1,720,959 research outputs found
Development of Hydrogen Peroxide Monopropellant Rocktes
Get PDFAlta S.p.A. (Italy) and DELTACAT Ltd. (United Kingdom) are conducting a study, funded by the European Space Agency, into the development of hydrogen peroxide monopropellant thrusters using advanced catalytic beds. The present paper focuses on the design of two different demonstration thrusters with nominal ratings of 5 N and 25 N. Design requirements and specifications are presented, followed by the main results of a concept study, which was conducted to define the approximate dimensions needed. Some details about the specific design of the two prototypes and the choice of the main components are provided, with particular regard to the sensors and transducers to be used during the experimentation. Different catalytic bed configurations, including pure silver gauzes and pellets coated with manganese oxide or platinum, are going to be tested in the prototype thrusters, in order to find the optimum one for further industrial development. A dedicated test bench, designed and r..
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
Experimental Characterization of a 5 N Hydrogen Peroxide Monopropellant Thruster Prototype
Get PDFIn the framework of the LET-SME program funded by the European Space Agency, ALTA S.p.A. (Italy) and DELTACAT Ltd. (United Kingdom) jointly investigated the use of advanced catalytic beds on ceramic supports as a cost-effective alternative to metal screen reactors for the decomposition of high-concentration hydrogen peroxide in small monopropellant rockets. To this purpose ALTA S.p.A. designed and realized a reconfigurable test bench for the characterization of the operation and propulsive performance of small rocket thrusters. The present paper illustrates the experimental campaign carried out on a 5 N thruster prototype operating with two platinum catalysts on g− alumina supporting spheres, especially developed by ALTA in collaboration with the Chemistry and Industrial Chemistry Department of Pisa University, Italy. The results indicated that Pt/Al2 O3 is an effective catalyst combination for the decomposition of 87.5% propellant grade hydrogen peroxide, with good stability and performance comparable to silver screen beds of equal geometric envelope and operational conditions. Incomplete hydrogen peroxide decomposition and the onset of flow oscillations in the reactor were observed at the tested levels of bed loading, residence time and flow pressure. Thermal stresses due to the large temperature gradients occurring during the decomposition of high grade hydrogen peroxide (87.5% by weight) caused the ceramic pellets to break and the progressive occlusion of the bed. Based on the analysis of the test results, several ways to overcome these problems in future investigations have been tentatively identified, together with the necessary modifications to the present experimental set-up
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
Experimental Characterization of Advanced Materials for the Catalytic Decomposition of Hydrogen Peroxide
Get PDFAlta S.p.A. (Italy) and DELTACAT Ltd. (United Kingdom) are conducting a study, funded by the European Space Agency, into the development of hydrogen peroxide monopropellant thrusters using advanced catalytic beds. The present paper focuses on the design of a dedicated test bench to assess the effectiveness of different catalyst samples when immersed in hydrogen peroxide. To date, the apparatus has been used to study powdered silver and three oxides of manganese. The evaluation of an analytical technique for determining the observed decomposition rates is also presented. In addition to devising a quantitative method for assessing the efficacy of the candidate catalysts, some qualitative studies of proposed metallic catalysts, in the form of wires immersed in hydrogen peroxide, are also described. Of the catalyst materials tested so far, preliminary results suggest that dimanganese trioxide offers slightly better performance than both manganese dioxide and silver
Dependence of pellet shape and size on pressure drop in thrusters
No full textThe most important parameters influencing the pressure drop over a reacting catalyst bed are analyzed using a multiphase multicomponent flow model. The model, in which the gas and liquid phases are treated as separate fluids,simulates the flow of highly concentrated hydrogen peroxide from a tank, through the injector, into the catalyst bed to the nozzle. It contains submodels to describe the interphase mass, momentum, and energy transfer occurring in thecatalyst bed, in which it is assumed there is a pellet-based catalyst structure. The main purpose is to investigate the influence of pellet shape and dimensions on the pressure drop over the bed and the required bed length. The model hasbeen verified and validated against experimental data and shows improved predictions of the pressure drop compared with traditionally employed pressure drop models. It is shown that cylindrical pellets with a diameter to length ratio larger than two give a lower pressure drop for a given bed length than spherical pellets. It is furthermore shown that this result is independent of the inlet mass flux and liquid volume fraction distribution and is reliable for high bed to pellet diameter ratios
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
Development of Green Hydrogen Peroxide Monopropellant Rocket Engines and Testing of Advanced Catalytic Beds
Get PDFWith the financial support of the European Space Agency, Alta S.p.A. in Italy and DELTACAT Ltd. in the United Kingdom are conducting a joint study on the development of two hydrogen peroxide monopropellant thruster prototypes (5 and 25 N vacuum thrust) using advanced catalytic beds. The present article illustrates the results of recent tests on the developed catalysts and the main aspects of the thruster design as well as of the technique used for quantitative determination of the observed decomposition rates. Preliminary results indicate that platinum deposited on a γ−alumina substrate yields the best performance with respect to the other solutions under consideration
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