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Image rotation makes fake images more realistic in geometric perspective, and the performance of existing JPEG image rotation angle estimation algorithms is easily disturbed by block artifacts and the image block size. It remains an imminent and challenging work for the rotation angle interval [1°,15°]. This study presents an effective algorithm to estimate the rotation angle of JPEG images based on block artifact spectral analysis. Firstly, the edges of the image are extracted and removed using a variant colony algorithm to highlight block effects. Secondly, the effect of image texture is further mitigated by cross-differentiation. Thirdly, extraneous peaks are removed in the Fourier transform domain by setting reasonable thresholds and using a Gaussian high-pass filter to reduce interference. Finally, the amplitude component of the Fourier spectrum is projected into the polar coordinates, and the polar angle corresponding to the peak in the polar coordinates is the estimation of rotation angle we need. The experimental results show that the average absolute error of the method is lower than that of the existing methods for the detection of small-size JPEG images whose rotation angle lies within the [1°,15°] interval. Besides, when the compression quality factor is gradually reduced, the performance of the proposed method is still better than the existing methods, and the robustness of the proposed method to JPEG compression is better. [ABSTRACT FROM AUTHOR]

First, polyacrylonitrile/polyvinyl pyrrolidone (PAN/PVP) fibrous membrane was prepared by electrospinning, and then porous polyacrylonitrile (PPAN) fibrous membrane was obtained by water impregnation. Fourier transform infrared (FTIR) spectra and thermogravimetric analysis (TGA) were used to explore the mechanism of fiber pore-forming, and X-ray photoelectron spectroscopy (XPS) was used to study the interaction between PAN and PVP molecules in the porous fibrous membrane. At the same time, the effects of mass ratio of PAN to PVP on the morphology, surface area, wettability, mechanical properties, and oil/water separation performance of fibrous membrane were investigated, and the optimal mass ratio was determined. Results showed that when m(PAN)/m(PVP) was 1∶2, PPAN fibrous membrane showed higher mechanical properties. The separation flux of the n-hexane/water mixture was (46 318 ± 3 879) L/(m2·h·bar) (1 bar=0.1 MPa), and the efficiency was (96.01 ± 0.38)%. It also realized the efficient separation of different kinds of oil/water mixtures. In addition, PPAN fibrous membrane showed excellent cyclic separation performance, and the flux loss rate was only 8.9% after ten cycles of separation. [ABSTRACT FROM AUTHOR]

For the complicated problem of groundwater flow to a partially penetrating well in a rectangular con- fined aquifer, a mathematical model describing the groundwater flow to a partially penetrating well pumped at a constant rate in a rectangular leaky-confined aquifer, was established. The analytical solutions of the 3D steady flow in the Cartesian coordinate system under different boundary conditions, were derived through the finite Fourier transform and the inverse transform. After the verification of the analytical solution of drawdown, the number of calculation items satisfying the calculation accuracy requirement was given, based on the analysis of the calculation accuracy of the analytical solution and the characteristics of the groundwater flow to a partially penetrating well. Moreover, the effects of orthotropy, well integrity and well location on the drawdown and seepage fields, were discussed. The engineering examples demonstrate the applicability of the proposed analytical method. [ABSTRACT FROM AUTHOR]

The influence of talc on polypropylene(PP) pipes after surface modification was studied. The main raw materials, talc, polypropylene, surface modifier were fully mixed in the plastic mixer to achieve several raw materials, become composite materials. The mechanical properties of the composites were tested by universal testing machine, and the microstructure and functional groups of the composites were studied by Fourier transform and XRD. The results showed that: after modification, the filler can be composite with polypropylene regularly, the microstructure distribution is uniform, and the functional groups have a great change, PP: talc (after modification) = 1:3, the mechanical properties of the composite are the best. [ABSTRACT FROM AUTHOR]

Inspired by the dynamic properties of hindered urea bonds (HUBs), prepolymer of polyurethane-acrylate (PUA) with HUBs was designed and synthesized using 1,3-bis(2-isocyanato-2-propyl)benzene (TMXDI) as hard segment, bis(2,2,6,6- tetramethyl-4-piperidyl) sebacate (TMPCA) as soft segment, isobornyl methacrylate (IBOMA) as reactive diluent, and 2-hydroxyethyl methacrylate (HEMA) as block agent. The prepolymer was subsequently UV-cured to obtain PUA photopolymer. The property and reaction mechanism of the incorporated dynamic HUBs were investigated via Differential Scanning Microcalorimetry (MicroDSC) and Fourier Transform Infrared (FT-IR) spectroscopy. And studies were carried out in terms of the repairability, shape memory and reshapability of the corresponding photopolymer. Results showed that the thermal effect of the HUB could be identified in MicroDSC analysis, as an endothermic peak appeared in the range of 46 ℃ to 56 ℃. In addition, the dynamic content variation of the isocyanate group (NCO) could be observed via temperaturedependent FT-IR in both prepolymer and cured resins. In the in-situ FT-IR spectra of prepolymer with HUBs, the characteristic peak of NCO was observed to increase when heated from 30 ℃ to 80 ℃, which later decreased when cooled down to 30 ℃. Also, the peak area of NCO characteristic peak increased in cured resins with increased temperature. The dynamic nature of HUBs allowed the obtained photopolymer to be repaired with a demonstrated improvement in mechanical properties. By drilling a 1 mm hole in the center of a testing sample, refilling prepolymer, and treating with UV-cure and postcure, the tensile strength of the material was observed to recover from 13.8 MPa to 18.4 MPa after repairing. The incorporated HUBs provided the PUA resin with shape memory and reshaping capacities, and the testing sample was able to reserve a 45 MPa flexural strength after being reshaped. [ABSTRACT FROM AUTHOR]

To identify the instantaneous frequencies of time-varying signals, the theoretical relationship between the frequency and rotational angle α in a signal was derived based on the definition of the fractional Fourier transform. Then the fractional Fourier transform was interpreted to be essentially an algorithm combining the ordinary Fourier transform with the dilation and translation window. A general expression of the signal instantaneous frequency in the fractional Fourier domain was thereafter formulated so that the structural instantaneous frequency can be extracted accordingly. The feasibility and reliability of the proposed method were verified with a simulated nonlinear frequency modulation signal and a numerical example of a 3DOF damped time-varying structure system. The results show that, the results of the proposed method are in good agreement with the theoretical values, and the method has a certain degree of anti-noise capability. Subsequently, the proposed method is applicable to the identification of the instantaneous frequencies of time-varying structures.. [ABSTRACT FROM AUTHOR]

