On the regimes of charge reversal

Charge reversal of the planar electrical double layer is studied by means of a well known integral equations theory. By a numerical analysis, a diagram is constructed with the onset points of charge reversal in the space of the fundamental variables of the system. Within this diagram two regimes of charge reversal are identified, referred to as oscillatory and non oscillatory. We found that these two regimes can be distinguished through a simple formula. Furthermore, a symmetry between electrostatic and size correlations in charge reversal is exhibited. The agreement of our results with other theories and molecular simulations data is discussed.Comment: 5 figure

Model charged cylindrical nanopore in a colloidal dispersion: charge reversal, overcharging and double overcharging

Using the hypernetted-chain/mean spherical approximation (HNC/MSA) integral equations we study the electrical double layer inside and outside a model charged cylindrical vesicle (nanopore) immersed into a primitive model macroions solution, so that the macroions are only present outside the nanopore, i.e., the vesicle wall is impermeable only to the external macroions. We calculate the ionic and local linear charge density profiles inside and outside the vesicle, and find that the correlation between the inside and outside ionic distributions causes the phenomena of overcharging (also referred to as surface charge amplification) and/or charge reversal. This is the first time overcharging is predicted in an electrical double layer of cylindrical geometry. We also report the new phenomenon of double overcharging. The present results can be of consequence for relevant systems in physical-chemistry, energy storage and biology, e.g., nanofilters, capacitors and cell membranes.Comment: 10 pages, 4 figure

Reengineering the process of manufacturing thermal-cryogenics tanks

Includes bibliographical references

The radial plot in meta-analysis : approximations and applications

Fixed effects meta-analysis can be thought of as least squares analysis of the radial plot, the plot of standardized treatment effect against precision (reciprocal of the standard deviation) for the studies in a systematic review. For example, the least squares slope through the origin estimates the treatment effect, and a widely used test for publication bias is equivalent to testing the significance of the regression intercept. However, the usual theory assumes that the within-study variances are known, whereas in practice they are estimated. This leads to extra variability in the points of the radial plot which can lead to a marked distortion in inferences that are derived from these regression calculations. This is illustrated by a clinical trials example from the Cochrane database. We derive approximations to the sampling properties of the radial plot and suggest bias corrections to some of the commonly used methods of meta-analysis. A simulation study suggests that these bias corrections are effective in controlling levels of significance of tests and coverage of confidence intervals

Partial match queries in relaxed K-dt trees

The study of partial match queries on random hierarchical multidimensional data structures dates back to Ph. Flajolet and C. Puech’s 1986 seminal paper on partial match retrieval. It was not until recently that fixed (as opposed to random) partial match queries were studied for random relaxed K-d trees, random standard K-d trees, and random 2-dimensional quad trees. Based on those results it seemed natural to classify the general form of the cost of fixed partial match queries into two families: that of either random hierarchical structures or perfectly balanced structures, as conjectured by Duch, Lau and Martínez (On the Cost of Fixed Partial Queries in K-d trees Algorithmica, 75(4):684–723, 2016). Here we show that the conjecture just mentioned does not hold by introducing relaxed K-dt trees and providing the average-case analysis for random partial match queries as well as some advances on the average-case analysis for fixed partial match queries on them. In fact this cost –for fixed partial match queries– does not follow the conjectured forms.Peer ReviewedPostprint (author's final draft

Fragmentation of the social fabric and polarisation in Venezuela

Since the death of Hugo Chávez last year, the economic, political and social vision of Venezuela has been uncertain. In this post, Mireya Lozada discusses the current state of fragmentation in the Venezuelan society, as well as the psychosocial impact of polarisation on large social sectors in the country and on the ruling government and its opposition. She also presents the challenges this situation entails for psychologists and social researchers working on the ground, and potential avenues to address them

Fractura del tejido social y polarización en Venezuela

Desde la muerte de Hugo Chávez el año pasado, la visión económica, política y social de Venezuela ha sido y continúa siendo incierta. En esta entrada, Mireya Lozada discute la situación de grandes fisuras en la sociedad venezolana, así como el impacto psicosocial de la polarización tanto en grandes sectores del país, como en actores políticos del gobierno y sus oponentes. Son presentados desafíos de esta situación para psicólogos e investigadores sociales con actuación en campo, así como posibles aproximaciones de abordaje

Overcharging of DNA in the presence of salt: Theory and Simulation

A study of a model rod-like polyelectrolyte molecule immersed into a monovalent or divalent electrolyte is presented. Results from the hypernetted-chain/mean spherical approximation (HNC/MSA) theory, for inhomogeneous charged fluids, {\ch are} compared with molecular dynamics (MD) simulations. As a particular case, the parameters of the polyelectrolyte molecule are mapped to those of a DNA molecule. An excellent qualitative, and in some cases quantitative, agreement between HNC/MSA and MD is found. Both, HNC/MSA and MD, predict the occurrence of overcharging, which is not present in the Poisson-Boltzmann theory. Mean electrostatic potential and local concentration profiles, $\zeta$-potential and charge distribution functions are obtained and discussed in terms of the observed overcharging effect. Particularly interesting results are a very non-monotonic behavior of the $\zeta$-potential, as a function of the rod charge density, and the overcharging by {\em monovalent} counterions.Comment: 11 pages, 8 figures, RevTex, published in J. Phys. Chem. B 2001, vol. 105, pags. 1098