1834 research outputs found
Sort by
Discrete time analysis of cognitive radio networks with imperfect sensing and saturated source of secondary users
No full textSensing is one of the most challenging issues in cognitive radio networks. Selection of sensing parameters raises several tradeoffs between spectral efficiency, energy efficiency and interference caused to primary users (PUs). In this paper we provide representative mathematical models that can be used to analyze sensing strategies under a wide range of conditions. The activity of PUs in a licensed channel is modeled as a sequence of busy and idle periods, which is represented as an alternating Markov phase renewal process. The representation of the secondary users (SUs) behavior is also largely general: the duration of transmissions, sensing periods and the intervals between consecutive sensing periods are modeled by phase type distributions, which constitute a very versatile class of distributions. Expressions for several key performance measures in cognitive radio networks are obtained from the analysis of the model. Most notably, we derive the distribution of the length of an effective white space; the distributions of the waiting times until the SU transmits a given amount of data, through several transmission epochs uninterruptedly; and the goodput when an interrupted SU transmission has to be restarted from the beginning due to the presence of a PUNational Research Foundation (South Africa
Factors influencing health behaviours in response to the air quality health index: a cross-sectional study in Hamilton, Canada
No full textResearch associating adverse health effects with air pollution exposure is robust. Public health authorities recognize the need to implement population health strategies that protect public health from air pollution exposure. The Air Quality Health Index (AQHI) is a public health initiative that is intended to protect the public's health from exposure to air pollution. The aim of this research was to identify and explain factors influencing AQHI adoption at the individual level and to establish intervention strategies. A cross-sectional survey with both quantitative and qualitative questions was administered in Hamilton, Ontario, Canada, during the months of June to October 2012. Logistic regression and the Health Belief Model are used to explore the data. Demographics (gender, age, education, and area of residence), knowledge/understanding, and individual risk perceptions (neighbourhood air effects on health) were found to be significant predictors of AQHI adoption. The perceived benefits of AQHI adoption included protection of health for self and those cared for via familial and (or) occupational duties, whereas the perceived barriers of AQHI adoption included lack of knowledge about where to check and lack of time required to check and follow AQHI health messages. Also, self-efficacy was uncovered as a factor influencing AQHI adoption. Accordingly, increases in AQHI adoption could be achieved via increasing AQHI knowledge among low socioeconomic status females, communicating the benefits of AQHI adoption to “at-risk” populations and implementing supports for males to follow AQHI health messages.National Research Foundation (South Africa
Female reproductive activity and its endocrine correlates in the African lesser bushbaby, Galago moholi
No full textSteroid hormones play an important role in female reproductive physiology and behaviour and are often used to monitor important female reproductive events. However, such studies are often attempted on captive populations alone, delivering limited data. One such example is the African lesser bushbaby, Galago moholi, for which contradicting observational data exist between captive and free-ranging populations, while hormonal analyses have only been obtained from a single captive population. To extend and rectify the limited information, we monitored faecal progestagen and oestrogen metabolite levels across various important life history stages of both captive and free-ranging G. moholi. We additionally recorded changes in vaginal state as well as the occurrence of reproductive and aggressive behaviour throughout the study. Data from our captive population revealed an ovarian cycle length of 33.44 ± 0.59 days (mean ± SD), with follicular and luteal phases of 14.2 ± 1.0 and 19.1 ± 1.5 days, respectively, and an average pregnancy length of 128 ± 3.3 days. The initiation of female reproductive activity was closely linked to an oestrus-related increase in faecal oestrogen metabolite levels. Four of the seven captive females monitored in our study conceived during the May mating period, with one additional female fertilised in September, supporting the idea that the September mating period functions as a back-up for female G. moholi. Identified benchmark faecal progestagen metabolite levels (non-pregnant: >1 µg/g dry weight (DW), pregnant: >9 µg/g DW) should help researchers to determine pregnancy status of randomly wild-caught females in even a cross-sectional study setup.National Research Foundation (South Africa
Sleep in the Cape Mole Rat: A Short-Sleeping Subterranean Rodent.
