ResearchSpace :: Browsing by Author "Smit, Jacoba E"

Browsing by Author "Smit, Jacoba E"

Now showing 1 - 18 of 18

Artificial vesicles with incorporated photosynthetic materials for potential solar energy conversion systems
(2009-07) Smit, Jacoba E; Grobler, AF; Karsten, AE; Sparrow, RW
Currently the primary source of energy for industrial and domestic use is based on fossil fuels. The supplies of these fuels are limited and are becoming depleted. Thus there is a search for alternative and more sustainable energy sources. One such source is solar energy, which has many advantages over fossil fuels. Thus research into harvesting, transferring, and converting light energy is of great significance. The most abundant and efficient light harvesting, energy transfer and transduction systems are found in nature with the process of photosynthesis. Previous work has shown that photosynthetic light harvesting material can be incorporated into artificial vesicles called Pheroid. In this study researchers are characterising the level of organisation of the incorporated light harvesting and energy transfer systems using steady state optical techniques such as absorption spectroscopy. The incorporation ratio of photosynthetic material, Pheroid has been investigated and preliminary results indicate that the loading capacity of the Pheroid differs depending on the photosynthetic membrane fractions used.
An assessment of the role of the k-e vertical mixing scheme in the simulation of Southern Ocean upper dynamics
(2016-11) Boodhraj, K; Vichi, M; Smit, Jacoba E
Following the work done by Reffrey, Calone and Bourdalle-Badie (2015) we implemented a one dimensional (1D) ocean physical model in the sub-Antarctic Southern Ocean using the Nucleus for the European Modelling of the Ocean(NEMO) model. The 1D model is a first attempt at studying sub-grid scale parameterizations in the region. It was used to test the effects of the k-e turbulence closure scheme on the simulation of vertical mixing in the water column structure in the North Pacific and Southern Ocean, using the available scattered data as comparison. This analysis also gives indications for the choice of the grid’s vertical levels.
Comparative attenuation spectra of liquid skin-like phantoms
(SAIP 2010, 2010-09) Singh, A; Smit, Jacoba E; Karsten, AE; Grobler, AF; Sparrow, RW
This study aims to extract and compare attenuation coefficients of different liquid skin-like phantoms representing Skin Types 1 to V1 with two methods, Spectrophotometric and Integrating Sphere methods. The correlation between the results of the 2 methods was excellent.
Estimation of stimulus attenuation in cochlear implants
(Elsevier Science, 2009-03) Smit, Jacoba E; Hanekom, T; Hanekom, JJ
Neural excitation profile widths at the neural level, for monopolar stimulation with Nucleus straight and contour arrays respectively, were simulated using a combined volume-conduction-neural model. The electrically evoked compound action potential profile widths at the electrode array level were calculated with a simple approximation method employing stimulus attenuation inside the cochlear duct, and the results compared to profile width data from literature. The objective of the article is to develop a simple method to estimate stimulus attenuation values by calculating the values that best fit the modelled excitation profile widths to the measured evoked compound action potential profile widths. Results indicate that the modelled excitation profile widths decrease with increasing stimulus attenuation. However, fitting of modelled excitation profile widths to measured evoked compound action potential profile widths show that different stimulus attenuation values are needed for different stimulation levels. It is suggested that the proposed simple model can provide an estimate of stimulus attenuation by calculating the value of the parameter that produces the best fit to experimental data in specific human subjects.
Forward and reverse middle ear frequency responses with various terminal loads
(ACTA Press, 2012-09) Thejane, T; Marwala, T; Smit, Jacoba E; Nelwamondo, Fulufhelo V
An analog network model of the human middle ear is used to study the effect of terminal loads on the middle ear frequency response. A new transformer ratio value is computed and used to improve the model of the middle ear through the use of an ideal transformer. The terminal loads are taken as the loads on either side of the middle ear. The forward and reverse frequency characteristics of the middle ear are computed using various cochlear and outer ear impedances as the terminal load, respectively. The cochlear loads used are an open circuit, a resistive load and an RCL load. The outer ear loads used are an open circuit, a outer ear transmission line model having a constant auditory canal radius and an outer ear transmission line model having a varying auditory canal radius. The components of the cochlear and outer ear loads are computed using previously published anatomical data. The RCL load proved to give the most accurate response for the forward frequency response whereas the open circuit response proved to be the most accurate for the reverse frequency response. The outer ear load models used give minimal accuracy as terminal loads and should thus be improved.
