Layers Of Different Density Research Articles

Spurious numerical mixing under strong tidal forcing: a case study in the south-east Asian seas using the Symphonie model (v3.1.2)

Abstract. The role of mixing between layers of different densities is key to how the ocean works and interacts with other components of the Earth's system. Correctly accounting for its effect in numerical simulations is therefore of utmost importance. However, numerical models are still plagued with spurious sources of mixing, originating mostly from the vertical advection schemes in the case of fixed-coordinate models. As the number of phenomena explicitly resolved by models increases, so does the amplitude of resolved vertical motions and the amount of spurious numerical mixing, and regional models are no exception to this. This paper provides a clear illustration of this phenomenon in the context of simulating the south-east Asian (SEA) seas along with a simple way to reduce its impact. This region is known for its particularly strong internal tides and the fundamental role they play in the dynamic of the region. Using the Symphonie ocean model, simulations including and excluding tides and using a pseudo-third-order upwind advection scheme on the vertical are compared to several reference datasets, and the impact on water masses is assessed. The high diffusivity of this advection scheme is demonstrated along with the importance of accounting for tidal mixing for a correct representation of water masses. Simultaneously, we present an improvement in this advection scheme to make it more suitable for use in the vertical. Simulations with the new formulation are added for comparison. We conclude that the use of a higher-order numerical diffusion operator greatly improves the overall performance of the model.

A Highly Responsive Graphene Oxide Humidity Sensor Based on PVA Nanofibers.

Graphene oxide (GO) humidity sensors based on poly(vinyl alcohol) (PVA) nanofibers have been proposed. The PVA nanofiber layers of different densities were obtained by adjusting the electrospinning time. Then, GO films were deposited on PVA nanofibers by a spin-coating method. The electrical properties of GO films are improved due to the increased distribution of PVA nanofibers in the GO films. The humidity sensors exhibit good sensitivity under a high relative humidity range of 40-80%. The response of sensors has reached 98.44% at a humidity level of 80% RH. The GO/PVA sensors have good stability at various humidity levels for 1 week. Furthermore, the GO/PVA sensors were used for respiration monitoring under different statuses. These sensors have good application prospects in the respiratory detection and analysis of diseases.

Equation of State of Autoclaved Aerated Concrete-Oedometric Testing.

This paper aims at investigating the triaxial behavior of Autoclaved Aerated Concrete (AAC) under extremely high pressures, and experimentally determine Equation of State (EOS) for several different AAC densities. Oedometric tests were carried out using a home-made high-pressure triaxial apparatus, and pressures up to ~500 MPa were applied. The complete pressure-bulk strain relationships were measured, and new findings and insights were obtained. The paper presents the testing set-up and the measurement system. The data processing method accounting for the AAC pronounced shortening during the ongoing test is described using a weighted functions procedure for the circumferential strains' calculation, with which the confining pressure was determined. The boundary conditions effects on the test results were investigated, and a new technique for specimen insulation was suggested to ensure loading without friction and the prevention of local shear failure. The experimental EOS for different AAC densities were obtained. EOS curves for different specimens with the same density demonstrated good to very good repeatability of the EOS curves over the entire pressure range. Based on the tests results and the density's span, three classes of AAC are proposed. A preliminary attempt to apply the newly obtained EOS curves has been carried out to examine the energy dissipation for three different dynamic load levels. Although this is a preliminary stage that is beyond the objective of this paper, early interesting results were observed where an optimal AAC density, for which the highest energy has been absorbed, was identified. This finding encourages inclusion of that preliminary study as a closure section. Numerical simulations of wave propagation through ACC layers of different densities, laid on rigid supporting slabs, was carried out. The minimum total impulse imparted to the rigid slab was found for the optimal AAC density that has been determined above.

Study of Moulding Sands to Create Three-Layer Magnesium Concrete

Abstract The article is devoted to the problem of creating energy-efficient building materials for enclosing structures. The aim of the research is to develop a recipe and a method for moulding sands placing to create heat-insulating concrete of a multilayer structure. The three-layer magnesium concrete containing layers of different densities is an object of a scientific research. Compositions of moulding sands for concrete’s central and surface layers have been developed and studied. Materials specially developed were used as raw materials for moulding sands; they are as follows: composite magnesial binder and porous filler obtained by low-temperature firing of a granular mixture based on sodium liquid glass and thermal energy waste (fly ash from thermal power plants, aluminosilicate microsphere). Possibility of regulating moulding sand’s properties for concrete’s central layer by varying the content and fractional composition of porous granules has been shown. There has been proposed the moulding sand for surface layers of three-layer magnesium concrete containing crushed porous sand. The related composition of moulding sands favours with adhesion of concrete’s different layers. Various technological methods for producing magnesium concrete of a complex structure have been studied. The research reveals technological and operational characteristics of three-layer magnesium concrete obtained by horizontal and vertical deposition of moulding sands.

