O(N2log2N) filtered backprojectionreconstruction algorithm for tomography

We present a new fast reconstruction algorithm for parallel beam tomography. The new algorithm is an accelerated version of the standard filtered backprojection (FBP) reconstruction, and uses a hierarchical decomposition of the backprojection operation to reduce the computational cost from O(N(3)) to O(N(2)log(2 )N). We discuss the choice of the various parameters that affect the behavior of the algorithm, and present numerical studies that demonstrate the cost versus distortion tradeoff. Comparisons with Fourier reconstruction algorithms and a multilevel inversion algorithm by Brandt et al., both of which also have O(N(2)log(2)N) cost, suggest that the proposed hierarchical scheme has a superior cost versus distortion performance. It offers RMS reconstruction errors comparable to the FBP with considerable speedup. For an example with a 512x512-pixel image and 1024 views, the speedup achieved with a particular implementation is over 40 fold, with reconstructions visually indistinguishable from the FBP.     

N2LMS: enhanced LMS algorithm for speech applications

A modified LMS algorithm, for the echo control of speech signals in a conference environment, has been analysed. Initial results show that the algorithm can provide lower misadjustment and more uniform speech-band cancellation compared with the conventional LMS algorithm at equal convergence rates, with very little additional computation     

（Li,Nb）掺杂SnO2压敏材料的电学非线性研究

研究了掺锂对SnO2压敏电阻器性能的影响.研究发现Li+对Sn4+的取代能明显提高陶瓷的烧结速度和致密度,且能大幅度改善材料的电学非线性性能.掺入x(Li2CO3)为1.0%的陶瓷样品具有最高的密度(P=6.77g/cm3)、最高的介电常数(ε=1851)、最低的视在势垒电场(EB=68.86V/mm)和最高的非线性常数(α=9.9).对比发现,Na+由于具有较大的离子粒半径,其掺杂改性性能相对较差.提出了SnO2@Li2CO3@Nb2O5晶界缺陷势垒模型.     

Temporal stability of circulating current in thin film Tl2Ba2CaCu2O8 and YBa2Cu3O7

The temporal stability of trapped transport current in annular thin film Tl₂Ba₂CaCu₂O₈ (TBCCO) and YBa₂Cu₃O₇ (YBCO) wafers has been accurately measured and has been found to be of suitable quality for the stringent requirements of nuclear magnetic resonance (NMR) magnets. No detectable decay, to the limit of the experimental apparatus (2*10^-14 Ω), was detected in those wafers with transport current at or below the critical current density J_c. The critical current density, as previously determined from 12 μm meander lines, was confirmed in a wafer with a width of 1.9 cm. The profile of trapped magnetic field resulting from induced current was modeled in order to assess its effect on the uniformity of an NMR magnet     

选频~(14)CO_2-~(12)CO_2同位素激光器

我们研制了一台~(14)CO_2-~(12)CO_2同位素激光器,测量到激光谱线80条,其中40条是~(14)CO_200°1-(10°0,02°0)_I带的激光跃迁谱线,强线输出功率达4.0W以上;实验还观察到同位素的竞争效应,发现即使~(14)CO_2成份低于~(12)CO_2,其激光辐射仍占优势.     

时滞时变对象参数辨识方法

针对时滞时变系统,提出了一种参数辨识的新方法.该算法一方面采用互相关函数来辨识滞后时间,并引进了快速傅里叶变换及其反变换,提高了计算效率;另一方面,在变参数增量估计递推最小二乘算法估计时变参数的基础上,引入误差级序列,改善了时变参数的辨识精度.最后通过仿真验证了该方法的良好性能.     

