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We propose a novel method to compute in an exact manner the left-hand cut discontinuity of the electron-Atom partial wave scattering amplitude in the complex energy plane within the static stage approximation. Zero energy dispersion relations for electron-Hydrogen scattering are computed numerically for illustration.
The theory of surface gravity waves scattering at vortex flows in the ocean is developed in this paper. A scattering amplitude is found in the Born approximation as a function of Vorticity that appears very convenient for investigation of scattering at simple localized flows.
Effect of the ring current ions in the real part of electromagnetic ion Cyclotron wave dispersion relation is studied on global scale. Recent Cluster observations by Engebretson et al. showed that although the temperature anisotropy of is energetic (> 10 keV) ring current protons was high during the entire 22 November 2003 perigee pass, electromagnetic ion cyclotron waves were observed only in conjunction with intensification of the ion fluxes below 1 keV by over an order of magnitude. To study the effect of the ring current ions on the wave dispersive properties and the corresponding global wave redistribution, we use a self-consistent model of interacting ring current and electromagnetic ion cyclotron waves, and simulate the May 1998 storm. The main findings of our simulation can be summarized as follows: First, the plasma density enhancement in the night MLT sector during the main and recovery storm phases is mostly caused by injection of suprathermal plasma sheet H + (approximately < 1 keV), which dominate the thermal plasma density. Second, during the recovery storm phases, the ring current modification of the wave dispersion relation leads to a qualitative change of the wave patterns in the postmidnight-dawn sector for L > 4.75. This "new" wave activity is well organized by outward edges of dense suprathermal ring current spots, and the waves are not observed if the ring current ions are not included in the real part of dispersion relation. Third, the most intense wave-induced ring current precipitation is located in the night MLT sector and caused by modification of the wave dispersion relation. The strongest precipitating fluxes of about 8 X 10(exp 6)/ (cm(exp 2) - s X st) are found near L=5.75, MLT=2 during the early recovery phase on 4 May. Finally, the nightside precipitation is more intense than the dayside fluxes, even if there are less intense waves, because the convection field moves ring current ions into the loss cone on the nightside, but drives them out of the loss cone on the dayside. So convection and wave scattering reinforce each other in the nightside, but interfere in the dayside sector.
A tissue simulating gel and a method for preparing the tissue simulating gel are disclosed. The tissue simulating gel is prepared by a process using water, gelatin, ethylene glycol, and a cross-linking agent. In order to closely approximate the characteristics of the type of tissue being simulated, other material has been added to change the electrical, sound conducting, and wave scattering properties of the tissue simulating gel. The result of the entire process is a formulation that will not melt at the elevated temperatures involved in hyperthermia medical research. Furthermore, the tissue simulating gel will not support mold or bacterial growth, is of a sufficient mechanical strength to maintain a desired shape without a supporting shell, and is non-hardening and non-drying. Substances have been injected into the tissue simulating gel prior to the setting-up thereof just as they could be injected into actual tissue, and the tissue simulating gel is translucent so as to permit visual inspection of its interior. A polyurethane spray often used for coating circuit boards can be applied to the surface of the tissue simulating gel to give a texture similar to human skin, making the tissue simulating gel easier to handle and contributing to its longevity.
Free-free transition is studied for electron-Hydrogen atom system in ground state at very low incident energies in presence of an external homogeneous, monochromatic and linearly polarized laser field. The incident electron is considered to be dressed by the laser in a non perturbative manner by choosing the Volkov solutions in both the channels. The space part of the scattering wave function for the electron is solved numerically by taking into account the effect of electron exchange, short range as well as of the long range interactions. Laser assisted differential as well as elastic total cross sections are calculated for single photon absorption/emission in the soft photon limit, the laser intensity being much less than the atomic field intensity. A strong suppression is noted in the laser assisted cross sections as compared to the field free situations. Significant difference is noted in the singlet and the triplet cross sections.
