THE PEAK WINDOWING FOR PAPR REDUCTION IN SOFTWARE DEFINED RADIO BASE STATIONS

The utilization of the techniques for Peak to Average Power Ratio (PAPR) reduction makes the wireless infrastructure conform to rigorous telecommunication standard specifications (error vector magnitude (EVM), bit error rate (BER), transmit spectrum mask (TSM)). In modern modulation schemes reduction of PAPR is important requirement for distortion free and energy-efficient operation of power amplifiers (PA). In this paper novel implementation of Peak Windowing method for PAPR reduction in Software Defined Radio (SDR) Base Stations (BS) is presented. The measurement results in terms of EVM and ACPR are given for 5MHz, 10MHz, 15MHz, 20MHz Long-Term Evolution (LTE) and Wideband Code Division Multiple Access (WCDMA) modulations. In case of 10MHz LTE signal, we achieved PAPR=8dB, EVM=2.0%, ACPR -52dBc at modulated PA output, antenna point

Effect of the cooling rate on microstructure and hardness of MAR-M247 Ni-based superalloy

The effect of cooling rate on the microstructure of MAR-M247 Ni-based superalloy was investigated via physical simulation of the casting process. Solidification experiments with cooling rates in the range of 0.25–10 K/s showed smooth temperature profiles with measured cooling rates matching the set values. The MAR-M247 showed cellular (0.25 K/s) and dendritic (1, 5 and 10 K/s) microstructures. Microconstituents also varied with cooling rates: γ/γ′ matrix with carbides and γ/γ′ eutectic at 0.25 K/s, γ/γ′ matrix with carbides at 1 K/s, and γ/γ′ matrix with carbides and γ/MC eutectic at 5 and 10 K/s. Moreover, the secondary dendritic arm spacing decreased and the hardness increased with the increase in the cooling rates

Nanomechanics of Single Crystalline Tungsten Nanowires

Single crystalline tungsten nanowires were prepared from directionally solidified NiAl-W alloys by a chemical release from the resulting binary phase material. Electron back scatter diffraction (EBSD) proves that they are single crystals having identical crystallographic orientation. Mechanical investigations such as bending tests, lateral force measurements, and mechanical resonance measurements were performed on 100–300 nm diameter wires. The wires could be either directly employed using micro tweezers, as a singly clamped nanowire or in a doubly clamped nanobridge. The mechanical tests exhibit a surprisingly high flexibility for such a brittle material resulting from the small dimensions. Force displacement measurements on singly clamped W nanowires by an AFM measurement allowed the determination of a Young's modulus of 332 GPa very close to the bulk value of 355 GPa. Doubly clamped W nanowires were employed as resonant oscillating nanowires in a magnetomotively driven resonator running at 117 kHz. The Young's modulus determined from this setup was found to be higher 450 GPa which is likely to be an artefact resulting from the shift of the resonance frequency by an additional mass loading

Preparation and caracterization of in situ composite materials based on the Ni-Si eutectic alloys

Orientador: Rubens Caram JuniorDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecanicaResumo: A busca por materiais estruturais para aplicações em temperaturas elevadas tem estimulado o interesse por ligas eutéticas. Em diversos sistemas, a estrutura eutética exibe estabilidade térmica inerente e pennite obter um material compósito, com microestrutura alinhada e finamente dispersa, diretamente do fundido através da solidificação direcional. Portanto, a solidificação direcional de ligas eutéticas constitui-se em uma ferramenta atraente para produzir uma gama de materiais compósitos, evitando as operações complexas associadas às altas temperaturas envolvidas. O presente trabalho abrangeu a investigação de liga eutética Ni-Si localizada na parcela rica em Ni do diagrama de fase Ni-Si. A elaboração do presente trabalho teve como objetivo principal a investigação da microestrutura de solidificação e as características de morfologia no tocante às condições de solidificação. A caracterização das amostras, além da microscopia óptica e eletrônica de varredura, incluiu o emprego das técnicas de análise ténnica, de difração de raios-X, de espectroscopia por dispersão de energia, bem como ensaios mecânicos. Os resultados obtidos indicam que a solidificação direcional do eutético Ni-Nh Si resulta em uma microestrutura lamelar bem alinhada, sem presença de dendritas ou colônias eutéticas. Além disso, a relação quantitativa entre o espaçamento lamelar e taxa de solidificação foi estabelecida. Os ensaios mecânicos mostraram que um material compósito de alta resistência mecânica e ductilidade razoável foi obtido. Finalmente, constatou-se que apesar da presença de uma fase intermetálica, uma estrutura com alta regularidade foi obtidaAbstract: The search for new high-temperature structural materiaIs has stimulated much interest in eutectic alloys. The eutectic microstructure of many systems posses inherent termal stability and it may result in a composite material, with an aligned, finely dispersed microstructure directly from the melt by directional solidification. Thus, the directional solidification of the eutectic alloys constitutes an attractive mean of producing a variety of composite materials avoiding many of the complex processing operations. The present work is concemed with investigation of the Ni-Si eutectic alloys from the Ni-rich part of the Ni-Si phase diagram. The basic aim was to study the solidification microstructure and morphology characteristics regarding the solidification conditions. The characterization included optical and scanning electron microscopy, thermal analasys, X-ray diffraction, energy dispersive spectometry and mechanical testing. The results obtained indicate that the Ni-NhSi eutectic is characterised by cell and dendrite-free and well-aligned lamellar structure on a micron scale. In addition, the scaling laws of the variation in lamellar spacing with growth rate are quantitatively developed. Mechanical testing showed that the high-strength composite material with a moderate ductility was developed. Finally, despite the presence of an intermetallic phase, highly regular structure was obtained.MestradoMateriais e Processos de FabricaçãoMestre em Engenharia Mecânic

