1,721,028 research outputs found
Characteristics of Particulate Emissions from Low Temperature Combustion and Renewable Fuels : Aerosol Mass Spectrometry of Refractory Carbonaceous Particles
Full text linkParticulate air pollution is one of the major causes of premature death in the world, and combustion-derived soot emissions contribute strongly to the particulate pollution to which humans are exposed. Black carbon (BC) is one such emission and denotes soot with strong light absorption in the ultraviolet to infrared spectrum. Combustion can also generate brown carbon (BrC) particles, with absorption confined to shorter wavelengths than BC and absorption Ångström exponents (AAEs) significantly higher than 1. When emitted to the atmosphere, BC and BrC can accelerate global warming by absorbing incoming solar radiation. The overall aim of this thesis is to improve the understanding of relationships between combustion conditions, physicochemical soot properties, and parameters which are of relevance for adverse health effects and climate impact.Soot emissions were studied from a miniCAST soot generator, a heavy-duty diesel engine, and from traditional and modern biomass based cook stoves. The soot particles were characterized for their optical properties, chemical composition, size, and carbon nanostructure (soot maturity). Soot formation and oxidation processes were studied by extracting particles from the cylinder of a heavy-duty diesel engine. The diesel engine was equipped with an exhaust gas recirculation system, and used either Swedish MK1 fossil diesel, a rapeseed methyl ester (RME) biodiesel, or a renewable hydrotreated vegetable oil (HVO) fuel. Immature soot was characterized by short and amorphous nanostructures, BrC absorption, high polycyclic aromatic hydrocarbon (PAH) fractions, and refractory organic carbon that partially formed pyrolytic carbon during thermal-optical analysis. Mature soot was characterized by ordered nanostructures, BC absorption, low PAH mass fractions, and mass dominated by elemental carbon. A novel methodology was introduced to investigate differences in soot maturity using a soot particle aerosol mass spectrometer (SP AMS). Mature soot, characterized by long fringe lengths, generated mainly low molecular weight carbon cluster fragments (C1-5+). In addition to C1-5+, immature soot with shorter fringe lengths produced signals from midcarbon and fullerene carbon clusters (C≥6+). The new methodology and interpretation can improve methods that use aerosol mass spectrometry for the source apportionment of combustion emissions. It can also aid in the development of new emission mitigation strategies, for example, with respect to the soot oxidation reactivity of relevance for diesel particulate filters. The results show that low temperature combustion conditions result in soot with immature characteristics, while higher temperatures result in more mature soot. The elevated AAEs and a major fraction of the BrC absorption were assigned to refractory soot components. Specifically, the analysis suggested that the progression from BrC to BC absorption as soot maturity increased was caused primarily by the growth of refractory aromatic units, which are the soot building blocks. This description of how combustion conditions may control soot properties can improve our understanding of processes related to light absorption in the atmosphere.The renewable HVO and RME fuels reduced particulate matter and BC emissions; the RME, in addition, reduced PAH emissions compared to fossil diesel. The formation of reactive oxygen species (ROS) is an important mechanism in particle-induced toxicity. The ability of soot particles to form ROS increased with increasing combustion temperatures. It was hypothesized from the analysis of soot properties that the diesel soot potential to form ROS with increasing combustion temperature in the first step increased due to more mature soot nanostructures, and in the second step due to increased oxidation and altered surface oxygen functional groups. This hypothesis can form a basis for future evaluations of drivers of soot particle toxicity that are of relevance for global air pollution problems
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
Anthropogenic influence on new particle formation in the marine boundary layer atmosphere
