Robust matrix 𝒟U‐stability analysis

In this paper, the problem of robust matrix root‐clustering is addressed. The studied matrices are subject to both polytopic and unstructured uncertainties. An original point is the large choice of clustering regions enabled by the proposed approach since these regions can be unions of possibly disjoint and non‐symmetric subregions of the complex plane. The precise purpose is, considering a specified polytope, to determine the greatest robustness bound on the unstructured uncertainty such that robust matrix root‐clustering is ensured. To reduce conservatism in the derivation of the bound, the reasoning relies on a framework based upon parameter‐dependent Lyapunov functions. The bound value is computed by solving an ?? ?? ? problem. Copyright © 2003 John Wiley & Sons, Ltd.     

An experimental evaluation of cross-layer routing in a wireless mesh backbone

Over the latest few years, cross-layer design in wireless networks has drawn great attention from the research community. One of the main arguments in favor of such techniques is that the hop-count metric alone is not enough to capture the specificities of wireless links (e.g., interferences, collisions, fading). In this paper, we address a simple yet fundamental question: What are the real improvements that cross-layering can bring to routing performance when compared to the simple hop-count metric? In our experiments, we consider the backbone of a real wireless mesh network composed of 12 routers deployed in an office building. We focus on the stability of routes and their persistence. In spite of the nature of cross-layer metrics that take into account information from different layers, lets them be very reactive to changes, we observe that using these metrics, pairs of nodes tend to mainly use the same set of two or three routes between them.     

Pore-network modeling of liquid water flow in gas diffusion layers of proton exchange membrane fuel cells

Fluid flow through the gas diffusion layer (GDL) of fuel cells is numerically studied using a pore network modeling approach. The model is developed based on an experimental visualization technique (fluorescence microscopy). The images obtained from this technique are analyzed to find patterns of flow inside the GDL samples with different hydrophobicity. Three different flow patterns are observed: initial invasion, progression, and pore-filling. The observation shows that liquid water flows into the majority of available pores on the boundary of the untreated GDL and several branches are segregated from the initial pathways. For the treated GDL, however, a handful of boundary pores are invaded and the original pathways extend toward the other side of the medium with minimum branching. The numerical model, developed based on an invasion percolation algorithm, is used to study the effects of GDL hydrophobicity and thickness on the flow configuration and breakthrough time as well as to determine the flow rate and saturation in different GDL samples. During the injection of water into the samples, it is numerically shown that the flow rates are monotonically decreasing for both treated and untreated samples. For the treated sample, however, the injection flow rate is constantly lower than that of the untreated sample, resulting in a lower overall water saturation at breakthrough. The numerical results also suggest that hydrophobic treatment of thick samples has minor effects on water management and overall performance. The developed model can be used to optimize the GDL properties for designing porous medium with effective transport characteristics.     

Optimization of optical single sideband configurations for radio over fiber transmission and multi-type data communication over a DWDM link

Two new optical single side band (OSSB) configurations for radio frequency (RF) transmission of data are proposed based on the structures that have been designed for baseband digital data transmission. The performances of these schemes are evaluated based on the relevant eye diagrams and bit error rate (BER). The proposed configurations are studied and analyzed mathematically. Eye diagrams and BER’s indicate an acceptable performance for the suggested structures. Feasible settings for the RF electrical power of the links are considered and the link performance for each setting is evaluated. A 4-dense wavelength division multiplexing (4-DWDM) link is considered for transmitting different types of data over a single mode fiber (SMF). Baseband digital data in the format of OSSB and RF-OSSB signals are transmitted over a 4-DWDM link. Furthermore, the link performance is considered for different electrical power settings of OSSB signal in order to achieve efficient transmission for DWDM network.     

