In a Markov chain started at a state x, the hitting time τ(y) is the first time that the chain reaches another state y. We study the probability Px(τ(y) = t) that the first visit to y occurs precisely at a given time t. Informally speaking, the event that a new state is visited at a large time t may be considered a “surprise”. We prove the following three bounds: In any Markov chain with n states, In a reversible chain with n states, For random walk on a simple graph with n ≥ 2 vertices, We construct examples showing that these bounds are close to optimal. The main feature of our bounds is that they require very little knowledge of the structure of the Markov chain. To prove the bound for random walk on graphs, we establish the following estimate conjectured by Aldous, Ding and Oveis-Gharan (private communication): For random walk on an n-vertex graph, for every initial vertex x,

In collaborative video communication systems, establishing co-orientation around physical objects, virtual objects and people is a critical requirement. This is problematic as the technical limitations of video fractures the display of conduct in the connected environments. We present the results of a study of one collaborative system, CamBlend, which aims to alleviate some of these problems by using screen based pointing tools to both physical spaces and virtual resources. We report on how participants achieved co-orientation when using this system. We relate these findings to previous research into the fractured ecologies of collaborative spaces, describing how the form and nature of fractures in CamBlend differ from earlier reported work.

One of the main driving forces of the growing adoption of virtualization is its dramatic simplification of the provisioning and dynamic management of IT resources. By decoupling running entities from the underlying physical resources, and by providing easy-to-use controls to allocate, deallocate and migrate virtual machines (VMs) across physical boundaries, virtualization opens up new opportunities for improving overall system resource use and power efficiency. While a range of techniques for dynamic, distributed resource management of virtualized systems have been proposed and have seen their widespread adoption in enterprise systems, similar techniques for dynamic power management have seen limited acceptance. The main barrier to dynamic, power-aware virtualization management stems not from the limitations of virtualization, but rather from the underlying physical systems; and in particular, the high latency and energy cost of power state change actions suited for virtualization power management.

CamBlend is a new focus-in-context panoramic video collaboration system designed to facilitate the interaction with and around objects in a lightweight, flexible package. As well as the ability to view very high resolution local and remote video that covers a full 180#176; field of view, the system contains a number of tools which facilitate bi-directional pointing between two remote spaces. In the first quasi-naturalistic exploratory study on a focus-in-context video system, we show a number of unique object referencing behaviours, including un-intentional or 'implicit' pointing and a number of scenarios where this was advantageous. Additionally the study highlighted some of the problems inherent in aligning between screen-based and real-world perspectives.

A multiple microprocessor system is described which was developed for real-time detection and classification of railroad track flaws. Multiple processors were necessary to achieve the desired test vehicle velocity while maintaining the desired density (rate) of testing. The system is organized logically as a tree-structured pipeline of processing stages where the effective data rate from data input toward classification decision output is successively reduced as processing function potential is increased. A corresponding partitioning of the pattern recognition process was organized as a set of hierarchies, where successive patterns are modeled as regular probabilistic grammars and their recognizers implemented as finite state procedures. Interprocessor communications was achieved using shared (2-port) memories. A system prototype was designed and implemented, using real-time data from earlier work to ensure a performance level equivalent to a vehicle velocity of 40 km/h. The resulting system, while applied to a railroad track problem, is applicable to other real-time environments, with suitable parameterization.