Wave Zone Research Articles

Two-zone analysis of wavy two-phase flow using micro-particle image velocimetry (micro-PIV)

Micro-scale particle imaging velocimetry (micro-PIV) has been applied to 20 two-phase air–water flows in the wavy regime and near the wavy/annular regime transition. Velocity profiles and fluctuation statistics have been calculated based on the particle image pairs produced, which were divided into base film and wave zones. A linear velocity profile is seen within the base film that extends farther from the wall than in turbulent single-phase channel flow. Axial velocities and fluctuation statistics are observed to be significantly higher in waves. An increase in the axial fluctuation intensity that stems from the difference between waves and base film is observed with increasing gas flow, which may be indicative of a regime transition. The possible sources of the fluctuations, including turbulence and the variable shear experienced by the film, are also outlined.

Laser conferral of a directed character to near-field energy transfer

With sufficient intensity, an off-resonant laser beam can modify the character of electromagnetic near-field radiation produced by a nanoscale point source, narrowing its spatial distribution. The mechanism, for which the laser frequency is significantly off-resonant from the emission radiation, is detailed and analyzed through a quantum electrodynamical analysis. Results are calculated for various positions of a polarization-sensitive probe relative to the point source, sited within the throughput beam, and contour maps exhibit variations in the registered signal over a range of input intensities. A key feature is the clear exhibition of directed propagation features, usually emergent only in the wave zone, within the near-field region of the source.

Infracambrian hydrocarbon source rock potential and petroleum prospectivity of NW Africa

Abstract Proven Infracambrian hydrocarbon plays occur in various parts of the world, including Oman, the former Soviet Union, India, Pakistan and Australia. Organic-rich strata also occur in NW Africa, and gas shows originating from Infracambrian hydrocarbon source rocks are known from well Abolag-1 in the Mauritanian part of the Taoudenni Basin. The distribution of Infracambrian source rocks in North Africa is patchy and deposition commonly occurred in half-graben and pull-apart basins. In these intra-shelf basins, marine, organic-rich shales and limestones were deposited beneath the turbulent wave zone, away from the coarse siliciclastic Pan-African molasse detritus. On the West African Craton (including the Taoudenni Basin) organic-rich horizons were also deposited earlier, in pre- and syn-Pan-African times between 0.5 and 2 Ga (Ga is 10 9 years). The long-lasting sedimentation history in this area contrasts with that of the Pan-African regions, such as Oman, which lies in the Pan-African province of the East African Orogen, where preserved sediments are rarely older than 640 Ma. Infracambrian black phyllites in the Anti-Atlas region of Morocco were deposited on a continental slope of a short-lived ocean lying to the north of the West African Craton. Hydrocarbons generated during Infracambrian times from these deposits, however, have a low preservation potential. Infracambrian organic-rich and/or black-pyritic deposits in North Africa are proven in the Taoudenni Basin, the Anti-Atlas and the Ahnet Basin. Thick carbonate successions exist in the Taoudenni Basin, indicating deposition in areas some distance from contaminating coarse siliciclastic hinterland influx. Infracambrian strata may also occur in the Tindouf Basin. However, their deep burial and consequent early maturation history may be unfavourable for the preservation of Infracambrian-sourced hydrocarbons in this area. Local development of Infracambrian source facies may also occur in the Reggane, Ahnet, Mouydir and Iullemeden basins, as indicated by black shales in wells MKRN-1 and MKRS-1 in the Ahnet Basin. Generally, however, these basins appear to be close to the active Pan-African orogenic belt and, consequently, probably received large quantities of coarse siliciclastic sediment, largely of continental facies, which may have diluted any significant hydrocarbon source potential.

