Background:To assess the influence of different spectral energy distribution on accommodation,vergence and reading performance.Methods:A Randomized experimental study was conducted after getting the approval of the Et...Background:To assess the influence of different spectral energy distribution on accommodation,vergence and reading performance.Methods:A Randomized experimental study was conducted after getting the approval of the Ethical Committee of University of Hyderabad.Forty participants with an age group of 18-21 years was integrated,out of which 50%was male and 50%was female.Subjects with emmetropia and no history of ocular pathology were included in the study.Near point of accommodation(NPA)&near point of convergence(NPC)was measured with the help of royal air force(RAF)ruler followed by near visual task of a readability passage.Results:A statistically significant result was obtained when reading rate,reading speed and NPC was compared among different spectral distribution of light(P<0.001)except NPA(P=0.43).Post hoc analysis showed a significant difference(P<0.001)when tungsten was compared with fluorescent light(FLOU),compact fluorescent light(CFL),and light emitting diode(LED)for reading rate,reading speed and NPC.But there is no noteworthy difference exist when fluorescent was compared with CFL for reading rate(P=0.530)&reading speed(P=0.595).Similarly,LED also showed no considerable difference when compared with CFL(P=0.682)and fluorescent(P=0.490)for NPC.When NPA was assessed within the group LED showed insignificant difference with CFL(P=0.205)and fluorescent(P=0.275)similar like fluorescent and tungsten(P=0.482).Conclusions:This study concluded that reading performance(reading rate and reading speed)and NPC has a significance change if we use inappropriate lighting during visual tasks.It will cause visual fatigue and strain after sustained near work.In addition,tungsten spectral energy influences the convergence which can also show an impact on reading and near visual tasks because of its brightness and miosis.Prolonged reading and working under this lighting can cause convergence disorders and visual fatigue.展开更多
The comparison of networks with different orders strongly depends on the stability analysis of graph features in evolving systems. In this paper, we rigorously investigate the stability of the weighted spectral distri...The comparison of networks with different orders strongly depends on the stability analysis of graph features in evolving systems. In this paper, we rigorously investigate the stability of the weighted spectral distribution（i.e., a spectral graph feature） as the network order increases. First, we use deterministic scale-free networks generated by a pseudo treelike model to derive the precise formula of the spectral feature, and then analyze the stability of the spectral feature based on the precise formula. Except for the scale-free feature, the pseudo tree-like model exhibits the hierarchical and small-world structures of complex networks. The stability analysis is useful for the classification of networks with different orders and the similarity analysis of networks that may belong to the same evolving system.展开更多
Many real-world systems can be modeled by weighted small-world networks with high clustering coefficients. Recent studies for rigorously analyzing the weighted spectral distribution（W SD） have focused on unweighted ...Many real-world systems can be modeled by weighted small-world networks with high clustering coefficients. Recent studies for rigorously analyzing the weighted spectral distribution（W SD） have focused on unweighted networks with low clustering coefficients. In this paper, we rigorously analyze the W SD in a deterministic weighted scale-free small-world network model and find that the W SD grows sublinearly with increasing network order（i.e., the number of nodes） and provides a sensitive discrimination for each input of this model. This study demonstrates that the scaling feature of the W SD exists in the weighted network model which has high and order-independent clustering coefficients and reasonable power-law exponents.展开更多
A heavy dust episode occurred from May 3 to 8,2017 in China,with an influenced area exceeding 1.63 million km2.In this work,the mixing state of aerosols and their spectral distributions were simultaneously observed in...A heavy dust episode occurred from May 3 to 8,2017 in China,with an influenced area exceeding 1.63 million km2.In this work,the mixing state of aerosols and their spectral distributions were simultaneously observed in the sand source region ofHohhot and the long-range dust transport regi on of Nanji ng by using a single-particle aerosol mass spectrometer(SPAMS).The duration time of this dust episode was 37-40 h in Hohhot and prolonged to 51-104 h in Nanjing.Totals of 336,135(Hohhot)and 235,840(Nanjing)particles in PM2.5 were successfully ionized to identify 10 main particle classes.During this episode,aerosol particles including OCEC(30.65%),K(22.42%),K-CN(17.03%),sodium(9.46%),heavy metal(8.96%),EC-sulfate(3.46%)and Al(3.22%)were prevailing in Hohhot and were dominated by EC-sulfate(22.26%),OCEC(15.21%),heavy metal(11.96%),K(13.68%),sodium(12.27%),Al(10.54%)and EC(9.02%)in Nanjing.The spectral distribution peaked at 0.66μm during the dust episode in Nanjing,0.12μm larger than the peak size in the non-dust episode.Strong signals at-62[NO3)and-61[HCO3]/-61[C5H]for aerosol particles were observed in Hohhot and Nanjing respectively.The proportions of K-CN,sodium,heavy mental,OCEC and EC-sulfate particles in the dust episode of Hohhot were 2.75,1.41,1.80,1.22 and 1.28 times as large as the values in the non-dust episode.For Nanjing,the fractions of EC-sulfate,EC,Al particles in the dust episode were 10.55,4.65 and 1.46 times higher than values in the non-dust episode.The proportions of EC-secondary and EC-nitate particles were found to decrease in the dust episode in the two regions.展开更多
