954 resultados para current-mode design


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A presente dissertação busca realizar a descrição e sistematização de categorias analíticas que contribuam com análises sobre as relações econômicas, políticas e sociais que sustentam a forma como se constituem historicamente no Brasil o Estado e as políticas públicas na área social, com especial atenção para a área de saúde. Tal objetivo se constituiu na observação das novas estratégias utilizadas pelo Estado para a execução de ações na área de saúde, como os projetos sociais. Tomamos o método do materialismo histórico dialético como referencial teórico, com especial atenção às categorias da filosofia da práxis práxis, totalidade, historicidade e contradição e a teoria marxista sobre a formação do Estado capitalista e suas transformações históricas, com ênfase na teoria sobre o Estado ampliado e o papel da sociedade civil na disputa entre as classes pela hegemonia. No segundo capítulo, abordamos a organização contemporânea do Estado brasileiro, buscando discutir escolhas políticas e econômicas, suas implicações para a organização dos trabalhadores e para a correlação de forças na disputa entre as classes. Foi feito breve levantamento histórico sobre os modelos de desenvolvimento econômico e social nas sociedades contemporâneas, com atenção à consolidação do ideário neoliberal, sua conceituação, as adequações que sofreu a partir do final dos anos 1990 e sua relação com a ideologia desenvolvimentista. Dedicamos o terceiro capítulo ao conceito de capital social, como maneira de compreender a atual forma de desenvolvimento das políticas públicas e em especial as políticas de saúde. A partir deste conceito buscou-se compreender a relação entre Estado e sociedade civil na atualidade e como este influencia as transformações por que passaram o Estado e as políticas sociais. Abordou-se o desenvolvimento das políticas públicas da área social no Estado brasileiro até sua conformação no neoliberalismo; as concepções de saúde em disputa na sociedade brasileira, focando no conceito ampliado de saúde e no de determinação social da saúde; e de que forma estes conceitos são impactados pelas mudanças no contexto do neoliberalismo. Finalmente, foi possível observar como as orientações neoliberais alteraram significativamente a forma de organização e atuação do Estado, a concepção e aplicação de políticas públicas, bem como as políticas de saúde e seu ideário. Mudanças que fizeram pender a atuação do Estado ainda mais a favor dos interesses do capital.

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Novel alternatives to the conventional single crystal diamond Schottky metal-intrinsic-p+ (m-i-p+) diode is presented in this work. The conduction mechanism of the device is analysed and structural modifications to enhance its performance are proposed. The periodic inclusion of highly p+ doped thin δ-layers and p+ spots in the intrinsic voltage blocking layer of the diode drastically improves the forward performance of these devices enhancing the forward current of the device by a factor of 10 - 17 with a maximum forward current density of ̃ 40 A/cm 2 for a 2 kV device.

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A detailed study of the design issues relevant to long-wavelength monolithic mode-locked lasers is presented. Following a detailed review of the field, we have devised a validated travelling wave model to explore the limits of mode-locking in monolithic laser diodes, not only in terms of pulse duration and repetition rate, but also in terms of stability. It is shown that fast absorber recovery is crucial for short pulse width, that the ratio of gain to absorption saturation is key in accessing ultrashort pulses and that low alpha factors give only modest benefit. Finally, optimized contact layouts are shown to greatly enhance pulse stability and the overall operational success. The design rules show high levels of consistency with published experimental data.

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We report the amplification of 10-100-pJ semiconductor diode pulses to an energy of 158 microJ and peak powers >100 kW in a multistage fiber amplifier chain based on a single-mode, large-mode-area erbium-doped amplifier design. To our knowledge these results represent the highest single-mode pulse energy extracted from any doped-fiber system.

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Understanding the energy dissipation mechanisms in single-crystal silicon MEMS/NEMS resonators are particularly important to maximizing an important figure of merit relevant for miniature sensor and signal processing applications: the Quality factor (Q) of resonance. This paper discusses thermoelastic dissipation (TED) as the dominant internal-friction mechanism in flexural mode MEMS/NEMS resonators. Criteria for optimizing the geometrical design of flexural mode MEMS/NEMS resonators are theoretically established with a view towards minimizing the TED for single-crystal silicon MEMS/NEMS flexural mode resonators.

