1834 research outputs found
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Particle swarm optimization with crossover: a review and empirical analysis
No full textSince its inception in 1995, many improvements to the original particle swarm optimization (PSO) algorithm have been developed. This paper reviews one class of such PSO variations, i.e. PSO algorithms that make use of crossover operators. The review is supplemented with a more extensive sensitivity analysis of the crossover PSO algorithms than provided in the original publications. Two adaptations of a parent-centric crossover PSO algorithm are provided, resulting in improvements with respect to solution accuracy compared to the original parent-centric PSO algorithms. The paper then provides an extensive empirical analysis on a large benchmark of minimization problems, with the objective to identify those crossover PSO algorithms that perform best with respect to accuracy, success rate, and efficiencyNational Research Foundation (South Africa
Health-seeking behaviours of older black women living with non-communicable diseases in an urban township in South Africa
No full textBackground: Various studies have shown that non-communicable diseases (NCDs) especially diabetes and hypertension are prevalent among older women living in South African urban areas, placing a heavy burden on the healthcare system. This study aimed to understand the health-seeking behaviour, healthcare practices and prevalence of traditional herbal medicine (THM) use among older women self-reporting NCDs from the Prospective Urban Rural Epidemiology study (PURE). Method: A homogenous purposive sampling of PURE participants was used to recruit women who were 50 years or older (n = 250). Descriptive statistics were used to examine the number of NCDs reported by the study sample, health seeking behaviour and practices as well as THM use. Logistic regression was also employed to investigate possible associations between reported conditions and THM use or medical pluralism. Results: Within the study sample, 72 % self-reported an NCD. Of those with self-reported NCDs, 46 % had one, and 54 % had two or more NCDs. Those with NCDs usually visited public clinics (80 %), relied on doctors (90 %) and nurses (85 %) for health information, and mostly used conventional medicine (CM) to manage high blood pressure (81 %). About 30 % of those with NCDs indicated using THM, of whom 29 (53 %) reported practicing medical pluralism. Participants with dental problems (OR: 3.24, 95 % CI: 1.30–8.20), headaches (OR: 2.42, 95 % CI: 1.24–4.94), heart burn (OR: 2.30, 95 % CI: 1.18–4.48) and severe tiredness (OR: 2.05, 95 % CI: 1.08–3.99) were more likely to use THM. Anxiety and allergies increased the likelihood to practise medical pluralism by five and 20 times, respectively. Conclusion: Self-reported NCD with co-morbidities was prevalent among the participants in the study. Most of the study participants utilized state-owned clinics and hospitals for the management of their chronic conditions. THM use was not very common. However, among those who used THM, medical pluralism was prevalent. Family history was the most common reason for THM use, with many THM patrons utilizing these for treatment of a health condition. Older black women with anxiety and allergies were more likely to practise medical pluralism.National Research Foundation (South Africa
Nest predation and maternal care in the Nile crocodile (Crocodylus niloticus) at Lake St Lucia, South Africa
No full textInformation regarding nest predation, nest abandonment, and maternal care in the Nile crocodile (Crocodylus niloticus) is largely restricted to anecdotal observations, and has not been studied quantitatively. Consequently, we investigated their nesting biology using camera-traps over four years at Lake St Lucia, South Africa. We obtained 4305 photographs (daylight captures = 90.1%, nocturnal = 9.9%) of 19 nest-guarding females. Of 19 monitored nests, 37% were raided by predators (mean = 12.1 ± 6.2 days subsequent to camera placement). All females returned to their nests following first predation, and on average returned three times between predator raids before nest abandonment. Water monitors (Varanus niloticus) and marsh mongoose (Atilax paludinosus) were the main egg predators. Nesting raids lasted 5.9 ± 1.6 days. Diurnally females were seldom on the nest, except during cool/cloudy weather or rain, preferring to guard from nearby shade. Females defended nests aggressively against non-human intruders. Five Nile crocodile females were observed liberating their hatchlings from nests. A detailed sequence of a mother excavating and transporting hatchlings revealed 13 excursions between nest and water over 32.5 h. This, after months of continual nest attendance and defence, is illustrative of the high level of maternal care in Nile crocodiles. Camera-trapping is an effective, non-invasive method for further crocodile nesting behaviour research.National Research Foundation (South Africa
HI observations of galaxies in the southern filament of the Virgo Cluster with the SKA Pathfinder KAT-7 and the WSRT
