Incoherent intensities of electromagnetic waves in a random medium layer and radiative transfer theory

Abstract

Equations for incoherent intensities are obtained for electromagnetic waves in a random medium layer with plane parallel boundaries. These are based on the Bethe–Salpeter equation under the ladder approximation. These equations are then compared with the radiative transfer equations for this problem. Differences between these two approaches are pointed out and discussed. The Müller matrix is derived based on a first-order approximation to the equations for incoherent intensities which is then used to highlight the significance of the above-mentioned differences in radar cross-section computations.     

Unsteady diffusion in a multi‐layer medium with immobilization reaction at the interfaces

Abstract

A mathematical model is developed to describe the unsteady diffusion in a multi‐layer medium with interfaces that have non‐zero thickness. A general interface condition is used to account for the secondary phenomena that may take place in the interfaces. Analytical solution is obtained by the use of the linear operator method. An example is given to show the effects of the secondary phenomena on the diffusion behavior in the diffusion process with membrane as the interfaces.     

Photon Migration in a Two-layer Turbid Medium a Diffusion Analysis

Abstract

We analyse the diffusion of photons in a two-layer turbid medium, paying specific attention to parameters suggested by the use of lasers for diagnostic purposes in a medical setting. The data produced by such experiments consists of an intensity profile measured on the surface of the medium, which is measured either as a function of time at a fixed distance from the input laser beam, or else as a function of distance keeping the measurement time fixed. In both cases we demonstrate that the presence of a second layer can be detected provided that physical properties of the two layers differ by a sufficient amount, and also show up in calculated values of such parameters as the mean travel time of a photon to the surface of the medium, and the distribution of the maximum depth reached by an arbitrary photon.     

Effect of rotation on a layer of micropolar ferromagnetic fluid heated from below saturating a porous medium

This paper deals with the theoretical investigation of the effect of rotation on a layer of micropolar ferromagnetic fluid heated from below saturating a porous medium subjected to a transverse uniform magnetic field. For a flat fluid layer contained between two free boundaries, an exact solution is obtained using a linear stability analysis theory and normal mode analysis method. For the case of stationary convection, the effect of various parameters like medium permeability, rotation, non-buoyancy magnetization, coupling parameter, spin diffusion parameter and micropolar heat conduction has been analyzed. The critical magnetic thermal Rayleigh number for the onset of instability are also determined numerically for sufficiently large values of magnetic parameter M₁ and results are depicted graphically. The principle of exchange of stabilities is found to hold true for the micropolar ferromagnetic fluid saturating a porous medium heated from below in the absence of micropolar viscous effect, microinertia and rotation. The oscillatory modes are introduced due to the presence of the micropolar viscous effect, microinertia and rotation, which were non-existent in their absence. The sufficient conditions for the non-existence of overstability are also obtained.     

Buoyancy effects on the laminar boundary layer heat transfer along vertically moving cylinders

Abstract

The effects of buoyancy forces on the laminar boundary layer flow and heat transfer along vertically moving cylinders are analyzed for the cases of prescribed surface temperature and prescribed wall heat flux in power of streamwise distance. Local similarity solutions are obtained to show the effects of buoyancy parameters and the transverse curvature of the cylinder on the surface friction and heat transfer rate.     

Mode selection for a piezoelectric layer in a bulk-acoustic-wave composite acoustic resonator

An analysis is made of the mode selection for a thin piezoelectric layer in a bulk-acoustic-wave composite layered acoustic resonator by transformation of the impedance using a set of quarter-wave layers. Depending on the number of layers, the impedance of the substrate on which the piezoelectric layer is deposited may be abruptly increased or sharply reduced. This serves to simulate a “fixed” or “free” surface. As a result, a mechanically strong resonator structure is produced, operating at the natural frequencies of a thin piezoelectric layer. A numerical simulation is made of multilayer structures formed by alternating quarter-wave layers of LiNbO₃ and LiTaO₃. It is shown that if these layers are of micron thickness and there is a sufficiently large number of them, the acoustic properties of the substrate do not influence the frequency characteristics and Q factor of the thin piezoelectric vibrating layer in the microwave range. Pis’ma Zh. Tekh. Fiz. 23, 35–41 (October 12, 1997)     

Developing a four‐layer system rutting model in highway

Abstract

A four‐layer rutting model was developed to account for material property changes in the progression of accumulated compressive plastic strains in all roadway layers on the basis of traffic passing in this study. This paper demonstrates that incorporating the mechanistic‐empirical approach in the prediction of rutting provides value information on the contribution of each layer to rutting in flexible pavements.     

