1,720,962 research outputs found
Spatial variability of leachate tables, leachate composition and hydraulic conductivity in a landfill stabilized by in situ aeration
No full textWithin the framework of the project iDS, four compartments of the Dutch landfill Braambergen have been treated by in-situ aeration since 2017. The aeration infrastructure comprises 230 wells with a spacing of 15 to 20 m, distributed over an area of around 10 ha, intercepting a waste body of 1.2 × 106 t of contaminated soils, soil treatment residues, bottom ashes and construction and demolition waste. The wells, used in an alternating fashion for air injection and gas extraction, can also be used to monitor water tables within the waste body. In order to describe the spatial variability of waste hydraulics, design a larger scale leachate pumping test and, eventually, support model predictions of the site’s water balance and emission potential, analyses of leachate composition and pumping tests on individual wells have been conducted. The spatial variability of leachate quality and water tables is very high. High differences prevail not only across the compartments, but also between directly neighbouring wells. Both the small scale differences in leachate tables as well as in leachate quality indicate a spatial pattern of zones with low horizontal connectivity within the waste body. Recovery rates of drawdown in the wells yielded preliminary estimates of horizontal waste hydraulic conductivity in the order of 1*10-7 to 6*10-4 m/s
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
Investigation of the Relationship between Gas Production and Sediment Properties in River Environments
No full textIn riverine environments under anaerobic conditions, methane and carbon dioxide are produced as a result of biological activity, causing degradation of organic matter. Under aerobic conditions, the bacteria present degrade the organic matter, whereby the concentration of dissolved oxygen may be lowered. Thus, issues experienced in the investigation area (the Port of Hamburg) are hindered construction operations, increased greenhouse gas emissions and the echo-sounding equipment used for sonic-depth finding for ships possibly showing an erroneous depth. The purpose of this investigation was to find out how gas generation and respiration relate to the basic sediment properties and what mathematical model with the highest accuracy can predict gas generation and respiration (separately), while maintaining within a given (precision) error (1%). Gas pressure was measured at the TU Delft for an incubation period of 100 days, which was later used to calculate the gas generation (mg C/g DW) with the use of the ideal gas law. Statistical methods used to analyze the data were: Pearson’s correlation coefficient, multiple regression analysis, adjusted coefficient of determination and error analysis. The results show that both gas generation and respiration have the highest Pearson’s correlation coefficient with TOC. Furthermore, in the multiple linear regression, gas generation had the highest coefficient of determination in a regression between TOC as the primary parameter and iron content (in solids) as the secondary parameter (푅2=0.91495). For respiration, it was displayed in a regression between TOC (as the primary parameter) and copper content in the solids (as the secondary parameter) (푅2=0.881). This concludes that organic matter degradation is driven by the quantity of organic matter. The residual sum of squares showed a decrease from the linear (and non-linear) model to the multiple linear regression model. The prob>|t| value (which determines the probability of error for the multiple linear regression) was much lower than 1% for all parameters in both the gas generation and respiration model, so it can be deduced that the variables are contributing to the model in a statistically significant way. Together with the previously mentioned highest coefficient of determination, the most accurate model for both gas generation and respiration found in this investigation was the multiple linear regression model, although the model for gas generation presented little difference to that of the simpler non-linear model. The exponential nature of the optimal fit for the data suggests that there is a threshold. In areas with low organic matter content, the organic matter present is much less degradable, falling into the “slow” pool category. It is recommended to investigate other mathematical models further. There is a possibility of a more accurate model (possibly a combination of a linear and non-linear model) for both gas generation and respiration which can model the parameters even better (higher coefficient of determination while still remaining within the permitted range of error). Furthermore, it is recommended to find out why the samples listed in tables 6 and 10 deviate more than accepted from the calculated value.BIOMUDApplied Earth Science
Comparative Study of Self Sealing and Self Healing in Clay and Concrete
