Effects of particle size of reactant on characteristics of combustion synthesis of TiC-Fe cermet

Four Ti-C-Fe powder mixtures, with a same molar ratio but a different particle size, were used for a combustion synthesis of TiC-Fe cermet to investigate effects of the particle size on the characteristics of the combustion synthesis. The results showed that the mixture with the finer Ti powder gave out a higher combustion temperature, a higher reaction velocity, a higher product density, a layer-shaped pore, and a greater size of TiC particles whether the Fe powder was finer or coarser. While in the case of the coarser Ti powder used, a small amount of residual phase remained in the product, and what is more interesting that the mixture with the finer Fe powder gave out a lower reaction velocity than that by the mixture with the coarser Fe powder. These effects were successfully explained with the previously proposed mechanisms of the combustion synthesis of TiC-Fe, and the mechanisms were proved to be valid thereby.     

Experimental investigation of the effect of injection of products of decomposition of pastelike coolant on the electrical conductivity of the flow of pulsed MHD generator

A large-scale model of the channel of a pulsed MHD generator is investigated in an applied electric field. It is demonstrated that the flow of plasma under conditions of wall protection by way of injecting the products of decomposition of a pastelike coolant is realized with a clearly pronounced core and thin boundary layers. In the case of injection on the insulating walls alone, the integral electrical conductivity of flow remains almost constant in a wide range of injection intensity up to the value of 4%. The injection into the electrode boundary layer causes a considerable reduction of its electrical conductivity     

Optimization of the power and control of the shape of amplified trains of laser pulses

We have performed an optimization study on a train of laser pulses in a Nd:YLF master-oscillator power amplifier chain. Instead of using a flat train of input pulses and proper timing of the input pulses with respect to the pump pulse to keep the output pulse flat, we used a pulse-shaping technique. Then the maximum gain could be used, resulting in a 70% increase in output pulse energy. We constructed a special feed-forward loop to control the temporal shape of the train. We compare the results with a computational model based on the rate equations in the Nd:YLF amplifiers.     

Aspects of the theory of graphene

Following a brief review of the device-friendly features of graphene, recent work on its Green's functions with and without a normal magnetic field are discussed, for an infinite graphene sheet and also for a quantum dot, with analyses of the Landau-quantized energy spectra of the sheet and dot. The random phase approximation dielectric response of graphene is reviewed and discussed in connection with the van der Waals interactions of a graphene sheet with atoms/molecules and with a second graphene sheet in a double layer. Energy-loss spectroscopy for a graphene sheet subject to both parallel and perpendicular particle probes of its dynamic, non-local response properties are also treated. Furthermore, we discuss recent work on the coupling of a graphene plasmon and a surface plasmon, yielding a collective plasma mode that is linear in wavenumber. Finally, we discuss the unusual aspects of graphene conduction and recent work on diffusive charge transport in graphene, in both the DC and AC regimes.     

Ranking of research output of universities on the basis of the multidimensional prestige of influential fields: Spanish universities as a case of study

A university may be considered as having dimension-specific prestige in a scientific field (e.g., physics) when a particular bibliometric research performance indicator exceeds a threshold value. But a university has multidimensional prestige in a field of study only if it is influential with respect to a number of dimensions. The multidimensional prestige of influential fields at a given university takes into account that several prestige indicators should be used for a distinct analysis of the influence of a university in a particular field of study. After having identified the multidimensionally influential fields of study at a university their prestige scores can be aggregated to produce a summary measure of the multidimensional prestige of influential fields at this university, which satisfies numerous properties. Here we use this summary measure of multidimensional prestige to assess the comparative performance of Spanish Universities during the period 2006–2010.     

Technique of Calibration of a Working Standard of the Energy Unit of Narrow-Pulse Laser Radiation and Results of Trial Use of the Standard

Questions related to the design and testing of a technique of calibrating a working energy unit of narrow-pulse laser radiation by means of an electrical working system and determining the degree of equivalence of the optical and electrical conversion ratios of a calorimetric detector are considered. Results from calibration of the standard in the course of a trial period are also presented.     

Multiplicity of hydrodynamic states of the flow of a reacting gas through a layer of catalyst

It is shown numerically for the example of a two-temperature quasistationary model of the processes occurring in a layer of catalyst that in a reactor operating with a fixed pressure differential a set of stationary states can in principle exist.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 58, No. 2, pp. 239–244, February, 1990.     

A general method of solution of two-dimensional problems in the theory of cracks

Original systems of singular integral equations of plane problems in the theories of elasticity, heat conduction and thermoelasticity for a solid containing a set of straight thermally isolated arbitrarily oriented cracks are developed.The problems such as those of a set of cracks in infinite and semi-infinite plates, a set of cracks in a circular disk and an infinite plane with a circular hole, a periodic and doubly periodic set of arbitrarily oriented cracks in an infinite plate, a periodic row of cracks in a half-plane are considered.Analytical solution of the equations obtained is performed by using a perturbation technique when cracks are wide apart or remote at a large distance from the boundary of a region; otherwise the equations are solved numerically.     

