Flash floods are the highest sediment transporting agent,but are inaccessible for in-situ sampling and have rarely been analyzed by remote sensing technology.Laboratory and field experiments were done to develop linea...Flash floods are the highest sediment transporting agent,but are inaccessible for in-situ sampling and have rarely been analyzed by remote sensing technology.Laboratory and field experiments were done to develop linear spectral unmixing(LSU)remote sensing model and evaluate its performance in simulating the suspended sediment concentration(SSC)in flash floods.The models were developed from continuous monitoring in the laboratory and the onsite spectral signature of river bed sediment deposits and flash floods in the Tekeze River and in its tributary,the Tsirare River.The Pearson correlation coefficient was used to determine the variability of correlations between reflectance and SSCs.The coefficient of determination(R2)and root mean square of error(RMSE)were used to evaluate the performance of the generated models.The results found that the Pearson correlation coefficient between SSCs and reflectance varied based on the level of the SSCs,geological colors,and grain sizes.The performance of the LSU model and empirical remote sensing approaches were computed to be R2?0.92,and RMSE-±0.76 g/l in the Tsirare River and R2-0.91,and RMSE-±0.73 g/l in the Tekeze River and R2?0.81,RMSE-±2.65 g/l in the Tsirare river and R2?0.76,RMSE-±10.87 g/l in the Tekeze River,respectively.Hence,the LSU approach of remote sensing was found to be relatively accurate in monitoring and modeling the variability of SSCs that could be applied to the upper Tekeze River basin.展开更多
Let G be a simple graph with n vertices and m edges.In this paper,we present some new upper bounds for the adjacency and the signless Laplacian spectral radius of graphs in which every pair of adjacent vertices has at...Let G be a simple graph with n vertices and m edges.In this paper,we present some new upper bounds for the adjacency and the signless Laplacian spectral radius of graphs in which every pair of adjacent vertices has at least one common adjacent vertex.Our results improve some known upper bounds.The main tool we use here is the Lagrange identity.展开更多
Visible, near-infrared and shortwave-infrared(VNIR-SWIR) spectroscopy is an efficient approach for predicting soil properties because it reduces the time and cost of analyses. However, its advantages are hampered by t...Visible, near-infrared and shortwave-infrared(VNIR-SWIR) spectroscopy is an efficient approach for predicting soil properties because it reduces the time and cost of analyses. However, its advantages are hampered by the presence of soil moisture, which masks the major spectral absorptions of the soil and distorts the overall spectral shape. Hence, developing a procedure that skips the drying process for soil properties assessment directly from wet soil samples could save invaluable time. The goal of this study was twofold:proposing two approaches, partial least squares(PLS) and nearest neighbor spectral correction(NNSC), for dry spectral prediction and utilizing those spectra to demonstrate the ability to predict soil clay content. For these purposes, we measured 830 samples taken from eight common soil types in Israel that were sampled at 66 different locations. The dry spectrum accuracy was measured using the spectral angle mapper(SAM) and the average sum of deviations squared(ASDS), which resulted in low prediction errors of less than 8% and 14%, respectively. Later, our hypothesis was tested using the predicted dry soil spectra to predict the clay content, which resulted in R^2 of 0.69 and 0.58 in the PLS and NNSC methods, respectively. Finally, our results were compared to those obtained by external parameter orthogonalization(EPO) and direct standardization(DS). This study demonstrates the ability to evaluate the dry spectral fingerprint of a wet soil sample, which can be utilized in various pedological aspects such as soil monitoring, soil classification,and soil properties assessment.展开更多
A trigonometric series expansion method and two similar modified methods for the Orr-Sommerfeld equation are presented. These methods use the trigonometric series expansion with an auxiliary function added to the high...A trigonometric series expansion method and two similar modified methods for the Orr-Sommerfeld equation are presented. These methods use the trigonometric series expansion with an auxiliary function added to the highest order derivative of the unknown function and generate the lower order derivatives through successive integra- tions. The proposed methods are easy to implement because of the simplicity of the chosen basis functions. By solving the plane Poiseuille flow (PPF), plane Couette flow (PCF), and Blasius boundary layer flow with several homogeneous boundary conditions, it is shown that these methods yield results with the same accuracy as that given by the conventional Chebyshev collocation method but with better robustness, and that ob- tained by the finite difference method but with fewer modal number.展开更多
Constant envelope with a fractional Fourier transformorthogonal frequency division multiplexing(CE-FrFT-OFDM)is a special case of a constant envelope OFDM(CE-OFDM),both being energy efficient wireless communication te...Constant envelope with a fractional Fourier transformorthogonal frequency division multiplexing(CE-FrFT-OFDM)is a special case of a constant envelope OFDM(CE-OFDM),both being energy efficient wireless communication techniques with a 0 dB peak to average power ratio(PAPR).However,with the proper selection of fractional order,the first technique has a high bit error rate(BER)performance in the frequency-time selective channels.This paper performs further analysis of CE-FrFT-OFDM by examining its spectral efficiency(SE)and energy efficiency(EE)and compare to the famous OFDM and FrFT-OFDM techniques.Analytical and comprehensive simulations conducted show that,the CE-FrFT-OFDM has five times the EE of OFDM and FrFT-OFDM systems with a slightly less SE.Increasing CE-FrFT-OFDM’s transmission power by increasing its amplitude to 1.7 increases its SE to match that of the OFDM and FrFT-OFDM systems while slightly reducing its EE by 20%to be four times that of OFDM and FrFTOFDM systems.OFDM and FrFT-OFDM’s amplitude fluctuations cause rapid changing output back-off(OBO)power requirements and further reduce power amplifier(PA)efficiency while CE-FrFTOFDM stable operational linear range makes it a better candidate and outperforms the other techniques when their OBO exceeds 1.7.Higher EE and low BER in time-frequency selective channel are attracting features for CE-FrFT-OFDM deployment in mobile devices.展开更多
