Microwave hybrid fast sintering of red clay ceramics

This work aimed to examine the performance of the hybrid sintering of clay ceramic in a microwave furnace, compared to the sintering process in a conventional furnace. The raw materials were subjected to X-ray fluorescence, loss on ignition (LOI), X-ray diffraction, particle size distribution, real specific mass, and thermogravimetric analyses. The red clay ceramic mass was prepared, extruded, pre-sintered in a conventional furnace at 600°C/60 min, and sintered at temperatures between 700 °C and 1100 °C. The sintering conventional (resistive oven) was carried out for 60 min with a heating rate of 10°C/min. In the microwave furnace, the sintering times were 5, 10, and 15 min, with a heating rate of 50°C/min, with a sintering chamber coated with silicon carbide (susceptor). The sintered specimens were characterized according to linear shrinkage, water absorption, apparent porosity, apparent specific mass, X-ray diffraction, Raman spectroscopy analysis, spectroscopy analysis in the ultraviolet and visible regions, microhardness, and scanning electron microscopy. The results showed that microwave sintering promoted an increase in the microhardness and apparent specific mass, and reduction in water absorption and apparent porosity values, due to greater densification in the microstructure. The best results occurred for specimens sintered at 1100°C.     

Estimation of breast tumor thermal properties using infrared images

The major goal of this paper is to help detect breast cancer early based on infrared images. Some procedures, protocols and numerical simulations were developed or performed. Two different issues are presented. The first is the development of a standardized protocol for the acquisition of breast thermal images including the design, construction and installation of mechanical apparatus. The second part is related to the greatest difficulty for the numerical computation of breast temperature profiles that is caused by the uncertainty of the real values of the thermophysical parameters of some tissues. Then, a methodology for estimating thermal properties based on these infrared images is presented. The commercial software FLUENT^TM was used for the numerical simulation. A Sequential Quadratic Programming (SQP) method was used to solve the inverse problem and to estimate the thermal conductivity and blood perfusion of breast tissues. The results showed that it is possible to estimate the thermophysical properties using the thermography. The next stage will be to use the geometry of a real breast for the numerical simulation in conjunction with a linear mapping of the temperatures measured over the breast volume.     

Brazilian Solar Resource Atlas CD-ROM

The Brazilian Solar Resource Atlas CD-ROM is intended to be a tool for solar system design, delivering information that relies on a large interactive database, including, also, a modern device for calculating the solar radiation collected by planes inclined at different tilt angles or tracking the sun around one or two axes. The spatial distribution of the daily solar radiation, monthly and yearly averaged, that hits Brazil is presented in 13 colored maps, together with the methodological procedures used for harmonizing the information and designing the maps. A map containing the location of pyranometric and actinographic terrestrial stations, the information which was used for designing the maps, is also presented. The period of collected data runs from 1978 to 1990. Similarly, the atlas contains 13 colored maps, including daily insolation, monthly and yearly averaged, in addition to the map containing the location of the heliographic stations. The CD-ROM stores a database that includes over 500 stations located in Brazil and on the borders of its neighboring countries. The information is given either as daily, monthly average global solar radiation, or daily, monthly average insolation. A search device is included in the database, allowing to navigate over the maps or to select a desired location. The information may be printed as a report. The CD-ROM also includes a software to perform the following calculations: solar radiation estimates on a fixed plane at any inclination on North-South orientation; estimates of solar radiation collected by a plane tracking the sun about one or two axes; generation of synthetic series based on Markov’s Transition Matrixes.     

A multiobjective approach to the short-term scheduling of ahydroelectric power system

This paper is concerned with the short-term scheduling of the Iguacu river hydroelectric power system, in Southern Brazil. The system comprises four power plants with an unusual high coupling, held by two different utilities. Even though government regulations establishes operation guidelines, electric utilities have their own interests. A multiobjective framework is adopted to study the operation of the power system. Dynamic programming is used to find optimal solutions, with an implementation based on the concept of differential dynamic programming. A case study shows the possibility of obtaining energetic gains with the adoption of nonconventional operation rules and the need of negotiation to avoid wasting energy     

Assessing Decisions on Multiple Uses of Water and Hydroelectric Facilities

Hydroelectric systems no longer stay aside from conflicts in the use of water and facilities. As water and good sites become scarce, negotiation on multiple uses of hydro resources and sharing of costs and gains is a need. This paper gives an overview of quantitative tools designed to facilitate settlement of contentions in Brazilian hydroelectric systems. Two case studies are discussed, addressing scheduling policies for different utilities operating on the same stream and the operation of hydroplants when a variety of other users step into the scene. A framework of multiple criteria optimization is adopted in both cases, with solution approaches and computation engines tailored for each problem.     