To explore the effect of production temperature on the adsorption performance and mechanism of cadmium by biochar, three different types of biochar derived from rice straw were prepared at 300 ℃, 500 ℃ and 700 ℃（defined as BC300, BC500 and BC700. Based on analysis of ash content determination, element analysis, Brunauer-Emmett-Teller（BET）, Fourier transform infrared（FT-IR） and X-ray diffraction（XRD, the adsorption characteristics and adsorption mechanism of Cd2+ and quantitatively analyze the adsorption of Cd2+were studied. The results showed that, compared with BC500 and BC300, BC700 possessed higher specific surface area. The adsorption of Cd2+ by BC500 and BC300, BC700 was investigated, indicating all reaction fitted well the pseudo-second-order kinetic model and the Langmuir model. The theoretical maximum adsorption capacity was 20. 3 mg·g-1. Cation exchange（Qi） was the primary adsorption mechanisms for Cd removal by biochar synthesized at low-temperature, while precipitation（Qp） had the highest proportion of adsorption on Cd by high-temperature prepared biochar. This study showed that the pyrolysis temperature not only affected the adsorption capacity of cadmium by biochar, but also affected the effect of contribution of different adsorption mechanisms. [ABSTRACT FROM AUTHOR]

In order to study the occurrence and removal of microplastics （MPs） in municipal wastewater treatment plant in China, a dual-process three-stage wastewater treatment plant in Taiyuan was selected as the research object, and a Stereo microscope combined with Fourier transform infrared microscope spectrometer was used to detect and identify MPs. The results showed that the concentration of MPs in the influent was 21.0 n/L, which was at a medium level; small size（<1 000 μm） accounted for the highest proportion（77.38%）,and the main shape was fibrous（90.95%）.The main polymer components detected were cellulose（47.22%） and rayon（35.00%）,followed by polyester（PET,5.56%） and polypropylene-polyethylene copolymer（PP-PE,4.44%）.The overall removal rate of system 1 and system 2 for MPs were 78.73% and 75.71%,respectively.The primary and secondary treatment stages played a major role in the removal of MPs, and the grit tank was the main structure in the primary treatment. The advanced treatment had a certain effect on the removal of MPs, and the filter was the main role in system 2.Although the concentration of MPs in the effluent from the wastewater treatment plant was 4.5 n/L and 5.1 n/L, there were still 609 billion MPs discharged into the freshwater environment through the wastewater treatment plant every year. [ABSTRACT FROM AUTHOR]

The CaO typed solid base with high catalytic efficiency was synthesized by high temperature calculation of crayfish shell. The preparing produce was facile, and the crude materials were cheap and readily available. The morphology, structure and the chemical compositions of solid bases were analyzed with X-ray diffraction（XRD）, Fourier transform infrared spectra（FT-IR） and nitrogen sorption technologies（N2 sorption）. The total basic amount and distribution of active sites with different basic strength were determined with acid-base titration and CO2-TPD technologies. The solid base synthesized at 750 ℃ showed the highest amount of basic sites and the optimized distribution of basic strength. The optimized solid base exhibited excellent catalytic performance in Knoevenagel condensation for various aldehydes, and the catalysts could be regenerated with calculations. This research will be of significance for high-valued utilization of biomass wastes. [ABSTRACT FROM AUTHOR]

The semi-classical QFT is a transformation in which a specific bit in the calculation circuit is measured and the next bit is controlled by classical information processing according to the measurement result. This paper proposed the t-bit semi-classical quantum phase estimation algorithm by the idea of semi-classical quantum Fourier transform, and it had been implemented on the IBM Q Experience quantum cloud platform, the IBM qiskit quantum simulator and the quantum simulator of the domestic source-Wuyuan cloud platform. The experiment shows that this method improves the estimation accuracy while reducing the need of the algorithm on the circuit scale and the two-bit controlled gate. [ABSTRACT FROM AUTHOR]

N,N’-di(4-propargyloxyphenyl) phosphoramide (DPPPA) was successfully synthesized by nucleophilic substitution of 4-propargyloxy aniline and phenylphosphonyl dichloride. The structure of DPPPA was characterized by nuclear magnetic resonance (NMR) and Fourier transformation infrared (FT-IR) analyses. DPPPA was used to mix with bisphenol A of dicyanate ester (BADCy) and bisphenol E of dicyanate ester (BEDCy) in solution. The DPPPA modified cyanate esters (BADCy/DPPPA and BEDCy/DPPPA) were obtained after the solvent was evaporated under vacuum. The thermal properties, limited oxygen index (LOI) and mechanical properties of the modified cyanate esters were studied. The results show that the residual yield at 800 ℃ in air of the cured BADCy/DPPPA and cured BEDCy/DPPPA increase from 0 to 33% and 26% in comparison with the cured neat cyanate esters, and the LOI of the cured modified cyanate esters reach 39.7% and 35.4%, but the glass transition temperatures of the cured modified cyanate esters decrease by 19 ℃ and 24 ℃, respectively. The flexural and tensile strength of the cured BADCy/DPPPA are 123 MPa and 45 MPa, which are higher than that of the cured BEDCy/DPPPA. The impact strength of the cured BADCy/DPPPA and BEDCy/DPPPA are 11 kJ/m² and 14 kJ/m², respectively. The water absorption of the cured neat cyanate esters decreases with blended with DPPPA. [ABSTRACT FROM AUTHOR]

To address the problem that most bearing remaining useful life (RUL) prediction methods based on artificial intelligence cannot well predict bearing RUL under different working conditions， a transfer learning method was proposed to predict bearing RUL under different working conditions. Fourier transform was applied to the raw vibration signals of the bearing to obtain the frequency-domain signals， and convolutional neural network (CNN) and long short-term memory network(LSTM) were used to extract the features between data of the bearing′s frequency-domain signals and mine temporal information. The method of combining global and local domain adaption was adopted to reduce the distribution differences of the bearing data under different working conditions. The effectiveness of the method was verified by the existing bearing data. Compared with the traditional deep learning models， the proposed method improves the accuracy of bearing RUL prediction under different working conditions. [ABSTRACT FROM AUTHOR]

