Thermodynamics of phase equilibrium of binary alloys containing nanprecipitates

A model of phase equilibrium in binary alloys has been developed taking into account the formation of phase precipitates of arbitrary (including nanometer) size. It has been shown that the phase composition of alloys substantially depends on the size of phase precipitates and, in the case of the formation of nano-precipitates, the phase composition can differ by a factor of several times from the phase composition of macroscopic precipitates. The proposed model has been used for calculating the dependence of the phase composition of some binary alloys (α-Fe-Cr at the temperature T = 773 K and Zr-Nb at the temperature T = 853−873 K) on the size of precipitates. The results of the calculation agree with experimental data obtained by other authors.     

Surface phase transformation induced by the dezincification of a beta Cu-Zn alloy on highly deformed systems

When Cu-Zn alloys are annealed under dynamical vacuum the Zn component evaporates. The process is called dezincification. This paper presents the results of the dezincification of highly mechanically deformed surfaces of samples initially in the beta (bcc) phase by a combination of in situ optical microscopy observations together with TEM measurements. It is shown that grinding lines remaining from the sample preparation process act as nucleation centers for the alpha (fcc) phase. Under this surface preparation conditions the new fcc phase nucleates with a different geometry than the one reported in previous papers in which surfaces were finished by electropolishing. In the present case, we observe individual fcc precipitates with a well defined geometry. The typical size of precipitates is in the micron range, and depends on the dezincification parameters: final temperature, dezincification time and prior surface preparation. TEM observations show that the fcc precipitates contain a large density of defects, mainly dislocations and twin boundaries.     

Study of the second harmonics in nonlinear scattering of interacting acoustic waves by a rigid cylinder

The field formed by the second harmonics in the case of the nonlinear scattering of interacting plane acoustic waves by a rigid cylinder is considered. The method of successive approximations is used to obtain the solutions to the inhomogeneous wave equation in the first and second approximations. Asymptotic expressions are derived for the components of the total acoustic pressure of the second harmonics, and the scattering diagrams for these components are presented.     

蠕变镍基单晶高温合金微观结构与界面特征的X射线小角散射研究

利用SAXS技术对蠕变过程中不同尺度范围的微观结构变化分析表明X射线小角散射(SAXS)与中子小角散射(SANS)测量的二维散射图具有明显的差异,由散射强度曲线的变化说明了蠕变过程中二次析出γ'相形貌和不同区域尺寸特征的改变情况.分析结果表明二次析出γ'相存在两类特征尺寸,在蠕变过程中沿[100]或[010]方向的变化趋势类似,均是在第一和第二阶段有所减小,在第三阶段又有所增大,相较而言,特征尺寸较大的γ'相变化也较为显著.二次析出γ'相在蠕变第二阶段元素扩散最严重,相表面最粗糙,在第三阶段两相界面又进一 关键词： 单晶高温合金 二次析出γ'相 X射线小角散射 微观结构     

Counterion phase transitions in dilute polyelectrolyte solutions

In dilute solutions of rodlike polyelectrolytes some counterions are distributed far from polyions while others are located in their vicinity in the regions of cylindrical symmetry of the electrostatic potential. For these cylindrical regions around rodlike polyelectrolytes we find an exact solution of the nonlinear Poisson-Boltzmann equation for the case of nonzero net charge in these regions. This exact solution implies three qualitatively different phases of counterion distribution around the polyions with second order phase transitions between these phases.     

Interaction of dislocations with nanoprecipitates of the metastable phase and dispersion strengthening of the Fe-Cu alloy

The interaction of dislocations with copper-enriched precipitates in the matrix of body-centered cubic iron has been investigated by the molecular dynamics method. It has been shown that dislocations stimulate the development of a phase instability of body-centered cubic copper precipitates in a specific range of their sizes. This process is accompanied by the pinning of dislocations by precipitates and makes a significant contribution to strengthening. The results obtained provide an adequate explanation for the observed dependence of the strengthening in the Fe-Cu system on the precipitate size.     

Measurement of the spatial phase shift in high-gain photorefractive materials

The correct determination of the spatial phase shift ?(p) in photorefractive materials is crucial to the proper characterization of novel materials. It is shown that the grating translation techniques commonly used for the measurement of ?(p) need to be reevaluated for high-gain materials. Strong energy and phase coupling leads to nonuniform slanted gratings, which result in an apparent dependence of the phase shift of the beam ratio and the optical polarization. A revised theory is presented, and analytical solutions are obtained for the special case of ?(p)?pi/2 . Numerical solutions for arbitrary ?(p) are in good agreement with measurements in a photorefractive polymer.     

Asymptotic solutions of the inhomogeneous Burgers equation

The method of the active second harmonic suppression in resonators is investigated in this paper both analytically and numerically. The resonator is driven by a piston which vibrates with two frequencies. The first one agrees with an eigenfrequency and the second one is equal to the two times higher eigenfrequency. The phase shift of the second piston motion is 180 deg. It is known that for this case it is possible to describe generation of the higher harmonics by means of the inhomogeneous Burgers equation. This model equation was solved for stationary state analytically by a number of authors but only for ideal fluids. Unlike their solutions, new asymptotic solutions are presented here which take into account dissipative effects. The asymptotic solutions are compared with numerical ones. For study of generation higher harmonics the solutions are developed in a spectral form.     

