Research works by PhD students of the College of Science and Technology https://dr.ur.ac.rw/handle/123456789/35 2026-05-25T07:15:09Z 2026-05-25T07:15:09Z NDACYAYISENGA, Theogene https://dr.ur.ac.rw/handle/123456789/2928 2026-05-19T13:43:57Z 2025-08-01T00:00:00Z

Analysis of Low-frequency solar Radio Bursts from the solar Corona and their space weathe rimplications NDACYAYISENGA, Theogene Space Weather is the term used to describe changes in the space environment around Earth, often occurring within a day or less, driven by solar activity. The most powerful effects arise when massive bursts of solar material known as Coronal Mass Ejections (CMEs) and their shock waves interact with Earth’s magnetic field. The extent of impact depends on the speed, size, and magnetic strength of these CMEs. Solar flares also modify the amount of solar radiation reaching Earth’s atmosphere, affecting its lower layers. High-energy particles from the Sun, known as solar energetic particles (SEPs), are also a major concern for astronauts traveling to the Moon and beyond. Solar radio observations are essential for space weather research, as solar radio bursts (SRBs) originate from regions where solar flares erupt, SEPs are accelerated, and CMEs are launched. SRBs arise from different altitudes in the solar atmosphere and span wavelengths from millimeters to decameters. Coronal properties such as electron density, magnetic field strength, and turbulence affect the generation of SRBs and vary with both the solar cycle phase and overall solar activity. This study investigated low-frequency SRBs and their space weather implications during the progression of Solar Cycle 25 (SC 25). Initially, type II SRBs were analyzed alongside their impact on the ionosphere, particularly enhancementsintotalelectroncontent(TEC)measuredthroughtherateofTECindex(ROTI).Observations were primarily conducted using the Compound Astronomical Low-cost Low-frequency Instrument for Spectroscopy and Transportable Observatory (CALLISTO). A dataset of 32 type II bursts was used to estimate shock and Alfv´en speeds, ranging from 504 to 1282 km/s and 368 to 826 km/s, respectively, at heliocentric distances of 1 – 2 solar radii (R⊙). The ambient magnetic fieldstrength,rangingfrom7.8to0.7Goverthisradialspan,wasmodeledasB(r) = 6.07r−3.96 G. The analysis showed that 19 of the 32 type II bursts were directly associated with radio blackouts and polar cap absorption events. For the first time, type II bursts were demonstrated to be reliable indicators of subsequent ionospheric irregularities in TEC. ROTI-based assessments revealed that diurnal TEC variability was influenced by the strength of associated solar flares and SEPs, with observed longitudinal variations linked to GPS station locations. In the second part of the study, 35 geomagnetic storms (Dst ≤−50 nT) were analyzed to characterize magnetic activity during SC 25. Correlation between SRBs and geomagnetic disturbances confirmed intense magnetic activity during the cycle’s ascending phase. The time delay between v SRBs and CME-driven magnetospheric impacts ranged from 48 to 120 hours, with an average of 79 hours, highlighting the potential of solar radio emissions as forecasting tools. The analysis confirms that space weather responses to geomagnetic storms exhibit event-specific variability, yet ionospheric storm activity remains a persistent feature, independent of geomagnetic storm magnitude. The third part examined the relationship between SRBs and large SEP events, focusing on their terrestrial impacts. This analysis covered three solar cycles (1997 – 2024) and 122 large SEP events were analyzed. Statistical results showed that SC 25 behaves similarly to SC 23 and exhibits higher activity than SC 24 regarding large SEP occurrences. Velocity dispersion analysis (VDA) revealed that 35 of the 122 SEP events were released either before or concurrently with the peaks of associated GOES X-ray solar flares, without any time lag. The observed correlation betweenSRBs andSEPevents provides insightsintothebehaviorof particlepopulationsdriven by solar flares and CMEs. WAVES/STEREO dynamic spectra indicated that 76% of SRBs extended into interplanetary space, demonstrating the dynamics of associated shocks and electron beams propagating along open or quasi-open magnetic field lines. As a whole, this study underscored the value of SRBs observation for a better understanding of the Sun – Earth interaction dynamics. The ascending phase of SC 25 has been comprehensively monitored and characterized, paving the way for future advancements in space weather modeling and forecasting. Doctoral Thesis

2025-08-01T00:00:00Z KAGABO, Abdou Safari https://dr.ur.ac.rw/handle/123456789/2927 2026-05-19T13:41:26Z 2025-08-01T00:00:00Z

