Investigation of Microwave Surface-Wave Plasma Deposited SiO_x Coatings on Polymeric Substrates

In this paper, we reported nano-scale SiOx coatings deposited on polyethylene terephthalate （PET） webs by microwave surface-wave assisted plasma enhanced chemical vapor deposition for the purpose of improving their barrier properties. Oxygen （O2） and hexamethyl- disiloxane （HMDSO） were employed as oxidant gas and Si monomer during SiOx deposition, re- spectively. Analysis by Fourier transform infrared spectroscope （FTIR） for chemical structure and observation by atomic force microscopy （AFM） for surface morphology of SiO~ coatings demon- strated that both chemical compounds and surface feature of coatings have a remarkable influence on the coating barrier properties. It is noted that the processing parameters play a critical role in the barrier properties of coatings. After optimization of the SiOx coatings deposition conditions, i.e. the discharge power of 1500 W, 2 ： 1 of O2 ： HMDSO ratio and working pressure of 20 Pa, a better barrier property was achieved in this work.

Catalyst-Free Growth of Graphene by Microwave Surface Wave Plasma Chemical Vapor Deposition at Low Temperature

Catalyst-free graphene films has been synthesized by microwave (MW) surface wave plasma (SWP) chemical vapor deposition (CVD) using hydrogenated carbon source on silicon substrates at low temperature (500℃). The synthesized process is simple, low-cost and possible for application on transparent electrodes, gas sensors and thin film resistors. Analytical methods such as Raman spectroscopy, transmission electron microscopy (TEM) and four points prove resistivity measurement and UV-VIS-NIR spectroscopy were employed to characterize properties of the graphene films. The formation of multilayer of graphene on silicon substrate was confirmed by Raman spectroscopy and TEM. It is possible to grow graphene directly on silicon substrate (without using catalyst) due to high radical density of MW SWP CVD. In addition, we also observed that the hydrogen had significant role for quality of graphene.

Joint Distribution of Wave Periods and Rate of Change of Wave Surface Elevation

The rate of change of wave surface elevation is of much importance in ocean engineering, especially for the determination of the limitation of wave breaking. This paper gives a kind of joint distribution of wave periods and the rate of change of wave surface elevation by means of calculation of the two-order to four-order moment of the frequency spectrum based on the linear wave theory. For the first time, the distribution density function of wave periods determined by peaks is provided, and the conclusion is drawn that the rate of change of wave surface elevation obeys the Rayleigh distribution.

The Statistical Distribution of the Horizontal Velocities of Water Particles at Wave Surface Maxima

On the basis of the linear model of random sea waves presented by Longuet-Higgins, the statistical distribution of the horizontal velocities of water particles at wave surface maxima is derived theoretically. The derived distribution is similar to that of wave surface maxima, and a new spectral width epsilon(u), which is defined as (1 - m(3)(2)/m(2)m(4))(1/2), is introduced in the distribution. When epsilon(u) tends to zero, the distribution is reduced to Rayleigh distribution and it is reduced to the normal distribution when epsilon(u) tends to unity. For a narrow spectrum, it is proved that epsilon is equal to 1/2 epsilon, where epsilon is (1 - m(2)(2)/m(0)m(4))(1/2) and is the commonly used spectral width.

Effect of trigger system on experimental dispersion characteristics of active surface wave testing

A trigger system is typically employed in active seismic testing to trigger and synchronize multichannel surface wave data acquisition.The effect of the trigger system on the dispersion image of surface waves is empirically known to be negligible,however,theoretical explanation regarding the effect of the trigger system is insufficient.This study systematically examines the theory for surface wave dispersion analysis and proves that the effect of the trigger system on a dispersion image is negligible via a solid theoretical explanation.Subsequently,based on the new theoretical explanation,an alternative method that uses only the relative phase difference between sensors to extract dispersion characteristics with better conceptual clarity is proposed.Two active surface wave testing cases are considered to validate the theory and method.The results indicate that(1)an accurate trigger system is not necessary for surface wave data acquisition,and(2)it is unnecessary to assume that the impact point is the generation point of the surface waves for the experimental dispersion analysis.

