Validation of University of New Brunswick Ionospheric Modeling Technique with ionosonde TEC estimation over South Africa

For more than a decade, ionospheric research over South Africa has been carried out using data from ionosondes geographically located at Madimbo (28.38°S, 30.88°E), Grahamstown (33.32°S, 26.50°E), and Louisvale (28.51°S, 21.24°E). The objective has been modelling the bottomside ionospheric characteristics using neural networks. The use of Global Navigation Satellite System (GNSS) data is described as a new technique to monitor the dynamics and variations of the ionosphere over South Africa, with possible future application in high frequency radio communication. For this task, the University of New Brunswick Ionospheric Modelling Technique (UNB-IMT) was applied to compute midday (10:00 UT) GNSS-derived total electron content (GTEC). GTEC values were computed using GNSS data for stations located near ionosondes for the years 2002 and 2005 near solar maximum and minimum, respectively. The GTEC was compared with the midday ionosonde-derived TEC (ITEC) measurements to validate the UNB-IMT results. It was found that the variation trends of GTEC and ITEC over all stations are in good agreement and show a pronounced seasonal variation for the period near solar maximum, with maximum values ( 80 TECU) around autumn and spring equinoxes, and minimum values ( 22 TECU) around winter and summer. Furthermore, the residual ΔTEC = GTEC − ITEC was computed. It was evident that ΔTEC, which is believed to correspond to plasmaspheric electron content, showed a pronounced seasonal variation with maximum values ( 20 TECU) around equinoxes and minimum ( 5 TECU) around winter near solar maximum. The equivalent ionospheric and total slab thicknesses were also computed and comprehensively discussed. The results verified the use of UNB-IMT as one of the tools for future ionospheric TEC research over South Africa

Mapping GPS-derived ionospheric Total Electron Content over Southern Africa during different epochs of solar cycle 23

The Southern African Development Community and the International Global Navigation Satellite Systems Service (GNSS) network of dual frequency Global Positioning System (GPS) receivers provide an opportunity to determine Total Electron Content (TEC) over Southern Africa by taking advantage of the dispersive nature of the ionospheric medium. For this task, the University of New Brunswick (UNB) ionospheric modelling technique which applies a spatial linear approximation of the vertical TEC above each station using stochastic parameters in Kalman filter estimation, primed with data from the Southern Africa GPS network, was used for mapping TEC at South African locations during selected days and hours of different epochs of solar cycle 23. Significant enhancements in the TEC value and features, which could be associated with frequent solar events, are evident around a day of extreme solar maximum. These observations are discussed and further investigated by analyzing the GOES 8 and 10 satellites X-ray flux (0.1–0.8 nm) and SOHO Solar EUV Monitor (26.0–34.0 nm) higher resolution data. Comparison of these physical quantities reveals that for each X-ray flare observed, there is an associated EUV flare event. The latter phenomenon causes photoionisation in the daytime ionosphere which results in significant TEC enhancement. The daytime UNB TEC compared with the International Reference Ionosphere (IRI) 2001 predicted TEC found both models to show a good agreement

Hexahydroquinolines are antimalarial candidates with potent blood-stage and transmission-blocking activity

Hexahydroquinolines are antimalarial candidates with potent blood-stage and transmission-blocking activityAntimalarial compounds with dual therapeutic and transmission-blocking activity are desired as high-value partners for combination therapies. Here, we report the identification and characterization of hexahydroquinolines (HHQs) that show low nanomolar potency against both pathogenic and transmissible intra-erythrocytic forms of the malaria parasite Plasmodium falciparum. This activity translates into potent transmission-blocking potential, as shown by in vitro male gamete formation assays and reduced oocyst infection and prevalence in Anopheles mosquitoes. In vivo studies illustrated the ability of lead HHQs to suppress Plasmodium berghei blood-stage parasite proliferation. Resistance selection studies, confirmed by CRISPR-Cas9-based gene editing, identified the digestive vacuole membrane-spanning transporter PfMDR1 (P. falciparum multidrug resistance gene-1) as a determinant of parasite resistance to HHQs. Haemoglobin and haem fractionation assays suggest a mode of action that results in reduced haemozoin levels and might involve inhibition of host haemoglobin uptake into intra-erythrocytic parasites. Furthermore, parasites resistant to HHQs displayed increased susceptibility to several first-line antimalarial drugs, including lumefantrine, confirming that HHQs have a different mode of action to other antimalarials drugs for which PfMDR1 is known to confer resistance. This work evokes therapeutic strategies that combine opposing selective pressures on this parasite transporter as an approach to countering the emergence and transmission of multidrug-resistant P. falciparum malaria.The authors thank T.T. Diagana (Novartis Institute for Tropical Diseases, Singapore) for provision of the compounds, the Red Cross (Australia and the USA) for the provision of human blood for cell cultures, and G. Stevenson for assistance with the triaging of compounds following screening. The authors acknowledge the Bill and Melinda Gates Foundation (grant OPP1040399 to D.A.F. and V.M.A. and grant OPP1054480 to E.A.W. and D.A.F.), the National Institutes of Health (grant R01 AI103058 to E.A.W. and D.A.F., grant R01 AI50234 to D.A.F, and R01 AI110329 to T.J.E.), the Australian Research Council (LP120200557 to V.M.A.) and the Medicines for Malaria Venture for their continued support. P.E.F. and M.I.V. are supported by the Northern Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (FEDER).info:eu-repo/semantics/publishedVersio

