The physical basis for Parrondo's games

Several authors have implied that the original inspiration for Parrondo's games was a physical system called a ``flashing Brownian ratchet''. The relationship seems to be intuitively clear but, surprisingly, has not yet been established with rigor. In this paper, we apply standard finite-difference methods of numerical analysis to the Fokker-Planck equation. We derive a set of finite difference equations and show that they have the same form as Parrondo's games. Parrondo's games, are in effect, a particular way of sampling a Fokker-Planck equation. Physical Brownian ratchets have been constructed and have worked. It is hoped that the finite element method presented here will be useful in the simulation and design of flashing Brownian ratchets.Comment: 10 pages and 2 figure

The ATLAS-SPT radio survey of cluster galaxies

Galaxy clusters are the largest gravitationally bound objects in the Universe. The study of galaxy clusters can give insights into the large-scale structure of the Universe and provide constraints on the cosmological parameters that dictate the evolution of the Universe. Bent-tail radio sources are a class of Active Galactic Nuclei (AGN) where the jets or lobes have been distorted significantly due to the relative movement through a dense medium. This behaviour is expected to occur in galaxy clusters, especially those of high mass. I have planned and carried out the observations for the ATLAS-SPT survey, a radio continuum survey of ~86 deg2 using the Australia Telescope Compact Array at a central observing frequency of 2.1GHz over a bandwidth of 2GHz, with the telescope in an extended array configuration with a maximum baseline length of 6 km. The calibrated dataset was imaged, deconvolved using a multi-frequency deconvolution algorithm, and corrected for wide-bandwidth primary beam effects to produce total intensity and spectral variation images for each pointing. The limited u, v coverage of the survey caused several imaging challenges; the most significant being a poorly behaved synthesised beam response pattern and sidelobes from moderately bright outlier sources producing image artefacts. I devised an imaging pipeline which minimised the outlier source artefacts by employing a two-stage imaging process: 1) each pointing was imaged well beyond the primary beam with a coarse pixel resolution to find bright outlying sources; 2) outlying sources with a brightness expected to produce a synthesised beam pattern above the thermal noise of the pointing were modelled and subtracted from the pointing dataset. After subtracting the outlying sources, imaging could proceed as normal. Once each pointing was imaged, they were convolved with a Gaussian to produce a common angular resolution of 800 and linearly mosaicked to produce two images of the entire field: one total intensity mosaic and a spectral index mosaic. Due to limitations in the mosaicking software, 9 overlapping mosaic tiles were produced and subsequently combined with a custom imaging script. The final combined total intensity mosaic contains approximately 43 000 x 40 000 px and has a median rms noise level of approximately 180 μJy. I have produced a radio source catalogue containing positions and flux densities of 6067 sources. 722 of these sources have sufficient signal-to-noise ratios to provide a reliable spectral index measurement which is also included in the catalogue. I conducted a completeness simulation which indicates that the catalogue is 100% complete at the 1.3mJy beam−1 flux density level. This simulation was also used to estimate the flux density and positional accuracies. Due to noise fluctuations, flux densities of the faintest catalogued sources (~0.36mJy beam−1) are boosted by ~30%, and the boosting level falls below 5% for sources ≥$0.74mJy beam−1. The extracted positions have a median offset of ≪1" from their simulated input positions with a standard deviation of σ = 1.6" for the faintest sources, improving to σ = 0.5" for sources with flux densities ≥$1.3mJy beam−1. The catalogue was also matched and compared with the ATCA-XXL survey which covered the inner 25 deg2 of the field to a greater sensitivity. The matched sources are shown to be in excellent flux density and positional agreement. I constructed a Euclidean-normalised differential source count using the ATLAS-SPT catalogue, incorporating the necessary flux density corrections from the completeness simulation. The source counts agree well with others from the literature. The result confirms that the ATLAS-SPT survey is most sensitive to AGN and the steepening of the source counts clearly show the evolution of these sources. The source counts toward the catalogue sensitivity limit show the characteristic flattening, indicating the increased population of star-forming galaxies at those flux densities. I have identified 50 bent-tail radio galaxy candidates from the ATLAS-SPT total intensity mosaic by visual inspection and cross-matched these sources with the deep 3.6 μm Spitzer– South Pole Telescope Deep Field (SSDF) catalogue of the field. I then cross-matched the SSDF sources to both the Blanco Cosmology Survey (BCS) and Dark Energy Survey (DES) Science Verification catalogues and provide photometric redshift estimates for 17 bent-tail candidates. I then cross-matched these bent-tail candidates with redshifts to known cluster catalogues (546 in total). I found that only 4 are associated with known clusters. Recent models when applied to this dataset predict that ~7 bent-tail sources should be associated with high-mass (M ≥ 10 15M.) clusters such as those from the SPT SZ cluster catalogue. Instead I find only one. The lack of bent-tail sources within clusters may be explained by various effects such as projection, resolution, and AGN duty cycle. However, the lack of clusters found around bent-tail sources is more problematic and suggests that bent-tails may reside in cluster of lower mass than expected

