Christian K. Hansen

Spurious exponentiality observed when incorrectly fitting a distribution to nonstationary data

Failure data for a repairable system can be represented either by a set of chronologically ordered arrival times at which the system failed, or by a set of interarrival times defined as the times observed between successive failures (ignoring repair times in both cases). The two representations are mathematically equivalent if the chronological order of the interarrival times is maintained. Methods aimed at describing the distribution of the observed interarrival times are meaningful only if the interarrival times are identically distributed. In all other cases, such analyses are meaningless and often result in maximally misleading impressions about the system behavior, as demonstrated here by several examples. That is, when the information in the chronological order of interarrival times is ignored, they often appear spuriously exponential, leading to the impression that the system can be modeled using a homogeneous Poisson process. Misunderstandings of this nature can be avoided by applying an appropriate test for trend before attempting to fit a distribution to the interarrival times. If evidence of trend is determined, then a nonstationary model such as the nonhomogeneous Poisson process should be fitted using the chronologically ordered data.

IEEE Reliability Society Technical Operations Annual Technical Report for 2010

The Annual Technical Report this year is focused on infrastructure reliability. Infrastructure constitutes those things that are apparent only in their absence. We take the infrastructure for granted, assuming it will always be there. We turn on our water facet, and drinkable water has always flowed out, for most of us, most of the time. Our infrastructure is subject to environment breakages (e.g., earthquakes), accidents (e.g., dig ups of cables), sabotage, intrusion, and compromise. Also everyday component, software or system failures can bring our infrastructure down. Our global connectivity and communications, as well as our world wide distributed development and maintenance systems, increase our productivity and efficiency, but can also increase our vulnerabilities. Our critical infrastructures can be found in many places.

Reliability prediction and simulation for a communications-satellite fleet

Telecommunications satellites are usually designed to operate in-orbit for as long as 10-15 years. This places a lot of focus on the reliability of the spacecraft from the early design phase, through the manufacturing process and up until after the spacecraft has been launched and put into service. In this paper, the authors discuss methods with primary focus on the reliability of an in-orbit satellite fleet, i.e. a collection of satellites that have been placed successfully in orbit. Traditional methods developed primarily for reliability predictions of a single satellite with no flight history are not adequate for this purpose. Realistic reliability predictions for an in-orbit satellite fleet must address the flight history (launch date and observed in-orbit failures) of each individual satellite, and furthermore spacecraft units are often observed to have nonconstant hazard rates, significantly different from those that can be calculated using military handbooks. To obtain reliability predictions for a satellite fleet with individual flight histories, nonconstant unit hazard rates, and complicated redundancy configurations, Monte-Carlo simulation is a very useful tool, because it can handle complex models in contrast to most analytical tools.

Undergraduates and research: Motivations, challenges, and the path forward

At last years conference, we organized a panel “Involving Undergraduates in Research: Motivations and Challenges” which was a great success with many interesting discussions. This has motivated us to develop a second iteration of this panel with an additional dimension - the Path Forward. We expect to have more discussions on how to extend what we have already learned from the past experiences to further enhance the way we involve undergraduates in doing research. Panelists will deliver a 5-minute overview of their research experiences with undergraduate students, including challenges they faced, lessons learned, and areas for improvement. The floor will then be opened for audience members to voice any concerns, questions, or comments. Student panel attendees will be given special consideration when presenting observations from their own perspective.

Keynote speech: Connecting the dots. Navigating an interconnected world through IoT and Big Data

Through the deployment of the Internet of Things (IoT) and the associated explosive evolution of connectivity, issues surrounding reliability, security, privacy and safety have become sources of ever increasing concern. Furthermore, as Big Data is becoming the fabric and currency that bonds the IoT, we have seen an increased demand for advanced data mining and analytics tools over the last decade. In this presentation we review some historical trends and challenges related to this evolution of networking and connectivity and discuss areas of most likely focus over the next decade. In particular, ongoing efforts and future directions for research led by IEEE and the IEEE Reliability Society will be discussed.