Modeling guided wave propagation with application to the long-range defect detection in railroad tracks

The aim of this work is to demonstrate the use of a commercial finite element package, ABAQUS EXPLICIT, to model ultrasonic guided waves in structural components. The particular application of interest is modeling the interaction of a broadband vertical bending mode with transverse-type defects in railroad tracks. This topic is part of a broader project on high-speed defect detection in rails by long-range ultrasonic inspections. Reflection coefficient spectra in the 20–45 kHz range are obtained for four different sizes and three different orientations of transverse head flaws. A preliminary study of Lamb waves in a free plate helps drawing modeling guidelines for the rail.     

Modeling and robust discrete LQ repetitive control of electrically driven robots

Discrete linear quadratic control has been efciently applied to linear systems as an optimal control.However,a robotic system is highly nonlinear,heavily coupled and uncertain.To overcome the problem,the robotic system can be modeled as a linear discrete-time time-varying system in performing repetitive tasks.This modeling motivates us to develop an optimal repetitive control.The contribution of this paper is twofold.For the frst time,it presents discrete linear quadratic repetitive control for electrically driven robots using the mentioned model.The proposed control approach is based on the voltage control strategy.Second,uncertainty is efectively compensated by employing a robust time-delay controller.The uncertainty can include parametric uncertainty,unmodeled dynamics and external disturbances.To highlight its ability in overcoming the uncertainty,the dynamic equation of an articulated robot is introduced and used for the simulation,modeling and control purposes.Stability analysis verifes the proposed control approach and simulation results show its efectiveness.     

Studying the electronic and phononic structure of penta-graphane

In this paper, we theoretically consider a two dimensional nanomaterial which is a form of hydrogenated penta-graphene; we call it penta-graphane. This structure is obtained by adding hydrogen atoms to the sp² bonded carbon atoms of penta-graphene. We investigate the thermodynamic and mechanical stability of penta-graphane. We also study the electronic and phononic structure of penta-graphane. Firstly, we use density functional theory with the revised Perdew–Burke–Ernzerhof approximation to compute the band structure. Then one–shot GW (G₀W₀) approach for estimating accurate band gap is applied. The indirect band gap of penta-graphane is 5.78 eV, which is close to the band gap of diamond. Therefore, this new structure is a good electrical insulator. We also investigate the structural stability of penta-graphane by computing the phonon structure. Finally, we calculate its specific heat capacity from the phonon density of states. Penta-graphane has a high specific heat capacity, and can potentially be used for storing and transferring energy.     

Experimental investigation and numerical modelling of the fire performance for epoxy resin carbon fibre composites of variable thicknesses

This paper applies a unique integrated approach to determine the flammability properties of a composite material (epoxy with carbon fibre) and compares its fire behaviour at two different thicknesses (2.1 and 4.2 mm) by performing small scale (thermo‐gravimetric analysis (TGA)/Fourier transform infrared radiation) and meso‐scale tests (cone calorimeter). For small‐scale tests, experiments were conducted in nitrogen using TGA coupled to gas analysis by Fourier transform infrared radiation. These results allow the determination of thermal stability, main degradation temperature and main gaseous emissions released during the thermal degradation. For meso‐scale tests, experiments were carried out using a cone calorimeter with sample dimensions of 100 × 100 mm at five heat fluxes (30, 40, 50, 60 and 70 kW/m²). The results show that the ignition time increases with an increase in the thickness of the material. Relative hazard classification of the fire performance of the current composites has also been compared with other materials using parameters obtained elsewhere. In addition, the effective ignition, thermal and pyrolysis properties obtained from the ignition and mass loss rate experiments for the 4.2‐mm thick samples were used in a numerical model for pyrolysis to predict well ignition times, back‐surface temperatures and mass pyrolysis rates for all heat fluxes as well as for the 2.1‐mm thick samples. Note that the ignition temperature obtained in the cone agrees with the main degradation temperature in the TGA. The flammability properties deduced here can be used to predict the heat release rate for real fire situations using CFD modelling. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of fuel type on structural and physicochemical properties of solution combustion synthesized CoCr2O4 ceramic pigment nanoparticles

Due to importance and wide applications, CoCr₂O₄ ceramic pigment nanoparticles were synthesized via low-temperature solution combustion route by different fuels including ethylenediamine/oxalic acid, ethylenediamine/citric acid, oxalic acid/citric acid and ethylenediamine/oxalic acid/citric acid. Physicochemical properties of the synthesized samples were determined by different techniques such as fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDX) and color/optical properties were evaluated based on CIELAB system by spectrophotometer. Moreover, thermodynamic considerations of combustion reactions for CoCr₂O₄ nanopigments formation in terms of calculated adiabatic flame temperature and enthalpy of combustion reaction were studied. The Comparison of results and data showed that cobalt chromite pigment nanoparticles synthesized by using ethylenediamine/citric acid and ethylenediamine/oxalic acid/citric acid fuels exhibited higher purity, smaller crystallite size and lower degree agglomeration.     

