On the characterisation of photovoltaic device parameters using light beam induced current measurements

Light Beam Induced Current (LBIC) measurement is a non-destructive technique used to perform localized characterization of solar cells using a light beam as a probe. The technique allows the determination of local photo response of a cell, the electrical parameters and defects that occur in the individual solar cell. The semiconductor materials used to create solar cells are not always defect free and these defects reduce the electrical performance of the device. It is therefore important to use a system that will allow the characterization and extract the solar cell parameters as can be done using the LBIC system. By analysing these parameters and cell defects, further studies can be done to enhance the cell’s lifetime and hence its efficiency. Light beam induced current (LBIC) is a technique that focuses light onto a solar cell device and thus creating a photo-generated current that can be measured in the external circuit for analyses. By scanning this beam probe across a solar cell while measuring the current-voltage characteristics, a map of various parameters can be obtained. This thesis presents the design of the LBIC system, the software interfacing of the data acquisition system and local photo-response within different solar cell technologies. In addition, this thesis represent two curve fitting algorithms namely: the Gradient Descent Optimisation and the Differential Evolution used for the extraction of solar cell device parameters. The algorithms are based on the one-diode solar cell model and make use of the light generated current-voltage (I-V) data obtained from the LBIC system. Different solar cell technologies namely; single crystalline (c-Si) and multicrystalline silicon (mc-Si) was used for analysis. LBIC maps and I-V characteristics of both technologies was obtained. The LBIC maps shows performance degrading defects present in the bulk and the surface of the solar cells as a function of spatial distribution. These localised defects acts as trapping mechanism for the charge carriers and therefore limits recombination within the solar cell and thus decreasing the performance of the solar cell device. The resulting I-V characteristics obtained from the LBIC system were used to determine the performance parameters using the two algorithms. The resultant effect of these parameters on the performance of the solar cells was observed. The overall results showed that LBIC is a useful tool for identifying and characterising defects in solar cells

Using ambient noise tomography to image the Eastern Cape-Karoo and Karoo regions, South Africa

The primary aim of this thesis was to explore the use of ambient seismic noise as a tool to map the subsurface of the Cape-Karoo and Karoo region of South Africa. The Karoo is an ideal laboratory to use ambient seismic signal to map the shallow subsurface, as it is a quiet and pristine environment with a relatively well known geology. Ambient seismic signals were continuously recorded at three independent networks (ArrayA, ArrayB and ArrayC). ArrayA and ArrayB comprised 17 temporary stand-alone seismic stations each and recorded ambient noise wavefields for a ten week period between August and October 2015. ArrayC comprised 19 temporary stand-alone seismic stations, recording ambient seismic noise for a period of six weeks between June and July 2016. ArrayA and ArrayB were installed in the south-eastern Cape-Karoo region, near the town of Jansenville and ArrayC was installed near the Cradock-Tarkastad region of South Africa. This thesis is made up of two separate studies. Firstly, the retrieval and coherency of Rayleigh surface waves extracted from the vertical component recordings. For the first time in the south-eastern Cape-Karoo and Karoo area, estimates of Green’s function from cross-correlating ambient noise data between stations pairs were reconstructed and shown, which can be successfully used to image the subsurface. The stacked cross-correlations between all station pairs show clear arrivals of the Rayleigh surface waves. The group velocities of the Rayleigh waves in the 2 to 7 seconds period range were picked and inverted to compute the 2-D group velocity maps. For ArrayA and ArrayB, the resulting 2-D group velocity maps at different periods resulted in a group velocity model from approximately 2 to 7 km depth, which generally show a high velocity anomaly in the north of the study area, most likely imaging the denser, thick sedimentary basin of the Karoo (Carboniferous-Permian). To the south, the low velocity anomaly likely corresponds to the overlying Jurassic- Cretaceous sequences of the younger Algoa Basin (Uitenhage Group). For ArrayC, the group velocity maps showed high velocity regions, which is consistent with the dolerite sill intrusions in the Karoo and the low velocity structures, which was interpreted as the Karoo sediments. Secondly, the study comprised of characterizing the ambient seismic noise source. The first order analysis of the symmetry of the cross-correlation function showed that, although the ambient noise sources are relatively homogeneously distributed in the study area, most (energetic) of the ambient seismic noise propagates from the coast of South Africa. This was verified by analyzing the azimuthal distribution of the ambient seismic noise

