Dynamic Assembly for System Adaptability, Dependability, and Assurance

(DASASA) ProjectAuthor-contributed print ite

Initial CONNECT Architecture

Interoperability remains a fundamental challenge when connecting heterogeneous systems which encounter and spontaneously communicate with one another in pervasive computing environments. This challenge is exasperated by the highly heterogeneous technologies employed by each of the interacting parties, i.e., in terms of hardware, operating system, middleware protocols, and application protocols. The key aim of the CONNECT project is to drop this heterogeneity barrier and achieve universal interoperability. Here we report on the development of the overall CONNECT architecture that will underpin this solution; in this respect, we present the following contributions: i) an elicitation of interoperability requirements from a set of pervasive computing scenarios, ii) a survey of existing solutions to interoperability, iii) an initial view of the CONNECT architecture, and iv) a series of experiments to provide initial validation of the architecture

Development and performance of self-healing and self-immune soil-cement systems subjected to freeze-thaw cycles

Soil-cement systems are used in a wide variety of engineering projects. However, soil-cement systems are vulnerable to cyclic freeze-thaw deterioration. The engineering properties of soil-cement systems, such as strength and permeability, can be substantially degraded under the action of freeze-thaw cycles. This durability problem substantially impairs the sustainability of soil-cement systems and raises their maintenance and repair costs. Thus, when subjected to freeze-thaw cycles, civil infrastructure projects that use soil-cement systems can suffer from decreased reliability. Although extensive research has been carried out to improve the freeze-thaw durability of soil-cement systems, no method associated with significant improvement has been developed thus far. Biological systems have recently provided inspiration for scholarly attempts to develop smart materials that comprise sustainable and resilient systems, which similarly can continually adapt and respond to their environment. Most of these efforts so far have focused on self-healing properties in polymers and concrete, and many of them have shown promising results. However, to date there has been very little work reported on the development of effective smart systems for geotechnical applications and there is very little literature focusing on the specific damage scenario caused by freeze-thaw cycles. Those systems (and their geotechnical applications) pose challenging problems that are distinct from those of, for instance, concrete. For this reason, they require a complete reimagining of how such smart systems ought to be designed. Therefore, the focus of this PhD project is on the development and performance of self-healing and self-immune soil-cement systems that can respond and adapt to freeze-thaw cycles. Two different materials, microcapsules (produced by Lambson, UK) and LUVOMAG MgO pellets (produced by Lehmann & Voss, Germany), were used to develop self-healing soil-cement systems, and their self-healing capability was investigated. It was found that the addition of Lambson microcapsules improved the self-healing capability of soil-cement systems considerably in terms of unconfined compressive strength (UCS). The addition of MgO pellets not only substantially improved the self-healing capability of soil-cement systems in UCS, but also showed great potential in terms of crack sealing. The microstructure investigations revealed that brucite and different types of hydrated magnesium carbonates, such as hydromagnesite and dypingite, were produced in the self-healed MgO pellet-embedded soil-cement samples after freeze-thaw cycles. Biological systems, provided insights that aided the development of a self-immune soil-cement system. This is a system that can protect itself from cyclic freeze-thaw action before damage is initiated, thus preventing the occurrence of the damage, partially or entirely. A special admixture, SikaAer® Solid air entraining microcapsules was introduced to develop such systems. These uniformly distributed small compressible microcapsules can serve as pressure vessels by buffering the excess pressure generated during water freezing. Although initial dry density and strength properties generally decreased with the addition of the microcapsules, the final results demonstrate that the freeze-thaw resistance of soil-cement systems was substantially improved. Based on the results of the physical properties of soil-cement systems after freeze-thaw cycles, the microscopic analysis and the high resolution X-ray computed microtomography, the self-immune mechanism of soil-cement with SikaAer® Solid microcapsules and its behaviour during freeze-thaw action was revealed. A superabsorbent polymer (BASF SAP A) was also used to develop self-immune soil-cement systems. Compared to SikaAer® Solid microcapsules, the addition of SAPs had little effect on the initial dry density, strength properties, and permeability of the soil-cement mixes, and the self-immune mechanism was slightly different. SAPs can absorb water during the mixing of soil-cement and they have the ability to release the absorbed water during the hydration and hardening processes. As a result, small cavities are created in the soil-cement system as the water within SAPs is donated for cement hydration. These uniformly distributed small pores can serve as small reservoirs and pressure vessels for water to enter and expand within the soil-cement matrix during the freeze-thaw process. This quality is captured in the results of the experiments, which demonstrated that the freeze-thaw resistance can be substantially improved by the addition of SAPs. Overall, the self-healing and self-immune systems developed in this study showed promising results in terms of improving the self-healing and self-immune capability of soil-cement systems subjected to freeze-thaw cycles. More broadly, these smart systems contribute to attempts to build more resilient and sustainable soil-cement systems that may undergo freeze-thaw deterioration in the engineering practice.China Scholarship Counci

Multi-functional applications of graphene related materials in cementitious composites

