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Detonation propagation in a stratified layer of combustible gas over an inert gas was investigated experimentally. The layer formed in a 12.7-mm-wide channel by opening a sliding door that initially separated a nitrogen-diluted stoichiometric hydrogen–oxygen mixture from argon, or nitrogen. As the lighter combustible gas layer spreads axially down the channel, diffusion across the interface produces a composition gradient across the layer height. A steady detonation wave, generated by deflagration-to-detonation transition in the driver section before the door location, was transmitted into the combustible layer. The axial distance the layer spreads and the amount of mass diffusion across the layer were controlled by the flame ignition delay time after the door opens. Schlieren video and soot foils were used to measure the extent of detonation propagation through the layer. It was shown that detonation propagation through the layer is self-limiting due to over-mixing at the layer leading edge. Three-dimensional numerical simulations, including viscous and multicomponent mass diffusion effects, predicted the composition distribution within the layer. The cell size distribution, calculated based on the theoretical ZND induction zone length, corresponding to the simulation composition distribution showed that a cell size gradient-based failure criterion successfully predicted the extent of propagation in the layer. [ABSTRACT FROM AUTHOR]

Seismic and geomagnetic observations suggest the presence of a stratified layer atop Earth's core. Previous laboratory experiments showed that this layer could be primordial, produced by a collision between the primitive Earth and a giant impactor. However, paleomagnetic data require turbulent flow motions in the core for the last 3.4 Ga. Such flows can erode an existing stratification. It is therefore unclear whether a primordial stratification still exists nowadays. Here, we use numerical simulations to investigate the erosion by thermal convection of a chemical layer atop Earth's core. Our scaling law predicts that a primordial layer thicker than 1 km with a density anomaly above 0.01% can survive 4.5 Ga of convective erosion. We conclude that the observed present‐day stratification could be a vestige of core formation. We also observe strong double‐diffusive flows in the layer. These might reconcile the existence of a stratification with the present‐day structure of the geomagnetic field. Key Points: We perform the first simulations on the erosion by thermal convection of a chemically stratified layer atop Earth's coreOur numerical scaling suggests that a primordial chemical stratification in Earth's core can persist up to the present dayThe stratification at the top of Earth's core, suggested by seismic and geomagnetic observations, could be a vestige of core formation [ABSTRACT FROM AUTHOR]

• The interface displacement has nonlinear relationships with physical conditions. • A new scaling law is proposed to predict the long-term interface displacement. • The scaling law depends on the elapsed time, vessel diameter, and competitive force. • The prediction of scaling law is in a good agreement with the experimental results. The distribution and mixing characteristics of hydrogen gas are important for assessing the hydrogen risk in nuclear power plants (NPPs) during severe accidents. To estimate such characteristics, analyzing the erosion mixing process of a stratified hydrogen layer subject to a turbulent impinging jet is necessary. In this paper, we propose a novel scaling law for the interface displacement of a stratified layer by erosion mixing as the result of a turbulent jet impingement in a long-term transient state. We show that interface displacement has nonlinear and time-dependent relationships with flow conditions such as the competitive force between the turbulent jet and stratified layer, as well as geometric parameters such as the vessel diameter. We extend the mass conservation law for the entrainment of a stratified layer over a long elapsed time by incrementally using a scaling law for the entrainment rate that is valid at a quasi-steady state. As a result, we show that the novel scaling law for the long-term interface displacement depends on the elapsed time, vessel diameter, and competitive force. The results obtained in previously reported containment flows experiments, as well as those obtained in the present study, are in good agreement with the prediction by the proposed scaling law, demonstrating that this law would be useful for predicting the behavior of the interface displacement of a stratified layer by erosion mixing under various conditions. [ABSTRACT FROM AUTHOR]

