scholarly journals The stripping process can be slow: Part I

2018 ◽  
Vol 53 (1) ◽  
pp. 76-139 ◽  
Author(s):  
Pu Gao ◽  
Michael Molloy
Keyword(s):  
2003 ◽  
Vol 13 (01) ◽  
pp. 47-53 ◽  
Author(s):  
ANKE MEYER-BÄSE ◽  
SERGEI S. PILYUGIN

The dynamics of cortical cognitive maps developed by self–organization must include the aspects of long and short–term memory. The behavior of the network is such characterized by an equation of neural activity as a fast phenomenon and an equation of synaptic modification as a slow part of the neural biologically relevant system. We present new stability conditions for analyzing the dynamics of a biological relevant system with different time scales based on the theory of flow invariance. We prove the existence and uniqueness of the equilibrium, and give a quadratic–type Lyapunov function for the flow of a competitive neural system with fast and slow dynamic variables and thus prove the global stability of the equilibrium point.


1995 ◽  
Vol 03 (02) ◽  
pp. 591-602 ◽  
Author(s):  
PIERRE AUGER ◽  
JEAN-CHRISTOPHE POGGIALE

The aim of this work is to show that at the population level, emerging properties may occur as a result of the coupling between the fast micro-dynamics and the slow macrodynamics. We studied a prey-predator system with different time scales in a heterogeneous environment. A fast time scale is associated to the migration process on spatial patches and a slow time scale is associated to the growth and the interactions between the species. Preys go on the spatial patches on which some resources are located and can be caught by the predators on them. The efficiency of the predators to catch preys is patch-dependent. Preys can be more easily caught on some spatial patches than others. Perturbation theory is used in order to aggregate the initial system of ordinary differential equations for the patch sub-populations into a macro-system of two differential equations governing the total populations. Firstly, we study the case of a linear process of migration for which the aggregated system is formally identical to the slow part of the full system. Then, we study an example of a nonlinear process of migration. We show that under these conditions emerging properties appear at the population level.


2004 ◽  
Vol 4 (1) ◽  
pp. 805-831 ◽  
Author(s):  
M. P. Sulzer

Abstract. We report the observation and analysis of ionization flashes associated with the decay of meteoroids (so-called head echos) detected by the Arecibo 430 MHz radar during regular ionospheric observations in the spring and autumn equinoxes. These two periods allow pointing well-above and nearly-into the ecliptic plane at dawn when the event rate maximizes. The observation of many thousands of events allows a statistical interpretation of the results, which show that there is a strong tendency for the observed meteoroids to come from the apex as has been previously reported (Chau and Woodman, 2003). The velocity distributions agree with Janches et al. (2003) when they are directly comparable, but the azimuth scan used in these observations allows a new perspective. We have constructed a simple statistical model which takes meteor velocities as input and gives radar line of sight velocities as output. The intent is to explain the fastest part of the velocity distribution. Since the speeds interpreted from the measurements are distributed fairly narrowly about nearly 60 km/s−1, double the speed of the earth in its orbit, the obvious interpretation is that many of the meteoroids seen by the Arecibo radar are moving in orbits about the sun with similar parameters as the earth, but in the retrograde direction. However, some aspects of the measured velocity distributions suggest that this is not a complete description even for the fast part of the distribution, and it certainly says nothing about the slow part first described in Janches et al. (2003). Furthermore, we cannot conclude anything about the entire dust population since there are probably selection effects that restrict the observations to a subset of the population.


Author(s):  
L. Fang ◽  
L. Shao ◽  
J. P. Bertoglio ◽  
L. P. Lu ◽  
Z. S. Zhang

In large eddy simulation of turbulent flow, because of the spatial filter, inhomogeneity and anisotropy affect the subgrid stress via the mean flow gradient. A method of evaluating the mean effects is to split the subgrid stress tensor into “rapid” and “slow” parts. This decomposition was introduced by Shao et al. (1999) and applied to A Priori tests of existing subgrid models in the case of a turbulent mixing layer. In the present work, the decomposition is extended to the case of a passive scalar in inhomogeneous turbulence. The contributions of rapid and slow subgrid scalar flux, both in the equations of scalar variance and scalar flux, are analyzed. A Priori numerical tests are performed in a turbulent Couette flow with a mean scalar gradient. Results are then used to evaluate the performances of different popular subgrid scalar models. It is shown that existing models can not well simulate the slow part and need to be improved. In order to improve the modeling, an extension of the model proposed by Cui et al. (2004) is introduced for the slow part, whereas the Scale-Similarity model is used reproduce the rapid part. Combining both models, A Priori tests lead to a better performance. However, the remaining problem is that none eddy-diffusion model can correctly represent the strong scalar dissipation near the wall. This problem will be addressed in future work.


