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DC-DC converters are dynamic systems consisting of the passive components. These components under the effect of thermal stress in a PV system generate power losses. The knowledge of these power losses is necessary to evaluate the conversion efficiency of the system. Using the polynomial approximation method, the equations for calculating losses in the different components were determined. The system is implemented under the MATLAB / Simulink software. The results show that for a PV application of 240 W supplied to the load, 18% are lost, only 82% are transferred.

The West African Sub-Saharan region (Fig. 1) is home to some 300 million people, with at least 60% engaged in agricultural activity. Climate change is now recognized as a major constraint to development worldwide. While climate change primarily relates to the future, historical trends give evidence of climate change already occurring. Temperature increases of 1 to 1.5◦C have been observed over the last 30 years in West Africa (EPA Ghana, 2001; IPCC, 2007) and there are projections of further warming of the West African region in the foreseeable future (2040–2069; Fig. 2a). The impact of climate change on West African rainfall is less clear. The analysis of historical data over the last 30 years shows that, whereas some zones experienced increased rainfall by as much as 20% to 40%, other locations experienced a decline in annual rainfall by about 15%. Future projections suggest a drier western Sahel (e.g., Senegal) but a wetter eastern Sahel (e.g., Mali, Niger; Fig. 2b). The southern locations of WestAfrica (e.g., Ghana) are projected to experience no change or slight increases in annual rainfall (Hulme et al., 2001). Irrespective of whether these zones will be dryer or not, there is historical evidence of shifts in rainfall patterns with extreme events (i.e., droughts and floods) becoming more frequent (Adiku and Stone, 1995) and it is probable that this trend may persist into the future.

En Gambie, la couverture végétale a subi des changements importants au cours des deux dernières décennies. Pour aider à la prise de décision politique, cette étude cherche à détecter les tendances des changements au cours des deux dernières décennies à l'aide d'une série chronologique d'images NDVI MODIS. L'approche méthodologique est basée sur le calcul de la corrélation de Kendall (τ) associée au test de p-significance au seuil de 10 %. Les résultats ont montré une tendance à l'augmentation de la productivité de la végétation au cours de la décennie 2000-2009 (98,37 % de la zone d'étude) dans presque toutes les régions administratives. Cette tendance est plus significative le long de la rivière. En revanche, au cours de la décennie 2010-2019, il a été noté une tendance globale significative à la baisse de la productivité (44,01 % de la Gambie) dans toutes les régions administratives, à l'exception de la région de la côte ouest et de Banjul, mais pas significative. Le résultat a montré que, sur l'ensemble de la période (2000-2019), 61,86% du territoire national était caractérisé par une tendance positive et 38,14% par une tendance négative ; et que le pourcentage de tendance positive significative est de 10%, le pourcentage de tendance négative significative est de 4%. Des tendances positives significatives sont observées beaucoup plus le long de la rivière et au centre de la région de la rivière Central ; des tendances négatives significatives sont observées principalement dans la partie ouest de la région de la côte ouest et à Banjul, à l'extrémité est de la région de la rive nord et dans la région de la rivière Upper. En Gambia, la cubierta vegetal ha sufrido cambios significativos en las últimas dos décadas. Para ayudar a la toma de decisiones políticas, este estudio busca detectar tendencias en los cambios en las últimas dos décadas utilizando una serie temporal de imágenes MODIS de NDVI. El enfoque metodológico se basa en el cálculo de la correlación de Kendall (τ) asociada con la prueba de significación p en el umbral del 10 %. Los resultados mostraron una tendencia al aumento de la productividad de la vegetación durante la década 2000-2009 (98,37% del área de estudio) en casi todas las regiones administrativas. Esta tendencia es más significativa a lo largo del río. En contraste, durante la década 2010-2019, se observó una tendencia general a la baja significativa en la productividad (44.01% de Gambia) en todas las regiones administrativas, excepto la región de la costa oeste y Banjul, aunque no significativa. El resultado mostró que, durante todo el período (2000-2019), el 61,86% del territorio nacional se caracterizó por una tendencia positiva y el 38,14% por una tendencia negativa; y que el porcentaje de tendencia positiva significativa es del 10%, el porcentaje de tendencia negativa significativa es del 4%. Las tendencias positivas significativas se observan mucho más a lo largo del río y en el centro de la Región del Río Central; las tendencias negativas significativas se observan principalmente en la parte occidental de la Región de la Costa Oeste y Banjul, en el extremo oriental de la Región de la Ribera Norte y en la Región del Río Superior. In The Gambia, the vegetation cover has undergone significant changes over the past two decades. To assist policy decision-making, this study seeks to detect trends in changes over the past two decades using a time series of NDVI MODIS images. The methodological approach is based on the calculation of the correlation of Kendall (τ) associated with the p-significance test at the 10 % threshold. The results showed a trend of increasing vegetation productivity during the decade 2000-2009 (98.37% of the study area) in almost all administrative regions. This trend is more significant along the river. In contrast, during the decade 2010-2019, it was noted overall significant downward trend in productivity (44.01% of The Gambia) in all administrative regions except West Coast Region and Banjul, however not significant. The result showed that, over the whole period (2000-2019), 61.86% of the national territory was characterized by a positive trend and 38.14% by a negative trend; and that the significant positive trend percentage is 10%, the significant negative trend percentage is 4%. Significant positive trends are observed much more along the river and central of the Central River Region; significant negative trends are observed mainly in the western part of West Coast Region and Banjul, at the eastern end of the North Bank Region and in the Upper River Region. في غامبيا، شهد الغطاء النباتي تغيرات كبيرة على مدى العقدين الماضيين. للمساعدة في صنع القرار السياسي، تسعى هذه الدراسة إلى اكتشاف الاتجاهات في التغييرات على مدى العقدين الماضيين باستخدام سلسلة زمنية من صور NDVI MODIS. يعتمد النهج المنهجي على حساب ارتباط كيندال (τ) المرتبط باختبار أهمية p عند عتبة 10 ٪. أظهرت النتائج اتجاهًا لزيادة إنتاجية الغطاء النباتي خلال العقد 2000-2009 (98.37 ٪ من منطقة الدراسة) في جميع المناطق الإدارية تقريبًا. هذا الاتجاه أكثر أهمية على طول النهر. على النقيض من ذلك، خلال العقد 2010-2019، لوحظ اتجاه هبوطي كبير بشكل عام في الإنتاجية (44.01 ٪ من غامبيا) في جميع المناطق الإدارية باستثناء منطقة الساحل الغربي وبانجول، ولكن ليس كبيرًا. أظهرت النتيجة أنه على مدار الفترة بأكملها (2000-2019)، اتسم 61.86 ٪ من الأراضي الوطنية باتجاه إيجابي و 38.14 ٪ باتجاه سلبي ؛ وأن نسبة الاتجاه الإيجابي الكبير هي 10 ٪، ونسبة الاتجاه السلبي الكبير هي 4 ٪. لوحظت اتجاهات إيجابية كبيرة على طول النهر ووسط منطقة النهر الوسطى ؛ لوحظت اتجاهات سلبية كبيرة بشكل رئيسي في الجزء الغربي من منطقة الساحل الغربي وبانجول، وفي الطرف الشرقي من منطقة الضفة الشمالية وفي منطقة النهر العليا.

