Interaction of acoustic scatterers

The interaction of scatterers under steady-state acoustic irradiation is studied for the case of scatterers in the form of elliptic cylinders taken as an example. The angular scattering characteristics of two interacting cylinders are calculated and compared with the angular characteristics of a single cylinder in a wide frequency band and in a wide angular range of irradiation. The parameters of interacting bodies (the angle of irradiation, the size with respect to the wavelength, and the distance between the bodies) at which the interaction is negligibly small are determined.     

On the Power-counting Renormalizability of a Lifshitz-type QFT in Configuration Space

Recently, Ho?ava (Phys. Rev. D. 79, 084008, 2009) proposed a theory of gravity in 3+1 dimensions with anisotropic scaling using the traditional framework of quantum field theory (QFT). Such an anisotropic theory of gravity, characterized by a dynamical critical exponent z, has proven to be power-counting renormalizable at a z=3 Lifshitz Point. In the present article, we develop a mathematically precise version of power-counting theorem in Lorentz violating theories and apply this to the Ho?ava-Lifshitz (scalar field) models in configuration space. The analysis is performed under the light of the systematic use of the concept of extension of homogeneous distributions, a concept tailor-made to address the problem of the ultraviolet renormalization in QFT. This becomes particularly transparent in a Lifshitz-type QFT. In the specific case of the \({\phi _{4}^{4}}\) -theory, we show that is sufficient to take z=3 in order to reach the ultraviolet finiteness of the S-matrix in all orders.     

The vibrations of glasses near the end of acoustic branches

The interest in measuring acoustic and optic vibrations of glasses at terahertz frequencies is explained. Techniques used for Brillouin spectroscopy at scattering vectors Q⩾1 nm⁻¹ are briefly described and compared. Experimental results, for example on vitreous silicas or glassy selenium, show that plane-wave acoustic excitations exhibit a crossover from propagation to strong scattering as Q is increased. Optical excitations at similar frequencies form a ‘boson peak’. These fairly local excitations can obey ‘molecular-like’ selection rules. The findings reveal a somewhat unexpected strong elastic inhomogeneity in the structure of glasses at the extended length scale of ∼5 nm, about which so little is known otherwise.     

Interaction of a Gaussian acoustic wave with a turbulent non-premixed flame

A Direct Numerical Simulation (DNS) of a turbulent non-premixed flame interacting with a Gaussian acoustic wave is carried out in this work. This numerical simulation takes into account detailed transport phenomena including the Soret effect as well as complete chemical kinetics on a very fine mesh. Turbulent non-premixed flame calculations are carried out both with and without an acoustic wave and results are recorded at the same time. By a simple difference it is then possible to obtain the influence of the acoustic wave/turbulent flame interaction. Using an extension of the non-linear Rayleigh criterion to a system with many species and elementary reactions, the obtained results can be further analysed. The initially planar acoustic wave develops strong perturbations along its transverse direction because of the interaction process, even at very early times. The amplitude of the pressure perturbation presents locally high positive as well as negative values, demonstrating the importance of focussing/defocussing effects and local amplification (resp. damping) phenomena. In the same way, the heat release rate is locally modified (either increased or decreased) during the interaction process. Finally, the presented Rayleigh criterion is used to identify regions where local amplification (respectively damping) takes place. Both amplification and damping zones coexist directly close to each other inside the reaction zone. The observed, resulting global effect is thus based on an average over highly varying local conditions within the flame front, leading to a smoothing effect. The complexity of the coupling procedure leading to this global wave amplification or damping is demonstrated by the present analysis.     

Scale invariant optical correlation using Mellin transforms

The use of optical Mellin transforms in matched spatial filter correlation of imagery that differs in scale is discussed. Theoretical considerations and initial experimental results are included. The intensity of the correlation peak is found to be independent of the input scale, and the scale difference between the two functions to be correlated can also be extracted from the location of the correlation peak.     

Aberration invariant optical/digital incoherent systems

We have developed a fundamental technique for control of important known and unknown lens aberrations. Control of lens aberrations through traditional means is very difficult in high-performance optical systems. Minimizing aberrations caused by deterministic design errors as well as statistical fabrication errors has often led to costly systems and fabrication techniques. By employing a special-purpose optical phase mask and digital signal processing we can form imaging systems that are invariant, or substantially insensitive, to a number of important lens aberrations.     

