Energy efficiency of mmWave massive MIMO precoding with low-resolution DACs

With the congestion of the sub-6 GHz spectrum, the interest in massive multiple-input multiple-output (MIMO) systems operating on millimeter wave spectrum grows. In order to reduce the power consumption of such massive MIMO systems, hybrid analog/digital transceivers and application of low-resolution digital-to-analog/analog-to-digital converters have been recently proposed. In this work, we investigate the energy efficiency of quantized hybrid transmitters equipped with a fully/partially-connected phase-shifting network composed of active/passive phase-shifters and compare it to that of quantized digital precoders. We introduce a quantized single-user MIMO system model based on an additive quantization noise approximation considering realistic power consumption and loss models to evaluate the spectral and energy efficiencies of the transmit precoding methods. Simulation results show that partially-connected hybrid precoders can be more energy-efficient compared to digital precoders, while fully-connected hybrid precoders exhibit poor energy efficiency in general. Also, the topology of phase-shifting components offers an energy-spectral efficiency trade-off: active phase-shifters provide higher data rates, while passive phase-shifters maintain better energy efficiency.Comment: Published in IEEE Journal of Selected Topics in Signal Processin

Influence of free fatty acid content in biodiesel production on non-edible oils

The use of alternative feedstock as waste cooking oils (WCO) and bovine tallow for biodiesel production has some advantages. It is cheaper than edible vegetable oils and it is a way to valorize a sub-product. Nevertheless, these oils possess some contaminants, specially free fatty acid (FFA) content, which can reduce the quality and yield of biodiesel production. This problem was solved by testing different operating conditions and different transesterification procedure and equipments for each stage of processing. Technological assessment of process was carried out to evaluate their technical benefits, limitations and quality of final product. In this work biodiesel was produced by an alkali-catalyzed transesterification and by a two step esterification/alkali-catalysed transesterification in cases which FFA content has above 3%. Evaluation of quality from raw materials and final biodiesel was performed according to standard EN 14214. Results show that all parameters analyzed meet the standard and legislation requirements. This evidence proves that in those operational conditions the biodiesel produced from WCO and bovine tallow can substitute petroleum-based diesel

Small sized pilot scale experiments on the recovery cooper and nickel hydroxide from galvanic sludge

The present work, carried out within the project VALMETAIS, proposes a hydrometallurgical process for copper and nickel recovery from galvanic sludges produced by Ni/Cr plating plants. The procedure has been developed on laboratory scale and the results validation was verified in a small sized pilot scale. The project starts with a leaching process of sludge in sulphuric acid solution in three stages followed by copper cementation step, using iron scrap as precipitating agent. It was found that metals dissolution was almost completed for the three stages of leaching process. Extraction rates of 99% for Cu and Ni were achieved under the leaching. The solid residue separated from the leaching solution is mostly constituted by gypsum (CaSO4), and presents heavy metal content below 1%. Copper cementation process was performed at a pH of 2. Such pH level led to insignificant precipitation of other metals present in the leaching solution, particularly chromium. The recovery rate of copper is about 99% with a purity grade of 99% which enables its application as a commercial product. Nickel hydroxide precipitation was performed by adding sodium hydroxide solution. Results showed a successfully nickel hydroxide extraction obtaining 99% with a purity grade of more than 98%. These evidences demonstrate the high potential of this methodology to treat and derive economic benefits from galvanic sludge. The end products cooper and nickel can be applied as a commercial product generating a profit and the gypsum based sludge from the leaching process can be reutilized as component of construction materials.QREN (NORTE-01-0202-FEDER-005509

Waste management in Portugal and Europe: an overview of the past, present and future

As word society has grown exponentially it was created more and more wastes. Each year European Union throws away 3 billion tons of waste, and some 90 million tons of that are hazardous. It is clear that treating and disposing of all this material - without harming the environment becomes a major trouble. In the early years 90 the amount of waste generated in Europe increased by 10%. Most of that was thrown away in incinerators, or dumped into landfill creating environmental damage. Landfill disposal not only takes valuable land space but also causes air, water and soil pollution, discharging carbon dioxide (CO2) and methane (CH4) into the atmosphere and chemicals and pesticides into the earth and groundwater. This situation is harmful to human health as well as to plants and animals. These events triggered urgency for a responsibility and appropriate legislation for correct waste management. EU and Portuguese policy main objective in the waste management are prevent and reduce waste production, and reduce their toxicity, through the reuse and modification of production processes, adopting cleaner technologies. Waste management must also avoid or at least reduce its risk to human health and to environment. In Portugal, wastes sector was suffered a revolution on the last years, due to the appearance of the Strategic Plan for Solid Waste I (PERSU I) in 1997 and by the constant pressure from the EU for their state members and waste producers. In December 2006 was created the PERSU II to correct all mistakes made in the previous plan. However soon realized that PERSU II had very ambitious goals and so unattainable that triggered the need to reformulate these objectives. The aim of this overview in waste management was to follow the goals outlined in PERSU II, identifying the progress of each operational system over the years. It was also the target compare those results to European statistics tracing possible ways to permit compliance with EU objectives in future

