Diffusion maps for changing data

Graph Laplacians and related nonlinear mappings into low dimensional spaces have been shown to be powerful tools for organizing high dimensional data. Here we consider a data set X in which the graph associated with it changes depending on some set of parameters. We analyze this type of data in terms of the diffusion distance and the corresponding diffusion map. As the data changes over the parameter space, the low dimensional embedding changes as well. We give a way to go between these embeddings, and furthermore, map them all into a common space, allowing one to track the evolution of X in its intrinsic geometry. A global diffusion distance is also defined, which gives a measure of the global behavior of the data over the parameter space. Approximation theorems in terms of randomly sampled data are presented, as are potential applications.Comment: 38 pages. 9 figures. To appear in Applied and Computational Harmonic Analysis. v2: Several minor changes beyond just typos. v3: Minor typo corrected, added DO

Combustion waves in a model with chain branching reaction and their stability

In this paper the travelling wave solutions in the adiabatic model with two-step chain branching reaction mechanism are investigated both numerically and analytically in the limit of equal diffusivity of reactant, radicals and heat. The properties of these solutions and their stability are investigated in detail. The behaviour of combustion waves are demonstrated to have similarities with the properties of nonadiabatic one-step combustion waves in that there is a residual amount of fuel left behind the travelling waves and the solutions can exhibit extinction. The difference between the nonadiabatic one-step and adiabatic two-step models is found in the behaviour of the combustion waves near the extinction condition. It is shown that the flame velocity drops down to zero and a standing combustion wave is formed as the extinction condition is reached. Prospects of further work are also discussed.Comment: pages 32, figures 2

Dynamic optimal taxation with human capital.

This paper revisits the dynamic optimal taxation results of Jones, Manuelli, and Rossi (1993, 1997). They use a growth model with human capital and find that optimal taxes on both capital income and labor income converge to zero in steady state. For one of the models under consideration, I show that the representative household's problem does not have an interior solution. This raises concerns since these corners are inconsistent with aggregate data. Interiority is restored if preferences are modified so that human capital augments the value of leisure time. With this change, the optimal tax problem is analyzed and, reassuringly, the Jones, Manuelli, and Rossi results are confirmed: neither capital income nor labor income should be taxed in steady state

Male Circumcision and STI Acquisition in Britain: Evidence from a National Probability Sample Survey.

BACKGROUND: It is well-established that male circumcision reduces acquisition of HIV, herpes simplex virus 2, chancroid, and syphilis. However, the effect on the acquisition of non-ulcerative sexually transmitted infections (STIs) remains unclear. We examined the relationship between circumcision and biological measures of three STIs: human papillomavirus (HPV), Chlamydia trachomatis and Mycoplasma genitalium. METHODS: A probability sample survey of 15,162 men and women aged 16-74 years (including 4,060 men aged 16-44 years) was carried out in Britain between 2010 and 2012. Participants completed a computer-assisted personal interview, including a computer-assisted self-interview, which asked about experience of STI diagnoses, and circumcision. Additionally, 1,850 urine samples from sexually-experienced men aged 16-44 years were collected and tested for STIs. Multivariable logistic regression was used to calculate adjusted odds ratios (AOR) to quantify associations between circumcision and i) self-reporting any STI diagnosis and ii) presence of STIs in urine, in men aged 16-44 years, adjusting for key socio-demographic and sexual behavioural factors. RESULTS: The prevalence of circumcision in sexually-experienced men aged 16-44 years was 17.4% (95%CI 16.0-19.0). There was no association between circumcision and reporting any previous STI diagnoses, and specifically previous chlamydia or genital warts. However, circumcised men were less likely to have any HPV type (AOR 0.26, 95% confidence interval (CI) 0.13-0.50) including high-risk HPV types (HPV-16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59 and/or 68) (AOR 0.14, 95% CI 0.05-0.40) detected in urine. CONCLUSIONS: Circumcised men had reduced odds of HPV detection in urine. These findings have implications for improving the precision of models of STI transmission in populations with different circumcision prevalence and in designing interventions to reduce STI acquisition

Producing interventions for AIDS-affected young people in Lesotho's schools: Scalar relations and power differentials

This is the post-print version of the final paper published in Geoforum. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2009 Elsevier B.V.Children and youth are a key target group for interventions to address southern Africa’s AIDS pandemic. Such interventions are frequently implemented through schools, and are often complex products of negotiation between a range of institutional actors including international agencies, NGOs, government departments and individual schools. These institutions not only stand in different (horizontally scaled) spatial relationships to students in schools; they also appear to operate at different hierarchical levels. Empirical research with policy makers and practitioners in Lesotho, however, reveals how interventions are produced through flows of knowledge, funding and personnel within and between institutions that make it difficult to assert that any intervention is manifestly more international or more local than any other. Scale theory offers the metaphor of a network or web which usefully serves to move attention away from discrete organisations, sectors and scalar positionings and onto the relationships and flows between them. Nevertheless, organisations and development interventions are often partly structured in scalar hierarchical ways that express substantive power differentials and shape the forms of interaction that take place, albeit not binding them to strict binaries or nested hierarchies. A modified network metaphor is useful in aiding understanding of how particular interventions are produced through intermeshing scales and diverse fluid interactions, and why they take the form they do.RGS-IB

An analysis of organisational adaptation to climate change: the case of the Bardiya National Park

