An engineering process for the verification of real-time systems

The complete verification of the timing properties of a large critical system cannot be undertaken in a single step or with a single method. In this paper we present a process that links together a number of techniques and approaches that cover all stages of development from requirements analysis to code testing. The key elements of the process are: a constrained form of timed automata that uses delay and deadline to define temporal behaviour, notions of rely and guarantee to cover temporal dependencies, model checking for design verification, SPARK and Ravenscar restrictions for programming, and scheduling and response time analysis for asserting implementation compliance. Extended examples of the use of the process are given.     

Overall cooling efficiency of a solar desiccant plant powered by direct-flow vacuum-tube collectors: simulation and experimental results

Using solar thermal energy is an interesting option for heat-driven air conditioning, e.g. desiccant cooling. In this article, the autonomous operations of a solar desiccant cooling plant powered by direct-flow vacuum-tube collectors are investigated. A model of the solar installation and the desiccant air handling unit is presented and implemented in the SPARK simulation environment and then it is validated experimentally. The overall cooling efficiency of the system is evaluated using simulation for humid and moderately humid climates and the effect of increasing the regeneration temperature on the cooling capacity, the overall cooling efficiency is studied and finally the overall efficiency of the collectors is calculated for the studied cases.     

Influence of precursors on formation of TiO2–CrTaO4 rutile solid solutions

Abstract

Rutile solid solutions Cr_x Ti_1-2xTa_xO₂ (0 < x < 0·5) have been synthesised by: firing mixtures of Cr₂O₃ , Ta₂O₅ , and TiO₂ (anatase); firing colloidal gels obtained from TiCl₄ , TaCl₅ , and CrCl₃ . 6H₂O; and firing polymeric gels prepared from Ti⁴⁺ isopropoxide, Ta⁵⁺ethoxide, and Cr³⁺ acetylacetonate at 300–1300°C. Samples were characterised by XRD, differential thermal and thermogravimetric analysis, UV visible spectroscopy, Cielab colour parameter measurements, and electron microscopy. In samples synthesised from oxide mixtures, CrTaO₄ (rutile structure) appeared as an intermediate phase in the formation of the solid solutions and a positive departure from Vegard's law was observed. Ta₂O₅ segregation in gel samples seems to prevent the formation of material consisting only of rutile. The distortion of MO₆ octahedra varies as x increases. The chemical, structural, and thermal stability, and the colouration obtained on glazes containing 3 wt-%samples, indicate their potential for use as ceramic pigments. Under the experimental conditions used, the materials prepared by sol–gel synthesis were not found to be better than those prepared from oxide mixtures.     

Effect of talc and bauxite on sintering,microstructure, and refractory properties of Egyptian dolomitic magnesite

Abstract

Refractories produced from mixes of Egyptian dolomitic magnesite with talc and low cost Chinese bauxite have been assessed as potential substitutes for the high temperature basic refractory bricks currently used in steelmaking and other industries. Fifteen batches of different compositions were prepared by firing for 2 h up to 1580° C. Six samples were selected for further investigation on the basis of their phase composition and densification parameters. The mineralogical composition and microstructure, pore size distribution, and mechanical and refractory properties of these samples were investigated. All six samples consisted mainly of MgO and MA spinel refractory phases, plus some calcium silicates and aluminoferrite phases. The latter phases contribute to densification during firing by promoting liquid phase formation. Most samples showed high refractoriness under load, good spalling resistance, better mechanical properties than current refractories, and compact microstructure. It is concluded that these new refractories are good candidate materials for the production of shaped linings for industrial kilns and furnaces.     

An Integrated Approach to High Integrity Software Verification

Using automated reasoning techniques, we tackle the niche activity of proving that a program is free from run-time exceptions. Such a property is particularly valuable in high integrity software, for example, safety- or security-critical applications. The context for our work is the SPARK Approach for the development of high integrity software. The SPARK Approach provides a significant degree of automation in proving exception freedom. Where this automation fails, however, the programmer is burdened with the task of interactively constructing a proof and possibly also having to supply auxiliary program annotations. We minimize this burden by increasing the automation, through an integration of proof planning and a program analysis oracle. We advocate a ‘cooperative’ integration, where proof-failure analysis directly constrains the search for auxiliary program annotations. The approach has been successfully tested on industrial data.     

