972 research outputs found
An Improvement Study of the Decomposition-based Algorithm Global WASF-GA for Evolutionary Multiobjective Optimization
The convergence and the diversity of the decompositionbased evolutionary algorithm Global WASF-GA (GWASF-GA) relies
on a set of weight vectors that determine the search directions for new non-dominated solutions in the objective space. Although using weight vectors whose search directions are widely distributed may lead to a well-diversified approximation of the Pareto front (PF), this may not be enough to obtain a good approximation for complicated PFs (discontinuous, non-convex, etc.). Thus, we propose to dynamically adjust the weight vectors once GWASF-GA has been run for a certain number of generations. This adjustment is aimed at re-calculating some of the weight vectors, so that search directions pointing to overcrowded regions of the PF are redirected toward parts with a lack of solutions that may be hard to be approximated. We test different parameters settings of the dynamic adjustment in optimization problems with three, five, and six objectives, concluding that GWASF-GA performs better when adjusting the weight vectors dynamically than without applying the adjustment.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
On Surface Plasmon Damping in Metallic Nanoparticles
Two possible mechanisms of surface plasmon (SP) oscillations damping in
metallic nanoparticles (MNPs), not connected with electron-phonon interaction
are investigated theoretically: a) the radiation damping of SP, b) resonant
coupling of SP oscillations with electronic transitions in matrix. It is shown
that the radiation damping rate is proportional to the number of electrons in
MNP and therefore this channel of energy outflow from MNP becomes essential for
relatively large particles. The investigation of second mechanism shows that
the rate of SP oscillations energy leakage from MNP dos not depend on particle
size and is fully determined by the optical characteristics of the matrix. It
is demonstrated that for very small MNPs of 3-5 nm size, where the strong 3D
size quantization effect suppresses the electron-phonon interaction, the
resonance coupling in certain cases provides an effective energy outflow.Comment: 6 pages; E-mail address: [email protected]
Determining appropriate approaches for using data in feature selection
Feature selection is increasingly important in data analysis and machine learning in big data era. However, how to use the data in feature selection, i.e. using either ALL or PART of a dataset, has become a serious and tricky issue. Whilst the conventional practice of using all the data in feature selection may lead to selection bias, using part of the data may, on the other hand, lead to underestimating the relevant features under some conditions. This paper investigates these two strategies systematically in terms of reliability and effectiveness, and then determines their suitability for datasets with different characteristics. The reliability is measured by the Average Tanimoto Index and the Inter-method Average Tanimoto Index, and the effectiveness is measured by the mean generalisation accuracy of classification. The computational experiments are carried out on ten real-world benchmark datasets and fourteen synthetic datasets. The synthetic datasets are generated with a pre-set number of relevant features and varied numbers of irrelevant features and instances, and added with different levels of noise. The results indicate that the PART approach is more effective in reducing the bias when the size of a dataset is small but starts to lose its advantage as the dataset size increases
Blue luminescence of Au nanoclusters embedded in silica matrix
Photoluminescence study using the 325 nm He-Cd excitation is reported for the
Au nanoclusters embedded in SiO2 matrix. Au clusters are grown by ion beam
mixing with 100 KeV Ar+ irradiation on Au [40 nm]/SiO2 at various fluences and
subsequent annealing at high temperature. The blue bands above ~3 eV match
closely with reported values for colloidal Au nanoclusters and supported Au
nanoislands. Radiative recombination of sp electrons above Fermi level to
occupied d-band holes are assigned for observed luminescence peaks. Peaks at
3.1 eV and 3.4 eV are correlated to energy gaps at the X- and L-symmetry
points, respectively, with possible involvement of relaxation mechanism. The
blue shift of peak positions at 3.4 eV with decreasing cluster size is reported
to be due to the compressive strain in small clusters. A first principle
calculation based on density functional theory using the full potential linear
augmented plane wave plus local orbitals (FP-LAPW+LO) formalism with
generalized gradient approximation (GGA) for the exchange correlation energy is
used to estimate the band gaps at the X- and L-symmetry points by calculating
the band structures and joint density of states (JDOS) for different strain
values in order to explain the blueshift of ~0.1 eV with decreasing cluster
size around L-symmetry point.Comment: 13 pages, 7 Figures Only in PDF format; To be published in J. of
Chem. Phys. (Tentative issue of publication 8th December 2004
Combination of linear classifiers using score function -- analysis of possible combination strategies
In this work, we addressed the issue of combining linear classifiers using
their score functions. The value of the scoring function depends on the
distance from the decision boundary. Two score functions have been tested and
four different combination strategies were investigated. During the
experimental study, the proposed approach was applied to the heterogeneous
