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Damian G. Stephen Wen-Hao Hsu Diana Young Elliot L. Saltzman Kenneth G. Holt Dava J. Newman Marc Weinberg Robert J. Wood Radhika Nagpal Eugene C. Goldfield 《Chaos, solitons, and fractals》2012,45(9-10):1201-1219
Previous research has considered infant spontaneous kicking as a form of exploration. According to this view, spontaneous kicking provides information about motor degrees of freedom and may shape multijoint coordinations for more complex movement patterns such as gait. Recent work has demonstrated that multifractal, multiplicative fluctuations in exploratory movements index energy flows underlying perceptual-motor information. If infant spontaneous kicking is exploratory and occasions an upstream flow of information from the motor periphery, we expected not only that multiplicativity of fluctuations at the hip should promote multiplicativity of fluctuations at more distal joints (i.e., reflecting downstream effects of neural control) but also that multiplicativity at more distal joints should promote multiplicativity at the hip. Multifractal analysis demonstrated that infant spontaneous kicking in four typically developing infants for evidence of multiplicative fluctuations in multiple joint angles along the leg (i.e., hip, knee, and ankle) exhibited multiplicativity. Vector autoregressive modeling demonstrated that only one leg exhibited downstream effects but that both legs exhibited upstream effects. These results confirm the exploratory aspect of infant spontaneous kicking and suggest chaotic dynamics in motor coordination. They also resonate with existing models of chaos-controlled robotics and noise-based interventions for rehabilitating motor coordination in atypically developing patients. 相似文献
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E. Kalfon‐Cohen H. Harel M. Saadon‐Yechezkia K. Timna T. Zhidkov A. Weinberg G. Marom 《先进技术聚合物》2010,21(12):904-910
Polyacrylonitrile (PAN) textile fibers, in the form of fabrics or threads, were compacted in a heat‐pressure cycle and crosslinked by nitrile polymerization to form a thermoset composite article, whose mechanical properties were found to surpass those of commercially available polypropylene (PP) fiber counterparts. Additional advantages of the PAN compacts included their significant thermal stability (>300°C, i.e., twice that of PP) in addition to their flame retardancy, thereby rendering them as the structural material of choice for applications where heat protection and fire resistance are essential. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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A complete classification of the individual types of singular points is given for irreducible real sextic curves. This classification
is derived by using the computer algebra system Maple. There are 191 types of singular points for real irreducible sextic
curves. We clarify that the classification is based on computing just enough of the Puiseux expansion to separate the branches.
A significant portion of the proof consists of a sequence of large symbolic computations that can be done nicely using Maple. 相似文献
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Solder materials occupy many of fields for technical application (e.g. solder joints in automotive control units or in microelectronic packages). They are required to provide electrical and mechanical connections between different components. Due to their wide range of applications solder alloys are subject to a great variety of microstructural changes such as phase separation and coarsening processes. The micromorphological variations influence strength and life expectation of solder materials, in particular, in very small components such as solder joints in microelectronic packages. In order to analyze the microstructural evolution with a diffusion theory of heterogeneous solid mixtures we employ an extended Cahn-Hilliard phase field model. The diffusion equation under consideration constitutes a partial differential equation involving spatial derivatives of fourth order. Thus, the variational formulation of the problem requires approximation functions which are piecewise smooth and globally C1-continuous. In our contribution we fulfil the continuity requirement by means of rational B-spline finite element basis functions. To illustrate the versatility of this approach numerical simulations of phase decomposition and coarsening controlled by diffusion and by mechanical loading are discussed and compared with experimental results. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Spectroscopic measurements were made of three high CaO content Nd3+-doped glasses, two of which could only be prepared via splat cooling. Cross-section determinations of the Nd3+ 1.06 μm lasting line were performed for each of these glasses via several methods. The use of absorption spectroscopy and the Judd-Ofelt crystal field calculations indicated that the lasting line cross-section, viewed as a function of CaO content in these glasses, possesses a maximum. Fluorescent decay-time measurements, however, suggested a monotonically increasing cross-section with increasing CaO concentration in the base glass composition. Non-radiative decay processes could be responsible for the discrepancy in these results. 相似文献