Alias-Component Matrices of Nonuniform Transmultiplexers

Nonuniform transmultiplexers can be used for interconversion of signals with different sampling rates between the time-division multiplexing format and the frequency-division multiplexing format. Here, we review the polyphase representation and discuss the ℋ_∞ model-matching design of finite impulse response nonuniform transmultiplexers by semidefinite programming. Then, we study the alias-component matrices. It will be shown that the alias-component matrices of nonuniform transmultiplexers are generalizations of those of linear periodically time-varying systems. In particular, it is shown that the output at any given frequency is only dependent on the input at a finite set of frequencies. This work was supported by the Natural Sciences and Engineering Research Council of Canada.     

Influence of temperature on structural and magnetic properties of Co0·5Mn0·5Fe2O4 ferrites

Co_0·5Mn_0·5Fe₂O₄ ferrites have been synthesized using a single-step sol-gel auto-combustion method in which the metal nitrate (MN)-to-citric acid (CA) ratio was adjusted to 0.5: 1 and pH to 7, respectively. The structural and magnetic properties of as-burnt and annealed samples were studied as a function of temperature. The inverse spinel structure was confirmed by X-ray diffraction (XRD) and crystallite size was estimated by the most intense peak (311) using Scherrer’s formula. Contrary to earlier studies reported in the literature, both as-burnt and annealed samples exhibit crystalline behaviour. Room temperature magnetic properties were studied using vibrating sample magnetometer (VSM) with field strengths up to ±10 kOe. Lattice constant and crystallite size increased as the annealing temperature was increased. However, the coercivity (H _c) initially increased and then decreased with the increase of crystallite size. The variation in coercivity is ascribed to the transition from a multi-domain to a single-domain configuration.     

Wurtzite-type ZnS nanoparticles by pulsed electric discharge

The synthesis of wurtzite-type ZnS nanoparticles by an electric discharge submerged in molten sulfur is reported. Using a pulsed plasma between two zinc electrodes of diameter 5 mm in molten sulfur, we have synthesized high-temperature phase (wurtzite-type) ZnS nanocrystals with an average size of about 20 nm. The refined lattice parameters of the synthesized wurtzite-type ZnS nanoparticles were found to be larger than those of the reported ZnS (JCPDS card no 36-1450). Synthesis of ZnMgS (solid solution of ZnS and MgS) was achieved by using ZnMg alloys as both cathode and anode electrodes. UV-visible absorption spectroscopy analysis showed that the absorption peak of the as-prepared ZnS sample (319 nm) displays a blue-shift compared to the bulk ZnS (335 nm). Photoluminescence spectra of the samples revealed peaks at 340, 397, 423, 455 and 471 nm, which were related to excitonic emission and stoichiometric defects.     

Robust FIR equalization for time-varying communication channels with intermittent observations via an LMI approach

The optimal design of finite impulse response (FIR) filters for equalization/deconvolution is investigated in this paper. Two practical yet challenging constraints are incorporated into the modeling of the equalization system: (1) The parameters of the communication channel model are arbitrarily time-varying within a polytope with finite known vertices; (2) at the received end, the received signal is usually intermittent due to network-induced packet dropouts which are modeled by a stochastic Bernoulli distribution. Under the stochastic theory framework, a robust design method for the FIR equalizer is proposed such that the equalization system can achieve the prescribed energy-to-peak performance even it is subject to uncertainties, external noise, and data missing. Sufficient conditions for the existence of the equalizer are derived by a set of linear matrix inequalities (LMIs). An illustrative design example demonstrates the design procedure and the effectiveness of the proposed method.     

A new analytical method for determination of discharge duration in tunnels subjected to groundwater inrush

Bulletin of Engineering Geology and the Environment - Unexpected water inrush to tunnels is one of the most hazardous events, especially in karst terrains that could take place during mechanized...     

Numerical and experimental investigation of cascade type serpentine flow field of reactant gases for improving performance of PEM fuel cell

The distribution of reactant gases in polymer electrolyte membrane fuel cells (PEMFCs) plays a pivotal role in current density distribution, temperature distribution, and water concentration. Problems such as flooding or drying of the membrane are caused by the non-uniformity of the above mentioned parameters resulting in a reduced membrane electrode assembly (MEA) life time. In this study, a new cascade type serpentine flow field is introduced and the concept of design is explained. The simulation results are in good agreement with the literature. The optimal channel to rib ratio is obtained using simulation results. The results show that the proposed flow field produces a uniform current density and local stoichiometry as well as an improved water management. It is also determined that the two phase numerical method can estimate experimental results correctly.     

Approximate Representation of a Compliance Contribution Tensor for a Cylindrical Inhomogeneity Normal to the Axis of Symmetry of a Transversely Isotropic Material

The paper focuses on the assessment of the effect produced by a strongly prolate spheroidal pore in a transversely-isotropic material when the axis of rotation of the spheroid is perpendicular to the axis of transverse isotropy. We propose a simple approximation method to get components of the pore compliance contribution tensor. The results are compared with exact numerical solution. It is shown that for moderate anisotropy (like one of cortical bone, for example) the method produces accurate results.     

Robust weighted H∞ filtering for networked systems with intermittent measurements of multiple sensors

In this paper, we investigate the robust weighted H_∞ filtering problem for networked systems with intermittent measurements under the discrete‐time framework. Multiple outputs of the plant are measured by separate sensors, each of which has a specific failure rate. Network‐induced delay, packet dropouts and network‐induced disorder phenomena are all incorporated in the modeling of the network link. The resulting closed‐loop system involves both delayed noise and non‐delayed noise. In order to make full use of the delayed information, we define a weighted H_∞ performance index. Sufficient delay‐dependent and parameter‐dependent conditions for the existence of the filter and the solvability of the addressed problem are given via a set of linear matrix inequalities. Two simulation examples are presented to illustrate the relationship between the minimal performance level and the weighting factor, which show the effectiveness of the proposed method. Copyright © 2010 John Wiley & Sons, Ltd.     

Properties of linear switching time-varying discrete-time systems with applications

We study two discrete-time, linear switching time-varying (LSTV) structures, each of which consists of a periodic switch connected to several linear time-invariant (LTI) systems. Such structures can be used to represent any linear periodically time-varying (LPTV) systems. We give basic properties associated with the LSTV structures in terms of their LTI building blocks, and then apply the results to solve a general approximation problem: How to optimally approximate an LPTV system with period p by an LPTV system with period ? The optimality is measured using norms. The study is extended to general multirate periodic systems.