runs both ways and that discrete changes in national output and income depend on both current and previous accumulation behaviour. The open economy analogue reveals how international capital movements can create external account imbalances that enhance income growth for both borrower and lender economies. (C) 2002 Elsevier Science B.V. All rights reserved.

Integrals for continuous-time Markov chains

This paper presents a method of evaluating the expected value of a path integral for a general Markov chain on a countable state space. We illustrate the method with reference to several models, including birth-death processes and the birth, death and catastrophe process. (C) 2002 Elsevier Science Inc. All rights reserved.

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.

Feeding ecology of a carnivorous bladderwort (Utricularia uliginosa, Lentibulariaceae)

The terrestrial carnivorous bladderwort, Utricularia uliginosa Vahl. (Lentibulariaceae) was studied to determine the species assemblage present in traps of these plants in situ across four sites over 15 months. The immediate soil environment was also sampled to determine the fauna present, and to compare the fauna present in traps with the fauna in the environment. The soil fauna consisted of 10 taxon types, which occupied either pelagic, epibenthic or interstitial microhabitats. All were found in traps of U. uliginosa, with the main prey being interstitial taxa followed by epibenthic and occasionally pelagic taxa. Numbers of individuals of the two most abundant soil taxa (nematodes, Elaphoidella) varied independently across the four sites over the 15 months of the study, as did numbers of Elaphoidella in the traps of U. uliginosa. Numbers of nematodes in the traps of U. uliginosa showed significant differences among sites, but not differences among times. Comparison of the trap fauna with the soil fauna revealed differences in relative abundance between soil samples and trap samples for two of the three taxa examined. There was an under-representation of nematodes in the traps relative to numbers in surrounding soil. There was an over-representation of the copepod Elaphoidella in the traps of U. uliginosa relative to numbers in soil at some of the times of sampling. Acarina were equally abundant in soil and trap samples. The patterns observed for Elaphoidella and nematodes may be due to selectivity in trapping by U. uliginosa, and/or differences in digestibility of the prey. Elaphoidella individuals were found to be attracted to U. uliginosa in a behavioural experiment. This may contribute to the over-representation of Elaphoidella in the traps of U. uliginosa in the field.

Habitat requirements for the conservation of arboreal marsupials in dry sclerophyll forests of Southeast Queensland, Australia

The habitat requirements of arboreal marsupials were investigated in the dry sclerophyll forests of southeast Queensland, Australia. Species richness and abundance of arboreal marsupials was correlated to the proportion of total stand basal area occupied by lemon-scented gum (Corymbia citriodora), the height of the tallest trees, and density of hollow-bearing trees. The first two factors suggested that the most productive forests were also the most suitable habitats for arboreal marsupials. Importantly, the number of hollow-bearing trees was a significant factor in determining species richness and abundance of arboreal marsupials in this study, with the maximum number of species reached at sites containing greater than or equal to4 hollow-bearing trees/ha, and maximum abundance occurring at sites with :6 hollow-bearingtrees/ha. The proportion of C. citriodora was significant for the presence of the common brushtail possum (Trichosurus vulpecula), greater glider (Petauroides volans), and the yellow-bellied glider (Petaurus australis), while understory Acacia sp. density was important for the presence of the sugar glider (Petaurus breviceps). The yellow-bellied glider was also affected by two other variables: the density of hollow-bearing trees >50 cm diameter at breast height (dbh), and the time since the last logging. Current Codes of Practice regulating the density of hollow-bearing trees and silvicultural practices in state-owned timber production forests appear to provide adequate protection for arboreal marsupials, but the recently introduced increase in timber extraction rates within state forests may be detrimental to the animals. Also, protective prescriptions do not apply to the privately owned and leasehold estates, which contain the majority of the dry sclerophyll forests in southeast Queensland.

Anticipation of a non-aversive reaction time task facilitates the blink startle reflex

The conditions under which blink startle facilitation can be found in anticipation of a reaction time task were investigated to resolve inconsistent findings across previous studies. Four groups of participants (n = 64) were presented with two visual stimuli, one predicting a reaction time task (S+) and the second presented alone (S-). Participants were asked to make a speeded response to the offset of the S+ (S1 paradigm) or were asked to respond to a tactile stimulus presented at the offset of the S+ (S1-S2 paradigm). Half of the participants in each paradigm condition received performance feedback. Overall, blink latency shortening and magnitude facilitation were larger during S+ than during S-. More detailed analyses, however, found these differences to be reliable only in the Feedback conditions. Ratings of S+ pleasantness did not change across the experiment. Electrodermal responses to S+ were larger than to S- in all groups with differential electrodermal responding emerging earlier in the S1 paradigm. Taken together, the data support the notion that startle facilitation can occur during non-aversive Pavlovian conditioning. (C) 2002 Elsevier Science B.V. All rights reserved.

A formal model of real-time program compilation

Program compilation can be formally defined as a sequence of equivalence-preserving transformations, or refinements, from high-level language programs to assembler code, Recent models also incorporate timing properties, but the resulting formalisms are intimidatingly complex. Here we take advantage of a new, simple model of real-time refinement, based on predicate transformer semantics, to present a straightforward compilation formalism that incorporates real-time constraints. (C) 2002 Elsevier Science B.V. All rights reserved.

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).

Efficient time-independent wave packet scattering calculations within a Lanczos subspace: H+O-2 (J=0) state-to-state reaction probabilities

An efficient Lanczos subspace method has been devised for calculating state-to-state reaction probabilities. The method recasts the time-independent wave packet Lippmann-Schwinger equation [Kouri , Chem. Phys. Lett. 203, 166 (1993)] inside a tridiagonal (Lanczos) representation in which action of the causal Green's operator is affected easily with a QR algorithm. The method is designed to yield all state-to-state reaction probabilities from a given reactant-channel wave packet using a single Lanczos subspace; the spectral properties of the tridiagonal Hamiltonian allow calculations to be undertaken at arbitrary energies within the spectral range of the initial wave packet. The method is applied to a H+O-2 system (J=0), and the results indicate the approach is accurate and stable. (C) 2002 American Institute of Physics.