Lyapunov controller design for transverse vibration of a cable-linked transporter system

Modeling and Lyapunov controller design for transverse vibration of a flexible cable transporter system with arbitrarily varying lengths are presented using Hamilton's principle and Lyapunov theory. The axial velocity of the system is assumed to be unknown in the model. This is different from existing literature where the axial velocity is assumed either to be constant or prescribed. The governing equations include two coupled non-linear Partial Differential Equations (PDEs) and boundary conditions. The interactions between the cables and the slider, pulleys, and motors are included in the model. Numerical solution of the derived governing equations is obtained using Galerkin's method. Based on the Lyapunov theory, we propose two boundary controllers and one domain point-wise controller, which suppress the transverse vibration of the cables effectively while assuring the attainment of the slider goal. The proposed controllers dissipate the vibration energy and guarantee the stability of the closed-loop system in Lyapunov sense. Simulation results demonstrate the effectiveness of the proposed controllers.A short version of this paper was presented in 2004 ASME International Mechanical Engineering Conference and Exposition, Anaheim CA, November 14-19, 2004.     

Jini home networking: a step toward pervasive computing

Jini connection technology forms a network of devices on the fly, without manual connection or configuration. It can also complement other technologies that strive for "anytime, anywhere" connectivity. The article looks at lookup and discovery services; reliability and scalability; Jini architectural requirements; service for non-Jini devices; Jini mobile edition for wireless devices; Jini implementations; and competing and related technologies.     

Performance comparison of battery power consumption in wireless multiple access protocols

Energy efficiency is an important issue in mobile wireless networks since the battery life of mobile terminals is limited. Conservation of battery power has been addressed using many techniques such as variable speed CPUs, flash memory, disk spindowns, and so on. We believe that energy conservation should be an important factor in the design of networking protocols for mobile wireless networks. In particular, this paper addresses energy efficiency in medium access control (MAC) protocols for wireless networks. The paper develops a framework to study the energy consumption of a MAC protocol from the transceiver usage perspective. This framework is then applied to compare the performance of a set of protocols that includes IEEE 802.11, ECMAC, PRMA, MDRTDMA, and DQRUMA*. The performance metrics considered are transmitter and receiver usage times for packet transmission and reception. The time estimates are then combined with power ratings for a Proxim RangeLAN2 radio card to obtain an estimate of the energy consumed for MAC related activities. The analysis here shows that protocols that aim to reduce the number of contentions perform better from an energy consumption perspective. The receiver usage time, however, tends to be higher for protocols that require the mobile to sense the medium before attempting transmission. The paper also provides a set of principles that could be applied when designing access protocols for wireless networks.*ECMAC: energyconserving MAC. PRMA: packet reservation multiple access. MDRTDMA: multiservices dynamic reservation TDMA. DQRUMA: distributedqueuing request update multiple access.     

Abel inversion of deflectometric measurements in dynamic flows

We present an Abel-inversion algorithm to reconstruct mean and rms refractive-index profiles from spatially resolved statistical measurements of the beam-deflection angle in time-dependent, axisymmetric flows. An oscillating gas-jet diffusion flame was investigated as a test case for applying the algorithm. Experimental data were obtained across the whole field by a rainbow schlieren apparatus. Results show that simultaneous multipoint measurements are necessary to reconstruct the rms refractive index accurately.     

Schiff bases of ethylenediamine as corrosion inhibitors of zinc in sulphuric acid

The work described here deals with the performance of ethylenediamine N,N^′-dibenzylidene, ethylenediamine N,N^′-di(p-methoxybenzylidene), ethylenediamine N,N^′-disalicylidene as corrosion inhibitors for zinc in sulphuric acid. The effect of various parameters on the efficiency of these inhibitors has been studied. Ethylenediamine N,N^′-di(p-methoxybenzylidene) and ethylenediamine N,N^′-disalicylidene give 99% protection under a variety of conditions. Activation energies in the presence and absence of inhibitors have been calculated. It appears that an efficient inhibitor is characterized by a relatively greater decrease in free energy of adsorption, relatively lower entropy of adsorption and relatively lower heat of adsorption. Galvanostatic polarisation studies indicate that these are basically cathodic inhibitors. Cathodic protection in the presence of these inhibitors has been studied. With an efficient inhibitor, cathodic protection is achieved at potentials much less negative than that required for plain acid. The difference between protective potential and corrosion potential appears to be less for an effective inhibitor. Mechanism of the action of inhibitors has been provided.     

