检索结果-南通市图书馆

Macro-pyramid in GaN Film

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Physics Letters 2001年第2期18卷 260-262页

作者： ZHOU Jing yang zhi-jian XU Shi-Fa ZHU Xing ZHANG Guo-Yi Mesoscopic Physics National Laboratory and Department of Physics Peking UniversityBeijing 100871

A thin film of GaN with the thickness of 1.0μm was grown onα-Al2O3 substrate by metal organic chemical vapour disposition and then a thick GaN film with thickness of 12μm was grown in the halide vapour phase epitaxy *** macro-pyramids appeared on the surface of the *** macro-pyramids made the surface of the GaN film rough,which was harmful to the devices made by GaN *** defects changed the distribution of carrier concentration and affected the optical properties of *** step height of the pyramids was about 30-40 nm measured by atomic force microscopy.A simple model was proposed to explain the macro-pyramid phenomenon compared with the growth *** growth of the macro-pyramid was relative to the physical conditions in the reaction *** increasing growth temperature and low pressure may reduce the pyramid size.

关键词： GaN 2μm pyramid

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Physics Letters 1998年第9期15卷 677-679页

作者： ZHAO Yi-guang CHENG Lei HUANG Xian-ling ZHANG Guo-yi LI Jing yang zhi-jian Department of Physics Peking UniversityBeijing 100871 National Laboratory for Superlattices and Microstructures Institute of SemiconductorsChinese Academy of SciencesBeijing 100083 Department of Physics Mesoscopic Physics LaboratoryPeking UniversityBeijing 100871

Using solid-phase regrowth technique,Pd/Ge contact has been made on the GaN layer,and very good ohmic behavior was observed for the *** Photoluminescence(PL)spectra for different structures formed by the Pd/Ge contact,GaN layer,sapphire substrate,and mirror were studied,and a defect-assisted transition was found at 450nm related to Ge *** results show that the microcavity effect strongly influences the PL spectra of the band-gap and defect-assisted transitions.

关键词： GaN sapphire ohmic

RESEARCH ANNOUNCEMENTS ON “DPK: DEEP NEURAL NETWORK APPROXIMATION OF THE FIRST PIOLA-KIRCHHOFF STRESS”

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

数学杂志 2022年第4期42卷 283-286页

作者： yang zhi-jian YUAN Cheng School of Mathematics and Statistics Wuhan UniversityWuhan 430072China

1 Introduction and Main Results Consider the first Piola-Kirchhoff stress P defined as[1]P(F)=?W(F)/?F,(1.1)where F and W refer to the deformation tensor and strain energy *** to the principle of material frame-indiff... 详细信息

关键词： density deformation stress

Magnetic navigation system assisted percutaneous coronary intervention： a comparison to the conventional approach in daily practice

在线全文

学校读者我要写书评

暂无评论

Chinese Medical Journal 2011年第2期124卷 233-236页

作者： LI Chun-jian WANG Hui yang zhi-jian CAO Ke-jiang Department of Cardiology First Affiliated Hospital of Nanjing Medical University Nanjing Jiangsu 210029 China

