New insights from inside-out Doppler tomography

We present preliminary results from our investigation into using an 'inside-out' velocity space for creating a Doppler tomogram. The aim is to transpose the inverted appearance of the Cartesian velocity space used in normal Doppler tomography. In a comparison between normal and inside-out Doppler tomograms of cataclysmic variables, we show that the inside-out velocity space has the potential to produce new insights into the accretion dynamics in these systems.Comment: 4 pages, 4 figures, conference: The Golden Age of Cataclysmic Variables and Related Objects II, Palermo 201

A deep photometric survey of the Abell cluster SO423 : a pilot study for the UCT SALT supercluster survey

Includes bibliographical references (leaves 99-101)

High specificity makes DNA screening the method of choice for diagnosis of familial hyper-cholesterolaemia

No Abstract

Editorial

High specificity makes DNA screening the method of choice for diagnosis of familial hypercholesterolaemia

Comparative advantage of potato production in seven regions of South Africa

The focus of this research was to investigate the comparative advantage of the potato industry in seven potato production regions in South Africa. Potatoes are the most important vegetable crop produced in South Africa. In 2008 it contributed more than 40% to the total production of vegetables in South Africa and it accounted for more than 20% of the value of all fresh produce sold on all the major national fresh produce markets. This study uses the Resource Cost Ratio (RCR) methodology that provides an explicit indication of the efficiency with which production alternatives uses domestic resources to generate or save foreign exchange. The Nominal Protection Ratio (NPR) and Effective Protection Coefficient (EPC) were also calculated. The results show that current policies that affects the input market for potato production in South Africa is constraining the potato industry. This was confirmed by the results obtained from the NPR and EPC analysis, and the size of the policy distortions was shown through the calculation of market and economic profitability. If current policies prevail potato production in the Eastern Free State will not have a comparative advantage, but in the absence of such policies all production regions have a comparative advantage.Crop Production/Industries,

Environmental factors influencing the distribution of Opuntia stricta, an invasive alien plant in the Kruger National Park, South Africa

Opuntia stricta (Cactaceae), an alien weed, has invaded an area of more than 35 000 ha in the Skukuza region of the Kruger National Park [KNP]. The distribution of the plant and features of the environment were used to identify biotic and abiotic factors which may be affecting the distribution and density of the plant. A Canonical Community Analysis revealed that none of the environmental factors that were monitored influenced the distribution or abundance of O. stricta in KNP. There were no apparent natural barriers that might limit the occurrence of O. stricta within the KNP. The study provides insight into the relationship between the invader and host environment, showing that there is a high probability that, unless there is appropriate intervention, O. stricta will eventually colonise the entire KNP

Factors influencing the distribution of Cactoblastis cactorum, a biological control agent of Opuntia stricta in Kruger National Park, South Africa

Cactoblastis cactorum, a phycitid moth, has been used with considerable success as a biological control agent against several different cactus species in many parts of the world, including Opuntia stricta in Kruger National Park [KNP], South Africa. Although the moth has become widespread and abundant in KNP, its populations have not reached levels where it is able to provide the desired level of control on the alien species which has invaded more than 35 000 ha of the park and continues to spread. Although several factors, especially acquired predators and parasitoids, are known to curb the abundance of C. cactorum in South Africa, the extent to which this applies in KNP is unknown. Logistic regression and Canonical Community Analysis were used to determine the biotic and abiotic factors affecting the distribution and abundance of C. cactorum in KNP. To do this, maps of the ranges of the insect and host plant were constructed and integrated with other environmental features. The logistic regression showed that O. stricta density had no influence on whether or not C. cactorum was present in an area. The Canonical Community Analysis suggested that a high fire frequency, the herbicide control programme and the presence of small host plants may be important in limiting the distribution of C. cactorum, either directly or indirectly, through impacts on associated predators or parasitoids