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排序方式: 共有6021条查询结果,搜索用时 15 毫秒
1.
针对单级LED驱动电源输出电流低频纹波大的问题,提出了一种基于隔离型交错并联Boost变换器的单级高功率因数LED驱动电源。分析了该驱动电源的工作原理以及低频电流纹波的抑制机理,给出了一种将漏感引起的电压尖峰能量反馈到负载侧,抑制输出侧低频电流纹波的控制策略,并进行了仿真验证。最后设计了一台满载功率为100 W的数字控制样机,实验结果验证了所提电路能有效降低LED电流的低频纹波,实现LED的无频闪工作。  相似文献   
2.
This study focused on the large band gap of TiO2 for its use as a photocatalyst under light emitting diode (LED) light irradiation. The photocatalytic activities of core–shell structured Au@TiO2 nanoparticles (NPs), nitrogen doped Au@TiO2 NPs, and Au@TiO2/rGO nanocomposites (NCs) were investigated under various light intensities and sacrificial reagents. All the materials showed better photocatalytic activity under white LED light irradiation than under blue LED light. The N-doped core–shell structured Au@TiO2 NPs (Au@N–TiO2) and Au@TiO2/rGO NCs showed enhanced photocatalytic activity with an average H2 evolution rate of 9205 μmol h?1g?1 and 9815 μmol h?1g?1, respectively. All these materials showed an increasing rate of hydrogen evolution with increasing light intensity and catalyst loading. In addition, methanol was more suitable as a sacrificial reagent than lactic acid. The rate of hydrogen evolution increased with increasing methanol concentration up to 25% in DI water and decreased at higher concentrations. Overall, Au@TiO2 core–shell-based nanocomposites can be used as an improved photocatalyst in photocatalytic hydrogen production.  相似文献   
3.
为研究抛物面型反光杯用于LED光源准直时的特点,基于TracePro仿真了LED光源在不同尺寸反光杯下的有效射程和光斑直径,分析了反光杯和LED尺寸对射程和光斑直径的影响。仿真结果表明:射程与反光杯的口径和深度都有关系。高度相同时,反光杯口径越大,射程越大;口径相同时,射程随反光杯高度增加先增大后减小。LED光源经反光杯准直,较短距离的光斑中心光强很低,形成光环。LED光源面积直接影响目标面光斑的大小,对射程影响较小。  相似文献   
4.
Deep-red light emitting phosphors are widely used in LEDs for indoor plant growth because of the critical role played by red light in plant growth. The luminescence properties of deep-red phosphors are still not well understood at present. An energy transfer strategy is a common and effective method to improve luminescence properties. In principle, the energy transfer process may occur when the sensitizer's emission spectra overlap with the activator's excitation spectra. In this work, Bi3+ and Mn4+ were incorporated into the matrix of Gd2MgTiO6 as sensitisers and activators, respectively. Mn4+ ions tend to occupy the [TiO6] octahedral site and the Bi3+ ions are expected to substituted in the site of Gd3+. The energy transfer process from Bi3+ to Mn4+ was realised and the photoluminescence (PL) intensity of Mn4+ increased with the doping content of Bi3+. Upon excitation at 375 nm, the PL intensity of Mn4+ increased to 116.4% when the doping concentration of Bi3+ reached 0.3%. Finally, the pc-LED devices were prepared by a Gd2MgTiO6:Bi3+, Mn4+ phosphor. The high red luminescence indicated that this phosphor has potential applications in indoor LED lighting.  相似文献   
5.
Access to electricity is still a challenge in many parts of sub-Saharan Africa. In Nigeria, over 70% of the rural dwellers do not have access to electricity. The purpose of this paper is to examine the potential of a smart microgrid for off-grid rural electrification in Nigeria. A combination of design thinking and model-based design methodology is employed to select a suitable microgrid configuration and to develop a smart microgrid model. A system consisting of a solar photovoltaic array, battery energy storage and a diesel generator is selected, and the model is developed in Simulink. Demand data from 10 rural communities in Nigeria are used to validate the performance of the model and the potential for demand management is considered. The use of energy efficient light bulbs is found to reduce the peak electricity demand of the case study communities by 42 to 76%. Combining the proposed system with the use of LED bulbs makes the system to have 56 to 81% less net present cost than a system with a diesel generator alone and incandescent light bulbs. The proposed smart microgrid is found to be more suitable for off-grid rural electrification in Nigeria than diesel generators which are currently used for off-grid electrification in Nigeria.  相似文献   
6.
为实现太阳模拟器的大辐照面积均匀照明,研究了大面积发散太阳模拟器光学系统的设计与仿真。分析了复眼透镜阵列组与发散投影系统工作原理及旁瓣效应产生机理;基于嵌套建模思想,结合多项式拟合方法,得出了氙灯轴上强度分布曲线,并根据氙灯发光能量对称性质,实现了氙灯空间光强分布模拟;结合提出的光学系统设计边界条件与参数,设计了光束整形系统、复眼透镜阵列组和发散投影系统。实验结果表明:当工作距离为20000mm,辐照面直径1500mm范围内,辐照均匀度为92.8%,满足了大面积发散太阳模拟器均匀照明的使用需求。  相似文献   
7.
