Using acoustic and satellite tracking data to better understand the factors associated with marine mammal habitat use and movements within urban coastal environments: dugongs in Moreton Bay, Queensland

Daniel Zeh studied dugong movements and established proof of concept that acoustic technology provides results comparable to satellite/GPS in two dimensional space use and extends to three dimensional space use. He found evidence of behavioural thermoregulation and the existence of a possible dugong movement corridor, extending current knowledge of dugong behavioural ecology

Arrow of time in a recollapsing quantum universe

We show that the Wheeler-DeWitt equation with a consistent boundary condition is only compatible with an arrow of time that formally reverses in a recollapsing universe. Consistency of these opposite arrows is facilitated by quantum effects in the region of the classical turning point. Since gravitational time dilation diverges at horizons, collapsing matter must then start re-expanding ``anticausally" (controlled by the reversed arrow) before horizons or singularities can form. We also discuss the meaning of the time-asymmetric expression used in the definition of ``consistent histories". We finally emphasize that there is no mass inflation nor any information loss paradox in this scenario.Comment: Many conceptual clarifications include

Quantum Theory and Time Asymmetry

The relation between quantum measurement and thermodynamically irreversible processes is investigated. The reduction of the state vector is fundamentally asymmetric in time and shows an observer-relatedness which may explain the double interpretation of the state vector as a representation of physical states as well as of information about them. The concept of relevance being used in all statistical theories of irreversible thermodynamics is shown to be based on the same observer-relatedness. Quantum theories of irreversible processes implicitly use an objectivized process of state vector reduction. The conditions for the reduction are discussed, and I speculate that the final (subjective) observer system might even be carried by a spacetime point.Comment: Latex version of a paper published in 1979 (with minor revisions), 18 page

Decoherence: Concepts and Examples

We give a pedagogical introduction to the process of decoherence - the irreversible emergence of classical properties through interaction with the environment. After discussing the general concepts, we present the following examples: Localisation of objects, quantum Zeno effect, classicality of fields and charges in QED, and decoherence in gravity theory. We finally emphasise the important interpretational features of decoherence.Comment: 24 pages, LATEX, 9 figures, needs macro lamuphys.sty, to appear in the Proceedings of the 10th Born Symposiu

Following a "Collapsing" Wavefunction

I study the quantum mechanics of a spin interacting with an ``apparatus''. Although the evolution of the whole system is unitary, the spin evolution is not. The system is chosen so that the spin exhibits loss of quantum coherence, or ``wavefunction collapse'', of the sort usually associated with a quantum measurement. The system is analyzed from the point of view of the spin density matrix (or ``Schmidt paths''), and also using the consistent histories approach. These two points of view are contrasted with each other. Connections between the results and the form of the Hamiltonian are discussed in detail.Comment: 30 pages, plain LaTex, 3 figures in a separate uuencoded fil

Efficient distributed machine learning via combinatorial multi-armed bandits

We consider the distributed stochastic gradient descent problem, where a main node distributes gradient calculations among n workers from which at most b ≤ n can be utilized in parallel. By assigning tasks to all the workers and waiting only for the k fastest ones, the main node can trade-off the error of the algorithm with its runtime by gradually increasing k as the algorithm evolves. However, this strategy, referred to as adaptive k-sync, can incur additional costs since it ignores the computational efforts of slow workers. We propose a cost-efficient scheme that assigns tasks only to k workers and gradually increases k. As the response times of the available workers are unknown to the main node a priori, we utilize a combinatorial multi-armed bandit model to learn which workers are the fastest while assigning gradient calculations, and to minimize the effect of slow workers. Assuming that the mean response times of the workers are independent and exponentially distributed with different means, we give empirical and theoretical guarantees on the regret of our strategy, i.e., the extra time spent to learn the mean response times of the workers. Compared to adaptive k-sync, our scheme achieves significantly lower errors with the same computational efforts while being inferior in terms of speed

Quick fix GPS technology highlights risk to dugongs moving between protected areas

Incidental capture in fishing gear is the most serious threat to the survival of many species of marine mammals. Fisheries closures developed to protect marine mammals have tended to concentrate on areas of high marine mammal density. Movement corridors have generally been less protected because they are often unknown and difficult to detect. Seagrass meadows in Moreton and Hervey Bays in south-eastern Queensland support significant populations of dugongs Dugong dugon. Pedigree analysis based on genetic and ancillary biological data indicates that there is substantial movement of dugongs between these bays, which are separated by open surf coasts where dugongs are occasionally caught in inshore shark nets set for the protection of bathers. This bycatch suggests that the dugong movement corridor between Moreton and Hervey Bays is close to the coast, a hypothesis not confirmed by nearly 30 yr of dugong satellite tracking using platform transmitter terminal (PTT) technology. Twenty-nine dugongs were captured in seagrass habitats on the eastern banks of Moreton Bay in 2012-2014 and were fitted with Quick Fix GPS and acoustic transmitters. One animal was captured and tracked twice. Four dugongs were tracked moving from Moreton Bay to Hervey Bay covering distances of 278-338 km over 5-9 d; 1 dugong made the return journey. Three of the 4 animals travelled along and very close to the coast; the exact track of the fourth animal is uncertain. These results suggest that dugongs would benefit from netting closures that extend beyond seagrass meadows

Entanglement and the Thermodynamic Arrow of Time

We discuss quantum entanglement in the context of the thermodynamic arrow of time. We review the role of correlations in entropy-decreasing events and prove that the occurrence of a transformation between two thermodynamic states constitutes a new type of entanglement witness, one not defined as a separating plane in state space between separable and entangled states, but as a physical process dependent on the local initial properties of the states. Extending work by Partovi, we consider a general entangled multipartite system that allows large reversals of the thermodynamic arrow of time. We describe a hierarchy of arrows that arises from the different correlations allowed in a quantum state and examine these features in the context of Maxwell's Demon. We examine in detail the case of three qubits, and also propose some simple experimental demonstrations possible with small numbers of qubits.Comment: 10 pages with 9 figure

On the Definition of Decoherence

We examine the relationship between the decoherence of quantum-mechanical histories of a closed system (as discussed by Gell-Mann and Hartle) and environmentally-induced diagonalization of the density operator for an open system. We study a definition of decoherence which incorporates both of these ideas, and show that it leads to a consistent probabilistic interpretation of the reduced density operator.Comment: 10 pages, LaTeX, SJSU/TP-93-1