Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Determination of parameters of microstructural inhomogeneity of deformation of metals by the method of modeling

The article suggests a method of evaluating the microstructural inhomogeneity of deformation of metals by modeling. The method includes the measurement of deformations of metal according to meshes of a dividing grid with small base and the calculation of the distribution parameters of microdeformations in model representation. It is shown that the modeling method makes it possible objectively to evaluate the microinhomogeneity of deformation of metals independently of the chosen mesh size of the dividing grid. New structural characteristics are introduced: the base and wave of variation expressing the degree of crumbling or amalgamation of metal grains by inhomogeneity of deformation.Translated from Problemy Prochnosti, No. 7, pp. 40–44, July, 1991.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Mathematical simulation of the front processes of combustion of condensed systems in view of the velocity of propagation of heat

It is suggested to use the hyperbolic heat equation for mathematical simulation of the front processes of combustion of energy-intensive condensed systems (CS). The correlation between the velocity of propagation of thermal wave with the velocity of front motion, the thermal effect of the reaction of thermal decomposition, and the value of heat flux delivered to the surface is analytically determined. Numerical solutions of hyperbolic heat equation are obtained for unsteady-state mode of ignition of energy-intensive materials. The agreement between calculated dependences and experimental data on the combustion of energy-intensive compounds is considered.     

方波幅度的测量不确定度

介绍了用众数法评价方波幅度时的不确定度分析和评价过程;讨论了主要的不确定度来源,包括众数判别区间的影响、波形测量系统幅度测量误差的影响等等;给出了减小不确定度的主要措施,并结合一个实例,给出了方波幅度的不确定度评价结果。     

Characteristics of mechanical properties of materials in studies of conditions of attainment of marginal states

It is shown that conditions of attainment of marginal states in the material of structural components are formulated on the basis of analysis of force and deformation criteria of formation and development of destruction. The parameters of these criteria are data on types of structural materials, standard and special characteristics of their mechanical properties, structural forms of considered elements of the equipment, and their operating stress loading. In this case, the construction of a system of state equations for describing interrelation of current damage, external actions, and responses to them is based on the concept of calculating variations in properties of materials at all stages of the design life cycle.     

Possibilities of Decreasing the Errors of Determination of the Height of the Pole of a Sessile Drop of Melt

We analyze the possibilities of decreasing the errors of measuring the height of the pole of a sessile drop of melt above its equator by determining the position of the equator according to the midpoints of vertical chords of the image of the drop. The optimal distance between these chords and the edge of the image of the drop is chosen within 10–20% of the radius of the equator. The proposed method guarantees the same level of errors of evaluation of the height of the pole and the radius of the equator, which enables one to substantially increase the accuracy of evaluation of the capillary constant and the surface energy of the melt according to the geometric parameters of the sessile drop.     

Effect of heterogeneity of materials and heat cycles on diffusion of hydrogen as a factor of the risk of development of hydrogen degradation of metals

Conclusions The analysis results show that in the presence of hydrogen the nonstationary nature of the thermal effects (heat changes, thermal cycles) in the presence of heterogeneities may on its own be a factor causing a high risk of hydrogen degradation and may be of the implicit type (hidden). The degree of risk depends, in particular, on the kinetics of thermal processes. These defects must be taken into account by estimating the properties of materials after the effect of hydrogen and solving the problems of ensuring safety of structures both in the design stage and controlling efficiency and in determining the optimum (permissible) operating conditions, and also in determining the residual service life. In certain cases the conditions of transition of thermal processes may be of controlling importance for the efficiency of materials in structures.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 6, pp. 7–20, November–December, 1992.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

Numerical study of methods of linearization of the output characteristics of radio-frequency sensors of the level of dielectric media

Different constructions of the sensing elements of radio-frequency level sensors based on sections of long lines are numerically investigated by means of the Matlab program for the purpose of minimizing the measurement error caused by the nonlinearity of the output characteristic. It is shown that the nonlinearity is lowest for U-shaped designs. The nonlinearity factor KN may be regulated by varying the capacitance of a correcting capacitor connected to the input of the sensing element and (or) the length of one of the sections of the long line. In selecting an optimal capacitance of the correcting capacitor KN ≤ 0.15% for control media with dielectric permittivity in the range 2.2–30.     

空压机轴承箱蜗壳温度探头油封改造

由于空压机进气侧轴承箱蜗壳温度探头密封效果不好,使空压机及其后续管道受到油污染。后将温度探头的O形圈密封改为骨架油封,杜绝了轴承箱漏油问题。文章简介空压机的结构和技术参数,详细介绍了骨架油封的制作和优点。     

Study of Flowability of Powders. Effect of the Addition of Lubricants

Abstract

In early paper we have studied the flow parameters of powders using a ring shear. Also, we have evaluated an adequate method to estimating flowability according to powder characteristics. The goal of this article is the study of the action of three lubricants, magnesium stearate, PRUV® and PRECIROL®, on the flowability of an excipient for direct compression, Maltrin® M510. Flow characteristics are evaluated with flowrate, repose angle and compressibility. The influence of concentration and mixing time is also evaluated. Compressibility did not discriminate the lubricant effect. The maximum correlation coefficient flowrate and the repose angle showed the best flowability for magnesium stearate mixtures.     

Analysis of anisotropy of properties on the basis of studies of texture of coarse-grained ingots of thermoelectric materials

An analysis of anisotropy of the properties of a Bi₂Se_0.3Te_2.7 solid solution was carried out using construction of demonstrative surfaces for thermoelectric effectiveness and thermal expansion coefficients. It is shown that the texture is an important factor forming anisotropy of properties and technological fitness of ingots for manufacturing modules. Anisotropy of properties based on the studies of the ingot textures obtained using the float-zone method and Bridgman method (growing thermoelectric plates in a flat cavity) was studied.     

Kinetics of drying of various materials and calculation of the duration of drying

This paper deals with methods of combining the drying curves obtained in different conditions into a single curve, the analysis of the kinetics of the process, and methods of calculating the duration of drying of materials. The proposed method of calculation is a development of Lykov's method.     

Extension of a model analysis of the degree of polarization of light

A theoretical approach is developed in which partially polarized radiation can be represented as a sum of coherent and incoherent components and also of the action of some imaginary device with time-dependent birefringence. This approach allows the Jones vector matrix method to be used for the calculations, which is important for theoretical calculations of the polarization state. Pis’ma Zh. Tekh. Fiz. 25, 74–78 (April 12, 1999)     

Calculation of the Heat of Combustion of Hydrocarbon Components of Fuels

Development is continued of the empirical method for the calculation of the heat of combustion of organic compounds and, in particular, of hydrocarbons of different structures by the additive scheme based on their chemical structure.     

Regularities of the influence of the aerodynamic coupling of blades on the formation of the spectrum of natural vibrations of the rims of turbine wheels of gas-turbine engines

We present the results of analytic and numerical investigations aimed at the evaluation of the influence of the aerodynamic coupling of blades on the formation of the spectrum of natural vibrations of the rims of turbine wheels regarded as a complex mechanical system with structural rotational symmetry with regard for the frequency detuning of blades.     

Evaluation of the reproducibility of the results of verification of counters. Case of water flowmeters

An approach to the analysis of the metrological comparability of control flowmeter instruments and different positions of the work table of an individual instrument is proposed. The results of experimental studies are presented.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.