Can the addition of a dielectric improve the figure of merit of a tunable material?

The influence of addition of a low-loss linear dielectric material to a tunable ferroelectric material has been investigated in terms of the electrostatic consideration. The calculations of the dielectric loss and dielectric non-linearity of ferroelectric-dielectric composites have been performed by using three different models. On the basis of results obtained, the figure of merit of the composite material has been evaluated. No improvement of the figure of merit of composite material compared to the pure ferroelectric has been observed for the considered models.     

Effect of a mass force on the combustion of the Ni−Al system

The effect ofg-load (in the range of 1 to 1000g) on the combustion of the Ni−Al system was studied experimentally. It is shown that a mass force has a significant effect on the burning rate of the mixture, compaction, and the chemical and phase compositions of the combustion products. A mechanism for the effect ofg-load on the burning rate and compaction of the system is proposed. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 1, pp. 34–38, January–February, 1998.     

Evaluation of the performance of a constructal mixer with the iodide–iodate reaction system

A novel fluidic mixer, which takes advantage of impingement mixing and is designed according to the constructal approach, is evaluated by the Villermaux/Dushman method. The effects of different configurations (including the structure of the fluid collector and the diameter of the nozzles on the fluid injector) on the mixing performance (i.e. the segregation index and the energy dissipation rate) are determined. The segregation index is smaller, or in other words the degree of mixing is better, when a branch type fluid collector or smaller nozzles are used, however, at the cost of higher energy dissipation rate. When the flow rate is sufficiently high, mixing caused by the impingement of streams is almost complete, rendering the mixing in the branched channels unnecessary. As a result, if very high degree of mixing is pursued, the collector with a simple empty space should be used in the mixer to reduce energy consumption.     

Combustion of a Mixture of Aluminum and a Titanium‐Containing Raw Material in the Presence of Additives

A model of the gasphase component of combustion of an aluminum mixture with metal oxides is described. By the example of titanium reduction from its oxide, it is shown that atomic oxygen formed thereby facilitates gasphase oxidation of aluminum and decreases metal yield. The effect of graphite, activated carbon, and diesel fuel on combustionwave velocity and temperature is considered. Two waves (cold and hot ones) are observed in the system titanium oxide–ferric oxide–aluminum–carboncontaining additives. Hydrocarbon additives inhibit the aluminumoxidation reaction by oxygen contained in air in the first wave, and graphite and activated carbon play the same role in the second wave in the titaniumreduction reaction. Experimental confirmation is found for the fact that the action of additives increases the amount of aluminum consumed directly for titanium reduction in the second wave, which enhances exothermality of the process.     

Initiation of Ignition by the Action of a High‐Current Pulsed Discharge on a Gas

The possibility of nonthermal initiation of chemical reactions by a uniform pulsed nanosecond discharge is demonstrated. Dependences of variation of the ignition delay on initial conditions are obtained. It is shown that the main role in combustion initiation under conditions of a pulsed gas discharge in the case of moderate electric fields and low degree of ionization belongs to reactions of dissociation quenching of electronexcited levels of nitrogen.     

Effect of a Gas‐Phase Reaction on the Combustion Performance of a Sandwich Layered System

This paper considers a sandwich layered combustion model (an oxidizer and a fuel) that takes into account condensed and gasphase chemical reactions and transverse heat and mass transfer. Under particular simplifications, algebraic expressions are obtained for the burning rates of the components and the temperature and concentration of gaseous reagents on the burning surface. Calculated dependences of the burning rate on the sandwich size agree with experiments.     