No full textThe Cape mole rat Georychus capensis is a solitary subterranean rodent found in the western and southern Cape of South Africa. This approximately 200-gram bathyergid rodent shows a nocturnal circadian rhythm, but sleep in this species is yet to be investigated. Using telemetric recordings of the electroencephalogram (EEG) and electromyogram (EMG) in conjunction with video recordings, we were able to show that the Cape mole rat, like all other rodents, has sleep periods composed of both rapid eye movement (REM) and slow-wave (non-REM) sleep. These mole rats spent on average 15.4 h awake, 7.1 h in non-REM sleep and 1.5 h in REM sleep each day. Cape mole rats sleep substantially less than other similarly sized terrestrial rodents but have a similar percentage of total sleep time occupied by REM sleep. In addition, the duration of both non-REM and REM sleep episodes was markedly shorter in the Cape mole rat than has been observed in terrestrial rodents. Interestingly, these features (total sleep time and episode duration) are similar to those observed in another subterranean bathyergid mole rat, i.e. Fukomys mechowii. Thus, there appears to be a bathyergid type of sleep amongst the rodents that may be related to their environment and the effect of this on their circadian rhythm. Investigating further species of bathyergid mole rats may fully define the emerging picture of sleep in these subterranean African rodents.National Research Foundation (South Africa
SEAmester-South Africa's first class afloat
No full textThe Department of Science and Technology's (DST's) 10-year Global Change Grand Challenge programme requires platforms to 'attract young researchers to the region and retain them by exciting their interest in aspects of global change; while developing their capacity and professional skills in the relevant fields of investigation'1. In addition, in July 2014, President Zuma officially launched Operation Phakisa and announced that a key target of this Oceans Economy initiative would be 'for the Department of Higher Education and Training to drive alignment between theoretical and workplace learning'2.
SEAmester - South Africa's recently established Class Afloat - achieves just that. SEAmester introduces marine science as an applied and cross-disciplinary field to students who have shown an affinity for core science disciplines. It identifies with government's National Development Plan3 on education, training and innovation - critical to South Africa's long-term development and investment in this sector.
SEAmester has a long-term vision aimed at building capacity within the marine sciences by coordinating and fostering cross-disciplinary research projects and achieving this goal through a highly innovative programme. The strength of SEAmester is that postgraduate students combine theoretical classroom learning with the application of this knowledge through ship-based, and more importantly, hands-on research. The state-of-the-art research vessel, SA Agulhas II, provides an ideal teaching and research platform for this programme; its size, comfort and shipboard facilities allow large groups of students and lecturers to productively interact over a period of 10 days.National Research Foundation (South Africa
South Africa in the Antarctic Circumnavigation Expedition: A multi-institutional and interdisciplinary scientific project.
No full textThe polar regions are more critically affected by climate change than any other region on our planet.1,2 On the Antarctic continent and in its surrounding oceans, the effects of climate change are likely to be dramatic,3 and include large-scale catastrophic ice melt, loss of habitat and biodiversity, and global sea level rise. The 'Southern Ocean' refers to the region where Atlantic, Indian and Pacific Ocean waters come together to encircle Antarctica. These waters connect the different ocean basins by linking the shallow and deep limbs of the global ocean current system ('overturning circulation') and play a critical role in storing and distributing heat and carbon dioxide (CO2). The Southern Ocean thus regulates not only the climate of the Antarctic, but of the entire earth system.1,4 By extension, the capacity of the global ocean to ameliorate earth's changing climate is strongly controlled by the Southern Ocean.
