1834 research outputs found
Sort by
The influence of environmental variability on the catch of chokka, Loligo reynaudii, off the coast of South Africa
No full textGlobally, cephalopod fisheries are being relied on more heavily due to the depletion of longer-lived teleost species. The South African chokka squid (Loligo reynaudii) fishery is a case in point. Although previously numerous squid were often caught as bycatch, the fishery has officially been in place since 1985. Since the inception of the chokka fishery in South Africa, several studies have investigated the relationship between environmental drivers and annual chokka squid catch, with varying degrees of success. Recently, in 2013, chokka squid catches hit a record low, prompting resurgence in the topic of the squid environment-catch relationship. This study was initiated in an attempt to provide a quantitative relationship between the chokka squid catch and environmental variability, and to build a predictive model that could be used in fisheries management strategies. Historical data were obtained from various sources and included the mean and standard deviation in ocean bottom temperature; the mean and standard deviation in sea surface temperature; the maximum and minimum as well as the variation in wind speed; the mean, predominant and standard deviation in wind direction; the mean and standard deviation in atmospheric pressure; the mean chlorophyll concentration; the number of upwelling events; the hours of easterly winds blowing per day; and two large variation-in-climate indices, namely, the oceanic Nino index and the Antarctic Oscillation index. The monthly catch data were also provided. These data were initially analysed for inter-annual and intra-annual cyclic trends and followed by analysis of the delay in response of catch to the environmental variables, anticipating some impact on the different stages of the chokka life cycle. These lagged data were incorporated into a negative binomial generalised linear model, as well as a generalised additive model, which revealed a strong relationship (r²=0.707) between the catch and environmental variability. The inclusion of all the parameters was necessary; however, the mean bottom temperature and the standard deviation in sea surface temperature were the only parameters that had a significant effect on the catch. These results were used to build a predictive model that indicated that, although the relationship was strong, the ability of the model to predict catch was weak, particularly from the year 2005 onwards.National Research Foundatio
The use of 3D geovisualisations for urban design: The case of informal settlement upgrading in South Africa
No full textInformal settlements are a common occurrence in South African due to housing backlogs and shortage of housing subsidies, and are often located on disputed land. To improve in-situ circumstances of these communities, informal settlement upgrades and urban design is required. Spatial data and maps are essential throughout the entire upgrading and urban design process in order to understand the current environment, plan new developments and communicate planned developments. All stakeholders need to understand maps to ensure active participation in the urban design process. Previous research demonstrated that a large number of planning professionals in South Africa have a relatively low level of map literacy, which is considered to be inadequate for effective planning. Many researchers proclaimed that because 3D visualisations resemble the real environment more than traditional maps, and are more intuitive, therefore 3D geovisualisations are easier to interpret. The goal of this research is to investigate the use of 3D geovisualisations (specifically 3D city models) for urban design in informal settlement upgrading in South Africa. To achieve this goal, the following topics were investigated: modelling processes (manual and procedural); visual design (visual characteristics, visual complexity and visual variables); and cognition related to spatial tasks on 3D geovisualisations and comparable alternatives (i.e. topographic maps, aerial photographs, 2D maps) when performing basic map reading tasks. Procedural modelling was found to be a feasible alternative to time-consuming manual modelling and has the capabilities to produce high-quality models. When investigating the visual design, the visualisation characteristics of 3D models of informal settlements, and relevance of a subset of visual variables for urban design activities of informal settlement upgrades were assessed. The results were used to produce various maps and 3D geovisualisations that were presented in quantitative user studies and expert interviews. The results of four user studies and expert interviews contributed to understanding the impact of various levels of complexity in 3D city models and map literacy of future geoinformatics and planning professionals when using aerial photographs, 2D maps and 3D models. The research results could assist planners in designing suitable 3D models for use throughout the entire urban design process.National Research Foundatio
Optimal sensor placement approaches for the design of inverse experiments by simulation
No full textThis dissertation serves to present the research conducted on sensor placement optimisation
(SPO) using sensitivity analyses of virtual experiments in order to design virtual inverse
problems. Two classes of SPO methods are considered namely mode-based and mode-free
approaches. The mode-based approaches make use of SIMPLS and SVD to extract useful
data by examining the correlation between the target variables (characterising variables)
and the sensor measurement variables, while the mode-free approaches eliminate the need of
spending the extra time required to extract modes, which ultimately leads to successful sensor
placement for solving inverse problems. The aim of the mode-free approach is to maximise the
variance explained subject to uniqueness of the information of each sensor. Both approaches
aim to maximise the potential of an experimental setup to solve an inverse problem by using
the right number of sensors and placing them at the optimal spatial positions. SPO is not only
capable of designing an experiment but it is also capable of classifying the well-posed or ill-
posed nature of an existing experiment that can be modelled, which saves both time and cost.
