Stress-Strain State of Elastic Plate with a Crack

Russian Physics Journal - The paper considers an infinite plate with a crack in the form of a narrow hole with a certain curvature at the tip of the crack. The stress-strain state parameters of...     

Switching between the Functions of Half-Wave Plate and Quarter-Wave Plate Simply by Using a Vanadium Dioxide Film in a Terahertz Metamaterial

We propose a switchable THz metamaterial that can be switched between two functions of half-wave plate and quarter-wave plate.The two switchable functions can be simply achieved by inserting a VO₂ film in the metamaterial design.Finite-difference time-domain(FDTD) simulation results show that the proposed metamaterial can convert x-polarized incident wave to y-polarized reflected wave when VO₂ is at metal phase,and convert x-polarized wave to circularly polarized wave when ...     

Power Flux along a Straight Crack in an Elastic Plate

Propagation of the edge waves along a straight crack in an elastic plate is studied. The power fluxes associated with these waves are calculated, and the modes of vibration are considered.     

Analysis of Second-Harmonic Generation of Low-Frequency Dilatational Lamb Waves in a Two-Layered Composite Plate

We analyze the effect of second-harmonic generation(SHG) of primary Lamb wave propagation in a two-layered composite plate, and then investigate the influence of interfacial properties on the said effect at low frequency. It is found that changes in the interfacial properties essentially affect the dispersion relation and then the maximum cumulative distance of the double-frequency Lamb wave generated. This will remarkably influence the efficiency of SHG. To overcome the complications arising from the inherent dispersion and multimode natures in analyzing the SHG effect of Lamb waves, the present work focuses on the analysis of the SHG effect of low-frequency dilatational Lamb wave propagation. Both the numerical analysis and finite element simulation indicate that the SHG effect of low-frequency dilatational Lamb wave propagation is found to be much more sensitive to changes in the interfacial properties than primary Lamb waves. The potential of using the SHG effect of low-frequency dilatational Lamb waves to characterize a minor change in the interfacial properties is analyzed.     

Thickness Determination for a Two-Layered Composite of a Film and a Plate by Low-Frequency Ultrasound

We present an ultrasonic method for determining the thickness of a composite consisting of a soft thin film attached to a hard plate substrate, by resonance spectra in the low frequency region, The interrogating waves can be incident only to the two-layered composite from the substrate side. The reflection spectra are obtained by FFT analysis of the compressive pulsed echoes from the composite, and the thicknesses of the film and the substrate are simultaneously inversed by the simulated annealing method from the resonant frequencies knowing other acoustical parameters in prior. The sensitivity of the method to individual thickness, its convergence and stability against experimental noises are studied, Experiment with interrogating wavelength 4 times larger than the film thickness in a sample of a polymer film （0.054mm） on an aluminium plate （6.24mm） verifies the validity of the method. The average relative errors in the measurement of the thicknesses of the film and the substrate are found to be -4.1% and -0.62%, respectively.     

Mass Transfer of the Liquid Phase in a Partially Saturated Porous Medium Under the Action of Low-Frequency Elastic Vibrations

We study the model of a partially saturated porous medium comprising a system of identical parallel cylindrical capillaries filled up with equal droplets. The basic features of the liquid-phase drift and the accompanying sound attenuation and droplet coalescence effects are analyzed in the case of external compression.     

Improved Adaptive Augmentation Control for a Flexible Launch Vehicle with Elastic Vibration