A importância da infra-estrutura de transportes públicos colectivos em aglomerados urbanos de pequena dimensão ma promoção de uma mobilidade sustentável

Os aglomerados urbanos de pequenas dimensões apresentam, habitualmente, padrões de mobilidade centrados na utilização do veículo privado em detrimento de modos de transporte mais sustentáveis, como são os casos do transporte público e dos modos suaves, fruto do tipo de actividades que aí se desenrolam. Assim, um desenvolvimento urbano mais sustentável deve promover a adopção de medidas de apoio para os modos de transporte menos poluentes e mais eficientes de ponto de vista da mobilidade. Para este efeito, o nível de infra-estruturação e equipamentos de apoio deve ser adequado às necessidades dos seus utilizadores e possuir uma boa visibilidade em contexto urbano. Desta forma, será apresentado uma proposta de intervenção e organização ao nível do transporte público colectivo de passageiros, nomeadamente ao nível do estudo, caracterização e desenho de paragens de autocarros, sendo apresentado o caso de estudo da Vila de Póvoa de Lanhoso

Acessibilidade pedonal em espaço público exterior: requalificação do centro urbano de Guimarães

Todo o espaço urbano é fruto de uma multiplicidade de vicissitudes históricas, bem como o resultado contingencial de uma ampla variedade de circunstâncias económicas e políticas. Excetuando situações extremas, o crescimento das cidades resulta de processos de expansão relacionados com o aumento da população, bem como de novos usos do solo e dos seus edifícios. O maior interesse de uma cidade reside no seu espaço, porque é nele que se desenvolvem as diversas atividades socioeconómicas. Deste modo, para avaliar a qualidade de vida de uma cidade importa desenvolver uma análise da qualidade dos seus espaços exteriores e dos seus elementos estruturais. O objetivo deste trabalho é o de propor ações de requalificação do ambiente pedonal urbano de forma a responder às necessidades dos peões, nomeadamente das pessoas com mobilidade reduzida, com vista a aumentar os níveis de conforto e qualidade de vida dos cidadãos e visitantes da cidade de Guimarães

Adsorption process onto an innovative eggshell-derived low-cost adsorbent in simulated effluent and real industrial effluents

ISBN 978-989-97429-1-8As the current global trend towards more stringent environmental standards, technical applicability and cost-effectiveness became key factors in the selection of adsorbents for water and wastewater treatment. Adsorption is by far the most versatile and widely used method for the removal of pollutants due to its high removal capacity and ease of operation at large scale. Recently, various low-cost adsorbents derived from agricultural waste, industrial by-products or natural materials, have been intensively investigated. In this respect, the eggshells from egg-breaking operations constitute significant waste disposal problems for the food industry, so the development of value-added by-products from this waste is to be welcomed. The egg processing industry is very competitive, with low profit margins due to global competition and cheap imports. Additionally, the costs associated with the egg shell disposal (mainly on landfill sites) are significant, and expected to continue increasing as landfill taxes increase. The aim of the present was to provide an overview on the adsorption process both on simulated and real effluents onto eggshell-derived adsorbent. This was accomplished by analyzing the uptake potential for selected contaminants. Real wastewater effluents were studied to determine the effectiveness of this low cost adsorbent. Results obtained shown that eggshell can remove several pollutants from different types of aqueous systems, with great efficiency

Feature selection for bankruptcy prediction: a multi-objective optimization approach

In this work a Multi-Objective Evolutionary Algorithm (MOEA) was applied for feature selection in the problem of bankruptcy prediction. The aim is to maximize the accuracy of the classifier while keeping the number of features low. A two-objective problem - minimization of the number of features and accuracy maximization – was fully analyzed using two classifiers, Logistic Regression (LR) and Support Vector Machines (SVM). Simultaneously, the parameters required by both classifiers were also optimized. The validity of the methodology proposed was tested using a database containing financial statements of 1200 medium sized private French companies. Based on extensive tests it is shown that MOEA is an efficient feature selection approach. Best results were obtained when both the accuracy and the classifiers parameters are optimized. The method proposed can provide useful information for the decision maker in characterizing the financial health of a company