Preliminary research on the relationship between long-range correlations and predictability

By establishing the Markov model for a long-range correlated time series （LRCS） and analysing its evolutionary characteristics, this paper defines a physical effective correlation length （ECL） T, which reflects the predictability of the LRCS. It also finds that the ECL has a better power law relation with the long-range correlated exponent γ of the LRCS： T = Kexp（-γ/0.3） ＋ Y, （0 〈 γ〈 1） the predictability of the LRCS decays exponentially with the increase of γ It is then applied to a daily maximum temperature series （DMTS） recorded at 740 stations in China between the years 1960-2005 and calculates the ECL of the DMTS. The results show the remarkable regional distributive feature that the ECL is about 10-14 days in west, northwest and northern China, and about 5-10 days in east, southeast and southern China. Namely, the predictability of the DMTS is higher in central-west China than in east and southeast China. In addition, the ECL is reduced by 1-8 days in most areas of China after subtracting the seasonal oscillation signal of the DMTS from its original DMTS; however, it is only slightly altered when the decadal linear trend is removed from the original DMTS. Therefore, it is shown that seasonal oscillation is a significant component of daily maximum temperature evolution and may provide a basis for predicting daily maximum temperatures. Seasonal oscillation is also significant for guiding general weather predictions, as well as seasonal weather predictions.

LONG-RANGE CORRELATIONS IN DNA SEQUENCES USING TWO-DIMENSIONAL DNA WALKS

The characterization of long-range correlations and fractal properties of DNA sequences has proved to be adifficult though rewarding task mainly due to the mosaic character of DNA consisting of many patches of various lengthswith different nucleotide constitutions.In this paper we investigate statistical correlations among different positions in DNAsequences using the two-dimensional DNA walk.The root-mean-square fluctuation F(l)is described by a power law.Theautocorrelation function C(l),which is used to measure the linear dependence and periodicity,exists a power law ofC(l)-l^(-μ).We also calculate the mean-square distance<R^2(l)>along the DNA chain,and it may be expressed as<R^2(l)>-l^(?)with 2>γ>1.Our investigations can provide some insights into long-range correlations in DNA sequences.

Characterizing Long-range Correlation Properties in Nucleotide Sequences

Using continuous wavelet transform as the analytical tool, the fractal characteristic of nucleotide sequences was studied. The fractal dimension of the exon and intron sequences for different species was calculated. We use the Mexican hat wavelet function as the mother wavelet and Hurst exponent to describe the long-range correlation. It is found that the Hurst exponent of intron sequence is larger than that of exon sequence for the same gene.

Long-range correlation analysis of urban traffic data

This paper investigates urban traffic data by analysing the long-range correlation with detrended fluctuation analysis. Through a large number of real data collected by the travel time detection system in Beijing, the variation of flow in different time periods and intersections is studied. According to the long-range correlation in different time scales, it mainly discuss the effect of intersection location in road net, people activity customs and special traffic controls on urban traffic flow. As demonstrated by obtained results, the urban traffic flow represents three-phase characters similar to highway traffic. Moreover, compared by the two groups of data obtained before and after the special traffic restrictions （vehicles with special numbered plates only run in a special workday） enforcement, it indicates that the rules not only reduce the flow but also avoid irregular fluctuation.

Electronic properties of one-dimensional systems with long-range correlated binary potentials

We study numerically the electronic properties of one-dimensional systems with long-range correlated binary potentials. The potentials are mapped from binary sequences with a power-law power spectrum over the entire frequency range, which is characterized by correlation exponent β. We find the localization length ζ increases withβ. At system sizes N →∞, there are no extended states. However, there exists a transition at a threshold ζ. Whenβ 〉 βc, we obtain ζ 〉 0. On the other hand, at finite system sizes, ζ≥ N may happen at certain β, which makes the system ＂metallic＂, and the upper-bound system size N＊ （β） is given.

Elastic Net方法在Cox模型变量选择中的研究

将Elastic Net方法运用于Cox模型的变量选择中,建立EN-Cox模型,证明了Cox模型的Elastic Net估计具有组效应性质.数值模拟验证了Elastic Net方法能将强相关变量全部选入Cox模型,而Lasso方法无此功效.数值实例验证了Elastic Net方法运用于Cox模型的可行性,表明EN-Cox在拟合效果和预测能力方面均优于传统Cox模型.

