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71.
Vladimir Macias Israel Becerra Edgar Martinez Rafael Murrieta-Cid Hector M. Becerrra 《Journal of The Franklin Institute》2021,358(9):4761-4792
In this paper, we propose a feedback-based control approach to execute the time optimal motion trajectories for a differential drive robot. These trajectories are composed of straight lines and rotations in place. We show that the evolution of the position of a single landmark over time, in a local reference frame, makes it possible to track a prescribed time-optimal robot’s trajectory, based on feedback of the landmark’s position. We also show that the closed-loop system is an exponentially stable one with a nonvanishing perturbation, and that globally uniformly ultimately boundedness of the tracking errors can be achieved. The two main results of this work are: 1) Our approach leverages visual servo control type of methods with tools from optimal control for executing time-optimal trajectories in the state space based on feedback information. 2) The approach is able to work with the minimum number of landmarks–only one–this represents a necessary and sufficientcondition for landmark-based navigation. Experiments in a physical robot, a nonholonomic differential drive system equipped with an omnidirectional laser sensor, are shown, which validate the proposed theoretical modelling. 相似文献
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The paper considers planar interception engagements against maneuverable targets using a linearized kinematic model with constant velocities. Both the interceptor and the target have bounded controls and first-order linear dynamics. Due to the linearization, the duration of the interception is prescribed. The target dynamics is fixed, but the interceptor has variable structure dynamics, switching from one mode to another once during the engagement. For such engagements the capture zone of a given linear feedback control is constructed. Numerical examples demonstrate that proper change of the interceptor dynamic mode leads to an enlarged capture zone. 相似文献
76.
Vladimir Sobkin 《International Journal of Inclusive Education》2013,17(2-3):293-303
The socioeconomic changes that took place in Russia in the 1990s defined both the ideology and practice of educational reform. The answer to the question: ‘Was the educational system democratized?’, is of key importance in evaluating the social outcomes of the educational reforms. In this paper, I discuss three aspects of the problem of inequality in school education in Russia: (a) social stratification and institutional changes in the school system; (b) regional features and inequality in education; and (c) the school as the site of social differentiation. The first and second aspects are concerned with macro tendencies, and I use official statistical data in discussing these. The third aspect has a socio-psychological orientation, and here I draw on material from research undertaken by the Centre of Sociology of Education in the Russian Academy of Education. 相似文献
77.
Martin Ebon Lawrence C. Soley John S. Nichols Olive Renier Vladimir Rubinstein Tran Van Dinh 《Communication Booknotes Quarterly》2013,44(5-6):44-45
THE SOVIET PROPAGANDA MACHINE by Martin Ebon (New York: McGraw-Hill, 1987—$22.95) CLANDESTINE RADIO BROADCASTING: A STUDY OF REVOLUTIONARY AND COUNTERREVOLUTIONARY ELECTRONIC COMMUNICATION by Lawrence C. Soley and John S. Nichols (New York: Praeger, 1987—$47.95) ASSIGNED TO LISTEN: THE EVESHAM EXPERIENCE, 1939–43 by Olive Renier and Vladimir Rubinstein (London: BBC External Services, 1986—L3.95, paper, plus 25% more to cover postage and packing outside of the U.K.) INDEPENDENCE, LIBERATION, REVOLUTION: AN APPROACH TO THE UNDERSTANDING OF THE THIRD WORLD by Tran Van Dinh (Norwood, NJ: Ablex, 1987—$37.50) FOLLOWING THE FOOTPRINTS: PROTECTING FILM AND TV RIGHTS IN THE WORLD SATELLITE MARKETPLACE edited by Charles Firestone and Daniel Brenner (Communications Law Program, UCLA School of Law, University of California, Los Angeles 90024—price not given, paper) 相似文献
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Robinson John P.; Andreyenkov Vladimir; Slepenkov Ivan; Kurbanov Erjan; Davidchinkova Lena 《Int. Journal of Public Opinion Research》1992,4(4):335-345
Dramatic changes in the perceptions of problems in the SovietUnion and in the USA are shown among samples of Soviet youthstudied over a three-year period, from 1988 to 1991. Growingdisillusionment with worsening domestic conditions was mirroredby a growing, unrealistic appreciation of life in the USA, reflectinga painful search for a new national identity. 相似文献
80.
How Much Does a Shared Name Make Things Similar? Linguistic Labels, Similarity, and the Development of Inductive Inference 总被引:6,自引:0,他引:6
This article examines the development of inductive generalization, and presents a model of young children's induction and two experiments testing the model. The model specifies contribution of linguistic labels and perceptual similarity to young children's induction and predicts a correspondence between similarity judgment and induction of young children. In Experiment 1, 4- to 5-year-olds, 7- to 8-year-olds, and 11- to 12-year-olds were presented with triads of schematic faces (a Target and two Test stimuli), which varied in perceptual similarity, with one of the Test stimuli sharing a linguistic label with the Target, and another having a different label. Participants were taught an unobservable biological property about the Target and asked to generalize the property to one of the Test stimuli. Although 4- to 5-year-olds' proportions of label-based inductive generalizations varied with the degree of perceptual similarity among the compared stimuli, 11- to 12-year-olds relied exclusively on labels, and 7- to 8-year-olds appeared to be a transitional group. In Experiment 2 these findings were replicated using naturalistic stimuli (i.e., photographs of animals), with perceptual similarity manipulated by "morphing" naturalistic pictures into each other in a fixed number of steps. Overall results support predictions of the model and point to a developmental shift from treating linguistic labels as an attribute contributing to similarity to treating them as markers of a common category-a shift that appears to occur between 8 and 11 years of age. 相似文献