1,720,976 research outputs found
Ceramics for chemical sensing
No full textMany types of sensors have been developed to detect chemical species in the gas phase. These include optical based on color change or fluoresence, surface acoustic wave (SAW) devices, electrochemical, chemoresistive/semiconductive, field effect transistors (FET), metal-insulator-semiconductor (MIS) diode devices, and many other. Among these, resistive type sensors based on ceramic oxides are particularly attractive because of their low cost, wide range of applications and potential for use in electronic nose. This article focuses mainly on the resistive/semiconductive, especially the surface conductive ceramic oxide type gas sensors. The main emphasis is on the basic principles involving gas-solid reactions. Also discussed are selected applications with an emphasis on sensor design issues. Since SnO2 can be used as a model system for oxide-based sensors, most of the discussions focuses on this system, though other systems are occasionally highlighted illustrating recent developments. (C) 2003 Kluwer Academic Publishers.Collaboration of Dr. Prabir Dutta and Dr. Bruce Patton on the selective CO sensor and sensor array work is acknowledged. Technical comments from Joe Trimbol and Dr. Ramamoorthy on the manuscript are greatly appreciated
Potentiometric CO2 gas sensor with lithium phosphorous oxynitride electrolyte
No full textPotentiometric cell, Au/LiCoO2 5 m/o Co3O4/Li2.88PO3.73N0.14/Li2CO3/Au, has been fabricated and investigated for monitoring CO2 gas. A LiCoO2-CO3O4 mixture was used as the solid-state reference electrode instead of a reference gas. The idea is to keep the lithium activity constant on the reference side using thermodynamic equilibrium at a given temperature. The thermodynamic stability of the reference electrode was studied from the phase stability diagram of Li-Co-C-O system. The Gibb's free energy of formation of LiCoO2 Was estimated at 500 degreesC from the measured value of the cell emf. The sensors showed good reversibility and fast response toward changing CO2 concentrations from 200 to 3000 ppm. The emf values were found to follow a logarithmic Nernstian behavior in the 400-500 degreesC temperature range. CH4 gas did not show any interference effect. Humidity and CO gas decreased the emf values of the sensor slightly. NO and NO2 gases affect this sensor significantly at low temperatures. However, increased operating temperature seems to reduce the interference. (C) 2001 Elsevier Science B.V. All rights reserved.This work was supported by a grant from the National Science Foundation (EEC-9523358) with matching support from the State of Ohio and an Industrial Consortium
Ceramic electrolytes and electrochemical sensors
No full textThe electrochemical method involving solid electrolytes has been known as a selective and an accurate way of sensing chemical species in the environment and even in liquid metal for some time. The most successful among the electrochemical sensors are the emission control sensor (lambda-sensor) for the automobile engine and the oxygen sensor used in steelmaking, both made of stabilized zirconia. This article presents an overview of basic principles of various types of electrochemical sensors including active (potentiometric) and passive (amperometric) sensors. Recent advances in oxygen (O-2), carbon dioxide (CO2) and hydrogen (H-2) sensors are also presented. (C) 2003 Kluwer Academic Publishers
Selective gas detection with catalytic filter
No full textSelectivity to a specific gas can be achieved by depositing catalytic filter layer over the SnO2 sensing element. Two kinds of filter materials are used: intrinsic Nb2O5 and n-type semiconducting SnO2 doped with Pt. Using a filter layer, hydrocarbon sensor and alcohol sensor with excellent selectivity were made. Pt doped SnO2 filter for hydrocarbon sensor gives negligible response to the interfering gases such as ethylalcohol and cigarette smoke. On the other hand, Nb2O5 filter exhibits small interference to breath and propane gas for the detection of alcohol gas. (C) 2002 Published by Elsevier Science B.V
The origin of oxygen dependence in a potentiometric CO(2) sensor with Li-ion conducting electrolytes
No full textWhen the electrochemical cell arrangement of type III, O(2), CO(2), Au, Li(2)CO(3)\Li(+) conductor\O(2), reference (a(Li2O) = constant) is used to measure the CO(2) concentration in air, the emf should depend only on the logarithmic concentration of CO(2). In reality, however, the sensor response is also affected by the oxygen present in the environment. The oxygen dependence of the CO(2) sensing electrochemical cell originates from an influence of electronic conduction in the electrolyte. The theoretical change of emf with oxygen pressure, which is predicted from the modified emf-equation for the electrochemical cell with a mixed conducting electrolyte, agrees well with the measured emf change. (C) 2002 Elsevier Science B.V. All rights reserved.The authors are very grateful to John Howarter for his assistance in experiments as well as to Dr. Rapp (Emeritus Professor) for critical reading of the manuscript. The work was supported by NSF through CISM and a Korean Research Foundation Grant
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
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