An Adaptive Interacting Wang-Landau Algorithm for Automatic Density Exploration

While statisticians are well-accustomed to performing exploratory analysis in the modeling stage of an analysis, the notion of conducting preliminary general-purpose exploratory analysis in the Monte Carlo stage (or more generally, the model-fitting stage) of an analysis is an area which we feel deserves much further attention. Towards this aim, this paper proposes a general-purpose algorithm for automatic density exploration. The proposed exploration algorithm combines and expands upon components from various adaptive Markov chain Monte Carlo methods, with the Wang-Landau algorithm at its heart. Additionally, the algorithm is run on interacting parallel chains -- a feature which both decreases computational cost as well as stabilizes the algorithm, improving its ability to explore the density. Performance is studied in several applications. Through a Bayesian variable selection example, the authors demonstrate the convergence gains obtained with interacting chains. The ability of the algorithm's adaptive proposal to induce mode-jumping is illustrated through a trimodal density and a Bayesian mixture modeling application. Lastly, through a 2D Ising model, the authors demonstrate the ability of the algorithm to overcome the high correlations encountered in spatial models.Comment: 33 pages, 20 figures (the supplementary materials are included as appendices

A population Monte Carlo scheme with transformed weights and its application to stochastic kinetic models

This paper addresses the problem of Monte Carlo approximation of posterior probability distributions. In particular, we have considered a recently proposed technique known as population Monte Carlo (PMC), which is based on an iterative importance sampling approach. An important drawback of this methodology is the degeneracy of the importance weights when the dimension of either the observations or the variables of interest is high. To alleviate this difficulty, we propose a novel method that performs a nonlinear transformation on the importance weights. This operation reduces the weight variation, hence it avoids their degeneracy and increases the efficiency of the importance sampling scheme, specially when drawing from a proposal functions which are poorly adapted to the true posterior. For the sake of illustration, we have applied the proposed algorithm to the estimation of the parameters of a Gaussian mixture model. This is a very simple problem that enables us to clearly show and discuss the main features of the proposed technique. As a practical application, we have also considered the popular (and challenging) problem of estimating the rate parameters of stochastic kinetic models (SKM). SKMs are highly multivariate systems that model molecular interactions in biological and chemical problems. We introduce a particularization of the proposed algorithm to SKMs and present numerical results.Comment: 35 pages, 8 figure

Assessing Order Effects in Online Community-based Health Forums

Measuring the quality of health content in online health forums is a challenging task. The majority of the existing measures are based on evaluations of forum users and may not be reliable. We employed machine learning techniques, text mining methods, and Big Data platforms to construct four measures of textual quality to automatically determine the similarity of a given answer to professional answers. We then used them to assess the quality of 66,888 answers posted on Yahoo! Answers Health section. All four measures of textual quality revealed a higher quality for asker-selected best answers indicating that askers, to some extent, have a proper judgment to select the best answers. We also studied the presence of order effects in online health forums. Our results suggest that the textual quality of the first answer positively influences the mean textual quality of the subsequent answers and negatively influences the quantity of subsequent answers

Early markers for myocardial ischemia and sudden cardiac death.

The post-mortem diagnosis of acute myocardial ischemia remains a challenge for both clinical and forensic pathologists. We performed an experimental study (ligation of left anterior descending coronary artery in rats) in order to identify early markers of myocardial ischemia, to further apply to forensic and clinical pathology in cases of sudden cardiac death. Using immunohistochemistry, Western blots, and gene expression analyses, we investigated a number of markers, selected among those which are currently used in emergency departments to diagnose myocardial infarction and those which are under investigation in basic research and autopsy pathology studies on cardiovascular diseases. The study was performed on 44 adult male Lewis rats, assigned to three experimental groups: control, sham-operated, and operated. The durations of ischemia ranged between 5 min and 24 h. The investigated markers were troponins I and T, myoglobin, fibronectin, C5b-9, connexin 43 (dephosphorylated), JunB, cytochrome c, and TUNEL staining. The earliest expressions (≤30 min) were observed for connexin 43, JunB, and cytochrome c, followed by fibronectin (≤1 h), myoglobin (≤1 h), troponins I and T (≤1 h), TUNEL (≤1 h), and C5b-9 (≤2 h). By this investigation, we identified a panel of true early markers of myocardial ischemia and delineated their temporal evolution in expression by employing new technologies for gene expression analysis, in addition to traditional and routine methods (such as histology and immunohistochemistry). Moreover, for the first time in the autopsy pathology field, we identified, by immunohistochemistry, two very early markers of myocardial ischemia: dephosphorylated connexin 43 and JunB

