Common mechanics of mode switching in locomotion of limbless and legged animals

Crawling using muscular waves is observed in many species, including planaria, leeches, nemertea, aplysia, snails, chitons, earthworms and maggots. Contraction or extension waves propagate along the antero-posterior axis of the body as the crawler pushes the ground substratum backward. However, the observation that locomotory waves can be directed forward or backward has attracted much attention over the past hundred years. Legged organisms such as centipedes and millipedes exhibit parallel phenomena; leg tips form density waves that propagate backward or forward. Mechanical considerations reveal that leg-density waves play a similar role to locomotory waves in limbless species, and that locomotory waves are used by a mechanism common to both legged and limbless species to achieve crawling. Here, we report that both mode switching of the wave direction and friction control were achieved when backward motion was induced in the laboratory. We show that the many variations of switching in different animals can essentially be classified in two types according to mechanical considerations. We propose that during their evolution, limbless crawlers first moved in a manner similar to walking before legs were obtained. Therefore, legged crawlers might have learned the mechanical mode of movement involved in walking long before obtaining legs.     

Forward/Backward Switching of Plasmonic Wave Propagation Using Sign‐Reversal Coupling

Backward waves with wave‐front propagation opposite in direction to that of energy flow have attracted considerable interest in the context of photonic metamaterials. However, switching between forward and backward waves in the same frequency range has remained a challenge. Here, on a platform of coupled designer surface plasmon resonators in the microwave regime, multiband forward/backward switching of plasmonic wave propagation is demonstrated. This approach makes use of sign‐reversal coupling that occurs when switching the coupling configuration between tightly confined photonic modes. Direct experimental measurements of plasmon dispersion curves confirm the forward/backward propagation of plasmonic waves in the same frequency range. This study provides a solution to forward/backward switching of subwavelength plasmonic wave propagation, and may find potential applications in photonic integrated systems.     

Characteristics of radiation generated during the conversion of backward bulk magnetostatic waves into electromagnetic waves

The directivity diagram of electromagnetic waves, generated during the propagation of backward bulk magnetostatic waves (BMSWs) in a ferrite plate tangentially magnetized by a decreasing field has been calculated using a model of the accelerated motion of magnetic charges. It is shown that the directivity diagram consists of two lobes, which are symmetric with respect to the ferrite plate surface and tilted back relative to the direction of backward BMSW propagation.     

Analysis of the left-handed corrugated circular waveguide

Infinite circular corrugated waveguide is analysed to investigate its ability to support modes with backward wave behaviour. Such waveguides provide an alternative structure, easier to manufacture than those already reported based on rectangular symmetry with corrugated walls or filled with frequency selective surfaces. The corrugations if sufficiently deep provide a guiding structure with the required series capacitance and shunt inductance to allow left-handed propagation within some frequency bands. These backward waves are analysed using the surface impedance model of propagation in corrugated waveguides to predict their properties. Interpreting the physical meaning of the analysis, the authors discuss how backward waves are related to resonances in corrugated structures. The relationship between power flows in the guide and the behaviour of the group velocity for such guides is shown. A full wave simulator is also applied to validate these results and the case of a dielectric filled waveguide is considered showing the improved ability to support left-handed modes. The authors present the results of a parametric study of how left-handed propagation depends on the corrugation depth. Potential applications of backward waves in corrugated circular waveguides are proposed.     

Hybridization of backward acoustic waves in piezoelectric plates

The phenomenon of hybridization of the backward acoustic waves propagating in a piezoelectric crystal plate has been studied. In an electrically free plate (in particular, of potassium niobate) with a crystal orientation for which a sagittal plane is the symmetry plane, the dispersion curves of backward acoustic waves exhibit points of intersection and hybridization is absent. However, for a small change in the direction of wave propagation, the dispersion curves exhibit “repulsion” and the waves become coupled. The degree of hybridization is quantitatively evaluated in terms of the hybridization coefficient, which is defined as the ratio of the total mutual energy density and the total energy density of the interacting waves. It is demonstrated that the extent of repulsion of the dispersion curves for the interacting waves is determined by the dependence of the hybridization coefficient on the product of the plate thickness and the wave frequency.     

