We used the Earth Gravitational Model （EGM2008） data sets to analyze the regional gravity anoma- lies and to study the underground structures in Cameroon. We first created a high-resolution Free-Air anomaly database...We used the Earth Gravitational Model （EGM2008） data sets to analyze the regional gravity anoma- lies and to study the underground structures in Cameroon. We first created a high-resolution Free-Air anomaly database, then corrected the gravity field of the topographic effect by using ETOPO1 DEM with a resolution of 0.01~ to obtain the Bouguer anomaly, then applied a multi-scale wavelet-analysis technique to separate the gravity-field components into different parts of shallow-to-deep origins, and finally used the logarithmic power spectrum technique to obtain detailed images and corresponding source depths as well as certain lateral inho- mogeneity of structure density. The anomalies of shallow origin show successive elongated gravity ＂highs＂ and ＂lows＂ attributable to subsurface Tertiary and lower Cretaceous undulations. Our results are in good agreement with previous investigations.展开更多
This study presents a method based on the experimental measurement of the short-circuit current (Icc) and the open circuit voltage (Vco) of the solar cell. It permits the determination of recombination parameters such...This study presents a method based on the experimental measurement of the short-circuit current (Icc) and the open circuit voltage (Vco) of the solar cell. It permits the determination of recombination parameters such as: diffusion length (L), back surface recombination velocity (Sb), intrinsic junction recombination velocity (Sjo), and macroscopic parameters in particular, the shunt and series resistances of a bifacial solar cell for various illumination levels (n). Illumination level effects on macroscopic parameters are highlighted.展开更多
As a good food supply for the local people in various Senegalese regions, the forest fruits are becoming very important. They are using between foods or main condiment for dishes in many part of Africa. These fruits r...As a good food supply for the local people in various Senegalese regions, the forest fruits are becoming very important. They are using between foods or main condiment for dishes in many part of Africa. These fruits represent non negligible sources of vitamins, carbohydrates and minerals. Instead of more commercialized species such as Adansonia digitata L., Detarium senegalensis J.F.Gmel., Saba senegalensis (A.DC.) Pichon, Tamarindus indica L., this article focused on nutritional values of other fruits with little interest or neglected. These species were Ficus gnaphalocarpa, L., Cordyla pinnata (Lepr. ex A.Rich.) Milne-Redh. and Icacina senegalensis, harvested in soudano-sahelian zone;while Sarcocephalus latifolius (Sm.) E.A. Bruce belongs to Sudanese zone. The fruit pulps were isolated and freeze dried before analysis. The results showed that acidity, vitamin C and total minerals were significantly different from one fruit to another. S. latifolius with the highest acidity content (402.43 mg/100 g) and best vitamin C content if 1488 mg/100 g were found. Also as results, S. latifolius provided high protein content nearby the 20%. The caloric contributing (kcal/100 g) were 102.5, 177 and 132 respectively for F. gnaphalocarpa, C. pinnata, and S. latifolius. The ash contents were the same for all species (4.5%), indicating the richness in mineral elements. Furthermore, all species in this study were good sources of iron, copper and zinc. However, small amounts of sodium were noticed in all samples. Analysis of total sugars and their profile showed that I. senegalensis and C. pinnata were more appreciated. These results predicted the useful incomes for forest fruits in human being. Lot of medicinal virtues has been recognized from these fruits. The increase in value and the preservation of the biodiversity are necessary particularly for C. pinnata which presents a serious threat because of the strong income for wood production.展开更多
This paper presents the results of research on speed regulation of a brushless DC motor</span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;">&l...This paper presents the results of research on speed regulation of a brushless DC motor</span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">. </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">This is mainly a comparative study between a PID regulator and a fuzzy regulator applied to the operation of this type of engine in order to find the best control. The BLDC engine must operate under various speed and load conditions with improved performance and robust and complex speed control. Because of this complexity, the traditional PID command encounters difficulties in controlling the speed of a BLDC. Another control technique is currently developing and is producing good results. This is the fuzzy controller that handles process control problems, that is, managing a process based on a given set point per action on the variables that describe the process. To achieve the desired results, the brushless DC machine model will be studied. With the model obtained, both types of regulator will be tested. A synthesis of the observed comparison results will enable a conclusion to be drawn on the performance of the two types of regulators driving a BLDC (Brushless DC)</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">.展开更多
From the dynamical equation of barotropic relaxing media beneath pressure perturbations, and using the reductive perturbative analysis, we investigate the soliton structure of a （1＋1）-dimensional nonlinear partial ...From the dynamical equation of barotropic relaxing media beneath pressure perturbations, and using the reductive perturbative analysis, we investigate the soliton structure of a （1＋1）-dimensional nonlinear partial differential evolution （NLPDE） equation δy（δη ＋ uδy ＋ （u^2/2）δy）u ＋ auy ＋ u = 0, describing high-frequency regime of perturbations. Thus, by means of Hirota＇s bilinearization method, three typical solutions depending strongly upon a characteristic dissipation parameter are unearthed.展开更多
The synthesis of geological and petroleum research undertaken in the coastal Sedimentary Basin of the Pointe-Noire region enabled the establishment of a lithostratigraphic scale. It has been observed that the order in...The synthesis of geological and petroleum research undertaken in the coastal Sedimentary Basin of the Pointe-Noire region enabled the establishment of a lithostratigraphic scale. It has been observed that the order in which the series observed in outcrop and those encountered by deep wells succeed each other has allowed a value to be given to this relative scale. The study area corresponds to a longitudinal tectonic accident, fault or flexure. It belongs to the Cretaceous and Tertiary coastal sedimentary basin covered by the Plio-Pleistocene age formations (series of circuses), formed of highly permeable sands comprising multiple resistant horizons that store large bodies of water whose reserves are considered very important. Hydrographic network is composed of four main basins with a mediocre size. The quality of this groundwater is considered to be satisfactory for household consumption, but the sustainable management of these reserves requires constant checks on their quality as well as on the level of the reserves. All these resources put the agglomeration of Pointe-Noire close to large exploitable water reserves that meet the need for drinking water, even if, on the whole, the agglomeration is still experiencing many difficulties in terms of its drinking water supply.展开更多
