https://repository.biust.ac.bw:443 The BIUSTRE digital repository system captures, stores, indexes, preserves, and distributes digital research material. 2026-03-14T14:00:59Z https://repository.biust.ac.bw/handle/123456789/726 Relativistic plane wave predictions of ( 𝒑⃗⃗,2𝒑⃗⃗ ) Polarization transfer observables on spherical nuclei Mello, Tumisang This study focuses on the application of the Relativistic Plane Wave Impulse Approximation (RPWIA) model for the predictions of (⃗p, 2⃗p ) polarization transfer observables and the unpo- larized triple differential cross sections on stable spherical nuclei: 208Pb, 40Ca and 12C. The predictions are for knockout from different single-particle states, namely: 3s1/2, 2d3/2, 1h11/2, 2d5/2 and 1g7/2 in 208Pb, 1d3/2 and 2s1/2 in 40Ca, and 1p3/2 state in 12C. The predictions are compared to experimental data from the Research Center for Nuclear Physics (RCNP) at inci- dent proton energies of 392 MeV and coplanar scattering angles: 32.5◦ and -50.0◦. Within the context of the RPWIA model, the relativistic transition amplitude is employed with the incident and outgoing proton wave functions treated as relativistic free Dirac plane waves (ignores the distortion effects). The Relativistic Impulse Approximation (RIA) is adopted for the nucleon-nucleon (N N ) interaction between the incident and the bound proton, the bound- state proton wave functions are extracted through the application of Quantum Hadrodynamics (QHD) and different Relativistic Mean Field (RMF) models: QHDII, NL3, FSUGold and FSUGold2. A computer code was developed and implemented in FORTRAN, to calculate the unpolar- ized triple differential cross sections and the complete set of polarization transfer observables for proton knockout from single-particle states in 208Pb, 40Ca and 12C. The predictions of the unpolarized triple differential cross sections and the analyzing powers were compared to the ex- perimental data from RCNP measured as functions of the kinetic energy of the outgoing proton [Ta′ (MeV)]. Some of the key points that this study seeks to address are to: test the predictive power of the RPWIA model for the predictions of unpolarized triple differential cross sections and the analyzing powers for (⃗p, 2⃗p ) knockout reactions compared to data, identify kinematic regions where the RPWIA predictions are closer to data and compare these predictions with the Relativistic Distorted Wave Impulse Approximation (RDWIA) predictions, investigate the possibilities of applying a model that does not rely on optical potentials, and to study the sen- sitivity of the polarization transfer observables to different RMF models applied in this study. It shows that the RPWIA predictions quantitatively describe the data for the unpolarized triple differential cross sections and the analyzing powers for knockout from most single-particle states. The RPWIA model describe the data within a range of ± 10 MeV [Ta′ (MeV)] from the peak of the unpolarized triple differential cross section for the analyzing power data. Within those regions, the RPWIA and the RDWIA predictions share intersection points for various po- larization transfer observables and nuclear states, showing that the RPWIA model is sufficient to predict the observables for those energies. The variations between the predictions of the complete set of polarization transfer observables using different RMF models are small which implies that the choice of the RMF model has a limited impact on the overall predictions of these observables, i.e., the observables are insensitive to the different RMF models. Thesis (MSc in Physics) ---Botswana International University of Science and Technology, 2025 2025-01-01T00:00:00Z https://repository.biust.ac.bw/handle/123456789/725 Security of quantum key distribution protocols: Towards practical realization Sekga, Comfort Quantum cryptography, or more specifically, quantum key distribution (QKD), guarantees information theoretical security-the Holy Grail of communication se- curity based on the principles of quantum physics. Since the primitive BB84 QKD protocol, great strides have been made both in theory and experiments to develop quantum technologies for real-life applications. Even though QKD has reached this milestone, most security analyses are based on the assumption that the QKD system’s preparation and measurement devices are idealized. However, such as- sumptions can be fatal to the security of a QKD system. As a result, we relax some of these assumptions and prove the security of several QKD protocols by using techniques that closely emulate the imprecisions in preparation and measurement devices and the environment in which the QKD is operated. For instance, we apply the post-selection technique to demonstrate the security of the six-state SARG04 protocol against general attacks with finite resources. Through this approach, one can derive a secure key from a multi-photon source while also taking into account an optimal coherent attack. Moreover, we employ the reference frame independence (RFI) concept, which eliminates the need for active alignment of reference frames to derive the security bounds for several proposed QKD protocols. Our security analyses also incorporate the loss-tolerant method, which allows us to prove the security of QKD by considering imperfections in the state preparation. Further- more, we propose the variants of the measurement-device-independent (MDI) QKD protocol, which utilizes a measurement device controlled by a third party, who may be an eavesdropper, thus removing the possibility of detector side-channel attacks. We also exploit quantum resources, such as biphotons, that