1,720,962 research outputs found
Efficient Light Harvesting/Extraction Schemes Employing Structure Designs from Microscale to Nanoscale for InGaN/GaN Devices
No full text在本篇論文中，我們將先討論氮化鎵系的太陽能電池，接著為氮化鎵系的發光二極體，最後是我們的總結。
首先，在氮化銦鎵系的多重量子井太陽能電池上，利用自組裝的銀奈米小球當作蝕刻遮罩，去做反應式離子蝕刻，製做出二氧化矽奈米柱陣列。由於光捕捉效應及折射率的匹配(在空氣及元件間)，使此二氧化矽奈米柱陣列可有效地降低元件的表面反射率(從330至570奈米波段)。電池在模擬太陽光源(air mass 1.5G)的照射下，其短路電流明顯提升，而轉換效率可增加21 %。模擬軟體的分析也進一步証明此表面結構能改善電池的光伏特性。
第二，將太陽能電池的p型氮化鎵層製做成微米鐘的結構，也可以顯著的提升其轉化效率達102 %之多。此微米鐘結構能降低元件表面的反射率，增加電池的光吸收能力，並提升短路電流及填充因子。此經由磊晶直接成長出微米鐘的方法，可有效的改善元件的光伏特性。
第三，二氧化矽奈米柱陣列/p型氮化鎵微米鐘的分層結構被應用在氮化銦鎵的多層量子井太陽能電池上，以當作光擷取層。同樣以自組裝的銀球當作蝕刻遮罩來做反應式離子蝕刻，來將二氧化矽奈米柱陣列製作於p型氮化鎵微米鐘之上。由於此粗糙結構的光捕捉效應以及奈米柱具匹配的折射率，使得介面的菲涅耳反射(Fresnel reflection)能被更有效地降低。具此分層結構的電池表現出優異的光伏特性，能提升短路電流及填充因子，進而使轉換效率增加1.47倍。此外，元件光吸收能力的增加與以有限差分時域法(finite-difference time-domain, FDTD)分析的結果相吻合。
最後，我們將此分層結構應用在LED上，發現能增加LED的出光強度。與表面未經粗化的LED相比，在20mA注入電流下，微米鐘LED出光強度增強16.7 %，而奈米柱/微米鐘LED則增強了36.8 %之多。此結果歸因於粗化結構能使出射光散射並提供一等效折射率，來降低元件的內部全反射，進而提高光萃取率。此LED出光強度的增加也同樣可由有限差分時域法來分析得到。In this thesis, we will firstly focus on InGaN/GaN solar cells, and secondly we move to GaN/InGaN light emitting diodes. The final is our conclusion.
First, SiO2 nanorod arrays (NRAs) are fabricated on InGaN-based multiple quantum well (MQW) solar cells using self-assembled Ag nanoparticles as the etching mask and subsequent reactive ion etching. The SiO2 NRAs effectively suppress the undesired surface reflections over the wavelengths from 330 to 570 nm, which is attributed to the light-trapping effect and the improved mismatch of refractive index at the air/MQW device interface. Under the air mass 1.5 global illumination, the conversion efficiency of the solar cell is enhanced by ~21 % largely due to increased short-circuit current from 0.71 to 0.76 mA/cm2. The enhanced device performances by the optical absorption improvement are supported by the simulation analysis as well.
Second, InGaN-based multiple quantum well (MQW) solar cells (SCs) employing the p-GaN microdome were demonstrated to significantly boost the conversion efficiency by 102 %. The improvements in short-circuit current density (Jsc, from 0.43 to 0.54 mA/cm2) and fill factor (from 44 % to 72 %) using the p-GaN microdome are attributed to enhanced light absorption due to surface reflection suppression. The concept of microdome directly grown during SC epitaxial growth preserving mechanical robustness and wafer-scale uniformity proves a promising way in promoting the photovoltaic performances of SCs without any additional process.
Third, the hierarchical structure of SiO2 nanorod arrays/p-GaN microdomes was applied as a light harvesting scheme on InGaN-based multiple quantum well solar cells. Using self-assembled Ag nanoparticles as the etching mask and subsequent reactive ion etching, SiO2 NRAs were fabricated upon the p-GaN microdomes. Due to the light trapping effect of the roughness and the improved match of refractive index by SiO2 nanorod arrays, the undesired Fresnel reflections are effectively suppressed. Cells with the hierarchical surfaces exhibit excellent photovoltaic performances including enhanced short-circuit current densities and fill factor, and the measured conversion efficiency is enhanced by 1.47-fold. The improved light absorption in device is consistent with the finite-difference time-domain analysis.
Finally, we report the enhanced light extraction efficiency of the hierarchical structure, SiO2 nanorods/p-GaN microdomes, fabricating on InGaN/GaN LEDs. Compared with conventional flat LEDs, the light output intensity of bare microdome LED presents an improvement of 16.7 % at 20 mA, yet it boosts to 36.8 % for SiO2 NRA/p-GaN microdome LED. The results are attributed to the scattering effect and the effective refraction indexes of the textured structures that reduce the total internal reflection, contributing to the most light extraction. The enhanced optical performances are supported by the improved light output power calculated by finite-difference time-domain analysis
The Research of Vibration Analysis and Optimal Design on Electric Vehicle Drive System
No full text本研究以華創/華擎車電開發之電動車為研究對象，進行電動車動力系統的振動分析和減振的優化設計。一開始根據文獻回顧，蒐集並歸納電動車動力系統（馬達、減速齒輪箱）模組化結構之振動原因，接著使用有限元素軟體Abaqus建立動力系統模型，並透過模態敲擊試驗驗證模型的準確性。本研究所建立之模型由實體元素和薄殼元素組成，且網格經適當分割，不僅品質較佳的網格可確保分析維持準確性，同時因大幅減少網格的數量，尚能節省大量軟體模擬運算時間。在振動分析中，分別就兩個主要影響振動的因素：馬達轉子動平衡，以及齒輪嚙合進行模擬，並探討個別因素對動力系統振動的影響程度。最後，透過改善振動源和增加結構剛性的方式，產出的優化設計可降低19.9%振動位移。This thesis studies the vibration influences on the whole drive system of vehicle for HAITEC/CECTEC’s EV car and proposes an optimal design which can reduce vibration. From literature review, this study summarizes the sources of vibration. Then this thesis uses finite element software: Abaqus to create whole model of the electric vehicle drive system. The accuracy of the finite element model is confirmed by the experiment of modal testing. The model is created by both solid and shell elements which is well meshed, so it has better quality and lower quantity of mesh elements, which can not only keep the precision of analysis but also decrease software simulation time. This thesis investigates and simulates two main sources of vibrations: rotor’s unbalance rotating mass and gear meshing during vibration analysis, then explores the importance between each reason and vibration of the whole drive system. At last, this thesis proposes a new optimal design which can lower 19.9% of vibration displacement by improving vibration sources and enhancing the stiffness of structure
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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