Full text linkThe most important parameter for estimates of the anthropogenic induced climate change is the radiative forcing. In a comparison of the earth’s radiative budget in the year 2011 relative to 1750, the intergovernmental panel on climate change concludes that the largest uncertainty in the total radiative forcing derives from aerosol particles and their ability to modify cloud properties as cloud condensation nuclei (CCN). This uncertainty may be reduced from increased knowledge of the spatial and temporal distribution of aerosol particles with CCN properties. In this project, aerosol particles formed in coastal and marine atmospheres through so called new particle formation (NPF) were analysed spatially and temporally and an assessment of the anthropogenic impact on the marine NPF was attempted. A method known as the NanoMap method was applied to infer the frequency of NPF in marine environments in the North Sea, Baltic Sea and the Mediterranean Sea. The results of the NanoMap analysis clearly identifies NPF frequently occurring in all three marine environments. The results suggested furthermore an increased probability of NPF in areas with heavy shipping. If the particles formed by the NPF grow to sizes with diameters larger than 50 nm, these may participate in the formation of clouds as CCN. To assess the anthropogenic impact on marine NPF, aerosol properties and NPF were simulated with the ADCHEM model. The input gas phase emissions to the model were emissions from anthropogenic, biogenic and natural sources. The simulations were carried out mainly over the the North Sea and the model was evaluated against the total particle volume measured in Høvsøre, Denmark. The model results were reasonably consistent with the observations. From the ADCHEM modelling results, it was concluded that anthropogenic marine emissions do influence NPF. The modelled particle size distribution at Høvsøre showed evidence of an increase in the NPF most likely as a result of anthropogenic emissions of condensable gases. However, particulate matter from shipping emissions were in some cases found to suppress the NPF. It was therefore concluded that new marine emission control legislations of sulphur-containing compounds may result in a decrease of marine NPF. If particulate emissions were also to be reduced, the result may instead be an increase of marine NPF. The ADCHEM model results were furthermore compared to the NanoMap analysis of the same period. The comparison showed that the modelled and the inferred NPF in the marine areas coincided to a large extent. The consistency between the modelled and the inferred NPF is an encouraging result and provides a first verification of the NanoMap analysis.Ville Berg Malmborg Skeppstrafiken ökar antalet nanopartiklar i atmosfären I den här studien där aerosoler, luft-partiklar, studerats i marin miljö visar resultaten att utsläpp från skeppstrafiken kan bidra till att öka antalet nanopartiklar i luften. De partiklar som studerats här är i första hand de allra minsta nanopartiklarna som bildas i atmosfären. Dessa bildas vid ungefär 1 nanometer genom nypartikelbildning (NPB) och om dessa växer kan de potentiellt få stor inverkan på klimatet och molnbildning i atmosfären. Skeppspartiklarna bildas framförallt direkt vid förbränning av fossilt bränsle och kallas primärpartiklar. Gasutsläpp från skeppstrafiken kan leda till att partiklar bildas vid ett senare tillfälle i atmosfären, så kallade sekundärpartiklar. Vid NPB bildas enbart sekundärpartiklar. NPB är en process där ett ämne i gas-fas kondenserar till flytande eller fast fas. NPB kan påverka klimatet när de små partiklarna växer till större storlekar och bildar så kallade kondensationskärnor. Kondensationskärnor är partiklar som tillåter vattenånga att kondensera vid de förhållanden som råder i atmosfären. Dessa partiklar är därför nödvändiga för bildandet av moln. Tidigare studier har visat att NPB kan bidra med 5-50 % av alla kondensationskärnor globalt sett och förändringar i NPB kan därför kraftigt påverka klimatet. För att studera den antropogena påverkan på NPB i marina miljöer tillämpades i studien två metoder. Förhållandena för NPB i den marina atmosfären över Nordsjön simulerades med hjälp av en aerosol-modell. Vidare användes en mätbaserad metod som kallas NanoMap för att påvisa var och hur ofta NPB sker i marina miljöer. Resultaten från NanoMap-studien visar att NPB är ett ganska vanligt fenomen i den marina atmosfären i både Nordsjön, Östersjön och Medelhavet. Ett viktigt resultat visar på en anmärkningsvärt hög sannolikhet för NPB i marina områden med kraftig mänsklig aktivitet. Figur 1 visar resultat från NanoMap-studien i östra Medelhavet samt inringade områden med kraftiga utsläpp från skeppstrafiken, enligt den europeiska samarbetsorganisationen EMEP. I modellstudien där NPB simulerades i Nordsjön framkom att stora antropogena utsläpp av primärpartiklar kan leda till mindre NPB. Dock visade resultaten att den sammanlagda effekten av utsläppen av både gaser och primärpartiklar från skeppstrafiken ger en ökning av NPB över hav och i kustnära miljöer. Den internationella sjöfartsorganisationen har möjlighet att reglera utsläppen från skeppstrafiken. Nya regleringar som träder i kraft den 1 januari 2015 skall minska skeppsutsläppen av svaveldioxid i Nordsjön till en tiondel av dagens värde. Enligt resultaten i denna studie kan detta leda till mindre frekvent NPB i Nordsjön. Eftersom den slutgiltiga ökningen eller minskningen i NPB kan få effekter för klimatet, då antalet kondensationskärnor i luften sannolikt kan påverkas, finns ett starkt behov av fler studier av NPB som klarlägger både antropogena och biogena källor till NPB. Handledare: Adam Kristensson, Pontus Roldin och Erik Swietlicki Examensarbete 60 hp i Fysik, 2014 Fysiska institutionen, Lunds Universite
