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91.
<正>We demonstrate a photonic band gap(PBG) from one-dimensional(1D) periodic structures created by a double-layer unit cell with an air layer and an anisotropic nonmagnetic left-handed metamaterial(LHM) layer whose permittivity elements are partially negative.The requirements imposed on the materials and structures to realize a PBG are derived when the frequency is above or below the cutoff frequency,and the transmission properties of the PBG are discussed by utilizing 4×4 transfer-matrix method with dispersive semiconductor metamaterial. 相似文献
92.
<正>With the development of the compressive sensing theory,the image reconstruction from the projections viewed in limited angles is one of the hot problems in the research of computed tomography technology.This paper develops an iterative algorithm for image reconstruction,which can fit most cases.This method gives an image reconstruction flow with the difference image vector,which is based on the concept that the difference image vector between the reconstructed and the reference image is sparse enough.Then the l_2-norm minimization method is used to reconstruct the difference vector to recover the image for flat subjects in limited angles.The algorithm has been tested with a thin planar phantom and a real object in limited-view projection data.Moreover,all the studies showed the satisfactory results in accuracy at a rather high reconstruction speed. 相似文献
93.
为了研究汽车尾气颗粒物的结构和氮的种态,使用扫描透射X射线显微成像(STXM)技术研究了桑塔纳3000和高尔汽车尾气颗粒物.STXM表明单颗粒物的粒径为500nm,颗粒物质量分布不均匀,有中间空洞.比较汽车尾气颗粒物和(NH4)2SO4和NaNO3中N的1sX射线近边吸收精细结构谱(NEXAFS),铵盐在406eV有显著的σ*吸收峰,有肩部结构;汽车尾气颗粒物和NaNO3中N的近边吸收谱在412eV和418.5eV有明显的σ吸收峰;(NH4)2SO4中N的近边吸收谱在413.5eV和421.8eV更宽的σ吸收峰.硝酸盐是汽车尾气颗粒物中的N化学种态的主要存在形式.在395—418eV能量范围内对桑塔纳3000汽车尾气颗粒物进行堆栈扫描,经过主成分分析和聚类分析,发现其表层主要为硝酸盐,内部有少量铵盐. 相似文献
94.
运用分子动力学方法具体模拟研究单个碳纳米管(CNTs)在加热过程中的结构变化.选择多组不同结构的单壁碳纳米管(SWCNTs)和双壁碳纳米管(DWCNTs)作为研究对象,加热温度从室温开始到4000 K,压强保持为1 atm.结果表明单壁碳管中手性型结构热稳定性最好,其次是扶手椅型和锯齿型,当手性角相同时,直径大的热稳定性更高;对于双壁碳管,研究表明当双壁中至少之一为手性结构时其热稳定好,而内外壁均为锯齿结构的稳定性最差,该结果进一步支持了有关单壁碳管的结论;还从理论上探索了描述结构热稳定性的方式,并在键层
关键词:
单壁碳纳米管
双壁碳纳米管
分子动力学方法
热稳定性能 相似文献
95.
Strain distributions and electronic structure of three-dimensional InAs/GaAs quantum rings 下载免费PDF全文
This paper presents a finite element calculation for the
electronic structure and strain distribution of self-organized
InAs/GaAs quantum rings. The strain distribution calculations are
based on the continuum elastic theory. An ideal three-dimensional
circular quantum ring model is adopted in this work. The electron
and heavy-hole energy levels of the InAs/GaAs quantum rings are
calculated by solving the three-dimensional effective mass
Schr?dinger equation including the deformation potential and
piezoelectric potential up to the second order induced by the
strain. The calculated results show the importance of strain and
piezoelectric effects, and these effects should be taken into
consideration in analysis of the optoelectronic characteristics of
strain quantum rings. 相似文献
96.
