Rwanda Journal of Engineering, Science, Technology and Environment

Coexistence of positive and negative potential nonlinear structures in a two positive ion plasma with Cairns distributed electrons

Xavier Mushinzimana — 2026-02-10

The effects of electron nonthermality on the stopbands in a two positive ion plasma, comprising a cold positive ion species, a warm positive ion species, and Cairns distributed electrons were investigated by Maharaj and Bharuthram. In this study, we extend the study by Maharaj and Bharuthram, and investigate the existence of negative solitons and their coexistence with positive solitons in the same plasma model. It is found that, depending on the combination of the plasma parameter values, the coexistence of solitary waves of both polarities exists in three different combinations: coexistence of positive KdV with negative non-KdV solitons, coexistence of positive non-KdV with negative KdV solitons, and coexistence of positive KdV with negative KdV solitons. The effects of the cold ion charge-to-mass ratio on the stopbands and the solitary wave existence and coexistence domains in the plasma parameter space are also investigated.

Moving objects and moving clocks

C´elestin Kurujyibwami — 2026-02-10

In Special Relativity, it is commonly accepted that a moving clock goes more slowly than a clock at rest in an inertial reference frame. In this paper, we use systematically the Lorentz transformations and prove that the statement is incorrect as long as the moving clock is not accelerating. We show that the statement results from an inexact interpretation of the proper time of objects moving at speeds less than that of light. The paper shows that the standards of length and time are not affected by the relative motion of inertial reference frames.

Effectiveness of the implementation of the informal settlement upgrading programme in Rwanda: Opportunities and challenges of Agatare cell, Nyarugenge Sector, Kigali, Rwanda

Muyombano Emmanuel — 2026-02-10

Informal settlements are residential areas developed outside formal planning and tenure systems, housing nearly one billion people globally and exacerbating urban challenges such as overcrowding and environmental degradation, particularly in developing countries. In Kigali, Rwanda, their growth has contributed to insecurity and limited access to basic services. To address these issues, the government, in collaboration with the World Bank, initiated upgrading programs such as the Agatare project, aiming to improve infrastructure and provide affordable housing. Sustainable urban development also requires attention to environmental concerns, including waste management and drainage. This study evaluates the effectiveness of informal settlement upgrading in Agatare Cell, Nyarugenge Sector, using a mixed-methods approach that combines field observations, questionnaire surveys, semi-structured interviews, and spatial data analysis. Findings indicate that the project generated local employment, enhanced housing quality, contributed to the provision of basic infrastructure and facilities. In addition, it fostered the improvement of the environment and increased public safety through street lighting. It also contributed to the attainment of Kigali’s urban development goals by promoting a secure and clean city. However, challenges were identified. These include the limited financial resources available to property owners to improve their dwellings which can trigger tenure insecurity, inadequate compensation during expropriation, and insufficient community participation. The study recommends the prioritization of tenure security and promoting inclusive community engagement that would strengthen the upgrading initiatives and support sustainable urban resilience.

Stochastic partial differential equations and their applications

Jean de Dieu Mutima — 2026-02-10

This research investigates the existence and uniqueness of solutions in investment forward performance Stochastic Partial Differential Equations (SPDEs). The study employs the Picard iteration method to establish the well-posedness of the SPDE and the convergence of the iterative solution methods. It is built on the seminal works of (Mykhaylo, Ronnie, & Zariphopoulou, 2016) who introduced forward investment strategies and optimal feedback portfolios. Their groundbreaking contributions significantly advanced the understanding of optimal portfolio selection in incomplete markets, guided by forward investment performance criteria. The key concepts such as consistency, limits, continuity, and memorability are employed to elucidate the dynamics of the processes under examination. These notions play a crucial role in characterizing the intricate behavior of the systems and ensuring the validity of the proposed hypotheses. The main focus of this work is exclusively on the theoretical aspects of the existence and uniqueness of solutions, without delving into estimation or calibration methods for model parameters. The parameters are treated as random in certain applications discussed herein. Thus, the primary objective is to explore theorems and methodologies that guarantee the well-posedness of the given SPDE. Particular emphasis is placed on the role of key assumptions such as coercivity, monotonicity, boundedness, hemi continuity, Lipchitz continuity and growth condition as well as initial conditions in ensuring the convergence of iterative methods. Rigorous mathematical tools, including Gronwall's lemma and Itô's formula, are applied to establish uniqueness results. The findings have potential applications in diverse fields, such as population dynamics and Crack propagation in composite materials and others.

