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Considering the nonlinear stiffness constraint action from the hydraulic cylinder in the four-high rolling mill process, the vertical vibration dynamic model with two degrees of freedom is established. The nonlinear vertical vibration equation of roll system contained the nonlinear stiffness of the hydraulic cylinder is established on the basis of D'Alembert's principle, and the amplitude-frequency response of the vibration system is obtained by using average method. According to the actual parameters of rolling mill, the influence of the nonlinear stiffness of the hydraulic cylinder and external force on the amplitude-frequency response of the rolling mill is analyzed. Based on it, the behavior of mill vibration under the effect of different nonlinear stiffness is studies. The results show that the nonlinear stiffness of the hydraulic cylinder is larger and the rolling mill system is more unstable. The mill vibration behavior will gradually converge to stability when the nonlinear stiffness is weaker, and the mill vibration will be in a state of instability and divergent when the nonlinear stiffness is stronger. This conclusion provides a theoretical basis to suppress vibration of rolling mill.

We have developed convolutional sparse coding (CSC) to attenuate noise in seismic data. CSC gives a data-driven set of basis functions whose coefficients form a sparse distribution. The noise attenuation method by CSC can be divided into the training and denoising phases. Seismic data with a relatively high signal-to-noise ratio are chosen for training to get the learned basis functions. Then, we use all (or a subset) of the basis functions to attenuate the random or coherent noise in the seismic data. Numerical experiments on synthetic data show that CSC can learn a set of shifted invariant filters, which can reduce the redundancy of learned filters in the traditional sparse-coding denoising method. CSC achieves good denoising performance when training with the noisy data and better performance when training on a similar but noiseless data set. The numerical results from the field data test indicate that CSC can effectively suppress seismic noise in complex field data. By excluding filters with coherent noise features, our method can further attenuate coherent noise and separate ground roll.

We have recast the forward pass of a multilayered convolutional neural network (CNN) as the solution to the problem of sparse least-squares migration (LSM). The CNN filters and feature maps are shown to be analogous, but not equivalent, to the migration Green’s functions and the quasi-reflectivity distribution, respectively. This provides a physical interpretation of the filters and feature maps in deep CNN in terms of the operators for seismic imaging. Motivated by the connection between sparse LSM and CNN, we adopt the neural network version of sparse LSM. Unlike the standard LSM method that finds the optimal reflectivity image, neural network LSM (NNLSM) finds the optimal quasi-reflectivity image and the quasi-migration Green’s functions. These quasi-migration Green’s functions are also denoted as the convolutional filters in a CNN and are similar to migration Green’s functions. The advantage of NNLSM over standard LSM is that its computational cost is significantly less and it can be used for denoising coherent and incoherent noise in migration images. Its disadvantage is that the NNLSM quasi-reflectivity image is only an approximation to the actual reflectivity distribution. However, the quasi-reflectivity image can be used as an attribute image for high-resolution delineation of geologic bodies.

Irregular topography can cause strong scattering and defocusing of propagating surface waves, so it is important to account for such effects when inverting surface waves for shallow S-wave velocity structures. We have developed a 3D surface-wave dispersion inversion method that takes into account the topographic effects modeled by a 3D spectral element solver. The objective function is the frequency summation of the squared wavenumber differences [Formula: see text] along each azimuthal angle of the fundamental mode or higher-order modes of Rayleigh waves in each shot gather. The wavenumbers [Formula: see text] associated with the dispersion curves are calculated using the data recorded along the irregular free surface. Numerical tests on synthetic and field data demonstrate that 3D topographic wave equation dispersion inversion (TWD) can accurately invert for the S-wave velocity model from surface-wave data recorded on irregular topography. Field data tests for data recorded across an Arizona fault demonstrate that, for this example, the 2D TWD model can be as accurate as the 3D tomographic model. This suggests that in some cases, the 2D TWD inversion is preferred over 3D TWD because of its significant reduction in computational costs. Compared to the 3D P-wave velocity tomogram, the 3D S-wave tomogram agrees much more closely with the geologic model taken from the trench log. The agreement with the trench log is even better when the [Formula: see text] tomogram is computed, which reveals a sharp change in velocity across the fault. The localized velocity anomaly in the [Formula: see text] tomogram is in very good agreement with the well log. Our results suggest that integrating the [Formula: see text] and [Formula: see text] tomograms can sometimes give the most accurate estimates of the subsurface geology across normal faults.