The onset of electrothermoconvection in a rotating Brinkman porous layer

The criterion for the onset of electrothermoconvection in a rotating horizontal layer of Brinkman porous medium is investigated for different types of velocity boundary conditions namely, (i) both boundaries stress-free, (ii) both boundaries rigid and (iii) lower rigid and upper free boundaries. Results indicate that the nature of boundaries and speed of rotation significantly influence the stability characteristics of the system. In the case of stress-free condition, it is shown that the necessary conditions for the occurrence of oscillatory onset are independent of an external electric field. Contrary to their stabilizing effect in the absence of rotation, increasing the ratio of viscosities Λ and decreasing the Darcy number Da show some destabilizing effect on the onset of stationary electrothermoconvection in the presence of rotation and some important observations are made on the stability characteristics of the system. Moreover, the similarities and differences between free-free, rigid-rigid and rigid-free boundaries are emphasized in triggering the onset of electrothermoconvection in a rotating porous layer. For small Taylor number domain, the stress-free boundaries is found to be always unstable than that of rigid-rigid and rigid-free boundaries. However, this trend is reversed at higher Taylor number domain because the stability of the stress-free case is increased more quickly than the other boundaries.     

Thiolated alginate-based multiple layer mucoadhesive films of metformin forintra-pocket local delivery: in vitro characterization and clinical assessment

Abstract

Introduction: Periodontal disease broadly defines group of conditions in which the supportive structure of the tooth (periodontium) is destroyed. Recent studies suggested that the anti-diabetic drug metformin hydrochloride (MF) has an osteogenic effect and is beneficial for the management of periodontitis.

Objective: Development of strong mucoadhesive multiple layer film loading small dose of MF for intra-pocket application.

Methodology: Multiple layer film was developed by double casting followed by compression method. Either 6% carboxy methyl cellulose sodium (CMC) or sodium alginate (ALG) constituted the inner drug (0.6%) loaded layer. Thiolated sodium alginate (TSA; 2 or 4%) constituted the outer drug free layers to enhance mucoadhesion and achieve controlled drug release. Optimized formulation was assessed clinically on 20 subjects.

Results: Films were uniform, thin and hard enough for easy insertion into periodontal pockets. Based on water uptake and in vitro drug release, CMC based film with 4% TSA as an outer layer was the optimized formulation with enhanced mucoadhesion and controlled drug release (83.73% over 12?h). SEM showed the effective fabrication of the triple layer film in which connective lines between the layers could be observed. FTIR examination suggests possibility of hydrogen bonding between the –NH groups of metformin and –OH groups of CMC. DSC revealed the presence of MF mainly in the amorphous form. Clinical results indicated improvement of all clinical parameters six months post treatment.

Conclusion: The results suggested that local application of the mucoadhesive multiple layer films loaded with metformin hydrochloride was able to manage moderate chronic periodontitis.     

Influence of a thin layer with arbitrary conductivity on the characteristics of acoustic waves in potassium niobate

The influence of a thin layer of arbitrary conductivity on the characteristics of acoustic waves in potassium niobate is investigated theoretically. The conductivity of a thin layer on the surface of a potassium niobate crystal or plate is shown to have a significant influence on the damping and velocity not only of symmetric Lamb waves and quasi-shear-horizontal waves but also of Gulyaev-Bleustein waves. It is found that a relative change in velocity as large as 50% can be achieved for quasi-shear-horizontal waves by altering the surface conductivity. The results obtained reveal great prospects of using potassium niobate to create acoustoelectronic devices with controllable characteristics. Pis’ma Zh. Tekh. Fiz. 25, 21–26 (April 26, 1999)     

Anisotropic scattering of polarized light in a ferrofluid layer

Previously unknown effects wherein the scattering of plane-polarized light in a ferrofluid layer depends on the orientation of the electric field of the polarized radiation relative to the direction of the applied magnetic field are found experimentally, and their physical nature is explained. Pis’ma Zh. Tekh. Fiz. 23, 7–10 (September 12, 1997)     

Diffraction of light by agglomerates in a layer of magnetic fluid situated in a magnetic field parallel to the plane of the layer

Previously unknown behavior observed when laser radiation propagates through a layer of magnetic fluid with and without an external magnetic field are established for the first time and their physical nature is explained. Pis’ma Zh. Tekh. Fiz. 23, 64–67 (February 12, 1997)     

Flexural vibration of a lithium niobate piezoelectric plate with a ferroelectric inversion layer

Abstract

Two-dimensional equations for flexural motions of a lithium niobate piezoelectric plate are derived from three-dimensional equations. The plate has a ferroelectric inversion layer where the piezoelectric constants reverse signs. The equations show an unconventional behavior that a uniform electric field along the plate thickness can produce bending. This offers many possibilities for new designs of devices. Waves in unbounded plates are examined for the accuracy of the equations. A piezoelectric energy harvester based on such a plate is analyzed as an example of the application of the equations derived in vibrations of finite plates.     

