Towards Formal Fault Tree Analysis using Theorem Proving

Fault Tree Analysis (FTA) is a dependability analysis technique that has been widely used to predict reliability, availability and safety of many complex engineering systems. Traditionally, these FTA-based analyses are done using paper-and-pencil proof methods or computer simulations, which cannot ascertain absolute correctness due to their inherent limitations. As a complementary approach, we propose to use the higher-order-logic theorem prover HOL4 to conduct the FTA-based analysis of safety-critical systems where accuracy of failure analysis is a dire need. In particular, the paper presents a higher-order-logic formalization of generic Fault Tree gates, i.e., AND, OR, NAND, NOR, XOR and NOT and the formal verification of their failure probability expressions. Moreover, we have formally verified the generic probabilistic inclusion-exclusion principle, which is one of the foremost requirements for conducting the FTA-based failure analysis of any given system. For illustration purposes, we conduct the FTA-based failure analysis of a solar array that is used as the main source of power for the Dong Fang Hong-3 (DFH-3) satellite.Comment: 1

Implications for Research Methods When Conducting Studies With the Users of Online Health Communities

Bournemouth Universit

Economic Efficiency of Malaysian Oleochemical Enterprises

This study comprises a rigorous Micro Econometric and Data Envelopment Analysis (DEA) of the performance of the Malaysian oleochemical enterprises over time. The analysis covers the following sectors: coconut oil, palm oil, palm kernel oil and other oils and fats, as well as twelve out of fifteen working oleochemical enterprises. The micro-economic data were graciously provided by Malaysian National Productivity Corporation (NPC), Malaysian Department of Statistics and some other respected sources: Panel data have been used in this study. The time series data and cross section data have been both pooled together to constitute panel data. Also maximum likelihood estimation has been incorporated for composed error models as well as DEA. Where appropriate, the literature has been updated. This study shows that the major advantage of the systematic application of the two frontier approaches, which are stochastic and deterministic (DEA), with multiple techniques on panel of data containing two levels, enables the comparison of synthesis of the results obtained to provide a comprehensive, detailed and insightful understanding of the producer behaviour. This approach is superior and informative than single eyed approaches. The results from all approaches consistently show that scale inefficiency and allocative inefficiency are the main problems in efficiency analysis. The scale inefficiency is mainly due to production operation at increasing returns to scale. This is noted specially in the coconut oil sector, the palm kernel oil sector and oleochemical enterprises. Allocative inefficiency is mainly due to under-utilisation of inputs relative to capital. Labour was under-utilised relative to capital in palm oil and other fat and oil sector. Allocative inefficiency due to underutilsation of inputs relative to capital is proved in this study. It is in consistent with that found by Seale (1990) in Egyptian Tileries, who claimed that Tileries on average were allocatively inefficient, employing too much capital relative to labour. The estimate of Malaysian oil and fat industry's total factor productivity (TFP) change is -3.705% for the period 1985 to 1996. The major contributor to this negative technological change is the palm oil sector and other oil and fat sector. The palm oil sector's negative contribution is at an average annual rate of 6.818% over the period of this study and other oil and fat sector is at an average annual rate of 5.8] 8%. This implies that the palm oil sector is ailing due to technological regress. It could be concluded that allocative efficiency requires first or second best pricing of final products; scale efficiency requires limitation on sub-optimal entry to the industry; technical efficiency requires cost minimisation by the incumbent firms; and finally product choice and dynamic efficiency require innovation by incumbents and new entrants

"Where does my health information come from?": Information sharing in peer-to-peer health communities.Abstract.

Peer-to-peer health networks such as online discussion forums have created new ways for people, especially those living with a long term condition, to access health information. There have however been concerns about the quality of information, and the ability of the public to understand and evaluate that information [1, 2]. The term “apomediation”[3] has been used to describe the shift from professionals as the information gatekeepers, to individual-led signposting or use of technology-based solutions such as bookmarking. This abstract presents the findings of a study analyzing how people using online discussion boards adopt this apomediation role, the types of information they share, and how they share this information

Analysis and Optimization of Incompressible Inviscid Flow around Split Flap Airfoils

Generally airfoils are designed for cruise flight conditions; but during take-off and landing, when the airplane flies at low speeds and small angles of attacks, the lift provided by single airfoils is not sufficient, and an extra lift is required for safe landing and take-off. In this condition the use of high lift devices is important. When an airfoil is accompanied by high lift devices the system is referred to as multi-component airfoil configuration. When high lift devices are deflected, the geometry of the airfoil is changed temporarily. As a result the effective chamber, angle of attack, and area of the airfoil are increased; consequently, the lift is increased too, since the lift is directly proportional to the chamber, the angle of attack, and the airfoil area. The advantage of this is that the landing and take-off speeds are reduced, a fact that gives the pilot more time to react, in case any accident happens during take-off or landing. At the same time, the runway length is also reduced. If the airplane is fast and it's carrying capacity is high, then the importance of using multi-component airfoils increases, because the value of the lift increment necessary for safe take-off and landing is high. At the present time, the importance of multi-component airfoils is increasing due to the high competition between airplane manufacturing companies, whose aim is to produce new models of airplanes with higher speeds and carrying capacities than the airplanes used today. Future airplanes should be fast, safe, and large. Achievement of these requirements in future airplanes is strongly related to the use of the appropriate multi-component airfoil designs. And this is why much experimental and computational work needs to be devoted to analyze and optimize the flow around multi-component airfoil configurations. When dealing with multi-component airfoil configurations computational methods are of great importance so as to focus the zone of the optimal flap position for the maximum lift coefficient. Then the experimental work is to be carried out within that zone. This saves long expensive wind tunnel, and flight test hours. In the investigation presented in this thesis, a computer program, which models incompressible inviscid flow around an airfoil with a split flap, has been developed. The program is based on the pioneering Hess and Smith panel method. The new program is referred to as MULTFOIL