Rapid urban sprawl and re-construction of old towns have been leading to great changes of land use in cities of China. To witness short-term urban land use changes, rapid or real time remote sensing images and effecti...Rapid urban sprawl and re-construction of old towns have been leading to great changes of land use in cities of China. To witness short-term urban land use changes, rapid or real time remote sensing images and effective detection methods are required. With the availability of short repeat cycle, relatively high spatial resolution, and weather-independent Synthetic Aperture Radar (SAR) remotely sensed data, detection of short-term urban land use changes becomes possible. This paper adopts newly released Sentinel-1 SAR data for urban change detection in Tianhe District of Guangzhou City in Southern China, where dramatic urban redevelopment practices have been taking place in past years. An integrative method that combines the SAR time series data and a spectral angle mapping (SAM) was developed and applied to detect the short-term land use changes. Linear trend transformations of the SAR time series data were first conducted to reveal patterns of substantial changes. Spectral mixture analysis was then conducted to extract temporal endmembers to reflect the land development patterns based on the SAR backscattering intensities over time. Moreover, SAM was applied to extract the information of significant increase and decrease patterns. The results of validation and method comparison showed a significant capability of both the proposed method and the SAR time series images for detecting the short-term urban land use changes. The method received an overall accuracy of 78%, being more accurate than that using a bi-temporal image change detection method. The results revealed land use conversions due to the removal of old buildings and their replacement by new construction. This implies that SAR time series data reflects the spatiotemporal evolution of urban constructed areas within a short time period and this study provided the potential for detecting changes that requires continuously short-term capability, and could be potential in other landscapes.展开更多
As concluded from physical theory and laboratory experiment,it is widely accepted that nonlinearities of sea state play an important role in the formation of rogue waves;however,the sea states and corresponding nonlin...As concluded from physical theory and laboratory experiment,it is widely accepted that nonlinearities of sea state play an important role in the formation of rogue waves;however,the sea states and corresponding nonlinearities of real-world rogue wave events remain poorly understood.Three rogue waves were recorded by a directional buoy located in the East China Sea during Typhoon Trami in August 2013.This study used the WAVEWATCHⅢmodel to simulate the sea state conditions pertaining to when and where those rogue waves were observed,based on which a comprehensive and full-scale analysis was performed.From the perspectives of wind and wave fields,wave system tracking,High-Order Spectral method simulation,and some characteristic sea state parameters,we concluded that the rogue waves occurred in sea states dominated by second-order nonlinearities.Moreover,third-order modulational instabilities were suppressed in these events because of the developed or fully developed sea state determined by the typhoon wave system.The method adopted in this study can provide comprehensive and full-scale analysis of rogue waves in the real world.The case studied in this paper is not considered unique,and rules could be found and confirmed in relation to other typhoon sea states through the application of our proposed method.展开更多
Due to the development of E-Commerce, collaboration filtering (CF) recommendation algorithm becomes popular in recent years. It has some limitations such as cold start, data sparseness and low operation efficiency. In...Due to the development of E-Commerce, collaboration filtering (CF) recommendation algorithm becomes popular in recent years. It has some limitations such as cold start, data sparseness and low operation efficiency. In this paper, a CF recommendation algorithm is propose based on the latent factor model and improved spectral clustering (CFRALFMISC) to improve the forecasting precision. The latent factor model was firstly adopted to predict the missing score. Then, the cluster validity index was used to determine the number of clusters. Finally, the spectral clustering was improved by using the FCM algorithm to replace the K-means in the spectral clustering. The simulation results show that CFRALFMISC can effectively improve the recommendation precision compared with other algorithms.展开更多
The goal of this study is to provide a stochastic method to investigate the eff ects of the randomness of soil properties due to their natural spatial variability on the response spectra spatial variation at sites wit...The goal of this study is to provide a stochastic method to investigate the eff ects of the randomness of soil properties due to their natural spatial variability on the response spectra spatial variation at sites with varying conditions. For this purpose, Monte Carlo Simulations are used to include the variability of both incident ground motion and soil parameters in the response spectra by mean of an appropriate coherency loss function and a site-dependent transfer function, respectively. The approach is built on the assumption of vertical propagation of SH type waves in soil strata with uncertain parameters. The response spectra are obtained by numerical integration of the governing equation of a single-degree-of-freedom (SDOF) system under non-stationary site-dependent and spatially varying ground motion accelerations simulated with non-uniform spectral densities and coherency loss functions. Numerical examples showed that randomness of soil properties signifi cantly aff ects the amplitudes of the response spectra, indicating that as the heterogeneity induced by the randomness of the parameters of the medium increases, the spectral ordinates attenuate.展开更多
