Principal arc analysis on direct product manifolds

We propose a new approach to analyze data that naturally lie on manifolds. We focus on a special class of manifolds, called direct product manifolds, whose intrinsic dimension could be very high. Our method finds a low-dimensional representation of the manifold that can be used to find and visualize the principal modes of variation of the data, as Principal Component Analysis (PCA) does in linear spaces. The proposed method improves upon earlier manifold extensions of PCA by more concisely capturing important nonlinear modes. For the special case of data on a sphere, variation following nongeodesic arcs is captured in a single mode, compared to the two modes needed by previous methods. Several computational and statistical challenges are resolved. The development on spheres forms the basis of principal arc analysis on more complicated manifolds. The benefits of the method are illustrated by a data example using medial representations in image analysis.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS370 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

Ensuring Successful International Teaching Assistants (ITAs)

To ensure the success of both the ITAs and their students, various types of training and support are needed

The Impact of the Madden-Julian Oscillation on Extreme Winter Weather in the United States

Winter weather has substantial impacts on human activity, but it is challenging to predict more than 7-10 days in advance. Subseasonal-to-seasonal (S2S) prediction is a rapidly developing field of meteorology that could be used to improve winter weather prediction at longer time scales. The Madden-Julian Oscillation (MJO) is a major driver of global S2S variability. This study seeks to examine how the MJO affects the frequency of winter weather over the contiguous United States, which will help further improve winter weather prediction in the future. This is done by comparing the frequency of winter weather reports and snow accumulation data at surface meteorological stations in a given phase of the MJO to its climatology. We find that the MJO has significant impacts on increasing the frequency of extreme winter weather in the Northeast when MJO convection is in the western Indian Ocean (phase 1), the Southern Great Plains when MJO convection is in the central Indian Ocean (phase 2), and the Northern Great Plains when MJO convection is over the Maritime Continent (phase 4). These results are primarily driven by the forcing of the MJO on the jet stream and its subsequent impacts on geopotential height, as well as temperature and wind in the lower atmosphere. MJO impacts on the frequency of extreme winter weather can be seen up to 15 days in advance, suggesting utility in S2S forecasting

Changing the world or reacting to a changed world? : the global politics of population after the International Conference on Population and Development

This thesis explores the global politics of population and reproduction since 1994, when the International Conference on Population and Development (ICPD) was held in Cairo. The thesis is presented within the disciplinary framework of International Relations in the understanding that debates about population and reproduction are intensely political. The central question is "Did the ICPD change the world, and if not, why not?" based upon the statement made by Nafis Sadik who, in 1994, was the Executive Director of UNFPA. Sadik's statement reflected the views of many in the international women's health movement, which played a major role in setting the agenda for the ICPD, as the thesis outlines. The thesis is organised in six chapters, analysing the micro and macro aspects of ICPD's Programme of Action (POA). It explores the transformative aspects of ICPD which are found in its micro agenda of women's empowerment, reproductive rights and reproductive health. The key concepts are explored and debates about them within the broad and diverse feminist movement, as well as with the conservative opponents, are analysed in the thesis. The macro context necessary for the achievement of the POA's micro agenda was inadequately considered by the major players at ICPD and, hence, poorly covered in the POA. Development was given little attention, and the already weak concept of sustainable development was further compromised by its contextualisation within a framework of economic growth. Consequently, the thesis concludes, the transformative micro agenda was given no support by this part of the POA. The thesis tracks developments in global political economy which were occurring alongside the UN conferences of the 1990s. It focuses particularly on the World Bank, which is a major player in global population politics. Indonesia provides a case study of the impacts of global economic trends on reproductive health in a country with a population program which in 1994 was viewed as a model for other developing countries. The macro context is also determined by approaches to population in environmental discourses since the framework of sustainable development in which population was placed in 1994 combined environmental and economic objectives. Neo-Malthusian views have provided the 'common sense' approach to population, particularly within Northern environmental organisations, and key documents are trawled to discern whether these views have been modified within some environmental and population organisations. The thesis concludes by considering the contribution that the ICPD has made to population and broader debates and by assessing the contribution that topics related to population and reproduction can make to the discipline of International Relations. Throughout the thesis, the writings of Southern feminists are sought wherever possible, and the impacts of population and health policies on poor women are the main focus. As the people on the receiving end of population policies, the success of the conference is best measured by improvements in their health and their greater access to the conditions which enable them to exercise their reproductive and other human rights

Carers' Perspectives on Sustainability of Informal Care for People With Dementia

The majority of people with dementia, even at advanced stages, receive most of their care and support from family members, friends, and neighbors, rather than formal support systems. This qualitative research undertaken in the Australian state of Queensland explored how family carers of people with dementia living in the community successfully manage and sustain informal caring. It also considers challenges these carers anticipated in continuing to support their family member with dementia in the future. What emerges through this analysis of the carers’ perspective on the sustainability of care is the impact of factors including the living arrangements, generational cohort and life stage of the carer, financial issues, and ability to effectively combine caring with their other roles and responsibilities in life

