1,720,970 research outputs found
Martian aqua : occurrence of water and appraisal of acquisition technologies
No full textThe production of water through in-situ resource utilization (ISRU) will be necessary for a sustainable human presence on Mars. Accessible water on Mars occurs as ice (pure and mixed with regolith), bounded water in the regolith (adsorbed and in hydrated minerals) and vapor in the atmosphere. Harvesting water from the atmosphere appears to be relatively challenging than obtaining it from the regolith. However, the potential landing sites for human exploration are unlikely to have easy access to near-surface ice of any form, while utilization of the atmosphere can be accomplished almost anywhere. Extensive research has been conducted on atmospheric water vapor, which is ubiquitous and renewable, yet provides only a thin water source across the planet. This paper provides an overview of water availability on Mars, investigates the volatiles (CO2, H2O) phase equilibria in the atmosphere-surface system of the planet, and compares water harvesting from the atmosphere to obtaining water from the regolith. The findings indicate that while atmospheric water harvesting does not appear to be feasible to serve as the primary water source, it might have potential to become a supplementary, decentralized clean water supply. Atmospheric water harvesting systems on Mars require more power and energy, but they offer greater simplicity and flexibility compared to water extraction from the regolith. This approach could prove valuable in regions where water extraction from the regolith is infeasible or as a temporary backup in the event of a primary water system failure. Such a distributed water harvesting method might enhance the resilience and flexibility of water supply systems for future human Mars missions and settlements. Ultimately, any technology developed for extraterrestrial environments can have important applications on Earth
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
Adsorption Ion Exchange And Catalysis Design Of Operations And Environmental Applications
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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
Chapter 7 Extraterrestrial Environment
Get PDFAbstract This chapter deals with some aspects of the extraterrestrial environment, which is relevant—directly or indirectly—to human development. Space waste is an emerging problem that poses serious threats to human activities in space and is approached at several different angles. The next subject is relevant to the greenhouse effect, and starting from the analysis of planetary evolution and climate principles takes the reader to a journey around the solar system discussing the amazing marvels and mysteries of greenhouse effects on other terrestrial moons and planets: Mars, Venus, Pluto, Titan, and Triton. Finally, the implications and potential uses of humble but magic extraterrestrial hydrated minerals are addressed. This chapter is not an ordinary one but demonstrates lessons that can be learned by studying our neighborhood that one day we may call home
Modeling of ion exchange of Pb2+ in fixed beds of clinoptilolite
No full textIon exchange of Pb2+ on natural clinoptilolite in fixed bed and batch operations has been studied and simple models on experimental data have been applied. The operations are conducted at ambient temperature, an initial concentration of 0.01 N and at pH 4. Paterson's model is used to describe batch kinetics, the Langmuir isotherm is used to correlate equilibrium data and a solid diffusion controlled process is used to describe the fixed bed operation. The evaluated operating capacity is in the range of 0.21-1 meq/g and the diffusion coefficient is in the range of (0.07-5.4) × 10 -12 m2/s. The experimental results obtained put the basic theory under question. According to these experiments, the capacity and diffusion coefficient in fixed bed systems are flow dependent and different from those measured in the batch-reactor systems. This could be explained if the type of experimental setup influenced both the equilibrium isotherm and the system behavior. © 2003 Published by Elsevier Inc
Experimental study of zeolitic diffusion by use of a concentration-dependent surface diffusion model
Full text linkSurface diffusivity in adsorption and ion exchange processes is probably the most important property studied expensively in the literature but some aspects, especially its dependence on solid phase concentration, is still an open subject to discussion. In this study a new concentration-dependent surface diffusion model, equipped with a flexible double selectivity equilibrium relationship is applied on the removal of Pb2+, Cr3+, Fe3+ and Cu2+ from aqueous solutions using a natural zeolite. The model incorporates the Chen-Yang surface diffusivity correlation able to deal with positive and negative dependence with surface coverage. The double selectivity equilibrium relationship successfully represents the experimental equilibrium data, which follow Langmurian isotherm type for Pb2+, sigmoidal for Cr3+ and Fe3+ and linear for Cu2+. The concentration-dependent surface diffusion model was compared with the constant diffusivity surface diffusion model and found to be moderately more accurate but considerably more useful as it provides more insights into the diffusion mechanism. The application of the model resulted in an average deviation of 8.56 ± 6.74% from the experimental data and an average solid phase diffusion coefficients between 10−9 and 10−10 cm2/s. The results showed that the diffusion of metal ions in the zeolite structure is unhindered following the surface diffusion mass transfer mechanism
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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