The study of grain orientation distributions and grain boundary misorientation distributions in 304 and 316L stainless steels

Orientation distribution functions in two recrystallized austenitic stainless steels (AISI types 304 and 316L) with known grain boundary misorientation distributions have been studied. Previously obtained data on grain boundary spectra in these steels have been re-examined and analyzed from the point of view of texture analysis.The results obtained have shown that there is no unambiguous relatonship between grain boundary misorientation distribution and grain orientation distribution (ODF) determined by the X-ray analysis in the materials under study. This ambiguity is due to the following reason. In the grain boundary misorientation statistics only nearest-neighbor grains are taken into account, but in the orientation distribution function orientations are averaged over the entire volume of the specimen independent as to whether the grains are adjacent or not. Two main results were established for the steels under study: (i) Textures of the two steels differ, though their grain boundary misorientation distributions are similar; and (ii) misorientations of the majority of grain boundaries can be described as rotations about the axes close to 110.     

How accurately can the diffusion profiles indicate multiple fiber orientations? A study on general fiber crossings in diffusion MRI

The q-space imaging techniques and high angular resolution diffusion (HARD) imaging have shown promise to identify intravoxel multiple fibers. The measured orientation distribution function (ODF) and apparent diffusion coefficient (ADC) profiles can be used to identify the orientations of the actual intravoxel fibers. The present study aims to examine the accuracy of these profile-based orientation methods by comparing the angular deviations between the estimated local maxima of the profiles and the real fiber orientation for a fiber crossing simulated with various intersection angles under different b values in diffusion-weighted MRI experiments. Both noisy and noise-free environments were investigated. The diffusion spectrum imaging (DSI), q-ball imaging (QBI), and HARD techniques were used to generate ODF and ADC profiles. To provide a better comparison between ODF and ADC techniques, the phase-corrected angular deviations were also presented for the ADC method based on a circular spectrum mapping method. The results indicate that systematic angular deviations exist between the actual fiber orientations and the corresponding local maxima of either the ADC or ODF profiles. All methods are apt to underestimation of acute intersection and overestimation of obtuse intersection angle. For a typical slow-exchange fiber crossing, the ODF methods have a non-deviation zone around the 90 degrees intersection. Before the phase-correction, the deviation of ADC profiles approaches a peak at the 90 degrees intersection, while after the correction the ADC deviations are significantly reduced. When the b factor is larger than 1000 s/mm2, the ODF methods have smaller angular deviations than the ADC methods for the intersections close to 90 degrees . QBI method demonstrates a slight yet consistent advantage over the DSI method under the same conditions. In the noisy environment, the mean value of the deviation angles shows a high consistency with the corresponding deviation in the nose-free condition.     

Elasticity tensor and ultrasonic velocities for anisotropic cubic polycrystal

The orientation distribution of crystallites in a polycrystal can be described by the orientation distribution function (ODF). The ODF can be expanded under the Wigner D-bases. The expanded coefficients in the ODF are called the texture coefficients. In this paper, we use the Clebsch-Gordan expression to derive an explicit expression of the elasticity tensor for an anisotropic cubic polycrystal. The elasticity tensor contains three material constants and nine texture coefficients. In order to measure the nine texture coefficients by ultrasonic wave, we give relations between the nine texture coefficients and ultrasonic propagation velocities. We also give a numerical example to check the relations. Supported by the National Natural Science Foundation of China (Grant Nos. 10562004 and 10662004), the Jiangxi Project to Nature Academic and Technical Leaders in Targeted Areas, and Research Fund for the Doctoral Program of Higher Education (Grant No. 20070403003)     

用谱拟合法计算强激光场中氢原子的高次谐波谱

介绍了一种新的求解含时薛定谔方程的谱拟合法 .该方法把含时波函数在少量且分布稀疏的网格点上拟合 ,结合泰勒级数展开 ,用相对简单的计算得到包括Δt高次项贡献的含时波函数 .并将这一方法用于强激光场中氢原子高次谐波谱的计算 ,得到了与其它方法一致的结果. A new spectral fitting method for solving the time-dependent Schrdinger equation has been developed and applied to the atom in intense laser fields. By using this method, the time-dependent wave functions are determined with few and far between discrete mesh points. And the high accuracy wave functions with contribution of high-order-term of Δt are obtained by using Taylor series expand method. Our method is proved by computing high order harmonic generation spectra of hydrogen in laser fields...     

