Discrete optical soliton scattering by local inhomogeneities

The nonlinear wave scattering by local inhomogeneities in discrete optical systems is studied both analytically and numerically. The presented theory describes the reflection and transmission of discrete optical solitons at a point defect. In particular, the derived expressions determine the reflected and transmitted pulses from the incident one. In the range of validity, the analytical results are in excellent agreement with the numerical simulations. It is demonstrated that the point defects in structured optical materials represent effective tool for controlling and manipulation of the nonlinear light pulses.     

Fast beating null strip during the reflection of pulsed Gaussian beams incident at the Rayleigh angle

It is well known that harmonic bounded Gaussian beams undergo a transformation into two bounded beams upon reflection on a solid immersed in a liquid. The effect is known as the Schoch effect and can be found at the Rayleigh angle for thick plates and at the different Lamb angles for thin plates. Here, a study is made on the effect of pulsed Gaussian beams reflected on solids. It is found experimentally that the Rayleigh wave phenomenon still generates two reflected bounded beams, whereas Lamb wave phenomena do not generate this effect. This fact may be explained intuitively by realizing that the Rayleigh phenomenon is a coincidental phenomenon that is generated in situ, whereas the Lamb wave phenomenon is a non-coincidental phenomenon that is generated only after incident sound is influenced by both sides of a thin plate. Another explanation is the fact that Rayleigh waves are not dispersive, whereas stimulation and propagation of Lamb waves is frequency dependent. A pulse contains many frequencies and therefore only a fraction of the incident pulse is transformed into a Lamb wave. In this paper, numerical simulations are performed that show that actually the Schoch effect does occur neither for Rayleigh waves, nor for Lamb waves. As a matter of fact, a pulse, incident at the Rayleigh angle, generates two reflected lobes with a null zone of a different kind. The null zone is beating several times during the passage of each pulse. This results in a 'null zone' having a lower mean intensity than any of the two lobes, still less outspoken than for the case of harmonic incident bounded beams. This effect does only occur for Rayleigh wave generation and is much less outspoken for Lamb wave generation.     

In-situ formation of local inhomogeneities in semiconductors

The transport properties of ionic conductors such as α-AgI and Li_0.23La_0.69Fe_0.3Ti_0.7O₃ and of electronically conducting semiconductors such as α-Ag₂S and Ag_xWO₃ as a result of the application of voltages smaller than the decomposition voltage by two ionically blocking electrodes were investigated. The mobile ionic as well as the mobile electronic species are shifted from one electrode side to the other one. The change in the stoichiometric composition within the sample as a result of this transport process causes the formation of local inhomogeneities leading to changes in the electrical and optical properties. The experimental results also show that Nernst's law is not only valid for ionic conductors but also for semiconductors as well when a steady state is reached for ionically blocking electrodes. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Experimental study of reflection from discrete random inhomogeneities

Acoustic-signal backscattering by fixed discrete inhomogeneities randomly situated on a plane is modeled. The following effects are detected experimentally and discussed: the effect on backscattering intensity of coherent reflection from a weakly reflecting substrate, the collective effect associated with correlation of the scatterer locations, and the effect of multiple scattering with high inhomogeneity concentrations.Nizhny Novgorod State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 8, pp. 832–835, August, 1993.     

On Rayleigh waves in incompressible orthotropic elastic solids

In this paper the secular equation for the Rayleigh wave speed in an incompressible orthotropic elastic solid is obtained in a form that does not admit spurious solutions. It is then shown that inequalities on the material constants that ensure positive definiteness of the strain-energy function guarantee existence and uniqueness of the Rayleigh wave speed. Finally, an explicit formula for the Rayleigh wave speed is obtained.     

Production and study of local inhomogeneities in semiconducting oxides

An electric-transport method is described for introducing impurities into semiconducting oxides. Local inhomogeneities may be produced in the samples in this process. Certain physical properties of the samples may be changed by electric transport.Translated from Izvestiya VUZ. Fizika, No. 2, pp. 16–18, February, 1970.     

Detection of inhomogeneities in biological tissues by the methods of confocal microscopy

The model of detection of local inhomogeneities of scattering and absorbing types in biological tissues by the methods of reflection and transmission confocal microscopy has been developed on the basis of the theory of vision in scattering media. General equations for calculation of the image contrast of an inhomogeneity against the background of a scattering medium are derived. The influence of the object characteristics and observation-system parameters on the maximum detection depth of inhomogeneities is analyzed. Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 5, pp. 625–639, May, 1998.     

