Medium Of Finite Conductivity Research Articles

Piezopotential‐Driven Redox Reactions at the Surface of Piezoelectric Materials

Themanipulation of charge-carrier conduction characteristics is a critical attribute governing the operation and efficiency of photovoltaic, catalytic, and other energy-converting systems that are based on electrochemical principles. This manipulation is often accomplished through the application of electrical-potential gradients by an external power supply and/or the creation of electronic-state discontinuities by heterojunction-interface engineering. For example, in electrochemical systems, the transport of charge across chemical phases is governed by the energy and density of electronic states within the disparate phases as well as any existing bias between said phases. Piezoelectric materials have long been used as a source of bias and mechanical displacement, relying on their mechanical to electrical coupling character for applications in sensors, actuators, and energy harvesters. In contrast to this historical precedent, contemporary integration of piezoelectric materials in semiconductor heterostructures capitalizes on the capability of the piezoelectric potential to manipulate charge carriers (i.e., piezotronics). For instance, the straining of a piezoelectric element in order to change its semiconducting properties has recently been investigated in zinc oxide nanomaterials, which have opened the doors to strain-gated logic operations and new possibilities for microelectronic circuitry elements. Straining effects in piezoelectric photoelectrochemical cells have also been shown to result in performance enhancements through manipulation of interface energetics. In principle, the piezoelectric modulation of charge carrier energetics should extend beyond the bounds of the buried electronic interfaces explored to date, thus allowing the direct enhancement or suppression of electrochemical processes that occur at the interface of a piezoelectric material and a solution (i.e., piezocatalysis). Preliminary experiments have shown an evolution of H2 and O2 from mechanically agitated piezoelectric BaTiO3 and ZnO microstructures in an aqueous sonication bath. In order to elucidate the intriguing piezocatalytic phenomenon, we report a systematic study of the piezoelectric-potentialdriven electrochemical H2 evolution process that takes place at the electrodes located on the surface of the material. The results compliment the general trends expected from the combinatorial assemblage of piezoelectricity and electrochemistry. The H2 evolution rates were dependent upon the oscillation frequency and amplitude of the piezoelectric material, in accordance with the combination of the direct piezoelectric effect and electrochemical reactions. A study of the piezocatalytic effect was conducted on a single-crystalline ferroelectric Pb(Mg1/3Nb2/3)O3-32PbTiO3 (PMN-PT) cantilever in a sealed chamber (see Figure S1 in the Supporting Information). The voltage output of the PMN-PT slab was first characterized in air (Figure 1a). The cantilever was mechanically oscillated with a fixed frequency and amplitude. When the piezoelectric cantilever was transitioned to the deionized water environment, the voltage amplitude decreased while the mechanical oscillation frequency and amplitude remained constant. In order to encompass the entire piezocatalytic system into a cohesive entity, an analogous circuit was constructed (Figure 1b). In this circuit, opposite and iteratively alternating sides of the piezoelectric material serve as both the working and counter electrodes, respectively. A strained piezoelectric material can be considered a charged capacitor, and thus the change in measured voltage is correlated with a change in piezoelectricity-induced surface charge (DQp). When a strained piezoelectric material is placed within an aqueous medium of finite conductivity and polarizability, its piezoelectricity-induced surface charge can be depleted through two primary pathways: Faradic (If) and capacitive (Ic=dCdVd/dt, in which Cd and Vd are the double layer capacitance and voltage drop across the double layer, respectively) currents:

Propagation constant of HE/sub 11/ mode near the cutoff frequency in a circular waveguide

In this letter, the propagation characteristics of normal mode near the cutoff region of a circular waveguide surrounded by a medium of finite conductivity and given permeability is discussed. Several real-time applications require an accurate solution of the characteristic equation at low computational cost. A fast computed approximate solution for external medium with infinite conductivity is available but inaccurate in the cut off region. Besides, field solvers and other numerical techniques give a precise solution in the whole frequency range, but unacceptable computational time. The proposed solution is derived by a perturbation approach once the characteristic equation has been expanded. A comparison between computed and exact values shows that the approximate solution is quite good for a wide range of conductivity and permeability values of the external medium.

A target signature for distinguishing perfect conductors from anisotropic media of finite conductivity

We exhibit a target signature obtainable from the electromagnetic far field pattern at fixed frequency that allows one to distinguish a perfect conductor from an anisotropic medium of finite conductivity.

