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
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
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
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
This study quantifies biomass,aboveground and belowground net productivity,along with additional environmental factors over a 2–3 year period in Barnawapara Sanctuary of Chhattisgarh,India through satellite remotesen...This study quantifies biomass,aboveground and belowground net productivity,along with additional environmental factors over a 2–3 year period in Barnawapara Sanctuary of Chhattisgarh,India through satellite remotesensing and GIS techniques.Ten sampling quadrates 20×20,5×5 and 1×1 m were randomly laid for overstorey(OS),understorey(US)and ground vegetation(GS),respectively.Girth of trees was measured at breast height and collar diameters of shrubs and herbs at 0.1 m height.Biomass was estimated using allometric regression equations and herb biomass by harvesting.Net primary productivity(NPP)was determined by summing biomass increment and litter crop values.Aspect and slope influenced the vegetation types,biomass and NPP in different forests.Standing biomass and NPP varied from 18.6 to 101.5 Mg ha^-1 and 5.3 to 12.7 Mg ha^-1 a^-1,respectively,in different forest types.The highest biomass was found in dense mixed forest,while net production recoded in Teak forests.Both were lowest in degraded mixed forests of different forest types.OS,US and GS contributed 90.4,8.7 and 0.7%,respectively,for the total mean standing biomass in different forests.This study developed spectral models for the estimation of biomass and NPP using Normalized Difference Vegetation Index and other vegetation indices.The study demonstrated the potential of geospatial tools for estimation of biomass and net productivity of dry tropical forest ecosystem.展开更多
In this work,we study boundary value problems for second-order differential equations with singularities of second kind inside an interval.First,we investigate properties of the spectrum,then prove a theorem on comple...In this work,we study boundary value problems for second-order differential equations with singularities of second kind inside an interval.First,we investigate properties of the spectrum,then prove a theorem on completeness of eigenfunctions,and study the inverse problem of reconstructing the differential equation from spectral characteristics.展开更多
This paper presents a complete two-step phase-shifting(TSPS) spectral phase interferometry for direct electric-field reconstruction(SPIDER) to improve the reconstruction of ultrafast optical fields. Here, complete TSP...This paper presents a complete two-step phase-shifting(TSPS) spectral phase interferometry for direct electric-field reconstruction(SPIDER) to improve the reconstruction of ultrafast optical fields. Here, complete TSPS acts as a balanced detection that can not only remove the effect of the dc term of the interferogram, but also reduce measurement noises,and thereby improve the capability of SPIDER to measure the pulses with narrow spectra or complex spectral structures.Some prisms are chosen to replace some environment-sensitive optical components, especially reflective optics to improve operating stability and improve signal-to-noise ratio further. Our experiments show that the available shear can be decreased to 1.5% of the spectral width, which is only about 1/3 compared with traditional SPIDER.展开更多
In this study,seven isotopic databases are presented and analyzed to identify mantle and crustal episodes on a global scale by focusing on periodicity ranging from 70 to 200 million years(Myr).The databases are the la...In this study,seven isotopic databases are presented and analyzed to identify mantle and crustal episodes on a global scale by focusing on periodicity ranging from 70 to 200 million years(Myr).The databases are the largest,or among the largest,compiled for each type of data-with an objective of finding some samples from every region of every continent,to make each database as global as conceivably possible.The databases contain zircon Lu/Hf isotopic data,whole-rock Sm/Nd isotopic data,U/Pb detrital zircon ages,U/Pb igneous zircon ages,U/Pb non-zircon ages,whole-rock Re/Os isotopic data,and large igneous province ages.Part I of this study focuses on the periodicities of age histograms and geochemical averages developed from the seven databases,via spectral and cross-correlation analyses.Natural physical cycles often propagate in exact integer multiples of a fundamental cycle,referred to as harmonics.The tests show that harmonic geological cycles of~93.5 and~187 Myr have persisted throughout terrestrial history,and the cyclicities are statistically significant for U/Pb igneous zircon ages,U/Pb detrital zircon ages,U/Pb zircon-rim ages,large igneous province ages,meanεHf(t)for all samples,meanεHf(t)values for igneous-only samples,and relative abundance of mafic rocks.Equally important,cross-correlation analyses show these seven time-series are nearly synchronous(±7 Myr)with a model consisting of periodicities of 93.5 and 187 Myr.Additionally,the similarities between peaks in the 93.5 and 187 Myr mantle cycles and terminal ages of established and suspected superchrons provide a framework for predicting and testing superchron periodicity.展开更多