Uniaxial experimental study of the acoustic emission and deformation behavior of composite rock based on 3D digital image correlation(DIC)

In this paper, uniaxial compression tests were carried out on a series of composite rock specimens with different dip angles, which were made from two types of rock-like material with different strength. The acoustic emission technique was used to monitor the acoustic signal characteristics of composite rock specimens during the entire loading process. At the same time, an optical non-contact 3 D digital image correlation technique was used to study the evolution of axial strain field and the maximal strain field before and after the peak strength at different stress levels during the loading process. The effect of bedding plane inclination on the deformation and strength during uniaxial loading was analyzed. The methods of solving the elastic constants of hard and weak rock were described. The damage evolution process, deformation and failure mechanism, and failure mode during uniaxial loading were fully determined. The experimental results show that the θ = 0?–45?specimens had obvious plastic deformation during loading, and the brittleness of the θ = 60?–90?specimens gradually increased during the loading process. When the anisotropic angle θincreased from 0?to 90?, the peak strength, peak strain,and apparent elastic modulus all decreased initially and then increased. The failure mode of the composite rock specimen during uniaxial loading can be divided into three categories:tensile fracture across the discontinuities(θ = 0?–30?), slid-ing failure along the discontinuities(θ = 45?–75?), and tensile-split along the discontinuities(θ = 90?). The axial strain of the weak and hard rock layers in the composite rock specimen during the loading process was significantly different from that of the θ = 0?–45?specimens and was almost the same as that of the θ = 60?–90?specimens. As for the strain localization highlighted in the maximum principal strain field, the θ = 0?–30?specimens appeared in the rock matrix approximately parallel to the loading direction,while in the θ = 45?–90?specimens it appeared at the hard and weak rock layer interface.

Use of a Digital Image Correlation Technique for Measuring the Material Properties of Beetle Wing

Beetle wings are very specialized flight organs consisting of the veins and membranes.Therefore it is necessary from a bionic view to investigate the material properties of a beetle wing experimentally.In the present study,we have used a Digital Image Correlation (DIC) technique to measure the elastic modulus of a beetle wing membrane.Specimens were prepared by carefully cutting a beetle hind wing into 3.0 mm by 7.0 mm segments (the gage length was 5 mm).We used a scanning electron microscope for a precise measurement of the thickness of the beetle wing membrane.The specimen was attached to a designed fixture to induce a uniform displacement by means of a micromanipulator.We used an ARAMISTM system based on the digital image correlation technique to measure the corresponding displacement of a specimen.The thickness of the beetle wing varied at different points of the membrane.The elastic modulus differed in relation to the membrane arrangement showing a structural anisotropy;the elastic modulus in the chordwise direction is approximately 2.65 GPa,which is three times larger than the elastic modulus in the spanwise direction of 0.84 GPa.As a result,the digital image correlation-based ARAMIS system was suc- cessfully used to measure the elastic modulus of a beetle wing.In addition to membrane's elastic modulus,we considered the Poisson's ratio of the membrane and measured the elastic modulus of a vein using an Instron universal tensile machine.The result reveals the Poisson's ratio is nearly zero and the elastic modulus of a vein is about 11 GPa.

Mechanical properties of wood materials using near-infrared spectroscopy based on correlation local embedding and partial least-squares

This study used near-infrared(NIR)spectroscopy to predict mechanical properties of wood.NIR spectra were collected in wavelengths 900–1700 nm,and spectra averaged by radial and tangential surface spectra were used to establish a partial least square(PLS)model based on correlation local embedding(CLE).Mongolian oak(Quercus mongolica Fisch.ex Ledeb.)was used to test the eff ectiveness of the model.The cross-validation method was used to verify the robustness of the CLE–PLS model.Ninety samples were tested as the calibration set and forty-fi ve as the validation set.The results show that the prediction coeffi cient of determination(R2 p)is 0.80 for MOR,and 0.78 for MOE.The ratio of performance to deviation is 2.23 for MOR and 2.15 for MOE.