SITE CHARACTERISATION: ASTRONOMICAL SEEING FROM A TURBULENCE-RESOLVING MODEL

A Lunar Laser Ranging (LLR) system is to form part of geodetic instrumentation to be located at a new fundamental space geodetic observatory for South Africa. For optimal efficiency, LLR requires optical resolution or so-called astronomical seeing conditions of ~1 arc-second in order to deliver usable ranging data. Site characterisation should include a description of astronomical seeing for various locations on-site and overall atmospheric conditions. Atmospheric turbulence degrades astronomical seeing. In-situ methods of determining astronomical seeing are difficult, time-consuming and costly. We propose the use of a turbulence-resolving model to determine and predict astronomical seeing at a site. Large Eddy Simulation NERSC (Nansen Environmental and Remote Sensing Centre) Improved Code (LESNIC) is a turbulence-resolving simulation code which models atmospheric turbulence. It has been used to compile a database of turbulence-resolving simulations, referred to as DATABASE64. This database consists of a collection of LESNIC runs for a stably stratified planetary boundary layer (SBL) over a homogeneous aerodynamically rough surface. Results from DATABASE64 for the nocturnal boundary layer are employed to render profiles of the vertical distribution of optical turbulence (CN 2 profiles). Seeing parameter values are also obtained by making use of DATABASE64 results. The CN 2 profiles and seeing parameter values obtained from DATABASE64 results are compared with general observational results that have been published in the literature. The values obtained are consistent with results from field campaigns as reported. Turbulence-resolving models, such as LESNIC, show potential for delivering and predicting profiles and parameters to characterise astronomical seeing, which are essential prerequisites for establishing an LLR system at the most suitable site and most suitable on-site location. A two-pronged approach is envisaged – in addition to modelling, quantitative seeing measurements obtained with an on-site seeing monitor will be used to verify and calibrate results produced by the LESNIC model.http://www.gssa.org.za/index.php?module=htmlpages&func=display&pid=5nf201

A new geodetic research data management system at the Hartebeesthoek Radio Astronomy Observatory

<p>The Hartebeesthoek Radio Astronomy Observatory (HartRAO) hosts two research programmes: radio astronomy and space geodesy. The Space Geodesy programme has four main co-located space geodetic techniques, making HartRAO a true fiducial site. These techniques are Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), geodetic Very Long Baseline Interferometry (VLBI) and Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS). Only GNSS data are stored on-site in a publicly accessible repository. The <em>HartRAO</em> <em>Space Geodesy Programme</em> is expanding its geodetic techniques with Lunar Laser Ranging (LLR) as well as a network of seismometers, accelerometers, tidal gauges and gravimeters. These instruments will be installed across the southern African region and will generate large volumes of data that will be streamed to and stored at HartRAO.</p> <p>Our objective is to implement a complete <em>Geodetic Research Data Management System (GRDMS)</em> to handle all HartRAO’s geodetic data on-site in terms of archiving, indexing, processing and extraction. These datasets and subsequent data products will be accessible to both the scientific community and general public through an intuitive and easy to use web-based frontend. As the first step in this process, we are currently working on establishing a new data centre. This opens up the possibility for the librarian to provide data services and support by working together with researchers and information technology staff.</p> <p>We discuss the rationale, role players and top-level system design of this GRDMS, as well as the current status and planned products thereof.</p

High average power Q-switched 1314 nm two-crystal Nd:YLF laser

A 1314 nm two-crystal Nd:YLF laser was designed and operated in both CW and actively Q-switched modes. Maximum CW output of 26.5W resulted from 125 W of combined incident pump power. Active Q-switching was obtained by inserting a Brewster-cut Acousto Optic Modulator. This setup delivered an average power of 18.6 W with a maximum of 5.6 mJ energy per pulse with a pulse duration of 36 ns at a pulse repetition frequency of 500 Hz.Inkaba yeAfrica (as managed by AEON-NMMU)https://www.osapublishing.org/ol/home.cfmhb201