This scientific paper presents a study investigating the effects of defects at the CdS/CIGS and CdS/SDL interfaces on the performance of CIGS solar cells. The objective of this study is to analyze the influence of def...This scientific paper presents a study investigating the effects of defects at the CdS/CIGS and CdS/SDL interfaces on the performance of CIGS solar cells. The objective of this study is to analyze the influence of defects at the interface between the CdS buffer layer and the CIGS absorber, as well as the surface defect layer (SDL), on CIGS solar cell performance. The study explores three key aspects: the impact of the conduction band offset (CBO) at the CdS/CIGS interface, the effects of interface defects and defect density on performance, and the combined influence of CBO and defect density at the CdS/ SDL and SDL/CIGS interfaces. For interface defects not exceeding 10<sup>13</sup> cm<sup>-2</sup>, we obtained a good efficiency of 22.9% when -0.1 eV analyzing the quality of CdS/SDL and SDL/CIGS junctions, it appears that defects at the SDL/CIGS interface have very little impact on the performances of the CIGS solar cell. By optimizing the electrical parameters of the CdS/SDL interface defects, we achieved a conversion efficiency of 23.1% when -0.05 eV < CBO < 0.05 eV.展开更多
In this manuscript, we used the SCAPS-1D software to perform numerical simulations on a perovskite solar cell. These simulations were used to study the influence of certain parameters on the electrical behavior of the...In this manuscript, we used the SCAPS-1D software to perform numerical simulations on a perovskite solar cell. These simulations were used to study the influence of certain parameters on the electrical behavior of the cell. We have shown in this study that electron mobility is strongly influenced by the thickness of the absorber, since electron velocity is reduced by thickness. The influence of the defect density shows that above 10<sup>16</sup> cm<sup>-3</sup> all the electrical parameters are affected by the defects. The band discontinuity at the interface generally plays a crucial role in the charge transport phenomenon. The importance of this study is to enable the development of good quality perovskite solar cells, while taking into account the parameters that limit solar cell performance.展开更多
Understanding metal accumulation at organ level in roots, leaves and seeds in O. glaberrima (OG) is crucial for improving physiological and metabolic aspects in growing Asian and African rice in salted areas. The micr...Understanding metal accumulation at organ level in roots, leaves and seeds in O. glaberrima (OG) is crucial for improving physiological and metabolic aspects in growing Asian and African rice in salted areas. The micro-analytical imaging techniques are required to reveal its accumulation and distribution within plant tissues. PIXE studies have been performed to determine different elements in rice plants. The existing microbeam analytical technique at the iThemba LABS will be applied for the 2D image mapping of fresh rice tissues to perform a concentration of low atomic mass elements (such as Al, Si, P, S, Cl, Ca, Ti, Mn, Fe, Cu, Br, Zn and K) with detection limits of typically 1-10 μg/g. Comparison of the distribution of the elements between leaves, root and seed samples using uptake and distribution of elements in particular environmental conditions with potential amount of salt in water have been performed. We are also expecting to indicate metal exclusion as salt tolerance strategies from leaves, root, and seed compartments using matrix correlation between samples and between elements on rice species.展开更多
Structural, electronic and optical properties of Sc-based aluminum-nitride alloy have been carried out with first-principles methods using both local density approximation (LDA) and Heyd-Scuseria-Ernzerhof (HSE) hybri...Structural, electronic and optical properties of Sc-based aluminum-nitride alloy have been carried out with first-principles methods using both local density approximation (LDA) and Heyd-Scuseria-Ernzerhof (HSE) hybrid functional. This latter provides a more accurate description of the lattice parameters, enthalpy of formation, electronic and optical properties of our alloy than standard DFT. We found the transition from wurtzite to rocksalt structures at 61% of Sc concentration. By increasing the scandium concentration, the lattice parameters and the band gap decrease. The HSE band gap is in good agreement with available experimental data. The existence of the strong hybridization between Sc 3d and N 2p indicates the transport of electrons from Sc to N atoms. Besides, it is shown that the insertion of the Sc atom leads to the redshift of the optical absorption edge. The optical absorption of Sc<sub>x</sub>Al<sub>1-x</sub>N is found to decrease with increasing Sc concentrations in the low energy range. Because of this, Sc<sub>x</sub>Al<sub>1-x</sub>N have a great potential for applications in photovoltaics and photocatalysis.展开更多
