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Density operator approach to turbulent flows in plasma and atmospheric fluids
No full textWe formulate a statistical wave-mechanical approach to describe dissipation and instabilities in two-dimensional turbulent flows of magnetized plasmas and atmospheric fluids, such as drift and Rossby waves. This is made possible by the existence of Hilbert space, associated with the electric potential of plasma or stream function of atmospheric fluid. We therefore regard such turbulent flows as macroscopic wave-mechanical phenomena, driven by the non-Hermitian Hamiltonian operator we derive, whose anti-Hermitian component is attributed to an effect of the environment. Introducing a wave-mechanical density operator for the statistical ensembles of waves, we formulate master equations and define observables: such as the enstrophy and energy of both the waves and zonal flow as statistical averages. We establish that our open system can generally follow two types of time evolution, depending on whether the environment hinders or assists the system’s stability and integrity. We also consider a phase-space formulation of the theory, including the geometrical-optic limit and beyond, and study the conservation laws of physical observables. It is thus shown that the approach predicts various mechanisms of energy and enstrophy exchange between drift waves and zonal flow, which were hitherto overlooked in models based on wave kinetic equations.</jats:p
Echocardiography nomograms in black South African neonates
No full textBackground: Quantitative estimation of cardiac cham
bers, valve annulus and great vessel dimensions in pae
diatric echocardiography is necessary in clinical man
agement. Various studies have already provided normal
values in the paediatric population that represent most
populations of the world but there is paucity of data
originating from sub-Saharan Africa, particularly in
neonates. We sought to establish reliable echocardio
graphy nomograms for cardiac chambers, valve annulus,
great vessels, and thymus dimensions in the Black South
African neonatal population.
Methods: This was a descriptive, cross-sectional study
evaluating cardiac chamber, valve annuli, thymus, and
great vessel dimensions in Black South African neonates
with normal hearts using echocardiography.
Results: This study recruited 386 neonates (51% females,
49% males; Weight range: 2.50 - 4.43kg [mean, 3.180; SD,
0.38]; BSA range: 0.17 - 0.24m2 [mean, 0.20; SD, 0.01]).
After controlling for the effects of confounders, good
correlation for most cardiac dimensions were observed.
Inter-observer variability revealed a strong correlation
(ICC=0.50-0.82) with most measurements. All cardiac
dimensions correlated well with body weight and were
within ±2 standard deviation with few exceptions.
Conclusion: This study presents nomograms from data
acquired from healthy neonates which contributes to
the current body of knowledge on cardiac dimensions in
the African neonatal age group
Deep reinforcement learning agents for dynamic spectrum access in television whitespace cognitive radio networks
No full textBusinesses, security agencies, institutions, and individuals depend on wireless communication to run their day-to-day activities successfully. The ever-increasing demand for wireless communication services, coupled with the scarcity of available radio frequency spectrum, necessitates innovative approaches to spectrum management. Cognitive Radio (CR) technology has emerged as a pivotal solution, enabling dynamic spectrum sharing among secondary users while respecting the rights of primary users. However, the basic setup of CR technology is insufficient to manage spectrum congestion, as it lacks the ability to predict future spectrum holes, leading to interferences. With predictive intelligence and Dynamic Spectrum Access (DSA), a CR can anticipate when and where other users will be using the radio frequency spectrum, allowing it to overcome this limitation. Reinforcement Learning (RL) in CRs helps predict spectral changes and identify optimal transmission frequencies. This work presents the development of Deep RL (DRL) models for enhanced DSA in TV Whitespace (TVWS) cognitive radio networks using Deep Q-Networks (DQN) and Quantile-Regression (QR-DQN) algorithms. The implementation was done in the Radio Frequency Reinforcement Learning (RFRL) Gym, a training environment of the RF spectrum designed to provide comprehensive functionality. Evaluations show that the DQN model achieves a 96.34 % interference avoidance rate compared to 95.97 % of QRDQN. Average latency was estimated at 1 millisecond and 3.33 milliseconds per packet, respectively. Therefore DRL proves to be a more flexible, scalable, and adaptive approach to dynamic spectrum access, making it particularly effective in the complex and constantly evolving wireless spectrum environment
