A permeable interface crack between dissimilar thermopiezoelectric media

Summary This paper presents an explicit treatment of the generalized 2D thermopiezoelectric problem of an interfacial crack between two dissimilar thermopiezoelectric media by means of the extend Stroh formalism. In comparison with the other relevant studies, the present work has two features: one is that the crack is assumed to be a permeable slit across which the normal electric displacement and the tangential electric field are continuous. The other is that the heat loading is applied at infinity, rather than on the crack faces. As a result, the field intensity factors and the electric field inside the crack are obtained in explicit closed-forms, respectively. As examples, the solutions of several particular cases, including that of an impermeable crack and that of a homogeneous material with a crack are also presented. It is shown that the electric field inside a crack may be singular and oscillatory for the case of an interfacial crack, while for the case of a crack in a homogeneous medium it is linearly variable. Moreover, it is also found that for a homogeneous medium with a crack the stress intensity factors based on the impermeable model and permeable model are same, but the intensity factor of the electric displacement is not.     

Polarized light-pulse transport through scattering media

The propagation of a polarized pulse in random media is investigated using the discrete-ordinates method to solve the transient vector radiative transfer. The angular analysis of the transient polarized features of scattering fluxes makes it possible to investigate subtle details of the polarization flip encountered for circularly polarized waves. We found that, depending on the geometry, the state of polarization, and the angle of detection, the degree of polarization decays at either a slower or faster rate when the beam is impinging at an angle far from the normal incidence. At normal incidence, our results confirm that, for large particles, the circular polarization maintains a greater degree of polarization.     

Fundamentals of the double – decomposition concept for turbulent transport in permeable media

Environmental impact analyses as well as engineering equipment design can both benefit from reliable modeling of turbulent flow in porous media. A number of natural and engineering systems can be characterized by a permeable structure through which a working fluid permeates. Turbulence models proposed for such flows depend on the order of application of time and volume average operators. Two methodologies, following the two orders of integration, lead to different governing equations for the statistical quantities. This paper reviews recently published methodologies to mathematically characterize turbulent transport in porous media. A new concept, called double‐decomposition, is here discussed and models for turbulent transport in porous media are classified in terms of the order of application of the time and volume averaging operators, among other peculiarities. Within this paper Instantaneous Local Transport Equations are reviewed for clear flow before Time and Volume Averaging Procedures are applied to them. The Double‐Decomposition Concept is presented and thoroughly discussed prior the derivation of macroscopic governing equations. Equations for Turbulent Transport follow, showing detailed derivation for the mean and turbulent field quantities.     

Advective transport through permeable sediments: A new numerical and experimental approach

Summary We investigate the flow through a porous medium both numerically and experimentally. The computer simulation solves a generalized non-linear extension to Darcy's law, known as Darcy-Brinkman-Lapwood-Forchheimer (DBLF) equation in a way that allows us to estimate the significance of each term in this equation. The numerical results have been validated against tracer transport data obtained using positron emission tomography (PET), a novel, non-invasive technique for flow-visualization. The results indicate that viscous diffusion is of significance over a narrow region, the Brinkman-layer, below the fluid-sediment interface, and that the Darcy equation alone is not sufficient to estimate the advective transport correctly.     

Development and comparison of models for light-pulse transport through scattering-absorbing media

We examine the transport of short light pulses through scattering-absorbing media through different approximate mathematical models. It is demonstrated that the predicted optical signal characteristics are significantly influenced by the various models considered, such as P(N) expansion, two-flux, and discrete ordinates. The effective propagation speed of the scattered radiation, the predicted magnitudes of the transmitted and backscattered fluxes, and the temporal shape and spread of the optical signals are functions of the models used to represent the intensity distributions. A computationally intensive direct numerical integration scheme that does not utilize approximations is also implemented for comparison. Results of some of the models asymptotically approach those of direct numerical simulation if the order of approximation is increased. In this study therefore we identify the importance of model selection in analyzing short-pulse laser applications such as optical tomography and remote sensing and highlight the parameters, such as wave speed, that must be examined before a model is adopted for analysis.     

Hybrid Monte Carlo for photon transport through optically thick scattering media

A Monte Carlo simulation code developed to model time-domain transillumination measurements with small-area detectors through an optically thick scattering slab is presented. A hybrid approach has been implemented to reduce calculation times. Most of the scattering slab is treated stochastically, albeit with variance reduction techniques and the isotropic diffusion similarity rule. The contribution to the output signal per unit area and time of photon packets propagating in a thin slice near the output face of the slab is calculated analytically after each propagation step. This approach drastically reduces the calculation time but produces spikes in the temporal signals.     

