Time Domain Full Waveform Inversion Based on Gradient Preconditioning with an Angle-Dependent Weighting Factor

There are lots of low wavenumber noises in the gradients of time domain full waveform inversion(FWI),which can seriously reduce the accuracy and convergence speed of FWI.Thus,we introduce an angle-dependent weighting factor to precondition the gradients so as to suppress the low wavenumber noises when the multi-scale FWI is implemented in the high frequency.Model experiments show that the FWI based on the gradient preconditioning with an angle-dependent weighting factor has faster convergence speed and higher inversion accuracy than the conventional FWI.The tests on real marine seismic data show that this method can adapt to the FWI of field data,and provide high-precision velocity models for the actual data processing.

Angle-dependent discoloration structures in wing scales of Morpho menelaus butterfly

The Morpho butterfly is famous for its typical structural color and has increasingly attracted the interest of scholars in a wide variety of research fields. Herein, it was found that the color of Morpho menelaus butterfly wings is not only structure-based but also viewing-angle-dependent. Firstly, the discoloration effect of this typical butterfly was confirmed by a series of experiments. Then, the general form, arrangements, and geometrical dimensions of the scales were observed using a stereomicroscope. Scanning electron microscopy was also used to examine the two-dimensional morphologies and structures of a single scale. Afterwards, one model with the optimized three-dimensional profile of the structure was described using Pro-engineer software. The associate model was then analyzed to reconstruct the process between the incident light and the model surface. Finally, the mechanism of the angle-dependent discoloration effect was analyzed by theoretical calculation and optical simulation. Different light propagation paths and the length of the incident light at different angles caused destructive or constructive interference between the light reflected from the different layers. The different spectra of the reflected light make the wings appear with different structural colors, thereby endowing the angle-dependent discoloration effect. The consistency of the calculation and simulation results confirms that these structures possess an excellent angle-dependent discoloration effect. This functional "biomimetic structure" would not only be of great scientific interest but could also have a great impact in a wide range of applications such as reflective displays, credit card security, and military stealth technology.

Optical and Nanomechanical Characteristics of Multilayer Structure Derived from Color-changing Beetle Popillia Indgigonacea Motsch

The architecture of multilayer acting in colorful appearance has been widely reported.In spite of this,it is interesting that dense multilayer in epicuticle for Popillia indgigonacea Motsch elytra not only helps presenting angle dependence color-changing,but also showing higher reduced modulus(Er)and hardness(H)to protect soft abdomen below.The optical and nanomechanical properties of elytron were investigated by structural observation,optical experiments,nanoindentation and coupled bionic model simulations.The peak reflectance gradually varies from 588 nm to 510 nm with color change from orange and yellow to green when the incidence angle switches from 0°to 60°,which is attributed to the regulated variation from refractive spectra between the layers in different angle.In addition,the relatively higher Er and H of elytron epicuticle and endocuticle could play a role in resisting force with its multilayer.To identify the multifunctional characteristics of multilayer,optical and mechanical simulations were conducted based on coupled bionic models,and a strong consistence between the experiments and simulations is obtained.The multilayer could resist force with lowest strain and stress,and the structural thickness is the most necessary factors that could adjust the colors in color-changing process.