1,721,027 research outputs found
Potential Pathway for Reliable Long-Term CO2 Storage as Clathrate Hydrates in Marine Environments
No full textA countermeasure to global warming is removing high CO2 amounts from the atmosphere and locating the emitted CO2 into long-term stable carbon storage sites. The sequestration technologies must be reliable, long-lasting, and environmentally friendly. An alternative and innovative approach that may meet the sequestration requirements is CO2 storage as clathrate hydrates in marine environments. Extensive research has been devoted to CO2-CH4 replacement in natural gas hydrates. Another option is the direct formation of CO2 hydrates into deep ocean water or into marine underfloor sediments. This article deals with the positioning of direct hydrate-based CO2 storage among the other traditional geological options and the discussion of new, by-far, state-of-the-art knowledge required for the development of a hydrate-based CO2 storage pathway that is reliable, stable, durable, efficient, and environmentally benign
Scale Effects in the Artificial Reproduction of Natural Gas Hydrates in Lab Vessels
No full textNatural gas hydrates (NGHs), as the largest hydrocarbon resource on Earth, offer a promising reservoir of sustainable fuels, particularly due to the potential of the CO2-CH4 replacement process. Most of the literature on the study of NGHs comes from laboratory experimental campaigns using reactors for the artificial reproduction of the conditions in which NGHs form in nature. In order to develop production technologies at the field scale and also compare experimental results obtained in different setups, it is crucial to assess the effects that a particular geometry or size has on the results, from both thermodynamic and kinetic points of view. In this perspective, the paper compares the hydrate formation process carried out in two different reactors with similar cylindrical geometry, one with a volume of 1 L and the other with a volume of 60 L. The analysis covers, for two different values of hydrate saturation (10% and 20%), the thermal aspects, in order to understand how hydrates form and grow inside the reactor, the quantity of hydrate formed and gas uptake, and the kinetic aspects. At 10%, the formation front behaves differently between the two reactors, while at higher saturation, hydrates similarly form in the upper section of the reactor and subsequently advance to the lower section. With regard to gas uptake, it is higher in the small reactor, resulting in a higher utilization of the gas phase for hydrate formation. Also, the kinetics differs with size, especially at higher saturations. The pressure reduction rate is generally higher in the 1 L reactor
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
On the cooling potential of retro reflective façades and pavement in urban canyons
No full textRetro-reflective (RR) materials represent an opportunity to reduce UHI phenomenon due to their ability to reflect most of the incident energy towards the same incoming direction. The optical properties of RR materials suggest that they could be effectively applied as coatings in order to reflect the solar radiation beyond the urban canyon.
The RR behaviour depends on the angular distribution of the incident energy: for small incident angle the radiation is reflected mainly backward in the incoming direction; for large angles RR materials reflect the radiation symmetrically with respect to the surface normal. To overtake the limit of RR materials of being mainly retroreflective only for small angles of incidence, the investigation is focused on the optic interaction between vertical and horizontal RR surfaces. Therefore, the aim of this paper is to investigate the synergic effect of RR pavements and façades on a physical model in which urban canyon layouts with H/D equal to 1 and 2 are represented. To evaluate the global cooling effect of RR pavements and façades, a new parameter, called equivalent albedo, is introduced and calculated over the canyon’s ceiling. The results show that a canyon with RR vertical surfaces and RR pavement reflects outward more radiation than a canyon with RR vertical surfaces and diffusive pavement due to the interaction of optical properties of the materials
Effects of aging on retro-reflective materials for building applications
No full textCool materials have been proposed for building applications given their potentialities in reducing building energy consumption, urban heat island effects, and global warming. Among cool materials, retro-reflective (RR) ones have been recently proposed for their ability to reflect backwards the incidental striking solar energy. This property is useful in densely urbanized areas, in urban canyons patterns, and in urban areas with buildings of different heights, because it avoids that the reflected energy contributes to the overheating of the neighbor buildings and structures. This study aims to predict the long-term performance of some RR tiles and paints intended for building applications. To this purpose, laboratory accelerated aging tests as described in the ASTM G154 were performed to determine the long-term material properties within a much shorter time than with outdoor weather aging. The samples show minimal changes in the reflectivity, directional reflection, and colorimetry. Finally, this paper shows that the RR character of the investigated materials and their urban cooling potential would be preserved
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