Modern electrical power disribution systems play a critical role in system operations. Therefore, early fault detection and isolation is essential to maintaining system safety and avoiding catastrophic failures. This paper discusses a fault isolation scheme based on a qualitative fault signature-based isolation mechanism that applies to abrupt, incipient and intermittent faults in the system. We discuss the isolation algorithms for a combination of these faults, and demonstrate their performance on a set of test cases generated from a NASA Ames spacecraft power distribution testbed. Our results show good isolation accuracy with 103 out of 134 faulty scenarios isolated correctly. Most of the isolation errors can be attributed to errors in the detection scheme.

Failure of electronic devices is a concern for future electric aircrafts that will see an increase of electronics to drive and control safety-critical equipment throughout the aircraft. As a result, investigation of precursors to failure in electronics and prediction of remaining life of electronic components is of key importance. DC-DC power converters are power electronics systems employed typically as sourcing elements for avionics equipment. Current research efforts in prognostics for these power systems focuses on the identification of failure mechanisms and the development of accelerated aging methodologies and systems to accelerate the aging process of test devices, while continuously measuring key electrical and thermal parameters. Preliminary model-based prognostics algorithms have been developed making use of empirical degradation models and physics-inspired degradation model with focus on key components like electrolytic capacitors and power MOSFETs (metal-oxide-semiconductor-field-effect-transistor). This paper presents current results on the development of validation methods for prognostics algorithms of power electrolytic capacitors. Particularly, in the use of accelerated aging systems for algorithm validation. Validation of prognostics algorithms present difficulties in practice due to the lack of run-to-failure experiments in deployed systems. By using accelerated experiments, we circumvent this problem in order to define initial validation activities.

Electrolytic capacitors are used in several applications ranging from power supplies for safety critical avionics equipment to power drivers for electro-mechanical actuators. Past experiences show that capacitors tend to degrade and fail faster under high electrical and thermal stress conditions that they are often subjected to during operations. This makes them good candidates for prognostics and health management. Model based prognostics captures system knowledge in the form of physics-based models of components in order to obtain accurate predictions of end of life based on their current state of health and their anticipated future use and operational conditions. The focus of this paper is on deriving first principles degradation models for thermal stress conditions and implementing Bayesian framework for making remaining useful life predictions. Data collected from simultaneous experiments are used to validate the models. Our overall goal is to derive accurate models of capacitor degradation, and use them to remaining useful life in DC-DC converters.

The integration of physical systems through computing and networking has become pervasive, a trend now known as cyber-physical systems (CPS). Functionality in CPS emerges from the interaction of networked computational and physical objects. System design and integration are particularly challenging because fundamentally different physical and computational design concerns intersect. The impact of these interactions is the loss of compositionality which creates tremendous challenges. The key idea in this article is to use passivity for decoupling the control design of networked systems from uncertainties such as time delays and packet loss, thus providing a fundamental simplification strategy that limits the complexity of interactions. The main contribution is the application of the approach to an experimental case study of a networked multi-robot system. We present a networked control architecture that ensures the overall system remains stable in spite of implementation uncertainties such as network delays and data dropouts, focusing on the technical details required for the implementation. We describe a prototype domain-specific modeling language and automated code generation tools for the design of networked control systems on top of passivity that facilitate effective system configuration, deployment, and testing. Finally, we present experimental evaluation results that show decoupling of interlayer interactions.

System integration is the elephant in the china store of large-scale cyber-physical system (CPS) design. It would be hard to find any other technology that is more undervalued scientifically and at the same time has bigger impact on the presence and future of engineered systems. The unique challenges in CPS integration emerge from the heterogeneity of components and interactions. This heterogeneity drives the need for modeling and analyzing cross-domain interactions among physical and computational/networking domains and demands deep understanding of the effects of heterogeneous abstraction layers in the design flow. To address the challenges of CPS integration, significant progress needs to be made toward a new science and technology foundation that is model based, precise, and predictable. This paper presents a theory of composition for heterogeneous systems focusing on stability. Specifically, the paper presents a passivity-based design approach that decouples stability from timing uncertainties caused by networking and computation. In addition, the paper describes cross-domain abstractions that provide effective solution for model-based fully automated software synthesis and high-fidelity performance analysis. The design objectives demonstrated using the techniques presented in the paper are group coordination for networked unmanned air vehicles (UAVs) and high-confidence embedded control software design for a quadrotor UAV. Open problems in the area are also discussed, including the extension of the theory of compositional design to guarantee properties beyond stability, such as safety and performance.

This paper describes ongoing work on making the deploy- ment and configuration functionality for cyber physical sys- tems reliable and tolerant to failures, while also supporting predictable and incremental online redeployment and reconfiguration of application functionality. Our work is currently designed and evaluated in the context of a system of frac- tionated spacecrafts, which is a representative CPS system.

Web applications are one of the most prevalent platforms for information and services delivery over Internet today. As they are increasingly used for critical services, web applications become a popular and valuable target for security attacks. Although a large body of techniques have been developed to fortify web applications and and mitigate the attacks toward web applications, there is little effort devoted to drawing connections among these techniques and building a big picture of web application security research. This paper surveys the area of web application security, with the aim of systematizing the existing techniques into a big picture that promotes future research. We first present the unique aspects in the web application development which bring inherent challenges for building secure web applications. Then we identify three essential security properties that a web application should preserve: input validity, state integrity and logic correctness, and describe the corresponding vulnerabilities that violate these properties along with the attack vectors that exploit these vulnerabilities. We organize the existing research works on securing web applications into three categories based on their design philosophy: security by construction, security by verification and security by protection. Finally, we summarize the lessons learnt and discuss future research opportunities in this area.