Larvicidal Effects of Citrus Peels Extracts against Culex Pipiens Mosquitoes

Background: Mosquitoes transmit severe diseases such as malaria, lymphatic filariasis, dengue fever, and yellow fever. These diseases result in significant morbidity and mortality in humans around the world. This study aimed to provide information on the larvicidal potential of different Citrus species peels against Culex mosquito larvae.Methods: Ethanol extracts of the peels of four Citrus species, such as Citrus sinensis (sweet orange), Citrus reticulata (tangerine), Citrus latifolia (lime), and Citrus paradisi (grape) fruits were tested for larvicidal properties against Culex pipiens at different concentration (3 mg, 5 mg, 7 mg and 8 mg in 100 mL) on 25 larva per concentration. Percentage mortality was recorded for each of the concentrations used. Results: Only Culex latifolia induced the death of all the mosquito larvae (100%) at 5 mg/mL concentration of the extract, meanwhile Culex reticulata resulted in the lowest mortality rate (80%). However, a hundred percent (100%) mortality of the larvae, was observed at 8 mg/mL of all the types of extracts evaluated.Conclusion: The result indicates that the peels of these Citrus species, especially Culex latifolia, hold potential for control of Culex pipiens mosquito larvae

Markovian Queueing Model for Throughput Maximization in D2D-Enabled Cellular Networks

Device-to-Device (D2D) communication has been considered a key enabling technology that can facilitate spectrum sharing in 4G and 5G cellular networks. In order to meet the high data rate demands of these new generation cellular networks, this paper considers the optimization of available spectrum resource through dynamic spectrum access. The utilization of continuous-time Markov chain (CTMC) model for efficient spectrum access in D2D-enabled cellular networks is investigated for the purpose of determining the impact of this model on the capacity improvement of cellular networks. The paper considers the use of CTMC model with both queueing and non-queueing cases called 13-Q CTMC and 6-NQ CTMC respectively with the aim of improving the overall capacity of the cellular network under a fairness constraint among all users. The proposed strategy consequently ensures that spectrum access for cellular and D2D users is optimally coordinated by designing optimal spectrum access probabilities. Numerical simulations are performed to observe the impact of the proposed Markovian queueing model on spectrum access and consequently on the capacity of D2D-enabled cellular networks. Results showed that the proposed 13-Q CTMC provide a more spectrum-efficient sharing scheme, thereby enabling better network performances and larger capabilities to accommodate more users

A mathematical model for studying the impact of climate variability on malaria epidemics in South Africa

Philosophiae Doctor - PhDMalaria is most prevalent in tropical climates, where there are sufficient rainfall for mosquitoes to breed and conducive temperatures for both the mosquito and protozoa to live. A slight change in temperature can drastically affect the lifespan and patterns of mosquitoes, and moreover, the protozoan itself can only survive in a certain temperature range. With higher temperatures, mosquitoes can mature faster, and thus have more time to spread the disease. The malaria parasite also matures more quickly at warmer temperatures. However, if temperatures become too high, neither mosquitoes nor the malaria pathogen can survive. In addition, stagnant water is also a major contributor to the spread of malaria, since most mosquito species breed in small pools of water. The correct amount and distribution of rainfall increases the possible breeding sites for mosquito larvae, which eventually results in more vectors to spread the disease. With little rainfall, there are few places for the mosquitoes to breed. For these reasons, and in order to control mosquito population, it is important to examine the weather parameters such as temperature and rainfall which are imperative in determining the disease epidemics. Accurate seasonal climate forecasts of these variables, together with malaria models should be able to drive an early warning system in endemic regions. These models can also be used to evaluate the possible change in regions under climate change scenarios, and the spread of malaria to new regions. In this study, we develop and analyse a mosquito model to study the population dynamics of mosquitoes. Ignoring the impact of climate, the model is further developed by introducing human compartments into the model. We perform both analytical and numerical analyses on the two models and verify that both models are epidemiological and mathematical well-posed. Using the next generation matrix method, the basic reproduction number of each system is calculated. Results from both analyses confirm that mosquito- and disease-free equilibria are locally asymptotically stable whenever R0 < 1 and unstable whenever R0 > 1. We further establish the global stability of the mosquito-free equilibrium using a Lyapunov function. In order to examine the effectiveness of control measures, we calculate the sensitivity coefficients of the reproductive number of the mosquito-human malaria model and highlight the importance of mosquito biting rate on malaria transmission. In addition, we introduce climate dependent parameters of Anopheles gambiae and climate data of Limpopo province into the malaria model to study malaria transmission over the province. Climate variables and puddle dynamics are further incorporated into the mosquito model to study the dynamics of Anopheles arabiensis. The climatedependent functions are derived from the laboratory experiments in the study of Maharaj [114], and we further verify the sensitivity of the model to parameters through sensitivity analysis. Running the climate data of Dondotha village in Kwazulu-Natal province over the mosquito model, it is used to simulate the impact of climate variables on the population dynamics of Anopheles arabiensis over the village. Furthermore, we incorporate human compartments into the climate-based mosquito model to explore the impact of climate variability on malaria incidence over KwaZulu-Natal province over the period 1970-2005. The outputs of the climate-based mosquito-human malaria model are further analysed with Principal Component Analysis (PCA), Wavelet Power Spectrum (WPS) and Wavelet Cross-coherence Analysis (WCA) to investigate the relationship between the climate variables and malaria transmission over the province. The results from the mosquito model fairly accurately quantify the seasonality of the population of Anopheles arabiensis over the study region and also demonstrate the influence of climatic factors on the vector population dynamics. The model simulates the population dynamics of both immature and adult Anopheles arabiensis and increases our understanding on the importance of mosquito biology in malaria models. Also, the simulated larval density produces a curve which is similar to observed data obtained from another study. In addition, the mosquito-malaria models produce reasonable fits with the observed data over Limpopo and KwaZulu Natal provinces. In particular, they capture all the spikes in malaria prevalence. Our results further highlight the importance of climate factors on malaria transmission and show the seasonality of malaria epidemics over the provinces. The results of the PCA on the model outputs suggest that there are two major process in the model simulation. One of the processes indicate high loadings on the population of Susceptible, Exposed and Infected humans, while the other is more correlated with Susceptible and Recovered humans. However, both processes reveal the inverse correlation between Susceptible-Infected and Susceptible-Recovered humans respectively. Through spectrum analysis, we notice a strong annual cycle of malaria incidence over the province and ascertain a dominant periodicity of one year. Consequently, our findings indicate that an average of 0 to 120-day lag is generally noted over the study period, but the 120-day lag is more associated with temperature than rainfall. The findings of this study would be useful in an early warning system or forecasting of malaria transmission over the study areas