变分代数能量自洽法研究Li_2分子部分电子态的解析势能

在课题组前期建立的计算双核分子体系解析势能函数的代数能量自洽法(algebraic energy consistent method,AECM)的基础上,引入了经改进得到的精确研究双核分子完全振动能谱的变分代数法(variational algebraic method,VAM),获得了计算双核分子体系精确解析势能函数的变分代数能量自洽法(variational algebraic energy consistent method,VAECM)。基于有限的精确实验振动能谱数据,利用VAECM方法研究了Li_2分子1~3Δ_g,3~3Σ_g~+,1~3Σ_g~-和b~3Π_u等4个电子态的完全振动能谱和解析势能函数。获得了各电子态包含高阶的振动光谱常数、完全振动能谱、振动力常数fn和势能展开系数an,并通过可调变分参数λ最终确定了VAECM解析势能函数的具体表达形式。计算结果与其他方法的研究结果进行了比较,VAECM方法获得的振动能谱数据和势能解析表达形式能更好地描述这些电子态在渐近区和离解区的物理行为,消除了利用前期AECM方法研究这些电子态在离解区出现的非物理势垒现象。     

Spectral moments and orientation correlation functions of asymmetric top molecules

A method for calculating the spectral moments of dipole absorption and Raman scattering by asymmetric top molecules is proposed. The method is based on the calculation of coefficients of expansion of the corresponding orientation correlation functions in a Taylor series using the formalism of the angular momentum theory.     

Investigation of multiparticle atomic correlations in α-Fe1−xSi2 by Mössbauer spectroscopy

A method of experimental investigation of the parameters of multiparticle atomic correlations based on the Mössbauer spectra of the samples investigated has been developed. The presentation of complex spectra as a superposition of simple subspectra, determined by the local environment of resonant nuclei, makes it possible to evaluate the existence of different atomic configurations, centered on the resonant nucleus. The methods of probability expansion, in a series of correlation moments, permit us to evaluate the latter.The method developed is used to analyze vacancy ordering and clarify its nature in the highest iron silicide α-Fe_1?xSi₂. The correlation parameters in vacancy distribution, including the multiparticle ones, are determined. These data were used to calculate energies of atomic interactions according to the method of cluster variations.     

Si-SiO2膜的椭圆偏振光谱

我们建立了椭圆偏振光谱仪装置,提出一种较简便的测定方法(测I_max,I_min,θ_min,算(ψ,Δ)-λ),并对具有不同厚度氧化硅膜的硅样品进行了测量。还在理论上计算了光谱曲线,与实验结果基本相符。最后,对比了测定膜厚的偏振光谱法与消光法。 关键词：     

用广角X射线衍射系列方法测试和表征高聚物各种相态的结构特征

系统地论述了广角X射线衍射系列方法：径向分布函数、圆柱分布函数、取向分布函数、Rietveld粉末衍射全谱图最小二乘拟合、纤维全谱图精修以及衍射全谱图分峰等方法的基础理论、实验方法、计算程序及其可获得的结构参数;阐明采用这些方法研究高聚物非晶相、取向非晶相、结晶相的进展情况;探讨了联用这些方法研究高聚物二相、三相共存结构的一种新思路和新方案。而且已取得一定进展;并展望这一研究框架的全面实现,将能进一步拓展亢矣物共混物结构的研究。     