In the factor analysis model with large cross-section and time-series dimensions,we pro- pose a new method to estimate the number of factors.Specially if the idiosyncratic terms satisfy a linear time series model,the ...In the factor analysis model with large cross-section and time-series dimensions,we pro- pose a new method to estimate the number of factors.Specially if the idiosyncratic terms satisfy a linear time series model,the estimators of the parameters can be obtained in the time series model. The theoretical properties of the estimators are also explored.A simulation study and an empirical analysis are conducted.展开更多
We consider the empirical spectral distribution （ESD） of a random matrix from the Gaussian Unitary Ensemble. Based on the Plancherel-Rotaeh approximation formula for Hermite polynomials, we prove that the expected e...We consider the empirical spectral distribution （ESD） of a random matrix from the Gaussian Unitary Ensemble. Based on the Plancherel-Rotaeh approximation formula for Hermite polynomials, we prove that the expected empirical spectral distribution converges at the rate of O（n^-1） to the Wigner distribution function uniformly on every compact intervals [u,v] within the limiting support （-1, 1）. Furthermore, the variance of the ESD for such an interval is proved to be （πn）^-2 logn asymptotically which surprisingly enough, does not depend on the details （e.g. length or location） of the interval, This property allows us to determine completely the covariance function between the values of the ESD on two intervals.展开更多
In this paper, we present the analysis of the spectral distributions of the scattered photons within a certain acceptance angle in Thomson scattering, in which the beam divergence, energy spread and spatial distributi...In this paper, we present the analysis of the spectral distributions of the scattered photons within a certain acceptance angle in Thomson scattering, in which the beam divergence, energy spread and spatial distribution are all considered. The analytical results are compared with the simulation results, and good agreement between the two approaches is obtained.展开更多
The radiation budget at the top of the atmosphere plays a critical role in climate research. Compared to the broadband flux, the spectrally resolved outgoing longwave radiation or flux （OLR）, with rich atmospheric i...The radiation budget at the top of the atmosphere plays a critical role in climate research. Compared to the broadband flux, the spectrally resolved outgoing longwave radiation or flux （OLR）, with rich atmospheric information in different bands, has obvious advantages in the evaluation of GCMs. Unlike methods that need auxiliary measurements and information, here we take atmospheric infrared sounder （AIRS） observations as an example to build a self-consistent algorithm by an angular distribution model （ADM）, based solely on radiance observations, to estimate clear-sky spectrally resolved fluxes over tropical oceans. As the key step for such an ADM, scene type estimations are obtained from radiance and brightness temperature in selected AIRS channels. Then, broadband OLR as well as synthetic spectral fluxes are derived by the spectral ADM and validated using both synthetic spectra and CERES （Clouds and the Earth＇s Radiant Energy System） observations. In most situations, the mean OLR differences between the spectral ADM products and the CERES observations are within -4-2 W m-2, which is less than 1% of the typical mean clear-sky OLR over tropical oceans. The whole algorithm described in this study can be easily extended to other similar hyperspectral radiance measurements.展开更多
Let {vij}, i, j = 1, 2, …, be i.i.d, random variables with Ev11 = 0, Ev11^2 = 1 and a1 = （ai1,…, aiM） be random vectors with {aij} being i.i.d, random variables. Define XN =（x1,…, xk） and SN =XNXN^T,where xi=ai...Let {vij}, i, j = 1, 2, …, be i.i.d, random variables with Ev11 = 0, Ev11^2 = 1 and a1 = （ai1,…, aiM） be random vectors with {aij} being i.i.d, random variables. Define XN =（x1,…, xk） and SN =XNXN^T,where xi=ai×si and si=1/√N（v1i,…, vN,i）^T. The spectral distribution of SN is proven to converge, with probability one, to a nonrandom distribution function under mild conditions.展开更多