To image deeper portions of the earth, geophysicists must record reflection data with much greater source-receiver offsets. The problem with these data is that the signal-to-noise ratio (S/N) significantly diminishes with greater offset. In many cases, the poor S/N makes the far-offset reflections imperceptible on the shot records. To mitigate this problem, we have developed supervirtual reflection interferometry (SVI), which can be applied to far-offset reflections to significantly increase their S/N. The key idea is to select the common pair gathers where the phases of the correlated reflection arrivals differ from one another by no more than a quarter of a period so that the traces can be coherently stacked. The traces are correlated and summed together to create traces with virtual reflections, which in turn are convolved with one another and stacked to give the reflection traces with much stronger S/Ns. This is similar to refraction SVI except far-offset reflections are used instead of refractions. The theory is validated with synthetic tests where SVI is applied to far-offset reflection arrivals to significantly improve their S/N. Reflection SVI is also applied to a field data set where the reflections are too noisy to be clearly visible in the traces. After the implementation of reflection SVI, the normal moveout velocity can be accurately picked from the SVI-improved data, leading to a successful poststack migration for this data set.

We present a theory for wave-equation inversion of Love-wave dispersion curves, in which the misfit function is the sum of the squared differences between the wavenumbers along the predicted and observed dispersion curves. Similar to inversion of Rayleigh-wave dispersion curves, the complicated Love-wave arrivals in traces are skeletonized as simpler data, namely, the picked dispersion curves in the [Formula: see text] domain. Numerical solutions to the SH-wave equation and an iterative optimization method are then used to invert these dispersion curves for the S-wave velocity model. This procedure, denoted as wave-equation dispersion inversion of Love waves (LWD), does not require the assumption of a layered model or smooth velocity variations, and it is less prone to the cycle-skipping problems of full-waveform inversion. We demonstrate with synthetic and field data examples that LWD can accurately reconstruct the S-wave velocity distribution in a laterally heterogeneous medium. Compared with Rayleigh waves, inversion of the Love-wave dispersion curves empirically exhibits better convergence properties because they are completely insensitive to the P-velocity variations. In addition, Love-wave dispersion curves for our examples are simpler than those for Rayleigh waves, and they are easier to pick in our field data with a low signal-to-noise ratio.

The 2D wave-equation dispersion (WD) inversion method is extended to 3D wave-equation dispersion inversion of surface waves for the shear-velocity distribution. The objective function of 3D WD is the frequency summation of the squared wavenumber [Formula: see text] differences along each azimuth angle of the fundamental or higher modes of Rayleigh waves in each shot gather. The S-wave velocity model is updated by the weighted zero-lag crosscorrelation between the weighted source-side wavefield and the back-projected receiver-side wavefield for each azimuth angle. A multiscale 3D WD strategy is provided, which starts from the pseudo-1D S-velocity model, which is then used to get the 2D WD tomogram, which in turn is used as the starting model for 3D WD. The synthetic and field data examples demonstrate that 3D WD can accurately reconstruct the 3D S-wave velocity model of a laterally heterogeneous medium and has much less of a tendency to getting stuck in a local minimum compared with full-waveform inversion.