Based on the theory of fractional-order strains, the thermomechanical dynamic responses of 3D elastomers under moving heat sources were studied. The governing equations under the theory of fractional-order strains were applied to the 3D semi-space model, and solved by means of the Laplace transform, the double Fourier transform and its numerical reverse transform. The distributions of non-dimensional temperatures, stresses, strains and displacements were obtained under different heating source velocities and different fractional-order parameters. The results show that, the fractional-order strain parameters have significant effects on mechanical waves but minor effects on heat waves, and the heat source velocity has significant effects on thermomechanical waves. [ABSTRACT FROM AUTHOR]

In order to improve the adsorption performance of ordinary ZrO2-SiO2 composite materials for dyes, methyl-modified ZrO2-SiO2(ieZrO2-MSiO2) composite materials were successfully synthesized based on the solgel technique. The material structures were characterized by Fourier transform infrared spectrum (FTIR), X-ray diffraction (XRD) and N2 adsorption-desorption methods. The Rhodamine B (RhB) was adsorbed by the prepared ZrO2-SiO2 composite materials, the effects of adsorbent dosage, pH, adsorption time, initial RhB concentration and temperature on the adsorption process were investigated. The adsorption mechanism was described by adsorption kinetics an disothermadsorption process. The results showed that Si—CH3 and Zr—O—Si bonds were formed in the ZrO2-MSiO2 composite materials, which indicated that the hydrophobic modification was successful and that the SiO2 was chemically bonded the ZrO2 particles, respectively. Under the experimental conditions of ZrO2-MSiO2 dosage of 0.05g, pH=9, adsorption time of 30min, RhB concentration of 150mg·L-1, temperature of 25°C, ZrO2-MSiO2 adsorption quantity reached182.4mg·g-1. The adsorption process of RhB on the ZrO2-MSiO2 composite materials followed the pseudo-first-order kinetic model and fitted the Langmuir isotherm adsorption model. [ABSTRACT FROM AUTHOR]

In order to solve the problem of obtaining high-precision tidal level in the port & waterway engineering far from the coast, the principle of medium and long distance GNSS positioning considering ocean water vapor, and the method coupled tide level extraction algorithm were studied and related software were developed. The instantaneous three-dimensional coordinates of GNSS antenna were measured by using PPK technology based on GPS and BDS, the instantaneous elevation of the sea surface was obtained by combining its coordinates in the hull coordinate system, the tide level in navigation was finally obtained through the Fourier transforming, wavelet filtering, and the conversion of the vertical datum. It has been proved by many tests and practical application that the accuracy of PPK technology in locating and acquiring tidal level in the medium and long distance waters can meet the requirements of horizontal positioning and tidal level in port & waterway engineering. [ABSTRACT FROM AUTHOR]

The wave model generated for laser plasma was discussed, which can be expressed as the Riemann problem of Burgers equations with initial value discontinuity. The singularly perturbed asymptotic solution of the Burgers equations with discontinuous initial values was obtained with the singularly perturbed expansion method. The solution was divided into 2 parts: an outer solution and an inner layer correction term. Since the initial condition is constant, the wave will generate the characteristic boundary in the process of propagation, and the correction term will make the parabolic characteristic boundary. The external solution was corrected at the internal layer along the characteristic lines. The existence and uniqueness of the asymptotic solution was proved through the HopfCole transform, Fourier transform and the extremum principle. Then the asymptotic expansion is obtained with the uniform validity proved. [ABSTRACT FROM AUTHOR]

The dynamic responses of 3D, 2D and 1D track-ground models under moving loads were analyzed based on the Fourier transformation technique. The track was modelled as a Timoshenko beam, and response discrepancies between the 3 models were compared in terms of different load speeds and ground thicknesses. The results indicate that, there is an equivalent ground stiffness in the 3D track-ground model, which is a function of the wave number and the frequency. The critical velocities of 2D and 3D track-ground models are almost the same, but are much smaller than that of the 1D model. When the load speed is less than the critical speed, the Timoshenko beam deflection of the 3D model is the smallest, that of the 2D model is the intermediate, and that of the 1D model is the largest. However, when the load speed reaches or exceeds the critical velocity, the T beam deflection of the 2D model becomes the largest, and the time history curves of the T beam deflection for the 3 models are significantly different. In the 2D and 3D models, the longitudinal ground displacement firstly increases with the soil depth to a peak value and then decreases, but the vertical displacement decreases continuously with the soil depth. [ABSTRACT FROM AUTHOR]

For the problem of the traditional partial matched filter( PMF) combined with fa st Fourier transform( FFT) could not accurately capture the time-division multiplexed binary offset carrier ( TMBOC) modulated signal, this paper proposed a capture method based on all-phase spectrum correction. Firstly, it received signal with PMF for partial correlation operation, then used the all-phase fast Fourier transform ( apFFT) algorithm to compensate the Doppler effect. Finally, the power spectrum was corrected in combination with the all-phase spectrum correction technique. The experimental results show that, under the same conditions, the proposed scheme improves the detection probability by about 3 dB than the PMF-FFT windowing algorithm, and shortens effectively the acquisition ti me . This algorithm captures the TMBOC signal more accurately than the PMF-FFT windowing algorithm. [ABSTRACT FROM AUTHOR]

In order to solve the problem of the fractional Fourier transform( FRFT) in estimating the multipath delay for Chirp signal, this paper proposed an improved FRFT multipath delay estimation algorithm based on the energy of each multipath component. The algorithm sequentially returned the estimated values of multipath components by iteration according to the energy magnitude of multipath components. In each iteration, there were a sub-iteration to accurately estimate the parameter and location of the current component, and then generated a time domain copy of the sounding signal, which was subtracted from the residual signal to reach separation of the multi path signal. This paper made some experiments which used channel model based on the characteristics of power delay distribution. The results show that the improved algorithm can estimate the multipath delay more accurately than the other three delay estimation approaches. [ABSTRACT FROM AUTHOR]