Interaction of acoustic waves with polycrystals

We analyze theoretically the structure of the field created in a semi-infinite polycrystal by an acoustic wave, coming from an isotropic homogeneous medium and incident normally onto its surface. The elastic anisotropy of the polycrystal is supposed to be small, and the perturbation theory is applied. It is shown that the effective medium approach is not valid. In addition to the transmitted wave propagating in the polycrystal with an effective sound speed, there is one more bulk wave, whose amplitude decreases at a distance of the order of the mean size of the grain from the interface. The structure of the reflected wave is the same as when reflecting from an isotropic solid. However, the relation between the amplitudes of reflected and transmitted waves differs from that in an isotropic solid.     

Interaction of a spherical acoustic wave with an elastic spherical shell

The interaction of a spherical acoustic wave with an elastic spherical shell is treated analytically. The solution includes the coupling between the acoustic sound field and vibration of the shell with any degree of fluid loading. The formulation for the far-field acoustic pressure is derived in terms of natural spherical wave functions, the properties of the acoustic medium, and the material constants of the shell. The far acoustic field is computed for a thin aluminum shell and several sound source locations over a large range of ka, where k is the wavenumber, and a is the shell radius. It is shown that the acoustic pressure depends significantly on whether the shell is in air or is submerged in water, particularly when the sound source is very near the surface. In air, the sound field of the shell is nearly identical to that of a rigid sphere but, in water, the shell is more compliant, which results in a damped radiation field that is characterized by vibrational resonances throughout the range of frequencies considered. As the sound sources is moved further away from the surface, however, this resonance response decreases very rapidly, and the sound field corresponds more closely to that of the shell in air.     

Interaction of an optical soliton with a dispersive wave

Scattering of a dispersive wave by optical solitons is studied experimentally in photonic crystal fibers in cases when the soliton and the dispersive wave have either identical or orthogonal polarization states. Observations of new resonant frequencies are reported. The experimental results are compared to numerical simulations and predictions from the recently derived wave vector matching conditions.     

Interaction of acoustic waves with porous layer

Interaction of sound impulse with porous layer is investigated. The presence of a barrier shielded by the layer and the gap between the porous layer and the barrier is possible. Method of calculation in linear approximation of pressures and tensions in the porous layer, gap, and on the barrier has been proposed. The method serves to interpret data on acoustic waves interaction with porous layer obtained experimentally or with the use of finite-difference methods. Specifics of acoustic wave propagation into the porous layer and further reflection from the barrier has been studied. Comparison of calculation data with experimental data of other authors on impulse propagation through the porous plate submerged in water has been carried out.     

Diffraction correlators invariant to the shift of optical elements

Linear in intensity image processing systems based on the principles of diffraction optics are considered in the paper. Influence of optical element shifts on calculation accuracy in the systems is studied. It is shown that image processing in the diffraction intensity correlators (vignetting, partial coherence, etc. are not taken into account) is absolutely invariant to longitudinal shifts of a holographic filter and, to a great extent, invariant to longitudinal shifts of objectives. The experiments show that the correlators operate rather stable with the optical elements shifted within 10% from the focal lengths of the objectives used, which is higher by two orders than the analogous limits in the diffraction amplitude correlators.     

声强谱频移补偿的波导不变量和距离估计方法

基于声强的距离一频率干涉结构,利用对水平阵不同阵元信号的声强谱进行频移补偿的方法估计波导不变量和距离。在波导不变量和距离其中一项已知的情况下,可以通过该方法估计另外一项。利用2011年12月北黄海水声实验中拖曳声源发射和海底水平阵接收的线性调频信号,通过上述方法估计了不同距离处的波导不变量。结果显示波导不变量的估计值在0.8到1.2之间变化,其均值与利用实测海洋环境计算的理论值符合良好。同时,利用相同的信号和波导不变量的理论计算值,通过上述方法在不同时刻进行距离估计,结果与GPS测量距离基本一致。     