The main objective of this study is to evaluate the seasonal performance of 20 MW solar power plants in Senegal. The analysis revealed notable seasonal variations in the performance of all stations. The most significa...The main objective of this study is to evaluate the seasonal performance of 20 MW solar power plants in Senegal. The analysis revealed notable seasonal variations in the performance of all stations. The most significant yields are recorded in spring, autumn and winter, with values ranging from 5 to 7.51 kWh/kWp/day for the reference yield and 4.02 to 7.58 kWh/kWp/day for the final yield. These fluctuations are associated with intense solar activity during the dry season and clear skies, indicating peak production. Conversely, minimum values are recorded during the rainy season from June to September, with a final yield of 3.86 kWh/kW/day due to dust, clouds and high temperatures. The performance ratio analysis shows seasonal dynamics throughout the year with rates ranging from 77.40% to 95.79%, reinforcing reliability and optimal utilization of installed capacity. The results of the capacity factor vary significantly, with March, April, May, and sometimes October standing out as periods of optimal performance, with 16% for Kahone, 16% for Bokhol, 18% for Malicounda and 23% for Sakal. Total losses from solar power plants show similar seasonal trends standing out for high loss levels from June to July, reaching up to 3.35 kWh/kWp/day in June. However, using solar trackers at Sakal has increased production by up to 25%, demonstrating the operational stability of this innovative technology compared with the plants fixed panel. Finally, comparing these results with international studies confirms the outstanding efficiency of Senegalese solar power plants, other installations around the world.展开更多
In geology, classification and lithological recognition of rocks plays an important role in the area of oil and gas exploration, mineral exploration and geological analysis. In other fields of activity such as constru...In geology, classification and lithological recognition of rocks plays an important role in the area of oil and gas exploration, mineral exploration and geological analysis. In other fields of activity such as construction and decoration, this classification makes sense and fully plays its role. However, this classification is slow, approximate and subjective. Automatic classification curbs this subjectivity and fills this gap by offering methods that reflect human perception. We propose a new approach to rock classification based on direct-view images of rocks. The aim is to take advantage of feature extraction methods to estimate a rock dictionary. In this work, we have developed a classification method obtained by concatenating four (4) K-SVD variants into a single signature. This method is based on the K-SVD algorithm combined with four (4) feature extraction techniques: DCT, Gabor filters, D-ALBPCSF and G-ALBPCSF, resulting in the four (4) variants named K-Gabor, K-DCT, KD-ALBPCSF and KD-ALBPCSF respectively. In this work, we developed a classification method obtained by concatenating four (4) variants of K-SVD. The performance of our method was evaluated on the basis of performance indicators such as accuracy with other 96% success rate.展开更多
The satisfaction rate of desired velocity in the case of a mixture of fast and slow vehicles is studied by using a cellular automaton method. It is found that at low density the satisfaction rate depends on the maxima...The satisfaction rate of desired velocity in the case of a mixture of fast and slow vehicles is studied by using a cellular automaton method. It is found that at low density the satisfaction rate depends on the maximal velocity. However, the behavior of the satisfaction rate as a function of the coefficient of variance is independent of the maximal velocity. This is in good agreement with empirical results obtained by Lipshtat [Phys. Rev. E 79 066110 (2009)]. Furthermore, our numerical result demonstrates that at low density the satisfaction rate takes higher values, whereas the coefficient of variance is close to zero. The coefficient of variance increases with increasing density, while the satisfaction rate decreases to zero. Moreover, we have also shown that, at low density the coefficient variance depends strongly on the probability of overtaking.展开更多
We have employed the density functional theory plane-wave pseudo potential method,with local density approximation and generalized gradient approximation to perform first-principles quantum mechanics calculations in o...We have employed the density functional theory plane-wave pseudo potential method,with local density approximation and generalized gradient approximation to perform first-principles quantum mechanics calculations in order to investigate the structural,elastic and mechanical properties of the intermetallic compound MgCu with a CsCl-type structure.The calculated equilibrium lattice constant is in good agreement with the experimental and theoretical values.The elastic constants were determined from a linear fit of the calculated stress-strain function according to Hooke’s law.From the elastic constants,the bulk modulus B,anisotropy factor A,shear modulus G,Young’s modulus E,Poisson’s ratio y,and the ratio B/G for MgCu compound are obtained.Our calculated results for the bulk modulus B,and Young’s modulus E are consistent with the experimental and theoretical data.The sound velocities and Debye temperature are also predicted from elastic constants.Finally,the linear response method has been used to calculate the thermodynamic properties.The temperature dependence of the enthalpy H,free energy F,entropy S,and heat capacity at constant volume Cv of MgCu crystal in a quasi-harmonic approximation have been obtained from phonon density of states and discussed for the first report.展开更多