Telerehabilitation during the COVID-19 pandemic in Sweden: a survey of use and perceptions among physiotherapists treating people with neurological diseases or older adults

Background : Telerehabilitation, i.e. rehabilitation at a distance using Information and Communication Technology (ICT), is a promising avenue for improving health among people with neurological diseases or older adults who often experience limited access to services. Still, little is known about physiotherapists’ use, perceptions and needs with regards to telerehabilitation services. Aims: To describe physiotherapists use and perceptions of, as well as needs for, telerehabilitation services for the rehabilitation of people with neurological diseases or older adults in Sweden. Methods: In this cross-sectional study, an author-created survey was sent out to members of the Swedish Association of Physiotherapists including questions about the use and perceptions of existing telerehabilitation services (e.g. telephone, internet-based applications and mobile applications) as well as needs of future telerehabilitation services. The results were presented descriptively as numbers and percentages. Results: Three hundred seven physiotherapists were included in this study with 139 (45%) treating people with neurological diseases and 168 (55%) treating older adults. Most respondents did not provide telerehabilitation before (74%) or during (51%) the COVID-19 pandemic. Telephone, which was predominantly used for administrative tasks, was the most frequent utilised ICT used by 68% of the physiotherapist using ICTs several days/week. Few respondents used internet-based applications (12%), mobile applications (3%) or SMS services (8%) and videoconferencing (3%). A majority of the respondents were interested in ICT (78%), felt comfortable using ICT (57%) and were interested in learning how ICT can be used in rehabilitation (92%). Still, few respondents perceived that people with neurological diseases or older adults can use existing ICTs for rehabilitation purposes (18%) and that existing reimbursement system within health care facilitates remote rehabilitation (16%). Important functionality of future ICT perceived by physiotherapists covered patient communication (e.g. chat, SMS and video), assessments (e.g. digital surveys and assessment of physical activity) and treatment (e.g. exercise prescription)

Using functional near-infrared spectroscopy to measure prefrontal cortex activity during dual-taskwalking and navigated walking: A feasibility study

While functional near-infrared spectroscopy (fNIRS) can provide insight into motor-cognitive deficits during ecologically valid gait conditions, the feasibility of using fNIRS during complex walking remains unknown.We tested the process and scientific feasibility of using an fNIRS device to measure cortical activity during complex walking tasks consisting of straight walking and navigated walking under single and dual-task (DT) conditions. Nineteen healthy people from 18 to 64 years (mean age: 45.7 years) participated in this study which consisted of three complex walking protocols: (i) straight walking, DT walking (walking while performing an auditory Stroop task) and singletask auditory Stroop, (ii) straight and navigated walking, and (iii) navigated walking and navigated DT walking

The role of environmental factors on health conditions, general health and quality of life in persons with spinal cord injuries in South Africa

The objective was to describe the individual items of the environmental factors and to investigate the relationship between the environmental factors to health conditions, general health and quality of life in people with SCI in South Africa. Methods: Two hundred persons with SCI participated in a cross-sectional survey design. This study formed part of the International Spinal Cord Injury (InSCI) Community Survey. Four major domains, environmental factors, health conditions, general health and quality of life of the survey questionnaire responses, were used for the analysis. Regression models were used to determine the association between the independent variable, which consisted of the specific environmental factors items, and the dependent variables comprising health conditions, general health and quality of life. Results: The commonly reported environmental barriers were public access, lack of short- and long-distance transport and finances. Environmental factors such as public access (p < 0.001), short- (p < 0.001) and long-distance transport (p = 0.001), and friends’ (p = 0.003) and colleagues’ (p < 0.001) attitudes and communication (p = 0.042) were significantly associated with the presence of secondary health conditions. Finances (p = 0.026), family attitudes (p = 0.037) and communication (p = 0.039) had a significant association with worsened mental health. Services (p = 0.022) and communication (p = 0.042) were also significantly associated with decreased general health