Numerical exploration of the motion of variable mass test particle on the perturbed circular restricted three-body configuration

This paper represents analytical and numerical investigations of the motion properties of a test particle having a variable mass according to Jeans’ law and subject to the influence of a heterogeneous primary having N layers of different densities of a part and a second body producing a modified Newton potential on the other hand. We also assume that the whole system is perturbed by Coriolis force and centrifugal force. The equations of motion that we derive, are used to determine the locations of equilibrium points, Poincaré surfaces of section, basins of attraction as well as to study questions related to the stability of equilibrium points.

Conserved Quantities of a Nonlinear Coupled System of Korteweg-De Vries Equations

The conserved vectors from a system of coupled Kortewegde Vries equations that have modelled the propagation of shallow water waves, ion-acoustic waves in plasmas, solitons, and nonlinear perturbations along internal surfaces between layers of different densities in stratified fluids, for example propagation of solitons of long internal waves in oceans. Notable applications have been to model shock wave formation, turbulence, boundary layer behavior, and mass transport. This paper illustrates the computation of conserved quantities using two approaches. First, by the multiplier method and by an application of new conservation theorem developed by Nail Ibragimov. 2010 Mathematics Subject Classification. 47B47; 47A30.

Lie Group Analysis of a Nonlinear Coupled System of Korteweg-de Vries Equations

In this paper, we consider coupled Korteweg-de Vries equations that model the propagation of shallow water waves, ion-acoustic waves in plasmas, solitons, and nonlinear perturbations along internal surfaces between layers of different densities in stratified fluids, for example propagation of solitons of long internal waves in oceans. The method of Lie group analysis is used to on the system to obtain symmetry reductions. Soliton solutions are constructed by use of a linear combination of time and space translation symmetries. Furthermore, we compute conservation laws in two ways that is by multiplier method and by an application of new conservation theorem developed by Nail Ibragimov.

Performance of snow density measurement systems in snow stratigraphies

Abstract Gravimetric and dielectric permittivity measurement systems (DMS) are applied to measure snow density, but few studies have addressed differences between the two measurement systems under complex snowpack conditions. A field experiment was conducted to measure the snow density using the two measurement systems in stratigraphical layers of different densities, liquid water content (LWC), hardness, and shear strength, and the performance of the two measurement systems was analyzed and compared. The results showed that the snow density from the DMS tended to underestimate by 9% in the dry snowpack and overestimate by 3% in the wet snowpack, expressed as the percentage of the mean density from the gravimetric measurement system (GMS). Compared with the GMS, the DMS has relatively low precision and accuracy in the dry snowpack and similar precision and accuracy in the wet snowpack. The accuracy and precision of the two measurement systems increased with the increase of hardness and shear strength of snow in the dry snowpack, but the accuracy and precision measured of the DMSs increased with the decrease of hardness and shear strength of snow in wet snowpack. The results will help field operators to choose a more reasonable measurement system based on snowpack characteristics to get reliable density data and optimize field measurements.

Variable low-density polylactic acid and microsphere composite material for additive manufacturing

Thermally expandable microspheres are extensively used in industry as a lightweight filler for many products. The spheres can expand up to 60 times the initial size and are used for different purposes, including material reduction and surface modification. In fused filament fabrication (FFF), a material is deposited in a layer-by-layer process. Typically, FFF objects need not be solid because such objects are typically used for applications with low mechanical stress. Low material infill percentages are commonly used inside a solid outer shell to reduce material usage, weight, and manufacturing time. This paper proposes a new composite filament for FFF consisting of polylactic acid (PLA) and thermally expandable Expancel microspheres in the form of masterbatch granules. These filaments contain unexpanded microspheres that can be expanded during printing by heating. Two types of filaments containing 2 wt% and 5 wt% of masterbatch granules were manufactured and tested. The filaments were successfully used with a commercial 3D printer to manufacture objects with a density of 45% compared to objects manufactured using standard PLA. The tensile strength of these objects changed linearly with density and was comparable to that of PLA objects of the same density prepared using infill patterns. The composite filaments are advantageous in that they can reduce the amount of material used, as is currently done by using different amounts of infill in a pattern. Further, by varying the nozzle temperature, their density can be adjusted directly during printing as well as during fabrication to produce layers of different densities in the same object.

