Relaxation Dynamics of Semiflexible Polymers

We study the relaxation dynamics of a semiflexible chain by introducing a time-dependent tension. The chain has one of its ends attached to a large bead, and the other end is fixed. We focus on the initial relaxation of the chain that is initially strongly stretched. Using a tension that is self-consistently determined, we obtain the evolution of the end-to-end distance with no free parameters. Our results are in good agreement with single molecule experiments on double stranded DNA

A theoretical and numerical study of a phase field higher-order active contour model of directed networks.

We address the problem of quasi-automatic extraction of directed networks, which have characteristic geometric features, from images. To include the necessary prior knowledge about these geometric features, we use a phase field higher-order active contour model of directed networks. The model has a large number of unphysical parameters (weights of energy terms), and can favour different geometric structures for different parameter values. To overcome this problem, we perform a stability analysis of a long, straight bar in order to find parameter ranges that favour networks. The resulting constraints necessary to produce stable networks eliminate some parameters, replace others by physical parameters such as network branch width, and place lower and upper bounds on the values of the rest. We validate the theoretical analysis via numerical experiments, and then apply the model to the problem of hydrographic network extraction from multi-spectral VHR satellite images

Application of the cross-entropy method to the buffer allocation problem in a simulation-based environment

The buffer allocation problem (BAP) is a well-known difficult problem in the design of production lines. We present a stochastic algorithm for solving the BAP, based on the cross-entropy method, a new paradigm for stochastic optimization. The algorithm involves the following iterative steps: (a) the generation of buffer allocations according to a certain random mechanism, followed by (b) the modification of this mechanism on the basis of cross-entropy minimization. Through various numerical experiments we demonstrate the efficiency of the proposed algorithm and show that the method can quickly generate (near-)optimal buffer allocations for fairly large production lines

Estructura financiera y logro empresarial en cooperativas agrarias: una aproximación empírica

[EN] This paper analyzes the economic and financial information of a sample of Spanish agricultural co-operatives in order to identify the variables that determine the nature and composition of its financial structure. A new variable named “business achievement” has been defined using the statistical technique of principal component analysis (PCA); this, and other ratios, have been used in the regression models. Results show no relationship between financial structure and “business achievement”, but they support the Pecking order theory, thus validating the hypothesis that, in absence of self-financing, the prevalent funding sources in agricultural cooperatives are debt and capitalization. Also, in line with the Agency theory, it has been shown that in these entities growths in sales, and therefore cash flow generation, lead to higher short-term debt, while the use of long-term debt decreases.[ES] Este trabajo utiliza la información económico-financiera de una muestra de cooperativas agrarias españolas para identificar las variables que determinan la naturaleza y composición de su estructura financiera. Se define una variable relativa al logro empresarial, a partir de la técnica estadística del análisis de componentes principales que, junto con otros ratios, se introduce en los modelos de regresión. Los resultados no evidencian relación entre estructura financiera y logro empresarial, pero sí corroboran la teoría del Pecking order, apoyando la hipótesis del endeudamiento y la capitalización como fuentes de financiación predominantes. También se verifica la Teoría de la agencia, ya que crecimientos de ventas conllevan un mayor endeudamiento a corto plazo.Los autores agradecen los comentarios anónimos de los revisores de la revista. Este trabajo se enmarca dentro del Proyecto DER2008-03475 “Pérdidas, disolución e insolvencia en la sociedad cooperativa”, financiado por el Ministerio de Ciencia e Innovación (IV Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica 2008-2011).Lajara-Camilleri, N.; Mateos-Ronco, A. (2012). Financial structure and business achievement in agricultural cooperatives: an empirical approach. Economía Agraria y Recursos Naturales - Agricultural and Resource Economics. 12(2):77-101. https://doi.org/10.7201/earn.2012.02.04SWORD7710112

Boundary lubrication properties of materials with expansive freezing

We have performed molecular dynamics simulations of solid-solid contacts lubricated by a model fluid displaying many of the properties of water, particularly its expansive freezing. Near the region where expansive freezing occurs, the lubricating film remains fluid, and the friction force decreases linearly as the shear velocity is reduced. No sign of stick-slip motion is observed even at the lowest velocities. We give a simple interpretation of these results, and suggest that in general good boundary lubrication properties will be found in the family of materials with expansive freezing.Comment: Version to appear in Phys. Rev. Let

Regression Error Characteristic Optimisation of Non-Linear Models.

Copyright © 2006 Springer-Verlag Berlin Heidelberg. The final publication is available at link.springer.comBook title: Multi-Objective Machine LearningIn this chapter recent research in the area of multi-objective optimisation of regression models is presented and combined. Evolutionary multi-objective optimisation techniques are described for training a population of regression models to optimise the recently defined Regression Error Characteristic Curves (REC). A method which meaningfully compares across regressors and against benchmark models (i.e. ‘random walk’ and maximum a posteriori approaches) for varying error rates. Through bootstrapping training data, degrees of confident out-performance are also highlighted

Identification of PhIL1, a Novel Cytoskeletal Protein of the Toxoplasma gondii Pellicle, through Photosensitized Labeling with 5-[125I]Iodonaphthalene-1-Azide

The pellicle of the protozoan parasite Toxoplasma gondii is a unique triple bilayer structure, consisting of the plasma membrane and two tightly apposed membranes of the underlying inner membrane complex. Integral membrane proteins of the pellicle are likely to play critical roles in host cell recognition, attachment, and invasion, but few such proteins have been identified. This is in large part because the parasite surface is dominated by a family of abundant and highly immunogenic glycosylphosphatidylinositol (GPI)-anchored proteins, which has made the identification of non-GPI-linked proteins difficult. To identify such proteins, we have developed a radiolabeling approach using the hydrophobic, photoactivatable compound 5-[125I]iodonaphthalene-1-azide (INA). INA can be activated by photosensitizing fluorochromes; by restricting these fluorochromes to the pellicle, [125I]INA labeling will selectively target non-GPI-anchored membrane-embedded proteins of the pellicle. We demonstrate here that three known membrane proteins of the pellicle can indeed be labeled by photosensitization with INA. In addition, this approach has identified a novel 22-kDa protein, named PhIL1 (photosensitized INA-labeled protein 1), with unexpected properties. While the INA labeling of PhIL1 is consistent with an integral membrane protein, the protein has neither a transmembrane domain nor predicted sites of lipid modification. PhIL1 is conserved in apicomplexan parasites and localizes to the parasite periphery, concentrated at the apical end just basal to the conoid. Detergent extraction and immunolocalization data suggest that PhIL1 associates with the parasite cytoskeleton

Tension Dynamics and Linear Viscoelastic Behavior of a Single Semiflexible Polymer Chain

We study the dynamical response of a single semiflexible polymer chain based on the theory developed by Hallatschek et al. for the wormlike-chain model. The linear viscoelastic response under oscillatory forces acting at the two chain ends is derived analytically as a function of the oscillation frequency . We shall show that the real part of the complex compliance in the low frequency limit is consistent with the static result of Marko and Siggia whereas the imaginary part exhibits the power-law dependence +1/2. On the other hand, these compliances decrease as the power law -7/8 for the high frequency limit. These are different from those of the Rouse dynamics. A scaling argument is developed to understand these novel results.Comment: 23 pages, 6 figure