用广角X射线衍射系列方法测试和表征高聚物各种相态的结构特征

系统地论述了广角X射线衍射系列方法 :径向分布函数、圆柱分布函数、取向分布函数、Rietveld粉末衍射全谱图最小二乘拟合、纤维全谱图精修以及衍射全谱图分峰等方法的基础理论、实验方法、计算程序及其可获得的结构参数 ;阐明采用这些方法研究高聚物非晶相、取向非晶相、结晶相的进展情况 ;探讨了联用这些方法研究高聚物二相、三相共存结构的一种新思路和新方案 ,而且已取得一定进展 ;并展望这一研究框架的全面实现 ,将能进一步拓展高聚物共混物结构的研究     

Relationship between elastic anisotropy and texture in metal-matrix composites

The relationship between elastic anisotropy and texture in two-phase metal-matrix composites has been developed under certain conditions. Using measurements of the six independent ultrasonic velocities V_ij in samples of the aluminium alloys 8091 and 7064 containing up to 20% SiC particles and the formulation given by Bunge, the fourt-order expansion coefficients of the orientation distribution function are determined. The Young's moduli in different directions are also obtained from ultrasonic velocity measurements. Linear correlations between anisotropy described by Young's moduli and texture determined by orientation distribution function expansion coefficients are obtained, and confirm developed relationships for two-phase metal-matrix composites. This result shows that ultrasonic measurements provide a technique for the characterization of texture and elastic anisotropy in these materials.     

NMR studies of single crystals of the topological insulator Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> at low temperatures

A powder sample and single-crystal plates of the topological insulator Bi₂Te₃ have been investigated using the ¹²⁵Te NMR method at room temperature and at low temperatures in the range from 12.5 to 16.5 K. The NMR spectra of the single-crystal plates have been studied in the orientation where the crystallographic axis c is directed parallel or perpendicular to the magnetic field. The spectra have been obtained by means of recording spin-echo signals and plotting their envelopes. It has been shown that the NMR spectra for the bismuth telluride powder and plates with the orientation c ⊥ B consist of two lines, which are presumably attributed to tellurium nuclei in two crystallographic positions in the bulk of the sample. The position and shape of the lines are determined by the chemical shift and the Knight shift. For the orientation of the plates c || B, the spectrum contains an additional component in the high-frequency region, which cannot appear due to the angular dependence of the line shifts caused by tellurium nuclei in the bulk of the topological insulator. At a low temperature, the additional line dominates in the spectrum.     

Nonlinear electromechanical analysis: a constitutive theory for perovskite type ferroelectrics

A constitutive theory is established in this paper to describe the nonlinear electromechanical behavior of perovskite type ferroelectrics subjected to external stress and external electric field. In the proposed theory, each domain is considered as an inclusion. The Helmholtz free energy and Gibbs free energy of a constituent element, that are derived by using micromechanics approaches, are functionals of the orientation distribution function (ODF) that depicts the domain distribution patterns. By applying the internal variable theory and expanding ODF in Fourier series, the yielding condition, the evolution of ODF, and the constitutive relation are obtained. In terms of the simplification of the constitutive relation, theoretical predictions are compared with experimental results. There is an agreement between the theoretical and the experimental results, indicating that the theory is reasonable and applicable. It should be pointed out that the constitutive model proposed in this paper is restricted to ferroelectric materials exhibiting transformation from cubic to tetragonal only.     

IR Dichroism of Langmuir–Blodgett Films Based on Fatty Acids

We propose a method of measurement and quantitative estimation of dichroic ratios of submicron laminated Langmuir–Blodgett films by the IR spectra of multiple attenuated internal reflection. The method has been used in calculating the angles of orientation of molecular chains of stearic and palmitic acids in the process of their molecular deposition on an optical substrate. It has been found that in the process of structural self-organization of ensembles the degree of orientation of macromolecules is the higher, the greater the number of links entering into the aliphatic chain.     

Solute-solvent interaction in liquids

The infrared absorption spectra of HCl and DCl in dilute CCl₄ have been recorded over a range of temperatures. The band shapes have been analysed using the method of moments, allowing both the rms torque and rms force acting on the solute to be determined as functions of temperature. It is shown that rotation-translation coupling makes a significant contribution to the dynamics of these polar molecules in solution.     

