Polyurethane‐infiltrated carbon foams: A coupling of thermal and mechanical properties

The thermal and mechanical properties of polyurethane‐infiltrated carbon foam of various densities were investigated. By combining the high thermal conductivity of the carbon foam with the mechanical toughness of the pure polyurethane, a mechanically tough composite (relative to the unfilled foam) that could be used at higher temperatures than the polyurethane's degradation was formed. Both the tensile strength and the modulus increased by an order of magnitude for the composites compared to unfilled foam, while the compressive and shear strengths and moduli of the composites approached values exhibited by pure polyurethane. At both 300 and 400°C, the rectangular blocks of pure polyurethane lost their mechanical integrity due to decomposition in air. Thermogravimetric analysis confirms substantial initial weight loss above 290°C. Filled carbon foam blocks, however, maintain their mechanical integrity at both 300 and 400°C indefinitely, although the bulk of the rectangular block mass is polyurethane. Three different carbon foam densities are examined. As expected, the higher density foams show greater heat transfer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2348–2355, 2003     

Transformation Toughening in Large-Grain-Size CeO2-Doped ZrO2 Polycrystals

The fracture and transformation behavior of tetragonal polycrystalline ZrO₂ alloys containing 18 mol% CeO₂ (Ce-TZP) was investigated. In the absence of applied stress the tetragonal phase was found to be stable in large-grained (>30 μm) samples at room temperature. The monoclinic phase was detected in regions of high residual stress near hardness indentations although no evidence of a wake of monoclinic phase along the fracture surface was observed. The fracture toughness increased from 4 to 7 MPa · m^1/2 as density and/or grain size increased. It is proposed that the relatively high toughness of these materials is due to the occurrence of stress-driven tetragonal-to-monoclinic transformation near the crack tip, which reverses when the crack has passed.     

Factors influencing the photofading of commercial anthraquinone dyes in solution

The photofading of two anthraquinone dyes has been studied in aqueous solution using ultraviolet-visible absorption spectroscopy and flash photolysis. The influence of alcohol concentration, pH, atmosphere, photosensitisers and stabilisers have been examined and these lead to some important conclusions on the mechanism of dye fading. Essentially, the results indicate the photoexcited triplet state of the dye undergoes a process of either electron or hydrogen-atom abstraction depending on the nature of the environment. Other factors such as aggregation and singlet oxygen also appear to play an important role in solution photofading. The relevance of these results to photofading in a polymeric phase is discussed.     

Microstructure and Mechanical Properties of Mullite–Silicon Carbide Composites

Mullite-SiC-whisker composites were prepared by powder processing using two commercial SiC whiskers. These composites were prepared by sintering rather than hot-pressing. A mulliteSlC-powder composite and a base line mallite material were also prepared for comparison with the two whisker composite materials. Fracture toughness measurements showed significant enhancement in only one of the whisker composite materials. The microstructure of the four materials was examined by scanning electron microscopy and transmission electron microscopy to assist in the explanation of the mechanical behavior of these composites. The examinations suggested that most of the toughening results from second-phase particles, with only limited toughening from effects associated with whiskers per se. In one case, higher toughness was partially associated with the formation of sialon phase by reaction with the whiskers and the furnace environment.     

Modeling the Value-Based Software Process with Object-Petri-Nets

Commercial organizations increasingly need software processes sensitive to busi- ness value, quick to apply, supportive of multi-stakeholder collaboration, and capable of early analysis for subprocess consistency and compatibility. This paper and a companion paper \Applying Value-Based Software Process: An ERP Example" present our experience in ap- plying a lightweight synthesis of a Value-Based Software Quality Achievement (VBSQA) process and an Object-Petri-Net (OPN) based process model to achieve a stakeholder win- win outcome for software quality achievement in an ERP software project in China. We attempt to answer such questions as (1) whether it is possible to model various project stakeholder perspectives using formal process modeling languages in a real-world project? (2) how to make stakeholders synchronize and stabilize their value propositions, activities and commitments as needed. The companion paper presents the VBSQA process and its application to the ERP project; this paper presents the OPN-based process modeling and its application. The application results of OPN process modeling conˉrmed that (1) the OPN- based process model provided project managers with a synchronization and stabilization framework for process activities, success-critical stakeholders and their value propositions; (2) process visualization and simulation tools signiˉcantly increased management visibility and controllability for the success of the software project.     

