Light coherence properties in optical fibres and visual receptors

The optical field on the end of an optical fibre can display varying degrees of spatial coherence. The classical analyses of the excitation of the fibre have relied on the assumptions that the coherence properties of this field can be approximated by either perfect coherence or total incoherence, and it has long been appreciated that the resulting excitations are markedly different. It is the purpose of the work presented in this thesis to investigate the effects of differing degrees of coherence of this excitation field. The investigation has been restricted in the main to the bound or guided power of the fibre, and the prime consideration has been of current practical communications fibres. Chapter I provides some necessary background information for the thesis and discusses the types of optical fibres to which the study is applied. Chapter II contains a discussion of the theory of partial coherence. The history of optical coherence theory is summarised and then the formal treatment of the theory is described. In the last part of the chapter, an alternative representation of a partially coherent field by an angular spectrum of plane waves is introduced. This is of considerable importance, as it has been used extensively in the work presented here in the framework of the geometric optics description of optical fibre excitation. The need to normalise the power launched into an optical fibre by a partially coherent source led to an investigation of the diffraction of partially coherent light. This is contained in Chapter III. After a discussion of the classical diffraction theory and of previous studies of the diffraction of partially coherent light, a vector formulation is presented, which is shown to have some advantages over the previous analyses. The angular spectrum representation is then used to examine the problem, and shown to give some very informative, if qualitative, results. The central problem of the excitation of an optical fibre by a partially coherent source is tackled in the next two chapters. In Chapter IV the excitation mechanism is discussed in terms of both mode theory and geometric optics. A general analysis for polychromatic partially coherent sources is then developed and the limiting forms of total coherence and total incoherence are derived. A quasimonochromatic approximation is also obtained from this general result. A separate derivation of the quasimonochromatic form is then presented. These analyses are restricted to large V fibres, but are independent of the fibre type. In Chapter V, the quasimonochromatic analysis is applied to the step index fibre, giving detailed results for V < 20 and asymptotic expressions for V >> 1 and for the two extremes of total coherence and total incoherence. A geometric optics treatment of the step index fibre is then presented, and shown to be a good approximation for V ^ 10 and for more incoherent excitations. The last part of the chapter examines the excitation of both step and graded index fibres using a more general and detailed geometric optics approach. This approach is shown to be very powerful, and is used to examine both the bound and leaky powers associated with the fibres. Particular examples of excitations are considered in Chapter VI. In the previous chapters, the source used was the optical field on the end of the fibre, with no reference being made to specific physical sources. In this chapter the two most important sources, the light emitting diode (LED) and semiconductor laser, are examined with reference to the results obtained in Chapter V, and with reference to the common approximations used. The effect of a lens to increase the coupling efficiency of the LED is also examined. The lens excitation in Chapter VI prompted the investigation of the propagation of spatial coherence that appears in Chapter VII. The propagation of the degree of spatial coherence along an optical fibre is investigated first, and the phenomena of coherence enhancement is shown to occur in this situation. The effect of the temporal coherence of the source, a reflection of the finite bandwidth of any physical source, is briefly discussed. A study of the degree of coherence in the image of a partially coherent object forms the last part of this chapter. The simple rule used in Chapter VI is initially derived from intuitive ideas, then shown to be supported by a more formal approach, and finally proved by the use of Fourier theory. The final chapter deals with the previously excluded small V fibres. These are of relevance to communications systems, in the guise of monomode fibres, and to vision research, where visual photoreceptors have been successfully modelled by small V optical waveguides. The relevance of the partially coherent excitation theories developed in this thesis is discussed with reference to these two examples of small V fibres

Environmental exposures: an underrecognized contribution to noncommunicable diseases