An FTIR study on the chlorophyll and apoprotein aggregation states in LHCII due to solvent effects
(2012-07) Smit, Jacoba E; Prinsloo, LC; Nel, JM
Photosynthesis provides us with the most abundant and efficient light-harvesting systems found in nature. The photosynthetic process is very much dependent on the aggregation state of the chlorophylls and secondary conformational structure of the apoproteins in the light-harvesting systems. The aim of this study was to test possible buffer influence on these in the light-harvesting complex (LHCII) of Photosystem II (PSII). LHCII was extracted from spinach leaves in a 20 mM Tricine buffer to stabilise the proteins, after which samples were diluted in 20 mM Tricine (pH 7.61) and 60 mM Tricine (pH 7.6) buffers respectively. Additionally, the 20 mM Tricine buffer was dialysed out of some of the LHCII stock samples directly into a 20 mM K2HPO4 / KH2PO4 buffer (pH 7.64) to prevent denaturing of the LHCII proteins. FTIR and absorbance spectra of samples were compared. Gaussian curve-fitting based on second order derivative resolution enhancement were performed on the Amide I region of all the FTIR spectra to reveal the overlapping component contributions of the chlorophylls and apoproteins in the light-harvesting complexes. FTIR results from the light-harvesting complexes in the Tricine buffers indicated a downward shift by about 25 cm-1 of the Amide I peak compared to the K2HPO4 / KH2PO4 buffer results. This leads to the assumption that the apoproteins has undergone a conformational shift from mostly a-helical to b-sheet structure. The curve-fitting method, however, predicted a smaller downward shift of between 3 and 7 cm-1 of the apoproteins, indicating a slight unfolding of the aproteins to a more unordered coil-structure, masked by the stronger Tricine peaks at around 1624 cm-1 in the Amide I region. Results also indicated that the chlorophylls associated with these apoproteins assumed a less aggregated state, confirmed as a slight blue shift in the absorbance spectra. The results were more pronounced in the higher concentrate Tricine buffer.
Harvesting sunlight energy: a biophysics approach
(2011-04) Smit, Jacoba E; Grobler, AF; Sparrow, RW
The most efficient light harvesting and energy transfer systems are found in nature as part of the photosynthesis process. In the photosynthetic system light energy is absorbed by antenna chlorophylls and this energy is then passed onto a reaction centre chlorophyll molecule where charge separation occurs in less than 100 ps and at about 95% efficiency. It has been shown that organised connective light harvesting complexes are required for long range energy transfer. By extracting these system fragments and maximising their organisational structure, similar artificial systems for energy sources and transfer system can potentially be developed. As a matrix to stabilize the system we are using a combination of fatty acids and nitrous oxide, rather than conventional phospholipid-based combinations, which enables the production of small, elastic artificial vesicles, called Pheroid™. Previous work has shown that photosynthetic light harvesting material can be incorporated into the Pheroid™. In this study we are characterising the level of organisation through protein aggregation on the incorporated light harvesting systems using absorption spectroscopy.
Improving broiler lifestyle: a CFD approach
(2014-01) Humbert, U; Wessels, GJC; Smit, Jacoba E; Ubbink, O
Climate change poses environmental risks which can negatively affect livestock production. To circumvent this, it is possible to move livestock into environmentally controlled animal housings. In South Africa, this is practiced in the broiler industry. To be economically viable, it is required to build energy and cost effective housing while not compromising the health of the broilers. A broiler’s physiology is sensitive to the environment it resides in and slight fluctuations can have detrimental effects and can negatively influence the growth or health of the broiler. These houses make use of different combinations of heaters, fans and inlets to warm, cool and ventilate the house. This needs to happen within very specific parameters or it can decrease broiler performance. We investigate how the equipment is used in current broiler houses and conclude that although this is a complex model to replicate and solve, computational fluid dynamics can assist in broiler house design.
Influence of the auditory canal number of segments and radius variation on the outer ear frequency response
(IEEE, 2012-01) Thejane, T; Nelwamondo, Fulufhelo V; Smit, Jacoba E; Marwala, T
A lumped transmission line model of the auditory canal is modified to study the influence of the number of segments used and the variation of the radius on the outer ear frequency response. A new second order polynomial is used to map the radius to the length along the narrow part of the auditory canal. The results found are compared to other literature results and expected theoretical results. The study shows that both an increase and decrease in the number of segments of the ear canal results in a distortion in the frequency response. The results obtained when using the radius-length mapping function show that the response found closely correlates with other literature results. The optimum representation of the frequency response was found when four number of segments and the radius-length mapping function were used. The use of a third order polynomial to further improve the relationship between the radius and the length of the ear canal is suggested for future research work.
