School of Mathematics and Physics - UQ eSpace

О разложениях по собственным функциям нелинейного оператора Штурма-Лиувилля с краевыми условиями, зависящими от спектрального параметра

Makin, A. S. og Thompson, H. B. — 2012-03-22T12:15:16Z

A basis for the symplectic group branching algebra

Kim, Sangjib og Yacobi, Oded — 2012-04-30T00:00:00Z

A Bayesian decision approach for sample size determination in phase II trials

Leung, Denis Heng-Yan og Wang, You-Gan — 2010-11-17T13:53:49Z

Stallard (1998, Biometrics 54, 279-294) recently used Bayesian decision theory for sample-size determination in phase II trials. His design maximizes the expected financial gains in the development of a new treatment. However, it results in a very high probability (0.65) of recommending an ineffective treatment for phase III testing. On the other hand, the expected gain using his design is more than 10 times that of a design that tightly controls the false positive error (Thall and Simon, 1994, Biometrics 50, 337-349). Stallard's design maximizes the expected gain per phase II trial, but it does not maximize the rate of gain or total gain for a fixed length of time because the rate of gain depends on the proportion of treatments forwarding to the phase III study. We suggest maximizing the rate of gain, and the resulting optimal one-stage design becomes twice as efficient as Stallard's one-stage design. Furthermore, the new design has a probability of only 0.12 of passing an ineffective treatment to phase III study.

A Bayesian-Decision Theoretic Approach to Model Error Modeling.

2009-02-04T00:00:00Z

Abstract: This paper takes a Bayesian-decision theoretic approach to transfer function estimation, nominal model estimation, and quantification of the resulting model error. Consistency of the nonparametric estimate of the transfer function is proved together with a rate of convergence. The required quantities can be computed routinely using reversible jump Markov chain Monte Carlo methods. The proposed methodology has connections with set membership identification which has been extensively studied for this problem.

Aberration compensation using nematic liquid crystals

2010-02-26T00:00:00Z

A Bethe ansatz study of the ground state energy for the repulsive Bose-Hubbard dimer

Links, Jon og Zhao, Shao-You — 2009-09-04T00:00:00Z

We employ an exact Bethe ansatz solution to study the repulsive Bose–Hubbard dimer model. Using a continuum approximation we solve for the ground state root density and in turn compute the ground state energy per particle. The formula so obtained is accurate for a finite-sized system in the weak coupling limit. Surprisingly, the formula diverges from the numerically calculated value as the number of particles increases. This indicates that the formula fails to predict the ground state energy per particle in the thermodynamic limit.

Ab initio excited-state dynamics of the photoactive yellow protein chromophore

2008-08-07T00:00:00Z

A binomial identity on the least prime factor of an integer

Hambleton, Samuel A. — 2011-10-30T00:00:00Z

An identity for binomial symbols modulo an odd positive integer

A boolean model of the gene regulatory network underlying mammalian cortical area development

Giacomantonio, Clare E. og Goodhill, Geoffrey J. — 2010-10-24T00:03:45Z

A brief summary of binary quadratic forms

Hambleton, Samuel A. — 2012-03-02T10:21:28Z

A bright future for quantum communications

Ralph, Timothy C. og Lam, Ping K. — 2009-12-13T00:00:00Z

Quantum information protocols based on continuous-variable entangled states are attractive because they exploit standard optical modulation and measurement equipment, and do not require single photons. Recent progress in the field is reversing initial concerns about the practicality of the approach.

Absolute absorption line-shape measurements at the shot-noise limit

2012-11-15T15:00:33Z

Here, we report a measurement scheme for determining an absorption profile with an accuracy imposed solely by photon shot noise. We demonstrate the power of this technique by measuring the absorption of cesium vapor with an uncertainty at the 2-ppm level. This extremely high signal-to-noise ratio allows us to directly observe the homogeneous line-shape component of the spectral profile, even in the presence of Doppler broadening, by measuring the spectral profile at a frequency detuning more than 200 natural linewidths from the line center. We then use this tool to discover an optically induced broadening process that is quite distinct from the well-known power broadening phenomenon.

