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Nonlinear dependence of the response rate on light intensity (form ula (ill.) is obtained in doped KNSBN crystals. One of them has a superlinear intensity-dependent re- sponse rate which cannot be explained by previous model. Ano...
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Nonlinear dependence of the response rate on light intensity (form ula (ill.) is obtained in doped KNSBN crystals. One of them has a superlinear intensity-dependent re- sponse rate which cannot be explained by previous model. Another anomalous phenomena are that the power coefficient x is nearly equal to 1 while the density of filled shallow trap is higher in reduced Co: KNSBN crystal. A new model of two types of carriers with multiple traps is proposed to explain the anomalous phenomena.
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In this work, we use a special nonlinear dependence of dielectric permittivity to study theoretically the effect of a decrease in the nonlinear response in near-surface layers of a medium, which occurs with an increase in the ampl...
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In this work, we use a special nonlinear dependence of dielectric permittivity to study theoretically the effect of a decrease in the nonlinear response in near-surface layers of a medium, which occurs with an increase in the amplitude of the electric field. We propose a model of nonlinearity in which the Kerr-type nonlinearity abruptly disappears with an increase in the field, and the dielectric permittivity becomes constant and independent of the field. Increasing the electric field leads to the formation of a local zone (optical domain) near the surface with linear optical properties where the dielectric permittivity becomes independent of the electric field. We formulate a nonlinear equation with stepwise dependence of the dielectric permittivity on electric field, and obtain its two types of exact solutions corresponding to the surface waves in media with positive (self-focusing) and negative (defocusing) nonlinear responses. We calculate and analyze the total power flows of thesurface waves of both types. We discuss in detail the features of the obtained solutions in comparison with previously published results. It is shown that the choice of a crystal with an appropriate nonlinear response makes it possible to increase or decrease the field intensity near the crystal surface with practically the same thickness of the near-surface layer with altered optical properties.
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Numerical models of ionospheric coupling with the neutral atmosphere are used to investigate perturbations of plasma density, vertically integrated total electron content (TEC), neutral velocity, and neutral temperature associated...
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Numerical models of ionospheric coupling with the neutral atmosphere are used to investigate perturbations of plasma density, vertically integrated total electron content (TEC), neutral velocity, and neutral temperature associated with large-amplitude acoustic waves generated by the initial ocean surface displacements from strong undersea earthquakes. A simplified source model for the 2011 Tohoku earthquake is constructed from estimates of initial ocean surface responses to approximate the vertical motions over realistic spatial and temporal scales. Resulting TEC perturbations from modeling case studies appear consistent with observational data, reproducing pronounced TEC depletions which are shown to be a consequence of the impacts of nonlinear, dissipating acoustic waves. Thermospheric acoustic compressional velocities are ～±250–300 m/s, superposed with downward flows of similar amplitudes, and temperature perturbations are ～300 K, while the dominant wave periodicity in the thermosphere is ～3–4 min. Results capture acoustic wave processes including reflection, onset of resonance, and nonlinear steepening and dissipation—ultimately leading to the formation of ionospheric TEC depletions “holes”—that are consistent with reported observations. Three additional simulations illustrate the dependence of atmospheric acoustic wave and subsequent ionospheric responses on the surface displacement amplitude, which is varied from the Tohoku case study by factors of 1/100, 1/10, and 2. Collectively, results suggest that TEC depletions may only accompany very-large amplitude thermospheric acoustic waves necessary to induce a nonlinear response, here with saturated compressional velocities ～200–250 m/s generated by sea surface displacements exceeding ～1 m occurring over a 3 min time period.
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Starting from physical insight on the energy transfer phenomena in wall turbulent flows, it is shown how modeling of subgrid stresses in large-eddy simulations can be improved. Each model should aim at reproducing the double featu...
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Starting from physical insight on the energy transfer phenomena in wall turbulent flows, it is shown how modeling of subgrid stresses in large-eddy simulations can be improved. Each model should aim at reproducing the double feature of energy sink and source of the small scales of wall flows which become relevant when large filter lengths are considered. Here we propose one possible choice where the main ingredient is the coupling of the classical linear formulation of eddy viscosity with the nonlinear anisotropic features of the velocity increments tensor. This approach, which actually presents most of the features of the mixed models, captures the near-wall dynamics for very large filter lengths reproducing the small scales source physics responsible for backward energy transfer. A posteriori tests show excellent agreement with direct numerical simulation of turbulent channel flows even when very coarse grids are considered. The capability of the balance of the filtered second order structure function as a post-processing tool to evaluate the physics of any model is also shown.
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In situ measurement of the elastic nonlinear site response is advantageous to provide optimal information for prediction of strong ground motion at a site. We report the first implementation of a technique known as Dynamic Acousto...
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In situ measurement of the elastic nonlinear site response is advantageous to provide optimal information for prediction of strong ground motion at a site. We report the first implementation of a technique known as Dynamic Acoustoelastic Testing (DAET) in situ with the ultimate goal of developing a new approach for site characterization. DAET has shown promising results at the laboratory scale for the study of nonlinear elasticity of Earth materials, detailing the full nonlinear elastic properties of the studied sample. We demonstrate the feasibility of DAET in situ and compare it to other methods (nonlinear resonance spectroscopy, wave amplitude dependence of propagation velocity, and wave distortion). Nonlinear elastic properties are characterized by DAET with the advantage of providing a local assessment compared to other methods, here at a depth of 4 m to 5 m. A vertical dynamic strain amplitude of 5 × 10~(?5) produces a relative change in compressional wave modulus of 6%. We measure an effective parameter of quadratic elastic nonlinearity of order ?10~3, the same order of magnitude measured at the laboratory scale in rocks and in packs of unconsolidated glass beads. Hysteresis is observed in the variation in soil elasticity as a function of the instantaneous dynamic strain that evolves as the dynamic strain amplitude is increased from 9 × 10~(?7) to 5 × 10~(?5).