In Vitro Angiogenic Behavior of HUVECs on Biomimetic SF/SA Composite Scaffolds

The 60Fc and 70Fc SF/SA blend scaffolds were prepared to mimic the functions of the native ECM for skin regeneration.Human Umbilical Vein Endothelial Cells (HUVECs) were used to examine the cell cytotoxicity,adhesion,growth factors secretion and the gene expression of associated angiogenic factors.Cell proliferation,adhesion and live-dead analyses showed that HUVECs could better attach,grow,and proliferate on the 70Fc scaffolds compared with 60Fc scaffolds and unmodified controls.Furthermore,the 70Fc scaffolds showed higher levels of specific angiogenic proteins and genes expression as well.This study suggests that the involvement of higher composition of SF (about 70%) than that of SA on the blended scaffolds could be advantageous as it is more suitable to promote angiogenesis,which is potential for vascularization during skin repair.     

An uncertainty compensator for robust control of wheeled mobile robots

This paper proposes an uncertainty compensator to design a novel robust control for mobile robots with dynamic and kinematic uncertainties. A novel gradient-based adaptive fuzzy estimator is developed to compensate uncertainties with minimum required feedback signals. As a novelty, the proposed approach uses the tracking error and its first time derivative to form the estimation error of uncertainty, and guarantees that both the estimation error and tracking error converge asymmetrically to ignorable value. Advantages of the proposed robust control are simplicity in design, robustness against uncertainties, guaranteed stability, and good control performance. The control approach is verified by stability analysis. Simulation results and experimental results illustrate the effectiveness of the proposed control. Experimental evaluation of the proposed controller is expressed for two different low-cost nonholonomic wheeled mobile robots. The proposed control design is compared with an adaptive control approach to confirm the superiority of the proposed approach in terms of precision, simplicity of design, and computations.     

Task-space control of robots using an adaptive Taylor series uncertainty estimator

An uncertainty estimation and compensation can improve the performance of control systems due to structured and unstructured uncertainty. This paper presents a robust task-space control approach using an adaptive Taylor series uncertainty estimator for electrically driven robot manipulators. It is worth noting that not only the lumped uncertainty is estimated and employed in the indirect form of robust controller, but also the upper bound of approximation error is estimated to form a robustifying term and the asymptotic convergence of tracking error and its time derivative are proven based on stability analysis. Finally, the effectiveness of the proposed controller is shown through simulation and comparison with two valuable control schemes applied on the Selective Compliance Assembly Robot Arm (SCARA) robot manipulator.     

Rule-based data mining for yield improvement in semiconductor manufacturing

We describe an automated system for improving yield, power consumption and speed characteristics in the manufacture of semiconductors. Data are continually collected in the form of a history of tool usage, electrical and other real-valued measurements—a dimension of tens of thousands of features. Unique to this approach is the inference of patterns in the form of binary regression rules that demonstrate a significantly higher or lower performance value for tools relative to the overall mean for that manufacturing step. Results are filtered by knowledge-based constraints, increasing the likelihood that empirically validated rules will prove interesting and worth further investigation. This system is currently installed in the IBM 300 mm fab, manufacturing game chips and microprocessors. It has detected numerous opportunities for yield and performance improvement, saving many millions of dollars.     

A low-overhead and reliable switch architecture for Network-on-Chips

This paper proposes and evaluates Low-overhead, Reliable Switch (LRS) architecture to enhance the reliability of Network-on-Chips (NoCs). The proposed switch architecture exploits information and hardware redundancies to eliminate retransmission of faulty flits. The LRS architecture creates a redundant copy of each newly received flit and stores the redundant flit in a duplicated flit buffer that is associated with the incoming channel of the flit. Flit buffers in the LRS are equipped with information redundancy to detect probable bit flip errors. When an error is detected in a flit buffer, its duplicated buffer is used to recover the correct value of the flit. In this way, the propagation of the erroneous flits in NoC is prevented without any need to credit signals and, retransmission buffers. Using an HDL-based NoC simulator, the LRS is compared to two other widely used reliability enhancement methods: the Switch-to-Switch (S2S) and the End-to-End (E2E) methods. The simulation results show that the LRS consumes less power and provides higher performance compared to those of the E2E and S2S methods. More importantly, unlike the E2E and the S2S methods, the LRS has constant overheads, which makes it applicable in all working conditions. To validate the comparison, an analytical performance and reliability model is developed for the LRS, S2S and E2E methods. The results of the model match those obtained from the simulations while the proposed model is significantly faster.