Myelin figures: the buckling and flow of wet soap

Myelin figures are interfacial structures formed when certain surfactants swell in excess water. Here, I present data and model calculations suggesting myelin formation and growth is due to the fluid flow of surfactant, driven by the hydration gradient at the dry surfactant/water interface; a simple model based on this idea qualitatively reproduces the various myelin growth behaviors observed in different experiments. From a detailed experimental observation of how myelins develop from a planar precursor structure, I identify a mechanical instability that may underlie myelin formation. These results indicate the mixed mechanical character of the surfactant lamellar structure, where fluid and elastic properties coexist, is what enables the formation and growth of myelins.Comment: 11 pages, 10 figures, to appear in Phys. Rev. E. Corrected figures/typo

Models and Estimation for Phylogenetic Trees

In this thesis, we consider Markov models for matched sequences. De¯ne fij(t) = P(X(t) = i; Y (t) = jjX(0) = Y (0)); where fij is the joint probability that, for a given site, the ¯rst and second sequences have the values i and j at a given site, given that they were the same at time 0. This can generalized to several sequences. The sequences (taxa) are then arranged in an evolutionary tree (phylogenetic tree) depicting how taxa diverge from their common ancestors. We develop tests and estimation methods for the parameters of di®erent models. Standard phylogenetic methods assume stationarity, homogeneity and reversibility for the Markov processes, and often impose further restrictions on the parameters. The parameters in these cases are estimated using many popular packages, including PHYLIP and PAUP*. We describe a new and more general method for calculating the joint probability distribution under stationary and homogeneous models for the more general models with some weakening of the stationarity and homogeneity assumptions. We describe the method for a two edged tree and then extend it to the case for a K tipped tree. We discuss the case of a ¯ve edged tree for a set of bacterial sequences for which stationarity and homogeneity are not present. This data set is very similar to that of Galtier and Gouy (1995), and the search for methods appropriate for its analysis has provided the raison d'etre for this work. The extension we propose is to allow non-stationarity, so that from the root of the tree we permit di®erent Markov processes to operate along different descendant lineages; furthermore, we permit non-homogeneous Markov processes to operate across the tree. We obtain methods tha

Structural and mechanical properties of nanocrystalline Zr co-sputtered a-C(:H) amorphous films

The aim of this study was to investigate the effect of Zr as alloying element to carbon films, particularly in respect to film structure and mechanical properties. The films were deposited by magnetron sputtering in reactive (Ar + CH4) and non-reactive (Ar) atmosphere with different Zr contents (from 0 to 14 at.%) in order to achieve a nanocomposite based films. With an increase of Zr content a broad peak was observed in X-ray diffraction spectra suggesting the presence of nanocrystalline (nc) ZrC phase for the coatings with Zr content higher than 4 at.%. The application of Scherrer formula yielded a grain sizes with a dimension of 1.0–2.2 nm. These results were supported by X-ray photoelectron spectroscopy showing typical charge transfer at Zr-C nanograins and carbon matrix interface. The nc-ZrC phase was also observed by transmission electron microscopy. The hardness of the coatings was approximately independent of Zr content. However, the Young modulus increased linearly. The residual stress of the coatings was strongly improved by the presence of nc-ZrC phase embedded in the a-C matrix. Finally, the incorporation of H into the matrix led to denser and harder films

Tratamento conservador do carcinoma do pênis - estudo retrospectivo de 10 anos

Conservative treatment of penile squamous cell carcinoma has been advocated as a method of choice for tumours at early stages. Thirty patients with a mean age of 63.2 years were treated with CO2 laser ablation, radical local excision with preputial flap, direct closure or healing by secondary intention, circumcision alone or associated with CO2 laser and topical imiquimod. Sixteen patients had local recurrence. Partial penectomy was necessary in 3 patients. Conservative treatments of penile squamous cell carcinoma in early stages (< T1a) do not seem to compromise the survival rate, so it may be advisable for this subset of patients

Transformations of Heun's equation and its integral relations

We find transformations of variables which preserve the form of the equation for the kernels of integral relations among solutions of the Heun equation. These transformations lead to new kernels for the Heun equation, given by single hypergeometric functions (Lambe-Ward-type kernels) and by products of two hypergeometric functions (Erd\'elyi-type). Such kernels, by a limiting process, also afford new kernels for the confluent Heun equation.Comment: This version was published in J. Phys. A: Math. Theor. 44 (2011) 07520

Optimizing Connectivity through Network Gradients for the Restricted Boltzmann Machine

