14,803 research outputs found
Discrete-Time Negative Imaginary Systems
Full text linkIn this paper we introduce the notion of a discrete-time negative imaginary system and we investigate its relations with discrete-time positivereal system theory. In the framework presented here, discrete-time negative imaginary systems are defined in terms of a sign conditionthat must be satisfied in a domain of analyticity of the transfer function, in analogy with the case of discrete-time positive real functions,as well as analogously to the continuous-time case. This means in particular that we do not need to restrict our notions and definitionsto systems with rational transfer functions. We also provide a discrete-time counterpart of the different notions that have appeared sofar in the literature within the framework of strictly positive real and in the more recent theory of strictly negative imaginary systems,and to show how these notions are characterized and linked to each other. Stability analysis results for the feedback interconnection ofdiscrete-time negative imaginary systems are also derived
Foundations of not necessarily rational Negative Imaginary systems theory: Relations between classes of Negative Imaginary and Positive Real systems
Full text linkIn this technical note we lay the foundations of a not necessarily rational negative imaginary systems theory and its relations with positive real systems theory. In analogy with the theory of positive real functions, in our general framework negative imaginary systems are defined in terms of a domain of analyticity of the transfer function and of a sign condition that must be satisfied in such domain. In this way, we do not require to restrict the attention to systems with a rational transfer function. In this work, we also define various grades of negative imaginary systems and aim to provide a unitary view of the different notions that have appeared so far in the literature within the framework of positive real and in the more recent theory of negative imaginary systems, and to show how these notions are characterized and linked to each other
Flight Control of a Quadrotor Vehicle Subsequent to a Rotor Failure
No full textIn this paper, the problemof designingacontrol lawincase ofrotor failure inquadrotor vehiclesis addressed. First, a nonlinear mathematical model for a quadrotor vehicle is derived, which includes translational and rotational dynamics. Then a robust feedback linearization controller isdeveloped, which sacrifices the controllability ofthe yaw state due to rotor failure to linearize the closed-loop system around a working point, where roll and pitch angles are zero and the angular speed around the vertical axis is a nonzero constant. An H∞ loop shaping technique is adopted to achieve regulationofthese variables around the chosen working point. Finally,anouter loopisproposed for achieving control of the linear displacement under the assumption of small angles approximation for the pitch and roll angles. The proposed control strategy allows the vehicle to use the remaining three functional rotors to enter a constant angular speed around its vertical axis, granting stability and representing an effective way to deal with a rotor failure in quadrotor vehicles
Douglas Alexander Stewart, poet, author and playwright
No full textDouglas Alexander Stewart, poet, author and playwrigh
Design of Robust Drag-Free Controllers with Given Structure
No full textIn this paper the problem of designing a robust controller with given structure for a plant describing a drag-free
satellite is addressed. From recent experiences in drag-free control design we first derive an uncertain plant set
representative of many drag-free missions with nonspherical test masses. The design plant is uncertain and a
performance requirement is imposed on the absolute acceleration of the test mass along a measurement axis. The
v-gap metric is first used to derive a simplified uncertain design plant. Then the main performance requirement is
broken down into requirements on the uncertain closed loop behavior of the simplified system. The fulfillment of this
new set of requirements guarantees robust achievement of the overall system goal. Then optimal single-input–singleoutput
controllers are designed that robustly achieve the desired level of performance. The method proposed allows
one to properly account for the uncertainties in the system retaining the decentralized structure of the controller
suggested by the peculiar features of the design plant
Incorporating smoothness into weight optimization for H∞ loop-shaping design
No full textSmoothness constraints are formulated for weights in H∞ loop-shaping design in order to ensure smooth variations in their magnitude response. Smoothness in the magnitude response of weights prevents the cancelation of lightly damped poles/zeros of the plant when the shaped plant is formed by cascading the nominal plant with the weights. It also allows fitting by low-order transfer functions when the smooth variations are computed point-wise in frequency. Gradients of weights, expressed in dB/decade, are used to formulate the smoothness constraints in LMI form as additional constraints to those on the singular values and condition numbers of weights in [Lanzon, 2005, Weight optimization in H∞ loop-shaping, Automatica, 41(1): 1018-1029]. The resulting solution algorithm maximizes the robust stability margin while simultaneously synthesizing smooth weights and a stabilizing controller subject to the shaped plant lying within a specified region that depicts the closed-loop design requirements. © 2010 IEEE
Author inscription in William Hazlitt, essayist and critic; selections from his writings, with a memoir, biographical and critical by Alexander Ireland
No full textAuthor's gift inscription, "To W. C. Hazlitt Esq with kind regards, from Alexr Ireland," with tipped-in review of the book.ASU Library edition has inscription from Ireland to Hazlitt [a child of William Hazlitt?].
Hazlitt , William, 1778-1830.
Ireland, Alexander, 1810-1894
A Feedback Linearization Approach to Fault Tolerance in Quadrotor Vehicles
No full textIn this paper the control problem of a quadrotor vehicle experiencing a rotor failure is investigated. First we derive a nonlinear mathematical model for the quadrotor including both translational and rotational drag terms. Then we use a feedback linearization approach to design a controller whose task is to make the vehicle enter a constant angular velocity spin around its vertical axis, while retaining zero angular velocities around the other axis. These conditions can be exploited to design a second control loop, which is used to perform trajectory following. The proposed double control loop architecture allows the vehicle to perform both trajectory and roll/pitch control when a rotor failure is present
The Author of the Alexander Romance
No full textThis paper, which is based on a portion of the introduction of the author’s edition of Il Romanzo di Alessandro (Mondadori: Fondazione Valla 2007), surveys the generic components of the Alexander Romance in an attempt to arrive at a definition of the work. The argument builds on Merkelbach’s categorisation of elements and uses Fusillo’s insight into the novel as an ‘encyclopaedic genre’ to propose that ‘historical novel’ is not, as Hägg contended, a misnomer for the work. The main components I discuss are: ‘life’; praxeis; chreiai; Cynic elements, including choliambic poetry and utopian perspectives; and the Egyptian aspects of the narrative. A concluding jeu d’esprit offers a characterisation of the putative author, his antecedents and his process of composition.Richard Stoneman was for 25 years editor for classics at Croom Helm and then Routledge. In 1997 he was appointed an Honorary Fellow in the department of classics, University of Exeter. After retiring from publishing in 2006 he has been pursuing his researches on the Alexander legends and teaching a course on the subject at Exeter. His Penguin translation of the Alexander Romance was published in 1991, and a volume of translated Legends of Alexander the Great appeared from Everyman in 1994. Also in 1994 he co-edited Greek Fiction with John Morgan. His edition of the Greek recensions of the Alexander Romance was published (volume I) by the Fondazione Valla in 2007 – volumes II and III will follow over the next few years – and his Alexander the Great: A Life in Legend appeared from Yale University Press in spring 2008. He is the author of a number of other books on Greek history and travel, and is writing a book on oracles
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