A Bayesian Approach to Deriving Ages of Individual Field White Dwarfs

We apply a self-consistent and robust Bayesian statistical approach to determining the ages, distances, and ZAMS masses of 28 field DA white dwarfs with ages of approximately 4 to 8 Gyrs. Our technique requires only quality optical and near-IR photometry to derive ages with < 15% uncertainties, generally with little sensitivity to our choice of modern initial-final mass relation. We find that age, distance, and ZAMS mass are correlated in a manner that is too complex to be captured by traditional error propagation techniques. We further find that the posterior distributions of age are often asymmetric, indicating that the standard approach to deriving WD ages can yield misleading results.Comment: 9 pages, 10 figures, accepted for publication in Ap

Preprocessing Solar Images while Preserving their Latent Structure

Telescopes such as the Atmospheric Imaging Assembly aboard the Solar Dynamics Observatory, a NASA satellite, collect massive streams of high resolution images of the Sun through multiple wavelength filters. Reconstructing pixel-by-pixel thermal properties based on these images can be framed as an ill-posed inverse problem with Poisson noise, but this reconstruction is computationally expensive and there is disagreement among researchers about what regularization or prior assumptions are most appropriate. This article presents an image segmentation framework for preprocessing such images in order to reduce the data volume while preserving as much thermal information as possible for later downstream analyses. The resulting segmented images reflect thermal properties but do not depend on solving the ill-posed inverse problem. This allows users to avoid the Poisson inverse problem altogether or to tackle it on each of $\sim$10 segments rather than on each of $\sim$10$^7$ pixels, reducing computing time by a factor of $\sim$10$^6$. We employ a parametric class of dissimilarities that can be expressed as cosine dissimilarity functions or Hellinger distances between nonlinearly transformed vectors of multi-passband observations in each pixel. We develop a decision theoretic framework for choosing the dissimilarity that minimizes the expected loss that arises when estimating identifiable thermal properties based on segmented images rather than on a pixel-by-pixel basis. We also examine the efficacy of different dissimilarities for recovering clusters in the underlying thermal properties. The expected losses are computed under scientifically motivated prior distributions. Two simulation studies guide our choices of dissimilarity function. We illustrate our method by segmenting images of a coronal hole observed on 26 February 2015

Hutchinson's sign as a marker of ocular involvement in HIV-positive patients with herpes zoster ophthalmicus

The original publication is available at http://www.samj.org.zaBackground. A positive Hutchinson's sign indicates an increased risk of ocular involvement in herpes zoster ophthalmicus (HZO). We examined the sensitivity of Hutchinson's sign as an indicator of ocular involvement in a consecutive series of patients presenting with HZO. Methods. We conducted a descriptive observational prospective study of patients ≥18 years old presenting with HZO and consenting to pre- and post-test counselling and HIV and CD4 testing. A full ophthalmological examination focused on the extent of ocular involvement, and the presence of Hutchinson's sign was confirmed by two clinicians. Results. Thirty-three patients were enrolled; 29 were HIV positive, of whom 18 (62%) had not been diagnosed with HIV prior to enrolment. Of the 29 HIV-positive patients, 21 (72%) were Hutchinson's sign positive (HSP), all of whom had intra-ocular involvement (95% confidence interval 88 - 100%). Of the 8 HIV-positive, Hutchinson's sign-negative (HSN) patients, 4 did and 4 did not display intra-ocular involvement. Neither the mean CD4 count nor the average age in the HSP group differed significantly from the HSN group. Conclusion. We confirmed that a Hutchinson's sign- and HIVpositive patient with HZO has a very high positive predictive value for intra-ocular involvement. Neither age nor CD4 count had predictive value for ocular involvement. Young adults presenting with HZO should be suspected of having HIV, and HIV-positive patients with HZO but HSN may still have ocular involvement. All patients with HZO should be seen by an ophthalmologist.Publishers' versio

Identifying Cancer-Related Cognitive Impairment Using the FACT-Cog Perceived Cognitive Impairment.