It is a popular method to deal with structural breaks using Fourier transformation, in which an integer frequency and a fractional frequency are respectively associated with transitory and permanent breaks, and hence is important in empirical applications. However, we still do not know how the integer and fractional frequencies affect the theoretical properties of unit root tests. This paper examines the properties of Dickey-Fuller tests when the true datagenerating process contains fractional Fourier-form breaks but ignored in testing procedures. We derive the limiting distributions by reparameterization, discuss the theoretical predictions of the limiting results on the properties of Dickey-Fuller tests, and give the conditions under which spurious rejection occurs. We use Monte Carlos simulations to confirm the predictions, finding that the theory is consistent with the simulation evidence. Our results imply that permanent breaks could more easily lead to spurious rejections than temporary breaks. Thus, ignoring a fractional frequency or specifying it as integer would cause misleading results. [ABSTRACT FROM AUTHOR]

Based on reviewing the structure and principle of the quadrupole linear ion trap, this review explains the core technical principles of the linear ion trap electronic system and cascade mass spectrometry, and introduces the stored waveform inverse Fourier transform technique in quadrupole linear ions. The application in the well, especially how to select the parent ion. The quadrupole linear ion trap is a magical analyzer that analyzes ions with a mass-to-charge ratio of thousands or more. In the full scan mode, the ion trap still has high sensitivity, and its sensitivity is often 10-1 000 times higher than that of the quadrupole. Compared to other types of analyzers, MSn of multi-stage tandem mass spectrometry can be achieved with a single linear ion trap, which is very useful for structural identification of analytes. The resonance-assisted alternating voltage is used to excite the parent ion and the fragment ion, which is the key to achieving cascade mass spectrometry. In addition, the quadrupole linear ion trap is relatively easy to manufacture, requires low processing accuracy, and is cost effective. This review will introduce the mechanical structure of the quadrupole linear ion trap and the technical principles of circuit implementation; describe how to apply collision induced dissociation and assisted RF to achieve linear ion trap tandem mass spectrometry; explain how to pass RF voltage and DC voltage in a linear ion trap. The cooperation is to capture and excite ions; finally, the practical application of the stored waveform inverse Fourier transform technique in selecting parent ions and separating adjacent mass ions is also demonstrated. [ABSTRACT FROM AUTHOR]

This study was conducted to examine the differences in adsorption of Pb on the root cell wall of maize"Huidan No.4”and "Ludan No.8”and identify the main functional groups by kinetics analysis and Fourier transform infrared（FTIR）characterization. The results indicated that the adsorption capacity of"Huidan No.4”was 7.05 mg·g-1 when the value reached equilibrium, suggesting that the ad⁃ sorption capacity was significantly higher than that"Ludan No.8"which showed a value of 6.36 mg·g-1. The desorption rate of"Huidan No.4"was 67.41%, which was significantly lower than that of"Ludan No.8"with a desorption rate of 76.95%. The cumulative adsorption capacity of Pb on the cell wall of"Huidan No.4"and"Ludan No.8"was reduced by 44.59% and 47.41%, respectively, after esterification modification. The cumulative adsorption capacity of Pb decreased by 28.60% and 24.86% after amino methylation modification and the cumulative adsorption amount of Pb decreased by 15.79% and 21.75% after pectinase modification, respectively. Furthermore, analysis of the functional groups showed that the cell wall structure did not change after Pb adsorption, but the position and content of some functional groups changed significantly, among which"Huidan No.4"and the characteristic peaks of hydroxy（-OH）or amino（-NH2）of"Ludan No. 8"showed significant shifts. After Pb adsorption treatment, the ratio of A3382/A2921 of"Huidan No.4"increased by 0.53 and ratio of"Ludan No.8"A3385/A2921 increased by 0.41. The variation range of"Huidan No.4"was obviously higher than that of"Ludan No.8", but the differ⁃ ence in the absorbance ratio of the carboxyl（COO-, CO）characteristic peak was not obvious. Our results indicate that"Huidan No.4"has a higher adsorption capacity for Pb and is more firm and more difficult to desorb. The hydroxyl or amino group participates in the adsorption process of Pb on the cell wall. The difference in the cumulative ability to Pb of"Huidan No.4"and"Ludan No.8"is mainly related to differences in the change in the content of hydroxyl or amino groups in the cell wall. [ABSTRACT FROM AUTHOR]

A Rife interpolation short-time fractional Fourier transform( STFRFT)-variable weight least square fitting( VWSF) algorithm is proposed for solving the problem of low parameter estimation accuracy of linear frequency modulation( LFM) signal under low signal-to-noise ratio( SNR). STFRFT is used to improve the aggregation of LFM signals,and the estimation accuracy of instantaneous frequency of signal is improved by VWSF,thus estimating the instantaneous frequency,initial frequency and modulation frequency of LFM signal. The Cramer-Rao lower bound( CRLB) of the signal parameters estimation is derived,and the factors affecting the estimated parameter CRLB and the variation of CRLB with it are analyzed. The simulated results show that the Rife interpolation STFRFT-VWSF algorithm has better estimation accuracy of LFM signal parameters,the parameter estimation and CRLB theoretical analysis are rational,and the feasibility of the algorithm is proven through sea test. [ABSTRACT FROM AUTHOR]

The water resources in the Tibetan Plateau have a profound impact on China’ s economic, social development and climate change. Based on gravity data from gravity recovery and climate experiment (GRACE) satellite , considering its filtering leakage error, this paper proposes the Forward ‐ Modeling method for quantitative estimation. In view of the glocial isostatic adjustment(GIA) effect, we first infer terrestrial water storage (TWS) changes in the Tibetan Plateau, and compare the results with the water‐global assessment and prognosis hydrology model(WGHM). Then we extract the time‐frequency spectrum of timeseries signals using short‐time Fourier transformation algorithm. In addition, we discuss the relationship between TWS and precipitation by combining with precipitation data from Global Presipitation Climatology Centre. The study finds that: (1) TWS shows obvious spatial differences after recovering leakage signal. In most of the period, TWS in the north and southeast is in large surplus, and TWS in the south and southwest is rapidly depleted. The spatial characteristics are basically consistent with the WGHM results. (2) The time‐frequency spectrum distribution of TWS is dominated by low‐frequency signals, and time‐series dynamic changes have obvious seasonal and periodic changes, with an annual amplitude of 7.5 cm. The increase rate of water storage in 2003―2004 was 3.89 cm/a. The loss rate in 2005―2010 was -0.31 cm/a. The rate of increase in 2011―2014 was 0.22 cm/a. (3) Precipitation is the main factor affecting the variation of TWS. In 2006 and 2009, precipitation was significantly lower, the water storage all decreased significantly. In 2010, there was heavy rainfall, the water storage increased significantly. The leakage error correction method and research results in this paper have important reference value for quantitative research on regional TWS varition. [ABSTRACT FROM AUTHOR]

