Densification behavior and properties of alumina–chrome ceramics: Effect of TiO2

Highly dense alumina–chrome bodies with low porosity are usually used as corrosion and thermal resistant refractories. Alumina–chrome refractory with molar ratio 1:1 was developed using chemical grade hydrated alumina and chromium (III) oxide by conventional sintering route. Batch materials were attrition milled, isostatically pressed and sintered in the temperature range from 1000 °C to 1700 °C with 2 h soaking at peak temperature. Phase development of the sintered materials with temperature was studied by X-ray diffraction. Sintering temperature, sintering condition and addition of sintering aid (TiO₂) have immense effect on the densification of the alumina–chrome refractory. Highly dense alumina–chrome refractory with almost nil apparent porosity was developed at 1500 °C in reducing atmosphere. Flexural strength of the sintered materials at room temperature and at 1200 °C was also measured. 1 wt% TiO₂ gives the optimum result with respect to densification and flexural strength.     

Stochastic ADC with random U-quadratic distributed reference voltages to uniformly distribute comparators trip point

Stochastic ADC with uniformly distributed comparators trip point is presented. A basic comparator will have an offset that follows Gaussian distribution. When the comparator offset is used as the trip points for stochastic ADC, only 68 % of the comparators will be in the useful input range. By adding voltages that follow random U-quadratic distribution to the comparators’ reference inputs, their trip points will shape into uniform distribution, and 80 % of them will lie within the useful input range. That will not only increase the resolution of stochastic ADC but also its input dynamic range.     

Thermal evolution of Al2O3–CaO–Cr2O3 castables in different atmospheres

Al₂O₃–CaO–Cr₂O₃ castables are required for various furnaces linings due to their excellent corrosion resistance. However, toxic and water-soluble Cr(VI) could be generated in these linings during service. In this study Al₂O₃–CaO–Cr₂O₃ castables were prepared and heated at 300–1500 °C in air and coke bed to simulate actual service conditions. The formations of various phases were investigated by XRD and SEM-EDS. The Cr(VI) compounds CaCrO₄ and Ca₄Al₆CrO₁₆ formed in air at 300–900 °C and 900–1300 °C respectively, while C₁₂A₇ and CA₂ were generated rather than forming Cr(VI) compounds in coke bed at 700–1300 °C. However, at 1500 °C, nearly all the chromium existed in the form of (Al_1-xCr_x)₂O₃ solid solution in both atmosphere. As a result, the specimens treated in air contained 185.0–1697.8 mg/kg of Cr(VI) at 500–1300 °C but only 17.2 mg/kg of Cr(VI) at 1500 °C, whereas specimens treated in coke bed exhibited extremely low Cr(VI) concentration in the whole temperature range studied. Moreover, in coke bed, the mutual diffusion between Cr₂O₃ and Al₂O₃ was suppressed and a trace of Cr₂O₃ would even be reduced to form chromium-containing carbides on its surface, which would hindered the sintering process and hence lower the density as well as strength of the castables.     

Product backlog rating: a case study on measuring test quality in scrum

Agile software development methodologies focus on software projects which are behind schedule or highly likely to have a problematic development phase. In the last decade, Agile methods have transformed from cult techniques to mainstream methodologies. Scrum, an Agile software development method, has been widely adopted due to its adaptive nature. This paper presents a metric that measures the quality of the testing process in a Scrum process. As product quality and process quality correlate, improved test quality can ensure high-quality products. Also, gaining experience from 8 years of successful Scrum implementation at SoftwarePeople, we describe the Scrum process emphasizing the testing process. We propose a metric Product Backlog Rating (PBR) to assess the testing process in Scrum. PBR considers the complexity of the features to be developed in an iteration of Scrum, assesses test ratings and offers a numerical score of the testing process. This metric is able to provide a comprehensive overview of the testing process over the development cycle of a product. We present a case study which shows how the metric is used at SoftwarePeople. The case study explains some features that have been developed in a Sprint in terms of feature complexity and potential test assessment difficulties and shows how PBR is calculated during the Sprint. We propose a test process assessment metric that provides insights into the Scrum testing process. However, the metric needs further evaluation considering associated resources (e.g., quality assurance engineers, the length of the Scrum cycle).     

Control of stationary and transportation fuel cell systems: Progress and opportunities

Fuel cell power systems have witnessed intense development in the recent years as they offer a clean and efficient alternative for power generation in stationary and transportation applications. In this paper, we present an overview of recent work on dynamic modeling and control design for stationary and transportation fuel cell systems including the research at United Technologies Corporation.The use of equation oriented modeling framework for system level dynamic modeling enabled by tools, such as Dymola and gPROMS is described. It is demonstrated that the non-linear system level models readily allow linear model derivation and the application of advanced control analysis and design techniques that provide more insight into the system level dynamic and control issues in fuel cell systems. The dynamic modeling and advanced control design research performed at UTC for a hydrogen fed PEMFC power plant for a bus and a natural gas fed PEMFC power plant for stationary power generation is described.We also identify, for future research, the challenges and opportunities in several areas relating to fuel cell systems ranging from power management and freeze startup to system level modeling, control, diagnostics and hardware-in-the-loop validation of the control system. The emphasis is on polymer electrolyte membrane fuel cell (PEMFC) systems but phosphoric acid fuel cell (PAFC) systems are also briefly discussed.