Agricultural Technology Adoption and Adaptation under Climate Change: Microevidence from Niger

Many regions of Sub-Saharan Africa (SSA) are experiencing fast increases in human population pressure and urbanization. By 2050, feeding a planet of 9 billion people will require an estimated 50 percent increase in agricultural production. Farmers in in the Sahel are exposed to a highly variable weather over time, and to their limited adaptive capacity, therefore often use livestock as income generator, export earnings, and as insurance against weather risk. There is an increasing demand for livestock products, which increase pressure on crop residues use on the land. In this study, I use panel socio-economic data combined with village rainfall level from Niger to investigate how different types of weather shocks including drought and wet conditions influence farmer’s inputs adaption. Using cluster and year fixed effects estimations, I find that exposure to drought results in a strong and deep decrease in use of crop residues on the soil, which is particularly concerning because crop residue is crucial for soil protection, and fertility. I also find that one of the reasons poor Nigerien farmers remove crop residues on their land, is for livestock feeding purposes. This results in a bad synergy because removing crop residues could decrease long-term food production, and might keep households in poverty trap. Other determinants affecting inputs adoption on the land including temperature increase, income, farm size, and rainfall level of the previous year. I discuss policy recommendations

Regulation, SME Performance and Growth in Cameroon's Manufacturing and Retail Sectors

Research into small business activity has grown impressively over the last decade, though studies on the impact of regulation on business performance remains relatively under-explored. SMEs in Africa face difficulties in infrastructure, finance, as well as in complying with regulations and other governmental requirements. Confronted with poor economic performance, Cameroon began looking at policies to improve SMEs performance and to promote economic growth. This study hence examined the impact of regulation on SMEs performance and growth in Cameroon. The Tax department and the Municipality are the most well-known regulators. Businesses that are aware of their status as SMEs also legally register their companies. However, regulatory compliance of SMEs is low. Therefore the study recommends the establishment of one-stop shop for SMEs registration in Cameroon

Dendritic poly(3-hexylthiophene) star copolymer systems for next generation bulk heterojunction organic photovoltaic cells

Philosophiae Doctor - PhDThe continuous increase in energy consumption and decrease in fossil fuels reserves are a primary concern worldwide; especially for South Africa. Therefore, there is an urgent need for alternative energy resources that will be sustainable, and environmentally friendly in order to tackle the ecological degradation generated by the use of fossil fuels. Among many energy ‘niches’, solar energy appears to be one of the most promising and reliable for the African continent because of the constant availability of sun light. Organic conjugated polymers have been identified as suitable materials to ensure proper design and fabrication of flexible, easy to process and cost-effective solar cells. Their tendency to exhibit good semiconducting properties and their capability to absorb photons from the sunlight and convert it into electrical energy are important features that justify their use in organic photovoltaic cells. Many different polymers have been investigated as either electron donating or electron accepting materials. Among them, poly(3-hexylthiophene) is one of the best electron donor materials that have been used in organic photovoltaic cells. It is a good light absorber and its Highest Occupied Molecular Orbital (HOMO) energy level is suitable to allow electron transfer into an appropriate electron acceptor. On the other hand, the molecular ordering found in dendrimers attracted some interest in the field of photovoltaics as this feature can ensure a constant flow of charges. In this work, I hereby report for the first time, the chemical synthesis of a highly crystalline dendritic star copolymer generation 1 poly(propylene thiophenoimine)-co-poly(3-hexylthiophene) (G1PPT-co-P3HT) with high molecular weight and investigate its application as donating material in bulk heterojunction organic photovoltaics

Conception de circuits micro-ondes multi-bandes et à fréquences agiles pour la réalisation de systèmes sans fil reconfigurables

RÉSUMÉ Les travaux effectués dans cette thèse sont centrés sur la conception et la réalisation de composantes et d’un système récepteur complet Radio Fréquence (RF) et Micro-onde qui possèdent des caractéristiques multifonctionnelles telles que des bandes de fréquences d’opération multiples et reconfigurables par l’utilisation des diodes varactors semi-conducteurs ou des matériaux ferroélectrique (BST) contrôlés par des tensions électriques. Dans la première partie de cette thèse, une méthode de mesure simple et rapide est développée et utilisée pour extraire la perte tangentielle et la constante diélectrique du matériel ferroélectrique (BST) à partir de mesures de capacités interdigitales BST. Un modèle électrique de la capacité BST est aussi obtenu à différentes tensions de polarisation du BST, afin de représenter ainsi la variation des pertes résistives et le pourcentage d’accordabilité de la capacitance par rapport à la tension de polarisation. De façon globale, les capacités interdigitales BST caractérisées présentent une accordabilité capacitive de 52% pour une tension appliquée variant de 0 à 25 volts. Dans le but de concevoir un démodulateur frontal six-port reconfigurable, deux coupleurs hybrides quadrature multi bande accordables contrôlés par une tenson à l’aide de diode varactor et par des capacités ferroélectriques (BST) sont caractérisés et comparés dans la seconde partie de cette thèse. Les deux structures sont composées de quatre sections de ligne de transmission microruban d’un quart de longueur d’onde à une fréquence centrale entre les deux fréquences d’opérations, et de deux paires de lignes de transmission ouvertes connectées en parallèle.---------- ABSTRACT The research work in this thesis concerned with the design and realization of radio frequency (RF) and microwave components, and a complete receiver system, with multiple functionality such as multi-bands and reconfigurable operation frequencies bands based on standard silicon or ferroelectric (BST – barium strontium-titanate) varactors. In the first part of this thesis, a simple and fast measurement technique is developed to extract BST loss tangent and dielectric constant through an interdigital BST capacitor. Also, the electrical model obtained for the BST capacitor presents features of resistive loss variation and capacitance tunability. Thin-film BST-based and conventional silicon varactor-based tunable dual-band quadrature hybrid couplers are characterized and compared in this thesis. Both structures are composed of four quarter-wavelength sections at a frequency located between the two operating frequencies and with two pairs of open-ended stubs. Frequency tuning makes use of both BST interdigital and silicon varactor diode capacitors connected at the open-ended stubs. The characterized BST interdigital capacitor (IDC) presents a capacitive-tunability of 52% through an applied voltage of 0 to 25 volt, while 82.5% is achieved for the selected commercial silicon varactor diode. The silicon varactor-tuned dual-band coupler exhibits 45.9 % and 5.2 % tuning range of center frequency for the first and the second band, respectively, while 29.2 % and 4.3 % are achieved for the BST tunable coupler. With two-tone non-linear characterization test, the BST tunable coupler biased at 0 and 25 volt presents an IIP3 of +25.45 and +35 dBm, respectively, while +11.5 and +34 dBm are obtained for the silicon varactor tunable coupler