Mathematical modeling and analysis of HIV/AIDS control measures

>Magister Scientiae - MScIn this thesis, we investigate the HIV/AIDS epidemic in a population which experiences a significant flow of immigrants. We derive and analyse a math- ematical model that describes the dynamics of HIV infection among the im- migrant youths and intervention that can minimize or prevent the spread of the disease in the population. In particular, we are interested in the effects of public-health education and of parental care.We consider existing models of public-health education in HIV/AIDS epidemi-ology, and provide some new insights on these. In this regard we focus atten-tion on the papers [b] and [c], expanding those researches by adding sensitivity analysis and optimal control problems with their solutions.Our main emphasis will be on the effect of parental care on HIV/AIDS epidemi-ology. In this regard we introduce a new model. Firstly, we analyse the model without parental care and investigate its stability and sensitivity behaviour.We conduct both qualitative and quantitative analyses. It is observed that in the absence of infected youths, disease-free equilibrium is achievable and is asymptotically stable. Further, we use optimal control methods to determine the necessary conditions for the optimality of intervention, and for disease eradication or control. Using Pontryagin’s Maximum Principle to check the effects of screening control and parental care on the spread of HIV/AIDS, we observe that parental care is more effective than screening control. However, the most efficient control strategy is in fact a combination of parental care and screening control. The results form the central theme of this thesis, and are included in the manuscript [a] which is now being reviewed for publication. Finally, numerical simulations are performed to illustrate the analytical results

Minimizing Interference in Ultra-Dense Femtocell Networks Using Graph-Based Frequency Reuse Technique

This paper investigates the performance of graph colouring schemes for frequency assignment in Long-Term Evolution (LTE) networks with ultra-dense femtocells. The aim of the study is to minimize interference in such networks while ensuring efficient spectrum use for these femtocells. The three schemes investigated are the conventional greedy graph colouring algorithm, the saturation degree algorithm and our proposed graph-based theory (GBT) algorithm. The process of frequency assignment is similar in the last two except that the proposed GBT partitions the femtocells into independent sets for an efficient frequency re-use. The performance of these three schemes was analyzed through extensive simulations to determine the SINR and network capacity that can be obtained with the deployment of these schemes using the ITU-R P1238-7 path loss model. The outcome of this study showed that with the absence of a dynamic frequency assignment scheme, interference level is increased as the number of femtocell users within a particular coverage is increased, leading to a reduction in the capacity of such networks. Simulation results showed that all three algorithms considered have the ability to allocate frequencies to femtocells and minimize interference in a densely deployed environment, thereby increasing network capacity. The proposed GBT assigned the least sub-band thereby ensuring spectral efficiency while minimizing harmful interference. Results show that the greedy algorithm has a disadvantage of inefficiently assigning sub-bands randomly, while the saturation degree assigns more sub-bands when compared with the GBT scheme.Keywords — Femtocell, graph colouring, frequency assignment, LTE

Sequentially Distributed Coalition Formation Game for Throughput Maximization in C-RANs