Measurement of the absorption coefficient of scattering liquid media by the calorimetric method

Using the example of a number of hydrosols (gold nanorods and nanoshells, silver nanoshells, zinc phthalocyanine nanoparticles), we show that the absorption coefficient of a scattering liquid medium can be measured from its heating by a short-time laser irradiation. The degree of heating was determined from expansion of the liquid in an ampoule with a capillary (the principle of liquid thermometer). Irradiation was performed at a wavelength of 671 or 1069 nm. From the transmission of samples of hydrosols at these wave-lengths, the sum of the absorption and scattering coefficients has been determined. To measure the absorption spectra of scattering liquids by this method, a laser with a tunable radiation wavelength is required. In the case of monodisperse colloidal solutions, the method ensures the measurement of the absorption and scattering cross-section ratio of particles.     

Thermal expansion in various phases of Nitinol using TMA

Phase transformation in the near-equiatomic, cold-worked Nitinol, exhibiting shape memory effect, has been investigated through the study of thermal expansion by employing thermomechanical analyser (TMA). The characteristic transformation temperatures determined by this method are compared with those obtained through DSC thermograms. The reliability and sensitivity of the thermal expansion probe have been discussed. The variation of thermal expansion coefficient with temperature in different heat treated samples has been studied in the range 30–120°C. Thermal expansion coefficient is found to be −ve during M↔A transformation and +ve in R↔A transformations. Thermal expansion coefficient in martensitic region in the presence and absence of R-phase has been determined.     

A Mössbauer spectroscopy study of antiferromagnetic iron arachidate Langmuir-Blodgett films

Langmuir-Blodgett multilayers of ferric arachidate (abbreviated: FeA) on silicon wafers have been investigated by means of conversion electron Mössbauer spectroscopy (CEMS) and absorption Mössbauer spectroscopy at different temperatures between room temperature and 4.2 K, without and with external magnetic fields up to 5 T. The films show a quasicrystalline structure with ac-axis orientation perpendicular to the plane and a random distribution of orientations in the plane of the films. All Mössbauer spectra show Fe³⁺. At low temperatures, antiferromagnetic ordering has been observed. The lines in both the room temperature and the low-temperature spectra are significantly broadened, which is due to a distribution of electric field gradients and hyperfine fields. The reason for this is a slightly disordered iron environment. The orientation and the distribution function of the internal magnetic fields have been determined.     

Electronic structure of strontium titanate

The spectra of three sets of optical functions for SrTiO₃ crystals are determined in a broad energy range of fundamental absorption. The calculations are carried out using the experimental reflectivity spectrum in the range 1–35 eV and two theoretical permittivity spectra in the ranges 0–30 eV and 0–14 eV. The special features of these spectra have been determined. The theoretical spectra of the optical functions are compared with the spectra determined using the experimental reflectivity spectrum.     

Orientation of liquid-crystal molecules on substrates exposed to argon-ion bombardment

The possibility for homogeneous orientation of liquid-crystal (LC) molecules was studied after argon-ion bombardment of substrates (Si, Ge) transparent in the infrared (IR) spectral region. The orientation of the LC molecules was monitored by IR spectroscopy. Nematic LC 4-methoxybenzylidene-4′-butylaniline (MBBA) was used to study the molecular orientation. Absorption spectra were analyzed near the band with maximum at 1630 cm⁻¹ corresponding to − CH=N-group vibrations along the long axis of the MBBA molecule. The type and degree of initial orientation of the LC molecules were determined from the correlation of the integrated absorptions of this band without and with an applied electric field (above the threshold voltage for the Fredericksz effect). It has been established that an increased ion fluence results in a planar orientation of the LC molecules and in a gradual transformation of the planar orientation of the molecules to a homeotropic one with preliminary argon-ion bombardment of substrates at energies of 250 eV and 1.25 keV, respectively. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 6, pp. 763–767, November–December, 2008.