1834 research outputs found
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Inertia control strategies for particle swarm optimization: too much momentum, not enough analysis
No full textParticle swarm optimization (PSO) is a population-based, stochastic optimization technique inspired by the social dynamics of birds. The PSO algorithm is rather sensitive to the control parameters, and thus, there has been a significant amount of research effort devoted to the dynamic adaptation of these parameters. The focus of the adaptive approaches has largely revolved around adapting the inertia weight as it exhibits the clearest relationship with the exploration/exploitation balance of the PSO algorithm. However, despite the significant amount of research efforts, many inertia weight control strategies have not been thoroughly examined analytically nor empirically. Thus, there are a plethora of choices when selecting an inertia weight control strategy, but no study has been comprehensive enough to definitively guide the selection. This paper addresses these issues by first providing an overview of 18 inertia weight control strategies. Secondly, conditions required for the strategies to exhibit convergent behaviour are derived. Finally, the inertia weight control strategies are empirically examined on a suite of 60 benchmark problems. Results of the empirical investigation show that none of the examined strategies, with the exception of a randomly selected inertia weight, even perform on par with a constant inertia weight.National Research Foundation (South Africa
Patient diagnostic rate as indicator of tuberculosis case detection, South Africa
No full textTo address the uncertainty of the indirectly measured tuberculosis case detection rate, we used survey data stratified by HIV status to calculate the patient diagnostic rate, a directly measurable indicator, in 8 communities in South Africa. Rates were lower among HIV-negative than HIV-positive persons. Tuberculosis programs should focus on HIV-negative persons.National Research Foundation (South Africa
HIV prevention and care-seeking behaviour among female sex workers in four cities in India, Kenya, Mozambique and South Africa
No full textAbstract
Objective: To identify gaps in the use of HIV prevention and care services and commodities for female sex workers, we conducted a baseline cross‐sectional survey in four cities, in the context of an implementation research project aiming to improve use of sexual and reproductive health services.
Methods
Using respondent‐driven sampling, 400 sex workers were recruited in Durban, 308 in Tete, 400 in Mombasa and 458 in Mysore and interviewed face‐to‐face. RDS‐adjusted proportions were estimated by nonparametric bootstrapping and compared across cities using post hoc pairwise comparison.
Results: Condom use with last client ranged from 88.3% to 96.8%, ever female condom use from 1.6% to 37.9%, HIV testing within the past 6 months from 40.5% to 70.9%, receiving HIV treatment and care from 35.5% to 92.7%, care seeking for last STI from 74.4% to 87.6% and having had at least 10 contacts with a peer educator in the past year from 5.7% to 98.1%. Many of the differences between cities remained statistically significant (P < 0.05) after adjusting for differences in FSWs' socio‐demographic characteristics.
Conclusion: The use of HIV prevention and care by FSWs is often insufficient and differed greatly between cities. Differences could not be explained by variations in socio‐demographic sex worker characteristics. Models to improve use of condoms and HIV prevention and care services should be tailored to the specific context of each site. Programmes at each site must focus on improving availability and uptake of those services that are currently least used.National Research Foundation (South Africa
Age differences between sexual partners, behavioural and demographic correlates, and HIV infection on Likoma Island, Malawi
No full textPatterns of age differences between sexual partners – “age-mixing” – may partially explain the magnitude of HIV epidemics in Sub-Saharan Africa. However, evidence of age-disparity as a risk factor for HIV remains mixed. We used data from a socio-centric study of sexual behaviour in Malawi to quantify the age-mixing pattern and to find associations between relationship characteristics and age differences for 1,922 participants. Three age difference measures were explored as predictors of prevalent HIV infection. We found that for each year increase in male participant age, the average age difference with their partners increased by 0.26 years, while among women it remained approximately constant around 5 years. Women in the study had larger within-individual variation in partner ages compared to men. Spousal partnerships and never using a condom during sex were associated with larger age differences in relationships of both men and women. Men who were more than five years younger than their partners had 5.39 times higher odds (95% CI: 0.93–31.24) of being HIV-infected than men 0–4 years older. The relationship between HIV-infection and age-asymmetry may be more complex than previously described. The role that women play in HIV transmission should not be under-estimated, particularly in populations with large within-individual variation in partner ages.National Research Foundation (South Africa
Conservation of scattered energy and asymmetry factor in the new rotationally symmetric spherical discretisation scheme