On the singular behavior of the Stokes drift in layered miscible fluids

Gravity waves of the Stokes-type in a system of two horizontal layers of inviscid, stratified and miscible fluids are studied by applying a Lagrangian description of fluid motion. It is shown that for the total vertically-integrated Stokes drift (the Stokes flux) to become zero, the density must be continuous at the interface. This is not the case in a system of two immiscible homogeneous layers of different densities. For miscible fluids, however, one can extend the density of the lower layer continuously to that of the upper layer through an infinitely thin interface. This introduces a negative Stokes drift with a delta-function behavior. The corresponding finite negative Stokes flux obtained by integrating the Stokes drift across this infinitely thin layer adds to the original positive Stokes fluxes in the upper and lower layer, yielding the required vanishing total Stokes flux between the bounding planes of the model. The delta-function behavior of the Stokes drift at the interface also induces additional Lagrangian mean displacements in the vertical so that the position of the Lagrangian mean interfacial level is the same as in the absence of waves.

Moisture transfer in outer walls with layers of different density

The need to protect external walls from excess moisture to improve heat-shielding properties is an urgent task. If the outer wall is created from expanded clay concrete blocks, then the most interesting are the blocks created by layer-by-layer moulding, in which each layer can have its own given density. In such blocks, each layer has its own coefficients of thermal conductivity and vapor permeability, which allows you to select the required heat transfer resistance and vapor permeability of the outer wall for a specific region, taking into account the characteristics of the climate. The ability to have external walls with different material densities inside makes it possible to implement energy saving tasks in the building. The article discusses options for external walls made of expanded clay concrete blocks with layers with different densities and coefficients of thermal conductivity and vapor permeability. Changing the location of layers with different densities inside the blocks changes the local values of the vapor permeability resistance, which leads to a different nature of the movement of water vapor inside the wall in winter. It is good when water vapor does not accumulate in the wall; it does not condense and freely goes into the external environment. A dry wall is more durable, it loses less heat in winter. Changes in partial pressures at full saturation and with existing humidity inside the expanded clay concrete block for layers of different densities in winter are considered to determine the possible condensation from water vapor inside the wall. Layer-by-layer moulding of building materials improves their properties to increase resistance to heat transfer and to form a dry and more durable outer wall.

Motion around triangular points in the restricted three-body problem with radiating heterogeneous primaries surrounded by a belt

The present paper studies the locations and linear stability of the triangular equilibrium points when both primaries are radiating and considered as heterogeneous spheroid with three layers of different densities. Additionally, we include the effects of small perturbations in the Coriolis and centrifugal forces and potential from a belt (circumbinary disc). It is observed that the positions of the triangular equilibrium points are substantially affected by all parameters (except a perturbation in Coriolis force) involved in the system.The stabilty of motion is found only when 0 < mu < mu_{c}, where mu_{c} is the critical mass value which depends on the combined effect of radiation pressures and heterogeneity of the primaries, small perturbations and the potential from a belt.It is also seen that the Coriolis force and the belt have stabilizing effect,while the centrifugal force, radiation and heterogeineity of the primaries have destabilizing behaviour.The net effect is that the size of the region of stability decreases when the value of these parameters increases where mu is the mass ratio and k_{1} ,k_{2} characterize heterogeneity of both primaries. A practical application of this model could be the study of motion of a dust grain near the heterogeneous and luminous binary stars surrounded by a belt.Finally, we carried out and discuss numerical experiments aiming at computing the positions of triangular points and critical masses of three binary systems: Archid, Xi Booties and Kruger 60.