The characteristics of nonlinear and supernonlinear Alfvén waves propagating in a multicomponent plasma composed of a double spectral electron distribution and positive and negative ions were investigated.The Sag...The characteristics of nonlinear and supernonlinear Alfvén waves propagating in a multicomponent plasma composed of a double spectral electron distribution and positive and negative ions were investigated.The Sagdeev technique was employed,and an energy equation was derived.Our findings show that the proposed system reveals the existence of a double-layer solution,periodic,supersoliton,and superperiodic waves.The phase portrait and potential analysis related to these waves were investigated to study the main features of existing waves.It was also found that decreasing the electron temperature helps the superperiodic structure to be excited in our plasma model.Our results help interpret the nonlinear and supernonlinear features of the recorded Alfvén waves propagating in the ionosphere D-region.展开更多
We investigate the spectral redshift of high-order harmonics of the H_2~＋（D_2~＋） molecule by numerically solving the non-Born–Oppenheimer time-dependent Schr ¨odinger equation（TDSE）. The results show that ...We investigate the spectral redshift of high-order harmonics of the H_2~＋（D_2~＋） molecule by numerically solving the non-Born–Oppenheimer time-dependent Schr ¨odinger equation（TDSE）. The results show that the spectral redshift of highorder harmonics can be observed by adding a weak pulse in the falling part of the trapezoidal laser pulses. Comparing with the H_2~＋ molecule, the shift of high-order harmonic generation（HHG） spectrum for the D_2~＋ molecule is more obvious.We employ the spatial distribution in HHG and time-frequency analysis to illustrate the physical mechanism of the spectral redshift of high-order harmonics.展开更多
The spectral distribution exp( ), where {} are the eigenvalues of the negative Laplacian -△=- in the (x^1,x^2)-plane, is studied for a variety of domains, where -∞< t <∞ and i=(1/2)(-1) . The dependence of (...The spectral distribution exp( ), where {} are the eigenvalues of the negative Laplacian -△=- in the (x^1,x^2)-plane, is studied for a variety of domains, where -∞< t <∞ and i=(1/2)(-1) . The dependence of (t)on the connectivity of a domain and the boundary conditions are analyzed. Particular attention is given to a general bounded domain Ω in R^2 with a smooth boundary Ω, where a finite number of piecewise smooth Dirichlet, Neumann and Robin boundary conditions on the piecewise smooth parts Γj(j = 1,……,n) of Ω are considered such that Some geometrical properties of Ω(e.g., the area of Ω, the total lengths of the boundary, the curvature of its boundary, etc.) are determined, from the asymptotic expansions of (t) for |t| → 0.展开更多
In this paper,we consider the limiting spectral distribution of the information-plus-noise type sample covariance matrices Cn=1/N（Rn＋σXn）（Rn＋σXn）,under the assumption that the entries of Xn are independent but...In this paper,we consider the limiting spectral distribution of the information-plus-noise type sample covariance matrices Cn=1/N（Rn＋σXn）（Rn＋σXn）,under the assumption that the entries of Xn are independent but non-identically distributed random variables.It is proved that,almost surely,the empirical spectral distribution of Cn converges weakly to a non-random distribution whose Stieltjes transform satisfies a certain equation.Our result extends the previous one with the entries of Xn are i.i.d.random varibles to a more general case.The proof of the result mainly employs the Stein equation and the cumulant expansion formula of independent random variables.展开更多
Context: Medical imaging has a wide range of applications in today’s society. Basic projectional radiography, CT scans, mammograms and a range of other advanced technologies all use x-rays to create a large number of...Context: Medical imaging has a wide range of applications in today’s society. Basic projectional radiography, CT scans, mammograms and a range of other advanced technologies all use x-rays to create a large number of examinations every day across the world. The most essential component of such medical equipment is the x-ray tube, which creates and produces x-rays. Objective: We describe and investigate an abstract model-geometry of a simple x-ray tube utilizing the open-source software package of BEAMnrc of the EGSnrcmp family, which is well validated by several studies over the years, for high and low energy photons generation. Methodology: Our research focuses on two different electron beam energies: 120 keV and 30 keV. The 120 keV is the typical energy for simple projectional radiographic exams and CT examinations, whereas the 30 keV is the typical energy of mammography. Results: Two different anode materials are used for each case, Gold (Au) and Tungsten (W) for 120 keV because these are the most common in projectional radiography and CT;Molybdenum (Mo) and Rhodium (Rh) for 30 keV because with these targets most mammography exams are carried out. The aim of this work is to show how the BEAMnrc software package can simulate effectively x-ray generation of low-energy photons which are utilized in modern medical imaging procedures. We describe useful information on anode-target characteristics, such as anode angle, anode material, and metal filter materials, based on previous quality studies even by using software other than BEAMnrc. Conclusion: We demonstrate that BEAMnrc can be efficiently used for Monte Carlo modeling of low-energy photons.展开更多