Abundance, distribution, morphometrics, reproductive aspects and diet of the catshark Holohalaelurus regani

2009-12-17T09:20:50Z

Holohalaelurus regani was caught in 38% of the 3314 bottom trawls conducted during routine demersal surveys o. the South African west and south coasts from 1986 to 1999. An index of biomass for H. regani has increased on the west coast, from 1606 t in 1986–1993 to 3012 t in 1994–1999, despite c. 130 t being taken annually as by–catch in the demersal fishery. On the south coast, there has also been an increase over the same period, from 793 to 1350 t. Females and juveniles were generally found in shallower water (<300 m) than males, suggesting an inshore nursery area. Male H. regani become mature at 450–500 mm LT, whereas females become mature at 400–450 mm LT. There is reproductive activity throughout the year and fecundity appears to be high. This species is a generalist feeder, with the diet comprising teleosts, crustaceans and cephalopods. H. regani also scavenges offal opportunistically. Its high fecundity, the relative protection of females and juveniles in shallow water that is rarely trawled, its opportunistic diet and its robust nature that may allow it to survive after it has been discarded, have enabled H. regani to increase in numbers, despite indirect fishing pressure.

Accommodating dynamic oceanographic processes and pelagic biodiversity in marine conservation planning

2011-02-11T00:00:00Z

Accounting for habitat dynamics in conservation planning

2010-03-22T00:00:00Z

Accounting for individual variability in the von Bertalanffy growth model

Wang, Y. G. og Thomas, M. R. — 2010-11-17T00:00:00Z

Accuracy of single quantum dot registration using cryogenic laser photolithography

2010-01-21T00:00:00Z

We have registered the position of single InGaAs quantum dots using a novel cryogenic laser photolithography technique. This would be useful in realizing solid state cavity quantum electrodynamics. By fabricating metal alignment markers around the quantum dot, it was registered with an accuracy of 50 nm. Following the marker fabrication process we demonstrated that the same quantum dot was reacquired, with an accuracy of 150 nm. The photoluminescence spectra from the quantum dots before and after processing were identical except for a small red shift (~1 nm), probably introduced during the reactive ion etching.

A central limit theorem for a discrete-time SIS model with individual variation

McVinish, R. og Pollett, P.K. — 2012-06-18T08:16:53Z

A discrete-time SIS model is presented that allows individuals in the population to vary in terms of their susceptibility to infection and their rate of recovery. This model is a generalisation of the metapopulation model presented in McVinish and Pollett (2010). The main result of the paper is a central limit theorem showing that fluctuations in the proportion of infected individuals around the limiting proportion converges to a Gaussian random variable when appropriately rescaled. In contrast to the case where there is no variation amongst individuals, the limiting Gaussian distribution has a nonzero mean.

A Century After A Nobel Prize: The Legacy of Lippmann's Colour Photography

Wegener, M. — 2010-03-16T00:00:00Z

A CH3CN and HCO+ survey towards southern methanols masers associated with star formation

2009-02-12T00:00:00Z

A compact holographic optical tweezers instrument

2013-04-30T16:18:45Z

Holographic optical tweezers have found many applications including the construction of complex micron-scale 3D structures and the control of tools and probes for position, force, and viscosity measurement. We have developed a compact, stable, holographic optical tweezers instrument which can be easily transported and is compatible with a wide range of microscopy techniques, making it a valuable tool for collaborative research. The instrument measures approximately 30×30×35 cm and is designed around a custom inverted microscope, incorporating a fibre laser operating at 1070 nm. We designed the control software to be easily accessible for the non-specialist, and have further improved its ease of use with a multi-touch iPad interface. A high-speed camera allows multiple trapped objects to be tracked simultaneously. We demonstrate that the compact instrument is stable to 0.5 nm for a 10 s measurement time by plotting the Allan variance of the measured position of a trapped 2 μm silica bead.We also present a range of objects that have been successfully manipulated.

A compactness argument in the additive theory and the polynomial method

Karolyi, Gyula — 2012-03-02T00:00:00Z

A comparative study of two matrix factorization methods applied to the classification of gene expression rate

2011-02-22T00:00:00Z

In microarray data analysis, dimension reduction is an important consideration in the construction of a successful classification algorithm. As an alternative to feature selection, we use a well-known matrix factorisation method. For example, we can employ the popular singular-value decomposition (SVD) or nonnegative matrix factorization. In this paper, we consider a novel algorithm for gradient-based matrix factorisation (GMF). We compare GMF and SVD in their application to five gene expression datasets. The experimental results show that our method is faster, more stable, and sensitive.

A comparison of cross-entropy and variance minimization strategies

2011-03-15T00:00:00Z

The variance minimization (VM) and cross-entropy (CE) methods are two versatile adaptive importance sampling procedures that have been successfully applied to a wide variety of difficult rare-event estimation problems. We compare these two methods via various examples where the optimal VM and CE importance densities can be obtained analytically. We find that in the cases studied both VM and CE methods prescribe the same importance sampling parameters, suggesting that the criterion of minimizing the cross- entropy distance might be asymptotically identical to minimizing the variance of the associated importance sampling estimator.