Multiscale analysis of viscoelastic laminated composite plates using generalized differential quadrature

In this paper, a laminated composite plate is analyzed using a multiscale method. At first, material properties of a lamina are obtained using an analytical micromechanical approach called simplified unit cell method (SUCM), and then in structural level, the generalized differential quadrature method (GDQM) is used to analyze a laminated composite plate. By means of the Boltzmann superposition principle, the viscoelastic behavior of the matrix is obtained. The Prony series is considered to define the compliance of matrix. To verify the results, graphiteT300/epoxy5208 composite material is analyzed and the results are compared with existing experimental data. The multiscale algorithm includes obtaining overall properties of the composite by SUCM; then, these properties are used to define the bending stiffness. Governing equations of motion of laminated composite plate are solved via GDQM and Newton–Raphson method. Variations of stresses and displacements versus time and volume fraction of the fibers are shown for laminated composite plates with different boundary conditions.     

Thermal degradation behavior and kinetic studies of polyacrylamide gel in TiO2 nanoparticles synthesis

Polyacrylamide gel (PAMG) method is a simple, fast and cheap method used for the synthesis of a wide variety of nanopowders. However, no adequate results have been reported on the thermal degradation behavior of PAMG which can be very effective on the final product properties. In this work, thermal degradation behavior of PAMG in the presence of TiCl₄ as a precursor salt for synthesis of TiO₂ nanoparticles was examined in comparison with linear polyacrylamide (LPAM) and pure PAMG by thermogravimetry/differential thermal analysis. Their thermal degradation kinetics was investigated, as well. The results showed that thermal degradation of all samples occurred in two stages at different onset temperatures. Despite the high thermal stability of pure PAMG compared to LPAM, the presence of TiCl₄ as a mineral material in PAMG structure decreases the thermal degradation onset temperature, considerably. Furthermore for LPAM and PAMG, majority of weight loss occurs in the second stage, but in PAMG with TiCl₄ the weight loss occurs mainly at the first stage. For more detailed investigation, residual materials were characterized by Fourier transform infrared spectroscopy and X-ray diffraction (XRD) techniques, attributing this trend to the presence of mineral materials in PAMG structure. XRD and transmission electron microscopy were also applied to confirm anatase crystalline structure and nanoscale distribution of the TiO₂ particles synthesized via PAMG method.     

MFLP: a low power encoding for on chip networks

Network on chip (NoC) has been proposed as an appropriate solution for today’s on-chip communication challenges. Power dissipation has become a key factor in the NoCs because of their shrinking sizes. In this paper, we propose a new encoding approach aimed at power reduction by decreasing the number of switching activities on the buses. This approach assigns the symbols to data word in such a way that the more frequent words are sent by less power consumption. This algorithm dedicates the symbols with less ones to high probability data and uses transition signaling to transmit data. The proposed method, unlike the existing low power encoding, does not rely on spatial redundancy and keeps the width of the bus constant. Experimental evaluations show that our approach reduces the power dissipation up to 46 % with 2.70, 0.51, and 15.43 % power, critical path and area overhead in the NoCs, respectively.     

Effects of aluminium nitride silane-treatment on the mechanical and thermal properties of polybenzoxazine matrix

A new kind of polymer composite, produced from the typical polybenzoxazine and 0–30 wt-% native and silane-treated aluminium nitride (T-AlN), was investigated. The mechanical tests revealed a significant increase in the microhardness and flexural properties upon adding the T-AlN particles compared to that obtained from the untreated ones. By adding 0–30 wt-% T-AlN, the tensile moduli were accurately reproduced by the Halpin-Tsai and Nielsen models. At 30 wt-% T-AlN, dynamic mechanical analysis showed a significant increase in the storage moduli and the glass transition temperature (T_g), reaching 3.2?GPa and 217°C, respectively. The thermal stability of these materials was significantly improved upon the addition of the T-AlN fillers. These improvements are attributed to the high thermal and mechanical properties of the fillers and their good dispersion and adhesion in and to the matrix as revealed by a morphological analysis.     

Isogeometric level set topology optimization for elastoplastic plane stress problems

International Journal of Mechanics and Materials in Design - This article aims to utilize IsoGeometric analysis (IGA) and Level set method for topology optimization of elastoplastic plane stress...