Numerical simulation of the effect of maldistribution in a fixed bed adsorber

The paper deals with the modeling of the effect of maldistribution in pollutant abatementtrichloroethylene(TCE)concerning low concentration(10~(-5)-10~(-8)kg·m~(-3))adsorption in an adsorber.Such a concentration range is rather typical in many an environmental application.Isotherms andbreakthrough curves for TCE adsorption are obtained both for a commercial activated carbonSorbonorit 4 and a laboratory adsorber of d_B/d_P=11.Two two-dimensional nonequilibrium isothermalmodels are developed to describe the mass transfer in the fixed bed taking into account the effect ofmaldistribution.It is found the simulation results with maldistribution are in very good agreementwith the experimental findings.Low concentration TCE adsorption in a fixed bed of activated carbonis found to be strongly influenced by maldistribution.The non-uniform distributions of concentrationand loading of the pollutant in the adsorber are predicted by the model.Maldistribution and its ef-fect on the initial breakthrough of TCE in the     

Characteristics of a melt of the corium–high alumina cement system

The characteristics (composition of the quenched samples, ingot, and evaporation products) are studied of the melt of the corium–high alumina cement system in a weight ratio of 1: 1. In the quenched samples of the melt and ingot, signs of phase separation in the molten state are found. Below a temperature of 2100°C above the melt, aerosol particles with trimodal size distribution are formed; however, above this temperature, the nature of the granulometry of aerosols is bimodal. Moreover, the formation rate of aerosols increases dramatically. The form of aerosol particles under all the experimental conditions was spherical.     

The flooding of a powder — the importance of particle size distribution

This paper reviews the development of a new annular shear cell for the characterisation of aerated powders, and studies in detail the flooding phenomena for an alumina powder. Results have shown a large reduction in shear stress for small quantities of air entrainment and transition from normal Coulomb-solid flow to liquid-like flow at high shear rates. Addition of fine particles is shown to enhance these effects, thereby increasing the likelihood of flooding. Addition of particles of size 40 μm and below is shown to be the main factor. An increase of 10% of particles in this size range shows a similar shear response to that obtained with a sample of alumina known to have flooded, although smaller quantities also have a significant effect. Such low quantities of additional fines could occur due to segregation, resulting in pockets of material with a high chance of flooding under normal powder handling conditions.     

Quickest Detection of Changes in the Generating Mechanism of a Time Series via the ε-Complexity of Continuous Functions

Abstract

A novel methodology for the quickest detection of abrupt changes in the generating mechanisms (stochastic, deterministic, or mixed) of a time series, without any prior knowledge about them, is developed. This methodology has two components: the first is a novel concept of the ε-complexity and the second is a method for the quickest change point detection (Darkhovsky, 2013 Darkhovsky , B. S. ( 2013 ). Detection of Changes in Random Sequence with Minimum Priori Information, Theory of Probability and Its Applications 58:585–590. (in Russian)  [Google Scholar]). The ε-complexity of a continuous function given on a compact segment is defined. The expression for the ε-complexity of functions with the same modulus of continuity is derived. It is found that, for the Hölder class of functions, there exists an effective characterization of the ε-complexity. The conjecture that the ε-complexity of an individual function from the Hölder class has a similar characterization is formulated. The algorithm for the estimation of the ε-complexity coefficients via finite samples of function values is described. The second conjecture that a change of the generating mechanism of a time series leads to a change in the mean of the complexity coefficients, is formulated. Simulations to support our conjectures and verify the efficiency of our quickest change point detection algorithm are performed.     

Simulation of the Behavior of Mixtures of Heavy Particles Behind a Shock‐Wave Front

The twodimensional inviscid nonstationary flow behind a shock wave passing through solid uranium dioxide or carbide particles suspended in liquid iron was simulated numerically. Such layers can appear inside planets in the vicinity of the planet's solid core. Shock waves passing in the interior of a planet (resulting from a possible asteroid impact on the planet) can change parameters of the layer. The calculations demonstrated that the local particle massconcentration behind the incident and reflected shock waves increases considerably, which can cause a transition of the layer into a supercritical state and a nuclear explosion inside the planet. The problem was solved taking into account possible particle collisions and their deformation and fission as well as changes in the fields of major thermodynamic parameters inside and outside each particle.     