Morphological and developmental studies on the eggs of four <I>Coryphopterus</I> species (Actinopterygii: Gobiidae) in the caribbean sea

Currently, the gobiid genus Coryphopterus Gill, 1863 includes 13 western Atlantic species (Victor 2008). The sand dwelling species have been reported to live in similar habitats and therefore the question arises in how far they differ in ecological aspects such as their reproductive biology. No information has been presented on that topic, in particular their egg morphology, mode of attachment and development of eggs. This study investigates the morphology of eggs as well as aspects of their development and compares the results within the genus and to other gobiids. Eggs of Coryphopterus venezuelae Cervigon, 1966; Coryphopterus dicrus Bohlke et Robins, 1960; Coryphopterus eidolon Bohlke et Robins, 1960; and Coryphopterus thrix Bohlke et Robins, 1960 were collected under laboratory conditions and studied under a scanning electron microscope (SEM). These species are of similar size, with a maximum length of 5–7 cm and live associated with coral reefs. Eggs are deposited under stones or rocks and guarded by the male till hatching (Thresher 1984). The eggshell is called zona radiata or chorion and has been reported to vary in thickness, surface structure, and adhesive filaments. In many cases the zona radiata can be used to identify species (Riehl 1995, Riehl and Patzner 1998, Giulianini and Ferrero 2000). Its main function is to protect the embryo from mechanical forces. Normally it measures between 5 and 15 μm in thickness, but may reach up to 100 μm in species like Agonus cataphractus (L.) (Actinopterygii: Agonidae), which deposit their eggs in tidal wave zones (Riehl 1995). Typically gobiid fishes lay their eggs in a dense patch of single layers on the underside of a solid structure e.g., stones, rocks or shells and the male guards them until they hatch (Miller 1984, Thresher 1984). A characteristic feature of gobiid eggs is the formation of a layer of filaments between the follicle granulosa and the zona radiata. These filaments are arranged around the micropylar pole to provide a mode of attachment for these demersal eggs (Miller 1984). Giulianini et al. (2001) have proved that spermatozoa can pass through ACTA ICHTHYOLOGICA ET PISCATORIA (2008) 38 (2): 97–102 DOI: 10.3750/AIP2008.38.2.03

2D model in near-field microwave temperature tomography with a scanning diffraction grating

Equations have been derived to solve the inverse problem of reconstructing the Fourier expansion coefficients for the temperature of a medium as a function of coordinate along elementary layers. These coefficients are reconstructed from the known similar expansion coefficients for the thermal energy flux at the diffraction grating output as a function of the grating displacement along the medium surface. The grating is in the inhomogeneous wave zone.

Corotational damping of discoseismic c modes in black hole accretion discs

Diskoseismic c-modes in accretion discs have been invoked to explain low-frequency variabilities observed in black-hole X-ray binaries. These modes are trapped in the inner-most region of the disc and have frequencies much lower than the rotation frequency at the disc inner radius. We show that because the trapped waves can tunnel through the evanescent barrier to the corotational wave zone, the c-modes are damped due to wave absorption at the corotation resonance. We calculate the corotational damping rates of various c-modes using the WKB approximation. The damping rate varies widely depending on the mode frequency, the black hole spin parameter and the disc sound speed, and is generally much less than 10% of the mode frequency. A sufficiently strong excitation mechanism is needed to overcome this corotational damping and make the mode observable.

Dynamics evolution of shock waves in laser–material interaction

In this work, the dynamics and internal structure of shock waves in picosecond laser–material interaction are explored at the atomistic level. The pressure of the shock wave, its propagation, and interaction zone thickness between the plume and ambience are evaluated to study the effect of the laser absorption depth, ambient pressure, and laser fluence. Sound agreement is observed between the MD simulation and theoretical prediction of shock wave propagation and mass velocity. Due to the strong constraint from the compressed ambient gas, it is observed that the ablated plume could stop moving forward and mix with the ambient gas, or move backward to the target surface, leading to surface redeposition. Under smaller laser absorption depth, lower ambient pressure, or higher laser fluence, the shock wave will propagate faster and have a thicker interaction zone between the target and ambient gas.