Surface wave inversion with unknown number of soil layers based on a hybrid learning procedure of deep learning and genetic algorithm

Surface wave inversion is a key step in the application of surface waves to soil velocity profiling.Currently,a common practice for the process of inversion is that the number of soil layers is assumed to be known before using heuristic search algorithms to compute the shear wave velocity profile or the number of soil layers is considered as an optimization variable.However,an improper selection of the number of layers may lead to an incorrect shear wave velocity profile.In this study,a deep learning and genetic algorithm hybrid learning procedure is proposed to perform the surface wave inversion without the need to assume the number of soil layers.First,a deep neural network is adapted to learn from a large number of synthetic dispersion curves for inferring the layer number.Then,the shear-wave velocity profile is determined by a genetic algorithm with the known layer number.By applying this procedure to both simulated and real-world cases,the results indicate that the proposed method is reliable and efficient for surface wave inversion.

The viscous strip approach to simplify the calculation of the surface acoustic wave generated streaming

In recent decades,the importance of surface acoustic waves,as a biocompatible tool to integrate with microfluidics,has been proven in various medical and biological applications.The numerical modeling of acoustic streaming caused by surface acoustic waves in microchannels requires the effect of viscosity to be considered in the equations which complicates the solution.In this paper,it is shown that the major contribution of viscosity and the horizontal component of actuation is concentrated in a narrow region alongside the actuation boundary.Since the inviscid equations are considerably easier to solve,a division into the viscous and inviscid domains would alleviate the computational load significantly.The particles'traces calculated by this approximation are excellently alongside their counterparts from the completely viscous model.It is also shown that the optimum thickness for the viscous strip is about 9-fold the acoustic boundary layer thickness for various flow patterns and amplitudes of actuation.

Crustal and uppermost mantle structure of the northeastern Qinghai-Xizang Plateau from joint inversion of surface wave dispersions and receiver functions with P velocity constraints

Lithospheric structure beneath the northeastern Qinghai-Xizang Plateau is of vital significance for studying the geodynamic processes of crustal thickening and expansion of the Qinghai-Xizang Plateau. We conducted a joint inversion of receiver functions and surface wave dispersions with P-wave velocity constraints using data from the Chin Array Ⅱ temporary stations deployed across the Qinghai-Xizang Plateau. Prior to joint inversion, we applied the H-κ-c method(Li JT et al., 2019) to the receiver function data in order to correct for the back-azimuthal variations in the arrival times of Ps phases and crustal multiples caused by crustal anisotropy and dipping interfaces. High-resolution images of vS, crustal thickness, and vP/vSstructures in the Qinghai-Xizang Plateau were simultaneously derived from the joint inversion. The seismic images reveal that crustal thickness decreases outward from the Qinghai-Xizang Plateau. The stable interiors of the Ordos and Alxa blocks exhibited higher velocities and lower crustal vP/vSratios. While, lower velocities and higher vP/vSratios were observed beneath the Qilian Orogen and Songpan-Ganzi terrane(SPGZ), which are geologically active and mechanically weak, especially in the mid-lower crust.Delamination or thermal erosion of the lithosphere triggered by hot asthenospheric flow contributes to the observed uppermost mantle low-velocity zones(LVZs) in the SPGZ. The crustal thickness, vS, and vP/vSratios suggest that whole lithospheric shortening is a plausible mechanism for crustal thickening in the Qinghai-Xizang Plateau, supporting the idea of coupled lithospheric-scale deformation in this region.

Theoretical analysis of surface waves in piezoelectric medium with periodic shunting circuits

The investigations of surface waves in the piezoelectric medium bring out great possibility in designing smart surface acoustic wave(SAW)devices.It is important to study the dispersion properties and manipulation mechanism of surface waves in the semi-infinite piezoelectric medium connected with periodic arrangement of shunting circuits.In this study,the extended Stroh formalism is developed to theoretically analyze the dispersion relations of surface waves under different external circuits.The band structures of both the Rayleigh wave and the Bleustein-Gulyaev(BG)wave can be determined and manipulated with proper electrical boundary conditions.Furthermore,the electromechanical coupling effects on the band structures of surface waves are discussed to figure out the manipulation mechanism of adjusting electric circuit.The results indicate that the proposed method can explain the propagation behaviors of surface waves under the periodic electrical boundary conditions,and can provide an important theoretical guidance for designing novel SAW devices and exploring extensive applications in practice.

