316 research outputs found
A memetic algorithm with adaptive hill climbing strategy for dynamic optimization problems
Copyright @ Springer-Verlag 2008Dynamic optimization problems challenge traditional evolutionary algorithms seriously since they, once converged, cannot adapt quickly to environmental changes. This paper investigates the application of memetic algorithms, a class of hybrid evolutionary algorithms, for dynamic optimization problems. An adaptive hill climbing method is proposed as the local search technique in the framework of memetic algorithms, which combines the features of greedy crossover-based hill climbing and steepest mutation-based hill climbing. In order to address the convergence problem, two diversity maintaining methods, called adaptive dual mapping and triggered random immigrants, respectively, are also introduced into the proposed memetic algorithm for dynamic optimization problems. Based on a series of dynamic problems generated from several stationary benchmark problems, experiments are carried out to investigate the performance of the proposed memetic algorithm in comparison with some peer evolutionary algorithms. The experimental results show the efficiency of the proposed memetic algorithm in dynamic environments.This work was supported by the National Nature Science Foundation of China (NSFC) under Grant Nos. 70431003 and 70671020, the National Innovation Research Community Science Foundation of China under Grant No. 60521003, and the National Support Plan of China under Grant No. 2006BAH02A09 and the Engineering and Physical Sciences Research Council (EPSRC) of UK under Grant EP/E060722/01
An Agent-Based Approach to Self-Organized Production
The chapter describes the modeling of a material handling system with the
production of individual units in a scheduled order. The units represent the
agents in the model and are transported in the system which is abstracted as a
directed graph. Since the hindrances of units on their path to the destination
can lead to inefficiencies in the production, the blockages of units are to be
reduced. Therefore, the units operate in the system by means of local
interactions in the conveying elements and indirect interactions based on a
measure of possible hindrances. If most of the units behave cooperatively
("socially"), the blockings in the system are reduced.
A simulation based on the model shows the collective behavior of the units in
the system. The transport processes in the simulation can be compared with the
processes in a real plant, which gives conclusions about the consequencies for
the production based on the superordinate planning.Comment: For related work see http://www.soms.ethz.c
Delegation of Obligations and Responsibility
Part 6: Policy Compliance and ObligationsInternational audienceIn this paper, we discuss the issue of responsibilities related to the fulfillment and the violation of obligations. We propose to formally define the different aspects of responsibility, namely causal responsibility, functional responsibility, liability as well as sanctions, and to examine how delegation influences these concepts. Our main aim is to identify the responsibility of each agent that is involved in the delegation of obligations. More precisely, we try to answer to the following questions: who is responsible for the obligation fulfillment? When a violation occurs, which agents are causally responsible for this violation? Who is liable for this violation and to whom? And finally, who must be sanctioned
Network of Earthquakes and Recurrences Therein
We quantify the correlation between earthquakes and use the same to
distinguish between relevant causally connected earthquakes. Our correlation
metric is a variation on the one introduced by Baiesi and Paczuski (2004). A
network of earthquakes is constructed, which is time ordered and with links
between the more correlated ones. Data pertaining to the California region has
been used in the study. Recurrences to earthquakes are identified employing
correlation thresholds to demarcate the most meaningful ones in each cluster.
The distribution of recurrence lengths and recurrence times are analyzed
subsequently to extract information about the complex dynamics. We find that
the unimodal feature of recurrence lengths helps to associate typical rupture
lengths with different magnitude earthquakes. The out-degree of the network
shows a hub structure rooted on the large magnitude earthquakes. In-degree
distribution is seen to be dependent on the density of events in the
neighborhood. Power laws are also obtained with recurrence time distribution
agreeing with the Omori law.Comment: 17 pages, 5 figure
First-principles extrapolation method for accurate CO adsorption energies on metal surfaces
We show that a simple first-principles correction based on the difference
between the singlet-triplet CO excitation energy values obtained by DFT and
high-level quantum chemistry methods yields accurate CO adsorption properties
on a variety of metal surfaces.
We demonstrate a linear relationship between the CO adsorption energy and the
CO singlet-triplet splitting, similar to the linear dependence of CO adsorption
energy on the energy of the CO 2* orbital found recently {[Kresse {\em et
al.}, Physical Review B {\bf 68}, 073401 (2003)]}. Converged DFT calculations
underestimate the CO singlet-triplet excitation energy ,
whereas coupled-cluster and CI calculations reproduce the experimental . The dependence of on is used
to extrapolate for the top, bridge and hollow sites for the
(100) and (111) surfaces of Pt, Rh, Pd and Cu to the values that correspond to
the coupled-cluster and CI value. The correction
reproduces experimental adsorption site preference for all cases and obtains
in excellent agreement with experimental results.Comment: Table sent as table1.eps. 3 figure
Molecular absorption lines toward star-forming regions : a comparative study of HCO+, HNC, HCN, and CN
Aims. The comparative study of several molecular species at the origin of the
gas phase chemistry in the diffuse interstellar medium (ISM) is a key input in
unraveling the coupled chemical and dynamical evolution of the ISM. Methods.