A comparison of nighttime TID characteristics between equatorial-ionospheric-anomaly crest and midlatitude regions, related to spread F occurrence

Bowman, G. G. — 2007-08-14T00:00:00Z

A comprehensive set of simulations studying the influence of gas expulsion on star cluster evolution

Baumgardt, H. og Kroupa, P. — 2012-01-24T00:00:00Z

A comprehensive software suite for optical trapping and manipulation

2011-03-17T00:00:00Z

A constraint on the biembedding of Latin squares

2009-09-03T00:00:00Z

A context-free and a 1-counter geodesic language for a Baumslag-Solitar group.

Elder, Murray — 2009-02-10T00:00:00Z

We give a language of unique geodesic normal forms for the Baumslag–Solitar group BS(1,2) that is context-free and 1-counter. We discuss the classes of context-free, 1-counter and counter languages, and explain how they are inter-related.

A continued fractions approach to a result of Feit

Robertson, John P. og Matthews, Keith R. — 2009-09-03T10:14:18Z

For primes that can be written as a sum of integer squares, p = asup2 + (2b)sup2, Kaplansky asked whether the binary quadratic for F = xsup2 - pysup2 always represents a and 4b. Feit and Mollin proved the F does always represent a and 4b using the theory of ideals and the class group structure of quadratic orders. Here, Robertson and Matthews present a mathematical approach showing that a standard continued fraction methods give a more elementary answer to Kaplansky's question than the solutions by Feit and Mollin.

Actin- and dynamin-dependent maturation of bulk endocytosis restores neurotransmission following synaptic depletion

2012-07-11T11:42:01Z

Active adaptive conservation of threatened species in the face of uncertainty

2010-07-11T00:00:00Z

Adaptive Bayesian compound designs for dose finding studies

2012-04-16T12:52:43Z

We consider the problem of how to efficiently and safely design dose finding studies. Both current and novel utility functions are explored using Bayesian adaptive design methodology for the estimation of a maximum tolerated dose (MTD). In particular, we explore widely adopted approaches such as the continual reassessment method and minimizing the variance of the estimate of an MTD. New utility functions are constructed in the Bayesian framework and are evaluated against current approaches. To reduce computing time, importance sampling is implemented to re-weight posterior samples thus avoiding the need to draw samples using Markov chain Monte Carlo techniques. Further, as such studies are generally first-in-man, the safety of patients is paramount. We therefore explore methods for the incorporation of safety considerations into utility functions to ensure that only safe and well-predicted doses are administered. The amalgamation of Bayesian methodology, adaptive design and compound utility functions is termed adaptive Bayesian compound design (ABCD). The performance of this amalgamation of methodology is investigated via the simulation of dose finding studies. The paper concludes with a discussion of results and extensions that could be included into our approach.

Adaptive independence samplers

2009-02-18T00:00:00Z

Markov chain Monte Carlo (MCMC) is an important computational technique for generating samples from non-standard probability distributions. A major challenge in the design of practical MCMC samplers is to achieve efficient convergence and mixing properties. One way to accelerate convergence and mixing is to adapt the proposal distribution in light of previously sampled points, thus increasing the probability of acceptance. In this paper, we propose two new adaptive MCMC algorithms based on the Independent Metropolis–Hastings algorithm. In the first, we adjust the proposal to minimize an estimate of the cross-entropy between the target and proposal distributions, using the experience of pre-runs. This approach provides a general technique for deriving natural adaptive formulae. The second approach uses multiple parallel chains, and involves updating chains individually, then updating a proposal density by fitting a Bayesian model to the population. An important feature of this approach is that adapting the proposal does not change the limiting distributions of the chains. Consequently, the adaptive phase of the sampler can be continued indefinitely. We include results of numerical experiments indicating that the new algorithms compete well with traditional Metropolis–Hastings algorithms. We also demonstrate the method for a realistic problem arising in Comparative Genomics.

Adaptive optical phase estimation using time-symmetric quantum smoothing

2012-05-21T00:00:00Z

We present an experimental demonstration of quantum smoothing, a non causal version of quantum parameter estimation that has applications from gravitational wave detection to quantum key distribution. An existing technique for this type of parameter estimation is quantum filtering, which uses past observations only. The technique presented here is time‐symmetric that uses past and future observations to obtain a more precise estimate. We couple this innovative estimation technique with an adaptive detection scheme to demonstrate an estimation of the optical phase of light measured to be 2.24 ± 0.14 times better than the standard quantum limit. This approaches our theoretically derived prediction of a mean square error improvement of 2math times over the standard quantum limit [1].