Monitoring land use challenges driven by peri-urbanisation around Kigali City, Rwanda

Uwayezu Ernest — 2026-02-10

Urbanisation is accelerating globally, with significant impacts in Sub-Saharan Africa, where peri-urban areas are rapidly expanding, often without adequate planning or infrastructures. This study investigates the environmental sustainability challenges driven by rapid peri-urbanisation in Runda Sector, Kamonyi District, on the fringes of the City of Kigali, Rwanda, between 2010 and 2024. Using a combination of remotely sensed data, GIS analysis, field observations, and semi-structured interviews with 53 local stakeholders, the study (1) examines the spatial patterns of urban expansion; (2) identifies land use changes and associated environmental challenges; and (3) proposes sustainable urban development and mitigation strategies for environmental challenges. Findings show that the built-up area expanded from 560.5 ha in 2010 to 895.0 ha in 2024, while forest cover decreased by 279.0 ha between 2010 and 2020, recovering slightly by 2024 due to reforestation. Similarly, wetlands initially declined from 529.3 ha in 2010 to 387.3 ha in 2020, but later increased to 573.6 ha by 2024, owing to wetland restoration programs. Grasslands declined by 322.2 ha, and cropland by 133.4 ha in 2020–2024. Built-up expansion also occurred on slopes exceeding 35%, increasing from 90 ha in 2010 to 195.4 ha in 2024, despite legal restrictions, raising concerns over erosion and flood risks. These findings demonstrate: (1) significant urban encroachment into environmentally sensitive areas; (2) inadequate enforcement of zoning laws and weak land governance; and (3) increasing vulnerability of natural ecosystems and agricultural land to unregulated development. To mitigate these challenges, the study recommends (1) strict enforcement of slope and wetland-based zoning; (2) participatory land use planning; and (3) investment in green infrastructures and affordable housing to curb outward migration and environmental degradation. These strategies are important for promoting balanced urban growth and environmental sustainability in Kigali's peri-urban areas and other rapidly urbanizing regions in Sub-Saharan Africa.

Development of a machine learning-based model for early diagnosis of neonatal sepsis in Rwanda. Case study: Kabgayi and Ruhengeri level II teaching hospitals

Marianne Icyimpaye — 2026-02-10

Neonatal sepsis is a major cause of death and morbidity in developing countries, particularly in Sub-Saharan Africa. It is a life-threatening condition that can cause multiple organ failure, so early detection is critical for better outcomes and more effective antibiotic use. Current diagnostic methods in Rwanda rely on physician judgment and traditional cultural techniques, which take time and can lead to delays in critical treatment decisions. However, there is limited used of automated, data-driven tools to support early diagnosis, especially at district hospitals where neonatal specialists and advanced laboratory diagnostics are often lacking. The study aimed to develop a machine learning based-model that could be used in Rwandan hospitals for early detection of neonatal sepsis. Using a retrospective cohort study, clinical data from all neonates born and hospitalized in 2023 at Kabgayi and Ruhengeri level II teaching hospitals were extracted from electronic medical records. A machine learning model based on the Artificial Neural Networks (ANN) architecture was developed to predict the risk of neonatal sepsis using clinical data extracted from Electronic Medical Records (EMRs) in neonatal units. Pre-processing steps were used to handle missing values and extract categorical features, and sepsis criteria were defined to identify at-risk neonates. The model underwent 20 training epochs with Adam optimization and included early stopping to prevent overfitting. When tested on a set of 100 samples, the model yielded a test accuracy of 85%, with 85.18% precision, 86.79% recall, and an F1 score of 85.98%. The area under the curve for Receiver Operating Characteristics (ROC-AUC) was 84.88%. The model predicted 54 cases of sepsis among the tested samples and 46 cases of non-sepsis. The classification report indicated a balanced classification performance between the two classes, with a sensitivity of 86.79%, and a specificity of 82.98%. These findings demonstrated the potential of machine learning-based approaches in improving the early diagnosis of neonatal sepsis in developing countries. However, the model should be retested in other hospitals before being considered for integration into the EMR system of neonatal units across the country.

