Population genetic structure of the malaria vector Anopheles nili in sub-Saharan Africa

<p>Abstract</p> <p>Background</p> <p><it>Anopheles nili </it>is a widespread efficient vector of human malaria parasites in the humid savannas and forested areas of sub-Saharan Africa. Understanding <it>An. nili </it>population structure and gene flow patterns could be useful for the development of locally-adapted vector control measures.</p> <p>Methods</p> <p>Polymorphism at eleven recently developed microsatelitte markers, and sequence variation in four genes within the 28s rDNA subunit (ITS2 and D3) and mtDNA (COII and ND4) were assessed to explore the level of genetic variability and differentiation among nine populations of <it>An. nili </it>from Senegal, Ivory Coast, Burkina Faso, Nigeria, Cameroon and the Democratic Republic of Congo (DRC).</p> <p>Results</p> <p>All microsatellite loci successfully amplified in all populations, showing high and very similar levels of genetic diversity in populations from West Africa and Cameroon (mean Rs = 8.10-8.88, mean He = 0.805-0.849) and much lower diversity in the Kenge population from DRC (mean Rs = 5.43, mean He = 0.594). Bayesian clustering analysis of microsatellite allelic frequencies revealed two main genetic clusters in the dataset. The first one included only the Kenge population and the second grouped together all other populations. High Fst estimates based on microsatellites (Fst > 0.118, P < 0.001) were observed in all comparisons between Kenge and all other populations. By contrast, low Fst estimates (Fst < 0.022, P < 0.05) were observed between populations within the second cluster. The correlation between genetic and geographic distances was weak and possibly obscured by demographic instability. Sequence variation in mtDNA genes matched these results, whereas low polymorphism in rDNA genes prevented detection of any population substructure at this geographical scale.</p> <p>Conclusion</p> <p>Overall, high genetic homogeneity of the <it>An. nili </it>gene pool was found across its distribution range in West and Central Africa, although demographic events probably resulted in a higher level of genetic isolation in the marginal population of Kenge (DRC). The role of the equatorial forest block as a barrier to gene flow and the implication of such findings for vector control are discussed.</p

Higher Order Spectral Analysis: a Tool for Fault Monitoring and Diagnostics

This paper concerns the application of signal processing techniques based on the Higher Order Spectra (HOS) to the condition monitoring of mechanical systems. These techniques give more information than the linear spectral analysis and are particularly useful in situations where only a single measurement sensor is available. A simple model is presented and analysed with the aim of showing the effectiveness of the so called \u201cpolyspectra\u201d in detecting different kinds of system non-linearities. The HOS analysis is used to interpret the signal structure and the system\u2019s physical characteristics. Particular effort is made in order to give an interpretation of the structure of the HOS estimators. The results show that both the third and the fourth order spectra seem to provide a possibility of using HOS analysis as a tool for the condition monitoring and diagnostics of mechanical systems

Condition Monitoring and Diagnostics in Automatic Machines: Comparison of Vibration Analysis Techniques

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Dynamic analysis of a motorbike engine timing system: Experimental and numerical investigation of the geartrain

The development of high-performance vehicle engines requires advanced investigations in order to provide engineers with proper analysis tools to optimize the system design. The elastodynamic behaviour of the engine powertrain may be critical at high velocities (when the flexibility of the system components can have a major role on the overall performance) with consequences on the valve timing and the transmission of dynamic loads. A thorough numerical/experimental investigation was performed on the timing system of a racing motorbike engine. The timing system included the geartrain, which transmits power from the crankshaft to the camshafts, and the valve train, formed by the camshafts and the cam-follower mechanisms for the valve actuation. An experimental campaign was designed and carried out with the purpose of inspecting the timing system behaviour for different velocities and different design parameters. A numerical model was developed in order to provide a simulation/analysis tool that permits the design optimization of the main system components. The present work focuses on the geartrain elastodynamic analysis, which is the main novelty of a long-lasting activity carried out by the authors in collaborations with Ducati Motor Holding S.p.a. (Bologna, Italy). The experimental campaign, the model development and validation, and some simulation results are reported and discussed

Modal Parameter Estimation of a PVC-product Cleaning Machine by means of Operational Modal Analysis

The prototype of a machine tool for the fine machining of PVC window casings was recently developed and tested. Preliminary tests pointed out that excessive vibrations arise during the execution of some operative motion laws, possibly affecting the product quality. Some structural modification of the machine is thus needed in order to reduce the vibration level. In this context, modal analysis of the machine prototype can be useful to guide the design modifications. In order to excite the system consistently with the operative working conditions, the operational modal analysis was considered more suitable than the traditional experimental modal analysis. The excitation was provided by executing of an impulsive motion law of the machine part hosting the tools, which provides a flat spectrum in the bandwidth of interest. This paper illustrates the main practical aspects of the experimental tests and the results that were obtained by using a commercial software