Background The benefits of the magnetic navigation system （MNS） for percutaneous coronary intervention （PCI）remain unclear,and a comparison of the MNS assisted approach to the conventional approach for PCl,when used in daily practice,is little *** study aimed to investigate the benefits of an MNS assisted technique as compared to the conventional technique for *** Forty-eight consecutive patients scheduled for PCI were recruited between December 2009 and April *** assisted PCls were performed on 54 target *** 45 patients with 54 target vessels undergoing conventional PCls were selected from a historical population of patients to match the MNS group according to the coronary lesion type （ACC/AHA classification）.Emergency PCls and chronic total occlusions were excluded from both *** were performed using Stata 9.2 statistical *** There were no significant differences between the baseline characteristics of the MNS group and the control *** success rates were 100.0% for the MNS assisted PCI and 98.1% for the conventional PCI,which did not reach a significant difference （P=1.000）;there were also no significant differences in terms of guide wire crossing time （（51.7±30.5） seconds vs.（57.5±49.4） seconds,P=0.448）,operation time （（28.4±15.9） minutes vs.（28.0±24.7） minutes,P=0.935）,X-ray exposure （（458.1±350.1） μGym^2 vs.（558.7±451.7） μGym^2,P=0.197;and （94.2±80.9） mGy vs.（96.2±77.3） mGy,P=0.895） or contrast usage （（7.3±4.0） ml vs.（6.1 ±3.7） ml,P=0.121 ） between the two ***,a trend toward shorter guide wire crossing time and less X-ray exposure were observed for the magnetic *** In daily practice,MNS assisted PCI resulted in a similar procedural success rate,operation time,and contrast usage,with a trend toward shorter guide wire crossing time and less X-ray exposure when compared to the conventional PCI.

关键词： magnetic navigation coronary artery disease percutaneous coronary intervention

P-Type GaN Directly Grown by Low Pressure Metalorganic Vapor Phase Epitaxy

在线全文

学校读者我要写书评

暂无评论

Chinese Physics Letters 1997年第8期14卷 637-640页

作者： ZHANG Guo-yi yang zhi-jian TONG Yu-zhen JIN Si-xuan DANG Xiao-zhong WANG Shu-min Department of Physics Mesoscopic Physics LaboratoryPeking UniversityBeijing 100871

P-type GaN was grown on AI3O2 substrate by low pressure metalorganic vapor phase epitaxy without any post *** p-type conduction of as-grown GaN has the typical characteristics of a light-doped or high-compensation semiconductor,that is a hole concentration of 2.2× 10^(17)cm^(-3) at 77K,which changes to n-type with an electron concentration of 2.7 × 10^(17) cm^(-3) at room *** thermal annealing under a N2 ambient,it showed the characteristics of a heavy-doped semiconductor and the hole concentration was enhanced reaching a hole concentrations of 4.2× 10^(17) at 77K and 5.7 × 10^(17) cm^(-3) at room temperature.

关键词： temperature. GaN Epitaxy

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

调制FFT及其在离散频谱校正技术中的应用

振动工程学报 2009年第6期22卷 632-637页

作者：杨志坚丁康华南理工大学机械与汽车工程学院广东广州510640 广东省汽车工程重点实验室广东广州510640

提出了一种调制快速傅立叶变换(FFT),通过时域调制对实信号进行移频,打破频域内的对称性,再进行传统的FFT。该算法克服了直接进行FFT计算结果有一半冗余的缺点,将频率分辨率提高了一倍,提高了频率定位的精确度,从而减小了最大的幅值和... 详细信息

提出了一种调制快速傅立叶变换(FFT),通过时域调制对实信号进行移频,打破频域内的对称性,再进行传统的FFT。该算法克服了直接进行FFT计算结果有一半冗余的缺点,将频率分辨率提高了一倍,提高了频率定位的精确度,从而减小了最大的幅值和相位误差,并进一步提高了抗噪性能。以比值校正法和相位差法为例,将调制FFT应用到离散频谱校正技术中,解决了基于FFT的离散频谱校正方法由于噪声影响而出现的一些问题,进一步提高了校正精度和抗噪性能。理论分析和Monte Carlo计算机模拟实验验证了上述结论的正确性。

关键词： FFT 频谱分析频谱校正调制FFT 抗噪性能

高斯白噪声背景下时移相位差校正法的频率估计精度分析

在线全文

学校读者我要写书评

暂无评论

振动工程学报 2007年第3期20卷 274-279页

作者：杨志坚丁康华南理工大学汽车工程学院

推导了高斯白噪声背景下加任意对称窗函数截断的谐波信号用时移相位差校正法进行离散频谱校正时的归一化频率估计误差的统计公式;针对加矩形窗和加Hanning窗,通过与仿真模拟结果的对比分析验证了其正确性,并分析了在某些情况下产生偏离... 详细信息

