Statistiek en inferensie*

Een van die mees vooraanstaande wiskundiges wat hierdie eeu geleef het, Von Neumann,6 het een keer ’n voordrag m et die volgende opm erking ingelei: „A discussion of the nature of intellectual work is a diffi cult task in any field, even in fields which are not so far removed from the central area of our common hum an intellectual effort as mathematics still is. A discussion of the nature of intellectual effort is difficult per se — at any rate, more difficult than the mere exercise of that particular effort. It is harder to understand the mechanism of an airplane, and the theories of the forces which lift and which propel it, than merely to ride in it, to be elevated and transported by it — or even to steer it. It is exceptional that one should be able to acquire the understanding of a process without having pre­viously acquired a deep familiarity with running it, with using it, before one has assimilated it in an instinctive and empirical way

Die rol van die kerk in die rehabilitasie van die Misdadiger en die bestryding van die misdaad

No Abstract

Variable selection by searching for good subsets

Machine learning and statistical models are increasingly used in a prediction context and in the process of building these models the question of which variables to include often arises. Over the last 50 years a number of procedures have been proposed, especially in the statistical literature. In this paper a newvariable selection procedure is introduced for linear models. A subset of variables is defined here to be “good at margin λ” if it has two properties, namely (i) its associated criterion of fit will be improved in relative terms by less than λ if any variable is added to it, and (ii) its criterion of fit will deteriorate in relative terms by at least λ if any variable inside it, is dropped from it. Thus, such a subset contains all variables that are individually important and none that are unimportant at a given margin λ ≥ 0. This paper discusses calculation of such λ-good subsets. The “good” approach extends readily to generalised linear and many other models by using an appropriate criterion of performance. The approach is illustrated on an artificial data set and a number of real data sets

A framework for normal mean variance mixture innovations with application to GARCH modelling

GARCH models are useful to estimate the volatility of financial return series. Historically the innovation distribution of a GARCH model was assumed to be standard normal but recent research emphasizes the need for more general distributions allowing both asymmetry (skewness) and kurtosis in the innovation distribution to obtain better fitting models. A number of authors have proposed models which are special cases of the class of normal mean variance mixtures. We introduce a general framework within which this class of innovation distributions may be discussed. This entails writing the innovation term as a standardised combination of two variables, namely a normally distributed term and a mixing variable, each with its own interpretation. We list the existing models that fit into this framework and compare the corresponding innovation distributions, finding that they tend to be quite similar. This is confirmed by an empirical illustration which fits the models to the monthly excess returns series of the US stocks. The illustration finds further support for the ICAPM model of Merton, thus supporting recent results of Lanne and Saikonnen (2006)

AfrikaBot : design of a robotics challenge to promote STEM in Africa

Abstract: Science, technology, engineering and mathematics education for high school learners in developing countries is a challenge for two significant reasons: equipment for education is expensive and complex, and economically-marginalized youth must be integrated in pre-engineering programs to prepare them for technical programmes at university. The goal of establishing AfrikaBot is to prepare high school learners to study engineering at the University of Johannesburg; thus to train teenagers from disadvantaged communities with no prior experience in STEM to participate in a challenge to build and program a robot. Also, AfrikaBot aims to equip teenagers from low-income households with technology and entrepreneurial skills in a repressed economy. AfrikaBot achieves the above with a build-it-yourself robot that can be used after the competition to invent systems with real world applications. Anticipated long-term outcomes of the AfrikaBot program will influence the structure of future robotics challenges, and promote a higher number of technical candidates from marginalized communities. By transferring enabling technology skills in a fun and engaging way, participants will rapidly build the confidence to pursue careers in STEM fields. Participants can also acquire entrepreneurial skills that may lead to the establishment of new businesses and the creation of local jobs in both the formal and informal sectors in Africa. This paper presents the organizational and physical design of AfrikaBot, a robotics challenge that will be held in the latter half of 2016