An experimental study was carried out on bricks using local materials in order to take into account the waste wood management to protect the environment and to reduce the cost of the habitat. Chips and sawdust were bu...An experimental study was carried out on bricks using local materials in order to take into account the waste wood management to protect the environment and to reduce the cost of the habitat. Chips and sawdust were built-in clay bricks in order to study their influence on the compressive strength, Young’s modulus and the speed for soundproofing. Testings in compressive strength were made on the parallelepiped clay bricks, stabilized with different percentages of cement, with incorporation to various percentages of sawdust or wood chips (Mahogany), using a universal press. Young’s modulus was measured from the speed of sound by the ultrasonic method. The results obtained show that the incorporation of mahogany tree chips in the stabilized brick at 8% of cement, does not have much effect on the compressive strength. It was found that the incorporation of chips or sawdust on the clay brick, does not improve the compressive strength. The Young’s modulus decreases with increasing content of sawdust and practically remains constant regardless of the content of chips at 4% and 6% of cement. The clay brick mixed with 8% of mahogany sawdust can be an acoustic barrier.展开更多
A theoretical analysis of the electricity production of a photovoltaic solar power plant of 22 MW for different sites in Senegal is presented. The study is carried out in two coastal regions (Dakar and Saint-Louis) an...A theoretical analysis of the electricity production of a photovoltaic solar power plant of 22 MW for different sites in Senegal is presented. The study is carried out in two coastal regions (Dakar and Saint-Louis) and two continental regions (Mbacké and Linguère). This study is done using the RET Screen clean energy project management software climate data. The amount of electricity exported to the grid is calculated for each site. The results show that the climatic conditions of the coastal and continental regions are different from November to June. From July to October, which corresponds to the rainy season in Senegal, the climatic conditions of the coastal and continental regions are similar. The results also show that although the efficiency of photovoltaic modules is better on the coast, electricity production varies little from one site to another. Climate conditions in Senegal therefore have no impact on electricity production.展开更多
This work deals with determining the optimum thickness of the base of an n<sup>+</sup>/p/p<sup>+</sup> silicon solar cell under monochromatic illumination in frequency modulation. The continuit...This work deals with determining the optimum thickness of the base of an n<sup>+</sup>/p/p<sup>+</sup> silicon solar cell under monochromatic illumination in frequency modulation. The continuity equation for the density of minority carriers generated in the base, by a monochromatic wavelength illumination (<i>λ</i>), with boundary conditions that impose recombination velocities (<i>Sf</i>) and (<i>Sb</i>) respectively at the junction and back surface, is resolved. The ac photocurrent is deduced and studied according to the recombination velocity at the junction, to extract the mathematical expressions of recombination velocity (<i>Sb</i>). By the graphic technique of comparing the two expressions obtained, depending on the thickness (<i>H</i>) of the base, for each frequency, the optimum thickness (Hopt) is obtained. It is then modeled according to the frequency, at the long wavelengths of the incident light. Thus, Hopt decreases due to the low relaxation time of minority carriers, when the frequency of modulation of incident light increases.展开更多
The prediction of the mechanical properties of wood and the evolution of its damage has been essential for its application in many fields such as bridges and houses construction, racks of trucks and so on. In more val...The prediction of the mechanical properties of wood and the evolution of its damage has been essential for its application in many fields such as bridges and houses construction, racks of trucks and so on. In more valorization of biomaterials following the example material wood arouses for a few years a?private interest on behalf of the populations. The experimental characterization?makes it possible to consider the mechanical properties local of Pericopsis elata (Assamela) according to various parameters (the wood turpentine, the orientation of wood fibers, water the content, the type of test …). From the?results, we evaluate the mechanical characteristics of Pericopsis elata (Assamela)?according to the three directions of Orthotropy. Then from the tests of load-discharge we measured the evolution of the damage using the variation of the Young modulus, which enabled us to note the reduction in the modulus of elasticity because of the damage following the three directions. Finally we noted a progressive and irreversible degradation of mechanical properties induced by the development of the microscopic cracks within material.展开更多
The modelling and determination of the geometric parameters of a solar cell are important data, which influence the evaluation of its performance under specific operating conditions, as well as its industrial developm...The modelling and determination of the geometric parameters of a solar cell are important data, which influence the evaluation of its performance under specific operating conditions, as well as its industrial development for a low cost. In this work, an n+/p/p+ crystalline silicon solar cell is studied under monochromatic illumination in modulation and placed in a constant magnetic field. The minority carriers’ diffusion coefficient (<em>D</em>(<em>ω</em>, <em>B</em>), in the (<em>p</em>) base leads to maximum values (Dmax) at resonance frequencies (<em>ωr</em>). These values are used in expressions of AC minority carriers recombination velocity (Sb(Dmax, H)) in the rear of the base, to extract the optimum thickness while solar cell is subjected to these specific conditions. Optimum thickness modelling relationships, depending respectively on Dmax, <em>ωr</em> and <em>B</em>, are then established, and will be data for industrial development of low-cost solar cells for specific use.展开更多