The crop residues auto-detection is an important technology for intelligent agriculture. However, the farmland condition is so complicated so that it’s difficult to detect the crop residues and calculate its coverage. The field is always unevenly distributed with clays and gullies, besides that, the crop residues have various shapes and sizes. Those variables affect the detection accuracy. The research shows that FFT (fast Fourier transformation) can distinguish both the high frequency and low frequency signals in the image. The high frequency signals characterize the outline of the image and the low frequency signals characterize the content of the image. The crop residues belong to high frequency information exactly. Meanwhile, SVM (support vector machine) has a high distinguishing ability for target recognition in complex backgrounds. It maps linearly indivisible data to high dimensional space through different kernel functions and converts it into linearly separable data. It establishes a maximum interval hyperplane in high dimensional space and two mutually parallel hyperplanes on both sides of the data hyperplane. On the basis above, this paper proposed a novel fusion algorithm for crop residues auto-detection with Fast Fourier Transformation (FFT) and Support Vector Machine (SVM). We also designed and realized an intelligent monitoring equipment for crop coverage auto-detection which consists camera, embedded board, location module, communication module and other sensors through 4G cloud network. In order to detect residues, we extracted the high frequency information (residues region) by designing high pass filter after FFT with different kernels. We tested three different filter kernels including square, circle and diamond filter with three shapes. The results of the experiments indicated that the square filter with size 11×11 was the best choice considering speed and accuracy. Then, an adaptive threshold segmentation method was put forward to process the normalization image we obtained. The threshold was set by calculate the energy score we defined based on the idea of integral. The experiments showed that 0.8 was the best threshold choice for our algorithm. It can preserve the most crop region and remove the un-crop region as much as possible. We used the segmentation result as the detection mask for the next step. On the other hand, we trained a SVM classifier using our database with different input sizes and kernels and selected the parameter group with best performance as final choice. The classifier was utilized to re-classify the adaptive threshold segmentation result. Finally, we found that the traditional image erosion and dilation algorithm treated all pixels without considering its credibility. So it was prone to misprocessing (including etching away areas that should be preserved, or expanding the noise area that should be removed). To avoid this misprocessing, we raised a multi-scale filter to erase noises and fill tiny holes which was similar to image pyramid. There were two filters with size 3×3 and 7×7. The bigger one was to filter the image noise with tinny size and the smaller one was to expand the residues region with holes. We benchmarked the algorithm on our database and the results indicated that our method was state of the art. The error was about 4.55% and it just used 0.05 s. [ABSTRACT FROM AUTHOR]

The naturally vuggy and fractured carbonate rock plays an important role in China' s oil and gas resources. Therefore, it is of great significance to study the characteristics of well bottom pressure in fracture-vug carbonate rock Tor hydraulic fractured wells. According to the basic principle of seepage mechanics, the well test model for carbonate reservoirs in view of the stress sensitivity and the threshold pressure gradient was established. The point source function method, the Laplace integral transform and the Fourier cosine integral transform were used to obtain the point source solution with impermeable top and hot torn and lateral infinite boundary in the Laplace space. The surface source solution was obtained with the integral of the point source solution; the real-space well bottom pressure solution was obtained through the Stehfest numerical inversion and the well test curves were drawn. The simplified model solution matches with the related literature calculation results as to the threshold pressure gradient. The larger the stress sensitivity coefficient is, the more obviously the pressure and the pressure derivative curve will go up; the larger the threshold pressure gradient is, the earlier the pressure derivative curve will rise up; the smaller the open degree is, the more obvious the spherical flow characteristics will be; the larger the interporosity flow coefficient is, the earlier the concavity ' will appear; the larger the elastic storage ratio is, the wider and deeper the ' concavity' will be. The proposed model can be effectively applied to analyze the well test curves of hydraulic fractured wells in naturally vuggy and fractured carbonate reservoirs of low permeability. [ABSTRACT FROM AUTHOR]

According to the harmonic resonance theory， when the continuous casting mold is non-sinusoidal oscillation and the vibration frequency is lower than the natural frequency of the oscillator in the mold， partial harmonics with a higher amplitude can lead to resonance because the harmonic frequencies is an integer multiple of the oscillation frequency， which can directly affect the quality of slab. Using Fourier transformation， the acceleration curve of non-sinusoidal oscillation of the mold is analyzed and the relationships between harmonic amplitude and other factors， such as initial amplitude， oscillation frequency， non-sinusoidal oscillation factor and harmonic order are obtained. Then， a theoretical method of restraining resonance can be given. When the natural frequency of the oscillator in the mold is known， the harmonic order of resonance under different oscillation frequencies is determined. The harmonic amplitude corresponding to the combination of different oscillation parameters can be given by the relationship between the harmonic amplitude and the variation of each oscillation parameter. Consequently， selecting an oscillation parameter combination with a smaller harmonic amplitude can reduce the adverse effect of resonance phenomenon on the oscillator in the mold， resulting to reduce the deflection of mold， maintain liquid level stabilizing and improve the working conditions of continuous casting machine. [ABSTRACT FROM AUTHOR]