Effects of toroidal HVDC ground electrode on earth‐return circuits

AbstractThis paper presents a method of evaluation of currents and potentials, excited by conductive effects of high‐voltage direct‐current (HVDC) transmission system, along two parallel earth‐return circuits such as pipelines and cables buried in the vicinity of a toroidal ground electrode. It is assumed that the system considered is linear and that the earth is an isotropic, homogeneous medium of finite conductivity. Conductive coupling between earth‐return circuits is taken into account, whereas the reaction of the conductors' currents on the electrode current is disregarded. The transmission line model of the conductor with earth‐return, a segmental linear approximation of the curve of the primary earth potential distribution along the conductor and the concept of superposition have been used in the method. It should be pointed out, that the method does not require the time consuming numerical integration. The technical applications of the method are illustrated by examples.

Integral Equations for Kinematic Dynamo Models

A new technique for the treatment of the kinematic dynamo problem is presented. The method is applicable when the dynamo is surrounded by a medium of finite conductivity and is based on a reformulation of the induction equation and boundary conditions at infinity into an integral equation.

Two-wave propagation and interaction for weakly nonlinear waves in a dissipative medium

An asymptotic approach is presented to study the propagation of two wave modes in a dissipative medium before their separation, as predicted by the theory based on the Burgers equation. This approach involves introducing a second-order nonlinear evolution equation of a special kind, which can be considered as a second-order Burgers equation. Some analytical solutions for this equation are found and discussed. An application of the general theory to MHD waves in a medium of finite conductivity is presented.

Propagation of nonlinear magnetoacoustic waves in a compressible medium of finite electrical conductivity

We study the one-dimensional propagation of weakly nonlinear waves in a compressible medium of finite electrical conductivity subjected to the action of a magnetic field. We obtain evolution equations that describe the wave processes under small and finite magnetic Reynolds numbers. It is shown that in a medium of finite conductivity the evolution of perturbations in a fluid is described by the modified Burger's equation. We find the stationary and automodel solution of this equation and use them as the basis for analyzing the influence of effects of electrical conductivity on the structure of weak shock waves.

Wave absorption at the Alfv�n resonance in a medium of finite conductivity

The paper considers wave transformation in the vicinity of the Alfven resonance in a finite conductivity medium with a magnetic field, the inclination angle of which is close to the critical.

The analytical solution of a growing steady-state mode III crack in an elastic perfectly plastic solid through an electrical analogy

An approximate analytical solution is found of a quasi-static growing steady-state mode III crack in an elastic perfectly plastic solid. The analysis makes use of a close analogy between the mode III crack problem and the problem of the thin electrical conducting plate that is embedded in a medium of finite conductivity through which electrical current flows. Plastic strain is calculated from the motion of nonredundant infinitesimal screw dislocations. Screw dislocations are Eshelby’s analogue of lines of electrical charge. Calculation of the dislocation crack tip shielding can be used to check the analysis. The plastic zone is a combined Dean & Hutchinson (DH) type unfocused fan plastic zone and a Chitaley & McClintock (CM) type focused fan plastic zone. The asymptotic solution at the crack tip is the CM one. The plastic zone found differs significantly in size and shape from the DH and the CM plastic zones. Novel features in the analysis are the use of a (dislocation density required) stress gradient boundary condition and the introduction of a shifting centre cylindrical coordinate system.

Resonant absorption of internal gravity waves in stellar atmospheres

An equation describing wave propagation in an incompressible medium of finite conductivity with a uniform tilted magnetic field has been derived. It is shown that magneto-gravity waves are absorbed in the vicinity of the cusp resonant level if the angle of inclination of the magnetic field is smaller than the critical and are transformed into nondamping Alfvenp-waves if the angle of inclination of the magnetic field is larger than the critical. An evaluation of the critical angle is given on the basis of simple physics.

Electromagnetic induction in an irregular layer overlying the earth. The 2nd paper A semi-infinite medium of finite conductivity having an undulatory surface.

Electromagnetic induction by a uniform magnetic field in a semi-infinite medium of finite conductivity having a sinusoidal undulation at the surface is studied. The source field is assumed to be parallel to the mean surface. The apparent resistivity (ρa) vs. period of variation (T) relation is obtained at various points over the undulating surface by means of conventional magneto-telluric technique. The phase vs. T and the transfer function vs. T relations are also obtained from the electric and magnetic fields studied in this paper.It turns out that the ρa-T relation is little affected by the surface undulation. The order of magnitude of ρa value at various points over the surface does not vary although ρa for a longer period variation takes on a relatively lower value at a depressed portion of the undulatory surface. On the other hand, the transfer function vs. T relation differs from observation point to observation point depending upon the position of observation point on the undulatory topography.

