The Effect of Latitude, Litter and Vegetation type on the Performance of the Invasive Species Impatiens glandulifera

Background and Aims Impatiens glandulifera is a blacklisted invasive alien plant species that exhibits high phenotypic variation along latitudinal gradients in its invaded range in Europe, with a preference for riparian, roadside and other moist or disturbed habitats. However, limited information exists on how different latitudinal populations perform in contrasting vegetation types. Furthermore, the impact of I. glandulifera litter on the performance of co-occurring species within different vegetation types has not been assessed. Methods In a greenhouse experiment, we compared performances of different latitudinal populations of I. glandulifera in two vegetation types (roadside vs. riverside) and with or without litter using a life-history trait-based approach. Key Results Performance of I. glandulifera was much lower in graminoid-dominated roadside vegetation turfs than in the herbaceous-dominated riverside vegetation turfs. Although the northern plants exhibited faster onset of flowering, they had lower growth rates, height at maturity and biomass than individuals from central and southern latitudes. Especially the northern plants had lower performance in the highly competitive roadside vegetation compared to the rest of the populations. Interestingly, I. glandulifera litter facilitated the performance of the invader but did not limit the biomass accumulation of the co-occurring species. Conclusions Our findings indicate that the performances of contrasting latitudinal populations of I. glandulifera depend on the invaded vegetation type. The southern and central latitudinal populations of I. glandulifera exhibited higher performances than the northern population. Although litter of I. glandulifera did not limit the performance of native species in invaded vegetation in our study, we show that litter can facilitate the invader s performance. Key words Competitive limitation, Himalayan Balsam, Impatiens glandulifera, invasiveness, invasibility, latitudinal gradient, life-history traits, litter, vegetation type

An Empirical Performance Comparison of Meta-heuristic Algorithms for School Bus Routing Problem

School Bus Routing Problem is an NP-hard Combinatorial Optimization problem. Thus, mega-heuristic algorithms are widely used to solve instances of the School Bus Routing Problem with large data. In this work we present a model of the School Bus Routing Problem and empirical performances comparison between three meta-heuristic algorithms named Simulated Annealing (SA), Tabu Search (TS) and Ant-Colony Optimization (ACO) on the problem. We have analyzed their performances in terms of solution quality. The results show that all three algorithms have the ability to solve the School Bus Routing Problem. In addition, computational results show that TS performed best when execution time is not restricted while ACO had relative good performance when time is restricted but poor when the time is unrestricted.Keywords:  School Bus Routing Problem; Combinatorial Optimization; Meta-heuristic Algorithm

Variability of High risk HPV Genotypes among HIV Infected Women in Mwanza, Tanzania- The Need for Evaluation of Current Vaccine Effectiveness in Developing Countries.

High risk (HR) human papilloma Virus (HPV) genotypes have been associated with cervical cancer. In Tanzania there is a limited data on the epidemiology of HPV and genotypes distribution among HIV infected women. Here we document varieties of HPV genotypes associated with cervical squamous intraepithelial lesions (SIL) among HIV- infected women at Bugando Medical Centre, Mwanza-Tanzania. A cross sectional hospital based study involving HIV infected women was conducted between August and October, 2014. Exfoliated cells from ectocervix and endocervix were collected using cytobrush. HPV genotypes were detected using polymerase chain reaction (PCR) followed by sequencing using specific primers targeting broad range of HPV types. Cytology was done to establish squamous intraepithelial lesions. Log binomial regression analysis was done to establish risk ratios (RR) associated with HPV infection using STATA version 11. A total of 255 HIV infected women with mean age 39.2 ± 9.1 years were enrolled in the study. HPV DNA was detected in 138/255 (54.1 %, 95 % CI: 47-60) of HIV infected women. Twenty six genotypes were detected in various combinations; of these 17(65.3 %) were of HR genotypes. HR genotypes were detected in 124(48.6 %) of HIV infected women. Common HR genotypes detected were HPV-52(26), HPV-58(21), HPV-35(20) and HPV-16(14). The risk of being HPV positive was significantly higher among women with CD4 counts <100 (RR: 1.20, 95 % CI: 1.05-1.35, P = 0.006) and women with SIL (RR: 1.37, 95 % CI: 1.11-1.68, P = 0.005). Significant proportion of HIV infected women with low CD4 counts have various grades of cervical SIL associated with varieties of uncommon HR genotypes. There is a need to evaluate the effectiveness of the current vaccine in preventing cervical cancer in developing countries where HIV is endemic