Cancer-related cognitive impairment (CRCI) is a concerning problem for many cancer survivors. Evaluating patients for CRCI has been a challenge, in part because of a lack of standardized practices. Self-report instruments are often used to assess CRCI, but there are no validated cutpoints. We present the results of receiver operating characteristic curve analysis identifying cutpoints of the Functional Assessment of Cancer Therapy-Cognition perceived cognitive impairment (PCI) in female breast cancer survivors for identifying CRCI cases. We defined presence of CRCI based on elevated complaints on the Patient's Assessment of Own Functioning Inventory compared with healthy control scores. Our results indicate that scores less than 54 in PCI scores using 18 items and scores less than 60 in PCI scores using 20 items exhibited good ability to discriminate CRCI cases from noncases (area under the receiver operating characteristic curve was 0.84 [95% CI = 0.73 to 0.94]). These preliminary results represent an important contribution toward standardizing practices across CRCI studies

Ses van die een en ‘n halfdosyn van die ander?

Die sentrum vir Akademiese en Professionele Taalpraktyk en die universiteitsbestuur van die Noordwes- Universiteit se Potchefstroomkampus ontvang gereeld navrae van studente en ouers oor die verpligte module Akademiese Geletterdheid (AGLA121) wat deur sommige leerders en ouers as ʼn duplisering van matriek Huistaal beskou word. Daar word aangevoer dat dié kursus ʼn negatiewe impak het op leerders se reeds beperkte studietyd. Daarom word die versoek dikwels gerig dat leerders wat A’s of B’s vir Afrikaans of Engels Huistaal in matriek gekry het, van die verpligte Toets van Akademiese Geletterdheidsvlakke (TAG), of die Engelse ekwivalent daarvan: die Test of Academic Literacy Levels (TALL), en AGLA121 vrygestel behoort te word. Die doel van hierdie artikel is om te bepaal of bogenoemde persepsie op feite gebaseer is en of die Noordwes-Universiteit (NWU) se Akademiese Geletterdheidskursus inderdaad slegs ʼn taalkursus is wat oorvleuel met dit wat reeds op skool onderrig is. Die artikel is hoofsaaklik konseptueel van aard. ʼn Ontleding word gemaak van die Curriculum and Assessment Policy Statement (CAPS) Graad 10-12, die konstruk van TAG wat akademiese geletterdheidsvlakke toets en die AGLA121-kursusinhoud om te bepaal in welke mate die inhoude van die matriek Huistaalsillabus ooreenstem met die konstruk van TAG en die kursusinhoude van AGLA121. Uit die studie behoort dit duidelik te wees of daar grootskaalse oorvleueling tussen CAPS aan die een kant en TAG en die AGLA121-module aan die ander kant is en of ʼn module in Akademiese Geletterdheid noodsaaklik is vir alle leerders op eerstejaarsvlak, omdat dit fokus op aspekte wat nie deur die skoolsillabus gedek word nie.Sleutelwoorde: akademiese geletterdheid, taalonderrig, huistaal, konstruk, universiteitskurrikulum, skoolsillabus, CAP

A Tale of Two Impostors: SN2002kg and SN1954J in NGC 2403

We describe new results on two supernova impostors in NGC 2403, SN 1954J(V12) and SN 2002kg(V37). For the famous object SN 1954J we combine four critical observations: its current SED, its Halpha emission line profile, the Ca II triplet in absorption in its red spectrum, and the brightness compared to its pre-event state. Together these strongly suggest that the survivor is now a hot supergiant with T ~ 20000 K, a dense wind, substantial circumstellar extinction, and a G-type supergiant companion. The hot star progenitor of V12's giant eruption was likely in the post-red supergiant stage and had already shed a lot of mass. V37 is a classical LBV/S Dor variable. Our photometry and spectra observed during and after its eruption show that its outburst was an apparent transit on the HR Diagram due to enhanced mass loss and the formation of a cooler, dense wind. V37 is an evolved hot supergiant at ~10^6 Lsun with a probable initial mass of 60 -80 Msun.Comment: To appear in the Astrophysical Journa

Detecting Unspecified Structure in Low-Count Images

Unexpected structure in images of astronomical sources often presents itself upon visual inspection of the image, but such apparent structure may either correspond to true features in the source or be due to noise in the data. This paper presents a method for testing whether inferred structure in an image with Poisson noise represents a significant departure from a baseline (null) model of the image. To infer image structure, we conduct a Bayesian analysis of a full model that uses a multiscale component to allow flexible departures from the posited null model. As a test statistic, we use a tail probability of the posterior distribution under the full model. This choice of test statistic allows us to estimate a computationally efficient upper bound on a p-value that enables us to draw strong conclusions even when there are limited computational resources that can be devoted to simulations under the null model. We demonstrate the statistical performance of our method on simulated images. Applying our method to an X-ray image of the quasar 0730+257, we find significant evidence against the null model of a single point source and uniform background, lending support to the claim of an X-ray jet