Irreversible evolution of tectono-magmatic processes at the Earth and Moon: Petrological data

The tectono-magmatic evolution of the Earth and Moon started after the solidification of their magmatic “oceans”, whose in-situ crystallization produced the primordial crusts of the planets, with the composition of these crusts depending on the depths of the “oceans”. A principally important feature of the irreversible evolution of the planetary bodies, regardless of their sizes and proportions of their metallic cores and silicate shells, was a fundamental change in the course of their tectono-magmatic processes during intermediate evolutionary stages. Early in the geological evolution of the Earth and Moon, their magmatic melts were highly magnesian and were derived from mantle sources depleted during the solidification of the magmatic “oceans”; this situation can be described in terms of plume tectonics. Later, geochemically enriched basalts with high concentrations of Fe, Ti, and incompatible elements became widespread. These rocks were typical of Phanerozoic within-plate magmatism. The style of tectonic activity has also changed: plate tectonics became widespread at the Earth, and large depressions (maria) started to develop at the Moon. The latter were characterized by a significantly thinned crust and basaltic magmatism. These events are thought to have been related to mantle superplumes of the second generation (thermochemical), which are produced (Dobretsov et al., 2001) at the boundary between the liquid core and silicate mantle owing to the accumulation of fluid at this interface. Because of their lower density, these superplumes ascended higher than their precursors did, and the spreading of their head parts resulted in active interaction with the superjacent thinned lithosphere and a change in the tectonic regime, with the replacement of the primordial crust by the secondary basaltic one. This change took place at 2.3–2.0 Ga on the Earth and at 4.2–3.9 Ga on the Moon. Analogous scenarios (with small differences) were also likely typical of Mars and Venus, whose vast basaltic plains developed during their second evolutionary stages. The change in the style of tectonic-magmatic activity was associated with important environmental changes on the surfaces of the planets, which gave rise to their secondary atmospheres. The occurrence of a fundamental change in the tectono-magmatic evolution of the planetary bodies with the transition from depleted to geochemically enriched melts implies that these planets were originally heterogeneous and had metal cores and silicate shells enriched in the material of carbonaceous chondrites. The involvement of principally different material (that had never before participated in these processes) in tectono-magmatic processes was possible only if these bodies were heated from their outer to inner levels via the passage of a heating wave (zone) with the associated cooling of the outermost shells. The early evolutionary stages of the planets, when the waves passed through their silicate mantles, were characterized by the of development of super-plumes of the first generation. The metallic cores were the last to melt, and this processes brought about the development of thermochemical super-plumes.

To the mechanisms of failure wave

Results of shock-wave experiments with free and prestressed samples of K8 and K14 crown glasses are presented. Controlled confinement pressure on the specimen of around 200 MPa was provided by installing a shrink-fit metal sleeve on the lateral surface of the sample disk. Results of measurements of the free surface velocity histories show that prestressing leads to earlier stopping of the failure wave. Thus, the compressive transverse stress increases the failure threshold that is in agreement with existing criteria of compressive fracture. However, sensitivity of the failure threshold to the confinement stress value is not as high as it could be expected. Measurements of the refractive indexes for the particles from the failure wave zone of recovered glass samples have shown their small increase whereas no index change for particles from the residual zone was found. It has been concluded that irreversible densification makes essential contribution to the mechanism of failure of glasses.

THE EFFICIENCY OF GRAVITATIONAL BREMSSTRAHLUNG PRODUCTION IN THE COLLISION OF TWO SCHWARZSCHILD BLACK HOLES

In this paper, we examine the efficiency of gravitational bremsstrahlung production in the process of head-on collision of two boosted Schwarzschild black holes. We construct initial data for the characteristic initial value problem in Robinson–Trautman space–times, which represent two instantaneously stationary Schwarzschild black holes in motion toward each other with the same velocity. The Robinson–Trautman equation is integrated for these initial data using a numerical code based on the Galerkin method. The resulting final configuration is a boosted black hole with Bondi mass greater than the sum of the individual masses of the individual initial black holes. Two relevant aspects of the process are presented. The first relates the efficiency Δ of the energy extraction by gravitational wave emission to the mass of the final black hole. This relation is fitted by a distribution function of nonextensive thermostatistics with entropic parameter q ≃ 1/2; the result extends and validates analysis based on the linearized theory of gravitational wave emission. The second aspect is a typical bremsstrahlung angular pattern in the early period of emission at the wave zone, a consequence of the deceleration of the black holes as they coalesce; this pattern evolves to a quadrupole form for later times.

