1,721,030 research outputs found
Exploiting spontaneous Raman scattering in hollow core anti-resonant and photonic bandgap fibres for simultaneous and multi-species quantitative gas sensing
No full textThe aim of the work described in this thesis is the development of a gas sensor, capable of high sensitivity and selectivity. Particularly, the requirement was for an instrument that could detect and distinguish gases in a mixture, even the ones with low concentration (e.g. 380ppm of CO2 in ambient air). This work was carried out as part of a collaborative project with IS-instruments, a company whose expertise are the design, development and manufacturing of spectrometers for remote and compact sensor applications. A key application area identified by IS-Instruments is in gas pipelines where the pressure of the gas mixture to be tested can reach 90 bar, so a further requirement on the sensor design was the potential for high pressure operation. One of the most studied and exploited spectroscopic techniques is Raman spectroscopy, based on Raman scattering. When applied to gas sensing, it can achieve real-time and simultaneous detection of single gases in a mixture. Several research groups have tested this techinque for a wide range of applications, from the industrial field, like the one Is-instruments is interested to develop, to the medical or environmental fields, like breath analysis, or pollution control (some examples can be found in references [1-7]).Raman scattering can be produced when a monochromatic beam hits matter, like a molecule in a gas. The scattered radiation might have the same frequency of the excitation radiation (Rayleigh scattering) or a shifted frequency (inelastic scattering) that may be caused by some change in the vibrational or rotational state of the molecule; when this happens, the scattered light is called Raman scattering. The energies required to produce such changes are fixed for the type of molecule under observation, meaning that every species needs a defined amount of energy to produce the vibrational or the rotational state change. The so-called Stokes and anti-Stokes Raman lines, shifted towards lower and higher frequency respectively from the excitation one, are the results of those energy changes and are species-specific. Thanks to this property, Raman spectroscopy can be used to distinguish one gas from another so it meets the requirement of specificity for the gas sensor we wanted to develop. However, Raman scattering depends on the scattering cross section of the molecule involved, which has an extremely low value for gases. For instance, considering Nitrogen at room temperature and pressure contained in a transparent cell in which a laser source of ~100 mW at 785 nm is focused (free-space setup), the order of magnitude of the Raman Stokes power is ~ 10-14 W, as the scattering cross section of N2 at 785nm is equal to 7.467 × 10-32 cm2/sr∙molecules [8]. A key limiting factor in the free-space experiment is the interaction length between the gas sample and the laser beam, which is just ~ twice the Rayleigh length of the focused beam [9].A promising solution to increase this interaction length is based on the use of hollow core photonic crystal fibres (HC-PCFs). The periodic cladding structure of these type of fibres allows the guidance in the lower refractive index hollow core. The possibility to introduce the gas under analysis into the guiding core of a HC-PCF, enables long interaction lengths between the light and the sample and a much more compact device than in a free space arrangement. The Raman signal strength (Stokes power) obtainable using this technique can be hundreds of times higher than what can be obtained in free-space [1]. Furthermore, the fibres can act like 9 probes for remote gas detection, an important requisite when it comes to environments in which it is necessary to control and detect dangerous or explosive gases, like the gas pipelines. In this thesis, we investigate the use of HC-PCFs for Raman based gas sensing and develop a sensing scheme which has the potential to meet the necessary requirements of high sensitivity, high selectivity and high-pressure operation. A key part of this work is the comparison of the performance of two different types of HC-PCFs in our sensing scheme.We will expose the results of experiments based in the use of the so-called photonic bandgap fibres (PBGFs), in which the photonic bandgap created by the periodic cladding is used to guide the light [10, 11]. Furthermore, for the first time we report the use of the so-called anti-resonant (or Kagome) HC-PCF, a type of hollow core fibre never used before in spontaneous Raman spectroscopy [12]. The motivation behind this comparison is that these two fibres types have different physical and optical properties which may or may not provide advantages for Raman gas sensing. For example, the guidance mechanism in anti-resonant fibres, allows for wider transmission windows than the ones achievable in PBGFs which has potential advantages in enabling simultaneous detection of gas species with widely different Raman shifts. In addition, there is more flexibility in the choice of the core size in an anti-resonant fibre and as larger cores can lead to faster loading of samples this can be important in the final application. Being part of a research group in which the hollow core fibres are constantly designed and fabricated, we have been able to employ custom-made fibres to well suit the requirements of the project.The report is divided in three sections plus the conclusion. In chapter 1, the fundamental theory behind Raman Effect and the hollow core fibres will be discussed. Moreover, the chapter will present a comparison between different spectroscopy techniques for gas sensing and the advantages of Raman spectroscopy based on hollow core fibres. In chapter 2, the setup used for the experiments and the reasons behind the choice of every component and parameter will be explained. Finally, the last chapter (chapter 3) will expose and analyse the results of the experiments that have been completed so far
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
Pappa Maria
No full text1 φωτογραφία : ασπρόμ.; 8,5Χ6εκ.Παππά Μαρία, μητέρα του Χρήστου Λυμούση, απεβίωσε στις 17 Ιουνίου 1964
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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