A bioeconomic analysis of the carbon sequestration potential of agroforestry systems: A case study of Grevillea robusta in South Western Uganda

Grevillea robusta is an agroforestry tree species that has been widely promoted under the carbon forestry schemes in South Western Uganda. The objective of the study was to estimate the amount of carbon sequestered and the profitability of carbon offsets in G. robusta woodlot andagroforestry management options under the Plan Vivo system and small-scale Clean Development Mechanism (CDM). An allometric equation forG. robusta was used to calculate the carbon stocks and merchantable wood volume in the woodlot and agroforestry management options over different crediting periods. The results indicated that G. robusta woodlots and agroforestry management options sequestered 470 and 225 t CO2 e ha-1 respectively, over a 20 year rotation. The net present values (NPVs) of the G. robusta agroforestry management option of US$4367 and 4447 ha-1 under the Plan Vivo and small-scale CDM, respectively, were higher than US$1358 and 1902 ha-1 in the G. robusta woodlot management option. The NPV of the traditional agroforestry system was US$ 3992 ha-1. These results show that, whereas the woodlot option stores more carbon, it is the least profitable option. Analysis also revealed that, although poor households were well represented in the Plan Vivo scheme, they preferred the agroforestry option. This suggests that forest carbon offsets on productive agricultural land, should focus on promoting agroforestry technologies in order to increase profitability and targeting of the poor households

A Simulated Annealing Algorithm for Solving the School Bus Routing Problem: A Case Study of Dar es Salaam

School bus routing is one of major problems facing many schools because student’s transportation system needs to efficient, safe and reliable. Because of this, the school bus routing problem (SBRP) has continued to receive considerable attention in the literature over the years. In short, SBRP seeks to plan an efficient schedule for a fleet of school buses where each bus picks up students from various bus stops and delivers them to their designated school while satisfying various constraints such as the maximum capacity of a bus, the maximum transport cost, the maximum travelling time of students in buses, and the time window to reach at school. Since school bus routing problems differ from one school to another, this paper aims to developing Simulated Annealing (SA) heuristic algorithms for solving   formulating a mathematical model for solving the student bus routing problem. The objective of the model is to minimize amount of time students in the buses from the point where they pickup to the school. We illustrate the developed model using data from five schools located at Dar es salaam, Tanzania. We present a summary of results which indicates good performance of the model. Keywords: bus stop, students, bus, simulated Annealing (SA), Objective function value, Current route, proposed route

Mathematical Formulation Model for a School Bus Routing Problem with Small Instance Data

This paper aims to describe the mathematical formulation model and an exact optimal solution analyses for a school bus routing problem with small instance data. The formulated model has been used  to compute the optimal solution of time spent by students at all bus stops, apart from that the bus stops are not necessary be linearly ordered. We also listed down five procedures of mathematical formulation model to reach an exact optimal solution for a school bus routing problem with small instance data. We assume that each bus has fixed pick up points, these generates the many possible routes for a bus, the number of routes that generated is equal to permutation of pick up points, for each route of a bus we computing the objective function and the route with smallest objective function value can be optimal route of a bus. The sample data from two schools located at Dar es Salaam are collected and validated in the model to shows the good performing of that model. The optimal solution results obtained shows that the students spent minimal minutes in new planned routes compared to current routes. Keywords: bus stop, students, buses, optimal value, optimal solution, set, pick up

Evaluation of Geometric Design Needs of Freeway Systems Based on Safety and Geometric Data