A threshold-voltage-based 2-D theoretical model for the Current–Voltage characteristics of the AlGaN/GaN high electron mobility transistors (HEMT’s) is developed. The present work proposes an improved charge-control...A threshold-voltage-based 2-D theoretical model for the Current–Voltage characteristics of the AlGaN/GaN high electron mobility transistors (HEMT’s) is developed. The present work proposes an improved charge-control model by employing the Robin boundary condition when introduced the solution of the 2-D Poisson’s equation in the density of charge depleted in the AlGaN layer. The dependence of 2-DEG sheet carrier concentration on the aluminum composition and AlGaN layer thickness has been investigated in detail. Current–voltage characteristics developed from the 2-DEG model in order to take into account the impact of gate lengths. The relation between the kink effect and existing deep centers has also been confirmed by using an electrical approach, which can allow to adjust some of electron transport parameters in order to optimize the output current.展开更多
In recent years, photovoltaic (PV) modules are widely used in many applications around the world. However, this renewable energy is plagued by dust, airborne particles, humidity<span style="font-family:Verdana...In recent years, photovoltaic (PV) modules are widely used in many applications around the world. However, this renewable energy is plagued by dust, airborne particles, humidity<span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> and high ambient temperatures. This paper studies the effect of dust soiling on silicon-based photovoltaic panel performance in a mini-solar power plant located in Dakar (Senegal, 14<span style="white-space:nowrap;">°</span>42'N latitude, 17<span style="white-space:nowrap;">°</span>28'W longitude). Results of the current</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">voltage (I - V) characteristics of photovoltaic panels tested under real conditions. We modeled a silicon-based PV cell in a dusty environment as a stack of thin layers of dust, glass and silicon. </span><span style="font-family:Verdana;">The </span><span style="font-family:;" "=""><span style="font-family:Verdana;">silicon layer is modeled as a P-N junction. The study performed under standard laboratory conditions with input data of irradiation at 1000 W/m</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">, cell temperature at 25<span style="white-space:nowrap;">°</span>C and solar spectrum with Air Mass (AM) at 1.5 for the monocrystalline silicon PV cell (m-Si). The analysis with an ellipsometer of dust samples collected on photovoltaic panels allowed to obtain the refraction indices (real and imaginary) of these particles which will complete the input parameters of the model. Results show that for a photon flux arriving on dust layer of 70 μm (corresponding to dust deposit of 3.3 g/m</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">) deposited on silicon-based PV cell</span></span><span style="font-family:Verdana;">s</span><span style="font-family:Verdana;">, short circuit current decreases from 54 mA (for a clean cell) to 26 mA. Also, conversion efficiency decreases by 50% compared </span><span style="font-family:Verdana;">to </span><span style="font-family:Verdana;">clean cell and the cell fill factor decreases by 76% - 50% compared to reference PV cell.</span>展开更多
The adsorption of CH3O and H on the (100) facet of gold was studied using self-consistent periodic density functional theory (DFT-GGA) calculations. The best binding site, energy, and structural parameter, as well as ...The adsorption of CH3O and H on the (100) facet of gold was studied using self-consistent periodic density functional theory (DFT-GGA) calculations. The best binding site, energy, and structural parameter, as well as the local density of states, of each species were determined. CH3O is predicted to strongly adsorb on the bridge and hollow sites, with the bridge site as preferred one, with one of the hydrogen atoms pointing toward a fourfold vacancy (bridge-H hollow). The top site was found to be unstable, the CH3O radical moving to the bridge –H top site during geometry optimization. Adsorption of H is unstable on the hollow site, the atom moving to the bridge site during geometry optimization. The 4-layer slab is predicted to be endothermic with respect to gaseous H2 and a clean Au surface.展开更多
