Flow-distributed spikes for Schnakenberg kinetics

This is the post-print version of the final published paper. The final publication is available at link.springer.com by following the link below. Copyright @ 2011 Springer-Verlag.We study a system of reaction–diffusion–convection equations which combine a reaction–diffusion system with Schnakenberg kinetics and the convective flow equations. It serves as a simple model for flow-distributed pattern formation. We show how the choice of boundary conditions and the size of the flow influence the positions of the emerging spiky patterns and give conditions when they are shifted to the right or to the left. Further, we analyze the shape and prove the stability of the spikes. This paper is the first providing a rigorous analysis of spiky patterns for reaction-diffusion systems coupled with convective flow. The importance of these results for biological applications, in particular the formation of left–right asymmetry in the mouse, is indicated.RGC of Hong Kon

The Divisive Power of Humour: Comedy, Taste and Symbolic Boundaries

Using British and Dutch interview data, this article demonstrates how people from different social classes draw strong symbolic boundaries on the basis of comedy taste. Eschewing the omnivorousness described in recent studies of cultural consumption, comedy audiences make negative aesthetic and moral judgements on the basis of comedy taste, and often make harsh judgements without the disclaimers, apologies and ambivalence so typical of ‘taste talk’ in contemporary culture. The article demonstrates how, in particular, Dutch and British middle class audiences use their comedy taste to communicate distinction and cultural superiority. We discuss several reasons why such processes of social distancing exist in comedy taste and not other cultural areas: the traditionally low status of comedy; the strong relation between humour and personhood; the continuity between comedy tastes and humour styles in everyday life; as well as the specific position of comedy in the British and Dutch cultural fields

The Extremes of Thermonuclear Supernovae

The majority of thermonuclear explosions in the Universe seem to proceed in a rather standardised way, as explosions of carbon-oxygen (CO) white dwarfs in binary systems, leading to 'normal' Type Ia supernovae (SNe Ia). However, over the years a number of objects have been found which deviate from normal SNe Ia in their observational properties, and which require different and not seldom more extreme progenitor systems. While the 'traditional' classes of peculiar SNe Ia - luminous '91T-like' and faint '91bg-like' objects - have been known since the early 1990s, other classes of even more unusual transients have only been established 20 years later, fostered by the advent of new wide-field SN surveys such as the Palomar Transient Factory. These include the faint but slowly declining '02es-like' SNe, 'Ca-rich' transients residing in the luminosity gap between classical novae and supernovae, extremely short-lived, fast-declining transients, and the very luminous so-called 'super-Chandrasekhar' SNe Ia. Not all of them are necessarily thermonuclear explosions, but there are good arguments in favour of a thermonuclear origin for most of them. The aim of this chapter is to provide an overview of the zoo of potentially thermonuclear transients, reviewing their observational characteristics and discussing possible explosion scenarios.Comment: Author version of a chapter for the 'Handbook of Supernovae', edited by A. Alsabti and P. Murdin, Springer. 50 pages, 7 figure

Evaluation of lightweight wheelchairs using ANSI/RESNA testing standards

Lightweight wheelchairs are characterized by their low cost and limited range of adjustment. Our study evaluated three different folding lightweight wheelchair models using the American National Standards Institute/Rehabilitation Engineering Society of North America (ANSI/RESNA) standards to see whether quality had improved since the previous data were reported. On the basis of reports of increasing breakdown rates in the community, we hypothesized that the quality of these wheelchairs had declined. Seven of the nine wheelchairs tested failed to pass the multidrum test durability requirements. An average of 194,502 +/- 172,668 equivalent cycles was completed, which is similar to the previous test results and far below the 400,000 minimum required to pass the ANSI/ RESNA requirements. This was also significantly worse than the test results for aluminum ultralight folding wheelchairs. Overall, our results uncovered some disturbing issues with these wheelchairs and suggest that manufacturers should put more effort into this category to improve quality. To improve the durability of lightweight wheelchairs, we suggested that stronger regulations be developed that require wheelchairs to be tested by independent and certified test laboratories. We also proposed a wheelchair rating system based on the National Highway Transportation Safety Administration vehicle crash ratings to assist clinicians and end users when comparing the durability of different wheelchairs