STUDY ON MECHANICAL INTERACTIONS BETWEEN SINGLE CARDIAC MYOCYTE AND ELASTIC SUBSTRATE

Quantitative investigation on mechanical characteristics of cardiac myocytes has important physiological significance. Based on elastic substrate technique, this paper develops a set of algorithms for high-efficiency cellular traction recovery. By applying a gradient-based digital image correlation method to track randomly distributed fluorescence microbeads on the deformed substrate induced by single cardiac myocyte, high-resolution substrate displacement field can readily be obtained. By using a numerical algorithm based on the integral Boussinesq solution, cell-substrate tractions are reconstructed in a stable and reliable manner. Finally, spatiotemporal dynamics of a single cardiac myocyte is investigated as it adheres to a polyacrylamide elastic substrate.

A first-principles study of the structural and elastic properties of orthorhombic and tetragonal Ca_3Mn_2O_7

The structural and elastic properties of multiferroic Ca3Mn2O7 with ferroelectric orthorhombic （O-phase） and paraelectric tetragonal structures （T-phase） have been studied by first-principles calculations within the generalized gradient approximation （GGA） and the GGA plus Hubbard U approaches （GGA ＋ U）. The calculated theoretical structures are in good agreement with the experimental values. The T-phase is found to be antiferromagnetic （AFM） and the AFM O-phase is more stable than the T-phase, which also agree with the experiments. On these bases, the single-crystal elastic constants （Cijs） and elastic properties of polycrystalline aggregates are investigated for the two phases. Our elasticity calculations indicate Ca3Mn2O7 is mechanically stable against volume expansions. The AFM O-phase is found to be a ductile material, while the AFM T-phase shows brittle nature and tends to be elastically isotropic. We also investigate the influence of strong correlation effects on the elastic properties, qualitatively consistent results are obtained in a reasonable range of values of U. Finally, the ionicity is discussed by Bader analysis. Our work provides useful guidance for the experimental elasticity measurements of Ca3Mn2O7, and makes the strain energy calculation in multiferroic Ca3Mn2O7 thin films possible.

Elastic constants characterization on graphite at 500℃ by the virtual fields method

In this paper the elastic constants of graphite at elevated temperature were experimentally investigated by using the virtual fields method （VFM）. A new method was presented for the characterization of mechanical properties at elevated temperature. The three-point bending tests were performed on graphite materials by an universal testing machine equipped with heating fumace. Based on the heterogeneous deformation fields measured by the digital image correlation （DIC） technique, the elastic constants were then extracted by using VFM. The measurement results of the elastic constants at 500℃ were obtained. The ef- fect on the experimental results was also analyzed. The successful results verify the feasibility of using the proposed method to measure the properties of graphite at high temperature, and the proposed method is believed to have a good potential for further applications.

Evaluation of Myocardial Strain and Aortic Elasticity in Patients with Bicuspid Aortic Valve

This study evaluated the myocardial strain and aortic elasticity in patients with bicuspid aortic valve（BAV） and then investigated the relation between them. Thirty-nine patients（30 males; mean age 44±19 years; range 6 to 75 years） with BAV were recruited as BAV group, and 29 age- and sex-matched healthy controls（21 males; mean age 42±11 years; range 20 to 71 years） served as control group. Aortic strain, distensibility and stiffness index were derived using M-mode echocardiography. Left ventricular global myocardial strain was acquired with speckle-tracking echocardiography. Correlation between aortic elasticity and myocardial strain was also analyzed. The results showed that aortic stiffness was higher（17.5±14.0 vs. 5.3±2.7, P〈0.001）, and aortic strain（4.9±4.7 vs. 11.0±4.1, P〈0.001） and distensibility（1.8±2.1 vs. 3.7±1.6, P〈0.001） were lower significantly in BAV group than in control group. Global circumferential strain（–19.1±4.2 vs. –22.5±3.7, P〈0.001）, radial stain（29.8±14.9 vs. 38.0±8.8, P〈0.001） and longitudinal stain（–18.4±3.4 vs. –20.8±3.5, P〈0.001） were significantly lower in BAV group than in control group. There was weak association between aortic elasticity and myocardial strain. These findings indicated BAV patients manifest reduced myocardial strain which had weak relationship with aortic elastic lesion.

