300 research outputs found
Experimental Comparisons of Derivative Free Optimization Algorithms
In this paper, the performances of the quasi-Newton BFGS algorithm, the
NEWUOA derivative free optimizer, the Covariance Matrix Adaptation Evolution
Strategy (CMA-ES), the Differential Evolution (DE) algorithm and Particle Swarm
Optimizers (PSO) are compared experimentally on benchmark functions reflecting
important challenges encountered in real-world optimization problems.
Dependence of the performances in the conditioning of the problem and
rotational invariance of the algorithms are in particular investigated.Comment: 8th International Symposium on Experimental Algorithms, Dortmund :
Germany (2009
Observations and modelling of a large optical flare on AT Microscopii
Spectroscopic observations covering the wavelength range 3600--4600\AA are
presented for a large flare on the late type M dwarf AT Mic (dM4.5e). A
procedure to estimate the physical parameters of the flaring plasma has been
used which assumes a simplified slab model of the flare based on a comparison
of observed and computed Balmer decrements. With this procedure we have
determined the electron density, electron temperature, optical thickness and
temperature of the underlying source for the impulsive and gradual phases of
the flare. The magnitude and duration of the flare allows us to trace the
physical parameters of the response of the lower atmosphere. In order to check
our derived values we have compared them with other methods. In addition, we
have also applied our procedure to a stellar and a solar flare for which
parameters have been obtained using other techniques.Comment: 11 pages, 8 tables, accepted by A&
Generalized multiobjective evolutionary algorithm guided by descent directions
This paper proposes a generalized descent directions-guided multiobjective algorithm
(DDMOA2). DDMOA2 uses the scalarizing fitness assignment in its parent and
environmental selection procedures. The population consists of leader and non-leader individuals.
Each individual in the population is represented by a tuple containing its genotype
as well as the set of strategy parameters. The main novelty and the primary strength of
our algorithm is its reproduction operator, which combines the traditional local search
and stochastic search techniques. To improve efficiency, when the number of objective
is increased, descent directions are found only for two randomly chosen objectives. Furthermore,
in order to increase the search pressure in high-dimensional objective space, we
impose an additional condition for the acceptance of descent directions found for leaders
during local search. The performance of the proposed approach is compared with those produced
by representative state-of-the-art multiobjective evolutionary algorithms on a set of
problems with up to 8 objectives. The experimental results reveal that our algorithm is able
to produce highly competitive results with well-established multiobjective optimizers on all
tested problems.Moreover, due to its hybrid reproduction operator, DDMOA2 demonstrates
superior performance on multimodal problems.This work has been supported by FCT Fundação para a Ciência e Tecnologia in the
scope of the project: PEst-OE/EEI/UI0319/2014
Analysis and modeling of high temporal resolution spectroscopic observations of flares on AD Leo
We report the results of a high temporal resolution spectroscopic monitoring
of the flare star AD Leo. During 4 nights, more than 600 spectra were taken in
the optical range using the Isaac Newton Telescope (INT) and the Intermediate
Dispersion Spectrograph (IDS). We have observed a large number of short and
weak flares occurring very frequently (flare activity > 0.71 hours-1). This is
in favour of the very important role that flares can play in stellar coronal
heating. The detected flares are non white-light flares and, though most of
solar flares belong to this kind, very few such events had been previously
observed on stars. The behaviour of different chromospheric lines (Balmer
series from H_alpha to H_11, Ca II H & K, Na I D_1 & D_2, He I 4026 AA and He I
D_3) has been studied in detail for a total of 14 flares. We have also
estimated the physical parameters of the flaring plasma by using a procedure
which assumes a simplified slab model of flares. All the obtained physical
parameters are consistent with previously derived values for stellar flares,
and the areas - less than 2.3% of the stellar surface - are comparable with the
size inferred for other solar and stellar flares. Finally, we have studied the
relationships between the physical parameters and the area, duration, maximum
flux and energy released during the detected flares.Comment: Latex file with 17 pages, 11 figures. Available at
http://www.ucm.es/info/Astrof/invest/actividad/actividad_pub.html Accepted
for publication in: Astronomy & Astrophysics (A&A
Hybrid simulation-optimization methods: A taxonomy and discussion
The possibilities of combining simulation and optimization are vast and the appropriate design highly depends on the problem characteristics. Therefore, it is very important to have a good overview of the different approaches. The taxonomies and classifications proposed in the literature do not cover the complete range of methods and overlook some important criteria. We provide a taxonomy that aims at giving an overview of the full spectrum of current simulation-optimization approaches. Our study may guide researchers who want to use one of the existing methods, give insights into the cross-fertilization of the ideas applied in those methods and create a standard for a better communication in the scientific community. Future reviews can use the taxonomy here described to classify both general approaches and methods for specific application fields.The possibilities of combining simulation and optimization are vast and the appropriate design highly depends on the problem characteristics. Therefore, it is very important to have a good overview of the different approaches. The taxonomies and classifications proposed in the literature do not cover the complete range of methods and overlook some important criteria. We provide a taxonomy that aims at giving an overview of the full spectrum of current simulation-optimization approaches. Our study may guide researchers who want to use one of the existing methods, give insights into the cross-fertilization of the ideas applied in those methods and create a standard for a better communication in the scientific community. Future reviews can use the taxonomy here described to classify both general approaches and methods for specific application fields. (C) 2014 Elsevier B.V. All rights reserved
Process Simulation and Control Optimization of a Blast Furnace Using Classical Thermodynamics Combined to a Direct Search Algorithm
Several numerical approaches have been proposed in the literature to simulate the behavior of modern blast furnaces: finite volume methods, data-mining models, heat and mass balance models, and classical thermodynamic simulations. Despite this, there is actually no efficient method for evaluating quickly optimal operating parameters of a blast furnace as a function of the iron ore composition, which takes into account all potential chemical reactions that could occur in the system. In the current study, we propose a global simulation strategy of a blast furnace, the 5-unit process simulation. It is based on classical thermodynamic calculations coupled to a direct search algorithm to optimize process parameters. These parameters include the minimum required metallurgical coke consumption as well as the optimal blast chemical composition and the total charge that simultaneously satisfy the overall heat and mass balances of the system. Moreover, a Gibbs free energy function for metallurgical coke is parameterized in the current study and used to fine-tune the simulation of the blast furnace. Optimal operating conditions and predicted output stream properties calculated by the proposed thermodynamic simulation strategy are compared with reference data found in the literature and have proven the validity and high precision of this simulation
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