Model reframing by feature context change

[EN] Many solutions to cost-sensitive classification (and regression) rely on some or all of the following assumptions: we have complete knowledge about the cost context at training time, we can easily re-train whenever the cost context changes, and we have technique-specific methods (such as cost-sensitive decision trees) that can take advantage of that information. In this work we address the problem of selecting models and minimising joint cost (integrating both misclassification cost and test costs) without any of the above assumptions. We introduce methods and plots (such as the so-called JROC plots) that can work with any off-the-shelf predictive technique, including ensembles, such that we re-frame the model to use the appropriate subset of attributes (the feature configuration) during deployment time. In other words, models are trained with the available attributes (once and for all) and then deployed by setting missing values on the attributes that are deemed inefective for reducing the joint cost. As the number of feature configuration combinations grows exponentially with the number of features we introduce quadratic methods that are able to approximate the optimal configuration and model choices, as shown by the experimental results. ([ES] Muchas de las soluciones para la clasificación y regresión sensible al coste se basan en alguna de las siguientes hipótesis: que tenemos un conocimiento completo sobre el contexto de coste en tiempo de entrenamiento, que podemos volver a entrenar con facilidad cada vez que cambia el contexto de costes, y que tenemos los métodos para una técnica especifica (tales como árboles de decisiones sensibles a los costes) que pueden aprovechar esa información. En este trabajo se aborda el problema de la selección de modelos y la minimización de los costes conjuntos (integrando tanto el coste de clasificación errónea como los costes de pruebas de atributos) sin ninguno de los supuestos anteriores. Introducimos métodos y gráficos (como los gráficos JROC) que pueden funcionar con cualquier técnica predictiva común, incluyendo ensembles, de tal manera que nos adapta el modelo para el subconjunto apropiado de atributos (la configuración de los atributos) durante el tiempo de despliegue. En otras palabras, los modelos son entrenados con los atributos disponibles (una vez y para siempre) y luego desplegados mediante el establecimiento de valores faltantes en los atributos que se consideran ineficaces para reducir el conjunto. Como el número de combinaciones de los atributos crece exponencialmente con el número de atributos se introducirán métodos cuadráticos que son capaces de aproximar la opción de configuración óptima y el modelo óptimo, como se muestra con los resultados experimentales.Maguedong Djoumessi, CP. (2013). Model reframing by feature context change. http://hdl.handle.net/10251/44662Archivo delegad

Analyse de l’efficacite des petits exploitants de legumes en zone de foret dans la region du sud-ouest cameroun

This study examines the efficiency of smallholder vegetable farmers in the forest zone of the Southwest region of Cameroon. Data used was collected by means of a field survey within the framework of the Humidtropics program. This study aims to evaluate the technical efficiency levels of small-scale vegetable producers and to identify the sources of inefficiency. It therefore has two specific objectives: i) estimate the technical efficiency of smallholder vegetable farmers, (ii) identify the determinants of the technical efficiency of smallholder vegetable farmers. The efficiency scores for a sample of 100 producers are obtained using Data Envelopment Analysis and a Tobit model is used to identify the sources of inefficiency. The calculated technical efficiency scores range from 12% to 100%, with a mean technical efficiency index of 70% for the constant returns to scale (CRS) model. The technical efficiency scores for the variable returns to scale (VRS) model range from 23% to 100% with a mean score of 79%. Scale efficiency ranges from 40% to 100% with a mean of 87%. The mean technical efficiency scores indicate that there exist better ways of using resources which can push the production of the average producer right to the frontier. The findings show that farm size and access to credit influence efficiency significantly and positively. Age, household size, experience, manure, farm-related training and extension contact improve the efficiency of farmers. Meanwhile, education and membership of farmers’ association have no effect on the productive performance of vegetable farmers. Public and private stakeholders should therefore focus on these factors in order to reduce technical inefficienc