The gradient preconditioning approach based on seismic wave energy can effectively avoid the huge memory consumption of the gradient preconditioning algorithms based on the Hessian matrix. However, the accuracy of this approach is prone to be influenced by the energy of reflected waves. To tackle this problem, the paper proposes a new gradient preconditioning method based on the energy of transmitted waves. The approach scales the gradient through a precondition factor, which is calculated by the ‘approximate transmission wavefield’ simulation based on the nonreflecting acoustic wave equation. The method requires no computing nor storing of the Hessian matrix and its inverse matrix. Furthermore, the proposed method can effectively eliminate the effects of geometric spreading and disproportionality in the gradient illumination. The results of model experiments show that the time-domain full waveform inversion (FWI) using the gradient preconditioning based on transmitted wave energy can achieve higher inversion accuracy for deep high-velocity bodies and their underlying strata in comparison with the one using the gradient preconditioning based on seismic wave energy. The field marine seismic data test shows that our proposed method is also highly applicable to the FWI of field marine seismic data.

Considering the two kinds of nonlinear constraints of rolling mill hydraulic cylinder, spring force and friction force, the vibration model of rolling mill system is established. The amplitude frequency response equations are obtained by using the average method. Comparing the time history curves of vertical vibration displacement of rolling mill system under the nonlinear spring force and friction force, the amplitude frequency characteristic curves are simulated. The external excitation amplitude is viewed as the bifurcation parameter, and the system bifurcation response changing with the external excitation amplitude is analyzed. The influence of the external excitation amplitude on the system stability is studied. The results indicate that the increase of the nonlinear spring force makes the rolling mill system’s unstable area to become wider, and the influence on the rolling mill system of nonlinear friction force behaves as the damping characteristics; the vibration of rolling mill system is alternating between the periodic, period-doubling, and the chaotic motion. The research results provide a theoretical support for restraining the vibration of the rolling mill system in the actual production process.

An all-solid dispersion-compensating photonic crystal fiber based on mode coupling mechanism in dual-concentric core has been proposed. The mode coupling characteristics, dispersion, confinement loss of the fiber, and the influence on dispersion of some structure parameters are simulated by full-vector finite element method. By using the relationship between phase matching wavelengths and coupling strength with the change of fiber microstructure parameters, an all-solid dual-concentric-core dispersion-compensating photonic crystal fiber is presented. The structure parameters on dispersion characteristic are investigated. The results demonstrate that the proposed fiber has a large negative dispersion value 8465 ps/(nm·km) at 1550 nm. The effective mode area and the splicing loss to the standard single mode fiber are 12.8 μm2 and 1.89 dB at 1550 nm, respectively. At 1550 nm, the confinement loss is less than 1 × 10−3 dB/km and the bending loss with 2 cm bending diameter is less than 1 × 10−2 dB/km.

The absorption spectrum of the Yb3+-doped photonic crystal fiber covers from 770 nm to 980 nm. A less flatness broadband continuous spectrum and a short peak are generated in the uniform Yb3+-doped photonic crystal fiber. Supercontinuum from 388 nm to 1590 nm is received in the tapered Yb3+-doped photonic crystal fiber, which covers almost two octaves, generating an ultra flat (7 dB) continuous spectrum coming from 926 nm to 1554 nm in the long waveband, and receiving a 62 nm width, high and violet peak from 388 nm to 450 nm in the purple waveband by femtosecond pulse. The up conversion efficiency of pump power in tapered Yb3+-doped photonic crystal fiber is up to 59.4%, while the uniform is only 6.3%.

According to the “Hill rolling force formula”, taking particular account of the influence from horizontal vibration of rolled piece in roll gap, a dynamic rolling force model is analyzed. Considering the interaction between vibration of strip and roll, the dynamic vibration model of rolling mill is established. On this basis, the time delayed feedback is introduced to control the vibration of the roll system. The amplitude frequency response of the coupled vibration control equation is obtained by using the multiple scales method. Different time delay parameters are selected to test the control effect. Research results show that the unstable vibration of the roll system can be suppressed with appropriate time delay feedback parameters. Because it is simpler and has good control effect in solving nonlinear mechanical vibration, so these results will make a difference for the research of strip mill vibration, and provide theoretical basis for strip steel production.

