Total Scattering Cross Section Research Articles

An electron-impact cross section data set (10 eV–1 keV) of DNA constituents based on consistent experimental data: A requisite for Monte Carlo simulations

This work provides the first cross section data set of DNA constituents for an impact of electrons in the energy range between about 10eV and 1keV on a DNA target. The data set is designed for an implementation in Monte Carlo simulations and consists of model functions, taking into account elastic scattering, ionization and excitation interactions with the DNA constituents tetrahydrofuran, trimethylphosphate, pyrimidine and purine. It was developed on the basis of experimentally determined absolute differential and total scattering cross sections in accordance with the available literature data. The data set will be available in the Geant4-DNA toolkit to allow secondary electron transport in a DNA-like medium down to the ionization threshold.

Collisional decoherence of polar molecules

The quantum state of motion of a large and rotating polar molecule can lose coherence through the collisions with gas atoms. We show how the associated quantum master equation for the center of mass can be expressed in terms of the orientationally averaged differential and total scattering cross sections, for which we provide approximate analytic expressions. The master equation is then utilized to quantify collisional decoherence in a interference experiment with polar molecules.

Elastic and total scattering cross section for halogen substituted fluoromethane molecules

The electron scattering elastic and total scattering cross section for CF3X and CF2X2 (where X=H, Cl, Br, and I) molecules are reported in this article for incident energies from 30 to 5000eV. These cross sections are relevant to various fields of applied interest, especially to plasma modelling. The calculations are performed using the quantum mechanical approach, where the potential representing the interaction dynamics between the incoming electron and the scattering centre of the molecule is formulated using spherical complex optical potential. This potential is then incorporated to Schrödinger equation, which is solved through partial wave analysis. The results obtained in the present calculation are compared with previously available experimental and theoretical data.

Interactions and low-energy collisions between an alkali ion and an alkali atom of a different nucleus

We study theoretically interaction potentials and low-energy collisions between different alkali atoms and alkali ions. Specifically, we consider systems such as X + , where X( is either Li(Cs+) or Cs(Li+), Na(Cs+) or Cs(Na+) and Li(Rb+) or Rb(Li+). We calculate the molecular potentials of the ground and first two excited states of these three systems using a pseudopotential method and compare our results with those obtained by others. We derive ground-state scattering wave functions and analyze the cold collisional properties of these systems for a wide range of energies. We find that, in order to get convergent results for the total scattering cross sections for energies of the order 1 K, one needs to take into account at least 60 partial waves. The low-energy scattering properties calculated in this paper may serve as a precursor for experimental exploration of quantum collisions between an alkali atom and an alkali ion of a different nucleus.

B-Scan in a Reverberation Chamber

In this paper, the B-scan technique is applied to a reverberation chamber (RC) for the first time to characterize the time-domain behavior of the chamber. Based on B-scan measurement results, three things are studied in this paper. 1) The statistical behavior of the fields in the time domain is investigated, and it is found that the received power of the impulse response follows chi-square distribution with one degree of freedom. 2) The stirrer efficiency is quantified based on the equivalent total scattering cross section (TSCS) of stirrers, and this definition is not sensitive to the antenna position and load in the RC. It is shown that the stirrer efficiency defined in this paper provides, for the first time, a quantitative way to evaluate the stirrer design and the chamber performance. 3) A time-gating technique is proposed which provides an alternative method to eliminate the early time response and obtain the chamber transfer function of the RC accurately. This could be potentially used to increase the stirrer efficiency without changing the stirrers physically. It is demonstrated that the B-scan technique is a very useful approach for the study and evaluation of an RC.

The Limit of the Total Scattering Cross Section of Electrically Large Stirrers in a Reverberation Chamber

The total scattering cross section (TSCS) has been proven to be an effective quantity to characterize the performance of stirrers in a reverberation chamber (RC). It is shown in this letter that the maximum TSCS is a quarter of the stirring surface area, and it is equal to the absorption cross section (ACS) of the same area with perfect radio absorbers. The mathematical proof is presented and measurements are performed to validate this limit. It is also shown that the TSCS and ACS are statistical dual quantities; related dual quantities are also given. The TSCS can be used to characterize how well a stirrer is designed or how close an RC is to a perfect RC.

Positronium collisions with rare-gas atoms

We calculate elastic scattering of positronium (Ps) by the Xe atom using the recently developed pseudopotential method (Fabrikant and Gribakin 2014 Phys. Rev. A 90 052717) and review general features of Ps scattering from heavier rare-gas atoms: Ar, Kr and Xe. The total scattering cross section is dominated by two contributions: elastic scattering and Ps ionization (break-up). To calculate the Ps ionization cross sections we use the binary-encounter method for Ps collisions with an atomic target. Our results for the ionization cross section agree well with previous calculations carried out in the impulse approximation. Our total Ps–Xe cross section, when plotted as a function of the projectile velocity, exhibits similarity with the electron-Xe cross section for the collision velocities higher than 0.8 a.u., and agrees very well with the measurements at Ps velocities above 0.5 a.u.