Long-range Dependence Characteristics of Forest Biological Disasters in China against the Background of Climate Change

Forest biological disasters(FBD) seriously impact energy flow and material cycling in forest ecosystems,while the underlying causes of FBD are complex. These disasters involve large areas and cause tremendous losses. As a result,the occurrence of FBDs in China( CFBD) threatens the country's ability to realize its strategic target of increasing both forested area(40 million ha) and forest volume(1.3 billion m^3) from 2005 to 2020. Collectively,China has officially named this effort to increase forest area and volume the "Two Increases" as national goals related to forestry. Based on Hurst index analysis from fractal theory,we analyzed the time series of the occurrence area and related data of FBDs from 1950 to 2007 to quantitatively determine the patterns of the macro occurrence of FBDs in China. Results indicates that,the time series of( CFBD) areas is fractal( self-affinity fractal dimension D = 1. 3548),the fluctuation of( CFBD) areas is positively correlated( auto-correlation coefficient C = 0. 2170),and the occurrence of the time series of( CFBD) is long-range dependent( Hurst index H =0. 6416),showing considerably strong trend of increases in FBDC area. Three different methods were further carried out on the original time series,and its two surrogate series generated by function surrogate in library t series,and function Surrogate Data in library in Wavelet software R,so as to analyze the reliability of Hurst indexes. The results showed that the Hurst indices calculated using different estimation methods were greater than 0. 5,ranging from 0. 64 to 0. 97,which indicated that the change of occurrence area data of FBDs was positively autocorrelated.The long-range dependence in forest biological disasters in China is obvious,and the spatial extent of FBDs tended to increase during this study period indicating this trend should be expected to persistent and worsen in the future.

Identification of Time-Varying Modal Parameters for Thermo-Elastic Structure Subject to Unsteady Heating

A time-varying modal parameter identification method combined with Bayesian information criterion(BIC)and grey correlation analysis(GCA)is presented for a kind of thermo-elastic structures with sparse natural frequencies and subject to an unsteady temperature field.To demonstrate the method,the thermo-elastic structure to be identified is taken as a simply-supported beam with an axially movable boundary and subject to both random excitation and an unsteady temperature field,and the dynamic outputs of the beam are first simulated as the measured data for the identification.Then,an improved time-varying autoregressive(TVAR)model is generated from the simulated input and output of the system.The time-varying coefficients of the TVAR model are expanded as a finite set of time basis functions that facilitate the time-varying coefficients to be time-invariant.According to the BIC for preliminarily determining the scope of the order number,the grey system theory is introduced to determine the order of TVAR and the dimension of the basis functions simultaneously via the absolute grey correlation degree(AGCD).Finally,the time-varying instantaneous frequencies of the system are estimated by using the recursive least squares method.The identified results are capable of tracking the slow time-varying natural frequencies with high accuracy no matter for noise-free or noisy estimation.

Many-Body Correlation Effects on the <i>x</i>_Bjorken-Dependence of Cross Section Ratios off Nuclei for 1 <<i>x</i>_Bjorken<2

Many-body correlations in nuclei determine the behavior of Deep-Inelastic-Scattering (DIS) and Quasi-Elastic Scattering (QES) cross section ratios off heavy over light nuclei especially for xBjorken > 1, obtained at Jefferson Lab. They can be described in terms of quark-cluster formation in nuclei due to wave-function overlapping, manifesting itself when the momentum transfer is high so that the partonic degrees of freedom are resolved. In clusters (correlated nucleons) the quark and gluon momentum distributions are softer than in single nucleons and extend to xBjorken > 1. The cluster formation probabilities are computed using a network-defining algorithm in which the initial nucleon density is either standard Woods-Saxon or is input from lower energy data while the critical radius for nucleon merging is an adjustable parameter. The exact choice of critical radius depends on the specific nucleus and it is anti-correlated to the rescaling of the xBjorken needed for bound nucleons. The calculations show that there is a strong dependence of the cross section ratios on the xBjorken in agreement with the data and that four-body correlations are needed to explain the experimental results even in the range 1 < xBjorken < 2. The dependence on the specific exponents of parton distributions in high-order clusters is weak.