推导了高斯白噪声背景下加任意对称窗函数截断的谐波信号用时移相位差校正法进行离散频谱校正时的归一化频率估计误差的统计公式;针对加矩形窗和加Hanning窗,通过与仿真模拟结果的对比分析验证了其正确性,并分析了在某些情况下产生偏离的原因;研究了谐波信号本身参数和校正方法选取的参数对估计误差的影响,并比较了加矩形窗和加Hanning窗时的估计误差。

关键词：离散频谱相位差误差高斯白噪声

在线全文

学校读者我要写书评

暂无评论

改变窗长相位差校正法的改进与抗噪性能分析

华南理工大学学报（自然科学版） 2007年第10期35卷 210-213页

作者：丁康杨志坚华南理工大学汽车工程学院广东广州510640

提出了一种改进的改变窗长相位差校正法来估计谐波信号的频率,与原方法相比,改进后的方法只需做一次快速傅立叶变换(FFT)和一次单点离散傅立叶变换(DFT),提高了运算速度.分析了改进方法的抗噪声性能,推导出了在高斯白噪声背景下频率估... 详细信息

提出了一种改进的改变窗长相位差校正法来估计谐波信号的频率,与原方法相比,改进后的方法只需做一次快速傅立叶变换(FFT)和一次单点离散傅立叶变换(DFT),提高了运算速度.分析了改进方法的抗噪声性能,推导出了在高斯白噪声背景下频率估计误差的方差公式,并通过仿真计算验证了推导公式的正确性.仿真结果表明改进后的方法具有更强的抗噪能力.

关键词：频率估计相位差抗噪频谱分析校正

Ba_5SiO_4Cl_6:Yb^(3+),Er^(3+),Li^+荧光粉的制备及上转换发光性质研究

在线全文

学校读者我要写书评

暂无评论

物理学报 2015年第13期64卷 394-399页

作者：杨健芝邱建备杨正文宋志国杨勇周大成昆明理工大学材料科学与工程学院昆明650093

本文采用高温固相反应法制备了Ba5SiO4Cl6:Yb3+,Er3+,Li+荧光粉,并对其上转换发光性质及其发光机理进行了研究.在980 nm激光的激发下,Ba5SiO4Cl6:Yb3+,Er3+荧光粉呈现较强的红色(662 nm)和较弱的绿色(550 nm)的上转换发光,红色和绿色的... 详细信息

本文采用高温固相反应法制备了Ba5SiO4Cl6:Yb3+,Er3+,Li+荧光粉,并对其上转换发光性质及其发光机理进行了研究.在980 nm激光的激发下,Ba5SiO4Cl6:Yb3+,Er3+荧光粉呈现较强的红色(662 nm)和较弱的绿色(550 nm)的上转换发光,红色和绿色的上转换发光分别对应于Er3+离子的4S3/2/2H11/2→4I15/2和4F9/2→4I15/2跃迁,且随着掺杂的Er3+和Yb3+离子浓度增加,样品的上转换发光强度增加,这是因为Yb3+离子和Er3+离子之间的能量传递效率增加引起的.在0.5—0.8 W功率激发下,样品属于双光子发射,而在0.9—1.2 W功率激发下样品具有新的上转换发光机理——光子雪崩效应.探讨了Li+掺杂对Ba5SiO4Cl6:Yb3+,Er3+样品的上转换发光性质的影响,Li+离子的掺杂引起Ba5SiO4Cl6:Yb3+,Er3+上转换发光强度增加,这是由于Li+离子的掺入降低了晶体场的对称性引起的.

关键词：上转换发光 Ba5SiO4Cl6:Yb3+ Er3+ Li+ 发光粉光子雪崩 Ba5SiO4Cl6:Yb3+ Er3+ Li+