Mössbauer and electron microscopy study of martensitic transformations in an Fe-Mn-Mo alloy

The kinetic, morphological, crystallographic, and magnetic characteristics of thermally induced martensites in Fe-13.4wt% Mn-5.2wt% Mo alloy were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Mössbauer spectroscopy. The experimental results reveal that two types of thermal-induced martensites, ? (hcp) and α′ (bcc) martensites, are formed in the as-quenched condition, and these transformations have athermal characters. Mo addition to the Fe-Mn alloy does not change the coexistence of ? and α′ martensites with the Mn content between 10wt% and 15wt%. Besides, Mössbauer spectra reveal a paramagnetic character with a singlet for the γ (fcc) austenite and ? martensite phases and a ferromagnetic character with a broad sextet for the α′ martensite phase. The volume fraction of α′ martensite forming in the quenched alloy is much more than that of the ? martensite.     

AFM quantitative analysis and determination of shear angle of {259}f martensitic surface relief

An attentive observation and quantitative analysis of {259}f martensitic surface relief in an Fe-23Ni-0.55C alloy are made by means of an atomic force microscope (AFM), and different martensitic variants' shear angles are determined in this paper. The experiments show that {259}f martensitic surface relief exhibits regular shape in many cases, which is in agreement with the prediction of invariant plane strain (IPS). Generally, {259}f martensitic surface relief appears to be "N"-shaped, but it is tent-shaped in the case of zigzag-shaped martensite. The compressed deformation of parent phase diminishes the surface relief in size but with little change of its relief angle. {259}f martensitic surface relief, large or small, has approximately the same relief angles, exhibiting a good "self-similar fractal". The determined values of different {259}f martensitic variants' shear angles are in fine agreement with the prediction of Wechsler-Liberman-Read (W-L-R) theory, with only a slight difference of less than 3.65°.     

Microstructure of ultrahigh carbon martensite

Recent experimental investigations suggest that the martensite formed by quenching carbon steels(0.2–1.26 mass %C) are composed of twins and nanoscale ω particles in twin boundaries, rather than carbon supersaturated uniform solutions. In order to probe the microstructure of the martensite with ultrahigh carbon content, a novel strategy is employed in the present study to obtain ultrahigh carbon martensite(approximate2.1 mass %C) by quenching ductile cast iron. The microstructure of the martensite was intensively characterized by high resolution transmitting electron microscopy. It is indicated that the microstructure of the ultrahigh carbon martensites is composed of ultrafine {112} 111 -type twins and high-density nano-scaled ω particles embedded in twin boundaries. These ω nanoparticles in twin boundaries could remarkably impede the deformation of the movement of the nanotwins in martensites, leading to poor ductility and strength of the quenched ductile cast iron. These findings not only reveal the substructures of ultrahigh carbon martensite, but also enhance the understanding of the mechanical behavior of high carbon steels and ductile cast irons.     

母配分系数与旋量玻色-爱因斯坦凝聚

研究了由自旋为1的玻色子组成的N-体系统的总自旋态.导出了具有{N}和{N-1,1}对称性的总自旋态的母配分系数.这些系数使有关矩阵元的计算大为方便.因而它们将有助于建立一个关于旋量玻色爱因斯坦凝聚的改进了的理论,其中总自旋S及它的Z-分量Sz均得以守恒.     

Retrieval of column-averaged volume mixing ratio of CO2 with ground-based high spectral resolution solar absorption

The total column-averaged volume mixing ratio of atmospheric carbon dioxide （Xco2） has been retrieved with high spectral resolution solar absorption data obtained from ground-based Fourier transform spectrometer （FTS） measurements at Xichong, a coastal site in the district of Shenzhen in southern China. Based on differential optical absorption spectroscopy （DOAS） theory, the Xco2 was retrieved by finding the best match of observed high spectral resolution solar absorption data and monochromatic radia- tion transfer model calculations. The averaged Xco2 in the whole observation period was about 394.9 ppm. The uncertainty of the retrieval was estimated to be 2.0 ppm （0.51%） by comparing retrievals at two bands. The preliminary results show that Xc% retrieved by this method can be used to validate satellite remote sensing of Xco2.     

广义逆的递推算法及其应用

在简化{1}-,{1,2}-和{1,2,3,4}-逆并给出{1,3}-,{1,2,3}-,{1,4}-和{1,2,4}-逆的基础上,得到了递推滤波、固定点平滑、固定滞后平滑和预报算法,并由此得到离散线性随机和定常系统状态的最佳线性最小无偏估计.证明了给出最佳线性无偏估计的充要条件而无需初始状态的先验统计知识.对于定常系统,给出了滤波、固定点平滑、固定滞后平滑和预报形式的无差状态观测器而无需系统是时不变和完全可观测性的.     

