High Frequency Part Research Articles

Optimal decay of the Boltzmann equation

The Boltzmann equation is a typical example of partially dissipative equations, where the linearized collision operator is positive definite with respect to the microscopic part and the dissipation of the hydrodynamic part is discovered from the coupling structure between the transport operator and the linearized collision operator. Guo and Wang (Comm. Partial Differential Equations, 37, 2012) developed a general energy method for proving the optimal time decay rates of the solution to such type of equations in the whole space; however, the decay rate of the highest order spatial derivatives of the solution is not optimal. In this paper, by incorporating the high‐low frequency decomposition in the energy estimates, both linearly and nonlinearly, we prove the optimal decay rates of any high order spatial derivatives of the low frequency part of the solution to the Boltzmann equation and the almost exponential decay rate of the high frequency part, which imply in particular the optimal decay rate of the highest order spatial derivatives of the solution. Moreover, the velocity‐weighted assumption of the initial data required in Guo and Wang (Comm. Partial Differential Equations, 37, 2012) is removed by capturing the time‐weighted dissipation estimates via the time‐weighted energy method. The method can be applied to the compressible Navier–Stokes equations and many partially dissipative equations in kinetic theory and fluid dynamics.

Equivalent static wind load based on displacement mode and load combination for high‐rise buildings

AbstractUnder the action of the fluctuating wind load, the low frequency part produces background response to the structures, while the high frequency part produces resonance response to the structures. In structural design, equivalent static wind load is usually used to equate the fluctuating wind load. Although there are various methods of evaluating the equivalent static wind load, they did not consider the correlation between modal responses or considered them insufficiently. Therefore, in this paper, the correlation between modal response is considered to evaluate the equivalent static wind load, the displacement response is decomposed by proper orthogonal decomposition (POD) method, the correlation between modal displacement is removed, the equivalent static wind load is expressed in the form of displacement mode, and then the correlation between modal response is fully considered in the extreme value combination. This paper combines the equivalent static wind loads in order to make the wind resistance design more reasonable for high‐rise buildings. First, the formulas of equivalent static wind loads expressed by displacement modes of background and resonant response are deduced based on modal decomposition and POD method. Second, the combination formulas of square‐root‐of‐sum‐square (SRSS) and complete‐quadratic‐combination (CQC) rules for the equivalent static wind loads considering the mean wind loads are proposed. Both the linear combination formula of SRSS for the equivalent static wind load and the weighting factor expressions of background and resonance equivalent static wind load are given. Third, the accuracy and validity of the formulas of equivalent static wind load are verified by a wind tunnel pressure test of a high‐rise building. Finally, the simplified combination coefficient formulas for the equivalent static wind loads are proposed, and the combination of the high‐rise building base's fluctuating equivalent static wind loads of along‐wind direction, across‐wind direction, and torsional direction is analyzed.

Roughness Evolution of Granite Flat Fracture Surfaces during Sliding Processes

Roughness is an essential factor affecting the shear process of discontinuous surfaces, and the evolution of roughness is closely related to the mechanical behavior of discontinuous surfaces. In this paper, with the help of granite specimens, a direct shear test was carried out on flat fracture surfaces obtained by sawing in order to study the evolution of roughness with shear slip. During the tests, the roughness evolution was evaluated using the arithmetic mean, root mean square and power spectral density of the roughness. The variation in these parameters all indicate that the friction surface with large slip tends to be rougher, at least under the loading conditions in this paper. And the increase in normal force will enhance this process, while the loading rate seems to have little effect on the roughness evolution. Finally, the analysis of the power spectral density shows that the roughness evolution in the spatial frequency of the profile line is mainly reflected in the middle– and low–frequency part, while the high–frequency part corresponding to the microscopic roughness body does not change much throughout the shear process.

