Power conversion for a novel AC/DC aircraft electrical distribution system

This paper proposes a novel and compact AC/DC electrical distribution system for new generation aircraft. In these new aircraft power systems, all loads are fed by two dc bus systems: at 28V and at +/-270V. The electrical distribution system, whose design and implementation are described in this paper, has only one primary AC source (360-900Hz at 230V) with all the required dc voltage levels being derived from this source. This solution enables elimination of the complex mechanical coupling apparatus currently used, for fixed frequency AC systems, to maintain the generator speed at constant level while the engines operate at variable speed. Under the proposed solution, all conversion stages needed to generate the various output voltage levels are implemented using power converters assembled in one unit. Each converter has a current control loop in order to regulate the output current even during output line short circuits and also to limit the inrush current to the circuit at turn-on. To prove the concept a 5 kW prototype was designed and tested, and demonstrated to meet all the specifications within relevant standards regarding input and output power quality

Um estudo de frases engraçadas que versam sobre bebida: Construção de sentido e Ethos

Nesta pesquisa, busca-se analisar a construção do sentido humorístico em frases engraçadas veiculadas no site Os Vigaristas e que têm como temática a bebida. Parte-se da hipótese de que o humor é construído na interação e que cumpre uma finalidade para além do fazer rir. Objetiva-se, também, discutir a constituição do ethos do bêbado e sua relação com a finalidade discursiva do humor nas frases. No que se refere à construção de sentido, utilizam-se os pressupostos teóricos da Linguística Textual de base sociocognitiva e interacionista, para a qual a significação textual se dá pela mobilização de conhecimentos prévios alocados na memória dos interactantes, por intermédio de processos cognitivos, como a inferência, e a partir dos elementos linguísticos explícitos na superfície do texto. Nessa perspectiva, são adotados principalmente os trabalhos de Van Dijk (2001, 2002), Koch (2003; 2006; 2008; 2010) e Marcuschi (2008). No que diz respeito ao humor, este é tomado enquanto efeito de sentido produzido nos textos humorísticos por meio de técnicas humorísticas que funcionam como gatilho na deflagração da comicidade. Portanto, são levados em consideração especialmente os estudos de Bergson (1900), Freud (1905), Raskin (1985), Propp (1976), Travaglia (1990; 1992; 1998), Possenti (1998; 2010), entre outros autores. Quanto ao ethos, consideram-se os postulados da Nova Retórica, que concebe a eficácia do discurso como proveniente da autoridade do orador. Este, no instante em que toma a palavra, em um contexto retórico, faz uma apresentação de si e do outro no discurso, mesmo que não fale expressamente sobre suas qualidades, de modo a conseguir a adesão do público-alvo. Para tanto, são relevantes os conceitos expostos por Reboul (2004), Perelman e Olbrechts-Tyteca (2005), Meyer (2007), Amossy (2008) e Ferreira (2010). Feitas as análises, constatou-se que o humor, nas frases engraçadas, dá-se pelo acionamento de conhecimentos prévios e por meio de técnicas humorísticas, entre as quais a mais recorrente é a inversão. No que tange à finalidade do humor nas frases, estas visam à liberação, através da subversão do discurso do Ministério da Saúde. A finalidade humorística, por sua vez, é sustentada pelo ethos positivo do bêbado, que é mostrado como o beneficiado pela ingestão da bebida

Experimental comparison of a matrix converter using Si IGBT and SiC MOSFETs

This paper presents an analytical and experimental comparison between comparable Silicon (Si) IGBTs and Silicon Carbide (SiC) MOSFETS when used in a direct AC/AC matrix converter circuit. The switching performance of the two devices is analysed and the efficiency / losses measured in order to develop a loss model which will help engineers to design and develop matrix converter circuits using these types of devices. Particular attention is given in the paper to the discrepancies found between the data-sheet values and the measured data. The EMI performance of the two matrix converters is also determined and the implication of using high speed devices from both an EMI and an efficiency point of view is formulated together with an improved input filter design

The experimental development of the mammary gland with special reference to the interaction of the pituitary and ovarian hormones

Publication authorized May 13, 1948.Digitized 2007 AES.Includes bibliographical references (pages 41-48)

Perfilhamento de Eragrostis plana Ness sob estresse hídrico.

CONGREGA

Oral effectiveness of the dimethyl ether of diethylstilbestrol and of various steroid hormones on the mammary glands of mice and rabbits

Publication authorized December 18, 1947Digitized 2007 AES.Includes bibliographical references (pages 31-33)

Organic-Inorganic Hybrid Coatings for Active and Passive Corrosion Protection

Organic-inorganic coatings based on poly(methyl methacrylate) (PMMA)-silica and PMMA-cerium oxide hybrids provide effective and active corrosion protection of metallic surfaces. For both hybrid materials, the covalent conjugation of inorganic silica or ceria nanodomains with the PMMA matrix, provided by molecular coupling agents, leads to homogenous and highly cross-linked nanocomposites, which act in the form of coatings as an efficient diffusion barrier. The addition of lithium salts (500–2000 ppm) into PMMA-silica hybrid and optimized ceria fraction in PMMA-cerium oxide coatings results in active corrosion inhibition by the self-healing effect. Results of electrochemical assays of aluminum- and steel-coated samples, performed in a 3.5% NaCl solution, show an excellent corrosion resistance (impedance modulus up to 100 GΩ cm2) and durability (up to 350 days) of the 10-μm-thick passive barrier layer. Time-of-flight secondary ion mass and X-ray photoelectron spectroscopies evidenced the self-healing ability of coatings induced by lithium/cerium ion leaching toward corrosion spots or artificial scratches, which are restored by a protective layer of precipitated phases. Results presented in this book chapter evidence the active role of lithium and cerium species in improving the hybrid structure and providing through self-healing a significantly extended service life of metallic components

Sobressemeadura de azevém (Lolium multiflorum L.) em campo nativo após controle de Eragrostis plana Ness em pós-florescimento com a máquina Campo Limpo.

CIC UFPelotas

Experimental efficiency comparison between a direct matrix converter and an indirect matrix converter based on efficiency using Si IGBT and SiC MOSFETs

This paper presents an experimental efficiency comparison study between two different direct AC-AC converter topologies: a direct matrix converter (DMC) and an indirect matrix converter (IMC). The evaluation is performed under variable load conditions using both discrete Silicon (Si) IGBTs and Silicon Carbide (SiC) MOSFETs working at power levels up to 9 kW. Each loss measurement is carried out using two power analyzers: one placed at the input and one at the output of the converter under study. To facilitate this measurement an output filter was necessary in addition to the normal input filter. Both converters are modulated the same traditional symmetrical space vector approach and feature an identical input/output filter design