Long-wave infrared (LWIR) spectral imaging technology has broad application prospects in mineral detection and identification of hazardous chemicals. Five kinds of common interference spectral imagers, such as two-sided Sagnac type, three-sided Sagnac type, static Michelson type, swing arm Michelson type and variable gap Fabry-Perot (F-P) type, are analyzed for the miniaturization and multi-platform application of LWIR spectral imaging technology. The advantages and disadvantages of these imagers are analyzed from the aspects of volume, stability, accuracy requirements, and optical system complexity. A prototype of variable gap F-P spectral imager was developed. The rearrangement, apodization, Fourier transform, spectral radiation calibration and other processing methods are used to accurately invert the target spectrum. The chemical DMMP was tested using the prototype imager, and the test result is consistent with that of MR170 high precision spectrometer. [ABSTRACT FROM AUTHOR]

In order to investigate the dynamic stability of a plate, the Mathieu-Hill equation of dynamic instability for a plate was derived by Galerkin method, then the critical excitation frequencies and amplitude frequency resonance for the plate without and with additional mass were solved by the eigenvalue method. In order to verify the analytical solution, the experimental research on the dynamic stability of a plate was further carried out, the dynamic resonances of the plate without and with additional mass under the excitation force of different amplitudes were obtained by the swept frequency tests. Three important stages in the process of parametric resonance instability and the variation trend of vibration period of a plate were detected by time domain analysis method. The measured critical excitation frequencies of the plate without and with additional mass under the excitation force of different amplitude were obtained. The corresponding measured amplitude frequency response were acquired by the Fourier transform of the dynamic response. It is shown that the process of the plate’ s instability owing to parametric resonance is from transient vibration to parametric resonance instability and finally restored to transient vibration, the trend of vibration amplitude increasing unlimitedly instability plate is limited by the geometrical nonlinearity which induces traction resonance vibration toward to the direction of large frequencies. Additional masses of a plate will cause the decrease of instability region, and the increase of critical excitation parameter and vibration amplitude. The experimental results are agreed well with theoretical ones. [ABSTRACT FROM AUTHOR]

In order to improve the reusable performance of nano-silver in catalytic reduction of p-nitrophenol, polyvinyl alcohol sponge (PVA-S) loaded with nano-silver particles (PVA-S-Ag) was prepared. Scanning electron microscope (SEM), Fourier transform infrared spectra (FT-IR) and X-ray diffraction (XRD) were used to characterize the structure of PVA-S-Ag. The effect of the catalytic reduction of p-nitrophenol by PVA-S-Ag in the presence of sodium borohvdride was investigated by UV-vis. The results show that PVA-S-Ag is an excellent catalyst for the reduction of p-nitrophenol. Resides, PVA-S-Ag still maintains good catalytic reduction effect on 4-NP after several cycles. [ABSTRACT FROM AUTHOR]

In industrial production, it is necessary to detect the running state of rolling bearings and diagnose their faults. When rolling bearing is damaged, the vibration signals collected often show the characteristics of non-stationary and modulation, and will inevitably be disturbed by strong noise, so it is very difficult to identify the fault features. How to effectively extract the components carrying fault feature information from complex non-stationary and modulated signals is the key of diagnosing bearing fault. Frequency slice wavelet transform (FSWT) uses frequency slice function based on the advantages of short-time Fourier transform (STFT) and wavelet transform (WT), which makes the traditional Fourier transform realize time-frequency analysis function. The traditional fault diagnosis method based on FSWT determines the most suitable center frequency and the faulty bandwidth by comparing the results of different frequency band processing, and realizes the reconstruction and description of arbitrary frequency band and local characteristics of the signal. However, this method is inefficient, non-adaptive and can not guarantee that the frequency band screened manually contains the required fault information. Aiming at the problem that traditional methods rely on manual operation and have no self-adaptability, an adaptive frequency slice wavelet transform (AFSWT) is proposed in this paper. Firstly, the signal spectrum is segmented continuously; spectrum segmentation covers the whole frequency band and avoids the process of manual selection of spectrum boundary. The method of equalization can improve the computational efficiency. Secondly, the spectral negative entropy is introduced as the evaluation basis to calculate the complexity of the signal in each frequency band in order to screen the cyclostationary information which may contain periodic shocks. Finally, the frequency band with the largest spectral negative entropy is selected and defined as the faulty center frequency and bandwidth. The signal components in the band are reconstructed and analyzed by envelope demodulation to realize fault diagnosis. The analysis results of a simulation signal show that the AFSWT method identifies the center frequency of 5 000 Hz and the bandwidth of 909 Hz, which is very close to the ideal result. Compared with fast spectral kurtosis, AFSWT has better applicability when the central frequency of signal is located in Fs/4, Fs/8 and Fs/16(Fs is the sampling frequency). Through the test of rolling bearing test-bench, the vibration signals of rolling bearing outer ring fault are collected and analyzed. After AFSWT analysis, the characteristic frequency and its 2-6 times frequency components can be clearly found in the envelope spectrum of the results. On the other hand, AFSWT takes 14.7 seconds to process test signals. The traditional FSWT needs repeated drawing of time-frequency distribution map, determination of central frequency band and selection of observation frequency, it often takes 5-10 minutes to determine the faulty center frequency and bandwidth. The above analysis shows that AFSWT can improve the calculation efficiency and screening accuracy by uniformly dividing the spectrum of the signal and screening the signal components according to the negative entropy of the spectrum. It is suitable for fault diagnosis of rolling bearings. [ABSTRACT FROM AUTHOR]

Non-invasive CAP(central aortic pressure)reconstruction is mostly based on the auto regressive eXogenous(ARX)model or Fourier transform in transfer function method， without considering the factors such as sampling frequency and data length. Based on the ARX model and the Fourier transform， the error of reconstruction CAP was analyzed for studing the effects of sampling frequency and data length on the CAP. The results show that when sampling frequency is 100Hz and data length is greater than 3s， CAP can be better reconstructed by ARX model(RMSE:(306.6±80.0)Pa; FIT: 89%). The algorithm based on the Fourier transform is insensitive to sampling frequency. When data length is set to 6s， the reconstructed CAP has a better performance(RMSE:(493.3±320.0)Pa，FIT:84%). [ABSTRACT FROM AUTHOR]

