1,721,307 research outputs found
A mechanism to accelerate the late ablation in pulsed plasma thrusters
No full textPulsed Plasma Thrusters (PPTs) are long standing electric propulsion thrusters that are reliable, relatively simple and low cost. One of the main issues with the PPT is its poor utilization of the propellant and low efficiency. Typically only 40-60% of the propellant contributes to the production significant impulse and the efficiency is around 8%. The cause of the PPT’s poor propellant utilization is the late time ablation (LTA), which has a major impact on the efficiency. LTA is the sublimation of propellant that takes place after the main discharge, due to the propellant, usually Polytetrafluoroethylene (Teflon®), being at a temperature above its sublimation point. The LTA produces a low speed gas and macro particles that do not contribute significantly to the thrust. This work presents a way of accelerating the late time ablation by employing an additional discharge after the main discharge, in a separate pair of electrodes. A new thruster, called the two-stage pulsed plasma thruster (TS-PPT) was built and tested. This thruster has two pair of electrodes: primary and secondary. The primary is placed in contact with the propellant surface, as in a regular PPT. The secondary is placed downstream, relatively far from the propellant. A new approach, dividing the PPT thrust generation in two phases, was envisioned. The first phase is responsible for the ablation process and takes place in the first pair of electrodes. The second phase takes place in the second pair of electrodes and is responsible for the acceleration process. The phase division allowed for propellant metering and better propellant utilization. Evidence was
found that a pair of electrodes placed downstream, further from the propellant surface is able to discharge in the late ablation portion of the propellant and can impart extra energy into the exhaust and improve propellant utilization. A simple analytical model was developed to predict trends. A prototype of a TS-PPT was designed and built. A vacuum facility was modified, adapted, partially designed and built. An average mass bit consumption test was carried out. A simple time-of-flight experiment revealed that the fastest portions of the plasma from the primary electrodes discharge were travelling at around 33 km/s. Several current measurements were performed and calculations of the total electrical resistance, total inductance, electromagnetic impulse bit, specific impulse, efficiency, and other parameters were calculated based on experimental data. Experimental results indicated that significant improvements in the specific impulse and efficiency are possible by utilising a two-stage PPT. Specific impulses as high as 4000s were calculated based on experimental results, indicating a better propellant utilization
A má ambiguidade na filosofia de Maurice Merleau-Ponty
Get PDFDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Filosofia e Ciências Humanas. Programa de Pós-Graduação em FilosofiaO presente trabalho busca refletir sobre a forma como Merleau-Ponty articula as noções de corpo e reflexão na obra Fenomenologia da Percepção. Apresentamos como o estudo da percepção empreendida por este filósofo resultou em uma má ambiguidade, tal como a declara no texto de candidatura ao College de France. Percorremos nossa discussão sobre a ambiguidade do corpo através da compreensão de uma estrutura existencial onde o corpo e o mundo estão interligados numa expressão perfeita como uma obra de arte. Vamos encontrar a má ambiguidade na tentativa de Merleau-Ponty de sair do equívoco da fundação cruzada, o Fundierung. A má ambiguidade se mostra como a simples mistura entre o universal e o particular. Não sendo possível compreender como pode ocorrer a passagem efetiva entre os extremos, assim Merleau-Ponty se mantém no interior dos quadros da tradição. O projeto da Fenomenologia da Percepção trouxe uma grande contribuição para a noção de corpo e mundo, contudo ao tentar resolver o equívoco pela correlação entre subjetividade e temporalidade houve uma centralidade na subjetividade tornando-o tributária da ontologia clássica que é sua crítica e tentativa de superação.The present work aims to reflect on how Merleau-Ponty articulates the