晶界内耗研究的新进展

由不同取向差的纯Al双晶的内耗实验观察到,不同类型晶界的弛豫参量有明显差别.用耦合模型对内耗数据的分析表明,小角度晶界内耗的基本机制是位错攀移,而大角度晶界内耗的基本机制是晶界扩散.在此基础上,对多晶中晶界内耗的一些特征也作了解释.     

晶界内耗研究的进展

固体在机械振动过程中由于材料内部原因引起的能量损耗称为内耗。晶界内耗峰是我国科 学家葛庭燧于1947 年用他发明的“葛氏扭摆” 在多晶纯铝中发现的。晶界内耗峰和相关的滞弹 性效应可以用滞弹性理论和粘滞性滑动模型给予合理的解释。这个内耗峰已被广泛地用来研究晶 界的动力学行为,杂质在晶界的偏聚,以及材料科学中相关的问题。 以往晶界内耗的研究大多数是用多晶试样进行的,其中包含了不同类型晶界的贡献。由于不 同类型晶界的结构和性质不同,因而多晶试样中的晶界内耗只能反映不同晶界的“平均效应”, 它的具体机制也难以解释清楚。 二十一世纪以来,人们对双晶试样（其中只包含单一晶界）中的晶界内耗进行了比较细致的 研究。实验结果表明,晶界内耗可以反映不同类型晶界的“个性”,因而可以应用于“晶界的设 计和控制”（或称“晶界工程”）。此外,新近还发现了晶界内耗中的“耦合效应” 和“补偿效 应”。这些发现加深了对晶界内耗机制的认识。 本文首先对以往多晶试样中的晶界内耗研究做一个简要的概述,然后介绍近年来双晶试样中 晶界内耗研究的新进展,并对晶界内耗的微观机制和应用前景进行分析和展望。     

晶界内耗的研究

晶界内耗是中国科学家葛庭燧开创的一个研究领域．以往晶界内耗的研究主要是用多晶试样进行的．最近作者用不同取向差的双晶试样研究了单个晶界的内耗，取得了一些新的结果．文章综述了研究晶界内耗的意义以及新近的进展．     

晶界力学弛豫研究的新成就

概括地介绍了近１０年来葛庭燧教授领导的中国科学院固体物理研究所内耗与固体缺陷开放研究实验室在晶界力学弛豫方面所做的大量的创造性工作，其中包括确证了晶界力学弛豫的来源，发现了低频高温范围若干新的力学弛豫现象和非线性效应，在晶界弛豫与晶界结构的联系上得到一些极有价值的实验结果．这是继１９４７年葛庭燧教授发现晶界内耗峰以来我国科学工作者对线性和非线性内耗研究领域发展作出的新的重大贡献。     

晶界弛豫研究50年

文章综述了我国科学工作者５０年来关于晶界弛豫研究的早期开拓和近期发展．前者包括扭摆内耗仪的发明、晶界内耗峰的发现和无序原子群晶界模型的提出．后者包括澄清了关于晶界内耗峰来源的争论,揭示了晶界弛豫具有一个临界温度,从而提出了一个适合于各种温度的综合的晶界模型．一个最重要的进展是关于竹节晶界内耗峰的发现与其机理的阐明,从而揭示了晶界附近的位错亚结构能够影响晶界本身的性质和结构．这对于研究多晶金属的力学性质提供了一个广阔的途径．另外,晶界与邻域位错的非线性交互作用的发现,为奠定非线性滞弹性这门新学科提供了实验基础     

用测量晶界内耗的方法研究蠕变断裂过程

本文研究了工业纯铝在不同断裂类型的蠕变过程中晶界内耗峰的变化。由晶界内耗曲线所包围的面积求出晶界弛豫度,而晶界弛豫度的下降意味着晶界强度增高。根据实验结果可以推知:在沿晶型断裂过程中,晶界不发生强化;在混合型断裂过程中,晶界发生了强化;在穿晶型断裂过程中,晶界则发生了显著的强化。这说明:发生不同类型的蠕变断裂,不仅决定于晶界和晶粒在蠕变试验前的相对强度,而且与蠕变过程中晶界强化的程度有关。     

晶界驰豫研究50年

文章综述了我国科学工作者５６０年来关于晶界驰豫研究的早期开拓和近期发展,前者包括扭摆内耗仪的民昌界内耗峰的发现和无序原子群晶界模型的提出,后者包括澄清了关于介内耗峰来源的争论,揭示限晶界弛豫具有一个临界温度,从而提出了一个适合于各种温度的综合的晶界模型,一个最重要的进展是关于竹节晶界内耗峰的发现与其机理的阐明,从而揭示了介附近的位错亚结构能够影响晶一身性质和结构,这对于研究多晶金属的力学性质提供了     