New concept of the discrete sources method in electromagnetic scattering problems

We propose and implement a new concept of the discrete sources method; by applying this concept, one can investigate dielectric scatterers with large wave numbers. It is shown that the total scattering cross section can be determined analytically by using the amplitudes of discrete sources. The numerical results are presented; they demonstrate a considerable gain obtained by using the new concept in comparison with the conventional concept.

Evaluation of a graphene-covered dielectric microtube as a refractive-index sensor in the terahertz range

We studied the scattering and absorption of the H-polarized plane wave by a graphene-covered circular dielectric cylinder and a hollow tube with a graphene cover on the outer boundary in the terahertz range. The analytical solution of the wave-scattering problem was based on the Maxwell equations and the use of the separation of variables in the polar coordinates. We assumed the resistive boundary conditions on the zero-thickness graphene cover where the graphene electron conductivity was included as a parameter and was determined from the Kubo formalism. The computed spectra of the total scattering cross section and the absorption cross section displayed several types of resonances: the localized-surface-plasmon (LSP) resonances of the graphene cover and the resonances on the whispering-gallery modes of a dielectric cylinder or dielectric tube. The computed data can be useful for the design of graphene-based sensors of the changes in the refractive index of the host medium. For this purpose, the sensitivities and the figure-of-merit values of the LSP resonances were computed; their comparison demonstrated advantages of a thin-tube configuration.

Invisibility of a finite dielectric cylinder under Fano resonance conditions

The effect of invisibility of a finite homogeneous dielectric cylinder due to a substantial decrease in the scattering of electromagnetic waves in specific spectral ranges has been investigated theoretically. A regime of invisibility of the cylinder in an air space without additional cloaking devices has been considered. The effect is based on the resonance suppression of scattered waves, which makes the cylinder invisible to an observer located at any point of the space. The invisibility condition is determined by the Fano resonance between the re-emitted Mie modes and the nonresonant scattering by the cylinder. The dependence of the spectra of the total scattering cross section on the ratio between the length and radius of the cylinder has been analyzed in detail. It has been shown that the transition from the model infinite cylinder to the cylinder of finite length is accompanied by the appearance of new resonances and additional scattering, which, however, does not disturb the lowest frequency region of invisibility at specific length-to-radius ratios of the cylinder.

Dispersion study on scattering cross section of metamaterial cloak due to various cloaking parameters

Electromagnetic cloak is a device that has the potential to conceal an object by minimizing its total scattering cross section over a desired frequency. But due to causality constraints the material properties become dispersive which reduces cloaking bandwidth. In this work, the emphasis is on the study of various cloaking parameters like dispersive material properties, cloak dimensions, material losses which influence the real implementation of cloak. This work rigorously investigated the scattering performance at the design frequency and cloaking bandwidth for aforementioned parameters on the cloak design by utilizing a widely accepted term called total scattering cross section.

Scattering Cross Sections of Impedance-Matched Bodies

Electromagnetic scattering from bodies with the surface impedance equal to the wave impedance of the surrounding medium shows a number of extremal features, including vanishing axial backscattering cross section in the case of bodies of revolution. This paper examines various scattering cross sections (mono- and bistatic, total scattering, absorption, and extinction) of electrically large arbitrarily shaped impedance-matched bodies, and it is shown that the backscattering cross section of arbitrarily shaped convex impedance-matched bodies vanishes in the optical limit. Furthermore, it is conjectured that considered as functions of the surface impedance, the mean total scattering cross section has a global minimum and the mean absorption cross section a global maximum when the body is illuminated by plane waves with random incidence direction and polarization.

Bandwidth enhancement of transformation optics-based cloak with reduced parameters

In this paper, dispersive cloak design with broad bandwidth and minimal scattering cross section is proposed by appropriately selecting a radial permeability for each shell in a discretized reduced cloak. The dispersive medium is constructed by artificially varying the inner radius of the cloak with frequency, and this variation results into unique material properties at every frequency. The variation of inner radius of the cloak with frequency is artificial since the actual physical dimension of inner radius remains invariant. The relation between bandwidth and geometrical parameters of cloak is obtained by ensuring that transformation media must satisfy the condition that group velocity must remain less than the speed of light along every direction for a finite frequency range. The proposed cloak provides $$8.9\,\%$$ bandwidth with respect to the center frequency for $$50\,\%$$ reduction in total scattering cross section, and at the design frequency, the minimum scattering cross section obtained is $$0.266$$ . The proposed dispersive cloak design is verified by numerical full-wave simulations results which also confirm good cloaking performance.