Influence of variation in eumelanin content on absorbance spectra of liquid skin-like phantoms
(Wiley Blackwell, 2011-01) Smit, Jacoba E; Grobler, AF; Sparrow, RW
The attenuation behaviour of two different types of skin-like phantoms representing the range of Skin Types I to VI were investigated and compared to real human skin. Intralipid and PheroidTM artificial lipid membrane vesicles respectively were added to synthetic eumelanin concentrations ranging from 0.0044 to 0.13 mg/mL to produce skin-like phantoms. Spectrophotometric absorbance and transmittance measurements were performed. Results predicted some of the non-monotonic trends observed in real human skin, albeit shifted more towards the visible wavelength range. There exist however an underlying difference in interaction between the melanin and the PheroidTM and Intralipid skin-like phantoms
Influence of variation in melanin content on absorbance spectra of liquid skin phantoms
(2010-09) Smit, Jacoba E; Karsten, AE; Grobler, AF; Sparrow, RW
This presentation looked at the influence of variation in melanin content on absorbance spectra of liquid skin phantoms. Reasons for studying melanin, plus skin pigments, melanocytes, melanosomes, and melanin in particular, are discussed. The phenomena of natural vs synthetic melanin, is also touched on.
Investigating the turbulence response of a 1-D idealized water column located in the sub-Antarctic zone with focus on the upper ocean dynamics
(2017-09) Boodhraj, Kirodh; Vichi, M; Smit, Jacoba E
A one-dimensional ocean physical model was implemented in the sub-Antarctic Southern Ocean using the Nucleus for the European Modelling of the Ocean (NEMO) model. It was used to examine the effects of the turbulence response of the simulation of vertical mixing in the water column structure in the Southern Ocean (SO), using the available scattered data as comparison. The Brunt Väisälä frequency, turbulent diffusivity and turbocline provided valuable information regarding the turbulence response of the water column and the effect of an entrapped warm water parcel below cool waters was observed.
Modelled temperature-dependent excitability behaviour of a generalised human peripheral sensory nerve fibre
(Springer Science and Business Media, 2009-09) Smit, Jacoba E; Hanekom, T; Hanekom, JJ
The objective of this study was to determine if a recently developed human Ranvier node model, which is based on a modified version of the Hodgkin-Huxley model, could predict the excitability behaviour in human peripheral sensory nerve fibres with diameters ranging from 5.0 – 15.0 µm. The Ranvier node model was extended to include a persistent sodium current and was incorporated into a generalised single cable nerve fibre model. Parameter temperature dependence was included. All calculations were performed in Matlab. Sensory nerve fibre excitability behaviour characteristics predicted by the new nerve fibre model at different temperatures and fibre diameters compared well with measured data. Absolute refractory periods deviated from measured data, while relative refractory periods were similar to measured data. Conduction velocities showed both fibre diameter and temperature dependence and were underestimated in fibres thinner than 12.5 µm. Calculated strength-duration time constants ranged from 128.5 µs to 183.0 µs at 37°C over the studied nerve fibre diameter range, with chronaxie times about 30% shorter than strength-duration time constants. Chronaxie times exhibited temperature dependence, with values overestimated by a factor 5 at temperatures lower than body temperature. Possible explanations include the deviated absolute refractory period trend and inclusion of a nodal strangulation relationship.
Modelling and verification of melanin concentration on human skin type
(Wiley, 2012-03) Karsten, AE; Smit, Jacoba E
Lasers are used in the minimalistic or noninvasive diagnosis and treatment of skin disorders. Less laser light reaches the deeper skin layers in dark skin types, due to its higher epidermal melanin concentration compared with lighter skin. Laser–tissue interaction modeling software can correct for this by adapting the dose applied to the skin. This necessitates an easy and reliable method to determine the skin’s type. Noninvasive measurement of the skin’s melanin content is the best method. However, access to samples of all skin types is often limited and skin-like phantoms are used instead. This study’s objective is to compare experimentally measured absorption features of liquid skin-like phantoms representing Skin Types I–VI with a realistic skin computational model component of ASAP®. Sample UV–VIS transmittance spectra were measured from 370 to 900 nm and compared with simulated results from ASAP® using the same optical parameters. Results indicated nonmonotonic absorption features towards shorter wavelengths, which may allow for more accurate ways of determining melanin concentration and expected absorption through the epidermal layer. This suggests possible use in representing optical characteristics of real skin. However, a more comprehensive model and phantoms are necessary to account for the effects of sun exposure.
