共查询到20条相似文献,搜索用时 250 毫秒
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Fetal heart rate complexity was examined on the basis of RR interval time series obtained in the second and third trimester of pregnancy. In each fetal RR interval time series, short term beat-to-beat heart rate changes were coded in 8 bit binary sequences. Redundancies of the 2(8) different binary patterns were reduced by two different procedures. The complexity of these sequences was quantified using the approximate entropy (ApEn), resulting in discrete ApEn values which were used for classifying the sequences into 17 pattern sets. Also, the sequences were grouped into 20 pattern classes with respect to identity after rotation or inversion of the binary value. There was a specific, nonuniform distribution of the sequences in the pattern sets and this differed from the distribution found in surrogate data. In the course of gestation, the number of sequences increased in seven pattern sets, decreased in four and remained unchanged in six. Sequences that occurred less often over time, both regular and irregular, were characterized by patterns reflecting frequent beat-to-beat reversals in heart rate. They were also predominant in the surrogate data, suggesting that these patterns are associated with stochastic heart beat trains. Sequences that occurred more frequently over time were relatively rare in the surrogate data. Some of these sequences had a high degree of regularity and corresponded to prolonged heart rate accelerations or decelerations which may be associated with directed fetal activity or movement or baroreflex activity. Application of the pattern classes revealed that those sequences with a high degree of irregularity correspond to heart rate patterns resulting from complex physiological activity such as fetal breathing movements. The results suggest that the development of the autonomic nervous system and the emergence of fetal behavioral states lead to increases in not only irregular but also regular heart rate patterns. Using symbolic dynamics to examine the cardiovascular system may thus lead to new insight with respect to fetal development. 相似文献
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The entropy production sigma is calculated in the time evolution processes toward a Turing-like pattern and a chaotic pattern in a two-dimensional reaction-diffusion system. The contributions of reaction and diffusion to the entropy production are evaluated separately. Though its contribution to total sigma is about 5%, the entropy production in diffusion foretells the moving direction of the dots (reaction spots) and the line-shaped patterns. The entropy production of the entire system sigma depicts well the cooperative dynamics and evolution of chaotic dot patterns. It is suggested that sigma can be a scalar measure for quantitative studies of hierarchic pattern dynamics. The relation is also discussed between the bifurcation parameter and the distance from thermodynamic equilibrium. 相似文献
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We investigate the role of the spatial pattern and temporal dynamics on the population properties of a diffusive Gause–Lotka–Volterra system. The average total population size is insensitive to the temporal dynamics, whereas a significant decrease of the population size can be found as the spatial diffusion effect is increased, implying that the spatial pattern plays an important role. At large diffusion coefficients, a saturation of the spatial pattern variation is observed, which can be understood by a spatial scaling analysis of the system. The existence of multiple attractors can also indicate that spatial patterns play a more important role than temporal dynamics in dominating the population size. 相似文献
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Local binary pattern (LBP) operators, which measure the local contrast within a pixel's neighborhood, have been successfully applied to texture analysis, visual inspection, and image retrieval. In the paper, we present a novel semi-fragile spatial watermarking method based on LBP operators by using the local pixel contrast for the embedding and extraction of watermarks. We also propose a general framework for multi-level image watermarking. Experimental results show that the proposed watermarking methods are robust against commonly-used image processing operations, such as additive noise, luminance change, contrast adjustment, color balance, and JPEG compression. At the same time, they achieve good invisibility, fragility, and image tamper detection and localization with less computational cost. 相似文献
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研究聚合物薄膜纳米尺度的动力学特性对于高性能材料的制备具有重要的意义.本文利用尼罗红单分子作为光学探针吸附在聚丙烯酸甲酯(PMA)聚合物链上,研究该聚合物薄膜的动力学特性.通过单分子散焦宽场荧光成像显微镜技术测量了单分子随PMA聚合物链转动弛豫的三维再取向特性,当环境温度高于PMA的玻璃点温度19 K时,发现处于PMA聚合物薄膜中的单分子光学探针的转动态和非转动态的持续时间概率密度服从指数截止的幂律分布.研究结果表明该温度下PMA聚合物薄膜的纳米环境动力学仍存在空间和时间异构性. 相似文献
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Modeling phase decomposition and patterning in binary alloy systems subjected to neutron irradiation
We study processes of phase decomposition and patterning in a model of a binary alloy system subjected to sustained irradiation. We exploit the reaction rate theory and generalize the Darken approach of vacancy diffusion to describe generation, recombination, annihilation and spatial interaction of point defects. It is shown that an increase in the defect production rate phase, decomposition processes are replaced by disordering and patterning with vacancy clusters' formation. At elevated damage rates, both phase separation and patterning are accompanied by pattern selection processes. In the framework of numerical simulations, dynamics of phase decomposition and vacancy clusters formation is studied in detail. A change in the morphology of vacancy clusters during irradiation and their statistical properties are discussed. 相似文献
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采用水电极介质阻挡放电装置,在大气压氩气放电中,在低电压区和高电压区,观察到两种具有不同时空特性的六边形点阵发光斑图.低压区的六边形斑图空间波长及单元直径均小于高压区的六边形斑图的相应量;高压区的六边形斑图具有较亮的背景,而低压区的六边形则没有.通过对两种六边形发光斑图进行时空动力学测量,发现低压区六边形是由两套长方形子点阵嵌套而成的,且这两套子点阵的出现顺序交替变化;而高压区六边形点阵斑图的所有单元基本是同步的.最后讨论了壁电荷对斑图的时空动力学行为的影响.