Study on fault characteristic of piezoelectric acceleration sensor

In order to explore the fault characteristics and failure mechanism of the sensor, staring from the working principle and structural characteristics of the piezoelectric acceleration sensor, the problems affecting the quality of the collected signal due to the fault of the component of the sensor are systematically studied. Firstly, according to the application scenario and structural characteristics of this kind of sensor, the main fault forms are analyzed, including: insufficient preload, crystal plate damage, crystal plate side loading and crystal plate phase loading reverse four kinds of faults. Secondly, the signal of the exciter is used to test the above sensors. It is found that except the sensor with insufficient preload does not affect the signal, other fault sensors will make the collected signal amplitude smaller, but the signal frequency does not change. In order to verify the accuracy of the exciter test results, the sensor signal test on rotor bearing vibration was continued. The test results show that not only the signal amplitude decreases, but also the high frequency part of the signal is seriously distorted. Finally, the fault characteristics of various components of piezoelectric acceleration sensor are obtained by combining the test results of the two groups.

An improved demosaicing method based on Hibbard algorithm

As computer vision become more widespread and deeper, the requirements for accuracy and clarity of an image gradually increase, and more accurate image reconstruction algorithms urgently need to be developed and researched. Existing image reconstruction algorithms mainly use the conversion of images into RGB or use the difference to predict certain regions to build mathematical models and then revert to images. The existing bilinear interpolation algorithm may reduce the resolution and damage the high frequency part, thus blurring the edges and making it difficult to achieve the expected results. The colorimetric constant method is greatly affected by noise, and the boundary problem is still unsolved. The gradient edge interpolation method only considers the horizontal and vertical directions, which is a single idea and does not meet the needs of oblique edges, and there will be problems such as color overflow. And based on some features near the oblique boundary, this paper focus on the case of large or small edge slope, and select the horizontal difference and vertical difference for algorithm improvement respectively by comparing the color difference along all four directions. Experimental results show that the PSNR value increases slightlyby 0.0013. It effectively optimizes the image and lays the foundation for feature perception in the image.

Removing Rain Streaks from Visual Image Using a Combination of Bilateral Filter and Generative Adversarial Network

Images acquired using vision sensors are easily affected by environmental limitations, especially rain streaks. These streaks will seriously reduce image quality, which, in turn, reduces the accuracy of the algorithms that use the resulting images in vision sensor systems. In this paper, we proposed a method that combined the bilateral filter with the generative adversarial network to eliminate the interference of rain streaks. Unlike other methods that use all the information in an image as the input to the generative adversarial network, we used a bilateral filter to preprocess and separate the high frequency part of the original image. The generator for the high-frequency layer of the image was designed to generate an image with no rain streaks. The high-frequency information of the image was used in a high-frequency global discriminator designed to measure the authenticity of the generated image from multiple perspectives. We also designed a loss function based on the structural similarity index to further improve the effect of removal of the rain streaks. An ablation experiment proved the validity of the method. We also compared images in synthetic and real-world datasets. Our method could retain more image information, and the generated image was clearer.

First-principles investigations of the crystal and electronic structures, dynamical and mechanical stabilities, Born effective charges and dielectric permittivities of a novel tetragonal zirconia

In this paper, a novel tetragonal ZrO2 phase has been predicted from first-principles calculations. The detailed crystal structural analysis shows that the tetragonal ZrO2 has a space group I41/amd (D4h19, No. 141) with 4 formula units per unit cell and 16 symmetry operations as well as six-fold cation coordination. The Zr atoms occupy 4a Wyckoff positions (0, 1/2, 1/4) and (1/2, 1/2, 1/2) and the O atoms occupy 8e Wyckoff positions (0, 0, z+1/8), (0, 1/2, z+3/8), (1/2, 0, -z+5/8) and (1/2, 1/2, -z+3/8) with z = 0.0761. The electronic structures, dynamical and mechanical stabilities investigations show the tetragonal ZrO2 is dynamical and mechanical stable as well as with a large direct band gap of 3.9015eV at Γ point. The phonon dispersion is divided into two regions: the low frequency part (0–8.6240 THz) and the high frequency part (10.3453–18.4034 THz) with a separation gap of 1.7213 THz. The magnitudes of Born effective charges are greater than the nominal chemical valences of +4 and −2 for Zr and O ions, respectively, reflecting a strong dynamic charge transfer from Zr to O atoms and thus a p-d hybridized Zr–O ionic bond. A diagonal and anisotropic static dielectric permittivity εij0 is obtained between ab-plane ε110=ε220=17.80 and along c axis ε330=14.77.