Enthalpies and heat capacities of dissolution, apparent molar heat capacities, and apparent molar volumes of some mono-, di-, tri-, and tetra-saccharides in water

Molar enthalpies of solution at very low molalities of some mono-, di, tri, and tetra-saccharides in water have been measured at 298.15 and 308.15 K using an isoperibol calorimeter. The molar heat-capacity changes ΔsolCp, m ∞on dissolution at 303.15 K were derived from molar enthalpies of solution. A Picker flow microcalorimeter and an Anton Paar digital density meter were used to measure apparent molar heat capacities Cp, 2, φ and apparent molar volumes V2, φ of solute at 298.15 K. The various compounds studied show large positive values of ΔsolCp, m∞ and Cp, 2∞. The experimental Cp, 2∞ values are found to be much higher than values estimated using additivity relations and heat capacities for the constituent groups derived from the heat capacities of monofunctional compounds. Results further indicate that the difference in Cp, 2∞(expt) and Cp, 2∞(est.) per hydroxyl group increases with an increase in the number of hydroxyl groups in a molecule. An attempt has been made to explain the Cp, 2infinity values of stereoisomers in terms of the compatibility of the aqueous-solution conformation of the compound and the tetrahedral order in water

Enthalpies of solution, partial molal heat capacities and apparent molal volumes of sugars and polyols in water

Integral enthalpies of solution of some sugars and polyols in water at low concentrations have been determined calorimetrically at 25 and 35°C. These data have been used to derive heat capacities of solution ΔC°p,2 at 30°C. Partial molal heat capacities C°p,2 have been obtained by combining ΔC°p with C p,2∗, the heat capacity of pure solid compounds. Apparent molal volumes have been obtained from density data. The sugars as well as polyols show significantly high positive ΔC°p and ΔC°p,2 values. The results have been explained in terms of a specific hydration model. The effect of substitution of -OH by glycosidic-OCH3 and of -CHOH by deoxy -CH2 are also discussed

Effect of presorbed water and temperature on adsorption of nitrogen and oxygen in NaCaA and NaMgA zeolites

15-21Adsorption of N2 and O2 has been studied on Ca2+ exchanged NaA zeolites (NaCaA) and on a NaMgA zeolite using elution gas chromatography. N2 specific retention volume and adsorption selectivity increase with increase in calcium content (0 to 97% exchange) of the zeolite. However, the increase in much higher at above 90% calcium exchange. Specific retention volumes and adsorption selectivity decrease with increase in temperature for both the adsorbates. N2 specific retention volume decreases with presorbed water in the zeolite. For zeolite samples NaA and NaCaA having > 90% calcium exchange even 0.9 mmol/g of presorbed water suppressed the N2 selectivity substantially. Zeolite NaMgA shows higher heats of adsorption and lower specific retention volume and selectivity compared to NaCaA with similar ion exchange for nitrogen. Pronounced decrease in N2 specific retention volume, selectivity and heat of adsorption is observed for NaMgA even with 0.9 mmol/g of presorbed water. These results have been explained in terms of interaction of adsorbate molecules with extra-framework cations and their distribution in zeolite A

Sorption of nitrogen, oxygen and argon in mordenite type zeolites

34-39Sorption of nitrogen, oxygen and argon is studied in mordenite type zeolites having different Si/Al ratios using elution gas chromatography. Sorption isotherms of water, benzene and nitrogen show that ZM-060 is a small pore zeolite. The higher values of nitrogen Henry constant, nitrogen selectivity and heats of sorption observed for ZM-060 have been attributed to the presence of Na+ ions in this sample. Comparison of heats of sorption of nitrogen and argon in ZM-060 with those in NaA and NaX reveal that the sorbate molecules experience higher interactions with extra-framework Na+ ion as well as lattice oxygen atoms in mordenite structure. Higher heats of sorption of nitrogen in mordenite ZM-060 have been attributed to the restricted rotational freedom of sorbed nitrogen molecules in the channels of mordenite.</span