No full textStudy of self-sealing and self-healing in clay is a fascinating topic which can be applied in many fields namely in construction sector or as the underground nuclear waste repository. However, lack of references still hinders the advancement of such field. Meanwhile, more advance researches are available for self-sealing and self-healing in concrete. Therefore, this project is held to find whether any valuable lessons from extensive researches of self-sealing and self-healing in concrete which can be applied to the development of the study in clay. This research is a comparative literature study of self-sealing and self healing mechanism between clay and concrete based on four aspects i.e. hydraulic, thermal, chemical and mechanical which based on the published papers from scientific journals and books. In terms of hydraulic aspect, hydraulic gradient plays an important role for sealing and healing mechanism in both clay and concrete. For thermal aspect, hydraulic conductivity is not affected by the temperature increased in clay while sealing and healing rate are improved for the similar condition in concrete. In chemical aspect, high pH environment increases sealing rate of concrete while high salinity decreases the capacity of sealing and healing of clay. For mechanical aspect, both concrete and clay experience a decreasing hydraulic conductivity under increasing confining stress. All of the results showed that both clay and concrete experience self-sealing and self healing mechanism with different influences by each aforementioned aspect.Final report of Additional Graduation Work (AES4011-10
A conceptual model describing Microbially Influenced Corrosion of sheet piles
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Gas flow through methane oxidation systems: A laboratory and numerical study for optimising system design
No full textEnglish: Landfills have been indicated as a major methane source. Methane oxidation systems are `low technology' systems that can treat these methane emissions. Yet, methane oxidation systems are herein still sub-optimal and leave room for improvement. A numerical model was established to research the effective gas permeability ratio between the gas distribution layer and the methane oxidation layer, and the centre-to-centre distance of the gas inlet points, necessary to achieve a spatial homogeneous methane load. In order to relate the permeability ratio to the design choice for the materials, laboratory experiments were performed to asses the influences of compaction level, hydraulic conditions and physical properties of a soil on the effective permeability of that soil. Overall, it is concluded that the effective permeability is predominantly influenced by the compaction level and soil texture. The water saturation only has a significant influence at near saturated levels. This means that the choice of suitable material and adequate construction practice has more effect on the effective permeability than seasonal changes in saturation levels in moderate climates. Furthermore, it is concluded that there are two parameters that govern the spatial homogeneity of the methane fluxes from the gas distribution layer into the methane oxidation layers: the permeability ratio between these layers, and the centre-to-centre distance between the inlet points. The required permeability ratio increases quadratically with an increasing centre-to-centre distance. Nederlands: Stortplaatsen zijn aangeduid als een belangrijke bron van methaanemissies. Methaanoxidatiesystemen zijn technisch simpele systemen die het stortgas kunnen saneren. Op dit moment zijn de bestaande methaanoxidatiesystemen nog weinig efficiënt en is het noodzakelijk om de homogeniteit van de laterale distributie van het stortgas te optimaliseren. Er is een numeriek model gegenereerd om inzicht te geven in de benodigde ratio tussen de effectieve permeabiliteit voor gas van de gasdistributielaag en van de methaanoxidatielaag, en in de maximale hart-op-hartafstand tussen de gasinlaatpunten om deze lateraal homogene methaan distributie te bereiken. Om de effectieve permeabiliteitsratio te relateren aan de materiaalselectie zijn er laboratoriumexperimenten uitgevoerd, die de invloeden van het compactieniveau, de hydraulische condities en de fysieke grondeigenschappen op de effectieve permeabiliteit voor gas vaststellen. Al met al kan worden geconcludeerd dat de effectieve permeabiliteit hoofdzakelijk wordt beïnvloed door het compactieniveau en de grondtextuur. Het watergehalte blijkt alleen significante invloed te hebben onder bijna verzadigde omstandigheden. Dit betekent dat een geschikte materiaalkeuze en adequate constructie de effectieve permeabiliteit voor gas meer beïnvloeden dan de seizoensgerelateerde veranderingen in het watergehalte in gematigde klimaten. Daarnaast kan worden geconcludeerd dat twee parameters bepalend zijn voor de laterale homogeniteit van de methaanstroom van de gasdistributielaag naar de methaanoxidatielaag: de ratio tussen de effectieve permeabiliteit voor gas tussen deze twee lagen, en de hart-op-hartafstand van de gasinlaatpunten. De benodigde permeabiliteitsratio neemt kwadratisch toe bij een toenemende hart-op-hartafstand.Applied Earth Science
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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