This research is concerned with understanding how the management authority of the Bardiya National Park (the BNPMA) is able to adapt to the pressures of increasing climate variability and change. To that end, this study employs a mixed-methods case study approach to elucidate the key drivers of change facing the BNPMA, the processes through which the organisation adapts to these challenges, and the factors that enable and constrain action. In doing so it intends to provide a more comprehensive understanding of the potential future effectiveness of adaptation interventions. Analysis of local weather data, in conjunction with data obtained from village level surveys, highlights a number of climatic trends which, along with related environmental changes are shown to have an important role in driving change within the BNPMA. A range of anthropogenic drivers are also shown to be relevant. The factors enabling and constraining the BNPMA’s ability to respond to these identified drivers of change are subsequently examined through the analysis of data obtained from Likert questionnaires, semi-structured interviews, focus groups, and field observations. Organisational systems, culture, internal resources and the process of knowledge generation and sharing are all found to play a pivotal role in determining the capacity of the BNPMA to respond to its drivers of change. The final analytical section of this thesis uses three examples to evaluate the learning processes through which the BNPMA operationalises its adaptive capacity and mobilises it as adaptive management interventions. Drawing on the results of semi-structured interviews, focus group discussions, official park documents, and fieldwork observations, three distinct types of learning are identified within the organisation. In conclusion, this study argues that learning plays a key role in adaptive management approaches to conservation and in operationalising organisational adaptive capacity, enabling the BNPMA to effectively respond to new challenges. However, further research is needed to assess the wider applicability of the drivers of change highlighted in this study, within Nepal and beyond, as well as the interplay of components of adaptive capacity in conservation organisations and the learning processes through which this capacity is mobilised

Estimating the horizontal and vertical direction-of-arrival of water-borne seismic signals in the northern Philippine Sea

Author Posting. © Acoustical Society of America, 2013. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 134 (2013): 3282, doi:10.1121/1.4818843.Conventional and adaptive plane-wave beamforming with simultaneous recordings by large-aperture horizontal and vertical line arrays during the 2009 Philippine Sea Engineering Test (PhilSea09) reveal the rate of occurrence and the two-dimensional arrival structure of seismic phases that couple into the deep ocean. A ship-deployed, controlled acoustic source was used to evaluate performance of the horizontal array for a range of beamformer adaptiveness levels. Ninety T-phases from unique azimuths were recorded between Yeardays 107 to 119. T-phase azimuth and S-minus-P-phase time-of-arrival range estimates were validated using United States Geological Survey seismic monitoring network data. Analysis of phases from a seismic event that occurred on Yearday 112 near the east coast of Taiwan approximately 450 km from the arrays revealed a 22° clockwise evolution of T-phase azimuth over 90 s. Two hypotheses to explain such evolution—body wave excitation of multiple sources or in-water scattering—are presented based on T-phase origin sites at the intersection of azimuthal great circle paths and ridge/coastal bathymetry. Propagation timing between the source, scattering region, and array position suggests the mechanism behind the evolution involved scattering of the T-phase from the Ryukyu Ridge and a T-phase formation/scattering location estimation error of approximately 3.2 km.This research is supported by the Office of Naval Research, both the Applied Research Laboratory program and Code 322(OA)

Epidemiology of Mycoplasma genitalium in British men and women aged 16–44 years: evidence from the third National Survey of Sexual Attitudes and Lifestyles (Natsal-3).

BACKGROUND: There are currently no large general population epidemiological studies of Mycoplasma genitalium (MG), which include prevalence, risk factors, symptoms and co-infection in men and women across a broad age range. METHODS: In 2010-–12, we conducted the third National Survey of Sexual Attitudes and Lifestyles (Natsal-3), a probability sample survey in Britain. Urine from 4507 sexually-experienced participants, aged 16–44 years, was tested for MG. RESULTS: MG prevalence was 1.2% [95% confidence interval (CI): 0.7–1.8%] in men and 1.3% (0.9–1.9%) in women. There were no positive MG tests in men aged 16–19, and prevalence peaked at 2.1% (1.2–3.7%) in men aged 25–34 years. In women, prevalence was highest in 16–19 year olds, at 2.4% (1.2–4.8%), and decreased with age. Men of Black ethnicity were more likely to test positive for MG [adjusted odds ratio (AOR) 12.1; 95% CI: 3.7–39.4). For both men and women, MG was strongly associated with reporting sexual risk behaviours (increasing number of total and new partners, and unsafe sex, in the past year). Women with MG were more likely to report post-coital bleeding (AOR 5.8; 95%CI 1.4–23.3). However, the majority of men (94.4%), and over half of women (56.2%) with MG did not report any sexually transmitted infection (STI) symptoms. Men with MG were more likely to report previously diagnosed gonorrhoea, syphilis or non-specific urethritis, and women previous trichomoniasis. CONCLUSIONS: This study strengthens evidence that MG is an STI. MG was identified in over 1% of the population, including in men with high-risk behaviours in older age groups that are often not included in STI prevention measures

Argumentation in school science : Breaking the tradition of authoritative exposition through a pedagogy that promotes discussion and reasoning

The value of argumentation in science education has become internationally recognised and has been the subject of many research studies in recent years. Successful introduction of argumentation activities in learning contexts involves extending teaching goals beyond the understanding of facts and concepts, to include an emphasis on cognitive and metacognitive processes, epistemic criteria and reasoning. The authors focus on the difficulties inherent in shifting a tradition of teaching from one dominated by authoritative exposition to one that is more dialogic, involving small-group discussion based on tasks that stimulate argumentation. The paper builds on previous research on enhancing the quality of argument in school science, to focus on how argumentation activities have been designed, with appropriate strategies, resources and modelling, for pedagogical purposes. The paper analyses design frameworks, their contexts and lesson plans, to evaluate their potential for enhancing reasoning through foregrounding the processes of argumentation. Examples of classroom dialogue where teachers adopt the frameworks/plans are analysed to show how argumentation processes are scaffolded. The analysis shows that several layers of interpretation are needed and these layers need to be aligned for successful implementation. The analysis serves to highlight the potential and limitations of the design frameworks