Perturbation approach to the time-resolved transmittance for a spatially varying scattering inclusion in a diffusive slab

In the framework of the perturbation approach to the diffusion equation, an analytical expression is derived to describe the effects on the time-resolved transmittance due to the presence of a spatially varying scattering inclusion hidden inside a diffusive slab. This formula assumes that the reduced scattering coefficient of the inclusion is spatially Gaussian distributed and complements that obtained for the absorptive case. The accuracy and the application range of the perturbed transmittance are investigated through comparisons with the numerical solutions of the time-dependent diffusion equation given by using the finite-element method. The proposed perturbation model is validated through a fitting procedure that determines the relative error in retrieving the scattering perturbation parameter of the inclusion located at the midplane of the slab.     

铸坯夹杂物的定量评价方法

目前评估铸坯夹杂物水平的主要依据是夹杂物的面积(体积)分数。借鉴现有的国内外标准,制定了两个评价铸坯夹杂物的指标:纯净度指数和级别数。应用结果表明:这两种指标很好地反映了铸坯夹杂物的含量及其对产品质量的影响程度,如304不锈钢磨砂板的合格率。     

Time-domain optical imaging: discrimination between scattering and absorption

A technique for discriminating between scattering and absorbing inclusions located in the center of a scattering slab is presented. The technique is based on an empirical model that provides a simple mathematical expression to describe the change in the time-resolved transmission resulting from the presence of an inclusion. Experimental results from various configurations show that the technique allows for proper recognition of the type of an inclusion whether it is scattering or absorbing. This technique is a significant step toward tissue differentiation.     

Effect of Flux Jump on Current Density Distributions in Type-II Superconductors

The effect of flux jump on the current density distributions is studied in type-II superconducting slab. The magnetothermal diffusion equations based on the Kim model in the regime of flux creep are presented to estimate the effect of flux jump on the distributions of current density inside the slab and the changes of surface current density in the flux jump process. Numerical results show that the current density distributions are dependent on the flux jump. It is intended that the flux jump analysis presented be useful to researchers interested in flux jump instability characteristics.     

Inclusion characterization in a scattering slab with time-resolved transmittance measurements: perturbation analysis

A procedure for the time-domain optical characterization of an inclusion in a scattering slab is investigated theoretically and experimentally. The method relies on the measurement of a contrast function, which is defined as the time-dependent relative change in the transmitted signal resulting from the presence of the inclusion. Analytical expressions for the contrast functions of absorptive and diffusive inclusions are obtained through a perturbation solution of the diffusion equation. This procedure is used successfully to determine the optical properties of absorptive, diffusive, and mixed inclusions located at midplane in a scattering slab by use of time-resolved transmittance measurements.     

Effect of Critical Current Density and Critical Temperature on ac Susceptibility

Based on the flux creep equation, the effect of critical current density and critical temperature on ac susceptibility is investigated numerically in a superconducting slab immersed in an ac magnetic field. The current density dependence of the flux creep activation barrier is employed as the logarithmic law. The fundamental ac susceptibilities of the slab as a function of temperature for the same ac field have been derived in a unified picture. The results show that ac susceptibility in flux creep regime is affected by critical current density and critical temperature.     

On stress controlled thermoviscoplastic shearing and higher order strain gradients

Summary We give a brief discussion on the stability and non-uniformity of shear in a slab of finite width and infinite extent made from a non-hardening, non-conducting, anisothermal viscoplastic material with stress controlled boundary conditions. The new ingredient in our analysis is the inclusion of higher-order strain gradients in the expression for the flow stress. It is shown that this inclusion allows for the development of non-uniformities for a certain condition between the thermomechanical parameters for which the classical model (absence of strain gradients) imposes a uniformly evolving stable solution.     