The luminescence properties of yellow-emitting Ce3+-doped Sr-containing sialon phosphor Sr(Al,Si)5(O,N)7:Ce3+ were notably improved by the Ce raw material selection. By changing the Ce raw material from oxides to nitrides or chlorides, the emission wavelength shifted to above 560 nm, which is beneficial for higher color rendering index white light-emitting diodes. This result from an increase in the covalency of the host crystal being associated with a decrease in the oxygen content. When Ce chloride was used, both the absorption and internal quantum efficiency increased, resulting in an increase in the external quantum efficiency up to 65%–72%. Inductively coupled plasma mass spectrometry, X-ray diffraction, and electron spin resonance measurements showed that the reason for the absorption increase is an increase in Ce3+ content and suppression of the generation of the second phase, and the reason for the increase in the internal quantum efficiency is a decrease in the host crystal absorption via suppression of anion vacancy generation. It was found that Ce chloride not only suppresses oxygen impurities but also acts as a flux that results in improved crystallinity.  相似文献   
8.
Cyan-emitting phosphors have attracted widespread attention as an integral part to realize full-spectrum lighting. Understanding the site occupation of luminescence centers is of great importance to design and clarify the luminescent mechanism for new cyan-emitting phosphors. Here, we report a cyan-emitting phosphor Ca18Na3Y(PO4)14:Eu2+ synthesized by the high-temperature solid-state method. The crystal structure is characterized by X-ray diffraction and refined by the Rietveld method. The diffuse reflectance spectra, excitation/emission spectra, fluorescence decay curves, thermal stability, and related mechanism are systematically studied. The results show that Ca18Na3Y(PO4)14:Eu2+ crystallizes in a trigonal crystal system with space group R3c. Under excitation at 350 nm, a broadband cyan emission can be obtained at 500 nm with a half-width of about 120 nm, which is caused by Eu2+ occupying five different sites in host, namely, Na2O12 (450 nm), (Ca3/Na1)O8 (485 nm), Ca2O8 (515 nm), Ca1O7 (565 nm), and (Ca4/Y)O6 (640 nm), respectively. Moreover, crystal structure, room and low temperature spectroscopy, and luminescence decay time are used to skillfully verify the site-selective occupation of Eu2+. Finally, a full-spectrum light-emitting diode (LED) lamp is fabricated with an improved color rendering index (∼90.3), CCT (∼5492 K), and CIE coordinates (0.332, 0.318). The results show that Ca18Na3Y(PO4)14:Eu2+ has the potential to act as a cyan emission phosphor for full-spectrum white LEDs.  相似文献   
9.
《Ceramics International》2021,47(19):27157-27164
Optical thermometry and white light-emitting diodes (WLEDs) are the research hotspots for Eu3+ doped phosphors. In this study, a series of Sr2TiSi2O8: Eu3+ red phosphors were developed in a solid-state reaction method. The luminescent properties of the Sr2TiSi2O8: Eu3+ phosphor illustrate that Sr2TiSi2O8: Eu3+ is effectively excited by the NUV LED chip and emit an intense red light with a peak of 618 nm due to the noninversion symmetry coordination of Eu3+ in Sr2TiSi2O8. The local coordination environment of Eu3+ was investigated in detail using crystallographic data, spectroscopic data and Judd–Ofelt parameters. In addition, the emission intensity of Sr2TiSi2O8:Eu3+ is extremely sensitive to temperature. The relative sensitivity of Sr2TiSi2O8:Eu3+ is 1.1% k-1@300 k, which is comparable to other Eu3+-activated temperature sensing materials. The possible mechanism of the temperature sensitive quenching characteristics was proposed. The results indicate that Sr2TiSi2O8:Eu3+ is a potential temperature sensing material.  相似文献   
10.
目的分析对比我国不同产区主要地方品种与进口羊腿肉的营养品质与质构差异。方法选取中东部农牧交错带肉羊优势区域主要产区:内蒙古锡林郭勒;西北肉羊优势区域的代表产区:新疆、甘肃和宁夏,以乌珠穆沁羊、滩羊、哈萨克羊3个地方品种为主,同时对比来自澳大利亚和新西兰的进口羊腿,品种分别为澳洲白与无角陶赛特羊。分析羊腿的蛋白、脂肪、脂肪酸及氨基酸、维生素、矿物质含量,以及质构参数。结果澳大利亚羊腿蛋白含量较高;甘肃肃北哈萨克羊脂肪酸组成最优;内蒙古锡林郭勒阿巴嘎旗乌珠穆沁羊的钙、磷、钾含量均较高。结论营养成分受品种、饲养方式、地理环境等综合影响:蛋白含量与品种有关,放牧会增加羊腿中不饱和脂肪酸的含量,地理环境与饲料共同影响羊腿的矿质元素含量特征;口感受饲养方式影响较大,放牧会导致羊肉硬度较高。  相似文献   
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