ESOLID—a system for exact boundary evaluation

We present a system, ESOLID, that performs exact boundary evaluation of low-degree curved solids in reasonable amounts of time. ESOLID performs accurate Boolean operations using exact representations and exact computations throughout. The demands of exact computation require a different set of algorithms and efficiency improvements than those found in a traditional inexact floating point based modeler. We describe the system architecture, representations, and issues in implementing the algorithms. We also describe a number of techniques that increase the efficiency of the system based on lazy evaluation, use of floating point filters, arbitrary floating point arithmetic with error bounds, and lower dimensional formulation of subproblems. ESOLID has been used for boundary evaluation of many complex solids. These include both synthetic datasets and parts of a Bradley Fighting Vehicle designed using the BRL-CAD solid modeling system. It is shown that ESOLID can correctly evaluate the boundary of solids that are very hard to compute using a fixed-precision floating point modeler. In terms of performance, it is about an order of magnitude slower as compared to a floating point boundary evaluation system on most cases

Segmenting CT prostate images using population and patient-specific statistics for radiotherapy: Segmenting CT prostate images for radiotherapy

Purpose: In the segmentation of sequential treatment-time CT prostate images acquired in image-guided radiotherapy, accurately capturing the intrapatient variation of the patient under therapy is more important than capturing interpatient variation. However, using the traditional deformable-model-based segmentation methods, it is difficult to capture intrapatient variation when the number of samples from the same patient is limited. This article presents a new deformable model, designed specifically for segmenting sequential CT images of the prostate, which leverages both population and patient-specific statistics to accurately capture the intrapatient variation of the patient under therapy

Social media-enabled learning and the curriculum in Australian higher education: A literature review

This study is centred on the impact of social media-enabled learning on the curriculum within higher education in Australia and focuses on curriculum in relation to distance education. The impact on curriculum design of the trend for rapid uptake of social media, but with less active contribution of user generated content, is discussed, as are the implications for higher education of other central ethical issues in relation to the protection of identity and development of trust in utilizing social media sites in higher education. The review explores the applicability of six curriculum models within a social media-enriched learning environment: curriculum as product, curriculum as a body of knowledge for transmission, curriculum as process curriculum, as praxis, curriculum as knowledge creation and community as curriculum. The importance of open and flexible design methodologies emerges; the conclusion being that social media-enabled learning moves higher education beyond a focus on content provision into a dynamic communal process of sense-making and knowledge

Three-dimensional quantitative evaluation method of nonrigid registration algorithms for adaptive radiotherapy

Purpose: Current radiotherapy is progressing to the concept of adaptive radiotherapy, which implies the adaptation of planning along the treatment course. Nonrigid registration is an essential image processing tool for adaptive radiotherapy and image guided radiotherapy, and the three-dimensional (3D) nature of the current radiotherapy techniques requires a 3D quantification of the registration error that existing evaluation methods do not cover appropriately. The authors present a method for 3D evaluation of nonrigid registration algorithms’ performance, based on organ delineations, capable of working with near-spherical volumes even in the presence of concavities. Methods: The evaluation method is composed by a volume shape description stage, developed using a new ad hoc volume reconstruction algorithm proposed by the authors, and an error quantification stage. The evaluation method is applied to the organ delineations of prostate and seminal vesicles, obtained by an automatic segmentation method over images of prostate cancer patients treated with intensity modulated radiation therapy. Results: The volume reconstruction algorithm proposed has been shown to accurately model complex 3D surfaces by the definition of clusters of control points. The quantification method, inspired by the Haussdorf–Chebysev distance, provides a measure of the largest registration error per control direction, defining a valid metric for concave-convex volumes. Summarizing, the proposed evaluation methodology presents accurate results with a high spatial resolution in a negligible computation time in comparison with the nonrigid registration time. Conclusions: Experimental results show that the metric selected for quantifying the registration error is of utmost importance in a quantitative evaluation based on measuring distances between volumes. The accuracy of the volume reconstruction algorithm is not so relevant as long as the reconstruction is tight enough on the actual volume of the organ. The new evaluation method provides a smooth and accurate volume reconstruction for both the reference and the registered organ, and a complete 3D description of nonrigid registration algorithms’ performance, resulting in a useful tool for study and comparison of registration algorithms for adaptive radiotherapy

Simulation-Based Joint Estimation of Body Deformation and Elasticity Parameters for Medical Image Analysis

Estimation of tissue stiffness is an important means of noninvasive cancer detection. Existing elasticity reconstruction methods usually depend on a dense displacement field (inferred from ultrasound or MR images) and known external forces. Many imaging modalities, however, cannot provide details within an organ and therefore cannot provide such a displacement field. Furthermore, force exertion and measurement can be difficult for some internal organs, making boundary forces another missing parameter. We propose a general method for estimating elasticity and boundary forces automatically using an iterative optimization framework, given the desired (target) output surface. During the optimization, the input model is deformed by the simulator, and an objective function based on the distance between the deformed surface and the target surface is minimized numerically. The optimization framework does not depend on a particular simulation method and is therefore suitable for different physical models. We show a positive correlation between clinical prostate cancer stage (a clinical measure of severity) and the recovered elasticity of the organ. Since the surface correspondence is established, our method also provides a non-rigid image registration, where the quality of the deformation fields is guaranteed, as they are computed using a physics-based simulation