Wave ionosphere perturbations with small periods under magnetic storm conditions

The characteristics of total electron content (TEC) variations obtained using the data of middle-latitude stations for receiving GPS satellite signals were studied. An analysis showed that perturbations of diurnal TEC variations during a geomagnetic storm were determined by strengthening of harmonics with periods of 4–5 and 6–8 h. Perturbations in diurnal TEC variations were retained for several days after a geomagnetic storm. An analysis of the frequency and amplitude characteristics of perturbed variations showed that differences between variations at different latitudes could be explained by the propagation of Poincaré planetary waves in an atmospheric wave channel. The atmospheric channel was formed because of increased heating of pole regions during geomagnetic storms. A comparative analysis of observations made at different stations was used to estimate the width of the atmospheric channel and Poincaré wave frequencies and wave vector components.     

Nonlinear effects in trapped modes of standing waves on the surface of shallow water

It was shown that traveling waves may coexist with standing waves in a planar infinitely long channel filled by ideal liquid with a free surface. The standing waves are localized near a dynamic inclusion—a massive die on an elastic base. The amplitude of the traveling waves may be turned to zero by appropriately selecting the vibration frequency of the die. The standing waves arise because the vibration eigenfrequencies have a mixed spectrum; that is, the discrete and continuous spectra superpose. Nonlinear effects were observed for the first time when standing waves form in shallow water. In particular, a relationship between the die weight necessary to excite trapped modes, die dimensions, and vibration frequency was derived. It was shown that the nonlinear effects cause double-frequency traveling waves with amplitudes of the next order of smallness. These traveling waves vanish if the die geometry is properly chosen, as for the waves of the zeroth order.     

Numerical analysis of bulk conical waves in anisotropic cylinders; application to stiffness tensor measurement

A point source-point receiver technique, based on laser generation and laser detection of acoustic waves, allows determination of mechanical properties of an anisotropic cylinder. The nature of the material and the geometry of the sample give a dispersive behaviour to the diffracted waves and make the acoustic signature difficult to interpret. To overpass the intricacies, wave fronts (conical waves in the volume and helical waves on the surface) are synthesized from signals provided by scanning the primitive line of the cylinder with a laser point source. In order to distinguish between direct bulk conical waves and other contributions in the acoustic response, some considerations on line surface waves and on reflected bulk conical waves are supplied. The identification of the stiffness tensor components, based on the inversion of the bulk waves phase velocities, is applied to signals simulated for a composite material.     

Diffraction of light by an acoustic wave with three frequency components

Collinear light diffraction by three-frequency sound is investigated theoretically. The amplitude distributions of transmitted and diffracted light waves along the cell are calculated for different amplitudes of sound signals. The dependence of the intensity of principal diffraction peaks on the frequency difference between acoustic signal components is studied for different amplitude ratios of these components. It is shown that the character of this dependence for a wave being in synchronism differs substantially from that for two other waves characterized by detuning. The dependence of the amplitudes of principal and parasitic diffraction peaks on the efficiency of acoustooptical interaction is investigated. It is demonstrated that parasitic sideband components in diffracted light can play a considerable role if the diffraction efficiency is sufficiently high and exceeds 80%.     

Wavelet analysis of ellipticity,dispersion, and dissipation properties of Rayleigh waves

This paper is devoted to the digital processing of multicomponent seismograms using wavelet analysis. The goal of this processing is to identify Rayleigh surface elastic waves and determine their properties. A new method for calculating the ellipticity parameters of a wave in the form of a time-frequency spectrum is proposed, which offers wide possibilities for filtering seismic signals in order to suppress or extract the Rayleigh components. A model of dispersion and dissipation of elliptic waves written in terms of wavelet spectra of complex (two-component) signals is also proposed. The model is used to formulate a nonlinear minimization problem that allows for a high-accuracy calculation of the group and phase velocities and the attenuation factor for a propagating elliptic Rayleigh wave. All methods considered in the paper are illustrated with the use of test signals.     