Adaptive phase measurements for narrowband squeezed beams

Berry, Domonic W. og Wiseman, Howard M. — 2007-08-15T00:00:00Z

We have previously [Phys. Rev. A 65, 043803 (2002)] analyzed adaptive measurements for estimating the continuously varying phase of a coherent beam, and a broadband squeezed beam. A real squeezed beam must have finite photon flux N and hence can be significantly squeezed only over a limited frequency range. In this paper we analyze adaptive phase measurements of this type for a realistic model of a squeezed beam. We show that, provided it is possible to suitably choose the parameters of the beam, a mean-square phase uncertainty scaling as (N/kappa)(-5/8) is possible, where kappa is the linewidth of the beam resulting from the fluctuating phase. This is an improvement over the (N/kappa)(-1/2) scaling found previously for coherent beams. In the experimentally realistic case where there is a limit on the maximum squeezing possible, the variance will be reduced below that for coherent beams, though the scaling is unchanged.

Adaptive strategy recommended for US ocean planning

2011-02-10T00:00:00Z

A dark excited state of fluorescent protein chromophores, considered as Brooker dyes

Olsen, Seth og McKenzie, Ross H. — 2010-05-30T00:07:03Z

The green fluorescent protein (GFP) chromophore is a dihydroxyarylmethine (oxonol) dye. Resonance and molecular orbital theories predict two low-lying excitations with distinct oscillator strength and polarization in these systems. Using a variational quantum-chemical model that reflects both theories, we estimate the energy of both states in resonant anionic and cationic forms of the chromophore. The energy of the higher, dark state in these forms is in the same range as the bright transition of the nonresonant neutral form, estimated by similar methods. This suggests interesting roles for the dark state in GFP photophysics. 2010 Elsevier B.V. All rights reserved.

Adding control to arbitrary unknown quantum operations

2011-10-02T00:00:00Z

A definition for the covalent and ionic bond index in a molecule

2009-09-03T00:00:00Z

Formulae for hermitian operators representing covalent, ionic, and total bond indices are derived. The eigenstates of these operators come in pairs, and can be considered as bonding, anti-bonding and lone-pair orbitals. The form of these operators is derived by generalising the rule that the bond order be defined as the net number of bonding electron pairs. The percentage of covalency and ionicity of a chemical bond may be obtained, and bond indices can also be defined between groups of atoms. The calculation of the bond indices depends only on the electron density operator, and certain projection operators used to represent each atom in the molecule. Bond indices are presented for a series of first and second row hydrides and fluorides, hydrocarbons, a metal complex, a Diels–Alder reaction and a dissociative reaction. In general the agreement between the bond indices is in accord with chemical intuition. The bond indices are shown to be stable to basis set expansion.

A dendronised polymer for bulk heterojunction solar cells

2011-12-04T00:00:00Z

A diabatic state model for donor-hydrogen vibrational frequency shifts in hydrogen bonded complexes

McKenzie, Ross H. — 2012-06-05T03:31:45Z

A simple diabatic two-state Hamiltonian is considered which describes hydrogen bonding and proton transfer between a donor (D) and an acceptor (A), including different classes of bonds (weak, low-barrier, and strong). The independent variables are the distance R and the difference in proton affinity ϵ between the donor and acceptor. With only two free parameters the model Hamiltonian gives a quantitative description of experimental data from a wide range of molecular complexes exhibiting correlations between R and ϵ and binding energies, D–H bond lengths, and the frequencies of D–H stretch and bend vibrations. The UV photo-dissociation of strong H-bonded complexes via an excited electronic state with an exalted vibrational frequency is predicted.