Channel impairments are major limiting factors in the performance of large-scale antenna systems.In this paper,we analyze the impacts of practical channel impairments caused by pilot contamination,Doppler shift,and ph...Channel impairments are major limiting factors in the performance of large-scale antenna systems.In this paper,we analyze the impacts of practical channel impairments caused by pilot contamination,Doppler shift,and phase noise on the downlink spectral efficiency of large-scale distributed antenna systems(L-DASs)with maximum ratio transmission(MRT)and zero-forcing(ZF)beamforming,in which per user power normalization is considered.Using a joint channel model that allows study of the simultaneous impacts of these channel impairments,we derive accurate and tractable closed-form approximations for the ergodic achievable downlink rate,thereby enabling spectral efficiency analysis of L-DASs and an efficient evaluation of the impacts of the channel impairments.It is shown that channel impairments reduce the downlink spectral efficiency and have a significant impact on ZF beamforming.The asymptotic user rate limit is also determined,from which we analyze the asymptotic performance of L-DASs with channel impairments.The analytical results show that MRT and ZF beamforming achieve the same asymptotic performance limit even with channel impairments.It is also found that the use of a large-scale antenna array at the base station sides can weaken the impacts of channel impairments.展开更多
Laser-induced breakdown spectroscopy(LIBS)is regarded as a promising technique for real-time sorting of scrap metals due to its capability of fast multi-elemental and in-air analysis.This work reports a method for sig...Laser-induced breakdown spectroscopy(LIBS)is regarded as a promising technique for real-time sorting of scrap metals due to its capability of fast multi-elemental and in-air analysis.This work reports a method for signal processing which ensures high accuracy and high speed during similar metal sorting by LIBS.Similar metals such as aluminum alloys or stainless steel are characterized by nearly the same constituent elements with slight variations in elemental concentration depending on metal type.In the proposed method,the original data matrix is substantially reduced for fast processing by selecting new input variables(spectral lines)using the information for the constituent elements of similar metals.Specifically,principal component analysis(PCA)of full-spectra LIBS data was performed and then,based on the loading plots,the input variables of greater significance were selected in the order of higher weights for each constituent element.The results for the classification test with aluminum alloy,copper alloy,stainless steel and cast steel showed that the classification accuracy of the proposed method was nearly the same as that of full-spectra PCA,but the computation time was reduced by a factor of 20 or more.The results demonstrated that incorporating the information for constituent elements can significantly accelerate classification speed without loss of accuracy.展开更多
Angular momentum,a fundamental physical quantity,can be divided into spin angular momentum(SAM)and orbital angular momentum(OAM)in electromagnetic waves.Helically-phased or twisted light beams carrying OAM that exploi...Angular momentum,a fundamental physical quantity,can be divided into spin angular momentum(SAM)and orbital angular momentum(OAM)in electromagnetic waves.Helically-phased or twisted light beams carrying OAM that exploit the spatial structure physical dimension of electromagnetic waves have benefited wide applications ranging from optical manipulation to quantum information processing.Using the two distinct properties of OAM,i.e.,inherent orthogonality and unbounded states in principle,one can develop OAM modulation and OAM multiplexing techniques for twisted optical communications.OAM multiplexing is an alternative space-division multiplexing approach employing an orthogonal mode basis related to the spatial phase structure.In this paper,we review the recent progress in twisted optical communications using OAM in free space and fiber.The basic concept of momentum,angular momentum,SAM,OAM and OAM-carrying twisted optical communications,key techniques and devices of OAM generation/(de)multiplexing/detection,high-capacity spectrally-efficient free-space OAM links,fiber-based OAM links,and OAM processing functions are presented.Ultra-high spectral efficiency and petabit-scale freespace data links are achieved benefiting from OAM multiplexing.The key techniques and challenges of twisted optical communications are also discussed.Twisted optical communications using OAM are compatible with other existing physical dimensions such as frequency/wavelength,amplitude,phase,polarization and time,opening a possible way to facilitate continuous increase of the aggregate transmission capacity and spectral efficiency through N-dimensional multiplexing.展开更多
Atmospheric reentry vehicles and planetary probes fly through the atmosphere at hypervelocity speed. At such speed, there is a significant proportion of heat load to the vehicle surface due to radiative heating. Accur...Atmospheric reentry vehicles and planetary probes fly through the atmosphere at hypervelocity speed. At such speed, there is a significant proportion of heat load to the vehicle surface due to radiative heating. Accurate prediction needs a good knowledge of the radiation spectrum properties. In this paper, a high-speed camera and spectrograph coupled to an intensified charge-coupled device have bee n impleme nted to inv estigate the rad i at io n flow over a semi-cylinder model. The experiments were carried out in the JF16 expansi on timnel with secondary shock velocity of 7.9 km·s^-1. Results show that the emissio n spectrum comprises several atomic lines and molecular band systems. We give detailed data of the radiation spectrum, shock shape, shock detached distance and radiation intensity varying with space and wavelength. This valuable experimental dataset will be helpful to validate computational fluid dynamics codes and radiation models, which equates to increased prediction accuracy of radiation heating. Also, some suggestions for spectral measurement in hypervelocity flow field were list in the end.展开更多
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.
