154 research outputs found
Geregtelike geneeskunde : die multidissiplinêre benadering
Ek vra u vergunning om by hierdie geleentheid enkele woorde van
dank en waardering uit te spreek.
Eerstens my dank aan die Universiteit van Pretoria vir die vertroue in
my gestel deur my in hierdie verantwoordelike pos aan te stel. Ek wil
graag onderneem om steeds my bes te doen om op 'n verantwoordelike
en bevredigende wyse aan die hoe eise en verwagtinge wat ek
weet wat gestel mag word, te voldoen.Digitised by the Department of Library Services in support of open access to information, University of Pretoria, 202
Genetic testing approaches for hereditary breast cancer: Perspectives from a private diagnostic laboratory
Breast cancer is highly prevalent in South Africa, and up to 10% of breast cancer cases may be hereditary. The landscape of genetic testing options for hereditary breast cancer (HBC) has changed significantly over the past decade, and healthcare providers are faced with multiple options when referring breast cancer patients for genetic testing. We have performed a retrospective study of 3 years’ worth of breast cancer genetic testing referrals to our laboratory. While Afrikaner and Ashkenazi Jewish founder screens may be appropriate as first-line tests in a limited subset of patients, we have shown that in the majority of cases it is more effective to adopt a multigene panel approach. While variants in the BRCA1 and BRCA2 genes still account for a significant proportion of cases, close to 40% of pathogenic variants were found in genes other than BRCA1 or BRCA2. There are many factors that healthcare providers should consider when requesting genetic testing for breast cancer patients and families, including family history, ancestral background, cost, medical aid scheme reimbursement and scope of testing. We summarise our findings and provide advantages and disadvantages of each approach, with the aim of assisting clinicians and genetic counsellors to make appropriate testing decisions
Properties of nitrogen-vacancy centers in diamond: group theoretic approach
We present a procedure that makes use of group theory to analyze and predict
the main properties of the negatively charged nitrogen-vacancy (NV) center in
diamond. We focus on the relatively low temperatures limit where both the
spin-spin and spin-orbit effects are important to consider. We demonstrate that
group theory may be used to clarify several aspects of the NV structure, such
as ordering of the singlets in the () electronic configuration, the
spin-spin and the spin-orbit interactions in the () electronic
configuration. We also discuss how the optical selection rules and the response
of the center to electric field can be used for spin-photon entanglement
schemes. Our general formalism is applicable to a broad class of local defects
in solids. The present results have important implications for applications in
quantum information science and nanomagnetometry.Comment: 30 pages, 6 figure
The negatively charged nitrogen-vacancy centre in diamond: the electronic solution
The negatively charged nitrogen-vacancy centre is a unique defect in diamond
that possesses properties highly suited to many applications, including quantum
information processing, quantum metrology, and biolabelling. Although the
unique properties of the centre have been extensively documented and utilised,
a detailed understanding of the physics of the centre has not yet been
achieved. Indeed there persists a number of points of contention regarding the
electronic structure of the centre, such as the ordering of the dark
intermediate singlet states. Without a sound model of the centre's electronic
structure, the understanding of the system's unique dynamical properties can
not effectively progress. In this work, the molecular model of the defect
centre is fully developed to provide a self consistent model of the complete
electronic structure of the centre. The application of the model to describe
the effects of electric, magnetic and strain interactions, as well as the
variation of the centre's fine structure with temperature, provides an
invaluable tool to those studying the centre and a means to design future
empirical and ab initio studies of this important defect.Comment: 24 pages, 6 figures, 10 table
Continuous-wave room-temperature diamond maser
The maser, older sibling of the laser, has been confined to relative
obscurity due to its reliance on cryogenic refrigeration and high-vacuum
systems. Despite this it has found application in deep-space communications and
radio astronomy due to its unparalleled performance as a low-noise amplifier
and oscillator. The recent demonstration of a room-temperature solid- state
maser exploiting photo-excited triplet states in organic pentacene molecules
paves the way for a new class of maser that could find applications in
medicine, security and sensing, taking advantage of its sensitivity and low
noise. However, to date, only pulsed operation has been observed in this
system. Furthermore, organic maser molecules have poor thermal and mechanical
properties, and their triplet sub-level decay rates make continuous emission
challenging: alternative materials are therefore required. Therefore, inorganic
materials containing spin-defects such as diamond and silicon carbide have been
proposed. Here we report a continuous-wave (CW) room-temperature maser
oscillator using optically pumped charged nitrogen-vacancy (NV) defect centres
in diamond. This demonstration unlocks the potential of room-temperature
solid-state masers for use in a new generation of microwave devices.Comment: 7 pages, 4 figure
Anisotropic interactions of a single spin and dark-spin spectroscopy in diamond
The nitrogen-vacancy (N-V) center in diamond is a promising atomic-scale
system for solid-state quantum information processing. Its spin-dependent
photoluminescence has enabled sensitive measurements on single N-V centers,
such as: electron spin resonance, Rabi oscillations, single-shot spin readout
and two-qubit operations with a nearby 13C nuclear spin. Furthermore, room
temperature spin coherence times as long as 58 microseconds have been reported
