Complexation between oppositely charged polyelectrolytes: beyond the Random Phase Approximation

We consider the phase behavior of polymeric systems by calculating the structure factors beyond the Random Phase Approximation. The effect of this correction to the mean-field RPA structure factor is shown to be important in the case of coulombic systems. Two examples are given: simple electrolytes and mixtures of incompatible oppositely charged polyelectrolytes. In this last case, all former studies predicted an enhancement of compatibility for increasing charge densities; we also describe the complexation transition between the polyelectrolytes. We determine a phase diagram of the polyelectrolyte mixture that includes both complexation and incompatibility.Comment: 18 pages, 4 figures. Submitted to EPJ-

Charge Distribution on Annealed Polyelectrolytes

We investigate the equilibrium charge distribution along a single annealed polyelectrolyte chain under different conditions. The coupling between the conformation of the chain and the local charge distribution is described for various solvent qualities and salt concentration. In salt free solution, we find a slight charge depletion in the central part of the chain: the charges accumulate at the ends. The effect is less important if salt is added to the solution since the charge inhomogeneity is localized close to the chain ends over a distance of order of the Debye length. In the case of poor solvent conditions we find a different charging of beads and strings in the framework of the necklace model. This inhomogeneity leads to a charge instability and a first order transition between spherical globules and elongated chains.Comment: 20 pages, 4 figure

Bayesian Analysis of a Probit Panel Data Model with Unobserved Individual Heterogeneity and Autocorrelated Errors

In this paper, we perform Bayesian analysis of a panel probit model with unobserved individual heterogeneity and serially correlated errors. We augment the data with latent variables and sample the unobserved heterogeneity component as one Gibbs block per individual using a flexible piecewise linear approximation to the marginal posterior density. The latent time effects are simulated as another Gibbs block. For this purpose we develop a new user-friendly form of the Efficient Importance Sampling proposal density for an Acceptance-Rejection Metropolis-Hastings step. We apply our method to the analysis of product innovation activity of a panel of German manufacturing firms in response to imports, foreign direct investment and other control variables. The dataset used here was analyzed under more restrictive assumptions by Bertschek and Lechner (1998) and Greene (2004). Although our results differ to a certain degree from these benchmark studies, we confirm the positive effect of imports and FDI on firms' innovation activity. Moreover, unobserved firm heterogeneity is shown to play a far more significant role in the application than the latent time effects.Dynamic latent variables; Markov Chain Monte Carlo; importance sampling

KNR4, a suppressor of Saccharomyces cerevisiae cwh mutants, is involved in the transcriptional control of chitin synthase genes

The KNR4 gene, originally isolated by complementation of a K9 killer-toxinresistant mutant displaying reduced levels of both 1,3-b-glucan and 1,3-bglucan synthase activity, was recloned from a YCp50 genomic library as a suppressor of Saccharomyces cerevisiae calcofluor-white-hypersensitive (cwh) mutants. In these mutants, which were characterized by increased chitin levels, the suppressor effect of KNR4 resulted, for some of them, in a lowering of polymer content to close to wild-type level, with no effect on the contents of b-glucan and mannan. In all cases, this effect was accompanied by a strong reduction in mRNA levels corresponding to CHS1, CHS2 and CHS3, encoding chitin synthases, without affecting expression of FKS1 and RHO1, two genes encoding the catalytic subunit and a regulatory component of 1,3-b-glucan synthase, respectively. Overexpression of KNR4 also inhibited expression of CHS genes in wild-type strains and in two other cwh mutants, whose sensitivity to calcofluor white was not suppressed by this gene. The physiological relevance of the KNR4 transcriptional effect was addressed in two different ways. In a wild-type strain exposed to a-factor, overexpression of this gene inhibited CHS1 induction and delayed shmoo formation, two events which are triggered in response to the pheromone, whereas it did not affect bud formation and cell growth in a chs1 chs2 double mutant. A chimeric protein made by fusing green fluorescent protein to the C terminus of Knr4p which fully complemented a knr4D mutation was found to localize in patches at presumptive bud sites in unbudded cells and at the incipient bud site during bud emergence. Taken together, these results demonstrate that KNR4 has a regulatory role in chitin deposition and in cell wall assembly. A mechanism by which this gene affects expression of CHS genes is proposed

First whole atmosphere night-time seeing measurements at Dome C, Antarctica

We report site testing results obtained in night-time during the polar autumn and winter at Dome C. These results were collected during the first Concordia winterover by A. Agabi. They are based upon seeing and isoplanatic angle monitoring, as well as in-situ balloon measurements 2 of the refractive index structure constant profiles Cn (h). Atmosphere is divided into two regions: (i) a 36 m high surface layer responsible of 87% of the turbulence and (ii) a very stable free atmosphere above with a median seeing of 0.36+-0.19 arcsec at an elevation of h = 30 m. The median seeing measured with a DIMM placed on top of a 8.5 m high tower is 1.3+-0.8 arcsec.Comment: accepted for publication in PASP (oct 2005