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     

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.     

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.     

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.     

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.     

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.     

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.     

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。     

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.     

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.     

Experimental evaluation of the interference method of measurement of displacements on the basis of illumination of the surface of a test object

Results from experimental studies of a laser displacement measurement device that implements a new interference method of measurement based on illumination of the surface of a test object are presented. Translated from Izmeritel’naya Tekhnika, No. 10, pp. 26–30, October, 2008.     

Problem of Drying of a Layer of Combustible Forest Materials

Physical and mathematical modeling of drying of a layer of combustible forest materials (CFMs) is considered in a conjugate formulation within the framework of which the equations of a binary boundary layer and the equations of heat and mass transfer in a layer of combustible forest materials are solved. Boundary conditions for the laws of conservation of mass and energy are written on the interface of media. It is found experimentally and theoretically that the velocities of the flow and radiation strongly affect the time of drying of a layer of combustible forest materials, whereas the effect of the angle of inclination (slope) between the underlying surface and the horizontal plane is insignificant.     

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.     

Mathematical simulation of the process of fine cleaning of suspensions

A mathematical model is considered of the process of interaction of filtrate within a pipe with a two-phase disperse mixture in the porous wall and outside of the pipe. The results of numerical solution of conjugate problem of heat and mass transfer demonstrate the advisability of preheating the substrate of a tubular filter for producing filtrate.     

Statistics of the contrast of coherent images

Contrast optimization, also known as image sharpening, is a method that can be used to estimate phase errors in coherent images. However, the contrast measure of a coherent image is a random variable because of the speckle present in coherent images. The variance of this measure puts a limit on the ability of contrast optimization to focus an image. We derive the probability distribution function of the most common contrast measure, the sum of the pixel intensities raised to a power. These statistics are then verified by a number of speckle simulations and compared with measured statistics from synthetic aperture sonar images. The developed statistics can be used as a tool to understand and improve the method of contrast optimization as well as assess its performance for a given imaging system. They can also be used to predict the effect of certain image processing operations on the contrast.     

Calculation of prolonged high-temperature sublimation refining of a material consisting of spherical parts

We demonstrate the possibility of calculating the time-dependent vapor composition and impurity distribution in a condensate for a prolonged high-temperature sublimation of a model material consisting of spherical parts differing in size (and identical in initial composition). The calculation procedure is based on the use of distillation equations for a binary substance in a nonequilibrium vaporization process. It has been shown that the condensate obtained through the sublimation of such a material has an increased impurity concentration compared to the condensate obtained through the sublimation of a single sphere.     

Rational Design of the Structure of a Tubular Element of a Cross-Reinforced Plastic

We propose a procedure of manufacturing tubular elements from a cross-reinforced plastic and their adhesive junctions with end reinforcement. Elements are created by winding a continuous fiber with the simultaneous attachment of metallic nozzles on the ends of a pipe in the process of its formation. The potentialities and advantages of the procedure are demonstrated. By a test of tubular elements for short-term strength, we established the form of a junction and the rational scheme of reinforcement of the material that provide the maximum strength on tension.     

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.