for N-V center ensembles. Here, we have developed an angle-resolved
magneto-photoluminescence microscopy apparatus to investigate the anisotropic
electron spin interactions of single N-V centers at room temperature. We
observe negative peaks in the photoluminescence as a function of both magnetic
field magnitude and angle that are explained by coherent spin precession and
anisotropic relaxation at spin level anti-crossings. In addition, precise field
alignment unmasks the resonant coupling to neighboring dark nitrogen spins that
are not otherwise detected by photoluminescence. The latter results demonstrate
a means of investigating small numbers of dark spins via a single bright spin
under ambient conditions.Comment: 13 pages, 4 figure
The MeerKAT Fornax Survey -- II. The rapid removal of HI from dwarf galaxies in the Fornax cluster
We present MeerKAT Fornax Survey atomic hydrogen (HI) observations of the
dwarf galaxies located in the central ~2.5 x 4 deg of the Fornax galaxy
cluster. The HI images presented in this work have a column density
sensitivity between 2.7 and 50 x 10 cm over 25 km s for
spatial resolution between 4 and 1 kpc. We are able to detect an impressive MHI
= 5 x 10 Msun 3 point source with a line width of 50 km s
at a distance of 20 Mpc. We detect HI in 17 out of the 304 dwarfs in our field
-- 14 out of the 36 late type dwarfs (LTDs), and 3 of the 268 early type dwarfs
(ETDs). The HI-detected LTDs have likely just joined the cluster and are on
their first infall as they are located at large clustocentric radii, with
comparable MHI and mean stellar surface brightness at fixed luminosity as blue,
star-forming LTDs in the field. The HI-detected ETDs have likely been in the
cluster longer than the LTDs and acquired their HI through a recent merger or
accretion from nearby HI. Eight of the HI-detected LTDs host irregular or
asymmetric HI emission and disturbed or lopsided stellar emission. There are
two clear cases of ram-pressure shaping the HI, with the LTDs displaying
compressed HI on the side closest to the cluster centre and a one-sided,
starless tail pointing away from the cluster centre. The HI-detected dwarfs
avoid the most massive potentials, consistent with massive galaxies playing an
active role in the removal of HI. We create a simple toy model to quantify the
timescale of HI stripping in the cluster. We find that a MHI = 10 Msun
dwarf will be stripped in ~ 240 Myr. The model is consistent with our
observations, where low mass LTDs are directly stripped of their HI from a
single encounter and more massive LTDs can harbour a disturbed HI morphology
due to longer times or multiple encounters being required to fully strip their
HI.Comment: Accepted in Astronomy & Astrophysics. 21 pages, 10 figures. Data
available at the MeerKAT Fornax Survey website
https://sites.google.com/inaf.it/meerkatfornaxsurve
The Shapes of BCGs and normal Ellipticals in Nearby Clusters
We compare the apparent axial ratio distributions of Brightest Cluster
Galaxies (BCGs) and normal ellipticals (Es) in our sample of 75 galaxy clusters
from the WINGS survey. Most BCGs in our clusters (69%) are classified as cD
galaxies. The sample of cDs has been completed by 14 additional cDs (non-BCGs)
we found in our clusters. We find that: (i) Es have triaxial shape, the
triaxiality sharing almost evenly the intrinsic axial ratios parameter space,
with a weak preference for prolateness; (ii) the BCGs have triaxial shape as
well. However, their tendence towards prolateness is much stronger than in the
case of Es. Such a strong prolateness appears entirely due to the sizeable
(dominant) component of cDs inside the WINGS sample of BCGs. In fact, while the
'normal'(non-cD) BCGs do not differ from Es, as far as the shape distribution
is concerned, the axial ratio distribution of BCG_cD galaxies is found to
support quite prolate shapes; (iii) our result turns out to be strongly at
variance with the only similar, previous analysis by Ryden et al.(1993)(RLP93),
where BCGs and Es were found to share the same axial ratio distribution; (iv)
our data suggest that the above discrepancy is mainly caused by the different
criteria that RLP93 and ourselves use to select the cluster samples, coupled
with a preference of cDs to reside in powerful X-ray emitting clusters; (v) the
GIF2 N-body results suggest that the prolateness of the BCGs (in particular the
cDs) could reflect the shape of the associated dark matter halos.Comment: 18 pages, 9 figures, 2 tables. Accepted for publication in MNRA
an overview of the MHONGOOSE survey: Observing nearby galaxies with MeerKAT
© Copyright owned by the author(s). MHONGOOSE is a deep survey of the neutral hydrogen distribution in a representative sample of 30 nearby disk and dwarf galaxies with H I masses from ∼ 106 to ∼ 1011 M, and luminosities from MR ∼ 12 to MR ∼ −22. The sample is selected to uniformly cover the available range in log(MHI). Our extremely deep observations, down to H I column density limits of well below 1018 cm−2 — or a few hundred times fainter than the typical H I disks in galaxies — will directly detect the effects of cold accretion from the intergalactic medium and the links with the cosmic web. These observations will be the first ever to probe the very low-column density neutral gas in galaxies at these high resolutions. Combination with data at other wavelengths, most of it already available, will enable accurate modeling of the properties and evolution of the mass components in these galaxies and link these with the effects of environment, dark matter distribution, and other fundamental properties such as halo mass and angular momentum. MHONGOOSE can already start addressing some of the SKA-1 science goals and will provide a comprehensive inventory of the processes driving the transformation and evolution of galaxies in the nearby universe at high resolution and over 5 orders of magnitude in column density. It will be a Nearby Galaxies Legacy Survey that will be unsurpassed until the advent of the SKA, and can serve as a highly visible, lasting statement of MeerKAT’s capabilities
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