Thin-film encapsulation of Al2O3 multidensity layer structure prepared by spatial atomic layer deposition

Aluminum oxide films deposited by spatial atomic layer deposition have been used for thin-film encapsulation of organic light-emitting diodes. In this study, a multidensity layer structure consisting of two Al2O3 layers of different densities was deposited at varying ozone flow rates. The structure improved moisture permeation barrier characteristics, as confirmed by the water vapor transmission rate (WVTR) measurement. The lowest WVTR of the multidensity layer structure was 5.3 × 10−5 g m−2 day−1, which is two orders of magnitude lower than that of a reference single-density Al2O3 layer. This improvement can be attributed to the location mismatch of paths in the film for atmospheric gases, such as oxygen and water, due to different layer densities. High-resolution transmission electron microscopy and x-ray photoelectron spectroscopy confirmed the multidensity layer structure’s superior characteristics as an encapsulation layer due to a location mismatch of the paths for oxidative species between the two layers.

Effect of heterogeneity on failure of natural rock samples

A carbonate sample extracted from the depth of about 10 kft was subjected to uniaxial loading while the confining stress remained constant. Post-experiment inspection of the sample showed an inclined crack at an angle less than 20° to the horizontal. This subhorizontal crack orientation was contrary to the expected 45° inclination, the plane of the maximum shear stress. Coincidentally, as shown by CT-scan prior to loading, there was a boundary between two layers of different density inside the sample located almost exactly where the crack appeared. This density difference has arguably translated into the contrast in the elastic properties at the boundary. The hypothesis is that because of this elastic heterogeneity, an incipient crack developed at the boundary due to the unavoidable tensile stressing of the sample as it was brought to the benchtop from its original state of high confining stress at depth. Controlled uniaxial compression made the sample slip along this crack, which then developed into a prominent feature. This assumption was corroborated by a numerical experiment showing a strong von Mises stress concentration at the elastic contrast boundary during hydrostatic tensile loading. Another sample, from the same formation, but without strong density heterogeneity, exhibited a classic 45° crack after uniaxial loading. These results provide a novel and important insight into the mechanics, breakage, and strength of natural rock.

Firn Clutter Constraints on the Design and Performance of Orbital Radar Ice Sounders

Radar sounding is a powerful tool for constraining subglacial conditions, which influence the mass balance of polar ice sheets and their contributions to global sea-level rise. A satellite-based radar sounder, such as those successfully demonstrated at Mars, would offer unprecedented spatial and temporal coverage of the subsurface. However, airborne sounding studies suggest that poorly constrained radar scattering in polar firn may produce performance-limiting clutter for terrestrial orbital sounders. We develop glaciologically constrained electromagnetic models of radar interactions in firn, test them against in situ data and multifrequency airborne radar observations, and apply the only model we find to be consistent with observation to assess the implications of firn clutter for orbital sounder system design. Our results show that in the very high-frequency (VHF) and ultrahigh-frequency (UHF) bands, radar interactions in the firn are dominated by quasi-specular reflections at the interfaces between layers of different densities and that off-nadir backscatter is likely the result of small-scale roughness in the subsurface density profiles. As a result, high frequency (HF) or low VHF center frequencies offer a significant advantage in near-surface clutter suppression compared to the UHF band. However, the noise power is the dominant constraint in all bands, so the near-surface clutter primarily constrains the extent to which the transmit power, pulselength, or antenna gain can be engineered to improve the signal-to-noise ratio. Our analysis suggests that the deep interior of terrestrial ice sheets is a difficult target for orbital sounding, which may require optimizations in azimuth processing and cross-track clutter suppression which complement existing requirements for sounding at the margins.

Internal Waves at the UK Continental Shelf: Automatic Mapping Using the ENVISAT ASAR Sensor

Oceanic internal waves occur within stratified water along the boundary between water layers of different density and are generated when strong tidal currents flow over seabed topography. Their amplitude can exceed 50 m and they transport energy over long distances and cause vertical mixing when the waves break. This study presents the first fully automated methodology for the mapping of internal waves using satellite synthetic aperture radar (SAR) data and applies this to explore their spatial and temporal distribution within UK shelf seas. The new algorithm includes enhanced edge detection and spatial processing to target the appearance of these features on satellite images. We acquired and processed over 7000 ENVISAT ASAR scenes covering the UK continental shelf between 2006 and 2012, to automatically generate detailed maps of internal waves. Monthly and annual internal wave climatology maps of the continental shelf were produced showing spatial and temporal variability, which can be used to predict where internal waves have the most impact on the seabed environment and ecology in UK shelf seas. These observations revealed correlations between the temporal patterns of internal waves and the seasons when the continental shelf waters were more stratified. The maps were validated using well-known seabed topographic features. Concentrations of internal waves were automatically identified at Wyville-Thomson Ridge in June 2008, at the continental shelf break to the east of Rosemary Bank in January 2010 and in the Faroe-Shetland Channel in June 2011. This new automated methodology has been shown to be robust for mapping internal waves using a large SAR dataset and is recommended for studies in other regions worldwide and for SAR data acquired by other sensors.