A flocculi model for the acoustic scattering from flocs

The objective of this paper is to suggest a methodology for the practical inversion of acoustic backscatter to obtain suspended mass concentration of marine flocs. Optical data collected using a LISST-100 at the same time as acoustic backscatter (ABS) measurements were made during a series of controlled flocculation laboratory experiments using kaolin (MacDonald et al., 2013) showed a consistent peak in the particle size distribution at around 10–20µm in 50 of the 75 experimental runs. This peak corresponds to the size of the strongest and most tightly bound of component floc structures referred to as ‘flocculi’ (Van Leussen, 1994; Lee et al., 2012). Log-normal distributions fitted to these peaks accounted for between 30.1% and 90.7% of the total volume of particles (median 50.4%). The equivalent mean floc sizes identified from the FLOCView camera system were between 38 and 92µm. It was hypothesised that the acoustic backscatter from the flocculated kaolin was occurring from the flocculi (and not the flocs per se) and that the flocculi could be treated as elastic spheres with density and acoustic wave propagation speeds equal to bulk kaolin. The ABS signals were inverted, using the methodology suggested by Lee and Hanes (1995), using the form function and total scattering cross section defined by Moate and Thorne (2009) for particles with a broad size distribution, to determine the particle size. Excluding the unflocculated runs the particle diameters were 15.5±4.9µm; the particle size tended to increase with concentration and with the ‘level’ of flocculation. The viscous attenuation, which cannot be neglected for particles of this size, was also estimated from the ABS data and was found to be consistent with Urick's (1948) model. It is concluded that the flocculi model of acoustic backscatter is supported by laboratory measurements on a simple suspension of kaolin, and may offer a practical way forward for the interpretation of marine field data.

Comparison of Refractive-Index Sensitivities of Optical-Mode Resonances on a Finite Comb-Like Grating of Silver Nanostrips

We investigate the interplay of several different types of resonances in the scattering of light by finite comb-like nanogratings made of silver strips, in the H- and E-polarization cases. The resonances studied correspond to the localized surface plasmon modes, the periodicity-induced grating mode, and the cavity modes. They show up as Fano shapes in the total scattering cross sections and absorption cross sections. We find that the grating-mode and the cavity-mode resonances have higher values of both bulk refractive-index sensitivity and figure-of-merit than the localized-surface-plasmon resonances, in the visible band.

Temperature controlled infrared broadband cloaking with the bilayer coatings of semiconductor and superconductor

The infrared broadband tunable cloaking have been proposed and investigated with the bilayer coating materials of semiconductor (n-Ge) and high-temperature superconductor (YBa2Cu3O7), whose cloaking frequency can be controlled by external temperature. The analytical solution is derived based on the scattering cancellation cloaking technique from the Mie scattering theory, and the full-wave numerical simulation is performed by the finite element method. The calculated and simulated results have demonstrated that this invisibility cloak may reduce the total scattering cross section of the composite structure of 90% over a broad frequency band of nearly 20THz, and the infrared cloaking frequency can be tuned by the external temperature. It can provide a feasible way to design a broadband tunable cloak.

Neutron-Nucleus Total Elastic Scattering

Using an exact and complete Yukawa Potential Energy (YPE), the neutron-triton and neutron-helium elastic total scattering cross section is estimated and extrapolated to zero energy. The estimated value agrees pretty well with the experimental value and the procedure can be extended to any neutron-nucleus total scattering. The results are extended to the case of 4He, 7Li, 9Be and 27Al nuclei also.

Partial-wave analysis of particular peaks in total scattering cross sections caused by a single partial wave

Certain broad low-energy peaks in the total cross sections relevant for electron-atom scattering are studied and found to be caused by a single partial wave. Such peaks are associated here with complex orbital angular momentum (Regge) pole trajectories. At the peak energies these S-matrix poles are in some neighborhood of an integer value and at the same time near its maximum real part value as a function of energy. Such peaks are found to have no time delays. Results are presented for the Dirac equation using three rational function Thomas-Fermi potential models, all with the same behavior at large and small radial distances.

Design of a two-dimensional metamaterial cloak with minimum scattering using a quadratic transformation function

The presence of extreme material properties and undesired scattering make practical implementation of transformation optics based cloaks an extremely challenging issue. To overcome these problems, a simplified quadratic cloak has been proposed which provides finite material properties at the inner radius of the cloak and impedance match with the free space at the outer radius of the cloak simultaneously. The simultaneous occurrence of finite material properties and impedance match with the free space at the respective boundaries reduces the scattering cross section significantly. The material properties of the proposed simplified quadratic cloak can be realized with two dimensional (2D) metamaterials. The performance of the proposed cloak is examined by plotting the normalized total scattering cross section (SCSt,norm), and the scattering patterns in azimuthal plane. The proposed simplified quadratic cloak shows 10 dB reduction of the scattered field in both the forward and backward directions with respect to the perfect electric conductor (PEC) cylinder.

Bounds on the average of total scattering cross section of random cylinder

Total scattering cross section (σT) of a PEC cylindrical scatterer is a function of it's scattering amplitude and is closely related to scatterer's cross section. It is difficult to determine σT analytically for arbitrary cross sections of scatterer, especially for random cross sections. Defining some bounds on the value of σT is therefore very helpful in its estimation. In this paper, σT of canonical shaped objects is used to define bounds on σT of random cylinder. The geometrical parameters of canonical scatterers are obtained from the geometric parameters of the random cylinder. A formulation is also developed to approximate the value of σT from its bounding values. This work therefore, helps to predict the σT of a random cylinder from its geometrical parameters, without solving an electromagnetic boundary value problem.