Assessment of the effects of urbanization-induced air pollution on human respiratory health in Rwanda KAGABO, Abdou Safari Urbanization-driven land use changes and urban activities contribute to environmental degradation, intensify climate change, and pose growing risks to public health. This thesis aimed to investigate the impact of urbanization-induced air pollution on respiratory health in Rwanda. Using Landsat satellite imagery and GIS tools, changes in Land Use and Land Cover (LULC) and associated urban indices from 1990 to 2020 were mapped for Kigali. The modified Mann-Kendall test and Sen’s slope estimator were applied to assess trends in air temperatures. Built-up areas increased at an average rate of 3.39 km²/year, while open lands declined by 5.81 km²/year. Simultaneously, air temperature showed significant upward trends, with minimum temperatures increasing by 0.51 °C per decade during the long dry season (JJA) and maximum temperatures increasing by 0.49 °C per decade in the short dry season (JF). Strong positive correlations (r > 0.61, p ≤ 0.05) were observed between air temperature and urban indices across all subregions. To evaluate the degree of personal exposure to air pollution, PM2.5 levels were monitored among 150 participants engaged in seven major urban activities across five rapidly growing cities of Rwanda over five consecutive days in dry season. PM2.5 concentrations in work microenvironments ranged from 12.67 μg/m³ to 192.64 μg/m³, higher than those recorded at home (11.69 to 72.54 μg/m³) and other microenvironments (13.25 µg/m3 to 113.58 µg/m3). Exposure contributions and personalambient differences were dominated by the work microenvironment, with some participants exposed to maximum PM2.5 concentrations up to 22 times higher than ambient levels. These findings indicate the significant effects of daily personal activities and visited microenvironments on personal exposure, and the importance of considering a personal lifestyle in understanding the true personal exposure. To investigate the interactive effects of temperature and ambient air pollution with a focus on differences in urbanization levels on hospital visits for Chronic obstructive pulmonary disease (COPD) and Acute Respiratory Infections (ARIs) over Rwanda, the sector territories were used and categorized into municipalities and agglomerations. Principal component multivariate analysis was applied to generate urban, temperature, and air quality indices, while correlation analysis was used to evaluate their respective relationships with health parameters. Results showed that municipalities recorded higher ambient pollution levels compared to agglomerations. These levels were associated with increased hospital visit rates for respiratory diseases, with correlation coefficients reaching up to ρ = 0.776 and τ = 0.584 for COPD, and ρ = vi 0.672 and τ = 0.494 for ARIs between respiratory disease incidences and air quality index. On the other hand, significant positive correlations were observed between urban index and ARIs in all sectors (ρ = 0.518; τ = 0.366) but the prevalence of respiratory diseases was more closely linked to air quality rather than simply the population size or density in municipalities. The findings of this thesis are valuable for assessing environmental challenges related to land use and for developing long-term strategies to mitigate its impacts on respiratory health. Doctoral Thesis

2025-08-01T00:00:00Z RWEMA, Michel https://dr.ur.ac.rw/handle/123456789/2926 2026-05-19T13:37:36Z 2025-09-01T00:00:00Z