Bacterial chemotaxis in thin fluid layers with free surface

Thin fluid layers are common natural habitats for various species of aerobic bacteria. Collective behaviors in bacterial colonies caused by chemotaxis can form complex bioconvection patterns, which often work in favor of the colony’s survival and growth. The connection between the biology of bacterial aerotaxis and the physics of buoyancy effects caused by non-uniform suspension density is numerically investigated for a suspension of oxytactic bacteria placed in the Petri dish. The upper surface is free and open to the atmosphere, and through it oxygen diffuses into the suspension. Surface tension and dynamic contact line are incorporated into the mathematical and numerical models. A comparison has been made between dynamic free surface and fixed free surface models, and differences have been revealed. The parametric study in the case of dynamic free surface has been performed, and the non-linear dynamics of the phenomenon has been investigated. Resulting from upward aerotaxis and downward gravitational force, Rayleigh–Taylor-like instabilities develop between layers of different densities in the suspension. Bacterial plume patterns and their dynamics, such as sinking, merging, and birth of new plumes, characterize the phenomenon for particular intervals of dimensionless parameters. Accordingly, categorization of the phenomenon based on bacterial plume evolution has been made, and significant intervals of dimensionless parameters have been extracted.

Quantitative Comparison of Cone Penetration Testing Tip Resistance Data with Ground-Penetrating Radar Amplitude Data

Abstract Both cone penetration test (CPT) tip resistance data and ground-penetrating radar (GPR) amplitude data vary at the interface of snow layers of different density. Therefore, relationships b...

ВПЛИВ МОРФОЛОГІЇ ПРИРОДНІХ ГРАФІТІВ НА ЕКРАНУЮЧІ ВЛАСТИВОСТІ КОМПОЗИТНИХ МАТЕРІАЛІВ

Optimization of composition for a composite material based on graphite was done in order to increase the effectiveness of electromagnetic shielding. Morphological studies were carried out by optical and electron microscopy. Surface conductivity was determined by a four-probe measurement method. The effectiveness of electromagnetic shielding was studied by the level of attenuation of electromagnetic energy through the sample and the power level of the reflected electromagnetic wave in front of the sample. The dependence of surface conductivity and the efficiency of electromagnetic shielding on the particle size distribution of graphite in a composite material, as well as its density and thickness, has been established. It was experimentally approved that low-density carbon-graphite coatings containing magnetite were sufficiently effective for electromagnetic shielding. The density of the coating depends on their mechanical processing, as well as on the polydispersity of the graphite material. Shielding efficiency can be enhanced by combining layers of different density. A new concept for the manufacture of protective coatings for electromagnetic shielding was proposed taking in the account characteristics of graphite material such as polydispersity and particle structure. Particular attention was paid to the production of new carbon-graphite composites for the manufacture of screens and absorbers of electromagnetic radiation. The radio-absorbing properties of carbon-graphite coatings with different granulometric and chemical composition were analyzed for the first time. Multifunctional composite coatings for electromagnetic shielding can have a wide range of applications such as following: in the military and medical practice, specialized protective clothing, in screens for shielding equipment, rooms, and others.

The Shallow-Water Magnetohydrodynamic Theory of Stratified Rotating Astrophysical Plasma Flows: Beta-Plane Approximation and Magnetic Rossby Waves

Rotating magnetohydrodynamic flows of a thin stratified plasma layer in a gravitational field with a free boundary in an external vertical magnetic field were investigated. Magnetohydrodynamic equations were obtained in the two-layer shallow-water approximation in an external magnetic field when plasma is divided into two layers of different densities. A system of shallow-water equations for rotating stratified plasma in an external magnetic field was obtained in the beta-plane approximation. A linear theory was developed, and solutions in the form of magnetic Rossby waves, along with corrections that describe the effects of stratification, were obtained for stationary solutions in the form of vertical or horizontal magnetic field. Qualitative analysis of dispersion curves reveals the presence of three-wave nonlinear interactions of magnetic Rossby waves for each of the stationary states. The existence of parametric instabilities was demonstrated and their increments were found.