黄连与甘草化学成分的相互作用研究之一——混浊汤剂中沉淀部分的成分研究

以黄连与甘草为配伍组成的复方是一种沉淀性配伍, 它属于仲景古方系列之一。其汤剂呈混浊状, 分别对离心分离后的溶液与沉淀物的成分进行研究。运用高效液相色谱(HPLC)、傅里叶变换红外光谱(FTIR)和飞行时间质谱(TOF-MS)的方法, 对单煎黄连、单煎甘草和混煎黄连与甘草的溶液和沉淀物的结构组成进行研究。文章着重报道沉淀物成分的研究, 同时还将混煎沉淀物和溶液的谱学行为做了比较。结果发现, 在混煎黄连与甘草的沉淀物中, 黄连的有些化学成分被保留下来, 有些成分却被抑制了;而甘草的化学成分基本都消失了;同时在混煎黄连与甘草的沉淀物中还产生了在单煎黄连与单煎甘草中所没有的一些新物质。此结果说明黄连与甘草在混煎后其沉淀物的结构组成发生了变化, 这是由于在此复方中发生了甘草与黄连化学成分的相互作用所致。根据飞行时间质谱的数据, 推测黄连与甘草发生的化学反应可能有加成反应、分解反应和缔合反应等类型。它表明甘草在此复方中起到了极为重要的作用。通过混煎沉淀物与溶液的研究结果比较还表明, 在沉淀物中可能含有比溶液中更多的化学活性成分,它为古方的药用和疗效提供了一定科学依据。     

Viscoelastic phase separation of protein solutions

In addition to the known behavior of normal phase separation and gelation, we report novel phase-separation behavior of protein solutions as their intermediate case. A network structure of the protein-rich phase may be formed even if it is the minority phase, contrary to the conventional wisdom. This behavior is characteristic of viscoelastic phase separation found in polymer solutions. This kinetic pathway may play crucial roles in the complex phase ordering of protein solutions, in particular, protein network formation in biological systems and foods.     

Modelling of the influence of dihedral angle,volume fractions,particle size and coordination on the driving forces for sintering of dual phase systems

The equilibrium shape of solid particles in an aggregate immersed in a liquid or in a gas results from the minimization of interface energy. A model is developed for expressing the dependence of the solid–solid and solid–second phase interface areas on the system parameters: phase volume fractions, dihedral angle, particle size and coordination. The model aims at allowing quantitative assessment of the role of these parameters on the driving force for sintering. The representative volume element is a cone of which the apex angle accounts for the average particle coordination. In order to comply with the uniformity of interface curvature, the solid–second phase interfaces are described using the mathematics of the Delaunay surfaces. The results are compared with the solutions obtained by approximating the interface shape by the revolution of an arc of circle around the cone axis. This approximation does not involve a significant loss of precision.     

V型原子系统中相干布居俘获的相干相位调制研究

在延迟脉冲激光场作用下的V型原子系统中，实现了对相干布居俘获，电磁感应透明的相干相位调制，选择适当的能级其调制频率可以达到飞秒量级.利用数值和解析分析得到了延迟脉冲和叠加态粒子数布居的关系，以及粒子布居受光场相位调制的特点和变化规律.利用这种机理可以实现飞秒量级的量子开关作用. 关键词： 相干相位调制 相干布居俘获 电磁感应透明 量子开关     

Extreme wave formation in unidirectional sea due to stochastic wave phase dynamics

The authors consider a stochastic model based on the interaction and phase coupling amongst wave components that are modified envelope soliton solutions to the nonlinear Schrödinger equation. A probabilistic study is carried out and the resulting findings are compared with ocean wave field observations and laboratory experimental results. The wave height probability distribution obtained from the model is found to match well with prior data in the large wave height region. From the eigenvalue spectrum obtained through the Inverse Scattering Transform, it is revealed that the deep-water wave groups move at a speed different from the linear group speed, which justifies the inclusion of phase correction to the envelope solitary wave components. It is determined that phase synchronization amongst elementary solitary wave components can be critical for the formation of extreme waves in unidirectional sea states.     

Calculation of phase diagrams for solid solutions of ferroelectrics

The integral equations for calculating ferroelectric and antiferroelectric phase transition temperatures, order parameters, and critical concentrations of solid solution components are derived. The electric dipoles randomly distributed in the system are treated as sources of random fields. The random field distribution function is constructed taking into account the contribution of nonlinear effects and the differences in the dipole orientations for different solid solution components. The dependence of the phase transition temperature on the composition of a binary solid solution in the ferroelectric-antiferroelectric and ferroelectric-paraelectric systems is calculated. Numerical calculations are carried out for the PbTi_xZr_1?x O₃ and BaZr_xTi_1?x O₃ solid solutions. The results obtained are in good agreement with the experimental phase diagrams of these systems. Analysis of the results indicates that any solid solution containing ferroelectric (antiferroelectric) and paraelectric components transforms into a relaxor state at sufficiently high concentrations of the paraelectric component.     

