共查询到18条相似文献,搜索用时 125 毫秒
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小叶章种群分布格局的分形特征I计盒维数 总被引:2,自引:0,他引:2
应用分形理论(Fractal theory)中的计盒维数(Box-counting dimension)对三江平原小叶章(Deyeuxia angustifolia)种群分布格局特征进行了研究。结果表明:三江平原小叶章种群分布格局具有分形特征。其计盒维数5-9月分别为1.524、1.769、1.711、1.615、1.701,表明其占据空间能力较强。季节动态自5月始至6月达到极大值,而后逐渐下降, 相似文献
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小叶章种群分布格局的分形特征Ⅱ信息维数与关联维数 总被引:8,自引:0,他引:8
应用分形理论中的信息维数(Information dimensoin)和关联维数(Carrelation dimensoin)研究了三江平原小叶章(Deyeuxia angustifloia)种群分布格局特征。结果表明,信息维数在5~9月分别为1.494、1.709、1.642、1.553、1.625,表明其结构较复杂,格局强度较高。关联维数则为1.662、1.861、1.766、1.750、1. 相似文献
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经颅磁刺激对癫痫病灶脑电相关维数的影响 总被引:5,自引:0,他引:5
利用脑功能指标——大鼠病灶区脑电的相关维数,研究低频经颅磁刺激对慢性颞叶癫痫大鼠脑功能改善的作用。对一组颞叶癫痫大鼠施予频率为0.5Hz、强度为0.4T、20次/日、连续一周的低频重复性经颅磁刺激(rTMS).在rTMS前后,分别测取颞叶癫痫大鼠责任病灶区皮层和海马区的脑电,重构时间延迟吸引子,用G-P算法估算反映对应脑区功能状态的相关维数。研究结果显示:施予适量的rTMS(0.4T、20次/日、连续一周),使颞叶癫痫大鼠海马和相应皮层脑电的相关维数比刺激前明显升高。研究表明适量的rTMS有抑制癫痫的作用。 相似文献
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油松(Pinus tabuliformis)耐低温、干旱和瘠薄,是我国温性针叶林中分布最广的树种,也是我国北方广大地区最主要的造林树种之一。2013年7月,在七里峪林场设置一块100 m×100 m的油松天然林样地,逐一测量并记录了每株油松的胸径、树高和冠幅,并确定它们的坐标位置。应用分形理论中的计盒维数、信息维数和关联维数研究了样地内油松种群空间格局的分形特征。结果表明,油松种群格局具有自相似性,其有较高的计盒维数(1.785)和关联维数(1.826),个体空间相关程度较高,种内竞争激烈,对空间有较强的占据能力。油松种群格局的信息维数较低(0.262),其格局强度尺度变化程度较低,个体分布比较均匀。3个分形维数相辅相承、相互影响,研究结果对全面准确地解释油松种群的空间格局特征具有重要意义。 相似文献
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应用分形理论中的信息维数(Information dimension)和关联维数(Carrelation dimension)研究了三江平原小叶章(Deyeuxia angustifolia)种群分布格局特征。结果表明:信息维数在5~9月分别为1.494、1.709、1.642、1.553、1.625,表明其结构较复杂,格局强度较高。关联维数则为1.662、1.861、1.766、1.750、1.807,说明小叶章个体空间相关程度较高。种内竞争强烈,对空间有较强的占据能力。两个维数的季节动态均自5月至6月达到极大值,而后逐渐下降,至9月略有回升。 相似文献
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一些生理信号,例如脑电是源自于高维混沌系统,因此低维混沌理论和方法不适用于分析这类高维混沌。采用投影追踪主分量分析法(Princiopal Component Analysis based on Projection Pursuit,PP PCA)对高维Lorenz模型系统进行了降维的研究。在用上述方法成功地对线性和非线性噪声-周期模型分别进行了PP PCA分析的基础上,对Lorenz高维混沌系统进行了PPPCA降维的研究。结果表明,正确选用非线性的投影追踪主分量分析法,可以通过简化原系统达到降维的目的,并能保留研究所关心的原系统的主要动态特性。同时也阐明了方法的稳定性和将该方法应用于高维脑电降维的可行性。 相似文献
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N. Sriraam 《Biomedical signal processing and control》2012,7(4):379-388
Transmission of long duration EEG signals without loss of information is essential for telemedicine based applications. In this work, a lossless compression scheme for EEG signals based on neural network predictors using the concept of correlation dimension (CD) is proposed. EEG signals which are considered as irregular time series of chaotic processes can be characterized by the non-linear dynamic parameter CD which is a measure of the correlation among the EEG samples. The EEG samples are first divided into segments of 1 s duration and for each segment, the value of CD is calculated. Blocks of EEG samples are then constructed such that each block contains segments with closer CD values. By arranging the EEG samples in this fashion, the accuracy of the predictor is improved as it makes use of highly correlated samples. As a result, the magnitude of the prediction error decreases leading to less number of bits for transmission. Experiments are conducted using EEG signals recorded under different physiological conditions. Different neural network predictors as well as classical predictors are considered. Experimental results show that the proposed CD based preprocessing scheme improves the compression performance of the predictors significantly. 相似文献
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《IRBM》2008,29(4):239-244
ObjectivesThe electroencephalogram (EEG) signal contains information about the state and condition of the brain. The aim of the study is to conduct a nonlinear analysis of the EEG signals and to compare the differences in the nonlinear characteristics of the EEG during normal state and the epileptic state.DataThe EEG data used for this study – which consisted of epileptic EEG and normal EEG – were obtained from the EEG database available with the Bonn University, Germany.ResultsThe attractors seen in normal and epileptic human brain dynamics were studied and compared. Surrogate data analyses were conducted on two nonlinear measures, namely the largest Lyapunov exponent and the correlation dimension, to test the hypothesis whether EEG signals were in accordance with linear stochastic models.DiscussionsThe existence of deterministic chaos in brain activity is confirmed by the existence of a chaotic attractor; also, saturation of the correlation dimension towards a definite value is the manifestation of a deterministic dynamics. Also a reduction is observed between the dimensionalities of the brain attractors from normal state to the epileptic state. The evaluation of the largest Lyapunov exponent also confirms the lowering of complexity during an episode of seizure.ConclusionIn case of Lyapunov exponent of EEG data, the change due to surrogating is small suggesting that it is not representing the system complexity properly but there is a marked change in the case of correlation dimension value due to surrogating. 相似文献
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Using phase space reconstruct technique from one-dimensional and multi-dimensional time series and the quantitative criterion
rule of system chaos, and combining the neural network; analyses, computations and sort are conducted on electroencephalogram
(EEG) signals of five kinds of human consciousness activities (relaxation, mental arithmetic of multiplication, mental composition
of a letter, visualizing a 3-dimensional object being revolved about an axis, and visualizing numbers being written or erased
