Truncating the loop series expansion for Belief Propagation

Recently, M. Chertkov and V.Y. Chernyak derived an exact expression for the partition sum (normalization constant) corresponding to a graphical model, which is an expansion around the Belief Propagation solution. By adding correction terms to the BP free energy, one for each "generalized loop" in the factor graph, the exact partition sum is obtained. However, the usually enormous number of generalized loops generally prohibits summation over all correction terms. In this article we introduce Truncated Loop Series BP (TLSBP), a particular way of truncating the loop series of M. Chertkov and V.Y. Chernyak by considering generalized loops as compositions of simple loops. We analyze the performance of TLSBP in different scenarios, including the Ising model, regular random graphs and on Promedas, a large probabilistic medical diagnostic system. We show that TLSBP often improves upon the accuracy of the BP solution, at the expense of increased computation time. We also show that the performance of TLSBP strongly depends on the degree of interaction between the variables. For weak interactions, truncating the series leads to significant improvements, whereas for strong interactions it can be ineffective, even if a high number of terms is considered.Comment: 31 pages, 12 figures, submitted to Journal of Machine Learning Researc

ANALYSIS OF THE EFFECTS OF ENVIRONMENTAL REGULATION ON PULP AND PAPER INDUSTRY STRUCTURE

Environmental regulations are hypothesized to have an impact on industry structure in manufacturing industries. A nonstationary Markov chain analysis shows that the capital expenditures required to meet environmental regulations is a statistically significant variable explaining increasing concentration of production capacity in the pulp and paper industry.Environmental Economics and Policy, Research Methods/ Statistical Methods,

Stability of Influence Maximization

The present article serves as an erratum to our paper of the same title, which was presented and published in the KDD 2014 conference. In that article, we claimed falsely that the objective function defined in Section 1.4 is non-monotone submodular. We are deeply indebted to Debmalya Mandal, Jean Pouget-Abadie and Yaron Singer for bringing to our attention a counter-example to that claim. Subsequent to becoming aware of the counter-example, we have shown that the objective function is in fact NP-hard to approximate to within a factor of $O(n^{1-\epsilon})$ for any $\epsilon > 0$. In an attempt to fix the record, the present article combines the problem motivation, models, and experimental results sections from the original incorrect article with the new hardness result. We would like readers to only cite and use this version (which will remain an unpublished note) instead of the incorrect conference version.Comment: Erratum of Paper "Stability of Influence Maximization" which was presented and published in the KDD1

High density culturing of porcine hepatocytes immobilized on nonwoven polyurethane-based biomatrices

Objective: Hepatocytes are increasingly used as functional units in bioartificial liver devices. The objective of the present study was to investigate the feasibility of culturing porcine hepatocytes in high density on a novel polyurethane-based nonwoven three-dimensional matrix. We investigated (1) the optimal cell density within this culture configuration, (2) the maintenance of liver-specific morphology and cell functions over long-term periods and (3) the necessity to apply an additional extracellular matrix component (collagen gel). Methods: Nonwoven polyurethane matrices were manufactured by a specially developed fiber extrusion technology. Pig hepatocytes were cultured at various cell densities of 0.1, 0.25, 0.5, 0.75, 1 and 2 x 10(6) cells/cm(2) on three-dimensional networks of nonwoven polyurethane matrices and cell adhesion as well as functional parameters (DNA of nonattached/attached cells, lactate dehydrogenase release and cytochrome P450 activity) were determined. To assess the performance of cells within this configuration albumin and urea excretion was measured over 8 days. The potentially beneficial effect of an additional extracellular matrix configuration was evaluated by comparing the average albumin synthesis in groups of identical cell numbers. Results: The optimal cell density in this three-dimensional culture configuration was 1 x 10(6) cells/cm(2). The functional capacity of hepatocytes was stable for 8 days at an average level of 53.7 +/- 5.6 ng/h/mug DNA and of 1.8 +/- 0.14 mug/h/mug DNA for albumin and urea excretion, respectively. The supplementation of an extracellular matrix configuration did not improve functional activity of cells. Average albumin synthesis was 35.6 ng/h/mug DNA (28.7, 42.8) and 32.7 ng/h/mug DNA (23.4, 49.2) for collagen-immobilized and control cultures, respectively, Conclusion: The results of the study indicate that nonwoven polyurethane sheets supply a biocompatible support structure for functionally active high density cultures. Thus, nonwoven polyurethane matrices should be further investigated on with respect to their role in the development, optimization and design of bioartificial liver systems. Copyright (C) 2001 S.Karger AG, Basel

Symmetric Brownian motor

In this paper we present a model of a symmetric Brownian motor (SBM) which changes the sign of its velocity when the temperature gradient is inverted. The velocity, external work and efficiency are studied as a function of the temperatures of the baths and other relevant parameters. The motor shows a current reversal when another parameter (a phase shift) is varied. Analytical predictions and results from numerical simulations are performed and agree very well. Generic properties of this type of motors are discussed.Comment: 8 pages and 10 figure

White noise flashing Brownian pump

A Brownian pump of particles powered by a stochastic flashing ratchet mechanism is studied. The pumping device is embedded in a finite region and bounded by particle reservoirs. In the steady state, we exactly calculate the spatial density profile, the concentration ratio between both reservoirs and the particle flux. A simple numerical scheme is presented allowing for the consistent evaluation of all such observable quantities

The dust morphology of the elliptical Galaxy M86 with SPIRE

We present Herschel-SPIRE observations at 250–500 μm of the giant elliptical galaxy M 86 and examine the distribution of the resolved cold dust emission and its relation with other galactic tracers. The SPIRE images reveal three dust components: emission from the central region; a dust lane extending north-south; and a bright emission feature 10 kpc to the south-east. We estimate that ~10^6 M_☉ of dust is spatially coincident with atomic and ionized hydrogen, originating from stripped material from the nearby spiral NGC 4438 due to recent tidal interactions with M 86. The gas-to-dust ratio of the cold gas component ranges from ~20–80. We discuss the different heating mechanisms for the dust features