PID controller tuning for a multivariable glass furnace process by genetic algorithm

Standard genetic algorithms (SGAs) are investigated to optimise discrete-time proportional-integral-derivative (PID) controller parameters, by three tuning approaches, for a multivariable glass furnace process with loop interaction. Initially, standard genetic algorithms (SGAs) are used to identify control oriented models of the plant which are subsequently used for controller optimisation. An individual tuning approach without loop interaction is considered first to categorise the genetic operators, cost functions and improve searching boundaries to attain the desired performance criteria. The second tuning approach considers controller parameters optimisation with loop interaction and individual cost functions. While, the third tuning approach utilises a modified cost function which includes the total effect of both controlled variables, glass temperature and excess oxygen. This modified cost function is shown to exhibit improved control robustness and disturbance rejection under loop interaction.     

Reviewing VTAM and NetView Security Controls

Abstract

The basic premise of developing any information system is to increase efficiency and manage information in an improved manner. Based on the definitions above, an information system is “a group of devices or artificial objects serving a common purpose to communicate knowledge or intelligence.” Most information systems evolve from processes that either manipulate much information or rely on complex calculations. In other words, information systems are developed either to manage information or to manipulate it. Systems are meant to receive input, manipulate the input, and provide output.     

Flow measurements in sewers based on image analysis: automatic flow velocity algorithm

Discharges of combined sewer overflows (CSOs) and stormwater are recognized as an important source of environmental contamination. However, the harsh sewer environment and particular hydraulic conditions during rain events reduce the reliability of traditional flow measurement probes. An in situ system for sewer water flow monitoring based on video images was evaluated. Algorithms to determine water velocities were developed based on image-processing techniques. The image-based water velocity algorithm identifies surface features and measures their positions with respect to real world coordinates. A web-based user interface and a three-tier system architecture enable remote configuration of the cameras and the image-processing algorithms in order to calculate automatically flow velocity on-line. Results of investigations conducted in a CSO are presented. The system was found to measure reliably water velocities, thereby providing the means to understand particular hydraulic behaviors.     

Samplinghelper a web-based tool to assess the reliability of sampling strategies in sewers and receiving waters

Sampling is a key step in the analysis of chemical compounds. It is particularly important in the environmental field, for example for wastewater effluents, wet-weather discharges or streams in which the flows and concentrations vary greatly over time. In contrast to the improvements that have occurred in analytical measurement, developments in the field of sampling are less active. However, sampling errors may exceed by an order of magnitude those related to analytical processes. We proposed an Internet-based application based on a sampling theory to identify and quantify the errors in the process of taking samples. This general theory of sampling, already applied to different areas, helps to answer questions related to the number of samples, their volume, their representativeness, etc. The use of the internet to host this application facilitates use of theoretical tools and raise awareness of the uncertainties related to sampling. An example is presented, which highlights the importance of the sampling step in the quality of analytical results.     

New integer linear programming approaches for course timetabling

The most complete form of academic timetabling problem is the population and course timetabling problem. In this problem, there may be multiple classes of each subject, and the decision on which students are to constitute each class is made in concert with the decision on the timetable for each class. In order to solve this problem, it is normally simplified or decomposed in some fashion. One simplification commonly used in practice is known as blocking: it is assumed that the classes can be partitioned into sets of classes (or blocks) that will be timetabled in parallel. This restricts clashing to occur only between classes in the same block, and essentially removes the timetabling aspect of the problem, which can be carried out once the blocks are constituted and the classes populated. The problem of constituting the blocks and populating the classes, known as the course blocking and population problem, is nevertheless a challenging problem, and provides the focus of this paper. We demonstrate, using data provided by a local high school, that integer linear programming approaches can solve the problem in a matter of seconds. Key features include remodelling to remove symmetry caused by students with identical subject selection, and the observation that in practice, only integrality of the block composition variables needs to be enforced; the class population aspects of the model have strong integrality properties.