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Periodic Fluctuation (periodic + fluctuation)
Selected AbstractsSpectral decomposition of periodic ground water fluctuation in a coastal aquiferHYDROLOGICAL PROCESSES, Issue 12 2008David Ching-Fang Shih Abstract This research accomplished by the descriptive statistics and spectral analysis of six kinds of time series data gives a complete assessment of periodic fluctuation in significant constituents for the Huakang Shan earthquake monitoring site. Spectral analysis and bandpass filtering techniques are demonstrated to accurately analyse the significant component. Variation in relative ground water heads with a period of 12·6 h is found to be highly related to seawater level fluctuation. Time lag is estimated about 3·78 h. Based on these phenomena, the coastal aquifer formed in an unconsolidated formation can be affected by the nearby seawater body for the semi-diurnal component. Fluctuation in piezometric heads is found to correspond at a rate of 1000 m h,1. Atmospheric pressure presents the significant components at periods of 10·8 h and 7·2 h in a quite different type, compared to relative ground water head and seawater level. Copyright © 2008 John Wiley & Sons, Ltd. [source] Morphological analysis of the tiger stripe on injection molding of polypropylene/ethylene-propylene rubber/talc blends dependent on based polypropylene designJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Koki Hirano Abstract Tiger stripe of injection molding of polypropylene (PP)/elastomer/talc blends was analyzed in terms of the morphology of the dispersed phase comprising elastomer components by using gloss and scanning electron microscopy (SEM). In addition, the contribution of the polymer design of PP, i.e., industrial block-type grade consisting of a homo-PP portion as the matrix and an ethylene propylene random copolymer portion as the domain is discussed. Local gloss measurement of the injected specimen along with the flow direction of the molten blends indicates a periodic fluctuation repeating higher and lower degrees of gloss, corresponding to the period of glossy and cloudy portions of the tiger stripe, respectively. These local gloss degrees are highly dependent on the morphologies of the dispersed phases near the surface layer of the injected specimen. The gloss increases when the ratio long axis (L) and diameter (D), L/D, of the dispersed phase are increased, and the gloss decreases when the L/D is decreased. Increasing the intrinsic viscosity of the ethylene-propylene rubber portion of the PP is an effective design factor for restricting the deformation against shear strain during injection process by giving the dispersed phases high elasticity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 192,199, 2007 [source] Circumferential strain in the wall of the common carotid artery: Comparing displacement-encoded and cine MRI in volunteersMAGNETIC RESONANCE IN MEDICINE, Issue 1 2008Alexander P. Lin The walls of conduit arteries undergo cyclic stretching from the periodic fluctuation of arterial pressure. Atherosclerotic lesions have been shown to localize to regions of excessive stretching of the arterial wall. We employed a displacement encoding with stimulated echoes (DENSE) sequence to image the motion of the common carotid artery wall and map the two-dimensional (2D) circumferential strain. The sequence utilizes a fully-balanced steady-state free-precession (SSFP) readout with 0.60 mm in-plane resolution. Preliminary results in volunteers at 1.5T (N = 4) and 3.0T (N = 17) are compared to measurements of the lumen circumference from cine images. The agreement between the two independent measurements at both field strengths (P , 0.001) supports the use of DENSE as a means to map the pulsatile strain in the carotid artery wall. Magn Reson Med 60:8,13, 2008. © 2008 Wiley-Liss, Inc. [source] Thermal Characteristics of the Embankment with Crushed Rock Side Slope to Mitigate Thaw Settlement Hazards of the Qinghai-Tibet RailwayACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 5 2009Guoyu LI Abstract: Permafrost (perennially frozen ground) appears widely in the Golmud-Lhasa section of the Qinghai-Tibet railway and is characterized by high ground temperature (,,1°C) and massive ground ice. Under the scenarios of global warming and human activity, the permafrost under the railway will gradually thaw and the massive ground ice will slowly melt, resulting in some thaw settlement hazards, which mainly include longitudinal and lateral cracks, and slope failure. The crushed rock layer has a thermal semiconductor effect under the periodic fluctuation of natural air. It can be used to lower the temperature of the underlying permafrost along the Qinghai-Tibet railway, and mitigate the thaw settlement hazards of the subgrade. In the present paper, the daily and annual changes in the thermal characteristics of the embankment with crushed rock side slope (ECRSS) were quantitatively simulated using the numerical method to study the cooling effect of the crushed rock layer and its mitigative ability. The results showed that the ECRSS absorbed some heat in the daytime in summer, but part of it was released at night, which accounted for approximately 20% of that absorbed. Within a year, it removed more heat from the railway subgrade in winter than that absorbed in summer. It can store approximately 20% of the "cold" energy in subgrade. Therefore, ECRSS is a better measure to mitigate thaw settlement hazards to the railway. [source] Strain-driven homogenization of inelastic microstructures and composites based on an incremental variational formulationINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2002Christian Miehe Abstract The paper investigates computational procedures for the treatment of a homogenized macro-continuum with locally attached micro-structures of inelastic constituents undergoing small strains. The point of departure is a general internal variable formulation that determines the inelastic response of the constituents of a typical micro-structure as a generalized standard medium in terms of an energy storage and a dissipation function. Consistent with this type of inelasticity