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The Flower Garden Banks National Marine Sanctuary (FGBNMS) is located in the northwestern Gulf of Mexico approximately 180 km south of Galveston, Texas. The sanctuary’s distance from shore combined with its depth (the coral caps reach to within approximately 17 m of the surface) result in limited exposure of this coral reef ecosystem to natural and human-induced impacts compared to other coral reefs of the western Atlantic. In spite of this, the sanctuary still confronts serious impacts including hurricanes events, recent outbreaks of coral disease, an increase in the frequency of coral bleaching and the massive Diadema antillarum die-off during the mid-1980s. Anthropogenic impacts include large vessel anchoring, commercial and recreational fishing, recreational scuba diving, and oil and gas related activities. The FGBNMS was designated in 1992 to help protect against some of these impacts. Basic monitoring and research efforts have been conducted on the banks since the 1970s. Early on, these efforts focused primarily on describing the benthic communities (corals, sponges) and providing qualitative characterizations of the fish community. Subsequently, more quantitative work has been conducted; however, it has been limited in spatial scope. To complement these efforts, the current study addresses the following two goals put forth by sanctuary management: 1) to develop a sampling design for monitoring benthic fish communities across the coral caps; and 2) to obtain a spatial and quantitative characterization of those communities and their associated habitats.

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We report the amplification of 10-100-pJ semiconductor diode pulses to an energy of 158 μJ and peak powers >100 kW in a multistage fiber amplifier chain based on a single-mode, large-mode-area erbium-doped amplifier design. To our knowledge these results represent the highest single-mode pulse energy extracted from any doped-fiber system. © 1997 Optical Society of America.

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Monolithic multisection mode-locked semiconductor lasers with an integrated distributed Bragg reflector (DBR) have recently been demonstrated to generate stable picosecond pulses at high repetition rates suitable for optical communication systems. However, there has been very little theoretical work on understanding the physical mechanisms of the device and on optimisation of the absorber modulator design. This article presents numerical modeling of the loss modulated mode-locking process in these lasers. The model predicts most aspects experimentally observed within this type of device, and the results show the output waveform, optical spectrum, instantaneous frequency chirp, and stable operating range.

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A continuous Gaussian profile matched to the fundamental mode was etched onto the aperture of a vertical cavity surface emitting laser (VCSEL). Single Gaussian spot emission was achieved over the entire operating current range.

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The software package Dymola, which implements the new, vendor-independent standard modelling language Modelica, exemplifies the emerging generation of object-oriented modelling and simulation tools. This paper shows how, in addition to its simulation capabilities, it may be used as an embodiment design tool, to size automatically a design assembled from a library of generic parametric components. The example used is a miniature model aircraft diesel engine. To this end, the component classes contain extra algebraic equations calculating the overload factor (or its reciprocal, the safety factor) for all the different modes of failure, such as buckling or tensile yield. Thus the simulation results contain the maximum overload or minimum safety factor for each failure mode along with the critical instant and the device state at which it occurs. The Dymola "Initial Conditions Calculation" function, controlled by a simple software script, may then be used to perform automatic component sizing. Each component is minimised in mass, subject to a chosen safety factor against failure, over a given operating cycle. Whilst the example is in the realm of mechanical design, it must be emphasised that the approach is equally applicable to the electrical or mechatronic domains, indeed to any design problem requiring numerical constraint satisfaction.

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A new method has been used to design a power semiconductor device which combines IGBT switching and thyristor on-state characteristics. A single gate signal controls the switching and triggers the transitions between the IGBT and thyristor modes of operation. This paper discusses single-gated devices with multiple modes and aspects of their switching behaviour.

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The aim of this paper is to describe the growth and optimization of carbon nanotube (CNT) and CNT/Zinc Oxide nanostructures to produce novel electron sources. The emitters studied in this project are based on regular array of vertically aligned 5 μm height and 50 nm diameter CNTs with a pitch of 10 μm as described previously (1). Such a cathode design allows us to minimize electric field shielding effects and thus to help in optimizing the emitted current density. We have previously obtained a current density of 1 A/cm 2 from such arrays in DC mode, and over 12 A/cm2 in pulsed mode at RF frequencies. © 2010 IEEE.

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The Interdisciplinary Design for the Built Environment (IDBE) Masters program offers practicing professionals a structured process of interdisciplinary education and professional development. The course aims to equip all its students with the skills needed to meet these challenges. Most of those taking the course have demonstrated their abilities in their core disciplines and are moving to strategic and leadership roles for which they may well be under-prepared. The objectives of the course include giving students a strategic overview of the construction industry and of the production and management of built environment, as well as a critical perspective on the everyday knowledge and assumptions made in practice. The course also raises awareness of current research in the sector and its potential and limitations, and provides an introduction to professional ethics and the responsibilities owed by engineers and their colleagues to society as a whole.

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The conventional technology for generating ultrashort pulses relies on soliton-like operation based mode-locking. In this regime, the pulse duration is limited by nonlinear optical effects[1]. One method to mitigate these effects is to alternate segments of normal and anomalous group velocity dispersion (GVD) fiber[1]. This configuration is known as dispersion-managed soliton design. It decreases the nonlinear optical effects and reduces the pulse duration[1]. © 2011 IEEE.