Establishing accelerometer cut-points to classify walking speed in people post stroke

While accelerometers could be used to monitor important domains of walking in daily living (e.g., walking speed), the interpretation of accelerometer data often relies on validation studies performed with healthy participants. The aim of this study was to develop cut-points for waistand ankle-worn accelerometers to differentiate non-ambulation from walking and different walking speeds in people post stroke. Forty-two post-stroke persons wore waist and ankle accelerometers (ActiGraph GT3x+, AG) while performing three non-ambulation activities (i.e., sitting, setting the table and washing dishes) and while walking in self-selected and brisk speeds. Receiver operating characteristic (ROC) curve analysis was used to define AG cut-points for non-ambulation and different walking speeds (0.41–0.8 m/s, 0.81–1.2 m/s and >1.2 m/s) by considering sensor placement, axis, filter setting and epoch length. Optimal data input and sensor placements for measuring walking were a vector magnitude at 15 s epochs for waist- and ankle-worn AG accelerometers, respectively

The Role of Environmental Factors on Health Conditions, General Health and Quality of Life in Persons with Spinal Cord Injuries in South Africa

Objective: The objective was to describe the individual items of the environmental factors and to investigate the relationship between the environmental factors to health conditions, general health and quality of life in people with SCI in South Africa. Methods: Two hundred persons with SCI participated in a cross-sectional survey design. This study formed part of the International Spinal Cord Injury (InSCI) Community Survey. Four major domains, environmental factors, health conditions, general health and quality of life of the survey questionnaire responses, were used for the analysis. Regression models were used to determine the association between the independent variable, which consisted of the specific environmental factors items, and the dependent variables comprising health conditions, general health and quality of life. Results: The commonly reported environmental barriers were public access, lack of short- and long-distance transport and finances. Environmental factors such as public access (p p p = 0.001), and friends’ (p = 0.003) and colleagues’ (p p = 0.042) were significantly associated with the presence of secondary health conditions. Finances (p = 0.026), family attitudes (p = 0.037) and communication (p = 0.039) had a significant association with worsened mental health. Services (p = 0.022) and communication (p = 0.042) were also significantly associated with decreased general health. Conclusion: The results provide insight into modifiable environmental factors policymakers need to consider or adapt to improve the lives of people with SCI in South Africa with respect to health (secondary health conditions), as well as general and mental health

Using functional near‐infrared spectroscopy to measure prefrontal cortex activity during dual‐task walking and navigated walking: A feasibility study

Abstract Introduction While functional near‐infrared spectroscopy (fNIRS) can provide insight into motor‐cognitive deficits during ecologically valid gait conditions, the feasibility of using fNIRS during complex walking remains unknown. We tested the process and scientific feasibility of using an fNIRS device to measure cortical activity during complex walking tasks consisting of straight walking and navigated walking under single and dual‐task (DT) conditions. Methods Nineteen healthy people from 18 to 64 years (mean age: 45.7 years) participated in this study which consisted of three complex walking protocols: (i) straight walking, DT walking (walking while performing an auditory Stroop task) and single‐task auditory Stroop, (ii) straight and navigated walking, and (iii) navigated walking and navigated DT walking. A rest condition (standing still) was also included in each protocol. Process feasibility outcomes included evaluation of the test procedures and participant experience during and after each protocol. Scientific feasibility outcomes included signal quality measures, and the ability to measure changes in concentration of deoxygenated and oxygenated hemoglobin in the prefrontal cortex. Results All participants were able to complete the three protocols with most agreeing that the equipment was comfortable (57.9%) and that the testing duration was adequate (73.7%). Most participants did not feel tired (94.7%) with some experiencing pain (42.1%) during the protocols. The signal qualities were high for each protocol. Compared to the rest condition, there was an increase in oxygenated hemoglobin in the prefrontal cortex when performing dual‐task walking and navigation. Conclusion We showed that our experimental setup was feasible for assessing activity in the prefrontal cortex with fNIRS during complex walking. The experimental setup was deemed acceptable and practicable. Signal quality was good during complex walking conditions and findings suggest that the different tasks elicit a differential brain activity, supporting scientific feasibility