we develop a new incremental variational formulation of the local constitutive response where a quasi-hyperelastic micro-stress potential is obtained from a local minimization problem with respect to the internal variables. It is shown that this local minimization problem determines the internal state of the material for finite increments of time. We specify the local variational formulation for a setting of smooth single-surface inelasticity and discuss its numerical solution based on a time discretization of the internal variables. The existence of the quasi-hyperelastic stress potential allows the extension of homogenization approaches of elasticity to the incremental setting of inelasticity. Focusing on macro-strain-driven micro-structures, we develop a new incremental variational formulation of the global homogenization problem where a quasi-hyperelastic macro-stress potential is obtained from a global minimization problem with respect to the fine-scale displacement fluctuation field. It is shown that this global minimization problem determines the state of the micro-structure for finite increments of time. We consider three different settings of the global variational problem for prescribed linear displacements, periodic fluctuations and constant stresses on the boundary of the micro-structure and discuss their numerical solutions based on a spatial discretization of the fine-scale displacement fluctuation field. The performance of the proposed methods is demonstrated for the model problem of von Mises-type elasto-visco-plasticity of the constituents and applied to a comparative study of micro-to-macro transitions of inelastic composites. Copyright © 2002 John Wiley & Sons, Ltd. [source] ORDINARY LEAST SQUARES LEARNING AND NONLINEARITIES IN MACROECONOMICSJOURNAL OF ECONOMIC SURVEYS, Issue 1 2010Orlando Gomes Abstract The paper reviews the literature on adaptive learning in macroeconomic settings where the formation of expectations is particularly relevant. Special attention will be given to simple two-period overlapping generations models with a unique fixed point perfect foresight equilibrium; in this kind of scenario, eventual long-term periodic and a-periodic cycles are exclusively the result of the process of learning. The outcome that high rates of money growth have a potentially destabilizing effect generating periodic fluctuations and chaos is emphasized. The persistence of systematic forecast errors in a scenario where agents are supposed to act rationally is relevant in this context and it will be thoroughly discussed resorting to the notions of self-fulfilling mistakes, consistent expectations equilibria and beliefs equilibria. [source] Estimation of the Dominating Frequency for Stationary and Nonstationary Fractional Autoregressive ModelsJOURNAL OF TIME SERIES ANALYSIS, Issue 5 2000Jan Beran This paper was motivated by the investigation of certain physiological series for premature infants. The question was whether the series exhibit periodic fluctuations with a certain dominating period. The observed series are nonstationary and/or have long-range dependence. The assumed model is a Gaussian process Xt whose mth difference Yt = (1 ,B)mXt is stationary with a spectral density f that may have a pole (or a zero) at the origin. the problem addressed in this paper is the estimation of the frequency ,max where f achieves the largest local maximum in the open interval (0, ,). The process Xt is assumed to belong to a class of parametric models, characterized by a parameter vector ,, defined in Beran (1995). An estimator of ,max is proposed and its asymptotic distribution is derived, with , being estimated by maximum likelihood. In particular, m and a fractional differencing parameter that models long memory are estimated from the data. Model choice is also incorporated. Thus, within the proposed framework, a data driven procedure is obtained that can be applied in situations where the primary interest is in estimating a dominating frequency. A simulation study illustrates the finite sample properties of the method. In particular, for short series, estimation of ,max is difficult, if the local maximum occurs close to the origin. The results are illustrated by two of the data examples that motivated this research. [source] The circatidal rhythm of the estuarine gastropod Hydrobia ulvae (Gastropoda: Hydrobiidae)BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2010SÓNIA VIEIRA Intertidal animals display a suite of cyclic behaviours that evolved as adaptations to the predictable cycle of inundation and exposure. In estuarine habitats, mud snails from the genus Hydrobia are among the most abundant grazers, and have received considerable attention with respect to the behavioural mechanisms mediating locomotion, dispersal, and feeding, although the nature of the control of these processes has remained elusive. In particular, it is not clear whether endogenous activity patterns are related to periodic changes of microphytobenthos biomass at the sediment surface, or whether they are timed to the tidal cycle at all. In the present study, we address the crawling activity of Hydrobia ulvae under constant conditions, as well as the effects of individual size and previous short-term exposure to tides of different range, by recording immersed individual snails under constant dark conditions. We show that the species displays an overt circatidal pattern of crawling, with activity peaks around high water, and that the start of inundation may act as an entrainment agent of the rhythm. Moreover, the results obtained indicate that smaller snails display higher levels of activity, although neither the size nor previous in situ influence of tidal range has an effect on the period and on the amplitude of the rhythm. These findings suggest that fluctuations of microphytobenthos biomass are not a sufficiently strong selective pressure to have shaped locomotor activity in H. ulvae. Moreover, feeding of H. ulvae should take place mostly during high water and be independent of periodic fluctuations of microphytobenthos biomass at the surface of the sediment. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 439,450. [source] | ||||||||||