No full textA Rotationally Symmetric Spherical Discretisation (RSSD) technique has recently been developed for the discretisation of scattering phase functions in the Discrete Ordinates Method (DOM) in a consistent and rational manner. RSSD has inherent energy conservation, is suitable for any quadrature scheme used, minimising run-time matrix calculation, and to date has been used for the S4, S6 and S8 ordinate sets. In this follow-up paper, the RSSD boundary intervals for the four weightings of the S10 ordinate set are presented. The effect of asymmetry factor g and angular resolution of the discrete input scattering phase function distribution “grid” on final RSSD errors (in scattered energy conservation and calculated asymmetry factor) is explored, making use of the Henyey–Greenstein (HG) family of distributions. It is shown that the RSSD scattered energy error is a strong function of the grid resolution, indicating that can be controlled down to user-required levels by judicious choice of grid resolution and by local grid refinement in regions of steep gradients and peaks in the scattering phase function distribution (in this paper error levels as low as 0.002% have been achieved). RSSD asymmetry factor error behaves differently to , however, displaying a strong grid resolution dependence in a “grid sensitivity zone” of combinations of coarse grid resolution and high values of prescribed g (for the HG family of scattering phase functions, above g values of 0.9, 0.95 and 0.98 for grid angular resolutions of 1°, 0.5° and 0.25° respectively). Outside of the “grid sensitivity zone” g error is insensitive to grid resolution and achieves maximum (positive and negative) values of between −2.7% and 1% between prescribed g values of 0.7 and 0.9. This band decreases to a range from −1% to 1% for the S4, S6 and S10 ordinate sets. The grid resolution conclusions are supported by examining RSSD discretisation for two real scattering phase function distributions: for a diffusely reflecting large sphere with an asymmetry factor of −0.4444, grid angular resolutions of 2°, 1°, 0.5° and 0.25° resulted in the decreasing maximum values of 0.0449%, 0.0136%, −0.0050% and −0.0015% respectively, but near-constant maximum values of −1.225%, −1.239%, −1.247% and −1.250% respectively, while for a transparent large sphere with an asymmetry factor of 0.660, grid angular resolutions of 1°, 0.5° and composite 0.5°/0.25° resolution resulted in the decreasing maximum values of 0.0685%, −0.0402% and −0.0046% respectively and near-constant maximum values of −1.286%, −1.310% and −1.313% respectively.National Research Foundation (South Africa
The Comparative Gastrointestinal Morphology of Jaculus jaculus (Rodentia) and Paraechinus aethiopicus (Erinaceomorpha)
No full textJaculus jaculus (Lesser Egyptian jerboa) and Paraechinus aethiopicus (Desert hedgehog) are small mammals which thrive in desert conditions and are found, among others, in the Arabian Peninsula. Jaculus jaculus is omnivorous while P. aethiopicus is described as being insectivorous. The study aims to describe the gastrointestinal tract (GIT) morphology of these animals which differ in diet and phylogeny. The GITs of J. jaculus (n = 8) and P. aethiopicus (n = 7) were weighed, photographed, and the length, basal surface areas, and luminal surface areas of each of the anatomically distinct gastrointestinal segments were determined. The internal aspects of each area were examined and photographed while representative histological sections of each area were processed to wax and stained using haematoxylin and eosin. Both species had a simple unilocular stomach which was confirmed as wholly glandular on histology sections. Paraechinus aethiopicus had a relatively simple GIT which lacked a caecum. The caecum of J. jaculus was elongated, terminating in a narrow cecal appendix which contained lymphoid tissue on histological examination. The internal aspect of the proximal colon of J. jaculus revealed distinct V-shaped folds. Stomach content analysis of J. jaculus revealed mostly plant and seed material and some insects, whereas P. aethiopicus samples showed plant material in addition to insects, indicating omnivorous feeding tendencies in areas where insects may be scarce.National Research Foundation (South Africa
Can Parallel Lines Ever Meet? The Strange Case of the International Standards on Sovereign Debt and Business and Human Rights
No full textSovereigns have a long history of defaulting on their debts. Despite the bitter lessons learned through this history, the international community has not yet developed an effective method for dealing with these events. As a result, each sovereign’s debt restructuring process is likely to be conflict ridden, inefficient and to have a high probability of resulting in a sub-optimal outcome. In fact, the risk of sub-optimal outcomes has increased as financial markets have become larger and more globalized so that sovereign debtors - at least those with access to financial markets - are able to borrow from a broader range of creditors. One consequence is that sovereign debt restructurings (SODRs), are difficult, often traumatic, experiences for the sovereign debtors and their populations, and frustrating and potentially costly for their creditors.
Given these high stakes, it is not surprising that efforts have been made over the past seventy years to improve the process. One recent manifestation of this effort has been the promulgation of a number of international norms and standards that either explicitly or implicitly are applicable to SODRs. Interestingly, the documents dealing with the SODR process all recognize that SODRs have substantial social and political effects in addition to their financial and economic consequences. In fact, they all appear to accept that the parties to the SODR will need to take these impacts into account in arranging a sustainable SODR. However, they do not provide detailed guidance to the parties on how they should deal with these social and political impacts in negotiating and agreeing on a sustainable SODR. This is surprising given the norms and standards that companies and states have developed for dealing with the social responsibilities of businesses, including in regard to human rights.
