Explosion of a cylindrical charge above a rigid surface

We investigated the explosion of a cylindrical charge, which lies on a rigid surface or is positioned at some height above it. The explosion is modeled by the jump between the background and the region occupied by gas at a high pressure, density, and temperature. In an analogous formulation, the explosion from the Tunguska meteorite impact [1–4] was modeled by spherical and cylindrical explosive waves which consider the gravitational back pressure. Explosions from charges with nontraditional shapes have been studied [5–8]. Reflections of an explosive wave from a point charge from a rigid surface have been examined [9–10]. A more complete review of investigations on the spatial effects of forming propagating explosive waves can be found in [11].Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 27, No. 6, pp. 131–134, November–December, 1991     

Propagation of a burning front over a condensed material from a focus

Measured propagation speeds are given for the combustion front in a blind gap in a condensed substance, which are related to gap height and mean pressure. The front may propagate monotonically, which is characteristic of relatively high pressures and wide gaps, or as a result of additional burning foci arising at a certain distance from the main front. At low pressures and particularly with small gap heights, the front propagates in an unstable fashion over the surface.Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 28, No. 4, pp. 49–53, July–August, 1992.     

Reflection of a shock wave in a dusty cloud

The problem of shock-wave passage along a cloud of particles adjacent to a solid surface is studied numerically and analytically. The wave pattern of the flow near the shock wave reflected from this surface is analyzed within the framework of the equilibrium approximation of mechanics of heterogeneous media. The conditions of the transition from regular to irregular reflection from the substrate of the refracted shock wave inside the cloud are obtained analytically. The results of numerical simulations of a nonequilibrium flow in the two-velocity two-temperature approximation are compared with data obtained in the equilibrium approximation. Nonequilibrium and equilibrium flows are found to become more similar as the particle size decreases. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 121–131, January–February, 2007.     

Free coating of a Newtonian liquid onto a vertical surface

The entrainment of Newtonian liquid films onto a vertical surface which is continuously withdrawn from a bath of the liquid is considered. A new theoretical treatment is presented which is significantly different from previous theoreis and which predicts accurately the relationship between the dimensionless thickness parameter, T₀, and the Capillary Number, Ca, up to a value of Ca of 2. Experimental results have been obtained using a capacitance technique for film thickness measurement for a variety of Newtonian fluids with viscosities ranging from 0·006 to 2·06 N. sec m^?2.     

Heat transfer from a grid jet in a large fluidized bed

Heat transfer from a vertical grid jet within a 2 ft diameter and 4 ft deep fluidized bed of cracking catalyst was studied. The test nozzle diameter was varied from ¼ to 1 in. and the nozzle velocity from 50 to 250 ft /sec which is within the range of industrial practice. The axial temperature data have been related to a Froude, a Reynolds and a Nozzle number: In (δT/δT_o) = –58.1 Fr^?0.562 No^1.08 Re^?0.112 A simple jet quenching model yielded heat transfer coefficients between the fluid bed and grid jet which ranged from 300 to 1200 Btu/ft² hr.^o F.     

Investigation of Diamond Synthesis from a Mixture of an Explosive with a Carbon Additive Using a Tracer Technique

The synthesis of detonation diamonds from a mixture of RDX labeled by C¹⁴ isotope with soot was studied experimentally. It was shown that a considerable portion of the diamonds (24.7 ± 3.4)% are formed from the carbon of RDX molecules. The degree of conversion of the carbon atoms of soot to the diamond phase is (16.0 ± 1.6)%. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 117–118, September–October, 2005.     

