5,550 research outputs found
Gas of self-avoiding loops on the brickwork lattice
An exact calculation of the phase diagram for a loop gas model on the
brickwork lattice is presented. The model includes a bending energy. In the
dense limit, where all the lattice sites are occupied, a phase transition
occuring at an asymmetric Lifshitz tricritical point is observed as the
temperature associated with the bending energy is varied. Various critical
exponents are calculated. At lower densities, two lines of transitions (in the
Ising universality class) are observed, terminated by a tricritical point,
where there is a change in the modulation of the correlation function. To each
tricritical point an associated disorder line is found.Comment: 19 pages, 6 figures. to appear in J. Phys. A : Math. & Ge
Brood patch and sex-ratio observations indicate breeding provenance and timing in New Zealand storm petrel (Fregetta maoriana)
We used measurements of brood patch and moult status to estimate the breeding phenology of New Zealand Storm-Petrel, using birds caught at sea within the Hauraki Gulf Marine Park near Auckland, New Zealand. Birds caught October–January had completely downy brood patches, whereas birds caught February–April had bare brood patches with an observed male bias in the February sex-ratio, consistent with a female pre-laying exodus typical of petrels and with the existence of an unknown colony in the region. No birds captured exhibited primary moult, which is known to occur in storm-petrels during their non-breeding season. Our data support the conclusion that the New Zealand storm-petrel breeds during January–June in northern New Zealand and that field surveys for the species on offshore islands in this region during this period are warrante
Epoch Dependent Dark Energy
We present a model in which the equation of state parameter w approaches -1
near a particular value of z, and has significant negative values in a
restricted range of z. For example, one can have w ~ -1 near z = 1, and w >
-0.2 from z = 0 to z = 0.3, and for z > 9. The ingredients of the model are
neutral fermions (which may be neutrinos, neutralinos, etc) which are very
weakly coupled to a light scalar field. This model emphasises the importance of
the proposed studies of the properties of dark energy into the region z > 1.Comment: 7pp., 2 figs. Invited talk at the 5th Int'l. Wkshp. on the Dark Side
of the Universe, 1-5 June 2009 Melbourne, DSU09; to appear in the proceeding
A dynamics-driven approach to precision machines design for micro-manufacturing and its implementation perspectives
Precision machines are essential elements in fabricating high quality micro products or micro features and directly affect the machining accuracy, repeatability and efficiency. There are a number of literatures on the design of industrial machine elements and a couple of precision machines commercially available. However, few researchers have systematically addressed the design of precision machines from the dynamics point of view. In this paper, the design issues of precision machines are presented with particular emphasis on the dynamics aspects as the major factors affecting the performance of the precision machines and machining processes. This paper begins with a brief review of the design principles of precision machines with emphasis on machining dynamics. Then design processes of precision machines are discussed, and followed by a practical modelling and simulation approaches. Two case studies are provided including the design and analysis of a fast tool servo system and a 5-axis bench-top micro-milling machine respectively. The design and analysis used in the two case studies are formulated based on the design methodology and guidelines
MSW-like Enhancements without Matter
We study the effects of a scalar field, coupled only to neutrinos, on
oscillations among weak interaction current eigenstates. The effect of a real
scalar field appears as effective masses for the neutrino mass eigenstates, the
same for \nbar as for \n. Under some conditions, this can lead to a
vanishing of , giving rise to MSW-like effects. We discuss some
examples and show that it is possible to resolve the apparent discrepancy in
spectra required by r-process nucleosynthesis in the mantles of supernovae and
by Solar neutrino solutions.Comment: 9 pages, latex, 1 figur
Improvement for Quenched Wilson Fermions
We briefly describe some of our recent results for the mass spectrum and
matrix elements using improved fermions for quenched QCD. Where possible
a comparison is made between improved and Wilson fermions.Comment: 6 pages, Latex, 11 figures, epsf.sty and buckow1.sty needed
(buckow1.sty included). Talk presented at the 31st Ahrenshoop Symposium on
the Theory of Elementary Particles, September 1997, Buckow, German
On the predictability of extremes: Does the butterfly effect ever decrease?
This is the peer reviewed version of the following article: Sterk, A. E., Stephenson, D. B., Holland, M. P. and Mylne, K. R. (2015), On the predictability of extremes: Does the butterfly effect ever decrease?. Quarterly Journal of the Royal Meteorological Society, which has been published in final form at http://dx.doi.org/10.1002/qj.2627. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving: http://olabout.wiley.com/WileyCDA/Section/id-820227.html#termsThis study investigates whether or not predictability always decreases for more extreme events. Predictability is measured by the Mean Squared Error (MSE), estimated here from the difference of pairs of ensemble forecasts, conditioned on one of the forecast variables (the 'pseudo-observation') exceeding a threshold. Using an exchangeable linear regression model for pairs of forecast variables, we show that the MSE can be decomposed into the sum of three terms: a threshold-independent constant, a mean term that always increases with threshold, and a variance term that can either increase, decrease, or stay constant with threshold. Using the generalised Pareto distribution to model wind speed excesses over a threshold, we show that MSE always increases with threshold at sufficiently high threshold. However, MSE can be a decreasing function of threshold at lower thresholds but only if the forecasts have finite upper bounds. The methods are illustrated by application to daily wind speed forecasts for London made using the 24 member Met Office Global and Regional Ensemble Prediction System from 1 January 2009 to 31 May 2011. For this example, the mean term increases faster than the variance term decreases with increasing threshold, and so predictability decreases for more extreme events.Engineering and Physical Sciences Research Council (EPSRC)Netherlands Organisation for Scientific Research (NWO
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