Are hydrodynamic interactions important in the kinetics of hydrophobic collapse?

We study the kinetics of assembly of two plates of varying hydrophobicity, including cases where drying occurs and water strongly solvates the plate surfaces. The potential of mean force and molecular-scale hydrodynamics are computed from molecular dynamics simulations in explicit solvent as a function of particle separation. In agreement with our recent work on nanospheres [J. Phys. Chem. B 116, 378 (2012)] regions of high friction are found to be engendered by large and slow solvent fluctuations. These slow fluctuations can be due to either drying or confinement. The mean first passage times for assembly are computed by means of molecular dynamics simulations in explicit solvent and by Brownian dynamics simulations along the reaction path. Brownian dynamics makes use of the potential of mean force and hydrodynamic profile that we determined. Surprisingly, we find reasonable agreement between full scale molecular dynamics and Brownian dynamics, despite the role of slow solvent relaxation in the assembly process. We found that molecular scale hydrodynamic interactions are essential in describing the kinetics of assembly.Comment: 6 figures, 13 page

Lo statuto regionale, dopo le riforme

Analisi critica e ricostruzione dogmatica dello statuto regionale dopo le riforme costituzionali e, soprattutto, dopo i nuovi statuti delle regioni ordinarie

Formal and informal sectors in a Social Accounting Matrix for Brazil

This paper presents a methodology to estimate a Social Accounting Matrix for Brazil in 2006 that separates between formal and informal sectors. The goal of this study is to estimate and to analyze the Social Accounting Matrix for Brazil in 2006. The shares of output by informal and formal sectors are applied as weights to estimate the size of the two sectors. The results reveal important structural linkages between the two sectors and may serve as data input for future Structuralist Calibrated models

The role of water and steric constraints in the kinetics of cavity-ligand unbinding

A key factor influencing a drug's efficacy is its residence time in the binding pocket of the host protein. Using atomistic computer simulation to predict this residence time and the associated dissociation process is a desirable but extremely difficult task due to the long timescales involved. This gets further complicated by the presence of biophysical factors such as steric and solvation effects. In this work, we perform molecular dynamics (MD) simulations of the unbinding of a popular prototypical hydrophobic cavity-ligand system using a metadynamics based approach that allows direct assessment of kinetic pathways and parameters. When constrained to move in an axial manner, we find the unbinding time to be on the order of 4000 sec. In accordance with previous studies, we find that the ligand must pass through a region of sharp dewetting transition manifested by sudden and high fluctuations in solvent density in the cavity. When we remove the steric constraints on ligand, the unbinding happens predominantly by an alternate pathway, where the unbinding becomes 20 times faster, and the sharp dewetting transition instead becomes continuous. We validate the unbinding timescales from metadynamics through a Poisson analysis, and by comparison through detailed balance to binding timescale estimates from unbiased MD. This work demonstrates that enhanced sampling can be used to perform explicit solvent molecular dynamics studies at timescales previously unattainable, obtaining direct and reliable pictures of the underlying physio-chemical factors including free energies and rate constants.Comment: 7 pages, 4 figures, supplementary PDF file, submitte

The lake of priest: socio-political and cultural mediation in the corregimientos of the lake Titicaca (1570-1650)

Este artículo analiza las prácticas sociales y políticas de los curas doctrineros encargados de la evangelización de los colectivos indígenas de los pueblos de reducción, englobados en los corregimientos del lago Titicaca entre fines del siglo XVI y mediados del siglo XVII. A partir de información contenida en protocolos notariales, expedientes judiciales y presentaciones ante instancias superiores de la administración colonial, indagamos el entramado del poder político local, toda vez que los curas doctrineros, junto a los caciques y los corregidores, conformaron las piezas claves en la dinámica política de cada pueblo de reducción. Proponemos establecer puentes comparativos entre experiencias de construcción de carreras políticas tanto de curas como de autoridades indígenas, e interrogar las instancias de intermediación socio cultural protagonizadas por ambos actores sociales.This article analyzes social and political practices deployed by curas doctrineros (rural priest) in charge of evaengelization of native groups within the pueblos de reducción (villages) of the Titicaca lake corregimientos (provinces) between the late-16th and the mid-17th centuries. Notarial protocols, court records and formal presentations to higher colonial administration levels are addressed to inquire about local political framework, given that curas doctrineros, as well as caciques and corregidores, played key roles in the political dynamics of each pueblo de reducción. We prone to settle comparative approaches on how curas and caciques built their political careers and to examine sociocultural intermediation instances carried out by both social actors.Fil: Morrone, Ariel Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto de Historia Argentina y Americana "Dr. Emilio Ravignani". Universidad de Buenos Aires. Facultad de Filosofía y Letras. Instituto de Historia Argentina y Americana "Dr. Emilio Ravignani"; Argentin