1,720,983 research outputs found
Investigating experimentally the performances of a natural gas reciprocating compressor adapted to pure hydrogen up to 30 MPa
Get PDFHydrogen as an energy carrier can be integrated into various value chains, enabling the decarbonization of hard-to-abate processes. Hydrogen storage is necessary to handle the intermittency of renewables. Moreover, it allows hydrogen to be deployed in sectors such as mobility and backup power. Currently, high-pressure vessels are typically used for hydrogen storage. The compression process is required since hydrogen production occurs at lower pressure than storage. This study examines a three-stage reciprocating compressor for natural gas, which is operated with pure hydrogen. The compressor, driven by a 3-kW electric motor, can deliver 30 MPa starting from pressures between 0.3 and 0.8 MPa. The aim is to assess the energy impact of compression on hydrogen production and analyze potential issues such as leakages or contamination that can arise after changing the fluid. The study involves measuring hydrogen flow rates, inlet and outlet pressures, and electric power consumption during the filling of a vessel. The experiment shows a specific power input of 1.2 kW/(Nm3/h), more than 1/3 of the lower heating value, maximum isothermal efficiency of 21% and maximum isentropic efficiency of 34%. The optimal compression ratio is found to be between 25 and 30. Based on the few data available in literature, the performances do not reach state-of-art levels of 55-80% isentropic efficiency. However, the device was optimized for the compression of natural gas, and the scope of this study was to use it with fewer possible modifications
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
Comparison of immediate versus delayed implant placement in a failed implant site: A retrospective analysis of early implant survival
No full textPurpose: To compare immediate and delayed implant replacement at failed implant sites to evaluate the factors associated with early failure of second implants after replacement. Materials and methods: Data regarding early implant failure followed by replacement with another fixture in a private practice setting between 2003 and 2019 were analysed retrospectively. Early failure was defined as loss of the dental implant within 6 months of placement. The impact of patient-level (age, sex, diabetes, smoking history) and implant-level (timing of implant replacement, timing of prosthetic loading, bone grafting) variables on the early failure rate of second implants after replacement was evaluated. Due to the hierarchical structure of the data, a multivariate multilevel mixed-effects Poisson regression analysis was performed. Results: A total of 109 patients (63 men and 46 women) diagnosed with early implant failure at 124 implant sites were included in the present study. Fifty-eight implants were immediately replaced at the time of removal of the failed implant (test group), whereas 66 were replaced after a healing period of 2 to 4 months (delayed approach; control group). A total of 15 implants failed after replacement in 11 patients during the first 6 months of follow-up. Of these, nine failures (15.25%) occurred in seven patients (13.21%) after immediate replacement, and six (9.09%) occurred in four patients (7.02%) who underwent delayed replacement. No statistically significant differences were detected between the two groups (P = 0.431). Conclusions: No significant differences in implant survival at sites of previous failure were found according to the timing of implant replacement
Experimental and numerical study of a microcogeneration stirling unit under on-off cycling operation
No full textStirling units are a viable option for micro-cogeneration applications, but they operate often with multiple daily startups and shutdowns due to the variability of load profiles. This work focused on the experimental and numerical study of a small-size commercial Stirling unit when subjected to cycling operations. First, experimental data about energy flows and emissions were collected during on-off operations. Second, these data were utilized to tune an in-house code for the economic optimization of cogeneration plant scheduling. Lastly, the tuned code was applied to a case study of a residential flat in Northern Italy during a typical winter day to investigate the optimal scheduling of the Stirling unit equipped with a thermal storage tank of diverse sizes. Experimentally, the Stirling unit showed an integrated electric efficiency of 8.9% (8.0%) and thermal efficiency of 91.0% (82.2%), referred to as the fuel lower and, between parenthesis, higher heating value during the on-off cycling test, while emissions showed peaks in NOx and CO up to 100 ppm but shorter than a minute. Numerically, predictions indicated that considering the on-off effects, the optimized operating strategy led to a great reduction of daily startups, with a number lower than 10 per day due to an optimal thermal storage size of 4 kWh. Ultimately, the primary energy saving was 12% and the daily operational cost was 2.9 €/day
Prosthetic Rehabilitation of Edentulous Patients with Implants Based on Facial Profile Assessment: A Case Report
No full textPurpose:To introduce a user-friendly protocol for implant-retained prosthetic rehabilitation of fully edentulous patients based on facial profile and the cephalometric intermaxillary relationship.Materials and Methods:The prosthetic rehabilitation of edentulous patients with implants based on facial profile assessment protocol commences with a clinical and cephalometric analysis, followed by a preliminary projection to obtain a harmonious interarch relationship, eventually stabilized by the preplanned prosthesis. The protocol is divided into the following 5 phases: Esthetic evaluation; cephalometric-occlusal assessment; surgery; provisionalization; and definitive prosthesis. Evaluation of patient's satisfaction from the treatment provided was performed through a preoperative and postoperative visual analogue scale scores.Results:The patient was granted immediate function and superior esthetics at day 1 of the treatment. These results were re-evaluated on an interval of 18 months and continued to be stable. The overall treatment time was significantly reduced.Conclusion:Our recommended protocol gives the clinician a chance to grasp results beyond the offered by traditional protocols by using a wider perspective of rehabilitation, involving the patient's facial profile, thus fulfilling the integration of both occlusal and cephalometric parameters in a unified surgical-prosthetic approach
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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