1834 research outputs found
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Monte Carlo simulation of slot-scanning X-ray imaging systems
No full textWe present a method for simulating slot-scanning X-ray imaging using the general-purpose Monte Carlo simulation package PENELOPE and pen Easy imaging. Different phantoms can be defined with the PENGEOM package, which defines bodies as combinations of volumes limited by quadric surfaces. The source-detector geometry, the position of the object, the collimator, the X-ray tube properties, the detector material and the pixel dimensions are defined. The output of the time-delay integration detector is simulated using sequential slot outputs derived from pen Easy Imaging. The simulations are validated using tungsten and aluminium test objects, which are both simulated and imaged. The simulations are compared to the X-ray images using standard image quality metrics. The MTF, NPS and DQE curves show that the real and simulated X-ray images are comparable in terms of spatial resolution, noise and frequency information. The implementation can be modified to suit alterations in the system being simulated.National Research Foundation (South Africa
Anthropometric measurements, serum reproductivehormonal levels and sexual development among boys in the rural Western Cape, South Africa.
No full textData on growth and sexual maturation among boys from the rural Western Cape in South Africa is limited. A cross-sectional study of 269 school boys was conducted testing for serum luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone, sex hormone binding globulin (SHBG) and estradiol (E2); height, weight and body mass index (BMI); sexual maturity (using Tanner Stages) and a questionnaire (demographic and medical history). The median age at pubertal onset (Tanner Stage 2) and Tanner Stage 5 was 11.6 and 14.7 years, respectively. The median testicular volume was 5.5 mL at Tanner Stage 2 increasing from 2.5 mL at Tanner Stage 1 to 14.7 mL at Tanner Stage 5. Height and weight measurements were <25th & 50th percentile references at Tanner Stages 1–3. Controlling for confounders, serum FSH and LH increased (p < 0.05) from Tanner Stage 1 to 4 (by 4.1 and 3 mL respectively), and serum testosterone and estradiol increased after Tanner Stage 2 (by 12.7 nmol/L and 59.5 pmol/L respectively). These results indicate some delays in pubertal development of boys in the rural Western Cape when compared to boys from other settings possibly due to nutritional, socio-economic and environmental exposures. Changes in serum hormone levels were consistent with other populations. Initiatives to improve nutrition amongst Western Cape rural communities are recommendedNational Research Foundation (South Africa
A survey of resource management toward 5G radio access networks
No full textThe next generation 5G radio access network (RAN) system is believed to be a true world-wide wireless web (WWWW). This is because such system will seamlessly and ubiquitously connect everything, and support at least 1000-fold traffic volumes, 100 billion connected wireless devices, and diversified use cases as well as quality of service (QoS) requirements (e.g., reliability, latency, data rates, coverage, security, and privacy) of multimedia applications by 2020. Recently, a number of research challenges including the explosive growth in mobile traffic volumes, unprecedented connected devices, and diversified use cases have been identified for the 5G RAN systems. In addition, specific technologies such as multitier communication, massive MIMOs, mmWave backhauling, extreme densifications of nodes (UDNs), full-duplex communications (FDCs), and energy harvesting techniques have emerged in the literature to resolve some of these challenges of the 5G RAN systems. However, the research activities defining specific technical advancements for 5G RAN systems are yet to continue in the next half decade before specifications for standardization and commercialization are concluded. Motivated by the limited number of existing surveys of such technical advancements in a broader perspective (i.e., interference, spectrum-efficient, and energy-efficient management schemes), this paper seeks to take stock of state-of-the-art (SOTA) on such technical developments. Our attention focuses on relevant radio interference and resource management (RIRM) schemes that have been proposed in the last five years. Our contribution lies in the analysis, synthesis, and summarized alignments of the conventional RIRM schemes toward overcoming the identified challenges for the 5G RAN systems. Finally, the review highlights a number of open research issues deduced from recently proposed RIRM schemes.National Research Foundation (South Africa
Designing reconfigurable manufacturing systems using reconfigurable object Petri nets
No full textIn reconfigurable manufacturing systems (RMSs), the structure of the system can be changed during its execution. This reconfiguration can be triggered by several motivations: a new requirement in the production process, avoiding some problems caused by machines breakdowns, etc. RMSs are characterised by their flexibility which guarantees productivity and efficiency. However, their design is more complicated and needs new techniques and paradigms. The use of high level Petri nets (PNs) offers the ability to design these systems and to analyse their properties. In this article, the authors apply reconfigurable object nets (RONs) for the modelling, simulation and analysis of RMSs. Indeed, a formal method is proposed, where the reconfiguration process is specified explicitly as a graph transformation, the simulation is realised using the RON-tool, and the analysis exploits the TINA-tool (timed nets analyser tool).National Research Foundation (South Africa
Fully human MAP-fusion protein selectively targets and eliminates proliferating CD64+ M1 macrophages
No full textClassical immunotoxins compromise a binding component (for example, a ligand, antibody or fragment thereof) and a cytotoxic component, usually derived from bacteria or plants (for example, Pseudomonas exotoxin A or ricin). Despite successful testing in vitro, the clinical development of immunotoxins has been hampered by immunogenicity and unsatisfactory safety profiles. Therefore, research has focused on fully human pro-apoptotic components suitable for the development of cytolytic fusion proteins (CFP). We recently reported that human microtubule-associated protein tau (MAP) can induce apoptosis when delivered to rapidly proliferating cancer cells. Here, we describe a new fully human CFP called H22(scFv)-MAP, which specifically targets CD64+ cells. We show that H22(scFv)-MAP can efficiently kill proliferating HL-60 pro-monocytic cells in vitro. In addition, the human CFP specifically eliminates polarized M1 macrophages in a transgenic mouse model of cutaneous chronic inflammation. Because M1 macrophages promote the pathogenesis of many chronic inflammatory diseases, targeting this cell population with H22(scFv)-MAP could help to treat diseases such as atopic dermatitis, rheumatoid arthritis and inflammatory bowel diseaseNational Research Foundation (South Africa
Fredholm theory in ordered Banach algebras
No full textSince its inception, Fredholm theory has become an important aspect of
spectral theory. Among the spectra arising within Fredholm theory is the
Weyl spectrum which has been intensively studied by several authors, both
in the operator case and in the general situation of Banach algebras.