Biodiversity and water quality of Mukura forest and biosphere reserve, Western Rwanda

Venuste Nsengimana — 2026-02-10

Mukura Forest is a biodiversity hotspot within the Albertine Rift essential for biodiversity conservation, climate regulation, and provision of water resources. Despite its importance, a comprehensive biodiversity and water quality assessment was lacking. This study surveyed plants, birds, mammals, amphibians, reptiles, terrestrial arthropods, butterflies, water macroinvertebrates, diatoms and water quality. Water macroinvertebrates were collected by using the kick-nets and hand searching, while diatoms were sampled by substrate scraping. Further, water physicochemical properties were measured in situ using HQ40d Multimeter. Terrestrial arthropods were sampled through hand collection, sweep nets and pitfall traps, while butterflies were sampled using the sweep-net and baited traps. Birds were recorded via point counts and opportunistic observations; reptiles and amphibians were sampled through active searching and visual encounter surveys; mammals were trapped using Sherman live traps while vegetation was sampled using circular plots for woody species and nested quadrats for herbaceous plants. Collected specimens were identified using identification keys to the family and to species levels where possible. Results have indicated a total of 1 523 individuals of water macroinvertebrates and 25 diatom species. Results have also indicated 4 044 individuals of arthropods including 24 butterfly species. Avian surveys documented 124 species, with 12 Albertine Rift endemics and the critically endangered Hooded Vulture. Amphibians and reptiles yielded 12 and five species, respectively. Identified small mammals included 12 species, with three new records for Mukura. The floristic assessment identified 255 species, with two newly recorded. These findings underscore the significance of Mukura for biodiversity conservation and water quality. There is a need to identify collected specimens to specie level, make continuous study in Mukura and other tropical forests of Rwanda.

Light-like parallel vector fields and Einstein’s equations of gravity

C´elestin Kurujyibwami — 2026-02-10

We prove that, contrary to the situation with time-like and space-like parallel vector fields, there are real gravitational fields satisfying Einstein’s equations of gravity and admitting non-trivial light-like parallel vector fields; we solve completely the field equations under this geometric constraint and obtain through Bianchi identities an interesting property for the Riemann curvature tensor corresponding with a real gravitational field admitting a non-trivial parallel vector field. The solutions we obtained turn out to be generically wave-like and then we prove by a geometric method that this class of solutions is quite different from the class of solutions corresponding with spherical waves.

Sets with the Baire property in topologies defined from Vitali selectors on the real line

Venuste Nyagahakwa — 2026-02-10

No abstract.

Preliminary survey of insect pollinator interaction with native and non-native plant species in Nyandungu Urban Wetland Eco-Tourism Park, Rwanda

Jean de Dieu Uwizelimana — 2026-02-10

Wetlands are among the most productive yet threatened ecosystems worldwide, whereas insects play a crucial role in the dynamics of wetland plants. A study on the interactions between insect pollinators and plant species was conducted in the Nyandungu Urban Wetland Eco-Tourism Park in Rwanda. The objectives were to assess types of insect pollinators and their abundance between native and non-native plant species, and examine the influence of flower color on insect pollinator preferences. Field sampling was conducted in April 2024 using both line transects and opportunistic methods. Plant species visitation events and flower color preferences of insect pollinators were recorded to compare pollinator preferences between native and non-native plant species. Recorded insect pollinators were classified into five groups, corresponding to four insect orders: bees (Hymenoptera), butterflies (Lepidoptera), flies (Diptera), wasps (Hymenoptera), and beetles (Coleoptera). Pollinator insects visited more non-native (56.48%) than native plant species (43.52%), but the statistical difference was not significant (t = 2.776, df = 4, p = 0.16). However, pollinators’ flower color preferences differed significantly (F = 3.475, df = 4, p = 0.014), with yellow being the most preferred color. Despite the short sampling period, this first study in Nyandungu Urban Wetland should serve as a baseline for future studies. A seasonal variation study is needed to yield more information on the ecology of pollinator-plant interactions at the Wetland. Similar studies should be extended to other Wetlands of Rwanda and the region.

Orders and families of terrestrial arthropods from Gishanda and Kanyeganyege wetlands in Eastern Province of Rwanda

Venuste Nsengimana — 2026-02-10

Wetlands are critical ecosystems providing ecological, economic, and social benefits to local communities. However, they are increasingly threatened by different kinds of human activities. This study assessed the effects of wetland use change on terrestrial arthropods in Kanyeganyege and Gishanda wetlands in Eastern Rwanda. Data were collected across line transects using hand searching, sweep-nets and pitfall traps. Collected specimens were identified to order and family levels using identification keys in the literature. A total of 3 665 individuals of arthropods belonging to 20 orders and 76 families were collected. Results showed that Kanyeganyege wetland dominated by rice farming harbored 2 259 individuals classified into 20 orders and 63 families, while Gishanda influenced by banana and maize cultivation, had 1 406 individuals distributed into 16 orders and 66 families. Formicidae were the most dominant family in both Gishanda and Kanyeganyege, making up over a third of all samples. Diversity indicated slightly higher taxa diversity in Gishanda (H’= 4.19) than in Kanyeganyege (H’=4.14), while rarefaction curves highlighted the need for further sampling, especially in Gishanda compared to Kanyeganyege. This research provides baseline data for wetland managers and policymakers, emphasizing the need for sustainable wetland management to conserve arthropod biodiversity.

