Space station integrated wall design and penetration damage control

A methodology was developed to allow a designer to optimize the pressure wall, insulation, and meteoroid/debris shield system of a manned spacecraft for a given spacecraft configuration and threat environment. The threat environment consists of meteoroids and orbital debris, as specified for an arbitrary orbit and expected lifetime. An overall probability of no penetration is calculated, as well as contours of equal threat that take into account spacecraft geometry and orientation. Techniques, tools, and procedures for repairing an impacted and penetrated pressure wall were developed and tested. These techniques are applied from the spacecraft interior and account for the possibility of performing the repair in a vacuum. Hypervelocity impact testing was conducted to: (1) develop and refine appropriate penetration functions, and (2) determine the internal effects of a penetration on personnel and equipment

Adopting Architectural Event Modules for Modular Coordination of Multiple Applications

Nowadays, large-scale software systems consist of multiple applications, which interact with each other to fulfill desired system-level requirements. It is usually required to coordinate the interactions of the constituent applications to ensure that the system-level requirements are fulfilled. In this paper, we outline a set of requirements that must be fulfilled to facilitate the modular composition of multiple applications. We introduce the concept of architectural event modules, which are abstractions to represent constituent applications and their coordination logic in a modular and uniform way. We explain the implementation of this concept in the EventReactor language, and define their formal semantics in processing events using the UPPAAL toolset. We illustrate the suitability of architectural event modules in achieving modularity and loose coupling in the composition of multiple applications by means of a case study in the domain of energy-efficient computing

On the Roles of Drosophila Notch Signaling and Atonal Autoregulation in the Specification of R8 Photoreceptors

Drosophila retinogenesis has long served as a paradigm of tissue patterning. Notch, an anciently conserved signaling pathway, is critical to both the formation of and proper spacing of founding R8 photoreceptors. Notch is intimately interwoven into the activity of Atonal (Ato), a proneural basic helix-loop-helix (bHLH) that is required for R8 specification. Ato is expressed through dual enhancers: ato-3\u27 and 5\u27-ato. ato-3\u27 is activated in response to Notch-independent signaling cues whereas 5\u27-ato exhibits complex dependence on Notch signaling. First, Notch is required for 5\u27-ato activation, eliciting formation of Ato intermediate groups (IGs, evenly spaced clusters of 10--20 cells). Subsequently, Notch is required to repress ato, to resolve its expression from IGs to isolated R8s. This is accomplished through the induction of E(spl)bHLH repressors to disrupt proneural function. The former process is independent of the Notch pathway transcription factor Suppressor of Hairless (SuH) and the latter requires Su(H). Current views regarding this process suggest that either 1) the Su(H)-dependent response may require a greater threshold of Notch signal activity before engaging, or 2) E(spl) repressors are initially expressed but lack proper posttranslational activation to repress ato. The work of Chapter 2 refutes both scenarios. We demonstrate that E(spl)bHLHs are expressed prior to the perceived activation of 5\u27-ato. E(spl) repressors are active at this time, as their removal elicits precocious de-repression of 5\u27-ato. Thus, both the Su(H)-independent and -dependent processes initiate simultaneously. These findings suggest that ato-3\u27 activity is crucial during IG formation. Analysis of the hypermorphic allele E( spl)D delineates a role for posttranslational activation of E(spl)M8 during the repressive phase of Ato patterning. The work of Chapter 3 further probes the importance of ato-3\u27 in the formation of IGs. Anterior open (Aop) has previously been characterized as an effector of MAPK and is an ortholog of tumor suppressor Tel/ETV6. Aop coexpresses with Ato only during early IG formation, prior to the onset of autoregulation via 5\u27-ato. We demonstrate that Aop is required cell-autonomously during early IG formation to promote continued expression from ato-3\u27. Furthermore, Aop is induced by Notch activity via Su(H), indicating that Su(H) co-opts Aop to instill a delay in Notch-mediated repression. The work of Chapter 4 assesses the role of ato in a broader context. The region of the developing eye that expresses Ato is referred to as the morphogenetic furrow (MF). The MF relies upon sophisticated signaling between Notch, Hedgehog (Hh) and Decapentaplegic (Dpp). Our work indicates that, in addition to Ato\u27s role in facilitating neurogenesis, it is proactive in the production of neural progenitors through its elicitation of Dpp, as assessed by a lacZ reporter. In total, these studies emphasize the complexity of the relationship between Notch and Ato and suggest interesting new studies into possible nodes of signaling crosstalk with Notch