Nonequilibrium processes at the shock wave front in inert gases with a small amount of Fe(CO)5 impurity

Nonequilibrium processes occurring in shock waves generated in argon and helium containing a small amount of Fe(CO)5 impurity are investigated experimentally and numerically. Nonequilibrium radiation peaks are found in the relaxation zone of the shock wave, and a dependence of the radiation intensity on the shock parameters and Fe(CO)5 concentration is obtained. Unresolved spectra of the resulting radiation in the range 400–700 nm are recorded. It is shown that the effects observed cannot be accounted for by high-energy collisions in the zone of shock translational relaxation. It is concluded that these nonequilibrium phenomena are related to electronic excitation of small iron clusters at fast condensation of supersaturated iron vapor arising due to Fe(CO)5 decomposition. A kinetic model describing the formation of excited clusters is suggested.

Electromagnetic Excitation of PEC Slotted Cones by Elementary Radial Dipoles—A Semi-Inversion Analysis

A novel method is presented that is based on the use of the Kontorovich-Lebedev integral transform and the semi-inversion technique, developed for building the efficient and accurate numerical solutions to the boundary-value problems of electromagnetic wave scattering by the 3D coaxial slotted cones. A generic structure under consideration consists of two semi-infinite coaxial circular perfectly electrical conducting and zero-thickness cones with periodic longitudinal slots excited by a radial dipole. The considered problem is reduced to an infinite set of linear algebraic equations of the Fredholm second kind that is truncated and solved numerically. A detail analysis of the accuracy and convergence of the method is presented. The basic electromagnetic characteristics such as the field behavior near the structure singularities, field patterns in the wave zone, and field polarization for various problem parameters are investigated for the cones excited by on-axis elementary dipoles. The slotted cones allow obtaining more directional patterns in wider band than the solid ones.

Experimental Study of Shock Wave / Turbulent Boundary Layer Interaction

Experimental study of separated flow in a zone of oblique shock wave / turbulent boundary layer interaction was carried out for Mach number 2 and Reynolds number Reθ = 2,7÷3,5 × 103. Streamwise pressure distribution on the model surface was obtained, Schlieren and oil-flow visualizations were performed. The paper gives detailed data of hot-wire anemometry measurements in upstream boundary layer, interaction and recovery regions. Unsteady nature of separated zone and reflected shock wave was discovered. The effect of side walls on quasi 2D structure of separated flow is described.

Coordination of Actin Filament and Microtubule Dynamics during Neurite Outgrowth

Although much evidence suggests that axon growth and guidance depend on well-coordinated cytoskeletal dynamics, direct characterization of the corresponding molecular events has remained a challenge. Here, we address this outstanding problem by examining neurite outgrowth stimulated by local application of cell adhesion substrates. During acute outgrowth, the advance of organelles and underlying microtubules was correlated with regions of attenuated retrograde actin network flow in the periphery. Interestingly, as adhesion sites matured, contractile actin arc structures, known to be regulated by the Rho/Rho Kinase/myosin II signaling cascade, became more robust and coordinated microtubule movements in the growth cone neck. When Rho Kinase was inhibited, although growth responses occurred with less of a delay, microtubules failed to consolidate into a single axis of growth. These results reveal a role for Rho Kinase and myosin II contractility in regulation of microtubule behavior during neuronal growth.

The Kirchhoff method for transition radiation from flat and concave targets

Transition radiation (TR) emitted by a charged particle incident obliquely on a perfectly conducting surface is considered. A method is proposed that allows one to calculate the characteristics of backward radiation at a finite distance, including in the so-called pre-wave zone. Particular cases of a flat target, as well as a target in the form of a cylindrical surface whose axis is perpendicular to the trajectory of the particle are considered. In the first case, the radiation characteristics in the wave zone, calculated by the model proposed, are in complete agreement with available results. In the second case, when a detector is situated in the pre-wave zone, the radiation is focused. The properties of radiation are discussed as a function of the shape of the target surface, the angle of incidence of a particle, and the distance to the detector.

Simulating binary neutron stars: Dynamics and gravitational waves

We model two mergers of orbiting binary neutron stars, the first forming a black hole and the second a differentially rotating neutron star. We extract gravitational waveforms in the wave zone. Comparisons to a post-Newtonian analysis allow us to compute the orbital kinematics, including trajectories and orbital eccentricities. We verify our code by evolving single stars and extracting radial perturbative modes, which compare very well to results from perturbation theory. The Einstein equations are solved in a first-order reduction of the generalized harmonic formulation, and the fluid equations are solved using a modified convex essentially non-oscillatory method. All calculations are done in three spatial dimensions without symmetry assumptions. We use the had computational infrastructure for distributed adaptive mesh refinement.