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.
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].
文摘This study quantifies biomass,aboveground and belowground net productivity,along with additional environmental factors over a 2–3 year period in Barnawapara Sanctuary of Chhattisgarh,India through satellite remotesensing and GIS techniques.Ten sampling quadrates 20×20,5×5 and 1×1 m were randomly laid for overstorey(OS),understorey(US)and ground vegetation(GS),respectively.Girth of trees was measured at breast height and collar diameters of shrubs and herbs at 0.1 m height.Biomass was estimated using allometric regression equations and herb biomass by harvesting.Net primary productivity(NPP)was determined by summing biomass increment and litter crop values.Aspect and slope influenced the vegetation types,biomass and NPP in different forests.Standing biomass and NPP varied from 18.6 to 101.5 Mg ha^-1 and 5.3 to 12.7 Mg ha^-1 a^-1,respectively,in different forest types.The highest biomass was found in dense mixed forest,while net production recoded in Teak forests.Both were lowest in degraded mixed forests of different forest types.OS,US and GS contributed 90.4,8.7 and 0.7%,respectively,for the total mean standing biomass in different forests.This study developed spectral models for the estimation of biomass and NPP using Normalized Difference Vegetation Index and other vegetation indices.The study demonstrated the potential of geospatial tools for estimation of biomass and net productivity of dry tropical forest ecosystem.
基金the University of Kashan under grant number 464151/7.
文摘In this work,we study boundary value problems for second-order differential equations with singularities of second kind inside an interval.First,we investigate properties of the spectrum,then prove a theorem on completeness of eigenfunctions,and study the inverse problem of reconstructing the differential equation from spectral characteristics.
基金the National Natural Science Foundation of China(Nos.61775142,61490710 and 61705132)China Postdoctoral Science Foundation(No.2017M612726)Shenzhen Basic Research Project on Subject Layout(No.JCYJ20170412105812811).
文摘This paper presents a complete two-step phase-shifting(TSPS) spectral phase interferometry for direct electric-field reconstruction(SPIDER) to improve the reconstruction of ultrafast optical fields. Here, complete TSPS acts as a balanced detection that can not only remove the effect of the dc term of the interferogram, but also reduce measurement noises,and thereby improve the capability of SPIDER to measure the pulses with narrow spectra or complex spectral structures.Some prisms are chosen to replace some environment-sensitive optical components, especially reflective optics to improve operating stability and improve signal-to-noise ratio further. Our experiments show that the available shear can be decreased to 1.5% of the spectral width, which is only about 1/3 compared with traditional SPIDER.
文摘In this study,seven isotopic databases are presented and analyzed to identify mantle and crustal episodes on a global scale by focusing on periodicity ranging from 70 to 200 million years(Myr).The databases are the largest,or among the largest,compiled for each type of data-with an objective of finding some samples from every region of every continent,to make each database as global as conceivably possible.The databases contain zircon Lu/Hf isotopic data,whole-rock Sm/Nd isotopic data,U/Pb detrital zircon ages,U/Pb igneous zircon ages,U/Pb non-zircon ages,whole-rock Re/Os isotopic data,and large igneous province ages.Part I of this study focuses on the periodicities of age histograms and geochemical averages developed from the seven databases,via spectral and cross-correlation analyses.Natural physical cycles often propagate in exact integer multiples of a fundamental cycle,referred to as harmonics.The tests show that harmonic geological cycles of~93.5 and~187 Myr have persisted throughout terrestrial history,and the cyclicities are statistically significant for U/Pb igneous zircon ages,U/Pb detrital zircon ages,U/Pb zircon-rim ages,large igneous province ages,meanεHf(t)for all samples,meanεHf(t)values for igneous-only samples,and relative abundance of mafic rocks.Equally important,cross-correlation analyses show these seven time-series are nearly synchronous(±7 Myr)with a model consisting of periodicities of 93.5 and 187 Myr.Additionally,the similarities between peaks in the 93.5 and 187 Myr mantle cycles and terminal ages of established and suspected superchrons provide a framework for predicting and testing superchron periodicity.
基金National Natural Science Foundation of China(NSFC)(Grant Nos.61501113,61571120,61271205,61521061,61372100,)Jiangsu Provincial Natural Science Foundation(Grant Nos.BK20150630,BK20151415).