A diabatic three-state representation of photoisomerization in the green fluorescent protein chromophore

Olsen, Seth og McKenzie, Ross H. — 2010-03-23T00:00:00Z

We give a quantum chemical description of the photoisomerization reaction of green fluorescent protein (GFP) chromophores using a representation over three diabatic states. Photoisomerization leads to nonradiative decay, and competes with fluorescence in these systems. In the protein, this pathway is suppressed, leading to fluorescence. Understanding the electronic states relevant to photoisomerization is a prerequisite to understanding how the protein suppresses it, and preserves the emitting state of the chromophore. We present a solution to the state-averaged complete active space problem, which is spanned at convergence by three fragment-localized orbitals. We generate the diabatic-state representation by block diagonalization transformation of the Hamiltonian calculated for the anionic chromophore model HBDI with multireference, multistate perturbation theory. The diabatic states are charge localized and admit a natural valence-bond interpretation. At planar geometries, the diabatic picture of the optical excitation reduces to the canonical two-state charge-transfer resonance of the anion. Extension to a three-state model is necessary to describe decay via two possible pathways associated with photoisomerization of the (methine) bridge. Parametric Hamiltonians based on the three-state ansatz can be fit directly to data generated using the underlying active space. We provide an illustrative example of such a parametric Hamiltonian.

A dilemma for the emergence of spacetime in canonical quantum gravity

Lam, Vincent og Esfeld, Michael — 2012-08-22T10:43:58Z

The procedures of canonical quantization of the gravitational field apparently lead to entities for which any interpretation in terms of spatio-temporal localization or spatio-temporal extension seems difficult. This fact is the main ground for the suggestion that can often be found in the physics literature on canonical quantum gravity according to which spacetime may not be fundamental in some sense. This paper aims to investigate this radical suggestion from an ontologically serious point of view in the cases of two standard forms of canonical quantum gravity, quantum geometrodynamics and loop quantum gravity. We start by discussing the physical features of the quantum wave functional of quantum geometrodynamics and of the spin networks (and spin foams) of loop quantum gravity that motivate the view according to which spacetime is not fundamental. We then point out that, by contrast, for any known ontologically serious understanding of quantum entanglement, the commitment to spacetime seems indispensable. Against this background, we then critically discuss the idea that spacetime may emerge from more fundamental entities. As a consequence, we finally suggest that the emergence of classical spacetime in canonical quantum gravity faces a dilemma: either spacetime ontologically emerges from more fundamental non-spatio-temporal entities or it already belongs to the fundamental quantum gravitational level and the emergence of the classical picture is merely a matter of levels of description. On the first horn of the dilemma, it is unclear how to make sense of concrete physical entities that are not in spacetime and of the notion of ontological emergence that is involved. The second horn runs into the difficulties raised by the physics of canonical quantum gravity.

A discrete level-set topology optimization code written in Matlab

Challis, Vivien — 2010-03-11T00:00:00Z

A discussion of constrained binary embeddings with applications to cryptanalysis of irregularly clocked stream ciphers

2009-03-18T00:00:00Z

Advances in cross-entropy methods

Taimre, T. — 2010-01-03T00:04:30Z

Advances in resistive pulse sensors: Devices bridging the void between molecular and microscopic detection

2011-10-12T00:00:00Z

Since the first reported use of a biological ion channel to detect differences in single stranded genomic base pairs in 1996, a renaissance in nanoscale resistive pulse sensors has ensued. This resurgence of a technique originally outlined and commercialized over 50 years ago has largely been driven by advances in nanoscaled fabrication, and ultimately, the prospect of a rapid and inexpensive means for genomic sequencing as well as other macromolecular characterization. In this pursuit, the potential application of these devices to characterize additional properties such as the size, shape, charge, and concentration of nanoscaled materials (10-900 nm) has been largely overlooked. Advances in nanotechnology and biotechnology are driving the need for simple yet sensitive individual object readout devices such as resistive pulse sensors. This review will examine the recent progress in pore-based sensing in the nanoscale range. A detailed analysis of three new types of pore sensors - in-series, parallel, and size-tunable pores - has been included. These pores offer improved measurement sensitivity over a wider particle size range. The fundamental physical chemistry of these techniques, which is still evolving, will be reviewed.

Advection in chaotically time-dependent open ﬂows

Neufeld, Z. og Tel, T. — 2012-06-28T00:00:00Z

The passive advection of tracer panicles is considered in open two-dimensional incompressible flows with chaotic time dependence. As illustrative examples we investigate flows produced by chaotically moving ideal point vortices. The advection problem can be seen as a chaotic scattering process in a chaotically driven Hamiltonian system. Studying the motion of tracer ensembles, we present numerical evidence for the existence of a bounded chaotic set containing infinitely many aperiodic trajectories never leaving the mixing region of the flow. These ensembles converge to filamental patterns which, however, do not follow self-similar scaling. Nevertheless, they possess a fractal dimension after averaging over several finite-time realizations of the flow. We propose random maps as simple models of the phenomenon.

A Dynamical N-body model for the central region of ω Centauri

2012-04-09T12:08:31Z