Experimental measurement of the angle of repose of a pile of soft frictionless grains

Piles of perfectly smooth spherical particles are able to sustain a non-zero angle of repose as a result of geometrical constraints. Here we report on a study of piles made of soft frictionless grains and their angle of repose. The piles are formed by a continuous bubbling of air into a soapy solution in a narrow container of rectangular cross section. For wide containers, the angle of repose of the pile is \(3.75\pm 0.11\) degrees, independent of bubble flow rate. However, we find that the angle of repose is sensitive to confinement effects. In contrast with sand piles, surface avalanches are nearly absent and the fluidized region along the interface is several layers deep. In addition, the bubble pile is metastable, i.e. upon interruption of the gas flux the slope relaxes back to zero as a result of liquid drainage.     

Increasing the Accuracy of Reproduction of Pressure by Means of the Ukrainian Secondary Standard of the Unit of Pressure

The estimated components of the error in the determination of the effective area of a measuring piston-cylinder assembly of a piston manometer with a non-sealed piston are reported. Such manometers are incorporated into the secondary standard of the unit of pressure.     

Rationalization of Sequential Monitoring of Reliability

A discussion is given of the problem of increasing the efficiency of monitoring the quality of industrial products for which the moments of occurrence of failures are distributed in accordance with a binomial law or a Weibull law with unknown scale parameters. A mathematical modeling method is used to perform a comparison of the properties of different criteria and a sequential criterion with parabolic boundaries of the acceptance and rejection zones is proposed which is most economic in a number of cases.     

Determination of the Distribution Laws of Random Errors of Secondary Standards

An example of a random error is used to indicate the dependence of the accuracy of an interval estimate of the error of a secondary standard on the knowledge of its actual distribution law. A problem is formulated for determining a model of the distribution law of the random error of a secondary standard.     

Prediction of compressive strength of concrete

The paper, which summarises a survey and an analysis of empirical strength laws, was undertaken with a view to formulating a strength law interrelating the water-cement ratio-which determines the porosity of the hardened cement-paste-and Powers's Gel/Space ratio, giving the relative strength of the cement stone. Accordingly, a graphical procedure is given for predicting the strength of ordinary concretes for a given water-cement ratio and lean air-entrained concretes for a given “equivalent” water-cement ratio. Compressive strength may also be predicted by means of numerical formulae.     

A Quantum-Chemical Model of Active Centers of Electrochemical Corrosion of Metals

On the atomic level, we consider a model of the formation of active centers on the surface of a metal, which control the course of corrosion and electrochemical processes. Our quantum-chemical computations demonstrate that a foreign tin atom in a Sn - Ni₈ - Ni cluster can favor the dissolution of nickel in an acid medium, and a zinc atom in a Zn - Ni₈ - Ni cluster induces its passivation. We also show that the introduction of an oxygen atom into a cluster favors the passivation of nickel.__________Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 1, pp. 12–18, January–February, 2005.     

Monitoring of the temperature modes of operation of autonomous objects

The problems of constructing a measuring converter for a system for monitoring the temperature based on a thermoresistor sensor using programmable logic circuits are considered.     

任意旋转壳的振动特性计算

本文由旋转薄壳的基本方程导出了一组等效的一阶微分方程,并采用离散变量法对其进行求解。对于子午线出现尖角及双层旋转壳相耦合的情况,推导了相应的计算公式。文末给出了算例。     

Analysis of the sensitivity properties of a model of vector-borne bubonic plague.

Model sensitivity is a key to evaluation of mathematical models in ecology and evolution, especially in complex models with numerous parameters. In this paper, we use some recently developed methods for sensitivity analysis to study the parameter sensitivity of a model of vector-borne bubonic plague in a rodent population proposed by Keeling & Gilligan. The new sensitivity tools are based on a variational analysis involving the adjoint equation. The new approach provides a relatively inexpensive way to obtain derivative information about model output with respect to parameters. We use this approach to determine the sensitivity of a quantity of interest (the force of infection from rats and their fleas to humans) to various model parameters, determine a region over which linearization at a specific parameter reference point is valid, develop a global picture of the output surface, and search for maxima and minima in a given region in the parameter space.     

Process of deposition of a material on the surface of a rotating body

A mathematical model for estimating the thickness of a coating deposited on the surface of a rotating body having a circular symmetry is proposed. A method has been developed for determining the law of control of the mass flow of a deposited material for the purpose of obtaining coatings homogeneous in thickness. It is shown that, in the case of deposition of a coating on the surface of a circular disk, the optimum mass flow of a deposited material is defined by a linear function. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 6, pp. 149–154, November–December, 2006.