notions of body and reflection in the work Phenomenology of Perception. Here as the perception study undertaken by this resulted in a poor philosopher ambiguity, as stated in the text of the application College de France. We went through our discussion of the ambiguity of the body through the understanding of an existential structure where the body and the world are interconnected in a perfect expression as a work of art. Let us find the bad ambiguity in Merleau-Ponty attempted to leave the dubious foundation cross the Fundierung. The bad ambiguity appears as a simple mixture between the universal and particular. Not being able to understand how effective the passage may occur between the extremes, and Merleau-Ponty remains within the frame of tradition. The project of the Phenomenology of Perception brought a great contribution to the concept of body and world, however when trying to resolve the ambiguity in the relationship between subjectivity and temporality was a centrality of subjectivity making it tax the classical ontology that is his criticism and attempt to overcome
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
A concentração na internet e o necessário controle social
Get PDFEstamos hoje no final de 2021 e os resquícios das ilusões do passado devem ser abandonados de vez. A regulação dos diferentes aspectos que conformam a internet e as aplicações que dela fazem uso é tarefa que urge. Precisamos da regulação pois, caso contrário, as consequências econômicas, sociais e políticas vão se agravar ainda mais para a maior parte da humanidade, ao passo que os privilegiados serão poucos. Afinal, está cada vez mais claro: as tecnologias de informação e comunicação que se expandiram sobretudo a partir da virada do século XX para o XXI estão hoje absolutamente submetidas às coerções das relações sociais capitalistas.Fil: Maurício, Patricía. Universidade Federal do Rio de Janeiro; BrasilFil: Moreno Marques, Rodrigo. Universidade Federal de Minas Gerais; BrasilFil: Bizberge, Ana Gabriela. Universidad Nacional de Quilmes. Departamento de Ciencias Sociales. Industrias Culturales y Espacio Público; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Efeito do estádio de desenvolvimento de lagartas sobre a eficiência de controle de inseticidas químicos e biológicos na cultura da soja
Get PDFA soja [Glycine Max (L.) Merr.] é a cultura de destaque no Brasil, com altos índices de produção. Um de seus entraves está ligado ao ataque de lagartas, responsáveis por perdas significativas. O objetivo do trabalho foi avaliar a eficiência de inseticidas sobre lagartas em diferentes estádios de desenvolvimento. Foram utilizadas lagartas das espécies Anticarsia gemmatalis e Chrysodeixis includens nos estádios de desenvolvimento L1 (lagartas de 1º instar) e L3 (lagartas de 3º instar). Foram testados os ingredientes ativos: clorantraniliprole, metilcarbamato de oxima, triflumuron e Bacillus thuringiensis (Bt), nas doses de 2g de ingrediente ativo (ia)/ha, 64,8g ia/ha, 240g ia/ha e 16g ia/ha, respectivamente, e um tratamento testemunha. Foram pulverizadas seis plantas de soja de cada tratamento. Cinco horas após a aplicação foram retiradas folhas das plantas, os pecíolos foram envolvidos em algodão embebido em água e colocadas em placas plásticas. Foram inseridas cinco lagartas de cada espécie em dois estádios de desenvolvimento, separadamente, totalizando 160 placas (5 tratamentos, 8 repetições, 2 estádios e 2 espécies de lagartas), em um delineamento inteiramente casualizado. As placas foram mantidas em BOD com temperatura de 25ºC e fotofase de 12h. A mortalidade foi avaliada 24, 48 e 72 horas após a inoculação. Os inseticidas clorantraniliprole, metilcarbamato de oxima e triflumuron, apresentaram desempenho satisfatório para o controle das lagartas A. gemmatalis e C. includens no 1º e 3º instar, atingindo eficiência de 100% ao fim das avaliações. A tolerância das lagartas variou de espécie para espécie, lagartas de C. includens em L3 se mostraram mais tolerantes ao tratamento com Bt, o que não ocorreu com lagartas de A. gemmatallisFil: Oliveira, Josiele. Universidade Federal de Sao Carlos (Brasil).Fil: Marques, Rodrigo. Universidade Federal de Sao Carlos (Brasil)
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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