Multipath channel identification by using global optimization in ambiguity function domain

A new transform domain array signal processing technique is proposed for identification of multipath communication channels. The received array element outputs are transformed to delay-Doppler domain by using the cross-ambiguity function (CAF) for efficient exploitation of the delay-Doppler diversity of the multipath components. Clusters of multipath components can be identified by using a simple amplitude thresholding in the delay-Doppler domain. Particle swarm optimization (PSO) can be used to identify parameters of the multipath components in each cluster. The performance of the proposed PSO-CAF technique is compared with the space alternating generalized expectation maximization (SAGE) technique and with a recently proposed PSO based technique at various SNR levels. Simulation results clearly quantify the superior performance of the PSO-CAF technique over the alternative techniques at all practically significant SNR levels.     

Diffusion bonding of electroless Ni plated WC composite to Cu and AISI 316 stainless steel

In this study, a composite containing WC (Tungsten Carbide) and Ni was produced by two different processing routes. Electroless Ni coated WC powders were consolidated and sintered at 1200 °C. Diffusion bonding couples of WC(Ni)-electrolytic Cu, WC(Ni)-AISI 316 stainless steel and WC(Ni)-WC(Ni) were manufactured by using a preloaded compression system under Ar atmosphere. Diffusion bonding was carried out at varying bonding temperatures; 750 °C for (WC)Ni-Cu diffusion couple and 1200 °C for (WC)Ni-(WC)Ni and (WC)Ni-AISI 316 stainless steel diffusion couples. Standard metallographic techniques, Scanning Electron Microscopy and a shear test were employed to characterize the microstructure of bondline and mechanical properties of each diffusion couple, respectively.     

Improved Incompressible Smoothed Particle Hydrodynamics method for simulating flow around bluff bodies

In this article, we present numerical solutions for flow over an airfoil and a square obstacle using Incompressible Smoothed Particle Hydrodynamics (ISPH) method with an improved solid boundary treatment approach, referred to as the Multiple Boundary Tangents (MBT) method. It was shown that the MBT boundary treatment technique is very effective for tackling boundaries of complex shapes. Also, we have proposed the usage of the repulsive component of the Lennard-Jones Potential (LJP) in the advection equation to repair particle fractures occurring in the SPH method due to the tendency of SPH particles to follow the stream line trajectory. This approach is named as the artificial particle displacement method. Numerical results suggest that the improved ISPH method which is consisting of the MBT method, artificial particle displacement and the corrective SPH discretization scheme enables one to obtain very stable and robust SPH simulations. The square obstacle and NACA airfoil geometry with the angle of attacks between 0° and 15° were simulated in a laminar flow field with relatively high Reynolds numbers. We illustrated that the improved ISPH method is able to capture the complex physics of bluff-body flows naturally such as the flow separation, wake formation at the trailing edge, and the vortex shedding. The SPH results are validated with a mesh-dependent Finite Element Method (FEM) and excellent agreements among the results were observed.     

Neural extension of experimental data to investigate using phosphogypsume in light brick production

In this study, usability of wastes produced in phosphoric acid plants in structural brick manufacture has been investigated. There are several parameters involved in using these wastes in brick production namely the rate of added waste, firing speed and firing temperature. The performance of these parameters can be measured by several criteria such as natural drying shortening, water absorption and weight loss. Therefore, so many experiments are needed to investigate the effects of these parameters on the bricks produced with these wastes. The result of a series of experiments were utilized to achieve this end. The results have shown that the industrial wastes considered improve the performance of the bricks in terms of the criteria mentioned above. However, the results have also shown that further investigations are needed to explore the effects of interim values on the performance of the bricks. To achieve that end, a neural experimental study is adopted. For this purpose, the results of the experiments conducted were used to construct an artificial neural network. The trained and tested network was then used to check the effects of 280 different combinations for each type of material mixtures mentioned. The outcome of these artificial tests have provided the optimal values for the waste addition rate, firing speed and firing temperature based on the four criteria mentioned previously.     