Context Oriented Software Middleware

Our middleware approach, Context-Oriented Software Middleware (COSM), supports context-dependent software with self-adaptability and dependability in a mobile computing environment. The COSM-middleware is a generic and platform-independent adaptation engine, which performs a runtime composition of the software's context-dependent behaviours based on the execution contexts. Our middleware distinguishes between the context-dependent and context-independent functionality of software systems. This enables the COSM-middleware to adapt the application behaviour by composing a set of context-oriented components, that implement the context-dependent functionality of the software. Accordingly, the software dependability is achieved by considering the functionality of the COSM-middleware and the adaptation impact/costs. The COSM-middleware uses a dynamic policy-based engine to evaluate the adaptation outputs and verify the fitness of the adaptation output with the application's objectives, goals and the architecture quality attributes. These capabilities are demonstrated through an empirical evaluation of a case study implementation

Aspect-Oriented Programming for Test Control

Distributed and multithreaded systems are usually much more complex to analyze or test due to the nondeterminism involved. A possible approach to testing nondeterministic systems is to direct the execution of the program under test to take a certain path for each test, so that a unique output can be observed. Considering specification-based testing, we assume that a test case is given together with a test constraint for directing the internal nondeterministic choices. To instruct the program under test to execute according to a given test constraint, the program under test needs to communicate with the tester. In this thesis, we propose to use the features in Aspect-Oriented Programs to realize such communication. This solution does not require the availability of the source code of the program under test. We provide an automated translation from a test constraint to a set of aspects using AspectJ

Effecting Runtime Reconfiguration in Managed Execution Environments

Managed execution environments such as Microsoftäó»s Common Language Runtime (CLR) and Sun Microsystemsäó» Java Virtual Machine (JVM) provide a number of services äóñ including but not limited to application isolation, security sandboxing, garbage collection and structured exception handling äóñ that are aimed primarily at enhancing the robustness of managed applications. However, none of these services directly enables performing reconfigurations, repairs or diagnostics on the managed applications and/or its constituent subsystems and components. In this paper we examine how the facilities of a managed execution environment can be leveraged to support runtime system adaptations, such as reconfigurations and repairs. We describe an adaptation framework we have developed, which uses these facilities to dynamically attach/detach an engine capable of performing reconfigurations and repairs on a target system while it executes. Our adaptation framework is lightweight, and transparent to the application and the managed execution environment: it does not require recompilation of the application nor specially compiled versions of the managed execution runtime. Our prototype was implemented for the CLR. To evaluate our framework beyond toy examples, we searched on SourceForge for potential target systems already implemented on the CLR that might benefit from runtime adaptation. We report on our experience using our prototype to effect runtime reconfigurations in a system that was developed and is in use by others: the Alchemi enterprise Grid Computing System developed at the University of Melbourne, Australia

End-to-end security in service-oriented architecture

A service-oriented architecture (SOA)-based application is composed of a number of distributed and loosely-coupled web services, which are orchestrated to accomplish a more complex functionality. Any of these web services is able to invoke other web services to offload part of its functionality. The main security challenge in SOA is that we cannot trust the participating web services in a service composition to behave as expected all the time. In addition, the chain of services involved in an end-to-end service invocation may not be visible to the clients. As a result, any violation of client’s policies could remain undetected. To address these challenges in SOA, we proposed the following contributions. First, we devised two composite trust schemes by using graph abstraction to quantitatively maintain the trust levels of different services. The composite trust values are based on feedbacks from the actual execution of services, and the structure of the SOA application. To maintain the dynamic trust, we designed the trust manager, which is a trusted-third party service. Second, we developed an end-to-end inter-service policy monitoring and enforcement framework (PME framework), which is able to dynamically inspect the interactions between services at runtime and react to the potentially malicious activities according to the client’s policies. Third, we designed an intra-service policy monitoring and enforcement framework based on taint analysis mechanism to monitor the information flow within services and prevent information disclosure incidents. Fourth, we proposed an adaptive and secure service composition engine (ASSC), which takes advantage of an efficient heuristic algorithm to generate optimal service compositions in SOA. The service compositions generated by ASSC maximize the trustworthiness of the selected services while meeting the predefined QoS constraints. Finally, we have extensively studied the correctness and performance of the proposed security measures based on a realistic SOA case study. All experimental studies validated the practicality and effectiveness of the presented solutions