1,720,988 research outputs found
IDENTIFICATION AND SIGNIFICANCE OF THE FIRST STRUCTURAL MODES OFVIBRATION OF TWO WHEELED VEHICLES
No full textIn motorcycles and scooters the structural modes of
vibration are important because they influence both vehicle’s
comfort and vehicle’s stability and handling. Some researchers
have shown that instabilities, which may occur when the
vehicle is running (weave and wobble), are influenced by the
modes of vibration, of the vehicle.
At the Motorcycle Dynamics Research Group of Padova
University many motorcycles have been tested with the method
of modal analysis. The results of this research highlight that the
whole motorcycle is a complex system that shows many kinds of
modes of vibration: rigid modes, in which the structural
components of the vehicle (chassis, fork, handlebars) behave as
rigid bodies and deflection is given by tires and suspensions;
local modes, in which deflection is concentrated in some subsystem
of the vehicle (e.g. handlebars) and the rest of the
motorcycle behaves as a system of rigid bodies; global modes
with relevant deflection of the whole vehicle.
This paper focuses on a specific issue, which is important
for motorcycle design: the identifications of the frequencies of
the first modes that show relevant deflection of the front fork
and swing-arm.
First, experimental equipment and testing methods are
presented and discussed. Then the modal properties (natural
frequencies, damping coefficients and modal shapes) of four
motorcycles of different categories are presented, the
characteristics of some modes are highlighted.
Finally, the paper focuses on the identification of the
frequencies that represent the borderline between rigid and
elastic behavior of front fork and swing-arm. A method that
requires the analysis of the characteristics of a small set of
frequency response functions, without carrying out a long and
expensive modal analysis of the whole vehicle, is presented. It
is based on the properties of rigid modes (variation in vibration
amplitude along a set of measurement points)
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
Scalar-tensor cosmologies without screening
Full text linkScalar-tensor theories are frequently only consistent with fifth force constraints in the presence of a screening mechanism, namely in order to suppress an otherwise unacceptably large coupling between the scalar and ordinary matter. Here we investigate precisely which subsets of Horndeski theories do not give rise to and/or require such a screening mechanism. We investigate these subsets in detail, deriving their form and discussing how they are restricted upon imposing additional bounds from the speed of gravitational waves, solar system tests and cosmological observables. Finally, we also identify what subsets of scalar-tensor theories precisely recover the predictions of standard (linearised) ΛCDM cosmologies in the quasi-static limit
On the non-linear behaviour of motorcycle shock absorbers
No full textMotorcycle shock absorbers exhibit a non-linear behaviour characterized by
hysteresis in the force–velocity diagram. The presence of hysteresis is the main obstacle in
the identification of parameters and the development of computationally efficient shock
absorber models. Gas compression, oil compressibility, mechanical compliance of chambers,
and oil inertia are the most important causes of hysteresis. This paper deals with experimental
research carried out on a twin-tube shock absorber equipped with pressure gauges in the
chambers. A physical model is developed to explain the behaviour of the shock absorber from
the measured pressures. The relevance of the various non-linear phenomena is discussed. The
friction, hydraulic, and compliance parameters are identified from the measurements. The
mathematical model fitted with the identified parameters is able to predict with accuracy the
force generated by the shock absorber
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
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