Using a formal specification contractually

A commonly made criticism of formal methods is that they increase costs. Selective use of formal methods to define critical requirements can, however, lead to a significant decrease in lifecycle costs. In particular the economic and technical benefits of outsourcing the development of software can be fully realized and the cost of outsourcing slightly reduced by use of a formal specification. In this paper we describe a development in which a formal specification prepared by the customer formed part of the contract with the supplier. We conclude that this use of a formal specification can reduce risks and costs for all concerned and can help foster fruitful and co-operative relations in situations which are often fraught with confrontation.Published with the permission of the controller of Her Britannic Majesty's Stationery Office.     

基于SPARK与随机森林的短信诈骗用户识别研究

当今数据时代电信诈骗现象日益增多,为了在短信诈骗份子实施诈骗前及时识别出其身份,根据目前电信行业需求及研究现状,在SPARK并行处理框架上,针对性地提出了分层子空间的加权随机森林算法。面对短信用户种类繁杂导致的数据类别不平衡带来的随机森林性能低下的问题,采用改进的分层子空间的方法,并根据评估出的每棵树的分类能力给决策树加权,相较于其他分类算法,改进的随机森林表现得更优异;针对电信行业海量数据的特点,选择分布式SPARK作为数据处理平台,并行化的平台缩短了模型训练和测试时间,提高了效率,实时、准确地识别电信短信诈骗用户,其准确率达到90%以上。     

Relationship between microstructure and mechanical properties of fired Ecuadorean clay

Abstract

Hardness and fracture toughness measurements are reported for individual phases and interfacial composites present in fired specimens of an Ecuadorian clay mineral. Each investigation used a half disc from strength tests previously done and reported elsewhere. The aim was to rationalise trends in the macroscopic strength and density to quantify contributions from the important components of the microstructure. This was achieved through application of an etching and gold coating procedure prior to microindentation testing. The coating technique improved the clarity of the indents and made the diagonal and radial crack measurements more accurate. Two peaks in the strength versus firing temperature curve are shown to arise from opposite trends in the toughness of the quartz grains and the matrix phase, together with a no-linear build up of the volume of interfacial composite material which confines any cracks initiated in the residual quartz crystals at high firing temperatures.     

Comparison between the conventional and recirculation modes in desiccant cooling cycles and deriving critical efficiencies of components

Desiccant evaporative systems are heat driven at moderate temperature and are usually coupled with solar collectors or with waste heat. The performance of desiccant systems is very sensitive to outside conditions and to the efficiency of the system components. In this paper the impact of these factors on the performance of two configurations of desiccant systems is investigated through simulation. First, a model of a desiccant air handling unit is briefly presented and validated experimentally. Then different efficiency combinations are studied and the critical efficiencies are derived. Finally, a comparison of the conventional and the recirculation configurations is made, based on outside conditions.     

Ceramic matrix composite production by directed melt oxidation of pure aluminium metal using spinel dopants

Abstract

The production of Al₂O₃ matrix composites by directed melt oxidation of pure Al externally doped with spinel type dopants has been investigated. The presence of any one of MgAl₂O₄ , LiAlO₂, and ZnAl₂O₄ resulted in oxide growths in a similar fashion to the growths produced using elemental Mg, Li, and Zn. Rapid growth was achieved at 1180°C with MgAl₂O₄ and at 900°C with LiAlO₂ . The growth rates at 1180°C of the samples doped with ZnAl₂O₄ were less rapid than the growth rates of the samples doped with MgAl₂O₄ . The fact that growth is initiated by mixed oxide spinel dopants is further evidence in support of the cyclic reaction sequences that have been proposed for directed melt oxidation.