enable us to achieve high dimensional encoding in our proposed protocols. Also, we utilize vector vortex and scalar beams to study the security of proposed protocols through a turbulent xvi atmospheric link under diverse weather conditions such as rain or haze. The sim- ulation results demonstrate that the proposed protocols can achieve a significant secret key rate at reasonable transmission distances comparable to the key rates obtained under an ideal environment with perfect preparation and measurement devices. Therefore, proving the security of QKD while allowing intrinsic errors due to signal preparation and measurement devices makes a giant step toward realizing practical QKD implementations. Thesis (MSc in Physics ---Botswana International University of Science and Technology, 2024 2024-10-01T00:00:00Z https://repository.biust.ac.bw/handle/123456789/724 Modelling COVID-19 Pandemic in Southern African Region Nyamajiwa, Violet Zivai The global impact of COVID-19 incidence and mortality propelled world leaders under the guid- ance of the World Health Organization to agree on strategies and goals to reduce infections and mortality. The Southern African region was more vulnerable to the disease due to the high preva- lence of comorbidities. Hence, it is crucial to estimate incidence, mortality, and administered vaccinations to continuously monitor this disease. This estimation generally requires a suitable distribution. Failure to find a suitable distribution can result in wrong inferences. Thus, this research aimed to identify generalized distributions that can best fit and model the COVID-19 data in the Southern African region. Graphical and numerical summaries were used to determine the most suitable probability distributions for modelling COVID-19 data in Southern Africa. Two generalized distributions and their sub-models, as well as the two classical distributions, were evaluated to estimate parameters and identify the most suitable distribution for describ- ing the characteristics of COVID-19 data in the region. The maximum likelihood estimation method was used to estimate the unknown parameters of the models. The results indicated that the Type I Heavy-Tailed Log-Logistic distribution provided a better fit for COVID-19 weekly incidence, mortality, and administered vaccinations in Southern Africa and at the seasonal level compared to its competitors. However, the Topp-Leone Half Logistic-Odd Burr X-Log-Logistic distribution o↵ered a better fit for incidence in the spring period. This study provides valuable insights in modelling heavy-tailed/non-monotonic distributions such as the COVID-19 datasets used in this research. Thesis (MSc in Statistics)---Botswana International University of Science and Technology, 2024 2024-10-23T00:00:00Z https://repository.biust.ac.bw/handle/123456789/723 A comprehensive study of tess maia star Tic 202431888 Kgwatalala, Lister Vivian We present a detailed study of Maia type variable star, TIC 202431888 observed by the TESS satellite (Ricker et al., 2015) for the first time in literature. A new group of variable stars with late B or early A-type characteristics was initially proposed based on radial velocity observations of the prototype star, Maia, which is a member of the Pleiades star cluster as indicated by Struve (1955) and by Struve et al. (1957). During the following years, several studies also identified a short list of possible Maia candidates, but they were later classified into different variability groups. Maia variables are characterized by multiple high frequencies that occur between the red edge of the Cephei and the blue edge of the Scuti instability strips. It is possible that these stars are being driven by a pulsating mechanism that is not yet understood, and the high frequencies observed in late B-type stars still lack an explanation based on our current knowledge. However, stellar variability is being rediscovered by recent space missions like TESS through analysing unprecedented data sets, allowing for the detection of oscillations with very low amplitudes and they have been promising in solving the classification puzzle of Maia phenomenon among B-type stars. This study aims to examine common characteristics of Maia variables (MAIA) to investigate comparable or distinct features in the star TIC 202431888 listed among the classified Maia stars by Balona & Ozuyar (2020). For this reason, the TESS pho- tometry and high-dispersion ground-based spectroscopy were used. Spectroscopic observations were obtained with the 2-m RCC telescope at Rozhen, Bulgaria. From the spectroscopic observations, the atmospheric parameters, the projected rotational velocity v sin i, and chemical abundance of selected elements of TIC 202431888 were determined as well as the evolutionary track of the star in the HR diagram has been presented. The frequency analysis of the TESS photometry resulted in the detection of the two highest peaks at f 1 = 19.32 d 1 and f 2 = 22.10 d 1 , along with a few combinations and harmonics. Our results indicate that TIC 202431888 is a Maia-type variable star with low amplitude and high frequency values exceeding 5 d 1 , and its stellar parameters are in line with those observed between Scuti and B-type variables, which are classified as MAIAU by Balona (2023a). Also, we are in agreement that MAIA should continue to refer to these stars by their observed dis- tinctive features, which are contrary to current models, until accurate classification distinctions for instability regions are established (Balona, 2023a) Thesis (MSc in Physics ) ---Botswana International University of Science and Technology, 2024 2024-10-01T00:00:00Z