1,721,050 research outputs found
Performance analysis of continuous tracking laser Doppler vibrometry applied to rotating structures in coast-down
No full textIn this paper a performance analysis of the so-called tracking continuous scanning laser
Doppler vibrometry (TCSLDV) exploited in coast-down has been performed. This non-contact
measurement system is able to scan continuously over a rotating surface during coast-down
and to determine vibration operational deflection shapes (ODSs) and natural frequencies in
short time, i.e. the temporal extent of the coast-down. The method is based on a laser Doppler
vibrometer (LDV) whose laser beam is driven to scan continuously over the whole rotor
surface synchronously with its rotation, so that the LDV output is modulated by the structure’s
ODSs. This technique has a full-field nature that enables it to measure simultaneously the time
and spatial dependence of the vibration in a unique measurement. However, the TCSLDV
presents some criticalities in practical applications, especially when applied to rotary transient
and fast processes. In fact, if the vibration is transient and decays very fast, then the laser beam
could not have had the time to scan the complete structure surface and the modulation of the
ODS could be partial. An analytical model reproducing a representative experiment has been
developed in order to evaluate the sensitivity of results to testing conditions. The laser beam
trajectory in both the fixed and rotating reference systems has been synthesized showing its
dependence on experimental parameters as the rotation speed variation during coast-down. It
has been demonstrated the decrease in speed induces the deformation of the laser trajectory
influencing the LDV output time history, spectrum and consequently the recovered ODS
Noise source localization on washing machines by conformal array technique and near field acoustic holography
No full text
Acoustic beamforming: analysis of uncertainty and metrological performances
No full textIn this paper, the metrological performances of the acoustic beamforming technique have been investigated, and in
particular, its accuracy in estimating the acoustic power of sources and in localizing their spatial position has been
analysed.
The uncertainty of the system has been determined combining the statistical effects of input parameters uncertainty
under the basic hypothesis that the sound source can be represented as a distribution of independent monopoles. This
analysis was performed using a Type B approach based on an analytical model according to the ISO Guide of the
expression of uncertainty in measurement and subsequently using a numerical model based on Monte Carlo simulation.
Systematic errors due to deviations of input parameters (e.g. speed of sound or source–array distance), affecting output
level and spatial accuracy have been analysed. Once these inaccuracies were quantified, suggestions to minimize them were
given.
Finally a criterion to optimize focussing of the beamforming technique based on acoustic image contrast maximization
has been developed
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
Post-traumatic cluster headache: from the periphery to the central nervous system?
No full textA correlation between head trauma and cluster headache is believed to exist. We report a case of post-traumatic episodic cluster headache that fulfills the criteria of the International Classification of Headache Disorders, 2nd edition. The distinctive features of this case are: a close temporal relation between head trauma and headache onset; pain ipsilateral to the side of trauma; mild severity of trauma; episodic course well-responsive to low doses of verapamil. Given the close temporal relation between the 2 events, multiple hypotheses can be advanced about a possible role of head trauma in the pathogenesis of cluster headache
- …