A speckle noise suppression method based on surface waves investigation and monitoring data

The internal energy distribution of waves can be described using ocean-wave spectra.In many ways,obtaining wave spectra on a global scale is critical.Surface waves investigation and monitoring onboard the Chinese-French oceanography satellite is the first space-borne instrument for detecting wave spectra specially,which was launched on October 29,2018.It can avoid the shortage of synthetic aperture radar detection results while still having some problems,especially with the effects of speckle noise.In this study,a method to suppress the speckle noise is proposed.First,the empirical formula for background speckle noise is established.Second,many spatio-temporal representative fluctuation spectra are classified and averaged.Third,rational transfer function filtering is used to obtain speckle noise close to the along-track direction.Finally,a signal-to-noise ratio threshold is used to suppress the abnormal speckle noise.This method solves the problems existing in previous denoising methods,such as excessive denoising in the along-track direction and the inability of some abnormal noises to be denoised in the two-dimensional directional wave spectra.

An ISGW Filtering Antenna with Spurious Modes and Surface Wave Suppression for Millimeter Wave Communications

In this paper,an integrated substrate gap waveguide(ISGW)filtering antenna is proposed at millimeter wave band,whose surface wave and spurious modes are simultaneously suppressed.A secondorder filtering response is obtained through a coupling feeding scheme using one uniform impedance resonator(UIR)and two stepped-impedance resonators(SIRs).To increase the stopband width of the antenna,the spurious modes are suppressed by selecting the appropriate sizes of the ISGW unit cell.Furthermore,the ISGW is implemented to improve the radiation performance of the antenna by alleviating the propagation of surface wave.And an equivalent circuit is investigated to reveal the working principle of ISGW.To demonstrate this methodology,an ISGW filtering antenna operating at a center frequency of 25 GHz is designed,fabricated,and measured.The results show that the antenna achieves a stopband width of 1.6f0(center frequency),an out-of-band suppression level of 21 dB,and a peak realized gain of 8.5 dBi.

Method of measuring one-dimensional photonic crystal period-structure-film thickness based on Bloch surface wave enhanced Goos–H?nchen shift

This paper puts forward a novel method of measuring the thin period-structure-film thickness based on the Bloch surface wave(BSW) enhanced Goos–Hanchen(GH) shift in one-dimensional photonic crystal(1DPC). The BSW phenomenon appearing in 1DPC enhances the GH shift generated in the attenuated total internal reflection structure. The GH shift is closely related to the thickness of the film which is composed of layer-structure of 1DPC. The GH shifts under multiple different incident light conditions will be obtained by varying the wavelength and angle of the measured light, and the thickness distribution of the entire structure of 1DPC is calculated by the particle swarm optimization(PSO) algorithm.The relationship between the structure of a 1DPC film composed of TiO_(2) and SiO_(2) layers and the GH shift, is investigated.Under the specific photonic crystal structure and incident conditions, a giant GH shift, 5.1 × 10^(3) times the wavelength of incidence, can be obtained theoretically. Simulation and calculation results show that the thickness of termination layer and periodic structure bilayer of 1DPC film with 0.1-nm resolution can be obtained by measuring the GH shifts. The exact structure of a 1DPC film is innovatively measured by the BSW-enhanced GH shift.

Helical streamers guided by surface electromagnetic standing waves

The streamer that is driven by the specific pulse DC discharge parameters can stably form a three-dimensional helical plasma channel in a long dielectric tube in the low-temperature plasma experiment,in cases when there were neither external background magnetic field or other factors that destroyed the poloidal symmetry of the tube.The formation mechanism and chirality of helical streamers are discussed according to the surface electromagnetic standing wave theory.The shape of the helical streamers and the characteristics of helical branches are quantitatively analyzed to further expand the application of plasma and streamer theory in the helix problem and chiral catalytic synthesis.