Exploring the use of pesticides from Nicotiana tabacum and Capsicum annuum for fall armyworm control in maize plantations

Eric Tuyambaze — 2026-02-10

This study examines the utilization of Nicotiana tabacum and Capsicum annuum as bioresources for the development of sustainable, organic pesticides aimed at controlling maize caterpillars. Conducted across Gatsata, Nyamata, and Byimana, the research evaluates the efficacy of plant extracts in reducing fall armyworm populations. Nicotiana tabacum leaves and Capsicum annuum fruit extract were prepared, steeped in water, strained, and refrigerated. Extracts were diluted into low, medium, and high concentrations to test the pesticidal effects on maize caterpillars. These extracts were applied to maize caterpillars in controlled and uncontrolled environments to monitor mortality rates. Caterpillar abundance was recorded across three sites using 10m x 10m plots. The study found Nicotiana tabacum and Capsicum annuum extracts have significant pesticidal activity, and the mortality of maize caterpillars ranges from 81 to 84%. These findings highlight the potential of these botanical extracts as eco-friendly alternatives to synthetic pesticides, promoting sustainable agriculture by reducing environmental impact and preserving beneficial insects. The research recommends optimizing the application methods and dosage of these extracts for effective pest management and further exploring their long-term effects on biodiversity.

Evaluation of the efficiency of Lasures for outdoor use on East African wood species

Gloria Hortence Muyizere — 2026-02-10

Timber, a renewable and sustainable building material, is significantly found in the tropical regions like Rwanda where, is used for construction and furniture. However, the tropical climate, with high humidity and temperature fluctuations, along with threats from termites and fungi, challenges the durability and performance of timber. Existing surface treatment techniques often fail to address the specific environmental and socioeconomic conditions of these regions. There is a lack of research on sustainable surface treatments suitable for Rwanda's timber industry. Through experimental testing, this study assesses the sustainability-oriented performance of water-based lasures, a type of surface treatment, on six East African wood species, including; Milicia excelsa (muvula), Markhamia lutea (umusave), Entandrophragma excelsum (libuyu), Cupressus lusitanica (cypress), Pinus callitris (pine), and Eucalyptus saligna (eucalyptus), compared with Fagus sylvatica (European beech) as a reference. It analyzes the physical and chemical changes of these woods over time, aiming to provide insights for local timber industries on the most effective surface treatment techniques and wood species for outdoor use. The research involved testing moisture content, water absorption, and coating integrity of samples treated with pigmented waterbased lasures against paint-coated and untreated samples under controlled conditions. Results revealed that lasure-treated specimens demonstrated lower water uptake, enhanced surface stability, and superior coating adhesion, especially in dense hardwoods. The findings indicate that water-based lasures are a sustainable, low-VOC alternative, capable of prolonging the lifespan and minimizing the maintenance needs of outdoor timber products in tropical climates. These findings also provide the essential guidance for sustainable wood utilization in East Africa and similar regions.

Health Technology Assessment (HTA) framework proposal for Rwanda

Tuyizere Denyse — 2026-02-10

The assessment of health technology offers a framework to analyze whether the costs of health interventions match benefits to patients. Achieving universal health coverage is an important goal for Rwanda. When choosing which new medical technology (medical devices) to adopt, health technology assessment processes should be applied. The objective of this study was to create health technology assessment framework for Rwanda. Quantitative study was conducted among 45 participants from unknown population by using systematic sampling technique. A self-made survey instrument called questionnaire was created for data collection. Data analysis was performed using Statistical Package for Social Sciences software version 21. Significance and correlation of health technology assessment application in healthcare decision-making were tested using binary logistic regression analysis and chi-square test, respectively. Based on the outcomes attained, 66.7% suggested that health facilities should use health technology assessment in decision-making based on health technology assessment framework. Chi-square (x² ) test and Binary logistic analysis test showed the significant correlation between health technology assessment framework and willingness to use health technology assessment in decision-making Health technology assessment has a well-recognized potential to enhance healthcare decision-making in Rwanda. And for future research studies, proposed health technology assessment framework needs to be validated through consultation with experts and policymakers.