The distribution and chemical properties of colored dissolved organic matter(CDOM)in the Yellow Sea and the East China Sea during December 2011-January 2012 were investigated.The input of freshwater and biological act...The distribution and chemical properties of colored dissolved organic matter(CDOM)in the Yellow Sea and the East China Sea during December 2011-January 2012 were investigated.The input of freshwater and biological activities had an evident influence on the CDOM levels(characterized by the light absorption coefficient at the wavelength of 355 nm a355)in the study area.The spatial distribution of CDOM levels displayed a gradually decreasing trend from the coastal waters(0.37m^-1)to the open sea(0.18m^-1).The spectral slope ratio(the slope ratio SR defined as S275-295:S350-400)during the cruise was correlated with salinity,and exhibited a large variation from inshore(average of 2.515)to offshore sites(average of 5.327)compared with the distribution of a355.The values of SR were related to CDOM molecular weight(MW).The a355,SR,and chlorophyll a in 37 samples collected from the surface microlayer were significantly correlated with those in the corresponding subsurface water samples,implying a strong exchange action between the microlayer and bulk water.The a355 and SR of CDOM exhibited significant microlayer enrichment,with mean enrichment factors(EFs)of 1.72 and 1.62,respectively.展开更多
INTERNODES is a general purpose method to deal with non-conforming discretizations of partial differential equations on 2D and 3D regions partitioned into two or several disjoint subdomains. It exploits two intergrid ...INTERNODES is a general purpose method to deal with non-conforming discretizations of partial differential equations on 2D and 3D regions partitioned into two or several disjoint subdomains. It exploits two intergrid interpolation operators, one for transfering the Dirichlet trace across the interfaces, and the other for the Neumann trace. In this paper, in every subdomain the original problem is discretized by either the finite element method (FEM) or the spectral element method (SEM or hp-FEM), using a priori non-matching grids and piecewise polynomials of different degrees. Other discretization methods, however, can be used. INTERNODES can also be applied to heterogeneous or multiphysics problems, that is, problems that feature different differential operators inside adjacent subdomains. For instance, in this paper we apply the INTERNODES method to a Stokes- Darcy coupled problem that models the filtration of fluids in porous media. Our results highlight the flexibility of the method as well as its optimal rate of convergence with respect to the grid size and the polynomial degree.展开更多
This paper is devoted to Professor Benyu Guo's open question on the C1-conforming quadrilateral spectral element method for fourth-order equations which has been endeavored for years. Starting with generalized Jac...This paper is devoted to Professor Benyu Guo's open question on the C1-conforming quadrilateral spectral element method for fourth-order equations which has been endeavored for years. Starting with generalized Jacobi polynomials on the reference square, we construct the C1-conforming basis functions using the bilinear mapping from the reference square onto each quadrilateral element which fall into three categories-interior modes, edge modes, and vertex modes. In contrast to the triangular element, compulsively compensatory requirements on the global C1-continuity should be imposed for edge and vertex mode basis functions such that their normal derivatives on each common edge are reduced from rational functions to polynomials, which depend on only parameters of the common edge. It is amazing that the C1-conforming basis functions on each quadrilateral element contain polynomials in primitive variables, the completeness is then guaranteed and further confirmed by the numerical results on the Petrov-Galerkin spectral method for the non-homogeneous boundary value problem of fourth-order equations on an arbitrary quadrilateral. Finally, a C1-conforming quadrilateral spectral element method is proposed for the biharmonic eigenvalue problem, and numerical experiments demonstrate the effectiveness and efficiency of our spectral element method.展开更多
The boundary control problem of a cantilever Euler-Bernoulli beam with input time delay is considered.In order to exponentially stabilize the system, a feedback controller is adopted.And we study the well-posedness an...The boundary control problem of a cantilever Euler-Bernoulli beam with input time delay is considered.In order to exponentially stabilize the system, a feedback controller is adopted.And we study the well-posedness and exponential stability of the closed-loop system.The approach used in this paper is done by several steps.Firstly, the well-posedness of this system is proved by semi-group theory.Secondly, the asymptotical expression of eigenvalue is investigated by spectral analysis.Thirdly, the exponential stability of the system is studied by multiplier technology.Finally, numerical simulations on the dynamical behavior of the system are given to support the results obtained.展开更多