Highlights • Hugoniot analysis is applied to stratified steam explosion. • Incomplete participation of melt and coolant taken into account. • Peak pressures and conversion ratios are evaluated. • The model is shown to predict reasonably the steam explosion features. Abstract Recent experimental results on stratified steam explosion are analyzed by the model of "non-ideal" thermal detonation based upon Hugoniot relations, with factors taking into account incomplete melt fragmentation and participation of liquid coolant. The pressure behind the shock wave and conversion ratio are obtained as functions of the mass fraction of melt undergoing fragmentation and mass fraction of coolant in the explosion zone. Calculations are performed for one of the recent experiments on stratified steam explosion carried out with simulant oxidic materials. It is confirmed that the idealized scheme for thermal detonation overestimates significantly the conversion ratio, while predicting very low pressure levels. Taking into account incomplete melt fragmentation and limited participation of coolant improved the agreement between the predictions and experiments. Ranges for the melt fragmentation fraction and mass fraction of participating coolant where the model predictions agree with experimental values are obtained. [ABSTRACT FROM AUTHOR]

The flow and heat transfer characteristics of a film jet inclined to different supersonic situations with a varying Mach number of the main flow were numerically investigated. In supersonic situations, complicated waves are generated by the obstacle of the film jet. In this work, extra pressure is exerted onto the film jet, causing better film attachment to the wall. The strengthening of attachment decreases mixing between the main flow and film jet, causing better film cooling. We observed multi-interfacial layered structures caused by the film jet under the complicated effect of shock waves. At the interfaces of the film jet and shock waves, additional pressure is exerted on the film towards the wall. The pressure increases as the Mach number of the main flow increases and contributes to the increased adhesion of the gas film, which causes the cooling enhancement under a supersonic condition. In the vicinity of the film hole exit, a local low pressure region is formed under the influence of the supersonic main flow. An aerodynamic convergent–divergent state was formed in the film hole, devastating the state of supersonic congestion of the film hole and further enhancing the film cooling effect.

The present paper deals with effectiveness of coagulation for removal of turbidity and biological growth in experimental salt gradient solar pond. The result obtained indicated that coagulation is not able to bring down the turbidity below 1 NTU, while at 10 NTU starting turbidity, the optimum alum dose comes out to be 75 mg/I and it is 60 and 45 mg/l for 5 and 3 NTU respectively. This acquired level of turbidity is within acceptable limits for solar ponds, hence the experimentation with higher dose was not continued.

Abstract: A novel hybrid hydrogel has been developed by combining bilayer-based lamellar structure of a self-assembled polymer surfactant and polymer network of conventional hydrogel system. A wide range of lamellar structure from micro-domain up to macro-domain (cm-scale) has been successfully generated in the hydrogel. Flat, infinitely large, and perfectly aligned lamellar macro-domain was formed by applying mechanical shear to the gel forming precursor solution containing monomer, cross-linker, and initiator. The obtained hydrogel system contains macroscopic, single-domain, periodical stacking of integrated microscopic lamellar bilayers inside the polymer matrix of the hydrogel. Periodical stacking of the bilayers in the hydrogel selectively diffract visible light to exhibit magnificent structural color. Due to the uniaxial orientation of the bilayer, the hydrogel possesses superb functions that have never been realized before, such as the one-dimensional swelling, anisotropic Young’s modulus, anisotropic molecular permeation, and diffusion. Furthermore, the hydrogel exhibits excellent color tuning ability over a wide spectrum range by mechanical stimuli. [Copyright &y& Elsevier]

Internal solitary waves (ISWs) have been detected at the interface of a stratified water column in the laboratory. This paper reports upon the propagation of an ISW in various pycnoclines. The thickness of the pycnocline was estimated from the resulting density profile in the vertical direction. Based on the results obtained, the dimensionless thickness (= B/H, where B is pycnocline; H the total depth of 50 cm) of the first test was 0-0.1 in ISW. Experimental results show that, as the thickness of the pycnoline increases, the values of all the physical parameters (e.g., wave amplitude, phase speed, and wave energy) decreases. The findings of this study should be beneficial to oceanography and advanced research regarding ISW propagation and the evolution of both laboratory experiments and in-situ measurements. [ABSTRACT FROM PUBLISHER]