Diagnosis of osteoporosis based on multi-scale wavelet parameters of ultrasonic guided waves

Evaluating bone regularly is important to prevent and control the disease of osteoporosis. Impact of osteoporosis on ultrasonic guided waves propagating in human long bones is studied in this paper. Multi-scale wavelet transform is proposed to process the received guided waves, and by analyzing energy changes in detail components of high order wavelet at different propagating distance to assess if osteoporosis happened. The guided waves signals are collected from the tibias of 13 volunteers. Based on the analysis of multi-scale wavelet transform, the high order detail components d6 and d5 changed dramatically with the propagation of ultrasonic guided waves along long bones, which means these 7 volunteers are diagnosed with osteoporosis. Compared with X-ray diagnosis, the effectiveness of this method can reach 92.3% in 13 volunteers. This suggests the multi-scale wavelet transform method is potential in ultrasonic assessment of bone quality.     

Energy-Momentum Pseudo-Tensor of Relic Gravitational Wave of Both the Polarized States

Unlike usual celestial gravitational waves, the relic gravitational waves （RGWs） form random signals in curved spacetime background. We calculate the energy-momentum pseudo-tensor of a certain component of the RGWs propagating along arbitrary directions in Cartesian coordinates. It is found that the energy density of RGWs is positive definitely, and the momentum density components have reasonable behaviour. Such results may provide a theoretical basis for the detection of RGWs.     

Wave nonreciprocity in inhomogeneous gyrotropic media and multilayer systems: II. Multilayer systems

The propagation of electromagnetic waves in multilayer systems with a naturally (or structurally) gyrotropic layer (layers) is considered. A new mechanism of wave nonreciprocity is revealed. In particular, the wave nonreciprocity in multilayer systems with gyrotropic layers is investigated and a simple multilayer system consisting of a layer of a cholesteric liquid crystal and a substrate is considered. It is shown that multilayer systems with strong nonreciprocity can be used as optical diodes or optical isolators (which transmit signals through an optical channel in one direction and block signals propagating in the opposite direction) and systems for accumulation of light energy.     

连续多阈值神经元反馈神经网络盲检测光基带信号

空间分集接收可补偿信道衰落,提出了一种基于幅相联合激励法的连续多阈值神经元反馈神经网络(RNNCMVN)的光基带信号直接盲检测方法。针对多进制相移键控(MPSK)信号的特点,设计了两种连续相位多阈值激励函数形式,并简要讨论了该两类激励函数参数的选择;分别推演基于幅相联合激励法的RNNCMVN光基带信号盲检测方法工作于同步和异步两种模式下的新能量函数及其相关证明。同时针对正交调幅(QAM)信号的特点,分别设计出连续振幅和相位多阈值激励函数形式,最后通过仿真验证了该方法的有效性。     

Simultaneous four channel wavelength conversion of 50Gbps CSRZ–DPSK signals in S and C bands using HNLF without additional pump signals

Optical wavelength conversion is expected to be an important technique for future advanced dense wavelength division multiplexing systems. It enhances wavelength routing capabilities, improves network reconfigurability and eliminating the problem associated with wavelength reuse in network. Here, simultaneous 50Gbps four channel wavelength conversion is established in S and C bands of ITU grid using four wave mixing (FWM) technique in high nonlinear fiber (HNLF) without additional pump signals. Since the four channel wavelength conversion is to be performed, the frequency spacing between the pairs of signal in S and C bands should be maintained in order to avoid the signal degradation by the effect of higher order FWM. Thereby the best frequency spacing between the pairs of signals in S and C bands is estimated to maintain good BER over the wavelength converted signals of both bands. So the selected frequency spacing between the pairs fulfills the freedom of selecting any frequency spacing within a pair of wavelengths in S and C band signals. It is also shown that CSRZ–DPSK modulated input signal enhances the BER of wavelength converted signals over the RZ–DPSK. In addition to this, uniform wavelength conversion over a wide bandwidth with a reduced length of HNLF is achieved and also the best power range is estimated to obtain good conversion efficiency.     

Multipath-enabled super-resolution for rf and microwave communication using phase-conjugate arrays

We demonstrate experimentally that phase-conjugate techniques can be used to achieve super-resolution focusing of electromagnetic waves in a multipath indoor environment at 2.45 GHz. The focusing phenomena was used to direct independent signals to two locations separated by approximately one-half wavelength, thereby creating two simultaneous channels at the same frequency. An increase in channel capacity is shown to be achievable by an experimental transmission of a 1 Mbps signal over two channels created using a four element phase-conjugate array.     