We have developed a methodology for detecting the presence of near-surface heterogeneities by naturally migrating backscattered surface waves in controlled-source data. The near-surface heterogeneities must be located within a depth of approximately one-third the dominant wavelength [Formula: see text] of the strong surface-wave arrivals. This natural migration method does not require knowledge of the near-surface phase-velocity distribution because it uses the recorded data to approximate the Green’s functions for migration. Prior to migration, the backscattered data are separated from the original records, and the band-passed filtered data are migrated to give an estimate of the migration image at a depth of approximately one-third [Formula: see text]. Each band-passed data set gives a migration image at a different depth. Results with synthetic data and field data recorded over known faults validate the effectiveness of this method. Migrating the surface waves in recorded 2D and 3D data sets accurately reveals the locations of known faults. The limitation of this method is that it requires a dense array of receivers with a geophone interval less than approximately one-half [Formula: see text].

Summary Least squares migration (LSM) finds the reflectivity distribution that minimizes the regularized sum of the squared differences between the predicted and observed data. Many studies show that LSM can sometimes reduce migration artifacts due to ringy source wavelets, sparse source-receiver sampling, and weak illumination in the subsurface due to defocusing/geometric spreading of seismic waves. The most significant liability of LSM is that it costs about two rounds of migration or more, and the goal is to reduce this cost to be about that for standard migration. We now overview the current procedures of applying LSM to seismic data, point out their benefits and challenges, and suggest possible “Roads Ahead” for the improvement of LSM.

We present a novel multi-hole core photonic crystal fiber for guiding and confining light in subwavelength-diameter low-refractive-index air holes of core, even when light is guided based on total internal reflection. The low-loss, broadband and single-mode guiding properties of the fiber are studied. The propagation mechanism in subwavelength and low-refractive-index holes is analyzed by evanescent wave coupling. Light confinement and enhancement are caused by large discontinuity of the electric field at dielectric interfaces. Multiple subwavelength air holes in the core can guide light together, coupling and coherent with each other. Arrays of air holes in the core can be used as a means of patterning light on a submicrometer regime. The high light intensity in multiple long holes enables a variety of applications in nonlinear light management, optical modulation, and gas sensing.

By employing the liquid crystal refractive index changes induced by applied electric field, a novel polarization rotator with low crosstalk and shorter length of rotation has been proposed and theoretically analyzed. The mode field distribution, birefringence of the fiber fundamental mode and the influence on birefringence of some parameters are simulated by full-vector finite element method. The results demonstrate that the polarization axis of the guided mode is determined by the rotation angle. When temperature is increased from 15 °C to 45 °C, the birefringence of tellurite photonic crystal fiber filled with liquid crystal gradually decreases. At the wavelength of 1.55 μm, the polarization angle of 45°, this kind of the polarization rotator have low crosstalk and shorter length of rotation. These distinguished features ensure its important applications in the integrated optical systems.

We theoretically investigate the modes, birefringence, dispersion, confinement loss, nonlinear coefficient and the temperature properties of tellurite photonic crystal fiber filled with nematic liquid crystal. The birefringence caused by the high index difference between ordinary and extraordinary refractive indices of nematic liquid crystal makes it possible for single-mode single-polarization guiding. The influence of rotation angle of the director of liquid crystal on the modal properties is also demonstrated. The results demonstrate that the dispersion curve of tellurite photonic crystal fiber filled with nematic liquid crystal along fast axis is more flatten than that along slow axis the fast axis. The tellurite photonic crystal fiber filled with nematic liquid crystal has low confinement loss and high nonlinear coefficient. When temperature is increased from 15 °C to 45 °C, the birefringence of tellurite photonic crystal fiber filled with nematic liquid crystal gradually decreases and the dispersion along slow axis gradually becomes flat, which is very useful for making compact and diverse polarization-manipulating devices.