Multi-scale data have had a wide-ranging level of performance in the area of urban change monitoring. Herein we investigate the correlation between the impervious surface fraction(ISF) and the Defense Meteorological S...Multi-scale data have had a wide-ranging level of performance in the area of urban change monitoring. Herein we investigate the correlation between the impervious surface fraction(ISF) and the Defense Meteorological Satellite Program/Operational Linescan System(DMSP/OLS) nighttime stable light(NTL) data with respect to the urban expansion in the main districts of Guangzhou. Landsat 5 Thematic Mapper and Landsat 8 Operational Land Image(OLI) data from 1988 to 2015 were used to extract the ISF using the linear spectral mixture analysis model and normal difference build-up index at the sub-pixel scale. DMSP/OLS NTL data from 1992 to 2013 were calibrated to illustrate the urban nighttime light conditions at the regional scale. Urban expansion directions were identified by statistics and kernel density analysis for the ISF study area at the sub-pixel scale. In addition, the correlation between the ISF and DMSP/OLS NTL data were illustrated by linear regression analysis. Furthermore, Profile Graph in ArcGIS was employed to illustrate the urban expansion from the differences in correlation in different directions. The conclusions are as follows: 1) The impervious surface(IS)in the study area has expanded to the northeast and the east, starting with the old urban zones, and the high-density IS area has increased by321.14 km~2. 2) The linear regression analysis reveals a positive correlation between the ISF and the DMSP/OLS NTL data. The multi-scale data changes are consistent with the actual urban planning of Guangzhou. 3) The DMSP/OLS NTL data overestimate the urban extent because of its saturation and blooming effects, causing its correlation with ISF to decrease. The pattern of urban expansion influences the saturation and blooming effects of the DMSP/OLS NTL data.展开更多
FM-to-AM conversion for angular filtering based on transmitted volume Bragg gratings(TBGs)is discussed.Simulation results show that a narrower spectral selectivity of TBGs led to stronger FM-to-AM conversion.Good angu...FM-to-AM conversion for angular filtering based on transmitted volume Bragg gratings(TBGs)is discussed.Simulation results show that a narrower spectral selectivity of TBGs led to stronger FM-to-AM conversion.Good angular selectivity and a wide bandwidth for the TBGs can be obtained by controlling the grating period and thickness.FM-to-AM conversion can be effectively suppressed and the distortion criterion for the filtered beam reduces to less than 5%.FMto-AM conversion of TBGs is demonstrated in the’Shenguang’ facility,and the results are in good agreement with the simulation.展开更多
Desert plants survive harsh environment using a variety of drought-resistant structural modifications and physio-ecological systems.Rolled-leaf plants roll up their leaves during periods of drought,making it difficult...Desert plants survive harsh environment using a variety of drought-resistant structural modifications and physio-ecological systems.Rolled-leaf plants roll up their leaves during periods of drought,making it difficult to distinguish between the external structures of various types of plants,it is therefore necessary to carry out spectral characteristics analysis for species identification of these rolled-leaf plants.Based on hyper-spectral data measured in the field,we analyzed the spectral characteristics of seven types of typical temperate zone rolled-leaf desert plants in the Hexi Corridor,China using a variety of mathematical transformation methods.The results show that:(1)during the vigorous growth period in July and August,the locations of the red valleys,green peaks,and three-edge parameters,namely,the red edge,the blue edge,and the yellow edge of well-developed rolled-leaf desert plants are essentially consistent with those of the majority of terrestrial vegetation types;(2)the absorption regions of liquid water,i.e.,1400-1500 and 1600-1700 nm,are the optimal bands for distinguishing various types of rolled-leaf desert plants;(3)in the leaf reflectance regions of 700-1250 nm,which is controlled by cellular structure,it is difficult to select the characteristic bands for differentiation rolled-leaf desert vegetation;and(4)after processing the spectral reflectance curves using a first-order differential,the envelope removal method,and the normalized differential ratio,we identify the other characteristic bands and parameters that can be used for identifying various types of temperate zone rolled-leaf desert plants,i.e.,the 510-560,650-700 and 1330-1380 nm regions,and the red edge amplitude.In general,the mathematical transformation methods in the study are effective tools to capture useful spectral information for species identification of rolled-leaf plants in the Hexi Corridor.展开更多
This paper focuses on performance of several efficient and accurate numerical methods for the long-wave short-wave interaction equations in the semiclassical limit regime. The key features of the proposed methods are ...This paper focuses on performance of several efficient and accurate numerical methods for the long-wave short-wave interaction equations in the semiclassical limit regime. The key features of the proposed methods are based on:(i) the utilization of the first-order or second-order time-splitting method to the nonlinear wave interaction equations;(ii) the ap-plication of Fourier pseudo-spectral method or compact finite difference approximation to the linear subproblem and the spatial derivatives;(iii) the adoption of the exact integration of the nonlinear subproblems and the ordinary differential equations in the phase space. The numerical methods under study are efficient, unconditionally stable and higher-order accurate, they are proved to preserve two invariants including the position density in L^1. Numerical results are reported for case studies with different types of initial data, these results verify the conservation laws in the discrete sense, show the dependence of the numerical solution on the time-step, mesh-size and dispersion parameter ε, and demonstrate the behavior of nonlinear dispersive waves in the semi-classical limit regime.展开更多
In this paper,we consider the r-uniform hypergraphs H with spectral radius at most r√(2+√5).We show that H must have a quipus-structure,which is similar to the graphs with spectral radius at most 2/3√2[Woo-Neumaier...In this paper,we consider the r-uniform hypergraphs H with spectral radius at most r√(2+√5).We show that H must have a quipus-structure,which is similar to the graphs with spectral radius at most 2/3√2[Woo-Neumaier,Graphs Combin.2007].展开更多
基金It gives us a great pleasure to acknowledge Addis Ababa University,Ethiopia,for providing partial cover of financial support for this research.We also interested to extend our acknowledgement to ASD Inc.,a PANalytical company,USA,for providing us the hand held Spectroradiometer.
