1,721,069 research outputs found
Synthesis, Curing, and Decomposition of Allylamine-Adducted 3,3’-Bismaleimidodiphenylsuhphone Resins
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Nonlinear backstepping active suspension design applied to a half-car model
No full text[[abstract]]A fresh nonlinear backstepping design scheme, which is developed for the control of half-car active suspension systems to improve the inherent tradeoff between ride quality and suspension travel, is proposed in this paper. Since ride quality is dependent on a combination of vertical and angular displacements of a vehicle body, the design of active suspensions must have the potential to minimize heave and pitch movements in order to guarantee the ride comfort of passengers. The other important factor to be emphasized in the design of active suspensions is the suspension travel which means the space variation between the car body and the tires. In order to avoid damaging vehicle components and generating more passenger discomfort, the active suspension controllers must be capable of preventing the suspension from hitting its travel limits. Our design strategy, with two intentionally additional nonlinear filters, shows the potential to achieve these conflicting control objectives. The novelty of our active suspension design is in the use of two particular nonlinear filters at both the front and rear wheels. The effective bandwidths of these two nonlinear filters depend on the magnitudes of the front and rear suspension travels, individually. When suspension travel is small, the proposed controllers soften the suspension for enhancing passenger comfort. However, our control design shifts its attention to rattlespace, utilization by stiffening the suspension when suspension travel approaches its limits. As a result, the improvement of tradeoff between ride quality and suspension travel can be guaranteed and is then demonstrated through comparative simulations.[[note]]SC
Nonlinearities enhance parameter convergence in strict feedback systems
No full text[[abstract]]Following the development of a parameter convergence analysis procedure for output-Feedback nonlinear systems, the authors shift their attention to strict feedback nonlinear systems in this paper. They develop an analytic procedure which allows us, given a specific nonlinear system and a specific reference signal, to determine a priori whether or not the parameter estimates will converge to their true values, simply by checking the Linear independence of the rows of a constant real matrix. Moreover, the authors show that this convergence is exponential. Finally, they prove that even if the rows of this constant matrix are not Linearly independent, partial parameter convergence is still achieved, in the sense that the parameter error vector converges asymptotically to the left nullspace of this matrix.[[note]]SC
Hybrid maximum likelihood frequency offset estimation in coherent OFDM systems
No full text[[abstract]]One of the well known problems in an orthogonal frequency division multiplexing (OFDM) system is its vulnerability to frequency offset. In practice, most coherent OFDM systems transmit pilot symbols on some of the subcarriers to estimate channel attenuation and also add a cyclic prefix (CP) to avoid intercarrier interference and intersymbol interference. A hybrid maximum likelihood estimation algorithm based on the redundancy of both cyclic prefix and pilot subcarriers is proposed for the correction of frequency offset. If the frame timing has been synchronised in advance, by considering the two kinds of redundancy simultaneously, the performance of the proposed hybrid algorithm could achieve significant improvement under low SNR and short CP. As to high SNR and long CP, the performance of this hybrid algorithm is almost identical to that of CP-based only algorithm. Some comparative simulations are given to illustrate the advantages of the proposed hybrid estimation scheme.[[note]]SC
Nonlinear backstepping control design of half-car active suspension systems
No full text[[abstract]]This paper develops a novel nonlinear backstepping design for the control of half-car active suspension systems to improve the inherent tradeoff between ride quality and suspension travel. Since ride quality depends on a combination of vertical displacement (heave) and angular displacement (pitch) of a vehicle body, an active suspension controller must be able to minimize heave and pitch movements in order to guarantee ride comfort of passengers. Suspension travel means the space variation between body and tire. To avoid damaging vehicle components and generating more passenger discomfort, the controller must be capable of preventing the suspension from hitting it travel limits. Our design with an additional nonlinear filter shows potentials to achieve these conflicting control objectives. The novelty is in the use of the nonlinear filter whose effective bandwidths depend on the magnitudes of linear combination of the front and rear suspension travels. This intentional introduction of nonlinearity, which is conveniently accommodated by backstepping, results in a design that is fundamentally different from previous active suspension designs. As the suspension travel changes, the nonlinear controller smoothly shifts its focus between the conflicting objectives of ride comfort and rattlespace utilization. The suspension is set to be soft when suspension travel is small, and it is adjusted to become stiff as it approaches the travel limits. Therefore, this nonlinear design allows the closed-loop system to behave differently in different operating regions, thereby eliminating the dilemma of whether to use a soft or stiff suspension setting. As a result, the improvement of tradeoff between ride quality and suspension travel is demonstrated through comparative simulations.[[note]]SC
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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