Enhanced Accessibility for People with Disabilities Living in Urban Areas

[Excerpt] People with disabilities constitute a significant proportion of the poor in developing countries. If internationally agreed targets on reducing poverty are to be reached, it is critical that specific measures be taken to reduce the societal discrimination and isolation that people with disabilities continue to face. Transport is an important enabler of strategies to fight poverty through enhancing access to education, employment, and social services. This project aims to further the understanding of the mobility and access issues experienced by people with disabilities in developing countries, and to identify specific steps that can be taken to start addressing problems. A major objective of the project is to compile a compendium of guidelines that can be used by government authorities, advocacy groups, and donor/loan agencies to improve the access of people with disabilities to transport and other services in urban areas

Die rol van die kerk in die rehabilitasie van die misdadiger en die bestryding van die misdaad

No abstract available

Culicoides species abundance and potential overwintering of African horse sickness virus in the Onderstepoort area, Gauteng, South Africa

In South Africa, outbreaks of African horse sickness (AHS) occur in summer; no cases are reported in winter, from July to September. The AHS virus (AHSV) is transmitted almost exclusively by Culicoides midges (Diptera: Ceratopogonidae), of which Culicoides imicola is considered to be the most important vector. The over-wintering mechanism of AHSV is unknown. In this study, more than 500 000 Culicoides midges belonging to at least 26 species were collected in 88 light traps at weekly intervals between July 2010 and September 2011 near horses in the Onderstepoort area of South Africa. The dominant species was C. imicola. Despite relatively low temperatures and frost, at least 17 species, including C. imicola, were collected throughout winter (June–August). Although the mean number of midges per night fell from > 50 000 (March) to < 100 (July and August), no midge-free periods were found. This study,using virus isolation on cell cultures and a reverse transcriptase polymerase chain reaction (RT-PCR) assay, confirmed low infection prevalence in field midges and that the detection of virus correlated to high numbers. Although no virus was detected during this winter period,continuous adult activity indicated that transmission can potentially occur. The absence of AHSV in the midges during winter can be ascribed to the relatively low numbers collected coupled to low infection prevalence, low virus replication rates and low virus titres in the potentially infected midges. Cases of AHS in susceptible animals are likely to start as soon as Culicoides populations reach a critical level

Prediking oor politieke sake - riglyne vanuit Romeine 12-15

Preaching on political issues is a very topical matter, especially in the current situation in South Africa. This matter is extensively dealt with in literature in the field of the Old and New Testament, Homiletics and Ethics. The aim with this article is to explore the Pauline paranesis in Romans 12-15 to discern concrete guidelines on handling political issues in preaching. As point of departure the expression God’s mercy (Romans 12:1) is investigated closely, as the concept of God’s mercy is the foundation stone of the total paranesis in Romans 12-15. Regarding preaching on political issues, the fact that the new aeon has already come and will finally come, leads to certain conclusions. The responsibility of the congregation to test and approve what God's will is - also in political matters - is stressed. The kingdom of God as the predominant kingdom, relativises earthly (political) kingdoms. The responsibility to equip the congregation to discern political issues in the light of Scripture is dealt with in this regard. Finally, perspectives are given on the relation between state and believer. In conclusion the command to Christians to love each other as believers, to live in peace with everyone and to love enemies is also highlighted

Carbon­yl(N-nitroso-N-oxido-1-naphtylamine-κ2 O,O′)(triphenyl­phosphine-κP)rhodium(I) acetone solvate

The title compound, [Rh(C10H7N2O2)(C18H15P)(CO)]·(CH3)2CO, is the second structural report of a metal complex formed with the O,O′-C10H7N2O2 (neocupferrate) ligand. In the crystal structure, the metal centre is surrounded by one carbonyl ligand, one triphenyl­phosphine ligand and the bidentate neocupferrate ligand, forming a distorted square-planar RhCO2P coordination set which is best illustrated by the small O—Rh—O bite angle of 77.74 (10)°. There are no classical hydrogen-bond inter­actions observed for this complex