The devitrification of glasses with composition 50GeO2-40PbO-10PbF2-xREF3, RE = Gd, Eu, 0 3+: β-PbF2 nanocrystals embedded in a glassy oxide matrix. This transformation is investigated using thermal analysis, X-ray d...The devitrification of glasses with composition 50GeO2-40PbO-10PbF2-xREF3, RE = Gd, Eu, 0 3+: β-PbF2 nanocrystals embedded in a glassy oxide matrix. This transformation is investigated using thermal analysis, X-ray diffraction and electron microscopy. A comparison with RE3+: β-PbF2 ceramics prepared by standard ceramic techniques is performed. The Rare Earth cations show a strong nucleating effect for the precipitation of the RE3++: β-PbF2 nanocrystals. The evolution of the unit cell parameters of the REF3: β-PbF2 solid solution results from a combined effect of Pb2+-RE3+ substitution and interstitial F– introduction. In the glass ceramics, RE3+: β-PbF2 nanocrystals are constrained by the glassy matrix when they form with a pressure equivalent to 1.6 GPa. The constrained nanocrystals can return to a relaxed state by chemical dissolution of the embedding glassy matrix, followed by thermal treatments.展开更多
This work deals with a second order linear general equation with partial derivatives for a two-variable function. It covers a wide range of applications. This equation is solved with a finite difference hybrid method:...This work deals with a second order linear general equation with partial derivatives for a two-variable function. It covers a wide range of applications. This equation is solved with a finite difference hybrid method: BTCS + CTCS. This scheme is simple, precise, and economical in terms of time and space occupancy in memory.展开更多
We have shown in our first articles [1] [2] that even after encapsulation, the first rapid phase of degradation mechanism observed has been attributed to oxidation of interfaces and an alteration of the charges collec...We have shown in our first articles [1] [2] that even after encapsulation, the first rapid phase of degradation mechanism observed has been attributed to oxidation of interfaces and an alteration of the charges collection process. A second phase slower is induced by the oxidation of the active film, namely a decrease in the absorption and a degradation of the charge transport process. We revealed that another decrease in power conversion efficiency which has been induced by a possible interfacial passivation occurred at the organic/cathode interface, owing to the presence of residual oxygen, moisture and other impurities. This is in reality the real cause of the first rapid phase of degradation mechanism observed.展开更多
<span style="font-family:Verdana;">This study aims to evaluate the optical losses of photovoltaic modules due to Saharan dust deposition in Dakar, Senegal, West Africa. For this purpose, an air-dust-gl...<span style="font-family:Verdana;">This study aims to evaluate the optical losses of photovoltaic modules due to Saharan dust deposition in Dakar, Senegal, West Africa. For this purpose, an air-dust-glass system is modeled to simulate optical losses in transmittance </span><span style="font-family:Verdana;">and reflectance. To do this, we have collected dust samples from Photo-Voltaic</span><span style="font-family:Verdana;"> (PV) surface in Dakar area (14<span style="white-space:nowrap;">°</span>42'N latitude, 17<span style="white-space:nowrap;">°</span>28'W longitude), Senegal. X-ray fluorescence reveals that silicon (Si), iron (Fe), calcium (Ca) and potassium (K) mainly </span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">compose</span></span></span></span></span><span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">d these dust samples. Then, dust refractive indices obtained from an ellipsometer were used as an input to be used in the model. Simulations show that for radiation (at normal incidence) arriving on a dust layer of 30 μm-thick (corresponding to a dust deposit of 1.63 g/m</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">), 79% of the visible spectrum is transmitted</span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">;</span></span></span></span><span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> 19% is reflected and 2% is absorbed. Overall, the transmittance decreases by more than 50% as of dust layer of 70 μm-thick corresponding to a dust deposit of 3.3 g/m</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">.</span></span></span></span></span>展开更多
We investigate the electronic transport in a simple mesoscopic cross structure made of two wires(stubs)grafted at the same point along a quantum waveguide.We show that the structure may exhibit important phenomena suc...We investigate the electronic transport in a simple mesoscopic cross structure made of two wires(stubs)grafted at the same point along a quantum waveguide.We show that the structure may exhibit important phenomena such as bound in continuum(BIC)states.These states are transformed into electromagnetically induced transparency(EIT)resonance by detuning slightly the lengths of the stubs.The last phenomenon is used to propose and study a mesoscopic demultiplexer device with an input waveguide and two output waveguides.We give closed-form expressions of the geometrical parameters that allow a selective transfer of a given state in the first waveguide without perturbing the second waveguide.The effect of temperature on the transmission resonances is also examined by using Landauer-Büttiker formula.The analytical results of the dispersion relation and transmission and reflection coefficient are obtained using the Green's function method.展开更多
