Entanglement decoherence in a gravitational well according to the event formalism

The event formalism is a non-linear extension of quantum field theory designed to be compatible with the closed time-like curves that appear in general relativity. Whilst reducing to standard quantum field theory in flat space-time the formalism leads to testably different predictions for entanglement distribution in curved space. In this paper we introduce a more general version of the formalism and use it to analyse the practicality of an experimental test of its predictions in the earth's gravitational well

Operations Research : an indispensable toolkit for the logistician

CITATION: Pienaar, W. J. 2005. Operations research : an indispensable toolkit for the logistician. ORiON, 21(1):77-91, doi:10.5784/21-1-20.The original publication is available at http://orion.journals.ac.zaENGLISH SUMMARY : This paper traces the origin of the word logistics, outlines its conceptual evolution, and explains its meaning in contemporary usage. The background that led to the introduction of Logistics Management and Operations Research (OR) as undergraduate fields of study at the University of Stellenbosch is sketched. The concept of Logistics Management is described and its strategic, tactical and operational tiers, as well as the different activities that form part of the logistics supply chain process are identified. The role and necessity of OR in decision-making within each activity and in the coordination between the various activities are outlined. OR techniques most pertinent to the field of logistics are identified and the analytical competencies that a logistician should possess are indicated.http://orion.journals.ac.za/pub/article/view/20Publisher's versio

Base exchange in soils : a study of the reproducibility of base exchange values for some South African soils, as indicated by leaching with normal ammonium acetate solution

A very reliable method for the total analysis of the ammonium acetate leachate has been outlined. This is both simple and straight forward and is more rapid than any which have been seen in the literature. It is particularly applicable where a worker must perform a large number of routine analyses in the minimum of time. Shirley (29) and other workers have shown that 1000 ml. of leaching solution is generally necessary to extract all the exchangeable gases. The present investigation has shown that the time of leaching makes no appreciable difference to the amounts of bases replaced, as long as this exceeds four hours. Two alternative methods have been introduced for the rapid determination of the total exchangeable bases in a soil and there are considered to be more reliable than that of Bray and White. It is suggested that the two new methods might yield a still greater degree of accuracy if larger aliquots were to be used for each determination. It is further pointed out that the values obtained by the chloride methods are more likely to represent correct values than the sum totals of the bases as determined individually, since these are arrived at by summing the results of four different estimations, each of which is liable to experimental error, whereas in the chloride methods there is only one perfectly straightforward determination. The values for the total exchangeable bases in the soils examined were found to vary over the range 2.50 to 14.28 m.e. per 100 g. soil, with a variance of up to ± 0.2sm.e. per 100 g., corresponding to a percentage error of up to ± 4.7%. These figures are based on the analysis of 12 separate leachings of each soil with normal ammonium acetate solution of pH 7.00. This rather wide variance can be attributed to the fact that the exchangeable bases in some soils are more easily replaceable than in other soils. It is regretted that the shortage of time and the non-availability of a complete range of samples of all typical South African soils has prevented the attainment of an original objective, namely, a statistical evaluation of the base exchange figures for all South African soil types. It would also have been of great interest to have been able to establish exactly the composition of the double salt of calcium and magnesium, whose existence has been postulated to explain the effect of the Ca/Mg ratio on the results yielded by the first chloride method. Summary, p. 67-68

Open timelike curves violate Heisenberg's uncertainty principle

Toy models for quantum evolution in the presence of closed timelike curves (CTCs) have gained attention in the recent literature due to the strange effects they predict. The circuits that give rise to these effects appear quite abstract and contrived, as they require non-trivial interactions between the future and past which lead to infinitely recursive equations. We consider the special case in which there is no interaction inside the CTC, referred to as an open timelike curve (OTC), for which the only local effect is to increase the time elapsed by a clock carried by the system. Remarkably, circuits with access to OTCs are shown to violate Heisenberg's uncertainty principle, allowing perfect state discrimination and perfect cloning of coherent states. The model is extended to wave-packets and smoothly recovers standard quantum mechanics in an appropriate physical limit. The analogy with general relativistic time-dilation suggests that OTCs provide a novel alternative to existing proposals for the behaviour of quantum systems under gravity

Diagnosis of childhood tuberculosis and host RNA expression in Africa

Improved diagnostic tests for tuberculosis in children are needed. We hypothesized that transcriptional signatures of host blood could be used to distinguish tuberculosis from other diseases in African children who either were or were not infected with the human immunodeficiency virus (HIV

The lesson of causal discovery algorithms for quantum correlations: Causal explanations of Bell-inequality violations require fine-tuning