Lateral stiffness of steel plate shear wall systems

The accuracy of the finite element method and strip method of analysis for calculating the lateral stiffness of steel plate shear wall (SPSW) systems is assessed by making comparisons with experimental findings. Comparisons revealed that while both methods provide acceptable accuracy, they also require the generation of sophisticated computer models. In this paper, two alternative methods are developed. The first one is an approximate hand method based on the deep beam theory. The classical deep beam theory is modified in the light of parametric studies performed on restrained thin plates under pure shear and pure bending. The second one is a computer method based on the truss analogy. Stiffness predictions using the two alternative methods are found to compare well with the experimental findings. In addition, lateral stiffness predictions of the alternate methods are compared against the solutions provided using finite element and strip methods of analysis for a class of test structures. These comparisons reveal that the developed methods provide estimates with acceptable accuracy and are simpler than the traditional analysis techniques.     

Exploiting the channel using uninterrupted collision‐free MAC adaptation over IEEE 802.11 WLANs

IEEE 802.11 wireless local area networks (WLANs) have reached an important stage and become a common technology for wireless access due to its low cost, ease of deployment, and mobility support. In parallel with the extensive growth of WLANs, the development of an efficient medium access control protocol that provides both high throughput performance for data traffic and quality of service support for real‐time applications has become a major focus in WLAN research. The IEEE 802.11 Distributed Coordination Functions (DCF/EDCA) provide contention‐based distributed channel access mechanisms for stations to share the wireless medium. However, performance of these mechanisms may drop dramatically because of high collision probabilities as the number of active stations increases. In this paper, we propose an adaptive collision‐free MAC adaptation. The proposed scheme prevents collisions and allows stations to enter the collision‐free state regardless of the traffic load (saturated or unsaturated) and the number of stations on the medium. Simulation results show that the proposed scheme dramatically enhances the overall throughput and supports quality of service for real‐time services over 802.11‐based WLANs. Copyright © 2013 John Wiley & Sons, Ltd.     

k‐strong privacy for radio frequency identification authentication protocols based on physically unclonable functions

This paper examines Vaudenay's privacy model, which is one of the first and most complete privacy models that featured the notion of different privacy classes. We enhance this model by introducing two new generic adversary classes, k‐strong and k‐forward adversaries where the adversary is allowed to corrupt a tag at most k times. Moreover, we introduce an extended privacy definition that also covers all privacy classes of Vaudenay's model. In order to achieve highest privacy level, we study low cost primitives such as physically unclonable functions (PUFs). The common assumption of PUFs is that their physical structure is destroyed once tampered. This is an ideal assumption because the tamper resistance depends on the ability of the attacker and the quality of the PUF circuits. In this paper, we have weakened this assumption by introducing a new definition k‐resistant PUFs. k‐PUFs are tamper resistant against at most k attacks; that is, their physical structure remains still functional and correct until at most k^th physical attack. Furthermore, we prove that strong privacy can be achieved without public‐key cryptography using k PUF‐based authentication. We finally prove that our extended proposal achieves both reader authentication and k‐strong privacy. Copyright © 2014 John Wiley & Sons, Ltd.     

Conductive polyaniline/poly(methyl methacrylate) films obtained by electropolymerization

Electrochemical polymerization of aniline, on a Pt foil electrode coated with poly(methyl methacrylate) (PMMA), produces a homogeneous, free-standing, flexible, and conductive polymer film. The conductivity of the films depends on the aniline content and reaches 0.1–0.2 S/cm for films having aniline content of 15% or more. The optimum thickness of precoated PMMA to obtain durable conducting films was found to be in the range of 10–15 μm. Cyclic voltammetric investigation revealed that aniline exhibits a similar electrochemical behavior on a PMMA coated platinum electrode similar to a bare Pt surface. The film gives a fast and reproducible response against ammonia gas within a concentration range of 1.0–0.01%. Scanning electron micrographs indicate that the films have a rough structure consisting of globular regions. © 1996 John Wiley & Sons, Inc.     

Stochastic wave energy calculation formulation

The wave energy potential is directly proportional to the wave period and second power of wave height averaged over a suitable time period. The wave height and period have temporal and spatial stochastic variations. It is the main purpose of this paper to derive the most general wave energy formulation by considering simultaneously the temporal variations both in the wave height and period. The correction factor is derived explicitly in terms of cross-correlation and the coefficients of variation. The application of the methodology is performed for wave measurement stations located in the Pacific Ocean off the west coast of the US.