冶金内耗相关的阻尼峰机理

介绍了作者等近年来，对铁基材料内耗谱和内耗机制，进行的针对性研究和取得的进展；讨论和评述了变形增强Snoek效应、Snoek-Kē-Koester（SKK）阻尼、B变形峰和K色峰等内耗现象机制。还讨论了一些相关的基本问题和有争议的问题。     

用内耗方法研究铜的蠕变断裂过程

在文献[1]关于工业纯铝研究的基础上,研究了工业纯铜在不同条件下蠕变过程中晶界内耗峰的变化,蠕变条件分为三类:(a)较高温度、较低应力;(b)中等温度、中等应力;(c)较低温度、较高应力;使试样分别发生晶间型、混合型和穿晶型的断裂。由晶界内耗峰的变化可以推知:在较高温度、较低应力的蠕变过程中,晶界强度变化不大;在中等温度、中等应力的蠕变过程中,晶界强度有一定程度的提高;在较低温度、较高应力的蠕变过程中,晶界强度则有比较显著的提高。这说明,在蠕变过程中,晶界强度是变化着的,在不同的蠕变条件下,晶界强化的程度不同,最终导致了不同类型的蠕变断裂。这对于“等强温度”概念是一个修正和补充。 关键词：     

6066Al/SiCp复合材料内耗性能研究

用粉末冶金方法制备了6066Al合金和不同SiCp含量的6066Al／SiCp复合材料，用多功能内耗仪在200～600K温度区间内测试了所研究材料在升温过程中的内耗变化趋势，探讨了6066Al／SiCp复合材料在不同温度区间的内耗机制。结果表明6066Al／SiCp的内耗值比6066Al合金内耗值高，特别是在高温阶段比6066Al合金内耗值高得多；6066Al／SiCp和6066Al合金在300-470K时的内耗主要是位错与第二相颗粒交互作用引起的位错内耗，在高温下内耗主要由Al／Al、Al／SiC的界面微滑移引起。     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Retrieval of ultraviolet skylight radiances and O3 slant column densities from balloon-borne limb spectrometer

With a novel light-weight and absolutely calibrated ultraviolet （UV） spectrometer, UV skylight radiances and O3 slant column densities are measured by balloon-borne limb measurements in Xinjiang area, China. UV skylight radiances measured at the height of 31 km are compared with the results from Modtran in the wavelength range from 290 to 420 nm. O3 slant column densities are derived from radiance spectra in the Huggins bands （320 - 335 nm） using differential optical absorption spectroscopy method. And the parameter exhibits a good correlation with the same value simulated by radiative transfer model （Tracy）. The O3 profile simultaneously measured by an O3 sonde is used as input in Tracy calculations. The O3 sonde is launched on the same balloon.     

Design optimization of highly sensitive LSPR enhanced surface plasmon resonance biosensors with nanoholes

For breaking through the sensitivity limitation of conventional surface plasmon resonance (SPR) biosensors, novel highly sensitive SPR biosensors with Au nanoparticles and nanogratings enhancement have been proposed recently.But in practice, these structures have obvious disadvantages.In this study, a nanohole based sensitivity enhancement SPR biosensor is proposed and the influence of different structural parameters on the performance is investigated by using rigorous coupled wave analysis (RCWA).Electromagnetic field distributions around the nanohole are also given out to directly explain the performance difference for various structural parameters.The results indicate that significant sensitivity increase is associated with localized surface plasmons (LSPs) excitation mediated by nanoholes.Except to outcome the weakness of other LSP based biosensors, larger resonance angle shift, reflectance amplitude, and sharper SPR curves' width are obtained simultaneously under optimized structural parameters.     

Polymer gratings based on photopolymerization for low-order distributed feedback polymer lasers

Novel polymer distributed feedback(DFB)gratings are fabricated based on photopolymerization to reduce lasing threshold of polymer lasers.A photopolymer formulation sensitive to 355-nm ultraviolet(UV)light is proposed for the fabrication of polymer gratings and it can be used to form polymer films by spin-coating process.A very low surface-relief depth ranging from 12.5 to about 1.0 nm has been demonstrated with a refractive-index modulation of about 0.012.The experimental results indicate that such polymer gratings have promising potentials for the fabrication of low-order DFB organic semiconductor lasers.     

A novel methodology for photometric compensation of projection display on patterned screen

We propose a novel methodology based on the projector-camera (ProCam) system to address the photometric compensation issue for the projection display on the patterned screen.The patterned screen is treated as the combination of a perfect white screen and a color modulator.The perfect white screen is used to automatically and accurately characterize the ProCam system offline using the polynomial model,and the parameters of the color modulator can be efficiently recovered by employing only two gray images based on the linear reflectance model.The experimental results show that the color artifacts of the display image can be greatly improved with this methodology,which demonstrates its feasibility and validity in the photometric compensation.