Emulating dynamic non-linear simulators using Gaussian processes

The dynamic emulation of non-linear deterministic computer codes where the output is a time series, possibly multivariate, is examined. Such computer models simulate the evolution of some real-world phenomenon over time, for example models of the climate or the functioning of the human brain. The models we are interested in are highly non-linear and exhibit tipping points, bifurcations and chaotic behaviour. However, each simulation run could be too time-consuming to perform analyses that require many runs, including quantifying the variation in model output with respect to changes in the inputs. Therefore, Gaussian process emulators are used to approximate the output of the code. To do this, the flow map of the system under study is emulated over a short time period. Then, it is used in an iterative way to predict the whole time series. A number of ways are proposed to take into account the uncertainty of inputs to the emulators, after fixed initial conditions, and the correlation between them through the time series. The methodology is illustrated with two examples: the highly non-linear dynamical systems described by the Lorenz and Van der Pol equations. In both cases, the predictive performance is relatively high and the measure of uncertainty provided by the method reflects the extent of predictability in each system

A Matlab Code for Univariate Time Series Forecasting

This M-File forecasts univariate time series such as stock prices with a feedforward neural networks. It finds best (minimume RMSE) network automatically and uses early stopping method for solving overfitting problem.Neural Networks, Time Series, Early Stopping, Forecasting

Homogenization of diffuse delamination in composite laminates

Diffuse delamination induced by transverse cracking is usually the secondary damage mode when a composite laminate experiences tensile loading. The fist damage mechanism in such a laminate is transverse cracking which has been widely investigated with both analytical methods and " mechanism-based" constitutive laws. Delamination induced by matrix cracking is already studied extensively by analytical approaches, however, a proper homogenization way has not been proposed yet. In this paper, a modification to an available cohesive constitutive law is proposed which is capable of considering the effect of diffuse delamination without the necessity of consideration of an actual discontinuity between the layers. The proposed constitutive law is then compared against its equivalent models containing interlaminar discontinuity and it is shown that the obtained results from both models are in good. Then the proposed modification is used in Double Cantilever Beam (DCB) specimen and the obtained results are found coincident with the equivalent model with diffuse discontinuities at the interface. Finally, a damaged cross-ply laminate is modeled under the boundary conditions of tensile loading and also 3-point bending with and without the proposed cohesive modification. In tensile loading, the results of both cases are similar; however, it is shown that in bending, the unmodified cohesive law predicts the lateral stiffness larger than the proposed modification. The lateral stiffness of the equivalent model with discontinuities as crack indicates that the proposed modification is able to properly consider the lateral stiffness decrease

Phase behaviour modelling of systems containing gas hydrates and asphaltenes

Abstract currently unavailable please refer to PD

UTJECAJ RAZLIČITIH DOZA SINTETIČKOG HORMONA LHRH-A2, NA RAZINE SPOLNIH HORMONA U SERUMU, POSTOTAK USPJEŠNOSTI OVULACIJE I STOPE VALJENJA JAJA PERZIJSKE JESETRE, Acipenser persicus