The approach followed in this study was to design a simple virtual inverse problem for which
the well or ill-posedness of the problem can be controlled. Numerous virtual experiments
were conducted that varied from well-posed to severely ill-posed to allow for rigorous testing
of the various approaches. The e ect of model error and stochastic noise on ability to reliably
place sensors is also investigated.National Research Foundatio
Investigating the application of Static Synchronous Compensator (STATCOM) for mitigating power transmission line losses
No full textVoltage instability and increased power loss on transmission lines are major challenges in power transmission due to ever increasing load growth. This work investigates the effect of Static Synchronous Compensator (STATCOM) to mitigate power losses and enhance the voltage stability of a transmission system. STATCOM, a shunt-connected power electronic device, operate as a Voltage Source Converter (VSC) to improve power transfer capacity of transmission lines by injecting a set of three-phase balanced sinusoidal current with controllable magnitude and phase angle into the transmission lines to regulate the line voltage and compensate for reactive power at the Point of Common Coupling (PCC).
To validate the capacity of STATCOM in this light, a modified model of IEEE 14 bus test system was simulated using DIgSILENT PowerFactory v15. Four different load profiles were included by increasing the base load in a step of 10%. In each case, power flow was run with and without STATCOM incorporated in the network with a view to determine the impact of STATCOM on bus voltage and transmission line losses.
The simulation results are obtained were recorded and analyzed. It is noted that there was sufficient improvement in the new voltage profile obtained for the weak buses of the system, the active and reactive power losses were mitigated by 17.73% and 24.80% respectively when STATCOM was incorporated at normal load.
The results showed that STATCOM could give quick voltage support to reduce the likelihood of voltage collapse and mitigate power losses along the transmission lines. Reduction of reactive power losses along the lines is higher than the active power losses resulting in the improvement of the voltage profile as the device is connected to the system.National Research Foundatio
Prevalence of high blood pressure among the University of Venda academic staff, South Africa
No full textHigh blood pressure is a global public health problem. High blood pressure shows no signs or
symptoms and it can only be detected through BP measurements by a health professionals. It’s
a chronic condition which requires long term management. Poor control of high blood pressure
can lead to complications and even death. The aim of the study was to determine the
prevalence of high blood pressure among University of Venda academic staff. UNIVEN is
situated in Thohoyandou, Vhembe District in Limpopo. A cross-sectional design was used. A
modified WHO stepwise questionnaire for non-communicable diseases version 3.1 was used to
collect data regarding demographic characteristics, BP status, and stress and lifestyle
characteristics. Charts and graphs were used to present the results of the study. The Statistical
Package of Social Sciences was used to analyse data. The Chi-square test was used to
determine the association between blood pressure and risk factors. A total of 179 respondents
were selected, their ages of were ranged from 22 to 68 years. Their blood pressure, weight and
height of the participants were also measured. The prevalence of high blood pressure was 20%,
while 46% were on prehypertension stage and about 34% had a normal BP. About 23% had
been previously diagnosed with HBP, while about 90% were on treatment for high blood
pressure. Only 13% had their BP under control. The prevalence of high blood pressure was
associated with gender, family history, vegetable intake and diabetes. Department of Sports
need to introduce sports among academic staff as a way of prevention and management of high
blood pressure.National Research Foundatio
Marinobufagenin and its relationship with systolic blood pressure in a young black and white population : the African-Predict study
No full textHypertension remains one of the foremost causes of cardiovascular morbidity and
mortality in sub-Saharan Africa. Importantly, the prevalence of hypertension within
black and white populations has been ascribed to distinct pathophysiological
mechanisms. Numerous studies have shown that black individuals are predisposed
to hypertension in part due to their genetic susceptibility to be salt-sensitive. Hence,
the scope of research investigating possible underlying mechanisms of saltsensitivity
remains a subject of growing interest.
There is emerging evidence indicating an association between salt-sensitivity and
the novel biomarker, MBG. This endogenous sodium-pump ligand’s role in blood
pressure regulation is attributed to its ability to inhibit both renal as well as
cardiovascular α1-Na+/K+-ATPase subunits. Studies have demonstrated a
vasoconstrictive response to MBG in Dahl salt-sensitive rats — with attenuated
pressure-natriuresis — as opposed to the expected homeostatic natriuretic
response. Accordingly, black populations portray a similar salt-sensitive phenotype
with an impaired pressure-natriuresis profile. Thus, we calculated the 24hr urinary
MBG/Na+ excretion ratio as a proposed estimate of Na+ excretion resistance to
higher levels of urinary MBG. A better understanding with regards to both ethnic and sex differences in MBG/Na+
and its association with measures of cardiovascular function, could provide new
insight into the possible role of MBG in the salt-sensitive hypertension phenotype.
