1,720,959 research outputs found
On the instability tongues of the Hill equation coupled with a conservative nonlinear oscillator
Full text linkWe study the asymptotics for the lengths of the instability tongues L_N(q) of Hill equations that arise as iso-energetic linearization of two coupled oscillators around a single-mode periodic orbit. We show that for small energies, i.e. q->0, the instability tongues have the same behavior that occurs in the case of the Mathieu equation: L_N(q)=O(q^N). The result follows from a theorem which fully characterizes the class of Hill equations with the same asymptotic behavior. In addition, in some significant cases we characterize the shape of the instability tongues for small energies. Motivation of the paper stems from recent mathematical works on the theory of suspension bridges
On the Timoshenko Beam vibrating under an Obstacle Condition
No full textThe dynamic impact problem for the Timoshenko beam against
a rigid frictionless obstacle is studied.
The unknown reaction is modeled as a positive measure
with support contained in the contact set
and acting on the centroid of the beam in the vertical direction.
Three independent invariant quantities of energy type for
the free beam are derived. These quantities turn out to be
useful in the description of the impact lines, the crucial assumption
being the conservation of the local energies in order to model
the perfectly elastic impact.
The problem of extending the solution after the first influence line is considered.
The strict hyperbolicity of the system leads to a free-boundary
problem similar to a previous one studied by L. AMERIO for the
impact of two strings with different propagation velocities.
In a ``generic'' case, a necessary
and sufficient condition for the solvability of the free-boundary
problem is provided
Asymmetric invariants for a class of strictly hyperbolic systems including the Thimoshenko beam
No full textWe introduce a set of conserved quantities of energy-type for a strictly hyperbolic system of two coupled wave equations in one space dimension. The system is subject to mechanical boundary conditions. Some of these invariants are asymmetric in the sense that their defining quadratic form contains second order derivatives in only one of the unknowns. We study their independence with respect to the usual energies and characterize their sign. In many cases, our results provide sharp well-posedness and stability results. Finally, we apply some of our conservation laws to the study of a singular perturbation problem previously considered by J. Lagnese and J. L. Lions
Transfer of energy from flexural to torsional modes for the Fish-bone Suspension bridge
Full text linkWe consider a conservative coupled oscillators systems which arises as a
simplified model of the interaction of flexural and torsional modes of
vibration along the deck of the so-called fish-bone model of suspension
bridges. The elastic response of the cables is supposed to be asymptotically
linear under traction, and asymptotically constant when compressed (a
generalization of the slackening regime). We show that for vibrations of
sufficiently large amplitude, transfer of energy from flexural modes to
torsional modes may occur provided a certain condition on the parameters is
satisfied. The main result is a non-trivial extension of a theorem in an our
previous article to the case when the frequencies of the normal modes are no
more supposed to be the same. Several numerical computations of instability
diagrams for various slackening models respecting our assumptions are
presented
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
- …