Transient simulation is indispensable for capturing the periodic disturbance between the rotor and stator for turbomachine applications. In order to avoid resonance risk, the turbomachine systems generally have prime number of components between the rotor and stator, which makes the periodic boundary conditions failed and the transient simulation must be carried out including all the passages. However, prohibitive computing resources and too much time cost are required to obtain detailed accurate simulations for the conventional methods of modeling all the passage. In this paper, 3 numerical approaches, the full passages simulation, the PT(Profile Transform) method with only 1 passage, the FT(fourier transform) method with double-passage, were respectively used to numerically predict the hydraulic performance and loading for the Francis99 turbine based on the k-ω SST turbulent model. The PT method overcame the unequal pitch problem by scaling the flow profile across the blade row interfaces. In the Fourier Transformation method, a phase-shifted boundary condition with Fourier data compression was used to account for the unequal pitch between the blade rows passages, and the solution history of circumferential boundary and rotational boundary was reasonably reconstructed. During the transient numerical simulations, the inlet and outlet boundary were given by the method of Profile Boundary Conditions. The mass flow with the velocity vector direction was prescribed on the inlet section, and the outlet was treated as a static pressure outlet where a static gauge pressure was specified. Compared with the experimental tests, the 3 simulation methods could accurately predict the hydraulic efficiency and the average pressure at different locations, and the static pressure distribution on the mid-span plane and pressure loading on runner blade were comparable. The hydraulic efficiency extracted by FT and PT methods were both higher than the result of the full passages simulation, which was attributed to the fact that the 2 simulation methods only included part of the flow passages and didn’t consider the hydraulic loss of volute, fixed guide vane and draft tube. The temporal variation of blade force and torque generated by the FT method showed in good agreement with the full passages method, expect for small deviation in pulsating amplitude. However, the PT method showed larger discrepancy with the full passages results for both of pulsating frequency and amplitude. In term of spectrum characteristics of pressure fluctuation, the numerical results extracted by the FT method yielded to a very good validation with the full passages and the experimental obtainment. Due to variable scaling or stretching at the Rotor-Stator interface, the passing frequency of the blade was captured in both the static domain and the rotating domain, and the pressure amplitude of PT method was lower than that of the full passages and the experimental. In addition, the time cost ratio among the full passages, the FT method and the PT method was about 1:0.375:0.23. We concluded that the FT method was capable of predicting the hydraulic performance and pressure fluctuation well with less computing resources and was a good alternative compared to the conventional full passage method. [ABSTRACT FROM AUTHOR]

In this paper, graphene was synthesized on sapphire substrate by chemical vapor deposition (CVD) method, and the effect of growth time on hydrophobic properties and microstructure of graphene was investigated. Contact-angle meter, Fourier transform infrared spectrometer, Raman spectrometer and field emission scanning electron microscopy were applied to study hydrophobic and microscopic structure of graphene, respectively. It shows that after growing 30 min, maximum contact angle of graphene is 129.96°, it presents hydrophobic properties. Meantime, infrared test shows only carbon-carbon double bonds. Raman analysis also indicates three characteristic peaks of graphene after growing 10-30 min. larger contact angle makes graphene as a potential hydrophobic material, and it can even be a promising superhydrophobic material by its hydrophobic modification. [ABSTRACT FROM AUTHOR]

A method based on Hough transform to detect the wheezes from the STFT spectrum of the lung sounds was presented. This method first clips the ROI region of the STFT spectrum of the digital lung sound data， then uses the Canny operator for image edge detection， and finally identifies the wheezes automatically based on the analysis of Hough transform data. The data for clinical analysis includes the clinical acquisition of lung sounds and the international shared lung sound files. Hough transform detection method got the accuracy rate of 87% in the detection of 60 cases of wheezes， and 74% for the 70 cases of normal respiratory sound. [ABSTRACT FROM AUTHOR]

Low altitude image matching with repeated texture may have a small amount of corresponding points or be unsuccessful because of ambiguous matching. To solve the problem, a phase correlation method supportes low altitude aerial image matching with repeated texture is proposed. The method estimates the traversal range of corresponding points, including translation, rotation, and scale space. The traversal range is estimated by a cross-power spectrum of the image Fourier transform and a complex conjugate of another image Fourier transform. Next, Harris-Laplace scale space is estimated by the scale traversal range and corners detection. Then, corresponding point matching is achieved by a correlation coefficient and epipolar constraint. The experimental results show that the method may be reliable and practical for low altitude images matching with a repeated texture, and obtains enough and well-distributed corresponding points. [ABSTRACT FROM AUTHOR]

Widely emerging in the fields of mathematics and mechanics, a class of 3rd-order nonlinear strong-damp disturbed partial differential evolution equations were studied. Firstly, a functional homotopic mapping was constructed to express the solution to the evolution equation in a form of power series with artificial parameters, which was substituted into the homotopic mapping to build a method of successive iteration for the solution to the nonlinear disturbed equation. Then the corresponding non-disturbed strong-damp evolution equation was analyzed with exact solution based on the theory of Fourier transform. Secondly, the found exact solution was used as the initial function of the homotopic mapping iteration, and the iteration expansion of the nonlinear disturbed equation was applied to solve the related equations with the Fourier transform method. Finally, both the exact and arbitrary-order approximate analytic solutions to the nonlinear strong-damp disturbed evolution equation were obtained. The proposed homotopic mapping method is proved to have the advantages of convenience and accuracy. [ABSTRACT FROM AUTHOR]

Aiming at solving the problem that fast fourier transformation (FFT) is hardly applied to extract the characteristics frequency of the bearing's signal, a fault diagnosis method based on empirical mode decomposition (EMD), kurtosis and Hilbert demodulation was pro-posed. Firstly, EMD was used to decompose the vibration signal into the intrinsic mode function (IMF). Then, some of the IMFs selected by the rule of kurtosis were used to recombine the new vibration signal. At last, the Hilbert envelope demodulation was adopted with the new signal to detect the fault information. Through analyzing the simulation signal and the inner vibration signal of fault rolling bearing respective-ly, the characteristics frequency could be clearly extracted. The results indicate hat the proposed method is effective in extracting the bearings' fault information and could be used in rolling bearings fault diagnosis. [ABSTRACT FROM AUTHOR]