Aim:
The aim of this study was to compare the MBG and 24hr urinary sodium profiles
between black and white, men and women. Furthermore, we aimed to investigate
the association of the MBG/Na+ excretion ratio with systolic blood pressure (SBP)
and hemodynamic parameters in this young bi-ethnic population.
Methods:
This cross-sectional study is affiliated with the African Prospective study on the Early
Detection and Identification of Cardiovascular Disease and Hypertension (African-
PREDICT), and was reviewed and approved by the Health Research Ethics
Committee (HREC) of the North-West University (NWU-00022-16-A1).
The overarching aim of the African-PREDICT study partly entails the early
identification of novel biomarkers involved in the development of CVD especially in
young black South Africans. We investigated the data of the first consecutive 331
participants (42.9% black, 43.8% men) with complete 24hr urinary data.
We obtained basic anthropometric measurements including height, weight and waist
circumference, after which the body mass index (kg/m2) as well as the waist:height
ratio were calculated. Cardiovascular measurements included central systolic blood
pressure (cSBP), 24hr SBP and beat-to-beat hemodynamic measurements including
heart rate, stroke volume and total peripheral resistance (TPR). Participants were
asked to collect 24hr urine samples in which the 24hr urinary sodium, potassium and MBG concentrations were determined. Furthermore, we used blood samples to
determine the high density lipoprotein cholesterol (HDL-C), total cholesterol, and γ-
glutamyltransferase (GGT), glycated haemoglobin (HbA1c) and aldosterone levels.
After performing interaction testing participants were stratified by sex and ethnicity.
Accordingly we used T-tests and Chi-square tests to compare means and
proportions between groups. Subsequent single, partial and multiple regression
analyses were performed to explore the relationship between MBG and the
MBG/Na+ excretion ratio with SBP and other hemodynamic variables. P-values ≤0.05
were considered significant.
Results:
Interaction testing performed in the entire cohort, indicated an interaction of sex on
the relationship between cSBP and MBG/Na+ excretion ratio (p=0.027), while there
was an interaction of ethnicity on the associations between cSBP and 24hr SBP with
MBG/Na+ in women (p=0.010 and p=0.012). Black men and women displayed a
higher cSBP and TPR with a lower stroke volume compared to whites, whereas
white men had higher 24hr SBP measures. We observed no apparent ethnic
differences in either MBG excretion or MBG/Na+ in men or women, although men
had a significantly higher salt intake of 8.58 g/day and MBG excretion when
compared to women.
Black women portrayed a significant positive trend in cSBP (p=0.003) as well as
nighttime systolic ABPM (p=0.013) across increasing MBG/Na+ quartiles.
Furthermore, in black women only single and multiple regression analyses indicated
a positive association of central SBP (R2=0.26; ß=0.28; p=0.039), 24hr SBP
(R2=0.46; ß=0.30; p=0.011) and stroke volume (R2=0.26; ß=0.29; p=0.036) with MBG/Na+, whereas a negative association was found between MBG/Na+ and TPR
(R2=0.21; ß=−0.33; p=0.018). Conversely, in white women a negative association
existed between MBG/Na+ and nighttime SBP (r=−0.20; p=0.038), which became
non-significant after adjusting for multiple covariates (R2=0.36; ß=−0.13; p=0.12).
There were no significant trends or associations in young black and white men with
regards to the MBG/Na+ excretion ratio.
Conclusion:
Compared with white women, black women might be more vulnerable to early
cardiovascular risk brought on by an apparent resistance to sodium excretion, based
on MBG/Na+ and its association with an increase in cSBP, 24hr SBP and stroke
volume. Yet, clear contrasting associations in young white women supports the
normal physiological natriuretic effect of MBG. Our results suggest that the interregulation
of MBG and Na+ may partially contribute to the prevalence of a saltsensitive
hypertension phenotype. The absence of any associations with the
MBG/Na+ excretion ratio in men requires further investigationNational Research Foundatio
Synthesis, crystal structures and molecular modelling of rare earth complexes with bis(2-pyridylmethyl)amine
No full textEight rare earth complexes with bis(2-pyridylmethyl)amine (DPA) were synthesised and
recrystallised, under air-sensitive or low moisture conditions. The crystal structures were
successfully determined, via SC-XRD, and the asymmetric units of five complexes (1, 3, 5, 6
and 7) were submitted for DFT molecular modelling calculations, which involved geometry
optimisation and frequency calculations.