This work addresses the problem of excitation of a parallel plate waveguide by an array of rectangular waveguides that arises in applications such as the continuous transverse stub (CTS) antenna and dual-polarized parabolic cylindrical reflector antennas excited by a scanning line source. In order to design the junction region between the parallel plate waveguide and the linear array of rectangular waveguides, waveguide sizes have to be chosen so that the input match is adequate for the range of scan angles for both polarizations. Electromagnetic wave scattered by the junction of a parallel plate waveguide by an array of rectangular waveguides is analyzed by formulating coupled integral equations for the aperture electric field at the junction. The integral equations are solved by the method of moments. In order to make the computational process efficient and accurate, the method of weighted averaging was used to evaluate rapidly oscillating integrals encountered in the moment matrix. In addition, the real axis spectral integral is evaluated in a deformed contour for speed and accuracy. The MoM results for a large finite array have been validated by comparing its reflection coefficients with corresponding results for an infinite array generated by the commercial finite element code, HFSS. Once the aperture electric field is determined by MoM, the input reflection coefficients at each waveguide port, and coupling for each polarization over the range of useful scan angles, are easily obtained. Results for the input impedance and coupling characteristics for both the vertical and horizontal polarizations are presented over a range of scan angles. It is shown that the scan range is limited to about 35 for both polarizations and therefore the optimum waveguide is a square of size equal to about 0.62 free space wavelength.
With large separations (10-24 deg heliocentric), it has proven possible to cleanly separate the horizontal and vertical components of supergranular flow with time-distance helioseismology. These measurements require very broad filters in the k-$\omega$ power spectrum as apparently supergranulation scatters waves over a large area of the power spectrum. By picking locations of supergranulation as peaks in the horizontal divergence signal derived from f-mode waves, it is possible to simultaneously obtain average properties of supergranules and a high signal/noise ratio by averaging over many cells. By comparing ray-theory forward modeling with HMI measurements, an average supergranule model with a peak upflow of 240 m/s at cell center at a depth of 2.3 Mm and a peak horizontal outflow of 700 m/s at a depth of 1.6 Mm. This upflow is a factor of 20 larger than the measured photospheric upflow. These results may not be consistent with earlier measurements using much shorter separations (<5 deg heliocentric). With a 30 Mm horizontal extent and a few Mm in depth, the cells might be characterized as thick pancakes.
The free-free transition is studied for an electron-hydrogen in the ground state at low incident energies in the presence of an external homogenous, monochromatic, and linearly polarized laser-field inside a hot dense plasma.The effect of plasma screening is considered in the Debye-Huckel approximation. The calculations are performed in the soft photon limit, assuming that the plasma frequency is much higher than the laser frequency. The incident electron is considered to be dressed by the laser field in a nonperturbative manner by choosing the Volkov solutions in both the initial and final channels. The space part of the scattering wave function for the electron is solved numerically by taking into account the electron exchange. The laser-assisted differential and total cross sections are calculated for single-photon absorption /emission and no photon exchange in the soft photon limit, the laser intensity being much less than the atomic field intensity. The calculations have been carried out for various values of Debye parameter, ranging from 0.005 to 0.12. A strong suppression is noted in the laser-assisted cross sections as compared to the field-free situation. A significant difference is noted for the singlet and triplet cross sections. The suppression is much more in the triplet states.
The free-free transition is studied for an electron-hydrogen atom in ground state when a low-energy electron (external) is injected into hydrogenic plasma in the presence of an external homogenous, monochromatic, and linearly polarized laser field. The effect of plasma screening is considered in the Debye-Huckel approximation. The calculations are performed in the soft photon limit. The incident electron is considered to be dressed by the laser field in a nonperturbative manner by choosing the Volkov solutions in both the initial and final channels. The space part of the scattering wave function for the electron is solved numerically by taking into account the electron exchange. The laser-assisted differential and total cross sections are calculated for single-photon absorption or emission and no-photon exchange in the soft photon limit, the laser intensity being much less than the atomic field intensity. The calculations have been carried out for various values of Debye parameter, ranging from 0.005 to 0.12. A strong suppression is noted in the laser-assisted cross sections as compared to the field-free situation. A significant difference is noted for the singlet and triplet cross sections. The suppression is much more in the triplet states.
A non-intrusive sensor for in-situ measurement of recession rate of heat shield ablatives. An ultrasonic wave source is carried in the housing. A microphone is also carried in the housing, for collecting the reflected ultrasonic waves from an interface surface of the ablative material. A time phasing control circuit is also included for time-phasing the ultrasonic wave source so that the waves reflected from the interface surface of the ablative material focus on the microphone, to maximize the acoustic pressure detected by the microphone and to mitigate acoustic velocity variation effects through the material through a de-coupling process that involves a software algorithm. A software circuit for computing the location off of which the ultrasonic waves scattered to focus back at the microphone is also included, so that the recession rate of the heat shield ablative may be monitored in real-time through the scan-focus approach.
