1,721,372 research outputs found
Review of methods of optical gas detection by direct optical spectroscopy with emphasis on correlation spectroscopy
No full textThis paper reviews the development of optical gas sensors, starting with an initial emphasis on optical-fibre remoted techniques and finishing with a particular focus on our own group's work on highly selective methods using correlation spectroscopy. This latter section includes extensive theoretical modelling of a correlation spectroscopy method, and compares theory with practice for a CO2 sensor. It should be mentioned, in passing that, there are many remote free-space laser methods involving LIDAR. One of the most useful is DIAL (DIfferential Absorption LIDAR), where a dual-wavelength laser pulse is directed into the atmosphere and the time-varying back-scattered signatures from light at each of the two wavelengths are compared to determine the differential absorption as a function of distance along the path. A non-linear method called CARS (Coherent Anti-Stokes Raman Scattering) has also been used. These methods, and also several other more complex alternatives using multi-photon processes, are unsuitable for use with optical fibres. Also a full description of these would fill a chapter in its own right, so the focus of this review will be restricted to direct absorption methods
Review of methods of optical gas detection by direct optical spectroscopy with emphasis on correlation spectroscopy
No full textGas sensors are of importance for a variety of environmental, industrial, medical, scientific and even domestic applications. The gas may be, for example, hazardous to human health, an atmospheric pollutant, or important, in terms of its concentration, for an industrial or medical process. Apart from systems merely providing an alarm signal, it is frequently required to obtain accurate real-time measurements of the concentration of a particular target gas, often in a mixture of other gases
Experimental investigation of precoding for EM exposure reduction
Full text linkReduction of human exposure to electromagnetic (EM) radiation from communications devices without compromising link quality is of importance as people spend more and more time using devices with wireless connectivity. This paper considers the idea of designing a low complexity baseband precoder to reduce user EM exposure for the user scenario of a laptop making an uplink connection to an access point terminal in a picocell environment. The design of the precoder is supported by channel sounding measurements and a ten-fold reduction in user exposure is indicated
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
Model to predict the response of correlation spectroscopy gas detection systems for CH<sub>4</sub>
No full textWe present a comprehensive model of a correlation spectroscopy gas sensor for CH4. Response and performance are predicted for typical fibre optic-coupled systems
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
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
Model to predict the response of a correlation spectroscopy system for the detection of oxygen gas
No full textWe present the first comprehensive model for the detection of a gas by absorption based correlation spectroscopy, and show the practically useful results obtained. Predictions of sensor response for a fibre-optic-coupled O detection limits have been derived
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
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