In order to accurately and automatically measure the light emitting diode(LED) colorimetric parameters,the design of a measurement system by adopting a high-performance spectrometer and looking-up table method was pre...In order to accurately and automatically measure the light emitting diode(LED) colorimetric parameters,the design of a measurement system by adopting a high-performance spectrometer and looking-up table method was presented based on the LabVIEW.First,the data of the LED relative spectral power distribution(SPD) were read by the spectrometer to measure LED chromaticity coordinate,and the slopes table were formed by the LED chromaticity coordinate and the equal stimulus point.Then,the CIE1931 chromaticity diagram was divided into 4 different regions to ensure the slopes table that had the character of monotonic decreasing.Finally,the LED dominant wavelength and purity were automatically calculated using the LabVIEW programs.The data of LEDs' colorimetric parameters have demonstrated that the measurement method in this paper can achieve higher precision result.展开更多
The transition radiation of a charged particle crossing the interface of two media having a monatomic impurity layer is investigated. It is shown that at sliding angles of incidence of a particle on the boundary of th...The transition radiation of a charged particle crossing the interface of two media having a monatomic impurity layer is investigated. It is shown that at sliding angles of incidence of a particle on the boundary of the media, the transition radiation is mainly determined by the properties of the surface layer. The possibility of using transition radiation to study the surface of substances is discussed. In addition, due to the hard radiation present in space, this research may be important for the use of light monoatomic layers as a material for satellite antennas, “solar sails” and cover layers in a future space (interstellar) mission.展开更多
In this paper,the backward Euler method and the shifted Grünwald-Letnikov formulas are utilized to discretize the space-fractional diffusion equations.The discretized result is a system of linear equations with a...In this paper,the backward Euler method and the shifted Grünwald-Letnikov formulas are utilized to discretize the space-fractional diffusion equations.The discretized result is a system of linear equations with a coefficient matrix being the sum of a diagonal matrix and a non-Hermitian Toeplitz matrix.By utilizing the Hermitian and skew-Hermitian splitting of the Toeplitz matrix,we develop a two-parameter DThsS iteration method to solve the linear systems.The convergence is also discussed.A DTHsS-t(α,γ)preconditioner is proposed and the preconditioned GMRES method combined with the proposed preconditioner is applied to solve the linear systems.The spectral analysis of the DThsS-τ(α,γ)preconditioned matrix is provided.Experimental results demonstrate the effectiveness of the proposed methods in solving the space-fractional diffusion equations.展开更多
Despite its utility in identifying patterns in celestial objects, the Hertzsprung-Russell diagram is not supported in dim or small stars;it struggles to provide insights into certain celestial objects such as brown dw...Despite its utility in identifying patterns in celestial objects, the Hertzsprung-Russell diagram is not supported in dim or small stars;it struggles to provide insights into certain celestial objects such as brown dwarfs [1]. The purpose of this experiment is to create an improved version of the diagram with a three-dimensional model that includes a third z-axis to accurately predict and chart the life cycles of all stars regardless of size. The values of the stars’ absolute magnitude and color indices were used to chart the surface gravity and metallicity, variables that were chosen due to their ease of collection and their likeliness to be within the range of values being assessed. To obtain the values for the model, data points from the database GAIA DR2 were utilized via the TAP protocol to query the SQL database. The data was transferred into a local CSV file to facilitate data manipulation. The data could be read and interpreted, as dim stars would likely have higher values of these variables, making it easier to include them in the diagram. The Pandas DataFrames tool on Python 3 was used to organize and manage the data efficiently. Matplotlib Graphs visualized the relationships between different stellar attributes by developing a linear regression line and an algorithm and creating scatter plots and sky maps to explore trends, hence designing three-dimensional diagrams. It was determined that the surface gravity diagram had a higher efficacy than metallicity due to their standard deviations of 0.4641441715272741 and 0.786577627976148, respectively.展开更多
