Binary Mixtures of Particles with Different Diffusivities Demix

The influence of size differences, shape, mass and persistent motion on phase separation in binary mixtures has been intensively studied. Here we focus on the exclusive role of diffusivity differences in binary mixtures of equal-sized particles. We find an effective attraction between the less diffusive particles, which are essentially caged in the surrounding species with the higher diffusion constant. This effect leads to phase separation for systems above a critical size: A single close-packed cluster made up of the less diffusive species emerges. Experiments for testing of our predictions are outlined.Comment: 5 figures in main text, 8 figures in Supplemental Materia

New conserved structural fields for supercooled liquids

By considering Voronoi tessellations of the configurations of a fluid, we propose two new conserved fields, which provide structural information not fully accounted for by the usual 2-point density field fluctuations (structure factor). One of these fields is scalar and associated to the Voronoi cell volumes, whereas the other one, termed the "geometrical polarisation", is vectorial, related to the very local anisotropy of the configurations. We study the static and dynamical properties of these fields in the supercooled regime of a model glass-forming liquid. We show in particular that the geometrical polarisation is both statically correlated to the force field and contrary to it develops a plateau regime when the temperature is lowered. We attribute this behaviour to the microsopic disorder of the underlying inherent structures (IS) which dictate the dynamics on time scales larger than the true microscopic time, in the strong supercooled regime. In this respect, this work raises the issue of to what extent the inter IS dynamics, intrinsically anisotropic and collective (cf. T.B. Schr{\o}der et al. {\it J. of Chem. Phys.}, {\bf 112}, 9834 (2000)), could be related to their polarisation field.Comment: submitted to EPJE the 09/30/201

Current reversal and exclusion processes with history-dependent random walks

A class of exclusion processes in which particles perform history-dependent random walks is introduced, stimulated by dynamic phenomena in some biological and artificial systems. The particles locally interact with the underlying substrate by breaking and reforming lattice bonds. We determine the steady-state current on a ring, and find current-reversal as a function of particle density. This phenomenon is attributed to the non-local interaction between the walkers through their trails, which originates from strong correlations between the dynamics of the particles and the lattice. We rationalize our findings within an effective description in terms of quasi-particles which we call front barriers. Our analytical results are complemented by stochastic simulations.Comment: 5 pages, 6 figure

Propagation and Relaxation of Tension in Stiff Polymers

We present a unified theory for the longitudinal dynamic response of a stiff polymer in solution to various external perturbations (mechanical excitations, hydrodynamic flows, electrical fields, temperature quenches ...) that can be represented as sudden changes of ambient/boundary conditions. The theory relies on a comprehensive analysis of the non--equilibrium propagation and relaxation of backbone stresses in a wormlike chain. We recover and substantially extend previous results based on heuristic arguments. Intriguing new experimental implications are pointed out.Comment: 4 pages, 3 figure

Psychological Issues in Online Adaptive Task Allocation

Adaptive aiding is an idea that offers potential for improvement over many current approaches to aiding in human-computer systems. The expected return of tailoring the system to fit the user could be in the form of improved system performance and/or increased user satisfaction. Issues such as the manner in which information is shared between human and computer, the appropriate division of labor between them, and the level of autonomy of the aid are explored. A simulated visual search task was developed. Subjects are required to identify targets in a moving display while performing a compensatory sub-critical tracking task. By manipulating characteristics of the situation such as imposed task-related workload and effort required to communicate with the computer, it is possible to create conditions in which interaction with the computer would be more or less desirable. The results of preliminary research using this experimental scenario are presented, and future directions for this research effort are discussed

Linear response of a grafted semiflexible polymer to a uniform force field

We use the worm-like chain model to analytically calculate the linear response of a grafted semiflexible polymer to a uniform force field. The result is a function of the bending stiffness, the temperature, the total contour length, and the orientation of the field with respect to that of the grafted end. We also study the linear response of a worm-like chain with a periodic alternating sequence of positive and negative charges. This can be considered as a model for a polyampholyte with intrinsic bending siffness and negligible intramolecular interactions. We show how the finite intrinsic persistence length affects the linear response to the external field.Comment: 6 pages, 3 figure

The use of happiness research for public policy

Research on happiness tends to follow a "benevolent dictator" approach where politicians pursue people's happiness. This paper takes an antithetic approach based on the insights of public choice theory. First, we inquire how the results of happiness research may be used to improve the choice of institutions. Second, we show that the policy approach matters for the choice of research questions and the kind of knowledge happiness research aims to provide. Third, we emphasize that there is no shortcut to an optimal policy maximizing some happiness indicator or social welfare function since governments have an incentive to manipulate this indicator

Constructing coproducts in locally Cartesian closed ∞\infty-categories

We prove that every locally Cartesian closed $\infty$-category with subobject classifier has a strict initial object and disjoint and universal binary coproducts

Entropic forces generated by grafted semiflexible polymers

The entropic force exerted by the Brownian fluctuations of a grafted semiflexible polymer upon a rigid smooth wall are calculated both analytically and by Monte Carlo simulations. Such forces are thought to play an important role for several cellular phenomena, in particular, the physics of actin-polymerization-driven cell motility and movement of bacteria like Listeria. In the stiff limit, where the persistence length of the polymer is larger than its contour length, we find that the entropic force shows scaling behavior. We identify the characteristic length scales and the explicit form of the scaling functions. In certain asymptotic regimes we give simple analytical expressions which describe the full results to a very high numerical accuracy. Depending on the constraints imposed on the transverse fluctuations of the filament there are characteristic differences in the functional form of the entropic forces; in a two-dimensional geometry the entropic force exhibits a marked peak.Comment: 21 pages, 18 figures, minor misprints correcte

Angular Distribution of Gamma-ray Bursts and Weak Lensing

We investigate whether Gamma-Ray Bursts (GRBs) from the Current BATSE Catalog have been affected by weak lensing by the nearby large scale structure. The redshift distribution of GRBs is believed to be broad, extending to z~5, so most events can be assumed to be at large redshifts, and hence subject to weak lensing, which would betray itself as projected (anti-)correlations between GRB events and galaxies or clusters that trace the intervening mass. Given the observed distribution of GRBs in fluence, and statistical positional error, e, we predict that most subsets drawn from BATSE Catalog will be anti-correlated with the foreground structure due to weak lensing, i.e. will show negative magnification bias. We find that GRBs are indeed anti-correlated with the APM galaxies (z~0.2-0.3) in the sense that galaxy density in circles of radii 1-1.5 deg (15-20 Mpc at z~0.3) centered on e<1 GRBs is about 10% lower than expected from a random distribution; the significance of GRB-APM anti-correlations reaches 99.7%. Cross-correlation between GRBs and distant rich Abell-Corwin-Olowin clusters is also negative. Standard cosmological models with Omega_matter ~ 0.3, Omega_Lambda ~ 0.7, and matter distribution on large scales following observed APM galaxy distribution with the biasing parameter of around 1 are not able to reproduce our GRB-APM anti-correlations. We propose a speculative model that does account for these anti-correlations as well as positive correlations found previously, between QSOs and APM galaxies. We briefly discuss if the proposed scheme is in conflict with observations of cosmic microwave background, galaxy surveys, cosmic velocity flows, and weak shear lensing