Leveraging sparse networks to connect successive layers in deep neural networks has recently been shown to provide benefits to large scale state-of-the-art models. However, network connectivity also plays a significant role on the learning performance of shallow networks, such as the classic Restricted Boltzmann Machines (RBM). Efficiently finding sparse connectivity patterns that improve the learning performance of shallow networks is a fundamental problem. While recent principled approaches explicitly include network connections as model parameters that must be optimized, they often rely on explicit penalization or have network sparsity as a hyperparameter. This work presents a method to find optimal connectivity patterns for RBMs based on the idea of network gradients (NCG): computing the gradient of every possible connection, given a specific connection pattern, and using the gradient to drive a continuous connection strength parameter that in turn is used to determine the connection pattern. Thus, learning RBM parameters and learning network connections is truly jointly performed, albeit with different learning rates, and without changes to the objective function. The method is applied to the MNIST and other datasets showing that better RBM models are found for the benchmark tasks of sample generation and input classification. Results also show that NCG is robust to network initialization, both adding and removing network connections while learning

Revestimentos decorativos pelo efeito SPR obtido pela adição de Au a matrizes dieléctricas

A SPR (ressonância dos plasmões de superfície) originada pela introdução de nanopartículas metálicas em matrizes dieléctricas possui um elevado leque de aplicações, sendo alvo de uma actividade intensa de investigação. De modo a tirar partido da forte extinção da luz em certas gamas do visível que estes sistemas proporcionam, foi objectivo deste trabalho desenvolver revestimentos nanocompósitos com efeito SPR para aplicações decorativas. Para tal, recorreu-se à técnica de pulverização catódica reactiva para depositar os revestimentos nanocompósitos consistindo em nanopartículas de Au dispersas em matrizes de WO3 e Al2O3. Por outro lado, pela aplicação de tratamentos térmicos pós-deposição foi promovido o crescimento das nanopartículas de Au. A incorporação crescente de diferentes teores em Au na matriz permitiu a presença de nanopartículas com tamanhos maiores. Além disso, os tratamentos térmicos influenciaram com sucesso o crescimento das nanopartículas de Au na matriz, permitindo alterar a posição, forma e intensidade dos picos de SPR e, onsequentemente, a coloração obtida para as amostras. Contudo, também as propriedades estruturais e dieléctricas da matriz foram afectadas pela temperatura de recozimento, como por exemplo um aumento do índice de refracção que promoveu um deslocamento da posição dos picos de SPR para o “vermelho” (sistema W-O+Au). Nos resultados alcançados houve por isso um efeito combinado entre o crescimento das nanopartículas e a variação do índice de refracção da matriz. Através da variação de três parâmetros, matriz, composição química e temperatura de recozimento, foi possível depositar revestimentos nanocompósitos de WO3+Au e AlO+Au com diferentes cores pelo ajuste dos picos de SPR das nanopartículas de Au.The deposition of thin films consisting of metallic clusters embedded in dielectric matrixes can originate a strong SPR (Surface Plasmon Resonance) signal that has a wide range of applications, being the subject of an intense research nowadays. The main idea of this research work was to utilize the strong extinction of light that arises in these systems in certain zones of the visible spectrum for decorative coatings. Nanocomposite coatings consisting of Au clusters embedded in a WO3 or Al2O3 matrix were prepared by reactive sputtering with different Au contents. The higher the Au contents in the coatings the larger the nanoparticles were. By further annealing these samples at increasing temperatures, the Au segregation in the matrix was promoted. Both events permit to determine the SPR peak position along with its shape and intensity and, consequently, the optical properties of the coatings. Moreover, the thermal treatments also influenced the optical characteristics of the matrix, e.g. the refractive index was increased, leading to the redishing of the SPR position. Thus, the final results attained in the SPR peak shape, intensity and position for each case were mainly due to a combined effect between the Au cluster size and the refractive index of the oxide matrix. By varying the three major experimental parameters, the oxide matrix, the Au composition and the annealing temperature, it was possible to achieve nanocomposite coatings of WO3+Au and AlO+Au with different colours by tailoring the SPR peak shape and position.FCT - DECOMAT (PTDC/CTM/70037/2006), FEDER, através do programa COMPETE - Programa Operacional Factores de Competitividade

Spillover and diffraction sidelobe contamination in a double-shielded experiment for mapping Galactic synchrotron emission

We have analyzed observations from a radioastronomical experiment to survey the sky at decimetric wavelengths along with feed pattern measurements in order to account for the level of ground contamination entering the sidelobes. A major asset of the experiment is the use of a wire mesh fence around the rim-halo shielded antenna with the purpose of levelling out and reducing this source of stray radiation for zenith-centered 1-rpm circular scans. We investigate the shielding performance of the experiment by means of a geometric diffraction model in order to predict the level of the spillover and diffraction sidelobes in the direction of the ground. Using 408 MHz and 1465 MHz feed measurements, the model shows how a weakly-diffracting and unshielded antenna configuration becomes strongly-diffracting and double-shielded as far-field diffraction effects give way to near-field ones. Due to the asymmetric response of the feeds, the orientation of their radiation fields with respect to the secondary must be known a priori before comparing model predictions with observational data. By adjusting the attenuation coefficient of the wire mesh the model is able to reproduce the amount of differential ground pick-up observed during test measurements at 1465 MHz.Comment: 14 pages, 17 eps + 1 gif figures and 4 Tables. Accepted for publication in A&AS. Fig.7 available at full resolution from http://www.das.inpe.br/~tello/publications.ht