Robust adaptive observer design for uncertain systems with bounded disturbances.

This paper presents a robust adaptive observer design methodology for a class of uncertain nonlinear systems in the presence of time-varying unknown parameters with absolutely integrable derivatives, and nonvanishing disturbances. Using the universal approximation property of radial basis function (RBF) neural networks and the adaptive bounding technique, the developed observer achieves asymptotic convergence of state estimation error to zero, while ensuring boundedness of parameter errors. A comparative simulation study is presented by the end.     

Applied theories of thermoelasticity of micropolar thin beams

In the present article, a system of rather general hypotheses is developed, on the basis of which with the account of transverse shears the applied theories of thermoelasticity of bending of micropolar thin beams are introduced: (a) With free fields of displacements and rotations; (b) with constrained rotation; (c) the reduced model. On the basis of the constructed models, specific problems of thermoelastic bending of micropolar beams are studied. Numerical analysis of the studied problems states the effectiveness of the micropolar material from the point of view of the beam rigidity compared with that of the classical case.     

Hydrocarbon potentiality and thermal maturity of the Cretaceous rocks in Al Baraka oil field,KomOmbo basin,south Egypt

This paper aims to evaluate the hydrocarbon potentiality and thermal maturity of the Cretaceous source rocks in Al Baraka oil field in KomOmbo basin, south Egypt. To achieve this aim, geochemical analyses (TOC), Rock eval pyrolysis and vitrinite reflectance measurements (R0) were carried out on the studied rocks. The analytical results of the samples that were collected from five exploratory oil wells revealed that almost Lower Cretaceous formations (Sabaya, Abu Ballas, Six Hills and KomOmbo C, B, A) and Upper Cretaceous formations (Dakhla, Duwi, Quseir, Taref and Maghrabi) are ranged from fair to excellent source rocks for hydrocarbon generation. Oil and gas are mainly the future products of the thermally transformed organic matters within almost samples of the Cretaceous formations, where the Lower and Upper Cretaceous formations contain mixed type II/III and III kerogen besides type II kerogen in KomOmbo (B) and Dakhla formations. The thermal maturity parameters clarified that the Lower Cretaceous formations are belonged to marginally mature (in Sabaya and Abu Ballas formations), whereas the rocks of KomOmbo (B) Formation are mature source rocks and fall in the stage of oil generation and reach to the late stage of oil generation (R0?=?1.25). On the contrary the Upper Cretaceous formations are ranged from immature to marginally mature source rocks and reach only the early stage of oil generation in Maghrabi Formation. This study indicated that there is still a good chance to find oil generated from the Dakhla, Duwi, Maghrabi, Sabaya and Abu Ballas formations if buried in greater depths as well as, KomOmbo B and A intervals which are source rock potentials.     

Constant switching frequency-based delta-sigma modulation of single-phase AC–AC zeta converter

Direct pulse width modulated (PWM) AC–AC converters, derived from their DC–DC counterparts, serve as promising media for AC–AC power conversion because they offer benefits, such as single-stage power conversion, absence of bulky DC links, and small footprint. In this study, a single-phase ( $1-\varphi$) AC–AC zeta converter was analyzed under buck, boost, and buck-boost operations. Delta-sigma modulation (DSM) technique, known for its simple logic implementation, excellent reference-tracking property, robust control, and fast transient response, was employed for the load voltage control of a $1-\varphi$ AC–AC zeta converter. However, the conventional DSM technique relies on a fixed hysteresis band (FHB) for restricting the integrated (sigma) error (delta) between the reference and estimated control voltages within a narrow band, which causes the converter to operate at a variable switching frequency (VSF). Although VSF enhances the converter performance with low total harmonic distortion (THD) and high degree of flexibility over waveform quality, it poses serious implications such as higher switching losses, putting more strain on thermal management of switches. This paper presents a constant switching frequency-based DSM technique based on an adaptive hysteresis band (AHB) for a $1-\varphi$ AC–AC zeta converter. The converter is controlled using FHB-DSM and AHB-DSM techniques, and a comparison is drawn between the two in terms of various performance indices. In this comparison, FHB-DSM serves as a benchmark and an optimum switching frequency based on AHB-DSM technique is determined, which exhibits low switching losses while maintaining the same THD limits, dynamic response, and waveform quality as that of FHB-DSM technique. The proposed strategy was validated by simulation studies in MATLAB/SIMULINK software. Furthermore, a real-time simulator, OPAL-RT (OP4510), was used to validate the study with real-time implementation.