Taking the advantage of Internet of Things(IoT)enabled measurements,this paper formulates the event detection problem as an information-plus-noise model,and detects events in power systems based on free probability th...Taking the advantage of Internet of Things(IoT)enabled measurements,this paper formulates the event detection problem as an information-plus-noise model,and detects events in power systems based on free probability theory(FPT).Using big data collected from phasor measurement units(PMUs),we construct the event detection matrix to reflect both spatial and temporal characteristics of power gird states.The event detection matrix is further described as an information matrix plus a noise matrix,and the essence of event detection is to extract event information from the event detection matrix.By associating the event detection problem with FPT,the empirical spectral distributions(ESDs)related moments of the sample covariance matrix of the information matrix are computed,to distinguish events from“noises”,including normal fluctuations,background noises,and measurement errors.Based on central limit theory(CLT),the alarm threshold is computed using measurements collected in normal states.Additionally,with the aid of sliding window,this paper builds an event detection architecture to reflect power grid state and detect events online.Case studies with simulated data from Anhui,China,and real PMU data from Guangdong,China,verify the effectiveness of the proposed method.Compared with other data-driven methods,the proposed method is more sensitive and has better adaptability to the normal fluctuations,background noises,and measurement errors in real PMU cases.In addition,it does not require large number of training samples as needed in the training-testing paradigm.展开更多
文摘Background:To assess the influence of different spectral energy distribution on accommodation,vergence and reading performance.Methods:A Randomized experimental study was conducted after getting the approval of the Ethical Committee of University of Hyderabad.Forty participants with an age group of 18-21 years was integrated,out of which 50%was male and 50%was female.Subjects with emmetropia and no history of ocular pathology were included in the study.Near point of accommodation(NPA)&near point of convergence(NPC)was measured with the help of royal air force(RAF)ruler followed by near visual task of a readability passage.Results:A statistically significant result was obtained when reading rate,reading speed and NPC was compared among different spectral distribution of light(P<0.001)except NPA(P=0.43).Post hoc analysis showed a significant difference(P<0.001)when tungsten was compared with fluorescent light(FLOU),compact fluorescent light(CFL),and light emitting diode(LED)for reading rate,reading speed and NPC.But there is no noteworthy difference exist when fluorescent was compared with CFL for reading rate(P=0.530)&reading speed(P=0.595).Similarly,LED also showed no considerable difference when compared with CFL(P=0.682)and fluorescent(P=0.490)for NPC.When NPA was assessed within the group LED showed insignificant difference with CFL(P=0.205)and fluorescent(P=0.275)similar like fluorescent and tungsten(P=0.482).Conclusions:This study concluded that reading performance(reading rate and reading speed)and NPC has a significance change if we use inappropriate lighting during visual tasks.It will cause visual fatigue and strain after sustained near work.In addition,tungsten spectral energy influences the convergence which can also show an impact on reading and near visual tasks because of its brightness and miosis.Prolonged reading and working under this lighting can cause convergence disorders and visual fatigue.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61402485,61303061,and 71201169)
文摘The comparison of networks with different orders strongly depends on the stability analysis of graph features in evolving systems. In this paper, we rigorously investigate the stability of the weighted spectral distribution（i.e., a spectral graph feature） as the network order increases. First, we use deterministic scale-free networks generated by a pseudo treelike model to derive the precise formula of the spectral feature, and then analyze the stability of the spectral feature based on the precise formula. Except for the scale-free feature, the pseudo tree-like model exhibits the hierarchical and small-world structures of complex networks. The stability analysis is useful for the classification of networks with different orders and the similarity analysis of networks that may belong to the same evolving system.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61402485,61573262,and 61303061)
文摘Many real-world systems can be modeled by weighted small-world networks with high clustering coefficients. Recent studies for rigorously analyzing the weighted spectral distribution（W SD） have focused on unweighted networks with low clustering coefficients. In this paper, we rigorously analyze the W SD in a deterministic weighted scale-free small-world network model and find that the W SD grows sublinearly with increasing network order（i.e., the number of nodes） and provides a sensitive discrimination for each input of this model. This study demonstrates that the scaling feature of the W SD exists in the weighted network model which has high and order-independent clustering coefficients and reasonable power-law exponents.
基金the National Key Research and Development Program of China(2016YFA0602003)the Ministry of Science and Technology of China(2017YFC0210000)+3 种基金the National Natural Science Foundation of China(41805096 and 41830965)the Natural Science Foundation of Jiangsu Province(BK20180801)the Natural Science Research Project for Universities of Jiangsu Province,China(18KJB170011)the China Postdoctoral Science Foundation(2018M640169).