In the present work,we investigate the structural and elastic properties of a new intermetallic hydride compound Mg 3 CuH 0.6.The theoretical study has been carried out based on density functional theory(DFT),within l...In the present work,we investigate the structural and elastic properties of a new intermetallic hydride compound Mg 3 CuH 0.6.The theoretical study has been carried out based on density functional theory(DFT),within local density approximation(LDA)and generalized gradient approximation(GGA).The calculated structural parameters of Mg 3 CuH 0.6 compound are consistent with the available experimental data in both approximations.The heat of formation found shows that this compound has a stable structure.According to Hooke’s law which leads to a linear relation between stress and strain,the elastic constants were determined.Once the elastic constants are obtained,the bulk modulus B,shear modulus G,Young’s modulus E,Poisson’s ratioσ,for Mg 3 CuH 0.6 compound were deduced using Voigt-Reuss-Hill(VRH)approximation.The results show that this alloy exhibit ductile property.Finally,the Debye temperature is also calculated and discussed for the first time.This will be considered as the first quantitative theoretical prediction of these properties.展开更多
AD = 1 position-dependent mass approach to constructing nonlinear quantum states for a modified Coulomb potential is used to generate Gazeau–Klauder coherent states. It appears that their energy eigenvalues are scale...AD = 1 position-dependent mass approach to constructing nonlinear quantum states for a modified Coulomb potential is used to generate Gazeau–Klauder coherent states. It appears that their energy eigenvalues are scaled down by the quantum number and the nonlinearity coefficient. We study the basic properties of these states, which are found to be undefined on the whole complex plane, and some details of their revival structure are discussed.展开更多
文摘This scientific paper presents a study investigating the effects of defects at the CdS/CIGS and CdS/SDL interfaces on the performance of CIGS solar cells. The objective of this study is to analyze the influence of defects at the interface between the CdS buffer layer and the CIGS absorber, as well as the surface defect layer (SDL), on CIGS solar cell performance. The study explores three key aspects: the impact of the conduction band offset (CBO) at the CdS/CIGS interface, the effects of interface defects and defect density on performance, and the combined influence of CBO and defect density at the CdS/ SDL and SDL/CIGS interfaces. For interface defects not exceeding 10<sup>13</sup> cm<sup>-2</sup>, we obtained a good efficiency of 22.9% when -0.1 eV analyzing the quality of CdS/SDL and SDL/CIGS junctions, it appears that defects at the SDL/CIGS interface have very little impact on the performances of the CIGS solar cell. By optimizing the electrical parameters of the CdS/SDL interface defects, we achieved a conversion efficiency of 23.1% when -0.05 eV < CBO < 0.05 eV.
文摘In this manuscript, we used the SCAPS-1D software to perform numerical simulations on a perovskite solar cell. These simulations were used to study the influence of certain parameters on the electrical behavior of the cell. We have shown in this study that electron mobility is strongly influenced by the thickness of the absorber, since electron velocity is reduced by thickness. The influence of the defect density shows that above 10<sup>16</sup> cm<sup>-3</sup> all the electrical parameters are affected by the defects. The band discontinuity at the interface generally plays a crucial role in the charge transport phenomenon. The importance of this study is to enable the development of good quality perovskite solar cells, while taking into account the parameters that limit solar cell performance.
文摘Understanding metal accumulation at organ level in roots, leaves and seeds in O. glaberrima (OG) is crucial for improving physiological and metabolic aspects in growing Asian and African rice in salted areas. The micro-analytical imaging techniques are required to reveal its accumulation and distribution within plant tissues. PIXE studies have been performed to determine different elements in rice plants. The existing microbeam analytical technique at the iThemba LABS will be applied for the 2D image mapping of fresh rice tissues to perform a concentration of low atomic mass elements (such as Al, Si, P, S, Cl, Ca, Ti, Mn, Fe, Cu, Br, Zn and K) with detection limits of typically 1-10 μg/g. Comparison of the distribution of the elements between leaves, root and seed samples using uptake and distribution of elements in particular environmental conditions with potential amount of salt in water have been performed. We are also expecting to indicate metal exclusion as salt tolerance strategies from leaves, root, and seed compartments using matrix correlation between samples and between elements on rice species.