Approximation method for determining scattering properties of electromagnetic waves by circular dielectric-coated conducting cylinders with arbitrary cross section
The extended method of equivalent inclusion developed is applied to study the specific wave problems of the transmission of elastic waves in an infinite medium containing a layer of inhomogeneity, and of the scattering of elastic waves in an infinite medium containing a perfect spherical inhomogeneity. The eigenstrains are expanded as a geometric series and the method of integration for the inhomogeneous Helmholtz operator given by Fu and Mura is adopted. The results obtained by using a limited number of terms in the eigenstrain expansion are compared with exact solutions for the layer problem and for a perfect sphere. Two parameters are singled out for this comparison: the ratio of elastic moduli, and the ratio of the mass densities. General trends for three different situations are shown.
The extended method of equivalent inclusions is applied to study the specific wave problems: (1) the transmission of elastic waves in an infinite medium containing a layer of inhomogeneity, and (2) the scattering of elastic waves in an infinite medium containing a perfect spherical inhomogeneity. Eigenstrains are expanded as a geometric series and a method of integration based on the inhomogeneous Helmholtz operator is adopted. This study compares results, obtained by using limited number of terms in the eigenstrain expansion, with exact solutions for the layer problem and that for a perfect sphere.
In the present investigation of radiation and scattering by objects when the wavelengths are much smaller than the characteristic dimensions of the radiator or scatterer, the boundary-element method is used to obtain computational accuracy and efficiency. The approach employed for wavelengths less than 5 percent of object characteristic dimensions involves cubic elements, approximate polynomial and asymptotic evaluations of the fundamental solution, and a tailoring of the order of the Gaussian quadrature according to the local demands dictated by the distance between sending and receiving points. The method addresses the propagation of low-frequency sound over large terrain features.
The design, development, and use of a focused-beam radar to measure the electromagnetic bias introduced by the scattering of radar waves by a roughened water surface are discussed. The bias measurements were made over wide ranges of environmental conditions in a wavetank laboratory. Wave-elevation data were provided by standard laboratory capacitance probes. Backscattered radar power measurements coincident in time and space with the elevation data were produced by the radar. The two data sets are histogrammed to produce probability density functions for elevation and radar reflectivity, from which the electromagnetic bias is computed. The experimental results demonstrate that the electromagnetic bias is quite variable over the wide range of environmental conditions that can be produced in the laboratory. The data suggest that the bias is dependent upon the local wind field and on the amplitude and frequency of any background wave field that is present.
A hybrid numerical method combining finite elements and the boundary integral representation is used to investigate the transient scattering of ultrasonic waves by a crack in a plate. The incident wave models the guided waves generated by a steel ball impact on the plate. Two surface-breaking cracks and one subsurface crack are studied here. The results show that the location and depth of cracks have measurable effects on the surface responses in time and frequency domains. Also, the scattered fields have distinct differences in the three cases.
Using amplitude data of radio beacons at 40, 140, and 360 MHz from ATS 6 (phase II), an attempt has been made to study scattering of these waves in the equatorial ionosphere. A comparison of observed scintillation index S sub 4 with the theoretical results of the multiple scattering approach and variation of autocorrelation time with frequency indicates that this theory explains the results to a large extent. A comparison of power spectra of amplitude records with the ionograms of a nearby equatorial station has led to the following conclusions: the change from a weak scattering regime to a strong scattering regime is gradual and occurs because of the gradual decrease in the scale size of the irregularities (i.e., broadening of the spectra) and the gradual increase in the thickness of the irregular region.
Quantum state coherent frequency conversion processes—such as Bragg-scattering four-wave mixing (BSFWM)—hold promise as a flexible technique for networking heterogeneous and distant quantum systems. In this Letter, we demonstrate BSFWM within an extended (1.2-m) low-confinement silicon nitride waveguide and show that this system has the potential for near-unity frequency conversion in visible and near-visible wavelength ranges. Using sensitive classical heterodyne laser spectroscopy at low optical powers, we characterize the Kerr coefficient (∼1.55 W −1 m −1 ) and linear propagation loss (∼0.0175 dB/cm) of this non-resonant waveguide system, revealing a record-high nonlinear figure of merit (NFM = γ / α ≈ 3.85 W −1 ) for BSFWM of near-visible light in non-resonant silicon nitride waveguides. We predict how, at high yet achievable on-chip optical powers, this NFM would yield a comparatively large frequency conversion efficiency, opening the door to near-unity flexible frequency conversion without cavity enhancement and resulting bandwidth constraints.