Excitation of the opposite acoustic flows in thermodynamically nonequilibrium gaseous media

It is shown that the acoustic wind direction may change in an acoustically active gaseous medium.     

Photoresonant ionization of gaseous media by excimer laser radiation

An identification is made of twenty five elements whose resonance lines overlap the emission lines of high-power pulsed ultraviolet gas lasers or lie in the immediate vicinity of them, so that the mechanism laser ionization based on resonance saturation (LIBORS) can be used to ionize the vapor of these elements. Resonance transitions of atoms and ions excited by the same laser (by krypton fluoride and xenon fluoride lasers, respectively) are observed for tantalum and uranium. It ishas been suggested that these elements may be used as “catalysts” for “ catalytic” resonance ionization (CATRION) of dense multicomponent gas mixtures. Experiments have been carried out to study the krypton fluoride laser irradiation of expanding vapor clouds of different elemental composition, created by the evaporation of targets with a ruby laser. Photographs obtained with an image converter, measurements of the refractive index gradient from the deflection of the laser beam, as well as probe and spectroscopic measurements indicate that the clouds undergo photoresonant ionization if they contain tantalum vapor but that the laser radiation has no influence otherwise. Pis’ma Zh. Tekh. Fiz. 23, 24–32 (May 12, 1997)     

Molecular effects in the energy loss of alpha particles in gaseous media

Previous measurements in gaseous hydrocarbon and carbon-oxygen compounds in the range 0.3 ≦ E_α ≦ 2.0 MeV revealed that the Bragg additive rule failed to give molecular stopping cross sections ε_α from the measured atomic solid carbon stopping cross section ε(C) and diatomic ε_expt(H₂) or ε_expt(o₂). For example, when hydrogen was present in the compound, the molecular data could be fitted either by using ε(C) and an ε'(H) which was higher than $\text{1}\text{2}\text{ε}{}_{\mathrm{expt}}\text{(H}{}_2\text{)}$ by as much as 21%, or by using $\text{1}\text{2}\text{ε}{}_{\mathrm{expt}}\text{(H}{}_2\text{)}$ and another ε'(C) which was greater than ε(C) by as much as 22%. A similar difficulty has also been encountered in interpreting the stopping cross sections recently measured for C-H-F and C-H-O compounds. ε(C), ε_expt(H₂) and ε_expt(O₂) can be used to fit (CH₃)₂O, but it is necessary to use ε'(C) and ε_expt(H₂) for C₂H₂F₂. Nevertheless, a closer examination of the stopping cross sections for eight hydrocarbon compounds reveals a correlation between the stopping cross sections of atomic hydrogen and carbon which are required to satisfy the Bragg rule, and the type of bond associated with the atomic carbon in the molecule. The stopping cross section of a carbon atom is greater when the atom is bound by a triple bond than a single bond, whereas that of a hydrogen atom is less in a triple-bond compound than in a single-bond compound. Double-bonded compounds yield a carbon stopping cross section between the single-bond and triple-bond values at lower energies and closer to the triple-bond values at higher energies.     

Effect of sound on heat- and mass-transfer processes in gaseous media

Expressions are derived for the dimensionless heat- and mass-transfer coefficients for bodies of simple shape and the calculated relations are compared with the existing experimental data. The limits of applicability of the results are considered.     

A fiber-optic frequency transducer of variable pressure in gaseous and liquid media

Fiber-optic sensors of variable pressure are proposed and implemented on fiber lasers with microoptomechanical resonance structures generating in automodulation regimes. Possibilities of sound pressure monitoring in gaseous and liquid media are considered, and the sensitivity of these fiber-optic sensors is estimated.     

Picoliter rheology of gaseous media using a rotating optically trapped birefringent microparticle

An optically trapped birefringent microparticle is rotated by a circularly polarized beam in a confined gaseous medium. By recording the terminal rotation velocity and the change in polarization of the incident trapping beam, we determine the viscosity by probing a picoliter volume of air, carbon dioxide, and argon in the vicinity of the microparticle. We also characterize the optical force acting on a trapped particle in air using the generalized Lorenz-Mie theory taking into account the aberrations present. This opens up a new potential application of optical tweezers for the accurate measurement of gas viscosity in confined geometries.     

Effect of gaseous media on the structure and thermal EMF of components of chromel-copel thermocouples

The article describes the results of an investigation of the thermal emf of chromel and copel against platinum and chromel-copel thermocouples tested under various conditions of time and temperature. The results were compared with data from X-ray diffraction and speetrographic analysis obtained for these alloys. The causes of thermoelectric instability of chromel-copel thermocouples were discussed. Foundations were laid for accelerated laboratory tests designed to verify the suitability of chromel-copel thermocouples for service in air.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 5, No. 6, pp. 666–669, November–December, 1969.