This paper introduces the fourth-order absorbing boundary condition (ABC) into staggered-grid finite difference forward modeling of the first-order stress–velocity acoustic equation, and develops a new method to optimize coefficients of the fourth-order ABC to further improve its overall absorbing effect. Theoretical analysis and the results of numerical tests demonstrate that the fourth-order ABC with optimized coefficients has much higher absorbing efficiency than both the conventional second-order and fourth-order ABCs without optimized coefficients, for waves with large incident angles. Compared with the perfectly matched layer (PML) with 40 layers, the fourth-order ABC not only has a much better absorbing effect, but also uses far less computer memory for calculation. We present the fourth-order ABC with optimized coefficients as an ideal artificial boundary for the simulation of the acoustic equation based on extensive and complex structure models.

A kind of sandwich structure photonic crystal fiber with diameter-increasing air holes is proposed. The sandwich structure is composed of the rectangular lattice in the center and triangular lattice in both sides, which is used to gain high birefringence. The air holes in the cladding, whose diameter in outer ring is always larger than the next inner ring, is used to reduce the confinement loss. The model field, dispersion, birefringence and confinement loss of the fiber fundamental mode are simulated by full-vector finite element method. It was shown from numerical results that it is possible to design a PCF with birefringence B = 3.8 × 10−3 and the fast axis confinement loss less than 10−3 dB/km at wavelength of 1550 nm.

Novel highly nonlinear photonic crystal fibers (HN-PCFs) with flattened dispersion are proposed by omitting 19 air holes as the fiber core. The simulation results show that the high nonlinearity and the flattened dispersion can be achieved simultaneously by employing only two types of air holes in the cladding. To reduce the confinement loss, the modified designs are presented. The confinement loss is below 0.1 dB/km at 1.55 μm, when seven layers of air-hole rings are introduced to the cladding. After modifying, the dispersion can change from −0.5 ps/(nm·km) to +0.5 ps/(nm·km) in the range from 1.35 μm to 2.06 μm, and the effective mode area is as low as 2.27 μm2 at 1.55 μm.

The effective index of the cladding fundamental space-filling mode in photonic crystal fiber (PCF) is simulated by the effective index method. The variation of the effective index with the structure parameters of the fiber is achieved. For the first time, the relations of the V parameter of Yb3+-doped PCF with the refractive index of core and the structure parameters of the fiber are provided. The single-mode characteristics of large-core Yb3+-doped photonic crystal fibers with 7 and 19 missing air holes in the core are analyzed. The large-core single-mode Yb3+-doped photonic crystal fibers with core diameters of 50 μm, 100 μm and 150 μm are designed. The results provide theory instruction for the design and fabrication of fiber.

The photonic bandgaps and modal properties of triangular lattice photonic bandgap photonic crystal fibers (PBG-PCFs) with interstitial holes are analyzed by the full-vector plane-wave expansion method. We analyzed the influence of the air holes array triangular lattice cladding and the interstitial holes on the photonic bandgaps and calculated the spectrum range of photonic bandgaps. We found that the PBG-PCFs with interstitial holes have a fundamental bandgap and a secondary bandgap. The transmission spectrum of PBG-PCFs is measured. The results indicate that there are two strong transmission bands in the near-infrared, but hardly any transmission phenomena in the visible region, which show that there are some bandgaps in near-infrared wavelength. The results of the experiments are consistent with the numerically simulative results using the full-vector plane-wave expansion method. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:233–236, 2012

The dual-concentric-core photonic crystal fiber composed of pure silica and air is proposed in this paper. Around 1.55 ¼m, it exhibits a negative chromatic dispersion as high as -5850 ps/km/nm. Based on multipole method, a systemic and in-depth simulation is realized to investigate the mode characteristics. The explanations to propagation states of the fundamental mode and the second mode are given elaborately. Finally, the variation of structural parameters is investigated to evaluate the tolerance of the fabrication. As a result, the designed fiber can be fabricated easily.

