The influence of Johnson–Cook material constants on finite element simulation of machining of AISI 316L steel

In literature, five different sets of work material constants used in the Johnson–Cook's (J–C) constitutive equation are implemented in a numerical model to describe the behaviour of AISI 316L steel. The aim of this research is to study the effects of five different sets of material constants of the J–C constitutive equation in finite-element modelling of orthogonal cutting of AISI 316L on the experimental and predicted cutting forces, chip morphology, temperature distributions and residual stresses. Several experimental equipments were used to estimate the experimental results, such as piezoelectric dynamometer for cutting forces measurements, thermal imaging system for temperature measurements and X-ray diffraction technique for residual stresses determination on the machined surfaces; while an elastic–viscoplastic FEM formulation was implemented to predict the local and global variables involved in this research. It has been observed that all the considered process output and, in particular the residual stresses are very sensitive to the J–C's material constants.     

Further improvement in high crystalline quality of homoepitaxial CVD diamond

High-quality homoepitaxial diamond (001) films with macroscopically flat surfaces have been successfully grown using a high-power microwave-plasma chemical-vapor-deposition (MWPCVD) method. In this study, further optimization of the homoepitaxial growth condition has been accomplished mainly by controlling off-angles to 5° along the <110> or <100> direction of high-pressure/high-temperature-synthesized Ib diamond (001) substrates. We have found that the homoepitaxial films deposited at reasonably high growth rates under the optimized growth condition including the off-angle of 3°–4° along the <110> direction have macroscopically flat surfaces, accompany very low or almost negligible densities of growth hillocks and yield strong free-exciton emissions in both steady-state cathodoluminescence and time-resolved photoluminescence spectra measured at room temperature. These indicate that apparent lateral growths suitable for high-quality homoepitaxial layers in the case of the high-power MWPCVD method, which are similar to those previously reported in the case of MWPCVD processes with low methane concentrations, rather quickly occur from step edges on (001) terraces and that they can be achieved more preferentially on the vicinal substrates at high temperatures and high methane concentrations.     

Admission and GoS control in a multiservice WCDMA system

We consider in this paper a WCDMA system with two types of calls: real time (RT) calls that have dedicated resources, and data non-real time (NRT) calls that are treated using a time-shared channel (such as the HDR or the HSDPA). We consider reservation of some resources for the NRT traffic and assume that this traffic is further assigned the resources left over from the RT traffic. The grade of service (GoS) of RT traffic is also controlled in order to allow for handling more RT calls during congestion periods, at the cost of degraded transmission rates. We consider both the downlink (with and without macrodiversity) as well as the uplink and study the blocking probabilities of RT traffic as well as the expected sojourn time of NRT traffic. We further study the conditional expected sojourn time of a data connection given its size and the state of the system. Finally, we extend our framework to handle handover calls.     

A steel surface defect inspection approach towards smart industrial monitoring

Journal of Intelligent Manufacturing - With the advance in Industry 4.0, smart industrial monitoring has been proposed to timely discover faults and defects in industrial processes. Steel is widely...     

A parallel image encryption method based on compressive sensing

Recently, compressive sensing-based encryption methods which combine sampling, compression and encryption together have been proposed. However, since the quantized measurement data obtained from linear dimension reduction projection directly serve as the encrypted image, the existing compressive sensing-based encryption methods fail to resist against the chosen-plaintext attack. To enhance the security, a block cipher structure consisting of scrambling, mixing, S-box and chaotic lattice XOR is designed to further encrypt the quantized measurement data. In particular, the proposed method works efficiently in the parallel computing environment. Moreover, a communication unit exchanges data among the multiple processors without collision. This collision-free property is equivalent to optimal diffusion. The experimental results demonstrate that the proposed encryption method not only achieves the remarkable confusion, diffusion and sensitivity but also outperforms the existing parallel image encryption methods with respect to the compressibility and the encryption speed.     

