2,679 research outputs found
A Dispersion Operator for Geometric Semantic Genetic Programming
Recent advances in geometric semantic genetic programming (GSGP) have shown that the results obtained by these methods can outperform those obtained by classical genetic programming algorithms, in particular in the context of symbolic regression. However, there are still many open issues on how to improve their search mechanism. One of these issues is how to get around the fact that the GSGP crossover operator cannot generate solutions that are placed outside the convex hull formed by the individuals of the current population. Although the mutation operator alleviates this problem, we cannot guarantee it will find promising regions of the search space within feasible computational time. In this direction, this paper proposes a new geometric dispersion operator that uses multiplicative factors to move individuals to less dense areas of the search space around the target solution before applying semantic genetic operators. Experiments in sixteen datasets show that the results obtained by the proposed operator are statistically significantly better than those produced by GSGP and that the operator does indeed spread the solutions around the target solution
A gravitationally lensed quasar discovered in OGLE
Indexación: Scopus; Web of Science.We report the discovery of a new gravitationally lensed quasar (double) from the Optical Gravitational Lensing Experiment (OGLE) identified inside the ~670deg2 area encompassing the Magellanic Clouds. The source was selected as one of ~60 'red W1-W2' mid-infrared objects from WISE and having a significant amount of variability in OGLE for both two (or more) nearby sources. This is the first detection of a gravitational lens, where the discovery is made 'the other way around', meaning we first measured the time delay between the two lensed quasar images of -132 < tAB < -76 d (90 per cent CL), with the median tAB ~-102 d (in the observer frame), and where the fainter image B lags image A. The system consists of the two quasar images separated by 1.5 arcsec on the sky, with I ~20.0mag and I ~19.6mag, respectively, and a lensing galaxy that becomes detectable as I ~21.5 mag source, 1.0 arcsec from image A, after subtracting the two lensed images. Both quasar images show clear AGN broad emission lines at z=2.16 in the New Technology Telescope spectra. The spectral energy distribution (SED) fitting with the fixed source redshift provided the estimate of the lensing galaxy redshift of z ~0.9 ± 0.2 (90 per cent CL), while its type is more likely to be elliptical (the SED-inferred and lens-model stellar mass is more likely present in ellipticals) than spiral (preferred redshift by the lens model). © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.https://academic.oup.com/mnras/article/476/1/663/483368
Autonomous clustering using rough set theory
This paper proposes a clustering technique that minimises the need for subjective
human intervention and is based on elements of rough set theory. The proposed algorithm is
unified in its approach to clustering and makes use of both local and global data properties to
obtain clustering solutions. It handles single-type and mixed attribute data sets with ease and
results from three data sets of single and mixed attribute types are used to illustrate the
technique and establish its efficiency
Dependence of Faraday effect on the orientation of terbium-scandium-aluminum garnet single crystal
Rough Set Theory as a Data Mining Technique:A Case Study in Epidemiology and Cancer Incidence Prediction
OGLE16aaa - a Signature of a Hungry Super Massive Black Hole
We present the discovery and first three months of follow-up observations of
a currently on-going unusual transient detected by the OGLE-IV survey, located
in the centre of a galaxy at redshift z=0.1655. The long rise to absolute
magnitude of -20.5 mag, slow decline, very broad He and H spectral features
make OGLE16aaa similar to other optical/UV Tidal Disruption Events (TDEs). Weak
narrow emission lines in the spectrum and archival photometric observations
suggest the host galaxy is a weak-line Active Galactic Nucleus (AGN), which has
been accreting at higher rate in the past. OGLE16aaa, along with SDSS J0748,
seems to form a sub-class of TDEs by weakly or recently active super-massive
black holes (SMBHs). This class might bridge the TDEs by quiescent SMBHs and
flares observed as "changing-look QSOs", if we interpret the latter as TDEs. If
this picture is true, the previously applied requirement for identifying a
flare as a TDE that it had to come from an inactive nucleus, could be leading
to observational bias in TDE selection, thus affecting TDE-rate estimations.Comment: Accepted in MNRAS Letter
Effect of structural defects on anomalous ultrasound propagation in solids during second-order phase transitions
The effect of structural defects on the critical ultrasound attenuation and
ultrasound velocity dispersion in Ising-like three-dimensional systems is
studied. A field-theoretical description of the dynamic effects of
acoustic-wave propagation in solids during phase transitions is performed with
allowance for both fluctuation and relaxation attenuation mechanisms. The
temperature and frequency dependences of the scaling functions of the
attenuation coefficient and the ultrasound velocity dispersion are calculated
in a two-loop approximation for pure and structurally disordered systems, and
their asymptotic behavior in hydrodynamic and critical regions is separated. As
compared to a pure system, the presence of structural defects in it is shown to
cause a stronger increase in the sound attenuation coefficient and the sound
velocity dispersion even in the hydrodynamic region as the critical temperature
is reached. As compared to pure analogs, structurally disordered systems should
exhibit stronger temperature and frequency dependences of the acoustic
characteristics in the critical region.Comment: 7 RevTeX pages, 4 figure
- âŠ