Stability of Noisy Metropolis-Hastings

Pseudo-marginal Markov chain Monte Carlo methods for sampling from intractable distributions have gained recent interest and have been theoretically studied in considerable depth. Their main appeal is that they are exact, in the sense that they target marginally the correct invariant distribution. However, the pseudo-marginal Markov chain can exhibit poor mixing and slow convergence towards its target. As an alternative, a subtly different Markov chain can be simulated, where better mixing is possible but the exactness property is sacrificed. This is the noisy algorithm, initially conceptualised as Monte Carlo within Metropolis (MCWM), which has also been studied but to a lesser extent. The present article provides a further characterisation of the noisy algorithm, with a focus on fundamental stability properties like positive recurrence and geometric ergodicity. Sufficient conditions for inheriting geometric ergodicity from a standard Metropolis-Hastings chain are given, as well as convergence of the invariant distribution towards the true target distribution

A query description model based on basic semantic unit composite Petri-Net for soccer video

Digital video networks are making available increasing amounts of sports video data. The volume of material on offer means that sports fans often rely on prepared summaries of game highlights to follow the progress of their favourite teams. A significant application area for automated video analysis technology is the generation of personalized highlights of sports events. One of the most popular sports around world is soccer. A soccer game is composed of a range of significant events, such as goal scoring, fouls, and substitutions. Automatically detecting these events in a soccer video can enable users to interactively design their own highlights programmes. From an analysis of broadcast soccer video, we propose a query description model based on Basic Semantic Unit Composite Petri-Nets (BSUCPN) to automatically detect significant events within soccer video. Firstly we define a Basic Semantic Unit (BSU) set for soccer videos based on identifiable feature elements within a soccer video, Secondly we design Composite Petri-Net (CPN) models for semantic queries and use these to describe BSUCPNs for semantic events in soccer videos. A particular strength of this approach is that users are able to design their own semantic event queries based on BSUCPNs to search interactively within soccer videos. Experimental results based on recorded soccer broadcasts are used to illustrate the potential of this approach

Guidelines for the presentation and visualisation of lifelog content

Lifelogs offer rich voluminous sources of personal and social data for which visualisation is ideally suited to providing access, overview, and navigation. We explore through examples of our visualisation work within the domain of lifelogging the major axes on which lifelogs operate, and therefore, on which their visualisations should be contingent. We also explore the concept of ‘events’ as a way to significantly reduce the complexity of the lifelog for presentation and make it more human-oriented. Finally we present some guidelines and goals which should be considered when designing presentation modes for lifelog conten

REveAL™ and CARElink™ (Real Care): Minimising the time taken to achieve a diagnosis in the implantable loop recorder population

Introduction Syncope accounts for ≈ 2.7/1000 population/year of presentations to UK healthcare, a figure believed to be underestimated by up to 30% due to misdiagnosis. For some patients the cause of their episode/s may remain unexplained. The implantable loop recorder (ILR) is effective for diagnosis of syncope and palpitations, with UK and European guidelines advising its use if symptoms are infrequent. However current follow-up regimes can lead to a slow diagnostic pathway for patients. Remote monitoring technology allows patients to send their ILR data to their clinic Research Questions 1) Does remote monitoring of ILRs reduce time to diagnosis and/or increase diagnostic yield? 2) What is the impact of remote monitoring on logged events requiring analysis? Method New ILR patients at a single implanting centre were recruited. Following informed consent, they were randomised into control or experimental groups. Patients in the control group were reviewed in the conventional manner with routine 6 monthly follow-ups plus additional ad hoc checks if symptoms occurred. Patients in the experimental group were asked to send transmissions fortnightly or following a symptom. All recordings were reviewed and classified as true or false events according to pre-defined criteria. Significant true event ECGs were reviewed blindly by a cardiologist. All data were verified by two physiologists or a physiologist and a cardiologist prior to analysis. The primary outcome variable was median time to clinical diagnosis. Results 37 patients were randomised, 19 to the control and 18 to the experimental group. The control group comprised 11 males and 8 females with a median age of 60 (36-86) years. The experimental group comprised 10 males and 8 females, median age 58 (36-84) years. Mann-Whitney U testing showed no significant differences in group demographics. Following randomisation 5526 events were logged, 1264 in the control and 4262 in the experimental group. 28 (76%) of patients had a true event, which led to a diagnosis in 23 (67%) of patients. There were 13 patients with true events and 10 diagnoses in the experimental group, with 15 true events and 13 diagnoses in the control group. Asystole was the most common event that led to a diagnosis, accounting for 35% of diagnoses. Kaplan-Meier analysis was used to assess the primary outcomes of time from event to follow-up, and time to clinical diagnosis. Compared to the control group, the median time from event to follow-up was reduced from 3 to 1 week (p=0.004). Median time to diagnosis was reduced from 13 to 6 weeks (p=0.049) when remote monitoring was used. Conclusion In patients with ILR, remote monitoring significantly reduced diagnostic delay although the overall diagnostic yield was not increased. However remote monitoring resulted in a three-fold increase in logged events that required analysis with only 1 in 328 proving to be true events: this will have significant resource implications

Dublin City University at the TRECVid 2008 BBC rushes summarisation task

We describe the video summarisation systems submitted by Dublin City University to the TRECVid 2008 BBC Rushes Summarisation task. We introduce a new approach to re- dundant video summarisation based on principal component analysis and linear discriminant analysis. The resulting low dimensional representation of each shot offers a simple way to compare and select representative shots of the original video. The final summary is constructed as a dynamic sto- ryboard. Both types of summaries were evaluated and the results are discussed

Mobile access to personal digital photograph archives

Handheld computing devices are becoming highly connected devices with high capacity storage. This has resulted in their being able to support storage of, and access to, personal photo archives. However the only means for mobile device users to browse such archives is typically a simple one-by-one scroll through image thumbnails in the order that they were taken, or by manually organising them based on folders. In this paper we describe a system for context-based browsing of personal digital photo archives. Photos are labeled with the GPS location and time they are taken and this is used to derive other context-based metadata such as weather conditions and daylight conditions. We present our prototype system for mobile digital photo retrieval, and an experimental evaluation illustrating the utility of location information for effective personal photo retrieval

My digital photos: where and when?

In recent years digital cameras have seen an enormous rise in popularity, leading to a huge increase in the quantity of digital photos being taken. This brings with it the challenge of organising these large collections. We preset work which organises personal digital photo collections based on date/time and GPS location, which we believe will become a key organisational methodology over the next few years as consumer digital cameras evolve to incorporate GPS and as cameras in mobile phones spread further. The accompanying video illustrates the results of our research into digital photo management tools which contains a series of screen and user interactions highlighting how a user utilises the tools we are developing to manage a personal archive of digital photos

Using text search for personal photo collections with the MediAssist system

The MediAssist system enables organisation and searching of personal digital photo collections based on contextual information, content-based analysis and semi-automatic annotation. One mode of user interaction uses automatically extracted features to create text surrogates for photos, which enables text search of photo collections without manual annotation. Our evaluation shows that this text search facility is effective for known-item search

Changes in Refractive Error During Young Adulthood: The Effects of Longitudinal Screen Time, Ocular Sun Exposure, and Genetic Predisposition

Changes in refractive error during young adulthood is common yet risk factors at this age are largely unexplored. This study explored risk factors for these changes, including gene–environmental interactions