Coexisting fast–slow dendritic traveling waves in a 3D-array electric field coupled neuronal network

Coexistence of fast and slow traveling waves without synaptic transmission has been found in hhhippocampal tissues,which is closely related to both normal brain activity and abnormal neural activity such as epileptic discharge. However, the propagation mechanism behind this coexistence phenomenon remains unclear. In this paper, a three-dimensional electric field coupled hippocampal neural network is established to investigate generation of coexisting spontaneous fast and slow traveling waves. This model captures two types of dendritic traveling waves propagating in both transverse and longitude directions: the N-methyl-D-aspartate(NMDA)-dependent wave with a speed of about 0.1 m/s and the Ca-dependent wave with a speed of about 0.009 m/s. These traveling waves are synaptic-independent and could be conducted only by the electric fields generated by neighboring neurons, which are basically consistent with the in vitro data measured experiments. It is also found that the slow Ca wave could trigger generation of fast NMDA waves in the propagation path of slow waves whereas fast NMDA waves cannot affect the propagation of slow Ca waves. These results suggest that dendritic Ca waves could acted as the source of the coexistence fast and slow waves. Furthermore, we also confirm the impact of cellular spacing heterogeneity on the onset of coexisting fast and slow waves. The local region with decreasing distances among neighbor neurons is more liable to promote the onset of spontaneous slow waves which, as sources, excite propagation of fast waves. These modeling studies provide possible biophysical mechanisms underlying the neural dynamics of spontaneous traveling waves in brain tissues.

Inverting the rock mass P-wave velocity field ahead of deep buried tunnel face while borehole drilling

Imaging the wave velocity field surrounding a borehole while drilling is a promising and urgently needed approach for extending the exploration range of the borehole point.This paper develops a drilling process detection(DPD)system consisting of a multifunctional sensor and a pilot geophone installed at the top of the drilling rod,geophones at the tunnel face,a laser rangefinder,and an onsite computer.A weighted adjoint-state first arrival travel time tomography method is used to invert the P-wave velocity field of rock mass while borehole drilling.A field experiment in the ongoing construction of a deep buried tunnel in southwestern China demonstrated the DPD system and the tomography method.Time-frequency analysis of typical borehole drilling detection data shows that the impact drilling source is a pulse-like seismic exploration wavelet.A velocity field of the rock mass in a triangular area defined by the borehole trajectory and geophone receiving line can be obtained.Both the borehole core and optical image validate the inverted P-wave velocity field.A numerical simulation of a checkerboard benchmark model is used to test the tomography method.The rapid convergence of the misfits and consistent agreement between the inverted and observed travel times validate the P-wave velocity imaging.

Analysis of complicated structure seismic wave fields

In western China seismic wave fields are very complicated and have low signal to noise ratio.In this paper,we focus on complex wave field research by forward modeling and indicate that density should not be ignored in wave field simulation if the subsurface physical properties are quite different.We use the acoustic wave equation with density in the staggered finite-difference method to simulate the wave fields.For this purpose a complicated geologic structural model with rugged surfaces,near-surface low-velocity layers,and high-velocity outcropping layers was designed.Based on the instantaneous wave field distribution,we analyzed the mechanism forming complex wave fields.The influence of low velocity layers on the wave field is very strong.A strong waveguide occurs between the top and base of a low velocity layer,producing multiples which penetrate into the earth and form strong complex wave fields in addition to reflections from subsurface interfaces.For verifying the correctness of the simulated wave fields,prestack depth migration was performed using different algorithms from the forward modeling.The structure revealed by the stacked migration profile is same as the known structure.

Numerical modeling of seismic wavefields in transversely isotropic media with a compact staggered-grid finite difference scheme

To deal with the numerical dispersion problem, by combining the staggeredgrid technology with the compact finite difference scheme, we derive a compact staggered- grid finite difference scheme from the first-order velocity-stress wave equations for the transversely isotropic media. Comparing the principal truncation error terms of the compact staggered-grid finite difference scheme, the staggered-grid finite difference scheme, and the compact finite difference scheme, we analyze the approximation accuracy of these three schemes using Fourier analysis. Finally, seismic wave numerical simulation in transversely isotropic （VTI） media is performed using the three schemes. The results indicate that the compact staggered-grid finite difference scheme has the smallest truncation error, the highest accuracy, and the weakest numerical dispersion among the three schemes. In summary, the numerical modeling shows the validity of the compact staggered-grid finite difference scheme.