The Weyl spectrum of a bounded linear operator T on a Banach space
X is the set T
K∈K(X) σ(T + K), where σ(T) denotes the spectrum of T and
K(X) the closed ideal of all compact operators on X. A recent result by E.
A. Alekhno shows that, if “Banach space" is replaced by an arbitrary complex
Banach lattice E, then the Weyl spectrum of T on E can be made more
precise, and takes on the form T
0≤K∈K(E) σ(T + K).
By an ordered Banach algebra (OBA) we mean a complex unital Banach algebra
A containing an algebra cone; that is, a subset C which contains the unit
of A and is closed under addition, multiplication and positive scalar multiplication.
As is well-known, the algebra of all bounded linear operators on
a complex Banach lattice is an important example of an OBA.
If A denotes an arbitrary OBA with algebra cone C, B a Banach algebra and
T : A → B a homomorphism with N(T) = {a ∈ A : Ta = 0} indicating the
null space of T, then the Weyl spectrum T
c∈N(T) σ(a + c) of a ∈ A is in general
strictly contained in the set T
c∈C∩N(T) σ(a + c) — see Example 4.1.13.
As a result of this, we investigate the latter set, which we shall refer to as
the upper Weyl spectrum of a ∈ A. In this work the concept of the upper Browder
spectrum of a will also be introduced and results related to these spectra
and the underlying sets of elements on which these spectra are defined will
be given.
This thesis aims to present initial steps taken in the effort of unifying the
theory of positivity in OBAs with the general Fredholm theory in Banach
algebras.National Research Foundatio
Nectar distribution and nectarivorous bird foraging behaviour at different spatial scales
No full textWhile foraging strategies of animals may be shaped by the distribution of their food resources, these strategies in turn also affect the ecology and evolution of their resources. In this regard, African systems, of all the different bird-pollination systems worldwide, have been least studied. I investigated the relationships between these aspects at population, community and landscape levels in the bird-pollination systems of the Cape Floristic Region. This biodiversity hotspot in the southwest of South Africa contains an unusually high number of bird-pollinated plant species relative to the number of pollinating bird species.
Chapter 2 describes how I experimentally tested which nectar resource traits affect sunbird foraging behaviour at the small scale within populations. Sunbirds’ behaviour was largely determined by visual signals and distances between nectar resources. The birds showed flower colour preferences, but no flower constancy (selective foraging only on one flower type).
The foraging behaviour of pollinators seems to influence plant community assembly. With the use of null models, I show in Chapter 3 that communities of Proteaceae, a diverse and dominant plant family in the Cape Floristic Region, are structured both by competition for and facilitation of pollination. This was deduced from the non-random structure of the plant communities with respect to pollination syndromes and style lengths, which are proxies of the degree of pollinator sharing and of interspecific pollen transfer.
While species traits were important driving forces of community assembly in natural habitat, I show in Chapter 4 that species and habitat traits may also be important factors structuring bird communities in novel environments such as human settlements. Through a questionnaire, I determined how well different species of nectarivorous birds are adjusting to urban environments and which traits facilitate and prevent this adjustment. Nectar-generalist birds were successful exploiters of urban resources and were most abundant in gardens with large vegetated areas, bird baths and feeders. Nectar-specialist birds were less successful at adjusting, due to their high dependence on nectar. The presence of sugar water feeders and the number of indigenous bird-pollinated plants in gardens best predicted the communities of nectar-specialist birds. All nectarivorous birds were negatively affected by dispersal barriers.
