New radio (MeerKAT and Parkes) and X-ray (XMM-Newton, Swift, Chandra, and NuSTAR) observations of PSR J1622-4950 indicate that the magnetar, in a quiescent state since at least early 2015, ...reactivated between 2017 March 19 and April 5. The radio flux density, while variable, is approximately 100× larger than during its dormant state. The X-ray flux one month after reactivation was at least 800× larger than during quiescence, and has been decaying exponentially on a 111 19 day timescale. This high-flux state, together with a radio-derived rotational ephemeris, enabled for the first time the detection of X-ray pulsations for this magnetar. At 5%, the 0.3-6 keV pulsed fraction is comparable to the smallest observed for magnetars. The overall pulsar geometry inferred from polarized radio emission appears to be broadly consistent with that determined 6-8 years earlier. However, rotating vector model fits suggest that we are now seeing radio emission from a different location in the magnetosphere than previously. This indicates a novel way in which radio emission from magnetars can differ from that of ordinary pulsars. The torque on the neutron star is varying rapidly and unsteadily, as is common for magnetars following outburst, having changed by a factor of 7 within six months of reactivation.
New radio (MeerKAT and Parkes) and X-ray (XMM-Newton, Swift, Chandra, and NuSTAR) observations of PSR J1622-4950 indicate that the magnetar, in a quiescent state since at least early 2015, ...reactivated between 2017 March 19 and April 5. The radio flux density, while variable, is approximately 100x larger than during its dormant state. The X-ray flux one month after reactivation was at least 800x larger than during quiescence, and has been decaying exponentially on a 111+/-19 day timescale. This high-flux state, together with a radio-derived rotational ephemeris, enabled for the first time the detection of X-ray pulsations for this magnetar. At 5%, the 0.3-6 keV pulsed fraction is comparable to the smallest observed for magnetars. The overall pulsar geometry inferred from polarized radio emission appears to be broadly consistent with that determined 6-8 years earlier. However, rotating vector model fits suggest that we are now seeing radio emission from a different location in the magnetosphere than previously. This indicates a novel way in which radio emission from magnetars can differ from that of ordinary pulsars. The torque on the neutron star is varying rapidly and unsteadily, as is common for magnetars following outburst, having changed by a factor of 7 within six months of reactivation.
In Swaziland, maize (
Zea mays L.) yield and production fluctuate from year to year mainly due to rainfall variability. Such fluctuations result in food insecurity, and therefore, forecasting of crop ...yields prior to harvest is required for early intervention in case of a deficit. The Normalised Difference Vegetation Index (NDVI) data derived from NOAA-Advanced Very Resolution Radiometer (AVHRR) has been used in several countries to forecast crop yields. The objective of the current study was to evaluate the potential usefulness of the NDVI in forecasting maize yield in Swaziland, and also to identify the best time for making a reliable forecast. Regression results showed that the NDVI can be used effectively to forecast maize yield in three of the four agro-ecological regions of the country. The models developed for each agro-ecological region accounted for 5, 61, 68 and 51% of maize yield variability in the Highveld, Middleveld, Lowveld and Lubombo Plateau, respectively. The best time for making an accurate forecast was found to be from the third dekad of January through to the third dekad of March depending on the agro-ecological region. Maize production forecasts using the developed models can be made at least 2 months before harvest, which would allow food security stakeholders enough time to secure maize imports in case of a deficit.
This paper models dairy farms in KwaZulu-Natal, South Africa, emphasising the complexities unique to this multi-product industry. Net and gross output approaches to measuring production are discussed ...and then tested using panel data from 37 dairy farms in KwaZulu-Natal from 1999 and 2007. Production functions for the three outputs: milk production, animals and farm-produced feed, are fitted as a simultaneous system to model the farms' production activities. This simultaneous model is complemented by a single equation reduced form that is fitted as a frontier, which allows estimation of the relative efficiencies of the individual farms. The results show that, with data this detailed, it is possible to refine the model until it fits very tightly. Indeed, in the gross output model that includes cows there is nothing left to call inefficiency and what was clearly a frontier becomes a mean response function.
Effects of hog slurry application to fertilized grassland on emissions of nitrous oxide (N2O) from feces and urine excreted by cattle grazing was determined. Feces from cattle grazing forage grass ...fertilized with two rates of plant available N from a hog slurry, (i) hog slurry as Split application in fall and spring, each 72kg N/ha (Split), and (ii) hog slurry each spring at 148kg N/ha (Single), and zero slurry (Control), were monitored in field experiments in 2004 and 2005. The slurry treatments resulted in total N of feces patches of 84 (Control), 86 (Split), and 106g N/m2 (Single). Three synthetic urine treatments of (i) 136g N/m2 (Low), (ii) 233g N/m2 (Medium), and (iii) 329g N/m2 (High) and no urine (Background) applied to simulate the range in levels possible for cattle grazing the grass fertilized with the slurry treatments were examined in 2005. Nitrous oxide emissions from feces of cattle grazing the Split and Single treatments were higher than Control. Cumulative N2O emissions from feces additions in the studies were 7, 31, and 91mg N/m2 for the Control, Single and Split treatments, respectively. Nitrous oxide emissions from feces increased with feces NO3− and soil NH4+ concentrations, and decreased with feces and soil moisture. Cumulative N2O emissions from urine treatments were much higher than from feces, being 165, 534 and 694mg/m2. Nitrous oxide emissions from urine increased with soil NO3−, NH4+ and NO2− concentrations and decreased with soil moisture. Nitrous oxide emissions estimated for excreta of grazing cattle were 27g/kg of direct soil emissions for grassland receiving no slurry (Control) and 104 and 73g/kg of direct emissions of the Split and Single slurry treatments. Findings indicate direct N2O emission estimates for hog cattle grazing production systems are enhanced more by hog slurry treatment than are emissions from excreta.