on a blackboard). Through comparative studies on the determinacy, the phase graph, the power spectra, the approximate entropy,
the correlation dimension and the Lyapunov exponent of EEG signals of 5 kinds of consciousness activities, the following conclusions
are shown: (1) The statistic results of the deterministic computation indicate that chaos characteristic may lie in human
consciousness activities, and central tendency measure (CTM) is consistent with phase graph, so it can be used as a division
way of EEG attractor. (2) The analyses of power spectra show that ideology of single subject is almost identical but the frequency
channels of different consciousness activities have slight difference. (3) The approximate entropy between different subjects
exist discrepancy. Under the same conditions, the larger the approximate entropy of subject is, the better the subject's innovation
is. (4) The results of the correlation dimension and the Lyapunov exponent indicate that activities of human brain exist in
attractors with fractional dimensions. (5) Nonlinear quantitative criterion rule, which unites the neural network, can classify
different kinds of consciousness activities well. In this paper, the results of classification indicate that the consciousness
activity of arithmetic has better differentiation degree than that of abstract. 相似文献
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Fractal dimension of electroencephalographic time series and underlying brain processes 总被引:2,自引:0,他引:2
Werner Lutzenberger Hubert Preissl Friedemann Pulvermüller 《Biological cybernetics》1995,73(5):477-482
Fractal dimension has been proposed as a useful measure for the characterization of electrophysiological time series. This
paper investigates what the pointwise dimension of electroencephalographic (EEG) time series can reveal about underlying neuronal
generators. The following theoretical assumptions concerning brain function were made (i) within the cortex, strongly coupled
neural assemblies exist which oscillate at certain frequencies when they are active, (ii) several such assemblies can oscillate
at a time, and (iii) activity flow between assemblies is minimal. If these assumptions are made, cortical activity can be
considered as the weighted sum of a finite number of oscillations (plus noise). It is shown that the correlation dimension
of finite time series generated by multiple oscillators increases monotonically with the number of oscillators. Furthermore,
it is shown that a reliable estimate of the pointwise dimension of the raw EEG signal can be calculated from a time series
as short as a few seconds. These results indicate that (i) The pointwise dimension of the EEG allows conclusions regarding
the number of independently oscillating networks in the cortex, and (ii) a reliable estimate of the pointwise dimension of
the EEG is possible on the basis of short raw signals.
Received: 1 September 1994/Accepted in revised form: 16 May 1995 相似文献
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Most of the physiological signals (EEG, ECG, blood flow, human gait, etc.) characterize by complex dynamics including both non-stationarities and non-linearities. These time series resemble red noise with long-range correlation and 1/(f beta) power spectrum. A question arises as to how to distinguish the characteristics of the process underlying the signal dynamics from the properties of the observed time series. The classical methods to determine possible non-linear (chaotic) dynamics (e.g. correlation dimension) often fail in such signals because of relatively short data records containing stochastic components and non-stationarities. We report an application of several approaches, aimed at (1) determining of the non-stationarities in the signals and (2) testing whether non-linear dynamics exists. Assessment of the intrinsic correlation properties of the dynamic process and distinguishing the same from external trends was performed using singular spectra and detrended fluctuation analysis. The existence of non-linear dynamics was tested by correlation dimension (modified algorithm of re-embedding) and by correlation integrals of real and surrogate data. The correlation integrals of real signal and surrogate data sets were statistically compared using Kolmogorov-Smirnov (K-S) test. The procedures were tested on EEG and laser-Doppler (LD) blood flow. Our suggestion is that no one approach taken alone is the best for our aims. Instead, a battery of methods should be used. 相似文献
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Ali Bülent Uşaklı 《Journal of computational neuroscience》2010,28(3):595-603
In bio-signal applications, classification performance depends greatly on feature extraction, which is also the case for electroencephalogram
(EEG) based applications. Feature extraction, and consequently classification of EEG signals is not an easy task due to their
inherent low signal-to-noise ratios and artifacts. EEG signals can be treated as the output of a non-linear dynamical (chaotic)
system in the human brain and therefore they can be modeled by their dimension values. In this study, the variance fractal
dimension technique is suggested for the modeling of movement-related potentials (MRPs). Experimental data sets consist of
EEG signals recorded during the movements of right foot up, lip pursing and a simultaneous execution of these two tasks. The
experimental results and performance tests show that the proposed modeling method can efficiently be applied to MRPs especially
in the binary approached brain computer interface applications aiming to assist severely disabled people such as amyotrophic
lateral sclerosis patients in communication and/or controlling devices. 相似文献