Root exudates of a legume tree as a nitrogen source for a tropical fodder grass

Exudation of nitrogenous compounds from the roots of dinitrogen-fixing plants is a potential source of nitrogen for adjacent plants in intercropping systems. We studied (1) the extent of N exudation from the roots of a tropical legume tree Gliricidia sepium (Jacq.) Kunth ex Walp., and (2) the ability of a C4 fodder grass Dichantium aristatum (Poir) C.E. Hubbard and its mycorrhizal symbionts to absorb N from tree exudates in a glasshouse experiment. Root exudates of ¹⁵N-labelled trees were collected in hydroponic culture and applied with irrigation water on grass grown in separate pots. During the 10-week experiment, the trees exuded 34.1 ± 5.0 mg of N, which represented 1.7 ± 0.2% of their total N by the end of the experiment. The total amount exuded would have been enough to supply 16% of grass N content by the end of the experiment. The grass, however, absorbed only 3.8–7.5% of ¹⁵N in exudates and gained 0.8–1.1% of its N from exudates. The low absorption of exudate N by grass was explained by probable soil microbial immobilisation and by the dilution of exuded N in the substantially larger pool of soil mineral N. A close contact between the root systems of N donor and recipient plants directly or via their mycorrhizal symbionts seems to be a precondition of the apparently direct N transfer earlier observed in field studies of the same soil-plant system.     

Photochemical diodes of a TiO2 film prepared by a sol-gel method

Photochemical diodes were prepared using a thin film of TiO₂ made from titanium isopropoxide by a sol-gel method. A half part of a conductive SnO₂ film plated on a quartz plate was coated with the TiO₂ film, and the other parts of the SnO₂ substrate were coated with a thin Pt film. The photochemical diode thus prepared shows photocatalytic activity for hydrogen evolution from aqueous ethanol solutions containing NaOH or HClO₄. No other products are detected in the gas phase. Hydrogen evolution from the Pt part is definitely observed, indicating electron transfer from the TiO₂ film to the Pt film through the SnO₂ film. Another type of photochemical diode, the TiO₂ film coated on a Pt plate, is found to show higher activity than the TiO₂/SnO₂/Pt device for the hydrogen photo-evolution without any support electrolyte. Hydrogen evolution on this device, however, occurs on the TiO₂ side but not on the Pt side. These results are discussed in terms of a photo-electrochemical mechanism at semiconductor surfaces.     

Adhesion promotion between a homopolymer probe and a glass substrate coated with a block copolymer monolayer

The adhesion between a homopolymer matrix and a diblock copolymer is shown to depend on the length of the non-adsorbing block that penetrates the matrix chains. The tack or short-time adhesion was measured using a probe-tack set-up consisting of a thick (∼100 μm) polystyrene, PS, adhesive layer with degree of polymerization (DP), 1923, brought into contact with a monolayer of poly(deuterated styrene-block-methyl methacrylate), dPS-b-PMMA, deposited on a glass substrate. Experiments performed at 130 °C, above the glass transition temperatures, show that the maximum debonding stress increases from 1.4 MPa for the glass to 2.3 MPa for the copolymer. Also, the adhesion energy increases dramatically as the non-adsorbing block length, N_dPS, increases from below to above the entanglement DP of PS. These observations suggest a difference in the debonding mechanism between the nude glass, which undergoes fragile rupture, and the glass covered by dPS-b-PMMA, which exhibits increasing cavity formation with increasing N_dPS. After normalizing by the chain areal density, the adhesion dissipation is observed to increase by a factor of 4 as N_dPS increases from 100 to ca. 1000. These results suggest that entanglements between matrix chains and the non-adsorbing block impart good stress transfer and interfacial strength across the interface.     

Growth of a Bonelike Apatite Layer on a Substrate by a Biomimetic Process

A dense and uniform bonelike apatite layer was formed on a substrate by the following biomimetic method. The substrate was first placed on granular particles of CaO, SiO₂-based glass soaked in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma and then soaked in another fluid highly supersaturated with respect to the apatite. The thickness of the apatite layer increased in proportion to the soaking time in the second solution. The rate of increase in the thickness of the apatite layer increased from 0.5 to 7.0 μm/day with increasing temperature of the second solution from 10° to 60°C, increased from 0.15 to 1.7 μm/day with increasing ion concentrations of the second solution from 0.2 to 1.5 times those of the SBF, and doubled by shaking the second solution. These results indicate that the growth of the apatite layer is controlled by mass transport across the interface between the crystal and the fluid.     