Evaluation of Nonbreaking Wave-Induced Mixing Parameterization Schemes Based on a One-Dimensional Ocean Model

Surface waves have a considerable effect on vertical mixing in the upper ocean.In the past two decades,the vertical mixing induced through nonbreaking surface waves has been used in ocean and climate models to improve the simulation of the upper ocean.Thus far,several nonbreaking wave-induced mixing parameterization schemes have been proposed;however,no quantitative comparison has been performed among them.In this paper,a one-dimensional ocean model was used to compare the performances of five schemes,including those of Qiao et al.(Q),Hu and Wang(HW),Huang and Qiao(HQ),Pleskachevsky et al.(P),and Ghantous and Babanin(GB).Similar to previous studies,all of these schemes can decrease the simulated sea surface temperature(SST),increase the subsurface temperature,and deepen the mixed layer,thereby alleviating the common thermal deviation problem of the ocean model for upper ocean simulation.Among these schemes,the HQ scheme exhibited the weakest wave-induced mixing effect,and the HW scheme exhibited the strongest effect;the other three schemes exhibited roughly the same effect.In particular,the Q and P schemes exhibited nearly the same effect.In the simulation based on observations from the Ocean Weather Station Papa,the HQ scheme exhibited the best performance,followed by the Q scheme.In the experiment with the HQ scheme,the root-mean-square deviation of the simulated SST from the observations was 0.43℃,and the mixed layer depth(MLD)was 2.0 m.As a contrast,the deviations of the SST and MLD reached 1.25℃ and 8.4 m,respectively,in the experiment without wave-induced mixing.

A Probability Distribution of Surface Elevation for Wind Waves in Terms of the Gram-Charlier Series

Laboratory experiments are conducted to study the probability distribution of surface elevation for wind waves and the convergence is discussed of the Gram-Charlier series in describing the surface elevation distribution. Results show that the agreement between the Gram-Charlier series and the observed distribution becomes better and better as the truncated order of the series increases in a certain range, which is contrary to the phenomenon observed by Huang and Long (1980). It is also shown that the Gram-Charlier series is sensitive to the anomalies in the data set which will make the agreement worse if they are not preprocessed appropriately. Negative values of the probability distribution expressed by the Gram-Charlier series in some ranges of surface elevations are discussed, but the absolute values of the negative values as well as the ranges of their occurrence become smaller gradually as more and mote terms are included. Therefore the negative values will have no evident effect on the form of the whole surface elevation distribution when the series is truncated at higher orders. Furthermore, a simple recurrence formula is obtained to calculate the coefficients of the Gram-Charlier series in order to extend the Gram-Charlier series to high orders conveniently.

Three dimensional shear wave velocity structure of the crust and upper mantle beneath China from ambient noise surface wave tomography

We determine the three-dimensional shear wave velocity structure of the crust and upper mantle in China using Green＇s functions obtained from seismic ambient noise cross-correlation. The data we use are from the China National Seismic Network, global and regional networks and PASSCAL stations in the region. We first acquire cross-correlation seismograms between all possible station pairs. We then measure the Rayleigh wave group and phase dispersion curves using a frequency-time analysis method from 8 s to 60 s. After that, Rayleigh wave group and phase velocity dispersion maps on 1°by 1°spatial grids are obtained at different periods. Finally, we invert these maps for the 3-D shear wave velocity structure of the crust and upper mantle beneath China at each grid node. The inversion results show large-scale structures that correlate well with surface geology. Near the surface, velocities in major basins are anomalously slow, consistent with the thick sediments. East-west contrasts are striking in Moho depth. There is also a fast mid-to-lower crust and mantle lithosphere beneath the major basins surrounding the Tibetan plateau （TP） and Tianshan （Junggar, Tarim, Ordos, and Sichuan）. These strong blocks, therefore, appear to play an important role in confining the deformation of the TP and constraining its geometry to form its current triangular shape. In northwest TP in Qiangtang, slow anomalies extend from the crust to the mantle lithosphere. Meanwhile, widespread, a prominent low-velocity zone is observed in the middle crust beneath most of the central, eastern and southeastern Tibetan plateau, consistent with a weak （and perhaps mobile） middle crust.

