Sensitivity analysis of the GTN damage parameters at different temperature for dynamic fracture propagation in X70 pipeline steel using neural network

In this paper, the initial and maximum load was studied using the Finite Element Modeling (FEM) analysis during impact testing (CVN) of pipeline X70 steel. The Gurson-Tvergaard-Needleman (GTN) constitutive model has been used to simulate the growth of voids during deformation of pipeline steel at different temperatures. FEM simulations results used to study the sensitivity of the initial and maximum load with GTN parameters values proposed and the variation of temperatures. Finally, the applied artificial neural network (ANN) is used to predict the initial and maximum load for a given set of damage parameters X70 steel at different temperatures, based on the results obtained, the neural network is able to provide a satisfactory approximation of the load initiation and load maximum in impact testing of X70 Steel.

Sources of Harmonic Force and Speed in Mechatronic Automatic Systems

To study resonance and near-resonance phenomena, a symbolic (complex) method was used, which makes it possible to significantly increase productivity, simplify and formalize mathematical transformations. Parallel and sequential connections of elements of a mechanical system with a source of harmonic force or a source of harmonic speed as a source of external mechanical harmonic action are considered. The analytical descriptions of resonance in theoretical mechanics courses correspond to parallel connection. There are devices, in a satisfactory approximation, capable of performing the functions of sources of force and sources of speed. The source of harmonic speed can be a crank-yoke drive and a flywheel with a large moment of inertia. The source of the harmonic force can be the rod of the pneumatic cylinder, the cavity of which communicates with the cavity of another pneumatic cylinder, the diameter of which is immeasurably higher than that of the first, and the piston performs harmonic oscillations. The mechanical harmonic influences described in the courses of theoretical mechanics correspond to the source of the force. Four modes are described — resonances and antiresonances of forces and velocities. The use of the symbolic (complex) method has significantly simplified the study of resonance and near-resonance phenomena, in particular, it has made it possible to deeply unify and formalize the consideration of various mechanical systems. The cumbersome and time-consuming operations associated with the preparation and solution of differential equations have been replaced by simple algebraic transformations. Resonance and antiresonance of forces, resonance and antiresonance of velocities are determined.

Approximation of the Separation Boundary in the Water-Hydrotrope-Oil Ternary Systems

In this work, we studied the ternary systems water – 2-butoxyethanol – toluene, water – methanol – chloroform and water – methanol – dichloromethane. The separation boundary was experimentally located and approximated by various functions. The main reasons are revealed that prevent a satisfactory approximation of the separation boundaries by empirical functions with a small number of optimized parameters. It is found that the approximation of the separation boundaries in ternary systems can be carried out by polynomial and piecewise smooth functions with an error comparable to the uncertainty of the measurement.

Neural-Network-Based Curve Fitting Using Totally Positive Rational Bases

This paper proposes a method for learning the process of curve fitting through a general class of totally positive rational bases. The approximation is achieved by finding suitable weights and control points to fit the given set of data points using a neural network and a training algorithm, called AdaMax algorithm, which is a first-order gradient-based stochastic optimization. The neural network presented in this paper is novel and based on a recent generalization of rational curves which inherit geometric properties and algorithms of the traditional rational Bézier curves. The neural network has been applied to different kinds of datasets and it has been compared with the traditional least-squares method to test its performance. The obtained results show that our method can generate a satisfactory approximation.

Thermodynamic properties of 2H-MoSe2 from first principles quasi-harmonic approximation

In this paper, we report the results of first-principles calculation of 2H-MoSe2 thermodynamic properties within the quasi-harmonic approximation. The focus of the article is on the temperature dependencies of the heat capacity up to 1000 ℃ and values of enthalpy of formation, enthalpy, and entropy at 298,15 K, and their comparative analysis with the existing experimental data. The results show good general agreement with the published experimental data sets allowing to use them as arbitration of existing discrepancies. Increasing deviations of the heat capacity above the room temperature suggest that factors not included in the quasi-harmonic approximation, such as vibrational anharmonicity, may have a significant influence on the thermodynamics of 2H-MoSe2 in this temperature region. Considering the inconclusive high-temperature data from the experiment, the present results may be recommended as a satisfactory approximation until the appearance of more reliable experimental data or calculation results, taking into account more finite-temperature effects.