Formation of a low-resistivity penetrating metal-Si layer under the action of CO2 laser radiation

Some characteristic features observed as a result of the action of CO₂ laser radiation on a metal-silicon layer are described, especially the formation of a low-resistivity penetrating layer. The assumption is put forward that this low-resistivity penetrating layer forms as a result of the solid-phase dissolution of metal in Si or by diffusion of the metal into defects formed by laser radiation. Pis’ma Zh. Tekh. Fiz. 24, 60–63 (February 12, 1998)     

Analysis of reaction layer formed on steel strips during hot dip aluminising

Abstract

Aluminised steel sheets are currently used in many applications where the surface properties of aluminium combined with the formability, mechanical strength, and economic advantages of sheet material are obtained. During aluminising by hot dipping, an intermetallic reaction occurs due to diffusion between the aluminium bath and the steel sheet. The phases formed within the intermetallic layer and its thickness are important for determining the behaviour of the coating. In the present work, low alloy, medium carbon, low carbon 9Γ2C (9G2S), and low carbon steel sheets are used for hot dipping in a commercial purity aluminium bath. The temperatures used for hot dipping were 710 and 770°C and the immersion times were 2, 4, and 6 min. The results indicate that the thickness of the intermetallic layer X increases with increasing bath temperature and immersion time t. The variation of X with t followed the relationship X=Ktⁿ, where the constant K and the exponent n were found to depend on the carbon content and on the total alloying element content in the steel strip. With increasing total alloying elements, the thickness decreased. Analysis of the reaction layer indicates the formation of FeAl₂ in most cases in addition to FeAl₃, Fe₂Al₅, and Fe₂Al₃.     

Self-action of Counterpropagating Axially Symmetric Light Beams in a Transparent Cubic-nonlinearity Medium

Abstract

The stationary effect of self-action of counterpropagating axially symmetric light beams in a medium with cubic nonlinearity is discussed. Self-similar solutions for initial radiation parameters and nonlinear medium characteristics in the case of slowly varying amplitudes of beams are found. The analysis of approximate solutions obtained on the basis of motion constants is carried out and results are compared with numerical experimental data.     

Arc deposited AlSi12 cladding layer on steel plate without zinc coating

ABSTRACT

AlSi12 cladding layer was fabricated on steel plate without zinc coating via cold metal transfer arc deposited technique. The wettability, morphologies, microstructures, and mechanical properties of the cladding layer were investigated. The cladding layer exhibited favourable wettability with steel plate. Large swing amplitude and high swing frequency were the key factors to achieve excellent wettability. The cladding layer was composed of primary Al dendrites and (Al?+?Si) eutectic structure, and the microstructures were refined. Continuous and thin intermetallic compound layer appeared at AlSi12/steel interface, and reliable bonding strength between the cladding layer and steel plate was achieved. The fracture surface exhibited both brittle fracture and ductile fracture.     

Penetrative ferroconvection in a porous layer

Penetrative convection in a horizontal ferrofluid-saturated porous layer in the presence of a uniform applied vertical magnetic field has been investigated via the internal heating model using the Brinkman-extended Darcy equation. The rigid-isothermal boundaries of the porous layer are considered to be either paramagnetic or ferromagnetic. The eigenvalue problem is solved numerically using the Galerkin method with either thermal or magnetic Rayleigh number as the eigenvalue. The stability of the system is significantly affected by the internal heating in the porous layer. It is noted that the paramagnetic boundaries with large magnetic susceptibility delay the onset of penetrative ferroconvection the most when compared to very low magnetic susceptibility as well as ferromagnetic boundaries. An increase in the value of magnetic Rayleigh number (R _m ), heat source strength (N _S ) and non-linearity of magnetization (M ₃) is to hasten the onset of ferroconvection. In addition, the stability of the system when heated from above and also in the absence of thermal buoyancy has been discussed in detail.     

Surface waves at a moving plasma layer

An analysis is made of stable and unstable surface electromagnetic waves at the boundary of a planar moving plasma layer. It is shown that unlike an isolated tangential velocity discontinuity, both slow and fast waves may exist inside the layer. The maximum spatial growth rate of the oscillations is achieved for directions of wave propagation other than the direction of motion of the layer. Symmetric and antisymmetric waves relative to the symmetry plane of the layer have different critical angles from which their growth evolves and the range of angles where the flux is stable is determined by the smaller of these. Pis’ma Zh. Tekh. Fiz. 25, 50–55 (December 12, 1999)     

Degradation of structure and properties of rail surface layer at long-term operation

ABSTRACT

The microstructure evolution and properties variation of the surface layer of rail steel after passed 500 and 1000 million tons of gross weight (MTGW) have been investigated. The wear rate increases to 3 and 3.4 times after passed 500 and 1000 MTGW, respectively. The corresponding friction coefficient decreases by 1.4 and 1.1 times. The cementite plates were destroyed and formed the cementite particles of around 10–50nm in size after passed 500 MTGW. The early stage dynamical recrystallisation was observed after passed 1000 MTGW. The mechanisms for these have been suggested. The large number of bend extinction contours is revealed in the surface layer. The internal stress field is evaluated.

This paper is part of a themed issue on Materials in External Fields.