Phantom skin absorption coefficients from spectrophotometric and integrating sphere methods: preliminary comparative results
(European Cells and Materials, 2010-12) Smit, Jacoba E; Singh, A; Tshoke, I; Grobler, AF; Sparrow, RW
Minimalistic or non-invasive diagnosis and treatment of skin disorders requires accurate information regarding skin optical properties. Spectrophotometric and Integrating Sphere (IS) methods are commonly used to extract information regarding absorption and scattering properties of samples, although in the field of skin optics the latter is used more widely. The aim of this study is to extract and compare absorption coefficients of liquid skin phantoms with these two methods.
Potential sustainable energy source: Pheroid™ with incorporated light harvesting materials
(CSIR, 2010-09-01) Smit, Jacoba E; Grobler, AF; Sparrow, RW
The most efficient light harvesting and energy transfer systems are found in nature as part of the photosynthesis process. By extracting these system fragments and maximising their organisational structure, researchers are developing similar artificial systems for use as potential sustainable energy sources
Predicting human epidermal melanin concentrations for different skin tones
(2011-07) Smit, Jacoba E; Karsten, AE; Sparrow, RW
In the past 50 years lasers has found numerous applications in medicine. One of their advantages is their use for minimalistic or non-invasive diagnosis and treatment. Often that means light penetration through skin and the correct dose required relies on accurate information regarding the skin’s optical properties. Light absorption in the epidermal layer is a major factor in determining the laser light fluency that reaches the deeper skin levels. Darker skin has an epidermal melanin volume fraction about twice that of lighter skin. Due to melanin absorption, fewer lasers light reach the deeper skin layers in dark skin tones. Laser-tissue interaction modelling software can correct for this by adapting the dose applied to the skin. To correctly apply such software it is important to characterise the skin in terms of skin tone with an easy and reliable method. Measuring the melanin content of the skin is the best method, but it needs to be done non-invasively. However, access to samples of all skin types is often limited and skin-like phantoms are used instead. The objective of this study is to compare experimentally measured absorption features of liquid skin-like phantoms representing Skin Types I to VI with computational simulated skin from the Realistic Skin Model (RSM) part of the ASAP® software from Breault Research. Skin-like phantoms were prepared by adding Intralipid (20% fat emulsion) to samples of increasing melanin concentration at pH ~ 7. UV-VIS transmittance spectra of the samples were measured over the wavelength range 370 to 900 nm and compared to simulated results from ASAP using the same optical parameters.
Unravelling complex interactions between urbanisation and coastal fisheries using a system dynamics approach
(2017-11) Smit, Jacoba E; Botha, Gerda N; Arabi, Sumaiya; Slinger, JH; Taljaard, Susan; Weerts, Steven P
Coastal zones are amongst the most heavily populated and exploited areas in many parts of the world. Burgeoning coastal urbanization and resource use is increasingly giving rise to conflict among users of coastal resources. One such conflict arises from wastewater disposal in urban areas causing degradation of coastal water quality and pollution impacts on other uses, such as fishing. This is especially significant in developing countries, where subsistence fishing is very important to coastal communities that rely on their catches as a source of food and for their livelihoods. Thus urbanisation in coastal areas is often a factor contributing to devaluing of ecosystem goods and services, and can impact other uses, such as subsistence fisheries. Natural questions which arise are how severe is this impact, and what could be done to mitigate, or at least minimize it? In this project we aim to develop a decision-support tool to support non-technical decision-makers in data poor environments to reach realistic solutions in these complex socio-ecological systems without having to rely on detailed data and information. Specifically, we focus on potential conflict between land-based wastewater inputs from a city on a coastal fishery. This paper presents a simplified conceptualization of the key elements in this conflict situation, and proposes a preliminary design of a system dynamics model. This model will be refined in an expert workshop forum as part of the next stage in this project. Once calibrated, the model will be used to test various wastewater scenarios, so as to assist in unravelling this complex interaction and, most importantly, inform future mitigation needs.

Browsing by Author "Smit, Jacoba E"

Results Per Page

Sort Options