文摘Structural, electronic and optical properties of Sc-based aluminum-nitride alloy have been carried out with first-principles methods using both local density approximation (LDA) and Heyd-Scuseria-Ernzerhof (HSE) hybrid functional. This latter provides a more accurate description of the lattice parameters, enthalpy of formation, electronic and optical properties of our alloy than standard DFT. We found the transition from wurtzite to rocksalt structures at 61% of Sc concentration. By increasing the scandium concentration, the lattice parameters and the band gap decrease. The HSE band gap is in good agreement with available experimental data. The existence of the strong hybridization between Sc 3d and N 2p indicates the transport of electrons from Sc to N atoms. Besides, it is shown that the insertion of the Sc atom leads to the redshift of the optical absorption edge. The optical absorption of Sc<sub>x</sub>Al<sub>1-x</sub>N is found to decrease with increasing Sc concentrations in the low energy range. Because of this, Sc<sub>x</sub>Al<sub>1-x</sub>N have a great potential for applications in photovoltaics and photocatalysis.
文摘The main objective of this study is to evaluate the seasonal performance of 20 MW solar power plants in Senegal. The analysis revealed notable seasonal variations in the performance of all stations. The most significant yields are recorded in spring, autumn and winter, with values ranging from 5 to 7.51 kWh/kWp/day for the reference yield and 4.02 to 7.58 kWh/kWp/day for the final yield. These fluctuations are associated with intense solar activity during the dry season and clear skies, indicating peak production. Conversely, minimum values are recorded during the rainy season from June to September, with a final yield of 3.86 kWh/kW/day due to dust, clouds and high temperatures. The performance ratio analysis shows seasonal dynamics throughout the year with rates ranging from 77.40% to 95.79%, reinforcing reliability and optimal utilization of installed capacity. The results of the capacity factor vary significantly, with March, April, May, and sometimes October standing out as periods of optimal performance, with 16% for Kahone, 16% for Bokhol, 18% for Malicounda and 23% for Sakal. Total losses from solar power plants show similar seasonal trends standing out for high loss levels from June to July, reaching up to 3.35 kWh/kWp/day in June. However, using solar trackers at Sakal has increased production by up to 25%, demonstrating the operational stability of this innovative technology compared with the plants fixed panel. Finally, comparing these results with international studies confirms the outstanding efficiency of Senegalese solar power plants, other installations around the world.
文摘In geology, classification and lithological recognition of rocks plays an important role in the area of oil and gas exploration, mineral exploration and geological analysis. In other fields of activity such as construction and decoration, this classification makes sense and fully plays its role. However, this classification is slow, approximate and subjective. Automatic classification curbs this subjectivity and fills this gap by offering methods that reflect human perception. We propose a new approach to rock classification based on direct-view images of rocks. The aim is to take advantage of feature extraction methods to estimate a rock dictionary. In this work, we have developed a classification method obtained by concatenating four (4) K-SVD variants into a single signature. This method is based on the K-SVD algorithm combined with four (4) feature extraction techniques: DCT, Gabor filters, D-ALBPCSF and G-ALBPCSF, resulting in the four (4) variants named K-Gabor, K-DCT, KD-ALBPCSF and KD-ALBPCSF respectively. In this work, we developed a classification method obtained by concatenating four (4) variants of K-SVD. The performance of our method was evaluated on the basis of performance indicators such as accuracy with other 96% success rate.
文摘The satisfaction rate of desired velocity in the case of a mixture of fast and slow vehicles is studied by using a cellular automaton method. It is found that at low density the satisfaction rate depends on the maximal velocity. However, the behavior of the satisfaction rate as a function of the coefficient of variance is independent of the maximal velocity. This is in good agreement with empirical results obtained by Lipshtat [Phys. Rev. E 79 066110 (2009)]. Furthermore, our numerical result demonstrates that at low density the satisfaction rate takes higher values, whereas the coefficient of variance is close to zero. The coefficient of variance increases with increasing density, while the satisfaction rate decreases to zero. Moreover, we have also shown that, at low density the coefficient variance depends strongly on the probability of overtaking.
基金This work is supported by the(ENMC)laboratory,University Setif 1.Algeria.
文摘We have employed the density functional theory plane-wave pseudo potential method,with local density approximation and generalized gradient approximation to perform first-principles quantum mechanics calculations in order to investigate the structural,elastic and mechanical properties of the intermetallic compound MgCu with a CsCl-type structure.The calculated equilibrium lattice constant is in good agreement with the experimental and theoretical values.The elastic constants were determined from a linear fit of the calculated stress-strain function according to Hooke’s law.From the elastic constants,the bulk modulus B,anisotropy factor A,shear modulus G,Young’s modulus E,Poisson’s ratio y,and the ratio B/G for MgCu compound are obtained.Our calculated results for the bulk modulus B,and Young’s modulus E are consistent with the experimental and theoretical data.The sound velocities and Debye temperature are also predicted from elastic constants.Finally,the linear response method has been used to calculate the thermodynamic properties.The temperature dependence of the enthalpy H,free energy F,entropy S,and heat capacity at constant volume Cv of MgCu crystal in a quasi-harmonic approximation have been obtained from phonon density of states and discussed for the first report.