In Chad, despite the multiple culinary uses of cassava leaves and tubers, their nutritional values are untapped. In this study, the physicochemical compositions and structure of nine cultivars were assessed. The prote...In Chad, despite the multiple culinary uses of cassava leaves and tubers, their nutritional values are untapped. In this study, the physicochemical compositions and structure of nine cultivars were assessed. The proteins were obtained by Kjeldahl’s method. Total sugars were determined according to the Luff-Schoorl method. For starch content, the polarimetric method of Earle and Milner was used. Mineral elements were carried out using an atomic absorption spectrophotometry. The cyanide was evaluated by the method of Williams and Edwards. Significant variability has been demonstrated in the leaves and dry tubers except for water content and dry matter. Analysis of the variances of the components of the tubers reveals that the water contents of the cultivars vary from 5.01% to 5.86%. The ash contents vary from 4.23% (cultivar DVA2) to 8.32% (cultivar DVL2). For total sugars, the values are between 53.63% (cultivar DVL2) and 57.99% (cultivars DVL12 and KA0303). The fiber contents are lower and vary from 1.74% (cultivar DVL12) to 1.92% (cultivars SB1366, DVA2, TL0101 and PG1314). The starch content varies from 28.93% (cultivar DVL12) to 31.05% (cultivar SB1366). The variations in mineral constituents of the tubers in mg/100g are Ca (145.21 - 250.08), Mg (83.89 - 165.22), P (147.34 - 360.78), K (1534.50 - 3064.09), Zn (0.75 - 0.82) and Mn (0.78 - 0.89). Iron concentrations are from 7.72 mg/100g (cultivar BA0909) to 60.62 mg/100g (cultivar DVA2</span><span style="font-family:Verdana;">)</span><span style="font-family:""><span style="font-family:Verdana;">. Analysis of the variances of the </span><span style="font-family:Verdana;">leaf constituents reveals high contents of Calcium for SB1366 (2108.41 mg/100g)</span><span style="font-family:Verdana;">, of iron (Fe 54.26 mg/100g) and potassium (K 1866.86 mg/100g) for DVL12, </span><span style="font-family:Verdana;">of phosphorus for TL0101 (471.87 mg/100g), of phosphorus (470.36 mg/100g)</span> <span style="font-family:Verdana;">and protein (30.74%) for PG1314, for magnesium for DVA2 (383.41 mg/100g)</span> <span style="font-family:Verdana;">and Copper for KA0303 (0.0147 mg/100g). The concentrations of hydrocyanic</span><span style="font-family:Verdana;"> acids are high in both leaves than fresh tubers (85 - 150 ppm). Lowest values are observed in tubers (10 - 15 ppm) for cultivar DVA2. Principal component analysis of the physicochemical characteristics of the leaves revealed four groups: the first very rich in calcium, magnesium and average potassium contents. Groups 2 and 3 are poor in calcium and magnesium but Group 2 </span><span style="font-family:Verdana;">ha</span></span><span style="font-family:Verdana;">s</span><span style="font-family:Verdana;"> the highest potassium content while Group 3 ha</span><span style="font-family:Verdana;">s</span><span style="font-family:Verdana;"> an intermediate conten</span><span style="font-family:""><span style="font-family:Verdana;">t. Group 4 is very rich in calcium but low in magnesium and potassium. </span><span style="font-family:Verdana;">According to tubers, three groups have been identified which are characterized</span><span style="font-family:Verdana;"> by low, intermediate </span><span style="font-family:Verdana;">and</span><span style="font-family:Verdana;"> high contents in phosphorus. Cultivars SB1366, DVA2, DVL2, TL0101 an</span><span style="font-family:Verdana;">d PG1314 show promising nutritional values and chemical constituents even if some have high levels of hydrocyanic acids. They could be recommended for the national selection program and for various applications.展开更多
Carbon nanotubes (CNTs) grown on plain substrates SiO2/Si(100) by a direct current and hot filaments catalytic chemical vapor deposition process have been studied by synchrotron X-ray absorption near edge spectroscopy...Carbon nanotubes (CNTs) grown on plain substrates SiO2/Si(100) by a direct current and hot filaments catalytic chemical vapor deposition process have been studied by synchrotron X-ray absorption near edge spectroscopy (XANES) technique to theoretically investigate the angular-dependence of carbone (C) K-edge π* and σ* transitions. Experimental XANES spectra show that π* resonance increases with the incidence angle from normal to grazing incidence angle while σ* resonance decreases. This has been explained by the sine-square and cosine-square dependencies of π* and σ* intensities, respectively. These results were confirmed by theoretical XANES curves of highly oriented pyrolytic graphite (HOPG) and CNTs plotted versus incidence angle. It has been shown that π* and σ* transitions strongly depend on the nature of polarized light (linearly or circularly). At the linear polarized light, π* resonance is a preference as well as at right-circular polarized. At the left-circular polarized light, σ* resonance is a preference. The π* intensities are high at parallel orientation and the σ* intensities are low at normal orientation. The smallest π* intensity is noticed at normal orientation, where the π* orbitals are supposed to be lying parallel to the surface plane for perfectly aligned HOPG or CNTs. This explains the incomplete extinction of π* intensity. We noticed at parallel orientation a region where any π* and σ* transitions did not expect because of the lack of polarization light.展开更多
The coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), dates back to December 29, 2019, in Wuhan, China. It quickly spreads like wildfire to all continents in ...The coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), dates back to December 29, 2019, in Wuhan, China. It quickly spreads like wildfire to all continents in the following months. In Guinea, the first case of COVID-19 and death were all reported respectively on March 12 and April 16, 2020. Since then, several studies have found a relationship between certain environmental conditions such as the meteorological factors to have the potential of contributing to the spread of the virus. Thus, this study aims at examining the extent to which observed meteorological factors might have contributed to the spread of the coronavirus disease 2019 (COVID-19) cases in Conakry, from March 1 to May 31, 2020. Meteorological factors such as temperature (T</span><sub><span style="font-family:Verdana;">min</span></sub><span style="font-family:Verdana;">, T</span><sub><span style="font-family:Verdana;">mean</span></sub><span style="font-family:Verdana;"> and T</span><sub><span style="font-family:Verdana;">max</span></sub><span style="font-family:Verdana;">) and relative humidity (RH</span><sub><span style="font-family:Verdana;">min</span></sub><span style="font-family:Verdana;">, RH</span><sub><span style="font-family:Verdana;">mean</span></sub><span style="font-family:Verdana;"> and RH</span><sub><span style="font-family:Verdana;">max</span></sub><span style="font-family:Verdana;">) were analyzed together with the data on the COVID-19. The dynamic of the COVID-19 in Guinea was analyzed along with that of some west African countries. The analysis on the dynamic of the COVID-19 pandemic in West Africa indicated Guinea as one of the most affected countries by the pandemic after Nigeria and Ghana. The study found that in general an increase in the temperature is linked to a decline in the COVID-19 number of cases and deaths, while an increase in the humidity is positively correlated to the number of cases and deaths. Nevertheless, from this study it was also observed that low temperature, mild diurnal temperature and high humidity are likely to favor its transmission. The study therefore, recommends that habitations and hospital rooms should be kept in relatively low humidity and relatively higher temperature to minimize the spread of the (SARS-CoV-2).展开更多
