Seminars & Discussions
Week beginning 4 October 2015
Monday 5 Oct 15 - 1:00pm
Language change in individuals and populations
Richard Blythe (University of Edinburgh)
Historical linguists study changes that occur in the structure of languages - for example, changes in word order - that occur over many human generations. Psycholinguists meanwhile investigate (amongst other things) changes that arise from language learning and use. The link between the individual- and population-level dynamics is unclear, and provides an opportunity for investigation within the framework of statistical physics, which is set up to do the same sort of thing for condensed matter systems. In this talk I will argue that a very broad class of models of individual learning in populations predict that the system size (number of speakers) should have a big effect on the rate of historical language change, which is apparently not a feature of the empirical data. I will further propose that this conflict can be resolved if one augments language-learning biases that are universal to all humans with a set of socially-acquired biases that vary between cultures and over time.
Wednesday 7 Oct 15 - 11:00am
The Majority Illusion in Social Networks
In this talk I will discuss the "Majority illusion" paradox in social networks. This paradox says that it is possible that a globally rare variant can be perceived locally as common by almost every agent in the network. I will explain why this is the case and show how to quantify the phenomenon. I will also link this paradox with the well-known "friend paradox". (No prior knowledge assumed)
Ref: Lerman, K., Yan, X., & Wu, X. Z. (2015). The Majority Illusion in Social Networks. arXiv preprint arXiv: 1506.03022.
Friday 9 Oct 15 - 11:30am
The heat released during catalytic turnover enhances the diffusion of an enzyme
Authors: Clement Riedel, Ronen Gabizon, Christian A. M. Wilson, Kambiz Hamadani, Konstantinos Tsekouras, Susan Marqusee, Steve Pressé & Carlos Bustamante
Speaker: Aidan Brown
Recent studies have shown that the diffusivity of enzymes increases in a substrate-dependent manner during catalysis. Although this observation has been reported and characterized for several different systems the precise origin of this phenomenon is unknown. Calorimetric methods are often used to determine enthalpies from enzyme-catalysed reactions and can therefore provide important insight into their reaction mechanisms. The ensemble averages involved in traditional bulk calorimetry cannot probe the transient effects that the energy exchanged in a reaction may have on the catalyst. Here we obtain single-molecule fluorescence correlation spectroscopy data and analyse them within the framework of a stochastic theory to demonstrate a mechanistic link between the enhanced diffusion of a single enzyme molecule and the heat released in the reaction. We propose that the heat released during catalysis generates an asymmetric pressure wave that results in a differential stress at the protein-solvent interface that transiently displaces ththe centre-of-mass of the enzyme (chemoacoustic effect). This novel perspective on how enzymes respond to the energy released during catalysis suggests a possible effect of the heat of reaction on the structural integrity and internal degrees of freedom of the enzyme.
227-230 (2015) pdf version
Counter Argument Paper Enhanced Diffusion of Enzymes that Catalyze Exothermic Reactions
author = Ramin Golestanian abstract
Enzymes have been recently found to exhibit enhanced diffusion due to their catalytic activities. A recent experiment [C. Riedel et al.
, Nature (London) 517
, 227 (2015)] has found evidence that suggests this phenomenon might be controlled by the degree of exothermicity of the catalytic reaction involved. Four mechanisms that can lead to this effect, namely, self-thermophoresis, boost in kinetic energy, stochastic swimming, and collective heating are critically discussed, and it is shown that only the last two can be strong enough to account for the observations. The resulting quantitative description is used to examine the biological significance of the effect.
article 108102 (2015) pdf version
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