The continuous development of spacecraft with large flexible structures has resulted in an increase in the mass and aspect ratio of launch vehicles, while the wide application of lightweight materials in the aerospace field has increased the flexible modes of launch vehicles. In order to solve the problem of deviation from the nominal control or even destabilization of the system caused by uncertainties such as unknown or unmodelled dynamics, frequency perturbation of the flexible mode, changes in its own parameters, and external environmental disturbances during the flight of such large-scale flexible launch vehicles with simultaneous structural deformation, rigid-elastic coupling and multimodal vibrations, an improved adaptive augmentation control method based on model reference adaption, and spectral damping is proposed in this paper, including a basic PD controller, a reference model, and an adaptive gain adjustment based on spectral damping. The baseline PD controller was used for flight attitude control in the nominal state. In the non-nominal state, the spectral dampers in the adaptive gain adjustment law extracted and processed the high-frequency signal from the tracking error and control-command error between the reference model and the actual system to generate the adaptive gain. The adjustment gain was multiplied by the baseline controller gain to increase/decrease the overall gain of the system to improve the system’s performance and robust stability, so that the system had the ability to return to the nominal state when it was affected by various uncertainties and deviated from the nominal state, or even destabilized.     

On the Feasibility of Forming a Multifactor Foreshock by Synchronous Registration of the Electric Field Variations in Different Low-Frequency Bands

A problem of identification of a multifactor foreshock by registration of the ELF electromagnetic field at global distances from a seismic center is considered. The foreshock is identified with the product of variations of the electromagnetic field components in several space and frequency separated receiving channels. Based on the conducted experiments, a method of the parameter identification and the parameter form are presented.     

Elastic interaction between defects in thin and 2D films

Elastic interactions between defects is investigated at the surface of thin layers, a question on which we have given a brief account [P. Peyla et al. Phys. Rev. Lett. 82, 787 (1999)]. Two isotropic defects do not interact in an unlimited medium, regardless of the spatial dimension, a result which can be shown on the basis of the Gauss theorem in electrostatics. Within isotropic elasticity theory, defects interact only (i) if they are, for example, at a surface (or at least if they feel a boundary), or if their action on the material is anisotropic (e.g. they create a non central force distribution, though the material elasticity is isotropic). It is known that two identical isotropic defects on the surface of a semi-infinite material repel each other. The repulsion law behaves as 1/r ³(r = defects separation). We first revisit the Lau-Kohn theory and extend it to anisotropic defects. Anisotropy is found to lead to attraction. We show that in thin films defects may either attract or repel each other depending on the local geometric force distribution caused by the defect. It is shown that the force distribution (or more precisely the forces configuration symmetry) fixes the exponent in the power law 1/r ⁿ (e.g. for a four-fold symmetry n = 4). We discuss the implication of this behaviour in various situations. We treat the interactions in terms of the symmetries associated with the defect. We argue that if the defects are isotropic, then their effective interaction in an unlimited 2D (or a thin film) medium arises from the induced interaction, which behaves as 1/r ⁴ for any defect symmetry. We shall also comment on the contribution to the interaction which arises from flexion of thin films. Received 7 October 2002 Published online 4 June 2003 RID="a" ID="a"e-mail: chaouqi.misbah@ujf-grenoble.fr     

Multipole Effects in a Toroidal Tunable Planar Metamaterial

JETP Letters - A tunable planar metamaterial with a high contribution of the toroidal dipole moment in the microwave range is theoretically and experimentally studied. The properties of such a...     

Resonant Interaction of an Air Flow with Bending Vibrations of a Finite Elastic Plate

Russian Physics Journal - Resonant interaction of an elastic plate with an air bypassing it and leading to the development of a wind instability is studied. The dispersive equation of bending...     

All‐Optical Photonic Band Control in a Quantum Metamaterial

Metamaterials made of periodic collections of dielectric nanorods are considered theoretically. When quantum resonators are embedded within the nanorods, one obtains a quantum metamaterial, whose electromagnetic properties depend upon the state of the quantum resonators. The theoretical model predicts that when the resonators are pumped and reach the inversion regime, the quantum metamaterial exhibits an all‐optical switchable conduction band. The phenomenon can be described by considering the pole stucture of the scattering matrix of the metamaterial.     