Research on the Seismic Wave Field of Karst Cavern Reservoirs near Deep Carbonate Weathered Crusts

Fracture and cavern hydrocarbon reservoirs in carbonates are an important pool type worldwide. The karst cavern reservoirs are easiest to identify on seismic reflection data. The prediction, exploration, and development of this type of reservoir require theoretical research on seismic wave fields reflected from complex inhomogeneous media. We compute synthetic seismic sections for fluidfilled cavern reservoirs of various heights and widths using random media models and inhomogeneous media elastic wave equations. Results indicate that even caverns significantly smaller than 1/ 4 wavelength are detectible on conventional band-width seismic sections as diffractions migrated into bead-type events. Diffraction amplitude is a function of cavern height and width. We introduce a width-amplitude factor which can be used to calculate the diffraction amplitude of a cavern with a limited width from the diffraction amplitude computed for an infinitely wide cavern.

Modeling of the whole process of shock wave overpressure of freefield air explosion

The waveform of the explosion shock wave under free-field air explosion is an extremely complex problem.It is generally considered that the waveform consists of overpressure peak,positive pressure zone and negative pressure zone.Most of current practice usually considers only the positive pressure.Many empirical relations are available to predict overpressure peak,the positive pressure action time and pressure decay law.However,there are few models that can predict the whole waveform.The whole process of explosion shock wave overpressure,which was expressed as the product of the three factor functions of peak,attenuation and oscillation,was proposed in the present work.According to the principle of explosion similarity,the scaled parameters were introduced and the empirical formula was absorbed to form a mathematical model of shock wave overpressure.Parametric numerical simulations of free-field air explosions were conducted.By experimental verification of the AUTODYN numerical method and comparing the analytical and simulated curves,the model is proved to be accurate to calculate the shock wave overpressure under free-field air explosion.In addition,through the model the shock wave overpressure at different time and distance can be displayed in three dimensions.The model makes the time needed for theoretical calculation much less than that for numerical simulation.

Numerical Simulation of Wave Field near Submerged Bars by PLIC-VOF Model

Investigating the wave field near structures in coastal and offshore engineering is of increasing significance. In the present study, simulation is done of the wave profile and flow field for waves propagating over submerged bars, using PLIC-VOF （Pieeewise Linear Interface Construction） to trace the free surface of wave and finite difference method to solve vertical 2D Navier-Stokes （N-S） equations. A comparison of the numerical results for two kinds of submerged bars with the experimental ones shows that the PLIC-VOF model used in this study is effective and can compute the wave field precisely.

Characteristic analysis of wind field and sea wave field over the NW Pacific Ocean

According to ship observation data over the NW Pacific Ocean during 1950 - 1995. taking 5°×5° grid, the characteristics and variation rule of wind, wave and swell are analyzed. This area is typical monsoon area. In the period of monsoon, the directions of wind, sea wave and swell are roughly consistent. Sea wave of northeasterly is always prevailing in equatorial zone. The monsoon in winter is stronger than in summer, correspondingly, average wave height is higher, and the frequencies of high sea and heavy swell are also bigger. Both of North Indian Ocean and adjacent sea area is also monsoon area, but characteristic is opposite. This paper provides specific data of wind field and wave field and variaton for ship navigation, operation and scientific experiment in the NW Pacific Ocean.

SCATTERING FAR FIELD SOLUTION OF SH-WAVE BY MOVABLE RIGID CYLINDRICAL INTERFACE INCLUSION

The Green's function is used to solve the scattering far fieldsolution of SH-wave by a mov- able rigid cylindrical interfaceinclusion in a linear elastic body. First, a suitable Green'sfunction is devel- oped, which is the fundamental displacementsolution of an elastic half space with a movable rigid half-cylin-drical inclusion impacted by out-of-plane harmonic line source loadedat any point of its horizontal surface.