Previous attempts to determine the degree to which exposure to environmental factors contribute to noncommunicable diseases (NCDs) have been very conservative and have significantly underestimated the actual contribution of the environment for at least two reasons. Firstly, most previous reports have excluded the contribution of lifestyle behavioral risk factors, but these usually involve significant exposure to environmental chemicals that increase risk of disease. Secondly, early life exposure to chemical contaminants is now clearly associated with an elevated risk of several diseases later in life, but these connections are often difficult to discern. This is especially true for asthma and neurodevelopmental conditions, but there is also a major contribution to the development of obesity and chronic diseases. Most cancers are caused by environmental exposures in genetically susceptible individuals. In addition, new information shows significant associations between cardiovascular diseases and diabetes and exposure to environmental chemicals present in air, food, and water. These relationships likely reflect the combination of epigenetic effects and gene induction. Environmental factors contribute significantly more to NCDs than previous reports have suggested. Prevention needs to shift focus from individual responsibility to societal responsibility and an understanding that effective prevention of NCDs ultimately relies on improved environmental management to reduce exposure to modifiable risks

Meta-analytical methods to identify who benefits most from treatments: daft, deluded, or deft approach?

Identifying which individuals beneft most from particular treatments or other interventions underpins so-called personalised or stratifed medicine. However, single trials are typically underpowered for exploring whether participant characteristics, such as age or disease severity, determine an individual's response to treatment. A meta-analysis of multiple trials, particularly one where individual participant data (IPD) are available, provides greater power to investigate interactions between participant characteristics (covariates) and treatment e?ects. We use a published IPD meta-analysis to illustrate three broad approaches used for testing such interactions. Based on another systematic review of recently published IPD meta-analyses, we also show that all three approaches can be applied to aggregate data as well as IPD. We also summarise which methods of analysing and presenting interactions are in current use, and describe their advantages and disadvantages. We recommend that testing for interactions using within-trials information alone (the def approach) becomes standard practice, alongside graphical presentation that directly visualises this

Developing a conformance methodology for clinically-defined medical record headings:a preliminary report.

Background: The Professional Records Standards Body for health and social care (PRSB) was formed in 2013 to develop and assure professional standards for the content and structure of patient records across all care disciplines in the UK. Although the PRSB work is aimed at Electronic Health Record (EHR) adoption and interoperability to support continuity of care, the current technical guidance is limited and ambiguous. Objectives: This project was initiated as a proof-ofconcept to demonstrate whether, and if so, how, conformance methods can be developed based on the professional standards. Methods: An expert group was convened, comprising clinical and technical representatives. A constrained data set was defined for an outpatient letter, using the subset of outpatient headings that are also present in the ep-SOS patient summary. A mind map was produced for the main sections and sub-sections. An openEHR archetype model was produced as the basis for creating HL7 and IHE implementation artefacts. Results: Several issues about data definition and representation were identified when attempting to map the outpatient headings to the epSOS patient summary, partly due to the difference between process and static viewpoints. Mind maps have been a simple and helpful way to visualize the logical information model and expose and resolve disagreements about which headings are purely for human navigation and which, if any, have intrinsic meaning. Conclusions: Conformance testing is feasible but nontrivial. In contrast to traditional standards-development timescales, PRSB needs an agile standards development process with EHR vendor and integrator collaboration to ensure implementability and widespread adoption. This will require significant clinical and technical resources

Secular changes in functional disability, pain, fatigue and mental well-being in early rheumatoid arthritis.:A longitudinal meta-analysis

Objectives: To conduct a systematic review and longitudinal meta-analysis of early rheumatoid arthritis (RA) cohorts with long-term data on pain, fatigue or mental well-being. Methods: Searches using PUBMED, EMBASE and PyscInfo were performed to identify all early RA cohorts with longitudinal measures of pain, fatigue or mental well-being, along with clinical measures. Using longitudinal meta-analyses, the progression of each outcome over the first 60-months was estimated. Cohorts were stratified based on the median recruitment year to investigate secular trends in disease progression. Results: Of 7,319 papers identified, 75 met the inclusion criteria and 46 cohorts from 41 publications provided sufficient data on 18,046 patients for meta-analysis. The Disease Activity Scores (DAS28) and the Short-Form 36 (SF-36) Physical Component Score (PCS) indicated that post-2002 cohorts had statistically significant improvements over the first 60-months compared to pre-2002 cohorts, with standardised mean differences (SMD) of 0.86 (95% Confidence Intervals 0.34 to 1.37) and 0.76 (95% CI 0.25 to 1.27) respectively at month-60. However, post-2002 cohorts indicated statistically non-significant improvements in pain, fatigue, functional disability and SF-36 Mental Component Score (MCS) compared to pre-2002 cohorts, with SMD of 0.24 (95% CI -0.25 to 0.74), 0.38 (95% CI -0.11 to 0.88), 0.34 (95% CI -0.15-0.84) and -0.08 (95% CI -0.41 to 0.58) at month-60 respectively. Conclusions: Recent cohorts indicate improved levels of disease activity and physical quality of life, however this has not translated into similar improvements in levels of pain, fatigue and functional disability by 60-months