Acipenser persicus is one of the economically valuable fishes in the Caspian Sea. Due to the economical and cultural importance of sturgeons in the world, understanding of sturgeon reproduction is necessary for successful management of their populations in aquaculture and nature. To improve the culture methods and to facilitate captive breeding programs to support restocking, it is necessary to understand the changes in steroid hormones during artificial reproduction. The administration of sturgeon luteinizing hormone - releasing hormone analogue (LHRH-A2) induces changes in serum sex steroid levels. To study the effects of different doses of LHRH-A2 hormone on induction of final maturation and ovulation of Persian sturgeon, 18 maturating females and 18 maturating males were used. All brooders were injected with LHRH-A2 in dosages of 4, 6 and 8 μg kg-1. In this study, LHRH-A2 successfully induced final maturation and ovulation in females, and the highest percentage of ovulated females was observed in the groups treated with dose of 4 μg kg-1 LHRH-A2. There were significant differences in serum cortisol (C), testosterone (T) and Gonado-tropin hormone (GTHII) concentrations at tested dosages. In hormonal treatment groups, the highest hatching rate was observed in the groups receiving 4 μg kg-1 LHRH-A2. Finally, the LHRH-A2 in dose of 4 μg kg-1 is effective in stimulating oocyte maturation and ovulation in Persian sturgeon.Acipenser persicus (Acipenseridae) jedna je od ekonomski važnijih vrsta riba u Kaspijskom moru. Poznavanje reproduktivnih karakteristika jesetre je važno zbog uspješnog upravljanja njihovim populacijama u akvakulturi te njihove ekonomske i kulturne važnosti u svijetu. Razumijevanje razina steroidnih hormona i njihovih promjena u serumu tijekom umjetne oplodnje pomaže poboljšanju kvalitete nasadnih metoda te olakšava izvedbu programa razmnožavanja u zatočeništvu u svrhu potpore poribljavanja. Primjenom sintetičkog luteinizirajućeg hormona jesetre - oslobađajućeg analognog hormona (LHRH-A2) - induciraju se promjene u razinama spolnih steroida u serumu. Za proučavanje učinka različitih doza hormona LHRH-A2 na izazivanje konačnog sazrijevanja i ovulacije Perzijske jesetre, korišteno je 18 odraslih ženki i 18 odraslih mužjaka. Sve muške i ženske spolno zrele jedinke su inducirane s LHRH-A2 u dozama od 4, 6 i 8 μg kg-1. U ovoj studiji primjenom LHRH-A2 uspješno je inducirano sazrijevanje gonada i ovulacije u ženki, dok je najveći postotak ovuliranih ženki uočen u skupini tretiranoj dozom od 4 μg kg-1 LHRH-A2. Postoje značajne razlike u koncentracijama kortizola (C), testosterona (T) i gonadotropina (GTHII) u serumu ispitivanih doza hormona. Najveći postotak valjenja uočen je u skupinama riba koje su primale 4 μg kg-1 LHRHA 2. U dozi od 4 μg kg-1, LHRH-A2 je učinkovit pri poticanju sazrijevanja oocita te ovulacije Perzijske jesetre

An Accurate Scheme for Distance Measurement using an Ordinary Webcam

Nowadays, image processing has become one of the widely used computer aided science. Two major branches of this scientific field are image enhancement and machine vision. Machine vision has many applications and demands in robotic and defense industries. Detecting distance of objects is one of the extensive research in the defense industry and robotic industries that a lot of annual projects have been involved in this issue both inside and outside the country. So, in this paper, an accurate algorithm is presented for measuring the distance of the objects from a camera. In this method, a laser transmitter is used alongside a regular webcam. The laser light is transmitted to the desired object and then the distance of the object is calculated using image processing methods and mathematical and geometric relations. The performance of the proposed algorithm was evaluated using MATLAB software. The accuracy rate of distance detection is up to 99.62%. The results also has shown that the presented algorithms make the obstacle distance measurement more reliable. Finally, the performance of the proposed algorithm was compared with other methods from different literatures

Ductile failure prediction of U-notched bainitic functionally graded steel specimens using the equivalent material concept combined with the averaged strain energy density criterion

The final publication is available at Springer via http://dx.doi.org/10.1134/S102995991903010XIn this paper, the ductile fracture of bainitic functionally graded steel has been studied. Fracture tests was performed on U-notched specimens made of bainitic functionally graded steel under mode I. The averaged strain energy density criterion combined with equivalent material concept was employed to predict the ductile fracture of bainitic functionally graded steel. For this purpose, first, based on equivalent material concept, the mechanical properties of virtual brittle functionally graded steel were obtained. Then the averaged value of strain energy density over a well-defined control volume was calculated by finite element analysis for U-notched virtual brittle functionally graded steel. After that, the fracture loads was obtained based on the averaged strain energy density criterion. The agreement between experimental fracture loads and theoretical predictions was good.Peer ReviewedPostprint (author's final draft

Improved Denoising Method for Ultrasonic Echo with Mother Wavelet Optimization and Best-Basis Selection

Weak features of ultrasonicnondestructive test signals are usually immersed in noisy signals. So, in this paper, we proposed an improved scheme for noise reduction and feature extraction based on discrete wavelet transform. The basis of the mother wavelet was selected to be matched to a given signal. Three different constraints were presented to minimize the error between the denoised and the given signal. It should be mentioned that such an optimum wavelet can represent the signal more compactly with a few large coefficients which can be considered as the signal features. Standard signals and simulated ultrasonic echo were used to evaluate the performance of the presented algorithms. Signal to error ratio was used to compare the designed wavelet performance with that of standard wavelets. Simulation results revealed that the proposed method outperformed the other presented methods and even standard wavelets. The results also has shown that the signal-based noise reduction algorithms make the feature extraction more reliable. Finally, the performance of the proposed algorithm was compared with other methods from different literatures