文摘A heavy dust episode occurred from May 3 to 8,2017 in China,with an influenced area exceeding 1.63 million km2.In this work,the mixing state of aerosols and their spectral distributions were simultaneously observed in the sand source region ofHohhot and the long-range dust transport regi on of Nanji ng by using a single-particle aerosol mass spectrometer(SPAMS).The duration time of this dust episode was 37-40 h in Hohhot and prolonged to 51-104 h in Nanjing.Totals of 336,135(Hohhot)and 235,840(Nanjing)particles in PM2.5 were successfully ionized to identify 10 main particle classes.During this episode,aerosol particles including OCEC(30.65%),K(22.42%),K-CN(17.03%),sodium(9.46%),heavy metal(8.96%),EC-sulfate(3.46%)and Al(3.22%)were prevailing in Hohhot and were dominated by EC-sulfate(22.26%),OCEC(15.21%),heavy metal(11.96%),K(13.68%),sodium(12.27%),Al(10.54%)and EC(9.02%)in Nanjing.The spectral distribution peaked at 0.66μm during the dust episode in Nanjing,0.12μm larger than the peak size in the non-dust episode.Strong signals at-62[NO3)and-61[HCO3]/-61[C5H]for aerosol particles were observed in Hohhot and Nanjing respectively.The proportions of K-CN,sodium,heavy mental,OCEC and EC-sulfate particles in the dust episode of Hohhot were 2.75,1.41,1.80,1.22 and 1.28 times as large as the values in the non-dust episode.For Nanjing,the fractions of EC-sulfate,EC,Al particles in the dust episode were 10.55,4.65 and 1.46 times higher than values in the non-dust episode.The proportions of EC-secondary and EC-nitate particles were found to decrease in the dust episode in the two regions.
基金This work was partially supported by the National Natural Science Foundation of China (Grant No.10471135)
文摘In the factor analysis model with large cross-section and time-series dimensions,we pro- pose a new method to estimate the number of factors.Specially if the idiosyncratic terms satisfy a linear time series model,the estimators of the parameters can be obtained in the time series model. The theoretical properties of the estimators are also explored.A simulation study and an empirical analysis are conducted.
文摘We consider the empirical spectral distribution （ESD） of a random matrix from the Gaussian Unitary Ensemble. Based on the Plancherel-Rotaeh approximation formula for Hermite polynomials, we prove that the expected empirical spectral distribution converges at the rate of O（n^-1） to the Wigner distribution function uniformly on every compact intervals [u,v] within the limiting support （-1, 1）. Furthermore, the variance of the ESD for such an interval is proved to be （πn）^-2 logn asymptotically which surprisingly enough, does not depend on the details （e.g. length or location） of the interval, This property allows us to determine completely the covariance function between the values of the ESD on two intervals.
基金Supported by National Natural Science Foundation of China (10735050)National Basic Research Program of China (973Program) (2007CB815102)
文摘In this paper, we present the analysis of the spectral distributions of the scattered photons within a certain acceptance angle in Thomson scattering, in which the beam divergence, energy spread and spatial distribution are all considered. The analytical results are compared with the simulation results, and good agreement between the two approaches is obtained.
基金supported by the National Natural Science Foundation of China (Grant No. 41105015)
文摘The radiation budget at the top of the atmosphere plays a critical role in climate research. Compared to the broadband flux, the spectrally resolved outgoing longwave radiation or flux （OLR）, with rich atmospheric information in different bands, has obvious advantages in the evaluation of GCMs. Unlike methods that need auxiliary measurements and information, here we take atmospheric infrared sounder （AIRS） observations as an example to build a self-consistent algorithm by an angular distribution model （ADM）, based solely on radiance observations, to estimate clear-sky spectrally resolved fluxes over tropical oceans. As the key step for such an ADM, scene type estimations are obtained from radiance and brightness temperature in selected AIRS channels. Then, broadband OLR as well as synthetic spectral fluxes are derived by the spectral ADM and validated using both synthetic spectra and CERES （Clouds and the Earth＇s Radiant Energy System） observations. In most situations, the mean OLR differences between the spectral ADM products and the CERES observations are within -4-2 W m-2, which is less than 1% of the typical mean clear-sky OLR over tropical oceans. The whole algorithm described in this study can be easily extended to other similar hyperspectral radiance measurements.
文摘Let {vij}, i, j = 1, 2, …, be i.i.d, random variables with Ev11 = 0, Ev11^2 = 1 and a1 = （ai1,…, aiM） be random vectors with {aij} being i.i.d, random variables. Define XN =（x1,…, xk） and SN =XNXN^T,where xi=ai×si and si=1/√N（v1i,…, vN,i）^T. The spectral distribution of SN is proven to converge, with probability one, to a nonrandom distribution function under mild conditions.