Theoretical study of the influence of intense femtosecond laser field on the evolution of the wave packet and the population of NaRb molecule

Employing the two-state model and the time-dependent wave packet method, we have investigated the influences of the parameters of the intense femtosecond laser field on the evolution of the wave packet, as well as the population of ground and double-minimum electronic states of the NaRb molecule. For the different laser wavelengths, the evolution of the wave packet of 6{ }^1／Sigma ^ ＋ state with time and internuclear distance is different, and the different laser intensity brings different influences on the population of the electronic states of the NaRb molecule. One can control the evolutions of wave packet and the population in each state by varying the laser parameters appropriately, which will be a benefit for the light manipulation of atomic and molecular processes.

Direct Generation of Intense Compression Waves in Molten Metals by Using a High Static Magnetic Field and Their Application

Compression waves propagating through molten metals are contributed to degassing, accelerating reaction rate,removing exclusions from molten metals and refining solidification structures during metallurgical processing of materials. In the present study, two electromagnetic methods are proposed to generate intense compression wavesdirectly in liquid metals. One is the simultaneous imposition of a high frequency electrical current field and a staticmagnetic field; the other is that of a high frequency magnetic field and a static magnetic field. A mathematical modelbased on compressible fluid dynamics and electromagnetic fields theory has been developed to derive pressure distributions of the generated waves in a metal. It shows that the intensity of compression waves is proportional to thatof the high frequency electromagnetic force. And the frequency is the same as that of the imposed electromagneticforce. On the basis of theoretical analyses, pressure change in liquid gallium was examined by a pressure transducerunder various conditions. The observed results approximately agreed with the predictions derived from the theoreticalanalyses and calculations. Moreover, the effect of the generated waves on improvement of solidification structureswas also examined. It shows that the generated compression waves can refine solidification structures when they wereapplied to solidification process of Sn-Pb alloy. This study indicates a new method to generate compression wavesby imposing high frequency electromagnetic force locally on molten metals and this kind of compression waves canprobably overcome the difficulties when waves are excited by mechanical vibration in high temperature environments.

Influence of laser fields on the vibrational population of molecules and its wave-packet dynamical investigation

The time-dependent wave packet method is used to investigate the influence of laser-fields on the vibrational population of molecules. For a two-state system in laser fields, the populations on different vibrational levels of the upper and lower electronic states are given by wavefunctions obtained by solving the Schrbdinger equation with the split- operator method. The calculation shows that the field parameters, such as intensity, wavelength, duration, and delay time etc. can have different influences on the vibrational population. By varying the laser parameters appropriately one can control the evolution of wave packet and so the vibrational population in each state, which will benefit the light manipulation of atomic and molecular processes.

Multidimensional manipulation of wave fields based on artificial microstructures

Artificial microstructures,which allow us to control and change the properties of wave fields through changing the geometrical parameters and the arrangements of microstructures,have attracted plenty of attentions in the past few decades.Some artificial microstructure based research areas,such as metamaterials,metasurfaces and phononic topological insulators,have seen numerous novel applications and phenomena.The manipulation of different dimensions(phase,amplitude,frequency or polarization)of wave fields,particularly,can be easily achieved at subwavelength scales by metasurfaces.In this review,we focus on the recent developments of wave field manipulations based on artificial microstructures and classify some important applications from the viewpoint of different dimensional manipulations of wave fields.The development tendency of wave field manipulation from single-dimension to multidimensions provides a useful guide for researchers to realize miniaturized and integrated optical and acoustic devices.

Numerical Simulation of the Protective Effect of Complex Boundaries Toward Shock Waves in a 3D Explosive Field

A numerical method is presented that simulates 3D explosive field problems. A code MMIC3D using this method can be used to simulate the propagation and reflected effects of all kinds of rigid boundaries to shock waves produced by an explosive source. These numerical results indicate that the code MMIC3D has the ability in computing cases such as 3D shock waves produced by air explosion, vortex region of the shock wave, the Mach wave, and reflected waves behind rigid boundaries.

Peak Profile Analysis in High Field Asymmetric Wave Ion Mobility Spectrometry

High field asymmetric wave ion mobility spectrometry （FAIMS） is a powerful tool to detect and characterize gas-phase ions, while the unsolvable partial differential equation of ions moving in ion drift tube poses a big challenge to FAIMS spectral peak analysis. In this work, a universal and effective model of FAIMS spectral peak profile has been proposed by introducing ion trajectory and loss height. With this model, the influence of the structure of ion drift tube, dispersion voltages, compensation voltages, and carrier gas flow rate on the FAIMS spectral peak characteristics like peak shape, full width at half maximum and peak height is analyzed and discussed. The results show that the influence of different factors on the FAIMS spectral peak profile can be qualitatively described by the model which agrees with the experimental data.

