1,720,958 research outputs found
OXIDATION RATES OF A SINGLE CHAR PARTICLE IN AN ELECTRODYNAMIC BALANCE
No full textThe changes in reaction rate of a carbon char with conversion in the temperature range 500-1200 K are followed by using an electrodynamic balance (EDB). This device allows, in a temperature range wider than in other apparatus, in situ measurements of mass, diameter, density, surface area, rate of reaction, and temperature for a single, suspended submillimeter particle as the reaction takes place. A synthetic char (Spherocarb) has been used because of its low ash and volatile matter contents and its spherical shape. The results on oxidation kinetics obtained in an EDB are compared with low-temperature reaction rate data, obtained by conventional thermogravimetric apparatus on Spherocarb, and with the data obtained in an entrained-flow reactor at temperatures typical of pulverized-fuels combustors. The correlation between all the data in the temperature range 500-2300 K is examined. EDB data can be combined with entrained-flow data to depict a sharp change in reaction regime from a chemical kinetic to an internal diffusion control. A simple Thiele analysis, considering different classes of pores, yields results that suggest pores in the 100-1000 nm range are responsible for diffusional constraints that cause the kinetic data to depart from the chemical regime
MORPHOLOGICAL-CHANGES DURING OXIDATION OF A SINGLE CHAR PARTICLE
No full textThe e v o l u t i o n of pore s i z e d i s t r i b u t i o n d u r i n g t h e o x i d a t i o n of
s i n g l e Spherocarb c h a r p a r t i c l e s has been measured u n d e r c h e m i c a l
c o n t r o l l e d c o n d i t i o n s . E l e c t r o d y n a m i c a l l y l e v i t a t e d p a r t i c l e s were
heated t o r e a c t i o n t e m p e r a t u r e u s i n g a l a s e r and t h e weight and s i z e
changes m o n i t o r e d . The l a s e r h e a t i n g was i n t e r r u y p t e d a t s e l e c t e d
c o n v e r s i o n s and t h e C 0 2 a d s o r p t i o n determined at ambient c o n d i t i o n s .
A s r e a c t i o n p r o c e e d s , p a r t i c l e s a r e found t o s h r i n k , t h e macropore
volume d e c r e a s e s i n p r o p o r t i o n t o t h e t o t a l p a r t i c l e volume,
m a i n t a i n i n g a c o n s t a n t m a c r o p o r o s i t y . The micropore volume, however,
d e c r e a s e s w i t h i n c r e a s i n g c o n v e r s i o n whereas t h e n o r m a l i z e d p o r e
size d i s t r i b u t i o n remains unchanged, s u g g e s t i n g t h a t t h e
d e n s i f i c a t i o n of t h e microporous volume which l e a d s to. p a r t i c l e
s h r i n k a g e r e s u l t s from pore e l i m i n a t i o n . A t t h e same time t h e
mesopore volume i n c r e a s e s with i n c r e a s i n g c o n v e r s i o n i n d i c a t i n g t h a t
t h e mesopores play a dominant r o l e i n t h e c h a r r e a c t i o
STUDY OF ADSORPTION DESORPTION OF CONTAMINANTS ON SINGLE SOIL PARTICLES USING THE ELECTRODYNAMIC THERMOGRAVIMETRIC ANALYZER
No full textThe isothermal adsorption and desorption of organic vapors on a single soil particle was studied with the aid of the electrodynamic thermogravimetric analyzer (EDTGA). Toluene and carbon tetrachloride were tested at room temperature during their adsorption on Spherocarb, montmorillonite, and Carbopack particles. The maximum amount of either organic compound adsorbed was comparable to that required for one monolayer coverage of the particle surface area. Significant differences among various pairs of solid-organic vapor examined were identified and correlated to differences in solid pore structure and chemical affinity between the organic compound and the solid
INCINERATION OF CONTAMINATED SOILS IN AN ELECTRODYNAMIC BALANCE
No full textUnderstanding contaminant evolution from landfill soils is important in several in-situ remediation processes as well as in thermal treatment and incineration of contaminated top soils. To delineate the rate-limiting processes in the absence of interparticle effects, single surrogate soil particles are examined in this work. The adsorption-desorption characteristics of toluene and carbon tetrachloride on single, surrogate soil particles have been studied using an electrodynamic balance (EDB) under ambient conditions (P = latm; T = 298K). The EDB offers high mass sensitivity (DELTA-m approximately 10(-9)g) in the absence of external mass transfer limitations and interparticle effects. In this work, three types of solid particles, 100-170-mu-m in diameter, were examined, namely montmorillonite, a clay, and two synthetic chars, Spherocarb and Carbopack, of very different pore structures. Three different values of relative pressures, P/P(o), were tested for each liquid by changing the saturator bath temperatures. Significant differences were identified among the various solid-organic compound pairs examined in adsorption-desorption sequences in the EDB. These are strongly correlated with differences in the solid pore structures
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
- …
