Analysis of electrocardiograms during atrial fibrillation

The research discussed in this article is motivated by the search for an optimal classification of the different types of atrial fibrillation (AF) on the basis of recorded atrial signals. This would facilitate the selection of an optimal therapy. This article focuses on the biophysical models of the genesis of ECG waveforms during AF. The model of the electric activity of the atria was found to have sufficient realism to be used to describe the electric sources during AF. The inclusion of the volume conduction model resulted in electrocardiographic signals that are in all aspects similar to those observed clinically. The model is currently applied to solve various problems related to optimal signal preprocessing and extraction of features in AF signals for the classification of AF abnormalities. The biophysical model of the atrial activity is an essential element in this research, since it is capable of describing the electric source specifications derived from different hypotheses relating to the etiology of AF     

Estimation of a human capital model of migration

"The main deficiency of the current literature on the determinants of migration is the large gap between theoretical analyses and empirical applications. If no direct link is established between a theoretical model and its empirical specification, the empirical results cannot validate the model. This paper develops a version of the human capital model of migration which permits empirical specification. The human capital model presented incorporates two important concepts from migration theory: (1) an index of characteristics that uniquely define a specific location; and (2) location-specific human capital. The empirical model is estimated with a data set consisting of a number of cases from the Michigan [United States] Panel Study of Income Dynamics (PSID) survey."     

Laboratory-scale liquefiers for natural gas: A design and assessment study

Exact knowledge of natural gas composition is essential in custody transfer to determine the energy content of the delivery. However, for liquefied natural gas (LNG), a reliable composition determination is difficult. Here, we describe the design of a laboratory-scale reference liquefier that enables the validation and calibration of optical spectroscopy sensors by providing them with a sample of metrologically traceable composition. Hence, it is crucial to avoid fractionation of the sample during liquefaction. This is realized by supercritical liquefaction of a reference gas mixture in conjunction with a special vapor–liquid-equilibrium (VLE) cell. As this is a demanding high-pressure application, low-pressure condensation as liquefaction method was also assessed. Through experimental investigations and VLE calculations, preservation of the composition of the produced liquid sample during condensation was studied. We conclude that under optimized conditions, validation, and calibration measurements of optical sensors can be performed on condensed liquids, which, however, needs further confirmation.     

Experimental-numerical study and optimization of sound insulation of a finite composite cylinder

The aircraft fuselage is idealized as a composite cylinder, its vibroacoustic properties are studied both experimentally and numerically, and a minimization of the inner pressure of a composite cylinder is conducted with the genetic algorithm (GA). In the optimization, the Acoustic Transfer Vector (ATV), which comes from the boundary element method, builds the relationship between the structural surface velocity and the sound pressure at the specific filed points. Results show that the noise reduction obtained by the experimental and numerical methods have a good agreement; the optimization method which combines GA and ATV show high efficiency and robustness; increase of the bending stiffness of the cylinder can improve the noise reduction at low frequencies; both the reduction of weight and the increase of noise insulation can be achieved by the optimization of the layup at different regions of the cylinder individually.     

THE IMPACT OF CHANGING BUSINESS AGGLOMERATION ECONOMIES ON METROPOLITAN GROWTH

ABSTRACT This paper aims to determine the impact of changes in the parameters measuring economies of scale in production on metropolitan growth. The degree of spatial concentration of sectoral economic activity and patterns of trade between two metropolitan areas are explained with a two-sector model borrowed from the international trade literature. It is shown that sectoral production will become more concentrated as the importance of intrasectoral economics of scale relative to intersectoral scale economics increases. An increase in the relative size of intrasectoral business agglomeration economics will not necessarily lead to complete specialisation by either metropolitan area.     