文摘A threshold-voltage-based 2-D theoretical model for the Current–Voltage characteristics of the AlGaN/GaN high electron mobility transistors (HEMT’s) is developed. The present work proposes an improved charge-control model by employing the Robin boundary condition when introduced the solution of the 2-D Poisson’s equation in the density of charge depleted in the AlGaN layer. The dependence of 2-DEG sheet carrier concentration on the aluminum composition and AlGaN layer thickness has been investigated in detail. Current–voltage characteristics developed from the 2-DEG model in order to take into account the impact of gate lengths. The relation between the kink effect and existing deep centers has also been confirmed by using an electrical approach, which can allow to adjust some of electron transport parameters in order to optimize the output current.
文摘In recent years, photovoltaic (PV) modules are widely used in many applications around the world. However, this renewable energy is plagued by dust, airborne particles, humidity<span style="font-family:Verdana;">,</span><span style="font-family:Verdana;"> and high ambient temperatures. This paper studies the effect of dust soiling on silicon-based photovoltaic panel performance in a mini-solar power plant located in Dakar (Senegal, 14<span style="white-space:nowrap;">°</span>42'N latitude, 17<span style="white-space:nowrap;">°</span>28'W longitude). Results of the current</span><span style="font-family:Verdana;">-</span><span style="font-family:Verdana;">voltage (I - V) characteristics of photovoltaic panels tested under real conditions. We modeled a silicon-based PV cell in a dusty environment as a stack of thin layers of dust, glass and silicon. </span><span style="font-family:Verdana;">The </span><span style="font-family:;" "=""><span style="font-family:Verdana;">silicon layer is modeled as a P-N junction. The study performed under standard laboratory conditions with input data of irradiation at 1000 W/m</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">, cell temperature at 25<span style="white-space:nowrap;">°</span>C and solar spectrum with Air Mass (AM) at 1.5 for the monocrystalline silicon PV cell (m-Si). The analysis with an ellipsometer of dust samples collected on photovoltaic panels allowed to obtain the refraction indices (real and imaginary) of these particles which will complete the input parameters of the model. Results show that for a photon flux arriving on dust layer of 70 μm (corresponding to dust deposit of 3.3 g/m</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">) deposited on silicon-based PV cell</span></span><span style="font-family:Verdana;">s</span><span style="font-family:Verdana;">, short circuit current decreases from 54 mA (for a clean cell) to 26 mA. Also, conversion efficiency decreases by 50% compared </span><span style="font-family:Verdana;">to </span><span style="font-family:Verdana;">clean cell and the cell fill factor decreases by 76% - 50% compared to reference PV cell.</span>
文摘The adsorption of CH3O and H on the (100) facet of gold was studied using self-consistent periodic density functional theory (DFT-GGA) calculations. The best binding site, energy, and structural parameter, as well as the local density of states, of each species were determined. CH3O is predicted to strongly adsorb on the bridge and hollow sites, with the bridge site as preferred one, with one of the hydrogen atoms pointing toward a fourfold vacancy (bridge-H hollow). The top site was found to be unstable, the CH3O radical moving to the bridge –H top site during geometry optimization. Adsorption of H is unstable on the hollow site, the atom moving to the bridge site during geometry optimization. The 4-layer slab is predicted to be endothermic with respect to gaseous H2 and a clean Au surface.
文摘The devitrification of glasses with composition 50GeO2-40PbO-10PbF2-xREF3, RE = Gd, Eu, 0 3+: β-PbF2 nanocrystals embedded in a glassy oxide matrix. This transformation is investigated using thermal analysis, X-ray diffraction and electron microscopy. A comparison with RE3+: β-PbF2 ceramics prepared by standard ceramic techniques is performed. The Rare Earth cations show a strong nucleating effect for the precipitation of the RE3++: β-PbF2 nanocrystals. The evolution of the unit cell parameters of the REF3: β-PbF2 solid solution results from a combined effect of Pb2+-RE3+ substitution and interstitial F– introduction. In the glass ceramics, RE3+: β-PbF2 nanocrystals are constrained by the glassy matrix when they form with a pressure equivalent to 1.6 GPa. The constrained nanocrystals can return to a relaxed state by chemical dissolution of the embedding glassy matrix, followed by thermal treatments.