Theorising the politics of curriculum responsiveness in a Cameroonian university
No full textContent is the epicentre of the educational experience without
which no meaningful learning can take place. Curriculum
is what gives direction to teaching and learning in higher
education and helps in the shaping of academic life for all
students, the direction their future would take as well as
the society they live in. As such, it is critical to explore the
curriculum of higher education courses to ascertain whether
what is being taught and why it is being taught contribute to
the overall goal or purpose of responsiveness. Under such
circumstances, this research was designed as a qualitative
case study of three literature modules. Data was generated
using semi-structured interviews, document analysis and
observation. Two major themes emerged from the data
generated: resistance to change through praise singing;
and advocates of change in leadership. The analysis of these
themes reveal that lecturers selected content based on their
ideological and political stance in society. While the one
resisted change through what they teach, the other advocated for change in the same manner. The paper concludes with
three key thoughts: first, curricula charges like educational
integrity and moral commitment are vital for the continuous
blossoming of the higher education; secondly, those in the
higher education sector must distinguish between their moral
and intellectual responsibility to train students who possess
the right kind of knowledge and skill to lead the nation in
the way it should go; thirdly, curriculum developers, content
selectors, lecturers, researchers, university management,
higher education governing bodies and quality assurance
entities must work hand in hand for the sustainability of the
higher education system
Can superfluid stars be mistaken for black holes in astronomical observations?
No full textWe consider a general relativistic model of a self-interacting complex scalar field with logarithmic nonlinearity motivated by studies of laboratory superfluids and Bose-Einstein condensates. Spherically-symmetric gravitational equilibria are shown in this model, which do not have event horizons but which are regular, singularity-free and asymptotically flat. They can be thus interpreted as compact stars whose stability against gravitational collapse is enhanced not only by the Heisenberg uncertainty principle but also by the property of superfluidity itself, their ``darkness'' comes naturally as a result of suppressed dissipative excitations. Such objects do not obey any absolute upper mass limit of a Tolman-Oppenheimer-Volkoff type, while their relativisticity and effective compactness values are comparable to those of black holes. Their spatial density distribution drops abruptly (at the Gaussian-like rate), which can be mistaken in realistic astronomical observations for the presence of an exact material surface. We therefore present logarithmic superfluid stars as dark compact objects and black hole mimickers
Application of mine tailings sand as construction material : a review
No full textAbstract. Tailings are found during the exploration and processing of mineral ores. They contain a mixture of grounded rocks, processed effluent, and some trace elements that have the potential to damage the environment. Recent urbanisation has led to a large stockpile of tailings in many mining environment constituting health hazard. It becomes very important to develop disposal techniques that will reduce the huge mountain of tailings in mining environment. One of such method is the application of tailings in sustainable concrete production. It is shown that physical and chemical characteristics of tailings are comparable to crusher sand used in engineering construction and therefore, tailings can be used to partially replace sand in bituminous and concrete mixtures. In this review, specific interest has been given to iron, copper, and gold tailings, this is due to their dominance in mining areas of Kwa-Zulu Natal province of South Africa
C6H18N4 behaviour on reinforcing-steel corrosion in concrete immersed in 0.5 M H2SO4
