1,720,985 research outputs found
Physico-chemical characterization of combustion generated inorganic nanoparticles
No full textCombustion generated particulate matter is widely recognized to be the major pollutant in urban areas because of stationary combustor and vehicular traffic sources. Particularly the ultrafine fraction was proven to have the highest impact on human health since its ability to deeply penetrate the lung and the circulatory system and to be enriched in toxic condensable species because of the large specific surface area. Up to recent times the nanometric fraction, i.e. below 10nm, was not taken in consideration, despite it is the most toxic, because it was assumed that such small particles meet and coagulate at gas kinetic rate so that their lifetime was negligible small. Some recent results on carbonaceous nanometric particles generated in laboratory flames showed that, at high temperatures, their coagulation as well their collection efficiencies drops dramatically orders of magnitude as their size decreases below 5nm. Consequently they could escape from combustors and filters and survive in the atmosphere in a not negligible amount. Ashes and additives present in practical fuels, biomass and wastes contain a not negligible amount of metals which brought at high temperature, cause the emission of ultrafine particles. The fraction with size smaller than 10nm of such inorganic particles was not yet studied neither measured at the exhaust of combustors despite it is well known that the addition of trace amount of metals to a flame causes the formation of nanoparticles. The aim of the research activity described in this thesis is to characterize such small toxic metal nanoparticles and to verify if they could be released at the exhaust of combustion systems because their coagulation and collection efficiency, at high temperature, follow the same trend of carbonaceous nanoparticles. The thesis is composed of three main part roughly corresponding to the three year of the research activity. The first two chapters contains the background information on combustion generated particles and aerosol dynamic. The chapters two and three describe the followed experimental methodologies while the third parts contain the results and the relative discussions. Reactors consisting of flat laminar premixed flames doped with real fuels or toxic metal particles precursors were developed and successively investigated. They allow to perform spatially resolved measurements, at several residence time in flame, of incipient inorganic nanoparticles generated in a well controlled environment. Diagnostics with high sensitivity to particles of few nanometers in size were chosen to this aim. They are on-line sampling probe high resolution Differential Mobility Analysis and in- situ Laser Light Scattering. Particles thermophoretic collection for extra-situ Atomic Force Analysis was widely used too
Reactor temperature profile during autothermal methane reforming on Rh/Al2O3 catalyst by IR imagin
No full textCatalytic autothermal reforming of methane was studied over a commercial rhodium catalyst as a function of feed flow rate, feed composition and oven temperature. The process is carried out in a catalytic fixed bed reactor inserted in a tubular oven. Temperature profile of the catalyst bed was measured by IR thermography and product composition was measured with a continuous gas analyzer. The effect of water addition at fixed flow rate on catalyst temperature profile was investigated in two ways. In one case, upon water addition, an equivalent amount of nitrogen was removed from the feed in order to keep oxygen and methane concentrations constant. With this protocol nitrogen to oxygen ratio varies as a function of amount of water in the feed. In the other case, upon water addition, nitrogen, oxygen and methane were all reduced to keep total flow rate constant, thus keeping both oxygen to methane and nitrogen to oxygen ratios constant. The effect of water addition on product composition was investigated as a function of reactor thermal level, regulated by acting on oven temperature
Temperature evolution on Rh/Al2O3 catalyst during Partial Oxidation of Methane in a Reverse Flow Reactor
No full textCatalytic partial oxidation of methane was investigated in a reverse flow reactor with commercial Rh/
Al2O3 catalyst in pellets. The process is carried out in a catalytic fixed bed reactor and switching of feed
flow direction is obtained through four electrovalves synchronized in pairs. Temperature profile along the
catalyst bed was measured by fast IR thermography and product composition was measured with a continuous
gas analyzer.
Feed direction switching time, water to methane ratio and inert section length were investigated as
process parameters.
Data of catalyst bed temperature evolution during the flow cycle are presented, discussed and related
to reactor performance as a function of reverse flow switching period.
The effect of water addition to the reacting mixture on the dynamics of catalyst bed temperature evolution
is also presented
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
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