An active area of research in the fields of machine learning and statistics is the development of causal discovery algorithms, the purpose of which is to infer the causal relations that hold among a set of variables from the correlations that these exhibit. We apply some of these algorithms to the correlations that arise for entangled quantum systems. We show that they cannot distinguish correlations that satisfy Bell inequalities from correlations that violate Bell inequalities, and consequently that they cannot do justice to the challenges of explaining certain quantum correlations causally. Nonetheless, by adapting the conceptual tools of causal inference, we can show that any attempt to provide a causal explanation of nonsignalling correlations that violate a Bell inequality must contradict a core principle of these algorithms, namely, that an observed statistical independence between variables should not be explained by fine-tuning of the causal parameters. In particular, we demonstrate the need for such fine-tuning for most of the causal mechanisms that have been proposed to underlie Bell correlations, including superluminal causal influences, superdeterminism (that is, a denial of freedom of choice of settings), and retrocausal influences which do not introduce causal cycles.Comment: 29 pages, 28 figs. New in v2: a section presenting in detail our characterization of Bell's theorem as a contradiction arising from (i) the framework of causal models, (ii) the principle of no fine-tuning, and (iii) certain operational features of quantum theory; a section explaining why a denial of hidden variables affords even fewer opportunities for causal explanations of quantum correlation

The S’Khokho ‘bushcan’ initiative: Kick a bush and condoms fall out

Background. People living in rural areas have limited access to condoms owing to distance, cost and time involved in travelling to public health facilities, around which most condom distribution efforts are centralised.Objective. In an effort to increase access to condoms in these areas, we explored the feasibility and efficacy of condom distribution by placing ‘condocans’ on trees along informal footpaths used by residents.Methods. From October 2012, steel condocans, typically seen in clinic settings, were erected on trees along pathways in bushy areas with high levels of foot traffic at several rural locations in the uMgungundlovu district of KwaZulu-Natal Province, South Africa (SA). Because of their location, the condocans were referred to as ‘bushcans’. Condom uptake was closely monitored, and the bushcans were restocked when necessary.Results. Following the introduction of the bushcans, male condom distribution increased by 237% from October 2012 to December 2012. Condom distribution in these areas increased on average by 187% from October 2012 to October 2015, with more than 408 000 condoms distributed over the 3-year period using the bushcans alone. Discussions with residents revealed that they were pleased about the increased access to condoms via the bushcans, and they recommended other areas for potential implementation of this initiative.Conclusions. The bushcan initiative highlighted the fact that condoms are not as easily accessible to all South Africans as is often thought. By providing access to condoms in a discreet and convenient manner, the bushcans have the potential to increase access to condoms in other rural and periurban areas in SA where communities face similar barriers to access

The Parkes Observatory Pulsar Data Archive

The Parkes pulsar data archive currently provides access to 144044 data files obtained from observations carried out at the Parkes observatory since the year 1991. Around 10^5 files are from surveys of the sky, the remainder are observations of 775 individual pulsars and their corresponding calibration signals. Survey observations are included from the Parkes 70cm and the Swinburne Intermediate Latitude surveys. Individual pulsar observations are included from young pulsar timing projects, the Parkes Pulsar Timing Array and from the PULSE@Parkes outreach program. The data files and access methods are compatible with Virtual Observatory protocols. This paper describes the data currently stored in the archive and presents ways in which these data can be searched and downloaded.Comment: Accepted by PAS

Access to housing in South Africa: An overview of dimensions and mechanisms

The historical background of influx control, group areas and the regulation of unlawful occupation of land (squatting), explain, to some extent, why unlawful occupation of land and informal settlements are still prevalent 18 years after the new Constitutional dispensation commenced. For many people in South Africa, access to land is still an ideal and not a reality. Not only have the “three pillars of apartheid” contributed to the dismal current state of affairs, but the multi-faceted and multi-dimensional nature of access to housing has also contributed to it being particularly complex. In this regard a human rights, a land reform and a property law dimension can be identified. The human rights dimension is imbedded in socio-economic rights and is founded on dignity; the land reform dimension is based on the premise that access to housing is interlinked with access to land, and the property law dimension involves the development of common law (Roman-Dutch) principles of property and ownership to provide for other (or alternative) forms of ownership. This article aims to provide an overview of the three-dimensional nature of access to housing and to highlight some of the mechanisms encapsulated within each dimension. An overview of statutory measures will be provided and, where relevant, certain aspects will be attended to in more detail. In light of its three-dimensional nature, it is clear that access to housing remains a major challenge for all role players involved