The simulation results presented in this paper provided nuanced policy options for redistribution in South Africa in the face of the looming expropriation of land without compensation. The simulation ...done through Computable General Equilibrium approach using the modified University of Pretoria General Equilibrium Model (UPGEM) which is solved using a GEMPACK solution software. The simulation revealed that there will be adjustment costs regardless of the option(s) chosen. The Inclusive Scenario came up as the most suitable policy option in terms of minimal adjustment costs and allowing the sector to continue to grow, albeit at a lower rate compared to the status quo.
The HIV/AIDS epidemic in Sub-Saharan Africa poses a massive diffusion and persuasion challenge for health professionals. Individuals working with adolescents to prevent the spread of HIV/AIDS must ...gain an understanding of adolescent's preference in obtaining information about HIV/AIDS and sexual behaviors. This study describes the primary and preferred sources of information regarding HIV/AIDS and sexual risk behavior in relation to several socio-demographic variables (
n=941) in Swaziland, Southern Africa. Although print/broadcast media was the primary source for HIV/AIDS and sexual risk behavior information for the students, most participants preferred information from the healthcare workers. This study suggests a greater role for healthcare providers in providing HIV/AIDS and sexual risk information.
The research conducted within the framework of this PhD thesis is devoted to the high-fidelity multi-physics (based on neutronics/thermal-hydraulics coupling) analysis of Pebble Bed Modular Reactor ...(PBMR), which is a High Temperature Reactor (HTR). The Next Generation Nuclear Plant (NGNP) will be a HTR design. The core design and safety analysis methods are considerably less developed and mature for HTR analysis than those currently used for Light Water Reactors (LWRs). Compared to LWRs, the HTR transient analysis is more demanding since it requires proper treatment of both slower and much longer transients (of time scale in hours and days) and fast and short transients (of time scale in minutes and seconds). There is limited operation and experimental data available for HTRs for validation of coupled multi-physics methodologies. This PhD work developed and verified reliable high fidelity coupled multi-physics models subsequently implemented in robust, efficient, and accurate computational tools to analyse the neutronics and thermal-hydraulic behaviour for design optimization and safety evaluation of PBMR concept The study provided a contribution to a greater accuracy of neutronics calculations by including the feedback from thermal hydraulics driven temperature calculation and various multi-physics effects that can influence it. Consideration of the feedback due to the influence of leakage was taken into account by development and implementation of improved buckling feedback models. Modifications were made in the calculation procedure to ensure that the xenon depletion models were accurate for proper interpolation from cross section tables. To achieve this, the NEM/THERMIX coupled code system was developed to create the system that is efficient and stable over the duration of transient calculations that last over several tens of hours. Another achievement of the PhD thesis was development and demonstration of full-physics, three-dimensional safety analysis methodology for the PBMR to provide reference solutions. Investigation of different aspects of the coupled methodology and development of efficient kinetics treatment for the PBMR were carried out, which accounts for all feedback phenomena in an efficient manner. The OECD/NEA PBMR-400 coupled code benchmark was used as a test matrix for the proposed investigations. The integrated thermal-hydraulics and neutronics (multi-physics) methods were extended to enable modeling of a wider range of transients pertinent to the PBMR. First, the effect of the spatial mapping schemes (spatial coupling) was studied and quantified for different types of transients, which resulted in implementation of improved mapping methodology based on user defined criteria. The second aspect that was studied and optimized is the temporal coupling and meshing schemes between the neutronics and thermal-hydraulics time step selection algorithms. The coupled code convergence was achieved supplemented by application of methods to accelerate it. Finally, the modeling of all feedback phenomena in PBMRs was investigated and a novel treatment of cross-section dependencies was introduced for improving the representation of cross-section variations. The added benefit was that in the process of studying and improving the coupled multi-physics methodology more insight was gained into the physics and dynamics of PBMR, which will help also to optimize the PBMR design and improve its safety. One unique contribution of the PhD research is the investigation of the importance of the correct representation of the three-dimensional (3-D) effects in the PBMR analysis. The performed studies demonstrated that explicit 3-D modeling of control rod movement is superior and removes the errors associated with the grey curtain (2-D homogenized) approximation.
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