Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign

Abstract: In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 109 M ⊙. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87’s spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded

Predictive modelling of Namibian fairy circles and their co-occurrence with Euphorbia species using Geographical Information Systems (GIS)

Fairy circles are an example of patterned vegetation and have only been documented to occur along the coastline of southern Africa, although a very similar vegetation pattern has recently been documented in north Western Australia. After several decades of investigation, the cause of fairy circles is still open to debate. The current Namibian-based project studied the “Euphorbia spp. allelopathy” theory which states that fairy circles are the product of a localized allelopathic affect in the soil caused by the previous presence and subsequent death of E. damarana and E. gummifera. In the first part of this study, a GIS-based site suitability analysis for the occurrence of fairy circles was done using rainfall, altitude and land cover as site selection criteria. Thereafter 100 random sample points, each within a 10 km radius, were generated within the predicted site and investigated using Google Earth. It was found that 65 of the 100 locations contained fairy circles including a large distribution of fairy circles located in the south east of Namibia and also in the Kalahari Desert, that had not previously been documented. It was observed from the satellite images that several of the random sites did not have grass cover, and therefore would not have ‘shown’ fairy circles if they were present. From the site suitability analysis several additional sites where fairy circles co-occur with Euphorbia spp. were documented. The second part of the study focused on the landscape scale characteristics of fairy circles, E. damarana and E. gummifera. Aerial and satellite imagery were used to make observations of Euphorbia plants over time, while a number of analytical techniques were used to compare the size and spatial patterning of fairy circles to Euphorbia plants. In terms of results, first, the aerial image comparison showed that E. gummifera is eventually replaced by fairy circles. Second, using a T-test it was found that there is no statistical difference in size between fairy circles and E. damarana. Third, the spatial patterning of fairy circles was examined and compared to the distribution of E. gummifera and E. damarana using a range of geospatial point pattern techniques. Sites where fairy circles co-occur with either E. damarana or E. gummifera were included in the point pattern analysis as mixed sites. The analysis using point pattern analysis showed that fairy circles have the most uniform distribution, compared to the Euphorbia and mixed plots. Interestingly, the regularity of the pattern associated with the mixed plots are in-between that of fairy circles and the Euphorbia plots. E. damarana have also been shown to have a regular spatial pattern, while the regularity of the pattern associated E. gummifera only slightly departs from complete spatial randomness.Dissertation (MSc)--University of Pretoria, 2019.Geography, Geoinformatics and MeteorologyMScUnrestricte

Dr. John Philip's observations regarding the Hottentots of South Africa

Treatise (M.A.) -- University of Stellenbosch, 1939.Full text to be digitised and attached to bibliographic record

Hypothalamic-pituitary-adrenal-axis dysregulation and double product increases potentiate ischemic heart disease risk in a Black male cohort: The SABPA study

Emotional distress has been associated with a poorer prognosis in myocardial infarction patients. Elevated adrenocorticotrophic hormone (ACTH), lower cortisol, dehydroepiandrosterone sulfate (DHEAS) and cortisol:DHEAS, as measures of emotional distress, might correlate with silent myocardial ischemia (SMI) and workload. Thus, we assessed the relationship between emotional distress, SMI and double product (systolic blood pressure (SBP) × heart rate). Cross-sectional South African biethnic single-set cohorts (N=378), aged 44.7±9.52 years, were investigated. Depressive symptoms (Patient Health Questionnaire-9), anthropometric, fasting blood, 24-h double product and 24-h 2-lead electrocardiogram (ST-segment depression) values were obtained. Blacks, mostly men, had increased depressive symptoms, hyperglycemia, SMI, double product, SBP hypertension and ACTH but lower cortisol, DHEAS and cortisol:DHEAS than their White counterparts. Black men had the highest combined SBP hypertension and below-median cortisol prevalence, 38%, compared with 5.9-13.8% in the other groups. Their SMI was associated with ACTH and cortisol:DHEAS (adj. R 0.29; β 0.27-0.31 (0.12-0.64); P≤ 1/20.05), double product (adj. R 0.29; β 0.38 (0.18-0.57); P=0.050) and SBP hypertension (area under the curve: 0.68 (95% CI: 0.56, 0.80); P=0.042; sensitivity/specificity 49/85%). Double product was positively associated with central obesity in all sex groups and with cortisol in the Black men (P\u3c0.05). A dysregulated hypothalamic-pituitary-adrenal-axis (HPAA) showed signs of a hyporesponsive adrenal cortex, suggesting chronic emotional stress in the Black male cohort. In this cohort, HPAA dysregulation and compensatory increases in double product occur as a potential defense mechanism to alleviate perfusion deficits, thereby potentiating ischemic heart disease risk. 2