驻波声场中单分散细颗粒的相互作用特性

利用外加声场促进悬浮在气相中的细颗粒发生相互作用,进而引起颗粒的碰撞和凝并,使得颗粒平均粒径增大、数目浓度降低,是控制细颗粒排放的重要技术途径.为探究驻波声场中单分散细颗粒的相互作用,建立包含曳力、重力、声尾流效应的颗粒相互作用模型,采用四阶经典龙格-库塔算法和二阶隐式亚当斯插值算法对模型进行求解.将数值模拟得到的颗粒声波夹带速度和相互作用过程与相应的解析解和实验结果进行对比,验证模型的准确性.进而研究颗粒初始条件和直径对相互作用特性的影响.结果表明,初始时刻颗粒中心连线越接近声波波动方向、颗粒位置越接近波腹点,颗粒间的声尾流效应就越强,颗粒发生碰撞所需要的时间就越短.研究还发现,颗粒直径对颗粒相互作用的影响取决于初始时刻颗粒中心连线偏离声波波动方向的程度.当偏离较小时,颗粒直径越大,颗粒发生碰撞所需要的时间越短;当偏离很大时,直径较小的颗粒能够发生碰撞,而直径较大的颗粒则无法发生碰撞.     

干涉型光纤声传感器的研究

本文对光纤声传感器的压力灵敏度作了理论分析,且分析讨论了非均匀压力下的灵敏度,实现了直流相位跟踪零差检测(PTDC)系统,并测定了声压与输出电信号的关系,采用5m长光纤得到声压检测阈值为200μPa.     

Properties of optical and acoustic phonons in diamond crystals

The dependence of the energy on the quasi-momentum of optical and acoustic phonons in diamond-type crystals is analyzed. It is shown that the dispersion relation of optical branches near the Brillouin zone center in such crystals can be derived based on the modified Klein-Gordon equation corresponding to quasiparticles (optical phonons) with negative effective mass. Analytical expressions are derived for dispersion curves of acoustic and optical branches in the entire Brillouin zone, based on the sinusoidal approximation. The obtained analytical dependences of dispersion relations are compared to the experimental results of the study of inelastic neutron scattering spectra in diamond crystals. The law of the coordinate and time transformation for optical phonons with negative effective rest mass when going to the new inertial reference frame, similar to Lorentz transformations in relativistic mechanics, is determined.     

Obtaining gauge invariant actions via symplectic embedding formalism

The concept of gauge invariance is one of the most subtle and useful concepts in modern theoretical physics. It is one of the Standard Model cornerstones. The main benefit due to the gauge invariance is that it can permit the comprehension of difficult systems in physics with an arbitrary choice of a reference frame at every instant of time. It is the objective of this work to show a path of obtaining gauge invariant theories from non‐invariant ones. Both are named also as first‐ and second‐class theories respectively, obeying Dirac's formalism. Namely, it is very important to understand why it is always desirable to have a bridge between gauge invariant and non‐invariant theories. Once established, this kind of mapping between first‐class (gauge invariant) and second‐class systems, in Dirac's formalism can be considered as a sort of equivalence. This work describe this kind of equivalence obtaining a gauge invariant theory starting with a non‐invariant one using the symplectic embedding formalism developed by some of us some years back. To illustrate the procedure it was analyzed both Abelian and non‐Abelian theories. It was demonstrated that this method is more convenient than others. For example, it was shown exactly that this embedding method used here does not require any special modification to handle with non‐Abelian systems.     

Generation of Superpositions of Coherent Interaction States Along a Straight Line via Raman Interaction

We present an alternative scheme for preparing the superpositions of coherent states along a straight line of a cavity field using degenerate atom-cavity field Raman interaction. In the scheme, a collection of A-type three-level atoms is orderly sent through the cavity to interact with the cavity field adjusted by a microwave source connected to it, followed by state-selective measurements. In this way, we can prepare the superpositions of several coherent states along a straight line with arbitrary weighting factors for the cavity field. In the scheme, the coherence of the atom-cavity system may be maintained and the second microwave field is unnecessary, which is prior to the previous scheme.     

Interaction between moving bubbles and an acoustic field: Controlling flows and nonlinear acoustic vision

Results from studying the interaction between gas bubbles and the field of a flow-through acoustic resonator, and the Raman scattering of acoustic waves by moving bubbles, are presented. The structure of the distribution of bubble concentration in the resonator is studied. It is shown that nonlinear scattering by moving bubbles can be used to image bubble objects.