Dynamics of high-frequency modulated waves in a nonlinear dissipative continuous bi-inductance network

This paper presents intensive investigation of dynamics of high frequency nonlinear modulated excitations in a damped bimodal lattice. The effects of the dissipation are considered through a linear dissipation coefficient whose evolution in terms of the carrier wave frequency is checked. There appears that the dissipation coefficient increases with the carrier wave frequency. In the linear limit and for high frequency waves, study of the asymptotic behavior of plane waves reveals the existence of two additional regions in the dispersion curve where the modulational phenomenon is observed compared to the lossless line. Based on the multiple scales method exploited in the continuum approximation using an appropriate decoupling ansatz for the voltage of the two different cells, it appears that the motion of modulated waves is described by a dissipative complex Ginzburg–Landau equation instead of a Korteweg–de Vries equation. We also show that this amplitude wave equation admits envelope and hole solitons in the high frequency mode. From basic sources, we design a programmable electronic generator of complex signals with desired characteristics, which delivers signals exploited as input waves for all our numerical simulations. These simulations are performed in the LTspice software that uses realistic components and give the results that corroborate perfectly our analytical predictions.     

Methods for calculating low-frequency surface reverberation at known sea roughness characteristics

The problem of estimating the parameters of a reverberation signal generated due to scattering of acoustic waves on a rough surface is considered for a bistatic localization scheme using the example of tone and tone-pulse signals. Relatively simple calculation schemes that make it possible to recalculate three-dimensional space-time roughness spectra into angular-frequency reverberation characteristics and determine the positions of the surface regions that mainly contribute to the integral reverberation level are found. A reverberation spectrum is calculated for the wind waves typical for shallow-water closed basins, and the positions of the scattering regions forming the components of this spectrum are determined.     

Highlight model of echoes from sonar targets

I.IntroductionTheecho-rangingapproachistheonlycffectiveapproachfordetectionandidentifi-cationofunderwatertargetifitisasilcntobkct.Echoformationisaphysicalprocessinwhichthetargetisexcitcdbyincidentwavc.Byechothecharactcristicinformationsoftargethavebcencarricd.Suchinformationsarejustfundamentalsofdetectionandiden-hficationappliedbyactivesonars.Classificationandidentificationareimportantdevelopmentsofreccntsonarsin-c1udingthehomersoftorpedocs.Thisneedsadecpunderstandingrcferredtoechobe-haviors…     

Study of a novel range-dependent propagation effect with application to the axial injection of signals from the Kaneohe source

A novel range-dependent propagation effect occurs when a source is placed on the seafloor in shallow water with a downward refracting sound speed profile, and sound waves propagate down a slope into deep water. Under these conditions, small grazing-angle sound waves slide along the bottom downward and outward from the source until they reach the depth of the sound channel axis in deep water, where they are detached from the sloping bottom and continue to propagate outward near the sound channel axis. This "mudslide" effect is one of a few robust and predictable acoustic propagation effects that occur in range-dependent ocean environments. As a consequence of this effect, a bottom mounted source in shallow water can inject a significant amount of acoustic energy into the axis of the deep ocean sound channel that can then propagate to very long ranges. Numerical simulations with a full-wave range-dependent acoustic model show that the Kaneohe experiment had the appropriate source, bathymetry, and sound speed profiles that allows this effect to operate efficiently. This supports the interpretation that some of the near-axial acoustic signals, received near the coast of California from the bottom mounted source located in shallow water in Kaneohe Bay, Oahu, Hawaii, were injected into the sound channel of the deep Pacific Ocean by this mechanism. Numerical simulations suggest that the mudslide effect is robust.     