No full textWe map the Hi distribution of galaxies in a ∼1.5∘×2.5∘ region located at the virial radius south of the Virgo cluster using the KAT−7 and the WSRT interferometers. Because of the different beam sizes of the two telescopes, a similar column density sensitivity of NHi∼1018cm−2 was reached with the two observations over 16.5 km/s. We pioneer a new approach to combine the observations and take advantage of their sensitivity to both the large and small scale structures. Out to an unprecedented extent, we detect an Hi tail of ∼60 kpc being stripped off NGC 4424, a peculiar spiral galaxy. The properties of the galaxy, together with the shape of the tail, suggest that NGC 4424 is a post-merger galaxy undergoing a ram pressure stripping as it falls towards the centre of the Virgo Cluster. We detect a total of 14 galaxies and 3 Hi clouds lacking optical counterparts. One of the clouds is a new detection with an Hi mass of 7×107M⊙ and a strong Hi profile with W50=73 km/s. We find that 10 out of the 14 galaxies present Hi deficiencies not higher than those of the cluster's late spirals, suggesting that the environmental effects are not more pronounced in the region than elsewhere in the cluster.National Research Foundation (South Africa
A Multi-frequency analysis of dark matter annihilation interpretations of recent anti-particle and γ-ray excesses in cosmic structures
No full textThe Fermi-LAT observation of a gamma-ray excess from the galactic-centre, as well as the PAMELA, AMS, and AMS-2 anti-particle excesses, and the recent claim of a Fermi-LAT excess in the Reticulum-2 dwarf galaxy have been put forward as signatures compatible with of neutralino dark matter. These are of particular interest as the neutralino annihilation models which fit these observations might have observable consequences from radio to gamma-ray emission. Since dark matter is expected to be a major matter constituent of cosmic structure, these multi-frequency consequences should also be common to structures across the mass spectrum. Thus, in this work we make predictions for the multi-frequency spectra of three well-known sources dominated by dark matter, e.g. the Coma cluster, the galaxy M81, and the Draco dwarf galaxy using models favoured by dark matter interpretations of the aforementioned observations. We pay special attention to the consequences for these models when their cross-sections are renormalised to reproduce the recent gamma-ray excess observed in the Reticulum-2 dwarf galaxy, which throw a dark matter interpretation of this excess into doubt. We find that the multi-frequency data of Coma and Draco disfavour the dark matter interpretation of the AMS, PAMELA and Fermi anti-particle excess. Models derived from Fermi-LAT galactic centre observations present somewhat lesser conflicts. We determine the detection prospects of the Square Kilometre Array, the Cherenkov Telescope Array, as well as the ASTROGAM and ASTRO-H satellites for the studied models. This demonstrates that ASTRO-H is well positioned to probe the X-ray emissions from neutralino annihilation. Thus, multi-frequency observation with the next generation experiments will allow for unprecedented sensitivity to the neutralino parameter space.National Research Foundation (South Africa
Increasing numbers and intercontinental spread of invasive insects on eucalypts
No full textNative to Australasia, Eucalyptus (sensu lato) is one of the most planted genera of trees in the world. However, the sustainability of Eucalyptus species as plantation trees in non-native areas is increasingly threatened by the introduction and spread of Eucalyptus-feeding insects from Australia. We examine patterns and potential trends with respect to the global spread of Eucalyptus-feeding insects. Likely pathways of introduction and drivers of the rapid distribution of these insects, as well as management options are considered. The rate of introductions is shown to have increased nearly fivefold since the 1980s. As a result, the number of non-native pests of eucalypts outside of Australia has doubled in less than three decades. Furthermore, the rate of secondary spread among continents has also increased. Surprisingly, we found no association between area planted and the number of pests or new introductions. Only a small number of countries have been the points of first detection outside the native range; these countries have acted as bridgeheads to other regions. Quarantine regulations aimed at reducing the spread of invasive organisms appear to be ineffective at a global scale, and pathways allowing these invasions to occur are poorly understood or unknown. An expanded suite of management options are needed to provide resilience against the rapid accrual and homogenization of eucalypt pests, thereby ensuring the sustainability of eucalypt forestry worldwide.National Research Foundation (South Africa
An exploration of human well-being bundles as identifiers of ecosystem service use patterns
No full textWe take a social-ecological systems perspective to investigate the linkages between ecosystem services and human well-being in South Africa. A recent paper identified different types of social-ecological systems in the country, based on distinct bundles of ecosystem service use. These system types were found to represent increasingly weak direct feedbacks between nature and people, from rural “green-loop” communities to urban “red-loop” societies. Here we construct human well-being bundles and explore whether the well-being bundles can be used to identify the same social-ecological system types that were identified using bundles of ecosystem service use. Based on national census data, we found three distinct well-being bundle types that are mainly characterized by differences in income, unemployment and property