Numerical experiments with two-dimensional elastic-viscoplastic bars

Numerical solutions of two-dimensional elastic-viscoplastic wave propagation in bars of various shapes are discussed. Hondo code with the addition of a new sub-program for Bodner-Partom's constitutive equation is used for the analysis. For a two-dimensional elastic bar and a one-dimensional elastic/linear-hardening plastic bar, Hondo numerical results agree well with available analytical or numerical solutions. For elastic-viscoplastic bar, numerical solutions show some interesting features of the dynamic responses. The responses for Bodner-Partom constitutive equation were found to lie between the results for elastic-plastic and purely elastic constitutive relation. The precursor wave always propagates at the speed of elastic wave. For a bar with both discontinuities of cross-section and material properties, the computation showed the disappearance of stress localization, which usually exists for single-material bar with a geometric discontinuity.     

A new technique for numerical simulation of dendritic solidification using a meshfree interface finite element method

A new technique for sharp‐interface modeling of dendritic solidification is proposed using a meshfree interface finite element method such that the liquid–solid interface is represented implicitly and allowed to arbitrarily intersect the finite elements. At the interface‐embedded elements, meshfree interface points without connectivity are imposed directly at the zero level set while meshfree interpolants are constructed using radial basis functions. This ensures both the partition of unity and the Kronecker delta properties are satisfied allowing for precise and easy imposition of Dirichlet boundary conditions at the interface. The constructed meshfree interpolants are also used for solving a variational level set equation based on the Ginzburg–Landau energy functional minimization such that reinitialization is completely eliminated and fast marching algorithms for interfacial velocity extension are not necessary resulting in an efficient algorithm with excellent volume conservation. The meshfree interface finite element method is used for modeling dendritic solidification in a pure melt where it is found suitable in handling the complex interfacial dynamics often encountered in dendritic growth. Mathematical formulation and implementation followed by numerical results and analysis will be presented and discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

Characterizing game dynamics in two-player strategy games using network motifs.

Many complex systems, whether biological, sociological, or physical ones, can be represented using networks. In these networks, a node represents an entity, and an arc represents a relationship/constraint between two entities. In discrete dynamics, one can construct a series of networks with each network representing a time snapshot of interaction among the different components in the system. Understanding these networks is a key to understand the dynamics of real and artificial systems. Network motifs are small graphs-usually three to four nodes-representing local structures. They have been widely used in studying complex systems and in characterizing features on the system level by analyzing locally how the substructures are formed. Frequencies of different network motifs have been shown in the literature to vary from one network to another, and conclusions hypothesized that these variations are due to the evolution/dynamics of the system. In this paper, we show for the first time that in strategy games, each game (i.e., type of dynamism) has its own signature of motifs and that this signature is maintained during the evolution of the game. We reveal that deterministic strategy games have unique footprints (motifs' count) that can be used to recognize and classify the game's type and that these footprints are consistent along the evolutionary path of the game. The findings of this paper have significance for a wide range of fields in cybernetics.     

Effect of steam treatment on the activities of Pt/NH4-MOR catalysts for n-pentane hydroisomerization and hydrocracking

The rationale of this work is to study the effect of using Pt containing catalysts supported on NH₄-MOR zeolite, before or after steaming, to show how steam treatments affect the activities of catalysts used primarily for the hydroconversion of light naphtha to improve its octane rating. Hence, the reactions of the hydroisomerization and hydrocracking of n-pentane, were investigated at temperatures between 250 and 500 °C in a pulsed microcatalytic reactor using catalysts containing 0.25, 0.35 and 0.60 wt.% Pt supported on NH₄-MOR. The effect of steaming on the dispersion of Pt, acid sites strength distribution, intraparticle diffusion resistance and the catalytic activities were investigated. Steaming was found to enhance catalytic activity deterioration. This effect was significantly increased with increasing Pt content in the catalysts. The calculated activation energy and entropy values using the current catalysts were correlated with the activity levels for hydroisomerization and hydrocracking of n-pentane.     

Effect of Hydrogen Charging on the Tensile and Constant Load Properties of an Austenitic Stainless Steel Weldment

The effect of cathodic hydrogen charging on the tensile and constant load properties was determined for an austenitic stainless steel weldment comprising a 304L steel in the solution treated condition as a base metal and a 308L filler steel as a weld metal. Part of the 304L solution treatedsteel was separately given additional sensitization treatment to simulate the microstructure that would develop in the heat affected zone. Tests were performed at room temperature on notched round bar specimens. Hydrogen charging resulted in a pronounced embrittlement of the tested     

Optic disc detection from normalized digital fundus images by means of a vessels' direction matched filter

