1,720,962 research outputs found
On chaotic graphs: A different approach for characterizing aperiodic dynamics
No full textFractal worlds with limited connectivity are the topological result of growing graphs from
chaotic series. We show how this model presents original characteristics which cannot be
detected by means of the standard network descriptors. In detail, intrinsic inaccessibility
to the fully connected configuration is demonstrated to be a universal feature associated
with this family of graphs and strictly related to the fractality of a specific ``chaotic source''.
Here we discuss the potential of our model to be a generator of fractal graphs and also a
self-consistent tool for differentiating chaotic dynamics from stochastic processes
Butterfly effect in a chemical oscillator
No full textThe strong sensitivity of aperiodic dynamics to initial conditions is one of the fingerprinting features of chaotic systems. While this dependence can be directly verified by means of numerical approaches, it is quite elusive and difficult to be isolated in real experimental systems. In this paper, we discuss a didactic and self-consistent method to show the divergent behaviour between two infinitesimally different solutions of the famous Belousov–Zhabotinsky oscillator simultaneously undergoing a transition to a chaotic regime. Experimental data are also used to give an intuitive visualization of the essential meaning of a Lyapunov exponent, which allows for a more quantitative characterization of the chaotic transient
On the Origin of Chaos in the Belousov-Zhabotinsky Reaction in Closed and Unstirred Reactors
No full textWe investigate the origin of deterministic chaos in the Belousov-Zhabotinsky (BZ) reaction carried out in closed and unstirred reactors (CURs). In detail, we develop a model on the idea that hydrodynamic instabilities play a driving role in the transition to chaotic dynamics. A set of partial differential equations were derived by coupling the two variable Oregonator-diffusion system to the Navier-Stokes equations. This approach allows us to shed light on the correlation between chemical oscillations and spatial-temporal dynamics. In particular, numerical solutions to the corresponding reaction-diffusion-convection (RDC) problem show that natural convection can change the evolution of the concentration distribution as well as oscillation patterns. The results suggest a new way of perceiving the BZ reaction when it is conducted in CURs. In conflict with the common experience, chemical oscillations are no longer a mere chemical process. Within this framework the evolution of all dynamical observables are demonstrated to converge to the regime imposed by the RDC coupling: chemical and spatial-temporal chaos are genuine manifestations of the same phenomenon
Chaotic dynamics in an unstirred ferroin catalyzed Belousov-Zhabotinsky reaction
No full textThe Belousov–Zhabotinsky (BZ) reaction is the best known example of far from equilibrium self-organizing
chemical reaction. Among the many dynamical behaviors that this reaction can exhibit, spatiotemporal
chaos attracted particular interest, both for the ferroin and cerium catalyzed systems. In recent
years transient chaos was found in the cerium catalyzed BZ reaction, when conducted in batch and
unstirred reactors. It was established that the chaotic oscillations, originated by the coupling among
chemical kinetics and transport phenomena, appeared and disappeared following a Ruelle–Takens–
Newhouse scenario. In this Letter, we show results about the ferroin catalyzed system conducted in batch
and unstirred reactors. An aperiodic transient regime was detected and we show that this is a genuine
manifestation of spatio-temporal chaos
Evidence for age-structured depensation effect in fragmented plant populations: The case of the Mediterranean endemic Anchusa sardoa (Boraginaceae)
No full textDepensation in a population growth rate, well-known as Allee effect, has dramatic implications for the dynamics and conservation of small or sparse populations, as it can drive low-density populations to extinction when their demographic size is below a critical threshold. Although rarely detected, depensation effects are believed to be common in nature. Here we present experimental evidence for Allee effect in one Mediterranean endemic plant: Anchusa sardoa. Depensation in the population growth rate is demonstrated through a density-based approach by showing the fingerprinting relationship which ties the population density to its per capita growth rate (. pgr) during specific stages of the plant life-cycle. The pgr-density plots derived from observational data qualitatively compare with a general 2nd order polynomial function which features one of the peculiar trends underlying an Allee mechanism. We found strong evidence for depensation in the seedling and sapling classes, whereas no-depensation effect could be clearly observed in the adult classes. We also point out a characteristic demographic structure of A. sardoa (i.e. number of juveniles. >. number of adults) which reflects a not common life strategy with respect to Mediterranean endemic plants. By combining dynamical and demographic information, the results of this study suggest a possible scenario by which A. sardoa population could go extinct, and are discussed in the context of the increasing mass tourism in Mediterranean coastal environments
Understanding oscillatory phenomena in molecular hydrogen generation via sodium borohydride hydrolysis
No full textChemical Control of Hydrodynamic Instabilities in Partially Miscible Two-Layer Systems
No full textHydrodynamic instabilities at the interface between two partially miscible liquids impact numerous applications, including CO2 sequestration in saline aquifers. We introduce here a new laboratory-scale model system on which buoyancy- and Marangoni-driven convective instabilities of such partially miscible two-layer systems can easily be studied. This system consists of the stratification of a pure alkyl formate on top of a denser aqueous solution in the gravitational field. A rich spectrum of convective dynamics is obtained upon partial dissolution of the ester into the water followed by its hydrolysis. The properties of the convective patterns are controlled by the miscibility of the ester in water, the feedback of the dissolved species on its own miscibility, as well as the reactivity of given chemicals in the aqueous solution with the solubilized ester
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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