MCMC inference for Markov Jump Processes via the Linear Noise Approximation

Bayesian analysis for Markov jump processes is a non-trivial and challenging problem. Although exact inference is theoretically possible, it is computationally demanding thus its applicability is limited to a small class of problems. In this paper we describe the application of Riemann manifold MCMC methods using an approximation to the likelihood of the Markov jump process which is valid when the system modelled is near its thermodynamic limit. The proposed approach is both statistically and computationally efficient while the convergence rate and mixing of the chains allows for fast MCMC inference. The methodology is evaluated using numerical simulations on two problems from chemical kinetics and one from systems biology

Generative probabilistic models for image retrieval

Searching for information is a recurring problem that almost everyone has faced at some point. Being in a library looking for a book, searching through newspapers and magazines for an old article or searching through emails for an old conversation with a colleague are some examples of the searching activity. These are some of the many situations where someone; the “user”; has some vague idea of the information he is looking for; an “information need”; and is searching through a large number of documents, emails or articles; “information items”; to find the most “relevant” item for his purpose. In this thesis we study the problem of retrieving images from large image archives. We consider two different approaches for image retrieval. The first approach is content based image retrieval where the user is searching images using a query image. The second approach is semantic retrieval where the users expresses his query using keywords. We proposed a unified framework to treat both approaches using generative probabilistic models in order to rank and classify images with respect to user queries. The methodology presented in this Thesis is evaluated on a real image collection and compared against state of the art methods

The Impact of Lower Extremity Venous Ulcers due to Chronic Venous Insufficiency on Quality of Life

Lower extremity venous ulcers comprise a complex medical and social issue. The conservative and/or surgical management of venous ulcers is often inadequate. In addition, the psychosocial aspect of the disease is often overlooked and most often undertreated. Common symptoms such as pain, low self-esteem and patient isolation are usually not recognized and therefore not adequately managed

Acoustic identification of Mexican bats based on taxonomic and ecological constraints on call design

1. Monitoring global biodiversity is critical for understanding responses to anthropogenic change, but biodiversity monitoring is often biased away from tropical, megadiverse areas that are experiencing more rapid environmental change. Acoustic surveys are increasingly used to monitor biodiversity change, especially for bats as they are important indicator species and most use sound to detect, localise and classify objects. However, using bat acoustic surveys for monitoring poses several challenges, particularly in mega-diverse regions. Many species lack reference recordings, some species have high call similarity or differ in call detectability, and quantitative classification tools, such as machine learning algorithms, have rarely been applied to data from these areas. 2. Here, we collate a reference call library for bat species that occur in a megadiverse country, Mexico. We use 4,685 search-phase calls from 1,378 individual sequences of 59 bat species to create automatic species identification tools generated by machine learning algorithms (Random Forest). We evaluate the improvement in species-level classification rates gained by using hierarchical classifications, reflecting either taxonomic or ecological constraints (guilds) on call design, and examine how classification rate accuracy changes at different hierarchical levels (family, genus, and guild). 3. Species-level classification of calls had a mean accuracy of 66% and the use of hierarchies improved mean species-level classification accuracy by up to 6% (species within families 72%, species within genera 71.2% and species within guilds 69.1%). Classification accuracy to family, genus and guild-level was 91.7%, 77.8% and 82.5%, respectively. 4. The bioacoustic identification tools we have developed are accurate for rapid biodiversity assessments in a megadiverse region and can also be used effectively to classify species at broader taxonomic or ecological levels. This flexibility increases their usefulness when there are incomplete species reference recordings and also offers the opportunity to characterise and track changes in bat community structure. Our results show that bat bioacoustic surveys in megadiverse countries have more potential than previously thought to monitor biodiversity changes and can be used to direct further developments of bioacoustic monitoring programs in Mexico

Increased Fluorodeoxyglucose Uptake Following Endovascular Abdominal Aortic Aneurysm Repair: A Predictor of Endoleak?

The main criterion for abdominal aortic aneurysm (AAA) repair is an AAA diameter ≥5.5 cm. However, some AAAs rupture when they are smaller. Size alone may therefore not be a sufficient criterion to determine rupture risk. Fluorodeoxyglucose (FDG) uptake is increased in the presence of inflammation and it was suggested that this may be a better predictor of rupture risk than AAA size. Furthermore, increased FDG uptake following endovascular AAA repair may be an indirect predictor of continuous AAA sac enlargement due to the presence of an endoleak (even if this is not detected by imaging modalities) and/or increased AAA rupture risk. The role of FDG uptake needs to be explored further in the management of AAAs

Hepatic Subcapsular Biloma: A Rare Complication of Laparoscopic Cholecystectomy

The development of an intra-abdominal bile collection (biloma) is an infrequent complication of laparoscopic cholecystectomy (LC). These bilomas develop in the subhepatic space most often secondary to iatrogenic injury of the extrahepatic ducts. We present a case of hepatic subcapsular biloma following LC and we discuss its etiology and management. Early diagnosis is crucial and percutaneous drainage under CT guidance should be employed to resolve this complication