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A van 't Hof

Publications and source records attributed to A van 't Hof.

5 recordsLinked to original sources
PubMed2006

Computing the starting state for Gibbs-Duhem integration.

Gibbs-Duhem integration implies the numerical integration of a Clapeyron equation. To start the numerical integration, an initial coexistence point and a corresponding initial slope of the Clapeyron equation are needed. In order to apply Gibbs-Duhem integration to all kinds of systems at diverse physical conditions, one has to investigate and assess the available methods that can be used to compute these initial values. This publication focuses on vapor-liquid equilibria in binary mixtures comprising chain molecules. The initial coexistence point is either computed with the NVbeta Gibbs ensemble or with the Npbeta+test molecule method with overlapping distributions, which is introduced in this publication. Although computationally demanding, the Npbeta+test molecule method with overlapping distributions is applicable at conditions where the NVbeta Gibbs ensemble fails. We investigated three methods that can be employed to compute the initial slope of the Clapeyron equation. The Widom method and the overlapping-distributions difference method provide correct values for the initial slope. The difference method does only provide the correct answer in special cases. The possibility to judge the reliability of the results makes the overlapping-distributions difference method the safest route to the initial slope. Gibbs-Duhem integration requires the frequent computation of the slope of the Clapeyron equation. This slope depends on ensemble averages of the composition. A new bias method for efficient sampling of the composition in a semigrand-canonical simulation of chain molecules is presented. This bias method considerably enhances the composition sampling in systems comprising chain molecules of different sizes.

Journal Article↗
PubMed2006

An advanced Gibbs-Duhem integration method: theory and applications.

The conventional Gibbs-Duhem integration method is very convenient for the prediction of phase equilibria of both pure components and mixtures. However, it turns out to be inefficient. The method requires a number of lengthy simulations to predict the state conditions at which phase coexistence occurs. This number is not known from the outset of the numerical integration process. Furthermore, the molecular configurations generated during the simulations are merely used to predict the coexistence condition and not the liquid- and vapor-phase densities and mole fractions at coexistence. In this publication, an advanced Gibbs-Duhem integration method is presented that overcomes above-mentioned disadvantage and inefficiency. The advanced method is a combination of Gibbs-Duhem integration and multiple-histogram reweighting. Application of multiple-histogram reweighting enables the substitution of the unknown number of simulations by a fixed and predetermined number. The advanced method has a retroactive nature; a current simulation improves the predictions of previously computed coexistence points as well. The advanced Gibbs-Duhem integration method has been applied for the prediction of vapor-liquid equilibria of a number of binary mixtures. The method turned out to be very convenient, much faster than the conventional method, and provided smooth simulation results. As the employed force fields perfectly predict pure-component vapor-liquid equilibria, the binary simulations were very well suitable for testing the performance of different sets of combining rules. Employing Lorentz-Hudson-McCoubrey combining rules for interactions between unlike molecules, as opposed to Lorentz-Berthelot combining rules for all interactions, considerably improved the agreement between experimental and simulated data.

Journal Article↗
PubMed1993

Recurrence of paroxysmal atrial fibrillation or flutter after successful cardioversion in patients with normal left ventricular function.

One hundred twenty-four consecutive patients (85%) with paroxysmal atrial fibrillation (AF) and 21 (15%) with atrial flutter (AFI) were studied immediately after pharmacologic or electrical cardioversion to sinus rhythm. Mean age was 59 +/- 13 years (range 23 to 79). Patients with reduced left ventricular function were excluded from the study. After restoration to sinus rhythm, the clinical course of all patients was followed for the first recurrence of paroxysmal AF or AFI irrespective of the therapeutic approach. Mean follow-up was 23 +/- 16 months. After 12 months of follow-up, 50% of all patients remained in sinus rhythm. Univariate analysis indicated that coronary artery disease (relative risk 1.9; 95% confidence interval 0.9-3.9), history of paroxysmal AF or AFI (2.3; 1.1-5.0), female sex (2.3; 1.1-4.6), pulmonary disease (3.9; 1.9-7.6) and valvular heart disease (4.4; 2.2-8.8) were associated with an increased risk for recurrent or frequent episodes of paroxysmal AF or AFI. No predictors were found to be associated with a decrease in length of the recurrence-free period after successful conversion to sinus rhythm. Multivariate analysis identified history of AF or AFI (odds ratio 2.5; 95% confidence interval 0.9-6.4), coronary artery disease (3.1; 1.1-8.2) and female sex (3.4; 1.3-8.9) as independent predictors for recurrent or frequent episodes of paroxysmal AF or AFI. The presence of these risk factors should be taken into account when prophylactic therapy with antiarrhythmic drugs is being considered in the treatment of paroxysmal AF or AFI.

Adult↗