Cementitious composites are the most widely used construction materials with 4.1 billion tonnes of cement being produced globally in 2017. However, cement production is associated with ~7% of the total global anthropogenic CO2 emissions. Moreover, concrete structures suffer from poor durability, with a fifth of the total civil engineering output in the UK being spent on repair and maintenance. The poor durability of concrete structures necessitates frequent inspections and an enhanced structural monitoring regime. Despite the advancements in material science over the years, cementitious composites remain passive structural materials and do not possess any functionalities. The motivation for this research was to take advantage of emerging graphene-related materials (GRMs) to solve the challenges associated with concrete infrastructure and to instigate additional functionalities that would make the material smarter. Initially, the homogenous dispersion of GRMs was experimentally investigated in detail, as this was recognised as a key challenge in the literature. The results showed that a combination of sonication and the use of a polycarboxylate superplasticiser, were effective in homogenously dispersing the main GRM material, graphene nanoplatelets (GNPs), in cementitious systems. Subsequently, the effect of the GRMs on the early age, mechanical and permeability performance of cement pastes and mortars was investigated. It was found that GNPs reduced the fluidity, delayed the hydration, and had a poor microstructural interaction with the cement hydration products. This consequently led to a reduction in the flexural and compressive strengths. An early age beneficial effect with GNPs was found for water, gas, and chloride permeability. The use of GRMs to improve the electrical conductivity performance was also investigated, with the aim to create electrically conductive networks in the composite that could then be used to monitor changes in loading or damage, by triggering a self-sensing response. Natural graphite and GNPs were found to be effective, however, their use in bulk applications would be challenging and instead, their use in coatings was proposed. Finally, an industry survey was carried out to understand the industry perceptions of this novel material and a Lifecycle Assessment (LCA) study was also undertaken to establish the sustainability performance of a novel GNP-cement composite. The results demonstrated the potential of GRMs to improve the permeability performance of cementitious composites and to instigate a functional behaviour.Engineering and Physical Research council (EPSRC) - Grant No. EP/L016095/1-EPSRC Centre for Doctoral Training in Future Infrastructure and Built Environment and Grant No. EP/P02081X/1 - Resilient Materials for Life (RM4L) Costain Group PL

How To Touch a Running System

The increasing importance of distributed and decentralized software architectures entails more and more attention for adaptive software. Obtaining adaptiveness, however, is a difficult task as the software design needs to foresee and cope with a variety of situations. Using reconfiguration of components facilitates this task, as the adaptivity is conducted on an architecture level instead of directly in the code. This results in a separation of concerns; the appropriate reconfiguration can be devised on a coarse level, while the implementation of the components can remain largely unaware of reconfiguration scenarios. We study reconfiguration in component frameworks based on formal theory. We first discuss programming with components, exemplified with the development of the cmc model checker. This highly efficient model checker is made of C++ components and serves as an example for component-based software development practice in general, and also provides insights into the principles of adaptivity. However, the component model focuses on high performance and is not geared towards using the structuring principle of components for controlled reconfiguration. We thus complement this highly optimized model by a message passing-based component model which takes reconfigurability to be its central principle. Supporting reconfiguration in a framework is about alleviating the programmer from caring about the peculiarities as much as possible. We utilize the formal description of the component model to provide an algorithm for reconfiguration that retains as much flexibility as possible, while avoiding most problems that arise due to concurrency. This algorithm is embedded in a general four-stage adaptivity model inspired by physical control loops. The reconfiguration is devised to work with stateful components, retaining their data and unprocessed messages. Reconfiguration plans, which are provided with a formal semantics, form the input of the reconfiguration algorithm. We show that the algorithm achieves perceived atomicity of the reconfiguration process for an important class of plans, i.e., the whole process of reconfiguration is perceived as one atomic step, while minimizing the use of blocking of components. We illustrate the applicability of our approach to reconfiguration by providing several examples like fault-tolerance and automated resource control

NASA Tech Briefs, April 1995

This issue of the NASA Tech Briefs has a special focus section on video and imaging, a feature on the NASA invention of the year, and a resource report on the Dryden Flight Research Center. The issue also contains articles on electronic components and circuits, electronic systems, physical sciences, materials, computer programs, mechanics, machinery, manufacturing/fabrication, mathematics and information sciences and life sciences. In addition to the standard articles in the NASA Tech brief, this contains a supplement entitled "Laser Tech Briefs" which features an article on the National Ignition Facility, and other articles on the use of Lasers

An algorithmic approach to system architecting using shape grammar-cellular automata

Thesis (Ph. D.)--Massachusetts Institute of Technology, Engineering Systems Division, 2008.Includes bibliographical references (p. 404-417).This thesis expands upon the understanding of the fundamentals of system architecting in order to more effectively apply this process to engineering systems. The universal concern about the system architecting process is that the needs and wants of the stakeholders are not being fully satisfied, primarily because too few design alternatives are created and ambiguity exists in the information required. At the same time, it is noted that nature offers a superb example of system architecting and therefore should be considered as a guide for the engineering of systems. Key features of nature's architecting processes include self-generation, diversity, emergence, least action (balance of kinetic and potential energy), system-of-systems organization, and selection for stability. Currently, no human-friendly method appears to exist that addresses the problems in the field of system architecture while at the same time emulating nature's processes. By adapting nature's self-generative approach, a systematic means is offered to more rigorously conduct system architecting and better satisfy stakeholders. After reviewing generative design methods, an algorithmic methodology is developed to generate a space of architectural solutions satisfying a given specification, local constraints, and physical laws. This approach combines a visually oriented human design interface (shape grammar) that provides an intuitive design language with a machine (cellular automata) to execute the system architecture's production set (algorithm). The manual output of the flexible shape grammar, the set of design rules, is transcribed into cellular automata neighborhoods as a sequenced production set that may include other simple programs (such as combinatoric instructions).(cont.) The resulting catalog of system architectures can be unmanageably large, so selection criteria (e.g., stability, matching interfaces, least action) are defined by the architect to narrow the solution space for stakeholder review. The shape grammar-cellular automata algorithmic approach was demonstrated across several domains of study. This methodology improves on the design's clarification and the number of design alternatives produced, which should result in greater stakeholder satisfaction. Of additional significance, this approach has shown value both in the study of the system architecting process, leading to the proposal of normative principles for system architecture, and in the modeling of systems for better understanding.by Thomas H. Speller, Jr.Ph.D