2004 ◽  
Vol 28 (2) ◽  
pp. 160-182 ◽  
Author(s):  
Carlo Caballero

In "What the Sorcerer Said," Carolyn Abbate proposed a reading of Dukas's Sorcerer's Apprentice (1897) focused on the possibility of musical narration. The present essay shifts that focus to the question of the work's uncanniness and excess. In particular, where Abbate finds that the slow part of the epilogue resonates with her understanding of the work as an instance of narration, I begin with the final two measures of the work, which suddenly revert to the fast tempo of the central scherzo. These final measures, which Abbate does not mention, produce a disturbing regression that suggests another reanimation of the broom. This "third beginning" (thus heard in relation to the two preceding moments of animation) marks the broom as an agent of the uncanny (heimlich and unheimlich) in the sense identified by Freud in his essay "Das Unheimliche" (1919). Indeed, Dukas's work as a whole is haunted by motives Freud later identified as uncanny: magic, the omnipotence of thought, animism, and involuntary repetition. The essay works backward from the final noise of the piece into a re-reading founded on musical details such as the representation of the brooms through minor- and major-third dyads, the role of the pitch-class Ab, the structure of the central "reanimation scene," and the dismal interplay of motives associated with the broom and the Apprentice. Close attention is given to Dukas's immediate literary source, Goethe's ballad "Der Zauberlehrling," whose use of assonance and repeating rhymes provides subtle structural cues echoed in Dukas's music; I argue that the relationship between the ballad and Dukas's score is more homologous than Abbate was willing to allow. A number of revisions to Abbate's account also emerge through reference to a descriptive note on The Sorcerer's Apprentice left by Dukas in manuscript (Paris B.N.F. Musique MS 1037). Finally, I suggest that this "symphonic scherzo after Goethe" conflates literary and musical logics into a peculiar kind of fiction that points to the uncanny nature of narrative itself. Dukas's work ultimately engages the issue of mastery by focusing the listener's attention on the failure of authority and the contingency of animation or de-animation. In this Lacanian "overflow" into the unknown, the musical work goes beyond its literary sources, for the broom, not the human figure of the Apprentice, becomes the true protagonist of Dukas's work.


2014 ◽  
Vol 751 ◽  
Author(s):  
Marcel Oliver

AbstractThis paper demonstrates that the shallow water semigeostrophic equations arise from a degenerate second-order Hamilton principle of very special structure. The associated Euler–Lagrange operator factors into a fast and a slow first-order operator; restricting to the slow part yields the geostrophic momentum approximation as balanced dynamics. While semigeostrophic theory has been considered variationally before, this structure appears to be new. It leads to a straightforward derivation of the geostrophic momentum approximation and its associated potential vorticity law. Our observations further affirm, from a different point of view, the known difficulty in generalizing the semigeostrophic equations to the case of a spatially varying Coriolis parameter.


2015 ◽  
Vol Volume 20 - 2015 - Special... ◽  
Author(s):  
Ali Moussaoui ◽  
Nguyen Ngoc Doanh ◽  
Pierre Auger

