289 research outputs found
Opkomst en ondergang van de apartheid in Zuid-Afrika
No full textBeyers Naudé-lezing uitgesproken door Casper Labuschagne emeritus hoogleraar Oude Testament aan de Rijksuniversiteit Groningen op 3 november 2011 Bij gelegenheid van de 90-jarige jubileumviering van het Christelijk Gymnasium Leeuwarden en het vijfde lustrum als Christelijk Gymnasium Beyers Naud
Opkomst en ondergang van de apartheid in Zuid-Afrika
No full textBeyers Naudé-lezing uitgesproken door Casper Labuschagne emeritus hoogleraar Oude Testament aan de Rijksuniversiteit Groningen op 3 november 2011 Bij gelegenheid van de 90-jarige jubileumviering van het Christelijk Gymnasium Leeuwarden en het vijfde lustrum als Christelijk Gymnasium Beyers Naud
Classifying aerosol type using in situ surface spectral aerosol optical properties
No full textKnowledge of aerosol size and composition is important for determining radiative forcing effects of aerosols, identifying aerosol sources and improving aerosol satellite retrieval algorithms. The ability to extrapolate aerosol size and composition, or type, from intensive aerosol optical properties can help expand the current knowledge of spatiotemporal variability in aerosol type globally, particularly where chemical composition measurements do not exist concurrently with optical property measurements. This study uses medians of the scattering Ångström exponent (SAE), absorption Ångström exponent (AAE) and single scattering albedo (SSA) from 24 stations within the NOAA/ESRL Federated Aerosol Monitoring Network to infer aerosol type using previously published aerosol classification schemes.
Three methods are implemented to obtain a best estimate of dominant aerosol type at each station using aerosol optical properties. The first method plots station medians into an AAE vs. SAE plot space, so that a unique combination of intensive properties corresponds with an aerosol type. The second typing method expands on the first by introducing a multivariate cluster analysis, which aims to group stations with similar optical characteristics and thus similar dominant aerosol type. The third and final classification method pairs 3-day backward air mass trajectories with median aerosol optical properties to explore the relationship between trajectory origin (proxy for likely aerosol type) and aerosol intensive parameters, while allowing for multiple dominant aerosol types at each station.
The three aerosol classification methods have some common, and thus robust, results. In general, estimating dominant aerosol type using optical properties is best suited for site locations with a stable and homogenous aerosol population, particularly continental polluted (carbonaceous aerosol), marine polluted (carbonaceous aerosol mixed with sea salt) and continental dust/biomass sites (dust and carbonaceous aerosol); however, current classification schemes perform poorly when predicting dominant aerosol type at remote marine and Arctic sites and at stations with more complex locations and topography where variable aerosol populations are not well represented by median optical properties. Although the aerosol classification methods presented here provide new ways to reduce ambiguity in typing schemes, there is more work needed to find aerosol typing methods that are useful for a larger range of geographic locations and aerosol population
Rehabilitation for Cas Labuschagne : good enough, timely enough?
No full textDATA BESKIKBAARHEIDSVERKLARING : Datadeling is nie van toepassing nie, aangesien geen nuwe
data in die studie geskep of ontleed is nie.This research is part of the project, ‘Contextualized Reformed Theology in South Africa’, directed by Dr Andre Ungerer of the Reformed Theological College, Faculty of Theology, University of Pretoria.Special Collection: Wim Dreyer Dedication, sub-edited by Jaco Beyers (University of Pretoria, South Africa).During the General
Church Assembly of 2010, the Netherdutch Reformed Church of Africa (NRCA) confessed her
previous justification of apartheid as wrongdoing. It led to serious dissatisfaction in the more
conservative part of the Church, eventually ending in the painful church schism of 2011.
Afterwards, the leadership had to handle several related issues. And then, out of the blue, an
outstanding matter arose from the past’s nebulae – unfinished business between the Church
and prof. Cas Labuschagne. He was a dissident with prof. Albert Geyser who acted against
the church’s justification of apartheid during the sixties. After a fierce struggle and much
desperation, he left South Africa for the Netherlands in 1967. Almost 40 years later, in 2008,
correspondence occurred between the NRCA and Labuschagne to see if reconciliation was possible,
but without any positive results. Labuschagne distrusted the Church’s motives and argued that
only a public excuse would settle matters. Due to the run-up to the decision in 2010 and the
church schism in 2011, the case gathered some cyber dust. Professors A.G. van Aarde, J.