The allelopathic, adhesive, hydrophobic and toxic latex of Euphorbia species is the cause of fairy circles investigated at several locations in Namibia

Abstract Background In this multidisciplinary study we present soil chemical, phytochemical and GIS spatial patterning evidence that fairy circles studied in three separate locations of Namibia may be caused by Euphorbia species. Results We show that matrix sand coated with E. damarana latex resulted in faster water-infiltration rates. GC-MS analyses revealed that soil from fairy circles and from under decomposing E. damarana plants are very similar in phytochemistry. E. damarana and E. gummifera extracts have a detrimental effect on bacteria isolated from the rhizosphere of Stipagrostis uniplumis and inhibit grass seed germination. Several compounds previously identified with antimicrobial and phytotoxic activity were also identified in E. gummifera. GIS analyses showed that perimeter sizes and spatial characteristics (Voronoi tessellations, distance to nearest neighbour ratio, pair correlation function and L-function) of fairy circles are similar to those of fairy circles co-occurring with E. damarana (northern Namibia), and with E. gummifera (southern Namibia). Historical aerial imagery showed that in a population of 406 E. gummifera plants, 134 were replaced by fairy circles over a 50-year period. And finally, by integrating rainfall, altitude and landcover in a GIS-based site suitability model, we predict where fairy circles should occur. The model largely agreed with the distribution of three Euphorbia species and resulted in the discovery of new locations of fairy circles, in the far southeast of Namibia and part of the Kalahari Desert of South Africa. Conclusions It is proposed that the allelopathic, adhesive, hydrophobic and toxic latex of E. damarana, E. gummifera, and possibly other species like E. gregaria, is the cause of the fairy circles of Namibia in the areas investigated and possibly in all other areas as well

Childhood trauma is associated with reduced frontal gray matter volume: A large transdiagnostic structural MRI study

Background Childhood trauma increases risk for psychopathology and cognitive impairment. Prior research mainly focused on the hippocampus and amygdala in single diagnostic categories. However, other brain regions may be impacted by trauma as well, and effects may be independent of diagnosis. This cross-sectional study investigated cortical and subcortical gray matter volume in relation to childhood trauma severity. Methods We included 554 participants: 250 bipolar-I patients, 84 schizophrenia-spectrum patients and 220 healthy individuals without a psychiatric history. Participants filled in the Childhood Trauma Questionnaire. Anatomical T1 MRI scans were acquired at 3T, regional brain morphology was assessed using Freesurfer. Results In the total sample, trauma-related gray matter reductions were found in the frontal lobe (β = -0.049, p = 0.008; q = 0.048), this effect was driven by the right medial orbitofrontal, paracentral, superior frontal regions and the left precentral region. No trauma-related volume reductions were observed in any other (sub)cortical lobes nor the hippocampus or amygdala, trauma-by-group (i.e. both patient groups and healthy subjects) interaction effects were absent. A categorical approach confirmed a pattern of more pronounced frontal gray matter reductions in individuals reporting multiple forms of trauma and across quartiles of cumulative trauma scores. Similar dose-response patterns were revealed within the bipolar and healthy subgroups, but did not reach significance in schizophrenia-spectrum patients. Conclusions Findings show that childhood trauma is linked to frontal gray matter reductions, independent of psychiatric morbidity. Our results indicate that childhood trauma importantly contributes to the neurobiological changes commonly observed across psychiatric disorders. Frontal volume alterations may underpin affective and cognitive disturbances observed in trauma-exposed individuals