The waves driven by the wind do not move on the water as ordinarily done by sailboats. Indeed, the movement of the waves driven by the wind is more complex than the sailboats’ translation movement that we know. The m...The waves driven by the wind do not move on the water as ordinarily done by sailboats. Indeed, the movement of the waves driven by the wind is more complex than the sailboats’ translation movement that we know. The movement of the wave in our particular case results from the chain-job done by wind’s stress and gravity forces: material is collected upstream (erosion phenomenon) and then deposited on the wave’s summit by the wind. This material deposited on the summit of the wave by the wind is then removed and dispatched on the downstream side of the wave by gravity forces. As always happens in any chain-job: if the wind works faster than gravity forces, great accumulation of material will occur at the summit of the wave that will lead to an increase in its (the wave in this case) height. If conversely the wind works more slowly, a deficit in material delivery will occur and gravity force goes directly to remove material on the wave’s summit and lead to a decrease in its height. In terms of Mechanics, we know that the main obstacle that can seriously disturb the work of the wind is the unavailability of water or so its viscosity. Given the complexity of the process to be studied, it seemed necessary for us to make a use of modulational instability theories such as the standard NLSE in order to better understand the contribution of wind and water viscosity to modulations of driven waves’ amplitudes (or phases): modulations which sometimes can accidentally trigger unpredictable rogue waves.展开更多
The aim for this present study was to evaluate the antioxidant potential of aqueous extracts (AE), hydro-ethanolic extracts (HE) and ethanolic extracts (EE) obtained from an aquatic plant (<em>L. schlechteri<...The aim for this present study was to evaluate the antioxidant potential of aqueous extracts (AE), hydro-ethanolic extracts (HE) and ethanolic extracts (EE) obtained from an aquatic plant (<em>L. schlechteri</em>) using a simple and fast method that is the CCM. This method revealed the presence of phenolics and flavonoids at different levels but with higher antioxidant activity in EE compared to AE. Among the two families of antioxidants evaluated, the phenolic compounds were found to be higher on the EE (5.85 mgEAG/MS) followed by the HE (5.06 mgEAG/MS) and less and less important on the AE (3.661 mgEAG/MS). While the less significantly elevated flavonoids showed values of 1.146 mgECa/MS for EE, 0.406 mgECa/MS for HE et 0.181 mgECa/MS for AE. However, the anti-free radical activity was also evaluated. Unlike the antioxidant activity, the ant-free radical activity with a greater IC50 was observed on AE with a rate of 66.66 mg/mL, then less on the hydro-ethanolic and ethanolic extracts, respectively at levels of 26.15 mg/mL et 19.18 mg/mL.展开更多
Observed rainfall data of the National Meteorological Service of Guinea (NMS) exhibit that synoptic station usually records the largest rainfall amount in Guinea. Only few studies have been done on this rainfall peak ...Observed rainfall data of the National Meteorological Service of Guinea (NMS) exhibit that synoptic station usually records the largest rainfall amount in Guinea. Only few studies have been done on this rainfall peak observed in Conakry. This work better analyses the atmospheric dynamics leading to rainfall particularity. Using NMS data from 1981 to 2010, the monthly contribution and mean seasonal cycle of each station has been done. These findings of the study show that between July and August (rainfall season peak), the coastline particularly Conakry records the largest amount of rainfall. Using Era Interim data for the common period (1981-2010), we also investigate the rainfall dynamics in the lower level (1000 hPa - 850 hPa) from precipitable water, divergence, and moisture flow transport. There is a west and southwest moisture flow transport explained by a strong moisture convergence in the coastal region (Lower-Guinea). Furthermore, values of precipitable water in the same region are found, in agreement with the high moisture flow transport gradient. These incoming flow (west and south-west) undergo a return by blocking’s Kakoulima range (foehn effect) and Fouta Djallon massif to initiate convection clouds on the Guinean coast. These processes enhance a convergence of moisture associated with orographic origin convection. This has an important effect by increasing the rainfall amount in Conakry.展开更多
A （2＋1）-dimensional nonlinear partial differential evolution （NLPDE） equation is presented as a model equation for relaxing high-rate processes in active barothropic media. With the aid of symbolic computation an...A （2＋1）-dimensional nonlinear partial differential evolution （NLPDE） equation is presented as a model equation for relaxing high-rate processes in active barothropic media. With the aid of symbolic computation and Hirota＇s method, some typical solitary wave solutions to this （2＋1）-dimensional NLPDE equation are unearthed. As a result, depending on the dissipative parameter, single and multivalued solutions are depicted.展开更多
