Source-free Medium Research Articles

Near-Field Behaviors of Internal Energy Flows of Free-Space Electromagnetic Waves Induced by Electric Point Dipoles

Both orbital and spin energy fluxes constitute the internal flows decomposed from a Poynting vector. For generic electromagnetic waves propagating through source-free media, these energy fluxes are quadratic in field variables so that their properties are not easily predictable. Notwithstanding, their near-field behaviors play important roles in nanoscale photonics. For time-oscillatory fields, we found two hitherto-overlooked distinctions between the two internal flows. The first is an unequal level between them because the vorticity of an orbital energy flux plays a role comparable to a spin energy flux itself. The second is regarding the electric-magnetic dual symmetry in handling the two internal flows, whence the reactive helicity plays a role as important as the electromagnetic helicity. By helicity conservation, an inter-electric-magnetic transport is possible for the spin angular momentum density, while the electric and magnetic constituents of orbital energy fluxes admit only respective intra-electric and intra-magnetic transports. We have tested the validities of all these claims by exemplarily taking the electromagnetic fields induced by an electric point dipole, either a linear or a circular one. We have thus made new contributions not only in deriving explicit forms of the internal energy flows but also in revealing the magnetic activities hidden under the electromagnetic waves induced by electric point dipoles.

Reduction of Electromagnetic Reflections in 3D Airborne Transient Electromagnetic Modeling: Application of the CFS-PML in Source-Free Media

To solve the problem of electromagnetic reflections caused by the termination of finite-difference time-domain (FDTD) grids, we apply the complex frequency-shifted perfectly matched layer (CFS-PML) to airborne transient electromagnetic (ATEM) modeling in a source-free medium. To implement the CFS-PML, two important aspects are improved. First, our method adopts the source-free Maxwell’s equations as the governing equations and introduces the divergence condition, consequently, the discrete form of Maxwell’s third equation is derived with regard to the CFS-PML form. Second, because our method adopts an inhomogeneous time-step, a recursive formula composed of convolution items based on a nonuniform time-step is proposed. The proposed approach is verified via a calculation of the electromagnetic response using homogeneous half-space models with different conductivities. The results show that the CFS-PML can reduce a 60 dB relative errors in late times. Moreover, this approach is also applied to 3D anomalous models; the results indicate that the proposed method can reduce reflections and substantially improve the identification of anomalous bodies. Consequently, the CFS-PML has good implications for ATEM modeling in a source-free medium.

Transverse Electromagnetic Modes of Menger Sponge

In this article, an analytical solution for the electromagnetic modes of a Menger sponge using field equations of fractional space is presented. In order to realize the electromagnetic modes in non-integer dimension space, the fields inside the Menger sponge are expressed using a fractional parameter 2 ≤ D ≤ 3. The modes are calculated under two conditions of boundaries i.e., PMC and PEC, for D = 3 correspond to ordinary integer dimension space. Generalized solution for lossless and source free medium is studied for non-integer dimension. As anticipated, the dimension of media have effect on electric and magnetic fields. The classical results are recovered when integer dimensional space is considered. The proposed solution is useful for deriving electromagnetic modes of fractal structures.

Hybrid-transport point kinetics for initially-critical multiplying systems

The paper presents an extension of the Hybrid Transport Point Kinetic (HTPK) model to initially-critical multiplying structures, i.e. in a source-free medium with transients starting from the equilibrium between neutron distribution and precursor concentrations. The mathematical model behind the HTPK methodology is derived from the detailed time-dependent balance equations and with reference to the limiting cases (i.e., point model and multi-collision models). Numerical simulations of transient systems demonstrate the interesting features of HTPK, which is shown to sensibly increase the accuracy of classical point kinetics models even at low truncation orders.