Characteristics of Particulate Emissions from Low Temperature Combustion and Renewable Fuels [Elektronisk resurs] : Aerosol Mass Spectrometry of Refractory Carbonaceous Particles
No full textParticulate air pollution is one of the major causes of premature death in the world, and combustion-derived soot emissions contribute strongly to the particulate pollution to which humans are exposed. Black carbon (BC) is one such emission and denotes soot with strong light absorption in the ultraviolet to infrared spectrum. Combustion can also generate brown carbon (BrC) particles, with absorption confined to shorter wavelengths than BC and absorption Ångström exponents (AAEs) significantly higher than 1. When emitted to the atmosphere, BC and BrC can accelerate global warming by absorbing incoming solar radiation. The overall aim of this thesis is to improve the understanding of relationships between combustion conditions, physicochemical soot properties, and parameters which are of relevance for adverse health effects and climate impact. Soot emissions were studied from a miniCAST soot generator, a heavy-duty diesel engine, and from traditional and modern biomass based cook stoves. The soot particles were characterized for their optical properties, chemical composition, size, and carbon nanostructure (soot maturity). Soot formation and oxidation processes were studied by extracting particles from the cylinder of a heavy-duty diesel engine. The diesel engine was equipped with an exhaust gas recirculation system, and used either Swedish MK1 fossil diesel, a rapeseed methyl ester (RME) biodiesel, or a renewable hydrotreated vegetable oil (HVO) fuel. Immature soot was characterized by short and amorphous nanostructures, BrC absorption, high polycyclic aromatic hydrocarbon (PAH) fractions, and refractory organic carbon that partially formed pyrolytic carbon during thermal-optical analysis. Mature soot was characterized by ordered nanostructures, BC absorption, low PAH mass fractions, and mass dominated by elemental carbon. A novel methodology was introduced to investigate differences in soot maturity using a soot particle aerosol mass spectrometer (SP AMS). Mature soot, characterized by long fringe lengths, generated mainly low molecular weight carbon cluster fragments (C1-5+). In addition to C1-5+, immature soot with shorter fringe lengths produced signals from midcarbon and fullerene carbon clusters (C≥6+). The new methodology and interpretation can improve methods that use aerosol mass spectrometry for the source apportionment of combustion emissions. It can also aid in the development of new emission mitigation strategies, for example, with respect to the soot oxidation reactivity of relevance for diesel particulate filters. The results show that low temperature combustion conditions result in soot with immature characteristics, while higher temperatures result in more mature soot. The elevated AAEs and a major fraction of the BrC absorption were assigned to refractory soot components. Specifically, the analysis suggested that the progression from BrC to BC absorption as soot maturity increased was caused primarily by the growth of refractory aromatic units, which are the soot building blocks. This description of how combustion conditions may control soot properties can improve our understanding of processes related to light absorption in the atmosphere. The renewable HVO and RME fuels reduced particulate matter and BC emissions; the RME, in addition, reduced PAH emissions compared to fossil diesel. The formation of reactive oxygen species (ROS) is an important mechanism in particle-induced toxicity. The ability of soot particles to form ROS increased with increasing combustion temperatures. It was hypothesized from the analysis of soot properties that the diesel soot potential to form ROS with increasing combustion temperature in the first step increased due to more mature soot nanostructures, and in the second step due to increased oxidation and altered surface oxygen functional groups. This hypothesis can form a basis for future evaluations of drivers of soot particle toxicity that are of relevance for global air pollution problems
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
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