Stationary heat conduction in an anisotropic slab containing a crack

The stationary temperature field in an anisotropic slab containing an internal longitudinal crack is investigated. On each face of the slab the temperature is presumed to have an arbitrary variation in one direction, while on the crack surface either heat flux or temperature is prescribed. The problem is reduced to a pair of Fredholm integral equations which can be solved numerically. As an illustrative example, the temperature distribution is computed for a slab having a temperature rise on one face and containing a central crack across which no heat is transferred. Numerical results are given for orthotropic and isotropic slabs with various ratios of crack length to slab thickness.     

Prediction of spatial distribution of the composition of inclusions on the entire cross section of a linepipe steel continuous casting slab

In the current study, the transformation in the composition of non-metallic inclusions from the molten steel to the solidified steel was studied and the composition distribution of inclusions on the cross section of a linepine continuous casting slab was predicted. During cooling and solidification of the continuous casting strand, Al₂O₃-CaO inclusions reacted with the bulk steel and transformed to CaS-Al₂O₃-MgO-(CaO) ones in the continuous casting slab. The composition of inclusions on the cross section of the slab varied with locations due to the varied cooling rate. A model was established to predict the distribution of the composition of inclusions on the cross section of the continuous casting slab, coupling solidification and heat transfer of the continuous casting slab, the kinetic mass transfer of the dissolved elements in the solid steel, and thermodynamic calculation of inclusion transformation at different temperatures. The composition transformation of inclusions mainly occurred at the temperature between the liquidus and solidus of the linepipe steel. Inclusions were mainly CaS-Al₂O₃-MgO-(CaO) in slab center and were MgO-Al₂O₃-CaO-CaS within the subsurface of the slab. In the slab, the transformation fraction of inclusions was less than 10 % at corners while it reached 70 % at 50 mm below the surface of the slab.     

相变材料蓄冷板凝固过程的传热研究

采用精确解法与积分近似相结合的方法,对一种自制相变材蓄冷材料充冷凝固过程的相变导热问题进行了求解.获得了该蓄冷介质在板式蓄冷器中凝固时的相界面移动速度,边界面热流密度随时间变化的规律,及不同工况下蓄冷板厚度与预测蓄冷时间的关系.计算结果与实验结果吻合较好.结果表明,边界面的热流密度随固相区厚度的增加而减小;预测蓄冷时间随冷媒流体温度的降低而减小,随平板厚度的增加而增加.     

Spectral measurement of angular neutron flux on the restricted surface of slab assemblies by the time-of-flight method

An experimental method of neutron angular spectrum measurement in a slab geometry with D-T neutrons has been developed and its characteristics were examined. This method separates collided flux from uncollided flux. A neutron collimator restricts the measuring area on the surface of a slab assembly and the detector-collimator response function was determined. The time-of-flight method with two discrimination levels was adopted using an NE213 scintillation detector with pulse shape discrimination to obtain an accurate efficiency. Such measurements provide useful information in fusion blanket research. The results of the spectrum measurement were compared with calculated neutron spectra. The estimated overall error of the spectrum was within 5%.     

Perturbations about a finite elastic inflation

An exact general analytic solution for a class of boundary value problems involving perturbations about a finite inflation of a slab containing a circular hole or inclusion is obtained. The equilibrium equations for the perturbed state are derived in terms of a general strain-energy function and solved exactly for Mooney-Rivlin materials. The method is not, however, restricted to this particular class of materials. Applications are made to the case where a perturbational uniaxial tension is acting at sections far from the cavity or inclusion and to the case where a small shear is applied at the edge of the hole. The deformation, the stress field and stress concentration around the hole are investigated in detail and computational results are presented graphically.     