Image Denoising Method Based on Harmonic Filtering and Non-Subsample Shear Wave Block Matching in Wavelength Domain

<p>Efficient noise filtering is the difficulty of image denoising on the premise of preserving the edge and internal texture information of the image. Therefore, this paper focused on adaptive Gaussian variational model and block matching image denoising method in the wave domain from the non-local point of view. At first, a 3D block match harmonic filtering model was establish in that wavelet domain, 3D transform was use to represent that real signals in the match block group in a sparse form, then the shrinkage threshold was used to achieve the purpose of pre-denoising, and the wavelet transform was then used to extract the high frequency part of the predictor image for filtering. In order to avoid edge blurring, Laplace-Gaussian algorithm was used to construct a new operator into the diffusion model, and the wavelet coefficients were reconstructed to obtain the final approximation of the original image. Secondly, a block matching denoising model based on shear wave was proposed. In order to avoid ill-conditioned problem, The multi-scale geometric analysis method using shearlet transform can improve the edge protection ability, and a block matching denoising model based on shearlet is proposed. The new model predicts the scaling threshold according to the statistical characteristics of the histogram, performs hard threshold filtering on the high-frequency sub-band to obtain the processed sub-band coefficients, and performs block matching 3D filtering on the decomposed low-frequency sub-band coefficients to obtain the processed coefficients. All processed subband coefficients are inversely transformed and reconstructed to obtain a denoised image. The analysis and simulation results showed that the two new models can effectively suppress noise and improve the clarity, and the block matching denoising based on shear wave had more advantages.</p> <p> </p>

An Image Denoising Model via the Reconciliation of the Sparsity and Low-Rankness of the Dictionary Domain Coefficients

Sparse coding has achieved great success in various image restoration tasks. However, if the sparse representation coefficients of the structure (low-frequency information) and texture (high-frequency information) components of the image are under the same penalty constraint, the restoration effect may not be ideal. In this paper, an image denoising model combining mixed norm and weighted nuclear norm as regularization terms is proposed. The proposed model simultaneously exploits the group sparsity of the high frequency and low-rankness of the low frequency in dictionary-domain. The mixed norm is used to constrain the high frequency part and the weighted nuclear norm is used to constrain the low frequency part. In order to make the proposed model easy to solve under the framework of alternative direction multiplier method (ADMM), iterative shrinkage threshold method and weighted nuclear norm minimization method are used to solve the two sub-problems. The validity of the model is verified experimentally through comparison with some state-of-the-art methods.

A novel virtual admittance droop based inertial coordination control for medium-voltage direct current ship with hybrid energy storage

In the Medium-Voltage DC (MVDC) ships, pulse load will cause great disturbance to DC bus voltage. Hybrid energy storage (HESS) including Supercapacitor, Lithium batteries and Flywheel will bring significant improvement to the energy regulation ability of the ship integrated power system (IPS). A novel virtual admittance droop control based on the traditional virtual resistor and capacitor droop (VRCD) control is proposed. Through the design of specific virtual admittance structure and parameters, the generator and the HESS can bear the high, medium and low frequency part of the transient power fluctuation according to their own characteristics. Moreover, the State of Charge (SOC) recovery control of energy storage does not depend on the secondary controller, which simplifies the control structure. Simulation and experiment verify the effectiveness of the proposed control strategy.

Experimental Research on Idle Combustion Noise of a Diesel Engine

Noise is one of the three major pollutants in the world, among which noise pollution complaints caused by fuel-powered vehicles account for more than 70%. Research on engine combustion noise is aimed at reducing pollution problems caused by it. Based on the Chinese national standard ‘Reciprocating internal combustion engines-Measurement method for combustion noise’, an experimental study on combustion noise of a certain type of diesel engine under idling conditions was carried out. In the test, by changing the calibration values of the engine, such as: pre-injection mass, rail pressure and other calibration parameters, the cylinder pressure at idle speed of the engine is calculated based on the theory of cylinder force. It is concluded that when the rotational speed is 750r/min, the increase of the pre-injection amount and the rail pressure leads to an increase in the mean value of the combustion parameters of each cylinder force stage and is concentrated in the high frequency part. This study provides a reference for optimizing the idling noise of diesel engines, which is conducive to reducing noise pollution in life.

