Chimera states in networks of phase oscillators: the case of two small populations

Chimera states are dynamical patterns in networks of coupled oscillators in which regions of synchronous and asynchronous oscillation coexist. Although these states are typically observed in large ensembles of oscillators and analyzed in the continuum limit, chimeras may also occur in systems with finite (and small) numbers of oscillators. Focusing on networks of $2N$ phase oscillators that are organized in two groups, we find that chimera states, corresponding to attracting periodic orbits, appear with as few as two oscillators per group and demonstrate that for $N>2$ the bifurcations that create them are analogous to those observed in the continuum limit. These findings suggest that chimeras, which bear striking similarities to dynamical patterns in nature, are observable and robust in small networks that are relevant to a variety of real-world systems.Comment: 13 pages, 16 figure

Temporal dynamics in the multisensory brain

Phd ThesisIn this work, I investigate the mechanisms with which the brain manages temporal coherence between sensory signals. An overview of relevant literature is given, and current theories about how sensory signals are combined in brain and behaviour are introduced. Key unknowns about the temporal dynamics of auditory-visual integration are identified and addressed within four investigations. In the first study, I assess whether cues to the onset of a auditory-visual pair affect sensitivity to their temporal asynchrony. It is shown that regularly timed cues shorten the temporal window of integration compared with irregular cues. This demonstrates that attention can affect how sensory signals are bound. In the second experiment, speech-like asynchronous stimuli are presented for an extended duration whilst perceptual simultaneity is monitored. In this manner, the time-course of temporal adaptation is tracked over time. Adaptation occurs when the presented asynchrony is visual-leading, but not when it is auditory-leading. This may suggest that temporal recalibration in the auditory-leading direction is not a consequence of adaptation. In the third investigation, the neural correlates of the time-course of temporal adaptation are measured. Increased activity in frontal and parietal areas occurred during perceptual asynchrony, this replicates previous work and further promotes that these regions provide top-down modulation of the mechanisms of temporal simultaneity. Increased activity is present in the posterior cingulate cortex whilst the brain is maintaining an adapted state, compared with during adaptation. This region may act as a con ict monitor and compensator for temporal asynchrony. Lastly, I investigate the extent to which a highly prevalent inhibitory neurotransmitter affects performance in a multisensory behavioural task. There is a possible correlation between the concentration of gamma-aminobutyric acid in the parietal lobe and the overall strength of integration effects. Finally, the impact and future directions of this work are discussed in the context of current literature.Wellcome Trust and the Institute of Neuroscienc

A comparison of six fingerprint enhancement techniques for the recovery of latent fingerprints from unfired cartridge cases

This work compared the effectiveness of six different enhancement methods on six different sizes of brass cartridges. One sebaceous fingerprint was deposited onto twenty-five of each size of cartridge to enable a statistical evaluation of the enhancement methods for each cartridge size to be undertaken. The enhancement methods compared were superglue followed by BY40, superglue followed by gun blue followed by BY40, gun blue only, superglue followed by palladium deposition, palladium deposition only, and powder suspension. The six different cartridges used in this study were .22s, .32s, 9mm, .38s, ribbed shotgun, and smooth shotgun. The study found that more potentially identifiable fingerprints were enhanced on the larger cartridge cases. This was due to the surface area on the smaller cartridges, and in particular the .22s provided little ridge detail. Two techniques provided the best results - superglue followed by gun blue followed by BY40, and superglue followed by palladium deposition. This showed that the combination of the cyanoacrylate fuming and the metal oxidation reactions is increasing the yield of potentially identifiable fingerprints compared with the use of the techniques separately. Both techniques were also found to give reproducible results. These two enhancement techniques were also compared statistically and no statistical difference in their effectiveness was found suggesting both techniques are equally as effective at enhancing fingerprints on brass cartridge cases

Socioeconomic deprivation as measured by the index of multiple deprivation and its association with low sex hormone binding globulin in women

