Enkele strategieë vir ekonomie se ontwikkeling in die informele sektor

Since 2 February 1990 the pace of change in South Africa has been accelerating on all fronts. One naturally thinks of political development,but this change applies equally to economic development in the black informal sector There is a need for national and local authorities as well as fo r the private sector to play a role in promoting informal business activities. Instead of legislating away the so-called problem, the reality of the economic situation in the informal sector should be recognised and managed in a supportive manner In a changing society high priority should be given to the nurturing of economic growth in the informal sector. The increasing numbers of the unemployed in South Africa, especially in urban areas, necessitates positive steps to deal with the realities of urbanisation and to ease the way in which honest income can be earned through various opportunities in the informal sector A healthy and growing small business in the informal sector is a vital ingredient to ensure widespread employment and income-creation in a market-orientated economy. This sector of the economy tends to be labour-intensive, is competitive by nature and is noted for the ease of entry - thus being a prime training gun d for entrepreneurship. It is absolutely clear that the growing debate surrounding the informal sector in South Africa should be coupled with the application of reformist development strategies throughout the sub-continent. It order to improve the current situation, some specific strategies to achieve social and economic upliftment in the informal part of the economy are identified by the author. Although the informal sector forms an integral part of the economy as a whole, the focal point of this article is the economic role and function of the black population in the informal sector

WSRT Faraday tomography of the Galactic ISM at \lambda \sim 0.86 m

We investigate the distribution and properties of Faraday rotating and synchrotron emitting regions in the Galactic ISM in the direction of the Galactic anti-centre. We apply Faraday tomography to a radio polarization dataset that we obtained with the WSRT. We developed a new method to calculate a linear fit to periodic data, which we use to determine rotation measures from our polarization angle data. From simulations of a Faraday screen + noise we could determine how compatible the data are with Faraday screens. An unexpectedly large fraction of 14% of the lines-of-sight in our dataset show an unresolved main component in the Faraday depth spectrum. For lines-of-sight with a single unresolved component we demonstrate that a Faraday screen in front of a synchrotron emitting region that contains a turbulent magnetic field component can explain the data.Comment: 5 pages, 5 figures. Accepted for publication as a Letter to the Editor in A&

Motion of a sphere through an aging system

We have investigated the drag on a sphere falling through a clay suspension that has a yield stress and exhibits rheological aging. The drag force increases with both speed and the rest time between preparation of the system and the start of the experiment, but there exists a nonzero minimum speed below which steady motion is not possible. We find that only a very thin layer of material around the sphere is fluidized when it moves, while the rest of suspension is deformed elastically. This is in marked contrast to what is found for yield-stress fluids that do not age.Comment: latex, 4 figure

The radio source B 1834+620: A double-double radio galaxy with interesting properties

We present a study of the peculiar radio galaxy B 1834+620. It is characterised by the presence of a 420-kpc large edge-brightened radio source which is situated within, and well aligned with, a larger (1.66 Mpc) radio source. Both sources apparently originate in the same host galaxy, which has a R_s-magnitude of 19.7 and a redshift of 0.5194, as determined from the strong emission-lines in the spectrum. We have determined the rotation measures towards this source, as well as the radio spectral energy distribution of its components. The radio spectrum of the large outer source is steeper than that of the smaller inner source. The radio core has a spectrum that peaks at a frequency of a few GHz. The rotation measures towards the four main components are quite similar, within $\sim\!2$ rad m$^{-2}$ of 58 rad m$^{-2}$. They are probably largely galactic in origin. We have used the presence of a bright hotspot in the northern outer lobe to constrain the advance velocity of the inner radio lobes to the range between 0.19c and 0.29c, depending on the orientation of the source. This corresponds to an age of this structure in the range between 2.6 and 5.8 Myr. We estimate a density of the ambient medium of the inner lobes of \la 1.6 \times 10^{-30} gr\,cm$^{-3}$ (particle density \la 8 \times 10^{-7} cm$^{-3}$). A low ambient density is further supported by the discrepancy between the large optical emission-line luminosity of the host galaxy and the relatively low radio power of the inner lobes.Comment: Accepted for publication in MNRA

Simplified SIMPs and the LHC

The existence of Dark Matter (DM) in the form of Strongly Interacting Massive Particles (SIMPs) may be motivated by astrophysical observations that challenge the classical Cold DM scenario. Other observations greatly constrain, but do not completely exclude, the SIMP alternative. The signature of SIMPs at the LHC may consist of neutral, hadron-like, trackless jets produced in pairs. We show that the absence of charged content can provide a very efficient tool to suppress dijet backgrounds at the LHC, thus enhancing the sensitivity to a potential SIMP signal. We illustrate this using a simplified SIMP model and present a detailed feasibility study based on simulations, including a dedicated detector response parametrization. We evaluate the expected sensitivity to various signal scenarios and tentatively consider the exclusion limits on the SIMP elastic cross section with nucleons.Comment: 18 pages, 7 figure

Constructing tree decompositions of graphs with bounded gonality

In this paper, we give a constructive proof of the fact that the treewidth of a graph is at most its divisorial gonality. The proof gives a polynomial time algorithm to construct a tree decomposition of width at most k, when an effective divisor of degree k that reaches all vertices is given. We also give a similar result for two related notions: stable divisorial gonality and stable gonality