故障关联矩阵下弹性配电网可靠性评估

配电网弹性是指系统受到干扰后恢复原有状态的能力,而自然灾害的频发要求配电网不仅在正常条件下能够可靠运行,而且还能够在极端灾害出现时保持必要能力。据此,提出一种基于故障关联矩阵(fault incidence matrix,FIM)的弹性配电网可靠性评价方法。通过建立FIM,使用简化的矩阵代数、布尔运算即可实现配电系统可靠性、弹性和供电能力的显式解析计算,避免了评估过程中故障枚举的重复性搜索工作,节省了计算时间,并且可适用于结构复杂的配电网,易于扩展。最后结果表明:采用文中方法的计算时间仅为约0.055 s,相较于故障扩散算法和分块算法分别减少87%和75%的时间。

高弹性橡胶止水模型实验及全周鼓起变形测量

针对涵洞、隧道等水工建筑物在长期运营过程中出现的渗漏问题,利用高弹性橡胶进行封堵止水是一种行之有效的措施.为了评价不同橡胶的封堵效果,提出一种高弹性橡胶止水实验模型,将橡胶安装在模型伸缩缝中,通过施加静水压力测试橡胶的封堵性能.同时,提出一种利用电动旋转台的全周三维数字图像相关(Digital Image Correlation, DIC)方法,利用单套三维DIC系统,即可测量得到内侧橡胶在不同静水压力、各个视角下的鼓起变形.按照1∶1比例浇筑了实物模型,开展了静水压力实验,并测得了所选橡胶能承受的最大水压力和全周鼓起变形,验证了止水模型实验的可行性和全周变形测量方法的有效性.

基于改进弹性网络回归的电容式电压互感器误差状态预测

为了探索各因素对电容式电压互感器(Capacitance Type Voltage Transformer,CVT)误差状态的影响程度,提高CVT误差状态预测的精度,提出一种基于改进弹性网络回归的CVT误差状态预测方法。首先,通过拉依达准则和K-最近邻填充方法对原始数据进行预处理;然后,构建改进的弹性网络回归模型,根据每个影响因素的皮尔逊相关系数在弹性网络回归模型中给与不同的惩罚权重,计算出该模型的最优系数;最后,利用具有最优系数的回归模型对CVT误差状态进行预测。结果表明所提方法具有更高的预测精度。

Impact of radiations on the long-range correlation of soil moisture: A case study of the A’rou superstation in the Heihe River Basin

Analyses of the soil moisture evolution trend and the influence of different types of radiation on soil moisture are of great significance to the simulation and prediction of soil moisture.In this paper,soil moisture(2–60 cm) and various radiation data from 2014–2015 at the A’rou superstation were selected.The radiation data include the net radiation(NR),shortwave and longwave radiation(SR and LR).Using adaptive fractal analysis(AFA),the long-range correlation(LRC) of soil moisture and long-range cross correlation(LRCC) between moisture and three types of radiation were analyzed at different timescales and soil depths.The results show that:(1) Persistence of soil moisture and consistency between soil moisture and radiation mutate at 18-d and 6-d timescales,respectively.The timescale variation of soil moisture persistence is mainly related to the influence process of radiation on soil moisture;(2) Both the soil moisture persistence and soil moisture-radiation consistency vary substantially with soil depth.The soil depth variation of soil moisture persistence is related to the influence intensity of radiation;(3) From 2–6 day timescales,LR displays the strongest influence on soil moisture at depths of 2–10 cm through negative feedback of radiation on the soil temperature.The influence intensity decreases with depth from 2–15 cm.Therefore,the soil moisture persistence is weak and increases with depth from 2–15 cm;and(4) At more than 6 day timescales,SR and NR display a stronger influence on the soil moisture persistence at depths of 2–40 cm through positive feedback of radiation on the soil temperature,especially at depths of 2–10 cm.This influence also weakens with depth.The soil moisture persistence at depths of 2–10 cm is the weakest and increases with depth from 2–40 cm.The research results are instructive for determining timescales and soil depths related to soil water in hydrological models.