水泥混凝土路面板早龄期湿度场数值模拟研究

基于Fick第二定律湿度扩散方程,采用有限差分方法,重点考虑面板温度变化、基层吸水及供水能力、自干燥对板内湿度的影响,开展了现场施工条件下水泥混凝土路面板早龄期湿度场数值模拟和性状特性研究,并与室内试验、四季不同的现场监测试验和国外类似研究结果进行了对比校验。研究表明采用的算法、模型和参数可较好模拟现场面板湿度场性状,数值模拟宜考虑面板内部温湿度耦合作用、采用基层湿度交换边界,基层绝湿边界可使面板湿度计算值显著偏高。现场施工条件下水泥混凝土路面湿度更易受到周围环境参数、施工铺筑时间和养护方式的显著影响,相比之下材料参数改变对面板湿度影响并不显著。建议进一步精细化研究板上下边界条件及参数,路面施工时尽量避免炎热季节,高温时段和基层过于预湿。     

Observation of NMR Signals from a Thin 3He Slab

NMR free precession signals from a slab of normal ³ He of thickness comparable to the superfluid coherence length have been observed using a SQUID NMR spectrometer at a frequency of 880 kHz. This spectrometer is based on a SQUID with Additional Positive Feedback, directly coupled to a low noise room temperature amplifier, and operated in flux locked loop mode using the direct offset integration technique, with a bandwidth of several MHz. The sensitivity is such that the signal from a 100 nm slab on a 1 cm ² surface, corresponding to 2×10 ¹⁷ spins, is clearly resolved.     

Numerical solution to a two-dimensional inverse heat conduction problem

The two-dimensional inverse heat conduction problem is solved using the method of dynamic programming. One problem involves determining two unknown heat flux histories imposed on two faces of a slab. Several numerical experiments were performed to ascertain the effects of noise and the weighting parameters.     

Modal Characteristics of Five-Layered Slab Waveguides with Double-Clad Metamaterials

The guided modes are investigated in a five-layered slab waveguide with double claddings of metamaterials using a new graphical method. The dispersion equations in the symmetric and asymmetric five-layered slab waveguide are derived from the presented graphical method, and corresponding field distributions are plotted for the oscillating guided and surface guided modes. The energy flux distribution along the axis is plotted for the surface TE₁ mode.     

The release into the atmosphere of hazardous volatiles Part II. Release from a slab of contaminated porous particles. The importance of free convection

The release of a volatile organic compound from a slab of porous particles imbued with an immobile oily phase containing the volatile is studied. The most important feature of the model is that it accounts for natural convection besides diffusion. The gas which fills the interparticle porosity of the contaminated slab has a composition, and thus a density, different from that of the surrounding atmosphere. Therefore, a natural convection flux may be established through the slab. The model shows that natural convection indeed plays an important role which increases with the vapor pressure of the component. For benzene it predominates the overall process.     

A BEM for time dependent infiltration from an irrigation channel

In this paper some two dimensional time dependent infiltration problems are considered. The problems involve infiltration from an irrigation channel into a homogenous soil and a soil which contains an impermeable finite inclusion. The problems are reduced to boundary integral equations which may be solved numerically using established procedures. Numerical results are obtained to provide the distribution of the matric flux potential for some particular impermeable inclusions and a particular channel shape. The results indicate how the distance from the channel influences the speed with which the matric flux potential reaches its steady state value. They also illustrate how the presence of an impermeable inclusion can increase the matric flux potential at points below the surface.     

Elastic ellipsoidal heat-conducting inclusion in a body under the action of a heat flux applied at infinity

We find the exact analytic solution of the system of four singular integrodifferential equations obtained as a result of reduction of the three-dimensional thermoelastic problem for a body containing a heatconducting elastic ellipsoidal inclusion. It is assumed that the body is subjected to the action of a uniform heat flux applied at infinity in the direction perpendicular to the median plane of the inclusion. As a result, we deduce the relations for the stress concentration near the inclusion, the level of stresses inside the inclusion, and the corresponding stress intensity factors K _II and K _III. The influence of the configuration of the inclusion on the stress concentration and intensity is analyzed for some special cases of the problem.     

Method for solving the steady-state problem of radiative-conductive heat transfer in a plane slab. II

An algorithm is described for solving the problem of radiative-conductive heat transfer in a plane slab of a nongray medium with opaque mirror boundaries. The influence of the total energy flux on the heat transfer is studied.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 31, No. 5, pp. 866–872, November, 1976.