Model checking response times in Networked Automation Systems using jitter bounds

Response time (RT) of Networked Automation Systems (NAS) is affected by timing imperfections induced due to the network, computing and hardware components. Guaranteeing RT in the presence of such timing imperfections is essential for building dependable NAS, and to avoid costly upgrades after deployment in industries.This investigation proposes a methodology and work-flow that combines modelling, simulation, verification, experiments, and software tools to verify the RT of the NAS during the design, rather than after deployment. The RT evaluation work-flow has three phases: model building, modelling and verification. During the model building phase component reaction times are specified and their timing performance is measured by combining experiments with simulation. During the modelling phase, component based mathematical models that capture the network architecture and inter-connection are proposed. Composition of the component models gives the NAS model required for studying the RT performance on system level. Finally, in the verification step, the NAS formal models are abstracted as UPPAAL timed automata with their timing interfaces. To model timing interfaces, the action patterns, and their timing wrapper are proposed. The formal model of high level of abstraction is used to verify the total response time of the NAS where the reactions to be verified are specified using a subset of timed computation tree logic (TCTL) in UPPAAL model checker. The proposed approach is illustrated on an industrial steam boiler deployment.     

Speech authentication by semi-fragile speech watermarking utilizing analysis by synthesis and spectral distortion optimization

This paper proposes an improved semi-fragile speech watermarking scheme by quantization of linear prediction (LP) parameters, i.e., the inverse sine (IS) parameters. The spectral distortion due to watermark embedding is controlled to meet the ‘transparency’ criterion in speech coding. A modified bit allocation algorithm combined with watermarking is developed to determine the quantization step so that the ‘transparency’ requirement is satisfied. Due to the statistical nature, the LP coefficients estimated from the watermarked speech signal are different from the watermarked LP coefficients even in the absence of attacks. This effect is the cause of increase in decoding error and minimum authentication length. To tackle this problem, an Analysis by Synthesis (AbS) scheme is developed to reduce the difference between the estimated LP coefficients and the watermarked ones. The watermark detection threshold and minimum authentication length are then derived according to the probability of error and the signal to noise ratio (SNR) requirements. Experimental results show that the proposed AbS based method can effectively reduce the difference between the watermarked IS parameter and the extracted IS parameter when there is no attacks. In addition, the modified bit allocation algorithm can automatically find the appropriate quantization step used in the odd-even modulation so that the transparency requirement is satisfied.     

Genetic algorithm approach for QoS-based tree topology construction in IEEE 802.16 mesh networks

The topological characteristics of an IEEE 802.16 mesh network including the tree’s depth and degree of its nodes affect the delay and throughput of the network.To reach the desired trade-off between delay and throughput,all potential trees should be explored to obtain a tree with the proper topology.Since the number of extractable tree topologies from a given network graph is enormous,we use a genetic algorithm(GA) to explore the search space and find a good enough trade-off between per-node,as well as network-wide delay and throughput.In the proposed GA approach,we use the Pruefer code tree representation followed by novel genetic operators.First,for each individual tree topology,we obtain expressions analytically for per-node delay and throughput.Based on the required quality of service,the obtained expressions are invoked in the computation of fitness functions for the genetic approach.Using a proper fitness function,the proposed algorithm is able to find the intended trees while different constraints on delay and throughput of each node are imposed.Employing a GA approach leads to the exploration of this extremely wide search space in a reasonably short time,which results in overall scalability and accuracy of the proposed tree exploration algorithm.     

Bounded Consensus Algorithms for Multi‐Agent Systems in Directed Networks

In this paper, the consensus problem is investigated via bounded controls for the multi‐agent systems with or without communication. Based on the nested saturation method, the saturated control laws are designed to solve the consensus problem. Under the designed saturated control laws, the transient performance of the closed‐loop system can be improved by tuning the saturation level. First of all, asymptotical consensus algorithms with bounded control inputs are proposed for the multi‐agent systems with or without communication delays. Under these consensus algorithms, the states’ consensus can be achieved asymptotically. Then, based on a kind of novel nonlinear saturation functions, bounded finite‐time consensus algorithms are further developed. It is shown that the states’ consensus can be achieved in finite time. Finally, two examples are given to verify the efficiency of the proposed methods.