Study of the fracture toughness and fracture morphology of polybenzimidazole

Polybenzimidazole (PBI) is a relatively new polymeric material exhibiting unusual properties that are attributable to its aromatic-heterocyclic monomer structure. Owing to its high strength, stiffness and excellent stability in hostile chemical and thermal environments, PBI is being used increasingly in critical applications. As a result, understanding the failure mechanisms of the material is vital. This paper presents the results of a study of the fracture toughness and fracture morphology of polybenzimidazole. The standard compact tension specimen was used as the basic experimental specimen in this study. The fracture tests were performed in an Instron tensile testing machine. The effects of varying the loading rate, and the ratio of the initial crack length,a, to the ligament length,W, were investigated. The fracture surface morphology was examined using optical and scanning electron microscopy. The results of this study indicate that the precracking technique significantly affects the measured fracture toughness. Also, an increase in the loading rate causes a significant decrease in fracture toughness. Examination of the fracture morphology reveals that PBI fracture surfaces exhibit many of the characteristics expected of a tough engineering plastic.     

Sequence-specific RNase H cleavage of gag mRNA from HIV-1 infected cells by an antisense oligonucleotide in vitro

We have used a ribonuclease protection assay to investigate RNase H cleavage of HIV-1 mRNA mediated by phosphorothioate antisense oligonucleotides complementary to the gag region of the HIV-1 genome in vitro. Cell lysate experiments in H9 and U937 cells chronically infected with HIV-1 IIIB showed RNase H cleavage of unspliced gag message but no cleavage of spliced message which did not contain the target gag region. RNase H cleavage products were detected at oligonucleotide concentrations as low as 0.01 microM and the RNase H activity was seen to be concentration dependent. Similar experiments with 1-, 3- and 5-mismatch oligonucleotides demonstrated sequence specificity at low concentrations, with cleavage of gag mRNA correlating with the predicted activities of the parent and mismatch oligonucleotides based on their hybridization melting temperatures. Experiments in living cells suggested that RNase H-specific antisense activity was largely determined by the amount of oligonucleotide taken up by the different cell lines studied. RNase H cleavage products were detected in antisense oligonucleotide treated MT-4 cells acutely infected with HIV-1 IIIB, but not in infected H9 cells treated with oligonucleotide under the same conditions. The data presented demonstrate potent and specific RNase H cleavage of HIV-1 mRNA mediated by an antisense oligonucleotide targeted to HIV-1 gag mRNA, and are in agreement with previous reports that the major obstacle to demonstrating antisense activity in living cells remains the lack of penetration of these agents into the desired cellular compartment.     

Horizontally polarized waves in inhomogeneous media--Energy conservation and reciprocity relationships

Full wave solutions for the electromagnetic fields of a horizontally polarized wave propagating through an inhomogeneous ionized medium are derived using a generalized WKB method. Both the electron density and the collision frequency of the horizontally stratified media are assumed to vary and special attention is given to permittivity profiles with critical coupling regions. The reflection and transmission coefficients and the characteristic surface impedance for an inhomogeneous layer of finite thickness are computed as functions of the transverse wave number for various permittivity profiles. Excitation of both propagating and evanescent waves are considered. For some special permittivity profiles considered, closed form analytical solutions for the electromagnetic fields are known. Computations derived from these solutions are in good agreement with those obtained using the generalized WKB method. The results are also shown to satisfy energy conservation and reciprocity relationships in electromagnetic theory.     

A hybrid technique for wire antennas in a cavity

Two numerical techniques for solving the current distribution on wire antennas, namely point matching and reaction matching, have been combined in a particular fashion to yield a new technique termed the "hybrid method." The hybrid method is well suited for a wire antenna mounted in a cavity. Over the antenna, piecewise sinusoidal basis functions with reaction matching are used, and on the support structure, point matching is used with pulse basis functions. The hybrid method has been applied to calculate the input impedance and the radiation efficiency of the three-turn loop antenna in an open circular cavity. Calculated input resistance of the antenna is found to agree quite well with measured data. Effects of varying the extent of recession of the antenna and varying the radius and the material of the antenna wire on the bandwidth, the efficiency, the antiresonance frequencies, and the general input reactance level of the antenna have been examined for a specific antenna geometry. The results are considered to be indicative of the general characteristics of a multiturn loop antenna with nearby support structure. The computer program that has been developed may be applied to a systematic parametric study of this type of antenna in order to optimize it for a particular application.