GaAs Based InAs/GaSb Superlattice Short Wavelength Infrared Detectors Grown by Molecular Beam Epitaxy 下载免费PDF全文
InAs/GaSb superlattice (SL) short wavelength infrared photoconduction detectors are grown by molecular beam epitaxy on GaAs(O01) semi-insulating substrates. An interfacal misfit mode AISb quantum dot layer and a thick GaSb layer are grown as buffer layers. The detectors containing a 200-period 2 ML/S ML InAs/GaSb SL active layer are fabricated with a pixel area of 800×800 μm^2 without using passivation or antirefleetion coatings. Corresponding to the 50% cutoff wavelengths of 2.05μm at 77K and 2.25 μm at 300 K, the peak detectivities of the detectors are 4 × 10^9 cm·Hz^1/2/W at 77K and 2 × 10^8 cm·Hz1/2/W at 300K, respectively. 相似文献
97.
LIU Yimin HUANG Gangming & BAO Chengguang . Department of Physics Zhongshan University Guangzhou China . Department of Physics Shaoguan University Shaoguan China 《中国科学G辑(英文版)》2004,47(5):521-530
1 Introduction Quantum dots (QDs), often referred to as artificial atoms, are currently under in-tense study because they provide ideal structures used in optical-electronic microdevices, so they are essential in developing microtechniques. They are also essential in the aca-demic aspect, because rich information on microstructures can be extracted both theo-retically and experimentally. Since the early fabrication of the QDs, external magnetic field has been used to control their propertie… 相似文献
98.
Photoemission spectra are measured for Yb covered surface of wet-chemically-etched H-Si (111). The results reveal that the lattice structure of the H-Si (111) surface is stable against the deposition of Yb atoms. X-ray photoemission spectra indicate the formation of a polarized (dipole) surface layer, with the silicon negatively charged. Ultraviolet photoemission spectra exhibit the semiconducting property of the interface below one monolayer coverage. Work function variation during the formation of the Yb/H-Si (111) interface is measured by the secondary-electron cutoff in the ultraviolet photoemission spectral line. The largest decrease of work function is ~1.65eV. The contributions of the dipole surface layer and the band bending to the work function change are determined to be ~1.15eV and ~0.5eV, respectively. The work function of metal Yb is determined to be ~2.80±0.05eV. 相似文献
99.
Consistency-dependent optical properties of lubricating grease studied by terahertz spectroscopy 下载免费PDF全文
The optical properties of four kinds of lubricating greases (urea, lithium, extreme pressure lithium, molybdenum disulfide lithium greases) with different NLGL (National Lubricant Grease Institute of America) numbers were investigated using terahertz time-domain spectroscopy. Greases with different NLGL grades have unique spectral features in the terahertz range. Comparison of the experimental data with predictions based on Lorentz--Lorenz theory exhibited that the refractive indices of each kind of lubricating grease were dependent on the their consistency. In addition, molybdenum disulfide (MoS2) as a libricant additive shows strong absorption from 0.2 to 1.4 THz, leading to higher absorption of MoS2-lithium grease than that of lithium grease. 相似文献
100.
利用脉冲激光沉积技术,通过改变沉积过程中的氧气压力,在蓝宝石(0001)基片上制备了一系列ZnMgO合金.通过X射线衍射、反射和透射光谱以及室温和变温荧光光谱,对薄膜的结构和光学性能进行了系统地表征,分析了工作气压对ZnMgO合金薄膜的结晶质量及光学特性的影响.研究结果表明:随着沉积环境中氧气压力的增大,ZnMgO薄膜的结晶质量下降,富氧环境下,与蓝宝石晶格平行的ZnO晶粒的出现是导致薄膜结晶质量下降的主要原因;相对于本征ZnO,不同氧气环境下沉积的ZnMgO薄膜的紫外荧光峰均出现了不同程度的蓝移.随着工
关键词:
ZnO
Mg掺杂
脉冲激光沉积
薄膜生长
光学特性 相似文献