1,720,957 research outputs found
Predictions of the response of optical gas sensing systems using correlation spectroscopy
No full textFor the control of combustion systems, it is advantageous to monitor O Analyses that show predictions of the magnitude of this modulation index and the anticipated signal to noise ratio in measurements, factors which indicate the expected minimum detectable gas concentration, are presented. The expected drift of these factors with changes in measurement cell temperature and pressure are also shown
Recent measurements with Ru2+ oxygen sensors using doped sapphire crystals both as a calibration aid and an integral temperature sensor
No full textRecent measurements are presented, using an improved, real-time, all-optical sensor for simultaneous measurement of dissolved oxygen and temperature. The sensor has a small Cr3+ - doped sapphire (ruby) thermal monitoring crystal mounted at the probe tip, to which is bonded a Ru3+-based oxygen-indicator membrane. The probe may be interrogated in real-time, using, for both temperature and oxygen monitoring, the same combination of blue LED, light source, optical filter set, photomultiplier detector and digital processor. The ruby crystal also provides a fluorescent intensity reference, for possible on-line self-testing of the interrogation hardware. By examining the relative intensities from ruby and the membrane, mechanical damage, detachment or photo-bleaching of the sensing membrane may also be recognised. Recent developments of our novel, Ti3+-doped sapphire fluorescence-lifetime calibration probe are reported. These confirm that the fluorescence lifetime of the probe can be thermally controlled-in a reliable manner. This calibration probe then allows multi-point calibration of Ru3+-chemical sensors
Predicted response of optical gas sensing systems using correlation spectroscopy for combustion monitoring
No full textTo control combustion systems it is advantageous to monitor Oodulation (CoSM), where two broadband light sources are intensity modulated in anti-phase, and where the first source is coupled to the measurement sample after passing through the reference sample, whereas the second is directly-coupled. These two beams are combined in such proportions that there is no net intensity modulation, and the resulting light then passes through the measurement sample. The subsequent difference in attenuation, that light originating from each source suffers in the measurement region, results in an amplitude modulation of the beam after transmission through the measurement cell. The amplitude modulation index is indicative of the concentration of target gas present in this measurement cell.
We present analyses to show predictions of the magnitude of this modulation index and the anticipated signal to noise ratio in measurements, factors which indicate the expected minimum detectable gas concentration. Spectral absorption data of the gases is obtained from the publicly available HITRAN database. It is assumed that a junction photo-diode, as used in many fibre-based systems, is used to evaluate output light intensity. Effects of changing the pressure and temperature of gases in the reference and measurement cells have also been modelled
Theoretical modelling studies of gas sensing systems using correlation spectroscopy
No full textMonitoring the concentration of gaseous O2, CO2 and CH4 is needed for many environmental, medical and industrial applications. We model the COSM method of correlation spectroscopy, where two broadband light sources are intensity modulated in antiphase, the first being directed via the measurement cell after first passing through the reference sample, the second being more directly-coupled. The subsequent difference in fractional attenuation in the measurement cell indicates the concentration of target gas in this cell. Using data from the HITRAN database, comprehensive analyses are presented to predict the optical modulation index and the signal to noise ratio at the detector, as a function of optical filter properties, and for various gas temperatures and pressures (concentrations). The predicted detection sensitivities are presented for each gas
Correlation spectroscopy gas sensor with photonic band-gap fibre reference cell
No full textGas-filled microstructured optical fibres [1-4], in particular photonic band-gap fibres (PBGFs), have been suggested as a replacement for bulk-optic cells in optical gas sensors. However, the extended filling time required (~ hours) limits their usefulness in most real-world applications. Recently, sealed gas-filled fibres have been employed as fixed wavelength references for telecommunications [3], where filling time is no longer important.We now demonstrate the use of a sealed gas-filled PBGF as reference cell in a high-selectivity correlation spectroscopy gas sensor. The advantages of using PBGFs in this application are:- their suitability to sensing hazardous gases (only ~1 µl.m-1 of gas is required); their capability for providing long effective path lengths (because of high overlap between the guided mode and enclosed gas, and very low fibre loss: ~0.05 dB.m-1); and the ability to produce compact gas cells by simply coiling the fibre
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
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