关键词:
介质阻挡放电
六边形斑图
时间相关性 相似文献
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The distribution of ordinal patterns in time series has been found to reflect important qualitative features of the underlying system dynamics. Abrupt changes in the dynamics typically result in clearly visible differences between the distributions before and after the break. Recurring dynamical regimes can be discovered by classifying the distributions in different parts of the time series. This paper discusses two algorithms which exploit the relation between ordinal pattern distributions and system dynamics for the segmentation and classification of time series. The first algorithm employs a kernel-based statistic, the Maximum Mean Discrepancy of ordinal pattern distributions, to detect and locate change points in the time series. The second algorithm uses clustering of the ordinal pattern distributions to classify time series segments with similar dynamics. The methodology is applied to various real-life time series from physiology and economics. 相似文献
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Kapilanjan Krishan 《Pramana》2008,70(4):669-678
We develop two measures to characterize the geometry of patterns exhibited by the state of spiral defect chaos, a weakly turbulent
regime of Rayleigh-Bénard convection. These describe the packing of contiguous stripes within the pattern by quantifying their
length and nearest-neighbor distributions. The distributions evolve towards a unique distribution with increasing Rayleigh
number that suggests power-law scaling for the dynamics in the limit of infinite system size. The techniques are generally
applicable to patterns that are reducible to a binary representation.
相似文献
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识别非周期神经放电节律是混沌还是随机一直是一个重要的科学问题. 在神经起步点实验中发现了一类介于周期k和周期k+1(k=1,2)节律之间非周期自发放电节律, 其行为是长串的周期k簇和周期k+1簇的交替. 确定性理论模型Chay模型展示出了周期k和周期k+1节律的共存行为. 噪声在共存区诱发出了与实验结果类似的非周期节律, 说明该类节律是噪声引起的两类簇的跃迁. 非线性预报及其回归映射揭示该节律具有确定性机理; 将两类簇分别转换为0和1得到一个二进制序列, 对该序列进行概率分析获得了两类簇跃迁的随机机理. 这不仅说明该节律是具有确定性结构的随机节律而不是混沌, 还为深入识别现实神经系统的混沌和随机节律提供了典型示例和有效方法. 相似文献
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Recently various models for spatially chaotic structures have been proposed. We study the diffraction patterns produced by plane chaotic waves incident on one-dimensional chaotic point scatterers. The spacing between the scatterers and the dynamics of the incident wave are given by a logistic map or standard map. We find a sharp diffraction peak when the incident dynamics is produced by the same map as the structure of the spatial configuration. The diffraction pattern is symmetric about the incident direction only if the map dynamics is invertible. Diffraction patterns with chaotic incident waves have a large signal-to-noise ratio and are well suited for pattern identification. We discuss possible applications to the scattering of microwaves from aperiodic structures. (c) 1997 American Institute of Physics. 相似文献
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Based on forbidden patterns in symbolic dynamics, symbolic
subsequences are classified and relations between forbidden patterns, correlation
dimensions and complexity measures are studied. A complexity measure
approach is proposed in order to separate deterministic (usually chaotic) series
from random ones and measure the complexities of different dynamic systems.
The complexity is related to the correlation dimensions, and the algorithm is simple and
suitable for time series with noise. In the paper, the complexity measure method is used
to study dynamic systems of the Logistic map and the H\'enon map with multi-parameters. 相似文献
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Yuye Li Bing Jia Xiaoli Zhang Yongxia Yang 《The European physical journal. Special topics》2018,227(7-9):821-835
It has been identified that autapse can modulate dynamics of single neurons and spatial patterns of neuronal networks. In the present paper, based on the results that autapse can induce type II excitability changed to type I excitability, spatial pattern transitions are simulated in a two-dimensional neuronal network composed of excitatory coupled neurons with autapse which can induce excitability transition. Different spatial patterns including random-like pattern, irregular wave, regular wave, and nearly synchronous behavior are simulated with increasing the percentage (σ) of neurons with type I excitability. When noise is introduced, spiral waves are induced. By calculating signal-to-noise ratio from the spatial structure function and the mean firing probability of neurons, regular waves and spiral waves exhibit optimal spatial correlation, implying the occurrence of spatial coherence resonance phenomenon. The changes of mean firing probability of neurons show that different firing frequency between type I excitability and type II excitability may be an important factor to modulate the spatial patterns. The results are helpful to understand the spatial patterns including spiral waves observed in the biological experiment on the rat cortex perfused with drugs which can induce single neurons changed from type II excitability to type I excitability and block the inhibitory couplings between neurons. The excitability transition, absence of inhibitory coupling, noise as well as the autapse are important factors to modulate the spatial patterns including spiral waves. 相似文献
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Ryszard Piasecki 《Physica A》2008,387(22):5333-5341
The statistical measure of spatial inhomogeneity for n points placed in χ cells each of size k×k is generalized to incorporate finite size objects like black pixels for binary patterns of size L×L. As a function of length scale k, the measure is modified in such a way that it relates to the smallest realizable value for each considered scale. To overcome the limitation of pattern partitions to scales with k being integer divisors of L, we use a sliding cell-sampling approach. For given patterns, particularly in the case of clusters polydispersed in size, the comparison between the statistical measure and the entropic one reveals differences in detection of the first peak while at other scales they well correlate. The universality of the two measures allows both a hidden periodicity traces and attributes of planar quasi-crystals to be explored. 相似文献