Determination of Toxic Elements in Nuts by Inductively Coupled Plasma Mass Spectrometry after Microwave-Induced Combustion

Microwave-induced combustion (MIC) of nuts in closed vessels was evaluated as a sample preparation method for further determination of As, Cd, and Pb by inductively coupled plasma mass spectrometry (ICP-MS) and Hg by flow injection cold vapor generation coupled to ICP-MS (FI-CVG–ICP-MS). Conventional microwave-assisted acid digestion (MW-AD) in pressurized vessels was also used for results comparison. Samples were wrapped in polyethylene films and combusted using 20 bar of oxygen and 50 μl of 6 mol l^?1 ammonium nitrate as aid for ignition. Sample masses up to 500 mg of hazelnuts, almonds, cashew nuts, Brazil nuts, and walnuts were combusted using 7 mol l^?1 HNO₃ as absorbing solution. Accuracy was evaluated using certified reference materials and an agreement better than 96% was obtained for all analytes. Using MIC, it was possible to obtain lower limits of detection (LODs) in comparison with those obtained by MW-AD. The LOD obtained using MIC was 3, 2, and 6 ng g^?1 for As, Cd, and Pb, respectively. The LOD for Hg by FI-CVG–ICP-MS was 7 ng g^?1. Residual carbon content obtained after decomposition by MW-AD and MIC was 20% and lower than 1.5%, respectively, showing the high efficiency of MIC and allowing the determination of toxic elements in samples with high fat content. With the use of MIC up to eight samples could be processed simultaneously and only diluted nitric acid was required minimizing physical interferences, reagent consumption, and waste generation.     

Bromine, Chlorine, and Iodine Determination in Soybean and its Products by ICP-MS After Digestion Using Microwave-Induced Combustion

A method for bromine, chlorine, and iodine determination in soybean and related products was developed by inductively coupled plasma mass spectrometry (ICP-MS) after digestion by microwave-induced combustion (MIC). Samples were pressed as pellets and combusted using pressurized oxygen (20 bar) and ammonium nitrate solution (50 μL of 6 mol L^?1) as the igniter. Analytes were absorbed in alkaline solution (100 mmol L^?1 NH₄OH), and a reflux step of 5 min, microwave power of 1,400 W, was applied after combustion in order to improve analyte recoveries. For Cl determination by ICP-MS, a dynamic reaction cell was used with ammonia as the reaction gas. The accuracy was evaluated using certified reference materials (CRMs) and spiked samples. Using MIC, the agreement with CRM values and spike recoveries was higher than 95 % for all analytes for certified reference materials of a similar composition (National Institute of Standards and Technology (NIST), corn bran and NIST, whole milk). Limits of detection were 0.03, 1.2, and 0.002 μg g^?1 for Br, Cl, and I, respectively. The residual carbon content in the digests obtained after MIC procedure was lower than 0.5 %. Blanks were always negligible and no memory effects were observed. Digestion by MIC allowed processing up to eight samples by each run in 25 min with high efficiency of digestion providing a suitable medium for further bromine, chlorine, and iodine determination by ICP-MS.     

A contribution to the midterm scheduling of large scalehydrothermal power systems

A concise mathematical model and nonlinear minimization algorithm were presented as a joint approach to set optimal midterm production targets for power systems with predominance of hydroelectric power generation. The algorithm uses the network structure of the problem and takes into account nondifferentiable points. The approach was successfully applied to the optimal midterm scheduling of a very large hydroelectric power system in southeastern Brazil. Further insight into the problem allowed the adoption of an optimization-simulation strategy which achieved a very good suboptimal solution with great savings in computer requirements. The main purpose of this research was to develop a working tool able to assist engineers in setting optimized midterm targets for the large power systems in Brazil, where more than 90% of the electric energy comes from hydraulic sources     

The Use of Active Methodologies for Teaching–Learning Systems in Telecommunications

This article discusses the adoption of the Problem Based Learning (PBL) and Project Based Learning (P2BL) approaches in the teaching/learning process of telecommunications. A computational environment was defined to combine these two approaches which focused on the teaching of courses that cover topics related to telecommunications systems. Newly graduated professionals face difficulties when entering the job market, as they have to deal with situations that are not experienced in the academic world. There is still a tendency to rely on traditional approaches for the teaching of telecommunications systems that have proved to be inefficient, as they are only concerned with content and not the applications that the student will require in the job market. The aim of this research is to investigate whether the adoption of PBL and P2BL in a computational environment can enhance student learning more effectively than the traditional teaching approach. This involved conducting an experiment in 7 undergraduate classes to compare the performance of the students that adopted PBL and P2BL with that of the students who were taught with the traditional approach. Data were collected on the grades obtained by the students in the courses and these were statistically analyzed. The results show that the adoption of PBL and P2BL led to the students achieving a 32% increase in performance. However, it was noted that the infrastructure of the institutions directly influences the way the approaches are adopted and, hence affects, the results.

     

A review and comparative study of upwind biased schemes for compressible flow computation. Part I: 1—D first—order schemes

Summary First-order upwind biased formulations for simulating 1-D compressible flows are presented within a unified framework. A detailed study and comparison of the different formulations is important, as high-resolution extensions are known to inherit both the good and bad features of the first-order formulations used for their construction. The most popular flux difference splitting, flux vector splitting and some recently proposed hybrid splitting methodologies are considered. A finite element solution approach is adopted, as this provides a framework for the multidimensional extension of the solvers. Representative one-dimensional test cases are considered in order to provide evidence of the effectiveness and performance of the formulations. The results that are presented, together with the corresponding exact solutions, provide a set of benchmark test cases for comparison purposes.