Daniel A. Macedo

A dependability evaluation tool for the Internet of Things

The Internet of Things (IoT) is a promising networking paradigm which immerses objects (cell phones, goods, watches, sensing motes, TVs, etc.) in a worldwide connection. Despite its high degree of applicability, the IoT faces some challenges. One of the most challenging problems is its dependability (reliability and availability), since a device failure might put people in danger or result in financial loss. The lack of a design tool for assessing the dependability of IoT applications at the early planning and design phases prevents system designers from optimizing their decisions so as to minimize the effects of such faults on the network devices. In this paper, we propose a dependability evaluation tool for IoT applications, when hardware faults and permanent link faults are considered.

A dependability evaluation for Internet of Things incorporating redundancy aspects

The Internet of Things (IoT) is a promising networking paradigm which immerses objects (cell phones, goods, watches, sensing motes, TVs, etc.) in a worldwide connection. Despite its high degree of applicability, the IoT faces some challenges. One of the most challenging problems is its dependability (reliability and availability), since a device failure might put people in danger or result in financial loss. An alternative to mitigate these consequences is the adoption of a strategy based on spare devices. If a primary device fails, the spare device could assume its functions in a safe way. Thus, this work proposes mathematical models based on Markov Chain which is able to estimate the reliability and availability of IoT applications considering redundancy aspects. The proposal can be used in order to provide valuable data at the early planning and design phases of an IoT application.

Preparação de compósitos alumina-mulita de baixo custo via sinterização reativa entre uma argila caulinítica da Paraíba e hidróxido de alumínio

This work aimed to evaluate the effects of processing on microstructure and properties of alumina-mullite composites via reactive sintering of a mixture of kaolinite clay and aluminum hydroxide. Cylindrical pellets were pressed at 40 MPa and sintered between 1300 and 1600 °C. The technological properties were determined as a function of sintering temperature. The evaluation of crystalline phases and microstructure was performed by X-ray diffraction and electron microscopy. Structural results indicate the attainment of mullite and alumina at 1300 °C. Apparent porosity below 0.8% and flexural strength higher than 40 MPa were obtained for sintering temperatures above 1450 °C. A flexural strength as high as 70 MPa was obtained after sintering at 1600 °C. This study demonstrates the possibility of preparing low cost alumina-mullite composites with technological properties compatible with those of ceramics produced by companies with large operations in the international market of refractory products.

Infrared Spectroscopy Techniques in the Characterization of SOFC Functional Ceramics

Infrared spectroscopy is certainly one of the most important analytical techniques available nowadays for scientists. One of the greatest advantages of infrared spectroscopy is that virtually any sample in any physical state can be analyzed. The technique is based on the vibrations of atoms of a molecule. An infrared spectrum is obtained by passing infrared radiation through a sample and determining what fraction of the incident radiation is absorbed at a particular energy. The energy at which any peak in an absorption spectrum appears corresponds to the frequency of a vibration of a part of a sample molecule (Stuart, 2004).

Residue Characterization from Polishing Granite Submitted to the Hydrocycloning Process

The waste generated in granite processing has caused great social and environmental concern due to the release of its solid effluents into landfills and other places. The recycling and reuse of waste from different industrial processes as new raw materials has been the object of various researches. The use of hydrocyclone in the treatment of residues can represent a very efficient tool for separation and purification of the granite residue. This work aims to characterize and analyse the technological properties of the granite sawdust residues submitted to the hydrocyclone process in comparison with the same residue without going through the hydrocyclone process. The results indicate that the material resulting from this process presented different characteristics from the material without the process, mainly in terms of granulometric distribution and technological properties.

Estudo da incorporação de pó de concha de marisco em massa de porcelanato

The fishing of shellfish is one of the most important commercial activities of the fishing community of the municipality of Cabedelo (Paraíba, Brazil). The step of processing, after the extraction of the mollusk, generates a large amount of shells, whose discharge, in considerable volume, causes silting of large areas and consequent environmental imbalance. In the search for the use of these residues (mollusk shells) and aiming at reducing the environmental problems caused, this work had the aim of studying the incorporation of mollusk shell powder in the mass of porcelain tile. Ceramic compositions were formulated from an industrial standard mass and mollusk shell powder or commercial CaCO3 ranging from 0 to 7% by weight. Samples prepared by uniaxial pressing had their technological properties evaluated as a function of the sintering temperature. The results indicated that the use of up to 7 wt% of the mollusk shell powder maintains the technological properties within the standards required by the ABNT (Brazil) for classification as BIa type porcelain tiles.