Buitendag and W.A. Dreyer played a prominent role in bringing the outstanding matter of Cas
Labuschagne to the attention of the author of this article. It led to a visit in 2017 and more
correspondence to clarify issues. Eventually, reconciliation had occurred only a few months
before he died in 2019.
CONTRIBUTION : This article contributes to revealing an untold story in which different leaders
of the NRCA played a prominent role. It is about a struggle for reconciliation, events behind
the scenes, and a story with a good end – events the church and the academic community
should know about.http://www.hts.org.zaam2024Reformed Theological CollegeNon
Wind generator impedance matching in small-scale passive wind energy systems
No full textCITATION: Labuschagne, C. J. J. & Kamper, M. J. 2021. Wind generator impedance matching in small-scale passive wind energy systems. IEEE Access, 9:22558-22568, doi:10.1109/ACCESS.2021.3056226.The original publication is available at https://ieeexplore.ieee.orgENGLISH ABSTRACT: In this paper, the improved turbine power matching of passive wind energy systems for dcconnected
battery storage applications with an impedance matching method is investigated. The passive
system uses a direct-drive permanent magnet synchronous generator and is directly connected via a diode
recti er to the dc xed-voltage battery storage. To improve power matching, an external inductance is added
to the passive system between the generator and the diode recti er. A static nite element based solution
method is proposed to accurately calculate the necessary external inductance to achieve near maximum power
point matching. It is shown that the proposed nite element based calculation method is computationally
ef cient and excellently suited for generator design optimization, which is critical for this application.
It is also shown that by rewinding existing machines for the correct cut-in speed and adding the external
inductance for improved power matching, existing machines can be effectively recycled for passive wind
energy systems. The proposed static nite element solution method's accuracy and improved power matching
are con rmed with measured results on a sub 5 kW power level.https://ieeexplore.ieee.org/document/9343816Publisher's versio
Variations of the chemical characteristics and source regions of aerosols at the Cape Point GAW station
No full textNitrogen is an essential component for life. The natural nitrogen cycle has been greatly disturbed by the production of fertilizer and use of fossil fuels, such that it has doubled the amount of reactive nitrogen (Nr) produced globally. Excessive additions of Nr to the environment can have negative effects, including eutrophication, loss of biodiversity, enhanced greenhouse gas emissions, acidification, increased tropospheric ozone, and damage to human health. Excess ammonia (NH3) and nitrogen oxide (NOx) emissions lead to increased aerosol loading via secondary aerosol formation processes. Increased aerosol loading has impacts on the climate and on human health. Furthermore, the aerosols formed from Nr from continental sources can get deposited to the open ocean, which is usually nitrogen limited. Knowing the concentrations of different aerosol species from a pollution free environment, such as the remote open ocean, can give insights into the natural preindustrial conditions and be used as a baseline for looking into the impacts of anthropogenic activities. This thesis focuses on establishing the Cape Point Global Atmosphere Watch (GAW) station as a site for collecting aerosol samples from pristine marine air masses. The use of a tower site allows for high temporal resolution sampling across multiple seasons and years, which is logistically difficult when relying on ship-based sampling of pristine marine environments. Results are presented from the chemical composition analysis of aerosols sampled at the Cape Point GAW station, including comparisons of two different aerosol sampling systems (tall-tower PM10 and ground-based sizesegregated). Furthermore, the installation and testing of a sector-controlled sampling system designed to reduce continental influence on samples is evaluated. Air mass back trajectories and radon (222Rn) concentrations were used to classify the air masses of each aerosol sample as either marine, modified marine, or continental. We found that continental samples had elevated concentrations of NH4 + , NO3 - , and non-sea-salt SO4 2- , whereas the marine samples had elevated concentrations of Cl- , and Na+ , as expected. A comparison of the tall-tower PM10 and ground-based size-segregated sampling systems showed that the ground-based sampler measured higher concentrations of coarse mode aerosols. This is attributed to the settling of large aerosols within the long sampling intake tube from the tower sampling system. The sector-controlled sampling system based on wind speed and direction was able to remove some of the influence of continental air masses, however some continental influence could not be avoided as the continental air masses circulated over the ocean before being sampled from the marine sector. This system could be improved by having additional cut-off limits defined for sampling, such as particle number, black carbon, or carbon monoxide (CO) concentrations
Hoe heilzaam is de bijbelwetenschap : de bijdrage van de bijbel(wetenschap) aan de cultuur
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