Lastly, in Chapter 5, I use biome-wide atlas databases for birds and proteas to show how nectar distribution affects bird abundances at a landscape scale. The non-significantly different flowering phenology patterns throughout the biome suggest that nectarivorous birds would not need to migrate seasonally. Instead, birds may be sustained within mountain ranges all year round by the complementary flowering of species of different genera. Low floral abundances in the dry months of the year may still produce resource bottlenecks and this may encourage birds to forage in areas of human settlement.
Though we have gained insight into some of the relationships between African nectarivorous birds and their nectar resource distributions in space and time, there is still much to learn. There is also an urgent need to understand the effects of land-use change on the long-term persistence of nectar-feeding birds of the Cape Floristic Region.National Research Foundatio
Comparison of the technical and economic feasibility of devulcanisation processes for recycling waste tyres in south africa
No full textThe problem of the accumulation of waste tyres is receiving increased attention in the 21st century as a result of environmental concerns as well as the economic undesirability of discarding the valuable materials still present in tyres at the end of their useful life. The difficulty associated with recycling waste tyres is linked to the stable thermoset network structure of the vulcanised rubber comprising the majority of a waste tyre’s mass.
The recovery of value from tyres via incineration for their relatively high calorific value has been a popular method of diverting tyres from landfills and stockpiles in the past, although newer methods such as pyrolysis and devulcanisation aim to recover more value than merely the energy content of tyres. Pyrolysis processes aim to recover and purify valuable chemicals generated by the thermal decomposition of the rubber compounds in tyres. Devulcanisation processes aim for the controlled breakdown of the vulcanised rubber network in such a way that the rubber regains its thermoplastic properties and can be moulded and revulcanised into new products, without a significant loss of the important mechanical properties associated with vulcanised rubber products.
The shortcomings identified in the literature include the lack of comparable technical data between devulcanisation technologies, and the near absence of any form of energy consumption and economic data associated with devulcanisation processes. This study aimed to identify promising devulcanisation technologies and address the shortcomings identified in the literature by generating comparable technical and economic data for the selected devulcanisation technologies. The devulcanisation technologies identified for further analysis included the extrusion-based mechanical and mechanochemical devulcanisation processes.
The experimental work showed that increasing extrusion temperature has a strong effect on increasing the extent of devulcanisation in both devulcanisation processes. Varying screw speed in the mechanical devulcanisation process showed a very weak effect on the extent of the devulcanisation reaction. Increasing concentration of the devulcanisation chemical in the mechanochemical devulcanisation process caused an increase in the extent of the reaction, although the effect was rather weak. Overall, the mechanochemical devulcanisation process resulted in a substantially higher selectivity for crosslink scission and therefore higher product quality in comparison to the mechanical devulcanisation process.
Economic analysis of the processes was conducted assuming various scales of operation from approximately 400 tons/year to 7000 tons/year, using scaled-up power consumption data generated during the experimental work. The mechanical devulcanisation process was found to be likely to outperform the mechanochemical devulcanisation process from an economic iii
perspective due to the high costs of the extra chemicals required for the mechanochemical devulcanisation process. It should be noted, however, that the economic analysis did not take into account the potentially higher market value of the reclaimed rubber produced by the mechanochemical devulcanisation process. Therefore, further market research will be required in order to come to a firm conclusion as to which process will be more economically viable. A sensitivity analysis also showed that the economics of both processes are very sensitive to the power consumption, which could be a major problem for devulcanisation processes in South Africa.National Research Foundatio
NRF Desmond Tutu doctoral training programme
No full textPresentations SA PhD Project Conference: Free State 25-26 February 2016
The influence of Methylphenidate Hydrochloride on the development of the forensically significant blow fly Chrysomya chloropyga (Diptera:Calliphoridae) in the Western Cape, South Africa
No full textForensic entomologists rely on insect development and successional data to estimate the post-mortem interval (PMI). Ante-mortem drug use prior to an individual's death may result in drug transmission to feeding insects and subsequent alteration of their development, thereby altering PMI estimates. This study investigated the influence of Ritalin (methylphenidate hydrochloride) (MPH) on the development of Chrysomya chloropyga. C. chloropyga larvae were reared on pig liver treated with MPH and exhibited a trend of expedited larval development and prolonged pupal development. Conservatively, the results suggest that MPH may expedite the larval stage by up to 17 hours and prolong the pupal stage by up to 16 hours. These preliminary findings suggest that, at the concentration investigated, MPH may alter the duration of C. chloropyga developmental stages, and consequently PMI estimates if MPH is not detected or its effects not considered. Furthermore, MPH was detected in both frozen and ethanol preserved specimens. MPH could still be detected from treated larvae, after 3.5 days incubation at ~30°C. This may suggest an improved stability of MPH in insects. Moreover, detection of MPH from ethanol preserved specimens suggests the qualitative toxicological utility of specimens maintained in this preservation liquid, despite stability and self-extraction concerns. These are the first entomotoxicological data on MPH generated for blow flies local to the Western Cape, South Africa.National Research Foundatio