文摘Flash floods are the highest sediment transporting agent,but are inaccessible for in-situ sampling and have rarely been analyzed by remote sensing technology.Laboratory and field experiments were done to develop linear spectral unmixing(LSU)remote sensing model and evaluate its performance in simulating the suspended sediment concentration(SSC)in flash floods.The models were developed from continuous monitoring in the laboratory and the onsite spectral signature of river bed sediment deposits and flash floods in the Tekeze River and in its tributary,the Tsirare River.The Pearson correlation coefficient was used to determine the variability of correlations between reflectance and SSCs.The coefficient of determination(R2)and root mean square of error(RMSE)were used to evaluate the performance of the generated models.The results found that the Pearson correlation coefficient between SSCs and reflectance varied based on the level of the SSCs,geological colors,and grain sizes.The performance of the LSU model and empirical remote sensing approaches were computed to be R2?0.92,and RMSE-±0.76 g/l in the Tsirare River and R2-0.91,and RMSE-±0.73 g/l in the Tekeze River and R2?0.81,RMSE-±2.65 g/l in the Tsirare river and R2?0.76,RMSE-±10.87 g/l in the Tekeze River,respectively.Hence,the LSU approach of remote sensing was found to be relatively accurate in monitoring and modeling the variability of SSCs that could be applied to the upper Tekeze River basin.
基金the National Natural Science Foundation of China(11471077)the Open Research Fund of Key Laboratory of Spatial Data Mining and Information Sharing of MOE(2018LSDMIS09)Foundation of Key Laboratory of Intelligent Metro of Universities in Fujian Province(53001703).
文摘Let G be a simple graph with n vertices and m edges.In this paper,we present some new upper bounds for the adjacency and the signless Laplacian spectral radius of graphs in which every pair of adjacent vertices has at least one common adjacent vertex.Our results improve some known upper bounds.The main tool we use here is the Lagrange identity.
基金the Porter School of Environmental Studies,the GEO-CRADLE Project(The European Union’s Horizon 2020 Research and Innovation Programme)(No.690133)the Ministry of National Infrastructures,Energy,and Water Resources of Israel(No.212-17-025)+1 种基金the Ministry of Agriculture of Israel(No.13-21-0002)for financial supportthe Israel Science Foundation(No.1457/13)for supporting her research.
文摘Visible, near-infrared and shortwave-infrared(VNIR-SWIR) spectroscopy is an efficient approach for predicting soil properties because it reduces the time and cost of analyses. However, its advantages are hampered by the presence of soil moisture, which masks the major spectral absorptions of the soil and distorts the overall spectral shape. Hence, developing a procedure that skips the drying process for soil properties assessment directly from wet soil samples could save invaluable time. The goal of this study was twofold:proposing two approaches, partial least squares(PLS) and nearest neighbor spectral correction(NNSC), for dry spectral prediction and utilizing those spectra to demonstrate the ability to predict soil clay content. For these purposes, we measured 830 samples taken from eight common soil types in Israel that were sampled at 66 different locations. The dry spectrum accuracy was measured using the spectral angle mapper(SAM) and the average sum of deviations squared(ASDS), which resulted in low prediction errors of less than 8% and 14%, respectively. Later, our hypothesis was tested using the predicted dry soil spectra to predict the clay content, which resulted in R^2 of 0.69 and 0.58 in the PLS and NNSC methods, respectively. Finally, our results were compared to those obtained by external parameter orthogonalization(EPO) and direct standardization(DS). This study demonstrates the ability to evaluate the dry spectral fingerprint of a wet soil sample, which can be utilized in various pedological aspects such as soil monitoring, soil classification,and soil properties assessment.
基金the National Natural Science Foundation of China(Nos.11221062,11521091,and 91752203).
文摘A trigonometric series expansion method and two similar modified methods for the Orr-Sommerfeld equation are presented. These methods use the trigonometric series expansion with an auxiliary function added to the highest order derivative of the unknown function and generate the lower order derivatives through successive integra- tions. The proposed methods are easy to implement because of the simplicity of the chosen basis functions. By solving the plane Poiseuille flow (PPF), plane Couette flow (PCF), and Blasius boundary layer flow with several homogeneous boundary conditions, it is shown that these methods yield results with the same accuracy as that given by the conventional Chebyshev collocation method but with better robustness, and that ob- tained by the finite difference method but with fewer modal number.
文摘Constant envelope with a fractional Fourier transformorthogonal frequency division multiplexing(CE-FrFT-OFDM)is a special case of a constant envelope OFDM(CE-OFDM),both being energy efficient wireless communication techniques with a 0 dB peak to average power ratio(PAPR).However,with the proper selection of fractional order,the first technique has a high bit error rate(BER)performance in the frequency-time selective channels.This paper performs further analysis of CE-FrFT-OFDM by examining its spectral efficiency(SE)and energy efficiency(EE)and compare to the famous OFDM and FrFT-OFDM techniques.Analytical and comprehensive simulations conducted show that,the CE-FrFT-OFDM has five times the EE of OFDM and FrFT-OFDM systems with a slightly less SE.Increasing CE-FrFT-OFDM’s transmission power by increasing its amplitude to 1.7 increases its SE to match that of the OFDM and FrFT-OFDM systems while slightly reducing its EE by 20%to be four times that of OFDM and FrFTOFDM systems.OFDM and FrFT-OFDM’s amplitude fluctuations cause rapid changing output back-off(OBO)power requirements and further reduce power amplifier(PA)efficiency while CE-FrFTOFDM stable operational linear range makes it a better candidate and outperforms the other techniques when their OBO exceeds 1.7.Higher EE and low BER in time-frequency selective channel are attracting features for CE-FrFT-OFDM deployment in mobile devices.
