Detecting abrupt changes in the spectra of high-energy astrophysical sources

Variable-intensity astronomical sources are the result of complex and often extreme physical processes. Abrupt changes in source intensity are typically accompanied by equally sudden spectral shifts, that is, sudden changes in the wavelength distribution of the emission. This article develops a method for modeling photon counts collected from observation of such sources. We embed change points into a marked Poisson process, where photon wavelengths are regarded as marks and both the Poisson intensity parameter and the distribution of the marks are allowed to change. To the best of our knowledge, this is the first effort to embed change points into a marked Poisson process. Between the change points, the spectrum is modeled nonparametrically using a mixture of a smooth radial basis expansion and a number of local deviations from the smooth term representing spectral emission lines. Because the model is over-parameterized, we employ an ℓ1ℓ1 penalty. The tuning parameter in the penalty and the number of change points are determined via the minimum description length principle. Our method is validated via a series of simulation studies and its practical utility is illustrated in the analysis of the ultra-fast rotating yellow giant star known as FK Com

Charge-tagged polar phosphine ligands in Pd-catalysed reactions in aqueous and ionic media

© 2018 Elsevier Ltd A new range of polar imidazolium and phosphate-containing ligands was synthesised from readily available starting materials in high yielding multi-step transformations. These ligands were used to generate Pd catalysts for Suzuki and Heck C–C coupling reactions in organic and organic/aqueous media. The catalysts performed well in aqueous media in the Suzuki reaction and less well in the Heck reaction, related to substrate solubility in the aqueous media. When moving to ionic liquids, the Heck reaction dramatically improved, especially in media compatible with the polar catalysts and the non-polar reagents. In all cases, the catalysts were stable to the formation of Pd black, a form of degradation that frequently befalls Pd catalysts. The catalysts could be successfully recycled without loss of activity

Knowledge, attitude and practices of patients receiving maintenance haemodialysis in Bloemfontein, South Africa

Introduction: In sub-Saharan Africa, a paucity of data exists in respect of the knowledge, attitudes and practices (KAP) of patientson maintenance haemodialysis (MHD) regarding the dietary adaptations they should make.Methods: In a descriptive, cross-sectional study, conducted in 2017, questionnaires were administered during structured interviews with 75 participants in five MHD-units in Bloemfontein to assess socio-demographics and KAP regarding the ‘renal’ diet.Results: The median age was 50.5 years; 70.7% of participants were male. Overall, 49.4% scored low (< 50%) on knowledge regarding restricted foods, food content of restricted minerals, and phosphate binders; 60.0% reported negative attitudes towards the diet, and 61.4% reported poor adherence practices. Participants with tertiary education (28.0%) had significantly higher knowledge scores than participants with only primary school education (6.7%) (95% CI 3.9%; 73.5%), or those who had only partially completed secondary school (17.3%) (95% CI 6.3%; 64.0%). Only 21.0% reported having received written, and 30.7% verbal, nutrition education in their home language, while 24.0% reported never receiving nutrition education in either their home or second language. Having received nutrition education in a home language and/or second language was associated with significantly higher knowledge scores (95% CI 3.7%; 49.5%). Most (77.3%) reported zero to one consultation with a dietitian per MHD year (NKF-K/DOQI recommends at least three/MHD year).Conclusion: This population on MHD presented with poor KAP regarding the ‘renal’ diet, and inadequate involvement of dietitians in their treatment. Receiving nutritional education in a first or second language significantly increased knowledge of, and insight into, the required dietary adaptations

Analysis of energy spectra with low photon counts via Bayesian posterior simulation

Over the past 10 years Bayesian methods have rapidly grown more popular as several computationally intensive statistical algorithms have become feasible with increased computer power. In this paper, we begin with a general description of the Bayesian paradigm for statistical inference and the various state-of-the-art model fitting techniques that we employ (e.g., Gibbs sampler and Metropolis- Hastings). These algorithms are very flexible and can be used to fit models that account for the highly hierarchical structure inherent in the collection of high-quality spectra and thus can keep pace with the accelerating progress of new space telescope designs. The methods we develop, which will soon be available in the CIAO software package, explicitly model photon arrivals as a Poisson process and, thus, have no difficulty with high resolution low count X-ray and gamma-ray data. We expect these methods to be useful not only for the recently launched Chandra X-ray observatory and XMM but also new generation telescopes such as Constellation X, GLAST, etc. In the context of two examples (Quasar S5 0014+813 and Hybrid-Chromosphere Supergiant Star alpha TrA) we illustrate a new highly structured model and how Bayesian posterior sampling can be used to compute estimates, error bars, and credible intervals for the various model parameters

Nutritional status of undergraduate healthcare students at the University of the Free State

