Evaluation of peak picking quality in LC-MS metabolomics data

The output of LC-MS metabolomics experiments consists of mass-peak intensities identified through a peak-picking/alignment procedure. Besides imperfections in biological samples and instrumentation, data accuracy is highly dependent on the applied algorithms and their parameters. Consequently, quality control (QC) is essential for further data analysis. Here, we present a QC approach that is based on discrepancies between replicate samples. First, the quantile normalization of per-sample log-signal distributions is applied to each group of biologically homogeneous samples. Next, the overall quality of each replicate group is characterized by the Z-transformed correlation coefficients between samples. This general QC allows a tuning of the procedure's parameters which minimizes the inter-replicate discrepancies in the generated output. Subsequently, an in-depth QC measure detects local neighborhoods on a template of aligned chromatograms that are enriched by divergences between intensity profiles of replicate samples. These neighborhoods are determined through a segmentation algorithm. The retention time (RT)-m/z positions of the neighborhoods with local divergences are indicative of either: incorrect alignment of chromatographic features, technical problems in the chromatograms, or to a true biological discrepancy between replicates for particular metabolites. We expect this method to aid in the accurate analysis of metabolomics data and in the development of new peak-picking/alignment procedures.     

Fast GL(n)-Invariant Framework for Tensors Regularization

We propose a novel framework for regularization of symmetric positive-definite (SPD) tensors (e.g., diffusion tensors). This framework is based on a local differential geometric approach. The manifold of symmetric positive-definite (SPD) matrices, P _n , is parameterized via the Iwasawa coordinate system. In this framework distances on P _n are measured in terms of a natural GL(n)-invariant metric. Via the mathematical concept of fiber bundles, we describe the tensor-valued image as a section where the metric over the section is induced by the metric over P _n . Then, a functional over the sections accompanied by a suitable data fitting term is defined. The variation of this functional with respect to the Iwasawa coordinates leads to a set of frac12n(n+1)frac{1}{2}n(n+1) coupled equations of motion. By means of the gradient descent method, these equations of motion define a Beltrami flow over P _n . It turns out that the local coordinate approach via the Iwasawa coordinate system results in very simple numerics that leads to fast convergence of the algorithm. Regularization results as well as results of fibers tractography for DTI are presented.     

Simultaneous optimal integration of water utilization and heat exchange networks using holistic mathematical programming

A systematic holistic mathematical programming (HMP) is proposed to formulate a mixed integer nonlinear programming (MINLP) model for one-step optimization of water-allocation and heat exchange network (WAHEN) designs with single- or multi-contaminant water streams. The proposed model formulation and solution strategy are believed to be superior to the available ones in the following aspects. First, a comprehensive representation combining two separate superstructures is adopted to capture the structural characteristics of the integrated WAHEN. Then, a hybrid optimization strategy integrating stochastic and deterministic components is developed for the resulting MINLP model and, also, an interactive iteration method is adopted based on sensitivity analysis to guide the search toward a potential global optimum. Finally, evolutionary strategies and manipulations are executed to enhance WAHEN configurations. Two illustrative examples are presented to demonstrate the validity and advantages of the proposed approach.     

Number-theoretic functions which are equivalent to number of divisors

Let d(n) denote the number of positive integral divisors of n. In this paper we show that the Möbius function, μ(N), can be computed by a single call to an oracle for d(n). We also show that any function that depends solely on the exponents in the prime factorization of N can be computed by at most log₂ N calls to an oracle for d(N).     

Stress relief forms of diamond-like carbon thin films under internal compressive stress

An optical microscope study of the stress relief forms of diamond-like carbon thin films is presented in this paper. The dimensions of the stress relief patterns are shown to be proportional to the film thickness. Three stress relief forms are distinguished. They are analysed in the framework of the linear theory of plate buckling. The forms of the stress relief correspond to two different solutions of the differential equations.     

移动式小型X线机综合防护装置

本文介绍一种移动式小型 X 线机综合防护装置。该装置把便于运输的部件、防护隔屏及暗室融为一体,为 X 线工作者、被检者和被检者提供了较好的防护。本文介绍一种移动式小型 X 线机综合防护装置。现将其基本构造和防护效果简介如下:     

Reallocating Water Resources in the Middle East through Market Mechanisms

The growing demand for water by countries in the eastern Mediterranean raises the need to explore ways and means to ameliorate water scarcity. Economists have for some time proposed methods of more efficient exploitation of existing water supplies. Specifically, by employing m arket incentive mechanisms to encou rage voluntary water sharing among countries and regions is likely to lead to greater efficiency in water utilization. This paper explores the efficiency gains associated with re-allocating fresh water resources in the eastern Mediterranean through water rights markets. The results suggest that all parties involved might benefit to a greater or lesser degree from trading in water rights.