A topological approach to the correlation of standard formation enthalpy with path index of benzenes derivatives

A mathematical model formulated as ΔfHθm(g)=a+sum from i=1 to 5bipi(i≠2) was constructed for the relationshipbetween standard formation enthalpy ΔfHθm(g) and path index Pi of substituted benzenes derivatives. An empiric equation for the calculation of ΔfHθm(g) was worked out. The calculated values of standard formation enthalpy based on this model are excellently consistent with those from experimental for 55 organic compounds. The model is shown to be simple and of practical usefulness, particularly when required experimental data are unavailable.     

Crystallographic similarity between the lath martensite and lower bainite in medium-carbon alloy steels

Progress in the crystallography of lath martensitic and lower bainitic transformations is briefly reviewed, followed by a presentation of the experimentally measured crystallographic characteristics of both lath martensite and lower bainite formed in mediumcarbon steels containing Si, Mn and Mo. It is found that the bainite plates relate to each other by a relative rotation of 54.7°or 60°about the normal to their common close-packed planes {110} b, which ensures a pseudo- {112}b twin relationship between two adjacent plates,and that all bainite variants formed in a single packet keep a unique G-T orientation relationship with the austenite matrix. These two types of OR of lower bainite are similar to that of the lath martensite, respectively. Furthermore, the measured habit planes of both the lower bainite and lath martensite are all {335} f type, which can verify the crystallographic similarity between the lath martensite and lower bainite.     

全局性N元F-强混沌系统的一个判据

设(X,f)是一个动力系统, 其中X是一个含至少2个点的完备度量空间,f是X上的一个连续自映射. 对给定的 Furstenberg 族F与整数 $N\geq2$,将F-混沌推广到N元F-混沌. 为此, 对于X的2个非空子集A,B, 借助集对(A,B)的F-往复点来引入F-攀援串的概念, 进而定义N元 F-混沌以及讨论N元F-混沌的一些性质. 最后以 Furstenberg 族理论为主要工具, 给出一个动力系统是全局性N元F-强混沌的一个判据, 并通过例子来阐述它在动力系统中的应用.     

La$_{{1-x}}$Sr$_{x}$TiO$_{3}$ 薄膜的高通量 X 射线衍射

高通量材料合成方法和高通量材料表征手段区别于传统低效率的 "试错法"材料发展方法, 极大地加速了材料科学的变革和发展. 通过设计程序进行了高通量 X 射线衍射实验, 在保证数据分辨率条件下, 高效地表征了 La$_{1-x}$Sr$_{x}$TiO$_{3}$ 薄膜上多个数据位点的晶体结构, 验证了其成分的连续变化性质, 为后续开展更多类型的高通量 X 射线衍射实验提供了指导.     

取向硅钢薄带形变再结晶组织及织构演变

利用背散射电子衍射微织构分析技术及X射线衍射织构分析技术,结合对取向硅钢薄带再结晶各阶段退火板磁性能的分析,系统研究了其形变再结晶过程中的组织及织构演变。结果表明,薄带内原始高斯晶粒取向发生绕TD轴向{111}<112>的转变,同时晶粒取向还表现出绕RD轴的附加转动,这种附加转动及其导致的表层微弱立方形变组织可为再结晶立方织构的形成提供核心。退火各阶段样品磁性能的变化对应了{110}-{100}<001>有益织构及其他织构的强弱转变以及再结晶晶粒不均匀程度的变化,综合织构类型及晶粒尺寸的变化推断发生了二次及三次再结晶过程。升温过程再结晶织构演变主要体现了织构诱发机制,也即与基体存在绕<001>轴取向关系的晶粒长大优势结合高斯织构的抑制效应发挥作用;而在高温长时间保温后三次再结晶过程,{110}低表面能诱发异常长大发挥主要作用使得最终得到锋锐的高斯织构。     