Marine phytoplankton (microscopic plants inhabiting the sunlit upper ocean) convert CO2 (an inorganic form of carbon) dissolved in surface waters into organic carbon through photosynthesis. This organic carbon fuels upper trophic levels such as fish, mammals and birds, and a portion sinks into the deep ocean where it remains stored for hundreds to thousands of years. This mechanism, which lowers the atmospheric concentration of CO2, is termed the 'biological pump'.5 The efficiency of the global ocean's biological pump is currently limited by the Southern Ocean, where the macronutrients (nitrate and phosphate) required for photosynthesis are never fully consumed in surface waters. In theory, increased consumption of these nutrients could drive higher organic carbon removal to the deep ocean, enhancing the oceanic uptake of atmospheric CO2. Indeed, more complete consumption of Southern Ocean nutrients is a leading hypothesis for the decrease in atmospheric CO2 that characterised the ice ages.6
Despite the global importance of the Southern Ocean, knowledge of the controls on and interactions among the physical, chemical and biological processes operating in Antarctic ecosystems is limited, largely because of a scarcity of in-situ observational data, compounded by the challenge of integrating siloed scientific fields. Given predictions that diverse aspects of Southern Ocean physics and carbon biogeochemistry are likely to change in the coming decades, a transdisciplinary approach to studying Antarctic systems is critical.National Research Foundation (South Africa
Modernising, Upgrading and Recommissioning the Indoor Antenna Range at Stellenbosch University
No full textThis paper describes the upgrade to the indoor antenna range at Stellenbosch University. The previous measurement process relied upon obsolescent control equipment and undocumented software; it was critical that these be replaced. Now, the antenna range supports three measurement types using a commercial integrated measurement control system that provides support for high gain and low gain antennas over a wide frequency range. These are spherical near-field, planar near-field and conventional far-field measurements, with the potential to implement cylindrical near-field. The antenna range potentially supports operations from 1 GHz up to 26.5 GHz, though the currently available probes do not cover the full band. The main physical upgrade was performed during October 2014, though investigations had already begun in 2011, and some supplementary tasks were still ongoing at the time of writing. Several innovative commissioning tests have been undertaken, some of which are only possible with near-field metrology, and these are described in the paper.National Research Foundation (South Africa
MonteCarlo simulation of a slotscanning digital mammography system for tomosynthesis
No full textBACKGROUND: Digital breast tomosynthesis (DBT) reconstructs planar slices of the breast based on two-dimensional angular projections. Early studies and clinical trials show that DBT is an improvement over full field digital mammography (FFDM) because it provides the radiologist with better image quality and more information.
OBJECTIVE: This paper presents a simulation system to model the performance of a slot-scanning FFDM and DBT system.
METHODS: A tissue-equivalent three dimensional (3D) breast phantom was constructed, validated for slot-scanning digital mammography and used in simulating digital breast tomosynthesis. The simulation system was validated by comparing images acquired with a slot-scanning mammography machine with simulated phantom images, using the edge-test method and image quality metrics modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE). Different two-dimensional (2D) projections of the 3D phantom were simulated and the phantom was reconstructed using filtered back projection.
RESULTS: Image quality metrics showed equivalence between simulated and real images.
CONCLUSIONS: The simulation tool is suitable for slot-scanning FFDM and DBT and may be used for the design and comparison of mammography systems.National Research Foundation (South Africa
Minimally invasive transcatheter aortic valve implantation for the treatment of rheumatic heart disease in developing countries
No full textIntroduction: The treatment of rheumatic heart disease presents a medical and surgical challenge, particularly in developing countries, where the disease is prevalent. Most of these countries find it prohibitively expensive to import heart valve prostheses that are required for treatment and are largely manufactured in the United States and Europe. Even if the valves were available, the absence of facilities to conduct open-heart surgery for valve replacement results in many people from developing countries dying needlessly of the disease. To address this problem, transcatheter aortic valve implantation, an emerging, minimally invasive, treatment strategy for rheumatic heart disease, has been proposed.
Areas covered: This paper reviews the literature on current valve technologies in use globally, and focuses on a minimally invasive transcatheter aortic valve implantation device and aortic valve prosthesis that have been developed by Strait Access Technologies Holdings in South Africa.
Expert commentary: This new technology holds the potential of making available heart valve replacements to millions of patients in the developing world who would otherwise have no recourse to treatment.National Research Foundation (South Africa
Comparison of MOF-5 and Cr-MOF-derived carbons for hydrogen storage applications
No full textNanoporous carbons which possess high surface areas and narrow pore size distributions have become one of the most important classes of porous materials with potential to be utilized for hydrogen storage. In recent times, several metal–organic frameworks (MOFs) have been shown to be promising precursors for creating nanoporous carbons due to their high surface areas and tunable pore sizes. The pore structure and surface area of the resultant carbon materials can be tuned simply by changing the calcination temperature. In this work, a zinc-based MOF (MOF-5) and a chromium-based MOF (Cr-MOF) were both used as precursors for syntheses of nanoporous carbons by the direct carbonization technique at different temperatures. The resultant carbon nanostructure from MOF-5 possessed higher surface area, higher pore volume and enhanced hydrogen storage capacity as compared to pristine MOF. Meanwhile, the derived carbons from Cr-MOF displayed lower surface areas, pore volumes and hydrogen uptake than the parent MOF due to the formation of chromium oxide and carbide species in the pores of the Cr-MOF-derived carbonsNational Research Foundation (South Africa