The lowest rotational lines of HCO+, HCN, HNC, and CN were observed at the
IRAM-30m telescope in absorption against the \lambda 3 mm and \lambda 1.3 mm
continuum emission of massive star-forming regions in the Galactic plane. The
absorption lines probe the gas over kiloparsecs along these lines of sight. The
excitation temperatures of HCO+ are inferred from the comparison of the
absorptions in the two lowest transitions. The spectra of all molecular species
on the same line of sight are decomposed into Gaussian velocity components.
Most appear in all the spectra of a given line of sight. For each component, we
derived the central opacity, the velocity dispersion, and computed the
molecular column density. We compared our results to the predictions of
UV-dominated chemical models of photodissociation regions (PDR models) and to
those of non-equilibrium models in which the chemistry is driven by the
dissipation of turbulent energy (TDR models). Results. The molecular column
densities of all the velocity components span up to two orders of magnitude.
Those of CN, HCN, and HNC are linearly correlated with each other with mean
ratios N(HCN)/N(HNC) = 4.8 1.3 and N(CN)/N(HNC) = 34 12, and more
loosely correlated with those of HCO+, N(HNC)/N(HCO+) = 0.5 0.3,
N(HCN)/N(HCO+) = 1.9 0.9, and N(CN)/N(HCO+) = 18 9. These ratios
are similar to those inferred from observations of high Galactic latitude lines
of sight, suggesting that the gas sampled by absorption lines in the Galactic
plane has the same chemical properties as that in the Solar neighbourhood. The
FWHM of the Gaussian velocity components span the range 0.3 to 3 km s-1 and
those of the HCO+ lines are found to be 30% broader than those of CN-bearing
molecules. The PDR models fail to reproduce simultaneously the observed
abundances of the CN-bearing species and HCO+, even for high-density material
(100 cm-3 < nH < 104 cm-3). The TDR models, in turn, are able to reproduce the
observed abundances and abundance ratios of all the analysed molecules for the
moderate gas densities (30 cm-3 < nH < 200 cm-3) and the turbulent energy
observed in the diffuse interstellar medium. Conclusions. Intermittent
turbulent dissipation appears to be a promising driver of the gas phase
chemistry of the diffuse and translucent gas throughout the Galaxy. The details
of the dissipation mechanisms still need to be investigated
Synthesis and physical properties of pyrochlore cobalt oxides Bi1.56-xCaxSb1.48Co0.96O7-δ
Abstract A new solid solution Bi1.56-xCaxSb1.48Co0.96O7-δ (0≤x≤0.3) with a pyrochlore-like structure (A2B2O7) was synthesized in air by chemical solid-state reaction. The solution crystallized in the cubic system with the Fd-3m space group. A regular decrease of the lattice parameter was observed when calcium replaced bismuth in the A site. The electric measurements showed that the electrical conductivity increased with the temperature and that high values of relative permittivity and dielectric loss were put in evidence. Measurements of magnetic susceptibility indicated a paramagnetic behavior of the samples with an effective moment included between 4.81 and 5.12 μB and at a low temperature para-ferromagnetic transition was observed for fractions x= 0.2 and 0.3
First detection of ND in the solar-mass protostar IRAS16293-2422
In the past decade, much progress has been made in characterising the
processes leading to the enhanced deuterium fractionation observed in the ISM
and in particular in the cold, dense parts of star forming regions such as
protostellar envelopes. Very high molecular D/H ratios have been found for
saturated molecules and ions. However, little is known about the deuterium
fractionation in radicals, even though simple radicals often represent an
intermediate stage in the formation of more complex, saturated molecules. The
imidogen radical NH is such an intermediate species for the ammonia synthesis
in the gas phase. Herschel/HIFI represents a unique opportunity to study the
deuteration and formation mechanisms of such species, which are not observable
from the ground. We searched here for the deuterated radical ND in order to
determine the deuterium fractionation of imidogen and constrain the deuteration
mechanism of this species. We observed the solar-mass Class 0 protostar
IRAS16293-2422 with the heterodyne instrument HIFI as part of the Herschel key
programme CHESS (Chemical HErschel Surveys of Star forming regions). The
deuterated form of the imidogen radical ND was detected and securely identified
with 2 hyperfine component groups of its fundamental transition in absorption
against the continuum background emitted from the nascent protostar. The 3
groups of hyperfine components of its hydrogenated counterpart NH were also
detected in absorption. We derive a very high deuterium fractionation with an
[ND]/[NH] ratio of between 30 and 100%. The deuterium fractionation of imidogen
is of the same order of magnitude as that in other molecules, which suggests
that an efficient deuterium fractionation mechanism is at play. We discuss two
possible formation pathways for ND, by means of either the reaction of N+ with
HD, or deuteron/proton exchange with NH.Comment: Accepted; To appear in A&A Herschel/HIFI Special Issu
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