This paper proposes a constitutive law and a method for characterizing highly preloaded viscoelastic materials subjected to linear （small-amplitude） vibrations. A multiplicative non-separable variables law has been ...This paper proposes a constitutive law and a method for characterizing highly preloaded viscoelastic materials subjected to linear （small-amplitude） vibrations. A multiplicative non-separable variables law has been suggested to model the behavior that depends on both stretch and time/frequency. This approach allows splitting the intricate combined test performed simultaneously on both stretch and frequency, generally in a limited experimental domain up to 100 Hz, into two independent tests. Thus, on one hand, the dynamic complex modulus dependent on frequency alone is evaluated on the basis of vibration tests in a large experimental domain up to 100 kHz. On the other hand, energetic parameters are determined from a quasi-static hyperelastic tensile test. The complex modulus, dependent on both stretch and frequency, is then deduced from the results acquired from uncoupled investigations. This work shows that, in extension, the elastic modulus increases with increasing stretch, and the loss factor decreases with increasing stretch; while, in compression, around the material undeformed state, the modulus increases as the stretch increases till a certain value of compression stretch （upturn point depending on material characteristics）, and then the modulus decreases as the stretch increases. Globally, preload rigidifies materials but reduces their damping property. These results closely match a well-known observation in solid mechanics.展开更多
In this article, we present the study of a double-pass air insulated by crushed millet stem mixed with gum arabic. The study is carried out based on mathematical models obtained by writing energy conservation laws in ...In this article, we present the study of a double-pass air insulated by crushed millet stem mixed with gum arabic. The study is carried out based on mathematical models obtained by writing energy conservation laws in the various components of the system, which made it possible to determine the evolution of the air temperature as a function of the length of the absorber and to make a comparison with the experimental results. After comparing the results obtained with those found in the literature, the influence of some physical and geometrical parameters on the performance of the solar thermal collector is presented.展开更多
基金supported by CAS-TWAS under grant FR 3240267248the National Natural Science Foundation of China(41021003)the Research Project of State Key Laboratory of Geodesy and Earth's Dynamics(SKLGED2013-4-1-Z)
文摘We used the Earth Gravitational Model （EGM2008） data sets to analyze the regional gravity anoma- lies and to study the underground structures in Cameroon. We first created a high-resolution Free-Air anomaly database, then corrected the gravity field of the topographic effect by using ETOPO1 DEM with a resolution of 0.01~ to obtain the Bouguer anomaly, then applied a multi-scale wavelet-analysis technique to separate the gravity-field components into different parts of shallow-to-deep origins, and finally used the logarithmic power spectrum technique to obtain detailed images and corresponding source depths as well as certain lateral inho- mogeneity of structure density. The anomalies of shallow origin show successive elongated gravity ＂highs＂ and ＂lows＂ attributable to subsurface Tertiary and lower Cretaceous undulations. Our results are in good agreement with previous investigations.
文摘This study presents a method based on the experimental measurement of the short-circuit current (Icc) and the open circuit voltage (Vco) of the solar cell. It permits the determination of recombination parameters such as: diffusion length (L), back surface recombination velocity (Sb), intrinsic junction recombination velocity (Sjo), and macroscopic parameters in particular, the shunt and series resistances of a bifacial solar cell for various illumination levels (n). Illumination level effects on macroscopic parameters are highlighted.
文摘As a good food supply for the local people in various Senegalese regions, the forest fruits are becoming very important. They are using between foods or main condiment for dishes in many part of Africa. These fruits represent non negligible sources of vitamins, carbohydrates and minerals. Instead of more commercialized species such as Adansonia digitata L., Detarium senegalensis J.F.Gmel., Saba senegalensis (A.DC.) Pichon, Tamarindus indica L., this article focused on nutritional values of other fruits with little interest or neglected. These species were Ficus gnaphalocarpa, L., Cordyla pinnata (Lepr. ex A.Rich.) Milne-Redh. and Icacina senegalensis, harvested in soudano-sahelian zone;while Sarcocephalus latifolius (Sm.) E.A. Bruce belongs to Sudanese zone. The fruit pulps were isolated and freeze dried before analysis. The results showed that acidity, vitamin C and total minerals were significantly different from one fruit to another. S. latifolius with the highest acidity content (402.43 mg/100 g) and best vitamin C content if 1488 mg/100 g were found. Also as results, S. latifolius provided high protein content nearby the 20%. The caloric contributing (kcal/100 g) were 102.5, 177 and 132 respectively for F. gnaphalocarpa, C. pinnata, and S. latifolius. The ash contents were the same for all species (4.5%), indicating the richness in mineral elements. Furthermore, all species in this study were good sources of iron, copper and zinc. However, small amounts of sodium were noticed in all samples. Analysis of total sugars and their profile showed that I. senegalensis and C. pinnata were more appreciated. These results predicted the useful incomes for forest fruits in human being. Lot of medicinal virtues has been recognized from these fruits. The increase in value and the preservation of the biodiversity are necessary particularly for C. pinnata which presents a serious threat because of the strong income for wood production.
文摘This paper presents the results of research on speed regulation of a brushless DC motor</span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">. </span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">This is mainly a comparative study between a PID regulator and a fuzzy regulator applied to the operation of this type of engine in order to find the best control. The BLDC engine must operate under various speed and load conditions with improved performance and robust and complex speed control. Because of this complexity, the traditional PID command encounters difficulties in controlling the speed of a BLDC. Another control technique is currently developing and is producing good results. This is the fuzzy controller that handles process control problems, that is, managing a process based on a given set point per action on the variables that describe the process. To achieve the desired results, the brushless DC machine model will be studied. With the model obtained, both types of regulator will be tested. A synthesis of the observed comparison results will enable a conclusion to be drawn on the performance of the two types of regulators driving a BLDC (Brushless DC)</span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">.
文摘From the dynamical equation of barotropic relaxing media beneath pressure perturbations, and using the reductive perturbative analysis, we investigate the soliton structure of a （1＋1）-dimensional nonlinear partial differential evolution （NLPDE） equation δy（δη ＋ uδy ＋ （u^2/2）δy）u ＋ auy ＋ u = 0, describing high-frequency regime of perturbations. Thus, by means of Hirota＇s bilinearization method, three typical solutions depending strongly upon a characteristic dissipation parameter are unearthed.