Low-loss polyimide-Ta2O5-SiO2hybrid ARROW waveguides

A low-loss polyimide-Ta₂O₅-SiO₂ hybrid antiresonant reflecting optical waveguide (ARROW) is presented. The ARROW device was fabricated using both the organic and dielectric thin-film technologies. It consists of the fluorinated polyimide, tantalum pentoxide (Ta₂O₅), and silicon dioxide (SiO₂) hybrid layers deposited on a Si substrate. For transverse electric polarized light, the propagation loss of the waveguide as low as 0.4 dB/cm was obtained at 1.31 μm. The propagation loss for transverse magnetic polarized light is 1.5 dB/cm. An ARROW waveguide fabricated using the polyimide-Ta₂O₅ -polyimide material system is also presented for comparison     

Low Rayleigh scatteringP2O5-F-SiO2 glasses

The Rayleigh scattering and infrared absorption losses of P₂ O₅-F-doped silica glass, which is a candidate material for ultra-low-loss optical fiber, were investigated experimentally. The Rayleigh scattering loss of 8.5 wt.% P₂O₅ and 0.3 wt.% F-doped SiO₂ glass is found to be 0.8 times that of pure silica glass. It is also found that the infrared absorption property of P₂O₅-F-SiO₂ glass is almost the same as that of pure silica glass. The minimum loss for the proposed composition is estimated to be 0.11 dB/km at 1.55 μm wavelength, and 0.21 dB/km at 1.3 μm wavelength     

二维图形封闭区域自动识别算法

在图形处理中,常需要从仅含有直线、弧线信息的原始图形中获取多边形这样的封闭区域信息。该算法首先生成原始图形中线和线各交点组成的稀疏图结构,然后采用以广度遍历算法为基础的单源搜索法识别出图形中所有封闭区域,最终以点集形式输出这些区域的信息。输出结果能直接作为很多其他图形算法的输入（如多边形合并,凸包寻找）。这种算法快速高效,能很好的应对如多重交点、线段重合等一些临界情况,并且支持对弧线的处理。     

Radioactive mineral identification based on FFT Radix-2 algorithm

A fast Fourier transform (FFT) Radix-2 based approach using a gamma-ray spectrometer for the identification of radioactive mineral is presented. The proposed method reduces the complexity of diagnosis associated with the spectrometer by transferring time-domain analysis to frequency-domain analysis. The operation of PDA/DSP is discussed pragmatically.     

Nonlinear optical properties ofK2La(NO3)5.2H2O and K2Ce(NO3)5.2H2O

The harmonic generating properties of potassium lanthanum nitrate (KLN) and potassium cerium nitrate (KCN) are described. These crystals have much larger nonlinear coefficients than potassium dihydrogen phosphate (KDP) and are nearly noncritically phase matched at room temperature for Type I frequency doubling of 1.064-μm light, and for Type II doubling of light near 0.95 μm. Thus, these crystals are useful for generating blue-green light by frequency doubling high-power near-infrared lasers. The crystal growth of KLN and KCN are described by the three component phase diagrams. Crystallographic data for KCN that confirms its structural similarity to KLN are presented. The optical absorption spectra of the two materials are discussed, and the linear refractive indexes are given     

Layered Al2O3-TiO2 compositedielectric resonators

Aluminium oxide displays a very low tanδ at microwave frequencies. It also possesses a remarkably high thermal conductivity, ideal for heat dissipation in high power satellite filters. However, its temperature coefficient of the resonant frequency (τ_f) is approximately 60 ppm/K. It is shown that the application of a film of titanium oxide which has a T_f of opposite sign (45O ppm/K) produces a composite in which the τ_f can be tuned to be zero over a wide temperature range. The tanδ of the composite at zero T_f is 3.3×10⁵ (Q=30000) at room temperature and at 10 GHz     

Laser4F3/2→4I9/2and4F3/2→4I13/2transitions in KY(WO4)2:Nd3+

We report the observation of lasing at 0.9137 μm and 1.3545 μm in neodymium-doped KY(WO4)2at 77 K. Transition cross sections, fluorescent line width, and branching ratios are given.     