体膨颗粒非均质裂缝封堵效果与改善

体膨颗粒已广泛应用于高温高盐裂缝性油藏控水,且其封堵效果与颗粒尺寸、颗粒分流率密切相关。采用人工造缝的碳酸盐岩露头岩芯组模拟非均质裂缝储层,在130℃、19.8×10⁴ mg/L条件下进行体膨颗粒裂缝堵水效果评价与改善实验。结果发现,粒径过大、窄裂缝分流率过高的体膨颗粒可能加剧裂缝产液的非均质性,而粒径过小的体膨颗粒不适用于出水强度较高的储层。将可固化覆膜颗粒与体膨颗粒联用,前者在油藏高温下固化于宽裂缝内形成不可动筛网段塞,令后者从宽裂缝中突破的压力梯度显著高于窄裂缝,进而可有效改善非均质裂缝的产液剖面,并消除因体膨颗粒尺寸、分流率不当对裂缝封堵带来的负面影响。研究有助于进一步认识体膨颗粒的非均质裂缝封堵行为,对提高裂缝油藏的控水效果具有积极意义。     

高温下钨断裂及氢影响钨断裂的分子动力学模拟

用分子动力学模拟在1000K温度下单晶钨在单轴应变的情形下断裂和氢对钨断裂的影响。结果表明:{100}面的辟裂比{110}面要容易。{100}面的辟裂与裂纹尖端的取向有关,模拟结果与低温下的实验结果符合得比较好。{110}面<111>方向的断裂不是辟裂方式。切应变的模拟结果也与实验相符。氢的加入对裂纹尖端影响比较大,能显著降低应力。     

Influence of slip system combination models on crystal plasticity finite element simulation of NiTi shape memory alloy undergoing uniaxial compression

The influence of various slip system combination models on crystal plasticity finite element simulation of Ni Ti shape memory alloy subjected to uniaxial compression deformation is investigated according to three combinations of slip systems, including combination of {010}100and {110}111slip modes, combination of {110}100and {110}111slip modes and combination of {110}100, {010}100and {110}111slip modes, which consist of 18, 18 and 24 slip systems, respectively. By means of simulating mechanical response,strain distribution, stress distribution and Schmid factor, it can be found that in terms of simulation accuracy,combination of {110}100and {110}111slip modes is in good agreement with combination of {110}100,{010}100and {110}111slip modes. The contribution of {110}100slip mode to plastic strain is primary in plastic deformation of Ni Ti shape memory alloy, whereas {010}100slip mode, which makes small contribution to plastic deformation, can be regarded as the unfavorable slip mode. In the case of large plastic strain, the {010}100slip mode contributes to the formation of(001) [010] texture component, while {110}100and {110}111slip modes facilitate the formation of γ-fibre(111) texture.     

一种基于DWT和DFT的数字图像水印算法

提出了一种基于小波变换和离散余弦变换的数字图像水印算法.此算法首先对原始图像进行一级小波分解,再对其低频系数进行离散余弦变换,调整DCT中频系数的相对值,最后把由{-1,1}组成的伪随机序列嵌入其中.试验结果显示,此算法对JPEG压缩、gauss噪音有较强的鲁棒性.     

Microstructure and texture evolution of cold-rolled deep-drawing steel sheet during annealing

In accordance with experimental results about the annealing microstructure and texture of cold-rolled deepdrawing sheet based on the compact strip production (CSP) process, a two-dimensional cellular automation simulation model, considering real space and time scale, was established to simulate recrystallization and grain growth during the actual batch annealing process. The simulation results show that pancaked grains form during recrystallization. {111} advantageous texture components become the main parts of the recrystallization texture. After grain growth, the pancaked grains coarsen gradually. The content of {111} advantageous texture components in the annealing texture increases from 55vol% to 65vol%; meanwhile, the contents of {112}〈110〉 and {100}〈110〉 texture components decrease by 4% and 8%, respectively, compared with the recrystallization texture. The simulation results of microstructure and texture evolution are also consistent with the experimental ones, proving the accuracy and usefulness of the model.     

Kinetics of C2(a3Πu) radical reactions with NO, N2O, O2, H2 and NH3

Pulsed laser photolysis/laser-induced fluorescence (LP-LIF) is utilized to measure rate constants for C₂(a³Π_u) reactions with NO, N₂O, O₂, H₂ and NH₃. Multiphoton dissociation of C₂Cl₄ at 266 nm is employed for the generation of C₂(a³Π_u) radicals. The C₂(a³Π_u) concentration is monitored by the fluorescence of the (0, 0) band of the (d³Π_g&#8596;a³Π_u) transition at 516.5 nm. C₂(a³Π_u) removal rate constants for the reactions are determined as k_NO = (5.46 ± 0.10) × 10^-11 cm³ molecule^-1 s^-1 , k_N2O = (1.63 ± 0.20) × 10^-13 cm³ molecule^-1 s^-1 , k_N2O = (1.58 ± 0.16) × 10^-11 cm³ molecule^-1 s^-1, k_O2 = (5.92 ± 1.00) × 10^-14 cm³ molecule^-1 s^-1, k_H2< 1.0× 10^-14 cm³ molecule^-1 s^-1. Based on the data analysis and theoretical calculation, we suggest that the C₂(a³Π_u) reactions with H₂ and NH₃ proceed via the hydrogen abstraction mechanism, barriers exist at the entrance channel of the reactions of C₂(a³Π_u) with H₂ and NH₃.     