Influence of the source of sulfur on the hydroconversion of 1-methylnaphthalene over a Pt–Pd/USY catalyst

Hydroconversion of 1-methylnaphthalene was performed over a Pt–Pd/USY catalyst in a batch reactor at 310 °C and 5 MPa of hydrogen pressure in cyclohexane as the solvent and in the presence of 800 ppm of sulfur resulting from different sources, hydrogen sulfide, thiophene and dibenzothiophene. In a general manner, hydrogenation of 1-methylnaphthalene into the corresponding mixture of methyltetralines is not significantly affected by the nature of the sulfur species present in the starting feed. On the contrary, going from hydrogen sulfide to thiophene and finally to dibenzothiophene, hydrogenation of methyltetralines into methyldecalines is lowered and ring-opening of methyltetralines to alkylbenzenes is enhanced. This would agree with the expected sequence of appearance of hydrogen sulfide in the feed.These results are in agreement with dissociation of hydrogen into protonic and hydride species, as already proposed in the presence of sulfided catalysts, i.e., protonic species would be involved for the hydrogenation steps and hydride species for the ring-opening steps. Hydrogen sulfide present as such or resulting from the transformation of thiophene or dibenzothiophene would then reduce the hydrogenation route, and, as a consequence, increase the hydrogenolysis route.     

Effect of the addition of a fugitive salt on electrospinnability of poly(?-caprolactone)

Described in this paper is a novel study focused on producing bead-free ultrafine fibers, with narrow fiber diameter distribution, from Poly(?-caprolactone) (PCL) via electrospinning. High quality product is achieved with the use of a new solvent system that involves an acid-base reaction to produce weak salt complexes, which serve to increase the conductivity of the polymer solution. Additionally, the salt formed dissociates easily and evaporates along with the solvent during the spinning process because its respective acid-base components are volatile at room temperature. This results into the formation of pure PCL nanofibers of ultrafine dimensions. Glacial acetic acid was used as the solvent for the polymer and the organic base pyridine was used to initiate the formation of salt complexes in the solution. Pyridine was added at six different levels to vary the conductivity and examine the latter's effect on fiber morphology. Along with the pyridine content, the polymer concentration was also varied to determine how the two interacted in influencing the size of the fiber and the quality of the structure obtained. It was found that bead-free fibers of sizes lying well within the nano range (140-340 nm) could be produced using the conducting solvent system. Two interesting effects were noted. For a given polymer concentration, the mean fiber diameter increased with increase in pyridine amount. And, lower the polymer concentration, higher was the amount of pyridine required to produce bead-free nanofibers. The combination of these effects along with the fact that the reproducibility of the results was high provided a means of producing fibers with predictable sizes.     

The mechanism of the ethane hydrogenolysis—a reconsideration of some kinetic data

In order to justify the deduction made previously from isokinetic effects of ethane hydrogenolysis, i.e., that the rate determining step of this reaction on Pt and Ni is the C-C bond breaking of the chemisorbed C₂H₅ unit, some kinetic data from literature are scrutinized. It turns out that the variation of the observed rate with ethane and/or hydrogen pressure is such as predicted by the simple mechanism C₂H₅* + H* +n* CH₃* + CH₃* +n*, where n means the number of free sites (*) involved. From an analysis of the kinetic data it is shown thatn=1.     

Improving the interfacial and flexural properties of carbon fiber–epoxy composites via the grafting of a hyperbranched aromatic polyamide onto a carbon fiber surface on the basis of solution polymerization

Hyperbranched aromatic polyamide (HBP) was grafted successfully onto carbon fibers (CFs) on the basis of solution polymerization to enhance the interfacial adhesion strength of CF-reinforced epoxy resin composites. The microstructure and interfacial properties of the CFs before and after decoration were researched. The results indicate that HBP was deposited uniformly onto the CFs with γ-aminopropyl triethoxysilane as the bridging agent. The active groups, roughness, and surface energy of the modified fiber [hyperbranched aromatic polyamide grafted carbon fiber (CF–HBP)] increased visibly in comparison with those of the untreated CFs. The CF–HBP composites revealed simultaneous remarkable enhancements (65.3, 34.3, and 84.8%) in their interfacial shear strength, flexural strength, and modulus, respectively; this was attributed to the improvement in the fiber–epoxy interface through enhanced chemical interactions, mechanical interlocking, and wettability. These agreed with the scanning electron microscopy observations from the fracture surface morphologies of the composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47232.     