Characterization of the annealing impact on La2O3/HfO2 and HfO2/La2O3 stacks for MOS applications

The impact of various rapid thermal annealing used during the integration on the La₂O₃/HfO₂ and HfO₂/La₂O₃ stacks deposited by Atomic Layer deposition was analyzed. The consequences of lanthanum localization in such stacks on the evolution of the films during the rapid thermal annealing are investigated in term of morphology, crystalline structure, silicate formation and film homogeneity as a function of the depth. It appeared that the La₂O₃ location has an impact on the temperature of the quadratic phase formation which could be linked to the formation of SiOHfLa silicate and the resistance of the films to dissolution in HF 0.05 wt%.     

CO_2-N_2-H_2O激光体系的振动弛豫过程

讨论了驰豫过程中的一些重要问题:CO_2(v_3)的分子内V-V传能机制;水对驰豫过程的重要效应的机制;CO_2的v_1与v_2间的共振传能;膨胀流与压缩流的弛豫速率的同异;不同转动能级间和同一振型的不同振动能级间存在不平衡的可能性.指出了需进一步研究的问题.此讨论的内容亦适用于其它气体激光体系.     

New far infrared CW optically pumped cis-C2H2F2laser

Lasing on 6 FIR lines is reported for the new laser molecule cis-C2H2F2with high conversion efficiencies up to 7 percent of the maximum theoretical limit. A set of molecular selection criteria was used to predict efficient FIR lasing from this molecule, and analysis of the laser performance has increased the basic understanding of the molecular parameter contribution to high conversion efficiency. From this work a refined set of selection criteria has evolved that may be used to predict additional efficient laser molecules.     

Studies of CW lasing action in CO2-CO,N2O-CO, CO2-H2O, and N2O-H2O mixtures pumped by blackbody radiation

A proof of principle experiment to evaluate the efficacy of CO and H₂O in increasing the power output for N₂O and CO ₂ lasing mixtures has been conducted and theoretically analyzed for a blackbody radiation-pumped laser. The results for N₂ O-CO, CO₂-CO, N₂O-H₂O and CO₂-H₂O mixtures are presented. Additions of CO to the N₂O lasant increased power up to 28% for N₂O laser mixtures, whereas additions of CO to the CO₂ lasant, and the addition of H₂O to both the CO₂ and N₂O lasants, resulted in decreased output power     

硫化镉纳米微晶掺杂Na2O—B2O3—SiO2系统玻璃的制备及光学性质 …

本文采用Ｓｏｌ－ｇｅｌ方法制备了掺杂ＣｄＳ纳米微晶的Ｎａ２Ｏ－Ｂ２Ｏ３－ＳｉＯ２系统玻璃,研究了这种玻璃材料的合成反应机理和结构特性。利用各种温度下玻璃中掺杂纳米尺寸ＣｄＳ半导体微晶的光致发光光谱,研究了其光致发光带的峰值能量和线宽对温度的信赖关系,拟合了其带隙发光带的线宽随温度的变化曲线,获得样品的非均匀线宽。ＣｄＳ微晶的非均匀线宽主要是由于微晶的尺寸分布引起的,可以利用ＣｄＳ微晶的非均匀宽化系     

Ho3+/Yb3+共掺的SiO2-Al2O3-BaO-BaF2微晶玻璃上转换发光研究

制备了Ho3+/Yb3+共掺的氧氟硅酸盐玻璃, 根据玻璃样品的差热分析进行微晶化处理, 测试了Ho3+/Yb3+共掺微晶玻璃的X射线衍射(XRD)图谱、吸收光谱和上转换发光光谱。结果发现, 在980 nm LD激发下, Ho3+/Yb3+共掺的含BaF2纳米晶的氧氟硅酸盐微晶玻璃可以同时观察到绿光(544 nm)和红光(656, 748 nm)上转换发光, 分别对应于Ho3+ 离子的5F4/5S2→5I8, 5F5→5I8和5F4/5S2→5I7能级跃迁, 与未热处理的玻璃样品相比, 微晶玻璃样品的绿光发光强度增强约347倍。研究结果表明含BaF2纳米晶的氧氟硅酸盐微晶玻璃是一种潜在的上转换基质材料。