The omnipresence of connected objects leads to the quasi-permanent presence of electromagnetic waves from different sources in our environment. This article presents a new electromagnetic energy harvesting device, rectenna type, which offers the advantage of being versatile. Indeed, the proposed prototype is compatible with three frequency bands of radio standards widely deployed today (UHF RFID, GSM-1800, and UMTS-2100), and its performances remain good for low to very low ambient power levels as well as for different loads depending on the targeted application. The proposed solution is based on a tri-band antenna with very good efficiency and a bandwidth of at least 80 MHz for each of the operating frequencies. Moreover, the associated rectifier circuit is also tri-band and offers good performance in terms of RF-to-DC conversion efficiency for input levels varying in a rather wide range of power levels. The study is based on a design phase by simulation until the realization of prototypes and their experimental characterization. The designed rectenna is compared with solutions found in the literature.

AbstractFullerene derivatives functionalized with isomeric phenyleneethynylene‐based dendrons possessing either 1,3,5‐triethynylbenzene or 1,2,4‐triethynylbenzene branching units have been prepared. The electrochemical properties of these compounds are not strongly dependent on the branching patterns since the corresponding redox processes are localized either on the C60 cage (acceptor unit) or on the dialkyloxybenzene moieties (donor units) at the dendron periphery. The photophysical investigations performed in CH2Cl2 have revealed an ultrafast dendron → C60 energy transfer in all these hybrid systems. Importantly, the different π‐conjugation patterns in the two series have a dramatic effect on their electronic properties as attested by the differences observed in their absorption and emission spectra. The lower lying absorption onset and the wider spectral profile of the dyads with 1,2,4‐triethynylbenzene branching units when compared to their 1,3,5‐triethynylbenzene analogues clearly points out an improved light harvesting capability. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

<span lang="EN-US">A multi-point model predictive control (MPMPC) is widely used for many applications, including wind energy system (WES), notably enhanced power characteristics and oscillation regulation. In this work, MPMPC is adapted to condense the fatigue load of the WES and improve the lifetime of the turbine assembly. The lifetime examination is carried out by considering the three chief parameters: basic lifetime until failure, short-time damage equivalent loads (DELs), and lifetime DELs. The simulation study is performed for two cases: blade root bending moments and tower top bending. Further, fatigue load examination is demonstrated to analyze the effectiveness of the proposed controller. The observed results show that the lifetime analysis of the wind turbine system displayed more excellent characteristics, i.e., 49.50% greater than MPC. Also, the fatigue load mitigation showed greater magnitude due to the control action of the proposed controller, about 37.38% grander than MPC. Therefore, the attained outcomes exhibit outstanding performance compared with conventional controllers.</span>