Co-gasification of a lignite/waste-tyre mixture in a moving bed

The thermal treatment of waste-tyre by co-gasification with lignite was investigated on a commercial scale during the Lurgi gasification process. The experiments proved that this material can be treated in a mixture with lignite in the process of oxygen–steam pressure co-gasification in a moving bed, because a waste-tyre admixture improves the net calorific value of the raw gas obtained by 3% in comparison with that from the gasification of lignite alone. Further, it was found that the H₂S and CH₃SH contents in the raw gas are lower in the case of co-gasification than those from the gasification of lignite alone. Considering the very low reactivity of the char from waste-tyre and the resultant unburned carbon in the ash, the optimal content of the waste-tyre admixture in the gasified feed should not exceed 10 wt.%, whereas short-term increases of up to 20 wt.% will not cause any technological problems or significant economic losses.     

Motion of a large object in a bubbling fluidized bed with a rotating distributor

This work studies the effect of a low-frequency rotating distributor on the motion of a large object immersed in a bubbling fluidized bed. The object size and density differ from those of the inert solids that conform the bed. Examples of objects moving in a bubbling fluidized bed include passive particles, catalysts and reactants. The rotation modifies the bed dynamics in the surroundings of the distributor and affects the motion of the object within the bed.A set of experiments was carried out in a lab-scale cylindrical bed, equipped with a perforated plate distributor that can rotate at around 1 Hz, for different bed aspect ratios, gas velocities, and object characteristics. Sizes were far larger than that of the solids of the dense phase and densities ranged from half the bed density to values around it. The experiments were video recorded, capturing the surface of the bed from above.As have often been noted, objects might remain in stagnant regions near the distributor and be “lost” or precluded to circulate. This can be avoided in most practical cases forcing the distributor to rotate. Also, the effect of rotation on the circulation time of the objects is presented, showing a general reduction of large circulation times.     

Propagation of a one-spot spinning wave in a thick-walled cylinder under adiabatic conditions

Propagation of a one-spot spinning wave in a cylindrical specimen with a coaxial internal channel is studied by numerical methods under the assumption of the absence of heat removal from the outer surface of the specimen and from the channel surface. Variations of the spinning wave characteristics [maximum temperature, longitudinal and circumferential (tangential) velocities, “pitch,” and time of rotation of the hot spot around the specimen centerline] are tracked for a specimen of a particular size with a varied channel radius, for specimens of different sizes with a fixed channel radius, and for specimens with a constant wall thickness. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 41–49, July–August, 2006.     

Characterization of a Mo-Nitrogenase Variant Containing a Citrate-Substituted Cofactor

Nitrogenase converts N₂ to NH₃, and CO to hydrocarbons, at its cofactor site. Herein, we report a biochemical and spectroscopic characterization of a Mo-nitrogenase variant expressed in an Azotobacter vinelandii strain containing a deletion of nifV, the gene encoding the homocitrate synthase. Designated NifDK^Cit, the catalytic component of this Mo-nitrogenase variant contains a citrate-substituted cofactor analogue. Activity analysis of NifDK^Cit reveals a shift of CO reduction from H₂ evolution toward hydrocarbon formation and an opposite shift of N₂ reduction from NH₃ formation toward H₂ evolution. Consistent with a shift in the Mo K-edge energy of NifDK^Cit relative to that of its wild-type counterpart, EPR analysis demonstrates a broadening of the line-shape and a decrease in the intensity of the cofactor-originated S=3/2 signal, suggesting a change in the spin properties of the cofactor upon citrate substitution. These observations point to a crucial role of homocitrate in substrate reduction by nitrogenase and the possibility to tune product profiles of nitrogenase reactions via organic ligand substitution.     

Numerical study of the transfer of shock-wave loading to a screened flat wall through a layer of a powdered medium and a subsequent air gap

The two-velocity, two-temperature model with two stresses in a mixture of a gas and solid particles contacting each other is used to numerically study the dynamic effect of an air shock wave incoming onto a solid wall with a screening layer of a porous powdered medium at some distance from the wall. The process is described for the case of one-dimensional planar motion of the gaseous and disperse phases under the assumption of a viscoelastic behavior of the powder skeleton. The effect of stepwise shock waves onto the porous powdered screen is considered. The influence of parameters of the screening layer and the air gap on the dynamics of loading of the screened solid wall is analyzed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 132–142, January–February, 2007.     