Improvement of a cementation process by ultrasound: case of the cadmium–zinc couple at a RDE

This paper describes the impact of low frequency (20kHz) ultrasound (US) on Cd(II)/Zn cementation implemented on a RDE geometry. With and without US the reaction is mass-transfer controlled with two-step first-order kinetics mainly connected to deposit evolution. US improves the kinetics but to a lower extent than expected from electrochemical Cd(II) reduction. The favourable turbulence enhancement due to the deposit without US is not present when applying US because the deposit is continually removed from the surface. The influence of parameters such as temperature, initial concentration of reactants and US power is also analysed.     

Experimental investigation of effects of the feed flow rate and “tail scoop-wall” clearance on the performance of a gas centrifuge by feeding a Freon mixture

Experimental study of the performance of a gas centrifuge can be appreciably simplified if instead of isotopic mixtures, a binary mixture of gases with large molecular weight difference is used. The current study undertook this approach by injecting a 53%–47% (w/w) mixture of “Freon12-Freon22” into a gas centrifuge. The two parameters, whose investigation was the objective of the current study were: the feed flow rate (F), and the clearance between tail scoop and the rotor wall (d). The results demonstrated that changing the scoop-wall clearance has the most significant effect on the cut (θ), so that by fixing “d”, “θ” becomes nearly invariant. The head separation factor (α) exhibited the same dependency, but it was more influenced by the “F” than the “d”. Apparently the following regression exists between the inspected parameters:

Decreasing “d” → Decreasing “θ” → Increasing “α”.

Variations of the tail separation factor (β) with “F” or “d” was quite slight, even though similar to “α”, it was lowered with increasing of the “F”. The separation capacity (δU) as the most significant parameter of a centrifuge was optimised at the highest value of “F = 40.5 g/h”, and lowest value of “d = 3 mm”. The study achieved a separation capacity and an overall separation factor equal to 195.53 kg Freon/y and 16.87, respectively. These values are several times larger than those of the isotopic mixtures, demonstrating that application of Freons is a useful mean for magnifying the features of a gas centrifuge.     

Effect of tartrate on the morphological characteristics of the copper–tin electrodeposits from a noncyanide acid bath

Copper and tin were electrodeposited on platinum substrates from a 1.0 M sulphuric acid plating bath in the presence and absence of tartrate. Voltammetric curves indicated two deposition processes, at –0.310 and –0.640 V, which do not shift upon addition of tartrate to the plating bath. The presence of tartrate decreased the current density in the region of the more cathodic process. The metals were electrodeposited at both deposition potentials and the deposits have the same proportions of copper and tin either with or without tartrate in the plating bath, as observed by AAS. X-ray spectra suggested that a mixture of Cu and -Cu₆Sn₅ alloy was deposited at the less cathodic potential. SEM analysis showed that tartrate affects the morphology of the films.     

Effect of multiple scattering on the critical density of the energy used to initiate a PETN–aluminum compound by a neodymium laser pulse

The radiative transfer equation and the Mie theory are used in this paper to determine the optical properties of PETN–aluminum nanoparticles compounds. In the case of laser initiation with a wavelength of 1064 nm, the illumination gain at a depth of 100 μm from the surface of the sample varies in the range of 1.070–3.308 for nanoparticles with radii of 20–200 nm. The minimum of the relationship between the density of the energy required to initiate an explosive decomposition and the mass fraction of nanoparticles can be determined by the maximum illumination gain in the sample. The relationships between the critical density of the energy required to initiate PETN–aluminum nanoparticles compounds by the pulses of the first and second harmonics of a neodymium laser and the nanoparticle radius with account for multiple light scattering are determined. It is shown that account for multiple light scattering improves the agreement between theory and experiment.