Invariant Imbedding and the Radiation Transfer in a Plane-Parallel Inhomogeneous Atmosphere

The invariant imbedding technique is applied to the problems of radiation transfer in a plane-parallel inhomogeneous atmosphere. All the parameters which describe the elementary event of scattering and the distribution of the energy sources are allowed to vary with depth. Mathematically, the considered standard problems of the theory are reduced to initial-value problems which are better adapted to capabilities of the modern high speed computers. The reflectance of an atmosphere is shown to play a prominent role in describing the diffusion process since all the other characteristics of the radiation field are expressed through it. Three transfer problems frequently encountered in astrophysical applications are discussed: the radiation diffusion in the source-free medium, in a medium with arbitrarily distributed energy sources, as well as the problem of finding the statistical mean quantities, characteristics of the multiple scattering in the atmosphere.

Explicit local time-stepping methods for Maxwell’s equations

Explicit local time-stepping methods are derived for time dependent Maxwell equations in conducting and non-conducting media. By using smaller time steps precisely where smaller elements in the mesh are located, these methods overcome the bottleneck caused by local mesh refinement in explicit time integrators. When combined with a finite element discretisation in space with an essentially diagonal mass matrix, the resulting discrete time-marching schemes are fully explicit and thus inherently parallel. In a non-conducting source-free medium they also conserve a discrete energy, which provides a rigorous criterion for stability. Starting from the standard leap-frog scheme, local time-stepping methods of arbitrarily high accuracy are derived for non-conducting media. Numerical experiments with a discontinuous Galerkin discretisation in space validate the theory and illustrate the usefulness of the proposed time integration schemes.

Photosynthetic apparatus in Roseateles depolymerans 61A is transcriptionally induced by carbon limitation.

Production of a photosynthetic apparatus in Roseateles depolymerans 61A, a recently discovered freshwater beta-Proteobacterium showing characteristics of aerobic phototrophic bacteria, was observed when the cells were subjected to a sudden decrease in carbon sources (e.g., when cells grown with 0.1 to 0.4% Casamino Acids were diluted or transferred into medium containing <or=0.04% Casamino Acids). Accumulation of bacteriochlorophyll (BChl) a was observed in the presence of oxygen and was enhanced under semiaerobic conditions (2% oxygen) but was reduced in the presence of light. Similarly to what has been reported regarding some aerobic phototrophic bacteria belonging to the alpha subclass of the Proteobacteria, viability of the cells in the carbon source-free medium was prolonged under aerobic-light (10 W m(-2)) conditions, possibly due to photosynthetic energy conversion, but was not prolonged under aerobic-dark conditions. The puf operon, which encodes most of the apoproteins of light-harvesting and reaction center complexes, was sequenced, and the effect of changes in Casamino Acids concentrations, oxygen, and light on its expression was estimated by the accumulation of its mRNA. The expression of the puf operon was induced by the decrease in carbon sources, similarly to what was observed for the accumulation of BChl a under aerobic and semiaerobic conditions (>or=0.2% O(2)), and was reduced in the presence of light. Transcription of the R. depolymerans puf operon is considered to be controlled by changes in carbon nutrients in addition to oxygen tension and light intensity.

Radiation transfer in a diffuse and specular reflecting slab with Rayleigh scattering

A method of analysis is presented for solving the radiative transfer problem in an absorbing, emitting, inhomogeneous, and anisotropically scattering plane-parallel medium with specular and diffuse reflecting boundaries and internal source (problem 1). Exact relations for the radiation heat flux at the boundaries of problem 1 are obtained in terms of the radiation density and albedos of the corresponding source-free medium with specular reflecting boundaries (problem 2). Two coupled integral equations for the radiation density and the second moment of the radiation intensity for problem 2 with Rayleigh phase functions are obtained. The Galerkin method is used to solve these equations. Albedos of problem 2 are compared with theF n method. Numerical results for radiation heat fluxes at the boundaries of problem 1 are tabulated for different forms of the internal source.