Mass transfer to a drop stream from a field liquid

Mass transfer from a stream of drops falling freely in a stagnant liquid was investigated. Drop streams were produced by a dripping method and by a jet breakup method. Water and isobutanol, mutually saturated, were used as the dispersed and the continuous phases. Sodium hydroxide was transferred from isobutanol to water drops which were initially free of solute. The mass transfer resistance is on the continuous phase side. The mass transfer coefficient and terminal velocity of drop streams were measured experimentally. The experimental results show that the mass transfer coefficient in the drop stream is affected by the shielding effect of the previous drops. The experimental data have been correlated as K_t/U_t^0.5 versus interdrop distance l, a relationship describing the effect of the interdrop distance on the mass transfer coefficient in the continuous phase.     

Formation of a specific layer on the surface of a metallic target interacting with a shaped-charge jet of boron-containing liners

Coatings on titanium targets are obtained under conditions of a shaped-charge explosion; the maximum microhardness of the coatings at certain segments of the target can reach 4000 kg/mm². A conical liner with a cone angle of 20° prepared from a mixture of fine powders of amorphous boron and ammonium nitrate is used in the experiments. A comparative quantitative X-ray powder diffraction analysis of various segments of the coating is performed. The values of the unit cell parameters indicate the formation of complex phases. The dynamics of the results of the X-ray study with the cone angle of the liner decreasing from 45 to 20° is demonstrated. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 2, pp. 121–127, March–April, 2006.     

Development of a superhydrophobic polyurethane-based coating from a two-step plasma-fluoroalkyl silane treatment

A method of achieving a superhydrophobic surface based upon a highly filled polyurethane (PU) paint coating has been demonstrated through the use of a combined oxygen/argon plasma pretreatment and a fluoroalkyl silane (FAS) final treatment.The combined plasma-FAS treated PU surface has been investigated and characterised using: field emission gun secondary electron microscope (FEG-SEM); X-ray photoelectron spectroscopy (XPS); energy-dispersive X-ray spectroscopy (EDX); water contact angle analysis (WCA); atomic force microscopy (AFM), and; Fourier transform infrared spectroscopy (FTIR).It was found that the oxygen/argon plasma treatment increased both the surface roughness (R_a) and surface free energy (SFE) of the PU paint coating from approximately 60–320 nm, and, from ~52 to ~80 mN/m respectively. It was also found that the plasma process created a multiscale roughened texture through the process of differential ablation between the PU polymer and the barium sulphate solid content, which is present in the paint as an extender, and other additives. In addition, the process also imparted favourable polar groups into the PU surface from the ionised and radical oxygen species in the plasma.When the FAS coating was subsequently applied to the PU without prior plasma treatment, there was a significant increases in water contact angles. This parameter increased from approximately 60° on untreated PU to around 130° with FAS applied. In this case, the SFE decreased to ~7.5 mN/m and showed 42.0 at% fluorine present as indicated by XPS.However, subsequently applying the FAS polymer after plasma pretreatment takes advantage of the known synergistic relationship that exists between surface roughness and low surface free energy coatings. The two processes combined to create superhydrophobicity with a surface that exhibited water contact angles up to 153.1°. With this optimised process, the apparent SFE was 0.84 mN/m with a more highly fluorinated surface present. In this case 47.2 at% surface fluorine was observed by XPS.In addition to changes in SFE, plasma treatment was also observed to alter levels of surface gloss and colour. After exposure to 600 s of plasma gloss levels are shown to reduce from values of from ~50 to ~21 (GU), with small but significant corresponding increases in the lightness and yellowness of the surface.     

Interaction of a shock pulse with a contact discontinuity

Passing of a triangular moderate-intensity pulse through a constant discontinuity is considered. Decay of the shock wave that passed into the second gas is analyzed. Damping of the detonation wave after burnout of the combustible mixture is discussed. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 4, pp. 102–107, July–August, 2007.     

Modeling of ignition of a solid-propellant plate by a low-temperature plasma jet

A problem of ignition of a semi-infinite solid-propellant plate by a low-temperature plasma jet formed in an igniter under a high-power electric discharge is considered. Particular attention is paid to formation and evolution of zones of forced gasification of the fuel under the action of a heat flux from the plasma to the propellant. The locations of these zones are determined by satisfying two conditions: the propellant surface reaches the gasification temperature and the heat flux exceeds a certain “threshold” value. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 1, pp. 23–28, January–February, 2007.