文摘The characteristics of nonlinear and supernonlinear Alfvén waves propagating in a multicomponent plasma composed of a double spectral electron distribution and positive and negative ions were investigated.The Sagdeev technique was employed,and an energy equation was derived.Our findings show that the proposed system reveals the existence of a double-layer solution,periodic,supersoliton,and superperiodic waves.The phase portrait and potential analysis related to these waves were investigated to study the main features of existing waves.It was also found that decreasing the electron temperature helps the superperiodic structure to be excited in our plasma model.Our results help interpret the nonlinear and supernonlinear features of the recorded Alfvén waves propagating in the ionosphere D-region.
基金Project supported by the National Natural Science Foundation of China(Grant No.61575077)the Graduate Innovation Fund of Jilin University(Grant No.2017107)
文摘We investigate the spectral redshift of high-order harmonics of the H_2~＋（D_2~＋） molecule by numerically solving the non-Born–Oppenheimer time-dependent Schr ¨odinger equation（TDSE）. The results show that the spectral redshift of highorder harmonics can be observed by adding a weak pulse in the falling part of the trapezoidal laser pulses. Comparing with the H_2~＋ molecule, the shift of high-order harmonic generation（HHG） spectrum for the D_2~＋ molecule is more obvious.We employ the spatial distribution in HHG and time-frequency analysis to illustrate the physical mechanism of the spectral redshift of high-order harmonics.
文摘The spectral distribution exp( ), where {} are the eigenvalues of the negative Laplacian -△=- in the (x^1,x^2)-plane, is studied for a variety of domains, where -∞< t <∞ and i=(1/2)(-1) . The dependence of (t)on the connectivity of a domain and the boundary conditions are analyzed. Particular attention is given to a general bounded domain Ω in R^2 with a smooth boundary Ω, where a finite number of piecewise smooth Dirichlet, Neumann and Robin boundary conditions on the piecewise smooth parts Γj(j = 1,……,n) of Ω are considered such that Some geometrical properties of Ω(e.g., the area of Ω, the total lengths of the boundary, the curvature of its boundary, etc.) are determined, from the asymptotic expansions of (t) for |t| → 0.
基金supported by the National Natural Science Foundation of China(11071213,11101362)Natural Science Foundation of Zhejiang Province(R6090034)Specialized Research Foundation for the Doctor Program of Higher Education(20100101110001)
文摘In this paper,we consider the limiting spectral distribution of the information-plus-noise type sample covariance matrices Cn=1/N（Rn＋σXn）（Rn＋σXn）,under the assumption that the entries of Xn are independent but non-identically distributed random variables.It is proved that,almost surely,the empirical spectral distribution of Cn converges weakly to a non-random distribution whose Stieltjes transform satisfies a certain equation.Our result extends the previous one with the entries of Xn are i.i.d.random varibles to a more general case.The proof of the result mainly employs the Stein equation and the cumulant expansion formula of independent random variables.
文摘Context: Medical imaging has a wide range of applications in today’s society. Basic projectional radiography, CT scans, mammograms and a range of other advanced technologies all use x-rays to create a large number of examinations every day across the world. The most essential component of such medical equipment is the x-ray tube, which creates and produces x-rays. Objective: We describe and investigate an abstract model-geometry of a simple x-ray tube utilizing the open-source software package of BEAMnrc of the EGSnrcmp family, which is well validated by several studies over the years, for high and low energy photons generation. Methodology: Our research focuses on two different electron beam energies: 120 keV and 30 keV. The 120 keV is the typical energy for simple projectional radiographic exams and CT examinations, whereas the 30 keV is the typical energy of mammography. Results: Two different anode materials are used for each case, Gold (Au) and Tungsten (W) for 120 keV because these are the most common in projectional radiography and CT;Molybdenum (Mo) and Rhodium (Rh) for 30 keV because with these targets most mammography exams are carried out. The aim of this work is to show how the BEAMnrc software package can simulate effectively x-ray generation of low-energy photons which are utilized in modern medical imaging procedures. We describe useful information on anode-target characteristics, such as anode angle, anode material, and metal filter materials, based on previous quality studies even by using software other than BEAMnrc. Conclusion: We demonstrate that BEAMnrc can be efficiently used for Monte Carlo modeling of low-energy photons.