International audience The purpose of this paper is to investigate the effects of conflicting tactics of resource acquisition on stage structured population dynamics. We present a population subdivided into two distinct stages (immature and mature). We assume that immature individual survival is density dependent. We also assume that mature individuals acquire resources required to survive and reproduce by using two contrasted behavioral tactics (hawk versus dove). Mature individual survival thus is assumed to depend on the average cost of fights while individual fecundity depends on the average gain in the competition to access the resource. Our model includes two parts: a fast part that describes the encounters and fights involves a game dynamic model based upon the replicator equations, and a slow part that describes the long-term effects of conflicting tactics on the population dynamics. The existence of two time scales let us investigate the complete system from a reduced one, which describes the dynamics of the total immature and mature densities at the slow time scale. Our analysis shows that an increase in resource value may decrease total population density, because it promotes individual (i.e. selfish) behavior. Our results may therefore find practical implications in animal conservation or biological control for instance. Le but de cet article est d'étudier les effets de comportements agressifs dans l'acquisition de ressources sur la dynamique d'une population structurée en deux classes d'âge. Nous considérons une population divisée en deux sous populations distinctes (immatures et adultes matures). Nous supposons que la survie individuelle de la population immature est densité dépendante. Nous supposons également que les individus matures sont en compétition pour acquérir les ressources nécessaires pour leur survie et leur reproduction. Les adultes utilisent deux tactiques comportementales (faucon et colombe). Lors de confrontations entre adultes, la survie d'un individu mature est supposée être affectée par le coût moyen des combats alors que la fécondité dépend du gain moyen obtenu en accédant à la ressource. Notre modèle comprend deux parties : une partie rapide qui décrit les rencontres et les combats basée sur les équations du réplicateur, et une partie lente qui décrit les effets à long terme des tactiques conflictuelles sur la dynamique de la population. L'existence de deux échelles de temps nous permet d'étudier le système complet à partir d'un système réduit, qui décrit la dynamique des densités totales des immatures et des adultes à l'échelle de temps lente. Notre analyse montre que le taux de croissance global de la population dépend de la valeur de la ressource et du coût des combats entre adultes. Nos résultats trouvent des implications pratiques dans la conservation des espèces et le contrôle biologique.


1982 ◽  
Vol 26 (01) ◽  
pp. 25-35
Author(s):  
Michael S. Triantafyllou

The preliminary design of mooring systems is formulated by separating the quasi-steady solution from the dynamic solution. A multiple time-scale expansion provides the appropriate equations, which are nonlinear for the quasi-steady part and linear space varying for the dynamic part. The fast dynamic solution consists of a fast varying and a slowly varying part with respect to space. An asymptotic solution is obtained by using the WKB method for the fast part, while an approximate expression is derived for the slow part. The resulting solution is simple and can be used to determine the dynamic behavior of complex systems, while permitting an extensive parametric search and the use of spectral techniques. This formulation leads to rational measures of the dynamic performance which, combined with cost considerations obtained from the static solution, permit an optimal selection of the system parameters. An example demonstrates the features of this methodology.


2008 ◽  
Vol 23 (3-4) ◽  
pp. 73-81 ◽  
Author(s):  
Yves Morel ◽  
Remy Baraille ◽  
Annick Pichon

2003 ◽  
Vol 3 (5) ◽  
pp. 311-320 ◽  
Author(s):  
S. Tinti ◽  
G. Pagnoni ◽  
A. Piatanesi

Abstract. The paper explores the potential of tsunami generation by pyroclastic flows travelling down the flank of the volcano Vesuvius that is found south of Naples in Italy. The eruption history of Vesuvius shows that it is characterised by large explosive eruptions of plinian or subplinian type during which large volume of pyroclastic flows can be produced. The most remarkable examples of such eruptions occurred in 79 AD and in 1631 and were catastrophic. Presently Vesuvius is in a repose time that, according to volcanologists, could be interrupted by a large eruption, and consequently proper plans of preparedness and emergency management have been devised by civil authorities based on a scenario envisaging a large eruption. Recently, numerical models of magma ascent and of eruptive column formation and collapse have been published for the Vesuvius volcano, and propagation of pyroclastic flows down the slope of the volcanic edifice up to the close shoreline have been computed. These flows can reach the sea in the Gulf of Naples: the denser slow part will enter the waters, while the lighter and faster part of the flow can travel on the water surface exerting a pressure on it. This paper studies the tsunami produced by the pressure pulse associated with the transit of the low-density phase of the pyroclastic flow on the sea surface by means of numerical simulations. The study is divided into two parts. First the hydrodynamic characteristics of the Gulf of Naples as regards the propagation of long waves are analysed by studying the waves radiating from a source that is a static initial depression of the sea level localised within the gulf. Then the tsunami produced by a pressure pulse moving from the Vesuvius toward the open sea is simulated: the forcing pulse features are derived from the recent studies on Vesuvian pyroclastic flows in the literature. The tsunami resulting from the computations is a perturbation involving the whole Gulf of Naples, but it is negligible outside, and persists within the gulf long after the transit of the excitation pulse. The size of the tsunami is modest. The largest calculated oscillations are found along the innermost coasts of the gulf at Naples and at Castellammare. The main conclusion of the study is that the light component of the pyroclastic flows produced by future large eruptions of Vesuvius are not expected to set up catastrophic tsunamis.


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