Focusing of a Flat Left-Handed Metamaterial Lens in a Heterogeneous and Lossy Medium

For applications such as near-field target detection and tumor hyperthermia with a fiat left-handed metamaterial （LHM） lens, a microwave will be focused in the heterogeneous and lossy medium. Different from the focusing of a fiat LHM lens in vacuum as reported in most previous studies, the medium loss and heterogeneity will affect the focusing performance of the LHM lens. Numerical simulations indicate that the medium loss will degrade the focusing resolution, while the heterogeneity of random variability within ±30% will affect the focusing resolution to a limited extent. Both the loss and heterogeneity of the medium will shift the focal point away from the image plane. When focusing in a medium with different permittivity values, an LHM lens will also have different focusing resolutions due to different electric thicknesses.     

弹性板水下爆炸冲击载荷的修正虚拟流体方法分析

研究非接触水下爆炸中板结构厚度和密度对冲击载荷和空化演变的影响.将近期发展的修正的虚拟流体方法推广应用于处理可压缩流体与弹性板结构的非线性相互作用.研究发现,假设结构不发生断裂破坏,较小的板厚度或密度可以减弱爆炸波对结构的冲击,冲击载荷随着厚度或密度的增大非线性地趋向于固壁边界下的结果.而且较小的板厚度或密度可以促使空化较早形成,产生较大的空化区,并推迟和减弱空化破裂对结构的二次冲击.     

Elastic scattering of holes by acoustic phonons in thin GaAs/GaAlAs quantum wells

The rates of scattering by acoustic phonons _γi→j${\gamma }_{i\to j}$ from subband i→j$i\to j$ are calculated for holes in a narrow GaAs quantum well using the deformation potential, the Luttinger hamiltonian and the Debye approximation. At room temperature, we find that the energy dependences for both intra- and inter-subband scattering rates follow roughly the behavior of the density of states in the subband to which the hole scatters. Moreover, we study the influence of the overlap between the initial and final states, and for elastic processes we find that, unlike for the case of wide quantum wells, for narrow ones integration over the phonon transverse wavevector _qz$q_z$ should be restricted to about 4% of the bulk Brillouin zone extent. In addition the impact of the well width on _γi→j${\gamma }_{i\to j}$ is investigated.     

Modulation of Ion-Cyclotron Turbulence by Low-Frequency Perturbations in a Magnetized Plasma

We consider nonlinear coupling of ion-cyclotron turbulence with low-frequency fast magneto-acoustic perturbations across the external magnetic field in a magnetized plasma. It is found that such coupling leads to instability. The growth rate and the threshold of this instability are calculated.     

Stimulated Low-Frequency Raman Scattering in a Single-Crystal Diamond with a Buried Graphitized Layer

Optics and Spectroscopy - The results of experimental observation of stimulated low-frequency Raman scattering (SLFRS) in a single-crystal diamond with a buried graphitized layer created as a...     

Transition between a Photonic Crystal and a Metamaterial with Electric Response in Dielectric Structures

JETP Letters - The feasibility of dielectric structures possessing metamaterial properties owing to electric Mie resonances is theoretically demonstrated. The structures are formed by homogeneous...     

Vibration analysis of a rectangular thin isotropic plate with a part-through surface crack of arbitrary orientation and position

In this paper, vibration analysis of a rectangular thin isotropic plate with a part-through surface crack of arbitrary orientation and position is performed by using the Kirchhoff plate theory. Simply supported (SSSS), clamped (CCCC) and simply supported–clamped (SCSC) boundary conditions are considered for the analysis. First, the governing differential equation of a cracked plate is formulated. A modified line spring model is then used to formulate the crack terms in the governing equation. Next, by the application of Burger's formulation, the differential equation is transformed into the well-known Duffing equation with cubic and quadratic nonlinearities. The Duffing equation is then solved by the method of multiple scales (MMS) to extract the frequency response curve. Natural frequencies are evaluated for different values of length, angle and position of a part-through surface crack. Some results are compared with the published literature. Amplitude variation with different values of length, angle and position of a part-through surface crack are presented, for all three types of the plate boundary conditions.