653,560 research outputs found
A new class of multiscale lattice cell (MLC) models for spatio-temporal evolutionary image representation
Spatio-temporal evolutionary (STE) images are a class of complex dynamical systems that evolve over both space and time. With increased interest in the investigation of nonlinear complex phenomena, especially spatio-temporal behaviour governed by evolutionary laws that are dependent
on both spatial and temporal dimensions, there has been an increased need to investigate model identification methods for this class of complex systems. Compared with pure temporal processes, the identification of spatio-temporal models from observed images is much more difficult and quite
challenging. Starting with an assumption that there is no apriori information about the true model but
only observed data are available, this study introduces a new class of multiscale lattice cell (MLC)
models to represent the rules of the associated spatio-temporal evolutionary system. An application to a chemical reaction exhibiting a spatio-temporal evolutionary behaviour, is investigated to demonstrate the new modelling framework
Angular momentum and mass evolution of contact binaries
Various scenarios of contact binary evolution have been proposed in the past,
giving hints of (sometimes contradictory) evolutionary sequence connecting
A-type and W-type systems. As the components of close detached binaries
approach each other and contact binaries are formed, following evolutionary
paths transform them into systems of two categories: A-type and W-type. The
systems evolve in a similar way but under slightly different circumstances. The
mass/energy transfer rate is different, leading to quite different evolutionary
results. An alternative scenario of evolution in contact is presented and
discussed, based on the observational data of over a hundred low-temperature
contact binaries. It results from the observed correlations among contact
binary physical and orbital parameters. Theoretical tracks are computed
assuming angular momentum loss from a system via stellar wind, accompanied by
mass transfer from an advanced evolutionary secondary to the main sequence
primary. Good agreement is seen between the tracks and the observed graphs.
Independently of details of the evolution in contact and a relation between
A-type and W-type systems, the ultimate fate of contact binaries involves the
coalescence of both components into a single fast rotating star.Comment: 11 pages, 5 figures, a short paragraph added on p. 6, MNRAS, in pres
Grey-box model identification via evolutionary computing
This paper presents an evolutionary grey-box model identification methodology that makes the best use of a priori knowledge on
a clear-box model with a global structural representation of the physical system under study, whilst incorporating accurate blackbox
models for immeasurable and local nonlinearities of a practical system. The evolutionary technique is applied to building
dominant structural identification with local parametric tuning without the need of a differentiable performance index in the
presence of noisy data. It is shown that the evolutionary technique provides an excellent fitting performance and is capable of
accommodating multiple objectives such as to examine the relationships between model complexity and fitting accuracy during the
model building process. Validation results show that the proposed method offers robust, uncluttered and accurate models for two
practical systems. It is expected that this type of grey-box models will accommodate many practical engineering systems for a better
modelling accuracy
On the Caudrey-Beals-Coifman System and the Gauge Group Action
The generalized Zakharov-Shabat systems with complex-valued Cartan elements
and the systems studied by Caudrey, Beals and Coifman (CBC systems) and their
gauge equivalent are studies. This includes: the properties of fundamental
analytical solutions (FAS) for the gauge-equivalent to CBC systems and the
minimal set of scattering data; the description of the class of nonlinear
evolutionary equations solvable by the inverse scattering method and the
recursion operator, related to such systems; the hierarchies of Hamiltonian
structures.Comment: 12 pages, no figures, contribution to the NEEDS 2007 proceedings
(Submitted to J. Nonlin. Math. Phys.
Cultural selection drives the evolution of human communication systems
Human communication systems evolve culturally, but the evolutionary mechanisms that drive this evolution are not well understood. Against a baseline that communication variants spread in a population following neutral evolutionary dynamics (also known as drift models), we tested the role of two cultural selection models: coordination- and content-biased. We constructed a parametrized mixed probabilistic model of the spread of communicative variants in four 8-person laboratory micro-societies engaged in a simple communication game. We found that selectionist models, working in combination, explain the majority of the empirical data. The best-fitting parameter setting includes an egocentric bias and a content bias, suggesting that participants retained their own previously used communicative variants unless they encountered a superior (content-biased) variant, in which case it was adopted. This novel pattern of results suggests that (i) a theory of the cultural evolution of human communication systems must integrate selectionist models and (ii) human communication systems are functionally adaptive complex systems
Barium & related stars and their white-dwarf companions II. Main-sequence and subgiant stars
Barium (Ba) dwarfs and CH subgiants are the less-evolved analogues of Ba and
CH giants. They are F- to G-type main-sequence stars polluted with heavy
elements by a binary companion when the latter was on the Asymptotic Giant
Branch (AGB). This companion is now a white dwarf that in most cases cannot be
directly detected. We present a large systematic study of 60 objects classified
as Ba dwarfs or CH subgiants. Combining radial-velocity measurements from
HERMES and SALT high-resolution spectra with radial-velocity data from CORAVEL
and CORALIE, we determine the orbital parameters of 27 systems. We also derive
their masses by comparing their location in the Hertzsprung-Russell diagram
with evolutionary models. We confirm that Ba dwarfs and CH subgiants are not at
different evolutionary stages and have similar metallicities, despite their
different names. Additionally, Ba giants appear significantly more massive than
their main-sequence analogues. This is likely due to observational biases
against the detection of hotter main-sequence post-mass-transfer objects.
Combining our spectroscopic orbits with the Hipparcos astrometric data, we
derive the orbital inclinations and the mass of the WD companion for four
systems. Since this cannot be done for all systems in our sample yet (but
should be with upcoming Gaia data releases), we also analyse the mass-function
distribution of our binaries. We can model this distribution with very narrow
mass distributions for the two components and random orbital orientation on the
sky. Finally, based on BINSTAR evolutionary models, we suggest that the orbital
evolution of low-mass Ba systems can be affected by a second phase of
interaction along the Red Giant Branch of the Ba star, impacting on the
eccentricities and periods of the giants.Comment: Accepted for publication in A&A on the 5th of April, 201
Evolutionary-based sparse regression for the experimental identification of duffing oscillator
In this paper, an evolutionary-based sparse regression algorithm is proposed and applied onto experimental data collected from a Duffing oscillator setup and numerical simulation data. Our purpose is to identify the Coulomb friction terms as part of the ordinary differential equation of the system. Correct identification of this nonlinear system using sparse identification is hugely dependent on selecting the correct form of nonlinearity included in the function library. Consequently, in this work, the evolutionary-based sparse identification is replacing the need for user knowledge when constructing the library in sparse identification. Constructing the library based on the data-driven evolutionary approach is an effective way to extend the space of nonlinear functions, allowing for the sparse regression to be applied on an extensive space of functions. The results show that the method provides an effective algorithm for the purpose of unveiling the physical nature of the Duffing oscillator. In addition, the robustness of the identification algorithm is investigated for various levels of noise in simulation. The proposed method has possible applications to other nonlinear dynamic systems in mechatronics, robotics, and electronics
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