文摘The synthesis of geological and petroleum research undertaken in the coastal Sedimentary Basin of the Pointe-Noire region enabled the establishment of a lithostratigraphic scale. It has been observed that the order in which the series observed in outcrop and those encountered by deep wells succeed each other has allowed a value to be given to this relative scale. The study area corresponds to a longitudinal tectonic accident, fault or flexure. It belongs to the Cretaceous and Tertiary coastal sedimentary basin covered by the Plio-Pleistocene age formations (series of circuses), formed of highly permeable sands comprising multiple resistant horizons that store large bodies of water whose reserves are considered very important. Hydrographic network is composed of four main basins with a mediocre size. The quality of this groundwater is considered to be satisfactory for household consumption, but the sustainable management of these reserves requires constant checks on their quality as well as on the level of the reserves. All these resources put the agglomeration of Pointe-Noire close to large exploitable water reserves that meet the need for drinking water, even if, on the whole, the agglomeration is still experiencing many difficulties in terms of its drinking water supply.
文摘An experimental study was carried out on bricks using local materials in order to take into account the waste wood management to protect the environment and to reduce the cost of the habitat. Chips and sawdust were built-in clay bricks in order to study their influence on the compressive strength, Young’s modulus and the speed for soundproofing. Testings in compressive strength were made on the parallelepiped clay bricks, stabilized with different percentages of cement, with incorporation to various percentages of sawdust or wood chips (Mahogany), using a universal press. Young’s modulus was measured from the speed of sound by the ultrasonic method. The results obtained show that the incorporation of mahogany tree chips in the stabilized brick at 8% of cement, does not have much effect on the compressive strength. It was found that the incorporation of chips or sawdust on the clay brick, does not improve the compressive strength. The Young’s modulus decreases with increasing content of sawdust and practically remains constant regardless of the content of chips at 4% and 6% of cement. The clay brick mixed with 8% of mahogany sawdust can be an acoustic barrier.
文摘A theoretical analysis of the electricity production of a photovoltaic solar power plant of 22 MW for different sites in Senegal is presented. The study is carried out in two coastal regions (Dakar and Saint-Louis) and two continental regions (Mbacké and Linguère). This study is done using the RET Screen clean energy project management software climate data. The amount of electricity exported to the grid is calculated for each site. The results show that the climatic conditions of the coastal and continental regions are different from November to June. From July to October, which corresponds to the rainy season in Senegal, the climatic conditions of the coastal and continental regions are similar. The results also show that although the efficiency of photovoltaic modules is better on the coast, electricity production varies little from one site to another. Climate conditions in Senegal therefore have no impact on electricity production.
文摘This work deals with determining the optimum thickness of the base of an n<sup>+</sup>/p/p<sup>+</sup> silicon solar cell under monochromatic illumination in frequency modulation. The continuity equation for the density of minority carriers generated in the base, by a monochromatic wavelength illumination (<i>λ</i>), with boundary conditions that impose recombination velocities (<i>Sf</i>) and (<i>Sb</i>) respectively at the junction and back surface, is resolved. The ac photocurrent is deduced and studied according to the recombination velocity at the junction, to extract the mathematical expressions of recombination velocity (<i>Sb</i>). By the graphic technique of comparing the two expressions obtained, depending on the thickness (<i>H</i>) of the base, for each frequency, the optimum thickness (Hopt) is obtained. It is then modeled according to the frequency, at the long wavelengths of the incident light. Thus, Hopt decreases due to the low relaxation time of minority carriers, when the frequency of modulation of incident light increases.
文摘The prediction of the mechanical properties of wood and the evolution of its damage has been essential for its application in many fields such as bridges and houses construction, racks of trucks and so on. In more valorization of biomaterials following the example material wood arouses for a few years a?private interest on behalf of the populations. The experimental characterization?makes it possible to consider the mechanical properties local of Pericopsis elata (Assamela) according to various parameters (the wood turpentine, the orientation of wood fibers, water the content, the type of test …). From the?results, we evaluate the mechanical characteristics of Pericopsis elata (Assamela)?according to the three directions of Orthotropy. Then from the tests of load-discharge we measured the evolution of the damage using the variation of the Young modulus, which enabled us to note the reduction in the modulus of elasticity because of the damage following the three directions. Finally we noted a progressive and irreversible degradation of mechanical properties induced by the development of the microscopic cracks within material.
文摘The modelling and determination of the geometric parameters of a solar cell are important data, which influence the evaluation of its performance under specific operating conditions, as well as its industrial development for a low cost. In this work, an n+/p/p+ crystalline silicon solar cell is studied under monochromatic illumination in modulation and placed in a constant magnetic field. The minority carriers’ diffusion coefficient (<em>D</em>(<em>ω</em>, <em>B</em>), in the (<em>p</em>) base leads to maximum values (Dmax) at resonance frequencies (<em>ωr</em>). These values are used in expressions of AC minority carriers recombination velocity (Sb(Dmax, H)) in the rear of the base, to extract the optimum thickness while solar cell is subjected to these specific conditions. Optimum thickness modelling relationships, depending respectively on Dmax, <em>ωr</em> and <em>B</em>, are then established, and will be data for industrial development of low-cost solar cells for specific use.
