Calibration artefacts in radio interferometry. I. Ghost sources in WSRT data

This work investigates a particular class of artefacts, or ghost sources, in radio interferometric images. Earlier observations with (and simulations of) the Westerbork Synthesis Radio Telescope (WSRT) suggested that these were due to calibration with incomplete sky models. A theoretical framework is derived that validates this suggestion, and provides predictions of ghost formation in a two-source scenario. The predictions are found to accurately match the result of simulations, and qualitatively reproduce the ghosts previously seen in observational data. The theory also provides explanations for many previously puzzling features of these artefacts (regular geometry, PSF-like sidelobes, seeming independence on model flux), and shows that the observed phenomenon of flux suppression affecting unmodelled sources is due to the same mechanism. We demonstrate that this ghost formation mechanism is a fundamental feature of calibration, and exhibits a particularly strong and localized signature due to array redundancy. To some extent this mechanism will affect all observations (including those with non-redundant arrays), though in most cases the ghosts remain hidden below the noise or masked by other instrumental artefacts. The implications of such errors on future deep observations are discussed.Comment: 19 pages, 15 figures, submitted to MNRA

Comparative growth and static allometry in the genus Chlorocebus

Characterizing variation in growth across populations is critical to understanding multiple aspects of development in primates, including within-taxon developmental plasticity and the evolution of life history patterns. Growth in wild primates has often been reported and directly compared across larger taxonomic groups and within social groups, but comparisons are rarely investigated across widely dispersed populations of a single taxon. With the Vervet Phenome-Genome Project and the International Vervet Research Consortium, we trapped 936 vervet monkeys of all ages representing three populations (Kenyan pygerythrus, South African pygerythrus, and sabaeus from St. Kitts & Nevis). We gathered 10 different body measurements from each including mass, body breadth and length, segmental limb lengths, and chest circumference. To gain a better understanding of how ontogenetic patterns vary in these populations, we calculated bivariate allometry coefficients, derived using PCA on log-transformed and z-standardized trait values, and compared them to isometric vector coefficients. Within all population samples, around weaning age most traits showed a negative allometric relationship to body length. As each population ages, however, distinct patterns emerge, showing population differences in onset and intensity of growth among traits. In concordance with other analyses on growth in these populations, our results suggest that there exist relative differences in patterns of growth between Chlorocebus populations, further suggesting selection for unique developmental pathways in each

The static allometry of sexual and non-sexual traits in vervet monkeys

Sexual traits vary tremendously in static allometry. This variation may be explained in part by body size-related differences in the strength of selection. We tested this hypothesis in two populations of vervet monkeys, using estimates of the level of condition dependence for different morphological traits as a proxy for body size-related variation in the strength of selection. In support of the hypothesis, we found that the steepness of allometric slopes increased with the level of condition dependence. One trait of particular interest, the penis, had shallow allometric slopes and low levels of condition dependence, in agreement with one of the most consistent patterns yet detected in the study of allometry, namely that of genitalia exhibiting shallow allometries.This research was supported by NIH grant R01RR0163009

The use of confocal microscopy in quantifying changes in membrane potential

Monitoring the plasma membrane potential and its changes can be a time consuming and challenging task especially when conventional electrophysiological techniques are used. The use of potentiometricfluorophores, namely tetramethylrhodamine methylester (TMRM), and digital imaging devices (laser scanning confocal microscopy) provides reliable and time efficient method. Two scorpion pore-forming peptides, namely PP and OP1, were used as a tool to induce depolarization of the plasma membrane potential of neuroblastoma cell line and cardiac myocytes. Alternative methods for the neuroblastoma cells and cardiac myocytes were used. Depolarization of the neuroblastoma cells was calibrated with 140 mM KCl solution with 1 ìM valinomycin, after which intensity readers were substituted in the Nernst equation for quantification. Calibration of the alternative method used of the cardiac myocytes’ plasma membrane potential changes was calibrated with the use of 5, 20, 40, and 80 mM KCl solutions with 1 ìM valinomycin. A calibration curve was then constructed from which plasma membrane potential could be calculate

Prescribed minimum benefits – quagmire or foundation for social health reform?