文摘Channel impairments are major limiting factors in the performance of large-scale antenna systems.In this paper,we analyze the impacts of practical channel impairments caused by pilot contamination,Doppler shift,and phase noise on the downlink spectral efficiency of large-scale distributed antenna systems(L-DASs)with maximum ratio transmission(MRT)and zero-forcing(ZF)beamforming,in which per user power normalization is considered.Using a joint channel model that allows study of the simultaneous impacts of these channel impairments,we derive accurate and tractable closed-form approximations for the ergodic achievable downlink rate,thereby enabling spectral efficiency analysis of L-DASs and an efficient evaluation of the impacts of the channel impairments.It is shown that channel impairments reduce the downlink spectral efficiency and have a significant impact on ZF beamforming.The asymptotic user rate limit is also determined,from which we analyze the asymptotic performance of L-DASs with channel impairments.The analytical results show that MRT and ZF beamforming achieve the same asymptotic performance limit even with channel impairments.It is also found that the use of a large-scale antenna array at the base station sides can weaken the impacts of channel impairments.
基金the R&D Center for Valuable Recycling(Global-Top R&BD Program)of the Ministry of Environment.(Project No.2016002250003).
文摘Laser-induced breakdown spectroscopy(LIBS)is regarded as a promising technique for real-time sorting of scrap metals due to its capability of fast multi-elemental and in-air analysis.This work reports a method for signal processing which ensures high accuracy and high speed during similar metal sorting by LIBS.Similar metals such as aluminum alloys or stainless steel are characterized by nearly the same constituent elements with slight variations in elemental concentration depending on metal type.In the proposed method,the original data matrix is substantially reduced for fast processing by selecting new input variables(spectral lines)using the information for the constituent elements of similar metals.Specifically,principal component analysis(PCA)of full-spectra LIBS data was performed and then,based on the loading plots,the input variables of greater significance were selected in the order of higher weights for each constituent element.The results for the classification test with aluminum alloy,copper alloy,stainless steel and cast steel showed that the classification accuracy of the proposed method was nearly the same as that of full-spectra PCA,but the computation time was reduced by a factor of 20 or more.The results demonstrated that incorporating the information for constituent elements can significantly accelerate classification speed without loss of accuracy.
基金the National Basic Research Program of China(Grant No.2014CB340004)the National Natural Science Foundation of China(Grant Nos.11574001,61761130082,11774116,11274131,and 61222502)+1 种基金the Royal Society-Newton Advanced Fellowship,the National Program for Support of Top-notch Young Professionals,the Yangtze River Excellent Young Scholars Program,the Natural Science Foundation of Hubei Province of China(Grant No.2018CFA048)the Program fot.HU ST Academic Frontier Youth Team.
文摘Angular momentum,a fundamental physical quantity,can be divided into spin angular momentum(SAM)and orbital angular momentum(OAM)in electromagnetic waves.Helically-phased or twisted light beams carrying OAM that exploit the spatial structure physical dimension of electromagnetic waves have benefited wide applications ranging from optical manipulation to quantum information processing.Using the two distinct properties of OAM,i.e.,inherent orthogonality and unbounded states in principle,one can develop OAM modulation and OAM multiplexing techniques for twisted optical communications.OAM multiplexing is an alternative space-division multiplexing approach employing an orthogonal mode basis related to the spatial phase structure.In this paper,we review the recent progress in twisted optical communications using OAM in free space and fiber.The basic concept of momentum,angular momentum,SAM,OAM and OAM-carrying twisted optical communications,key techniques and devices of OAM generation/(de)multiplexing/detection,high-capacity spectrally-efficient free-space OAM links,fiber-based OAM links,and OAM processing functions are presented.Ultra-high spectral efficiency and petabit-scale freespace data links are achieved benefiting from OAM multiplexing.The key techniques and challenges of twisted optical communications are also discussed.Twisted optical communications using OAM are compatible with other existing physical dimensions such as frequency/wavelength,amplitude,phase,polarization and time,opening a possible way to facilitate continuous increase of the aggregate transmission capacity and spectral efficiency through N-dimensional multiplexing.
基金the National NaturalScience Foundation of China (Grants 11602275. 11672308, 11672312.and 11532014.).
文摘Atmospheric reentry vehicles and planetary probes fly through the atmosphere at hypervelocity speed. At such speed, there is a significant proportion of heat load to the vehicle surface due to radiative heating. Accurate prediction needs a good knowledge of the radiation spectrum properties. In this paper, a high-speed camera and spectrograph coupled to an intensified charge-coupled device have bee n impleme nted to inv estigate the rad i at io n flow over a semi-cylinder model. The experiments were carried out in the JF16 expansi on timnel with secondary shock velocity of 7.9 km·s^-1. Results show that the emissio n spectrum comprises several atomic lines and molecular band systems. We give detailed data of the radiation spectrum, shock shape, shock detached distance and radiation intensity varying with space and wavelength. This valuable experimental dataset will be helpful to validate computational fluid dynamics codes and radiation models, which equates to increased prediction accuracy of radiation heating. Also, some suggestions for spectral measurement in hypervelocity flow field were list in the end.