Stephen P. Williams

Learn More
— Recently, it has been discovered that the giant ice sheets covering Greenland and Antarctica have been shrinking at an accelerated rate. While it is believed that these regions hold important information related to global climate change, there is still insufficient data to be able to accurately predict the future behavior of those ice sheets. Satellites(More)
—Satellite-based instruments are now routinely used to map the surface of the globe or monitor weather conditions. However , these orbital measurements of ground-based quantities are heavily influenced by external factors, such as air moisture content or surface emissivity. Detailed atmospheric models are created to compensate for these factors, but the(More)
WorldWide Web proxy servers that cache documents can potentially reduce three quantities: the number of requests that reach popular servers, the volume of network traffic resulting from document requests, and the latency that an end-user experiences in retrieving a document. This paper examines the first two using the measures of cache hit rate (or fraction(More)
Repeated measurements and multimodal data are common in neuroimaging research. Despite this, conventional approaches to group level analysis ignore these repeated measurements in favour of multiple between-subject models using contrasts of interest. This approach has a number of drawbacks as certain designs and comparisons of interest are either not(More)
Bundle Adjustment is a key process to enhance the global accuracy of the 3D camera pose and structure estimation in the framework of structure from motion over long video sequences. However, most bundle adjustment algorithms require sufficient visual feature correspondences from each camera frame to its neighboring frames in video sequences, which are hard(More)
We report a rare case of chronic cough as the presenting symptom of a primary brainstem lesion. A 69-year-old gentleman presented with chronic cough followed by onset of progressive truncal ataxia, incoordination and nystagmus. Contrast-enhanced imaging showed a midbrain lesion extending into the cerebellum, confirmed as lymphoma by stereotactic brain(More)
The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Abstract—This paper presents a novel algorithm for integrating real-time filtering of navigation data with full map/trajectory smoothing. Unlike conventional mapping strategies, the result of loop closures within the smoother serve to(More)
—The capability to monitor natural phenomena using mobile sensing is a benefit to the Earth science community given the potentially large impact that we, as humans, can have on naturally occurring processes. Observable phenomena that fall into this category of interest range from static to dynamic in both time and space (i.e. temperature, humidity, and(More)
  • 1