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Nuovi approcci spettroscopici per l'analisi di miscele gassose complesse
No full textL'analisi di campioni di gas complesse riveste un aspetto cruciale nel campo della sensoristica, con numerose applicazioni, tra cui il monitoraggio ambientale in aree industriali e urbane, la rilevazione di perdite, l'analisi del gas naturale per l'esplorazione petrolifera e applicazioni biomediche. La complessità di questi campioni di gas deriva dall'interferenza e dall'interazione tra le diverse specie gassose nella miscela, che possono influenzare il rilevamento dell'analita target. A causa della coesistenza di molteplici analiti, ottenere alta selettività e sensibilità nelle miscele di gas complesse può rappresentare una sfida non banale. Inoltre, queste applicazioni richiedono monitoraggio in tempo reale e sul campo, oltre a un elevato livello di compattezza e portabilità.
Le tecnologie attuali includono la gascromatografia, i sensori elettrochimici, i sensori a semiconduttore e i sensori ottici, ciascuno dei quali offre vantaggi differenti in base al tipo di gas monitorato, all’ambiente operativo e all’applicazione specifica. La gascromatografia può fornire un'analisi sensibile e selettiva delle miscele di gas complesse, ma non offre una risposta in tempo reale a causa della necessità di preparare i campioni; inoltre, è generalmente costosa e inadatta per misurazioni sul campo. I sensori a semiconduttore e quelli elettrochimici possono offrire un'elevata compattezza, monitoraggio in tempo reale e alta sensibilità, ma sono suscettibili a problemi come isteresi, saturazione e deriva, con prestazioni significativamente influenzate da fattori ambientali come temperatura e umidità. Le tecniche ottiche che utilizzano sorgenti laser consentono un rilevamento altamente selettivo e sensibile di molecole/composti all'interno di miscele contenenti potenziali interferenti su un ampio range di concentrazioni.
Le tecniche ottiche possono essere classificate in due principali categorie, in base ai principi fisici che regolano il processo di rilevamento. Nella spettroscopia di assorbimento diretto, la lunghezza d'onda di emissione della sorgente laser è scelta in base alle linee di assorbimento tipiche di una specie gassosa. Questo si traduce in una riduzione della intensità del segnale misurato, dipendente dalla lunghezza d'onda a causa dell'assorbimento, rilevabile da un fotorilevatore. La spettroscopia di assorbimento diretto basata sull' utilizzo di laser (TDLAS) è una delle tecniche più impiegate per misurare la concentrazione di specie gassose e ricostruire il loro profilo di assorbimento.
Al contrario, le tecniche di assorbimento indiretto si basano sul rilevamento di effetti non radiativi derivanti dall'assorbimento della luce, come l'effetto fotoacustico o fototermico. Il principio base della spettroscopia fotoacustica (PAS) consiste nel rilevare onde sonore indotte dal rilassamento non radiativo del gas come conseguenza dell'assorbimento di luce modulata nell'infrarosso. Un trasduttore viene utilizzato per convertire l'onda acustica foto-indotta in un segnale elettrico proporzionale alla concentrazione della specie assorbente.
I diapason in quarzo (QTF) sono stati impiegati sia come trasduttori nella spettroscopia fotoacustica (QEPAS) sia recentemente come fotorilevatori nella TDLAS (LITES).
L'attività di ricerca svolta durante il mio dottorato si è concentrata sullo sviluppo di sensori basati su QEPAS e LITES per l'analisi di miscele di gas complesse, quali metano e i suoi isotopi, acido solfidrico e idrogeno. In ciascun lavoro, è stato esaminato a fondo lo scenario spettrale, e si è selezionata un range spettrale adeguato a rilevare la molecola target minimizzando le interferenze da parte di altre specie gassose. Inoltre, per sensori basati sulla tecnica QEPAS, sono state attentamente studiate le non-linearità derivanti da correlazioni non spettrali tra le specie gassose presenti nella miscela.The analysis of complex gas samples is a major issue in the field of sensing technology, with many applications including environmental monitoring in industrial and urban areas, leaks detection , natural gas analysis for petroleum exploration and biomedical applications. Complexity of these gas sample arises from the interference and interaction between the several gas species in the mixture, which could affect the detection of the target analyte. Due to the coexistence of multiple analytes, high selectivity and sensitivity in complex gas mixtures can represent a non-trivial task. Moreover, these application demand for real-time and in-situ operation as well as a high level of compactness and portability.
The state-of-the-art technologies include gas chromatography, electrochemical sensors, semiconductor sensors and optical sensors each offering distinct advantages based on the type of gas being monitored, the operational environment and the specific application. Gas chromatography can provide a sensitive and selective analysis of complex gas mixtures, but do not offer real-time response due to the need for sample preparation, is generally expensive and not suitable for on-field measurements. Semiconductor and electrochemical sensors can provide high compactness, real-time monitoring and high sensitivity. However, they are susceptible to issues like hysteresis, saturation, and drift, with their performance being significantly influenced by environmental factors, including temperature and humidity. Gas spectroscopy utilizing laser sources is a reliable technique that enables highly selective and sensitive detection of target molecules/compounds within mixtures containing several potential interferents in a wide concentration range.
Optical detection techniques can be classified into two main categories, based on the physical principles governing the detection process. In direct absorption spectroscopy the emission wavelength of the laser source is tuned along the typical absorption lines of a gas species. This results in a wavelength dependent reduction in the measured signal intensity due to absorption, which can be detected by a suitable photodetector. Tunable diode laser absorption spectroscopy (TDLAS) is one of the most employed techniques to measure the concentration of gas species and reconstruct their absorption profile. A basic TDLAS setup consists of a tunable diode laser light source , an absorbing sample and a photodetector.
Conversely, the indirect absorption techniques rely on the detection of non-radiative effects resulting from light absorption, e.g. photoacoustic or photothermal effect. Photoacoustic spectroscopy (PAS) basic principle consists in detecting sound waves induced by gas non-radiative energy relaxation as consequence of infrared modulated light absorption. A transducer is used to convert the photo-induced acoustic wave in an electrical signal proportional to the concentration of the absorbing species.
Quartz tuning forks (QTFs) have been employed both as sharply resonant transducers for PAS, namely quartz-enhanced photoacoustic spectroscopy (QEPAS) and recently as infrared detector in TDLAS, namely light induced thermoelastic spectroscopy (LITES).The research activity carried out during my Ph.D. was focused on the development of both QEPAS and LITES-based sensors for the analysis of complex gas mixtures, e.g., hydrogen sulfide, methane and its isotopologues, and hydrogen. In each work, the spectral scenario was thoroughly analysed, and an appropriate spectral range was selected to detect the target molecule while minimizing interference from other gas species. Additionally, for the QEPAS-based sensor, the non-linearities arising from non-spectral cross-correlations between the gas species in the mixture were carefully investigated
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
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
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
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