ACKNOWLEDGEMENTS M.L., I.L. and A.H.H. participated in the study concept and design, acquisition of data, study analysis, interpretation of data, drafting of the manuscript. D.M. provided statistical expertise. R.D., A.J.H., and A.F. participated in the interpretation of data and critical revision of the manuscript.Peer reviewedPublisher PD

Bioremoval of arsenic in purpose designed laboratory-scale bioreactors

Laboratory scale bioreactors were used to investigate the treatment of arsenic species deliberately contaminated groundwater. A mixed culture of sulphate-reducing bacteria (SRB) with molasses as carbon source was immobilised on a polystyrene support matrix. The artificial groundwater contained either As(III) or As(V) at concentrations of 20, 10, 5, 1 or 0.1 mg/l as well as 0.1 mg/l of a mixture with As(III) accounting for a total of 20, 30, 40, 60 and 80%. More than 90 and 60% of the As(V) and As(III), respectively, were removed by the end of a 14-day experiment. Total arsenic had been reduced to below the WHO acceptable level of 10 μg/l when the proportion of As(III) was 20 and 30%, while at 40% As(III), this level was reached only after 21 days treatment. The efficiency of As(III) removal was increased by first oxidising it to As(V) using MnO2.Keywords: Arsenite, arsenate, bioreactor, polystyrene, sulphate-reducing bacteriaAfrican Journal of Biotechnology Vol. 12(21), pp. 3260-327

Application of Microsatellites in Genetic Diversity Analysis and Heterotic Grouping of Sorghum and Maize

Sorghum and maize are major cereal crops worldwide and key food security crops in Sub-Saharan Africa. The difference in the mating systems, maize as predominantly a cross-fertilizer and sorghum as a self-fertilizer is reflected in differences in visible phenotypic and genotypic variations. The reproductive differences dictate the level of genetic variation present in the two crops. Conventionally, a heterotic group assignment is made based on phenotypic values estimated through combining ability and heterosis analyses. However, phenotypic evaluation methods have their limitation due to the influence of the environment and may not reflect the heterotic pattern of the lines accurately. Therefore, more effective and complementary methods have been proposed for heterotic grouping of candidate lines. Estimation of molecular-based genetic distance has proven to be a useful tool to describe existing heterotic groups, to identify new heterotic groups, and to assign inbreds into heterotic groups. Among the molecular markers, microsatellites markers have proved to be a powerful tool for analyzing genetic diversity and for classifying inbred lines into heterotic groups. Therefore, the aim of this chapter was to elucidate the use of microsatellite markers in genetic diversity analysis and heterotic grouping of sorghum and maize

Analysis of laboratory and field measurements of directionally spread nonlinear ocean waves

Surface gravity waves exist in the oceans as multi-directional nonlinear phenomena. Understanding how these two properties interact is intrinsically important in itself. Furthermore, an understanding of this relationship may be used to gain insight into other oceanic phenomena. This thesis first describes an experimental investigation into the relationship between directionality and non-linearity (Part I). This relationship was then used as a tool to estimate the directional spreading of field data (Part II). Experiments have been conducted in which directionally spread focused wave groups were created in a wave tank. The relationship between the degree of directional spreading and the second-order bound harmonics of the wave groups was examined, in particular the formation of a `set-up'. These measurements were then compared to predictions from second-order theories, finding good agreement. The two-dimensional structure of the bound waves was explored giving new insight into the underlying physics. Experiments were then carried out for directionally spread crossing wave groups. It is believed that the crossing of two sufficiently separated wave groups may be the cause of an anomalous set-up in the second-order bound waves observed for some extreme and potentially freak waves. This set-up is reproduced experimentally. Again, the results of these test agreed very well when compared to second-order theory. The insight gained from the foregoing experiments was then utilised in the analysis of field data. A method, which requires only a single measurement to estimate the observed degree of directional spreading, was applied to a large dataset of field measurements from the North Alwyn platform in the North Sea. This method was then compared to conventional approaches, which require multiple concurrent measurements. The method that requires only a single measurement was shown to be effective, and presents a promising approach to gaining additional insight about the directional spreading of point observations