Laser Pulses Shortening at Transient Backward SRS and Forward Scattering Suppression

Abstract

Mathematical simulation of the transient SRS process is performed taking into account backward scattering and Stokes-anti-Stokes parametric coupling of the forward waves. It is shown that the parametric coupling has a slight influence on the suppression of forward scattering. A main contribution to the SRS asymmetry is made by pumping exhaustion by the backward Stokes waves. The dynamics of scattering radiation formation is studied and the conditions for obtaining high-contrast pulses at SRS compression are formulated.     

High-power pumping wave influence on the volume spin wave propagation in a ferrite film

The influence of a high-power pumping wave on the propagation of backward volume spin waves in a longitudinally magnetized ferrite film was experimentally studied. Narrowing of the frequency band of propagation and the subsequent complete suppression of the volume spin waves with an increase of the pumping power were observed for the magnetic fields and frequencies allowing three-wave processes of the volume wave splitting.     

Propagation properties of an elliptical anisotropic metamaterial cylinder

The propagation characteristics were investigated of an open elliptical cylinder comprising a uniaxial anisotropic metamaterial. The dispersion relation for hybrid modes in this cylinder was examined theoretically. It is shown that forward and backward waves can be supported by such a metamaterial cylinder. Even and odd modes have different losses in a realistic anisotropic elliptical cylinder. The forward wave can propagate longer distances than the backward wave because of its lower loss. The light can propagate backward on the cylinder without the limit of structure size. The odd modes have higher operating wavelengths than the even modes. The extraordinary properties in this structure are identified as multilayer plasmons. The validity of the effective medium approximation of this structure is examined.     

Development of an ultrastable fiber optic frequency distributionsystem using an optical delay control module [for frequency standard andVLBI]

An ultrastable fiber optic frequency distribution system is described. The ultrastable phase stability is achieved by configuring a closed phase-locked loop with a single-mode optical fiber transmission line in which two optical carrier signals with different wavelengths are transmitted as a forward and a backward signal, and installing an optical delay control module which has no differential dispersion effect between the two optical carrier waves and induces no electrical noise. A phase stabilized optical fiber (PSOF) is used for the signal transmission line. The stabilities of this system are 7.5×10^-17 and 1.1×10^-17 in Allan standard deviation at 1000 and 10000 s averaging time, respectively, while the environmental temperature of the PSOF cable varies as much as the range of 10°C and the rate of 10°C/12 h     

Nearly backward reflection of elastic waves in an acousto-optic crystal of paratellurite

Some features of the propagation and reflection of acoustic waves in the XY plane of a paratellurite crystal have been studied. It is established that the acoustic waves exhibit an unusual backward reflection from the side crystal facet in the case of glancing incidence onto the crystal-vacuum interface. The experimental results are in good agreement with theoretical predictions.     

长春花微弱电信号的ARIMA模型

依据长春花(Catharanthus roseus)植物电信号小波软阈值消噪后的数据进行其电信号时间序列的求和自回归移动平均(ARIMA)模型分析.长春花植物微弱低频电信号的模型是Xt=2Xt-1+Xt-2+tε-0.119 04tε-1-0.361 83tε-2-0.155 47tε-3-0.363 66tε-4.长春花电信号幅值后向10个点的真实值与预测值的相对误差小于15%,表明利用自回归移动平均(ARIMA)模型对植物微弱电信号特性进行预测是可行的.预测数据可作为以节能为目标依据植物自适应电信号特性建立温室和/或塑料大棚智能自动化控制系统的重要参数.     

旋转层合圆板的行波动力学特性分析

基于一阶剪切变形理论和哈密顿原理,建立了旋转层合圆板动力学运动方程和相应的边界条件。运用伽辽金法对旋转层合圆板横向振动的行波动力学特性进行了模拟,给出了其前行波、后行波振动频率随层合圆板铺层几何特征、材料参数、旋转速度等的变化规律,并对旋转层合圆板几何和材料参数对其动力失稳临界转速的影响进行了讨论。     

Wideband design of nonreciprocal phase shift magneto-optical isolators using phase adjustment in Mach-Zehnder interferometers

A wideband design is proposed for nonreciprocal phase shift magneto-optical isolators based on Mach-Zehnder interferometers. The wavelength dependence of nonreciprocal phase difference between the backward waves propagating in two interferometer arms is compensated for by that of reciprocal phase difference. This is realized by introducing an appropriate phase bias in one of interferometer arms. Two design examples are presented with a backward loss of >30 dB in the wavelength range of 1.40-1.63 microm for a magnetic garnet waveguide isolator and of 1.485-1.630 microm for a Si-wire waveguide isolator.     