基金Key Program of the National Natural Science Foundation of China (Grant No. U1301253)Guangdong Provincial Science and Technology Project (Nos. 2017A050501031 and2017A040406022)+1 种基金Guangzhou Science and Technology Projects (Nos. 201807010048 and 201804020034)the International Postdoctoral Exchange Fellowship Program 2017 (No. 20170029). The authors would like to express their thanks to European Space Agency for providing Sentinel-1 SAR data as well as ESA-SNAP software in conducting research, our colleagues Haiyan Deng and Li Zhao for their assistance in collecting field validation, and processing images, and the colleagues from the Guangzhou Urban Renewal Bureau for their good suggestions. We also would like to thank the editors and anonymous reviewers for their instructive comments.
文摘Rapid urban sprawl and re-construction of old towns have been leading to great changes of land use in cities of China. To witness short-term urban land use changes, rapid or real time remote sensing images and effective detection methods are required. With the availability of short repeat cycle, relatively high spatial resolution, and weather-independent Synthetic Aperture Radar (SAR) remotely sensed data, detection of short-term urban land use changes becomes possible. This paper adopts newly released Sentinel-1 SAR data for urban change detection in Tianhe District of Guangzhou City in Southern China, where dramatic urban redevelopment practices have been taking place in past years. An integrative method that combines the SAR time series data and a spectral angle mapping (SAM) was developed and applied to detect the short-term land use changes. Linear trend transformations of the SAR time series data were first conducted to reveal patterns of substantial changes. Spectral mixture analysis was then conducted to extract temporal endmembers to reflect the land development patterns based on the SAR backscattering intensities over time. Moreover, SAM was applied to extract the information of significant increase and decrease patterns. The results of validation and method comparison showed a significant capability of both the proposed method and the SAR time series images for detecting the short-term urban land use changes. The method received an overall accuracy of 78%, being more accurate than that using a bi-temporal image change detection method. The results revealed land use conversions due to the removal of old buildings and their replacement by new construction. This implies that SAR time series data reflects the spatiotemporal evolution of urban constructed areas within a short time period and this study provided the potential for detecting changes that requires continuously short-term capability, and could be potential in other landscapes.
基金Supported by the National Key Research and Development Program of China(Nos.2016YFC1402004,2016YFC1401805).
文摘As concluded from physical theory and laboratory experiment,it is widely accepted that nonlinearities of sea state play an important role in the formation of rogue waves;however,the sea states and corresponding nonlinearities of real-world rogue wave events remain poorly understood.Three rogue waves were recorded by a directional buoy located in the East China Sea during Typhoon Trami in August 2013.This study used the WAVEWATCHⅢmodel to simulate the sea state conditions pertaining to when and where those rogue waves were observed,based on which a comprehensive and full-scale analysis was performed.From the perspectives of wind and wave fields,wave system tracking,High-Order Spectral method simulation,and some characteristic sea state parameters,we concluded that the rogue waves occurred in sea states dominated by second-order nonlinearities.Moreover,third-order modulational instabilities were suppressed in these events because of the developed or fully developed sea state determined by the typhoon wave system.The method adopted in this study can provide comprehensive and full-scale analysis of rogue waves in the real world.The case studied in this paper is not considered unique,and rules could be found and confirmed in relation to other typhoon sea states through the application of our proposed method.
基金the National Natural Science Foundation of China (Grant No. 61762031)Guangxi Key Research and Development Plan (Gui Science AB17195029, Gui Science AB18126006)+3 种基金Guangxi key Laboratory Fund of Embedded Technology and Intelligent System, 2017 Innovation Project of Guangxi Graduate Education (No. YCSW2017156)2018 Innovation Project of Guangxi Graduate Education (No. YCSW2018157)Subsidies for the Project of Promoting the Ability of Young and Middleaged Scientific Research in Universities and Colleges of Guangxi (KY2016YB184)2016 Guilin Science and Technology Project (Gui Science 2016010202).
文摘Due to the development of E-Commerce, collaboration filtering (CF) recommendation algorithm becomes popular in recent years. It has some limitations such as cold start, data sparseness and low operation efficiency. In this paper, a CF recommendation algorithm is propose based on the latent factor model and improved spectral clustering (CFRALFMISC) to improve the forecasting precision. The latent factor model was firstly adopted to predict the missing score. Then, the cluster validity index was used to determine the number of clusters. Finally, the spectral clustering was improved by using the FCM algorithm to replace the K-means in the spectral clustering. The simulation results show that CFRALFMISC can effectively improve the recommendation precision compared with other algorithms.
