1,721,850 research outputs found
Biomethane liquefaction: A systematic comparative analysis of refrigeration technologies
No full textThis work presents a comparative technical and economic analysis of alternative refrigeration technologies for the production of liquefied biomethane (a liquid biofuel also known as bio-LNG). These processes are designed for biogas plants (size: 1–10 tCH4/day), where they can be installed downstream of the biogas upgrading step, to bring biomethane (essentially pure CH4)from the gaseous to the liquid phase, at −152 °C and 2 bar. Five technologies are considered: liquid nitrogen vaporization (benchmark); reverse Rankine cycle with mixed refrigerant; reverse Brayton cycle; Claude cycle; reverse Stirling cycle. The energetic and economic analyses are carried out, under a consistent methodology (reference production capacity of 4.6 tCH4/day), based on Aspen Plus process modelling and simulation for the calculation of the heat and mass balances, linked with ad-hoc Matlab algorithms for equipment sizing and cost estimation, and adopting the PGS-COM numerical optimizer for the selection of the optimal process conditions. The Rankine cycle with mixed-refrigerant turns out to be the best option, with an electric consumption of 3061 kJ/kgCH4, and a levelized biomethane liquefaction cost of 6.3 €/GJLHV. However, for liquid nitrogen supply costs lower than 66 €/tN2, liquid nitrogen vaporization, the least capital-intensive option, becomes the favourite solution. Finally, sensitivity analysis on the key variables is carried out to give a broader perspective to the techno-economic assessment
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
Biomechanical comparison between stainless steel, titanium and carbon-fiber reinforced polyetheretherketone volar locking plates for distal radius fractures
No full textIntroduction: As the popularity of volar locked plate fixation for distal radius fractures has increased, so have the number and variety of implants, including variations in plate design, the size and angle of the screws, the locking screw mechanism, and the material of the plates. Hypothesis: Carbon-fiber reinforced polyetheretherketone (CFR-PEEK) plate features similar biomechanical properties to metallic plates, representing, therefore, an optimal alternative for the treatment of distal radius fractures. Materials and methods: Three different materials-composed plates were evaluated: stainless steel volar lateral column (Zimmer); titanium DVR (Hand Innovations); CFR-PEEK DiPHOS-RM (Lima Corporate). Six plates for each type were implanted in sawbones and an extra-articular rectangular osteotomy was created. Three plates for each material were tested for load to failure and bending stiffness in axial compression. Moreover, 3 constructs for each plate were evaluated after dynamically loading for 6000 cycles of fatigue. Results: The mean bending stiffness pre-fatigue was significantly higher for the stainless steel plate. The titanium plate yielded the higher load to failure both pre and post fatigue. After cyclic loading, the bending stiffness increased by a mean of 24% for the stainless steel plate; 33% for the titanium; and 17% for the CFR-PEEK plate. The mean load to failure post-fatigue increased by a mean of 10% for the stainless steel and 14% for CFR-PEEK plates, whereas it decreased (−16%) for the titanium plate. Statistical analysis between groups reported significant values (P < 001) for all comparisons except for Hand Innovations vs. Zimmer bending stiffness post fatigue (P = 0.197). Discussion: The significant higher load to failure of the titanium plate, makes it indicated for patients with higher functional requirements or at higher risk of trauma in the postoperative period. The CFR-PEEK plate showed material-specific disadvantages, represented by little tolerance to plastic deformation, and lower load to failure. Level of evidence: N/A
Giant sigmoid lipoma covered by a villous adenoma
No full textLipomas arise in the colon with an incidence of up to 4.4%. Usually asymptomatic, they can reach big dimensions causing bleeding, obstruction, intussusception and prolapse.
The occurrence of adenomas overlying a colonic lipoma is rare.
The authors report a case of a giant sigmoid lipoma with a wide villous adenoma in the lining mucosa. They also suggest a pathogenetic hypothesis of this event
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