Relative contribution of the anthropogenic forcing and natural variability to the interdecadal shift of climate during the late 1970s and 1990s

Global warming accelerated after the late 1970s and slowed down after the late 1990s, accompanying the significant interdecadal changes in the regional climate. We hypothesized that the interdecadal changes linearly consisted of two independent components, anthropogenic forcing and natural decadal variability, which can be represented simply by the radiative forcing effect of carbon dioxide \((\text{RF}_{\text {CO}_2})\) and the Pacific Decadal Oscillation (PDO), respectively. The combined effect of the \(\text{RF}_{\text {CO}_2}\) and PDO could explain the majority of the surface temperature changes during the late 1970s and 1990s, but the magnitudes of the relative contribution of the \(\text{RF}_{\text {CO}_2}\) and the PDO are inconsistent in different regions. For both the surface temperature and geopotential height, the \(\text{RF}_{\text {CO}_2}\) could induce significantly positive anomalies over almost the entire globe for these two shifts, exhibiting a larger magnitude in the mid–high latitudes and in the late 1990s shift. The PDO could induce opposite anomalies for the two interdecadal shifts due to its phase transitions (negative-positive–negative). Furthermore, for the shift in the late 1970s, both the \(\text{RF}_{\text {CO}_2}\) (53.7 %–66.7 %) and the PDO (33.3 %–46.3 %) were important in regulating the tropical geopotential height, whereas the \(\text{RF}_{\text {CO}_2}\) dominated the changes in the mid-latitudes. For the western Pacific subtropical high, the \(\text{RF}_{\text {CO}_2}\) (PDO) could explain 52.3 %–62.1 % (37.9 %–47.7 %) of the change. The negative effect of the PDO counteracted most of the \(\text{RF}_{\text {CO}_2}\) effects for the late 1990s shift.     

广义逆矩阵｛2｝-逆充分必要性的一些新结论

在相关的广义逆矩阵理论基础上,通过研究广义逆矩阵中某些满足一定条件的{2}-逆的充分必要性,获得了一些新结果。拓广补充了相关结论,这对于{2}-逆的应用具有一定意义。     

二硫化钼-氧化石墨烯纳米粒子的添加量对水性聚氨酯丙烯酸树脂涂层防腐蚀性能的影响

金属腐蚀给世界经济带来巨大损失, 防止金属腐蚀成为人们关注的焦点. 采用一种简单的方法合成二硫化钼-氧化石墨烯 (molybdenum disulfide-graphene oxide, MoS$_{2}$-GO), 将其作为纳米填料加入水性聚氨酯丙烯酸树脂 (waterborne polyurethane acrylic, WPUA) 涂层, 解决金属腐蚀的问题. 首先, 利用氨基丙基三乙氧基硅烷 (aminopropyltriethoxysilane, APTES) 对二硫化钼进行改性合成硅烷偶联剂改性二硫化钼 (molybdenum disulfide modified by silane coupling agent, A-MoS$_{2}$); 然后, 将 A-MoS$_{2}$ 与氧化石墨烯 (graphene oxide, GO) 在 N, N-二甲基甲酰胺 (dimethyl formamide, DMF) 中进行反应得到 MoS$_{2}$-GO 纳米粒子; 最后, 按照不同添加量 (0%、0.2%、0.4%、0.6%、 0.8% 和 1.0%) 将其加入 WPUA 涂层. 结果显示: MoS$_{2}$-GO 纳米粒子成功合成, 对比发现其中 0.4%MoS$_{2}$-GO/WPUA 涂层的表面平整致密, 接触角为 99.67$^{\circ}$; 在 3.5% NaCl 溶液中浸泡 28 d Bode 图中 $\vert Z\vert _{0.01{\rm Hz}}$ 为 3.19$\times $10$^{7} \Omega\cdot $cm², Nyquist 图为 1 个半圈, 相角图表现为 90$^{\circ}$ 的单峰, 表明具有更好的防腐蚀性能.