采用超声导波特征参量的骨质疏松识别方法

骨质的定期检测对骨质疏松的防治至关重要。本文研究了骨质疏松对超声导波在人体长骨中传播的影响。提出采用多尺度小波变换方法对接收到的导波信号进行处理,通过分析在不同传播距离下高阶小波细节分量所占信号总能量的变化,来判断是否患有骨质疏松症。在13位志愿者的小腿胫骨上进行超声测量,得到导波信号。经多尺度小波变换方法的分析处理结果显示在13位志愿者中,有7位志愿者的超声导波信号随着传播距离的改变,其主要频率成分发生了明显的变化,显示这7位志愿者患有骨质疏松症。这一诊断结果与X射线技术诊断结果相比,准确率可以达到92.3%,表明本文所提出的利用小波多尺度变换方法对长骨进行超声诊断具有较好的潜力。      

多通道超声兰姆波检测板状结构中的裂纹

超声兰姆(Lamb)波在结构缺陷检测方面愈来愈受到重视,但目前Lamb波的应用局限于单信号源激励,单通道接收的方法,容易受到噪声干扰,其后续的信号分析处理也比较复杂。本文旨在采用多通道Lamb波对板状结构中的裂纹进行定量分析与诊断。在铝板的表面凿刻出不同深度的凹槽作为裂纹,通过线阵换能器采集在一定传播距离内的多通道Lamb波信号,并采用二维傅里叶变换分析在不同深度的裂纹下,Lamb波模式能量的变化规律。结果表明,相对于完好铝板中的Lamb波信号,裂纹的存在会使Lamb波发生模式转换现象,并且转换模式能量百分比随裂纹深度的增加而线性增加。其结果为Lamb波评价板状结构中的裂纹状况提供了一种可能的方法。     

Fundamental study on subharmonic imaging by irradiation of amplitude-modulated ultrasound waves

The second harmonic and subharmonic components, the frequencies of which are twice and one half the fundamental frequency, are included in echoes from contrast agents. An imaging method, which employs a second harmonic (second harmonic imaging), is widely used in medical diagnoses. On the other hand, subharmonic is expected to provide a higher contrast between biological tissues and blood flow because echo signals are generated only from blood containing the contrast agents. However, the subharmonic component echo signal power from contrast agents is relatively low. This has resulted in little progress in the field of subharmonic imaging. In this study, a new imaging method is proposed using amplitude-modulated waves as transmitted waves combined with the pulse inversion method to enhance subharmonic echo signals. Two optimal frequencies are set, including the modulated waves, F(1) and F(2), so that the subharmonic frequency of F(1) and the second harmonic frequency of F(2) may result in the same value. This allows a more powerful signal at the frequency band because the second harmonic and subharmonic components are integrated. Furthermore, a B-mode ultrasound image of an agar phantom that imitated biological tissue and showed the effectiveness of our method was reconstructed. As a result, the echo power of the subharmonic component was enhanced by approximately 11.8 dB more than the conventional method and the signal to noise ratio showed an improvement of 7.6 dB.     

钠离子和钾离子通道噪声扰动对神经网络 时空模式的影响

研究了钠离子和钾离子通道噪声扰动对Hodgkin-Huxley神经网络放电时空模式的影响. 发现无论钠离子通道噪声还是钾离子通道噪声扰动, 当取定一组温度、噪声强度, 随着耦合强度的增大, 神经网络放电时空斑图总能演化出螺旋波, 而且存在形成螺旋波所需的临界耦合强度. 分析发现钠离子通道噪声有利于神经网络螺旋波的形成, 而钾离子通道噪声不利于螺旋波形成. 结果还表明较低的温度能够使神经网络对噪声更加敏感. 最后, 讨论了特定参数下螺旋波与靶波之间的转化现象.     

Boson peak, flickering noise, backscattering processes and radiative transfer in random media

The method of matrix Green’s functions in the classical theory of electromagnetic waves is stated. This method allows to obtain a closed equation system in the presence of the random media for the calculation both coherent, and incoherent (fluctuating) components of radiation. The density and heterogeneity of scattering media can be arbitrary. The coherent channel is calculated independently. The fluctuating radiation distribution in the medium is developed initially by an interference pattern generated by the coherent channel. The limitations of the processes speed are absent. The theory embraces such phenomena as the boson peak, flickering noise, memory effect, backscattering processes and also conventional radiative transfer equation and Fresnel’s formulae.