Analysis of wave propagation in cylindrical pipes with local inhomogeneities

In this paper, we present a numerical approach to study the guided elastic wave propagation in cylindrical pipes with local inhomogeneities. A hybrid wave finite element (WFE) and finite element (FE) technique is introduced to investigate the dispersion and wave scattering in pipes by taking full advantage of the existing FE codes. Dynamic reduction technique is employed to improve the computational efficiency, which is particularly suitable for the pipes with standard local features. Numerical examples indicate that the proposed technique provides an effective way to calculate the dispersion relationship and the scattered field. Both the axisymmetric and non-axisymmetric wave scattering problems are considered.     

Radiation reflection from inhomogeneities moving in a medium with a plasma dispersion law

The dependence of the complex frequency of radiation reflected from an inhomogeneity moving in a medium on the frequency of the incident radiation is found for inhomogeneous wave regimes. Explicit expressions for the plasma dispersion law of the medium are presented. The complex Doppler effect, where one (real) frequency of the incident radiation corresponds to two complex frequencies of the reflected radiation, is demonstrated.     

Determining local inhomogeneities of rotating plasma density via microwave refraction

A method for determining local inhomogeneities of the rotating plasmas is proposed. This method is based on spectral and correlation analysis of the reflected signals from the plasma at normal and oblique microwave incidence. Experimental approbation of the method is made.     

Method for calculating the scattering of solitons from local inhomogeneities

A special mathematical method combining analytical and numerical tools is developed to study how solitons are scattered from local inhomogeneities. As an example the method is used to investigate the scattering of a Toda-lattice soliton from a mass impurity.     

Detection of trace of impurities in some solids by proton spin-relaxation measurements

The amount of diamagnetic impurities occluded in the potassium hydrogen dibenzoate sample was estimated by proton spin-lattice relaxation measurements.     

NMR imaging of solids with magic angle spinning.

Different aspects of solid state NMR imaging are reviewed, with emphasis on imaging in combination with line narrowing, especially in combination with magic angle spinning. Experimental results obtained with the latter technique are discussed, along with the implications of magic angle spinning on slice selection.     

Inhomogeneous interactions in solids under slow off-magic angle spinning.

The central band of an inhomogeneous interaction under slow off-magic angle spinning (off-MAS) is no longer a scaled static spectrum with scaling factor P2(cos upsilon), that is, the spectrum distortion occurs in comparison with that under the rapid rotation condition. The dependence of this distortion in the chemical shift spectrum, for instance, on anisotropy, the asymmetry parameter, spinning rate and the angle between the spinning axis and the applied magnetic field is studied in this paper. It is shown that the distortion can be partly eliminated by using TOSS in certain circumstances. Experimental evidence is presented in this study.     

On the reflection of a radiowave beam from a plasma layer with large-scale inhomogeneities

Using the method of parabolic equation (MPE), we obtain transfer equations for the mean field, the space-coherence function, and the ray intensity of a radiowave beam as it is reflected from a plasma layer with random inhomogeneities. The general solutions of these equations are found. Special attention is given to the case of radiowave beam reflection from a linear plasma layer with large-scale electron-density inhomogeneities. If a weakly directed transceiving SW antenna is used, the shortwave scattering can lead to a pronounced (of the order of 3 dB) decrease in the intensity of a vertical-sounding signal reflected from the ionospheric F2 layer only under the conditions of abnormally strong ionospheric electron-density perturbations. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 8, pp. 955–965, August, 1998.     

A local mixing model for deuterium replacement in solids

A new model for hydrogen isotope exchange by ion implantation has been developed. The basic difference between our approach and previous work is that we include the depth distribution of the implanted species. The outstanding feature of this local mixing model is that the only adjustable parameter is the saturation hydrogen concentration which is specific to the target material and dependent only on temperature. The model is shown to give excellent agreement both with new data on H/D exchange in the low Z, coating materials VB₂, Tie, TiB₂, and B reported here and with previously reported data on stainless steel. The saturation hydrogen concentrations used to fit these data were 0.15, 0.25, 0.15, 0.45, and 1.00 times atomic density respectively. This model should be useful in predicting the recycling behavior of hydrogen isotopes in tokamak limiter and wall materials.