8,311 research outputs found
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 rad m of 58 rad m. 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 (particle density
\la 8 \times 10^{-7} cm). 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
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