3,581 research outputs found

    Taurine uptake across the human intestinal brush-border membrane is via two transporters: H+-coupled PAT1 (SLC36A1) and Na+- and Clāˆ’-dependent TauT (SLC6A6)

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    Taurine is an essential amino acid in some mammals and is conditionally essential in humans. Taurine is an abundant component of meat and fish-based foods and has been used as an oral supplement in the treatment of disorders such as cystic fibrosis and hypertension. The purpose of this investigation was to identity the relative contributions of the solute trans-porters involved in taurine uptake across the luminalmembrane of human enterocytes. Distinct transport characteristics were revealed following expression of the candidate solute trans-porters in Xenopus laevis oocytes: PAT1 (SLC36A1) is a H+-coupled, pH-dependent, Na+-and Clāˆ’-independent, low-affinity, high-capacity transporter for taurine and Ī²-alanine; TauT (SLC6A6) is a Na+- and Clāˆ’-dependent, high-affinity, low-capacity transporter of taurine and Ī²-alanine; ATB0,+ (SLC6A14) is a Na+- and Clāˆ’-dependent, high-affinity, low-capacity transporter which accepts Ī²-alanine but not taurine. Taurine uptake across the brush-border membrane of human intestinal Caco-2 cell monolayers showed characteristics of both PAT1-and TauT-mediated transport. Under physiological conditions, Clāˆ’-dependent TauT-mediated uptake predominates at low taurine concentrations, whereas at higher concentrations typical of diet, Clāˆ’-independent PAT1-mediated uptake is the major absorptive mechanism. Real-tim

    Markov chain aggregation and its application to rule-based modelling

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    Rule-based modelling allows to represent molecular interactions in a compact and natural way. The underlying molecular dynamics, by the laws of stochastic chemical kinetics, behaves as a continuous-time Markov chain. However, this Markov chain enumerates all possible reaction mixtures, rendering the analysis of the chain computationally demanding and often prohibitive in practice. We here describe how it is possible to efficiently find a smaller, aggregate chain, which preserves certain properties of the original one. Formal methods and lumpability notions are used to define algorithms for automated and efficient construction of such smaller chains (without ever constructing the original ones). We here illustrate the method on an example and we discuss the applicability of the method in the context of modelling large signalling pathways

    Fuzzy integral for rule aggregation in fuzzy inference systems

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    The fuzzy inference system (FIS) has been tuned and re-vamped many times over and applied to numerous domains. New and improved techniques have been presented for fuzzification, implication, rule composition and defuzzification, leaving one key component relatively underrepresented, rule aggregation. Current FIS aggregation operators are relatively simple and have remained more-or-less unchanged over the years. For many problems, these simple aggregation operators produce intuitive, useful and meaningful results. However, there exists a wide class of problems for which quality aggregation requires non- additivity and exploitation of interactions between rules. Herein, we show how the fuzzy integral, a parametric non-linear aggregation operator, can be used to fill this gap. Specifically, recent advancements in extensions of the fuzzy integral to \unrestricted" fuzzy sets, i.e., subnormal and non- convex, makes this now possible. We explore the role of two extensions, the gFI and the NDFI, discuss when and where to apply these aggregations, and present efficient algorithms to approximate their solutions

    ADvanced IMage Algebra (ADIMA): a novel method for depicting multiple sclerosis lesion heterogeneity, as demonstrated by quantitative MRI.

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    There are modest correlations between multiple sclerosis (MS) disability and white matter lesion (WML) volumes, as measured by T2-weighted (T2w) magnetic resonance imaging (MRI) scans (T2-WML). This may partly reflect pathological heterogeneity in WMLs, which is not apparent on T2w scans

    Fast Ensemble Smoothing

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    Smoothing is essential to many oceanographic, meteorological and hydrological applications. The interval smoothing problem updates all desired states within a time interval using all available observations. The fixed-lag smoothing problem updates only a fixed number of states prior to the observation at current time. The fixed-lag smoothing problem is, in general, thought to be computationally faster than a fixed-interval smoother, and can be an appropriate approximation for long interval-smoothing problems. In this paper, we use an ensemble-based approach to fixed-interval and fixed-lag smoothing, and synthesize two algorithms. The first algorithm produces a linear time solution to the interval smoothing problem with a fixed factor, and the second one produces a fixed-lag solution that is independent of the lag length. Identical-twin experiments conducted with the Lorenz-95 model show that for lag lengths approximately equal to the error doubling time, or for long intervals the proposed methods can provide significant computational savings. These results suggest that ensemble methods yield both fixed-interval and fixed-lag smoothing solutions that cost little additional effort over filtering and model propagation, in the sense that in practical ensemble application the additional increment is a small fraction of either filtering or model propagation costs. We also show that fixed-interval smoothing can perform as fast as fixed-lag smoothing and may be advantageous when memory is not an issue
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