1,720,990 research outputs found
Disturbance attenuation in nonlinear perturbed diffusion processes by sampled-in-space sensing and actuation
No full textA diffusion equation perturbed by uncertain disturbances
of both matching and unmatching nature is considered.
The problem of disturbance attenuation is tackled by
means of the sliding-mode control approach. It is assumed that
only a finite number of pointwise sensing and actuation devices,
suitably located in an equi-spaced manner along the spatial
domain of interest, is available. We show that an arbitrary level
of the unmatching disturbance attenuation can be achieved by
employing a sufficiently high number of sensing and actuation
devices. We also show that matching disturbances entering the
control channels can be fully rejected by the proposed design
On multi-input chattering-free second order sliding mode control
No full textA solution to the problem of eliminating the chattering effect, which is always associated with practical implementations of variable structure control, is presented in this paper with reference to a class of uncertain multi-input nonlinear systems. The solution procedure relies on the application of an original control approach capable of enforcing a second-order sliding mode (i,e., a sliding regime on a surface s[x(t)] = 0 in the system state space, with (s) over dot [x(t)] identically equal to zero, a regime enforced by a control signal depending on s[x(t)], but directly acting only on s[m(t)]). Such an approach, in its original formulation, only applies to single-input nonlinear systems with particular types of uncertainties. In the present paper, its validity is extended to multi-input nonlinear systems characterized by uncertainties of more general nature, covering a wide class of real processes
Second Order Chattering-Free Sliding Mode Control for some Classes of Multi-Input Uncertain Nonlinear Systems
No full textSliding Mode Optimization in Robot Dynamics with LPV Controller Design
Full text linkThis letter extends previous results on constrained optimization control problems of uncertain robot systems based on sliding modes generation. An equivalent linear parameter varying (LPV) state-space representation of the nonlinear robot model is considered to design a stabilizing state-feedback control law by solving linear matrix inequalities (LMI) with structural constraints. The finite-time regulation of the state trajectory to a desired reference, while minimizing a pre-specified cost function with state constraints, is then solved by a sliding mode approach relying on the considered parameter-dependent structure of the robot system. Stability conditions of the proposed approach are provided, and a realistic numerical example verifies the effectiveness of the proposed technique
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