Sc-doped ZnO transparent conductive films are deposited on glass substrates by radio-frequency sputtering. The influence of post-annealing on the structural, morphologic, electrical, and optical properties of the films is investigated by energy dispersion X-ray spectroscopy, X-ray diffraction, Hall measurement, and optical transmission spectroscopy. The experimental results show that these films are polycrystalline with a preferred [0 0 1] orientation. The lowest resistivity of 2.6 × 10 −4 Ω cm is obtained from the film annealed at 500 °C. The average optical transmittance of the films is over 90%. These results suggest that Sc-doped ZnO is a good candidate for fabricating high performance transparent conductive films.

A double-cladding microstructured fiber (MF) is proposed in this paper. The inner cladding of this optical fiber is composed of elliptical air holes and silica. The dependence of dispersion on the diameter of the air holes, the pitch, and the axes of the elliptical holes is investigated numerically. The proposed fiber possesses an ultra flattened dispersion curve over a wide wavelength range, and its dispersion value is small. The effective mode area is approaching to 60 μm 2 , and the confinement loss is as low as

In the light of the major problems existing in the current laser engraving image processing software such as lack of third-dimension and lifelikeness, missing detail information, having pattern trace, this thesis using visual characteristics of the human eye, the pattern dithering method in print areas apply to the process of gray image field of laser engraving. In addition, improvement on the traditional dithering method, pattern matrix becomes homogeneous matrix by calculating, solves the problem of trace pattern, and improves the quality of carving. KeywordsLaser Carving ; Threshold ; Tseudo-Gray ; Image processing ; Digital halftoning technique

A full-vector plane-wave method is introduced, particularly in calculating the photonic crystal in-plane photonic bandgap of a 2D triangular structure. Using numerical simulation, we can obtain the in-plane bandgap structure of a hollow-core photonic crystal fiber. In the experiments, we measured the transmission spectra of a hollow-core photonic crystal fiber and a silica rod. And using the numerical calculation we can get the relative transmission spectrum of a hollow-core photonic crystal fiber. Compared with the result of theoretical simulation, we found that they are in accordance with each other, i.e. they have the same bandgap in about the same normalized frequency.

A highly nonlinear dispersion flattened microstructured fiber is proposed. The new structure adopts two claddings with different pitches, air-holes diameters and air-holes arrayed fashions. The characteristics of such microstructured fiber such as nonlinearity and dispersion properties are investigated. The influence of the cladding structure parameters on the nonlinear coefficient and geometric dispersion is analyzed by full-vector finite element method with perfectly matched layer. Highly nonlinear coefficient and the dispersion properties of fibers are tailored by adjusting the cladding structure parameters. A novel microstructured fiber with highly nonlinear coefficient and dispersion flattened which is suited for supercontinuum generation is designed.

In the simulation of photonic crystal fibers, the fixed value of the normalized equivalent core radius (p/Lambda) in the fully vectorial effective index method is inaccurate. For what is believed to be the first time, the relation of p/Lambda with normalized frequency (Lambda/lambda) and hole-to-pitch ratio (d/Lambda) is obtained. The improved fully vectorial effective index method (IFVEIM) is proposed. The modal properties computed with the IFVEIM, such as the effective index and the total dispersion, are closely matched to those of the multipole method as well as to experimental values, and the errors of the effective index have been reduced by 2 to 3 orders of magnitude.

Photonic crystal fibers with three and four zero-dispersion wavelengths are presented through special design of the structural parameters, in which the closing to zero and ultra-flattened dispersion can be obtained. The unique phase-matching properties of the fibers with three and four zero-dispersion wavelengths are analyzed. Variation of the phase-matching wavelengths with the pump wavelengths, pump powers, dispersion properties, and fiber structural parameters is analyzed. The presence of three and four zero-dispersion wavelengths can realize wavelength conversion of optical soliton between two anomalous dispersion regions, generate six phase-matching sidebands through four-wave mixing and create more new photon pairs, which can be used for the study of supercontinuum generation, optical switches and quantum optics.