No Abstract South African Medical Journal Vol. 97 (6) 2007: pp. 446-45

Identifying sequence variation in cation channel sperm associated genes in Cape mountain zebra (Equus zebra zebra)

The Cape mountain zebra (Equus zebra zebra) has recovered from near extinction over more than eight decades. While their numbers have increased, populations remain isolated with low genetic diversity. With more than 75 new populations being founded and more than 4800 extant animals, conservation management strategies are being implemented to mitigate risk of losses in genetic diversity and reproductive fitness. One objective is to identify reproductive characteristics that may improve population growth. Cation channel sperm (CatSper) genes play an important role in hyperactivation of sperm during fertilization. Mutations in these genes lead to reduced fertility and even infertility. Ten male zebras were sampled from a group that were translocated in 2016 in order to found a new population. Single nucleotide polymorphisms (SNPs) were identified in three of the CatSper genes (1 - 3). Lack of variation was observed in all exons, with only four SNPs being identified in the intronic regions in close proximity to exons 1, 2, 7, 8, and 9 of CatSper 1. These results may contribute to the pre-identification of males for new founder populations to ensure population growth and viability, and may be a useful tool for selection against low-producing individuals

Redundant interferometric calibration as a complex optimization problem

Observations of the redshifted 21-cm line from the epoch of reionization have recently motivated the construction of low frequency radio arrays with highly redundant configurations. These configurations provide an alternative calibration strategy - "redundant calibration" - and boosts sensitivity on specific spatial scales. In this paper, we formulate calibration of redundant interferometric arrays as a complex optimization problem. We solve this optimization problem via the Levenberg-Marquardt algorithm. This calibration approach is more robust to initial conditions than current algorithms and, by leveraging an approximate matrix inversion, allows for further optimization and an efficient implementation ("redundant StEfCal"). We also investigated using the preconditioned conjugate gradient method as an alternative to the approximate matrix inverse, but found that its computational performance is not competitive with respect to "redundant StEfCal". The efficient implementation of this new algorithm is made publicly available.Comment: 11 pages, 7 figures, MNRAS accepte

Content validation of Mental Health Literacy Scale (MHLS) for primary health care workers in South Africa and Zambia a heterogeneous expert panel method

Background: The lack of public knowledge and the burden caused by mental-health issues' effect on developing and implementing adequate mental-health care for young and adolescent in low- and middle-income countries (LMIC). Primary health care could be the key in facing the challenge, but it suffers from insufficient resources and poor mental health literacy. This study's aim was to adapt the content validity of the Mental Health Literacy Scale (MHLS) developed by O'Connor & Casey (2015) with researchers and primary health-care workers in low- and middle-income contexts in South Africa (SA) and in Zambia. Objectives: The study population comprised two expert panels (N = 21); Clinical Experts (CE) (n = 10) from Lusaka, Zambia and Professional Research Experts (PE) (n = 11) from the MEGA project management team were recruited to the study. Methods: MHLS was validated in a South African and a Zambian context using a heterogeneous expert-panel method. Participants were asked to rate the 35 MHLS items on a 4-point scale with 1 as not relevant and 4 as very relevant After the rating, all 35 MHLS items were carefully discussed by the expert panel and evaluated according their relevance. The data were analyzed using an item-level content validity index (I-CVI) and narrative and thematic analyses. Results: All 35 items ranked by the PREs met the cutoff criteria (>= 0.8), and ten (n = 10) items were seen as relevant by CE when calculating I-CVIs. Based on the results of ratings and discussion, a group of sixteen (n = 16) of all items (n = 35) were retained as original without reviewing. A total of nineteen (n = 19) items were reviewed. Conclusion: This study found the MHLS to have sufficient validity in LMICs' context but also recognized a gap between professional researchers' and clinical workers' knowledge and attitudes related to mental health.</div

A Clinical Study of the Effectiveness of Two Different 10% Carbamide Peroxide Bleaching Products: A 6-Month Followup

The purpose of this study was to evaluate the efficacy of two different 10% carbamide peroxide bleaching products just after treatment and after a 6-month follow-up period. Methods. Two 10% carbamide peroxide products (Opalescence PF and Nite White ACP) were applied nightly for 14 days, according to the manufacturers' instructions. The color of teeth 11 and 21 of thirty-four subjects having A2 or darker teeth were measured with a spectrophotometer (L∗; a∗; b∗) before treatment, just after treatment (14 days) and after 6 months. Results and Conclusions. Both products produced significant whitening of teeth with total color change (ΔEab∗) of approximately 5.20 units. There was a significant improvement in all 3 color coordinates (L*, a*, and b∗) for up to 6 months postbleaching (P < .05). Nite White showed a higher degree of relapse (27%) than Opalescence (18%) over the 6-month period. It is suggested that rebleaching after 6 months is not necessary