ensemble and it was compared to two reference methods -- majority voting and
model averaging respectively. The comparison was made in terms of seven
different quality criteria. The result shows that combination strategies based
on simple average, and trimmed average are the best combination strategies of
the geometrical combination
Lattice-gas simulations of Domain Growth, Saturation and Self-Assembly in Immiscible Fluids and Microemulsions
We investigate the dynamical behavior of both binary fluid and ternary
microemulsion systems in two dimensions using a recently introduced
hydrodynamic lattice-gas model of microemulsions. We find that the presence of
amphiphile in our simulations reduces the usual oil-water interfacial tension
in accord with experiment and consequently affects the non-equilibrium growth
of oil and water domains. As the density of surfactant is increased we observe
a crossover from the usual two-dimensional binary fluid scaling laws to a
growth that is {\it slow}, and we find that this slow growth can be
characterized by a logarithmic time scale. With sufficient surfactant in the
system we observe that the domains cease to grow beyond a certain point and we
find that this final characteristic domain size is inversely proportional to
the interfacial surfactant concentration in the system.Comment: 28 pages, latex, embedded .eps figures, one figure is in colour, all
in one uuencoded gzip compressed tar file, submitted to Physical Review
Mechanical and Electronic Properties of MoS Nanoribbons and Their Defects
We present our study on atomic, electronic, magnetic and phonon properties of
one dimensional honeycomb structure of molybdenum disulfide (MoS) using
first-principles plane wave method. Calculated phonon frequencies of bare
armchair nanoribbon reveal the fourth acoustic branch and indicate the
stability. Force constant and in-plane stiffness calculated in the harmonic
elastic deformation range signify that the MoS nanoribbons are stiff quasi
one dimensional structures, but not as strong as graphene and BN nanoribbons.
Bare MoS armchair nanoribbons are nonmagnetic, direct band gap
semiconductors. Bare zigzag MoS nanoribbons become half-metallic as a
result of the (2x1) reconstruction of edge atoms and are semiconductor for
minority spins, but metallic for the majority spins. Their magnetic moments and
spin-polarizations at the Fermi level are reduced as a result of the
passivation of edge atoms by hydrogen. The functionalization of MoS
nanoribbons by adatom adsorption and vacancy defect creation are also studied.
The nonmagnetic armchair nanoribbons attain net magnetic moment depending on
where the foreign atoms are adsorbed and what kind of vacancy defect is
created. The magnetization of zigzag nanoribbons due to the edge states is
suppressed in the presence of vacancy defects.Comment: 11 pages, 5 figures, first submitted at November 23th, 200
Atomistic simulations of self-trapped exciton formation in silicon nanostructures: The transition from quantum dots to nanowires
Using an approximate time-dependent density functional theory method, we
calculate the absorption and luminescence spectra for hydrogen passivated
silicon nanoscale structures with large aspect ratio. The effect of electron
confinement in axial and radial directions is systematically investigated.
Excited state relaxation leads to significant Stokes shifts for short nanorods
with lengths less than 2 nm, but has little effect on the luminescence
intensity. The formation of self-trapped excitons is likewise observed for
short nanostructures only; longer wires exhibit fully delocalized excitons with
neglible geometrical distortion at the excited state minimum.Comment: 10 pages, 4 figure
An ecological approach to anomaly detection: the EIA Model.
The presented work proposes a new approach for anomaly
detection. This approach is based on changes in a population of evolving agents under stress. If conditions are appropriate, changes in the population (modeled by the bioindicators) are representative of the alterations to the environment. This approach, based on an ecological view, improves functionally traditional approaches to the detection of anomalies.
To verify this assertion, experiments based on Network Intrussion Detection Systems are presented. The results are compared with the behaviour of other bioinspired approaches and machine learning techniques
What is a Cool-Core Cluster? A Detailed Analysis of the Cores of the X-ray Flux-Limited HIFLUGCS Cluster Sample
We use the largest complete sample of 64 galaxy clusters (HIghest X-ray FLUx
Galaxy Cluster Sample) with available high-quality X-ray data from Chandra, and
apply 16 cool-core diagnostics to them, some of them new. We also correlate
optical properties of brightest cluster galaxies (BCGs) with X-ray properties.
To segregate cool core and non-cool-core clusters, we find that central cooling
time, t_cool, is the best parameter for low redshift clusters with high quality
data, and that cuspiness is the best parameter for high redshift clusters. 72%
of clusters in our sample have a cool core (t_cool < 7.7 h_{71}^{-1/2} Gyr) and
44% have strong cool cores (t_cool <1.0 h_{71}^{-1/2} Gyr). For the first time
we show quantitatively that the discrepancy in classical and spectroscopic mass
deposition rates can not be explained with a recent formation of the cool
cores, demonstrating the need for a heating mechanism to explain the cooling
flow problem. [Abridged]Comment: 45 pages, 19 figures, 7 tables. Accepted for publication in A&A.
Contact Person: Rupal Mittal ([email protected]
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