1,721,021 research outputs found
Experimental Characterization of Synchronization Protocols for Instrument Wireless Interface
No full textThe architecture and operation of a wireless instrumentation bus based on the Bluetooth standard are presented together with a detailed characterization. The bus, via suitable wireless interface boards, allows measurement instruments equipped with standard RS232, IEEE488, universal serial bus, and local area network interface ports to be simply connected within the wireless area without any firmware modification. In addition, a comparison with traditional wired interface buses is carried out in terms of communication reliability and throughput with reference to some basic operating modes. Finally, the results of distance tests and a detailed evaluation of power consumption for each wireless interface module are reported. This will enable measurement system designers to evaluate the convenience of the solution for their application requirements
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
Quality assessment of VoIP services: a proposal based on the measurement of the IP Packet Delay Variation
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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
An Internet protocol packet delay variation estimator for reliable quality assessment of video-streaming services
No full textMeasurement of Internet Protocol Packet Delay Variation (IPDV) is a relevant issue in real-time video-streaming services. To assess the Quality of Service (QoS) to the end user, IPDV measures are commonly compared to conventional thresholds, whose values depend on the application requirements. However, exceeding these thresholds only for short time intervals and with relatively low repetition rates does not generally imply a significant decrease of the quality perceived by the users. Viceversa, IPDV values not exceeding the admitted threshold but very close to this value for long time intervals and characterized by relatively high repetition rates can significantly affect the quality perceived by the users. Consequently, studying the correlation between IPDV measures and some performance metrics directly related to the quality perceived by the end user is a very useful and challenging issue. Literature concerning with IPDV evaluation does not provide relevant information about the measurement procedure, such as measurement rate, way of collecting the obtained results in a single estimator, time interval during which the estimator is evaluated, and so on. The absence of these important aspects makes the comparison between IPDV measures and the aforementioned thresholds very critical, thus making even more ambiguous the evaluation of the QoS to the end user. In this framework, the aim of this paper is twofold. From one side, it aims at experimentally assessing and correlating the values that some performance metrics assume at different layers of a wide area network (WAN) supporting video-streaming applications for several values of IPDV; from the other side, it aims at deducing helpful and practical hints for designers and technicians, in order to efficiently assess and enhance the performance of a WAN supporting video streaming, in some suitable setup conditions affected by IPDV. The final goal of the research activity is to identify and fine tune an IPDV estimator able to reliably estimate and detect the objective service degradation from the user perspective. The obtained estimator should be sensitive to service degradation that disregards the user’s expectations, and at the same time, it should be insensitive to disturbs that do not cause a perceptible service degradation
On the Use of Complex Excitation Sequences for Eddy Current Testing
No full textEddy Current Testing (ECT) is a Non Destructive technique widely used in many industrial
application fields in which it is very important to detect the presence of thin defects ( generally called cracks) in
conductive materials. Features of this technique are the cost-effective implementation and the kind of retrieved
measured data that make possible estimating geometrical characteristics of a crack as position, length, width and
depth. The analysis of these characteristics allows the user to accept or discard realized components then
improving the production chain. To accomplish for this task some aspects have to be taken into account during
the measurement process. They mainly concern with the realization of suitable measurement setup and post
processing stages. As far as the measurement setup is concerned, crucial aspects are the choice of measurement
and excitation devices. As for the former, in the past years the literature deeply explored many types of
measurement probes highlighting advantages and disadvantages of different solutions. The choice of optimized
excitation devices and strategies is now interesting recent studies about Non Destructive ECT (ND-ECT):
together with common aspects as the amplitude and the frequency of the exciting signal, recently the attention
has been paid to issues as the type of signal to be adopted. In particular it has been found as the use of complex
excitation signals, meant as signals different from the sinusoidal ones and with wide frequency content, might
raise eddy current responses trying to support the measurement, detection and characterization stages when
“difficult cases” are explored (i.e. very short or annealed cracks). In this paper the authors propose an
experimental comparison of different excitation signal designed to improve the quality of experimental data
when difficult cases are experienced (such as annealed and small cracks) and consequently to obtain a more
reliable extraction of defects geometrical features
Internet Protocol Packet Delay Variation measurements in communication networks: how to evaluate measurement uncertainty?
No full textMeasurement of Quality of Service (QoS) parameters is a relevant task in communication networks. Similarly to other contexts, the measurement result has to be completed with the related uncertainty in order to provide information about the significance and reliabil- ity of the overall measurement process. This aspect is particularly crucial in communica- tion networks. In fact, the measured values of QoS parameters have often to be compared against suitable thresholds to check their compliance with required quality con- straints (QoS levels delivered to the user are generally offered for a fee) or to reliably verify the effect of new services conveyed by the network on its performance. Nevertheless, uncertainty estimation in QoS parameters measurement is still an open issue. Most literature concerning communication and computer networks test and mea- surement clearly evidences the lack of the advisable practice of uncertainty evaluation in QoS parameters measurement according to the guide for the expression of uncertainty in measurements (GUM). In addition, it is worth emphasizing that uncertainty modeling and evaluation in QoS parameters measurement are not trivial tasks because several aspects are involved in a QoS measurement process. All these aspects can be thought of as sources of measurement uncertainty, capable of significantly influencing the reliability of measurement results. The paper investigates these issues by promoting and assessing the applicability of GUM tothespecific andcriticalcontextofcommunicationandcomputernetworkstestandmea- surement. More specifically, a simple model for uncertainty evaluation in Internet Protocol Packet Delay Variation measurement is proposed: a fundamental QoS parameter in Voice over IP and real time video streaming applications. The model is based on two main con- tributions: the former accounting for the instrumental measurement uncertainty and the latter for the measurand variability. A number of tests in a simulated scenario proves the effectiveness of the proposed model. To exemplify its practical application, some experiments in a real test-bed, i.e. the local area network of the University of Cassino and Southern Lazio, are finally conducted
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