4,596 research outputs found
Community reactions to the introduction of an educare programme at a home for Black aged in KwaMashu.
KwaMashu Christian Care Society, Zamazulu Nkosi Centre for the Aged and Daycare Centre
Population studies on Phytophthora infestans on potatoes and tomatoes in southern Germany
Fifty-seven isolates of Phytophthora infestans from blighted potato foliage were collected in 1995 in southern Germany and analysed for mating type and sensitivity to metalaxyl. Fifty-six of them were characterised as A1 and one as A2 mating types. Resistance to metalaxyl was observed frequently: 53 isolates were resistant, three were partially sensitive, and one was sensitive. In a subsequent field study in 1999, 84 isolates collected from blighted potato and tomato foliage were analysed for mating type. Seventy-two were characterised as A1 and twelve as A2 mating types. The response of 76 isolates to metalaxyl and to propamocarb was tested. The majority (42) of the 76 isolates was classified as resistant to metalaxyl; 31 were partially sensitive and only three isolates were sensitive. The results with propamocarb were less discrete; 10 isolates were classified as resistant and three were clearly sensitive. AFLP fingerprinting was used to examine the genetic structure of the southern German P. infestans population collected in 1999 and indicated that the tested population can be sub-divided into a tomato group, a potato group and a mixed group containing isolates collected from both crops. The presence of Ia and IIa mitochondrial DNA haplotypes indicates that the German P. infestans isolates belong to the new pathogen population that has also been reported in neighbouring regions of Europe. The present study indicates that at the beginning of the season only a few genotypes were present, and the population became genetically more variable at the end of the growing season
Poverty and quality of life among Blacks in South Africa
Presented at the Second Carnegie Inquiry into Poverty and Development in Southern Africa, Cape Town, 13-19th April, 1984Human Sciences Research Council
Centre for Applied Social Sciences, University of Natal
Council for Scientific and Industrial Research
Urban Foundatio
Scalar field theory on kappa-Minkowski spacetime and translation and Lorentz invariance
We investigate the properties of kappa-Minkowski spacetime by using
representations of the corresponding deformed algebra in terms of undeformed
Heisenberg-Weyl algebra. The deformed algebra consists of kappa-Poincare
algebra extended with the generators of the deformed Weyl algebra. The part of
deformed algebra, generated by rotation, boost and momentum generators, is
described by the Hopf algebra structure. The approach used in our
considerations is completely Lorentz covariant. We further use an adventages of
this approach to consistently construct a star product which has a property
that under integration sign it can be replaced by a standard pointwise
multiplication, a property that was since known to hold for Moyal, but not also
for kappa-Minkowski spacetime. This star product also has generalized trace and
cyclic properties and the construction alone is accomplished by considering a
classical Dirac operator representation of deformed algebra and by requiring it
to be hermitian. We find that the obtained star product is not translationally
invariant, leading to a conclusion that the classical Dirac operator
representation is the one where translation invariance cannot simultaneously be
implemented along with hermiticity. However, due to the integral property
satisfied by the star product, noncommutative free scalar field theory does not
have a problem with translation symmetry breaking and can be shown to reduce to
an ordinary free scalar field theory without nonlocal features and tachionic
modes and basicaly of the very same form. The issue of Lorentz invariance of
the theory is also discussed.Comment: 22 pages, no figures, revtex4, in new version comments regarding
translation invariance and few references are added, accepted for publication
in Int. J. Mod. Phys.
Coupling of whispering-gallery modes in size-mismatched microdisk photonic molecules
Mechanisms of whispering-gallery (WG) modes coupling in microdisk photonic
molecules (PMs) with slight and significant size mismatch are numerically
investigated. The results reveal two different scenarios of modes interaction
depending on the degree of this mismatch and offer new insight into how PM
parameters can be tuned to control and modify WG-modes wavelengths and
Q-factors. From a practical point of view, these findings offer a way to
fabricate PM microlaser structures that exhibit low thresholds and directional
emission, and at the same time are more tolerant to fabrication errors than
previously explored coupled-cavity structures composed of identical
microresonators.Comment: 3 pages with 5 figures (to appear in Opt. Lett. 2007
Dust absorption along the line of sight for high-redshift objects
We estimate the optical depth distribution of dust present in absorption
systems along the line of sight of high redshift galaxies and the resulting
reddening. We characterize the probability distribution of the transmission to
a given redshift and the shape of the effective mean extinction law by means of
analytical estimates and Monte Carlo simulations. We present our results in a
format useful for applications to present samples of high redshift galaxies and
discuss the implications for observations with the James Webb Space Telescope.
Our most realistic model takes into account the metallicity evolution of Damped
Lyman Alpha absorbers and predicts that the effects of dust absorption are
modest: at redshift z \gtrsim 5 the transmission is above 0.8 at an emitted
wavelength \lambda_e = 0.14 \mu m with probability 90%. Therefore dust
obscuration along the line of sight will affect only marginally observations at
very high redshift.Comment: 27 pages, 9 figures, ApJ accepte
Using Gravitational Lensing to study HI clouds at high redshift
We investigate the possibility of detecting HI emission from gravitationally
lensed HI clouds (akin to damped Lyman- clouds) at high redshift by
carrying out deep radio observations in the fields of known cluster lenses.
Such observations will be possible with present radio telescopes only if the
lens substantially magnifies the flux of the HI emission. While at present this
holds the only possibility of detecting the HI emission from such clouds, it
has the disadvantage of being restricted to clouds that lie very close to the
caustics of the lens. We find that observations at a detection threshold of 50
micro Jy at 320 MHz (possible with the GMRT) have a greater than 20%
probability of detecting an HI cloud in the field of a cluster, provided the
clouds have HI masses in the range 5 X 10^8 M_{\odot} < M_{HI} < 2.5 X 10^{10}
M_{\odot}. The probability of detecting a cloud increases if they have larger
HI masses, except in the cases where the number of HI clouds in the cluster
field becomes very small. The probability of a detection at 610 MHz and 233 MHz
is comparable to that at 320 MHz, though a definitive statement is difficult
owing to uncertainties in the HI content at the redshifts corresponding to
these frequencies. Observations at a detection threshold of 2 micro Jy
(possible in the future with the SKA) are expected to detect a few HI clouds in
the field of every cluster provided the clouds have HI masses in the range 2 X
10^7 M_{\odot} < M_{HI} < 10^9 M_{\odot}. Even if such observations do not
result in the detection of HI clouds, they will be able to put useful
constraints on the HI content of the clouds.Comment: 21 pages, 7 figures, minor changes in figures, accepted for
publication in Ap
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