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R C Ball

Publications and source records attributed to R C Ball.

7 recordsLinked to original sources
PubMed2003

From plasticity to a renormalization group.

The marginally rigid state is a candidate paradigm for what makes granular material a state of matter distinct from both liquid and solid. The coordination number is identified as a discriminating characteristic, and for rough-surfaced particles we show that the low values predicted are indeed approached in simple two-dimensional experiments. We show calculations of the stress transmission, suggesting that this is governed by local linear equations of constraint between the stress components. These constraints can in turn be related to the generalized forces conjugate to the motion of grains rolling over each other. The lack of a spatially coherent way of imposing a sign convention on these motions is a problem for scaling up the equations, which leads us to attempt a renormalization-group calculation. Finally, we discuss how perturbations propagate through such systems, suggesting a distinction between the behaviour of rough and smooth grains.

Journal Article↗
PubMed2003

Diffusion-controlled growth: theory and closure approximations.

We expand upon a new theoretical framework for diffusion-limited aggregation and associated dielectric breakdown models in two dimensions [R. C. Ball and E. Somfai, Phys. Rev. Lett. 89, 135503 (2002)]. Key steps are understanding how these models interrelate when the ultraviolet cut-off strategy is changed, the analogy with turbulence, and the use of logarithmic field variables. Within the simplest, Gaussian, truncation of mode-mode coupling, all properties can be calculated. The agreement with prior knowledge from simulations is encouraging, and a new superuniversality of the tip scaling exponent is discussed. We find angular resonances relatable to the cone angle theory, and we are led to predict a new screening transition in the DBM at large eta.

Journal Article↗
PubMed2002

Theory of diffusion controlled growth.

We present a new theoretical framework for diffusion limited aggregation and associated dielectric breakdown models in two dimensions. Key steps are understanding how these models interrelate when the ultraviolet cutoff strategy is changed, the analogy with turbulence and the use of logarithmic field variables. Within the simplest, Gaussian, truncation of mode-mode coupling, all properties can be calculated. The agreement with prior knowledge from simulations is encouraging, and a new superuniversality of the tip scaling exponent is both predicted and confirmed.

Journal Article↗
PubMed2001

How many conformations can a protein remember?

We show that a protein can be trained to recognize multiple conformations, analogous to an associative memory, and provide capacity calculations based on energy fluctuations and information theory. Unlike the linear capacity of a Hopfield network, the number of conformations which can be remembered by a protein sequence depends on the size of the amino acid alphabet as lnA, independent of protein length. This admits the possibility of certain proteins, such as prions, evolving to fold to independent stable conformations, as well as novel possibilities for protein and heteropolymer design.

Protein Conformation↗
PubMed2000

Universal aging features in the restructuring of fractal colloidal gels.

We use multispeckle dynamic light scattering to measure the dynamic structure factor, f(q,tau), of gels formed by aggregation of colloids. Although the gel is an elastic solid, f(q,tau) nearly completely decays on long time scales, with an unusual form, f(q, tau) approximately exp{-(tau/tau(f))(mu)}, with mu approximately 1.5 and with tau(f) proportional variant q(-1). A model for restructuring of the gel with aging correctly accounts for this behavior. Aging leads to a dramatic increase in tau(f); however, all data can be scaled on a single master curve, with tau(f) asymptotically growing linearly with age. This behavior is strikingly similar to that predicted for aging in disordered glassy systems, offering convincing proof of the universality of these concepts.

Journal Article↗
PubMed1996

A survey to investigate potential dehydration in slaughtered broiler chickens.

A survey of 800 broilers arriving at two commercial slaughterhouses with a combined annual throughput of 40 million birds was carried out. Each plant was visited on four occasions throughout summer and winter and blood samples were collected from 100 broilers at exsanguination throughout the day of each visit. In all, the survey covered 16 lorry loads of broilers delivered to one plant and 20 loads delivered to the other. The blood collected was analysed for packed cell volume (PCV), plasma creatine kinase, total protein, sodium, glucose, osmolality and corticosterone. Based on the measures of PCV, plasma total protein, sodium and osmolality there was no evidence of dehydration amongst the lorry loads of birds delivered to the plants. There were differences between the two plants in the levels of all of the blood variables that were measured, except for those of plasma corticosterone.

Abattoirs↗