The study of perfectly matched layer absorbing boundaries for SH wave fields

When modeling wave propagation in infinite space, it is necessary to have stable absorbing boundaries to effectively eliminate spurious reflections from the truncation boundaries. The SH wave equations for Perfectly Matched Layers （PML） are deduced and their Crank-Nicolson scheme are presented in this paper. We use the second-, sixth-, and tenth-order finite difference and pseudo-spectral algorithms to compute the spatial derivatives. Two numerical models, a homogeneous isotropic medium and a multi-layer model with a cave, are designed to investigate how the absorbing boundary width and the algorithms determine PML effects. Numerical results show that, for PML, the low-order finite difference algorithms have fairly good absorbing effects when the absorbing boundary is thin, whereas, high-order algorithms always have good absorption when the boundary is thick. Finally, we discuss the reflection coefficient and point out its shortcomings, which is why we use the SNR to quantitatively scale the PML effects,

Nearshore Wave Field Analysis Using SAR Images

Satellite remote sensing technique offers a wide range of information, and is one of the tools for ocean wave observation. This paper discusses the limitations of Synthetic Aperture Radar (SAR) images in wave field analysis. It is found that the wave field analysis is affected by the gray value distribution of image and the relationship between satellite travel and wave propagation directions. Since human activities and coastal engineering are performed in nearshore areas, some issues are discussed for nearshore SAR image analysis. Several case studies show that the wave parameters estimated from nearshore SAR images are quite different from in situ measurements, suggesting that the wave information derived from nearshore SAR images cannot appropriately represent the wave characteristics. One of the reasons is that the wave field is non homogeneous in the nearshore area.

WAVE FIELD EXTRAPOLATION IN VISCOELASTIC MEDIUM AND VARIABLE FOCUS METHOD TO SEPARATE SEISMIC COMPOUND WAVE

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Mathematical model of wave transformation over radial sand ridge field on continental shelf of South Yellow Sea

According to a deformed mild-slope equation derived by Guang-wen Hong and an enhanced numerical method, a wave refraction-diffraction nonlinear mathematical model that takes tidal level change and the high-order bathymetry factor into account has been developed. The deformed mild-slope equation is used to eliminate the restriction of wave length on calculation steps. Using the hard disk to record data during the calculation process, the enhanced numerical method can save computer memory space to a certain extent, so that a large-scale sea area can be calculated with high-resolution grids. This model was applied to wave field integral calculation over a radial sand ridge field in the South Yellow Sea. The results demonstrate some features of the wave field： （1） the wave-height contour lines are arc-shaped near the shore; （2） waves break many times when they propagate toward the shore; （3） wave field characteristics on the northern and southern sides of Huangshayang are different; and （4） the characteristics of wave distribution match the terrain features. The application of this model in the region of the radial sand ridge field suggests that it is a feasible way to analyze wave refraction-diffraction effects under natural sea conditions.

Development of a helicon-wave excited plasma facility with high magnetic field for plasma-wall interactions studies

The high magnetic field helicon experiment system is a helicon wave plasma（HWP）source device in a high axial magnetic field（B0）developed for plasma–wall interactions studies for fusion reactors.This HWP was realized at low pressure（5×10^-3-10 Pa）and a RF（radio frequency,13.56 MHz）power（maximum power of 2 k W）using an internal right helical antenna（5 cm in diameter by 18 cm long）with a maximum B0of 6300 G.Ar HWP with electron density～10^18–10^20m^-3 and electron temperature～4–7 e V was produced at high B0 of 5100 G,with an RF power of 1500 W.Maximum Ar^＋ion flux of 7.8×10^23m^-2s^-1 with a bright blue core plasma was obtained at a high B0 of 2700 G and an RF power of 1500 W without bias.Plasma energy and mass spectrometer studies indicate that Ar^＋ ion-beams of 40.1 eV are formed,which are supersonic（～3.1cs）.The effect of Ar HWP discharge cleaning on the wall conditioning are investigated by using the mass spectrometry.And the consequent plasma parameters will result in favorable wall conditioning with a removal rate of 1.1×10^24N2/m^2 h.