文摘In Chad, despite the multiple culinary uses of cassava leaves and tubers, their nutritional values are untapped. In this study, the physicochemical compositions and structure of nine cultivars were assessed. The proteins were obtained by Kjeldahl’s method. Total sugars were determined according to the Luff-Schoorl method. For starch content, the polarimetric method of Earle and Milner was used. Mineral elements were carried out using an atomic absorption spectrophotometry. The cyanide was evaluated by the method of Williams and Edwards. Significant variability has been demonstrated in the leaves and dry tubers except for water content and dry matter. Analysis of the variances of the components of the tubers reveals that the water contents of the cultivars vary from 5.01% to 5.86%. The ash contents vary from 4.23% (cultivar DVA2) to 8.32% (cultivar DVL2). For total sugars, the values are between 53.63% (cultivar DVL2) and 57.99% (cultivars DVL12 and KA0303). The fiber contents are lower and vary from 1.74% (cultivar DVL12) to 1.92% (cultivars SB1366, DVA2, TL0101 and PG1314). The starch content varies from 28.93% (cultivar DVL12) to 31.05% (cultivar SB1366). The variations in mineral constituents of the tubers in mg/100g are Ca (145.21 - 250.08), Mg (83.89 - 165.22), P (147.34 - 360.78), K (1534.50 - 3064.09), Zn (0.75 - 0.82) and Mn (0.78 - 0.89). Iron concentrations are from 7.72 mg/100g (cultivar BA0909) to 60.62 mg/100g (cultivar DVA2</span><span style="font-family:Verdana;">)</span><span style="font-family:""><span style="font-family:Verdana;">. Analysis of the variances of the </span><span style="font-family:Verdana;">leaf constituents reveals high contents of Calcium for SB1366 (2108.41 mg/100g)</span><span style="font-family:Verdana;">, of iron (Fe 54.26 mg/100g) and potassium (K 1866.86 mg/100g) for DVL12, </span><span style="font-family:Verdana;">of phosphorus for TL0101 (471.87 mg/100g), of phosphorus (470.36 mg/100g)</span> <span style="font-family:Verdana;">and protein (30.74%) for PG1314, for magnesium for DVA2 (383.41 mg/100g)</span> <span style="font-family:Verdana;">and Copper for KA0303 (0.0147 mg/100g). The concentrations of hydrocyanic</span><span style="font-family:Verdana;"> acids are high in both leaves than fresh tubers (85 - 150 ppm). Lowest values are observed in tubers (10 - 15 ppm) for cultivar DVA2. Principal component analysis of the physicochemical characteristics of the leaves revealed four groups: the first very rich in calcium, magnesium and average potassium contents. Groups 2 and 3 are poor in calcium and magnesium but Group 2 </span><span style="font-family:Verdana;">ha</span></span><span style="font-family:Verdana;">s</span><span style="font-family:Verdana;"> the highest potassium content while Group 3 ha</span><span style="font-family:Verdana;">s</span><span style="font-family:Verdana;"> an intermediate conten</span><span style="font-family:""><span style="font-family:Verdana;">t. Group 4 is very rich in calcium but low in magnesium and potassium. </span><span style="font-family:Verdana;">According to tubers, three groups have been identified which are characterized</span><span style="font-family:Verdana;"> by low, intermediate </span><span style="font-family:Verdana;">and</span><span style="font-family:Verdana;"> high contents in phosphorus. Cultivars SB1366, DVA2, DVL2, TL0101 an</span><span style="font-family:Verdana;">d PG1314 show promising nutritional values and chemical constituents even if some have high levels of hydrocyanic acids. They could be recommended for the national selection program and for various applications.
文摘Carbon nanotubes (CNTs) grown on plain substrates SiO2/Si(100) by a direct current and hot filaments catalytic chemical vapor deposition process have been studied by synchrotron X-ray absorption near edge spectroscopy (XANES) technique to theoretically investigate the angular-dependence of carbone (C) K-edge π* and σ* transitions. Experimental XANES spectra show that π* resonance increases with the incidence angle from normal to grazing incidence angle while σ* resonance decreases. This has been explained by the sine-square and cosine-square dependencies of π* and σ* intensities, respectively. These results were confirmed by theoretical XANES curves of highly oriented pyrolytic graphite (HOPG) and CNTs plotted versus incidence angle. It has been shown that π* and σ* transitions strongly depend on the nature of polarized light (linearly or circularly). At the linear polarized light, π* resonance is a preference as well as at right-circular polarized. At the left-circular polarized light, σ* resonance is a preference. The π* intensities are high at parallel orientation and the σ* intensities are low at normal orientation. The smallest π* intensity is noticed at normal orientation, where the π* orbitals are supposed to be lying parallel to the surface plane for perfectly aligned HOPG or CNTs. This explains the incomplete extinction of π* intensity. We noticed at parallel orientation a region where any π* and σ* transitions did not expect because of the lack of polarization light.
文摘The coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), dates back to December 29, 2019, in Wuhan, China. It quickly spreads like wildfire to all continents in the following months. In Guinea, the first case of COVID-19 and death were all reported respectively on March 12 and April 16, 2020. Since then, several studies have found a relationship between certain environmental conditions such as the meteorological factors to have the potential of contributing to the spread of the virus. Thus, this study aims at examining the extent to which observed meteorological factors might have contributed to the spread of the coronavirus disease 2019 (COVID-19) cases in Conakry, from March 1 to May 31, 2020. Meteorological factors such as temperature (T</span><sub><span style="font-family:Verdana;">min</span></sub><span style="font-family:Verdana;">, T</span><sub><span style="font-family:Verdana;">mean</span></sub><span style="font-family:Verdana;"> and T</span><sub><span style="font-family:Verdana;">max</span></sub><span style="font-family:Verdana;">) and relative humidity (RH</span><sub><span style="font-family:Verdana;">min</span></sub><span style="font-family:Verdana;">, RH</span><sub><span style="font-family:Verdana;">mean</span></sub><span style="font-family:Verdana;"> and RH</span><sub><span style="font-family:Verdana;">max</span></sub><span style="font-family:Verdana;">) were analyzed together with the data on the COVID-19. The dynamic of the COVID-19 in Guinea was analyzed along with that of some west African countries. The analysis on the dynamic of the COVID-19 pandemic in West Africa indicated Guinea as one of the most affected countries by the pandemic after Nigeria and Ghana. The study found that in general an increase in the temperature is linked to a decline in the COVID-19 number of cases and deaths, while an increase in the humidity is positively correlated to the number of cases and deaths. Nevertheless, from this study it was also observed that low temperature, mild diurnal temperature and high humidity are likely to favor its transmission. The study therefore, recommends that habitations and hospital rooms should be kept in relatively low humidity and relatively higher temperature to minimize the spread of the (SARS-CoV-2).