The neutral complexes obtained were bis(bis(2-pyridylmethyl)amine)-trichloro-lanthanum(III)
[LaCl3(DPA)2] (1), bis(bis(2-pyridylmethyl)amine)-trichloro-cerium(III)) [CeCl3(DPA)2] (2),
bis(µ2-chloro)-diaqua-tetrachloro-bis(bis(2-pyridylmethyl)amine)-di-praseodymium(III)
[PrCl2(µ-Cl)(DPA)(OH2)]2 (3) and bis(µ2-methoxo)-bis(bis(2-pyridylmethyl)amine)-
tetrachloro-di-dysprosium(III) [DyCl2(µ-OCH3)(DPA)]2 (4).
The cationic complexes obtained in this study were dichloro-bis(bis(2-pyridylmethyl)amine)-
neodymium(III) chloride methanol solvate [NdCl2(DPA)2]Cl·CH3OH (5), dichloro-bis(bis(2-
pyridylmethyl)amine)-dysprosium(III) chloride methanol solvate [DyCl2(DPA)2]Cl·CH3OH
(6), dichloro-bis(bis(2-pyridylmethyl)amine)-yttrium(III) chloride methanol solvate
[YCl2(DPA)2]Cl·CH3OH (7) and dichloro-bis(bis(2-pyridylmethyl)amine)-lutetium(III)
chloride methanol solvate [LuCl2(DPA)2]Cl·CH3OH (8).
The ‘Quantum theory of atoms in molecules’ approach was used to investigate the electron
density topology, primarily in order to investigate the hydrogen and coordination bonds for
three of the eight complexes. Two of the neutral complexes contain the ‘early’ rare earth
elements lanthanum and praseodymium and one cationic complex contains the ‘late’ lanthanide
element dysprosium. Noncovalent interaction analysis was also performed on the
aforementioned complexes in order to gain a deeper understanding of the intra-molecular
stereo-electronic interactions. Spin density analysis was used to investigate the distribution of
unpaired electron density at and around the metal centres of the aforementioned paramagnetic
Pr- and Dy-complexes.
A ligand conformation search for DPA was undertaken and 32 low energy conformers were
identified and their relative energies were determined using two DFT functionals, namely M06
and M06-2X.National Research Foundatio
Elucidation of African elephant beta casein phosphorylation state and casein micelle structure
No full textThe exact structure of casein micelles still remains a debated subject. While most of the experimental work on cow caseins and casein micelles has provided a wealth of data, data of caseins and casein micelles of non-bovine origin provide a new insight into the structure of casein micelles. Microscopic examination of cow, sheep, horse, human and African elephant milk casein micelles show that the respective casein micelles are all spherical in shape but differ in size as well as surface appearances. Human casein micelles were the largest of the casein micelles whereas sheep casein micelles were the smallest. Apart from their smaller size, sheep micelles also had a smooth surface compared to a rough surface observed on the rest of the casein micelles. African elephant casein micelles were the second largest of the five casein micelles compared. It may be derived that, although casein micelle shape and size seem to be species specific, the differences observed may be a result of the differences in total casein content, the proportions of the individual casein types and the presence and or absence of some of the casein types.
The elucidation of African elephant β-casein phosphorylation state by LC MS/MS, showed the presence of a single phosphorylation site at Ser9. In contrast, electrophoresis analysis showed that there are up to five phosphoforms of African elephant β-casein. The LC MS/MS also showed that the presence of a short length African elephant β-casein that is 200 amino acids long and that the gene sequences coded for by exons 4 and 5 have been truncated. Homology modeling of cow, sheep, horse, human and African elephant caseins showed that the secondary structure of α-caseins predominantly consist of α-helices, whereas the secondary structure of β- and κ-caseins is dominated by random coils. Alpha caseins give micelles a slightly compact structure whereas random coils result in a more open and larger size of micelles. These structural differences of caseins could possibly explain the varied size of casein micelles in milk. Comparative genomics of casein genes across mammalian species shows that several mammalian species are devoid of CNS1S1 and CSN1S2 genes. Considering the evolution of the casein gene locus organization, it appears that the CNS1S1 gene has been lost whereas the CSN1S2 gene has not been gained or developed in these species. In contrast, the CSN2 and CSN3 genes have been preserved and gained respectively, in most mammalian species. This suggests that these genes have a more important role in casein micelle formation and consequently the sequestration of large amounts of calcium and phosphate. Evidence from this study suggests that studying of non-cow caseins may shed more light on the casein micelle structure.National Research Foundatio