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Semiactive control of rigid blocks under earthquake excitation
No full textThis paper investigates the usefulness of a semiactive control to reduce the overturning vulnerability of a rigid block on a rigid plane under earthquake excitation. The proposed feedback law is used to set the stiffness of restraints placed at the 2 lower corners of the block. The performance of the semiactive control is numerically validated by subjecting the block to 100 recorded accelerograms. Specific simulations are performed to study the effect of different anchorage design parameters on the utility of the control. Finally, the robustness of the proposed control is addressed with respect to typical issues of the real-world implementation
Vibration and buckling of open TWBs with local weakening
No full textFree vibration and Ljapounov stability of compressed open thin-walled beams with a cross-section reduction are studied by a in-house finite differences numerical code, based on a refined direct beam model and allowing for investigating elastic stability of non-trivial equilibrium paths in a dynamic setting. The benchmark is a beam with doubly symmetric cross-section and non-zero warping rigidity, under free, semi-, and fully restrained warping at its ends. In all cases, the results of the direct model are compared to finite element and/or experimental ones. The reduction in the cross-section rigidity induces a weakening that may model a local damage; thus, the present investigation may be useful with an outlook to damage monitoring and identification
Single and multiple crack localization in beam-like structures using a Gaussian process regression approach
No full textA crack or a localized damage in a structure provokes a discontinuity in the rotation. Consequently, mode-shapes are nonsmooth at the damage position and the first derivative (strictly related to the rotation) presents a jump discontinuity. Based on this simple concept, a new approach has been developed in order to predict the location of the mode-shape derivative discontinuities, and therefore the location of damage, without the need to directly differentiate. This approach applies a Gaussian process regression to the mode-shape data, using a covariance function which allows for a nonsmooth point; this point, which indicates the crack position, can be determined by a maximum likelihood algorithm. Using a finiteelement model of a cracked beam, the performance of this methodology has been analyzed for the case of single crack and multiple cracks, for increasing amounts of noise. The effects of several parameters (damage position, damage severity, number of measurement points and of considered mode-shapes) on the approach accuracy have also been investigated. Finally, the method has been verified using experimental data coming from a vibrating steel beam with a cut. Results are encouraging and indicate that further developments of the technique for nondestructive testing of beam-like structures would be highly worthwhile
Utilization of industrial lignin as fire retardant additive in intumescent system for textile applications
No full textA design strategy for AM/PM compensation in GaN Doherty Power Amplifiers
No full textThis paper presents the theoretical analysis of phase distortion (AM/PM) mechanisms in Gallium Nitride (GaN) Doherty power amplifiers (DPAs) and a novel approach to optimize the tradeoff between linearity and efficiency. In particular, it is demonstrated how it is possible to mitigate the AM/PM by designing a suitable mismatch at the input of the active devices, based on the identification of constant AM/PM and gain contour circles. The proposed theory is experimentally confirmed by source- and load-pull measurements and further validated through the design and realization of a 7 GHz 10W DPA based on GaN monolithic technology
Integrating urban agriculture and urban planning in Mashhad, Iran; a short survey of current status and constraints
No full textThis article addresses the role of urban and peri-urban agriculture (UPA) in Mashhad in a perspective of sustainable development. To this end the article seeks to point out the conditions that hinder this development and the factors that could favor it. The article is structured as follows: in the first section the UPA phenomenon is framed with reference to some significant planning experiences in progress in Western and Islamic countries. In the second section, an outline of Mashhad as a "city in transition" is provided highlighting its main factors of change. In the third section, the institutional framework of present urban planning in Mashhad is described, also showing the weak enforcement mechanisms of planning policy for UPA. Section four presents both a conceptual and material network of un-built areas potentially suitable for agricultural uses, articulated in three different classes. By referring to city maps and recent urban schemes, the study summarizes the physical characteristics, the ownership, and the resources of each class, from inside the compact city to its peripheral belt. The article concludes by indicating the three domains of policy, education, and social commitment as the main factors that can favor effective policies and practices for a multifunctional urban agriculture
Investigation on the Demodulation of Multi-Tone Interference in Feedback OpAmps
No full textIn this paper the effect of multi-tone interference on feedback Operational Amplifiers is explored. An analytical model is derived under the assumption of weak non-linearity. It can be used to predict the output offset induced by the superposition of an arbitrary number of sinusoidal disturbance and to evaluate the intermodulation distortion caused by two-tone interference. The proposed model is validated through comparison with computer simulations