One-step synthesis and microstructure of CuO-SDC composites

An in situ one step synthesis route based on the polymeric precursor method was used to produce dual phase CuO-samaria doped ceria (SDC) nanocomposite powders. This chemical route allowed to obtain composite powders with reduced particle size and uniform distribution of Cu, Ce and Sm elements. The particulate material was characterized by powder X-ray diffraction (XRD) combined with Rietveld refinement. CuO-SDC sintered in air between 950 to 1050 °C and subsequently reduced to Cu-SDC cermets were further characterized by XRD and scanning electron microscopy. The open porosity was measured using the Archimedes’ principle. Suitable microstructures for both charge transfer and mass transport processes (30 to 45% porosity) were attained in Cu-SDC cermets previously fired at 1000 to 1050 °C. Overall results indicated that CuO-SDC composites and Cu-SDC cermets with potential application as anodes for solid oxide fuel cells (SOFCs) can be obtained by microstructural design. An anode supported half-cell was prepared by co-pressing and co-firing gadolinia doped ceria (CGO) and the herein synthesized CuO-SDC nanocomposite powder.

Citrate-Hydrothermal Synthesis and Electrochemical Characterization of La0.6Sr0.4Co0.2Fe0.8O3 for Intermediate Temperature SOFC

Lanthanum cobaltites doped with strontium and iron (La1-xSrxCo1-yFeyO3) have been intensively studied as cathode materials for solid oxide fuel cells (SOFC). In this work, powders of composition La0.6Sr0.4Co0.2Fe0.8O3 (LSCF6428) were synthesized by a combination of citrate and hydrothermal methods. As-prepared and calcined powders were investigated by different material characterization techniques. LSCF films were obtained on gadolinium doped ceria substrates (CGO) after sintering at 1200 °C. The effects of the sintering conditions on the microstructure and electrochemical performance of the electrodes were evaluated by scanning electron microscopy and impedance spectroscopy. The electrochemical characterization was assessed using a symmetrical cell configuration (LSCF/CGO/LSCF) at temperatures ranging from 650 to 800 °C. The area specific resistance showed strong relationship with microstructure. The best electrochemical behavior (0.18 ohm.cm2 at 800 °C) was obtained by using sintering dwell time of 2 h.

Study on the Viability of Using Drill Cuttings from the Potiguar Basin in the Production of Ceramic Products: Influence of Concentration and Firing Temperature

Drill cuttings are wastes produced on a large scale during the drilling of oil wells. Although there are several treatment techniques, there is still no consensus on which one are the best for the economy and environmental. On the other hand, one of the alternatives for the reuse of this waste, and purpose of the present study, is the incorporation of drill cuttings in clay matrixes. The raw materials used in this work, a mixture of clays and drill cuttings, were investigated by two basic techniques of characterization. X-ray fluorescence and X-ray diffraction. In order to evaluate the effect of the content of drill cuttings on the technological properties of sintered ceramics, different formulations containing from 0 wt.% to 100 wt.% of drill cuttings in a clay matrix were obtained. Ceramic samples were obtained by firing at temperatures ranging from 850 °C to 1050 °C. The fired specimens were characterized by water absorption, firing linear shrinkage, resistance to bending three points and scanning electron microscopy analysis. The results indicated that the incorporation of drill cuttings is a viable alternative for the manufacture of several ceramics products, such as solid masonry bricks and ceramic blocks, at certain concentrations and firing temperatures.

Microwave-assisted hydrothermal synthesis of NiO-Ce1-XEuxO2-δ powders for fuel cell catalytic anodes

Universidade Estadual Paulista Julio de Mesquita Filho,Instituto de Quimica de Araraquara, Araraquara, Rua Prof. Francisco Degni, 55, Quitandinha, CEP 14801970, SP, Brasil