Freeways are arterial highways characterized by high levels of safety and high speed vehicular traffic. Access to and from the freeways is provided through ramps. Geometric elements making up freeway facilities include the roadway, median shoulders, grades, and ramps to and from the traveled way at selected locations, shoulders, radius of curvature, lane width, and speed-change lanes. With the increase of traffic using the freeway systems, there arises more traffic weaving movements within the elements making up the freeway systems. This causes traffic flow to compete at the limited spaces available and reduces safety performance of freeway system. In studies on safety issues of freeway systems, geometric elements of freeways have been evaluated for their safety effects on crashes occurring on the freeways. These studies have included interchange spacing, number of through lanes, median shoulder width and type, ramp spacing, length of segment, speed change lanes, and lengths for limited and extended lanes. Their findings revealed that freeway safety issues are associated with freeway geometric characteristics. However, the previous studies did not consider the safety impact of all segment types on the crash frequency on freeways. This study observed four types of segments when a freeway is divided into segments with Exit and Entry terminals. These segments were defined as EN-EN, EX-EX, EN-EX, EX-EN segments where EX stands for Exit from the freeway and EN stands for Entrance to the freeway. The study also extends types of weaving movements taking place in weaving segments. Crash rate and severity models were developed in this study based on the data collected for every freeway segment type. A complete set of geometric data was included in the data for each freeway segment type. Models for individual freeway segment type (EN-EN, EX-EX, EN-EX, and EX-EN) were developed. The results indicated that for EN-EN segment type; only two freeway characteristics had an impact: median width and segment length. Wider median and long segments both reduced crash while they were insignificant for severity model. For EX-EX segment type, the number of through lanes, median width, and AADT had an impact on average crash rate while for a severity model, only the number of through lanes had an impact. Specifically, it was found that, the number of through lanes reduced both average crash rate and high severity crashes when all through lanes were combined together. However, on individual segment type in a specific freeway, it was found that, the number of through lanes on I-15 increased average crash rate while they reduced average crash rate on I-215. Wider median reduced average crash rate while it increased high severity crashes. Traffic volume increased average crash rate while it was found insignificant on severity model. At a freeway level, EX-EX segment type reduced average crash rate compared to both I-215 and US95 while it reduced average crash rate for I-215 compared to I-15 and US95. For EN-EX segment type, shoulder width had a significant impact on average crash rates while the number of through lanes, median width, length of segment, and curve radius indicated significant impact on severity crashes. Wider shoulders on I-15 reduced average crash rate. The number of through lanes increased high severity crashes when all number of lanes were combined together. However, on individual freeways, the number of through lanes on reduced high severity crashes while they were insignificant on I-215 and US95. Wider median increased high severity crashes when all freeways were combined together while they reduced high severity crashes on I-15. Long segment increased high severity crashes when all EN-EX segment type from all freeways was combined together. Segments with large radius of curvature reduced high severity crashes when all for combined freeways while they increased high severity crashes for I-15. At a freeway level, I-15 increased both average crash rate and high severity crashes compared to I-215 and US95. For EX-EN segments, shoulder and AADT had a significant impact on average crash rate while the number of through lanes, median width, radius curvature and lane changes from ramp-to-freeway had a significant impact on severity crashes. Wider shoulder reduced average crash rate for combined data from all freeways but increased crash rate on I-215.Wider median increased high severity crashes for combined data from all freeways while they were insignificant on average crash rate models. Segments with large radius of curvature increased high severity crashes while it was insignificant on average crash rate model. Lane changes from ramp-to-freeway increased high severity crashes. AADT increased average crash rate while it was found insignificant on severity crashes

An Empirical performances comparison of meta-heuristic algorithms for school bus routing problem

Paper presented at the 4th Strathmore International Mathematics Conference (SIMC 2017), 19 - 23 June 2017, Strathmore University, Nairobi, Kenya.School Bus Routing Problem is an NP-hard Combinatorial Optimization problem, and hence solving the School Bus Routing Problem, requires the application of one or more of the metaheuristic algorithms. This work presents a model of the School Bus Routing Problem and empirical performances comparison between three meta- heuristic algorithms namely, Simulated Annealing, Tabu Search and Ant Colony for solving a real-life School Bus Routing Problem. We have analyzed their performances in terms of computation time, efficiency and solution quality. All the three algorithms have effectively demonstrated the ability to solve the School Bus Routing Problem. The computational results show that better solution quality and fastest execution time of the Meta-heuristic algorithms depends on the number of buses and stops. The results also show that Ant Colony Algorithm produces better solution, followed by Simulated Annealing, then Tabu Search for those schools with a large number of buses and stops.Dar es Salaam University College of Educatio

Achieving sustainable operation and maintenance of water and sanitation facilities: findings from selected primary schools in Northern Uganda

A number of stakeholders including the local government, non-governmental organizations and donors have invested large sums of money towards improving access to safe water, sanitation and hygiene practices in Uganda. However, communities still encounter water related challenges because the facilities are poorly maintained. This paper specifically discusses findings of the O&M of rainwater harvesting tanks in selected primary schools in Northern Uganda districts including Gulu, Kitgum, Lamwo, Pader and Agago. Roles of key stakeholder towards good O&M of Water, Sanitation and Hygiene facilities in schools are suggested as means to ensure sustainability of the facilities