文摘The goal of this study is to provide a stochastic method to investigate the eff ects of the randomness of soil properties due to their natural spatial variability on the response spectra spatial variation at sites with varying conditions. For this purpose, Monte Carlo Simulations are used to include the variability of both incident ground motion and soil parameters in the response spectra by mean of an appropriate coherency loss function and a site-dependent transfer function, respectively. The approach is built on the assumption of vertical propagation of SH type waves in soil strata with uncertain parameters. The response spectra are obtained by numerical integration of the governing equation of a single-degree-of-freedom (SDOF) system under non-stationary site-dependent and spatially varying ground motion accelerations simulated with non-uniform spectral densities and coherency loss functions. Numerical examples showed that randomness of soil properties signifi cantly aff ects the amplitudes of the response spectra, indicating that as the heterogeneity induced by the randomness of the parameters of the medium increases, the spectral ordinates attenuate.
基金the National Key Research and Development Program of China(No.2016YFA0601304)the National Natural Science Foundation for Creative Research Groups(No.41521064)+2 种基金the National Natural Science Foundation of China(No.41320104008)the AoShan Talents Program of Qingdao National Laboratory for Marine Science and Technology(No.2015ASTP)the Fundamental Research Funds for the Central Universities.
文摘The distribution and chemical properties of colored dissolved organic matter(CDOM)in the Yellow Sea and the East China Sea during December 2011-January 2012 were investigated.The input of freshwater and biological activities had an evident influence on the CDOM levels(characterized by the light absorption coefficient at the wavelength of 355 nm a355)in the study area.The spatial distribution of CDOM levels displayed a gradually decreasing trend from the coastal waters(0.37m^-1)to the open sea(0.18m^-1).The spectral slope ratio(the slope ratio SR defined as S275-295:S350-400)during the cruise was correlated with salinity,and exhibited a large variation from inshore(average of 2.515)to offshore sites(average of 5.327)compared with the distribution of a355.The values of SR were related to CDOM molecular weight(MW).The a355,SR,and chlorophyll a in 37 samples collected from the surface microlayer were significantly correlated with those in the corresponding subsurface water samples,implying a strong exchange action between the microlayer and bulk water.The a355 and SR of CDOM exhibited significant microlayer enrichment,with mean enrichment factors(EFs)of 1.72 and 1.62,respectively.
文摘INTERNODES is a general purpose method to deal with non-conforming discretizations of partial differential equations on 2D and 3D regions partitioned into two or several disjoint subdomains. It exploits two intergrid interpolation operators, one for transfering the Dirichlet trace across the interfaces, and the other for the Neumann trace. In this paper, in every subdomain the original problem is discretized by either the finite element method (FEM) or the spectral element method (SEM or hp-FEM), using a priori non-matching grids and piecewise polynomials of different degrees. Other discretization methods, however, can be used. INTERNODES can also be applied to heterogeneous or multiphysics problems, that is, problems that feature different differential operators inside adjacent subdomains. For instance, in this paper we apply the INTERNODES method to a Stokes- Darcy coupled problem that models the filtration of fluids in porous media. Our results highlight the flexibility of the method as well as its optimal rate of convergence with respect to the grid size and the polynomial degree.
文摘This paper is devoted to Professor Benyu Guo's open question on the C1-conforming quadrilateral spectral element method for fourth-order equations which has been endeavored for years. Starting with generalized Jacobi polynomials on the reference square, we construct the C1-conforming basis functions using the bilinear mapping from the reference square onto each quadrilateral element which fall into three categories-interior modes, edge modes, and vertex modes. In contrast to the triangular element, compulsively compensatory requirements on the global C1-continuity should be imposed for edge and vertex mode basis functions such that their normal derivatives on each common edge are reduced from rational functions to polynomials, which depend on only parameters of the common edge. It is amazing that the C1-conforming basis functions on each quadrilateral element contain polynomials in primitive variables, the completeness is then guaranteed and further confirmed by the numerical results on the Petrov-Galerkin spectral method for the non-homogeneous boundary value problem of fourth-order equations on an arbitrary quadrilateral. Finally, a C1-conforming quadrilateral spectral element method is proposed for the biharmonic eigenvalue problem, and numerical experiments demonstrate the effectiveness and efficiency of our spectral element method.
基金the National Natural Science Foundation of China (Grant No.61174080).
文摘The boundary control problem of a cantilever Euler-Bernoulli beam with input time delay is considered.In order to exponentially stabilize the system, a feedback controller is adopted.And we study the well-posedness and exponential stability of the closed-loop system.The approach used in this paper is done by several steps.Firstly, the well-posedness of this system is proved by semi-group theory.Secondly, the asymptotical expression of eigenvalue is investigated by spectral analysis.Thirdly, the exponential stability of the system is studied by multiplier technology.Finally, numerical simulations on the dynamical behavior of the system are given to support the results obtained.
基金Under the auspices of the Special Project of Science and Technology Development (No. 2017GDASCX-0101)the Science and Technology Planning Project of Guangdong Province (No. 2017A020217005, 2018B020207002)Guangdong Innovative and Entrepreneurial Research Team Program (No. 2016ZT06D336).