Abstract: Barodiffusion is the tendency of light elements to migrate down a pressure gradient. In the Earth’s outer core, this effect can lead to the development of a chemically stable layer beneath the core–mantle boundary (CMB). Barodiffusion has so far been considered unimportant relative to other effects, but here we show that it dominates at the CMB and leads to an order-100km-thick layer that is rich in light elements and stably stratified. Barodiffusion changes not only the equations governing molecular diffusion of light elements in the core but also the boundary condition at the CMB to a non-zero compositional gradient, a point missed by previous studies. The mathematical problem has the same form as the recently-proposed migration of light elements passing from the mantle into the core; the effect of barodiffusion is comparable provided all light elements in the outer core are included, not just the light element driving the convection as in previous studies. We therefore conclude that a substantial stable layer can exist at the top of the core independent of any mass flux across the CMB. We solve the relevant diffusion equations in a thin layer beneath the CMB for barodiffusion of oxygen, sulphur and silicon over the whole history of the core using diffusion constants obtained from first principles calculations. The lower boundary of the layer is defined to be the neutrally stable level where the stabilising barodiffusive gradient is equal and opposite to the destabilising gradients associated with buoyancy sources in the well-mixed bulk of the core. We assume no mass flux across the CMB, and find the compositional gradient imposed by barodiffusion to be so large that its stable density gradient could not be overcome by any destabilising gradient at any time. The light layer therefore develops at the top of the core immediately after core formation; solving the diffusion equations shows it to grow to a thickness of order 100km. The final thickness is remarkably insensitive to the model of core cooling used to specify the destabilising gradients in the well-mixed region of the core. We consider a variety of instability mechanisms and argue that the stratification is strong enough to inhibit virtually all radial motion within the layer, although conclusive evidence for the existence of stratification can only come from observations. The variation in composition is sufficiently strong to produce geomagnetic effects and seismic velocity anomalies of a fraction of a percent that could be, and may already have been, detected. Differences in the diffusion parameters for the three light elements cause differences in their relative concentrations in the layer, leaving the layer oxygen-rich relative to sulphur or silicon. [Copyright &y& Elsevier]

Abstract: The paper investigates time-harmonic wave propagation in continuously stratified solids and provides the results of a reflection-transmission process generated by a layer sandwiched between homogeneous half-spaces. The layer is continuously stratified and allows for jump discontinuities at a finite number of planes. The dissipative effects are accounted for through the classical Boltzmann law of viscoelasticity. By using displacement and traction as convenient vector variables, the governing equations are considered in a vector Volterra integral equation and the solution is determined by means of a matricant. Next the matricant is applied to determine the reflection and transmission coefficients of a layer, with a generic piecewise continuous profile of the material properties. The reflection-transmission process produced by an obliquely incident wave, is considered for horizontally-polarized waves. The low-frequency approximation is derived for the reflection and transmission coefficients. Next, the high-frequency approximation is investigated by a WKB-like procedure which involves a complex valued frequency-dependent shear modulus. The displacement solution is obtained for the forward- and the backward-propagating waves in the layer along with the reflection and transmission coefficients. [Copyright &y& Elsevier]

THE PAPER INVESTIGATES the reflection-transmission process of acoustic waves, generated by an inhomogeneous fluid layer of finite thickness, which is sandwiched between two semi-infinite homogeneous half-spaces. First a direct problem is solved by determining the reflection and transmission coefficients along with the wave solution in the layer, produced by a known incident wave. Owing to the planar stratification of the layer, the unknown acoustic pressure is looked at as a generalized plane wave. Upon the Fourier transformation, the second-order wave equation is written as a first-order system of equations for the dependence on the depth of the pressure and the partial derivative. The corresponding Volterra integral equation gives the pressure in the layer as a series of repeated integrals of powers of the pertinent depth-dependent matrix of the system. The reflection and transmission coefficients of the layer are then determined for any incidence angle. Next an inverse problem is investigated. The derivatives of the reflection coefficient, with respect to the frequency, are shown to provide the thickness of the layer, the speed beyond the layer and the moments, of any order, of the refractive index. [ABSTRACT FROM AUTHOR]

