Exposure to Intermittent Noise Exacerbates the Cardiovascular Response of Wistar-Kyoto Rats to Ozone Inhalation and Arrhythmogenic Challenge.

Noise has become a prevalent public health problem across the world. Although there is a significant amount of data demonstrating the harmful effects of noise on the body, very little is known about how it impacts subsequent responses to other environmental stressors like air pollution, which tend to colocalize in urban centers. Therefore, this study was conducted to determine the effect of intermittent noise on cardiovascular function and subsequent responses to ozone (O).

Determination of the equilibrium charge distribution for polyampholytes of different compactness in a single computer experiment.

The conformational properties of charge-balanced polyampholytes described by the end-to-end distance or radius of gyration depend on parameters such as the temperature and pH as well as on the detailed charge distribution along the backbone. In this work we present a method to determine the charge distribution along a semi-stiff polyampholyte backbone which will result in a thermodynamically stable structure for the compactness of interest, from several loops to an uncoiled structure, performed in a single computer experiment.

Method for sampling compact configurations for semistiff polymers.

The sampling of compact configurations is crucial when investigating structural properties of semistiff polymers, like proteins and DNA, using Monte Carlo methods. A sampling scheme for a continuous model based on configuration biasing is introduced, tested, and compared with conventional methods. The proposed configuration biased Monte Carlo method, used together with the Wang-Landau sampling scheme, enables us to obtain any thermodynamic property within the statistical ensemble in use.

Number fluctuations of the condensing agent affects the coil-toroid coexistence for semi-stiff polyelectrolytes.

A semi-stiff charged polymer with counterions and salt was investigated using a Monte Carlo method with the Wang-Landau sampling scheme. Simulations show the coexistence of thermodynamically stable structures-prolonged and compact (toroidal-like). The transition between the two states is accompanied by concentration fluctuations for the condensing agent.

Effects of Discrete Charge Clustering in Simulations of Charged Interfaces.

A system of counterions between charged surfaces is investigated, with the surfaces represented by uniform charged planes and three different arrangements of discrete surface charges - an equispaced grid and two different clustered arrangements. The behaviors of a series of systems with identical net surface charge density are examined, with particular emphasis placed on the long ranged corrections via the method of "charged slabs" and the effects of the simulation cell size. Marked differences are observed in counterion distributions and the osmotic pressure dependent on the particular representation of the charged surfaces; the uniformly charged surfaces and equispaced grids of discrete charge behave in a broadly similar manner, but the clustered systems display a pronounced decrease in osmotic pressure as the simulation size is increased.

Decreased osmotic pressure via interfacial charge clustering.

Behaviors of a model interfacial system featuring the clustering of discrete, mobile wall charges and a counterion solution are investigated. The results demonstrate that even very small localized charge clusters produce significant effects for the osmotic pressure, effects that are not adequately represented in common colloidal models. We observe a pronounced decrease in osmotic pressure where a certain level of clustering is attained, with potentially significant implications for theories of colloidal stability and biochemical processes at microscopic length scales.

Interaction between charged surfaces mediated by rodlike counterions: the influence of discrete charge distribution in the solution and on the surfaces.

The interaction between two charged surfaces, with discrete or uniform charge distributions, embedded in a solution of rodlike counterions has been studied. Monte Carlo simulations and density functional theory have been applied to study the concentration profiles of counterions and the force between the charged surfaces. We show that for low surface charge densities the repulsive force between like-charged surfaces is observed regardless of the rod length.

The influence of discrete surface charges on the force between charged surfaces.

The force between two parallel charged flat surfaces, with discrete surface charges, has been calculated with Monte Carlo simulations for different values of the electrostatic coupling. For low electrostatic coupling (small counterion valence, small surface charge, high dielectric constant, and high temperature) the total force is dominated by the entropic contribution and can be described by mean field theory, independent of the character of the surface charges. For moderate electrostatic coupling, counterion correlation effects lead to a smaller repulsion than predicted by mean field theory.

A scalable parallel Monte Carlo method for free energy simulations of molecular systems.

We present a method of parallelizing flat histogram Monte Carlo simulations, which give the free energy of a molecular system as an output. In the serial version, a constant probability distribution, as a function of any system parameter, is calculated by updating an external potential that is added to the system Hamiltonian. This external potential is related to the free energy.