Towards informed decision making: the importance of baseline academic literacy assessment in promoting responsible university access and support

Low levels of academic literacy in the language(s) of teaching and learning are regarded as one of the main reasons for a lack of academic success amongst undergraduate students. Indeed, at Unisa, current concerns about the predictive validity of the National Senior Certificate has motivated a need for a reliable and valid instrument, used under standardised conditions, to measure the academic literacy levels of first year students. The aims of this project were to gather diagnostic data and empirical evidence about the current levels of academic literacy of prospective students of Unisa, and to identify specific reasons for their poor performance during the NQF5 in-service training. A quantitative research approach in the form of an interrupted time-series design was followed. A simple random sample of students, who underwent in-service training in 2009, was drawn, and the Test of Academic Literacy Levels (TALL) was employed as measuring instrument. T-tests were performed on the data to compare the actual differences between the pre- and post-test scores and regression analyses were used to determine the correlation between the two tests. The article concludes with recommendations on how language tests, like TALL, can assist higher education to make more informed, and thus responsible, decisions about issues of access.Lae vlakke van akademiese geletterdheid in die onderrig- en leertaal, of -tale, word beskou as een van die hoofredes vir gebrek aan akademiese sukses by voorgraadse studente. By Unisa het die heersende kommer oor die voorspellingsgeldigheid van die Nasionale Senior Sertifikaat inderdaad gelei tot &rsquo;n behoefte aan &rsquo;n betroubare en geldige instrument wat in vasgestelde omstandighede gebruik kan word om akademiese geletterdheidsvlakke onder eerstejaarstudente te meet. Die oogmerke met hierdie projek was om diagnostiese data en empiriese getuienis oor die bestaande akademiese geletterdheidsvlakke onder voornemende studente aan Unisa te versamel, en om spesifieke redes vir hulle swak prestasie tydens NKR 5-indiensopleiding uit te wys. &rsquo;n Kwantitatiewe navorsingsbenadering in die vorm van &rsquo;n onderbroketydreeks-ontwerp is gebruik. &rsquo;n Eenvoudige ewekansige steekproef is geneem van studente wat in 2009 indiensopleiding ondergaan het, en die Toets van Akademiese Geletterdheidsvlakke (TAG) is as meetinstrument gebruik. T-toetse is op die data uitgevoer om die werklike verskille tussen die voortoets- en natoetstellings te vergelyk, terwyl regressieontledings uitgevoer is om die korrelasie tussen die twee toetse te bepaal. Die artikel sluit af met aanbevelings oor hoe taaltoetse soos TAG ho&euml;r onderwys van hulp kan wees om meer ingeligte &ndash; en gevolglik meer verantwoordelike &ndash; besluite oor toelatingskwessies te neem.Keywords: academic readiness, academic literacy, first-year, Test of Academic Literacy Levels (TALL), throughput rates assessment, under-preparedness, university accessThe article is in English

Satisfaction with retention factors as predictors of the job embeddedness of medical and information technology services staff

The objective of the study was to determine whether employees’ satisfaction with retention factors (measured by the Retention Factors Scale) significantly predicted their job embeddedness (measured by the Job Embeddedness Scale). A quantitative survey was conducted on a purposive sample (n=206) of early career medical and information technology services staff, identified as scarce skills in a South African client services company. Retention factors such as training and development, career opportunities, supervisor support and the characteristics of the job (skills variety, challenge and autonomy) were shown to significantly predict the participants’ sense of job embeddedness. Satisfaction with training and development opportunities was the best predictor of organisational fit, while satisfaction with career opportunities was the best predictor of organisational sacrifice. The findings add valuable new knowledge that may be used to inform retention strategies for professional staff with scarce skills in the medical and information technology services sector.Key words: retention factors, perceived job embeddedness, training and development, career opportunities, job characteristics, supervisor suppor