The effect of yeast extract addition on bread quality parameters

The effects of yeast extract addition, with varied quantities of salt and sugar, on the chemical and mineral composition, colour and sensory properties of spelt bread, in order to obtain new products were investigated. The addition of 5 % yeast extract positively influenced the mineral characteristics and increased protein content by 30.77 %. As a salt substitution, addition of yeast extract improved appearance without deteriorating texture descriptors and breadcrumb quality, while the taste became more complex, but without increasing salty taste. Addition of sugar in samples with yeast extract, improved most sensory characteristics. The developed mathematical models of bread with yeast extract quality parameters were statistically significant, indicating the satisfactory approximation of the bread quality parameters within the varied formula. Bread samples with addition of 5 % yeast extract, 1.5 % of salt and 0 % sugar were determined as the best from the aspect of overall quality. A new product was obtained with good total quality, higher level of nutritional value and reduced salt content.

Hydrodynamics of micro-swimmers in films

One of the principal mechanisms by which surfaces and interfaces affect microbial life is by perturbing the hydrodynamic flows generated by swimming. By summing a recursive series of image systems, we derive a numerically tractable approximation to the three-dimensional flow fields of a stokeslet (point force) within a viscous film between a parallel no-slip surface and a no-shear interface and, from this Green’s function, we compute the flows produced by a force- and torque-free micro-swimmer. We also extend the exact solution of Liron & Mochon (J. Engng Maths, vol. 10 (4), 1976, pp. 287–303) to the film geometry, which demonstrates that the image series gives a satisfactory approximation to the swimmer flow fields if the film is sufficiently thick compared to the swimmer size, and we derive the swimmer flows in the thin-film limit. Concentrating on the thick-film case, we find that the dipole moment induces a bias towards swimmer accumulation at the no-slip wall rather than the water–air interface, but that higher-order multipole moments can oppose this. Based on the analytic predictions, we propose an experimental method to find the multipole coefficient that induces circular swimming trajectories, allowing one to analytically determine the swimmer’s three-dimensional position under a microscope.

Research on Nonlinear Modeling Method of Support Vector Machine with Wavelet Derivation Kernel Function

The model capability of Support Vector Machine (SVM) relies on the selection of kernel function. To obtain a better application modeling of SVM, the wavelet kernel function that satisfies Merce condition is introduced to use the kernel function of SVM, achieving a good effect. In the paper, on the basis of wavelet kernel function, a wavelet derivation kernel function is proposed in the application of SVM for higher accuracy. An actual example on nonlinear function approximation shows that SVM regression model has a satisfactory approximation effect, and also support an effective nonlinear modeling method.

Identification of Multimodel LPV Models with Asymmetric Gaussian Weighting Function

This paper is concerned with the identification of linear parameter varying (LPV) systems by utilizing a multimodel structure. To improve the approximation capability of the LPV model, asymmetric Gaussian weighting functions are introduced and compared with commonly used symmetric Gaussian functions. By this mean, locations of operating points can be selected freely. It has been demonstrated through simulations with a high purity distillation column that the identified models provide more satisfactory approximation. Moreover, an experiment is performed on real HVAC (heating, ventilation, and air-conditioning) to further validate the effectiveness of the proposed approach.

FORECASTING BANK STOCK MARKET PRICES WITH A HYBRID METHOD: THE CASE OF ALPHA BANK / VERTYBINIŲ POPIERIŲ KAINŲ PROGNOZAVIMAS HIBRIDINIU METODU: ALPHA BANK PAVYZDYS

The present study aims at constructing Confidence Intervals (C.I) for the predicted values of a Time Series with the application of a Hybrid method. The presented methodology is complicated and thus is completed in different stages. Initially the Artificial Neural Networks (ANNs) is applied on the raw time series in order to estimate C.I of the forecasts. Then, the Bootstrap method is employed on the residuals generated by the preceded process. On the upper and lower limit of the estimated C.I., two new ANNs are employed in order to make point estimations (of the upper and lower limits) using of Object Oriented Programming. For the empirical analysis daily observations of the closing prices of Alpha Bank stocks have been used. The sample period is extended from 28/01/2004 until 30/11/2005. The nonstationarity of the time series employed in our study is not a forbidding condition for the estimation of the confidence intervals, in our case, since the level of bootstrap still provides a satisfactory approximation for the roots arbitrarily close to unity (Berkowitz, Kilian 1996). The accuracy of the forecasts was surveyed with the use of different criteria and the results were satisfactory.