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We conduct a theoretical study of the nonlinear optical response of a two-dimensional semiconductor quantum-dot supercrystal subjected to a quasiresonant continuous-wave excitation. A constituent quantum dot is modeled as a three-...
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We conduct a theoretical study of the nonlinear optical response of a two-dimensional semiconductor quantum-dot supercrystal subjected to a quasiresonant continuous-wave excitation. A constituent quantum dot is modeled as a three-level ladderlike system (comprising the ground, the one-exciton, and the biexction states). To study the stationary response of the supercrystal, we propose an exact linear parametric method of solving the nonlinear steady-state problem, while to address the supercrystal optical dynamics qualitatively, we put forward a method to calculate the bifurcation diagram of the system. Analyzing the dynamics, we demonstrate that the supercrystal can exhibit multistability, periodic and aperiodic self-oscillations, and chaotic behavior, depending on parameters of the supercrystal and excitation conditions. The effects originate from the interplay of the intrinsic nonlinearity of quantum dots and the retarded interdot dipole-dipole interaction. The latter provides a positive feedback which results in the exotic supercrystal optical dynamics. These peculiarities of the supercrystal optical response open up a possibility for all-optical applications and devices. In particular, an all-optical switch, a tunable generator of THz pulses (in self-oscillating regime), a noise generator (in chaotic regime), and a tunable bistable mirror can be designed.
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In the context of event-by-event hydrodynamic description, we analyze the implications of two models characterized by distinct initial conditions. The initial energy density of the first model adopts a Gaussian-type distribution, ...
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In the context of event-by-event hydrodynamic description, we analyze the implications of two models characterized by distinct initial conditions. The initial energy density of the first model adopts a Gaussian-type distribution, while those of the second one are features by high energy peripheral tubes. We calibrate the initial conditions of both models so that their initial probability distribution of eccentricity are mostly identical. Subsequently, the resultant scaled probability distributions of collective flow and the correlations between flow harmonic and eccentricity coefficients are investigated. Besides, the calculations are carried out for particle correlations regarding the symmetric cumulant, mixed harmonics, and nonlinear response coefficients. Although the resultant two-particle correlations possess similar shapes, numerical calculations indicate a subtle difference between the two models. To be specific, the difference resides in more detailed observables such as the probability distributions of elliptic flow as well as Pearson correlation coefficient regarding higher-order harmonics. We discuss several essential aspects concerning the linearity and nonlinearity between initial eccentricities and final state anisotropies. Further implications are addressed.
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Stiffening behavior can result from interaction between a structure(base system)and its surrounding environment as in the bridge soil-structure interaction. In this paper the base single-degree-of-freedom(B-DSOF)systems are design...
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Stiffening behavior can result from interaction between a structure(base system)and its surrounding environment as in the bridge soil-structure interaction. In this paper the base single-degree-of-freedom(B-DSOF)systems are designed for several ductility factors and then the effects of different interacting environments(defined in terms of stiffness, strength and gap size)on its dynamic response are investigated. For this, nonlinear time history analyses are performed using an earthquake record scaled to an elastic design response spectrum at each period.
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We examine the delayed response of a diatomic gas to a polarizing laser field with the goal of obtaining computationally efficient methods for use with laser pulse propagation simulations. We demonstrate that for broadband pulses,...
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We examine the delayed response of a diatomic gas to a polarizing laser field with the goal of obtaining computationally efficient methods for use with laser pulse propagation simulations. We demonstrate that for broadband pulses, heavy molecules such as 02 and N2, and typical atmospheric temperatures, the initial delayed response requires only classical physics. The linear kinetic Green's function is derived from the Boltzmann equation and shown to be in excellent agreement with full density-matrix calculations. A straightforward perturbation approach for the fully nonlinear, kinetic impulse response is also presented. With the kinetic theory a reduced fluid model of the diatomic gas' orientation is derived. Transport coefficients are introduced to model the kinetic phase mixing of the delayed response. In addition to computational rapidity, the fluid model provides intuition through the use of familiar macroscopic quantities. Both the kinetic and the fluid descriptions predict a nonlinear steady-state alignment after passage of the laser pulse, which in the fluid model is interpreted as an anisotropic temperature of the diatomic fluid with respect to motion about the polarization axis.
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The goal of this paper is to elucidate the theoretical underpinnings of the metastable electronic state approach (MESA) and demonstrate its utility for the evaluation of the nonlinear optical response of noble-gas atoms with empha...
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The goal of this paper is to elucidate the theoretical underpinnings of the metastable electronic state approach (MESA) and demonstrate its utility for the evaluation of the nonlinear optical response of noble-gas atoms with emphasis on the application of the method to the propagation of multicolor optical fields in large-scale, spatially resolved simulations. More specifically, single-active-electron models of various atoms are employed to calculate their nonlinear properties both within the adiabatic approximation, involving a single metastable state and beyond, capturing inertial effects, and wavelength-dependent ionization. Simulations for excitation pulses at different center wavelengths as well as ionization in two-color pulses are presented and compared with numerical solutions of the time-dependent Schr?dinger equation. Illustrative examples of the numerical simulation of high-power pulse propagation incorporating MESA data are also presented and showcase the successful application to optical filamentation in the midinfrared region.
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