This paper introduces Fourier transformation, and its important role of fast Fourier transform (FFT) in the analysis of signal spectrum. According to the important properties of polymer materials--viscoelasticity, the paper deals with the spectral analysis by using fast Fourier transform and computer software MATLAB. It explores possibility of spectrum analysis of the methods using polymer materials by using fast Fourier transform, at least the possibilities in the experimental polymer material impact on the spectrum. From these results, it maybe extend the application of Fourier transform. [ABSTRACT FROM AUTHOR]

There are many methods to extract seismic signals from the background noise. In extraction of single frequency signa, seismic wave noise are mixed. There are much limitation of the classic Fourier transformation and the traditional wavelet transformation denoising methods. From the characteristics of seismic wave, we can take environmental noise collected a few second before source emission as noise signal in the process of the whole signal processing. The wavelet denoising method can obtain efective denoising results. And the extraction of earthquake wave signal by using this method to weight drop production, can provide a good basis for subsequent seismic wave information utilization. [ABSTRACT FROM AUTHOR]

The time spectral method casts a time-periodic flow computation into the solution of N coupled steady computations, where N indicates the number of time intervals. This method solves the periodic state directly without resolving transients, by enforcing periodicity and using a Fourier representation in time. This technique is presented to solve time periodic unsteady Navier-Stokes equations for unsteady viscous flow over an oscillating airfoil. The Roe's FDS scheme is used to discrete convective terms, and physical time derivative terms are discretized by a Fourier representation, in which the time derivative is formulated with the combination of flow variables at all time levels, leading to spectral accuracy. A pseudo-time derivative term is added into the original equations and the fully implicit BLU-SGS method in the pseudo-time direction is employed. The solution is obtained by marching towards a steady-state in the pseudo-time variable. A subsonic case and a transonic case about the NACA0012 airfoil are calculated. Baldwin-Lomax turbulence mode has been used in viscous flow analysis. The numerical results agree well with the experimental data. The computational results show that the small number of time intervals is sufficient to capture the flow physics phenomena. [ABSTRACT FROM AUTHOR]

Based on the Radon-Wigner transform (RWT), the Doppler resolution and extraction are studied for velocity and acceleration of maneuvering target. The pulse Doppler radar echo model of maneuvering target and the Fourier transformation processing method are offered. The RWT method is used to estimate the parameters of maneuvering targets. The Taylor analytical expression, the velocity and acceleration independent resolution expression and the joint resolution expression are proposed. It is indicated that the motion parameters can be distinguished if the path deviation between different maneuvering targets reaches one-half wavelength. The resolution capabilities of Fourier transform, Radon-ambiguity transform (RAT) and RWT method are simulated and compared. The simulation results show that RWT has the strong resolution capability of velocity and acceleration. The joint resolution condition of velocity and acceleration is validated. [ABSTRACT FROM AUTHOR]

The vibration equation is developed by semi-analytical finite element method. The mode-decoupling and Fourier transform are used to deal with the vibration equation, and the expression of dynamic stiffness is obtained. Considering the randomness of structural parameters, the random expression of dynamic stiffness is deduced by Taylor expansion and the random factor method. The influences of random factors on the means and variation coefficient of dynamic stiffness are discussed. The calculation resuits show that the standard deviation of elastic modulus random factor has a significant influence on the randomness of dynamic stiffness, and if all other factors are equal and the standard deviation of elastic modulus random factor is doubled, the decreasing ratios of all dynamic stiffness mean values in three minimum points are 46.7%, and are 27.4% and 3.6% for two maximum points in proper order. Furthermore, when the variability of structural parameters belongs to week degree, the variability of dynamic stiffness in extreme points belong to moderate degree, even strong degree. [ABSTRACT FROM AUTHOR]

The Fourier transform infrared spectrometer was used to measure the emissivity of natural surface objects in Shuixigou coalfield fires area of Xinjiang. The smooth spectral iterative method was used to separate the temperature and emissivity, and the accurate temperature and emissivity of the surface objects were obtained. The thermal infrared emissivity spectral characteristics of seven typical types natural surface objects were analyzed, and five ASTER thermal infrared bands were selected to conduct the data simulation. The results show that: 1 The characteristics of thermal infrared emissivity spectrum show distinct differences in wavelength range of 8 ~ 13 µ m, especially in 8. 5 ~ 10,11.3 and 12~13 µm. Therefore these bands can be used as identifying characteristics of different bands; 2 Emissivity spectrum shows a characteristic difference at five ASTER thermal infrared bands it is practically useful in the process of using remote sensing images to extract information for surface objects in coalfield fires areas; 3 The emissivity can provide surface temperature retrieval with a precise parameter, so as to improve precision of temperature retrieval. [ABSTRACT FROM AUTHOR]

According to Split Hopkinson Pressure Bar (SHPB) test signal characteristic with high noise, short lasting time, mutant fast,the Hilbert-Huang transform (HHT) analysis technique was used to de-noise testing signal on the coal impact failure. The intrinsic mode function (IMF) components and its' frequency spectrum and the energy percentages of IMF components were got by using empirical mode decomposition (EMD) decomposition to measure coal impact damage SHPB test signal. Thus the high frequency noises were effectively separated out from the original signal by the low-pass filtering. Through the comparison of original signal and de-noised signal characteristic by using fast Fourier transform (FFT) spectrum and Morlet spectrum analysis, the qualitative conclusion that the HHT method could be used in coal impact damage SHPB testing signal de-noising were obtained. From the calculation of the denoised signal noise ratios and energy percentages, it was indicated that the de-noised signals were fully retained the signals' transient non-stationary featured and the de-noising effect was obvious by HHT method in quantitative description. The HHT method, which is applied for coal impact damage SHPB testing signal de-noising, is simple and can obtain reliable results. [ABSTRACT FROM AUTHOR]

The time delay estimation for linear frequency-modulated (LFM) pulse based on the fractional Fourier transform was analyzed in the fractional Fourier domain, taken the time domain performance of linear frequency-modulated pulse compression as reference. Also, the difference between these two methods was discussed in digital signal processing. It is found that they have almost the same output signal to noise ratio, pulse-width compression ratio and peak amplitude ratio. Furthermore, the latter has higher precision in the time delay estimation in digital implementation, needs less data rate, and has more potential. [ABSTRACT FROM AUTHOR]