No full textThis paper studies C6 H18 N4 (Triethylenetetramine; TETA) corrosion-resistance behavior on reinforcing-steel in concreteimmersed in 0.5 M H2 SO4. Analyses showed that the corrosion inhibition efficiency increases as theconcentration of C6 H18 N4 admixture increases, whereby the inhibition efficiency also portrayed excellent correlation model (at r = 98.82%, Nash Sutcliffe Efficiency (NSE) = 97.65%, Analysis of Variance (ANOVA) p-value = 0.0350) with function of the C6 H18 N4 concentration admixed in the concrete. The optimal resistance to reinforcing-steel corrosion, in the study, was exhibited in the concrete sample having 0.1824 M C6 H18 N4 admixture, from which inhibition efficiency η = 94.78% was attained. The results support the suitability of C6 H18 N4 for inhibiting reinforcing-steel corrosion in concrete for the industrial/microbial medium, simulated by the 0.5 M H2 SO4
Dropouts in gamified promotions :how retailers can manage them
No full textRetailers are increasingly losing the attention of consumers (Stipp, 2018) and are therefore looking for new, attention-grabbing advertising methods such as gamification (Högberg et al., 2019). Gamification uses game elements to motivate consumers to behave in a certain way in non-game contexts (Deterding et al., 2011; Seaborn and Fels, 2015). Retailers can use gamified promotions that combine a traditional promotion with game elements such as digital prize wheels. Although such gamified promotions can potentially increase sales (Bauer et al., 2020), they can also lead to negative public and consumer perceptions. Previous literature has observed negative effects of gamification on consumer purchase intention (Högberg et al., 2019). These findings suggest that positive effects of gamification cannot be taken for granted. For example, some consumers may ignore gamified advertising or abandon the game. This behavior could have a negative impact on attitudes towards the app and the retailer. We conducted three studies using scenario experiments with a mock-up app to investigate the dropouts of a gamified promotion. The results of studies 1 to 3 show that gamified promotion dropouts have a more negative attitude towards the app and the retailer than players. The results of studies 2 and 3 show that the difference between dropouts and players can be explained by consumer reactance. In addition, study 3 shows that consumer reactance can be reduced if the prize is announced before (vs. after) playing and that retailers should implement a feedback option, e.g. in the form of a push message, so that consumers can decide whether they want to receive the option to play a game next time. The contribution of our work is threefold. First, we examine the effect of dropouts (vs. players) of a gamified promotion on consumers’ attitude toward the app and the retailer. Second, we consider reactance theory by Brehm (1966) to explain the abovementioned effect. Third, we contribute to existing literature by providing implications on how retailers should manage dropouts. In addition, our work highlights the importance of considering dropouts and provides insights into how retailers can deal with them
An evaluation of factors triggering accidents on construction sites
No full textA research dissertation submitted in fulfilment of the academic requirements for Master of the Built Environment: Construction Management, Durban University of Technology, Durban, South Africa, 2025.The Construction Industry (CI) continues to be one of the most physically demanding and
risky industries, especially in developing countries where construction activities are more
labor-intensive and key issues of health and safety are not adequately addressed when
compared with construction practice in the developed countries. Reports of fatal
occupational health and safety incidents in the South African construction industry
indicate an increase in construction site accidents. This study aims to identify key factors
contributing to construction site accidents and propose effective management strategies
for mitigating occupational injuries in KwaZulu Natal's construction sector. Thus, this study
adopted a quantitative research method, utilising the questionnaire survey as a data
collection tool. A purposive sample size of 100 South African Council for the Project and
Construction Management Professions (SACPCMP) practitioners were recruited as
respondents. Out of the 100 questionnaires distributed among the respondents, only 65
were filled out, returned and valid, yielding a response rate of 65%. The data collected
was analyzed using percentages, mean scores and standard deviations, and all the
questions contained in the questionnaires were rated using the SPSS statistical package.