ownership. The distribution of these well-being bundles approximates the distribution of ecosystem service use bundles to a substantial degree: High levels of income and education generally coincided with areas characterised by low levels of direct ecosystem service use (or red-loop systems), while the majority of low well-being areas coincided with medium and high levels of direct ecosystem service use (or transition and green-loop systems). However, our results indicate that transformations from green-loop to red-loop systems do not always entail an immediate improvement in well-being, which we suggest may be due to a time lag between changes in the different system components. Using human well-being bundles as an indicator of social-ecological dynamics may be useful in other contexts since it is based on socio-economic data commonly collected by governments, and provides important insights into the connections between ecosystem services and human well-being at policy-relevant sub-national scales.National Research Foundation (South Africa
Surfactant protein-d is essential for immunity to helminth infection
No full textPulmonary epithelial cell responses can enhance type 2 immunity and contribute to control of nematode infections. An important epithelial product is the collectin Surfactant Protein D (SP-D). We found that SP-D concentrations increased in the lung following Nippostrongylus brasiliensis infection; this increase was dependent on key components of the type 2 immune response. We carried out loss and gain of function studies of SP-D to establish if SP-D was required for optimal immunity to the parasite. N. brasiliensis infection of SP-D-/- mice resulted in profound impairment of host innate immunity and ability to resolve infection. Raising pulmonary SP-D levels prior to infection enhanced parasite expulsion and type 2 immune responses, including increased numbers of IL-13 producing type 2 innate lymphoid cells (ILC2), elevated expression of markers of alternative activation by alveolar macrophages (alvM) and increased production of the type 2 cytokines IL-4 and IL-13. Adoptive transfer of alvM from SP-D-treated parasite infected mice into naïve recipient’s enhanced immunity to N. brasiliensis. Protection was associated with selective binding by the SP-D carbohydrate recognition domain (CRD) to L4 parasites to enhance their killing by alvM. These findings are the first demonstration that the collectin SP-D is an essential component of host innate immunity to helminths.National Research Foundation (South Africa
IL-13 signals independent of IL-4 receptor-alpha chain to drive ovalbumin-induced dermatitis
No full textAtopic dermatitis (AD) is an allergic skin condition that can result from intrinsic genetic factors or repetitive occupational damage. Disruption of the skin barrier leads to sensitization to allergens followed by local inflammation (Leung et al., 2004, Pigatto et al., 1992). Strong evidence has shown that the T helper-2 (Th2) cytokine, IL-13, is the dominant disease-causing factor in the pathogenesis of AD in mice (Nieuwenhuizen et al., 2009, Sivaprasad et al., 2010, Tazawa et al., 2004). Hence, it is possible that patients with AD would benefit from treatments specifically targeting IL-13 signaling pathways. However, current treatment strategies are limited to broader therapies, such as emollients, topical glucocorticoids, and calcineurin inhibitors (Beck et al., 2014, De Benedetto et al., 2012, Gittler et al., 2012). A recent study by Beck et al. (2014), which used the monoclonal antibody dupilumab to block IL-4 receptor-alpha (IL-4Rα) signaling, showed promise in targeting specific immunological pathways. Until recently, IL-13 was thought to signal only through the IL-4Rα/IL-13Rα1 complex; however, recent data suggest that IL-13 may also signal via IL-13Rα2, previously known as a decoy receptor. In AD, the signaling pathway of IL-13 remains to be defined. In this study we addressed this problem by using a combination of IL-4Rα–deficient mice that lacked or overexpressed IL-13 to determine if IL-13 can signal independently of the IL-4Rα chain to mediate AD. Our results may have potential implications for therapeutic strategies, such as using IL-4Rα–antagonists to treat the disease.National Research Foundation (South Africa
Virgins and virtue: African masculinities and femininities in the making of teenage sexual cultures
No full textIn KwaZulu-Natal, South Africa, the ways in which teenage Africans construct sexuality is imbued with high cultural value that honours virginity and female respectability. Of what significance, do the cultural practices that endorse chastity and virginity play in the lives of 16- turning 17-year-old teenage Africans in a township context of KwaZulu-Natal? By drawing on focus-group discussions with teenage men and women, this article explores the saliency of virginity and cultural constructs in African teenage men and women’s account of sexuality. The article argues that African teenagers’ defence of virginity is grounded in and inspired by deep cultural connections and is an important resource to claim respectability, status and an identity. Both teenage men and women centred on and idealized virginity and respect. In doing so their meanings weave into gendered patterns of inequalities. Implications that take heed of local cultural patterns in construction of teenage sexualities are discussed in the conclusion.National Research Foundation (South Africa