Su(3) Algebraic Structure of the Cuprate Superconductors Model based on the Analogy with Atomic Nuclei

A cuprate superconductor model based on the analogy with atomic nuclei was shown by Iachello to have an $su(3)$ structure. The mean-field approximation Hamiltonian can be written as a linear function of the generators of $su(3)$ algebra. Using algebraic method, we derive the eigenvalues of the reduced Hamiltonian beyond the subalgebras $u(1)\bigotimes u(2)$ and $so(3)$ of $su(3)$ algebra. In particular, by considering the coherence between s- and d-wave pairs as perturbation, the effects of coherent term upon the energy spectrum are investigated

Preferred Basis in a Measurement Process

The effect of decoherence is analysed for a free particle, interacting with an environment via a dissipative coupling. The interaction between the particle and the environment occurs by a coupling of the position operator of the particle with the environmental degrees of freedom. By examining the exact solution of the density matrix equation one finds that the density matrix becomes completely diagonal in momentum with time while the position space density matrix remains nonlocal. This establishes the momentum basis as the emergent 'preferred basis' selected by the environment which is contrary to the general expectation that position should emerge as the preferred basis since the coupling with the environment is via the position coordinate.Comment: Standard REVTeX format, 10 pages of output. Accepted for publication in Phys. Rev

Interactions of B = 4 Skyrmions

It is known that the interactions of single Skyrmions are asymptotically described by a Yukawa dipole potential. Less is known about the interactions of solutions of the Skyrme model with higher baryon number. In this paper, it is shown that Yukawa multipole theory can be more generally applied to Skyrmion interactions, and in particular to the long-range dominant interactions of the B = 4 solution of the Skyrme model, which models the alpha-particle. A method that gives the quadrupole nature of the interaction a more intuitive meaning in the pion field colour picture is demonstrated. Numerical methods are employed to find the precise strength of quadrupole and octupole interactions. The results are applied to the B = 8 and B = 12 solutions and to the Skyrme crystal.Comment: 21 pages, 11 figure

Dissolution dominating calcification process in polar pteropods close to the point of aragonite undersaturation

Thecosome pteropods are abundant upper-ocean zooplankton that build aragonite shells. Ocean acidification results in the lowering of aragonite saturation levels in the surface layers, and several incubation studies have shown that rates of calcification in these organisms decrease as a result. This study provides a weight-specific net calcification rate function for thecosome pteropods that includes both rates of dissolution and calcification over a range of plausible future aragonite saturation states (Omega_Ar). We measured gross dissolution in the pteropod Limacina helicina antarctica in the Scotia Sea (Southern Ocean) by incubating living specimens across a range of aragonite saturation states for a maximum of 14 days. Specimens started dissolving almost immediately upon exposure to undersaturated conditions (Omega_Ar,0.8), losing 1.4% of shell mass per day. The observed rate of gross dissolution was different from that predicted by rate law kinetics of aragonite dissolution, in being higher at Var levels slightly above 1 and lower at Omega_Ar levels of between 1 and 0.8. This indicates that shell mass is affected by even transitional levels of saturation, but there is, nevertheless, some partial means of protection for shells when in undersaturated conditions. A function for gross dissolution against Var derived from the present observations was compared to a function for gross calcification derived by a different study, and showed that dissolution became the dominating process even at Omega_Ar levels close to 1, with net shell growth ceasing at an Omega_Ar of 1.03. Gross dissolution increasingly dominated net change in shell mass as saturation levels decreased below 1. As well as influencing their viability, such dissolution of pteropod shells in the surface layers will result in slower sinking velocities and decreased carbon and carbonate fluxes to the deep ocean