Lithospheric structure and deformation in SE Tibet revealed by ambient noise and earthquake surface wave tomography: Recent advances and perspectives

High-resolution lithospheric structure is essential for understanding the tectonic evolution and deformation patterns of the southeastern Tibetan plateau. This is now possible due to recent advances in ambient noise and earthquake surface wave tomography, and great improvements in data coverage from dense portable array stations deployed in SE Tibet. In this review paper, I first give a brief overview of the tomographic methods from ambient noise and earthquake surface waves, and then summarize the major findings about the lithospheric structure and deformation in SE Tibet revealed by ambient noise and earthquake surface wave tomography as well as by other seismic and geophysical observations. These findings mainly include the 3-D distribution of mechanically weak zones in the mid-lower crust, lateral and vertical variations in radial and azimuthal anisotropy, possible interplay of some fault zones with crustal weak zones, and importance of strike-slip faulting on upper crustal deformation. These results suggest that integration of block extrusion in the more rigid upper-middle crust and channel flow in the more ductile mid-lower crust will be more compatible with the current geophysical observations. Finally I discuss some future perspective researches in SE Tibet, including array-based tomography, joint inversion using multiple seismic data, and integration of geodynamic modeling and seismic observations.

Shear velocity structure of crust and uppermost mantle in China from surface wave tomography using ambient noise and earthquake data

We present a 3D model of shear velocity of crust and upper mantle in China and surrounding regions from surface wave tomography. We combine dispersion measurements from ambient noise correlation and traditional earthquake data. The stations include the China National Seismic Network, global networks, and all the available PASSCAL stations in the region over the years. The combined data sets provide excellent data coverage of the region for surface wave measurements from 8 to 120 s, which are used to invert for 3D shear wave velocity structure of the crust and upper mantle down to about 150 kin. We also derive new models of the study region for crustal thickness and averaged S velocities for upper, mid, and lower crust and the uppermost mantle. The models provide a fundamental data set for understanding continental dynamics and evolution. The tomography results reveal significant features of crust and upper mantle structure, including major basins, Moho depth variation, mantle velocity contrast between eastern and western North China Craton, widespread low-velocity zone in mid- crust in much of the Tibetan Plateau, and clear velocity contrasts of the mantle lithosphere between north and southern Tibet with significant E-W variations. The low velocity structure in the upper mantle under north and eastern TP correlates with surface geological boundaries. A patch of high velocity anomaly is found under the eastern part of the TP, which may indicate intact mantle lithosphere. Mantle lithosphere change from the western to The Tanlu Fault appears boundary. shows striking systematic eastern North China Craton. to be a major lithosphere

Dynamic modeling of wave driven unmanned surface vehicle in longitudinal profile based on D-H approach

Wave driven unmanned surface vehicle(WUSV) is a new concept ocean robot drived by wave energy and solar energy,and it is very suitable for the vast ocean observations with incomparable endurance.Its dynamic modeling is very important because it is the theoretical foundation for further study in the WUSV motion control and efficiency analysis.In this work,the multibody system of WUSV was described based on D-H approach.Then,the driving principle was analyzed and the dynamic model of WUSV in longitudinal profile is established by Lagrangian mechanics.Finally,the motion simulation of WUSV and comparative analysis are completed by setting different inputs of sea state.Simulation results show that the WUSV dynamic model can correctly reflect the WUSV longitudinal motion process,and the results are consistent with the wave theory.

Wave height measurement in the Taiwan Strait with a portable high frequency surface wave radar

As an important equipment for sea state remote sensing, high frequency surface wave radar （HFSWR） has received more and more attention. The conventional method for wave height inversion is based on the ratio of the integration of the second-order spectral continuum to that of the first-order region, where the strong external noise and the incorrect delineation of the first- and second-order Doppler spectral regions due to spectral aliasing are two major sources of errors in the wave height. To account for these factors, two more indices are introduced to the wave height estimation, i.e., the ratio of the maximum power of the second-or- der continuum to that of the Bragg spectral region （RSCB） and the ratio of the power of the second harmonic peak to that of the Bragg peak （RSHB）. Both indices also have a strong correlation with the underlying wave height. On the basis of all these indices an empirical model is proposed to estimate the wave height. This method has been used in a three-months long experiment of the ocean state measuring and analyzing ra- dar, type S （OSMAR-S）, which is a portable HFSWR with compact cross-loop/monopole receive antennas developed by Wuhan University since 2006. During the experiment in the Taiwan Strait, the significant wave height varied from 0 to 5 m. The significant wave heights estimated by the OSMAR-S correlate well with the data provided by the Oceanweather Inc. for comparison, with a correlation coefficient of 0.74 and a root mean square error （RMSE） of 0.77 m. The proposed method has made an effective improvement to the wave height estimation and thus a further step toward operational use of the OSMAR-S in the wave height extraction.