High Temperature Materials - EUROMAT 2019 / Area B: Structural Materials

EUROMAT 2019 / Area B: Structural MaterialsThe aspiration for improved thermal efficiency in energy conversion and aircraf propulsion systems is now dramatically increasing the demand for structural materials capable of operating at ever-higher temperatures and stresses. To meet this plea, there has been considerable progress in the development and enhancement of established materials such as steels and nickel-base superalloys through improvements in both alloy composition and production processing methods. Recently, there has also been active development of alternative metallic and intermetallic materials that may meet some of these requirements. Some of these materials, such as TiAl, are reaching a level of maturity, which may soon see their more widespread use, particularly in gas-turbine applications, whilst others, such as refractory metal silicides show promise for the future. This symposium also aims to be a meeting point for those interested in alloys (steels, oxide dispersion strengthened alloys, intermetallics) for structural applications under extreme environments in energy generation systems where superior corrosion and creep resistance are paramount. The High Temperature Alloys Symposium will focus on the latest progress and developments related to microstructure, processing, properties and applications of high temperature alloys (e.g. Heat resistant steels, Superalloys, Intermetallics). Topics of interest range from fundamentals of phase constitution, stability and transformations, over alloy development, microstructure, mechanical and environmental response, to developments in processing methods and in technological aspects for successful commercial applications. Contributions are welcome of both experimental and modelling nature

Mechanical properties and fracture behavior of directionally solidified nial-v eutectic composites

Directional solidification of eutectic alloys has been recognized as promising technique for producing in situ composite materials exhibiting balance of properties. Therefore, an in situ NiAl-V eutectic composite has been successfully directionally solidified using Bridgman technique. The mechanical behavior of the composite including fracture resistance, microhardness, and compressive properties at room and elevated temperatures was investigated. Damage evolution and fracture characteristics were also discussed. The obtained results indicate that the NiAl-V eutectic retains high yield strength up to 1073 K (800 °C), above which there is a rapid decrease in strength. Its yield strength is higher than that of binary NiAl and most of the NiAl-based eutectics. The exhibited fracture toughness of 28.5 MPa√m is the highest of all other NiAl-based systems investigated so far. The material exhibited brittle fracture behavior of transgranular type and all observations pointed out that the main fracture micromechanism was cleavage462557565FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPNão temFunding of the Project NECTAR (PCIG10-GA-2011-303409) by the Marie Curie Actions Grant FP7-PEOPLE-2011-CIG program is gratefully acknowledged. SM acknowledges the Ramon y Cajal fellowships from the Spanish Ministry of Economy and Competitiveness. The financial support from the São Paulo State Research Foundation (FAPESP, Brazil) is acknowledge

Wettability and Infiltration of Liquid Silicon on Graphite Substrates

The energy crisis has stimulated a rapid growth of developments in the photovoltaic industry in recent years. To reduce the high cost and the toxicity of classical metallurgical routes, new methods, such as vacuum refining of silicon, have been developed. Moreover, at the industry level, parameters such as the porosity in crucibles and dies are not controlled, so wettability, infiltration, and reaction between silicon and graphite are the key factors in the purification process. In this work, the behavior of several refractory substrates against melted silicon was studied by the classic sessile drop method. The most important phenomena, i.e., wettability and infiltration, were compared with the properties of the substrates. According to the results, for the carbonaceous materials, the reaction of triple line silicon-graphite manages these phenomena, whereas for alumina, a passive layer is formed due to the presence of oxygen, which is subsequently eliminated by the chemical reactions, delaying the process. Regarding the contact angle and infiltration behavior, alumina showed the best results, but due to its reactivity, it contaminates Si, so that this material is not recommended for solar silicon application. However, composite 2 is compatible with the application, as it shows good results in comparison with the other materials

Rapid fabrication and characterization of AISI 304 stainless steels modified with Cu additions by additive alloy melting (ADAM)

Rapid alloy prototyping is quickly emerging as a manufacturing approach to design novel structural alloys since allows producing low volume of high quality castings quickly at low cost. Thus, a large number of alloys can be produced and tested for finding the optimal composition in an alloy system. In this work, a new high throughput method for rapid alloy manufacturing has been developed and employed to cast AISI 304 stainless steel samples modified with an addition of Cu in the range of 1–4 wt.%. The homogeneity of the microstructure and chemical composition of as-cast materials has been characterized at the macro- and micro-scale, using optical and scanning electron microscopy, X-ray fluorescence, X-ray diffraction and electron probe microanalysis. At the macro-scale, no compositional variations have been found, while variations in the distribution of phases in the microstructure were related to variations in the cooling rate and thermal path undergone across the solidifying ingot. At the micro-scale, it has been found that segregation of austenite and ferrite stabilizing elements occurs during solidification, as expected from the phase diagram. Additive alloy melting (ADAM) has been demonstrated to be a suitable, rapid and versatile casting method for manufacturing metallic samples on a laboratory scale with good chemical homogeneity at the macro-scale. Keywords: AISI 304 stainless steel, Rapid alloy manufacturing, Additive alloy melting, Solidification, Microstructural characterizatio