Physical optics of photonic crystals

A one-dimensional harmonic model of a photonic crystal is considered using the methods of physical optics. The theoretical formalism is based on the notion of the Fresnel volume reflection and the system of two first-order differential equations, which are equivalent to the wave equation. Using the Rayleigh layer as an example, it is shown that the volume reflection plays a role of the friction, similar to the friction in oscillations of a pendulum, and, in a strongly inhomogeneous medium, can suppress field oscillations and turn the group velocity to zero. In the approximation of small modulation factor, the models of two, four, and six waves are considered. In the two-wave model, the dispersion relation contains a zone of inhomogeneous waves, whose width is determined by the Fresnel reflection coefficient from one period. The refinement in terms of the four-wave or six-wave model yields only a small correction to the position of the zone, retaining its width unchanged. The wavenumber as a function of frequency is described by a circle inside the zone of inhomogeneous waves and by a hyperbola outside this zone. Mathematically, the method used is significantly simpler than those based on the application of the Floquet theorem to the wave equation. It is shown that the notion of forbidden zones is inconsistent with respect to photonic crystals, and the term zones of inhomogeneous waves is proposed instead.

Structure of detonation waves in pressed 2′,2′,2′-trinitroethyl-4,4,4-trinitrobutyrate

The reaction zones of steady detonation waves in pressed 2′,2′,2′-trinitroethyl-4,4,4-trinitrobutyrate (TNETB) charges with densities within 1.23–1.79 g/cm3 and initial powder dispersities of 5 and 80 μm were studied with the use of a VISAR interferometer. It was demonstrated that the boundaries of the initial density range within which a pressure growth is observed instead of a chemical spike, predicted by the theory, are determined by the HE dispersity. The measured dependence of the detonation velocity on the initial HE density exhibits features suggestive of an underdriven detonation wave without a chemical spike. The peculiarities observed are accounted for by the heterogeneous structure of pressed HEs, the decomposition of which is of hot-spot character, occurring partly in the compression wave front.

Super-reflection in fluid discs: corotation amplifier, corotation resonance, Rossby waves and overstable modes

In differentially rotating discs with no self-gravity, density waves cannot propagate around the corotation, where the wave pattern rotation speed equals the fluid rotation rate. Waves incident upon the corotation barrier may be super-reflected (commonly referred to as corotation amplifier), but the reflection can be strongly affected by wave absorptions at the corotation resonance/singularity. The sign of the absorption is related to the Rossby wave zone very near the corotation radius. We derive the explicit expressions for the complex reflection and transmission coefficients, taking into account wave absorption at the corotation resonance. We show that for generic discs, this absorption plays a much more important role than wave transmission across the corotation barrier. Depending on the sign of the gradient of the vortensity of the disc, ζ=κ2/(2ΩΣ) (where Ω is the rotation rate, κ is the epicyclic frequency and Σ is the surface density), the corotation resonance can either enhance or diminish the super-reflectivity, and this can be understood in terms of the location of the Rossby wave zone relative to the corotation radius. Our results provide the explicit conditions (in terms of disc thickness, rotation profile and vortensity gradient) for which super-reflection can be achieved. Global overstable disc modes may be possible for discs with super-reflection at the corotation barrier.

Cost effective combustion synthesis of silicon nitride

The feasibility of mechanical activation (MA)-assisted combustion synthesis (CS) of Si 3N 4 was demonstrated by using Si/NH 4Cl as reactants under a nitrogen pressure of 2 MPa. MA treatment significantly enhances the reactivity of Si powders, which effectively promotes the nitridation of silicon. The NH 4Cl had the same effect as Si 3N 4 diluent in preventing extensive melting of Si within the combustion wave zone. Full nitridation of Si was achieved at diluent levels as low as 5 wt%. Si 3N 4 powders with α-phase contents of up to 90.6 wt% were obtained. The temperature gradient induced by heat release through radiation was responsible for discrepancies in the phase composition and morphologies of the as-synthesized product at different locations.