Investigation on the reconstruction of wave bimodal spectrum in the lagoon near islands and reefs

Due to the intricate topography and geomorphology of coral reefs, waves propagating from deep water areas to transitional or shallow water near islands and reefs will exhibit features of wave spectra that are very different from those in the deep sea. Thus, a reconstruction of the wave spectra is necessary. In this study, double Gaussian functions are first proposed to identify the characteristic frequencies of wave bimodal spectra, such as peak frequencies corresponding to the low frequency part and high frequency part, and separation frequencies differentiating between the low frequency part and the high frequency part, based on the observed data of wave spectra in the lagoon near islands and reefs of the South China Sea (SCS). The wave bimodal spectra close to the islands and reefs are then rebuilt using the Ochi-Hubble spectrum type. The high frequency and low frequency portions of the bimodal wave spectra are used to determine the significant wave heights, peak frequency and shape characteristics, respectively. The wave motions exhibit basically linear characteristics when two typical sea conditions, such as summer typhoon waves and winter Northeast monsoon waves, are investigated in detail. The superposition of wind waves and swells on the one hand, and the presence of the bottom on the other, have an impact on the generation of the bi-modal spectrum. The bi-modal spectra that were reconstructed and those that were observed have a correlation coefficient that is greater than 90%. The study on the reconstruction of the bimodal spectrum in the paper will provide a reference for the description of the bimodal spectrum near islands and reefs.

Displacement reconstruction of beams subjected to moving load using data fusion of acceleration and strain response

Displacement response induced by moving load is important for health monitoring and safety assessment of beams. It contains displacement representing the high frequency part and pseudo-static displacement (PSD) representing the low frequency part. It is normally difficult to reconstruct the PSD due to its approximately zero frequency and inaccurate assumption of the neutral axis position of the structural cross-section. This paper presents a moving load induced displacement reconstruction method using data fusion of acceleration and strain response with special attention on PSD extraction. Firstly, the displacements are derived from the acceleration and strain, which are deemed as the acceleration-derived displacement (ADD) and the strain-derived displacement (SDD), respectively. Subsequently, a correction factor is proposed based on the ADD and SDD to determine the neutral axis position of the structural cross-section. Then the PSD is extracted from the SDD based on the correction factor and a designed low-pass filter. Finally, the performance of proposed method is investigated by numerical and experimental examples. The results manifest that the correction factor can determine the neutral axis position with high accuracy, and the proposed method can obtain more accurate reconstructed displacement than using the acceleration or the strain alone.

On the frequency up-conversion mechanism due to a soft stopper by the example of an electrostatic kinetic energy harvester

Micro- and meso-scale electrostatic energy harvesting systems have high efficiency at the higher-frequency part of the spectrum due to the natural frequencies of micro-structures lying over a range from hundreds of hertz to megahertz. However, many real-life applications related, in particular, to wearable systems, structural monitoring, or the Internet of Things, are characterized by low-frequency environmental forces. The main goal of this letter is to demonstrate that the placement of a stopper that limits the motion of the proof mass and causes soft impacts in an electrostatic kinetic energy harvester is responsible for an effect known as frequency up-conversion. This means that there is a significant response to “non-resonant” frequencies away from the natural frequency of the structure leading to effective energy conversion to the electrical domain. The concept summarizing this effect is presented and modeled, and an experiment carried out on a microscopic electrostatic harvester is presented to prove the concept.

A General Equivalent Electrical Circuit Model for the Characterization of MXene/Graphene Oxide Hybrid-Fiber Supercapacitors By Electrochemical Impedance Spectroscopy