Debris Disks of Members of the Blanco 1 Open Cluster

We have used the Spitzer Space Telescope to obtain Multiband Imaging Photometer for Spitzer (MIPS) 24 um photometry for 37 members of the ~100 Myr old open cluster Blanco 1. For the brightest 25 of these stars (where we have 3sigma uncertainties less than 15%), we find significant mid-IR excesses for eight stars, corresponding to a debris disk detection frequency of about 32%. The stars with excesses include two A stars, four F dwarfs and two G dwarfs. The most significant linkage between 24 um excess and any other stellar property for our Blanco 1 sample of stars is with binarity. Blanco 1 members that are photometric binaries show few or no detected 24 um excesses whereas a quarter of the apparently single Blanco 1 members do have excesses. We have examined the MIPS data for two other clusters of similar age to Blanco 1 -- NGC 2547 and the Pleiades. The AFGK photometric binary star members of both of these clusters also show a much lower frequency of 24 um excesses compared to stars that lie near the single-star main sequence. We provide a new determination of the relation between V-Ks color and Ks-[24] color for main sequence photospheres based on Hyades members observed with MIPS. As a result of our analysis of the Hyades data, we identify three low mass Hyades members as candidates for having debris disks near the MIPS detection limit.Comment: Accepted to Ap

The DetectDeviatingCells algorithm was a useful addition to the toolkit for cellwise error detection in observational data

OBJECTIVE: We evaluated the error detection performance of the DetectDeviatingCells (DDC) algorithm, which flags data anomalies at observation (casewise) and variable (cellwise) level in continuous variables. We compared its performance to other approaches in a simulated dataset. STUDY DESIGN AND SETTING: We simulated height and weight data for hypothetical individuals aged 2-20 years. We changed a proportion of height values according to pre-determined error patterns. We applied the DDC algorithm and other error-detection approaches (descriptive statistics, plots, fixed-threshold rules, classic and robust Mahalanobis distance) and we compared error detection performance with sensitivity, specificity, likelihood ratios, predictive values and ROC curves. RESULTS: At our chosen thresholds, error detection specificity was excellent across all scenarios for all methods and sensitivity was higher for multivariable and robust methods. The DDC algorithm performance was similar to other robust multivariable methods. Analysis of ROC curves suggested that all methods had comparable performance for gross errors (e.g. wrong measurement unit), but the DDC algorithm outperformed the others for more complex error patterns (e.g. transcription errors that are still plausible, although extreme). CONCLUSIONS: The DDC algorithm has the potential to improve error detection processes for observational data

A Resolved Ring of Debris Dust around the Solar Analog HD 107146

We present resolved images of the dust continuum emission from the debris disk around the young (80-200 Myr) solar-type star HD 107146 with CARMA at λ = 1.3 mm and the CSO at λ = 350 μ. Both images show that the dust emission extends over an approximately 10" diameter region. The high-resolution (3") CARMA image further reveals that the dust is distributed in a partial ring with significant decrease in a flux inward of 97 AU. Two prominent emission peaks appear within the ring separated by ~140° in the position angle. The morphology of the dust emission is suggestive of dust captured into a mean motion resonance, which would imply the presence of a planet at an orbital radius of ~45-75 AU

The Report of the Ecological Society of America Committee on the Scientific Basis for Ecosystem Management

Ecosystem management is management driven by explicit goals, executed by policies, protocols, and practices, and made adaptable by monitoring and research based on our best understanding of the ecological interactions and processes necessary to sustain ecosystem composition, structure, and function