Imaging of earthquake sources

Elastic waves, produced by temporally and spatially finite fault ruptures during earthquakes, propagate through the Earth. Recordings of these waves at the Earth's surface provide the data for reconstruction of the source properties, including location, spatial and temporal extents, and rupture velocities. A 2D finite-difference solution of the elastic wave equation is used to numerically extrapolate synthetic observations backward in time to create images of the energy release during an earthquake.     

Nondispersive delay line on magnetostatic waves

A new approach to the design of a nondispersive delay line on magnetostatic waves is proposed, whereby the cascades operating on the surface waves and the backward volume waves have a common passband in the same magnetic system due to a difference in the crystallogrphic orientations of ferrite waveguides cut from a {100} yttrium iron garnet film. The possibility to obtain a pulse delay time of up to 113 ± 3 ns in a 300-MHz-wide frequency band is experimentally demonstrated. The central frequency of this band can be tuned within 4–6 GHz by changing the applied magnetic field.     

The spectrum study of blood pressure during the disturbance of organic vascular beds

Abstract

Like electrical circuit components, the vascular beds in organs present impedance to waves in systemic circulation. In this study, the authors design an animal experiment to study the effect of the impedance to the pressure waves. We view the systemic circulation as an electrical circuit network, and interpret the vascular beds in organs as lumped components in the electrical circuit. Nature's designing of the systemic circulation minimizes the pressure wave reflection, and maximizes blood distribution. This is very similar to the concept adopted by electrical engineers in designing electrical circuits.     

Direct observation of a propagating spin wave induced by spin-transfer torque

Spin torque oscillators with nanoscale electrical contacts are able to produce coherent spin waves in extended magnetic films, and offer an attractive combination of electrical and magnetic field control, broadband operation, fast spin-wave frequency modulation, and the possibility of synchronizing multiple spin-wave injection sites. However, many potential applications rely on propagating (as opposed to localized) spin waves, and direct evidence for propagation has been lacking. Here, we directly observe a propagating spin wave launched from a spin torque oscillator with a nanoscale electrical contact into an extended Permalloy (nickel iron) film through the spin transfer torque effect. The data, obtained by wave-vector-resolved micro-focused Brillouin light scattering, show that spin waves with tunable frequencies can propagate for several micrometres. Micromagnetic simulations provide the theoretical support to quantitatively reproduce the results.     

Polarimetric Study of the Phase Conjugate Wave in an Isotropic Medium

Abstract

We derive expressions for the third-order nonlinearities responsible for the optical phase conjugation via backward degenerate four-wave mixing using various combinations of left and right circularly polarized beams in isotropic media. The effects of polarization conjugation and the nulling effect of phase conjugate waves are also discussed in an isotropic medium.     

Scattering by a dense finite layer of infinite cylinders at oblique incidence

This paper presents the scattering solution for a finite dense layer of cylinders irradiated by an arbitrarily polarized plane wave at a general incident direction. The theoretical formulation utilizes the effective field approach and quasi-crystalline approximation to derive the governing equations for the propagation constant and amplitudes of the effective waves. The finite layer thickness gives rise to effective waves propagating in both the forward and backward directions inside the dense medium. Formulas are developed for the far-field coherent and incoherent scattered intensities, as well as the extinction and scattering cross sections of the dense layer. The forward peak of the incoherent scattered intensity is shown to be shifted to the propagating direction of the effective waves. The influence of incident direction, layer thickness, and solid volume fraction on the scattering properties is illustrated by means of a numerical example.     

Conditions for the existence of backward surface magnetostatic waves in a ferrite-insulator-metal structure

A theoretical analysis is made of the dispersion of surface magnetostatic waves (SMSWs) at different frequencies propagating in ferrite-insulator-metal (FIM) structures magnetized by a uniform magnetic field. It is established that depending on the ratio between the thicknesses of the ferrite and insulating layers in FIM structures, backward SMSWs exist in different frequency ranges and have different wave numbers and directions of propagation. The conditions for which backward SMSWs may be observed directly in FIM structures are determined. Pis’ma Zh. Tekh. Fiz. 24, 1–7 (July 12, 1998)