The seeming disconnect between the developments in regard to the SODR process and to business and human rights is intriguing, particularly because many of the world’s most significant financial institutions have publicly available human rights policies that, at least prima facie, are applicable to all their business operations and relations.
The disconnect between these two developments raises at least two questions. First, should the human rights and business standards be applied to the SODR process. Second, if they should be applied to the SODR process, how should they be applied? The primary purpose of this article is to answer these two questions. This exercise serves three purposes. First, it will enable us to see if these human rights and business standards can add value to SODRs in the sense of reducing their human rights costs without unduly increasing their financial costs. Second, it will provide some additional insight into how easily human rights law can be adapted to financial transactions specifically and to business more generally. Third, this exercise might help us better understand how to plug the gap in global economic governance that allows different actors in global governance to develop international standards on SODR and on business and human rights on parallel tracks that do not seem to communicate with each other.National Research Foundation (South Africa
β-Glucan exacerbates allergic airway responses to house dust mite allergen
No full textβ-(1,3)-Glucan is present in mould cell walls and frequently detected in house dust mite (HDM) faeces. β-Glucan exposure is thought to be associated with pulmonary allergic inflammation in mouse and man, although the published data are inconsistent. Here, we show that highly purified β-glucan exacerbates HDM-induced eosinophilic, T helper 2 type airway responses by acting as an adjuvant, promoting activation, proliferation and polarisation of HDM-specific T cells (1-Derβ T cells). We therefore provide definitive evidence that β-glucan can influence allergic pulmonary inflammation.National Research Foundation (South Africa
Role of IL-4 receptor α-positive CD4+ T cells in chronic airway hyperresponsiveness
No full textBACKGROUND: TH2 cells and their cytokines are associated with allergic asthma in human subjects and with mouse models of allergic airway disease. IL-4 signaling through the IL-4 receptor α (IL-4Rα) chain on CD4(+) T cells leads to TH2 cell differentiation in vitro, implying that IL-4Rα-responsive CD4(+) T cells are critical for the induction of allergic asthma. However, mechanisms regulating acute and chronic allergen-specific TH2 responses in vivo remain incompletely understood.
OBJECTIVE: This study defines the requirements for IL-4Rα-responsive CD4(+) T cells and the IL-4Rα ligands IL-4 and IL-13 in the development of allergen-specific TH2 responses during the onset and chronic phase of experimental allergic airway disease.
METHODS: Development of acute and chronic ovalbumin (OVA)-induced allergic asthma was assessed weekly in CD4(+) T cell-specific IL-4Rα-deficient BALB/c mice (Lck(cre)IL-4Rα(-/lox)) and respective control mice in the presence or absence of IL-4 or IL-13.
RESULTS: During acute allergic airway disease, IL-4 deficiency did not prevent the onset of TH2 immune responses and OVA-induced airway hyperresponsiveness or goblet cell hyperplasia, irrespective of the presence or absence of IL-4Rα-responsive CD4(+) T cells. In contrast, deficiency of IL-13 prevented allergic asthma, irrespective of the presence or absence of IL-4Rα-responsive CD4(+) T cells. Importantly, chronic allergic inflammation and airway hyperresponsiveness were dependent on IL-4Rα-responsive CD4(+) T cells. Deficiency in IL-4Rα-responsive CD4(+) T cells resulted in increased numbers of IL-17-producing T cells and, consequently, increased airway neutrophilia.
CONCLUSION: IL-4-responsive T helper cells are dispensable for acute OVA-induced airway disease but crucial in maintaining chronic asthmatic pathology.National Research Foundation (South Africa
High sensitivity phased array receivers for radio astronomy
No full textPhased arrays have a long history in radio astronomy. Large, sparse synthesis arrays have been in use for decades to capture high-resolution images of deep space objects. More recent work has extended the range of applications to other types of arrays, including aperture arrays (AAs) and phased array feeds (PAFs) for multibeam reflector antennas. The extreme sensitivity required for astronomical instrumentation is driving advances in numerical electromagnetic modeling, design optimization of large arrays, low noise amplifiers, minimization of receiver noise, cryogenic PAFs, array calibration, optimal beamforming, interferometric imaging, and array signal processing algorithms for radio-frequency interference mitigation. We give an overview of research progress, current and planned array-based instruments, and open challenges in these areas related to the new generation of sparse arrays, PAFs, and AAs that are in development for astronomical observatories around the world.National Research Foundation (South Africa