Study findings indicate that poor scaffolding, contact with energized power sources, and
substandard materials significantly contributes to construction site accidents. These
issues have key resultant effects such as the cost of case litigation processes, damage
to plant and equipment, damage to the reputation of the employer, settlement payments
for injuries and death, and the disruption of site operations. This study recommends
enhanced training, stricter safety regulations and improved site inspections as key
measures to reduce accident rates. However, the study further recommends structured
training programs, policy enhancements and stricter enforcement of safety standards to
mitigate site accidents and improve construction safety culture in South Africa
Corrosion rate measurement of sheet pile wall in the port of Durban
No full textSubmitted in fulfilment of the requirements for the degree of Master of Engineering: Civil Engineering and Geomatics, Durban University of Technology, Durban, South Africa, 2024.Ports and harbours are typically located along coastal and inland waterways. Harbours
refer to water bodies adjacent to the shore that shelter watercrafts from stormy
weather and provide anchorage for ships. Ports, on the other hand, denote
infrastructure designed for docking vessels that transport passengers and cargo to
and from land. In essence, harbours become ports when they are utilised for
commercial activities, such as loading and unloading cargo, embarking passengers,
or any other revenue-generating operations. At the Port of Durban, steel sheet piles
were installed beneath the quay walls to protect against rising sea levels, prevent soil
erosion, and support the riprap beneath the deck of the pile quay wall. However, these
steel sheet piles have reached the end of their design life. Furthermore, the thickness
of the steel sheet piles at several berths has decreased due to corrosion.
The aim of this study was to determine the corrosion rate (mm/year) and estimate the
remaining thickness of steel sheet pile walls at Island View Berth 3 and Maydon Wharf
Berth 12 in the Port of Durban. This investigation provided an estimation of the quay
wall’s functionality and determine whether maintenance, reinforcement, or
replacement is necessary. Additionally, the determined corrosion rate will inform future
designs of steel sheet piles.
Island View Berth 3 was constructed in 1993 using the ARBED BZ 7 sheet pile type,
while Maydon Wharf Berth 12 Berth was rebuilt in 2012 with the new HZM/AZ
combined sheet pile wall system. The latter utilised over 2 800 tonnes of HZ 1180M
A-24 king piles and 440 tonnes of AZ 18-700 sheet pile pairs as intermediate piles. A
significant challenge at the Port of Durban was the development of excessive
sinkholes behind berths, believed to result from erosion caused by deteriorating sheet
pile structures. Currently, the Port lacks mechanisms to measure the remaining
thickness of the steel sheet piles or perform underwater maintenance of these
structures. Furthermore, no system is in place to monitor or track the condition of the
sheet piles, making it difficult to determine when replacement or maintenance is
necessary.
During the inspections, 42 points were examined: 22 in Island View Berth 3 and 20 in
Maydon Wharf Berth 12. Island View Berth 3 was inspected over two days in January
2020, while Maydon Wharf Berth 12 was inspected over 14 days. Prior to measurements, divers cleaned 200 mm x 200 mm patches of the steel sheet pile wall.
Marine growths were manually removed using a steel scraper, hammer, and wire
brush. The outer flanges surface of the steel sheet pile was cleaned from top of pile to
the bottom of sheet pile.
An ultrasonic thickness (UT) gauge was employed to assess the remaining thickness
of steel sheet piles at both berths. This device emits high-frequency sound pulses
through a hand-held probe in contact with the metal, measuring the time taken sound
waves to travel through the material, reflect off the back wall, and return to the probe.
The remaining thickness was determined by calculating the sound speed in steel and
using half the total travel time. Corrosion rates were calculated using the formula icorr
=(To−Ta)/t, where To is the original thickness, Ta is the actual thickness, and t is the
exposure time in years. This data can inform the design of new steel sheet pile
structures for ports.
At Island View Berth 3, the average corrosion rate 28 years after installation was
0.0516 mm/year. Maydon Wharf Berth 12 showed varying corrosion rates by zone:
0.0545 mm/year (splash zone), 0.0485 mm/year (tidal zone), 0.0345 mm/year (lowwater zone), and 0.0290 mm/year (immersion zone), with an overall corrosion rate of
0.0466 mm/year. This study highlights significant corrosion variability across studied
zones and emphasises the need for a comprehensive maintenance plan. These
findings provide essential insights for future design and preservation strategies of
marine structures at the Port of Durban.