The flow and heat transfer characteristics of a film jet inclined to different supersonic situations with a varying Mach number of the main flow were numerically investigated. In supersonic situations, complicated waves are generated by the obstacle of the film jet. In this work, extra pressure is exerted onto the film jet, causing better film attachment to the wall. The strengthening of attachment decreases mixing between the main flow and film jet, causing better film cooling. We observed multi-interfacial layered structures caused by the film jet under the complicated effect of shock waves. At the interfaces of the film jet and shock waves, additional pressure is exerted on the film towards the wall. The pressure increases as the Mach number of the main flow increases and contributes to the increased adhesion of the gas film, which causes the cooling enhancement under a supersonic condition. In the vicinity of the film hole exit, a local low pressure region is formed under the influence of the supersonic main flow. An aerodynamic convergent–divergent state was formed in the film hole, devastating the state of supersonic congestion of the film hole and further enhancing the film cooling effect. [ABSTRACT FROM AUTHOR]

• Chemical interactions at the core-mantle boundary (CMB) lead to oxygen transfer to the core. • Lower mantle temperatures may have been supersolidus after core formation, facilitating rapid oxygen transfer. • We assess this transfer using a new model of coupled core-magma ocean evolution. • Oxygen transfer following core formation can account for 10-50% of present-day core concentration. • FeO loss to the core hastens the complete crystallization of the magma ocean. Chemical interactions between metal and silicates at the core-mantle boundary (CMB) are now thought to lead to transfer of oxygen into Earth's liquid core. Establishing the nature and extent of this transfer is important for constraining the conditions under which the core formed, the origin of a stably stratified region below the CMB and the possible precipitation of oxides within the core. Previous models of FeO transfer have considered a solid mantle; however, several lines of evidence suggest that the lowermost mantle could have remained above its solidus long after core formation was complete, which would allow much faster mass transfer. We investigate this scenario by developing a time-dependent model of FeO exchange between a diffusive stratified layer at the top of the core and a long-lived molten magma ocean. Core FeO concentration, c ¯ F e O c , is evolved subject to a time-dependent mass flux at the CMB, radius r cmb , which depends on the FeO concentration at the bottom ( c ¯ F e O m (r cmb)) and top ( c ¯ F e O m (r bulk)) of the chemical boundary layer above the CMB. Coupled core-magma ocean evolution arises because c ¯ F e O m (r cmb) and c ¯ F e O c (r cmb) are linked through the partition coefficient P = c ¯ F e O c (r cmb) / c ¯ F e O m (r cmb). c ¯ F e O m (r bulk) is held constant in No Crystallization (NC) models and evolves in Middle-Out Crystallization (MOC) models according to the basal magma ocean model of Labrosse et al. (2007) , generalised to account for FeO loss to the core. In the first 1 Gyr, FeO transfer in all models with ≥10% FeO in the magma ocean and P ≥ 5 produces pure FeO compositions at the CMB, stably stratified layers of 60 − 80 km and accounts for 15 − 50 % of the total present-day core oxygen content. In NC models the magma ocean does not completely freeze in 4 Gyr, in which time the stable layer reaches 120 − 150 km and FeO transfer can account for all of the present-day O in the core. However, in MOC models FeO loss to the core causes the magma ocean to completely freeze in the first 1-3 Gyrs following core formation. Our results suggest that the present-day core composition may not provide a strong constraint on models of core formation and that FeO could have precipitated at the top of the core. [ABSTRACT FROM AUTHOR]