Reduced percolation concentration in polypropylene/expanded graphite composites: Effect of viscosity and polypyrrole

With the goal to obtain material combining electrical and thermal conductivity at low filler loadings, composites based on polypropylenes (PP) and expanded graphite (EG) have been prepared. The effects of matrix viscosity and of coating the EG particles with polypyrrole (PPy, EG/PPy = 37.5/62.5 by weight) on the EG dispersibility and formation of percolation structures have been analyzed. When increasing the EG amount from 6 to 8 wt %, the electrical conductivity of PP/EG composites increased by 7–9 orders of magnitude, independent of matrix viscosity. When EG‐PPy is added, percolation was observed between 8 and 12 wt % EG‐PPy (3 and 4.5 wt % EG) in case of PP with higher viscosity and 6 wt % EG (2.25 wt % EG) in case of PP with lower viscosity, exhibiting a strong synergistic effect of EG and PPy in the latter case. In contrast, PPy does not contribute to reduction of thermal percolation concentration. Thermal percolation is observed at 8 wt % EG in PP/EG composites, but no percolation was found in PP/EG‐PPy composites with EG‐PPy contents of up to 20 wt %, corresponding to 7.5 wt % EG. Analyzing the melt rheology it becomes clear that the contribution of PPy to the formation of a filler network is strongly dependent on the matrix viscosity. The comparison of thermal, electrical and rheological percolation reveals that PPy participates in electron transport reducing the electrical percolation but not to heat transport. Overall, we found a good correlation between electrical, thermal, and melt rheological percolation concentrations. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41994.     

Prospective Validation of a Comprehensive In silico hERG Model and its Applications to Commercial Compound and Drug Databases

Ligand‐based in silico hERG models were generated for 2 644 compounds using linear discriminant analysis (LDA) and support vector machines (SVM). As a result, the dataset used for the model generation is the largest publicly available (see Supporting Information). Extended connectivity fingerprints (ECFPs) and functional class fingerprints (FCFPs) were used to describe chemical space. All models showed area under curve (AUC) values ranging from 0.89 to 0.94 in a fivefold cross‐validation, indicating high model consistency. Models correctly predicted 80 % of an additional, external test set; Y‐scrambling was also performed to rule out chance correlation. Additionally models based on patch clamp data and radioligand binding data were generated separately to analyze their predictive ability when compared to combined models. To experimentally validate the models, 50 of the predicted hERG blockers from the Chembridge database and ten of the predicted non‐hERG blockers from an in‐house compound library were selected for biological evaluation. Out of those 50 predicted hERG blockers, tested at a concentration of 10 μM , 18 compounds showed more than 50 % displacement of [³H]astemizole binding to cell membranes expressing the hERG channel. K_i values of four of the selected binders were determined to be in the micromolar and high nanomolar range (K_i (VH 01 )=2.0 μM , K_i (VH 06 )=0.15 μM , K_i (VH 19 )=1.1 μM and K_i (VH 47 )=18 μM ). Of these four compounds, VH 01 and VH 47 showed also a second, even higher affinity binding site with K_i values of 7.4 nM and 36 nM , respectively. In the case of non‐hERG blockers, all ten compounds tested were found to be inactive, showing less than 50 % displacement of [³H]astemizole binding at 10 μM . These experimentally validated models were then used to virtually screen commercial compound databases to evaluate whether they contain hERG blockers. 109 784 (23 %) of Chembridge, 133 175 (38 %) of Chemdiv, 111 737 (31 %) of Asinex and 11 116 (18 %) of the Maybridge database were predicted to be hERG blockers by at least two of the models, a prediction which could, for example, be used as a pre‐filtering tool for compounds with potential hERG liabilities.     

Improved self-organization with an alternative inhibition gradient in CALMMap networks

Phaf et al. (2001, Connection Science, 13 (4): 293-321) described a self-organizing variant of the CALM modular neural network model (Murre et al., 1992, Neural Networks, 5: 55-82), which has been coined CALMMap. The self-organization mechanism is driven by a specific inhibition gradient formula. The disadvantage of this formula is that it introduces new parameters and is not optimally adjusted to the size of a module. This research note provides an alternative to this inhibition gradient formula, with the benefit that it performs autonomously. In other words, no extra parameters are introduced and the strength of inhibition adapts to the size of a module. Simulations are described to show the effectiveness of the alternative inhibition gradient function.