Phase shifting algorithms for non-sinusoidal waveforms with phase shift errors

In phase shifting interferometry, phase errors due to harmonic components of a fringe signal can be minimized by applying synchronous phase shifting algorithms with more than four samples. However, when the phase shift calibration is inaccurate, these algorithms cannot eliminate the effects of a non-sinusoidal waveform. It is shown that by taking a number of samples beyond one period of the fringe pattern, phase errors due to the harmonic components of the fringe signal can be eliminated, even when there exists a constant error in the phase shift interval. A general procedure for constructing phase shifting algorithms that eliminate these errors is derived. A seven-sample phase shifting algorithm is derived as an example, in which the effect of the second harmonic component can be eliminated in the presence of a constant error in the phase shift interval.     

Viscoelastic model of phase separation in colloidal suspensions and emulsions

We propose a simple physical model of phase separation of colloidal suspensions and emulsions, which we call the "viscoelastic model." On the basis of this model, we consider two poorly understood phenomena: (i) phase separation accompanying the formation of a transient gel, and its collapse, and (ii) shear effects on composition fluctuations and phase separation. These phenomena can be explained by "asymmetric stress division" between the components of a mixture due to their size difference; the interaction network of particles can store elastic energy, while a fluid component cannot. The importance of the bulk stress stemming from an interaction network is discussed, using a concept of self-induced elastic constraint due to connectivity. We argue that there are common features to polymer solutions, colloidal suspensions, emulsions, and possibly protein solutions. They originate from dynamic asymmetry between the components and the resulting interaction network of the slower component of a mixture, which leads to the formation of a transient gel.     

Scattering phase functions of horizontally oriented hexagonal ice crystals

Finite-difference time domain (FDTD) solutions are first compared with the corresponding T-matrix results for light scattering by circular cylinders with specific orientations. The FDTD method is then utilized to study the scattering properties of horizontally oriented hexagonal ice plates at two wavelengths, 0.55 and 12 μm. The phase functions of horizontally oriented ice plates deviate substantially from their counterparts obtained for randomly oriented particles. Furthermore, we compute the phase functions of horizontally oriented ice crystal columns by using the FDTD method along with two schemes for averaging over the particle orientations. It is shown that the phase functions of hexagonal ice columns with horizontal orientations are not sensitive to the rotation about the principal axes of the particles. Moreover, hexagonal ice crystals and circular cylindrical ice particles have similar optical properties, particularly, at a strongly absorbing wavelength, if the two particle geometries have the same length and aspect ratio defined as the ratio of the radius or semi-width of the cross section of a particle to its length. The phase functions for the two particle geometries are slightly different in the case of weakly absorbing plates with large aspect ratios. However, the solutions for circular cylinders agree well with their counterparts for hexagonal columns.     

Ni4Ti3沉淀相对NiTi形状记忆合金相变行为的影响

采用第二近邻修正型嵌入原子势的分子动力学方法,建立了共格沉淀相与半共格沉淀相块状/柱状模型,模拟了温度诱发相变和应力诱发相变,分析了Ni₄Ti₃沉淀相对Ni Ti形状记忆合金相变行为的影响．结果表明,Ni₄Ti₃沉淀相本征应变诱发的弹性应力场对相变中马氏体变体类型、形核位置、分布等有重要影响.在温度诱发相变时,共格沉淀相促进部分马氏体变体的形核生长,能显著提高Ni Ti超弹性形状记忆合金的马氏体相变开始温度;在应力诱发相变时,Ni₄Ti₃沉淀相使马氏体早于无沉淀相区域形核,导致了相变应力降低、抑制了马氏体解孪,减小了应力-应变曲线的滞回环.     

Coherent phase control in electron argon scattering in a bichromatic laser field

This paper theoretically investigates the coherent phase control in electron--argon scattering assisted by a bichromatic laser field. The laser field is composed of a fundamental component and its second harmonic. The incoming and out going states of electron are described by the Volkov wave functions, and the electron--target interaction is treated as a screening potential. Numerical results for differential cross section of multiphoton processes vs the phase difference between the two components of laser field are discussed for several scattering angles and impact energies.     

High intensity Compton scattering in a strong plane-wave field of general form

Photon emission by an electron embedded in a strong external field of general form is studied theoretically. The external field considered is a plane-wave electromagnetic field of any number of components, period and polarisation. Exact, Volkov solutions of the Dirac equation with the 4-potential of the general external field are obtained. The photon emission is considered in the usual perturbation theory using the Volkov solutions to represent the electron. An expression for the transition probability of this process is obtained after the usual spin and polarisation sums, trace calculation and phase space integration. The final transition probability in the general case contains a single sum over contributions from external field photons, an integration over one of the phase space components and the Fourier transforms of the Volkov phases. The validity of the general expression is established by considering specific external fields. Known specific analytic forms of the transition probability are obtained after substitution of the 4-potential for a circularly polarised and constant crossed external field. As an example usage of the general result for the transition probability, the case of two circularly polarised external fields separated by a phase difference is studied both analytically and numerically.