1,720,968 research outputs found
Design of a novel PWV-Varying Arterial Simulator for biomedical applications: a preliminary study
No full textThe increasing trend of cardiovascular diseases recently led to a growing interest in evaluating methods and systems to diagnose and prevent them. Nowadays, one of the key indexes used to assess the health status of the cardiovascular tree is the Pulse Wave Velocity (PWV) which is strictly related to the mechanical and geometrical characteristics of blood vessels. It is currently measured as the ratio between the distance of two transducers located on the human body and the time the pulse takes to travel along the two chosen sites. Unfortunately, to date, the current measurement devices employed show a limited accuracy in PWV assessment, especially due to distance inaccuracy. The development of arterial simulators could potentially improve the current measurement systems accuracy by means of a better calibration. Despite the fact that many systems have been developed through time, they mainly focus on different aspects regarding the relationship between PWV and meaningful hemodynamic quantities rather than trying to provide a PWV measurement reference to test currently available devices. This results in a lack of information on the design of an in vitro experimental set-up specifically able to vary PWV according to different adjustable mechanical characteristics. In such a context, the present study aims at providing a numerical simulation, based on a previously developed mathematical model, as a next step for the design of a novel experimental set-up, constituted by an elastic tube as aortic surrogate (AS), able to simulate a desired PWV range according to different AS inner and outer pressures conditions
A novel experimental set-up for Young Modulus Assessment through Transit Time measurements in Biomedical applications
No full textYoung Modulus estimation in arteries is a relevant issue, since such parameter is characteristic of their mechanical and structural properties. It is well-known that human arteries undergo modifications due to physiological aging and/or cardiovascular pathologies resulting in Young Modulus variations through time. In literature, the validation of specific techniques for in vivo monitoring of arterial stiffness is carried out through vessel phantoms that reproduce the pressure waves propagation for different stiffness conditions. A physical model widely used in the current state of the art is based on the well-known Moens-Korteweg equation which correlates the Young Modulus to the Pulse Wave Velocity (PWV). In the present work a novel experimental set-up has been designed and tested to simulate Young Modulus variation of a natural rubber (NR) tube through the application of different tensioning states. Such variation has been estimated by transit time measurements on the pressure waves acquired through Linear Variable Differential Transformer (LVDT) sensors. The relevance of the present study lies in the possibility to simulate human vessel stiffness increase and to provide a testing device for the validation of in vivo techniques able to assess arterial stiffness
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
A preliminary study on an image analysis based method for lowest detectable signal measurements in Pulsed Wave Doppler ultrasounds
Full text linkNowadays, Doppler system performance evaluation is a widespread issue because a shared worldwide standard is still awaited. Among the recommended Doppler test parameters, the lowest detectable signal could be considered mandatory in Quality Control (QC) protocols for Pulsed Wave (PW) Doppler. Such parameter is defined as the minimum signal level that can be clearly distinguished from noise and therefore, it is considered as related to PW Doppler sensitivity. The present study focuses on proposing and validating a novel image analysis based method for the estimation of the Lowest Detectable Signal in the spectrogram image (LDSIMG), namely Automatic Doppler Sensitivity Measurement Method (ADSMM), as well as to compare its results with the outcomes retrieved from the Naked Eye Doppler Sensitivity Method (NEDSM), based on the mean judgment of three independent observers. Data have been collected from a Doppler flow phantom, through three ultrasound systems for general purpose imaging, equipped with two linear array probes each and with two configuration settings. Results are globally compatible among the proposed methods, US systems and settings. Further studies could be carried out on a higher number of US diagnostic systems, Doppler frequencies and observers, as well as with different probe and phantom models
Lowest detectable signal in medical PW doppler quality control by means of a commercial flow phantom: A case study
No full textPW Doppler Ultrasound (US) is commonly used in clinical practice for cardiovascular applications.Nowadays,theperformancesofaDoppler system are difficult to assess because a shared worldwide standard is lacking. This work aims at giving a contribution in the field, by defining a new index for PW Doppler Quality Control (QC) by using a commercial flow phantom, namely, the Lowest Detectable Signal in the spectrogram image, which scientific literature referred to as an index of PW Doppler sensitivity. A novel automatic algorithm for the estimation of such an index has been developed and validated through the results comparison with an observer judgement. Finally, a Monte Carlo Simulation has been carried out for the uncertainty analysis and robustness testing
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