Propagation Constant Below Cutoff Frequency in a Circular Waveguide with Conducting Medium

Exact and approximate propagation characteristics of normal modes in the cutoff region of a circular waveguide surrounded by a medium of finite conductivity are discussed. An exact solution is obtained by numerical analysis, and an approximate one is derived by expanding the characteristic equation considering the finite conductivity of the cylinder wall. The computed values are compared with experimental ones. It is shown that the attenuation of TM/sub 01/ mode at frequencies that are much lower than the cutoff frequency is constant, i.e., independent of frequency and the material constants of the external medium, and this mode is the most suitable one for realizing a precision circular piston attenuator.

Electromagnetic radiation from line sources embedded in a uniaxial dielectric or plasma half-space backed by a medium of finite conductivity

This paper treats the problem of electromagnetic radiation from the electric and magnetic line sources embedded in a uniaxially anisotropic dielectric or plasma half-space backed by a finitely conducting medium. The anisotropy of the uniaxial medium is taken along the x direction and the line source is aligned parallel with the z axis. For the envisaged geometry, E and H modes are independently excited by a magnetic and an electric line source, respectively. Expressions for the far-zone radiation field and the radiation pattern are obtained via the saddle-point technique of integration. It is noted that the radiation from an electric line source remains unaffected by the anisotropy of the medium and possesses only a radial component of the Poynting vector. In contrast, the radiation from a magnetic line source not only depends on the anisotropy of the medium but has, in addition to the radial component, a circumferential component of the Poynting vector indicating deviation of the resultant energy flow from the radial direction. Numerical results for the radiation pattern and also for the angle of deviation of the power flow from the radial direction, for the magnetic line source, are presented for a wide range of parameters characterizing the anisotropy of the uniaxial medium, the location of the line source, electron-plasma density, and the conductivity of the half-space backing the uniaxial medium. It is revealed that in the case of a uniaxial plasma or dielectric backed by a perfect conductor, the radiation has a finite strength of unity both in directions ϑ=0 and ϑ=π, in contrast to the case of a medium backed by a finitely conducting medium.

Reflection and refraction of an obliquely incident plane electromagnetic wave interacting with a moving magnetized plasma slab baked by a medium of finite conductivity

The interaction of an electromagnetic wave incident from vacuum (or dielectric) at a moving magnetoplasma slab backed by a finitely conducting medium is studied. Expressions for the power reflection and transmission coefficients and the phase shifts in the reflected and the transmitted waves are obtained both for incident E and H waves. It is found that the power reflection and transmission coefficients depend on the direction of the slab motion even for normal incidence, as against the cases of isotropic plasma slab or a magnetoplasma slab surrounded by media characterized by equal values for the wave impedance [√(µ/ ∈)]. In addition, for a magnetized plasma slab sandwiched between two dissimilar media, the direction of the static magnetic field also influences the reflection and the transmission coefficients; at normal incidence, the effect of the field reversal is the same as that produced by reversing the direction of the slab motion. Numerical results on the phase function referring to an incident H ...

Wake field of a charged particle in a conducting medium

A closed form solution for the electromagnetic field of a charged particle passing through a medium of finite conductivity σ is presented. The wake field of the particle extends over a region of a characteristic length 1/μ0σv, and is confined behind a plane which contains the particle. The electric lines of force reverse themselves, indicating current neutralization by the changing magnetic field. It is noted that the induced current around the charge has no dc component.

Mechanism of Inclusion Damage in Laser Glass

The mechanism of inclusion damage in laser glass is associated with the temperature rise of particles, or surface regions of particles, relative to the surrounding glass. The particles of greatest concern are metallic, although at very high-power levels ceramic inclusions containing large concentrations of highly absorbing ions can likewise result in failure. Solutions to the heat-flow problems of a perfectly conducting sphere in a medium of finite conductivity and of the infinite composite solid indicate that temperatures of metal particles subject to a 20-J/cm−2, 30-nsec laser pulse can exceed 10 000°K for a range of particle sizes. These high temperatures produce stresses in the glass adjacent to the particles which can exceed the theoretical strength of the glass, and result in failure. The effects on the breakdown condition of flux level and pulse time, as well as the size, shape, thermal expansivity, and spectral emissivity of the particle, and the heat capacity and thermal conductivity of particle and glass are specified. Observations of damage morphologies are reported and related to the results of the calculations. A fatigue phenomenon is anticipated under certain conditions, and the phenomenon of phase separation is not expected to affect significantly the process of inclusion damage. Likely sources of metallic inclusion particles in laser glasses are considered, and melting conditions most suitable for their avoidance are discussed.

On the motion of a plane piston in a medium of finite conductivity under the influence of an electromagnetic field

On the motion of a plane piston in a medium of finite conductivity under the influence of an electromagnetic field