Elm Farm Organic Research Centre December 2006

The Organic Research Centre. Elm Farm Research Centre Bulletin with Technical Updates from The Organic Advisory Service is a regular publication from The Organic Research Centre. The current issue covers: Report from 2006 Cirencester Conference; Quest for more home produced organic food; in a world where bread matters; Improving wheat with plenty of parents; Unlocking the secrets of the ancient (cereal varieties); Brain food- a good read; Not to late to protect the future: The organic role; Bumper Oat yields- Tradis trials top ten tonnes; Multiage flocks- a viable solution to wheigh variability; Letters

The Spatial Correlation of Bent-Tail Galaxies and Galaxy Clusters

We have completed a deep radio continuum survey covering 86 square degrees of the Spitzer-South Pole Telescope deep field to test whether bent-tail galaxies are associated with galaxy clusters. We present a new catalogue of 22 bent-tail galaxies and a further 24 candidate bent-tail galaxies. Surprisingly, of the 8 bent-tail galaxies with photometric redshifts, only two are associated with known clusters. While the absence of bent-tail sources in known clusters may be explained by effects such as sensitivity, the absence of known clusters associated with most bent-tail galaxies casts doubt upon current models of bent-tail galaxies.Comment: Accepted by MNRA

Analyzing Multidisciplinary Team Effectiveness in an Engineering Environment: A Case Study of the West Point Steel Bridge Design Team

The West Point Steel Bridge Design Team is a group of five undergraduate seniors working to design and build a steel bridge for the annual ASCE Steel Bridge Competition. The purpose of our group’s research is to discover how multidisciplinary teams perform in academically competitive environments. This project provides a unique opportunity in the field of multidisciplinary collaborative work because the team’s success can be objectively measured against this year’s competitors and the team’s performance in previous years. The traditional structure of the West Point team consisted of three-to-five civil engineering majors. This year’s team includes a law and legal studies major and five civil engineers, two of which recently switched from systems engineering. Past designs have relied heavily on the work of previous years, which has led to stagnant performance at competitions. Our hypothesis is that by entering different perspectives into the group at an early stage, a revolutionary approach will ensue and overall performance will increase. The team did not completely disregard the designs and methods of previous teams, but the reliance on their decision-making process was more heavily scrutinized with the current multidisciplinary team. Our research is not solely limited to competitive performance. We also analyzed the decision-making process of this year’s team in comparison to previous years. While data on decision-making is not readily available, both the faculty advisor and two current team members who served on the team last year were able to provide personal insight into how the teams compare. Ultimately, this research seeks to provide groups in similar academically competitive environments an indication of whether a multidisciplinary composition will provide benefit to their team’s performance.Cockrell School of Engineerin

Resting-State Functional Connectivity in Late-Life Depression: Higher Global Connectivity and More Long Distance Connections

Functional magnetic resonance imaging recordings in the resting-state (RS) from the human brain are characterized by spontaneous low-frequency fluctuations in the blood oxygenation level dependent signal that reveal functional connectivity (FC) via their spatial synchronicity. This RS study applied network analysis to compare FC between late-life depression (LLD) patients and control subjects. Raw cross-correlation matrices (CM) for LLD were characterized by higher FC. We analyzed the small-world (SW) and modular organization of these networks consisting of 110 nodes each as well as the connectivity patterns of individual nodes of the basal ganglia. Topological network measures showed no significant differences between groups. The composition of top hubs was similar between LLD and control subjects, however in the LLD group posterior medial-parietal regions were more highly connected compared to controls. In LLD, a number of brain regions showed connections with more distant neighbors leading to an increase of the average Euclidean distance between connected regions compared to controls. In addition, right caudate nucleus connectivity was more diffuse in LLD. In summary, LLD was associated with overall increased FC strength and changes in the average distance between connected nodes, but did not lead to global changes in SW or modular organization

LMC X-1: A New Spectral Analysis of the O-star in the binary and surrounding nebula

We provide new observations of the LMC X-1 O star and its extended nebula structure using spectroscopic data from VLT/UVES as well as H$\alpha$ imaging from the Wide Field Imager on the Max Planck Gesellschaft / European Southern Observatory 2.2m telescope and ATCA imaging of the 2.1 GHz radio continuum. This nebula is one of the few known to be energized by an X-ray binary. We use a new spectrum extraction technique that is superior to other methods to obtain both radial velocities and fluxes. This provides an updated spatial velocity of $\simeq 21.0~\pm~4.8$ km s$^{-1}$ for the O star. The slit encompasses both the photo-ionized and shock-ionized regions of the nebula. The imaging shows a clear arc-like structure reminiscent of a wind bow shock in between the ionization cone and shock-ionized nebula. The observed structure can be fit well by the parabolic shape of a wind bow shock. If an interpretation of a wind bow shock system is valid, we investigate the N159-O1 star cluster as a potential parent of the system, suggesting a progenitor mass of $\sim 60$ M$_{\odot}$ for the black hole. We further note that the radio emission could be non-thermal emission from the wind bow shock, or synchrotron emission associated with the jet inflated nebula. For both wind and jet-powered origins, this would represent one of the first radio detections of such a structure.Comment: 7 Figures, 4 Table