1,720,959 research outputs found
On the reachability and weak reachability of single-input positive switched systems
No full textAbstract—In the first part of the paper the reachability
property for positive switched systems which commute among n
single-input n-dimensional systems is investigated. By referring
to a (hard to check) necessary and sufficient condition for
the reachability of this class of systems [8], we develop new
algebraic tools which allow us to derive sufficient reachability
conditions which are easy to test. In the second part of the paper
weak reachability is introduced and a sufficient condition for
this property to hold is provided
An algebraic approach to the structural properties of switched positive systems
No full textSwitched positive systems deserve investigation both for theoretical reasons
and for practical applications. Indeed, switching among different system
models naturally arises as a way to mathematically formalize the fact that
the system laws change under different operating conditions. This is true,
e.g., when resorting to compartmental models; each of them may satisfactorily
capture the behavior of a physiological system only under specific working
conditions, so when these conditions change the system model has to switch to a different structure. For instance, the insulin-sugar metabolism is captured
by two different compartmental models: one valid in steady-state and the
other which is suitable to describe the evolution under perturbed conditions,
following an oral assumption or an intravenous injection.
The aim of this paper is to define controllability and reachability properties
for continuous time switched positive systems, and to provide some preliminary
characterizations of these properties
Recent advances on the reachability of single-input positive switched systems
No full textIn this paper the reachability property for singleinput
continuous-time positive switched systems is investigated.
By referring to an existing (and hard to check) characterization
of the reachability of the class of positive switched systems
which commute among n single-input n-dimensional systems
[9], we develop new algebraic tools which allow us to derive
sufficient reachability conditions which are easier to evaluate
Zero patterns and dominant modes of the state evolutions of autonomous continuous-time positive systems
No full textAbstract—In this paper, the zero pattern properties and
the asymptotic evolution of the trajectories of an autonomous
continuous-time positive system are investigated. To this end, a
normal form for the exponential of a Metzler matrix is provided,
and the concept of “echelon basis” is introduced. By making
use of these two ingredients, the dominant mode of each single
block appearing in the normal form of the exponential matrix is
determined. As a result, the zero pattern as well as the dominant
mode of every state evolution, depending on the zero pattern
of the initial state, can be easily inferred
On the reachability properties of continuous-time positive switched systems
No full textIn this paper we address the reachability of
continuous-time positive switched systems. In detail, we first
provide the reachability definition and a necessary condition
for its existence. We then fully explore the “pattern reachability”
problem, namely the problem of reaching, for every
subset S of {1, 2, . . . , n}, at least one nonnegative state vector
whose nonzero entries are exactly those corresponding to the
elements of S. Finally, for the class of n-dimensional singleinput
systems switching among n subsystems, necessary and
sufficient conditions for reachability are given
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
Variations on the Author
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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