Mobile health to promote physical activity in people post stroke or transient ischemic attack – study protocol for a feasibility randomised controlled trial

Abstract Background Physical activity is essential to improve health and reduce the risk of recurrence of stroke or transient ischemic attack (TIA). Still, people post stroke or TIA are often physically inactive and the availability of physical activity promotion services are often limited. This study builds on an existing Australian telehealth-delivered programme (i-REBOUND– Let’s get moving) which provides support for home-based physical activity for people post stroke or TIA. The aim of this study is to test the feasibility, acceptability, and preliminary effects of a mobile Health (mHealth) version of the i-REBOUND programme for the promotion of physical activity in people post stroke or TIA living in Sweden. Methods One hundred and twenty participants with stroke or TIA will be recruited via advertisement. A parallel-group feasibility randomised controlled trial design with a 1:1 allocation ratio to 1) i-REBOUND programme receiving physical exercise and support for sustained engagement in physical activity through behavioural change techniques, or 2) behavioural change techniques for physical activity. Both interventions will proceed for six months and be delivered digitally through a mobile app. The feasibility outcomes (i.e., reach, adherence, safety and fidelity) will be monitored throughout the study. Acceptability will be assessed using the Telehealth Usability Questionnaire and further explored through qualitative interviews with a subset of both study participants and the physiotherapists delivering the intervention. Clinical outcomes on preliminary effects of the intervention will include blood pressure, engagement in physical activity, self-perceived exercise self-efficacy, fatigue, depression, anxiety, stress and health-related quality of life and will be measured at baseline and at 3, 6 and 12 months after the baseline assessments. Discussion We hypothesise that the mHealth delivery of the i-REBOUND programme will be feasible and acceptable in people post stroke/TIA living in rural and urban regions of Sweden. The results of this feasibility trial will inform the development of full-scale and appropriately powered trial to test the effects and costs of mHealth delivered physical activity for people after stroke or TIA. Trial registration ClinicalTrials.gov Identifier: NCT05111951. Registered November 8, 2021

Earth Stewardship Science—Transdisciplinary Contributions to Quantifying Natural and Cultural Heritage of Southernmost Africa

Evaluating anthropogenic changes to natural systems demand greater quantification through innovative transdisciplinary research focused on adaptation and mitigation across a wide range of thematic sciences. Southernmost Africa is a unique field laboratory to conduct such research linked to earth stewardship, with &lsquo;earth&rsquo; as in our Commons. One main focus of the AEON&rsquo;s Earth Stewardship Science Research Institute (ESSRI) is to quantify the region&rsquo;s natural and cultural heritage at various scales across land and its flanking oceans, as well as its time-scales ranging from the early Phanerozoic (some 540 million years) to the evolution of the Anthropocene (changes) following the emergence of the first human-culture on the planet some 200 thousand years ago. Here we illustrate the value of this linked research through a number of examples, including: (i) geological field mapping with the aid of drone, satellite and geophysical methods, and geochemical fingerprinting; (ii) regional ground and surface water interaction studies; (iii) monitoring soil erosion, mine tailing dam stability and farming practices linked to food security and development; (iv) ecosystem services through specific biodiversity changes based on spatial logging of marine (oysters and whales) and terrestrial (termites, frogs and monkeys) animals. We find that the history of this margin is highly episodic and complex by, for example, the successful application of ambient noise and groundwater monitoring to assess human-impacted ecosystems. This is also being explored with local Khoisan representatives and rural communities through Citizen Science. Our goal is to publicly share and disseminate the scientific and cultural data, through initiatives like the Africa Alive Corridor 10: &lsquo;Homo Sapiens&rsquo; that embraces storytelling along the entire southern coast. It is envisioned that this approach will begin to develop the requisite integrated technological and societal practices that can contribute toward the needs of an ever-evolving and changing global &lsquo;village&rsquo;