Main text :Performance engineering of electrochemical energy-storage devices such as Supercapacitors (SCs) requires updated modelling capable of characterizing their electrical output in unique device geometries. In this work, an Equivalent Electrical Circuit (EEC) is developed to fit the impedance data of MXene/reduced Graphene Oxide (rGO) hybrid fiber-shaped supercapacitors (FSCs) fabricated by wet-spinning [1]. The model is applied for the interpretation of impedance data measured on FSCs using different active materials - rGO and MXene in the case of pseudo-capacitors (Figure - upper right side) and pure carbon in the case of Electrical Double-Layer Capacitors (EDLCs) - and polyvinylalcohol (PVA) gel infiltrated with sulfuric acid as the electrolyte and separator.The FSC charge storage behavior is modelled using a Transmission Line Model (TLM) including a finite Warburg impedance for pseudo-capacitance [2], and a Constant-Phase Element (CPE) for the electrostatic contribution (Figure – upper left side). The high frequency part of the Nyquist plots is characterized by a 45° straight line and the use of a TLM clearly improves the fit quality compared to a Randles circuit usually used for pseudo-capacitor modeling [1,2]. The 45° high frequency line and the difference between the two circuits becomes more visible as the length of the SC yarns increases (Figure – lower left side), which is consistent with the observed increase in internal resistance with fiber length evidenced with the TLM. Finally, the low frequency part of the spectra is correctly modeled by a CPE without any leakage resistance, showing that self-discharge is not a significant issue for the electrostatic contribution, at least in the frequency range tested.The fitting results on all tested devices indicate that the internal resistance of the TLM predominantly corresponds to the electrical resistance of the fiber (Figure – lower right side), i.e. the electron conductive phase of the electrode, instead of the electrolyte ionic resistance in usual SCs [2-4].[1] N. He, Q. Pan, Y. Liu and W. Gao, "Graphene-Fiber-Based Supercapacitors Favor N-Methyl-2-pyrrolidone/Ethyl Acetate as the Spinning Solvent/Coagulant Combination," ACS Appl. Mater. Interfaces, vol. 9, pp. 24568-24576, 2017.[2] S. Touhami, J. Mainka, J. Dillet, S. Ait Hammou Taleb and O. Lottin, "Transmission Line Impedance Models Considering Oxygen Transport Limitations in Polymer Electrolyte Membrane Fuel Cells," J. Electrochem. Soc., vol. 166, no. 15, pp. F1209-F1217, 2019.[3] L. M. Da Silva, R. Cesar, C. M. Moreira, J. H. Santos, L. G. De Souza, B. Morandi Pires, R. Vicentini, W. Nunes and H. Zanin, "Reviewing the fundamentals of supercapacitors and the difficulties involving the analysis of the electrochemical findings obtained for porous electrode materials," Energy Storage Mater., vol. 27, pp. 555-590, 2020.[4] D. I. Abouelamaiem, G. He, T. P. Neville, D. Patel, S. Ji, R. Wang, I. P. Parkin, A. B. Jorge, M.-M. Titirici, P. R. Shearing and D. J. Brett, "Correlating electrochemical impedance with hierachical structure for porous carbon-based supercapacitors using a truncated transmission line model," Electrochim. Acta, vol. 284, pp. 597-608, 2018.Figure caption:(Left) Experimental impedance spectra measured on rGO/MXene fibers-shaped supercapacitors (FSCs) of different length and fitting curves obtained with the herein developed equivalent electrical circuit (EEC). (Right) Internal resistance of the EEC identified by fitting the spectra on the left side per unit length of the FSCs and electric resistance of the rGO/MXene fibers of the electrodes. Figure 1

Efficient 2D image Upscaling using Iterative Optimized Sharpening filtering

In real-time image interpolation, polynomial-based approaches are used because they are simple and practical. The unknown pixels in the image grid are obtained using polynomial-based upscaling by taking into account the weighted average of adjacent pixels. It causes degradation in high frequency (HF) parts of the image due to blurring artifacts. Numerous edge-directed and learning-based techniques are discussed in the literature, which also introduces blurring in the image’s high variance region. To address the aforementioned issue, one pre-processing method based on the concept of unsharp masking is proposed in order to generate sharpened high resolution (HR) images from low resolution (LR) images. The LR image is blurred using a weighted average filter, which is based on the concept of unsharp masking. The difference between the LR image and the blurred LR image is then extracted to represent the loss edge portion of the image. This error or degraded HF image is sharpened iteratively using a cuckoo optimized sharpening filter known as the Iteratively Optimized Sharpening (IOS) filter. The subtle is then collected by iteratively applying ISO and combining it with the LR image using one optimized gain factor, resulting in a sharpened LR image. This pre-processing is done prior to interpolation to compensate for the loss of HF details. To up-sample the sharpened LR image, the MAKIMA scheme is used. Because of MAKIMA, the image’s edges and boundaries are preserved. As a result, an HR image with sharpened edges and texture details can be obtained. In comparison to existing techniques, the proposed algorithm yields better results in terms of visual quality and objectivity. Various image databases are used to assess the efficiency of the proposed method.

