774 research outputs found
SPH simulations of the chemical evolution of bulges
We have implemented a chemical evolution model on the parallel AP3M+SPH DEVA
code which we use to perform high resolution simulations of spiral galaxy
formation. It includes feedback by SNII and SNIa using the Qij matrix
formalism. We also include a diffusion mechanism that spreads newly introduced
metals. The gas cooling rate depends on its specific composition. We study the
stellar populations of the resulting bulges finding a potential scenario where
they seem to be composed of two populations: an old, metal poor,
-enriched population, formed in a multiclump scenario at the beginning
of the simulation and a younger one, formed by slow accretion of satellites or
gas, possibly from the disk due to instabilities.Comment: 2 pages, 3 figures. Proceedings of IAUS 245 "Formation and Evolution
of Galaxy Bulges
A new fractional derivative without singular kernel: Application to the modelling of the steady heat flow
In this article we propose a new fractional derivative without singular
kernel. We consider the potential application for modeling the steady
heat-conduction problem. The analytical solution of the fractional-order heat
flow is also obtained by means of the Laplace transform.Comment: 1 figur
Large Scale Morphological Segregation in Optically Selected Galaxy Redshift Catalogs
We present the results of an exhaustive analysis of the morphological
segregation of galaxies in the CfA and SSRS catalogs through the scaling
formalism. Morphological segregation between ellipticals and spirals has been
detected at scales up to 15-20 h Mpc in the CfA catalog, and up to 20-30
h Mpc in the SSRS catalog. Moreover, it is present not only in the
densest areas of the galaxy distribution, but also in zones of moderate
density.Comment: 9 pages, (1 figure included), uuencode compressed Postscript,
(accepted for publication in ApJ Letters), FTUAM-93-2
Fractional Dynamics in Forest Fires
Every year forest fires consume large areas, being a major concern in many countries like
Australia, United States and Mediterranean Basin European Countries (e.g., Portugal,
Spain, Italy and Greece). Understanding patterns of such events, in terms of size and
spatiotemporal distributions, may help to take measures beforehand in view of possible
hazards and decide strategies of fire prevention, detection and suppression. Traditional
statistical tools have been used to study forest fires. Nevertheless, those tools might not be
able to capture the main features of fires complex dynamics and to model fire behaviour
[1]. Forest fires size-frequency distributions unveil long range correlations and long memory
characteristics, which are typical of fractional order systems [2]. Those complex correlations
are characterized by self-similarity and absence of characteristic length-scale, meaning
that forest fires exhibit power-law (PL) behaviour. Forest fires have also been proved to
exhibit time-clustering phenomena, with timescales of the order of few days [3]. In this
paper, we study forest fires in the perspective of dynamical systems and fractional calculus
(FC). Public domain forest fires catalogues, containing data of events occurred in Portugal,
in the period 1980 up to 2011, are considered. The data is analysed in an annual basis,
modelling the occurrences as sequences of Dirac impulses. The frequency spectra of such
signals are determined using Fourier transforms, and approximated through PL trendlines.
The PL parameters are then used to unveil the fractional-order dynamics characteristics
of the data. To complement the analysis, correlation indices are used to compare and find
possible relationships among the data. It is shown that the used approach can be useful to
expose hidden patterns not captured by traditional tools
Dynamical analysis of the global warming
Global warming is a major concern nowadays. Weather conditions are changing, and it seems
that human activity is one of the main causes. In fact, since the beginning of the industrial
revolution, the burning of fossil fuels has increased the nonnatural emissions of carbon dioxide to
the atmosphere. Carbon dioxide is a greenhouse gas that absorbs the infrared radiation produced
by the reflection of the sunlight on the Earth’s surface, trapping the heat in the atmosphere. Global
warming and the associated climate changes are being the subject of intensive research due to
their major impact on social, economic, and health aspects of human life. This paper studies the
global warming trend in the perspective of dynamical systems and fractional calculus, which is a
new standpoint in this context. Worldwide distributed meteorological stations and temperature
records for the last 100 years are analysed. It is shown that the application of Fourier transforms
and power law trend lines leads to an assertive representation of the global warming dynamics
and a simpler analysis of its characteristics
Symmetry in Complex Systems
Complex systems with symmetry arise in many fields, at various length scales, including financial markets, social, transportation, telecommunication and power grid networks, world and country economies, ecosystems, molecular dynamics, immunology, living organisms, computational systems, and celestial and continuum mechanics. The emergence of new order and structure in complex systems means symmetry breaking and transition from unstable to stable states. Modeling complexity attracted many researchers from different areas, dealing both with theoretical concepts and practical applications. This Special Issue seeks to fill the gap between the theory of symmetry-based dynamics and its application to model and analyze complex systems. This Special Issue focuses on the synergies between the theory of symmetry-based dynamics and its application to model and analyze complex systems. It includes 7 manuscripts addressing novel issues and specific topics that illustrate symmetry in complex systems. In the follow-up the selected manuscripts are presented in alphabetic order.info:eu-repo/semantics/publishedVersio
Dynamic analysis of earthquake phenomena by means of pseudo phase plane
This paper analyses earthquake data in the
perspective of dynamical systems and its Pseudo
Phase Plane representation. The seismic data is collected
from the Bulletin of the International Seismological
Centre. The geological events are characterised
by their magnitude and geographical location and described
by means of time series of sequences of Dirac
impulses. Fifty groups of data series are considered,
according to the Flinn-Engdahl seismic regions of
Earth. For each region, Pearson’s correlation coefficient
is used to find the optimal time delay for reconstructing
the Pseudo Phase Plane. The Pseudo Phase
Plane plots are then analysed and characterised
Analysis of temperature time-series: embedding dynamics into the MDS method
Global warming and the associated climate changes are being the subject of intensive
research due to their major impact on social, economic and health aspects of the human
life. Surface temperature time-series characterise Earth as a slow dynamics spatiotemporal
system, evidencing long memory behaviour, typical of fractional order systems. Such phenomena
are difficult to model and analyse, demanding for alternative approaches. This
paper studies the complex correlations between global temperature time-series using
the Multidimensional scaling (MDS) approach. MDS provides a graphical representation
of the pattern of climatic similarities between regions around the globe. The similarities
are quantified through two mathematical indices that correlate the monthly average temperatures
observed in meteorological stations, over a given period of time. Furthermore,
time dynamics is analysed by performing the MDS analysis over slices sampling the time
series. MDS generates maps describing the stations’ locus in the perspective that, if they
are perceived to be similar to each other, then they are placed on the map forming clusters.
We show that MDS provides an intuitive and useful visual representation of the complex
relationships that are present among temperature time-series, which are not perceived
on traditional geographic maps. Moreover, MDS avoids sensitivity to the irregular distribution
density of the meteorological stations
Root-locus practical sketching rules for fractional-order system
For integer-order systems, there are well-known practical rules for RL sketching. Nevertheless, these rules cannot be directly applied to fractional-order (FO) systems. Besides, the existing literature on this topic is scarce and exclusively focused on commensurate systems, usually expressed as the ratio of two noninteger polynomials. The practical rules derived for those do not apply to other symbolic expressions, namely, to transfer functions expressed as the ratio of FO zeros and poles. However, this is an important case as it is an extension of the classical integer-order problem usually addressed by control engineers. Extending the RL practical sketching rules to such FO systems will contribute to decrease the lack of intuition about the corresponding system dynamics. This paper generalises several RL practical sketching rules to transfer functions specified as the ratio of FO zeros and poles. The subject is presented in a didactic perspective, being the rules applied to several examples
- …