Cloud radio access network (C-RAN) has been proposed as a solution to reducing the huge cost of network upgrade while providing the spectral and energy efficiency needed for the new generation cellular networks. In order to reduce the interference that occur in C-RAN and maximize throughput, this paper proposes a sequentially distributed coalition formation (SDCF) game in which players, in this case the remote radio heads (RRHs), can sequentially join multiple coalitions to maximize their throughput. Contrary to overlapping coalition formation (OCF) game where players contribute fractions of their limited resources to different coalitions, the SDCF game offers better stability by allowing sequential coalition formation depending on the availability of resources and therefore providing a balance between efficient spectrum use and interference management. An algorithm for the proposed model is developed based on the merge-only method. The performance of the proposed algorithm in terms of stability, complexity and convergence to final coalition structure is also investigated. Simulation results show that the proposed SDCF game did not only maximize the throughput in the C-RAN, but it also shows better performances and larger capabilities to manage interference with increasing number of RRHs compared to existing methods

Preservation and conservation of library materials in university libraries in Southwest, Nigeria

Libraries in third world countries despite the constraints of finance confronting them still make huge investment on acquisition of library resources. Deterioration of library resources has been one of the greatest challenges plaguing the libraries. In order to savage these library resources and the libraries from a colossal loss of her heritage, this study examines preservation and conservation of library materials in university libraries in Southwest, Nigeria. The study adopted a descriptive survey design. A total enumeration technique was used for selecting 308 respondents for the study. Questionnaire was used for data collection and was analyzed using descriptive statistics. The findings revealed that library security is the most used measure of preservation and conservation practices. Dust and particulate matter are the greatest causes of deterioration to library materials. The finding further revealed that dusting, cleaning and proper shelving are the major techniques adopted by the libraries. The study concluded that lack of proper preservation and conservation practices in the universities are the cause of resource loss and deterioration. Therefore, the study recommended that libraries should deploy modern preservation and conservation tools such as technologically enabled ICT devices which will aid adequate storage and enhance the durability and longevity of information materials in the libraries

Effect of Correlations on Type 1 Error Rates of Some Multivariate Normality Tests

Normality assumption of multivariate data is a prerequisite to the use of multivariate statistical data analysis methods before inference could be valid and reliable. Tests developed to validate this assumption including Doornik-Harsen (DH), Shapiro-Francia (SF), Mardia Skewness (MS), Mardia Skewness for small sample (MSS) and Kurtosis (MK), Skewness (S) and Kurtosis(K), Shapiro-Wilk(SW), Royston (R), Desgagne-Micheaux (DM), Henze-Zirkler (HZ), Energy (E), Gel-Gastwirth (GG) and Bontemps-Meddahi (BM) tests often result into different conclusions. These differences can be misleading. Consequently, this paper examined the effect of correlations on the Type 1 error rates of multivariate tests of normality. Monte Carlo experiments were conducted one thousand (1000) times taking into consideration the dimensions, correlations and sample sizes of the multivariate data. A test is affected by correlation if its estimated Type 1 error rate changes as correlation changes. A test is considered good if its estimated error rate approximates the true error rate and best if the number of times it approximates the estimated error rate when counted over the levels of correlations, sample sizes and levels of significance is the highest, the mode. Results show that Type 1 error rates of DH, SF, SW, R, DM, GG and BM tests are affected by correlations and are relatively not good; where as the Type 1 error rates of HZ, MS, MK, MSS, S, K and E tests are not only unaffected by correlations but are also relatively good. Consequently, MS, R, MSS, HZ and E tests have good Type 1 error rates but that of E and HZ tests are best. They are therefore recommended for practitioners

Investigating the resurgence of malaria prevalence in South Africa between 2015 and 2018: A scoping review

Malaria remains a serious concern in most African countries, causing nearly one million deaths globally every year. This review aims to examine the extent and nature of the resurgence of malaria transmission in South Africa. Methods: Using the Arksey and O'Malley framework, this scoping review includes articles published between the years 2015 and 2018 on the resurgence of malaria occurrence in South Africa. Articles were searched between October 2018 to January 2019 using the following electronic databases: CINAHL, Pubmed, Science Direct and SCOPUS. Grey literature from Google Scholar was also hand searched. Key search terms and subject headings such as climate variables, climate changes, climatic factors, malaria resurgence, malaria reoccurrence and malaria increase over epidemic regions in South Africa were used to identify relevant articles. Three independent reviewers performed the selection and characterization of articles, and the data collected were synthesized qualitatively. Results: A total number of 534 studies were identified. Among these, 24 studies met the inclusion criteria

A model of malaria population dynamics with migrants

We present a compartmental model in ordinary differential equations of malaria disease transmission, accommodating the effect of indoor residual spraying on the vector population. The model allows for influx of infected migrants into the host population and for outflow of recovered migrants. The system is shown to have positive solutions. In the special case of no infected immigrants, we prove global stability of the disease-free equilibrium. Existence of a unique endemic equilibrium point is also established for the case of positive influx of infected migrants. As a case study we consider the combined South African malaria region. Using data covering 31 years, we quantify the effect of malaria infected immigrants on the South African malaria region