Quasispecies evolution in general mean-field landscapes

I consider a class of fitness landscapes, in which the fitness is a function of a finite number of phenotypic "traits", which are themselves linear functions of the genotype. I show that the stationary trait distribution in such a landscape can be explicitly evaluated in a suitably defined "thermodynamic limit", which is a combination of infinite-genome and strong selection limits. These considerations can be applied in particular to identify relevant features of the evolution of promoter binding sites, in spite of the shortness of the corresponding sequences.Comment: 6 pages, 2 figures, Europhysics Letters style (included) Finite-size scaling analysis sketched. To appear in Europhysics Letter

Campaign advertising and democratic citizenship

Concern about the state of American democracy is a staple of political science and popular commentary. Critics warn that levels of citizen participation and political knowledge are disturbingly low and that seemingly ubiquitous political advertising is contributing to the problem. We argue that political advertising is rife with both informational and emotional content and actually contributes to a more informed, more engaged, and more participatory citizenry. With detailed advertising data from the 2000 election, we show that exposure to campaign advertising produces citizens who are more interested in the election, have more to say about the candidates, are more familiar with who is running, and ultimately are more likely to vote. Importantly, these effects are concentrated among those citizens who need it most: those with the lowest pre-existing levels of political information

Political advertising is not polarizing the American public

There is little doubt that American politics has become more partisan and acrimonious in recent decades. While there are many potential sources of this rise in polarization, many point to the growth in political advertising as one potential cause. By combining survey and advertising data from US media markets, Travis N. Ridout, Erika Franklin Fowler, Michael Franz, and Ken Goldstein were able to investigate the effects of political advertising. They find that there is no link between political advertising and polarization or between the amount of negative or contrasting advertising and polarization

Understanding the effect of political advertising on voter turnout: A response to Krasno and Green

Krasno and Green have argued that political advertising has no impact on voter turnout. We remain unconvinced by their evidence, given concerns about how they measure the advertising environment, how they measure advertising tone, their choice of modeling techniques and the generalizability of their findings. These differences aside, we strongly agree that political advertising does little to undermine voter participation. © 2008 Southern Political Science Association

Evaluating measures of campaign advertising exposure on political learning

Scholars employ various methods to measure exposure to televised political advertising but often arrive at conflicting conclusions about its impact on the thoughts and actions of citizens. We attempt to clarify one of these debates while validating a parsimonious measure of political advertising exposure. To do so, we assess the predictive power of six different measurement approaches - from the simple to the complex - on learning about political candidates. Two datasets are used in this inquiry: (1) geo-coded political advertising time-buy data, and (2) a national panel study concerning patterns of media consumption and levels of political knowledge. We conclude that many traditional methods of assessing exposure are flawed. Fortunately, there is a relatively simple measure that predicts knowledge about information featured in ads. This measure involves combining a tally of the volume of advertisements aired in a market with a small number of survey questions about the television viewing habits of geo-coded respondents

Statistical Physics of the Glass Phase

This paper gives an introduction to some of the statistical physics problems which appear in the study of structural glasses. It is a shortened and updated version of a more detailed review paper which has appeared in cond-mat/0005173.Comment: 10 pages, 4 figures, Proceedings of Statphys 2

Statistical Physics of Structural Glasses

This paper gives an introduction and brief overview of some of our recent work on the equilibrium thermodynamics of glasses. We have focused onto first principle computations in simple fragile glasses, starting from the two body interatomic potential. A replica formulation translates this problem into that of a gas of interacting molecules, each molecule being built of $m$ atoms, and having a gyration radius (related to the cage size) which vanishes at zero temperature. We use a small cage expansion, valid at low temperatures, which allows to compute the cage size, the specific heat (which follows the Dulong and Petit law), and the configurational entropy. The no-replica interpretation of the computations is also briefly described. The results, particularly those concerning the Kauzmann tempaerature and the configurational entropy, are compared to recent numerical simulations.Comment: 21 pages, 6 figures, to appear in the proceedings of the Trieste workshop on "Unifying Concepts in Glass Physics

Inherent Structures, Configurational Entropy and Slow Glassy Dynamics

We give a short introduction to the inherent structure approach, with particular emphasis on the Stillinger and Weber decomposition, of glassy systems. We present some of the results obtained in the framework of spin-glass models and Lennard-Jones glasses. We discuss how to generalize the standard Stillinger and Weber approach by including the entropy of inherent structures. Finally we discuss why this approach is probably insufficient to describe the behavior of some kinetically constrained models.Comment: 16 pages, 8 figures, Contribution to the ESF SPHINX meeting `Glassy behaviour of kinetically constrained models' (Barcelona, March 22-25, 2001

The Poggendorff illusion affects manual pointing as well as perceptual judgements

Pointing movements made to a target defined by the imaginary intersection of a pointer with a distant landing line were examined in healthy human observers in order to determine whether such motor responses are susceptible to the Poggendorff effect. In this well-known geometric illusion observers make systematic extrapolation errors when the pointer abuts a second line (the inducer). The kinematics of extrapolation movements, in which no explicit target was present, where similar to those made in response to a rapid-onset (explicit) dot target. The results unambiguously demonstrate that motor (pointing) responses are susceptible to the illusion. In fact, raw motor biases were greater than for perceptual responses: in the absence of an inducer (and hence also the acute angle of the Poggendorff stimulus) perceptual responses were near-veridical, whilst motor responses retained a bias. Therefore, the full Poggendorff stimulus contained two biases: one mediated by the acute angle formed between the oblique pointer and the inducing line (the classic Poggendorff effect), which affected both motor and perceptual responses equally, and another bias, which was independent of the inducer and primarily affected motor responses. We conjecture that this additional motor bias is associated with an undershoot in the unknown direction of movement and provide evidence to justify this claim. In conclusion, both manual pointing and perceptual judgements are susceptible to the well-known Poggendorff effect, supporting the notion of a unitary representation of space for action and perception or else an early locus for the effect, prior to the divergence of processing streams

Connected Network of Minima as a Model Glass: Long Time Dynamics

A simple model to investigate the long time dynamics of glass-formers is presented and applied to study a Lennard-Jones system in supercooled and glassy phases. According to our model, the point representing the system in the configurational phase space performs harmonic vibrations around (and activated jumps between) minima pertaining to a connected network. Exploiting the model, in agreement with the experimental results, we find evidence for: i) stretched relaxational dynamics; ii) a strong T-dependence of the stretching parameter; iii) breakdown of the Stokes-Einstein law.Comment: 4 pages (Latex), 4 eps figure