基金National Natural Science Foundation of China (No. 51105289)Doctoral Program Foundation of Self-determined and Innovative Research Funds of WUT,China (No. 2010-ZY-JD-034)
文摘In order to accurately and automatically measure the light emitting diode(LED) colorimetric parameters,the design of a measurement system by adopting a high-performance spectrometer and looking-up table method was presented based on the LabVIEW.First,the data of the LED relative spectral power distribution(SPD) were read by the spectrometer to measure LED chromaticity coordinate,and the slopes table were formed by the LED chromaticity coordinate and the equal stimulus point.Then,the CIE1931 chromaticity diagram was divided into 4 different regions to ensure the slopes table that had the character of monotonic decreasing.Finally,the LED dominant wavelength and purity were automatically calculated using the LabVIEW programs.The data of LEDs' colorimetric parameters have demonstrated that the measurement method in this paper can achieve higher precision result.
文摘The transition radiation of a charged particle crossing the interface of two media having a monatomic impurity layer is investigated. It is shown that at sliding angles of incidence of a particle on the boundary of the media, the transition radiation is mainly determined by the properties of the surface layer. The possibility of using transition radiation to study the surface of substances is discussed. In addition, due to the hard radiation present in space, this research may be important for the use of light monoatomic layers as a material for satellite antennas, “solar sails” and cover layers in a future space (interstellar) mission.
基金the National Natural Science Foundation of China(No.11971215)Science and Technology Project of Gansu Province of China(No.22JR5RA391)+1 种基金Center for Data Science of Lanzhou University,Chinathe Key Laboratory of Applied Mathematics and Complex Systems of Lanzhou University,China.
文摘In this paper,the backward Euler method and the shifted Grünwald-Letnikov formulas are utilized to discretize the space-fractional diffusion equations.The discretized result is a system of linear equations with a coefficient matrix being the sum of a diagonal matrix and a non-Hermitian Toeplitz matrix.By utilizing the Hermitian and skew-Hermitian splitting of the Toeplitz matrix,we develop a two-parameter DThsS iteration method to solve the linear systems.The convergence is also discussed.A DTHsS-t(α,γ)preconditioner is proposed and the preconditioned GMRES method combined with the proposed preconditioner is applied to solve the linear systems.The spectral analysis of the DThsS-τ(α,γ)preconditioned matrix is provided.Experimental results demonstrate the effectiveness of the proposed methods in solving the space-fractional diffusion equations.
文摘Despite its utility in identifying patterns in celestial objects, the Hertzsprung-Russell diagram is not supported in dim or small stars;it struggles to provide insights into certain celestial objects such as brown dwarfs [1]. The purpose of this experiment is to create an improved version of the diagram with a three-dimensional model that includes a third z-axis to accurately predict and chart the life cycles of all stars regardless of size. The values of the stars’ absolute magnitude and color indices were used to chart the surface gravity and metallicity, variables that were chosen due to their ease of collection and their likeliness to be within the range of values being assessed. To obtain the values for the model, data points from the database GAIA DR2 were utilized via the TAP protocol to query the SQL database. The data was transferred into a local CSV file to facilitate data manipulation. The data could be read and interpreted, as dim stars would likely have higher values of these variables, making it easier to include them in the diagram. The Pandas DataFrames tool on Python 3 was used to organize and manage the data efficiently. Matplotlib Graphs visualized the relationships between different stellar attributes by developing a linear regression line and an algorithm and creating scatter plots and sky maps to explore trends, hence designing three-dimensional diagrams. It was determined that the surface gravity diagram had a higher efficacy than metallicity due to their standard deviations of 0.4641441715272741 and 0.786577627976148, respectively.
基金supported by the National Key Research and Development Program of China(No.2021YFB2401302)。
文摘Taking the advantage of Internet of Things(IoT)enabled measurements,this paper formulates the event detection problem as an information-plus-noise model,and detects events in power systems based on free probability theory(FPT).Using big data collected from phasor measurement units(PMUs),we construct the event detection matrix to reflect both spatial and temporal characteristics of power gird states.The event detection matrix is further described as an information matrix plus a noise matrix,and the essence of event detection is to extract event information from the event detection matrix.By associating the event detection problem with FPT,the empirical spectral distributions(ESDs)related moments of the sample covariance matrix of the information matrix are computed,to distinguish events from“noises”,including normal fluctuations,background noises,and measurement errors.Based on central limit theory(CLT),the alarm threshold is computed using measurements collected in normal states.Additionally,with the aid of sliding window,this paper builds an event detection architecture to reflect power grid state and detect events online.Case studies with simulated data from Anhui,China,and real PMU data from Guangdong,China,verify the effectiveness of the proposed method.Compared with other data-driven methods,the proposed method is more sensitive and has better adaptability to the normal fluctuations,background noises,and measurement errors in real PMU cases.In addition,it does not require large number of training samples as needed in the training-testing paradigm.
