Search results for "RCA"

Dzīvsudraba akumulācija asara Perca fluviatilis audos Rīgas līča piekrastē

2019

Dzīvsudraba akumulācija asara Perca fluviatilis audos Rīgas līča piekrastē. Darbā tika kvantitatīvi noteikts Hg saturs asara audos noskaidrojot Hg atkarību no asaru izmēra, masas, vecuma un sezonas, kā arī izpētīta barības bāzes ietekme uz Hg saturu asaros. Hg izpēte ir aktuāla, jo ūdens ekosistēmās Hg biomagnificējas augstāko koncentrāciju sasniedzot zivīs, pēc to veselības ir iespējams spriest par ūdens vides ekoloģisko stāvokli. Samazinot Hg slodzes, tā saturs jūras ūdenī ir zems, bieži zem noteikšanas robežas, tomēr atsevišķām zivju sugām novērota augsta Hg bioakumulācija. Eksperimentālajā daļā tika ievākti 642 asari 8-30 cm. Tika konstatēts, ka visi paraugi bija piesārņoti ar Hg diapaz…

Europa en la hoguera

1989

La industria exógena en la periferia occidental del área metropolitana de Valencia (A.M.V.)

1991

En el tejido industrial de las comarcas occidentales del A. M. V., el Camp de Túria y la Hoya de Buñol-Chiva, hallamos una dualismo respecto al origen de los establecimientos industriales ubicados en ambas comarcas: la industria autóctona y la actividad fabril foránea. Tras analizar los factores que condicionan la localización de estas industrias exógenas definiremos qué rasgos las caracterizan así como el nivel de integración con respecto al espacio que las acoge. En la industria foránea hemos diferenciado aquellos establecimientos industriales que se han instalado tras un traslado de aquéllos otros de nueva creación producto de la iniciativa foránea

A Seven Mode Truncation of the Kolmogorov Flow with Drag: Analysis and Control

2009

The transition from laminar to chaotic motions in a viscous °uid °ow is in- vestigated by analyzing a seven dimensional dynamical system obtained by a truncation of the Fourier modes for the Kolmogorov °ow with drag friction. An- alytical expressions of the Hopf bifurcation curves are obtained and a sequence of period doubling bifurcations are numerically observed as the Reynolds num- ber is increased for ¯xed values of the drag parameter. An adaptive stabilization of the system trajectories to an equilibrium point or to a periodic orbit is ob- tained through a model reference approach which makes the control global. Finally, the e®ectiveness of this control strategy is numerically illustra…

Remarks on the economic interpretation of Hopf bifurcations

1999

Abstract The Hopf bifurcation theorem has become a frequently used tool in the study of nonlinear dynamical economic systems. In this paper, it is shown that phenomena like multiple limit cycles, hysteresis loops and catastrophic transitions may possibly accompany a Hopf bifurcation. The theoretical argument is illustrated in Foley's liquidity cost–business cycle model.

Coexistence of periods in a bifurcation

2012

Abstract A particular type of order-to-chaos transition mediated by an infinite set of coexisting neutrally stable limit cycles of different periods is studied in the Varley–Gradwell–Hassell population model. We prove by an algebraic method that this kind of transition can only happen for a particular bifurcation parameter value. Previous results on the structure of the attractor at the transition point are here simplified and extended.

Complex Dynamics in a Harmonically Excited Lennard-Jones Oscillator: Microcantilever-Sample Interaction in Scanning Probe Microscopes1

1998

In this paper we model the microcantilever-sample interaction in an atomic force microscope (AFM) via a Lennard-Jones potential and consider the dynamical behavior of a harmonically forced system. Using nonlinear analysis techniques on attracting limit sets, we numerically verify the presence of chaotic invariant sets. The chaotic behavior appears to be generated via a cascade of period doubling, whose occurrence has been studied as a function of the system parameters. As expected, the chaotic attractors are obtained for values of parameters predicted by Melnikov theory. Moreover, the numerical analysis can be fruitfully employed to analyze the region of the parameter space where no theoret…

A SUBCRITICAL BIFURCATION FOR A NONLINEAR REACTION–DIFFUSION SYSTEM

2010

In this paper the mechanism of pattern formation for a reaction-diffusion system with nonlinear diffusion terms is investigated. Through a linear stability analysis we show that the cross-diffusion term allows the pattern formation. To predict the form and the amplitude of the pattern we perform a weakly nonlinear analysis. In the supercritical case the Stuart-Landau equation is found, which rules the evolution of the amplitude of the most unstable mode. With the increasing distance from the bifurcation value of the cross-diffusion parameter, the weakly nonlinear analysis fails and a Fourier–Galerkin approach is adopted. In the subcritical case the weakly nonlinear analysis must be pushed u…

Transitions in a stratified Kolmogorov flow

2016

We study the Kolmogorov flow with weak stratification. We consider a stabilizing uniform temperature gradient and examine the transitions leading the flow to chaotic states. By solving the equations numerically we construct the bifurcation diagram describing how the Kolmogorov flow, through a sequence of transitions, passes from its laminar solution toward weakly chaotic states. We consider the case when the Richardson number (measure of the intensity of the temperature gradient) is $$Ri=10^{-5}$$ , and restrict our analysis to the range $$0<Re<30$$ . The effect of the stabilizing temperature is to shift bifurcation points and to reduce the region of existence of stable drifting states. The…

The period function of reversible quadratic centers

2006

Abstract In this paper we investigate the bifurcation diagram of the period function associated to a family of reversible quadratic centers, namely the dehomogenized Loud's systems. The local bifurcation diagram of the period function at the center is fully understood using the results of Chicone and Jacobs [C. Chicone, M. Jacobs, Bifurcation of critical periods for plane vector fields, Trans. Amer. Math. Soc. 312 (1989) 433–486]. Most of the present paper deals with the local bifurcation diagram at the polycycle that bounds the period annulus of the center. The techniques that we use here are different from the ones in [C. Chicone, M. Jacobs, Bifurcation of critical periods for plane vecto…