文摘The waves driven by the wind do not move on the water as ordinarily done by sailboats. Indeed, the movement of the waves driven by the wind is more complex than the sailboats’ translation movement that we know. The movement of the wave in our particular case results from the chain-job done by wind’s stress and gravity forces: material is collected upstream (erosion phenomenon) and then deposited on the wave’s summit by the wind. This material deposited on the summit of the wave by the wind is then removed and dispatched on the downstream side of the wave by gravity forces. As always happens in any chain-job: if the wind works faster than gravity forces, great accumulation of material will occur at the summit of the wave that will lead to an increase in its (the wave in this case) height. If conversely the wind works more slowly, a deficit in material delivery will occur and gravity force goes directly to remove material on the wave’s summit and lead to a decrease in its height. In terms of Mechanics, we know that the main obstacle that can seriously disturb the work of the wind is the unavailability of water or so its viscosity. Given the complexity of the process to be studied, it seemed necessary for us to make a use of modulational instability theories such as the standard NLSE in order to better understand the contribution of wind and water viscosity to modulations of driven waves’ amplitudes (or phases): modulations which sometimes can accidentally trigger unpredictable rogue waves.
文摘The aim for this present study was to evaluate the antioxidant potential of aqueous extracts (AE), hydro-ethanolic extracts (HE) and ethanolic extracts (EE) obtained from an aquatic plant (<em>L. schlechteri</em>) using a simple and fast method that is the CCM. This method revealed the presence of phenolics and flavonoids at different levels but with higher antioxidant activity in EE compared to AE. Among the two families of antioxidants evaluated, the phenolic compounds were found to be higher on the EE (5.85 mgEAG/MS) followed by the HE (5.06 mgEAG/MS) and less and less important on the AE (3.661 mgEAG/MS). While the less significantly elevated flavonoids showed values of 1.146 mgECa/MS for EE, 0.406 mgECa/MS for HE et 0.181 mgECa/MS for AE. However, the anti-free radical activity was also evaluated. Unlike the antioxidant activity, the ant-free radical activity with a greater IC50 was observed on AE with a rate of 66.66 mg/mL, then less on the hydro-ethanolic and ethanolic extracts, respectively at levels of 26.15 mg/mL et 19.18 mg/mL.
文摘Observed rainfall data of the National Meteorological Service of Guinea (NMS) exhibit that synoptic station usually records the largest rainfall amount in Guinea. Only few studies have been done on this rainfall peak observed in Conakry. This work better analyses the atmospheric dynamics leading to rainfall particularity. Using NMS data from 1981 to 2010, the monthly contribution and mean seasonal cycle of each station has been done. These findings of the study show that between July and August (rainfall season peak), the coastline particularly Conakry records the largest amount of rainfall. Using Era Interim data for the common period (1981-2010), we also investigate the rainfall dynamics in the lower level (1000 hPa - 850 hPa) from precipitable water, divergence, and moisture flow transport. There is a west and southwest moisture flow transport explained by a strong moisture convergence in the coastal region (Lower-Guinea). Furthermore, values of precipitable water in the same region are found, in agreement with the high moisture flow transport gradient. These incoming flow (west and south-west) undergo a return by blocking’s Kakoulima range (foehn effect) and Fouta Djallon massif to initiate convection clouds on the Guinean coast. These processes enhance a convergence of moisture associated with orographic origin convection. This has an important effect by increasing the rainfall amount in Conakry.
文摘A （2＋1）-dimensional nonlinear partial differential evolution （NLPDE） equation is presented as a model equation for relaxing high-rate processes in active barothropic media. With the aid of symbolic computation and Hirota＇s method, some typical solitary wave solutions to this （2＋1）-dimensional NLPDE equation are unearthed. As a result, depending on the dissipative parameter, single and multivalued solutions are depicted.
文摘This paper proposes a constitutive law and a method for characterizing highly preloaded viscoelastic materials subjected to linear （small-amplitude） vibrations. A multiplicative non-separable variables law has been suggested to model the behavior that depends on both stretch and time/frequency. This approach allows splitting the intricate combined test performed simultaneously on both stretch and frequency, generally in a limited experimental domain up to 100 Hz, into two independent tests. Thus, on one hand, the dynamic complex modulus dependent on frequency alone is evaluated on the basis of vibration tests in a large experimental domain up to 100 kHz. On the other hand, energetic parameters are determined from a quasi-static hyperelastic tensile test. The complex modulus, dependent on both stretch and frequency, is then deduced from the results acquired from uncoupled investigations. This work shows that, in extension, the elastic modulus increases with increasing stretch, and the loss factor decreases with increasing stretch; while, in compression, around the material undeformed state, the modulus increases as the stretch increases till a certain value of compression stretch （upturn point depending on material characteristics）, and then the modulus decreases as the stretch increases. Globally, preload rigidifies materials but reduces their damping property. These results closely match a well-known observation in solid mechanics.
文摘In this article, we present the study of a double-pass air insulated by crushed millet stem mixed with gum arabic. The study is carried out based on mathematical models obtained by writing energy conservation laws in the various components of the system, which made it possible to determine the evolution of the air temperature as a function of the length of the absorber and to make a comparison with the experimental results. After comparing the results obtained with those found in the literature, the influence of some physical and geometrical parameters on the performance of the solar thermal collector is presented.