Optic disc (OD) detection is a main step while developing automated screening systems for diabetic retinopathy. We present in this paper a method to automatically detect the position of the OD in digital retinal fundus images. The method starts by normalizing luminosity and contrast through out the image using illumination equalization and adaptive histogram equalization methods respectively. The OD detection algorithm is based on matching the expected directional pattern of the retinal blood vessels. Hence, a simple matched filter is proposed to roughly match the direction of the vessels at the OD vicinity. The retinal vessels are segmented using a simple and standard 2-D Gaussian matched filter. Consequently, a vessels direction map of the segmented retinal vessels is obtained using the same segmentation algorithm. The segmented vessels are then thinned, and filtered using local intensity, to represent finally the OD-center candidates. The difference between the proposed matched filter resized into four different sizes, and the vessels' directions at the surrounding area of each of the OD-center candidates is measured. The minimum difference provides an estimate of the OD-center coordinates. The proposed method was evaluated using a subset of the STARE project's dataset, containing 81 fundus images of both normal and diseased retinas, and initially used by literature OD detection methods. The OD-center was detected correctly in 80 out of the 81 images (98.77%). In addition, the OD-center was detected correctly in all of the 40 images (100%) using the publicly available DRIVE dataset.     

The electrochemical behavior of Sn–Ag binary alloys in sulfate solutions

The corrosion and passivation behavior of four binary xSn–Ag (x = 26, 50, 70, and 96.5 wt%) alloys and their pure metal components was investigated in sodium sulfate solutions using electrochemical techniques. The influence of two different electrolytic parameters, namely, concentration (0.01–1.0 M ) and pH (3.0–11.0) were studied while the specimens were potentiodynamically polarized between ?1000 and 500 mV versus saturated calomel electrode (SCE). The results showed that the corrosion current density (i_corr) increases with increasing either the tin content in the alloy or the ions concentration in the electrolyte. Increasing the pH value of a constant composition sulfate solution was found to improve the corrosion resistance of the tin‐richer alloys (x = 50–96.5 wt%), and decreases a little the stability of the silver‐rich one (74 wt% Ag). Impedance measurements at the free corrosion potential (E_corr) give good support for these results, where a small addition of tin to silver up to the intermetallic ratio (x = 26 wt%) gives an alloy with better corrosion resistance to the aggressive sulfate medium. In terms of the tin ratio, the order of surface film stability on the tested samples, generally follows the ranking: 26 > 96.5 > 50 > Ag > 70 > Sn. The good corrosion resistance of the tin‐rich alloy (x = 96.5 wt%), surpassing those for the pure constituents tin and silver can be attributed to the homogenous phase structure of this eutectic mixture.     

Effect of strain rate and temperature on the tensile properties of MANET II steel

MANET II, a modified 12% Cr steel with the German designation DIN 1.4914, is a candidate structural material for the first wall and blanket in fusion reactors. In the present study, the tensile properties of this steel were investigated in the temperature range of 25 to 350 °C at strain rates of 5 x 10^-5 ,1.2 x 10^-4, and 1.2 x 10^-3s-1, Both microstructure and fracture surfaces were examined using optical and scanning electron microscopic (SEM) techniques. The results showed that the steel suffers dynamic strain aging, although no serrated flow was observed. Yield strength, ultimate strength, and elongation showed negative strain rate sensitivity. Dynamic strain aging also affected the strain hardening rate. Results are discussed with regard to the chemical composition and fracture surface morphology.     

Characteristics and effect of thermal treatment on surface texture of ultrafine zirconia powders

Yttria-stabilized zirconia ultrafine powders were prepared by the hydrolysis of their hydroxide at 200° C. The powders obtained were investigated for their crystal structure and degree of fineness. The surface characteristics of the prepared powders were determined by nitrogen gas adsorption. The effect of calcination conditions on the powder characteristics were thoroughly investigated and the results discussed in relation to their surface textures and degree of crystallinity.     

Efficient Data Compression of ECG Signal Based on Modified Discrete Cosine Transform

This paper introduced an efficient compression technique that uses the compressive sensing (CS) method to obtain and recover sparse electrocardiography (ECG) signals. The recovery of the signal can be achieved by using sampling rates lower than the Nyquist frequency. A novel analysis was proposed in this paper. To apply CS on ECG signal, the first step is to generate a sparse signal, which can be obtained using Modified Discrete Cosine Transform (MDCT) on the given ECG signal. This transformation is a promising key for other transformations used in this search domain and can be considered as the main contribution of this paper. A small number of wavelet components can describe the ECG signal as related work to obtain a sparse ECG signal. A sensing technique for ECG signal compression, which is a novel area of research, is proposed. ECG signals are introduced randomly between any successive beats of the heart. MIT-BIH database can be represented as the experimental database in this domain of research. The MIT-BIH database consists of various ECG signals involving a patient and standard ECG signals. MATLAB can be considered as the simulation tool used in this work. The proposed method's uniqueness was inspired by the compression ratio (CR) and achieved by MDCT. The performance measurement of the recovered signal was done by calculating the percentage root mean difference (PRD), mean square error (MSE), and peak signal to noise ratio (PSNR) besides the calculation of CR. Finally, the simulation results indicated that this work is one of the most important works in ECG signal compression.