Climate trends and farmers’ perceptions in the Eastern Province of Rwanda RWEMA, Michel This dissertation presents a comprehensive assessment of climate trends and farmers’ perceptions in Rwanda’s Eastern Province by analyzing meteorological data from 1981 to 2021 alongside local knowledge gathered from farmer surveys. Employing robust statistical methods, the study investigates spatial and temporal variations in precipitation and temperature, characterizes drought dynamics, and examines smallholder farmers’ awareness and adaptation strategies in response to ongoing climatic changes. Analyses of precipitation trends across 56 meteorological stations reveal a complex seasonal variability. During the March–May (MAM) season, 39 stations recorded declining rainfall trends, with eight stations in the southern part showing statistically significant decreases. Conversely, in the September–December (SOND) season, 31 stations exhibited declining rainfall, but with only one significant station, while increasing rainfall trends were observed at 25 stations in SOND, with one significant. Regionally, MAM rainfall trends showed a non-significant decrease, whereas SOND demonstrated a slight but non-significant increase. Notably, season duration expanded in SOND across 43 stations, attributed primarily to earlier onset dates, which showed significant decreasing trends at 41 stations. The timing of trend change points generally clustered between 2000 and 2020, coinciding with critical shifts in regional agroclimatic conditions that have influenced cropping practices and heightened crop failure risks. Concurrently, temperature trend analysis highlights substantial warming, especially in minimum and mean temperatures. The annual minimum temperature increased significantly by 2.95 °C (95% CI: 1.64–4.45 °C), with the June–August season showing the greatest rise of 3.37 °C (1.75–4.81 °C). Mean temperature rose by 1.87 °C regionally (0.61–3.19 °C), while maximum temperature changes were not statistically significant. Temporal trends exhibited non-linear behavior, with a plateau in warming from 1990 to 2010, followed by accelerated increases post-2010. Among the identified climatic zones, Northwestern, Central, and Southeastern, the Northwestern zone experienced the most pronounced temperature rise, particularly in seasonal minimum temperatures, underscoring its heightened vulnerability to climate-related stressors. Drought analyses vi reveal an intensification of frequency, duration, and severity since 2010, with geographic variability intimating complex underlying environmental drivers. The Central zone exhibited the highest drought frequency, whereas the Northwestern and Southeastern zones displayed distinct patterns of short- and long-term drought extremes. Complementing the climatic assessment, a socio-environmental inquiry involving 204 farmers across five districts of the Eastern Province examined perceptions, indigenous knowledge, and adaptive responses. The majority (85%) acknowledged the reality of climate change, with over half observing rising temperatures (54%) and nearly 40% noting decreased rainfall. These perceptions are closely aligned with observed meteorological data, reinforcing the reliability of local knowledge systems. Farmers attributed climate change primarily to deforestation, linking it to adverse outcomes such as crop failures, yield reduction, and food shortages. Adaptation strategies employed were diverse, including agroforestry, crop varietal changes, and fertilizer use; however, financial constraints, lack of access to information, and limited availability of inputs present major obstacles to widespread adoption. Importantly, indigenous forecasting methods based on meteorological indicators remain a vital resource for many, enhancing decision-making despite limited formal education among respondents. This integrated analysis elucidates the multifaceted nature of climate change impacts in Eastern Rwanda, revealing significant shifts in climate drivers alongside tangible effects on vulnerable farming communities. The findings emphasize the importance of incorporating localized indigenous knowledge into adaptation planning and underscore the need for supportive policies that address both environmental changes and socioeconomic barriers. Together, these results provide an essential foundation for developing targeted resilience-building initiatives that foster sustainable agricultural practices and improve livelihoods amid evolving climatic challenges. Doctoral Thesis

2025-09-01T00:00:00Z MAVHEMWA, Prudence Munyaradzi https://dr.ur.ac.rw/handle/123456789/2925 2026-05-19T13:28:30Z 2025-09-05T00:00:00Z

Improved usable-security in user authentication of the internet of medical things MAVHEMWA, Prudence Munyaradzi The ever-increasing global disease burden, exacerbated by pandemics like COVID-19 and other global scourges, underscores the critical need for robust healthcare solutions that complement often overburdened medical staff. The Internet of Medical Things (IoMT) offers a transformative possibility, especially for regions such as Sub-Saharan Africa (SSA), where conventional healthcare models are predominant, yet they encounter significant challenges. However, the successful adoption of IoMT is hampered by prevalent cybersecurity threats, mostly stemming from the increased online activity of untrained users and the inherent security and usability deficiencies of current authentication systems. This thesis contributes to addressing these critical gaps by developing and evaluating a novel Machine Learning (ML) based adaptive user authentication framework aimed at improving secure and seamless access to medical IoT resources. The framework employs an edge-centric methodology, fusing the Naive Bayes classifier with the CoFRA model to dynamically evaluate the authenticity and associated risk of a login attempt. This risk assessment is based on a comprehensive set of inputs, including biometric wearable sensor data, non-biometric smartphone sensor data, and predefined user contextual information. Through a User-Centred Design (UCD) methodology, an Android application was developed and tested with a PineTime smartwatch connected via Bluetooth Low Energy, demonstrating the practical application of the model. Our results show that users consistently prefer basic physiological biometrics for authentication, regardless of their age, experience, or level of ICT proficiency. Simulation was conducted and comparative analyses across various ML algorithms, including Naive Bayes variations, Decision Trees, SVM, XGB, and Random Forests, demonstrated superior performance with weighted datasets, highlighting the importance of data characteristics and splitting methodologies. Other classifiers performed exceptionally well in multi-classification circumstances, whereas Naive Bayes demonstrated optimum performance for up to three authentication classes. Despite noted shortcomings, including class imbalance and a 19% false rejection rate, post-deployment evaluations verified good accuracy (100% and 98.6% in useful security metrics) and great user acceptability of the application. ______________________________________________________________________ ii Ultimately, this research provides a user-centric and context-aware authentication solution that adapts to individuals’ personal profiles such as age, risk scores, and health conditions, enabling secure access while striking a balance between security rigor and usability. By enhancing technology adherence and fostering confidence in digital health solutions, this adaptive authentication model significantly contributes to improving patient care, easing caregiver burdens, and advancing the attainment of Sustainable Development Goal (SDG) 3: Ensure healthy lives and promote well-being for all at all ages. Future work will explore explainable AI and advanced risk assessments to further refine the framework's capabilities. Doctoral Thesis

2025-09-05T00:00:00Z