Effect of Green Tea Extract on Growth of Intestinal Bacteria

Growth responses of a variety of human intestinal bacteria to methanol extracts of green tea ( Thea sinensis L.) were investigated in vitro . The extracts moderately enhanced growth of some bifidobacteria strains in tests on carbon source containing media but not carbon source-free media, suggesting that bifidus factor(s) might be involved. It did not stimulate growth of clostridia, bacteroides, eubacteria or Escherichia coli . However, the extract was found to be selectively inhibitory against the growth of some clostridia including C. difficile , C. paraputrificum and C. perfringens ; this effect was not observed with bifidobacteria. eubacteria or E. coli . Keywords: Bifidus factor(s); Growth inhibition; Green tea ( Thea sinensis L.); Intestinal bacteria; Bifidobacterium ; Clostridium .

The energy deposition of slowing down particles in heterogeneous media

Abstract Energy deposition by atomic particles in adjacent semi-infinite, amorphous media is described using the forward form of the Boltzmann transport equation. A transport approximation to the scattering kernel, developed elsewhere, incorporating realistic energy transfer is employed to assess the validity of the commonly used isotropic-scattering and straight-ahead approximations. Results are presented for integral energy deposition rates due to a plane, isotropic and monoenergetic source in one half-space for a range of mass ratios between 0.1 and 5.0. Integral profiles for infinite and semiinfinite media are considered and the influence of reflection for different mass ratios is evaluated. The dissimilar scattering properties of the two media induce a discontinuity at the interface in the energy deposition rate the magnitude of which is sensitive to the source position relative to the interface. A comprehensive evaluation of the total energy deposited in the source free medium is presented for a ran...

Asymptotic developments and scattering theory in terms of a vector combining the electric and magnetic fields

The vector combination <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\overrightarrow{M}=(\frac{\mu}{\epsilon})^{1/4} \overrightarrow{H} + j (\frac {\epsilon}{\mu})^{1/4} \overrightarrow{E}</tex> which was in principle introduced by Bateman and Silberstein in order to shorten Maxwell's equations for homogeneous media, also proves to be useful for the treatment of inhomogeneous media <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\epsilon</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\mu</tex> not depending on the time). The vector <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M\rightarrow</tex> is to be considered together with its conjugated quantity <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M^{x}\rightarrow</tex> obtained by replacing the imaginary unit <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">j</tex> by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-j</tex> . In a source-free medium the Maxwell equations reduce to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">curl \overrightarrow{M} + \frac{j}{c} (\epsilon \mu)^{1/2}\partial \overrightarrow{M}/ \partial^{f} = \frac{1}{4} grad \log \frac{\mu}{epsilon} \wedge \overrightarrow{M}^{x}</tex> and to the equation obtained by taking the conjugated complex value. This relation shows how an interaction between <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M\rightarrow</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M^{x}\rightarrow</tex> is produced only by the inhomogeneity of the medium. The theory of scattering by special volume elements, as well as that of partial reflections against layers with rapidly changing <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\epsilon</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\mu</tex> , can be based on the single relation (1) while fully accounting for the vectorial character of the field, The introduction of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M\rightarrow</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M^{x}\rightarrow</tex> also enables one to put many results of Luneberg-Kline's theory concerning asymptotic developments in a very simple form. As an example we mention the equation: <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">grad S \wedge \overrightarrow{m}_{r} - i_r \mu)^{1/2}m_{r} = c curl \overrightarrow {m_{r-1}} - \frac{c}{\epsilon} grad \log \frac{\mu}{\epsilon} \wedge \overrightarrow {m_{r-1^{x}}}</tex> , which fixes all recurrence relations between the consecutive terms of geometric-optical expansions; these expansions are defined by the asymptotic development <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\overrightarrow{M} =e^{ik^{s}} \Sigma \min{r=0} \max{\infty}(\frac{i}{kc))^{r} \overrightarrow {m_{r}}</tex> , for monochromatic solutions corresponding to some eiconal function <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</tex> .