Safety Analysis of Freeway segments with unobserved heterogeneity and Second order spatial effects

Safety analysis of freeway networks entails the quantification of crash frequency influencing factors which include roadway and traffic characteristics, environmental factors as well as human factors. This quantification can be used to detect locations with large impacts on the occurrence of crashes which in turn assist engineers and planners to improve safety levels of the network. Roadway characteristics are comprised of the physical elements of the road geometry such as section length, median and right shoulders, speed-exchange lanes, the number of main facility as well as geometry of the entrance from and exit to the main freeway facility. Traffic characteristics are comprised of traffic flow and vehicular volumes while environmental factors include weather conditions, pavement surface conditions, work zone areas conditions, and lighting conditions along the travel facility. Human factors are comprised of aging, aggressiveness while driving, mental stability, fatigue, alcoholism, acute psychological stress, suicidal behavior, drowsiness, and temporary distraction. Variability in the crash frequency is captured by the interaction of the aforementioned factors either in a multiplicative or additive nature through the use of statistical model formulation. When all factors believed to influence the occurrence of crashes are included in a mathematical formulation and all the assumptions underlying the statistical model are met, variability in the crash frequency referred to as observed heterogeneity can be fully explained. However, not all information believed to generate crashes is available. Some of the factors are latent in nature and some are either not available at the time of analysis or require time and high cost to be established. When such conditions exist, a formulated model does not fully explain observed heterogeneity in the crash frequency. Lack of information to fully explain variability in crash frequency as a result of excluding some factors leads to unobserved heterogeneity problems which results in biased and inconsistent safety estimators. Specifically, when observed crash counts are considered as clusters, analytical approach should consider the possibility of dependence within clustered crash counts. Correlation within clusters may be due to variation being induced by common unobserved cluster-specific factors. Ignoring cluster-effects increases the likelihood in drawing conclusion based on unrealistic inferences because safety estimator standard errors are likely to be underestimated and the usual conditional mean is no longer correctly specified. Cross sectional dependence may also arise when the crash counts have a spatial dimension due to contiguous freeway segments. Such conditions lead to what is known as spatial autocorrelation. This is the presence of spatial pattern in crash frequency over space due to geographic proximity whereby high values of crash frequency tend to cluster together in adjacent freeway segments or high crash frequencies are contiguous with low values of crash frequencies. When the distribution of crash frequency over space exhibit the aforementioned pattern, safety analysis techniques based on the distributional assumption of independence of crash frequency is violated. This study has two objectives: First, analyze safety of freeway geometric features while accounting for the effect of unobserved influencing factors and cluster-specific effects; Second, analyze safety of freeway geometric elements in the presence of spatial autocorrelation due to geographical proximity effects. To achieve the first objective, four models are compared: Two are standard Poisson and Negative binomial regression models which do not account for cluster effects. The other two are mixed effects Poisson and Negative binomial regression models which in addition to fixed effects parts they account for the effects of randomness arising from heterogeneity and clustering. The empirical results indicate that 13.9% of the variation in crash frequency is unaccounted for, which is an indication of the existence of unobserved factors influencing the occurrence of crashes. It is also revealed that weaving segments (EN-EX) had the highest between segment variance compared to non-weaving segments. More vehicles and short segments increased crash frequency while wider right shoulder decreased the crash frequency. It is also observed that weaving segments decreased crash frequency compared to non-weaving segments. These results indicate that by allowing parameters to vary within the weaving and non-weaving segments it is possible to capture and quantify unobserved factors. Ignoring these factors results in biased coefficients because the estimate of the standard errors required determining inferential statistics will be wrong. To achieve the second objective, Conditional Autoregressive models in Bayesian setting framework (CAR) is used. CAR models recognize the presence of spatial dependence which helps to obtain unbiased estimates of parameters quantifying safety levels since the effects of spatial autocorrelation is accounted for in the modeling process. Based on CAR models, approximately 51% of crash frequencies across contiguous freeway segments are spatially autocorrelated. The incident rate ratios revealed that wider shoulder and weaving segments decreased crash frequency by factors of 0.84 and 0.75 respectively. The marginal impact graphs showed that an increase in longitudinal space for segments with two lanes decreased crash frequency. However, an increase of facility width above three lanes results in more crashes which indicates an increase in traffic flows and driving behavior leading to crashes. These results call an important step of analyzing contagious freeway segments simultaneously to account for the existence of spatial autocorrelation