Analysis and experimental verification of dual frequency ultrasonic transducer with contour and thickness vibration modes

The contour mode is introduced with normal thickness mode to generate dual frequency ultrasonic waves in a single element transducer. The proposed dual frequency transducers are analyzed and designed by finite element analysis. Based on the results of simulation analysis, the four transducers prototypes are fabricated and tested. For dual frequency transducer with optimized matching layer, the pulse echo characteristics of low frequency part are similar with the comparison characteristics of 1–3 composites transducer. The dual frequency transducer still simultaneously owns effective high frequency part. The results demonstrate that the proposed contour vibration mode can work with thickness vibration mode to realize dual frequency with a high performance.

Research and Implementation of Image Rain Removal Based on Deep Learning

Abstract The traditional rain removal algorithm needs to optimize a large number of parameters, and it is only effective for rain of a specific shape, and the model generalization ability is poor. In recent years, the performance of rain removal methods based on deep learning is better than many traditional methods, but there are problems such as incomplete or excessive rain removal, and incomplete texture reconstruction of background details. This paper proposes a rain removal network based on generative confrontation, which connects the high and low frequency parts and integrates them into the model. At the same time, the attention mechanism cyclic neural network is organically combined, which can better preserve the background texture while removing rain. Theoretical can produce better rain streak removal with better color distortion.

A General Equivalent Electrical Circuit Model for the characterization of MXene/graphene oxide hybrid-fiber supercapacitors by electrochemical impedance spectroscopy – Impact of fiber length

Performance engineering of electrochemical energy-storage devices such as Supercapacitors (SCs) requires updated modeling capable of characterizing their electrical output in unique device geometries. In this work, an Equivalent Electrical Circuit (EEC) is developed to fit the impedance data of pseudo-capacitive and electrostatic fiber-shaped supercapacitors (FSCs). The model is applied for the interpretation of impedance data measured on FSCs made of reduced Graphene Oxide (rGO) and MXene in the case of pseudo-capacitors and pure carbon in the case of Electrical Double-Layer Capacitors (EDLCs) as active electrode materials, and polyvinylalcohol (PVA) gel infiltrated with sulfuric acid as the electrolyte and separator. The FSC charge storage behavior is modeled using a Transmission Line Model (TLM) including a finite Warburg impedance for pseudo-capacitance, and a Constant-Phase Element (CPE) for the electrostatic contribution. The high frequency part of the Nyquist plots is characterized by a 45° straight line and the use of a TLM clearly improves the fit quality compared to a Randles circuit usually used for pseudo-capacitor modeling. The difference between the two ciruits becomes more visible as the length of the SC yarns increases, which is consistent with the observed increase in internal resistance with fiber length evidenced with the TLM. Furthermore, the fitting results indicate that the internal resistance of the TLM predominantly corresponds to the electrical resistance of the fiber, i.e. the electron conductive phase of the electrode, instead of the electrolyte ionic resistance in usual SCs. Finally, the low frequency part of the spectra is correctly modeled by a CPE without any leakage resistance, showing that self-discharge is not a significant issue for the electrostatic contribution, at least in the frequency range tested.

Multifrequency ultrasonic transducers based on dual vibration and harmonic mode

Multifrequency ultrasonic transducers have broad application prospects in the field of biomedical due to their high imaging resolution and detection depth. This paper proposed a design method of triple frequency single-element transducers by finite element method(FEM). The triple frequency transducers are based on contour mode, thickness mode and the third harmonic of thickness mode. Nine micro single element transducers with different widths and matching layers were fabricated and characterized to verify the design method. The traditional 30 MHz single frequency transducer and 2.3 MHz 1–3 piezoelectric composite transducer were used to compare with high frequency part and low frequency part of the triple frequency transducers, respectively. The pulse-echo characteristics of the triple frequency transducers have impressive low and middle frequency part. The high frequency part is similar with traditional transducer except the sensitivity is 0.5 times. The results certify the feasibility of a triple-Frequency transducer based on dual vibration and harmonic modes.