文摘Multi-scale data have had a wide-ranging level of performance in the area of urban change monitoring. Herein we investigate the correlation between the impervious surface fraction(ISF) and the Defense Meteorological Satellite Program/Operational Linescan System(DMSP/OLS) nighttime stable light(NTL) data with respect to the urban expansion in the main districts of Guangzhou. Landsat 5 Thematic Mapper and Landsat 8 Operational Land Image(OLI) data from 1988 to 2015 were used to extract the ISF using the linear spectral mixture analysis model and normal difference build-up index at the sub-pixel scale. DMSP/OLS NTL data from 1992 to 2013 were calibrated to illustrate the urban nighttime light conditions at the regional scale. Urban expansion directions were identified by statistics and kernel density analysis for the ISF study area at the sub-pixel scale. In addition, the correlation between the ISF and DMSP/OLS NTL data were illustrated by linear regression analysis. Furthermore, Profile Graph in ArcGIS was employed to illustrate the urban expansion from the differences in correlation in different directions. The conclusions are as follows: 1) The impervious surface(IS)in the study area has expanded to the northeast and the east, starting with the old urban zones, and the high-density IS area has increased by321.14 km~2. 2) The linear regression analysis reveals a positive correlation between the ISF and the DMSP/OLS NTL data. The multi-scale data changes are consistent with the actual urban planning of Guangzhou. 3) The DMSP/OLS NTL data overestimate the urban extent because of its saturation and blooming effects, causing its correlation with ISF to decrease. The pattern of urban expansion influences the saturation and blooming effects of the DMSP/OLS NTL data.
基金supported by the National Key R&D Program of China(No.2016YFF0100903)National Natural Science Foundation of China(NSFC)(Nos.61775153,61705153,and 11504255)Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).
文摘FM-to-AM conversion for angular filtering based on transmitted volume Bragg gratings(TBGs)is discussed.Simulation results show that a narrower spectral selectivity of TBGs led to stronger FM-to-AM conversion.Good angular selectivity and a wide bandwidth for the TBGs can be obtained by controlling the grating period and thickness.FM-to-AM conversion can be effectively suppressed and the distortion criterion for the filtered beam reduces to less than 5%.FMto-AM conversion of TBGs is demonstrated in the’Shenguang’ facility,and the results are in good agreement with the simulation.
基金the National Natural Science Foundation of China(31760241,41671528)the Gansu Provincial Natural Science Foundation(17JR5RA061)+1 种基金the Gansu Province Basic Research Innovation Group Project(1506RJIA155)the Opening Foundation of the State Key Laboratory Breeding Base of Desertification and Aeolian Sand Disaster Combating,Gansu Desert Control Research Institute(GSDC201503).
文摘Desert plants survive harsh environment using a variety of drought-resistant structural modifications and physio-ecological systems.Rolled-leaf plants roll up their leaves during periods of drought,making it difficult to distinguish between the external structures of various types of plants,it is therefore necessary to carry out spectral characteristics analysis for species identification of these rolled-leaf plants.Based on hyper-spectral data measured in the field,we analyzed the spectral characteristics of seven types of typical temperate zone rolled-leaf desert plants in the Hexi Corridor,China using a variety of mathematical transformation methods.The results show that:(1)during the vigorous growth period in July and August,the locations of the red valleys,green peaks,and three-edge parameters,namely,the red edge,the blue edge,and the yellow edge of well-developed rolled-leaf desert plants are essentially consistent with those of the majority of terrestrial vegetation types;(2)the absorption regions of liquid water,i.e.,1400-1500 and 1600-1700 nm,are the optimal bands for distinguishing various types of rolled-leaf desert plants;(3)in the leaf reflectance regions of 700-1250 nm,which is controlled by cellular structure,it is difficult to select the characteristic bands for differentiation rolled-leaf desert vegetation;and(4)after processing the spectral reflectance curves using a first-order differential,the envelope removal method,and the normalized differential ratio,we identify the other characteristic bands and parameters that can be used for identifying various types of temperate zone rolled-leaf desert plants,i.e.,the 510-560,650-700 and 1330-1380 nm regions,and the red edge amplitude.In general,the mathematical transformation methods in the study are effective tools to capture useful spectral information for species identification of rolled-leaf plants in the Hexi Corridor.
基金the the National Natural Science Foundation (Grant No. 11571181)the Natural Science Foundation of Jiangsu Province (Grant No. BK20171454)Qing Lan project, thank the reviewers for their many valuable suggestions. This work was partially done while the first author was visiting Beijing Computational Science Research Center from October 3, 2013 to March 3, 2014.
文摘This paper focuses on performance of several efficient and accurate numerical methods for the long-wave short-wave interaction equations in the semiclassical limit regime. The key features of the proposed methods are based on:(i) the utilization of the first-order or second-order time-splitting method to the nonlinear wave interaction equations;(ii) the ap-plication of Fourier pseudo-spectral method or compact finite difference approximation to the linear subproblem and the spatial derivatives;(iii) the adoption of the exact integration of the nonlinear subproblems and the ordinary differential equations in the phase space. The numerical methods under study are efficient, unconditionally stable and higher-order accurate, they are proved to preserve two invariants including the position density in L^1. Numerical results are reported for case studies with different types of initial data, these results verify the conservation laws in the discrete sense, show the dependence of the numerical solution on the time-step, mesh-size and dispersion parameter ε, and demonstrate the behavior of nonlinear dispersive waves in the semi-classical limit regime.
基金the National Natural Science Foundation of China(Grant No.11601368).
文摘In this paper,we consider the r-uniform hypergraphs H with spectral radius at most r√(2+√5).We show that H must have a quipus-structure,which is similar to the graphs with spectral radius at most 2/3√2[Woo-Neumaier,Graphs Combin.2007].