Objectives: This study aimed to evaluate the lifestyle habits of South African students preparing for careers in health care that could influence the efficacy of their counselling practices on risk factors for noncommunicable diseases (NCDs) as future healthcare professionals.Design: Cross-sectional descriptive study.Setting and subjects: One hundred and sixty-one students (median age 21.5 years, 75.8% women) enrolled in the Faculty of Health Sciences at the University of the Free State.Outcome measures: Anthropometry was measured and structured questionnaires administered to assess dietary and lifestyle habits.Results: Many students were at risk of NCDs, with 19.8% being overweight or obese (body mass index > 25 kg/m2), 11.8% had a waist circumferences above gender-specific cut-off points, 98.1% consumed < 3 servings of vegetables/day, 58.4% consumed < 2 servings of fruit/day, 83% consumed < 2 servings of dairy products/day, 60% did not eat a beta-carotenerich fruit or vegetable daily, 31% did not eat a vitamin C-rich fruit or vegetable daily, 62% never consumed legumes, 43% reported a high intake of fats and sweets, 11% smoked a median of 3.5 cigarettes/day and 63% consumed a median of three drinks of alcohol/day on a median of four days (95% weekend days) per month. Fifty-nine per cent were active and 39% were very active owing to busy class schedules, but only 32% participated in formal exercise and sports.Conclusion: The poor dietary and lifestyle habits of most participants highlight the need to not just educate, but better empower these students to deal with the growing public health problem of obesity and related NCDs in the country.Keywords: students, healthcare professionals, diet, anthropometry, lifestyl

The impact of large terrestrial carnivores on Pleistocene ecosystems

At very high densities, populations of the largest herbivores, such as elephants, have devastating effects on the environment. What prevented widespread habitat destruction in the Pleistocene, when the ecosystem sustained many species of huge herbivores? We use data on predator–prey body mass relationships to predict the prey size ranges of large extinct mammalian carnivores, which were more diverse and much larger than living species. We then compare these prey size ranges with estimates of young mammoth sizes and show that juvenile mammoths and mastodons were within predicted prey size ranges of many of the Pleistocene carnivores. From this and other fossil evidence we argue that, by limiting population sizes of megaherbivores, large carnivores had a major impact on Pleistocene ecosystems

The Canonical Perfect Bose Gas in Casimir Boxes

We study the problem of Bose-Einstein condensation in the perfect Bose gas in the canonical ensemble, in anisotropically dilated rectangular parallelpipeds (Casimir boxes). We prove that in the canonical ensemble for these anisotropic boxes there is the same type of generalized Bose-Einstein condensation as in the grand-canonical ensemble for the equivalent geometry. However the amount of condensate in the individual states is different in some cases and so are the fluctuations.Comment: 23 page

Molecular Imaging Approaches in Dementia

The increasing prevalence of dementia worldwide places a high demand on healthcare providers to perform a diagnostic work-up in relatively early stages of the disease, given that the pathologic process usually begins decades before symptoms are evident. Structural imaging is recommended to rule out other disorders and can only provide diagnosis in a late stage with limited specificity. Where PET imaging previously focused on the spatial pattern of hypometabolism, the past decade has seen the development of novel tracers to demonstrate characteristic protein abnormalities. Molecular imaging using PET/SPECT is able to show amyloid and tau deposition in Alzheimer disease and dopamine depletion in parkinsonian disorders starting decades before symptom onset. Novel tracers for neuroinflammation and synaptic density are being developed to further unravel the molecular pathologic characteristics of dementia disorders. In this article, the authors review the current status of established and emerging PET tracers in a diagnostic setting and also their value as prognostic markers in research studies and outcome measures for clinical trials in Alzheimer disease

Molecular Imaging Approaches in Dementia

The increasing prevalence of dementia worldwide places a high demand on healthcare providers to perform a diagnostic work-up in relatively early stages of the disease, given that the pathologic process usually begins decades before symptoms are evident. Structural imaging is recommended to rule out other disorders and can only provide diagnosis in a late stage with limited specificity. Where PET imaging previously focused on the spatial pattern of hypometabolism, the past decade has seen the development of novel tracers to demonstrate characteristic protein abnormalities. Molecular imaging using PET/SPECT is able to show amyloid and tau deposition in Alzheimer disease and dopamine depletion in parkinsonian disorders starting decades before symptom onset. Novel tracers for neuroinflammation and synaptic density are being developed to further unravel the molecular pathologic characteristics of dementia disorders. In this article, the authors review the current status of established and emerging PET tracers in a diagnostic setting and also their value as prognostic markers in research studies and outcome measures for clinical trials in Alzheimer disease

ON COMPUTING UPPER LIMITS TO SOURCE INTENSITIES

A common problem in astrophysics is determining how bright a source could be and still not be detected. Despite the simplicity with which the problem can be stated, the solution involves complex statistical issues that require careful analysis. In contrast to the confidence bound, this concept has never been formally analyzed, leading to a great variety of often ad hoc solutions. Here we formulate and describe the problem in a self-consistent manner. Detection significance is usually defined by the acceptable proportion of false positives (the TypeI error), and we invoke the complementary concept of false negatives (the TypeII error), based on the statistical power of a test, to compute an upper limit to the detectable source intensity. To determine the minimum intensity that a source must have for it to be detected, we first define a detection threshold, and then compute the probabilities of detecting sources of various intensities at the given threshold. The intensity that corresponds to the specified TypeII error probability defines that minimum intensity, and is identified as the upper limit. Thus, an upper limit is a characteristic of the detection procedure rather than the strength of any particular source and should not be confused with confidence intervals or other estimates of source intensity. This is particularly important given the large number of catalogs that are being generated from increasingly sensitive surveys. We discuss the differences between these upper limits and confidence bounds. Both measures are useful quantities that should be reported in order to extract the most science from catalogs, though they answer different statistical questions: an upper bound describes an inference range on the source intensity, while an upper limit calibrates the detection process. We provide a recipe for computing upper limits that applies to all detection algorithms.Comment: 30 pages, 12 figures, accepted in Ap