文摘This work deals with a second order linear general equation with partial derivatives for a two-variable function. It covers a wide range of applications. This equation is solved with a finite difference hybrid method: BTCS + CTCS. This scheme is simple, precise, and economical in terms of time and space occupancy in memory.
文摘We have shown in our first articles [1] [2] that even after encapsulation, the first rapid phase of degradation mechanism observed has been attributed to oxidation of interfaces and an alteration of the charges collection process. A second phase slower is induced by the oxidation of the active film, namely a decrease in the absorption and a degradation of the charge transport process. We revealed that another decrease in power conversion efficiency which has been induced by a possible interfacial passivation occurred at the organic/cathode interface, owing to the presence of residual oxygen, moisture and other impurities. This is in reality the real cause of the first rapid phase of degradation mechanism observed.
文摘<span style="font-family:Verdana;">This study aims to evaluate the optical losses of photovoltaic modules due to Saharan dust deposition in Dakar, Senegal, West Africa. For this purpose, an air-dust-glass system is modeled to simulate optical losses in transmittance </span><span style="font-family:Verdana;">and reflectance. To do this, we have collected dust samples from Photo-Voltaic</span><span style="font-family:Verdana;"> (PV) surface in Dakar area (14<span style="white-space:nowrap;">°</span>42'N latitude, 17<span style="white-space:nowrap;">°</span>28'W longitude), Senegal. X-ray fluorescence reveals that silicon (Si), iron (Fe), calcium (Ca) and potassium (K) mainly </span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">compose</span></span></span></span></span><span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;">d these dust samples. Then, dust refractive indices obtained from an ellipsometer were used as an input to be used in the model. Simulations show that for radiation (at normal incidence) arriving on a dust layer of 30 μm-thick (corresponding to a dust deposit of 1.63 g/m</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">), 79% of the visible spectrum is transmitted</span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">;</span></span></span></span><span><span><span><span style="font-family:;" "=""><span style="font-family:Verdana;"> 19% is reflected and 2% is absorbed. Overall, the transmittance decreases by more than 50% as of dust layer of 70 μm-thick corresponding to a dust deposit of 3.3 g/m</span><sup><span style="font-family:Verdana;">2</span></sup><span style="font-family:Verdana;">.</span></span></span></span></span>
文摘We investigate the electronic transport in a simple mesoscopic cross structure made of two wires(stubs)grafted at the same point along a quantum waveguide.We show that the structure may exhibit important phenomena such as bound in continuum(BIC)states.These states are transformed into electromagnetically induced transparency(EIT)resonance by detuning slightly the lengths of the stubs.The last phenomenon is used to propose and study a mesoscopic demultiplexer device with an input waveguide and two output waveguides.We give closed-form expressions of the geometrical parameters that allow a selective transfer of a given state in the first waveguide without perturbing the second waveguide.The effect of temperature on the transmission resonances is also examined by using Landauer-Büttiker formula.The analytical results of the dispersion relation and transmission and reflection coefficient are obtained using the Green's function method.
基金This work is supported by the(ENMC)laboratory,Uni-versity Ferhat Abbas Setif-1,Algeria.
文摘In the present work,we investigate the structural and elastic properties of a new intermetallic hydride compound Mg 3 CuH 0.6.The theoretical study has been carried out based on density functional theory(DFT),within local density approximation(LDA)and generalized gradient approximation(GGA).The calculated structural parameters of Mg 3 CuH 0.6 compound are consistent with the available experimental data in both approximations.The heat of formation found shows that this compound has a stable structure.According to Hooke’s law which leads to a linear relation between stress and strain,the elastic constants were determined.Once the elastic constants are obtained,the bulk modulus B,shear modulus G,Young’s modulus E,Poisson’s ratioσ,for Mg 3 CuH 0.6 compound were deduced using Voigt-Reuss-Hill(VRH)approximation.The results show that this alloy exhibit ductile property.Finally,the Debye temperature is also calculated and discussed for the first time.This will be considered as the first quantitative theoretical prediction of these properties.
文摘AD = 1 position-dependent mass approach to constructing nonlinear quantum states for a modified Coulomb potential is used to generate Gazeau–Klauder coherent states. It appears that their energy eigenvalues are scaled down by the quantum number and the nonlinearity coefficient. We study the basic properties of these states, which are found to be undefined on the whole complex plane, and some details of their revival structure are discussed.