3,569 research outputs found
Data exploration systems for databases
Data exploration systems apply machine learning techniques, multivariate statistical methods, information theory, and database theory to databases to identify significant relationships among the data and summarize information. The result of applying data exploration systems should be a better understanding of the structure of the data and a perspective of the data enabling an analyst to form hypotheses for interpreting the data. This paper argues that data exploration systems need a minimum amount of domain knowledge to guide both the statistical strategy and the interpretation of the resulting patterns discovered by these systems
Detecting perceptual groupings in textures by continuity considerations
A generalization is presented for the second derivative of a Gaussian D(sup 2)G operator to apply to problems of perceptual organization involving textures. Extensions to other problems of perceptual organization are evident and a new research direction can be established. The technique presented is theoretically pleasing since it has the potential of unifying the entire area of image segmentation under the mathematical notion of continuity and presents a single algorithm to form perceptual groupings where many algorithms existed previously. The eventual impact on both the approach and technique of image processing segmentation operations could be significant
Dual Supermassive Black Hole Candidates in the AGN and Galaxy Evolution Survey
Dual supermassive black holes (SMBHs) with kiloparsec scale separations in
merger-remnant galaxies are informative tracers of galaxy evolution, but the
avenue for identifying them in large numbers for such studies is not yet clear.
One promising approach is to target spectroscopic signatures of systems where
both SMBHs are fueled as dual active galactic nuclei (AGNs), or where one SMBH
is fueled as an offset AGN. Dual AGNs may produce double-peaked narrow AGN
emission lines, while offset AGNs may produce single-peaked narrow AGN emission
lines with line-of-sight velocity offsets relative to the host galaxy. We
search for such dual and offset systems among 173 Type 2 AGNs at z<0.37 in the
AGN and Galaxy Evolution Survey (AGES), and we find two double-peaked AGNs and
five offset AGN candidates. When we compare these results to a similar search
of the DEEP2 Galaxy Redshift Survey and match the two samples in color,
absolute magnitude, and minimum velocity offset, we find that the fraction of
AGNs that are dual SMBH candidates increases from z=0.25 to z=0.7 by a factor
of ~6 (from 2/70 to 16/91, or 2.9% to 18%). This may be associated with the
rise in the galaxy merger fraction over the same cosmic time. As further
evidence for a link with galaxy mergers, the AGES offset and dual AGN
candidates are tentatively ~3 times more likely than the overall AGN population
to reside in a host galaxy that has a companion galaxy (from 16/173 to 2/7, or
9% to 29%). Follow-up observations of the seven offset and dual AGN candidates
in AGES will definitively distinguish velocity offsets produced by dual SMBHs
from those produced by narrow-line region kinematics, and will help sharpen our
observational approach to detecting dual SMBHs.Comment: 10 pages, 8 figures, accepted for publication in Ap
Hybridization, Inter-Ion Correlation, and Surface States in the Kondo Insulator SmB6
As an exemplary Kondo insulator, SmB6 has been studied for several decades;
however, direct evidence for the development of the Kondo coherent state and
the evolution of the electronic structure in the material has not been obtained
due to the rather complicated electronic and thermal transport behavior.
Recently, these open questions attracted increasing attention as the emergence
of a time-reversal invariant topological surface state in the Kondo insulator
has been suggested. Here, we use point-contact spectroscopy to reveal the
temperature dependence of the electronic states in SmB6. We demonstrate that
SmB6 is a model Kondo insulator: below 100 K, the conductance spectra reflect
the Kondo hybridization of Sm ions, but below ~ 30 K, signatures of inter-ion
correlation effects clearly emerge. Moreover, we find evidence that the
low-temperature insulating state of this exemplary Kondo lattice compound
harbors conduction states on the surface, in support of predictions of
nontrivial topology in Kondo insulators.Comment: Accepted for publication in Physical Review
The effects of entry on incumbent innovation and productivity
How does firm entry affect innovation incentives in incumbent firms? Microdata suggest that there is heterogeneity across industries. Specifically, incumbent productivity growth and patenting is positively correlated with lagged greenfield foreign firm entry in technologically advanced industries, but not in laggard industries. In this paper we provide evidence that these correlations arise from a causal effect predicted by Schumpeterian growth theory—the threat of technologically advanced entry spurs innovation incentives in sectors close to the technology frontier, where successful innovation allows incumbents to survive the threat, but discourages innovation in laggard sectors, where the threat reduces incumbents' expected rents from innovating. We find that the empirical patterns hold using rich micro panel data for the United Kingdom. We control for the endogeneity of entry by exploiting major European and U.K. policy reforms, and allow for endogeneity of additional factors. We complement the analysis for foreign entry with evidence for domestic entry and entry through imports
Mirror Maps in Chern-Simons Gauge Theory
We describe mirror symmetry in N=2 superconformal field theories in terms of
a dynamical topology changing process of the principal fiber bundle associated
with a topological membrane. We show that the topological symmetries of
Calabi-Yau sigma-models can be obtained from discrete geometric transformations
of compact Chern-Simons gauge theory coupled to charged matter fields. We
demonstrate that the appearence of magnetic monopole-instantons, which
interpolate between topologically inequivalent vacua of the gauge theory,
implies that the discrete symmetry group of the worldsheet theory is realized
kinematically in three dimensions as the magnetic flux symmetry group. From
this we construct the mirror map and show that it corresponds to the
interchange of topologically non-trivial matter field and gauge degrees of
freedom. We also apply the mirror transformation to the mean field theory of
the quantum Hall effect. We show that it maps the Jain hierarchy into a new
hierarchy of states in which the lowest composite fermions have the same
filling fractions.Comment: 40 pages LaTeX, 4 postscript files, uses psfig.sty; minor textual
changes, typos corrected, references adde
An unusual case of small bowel obstruction post caesarean section
Small bowel obstruction (SBO) is a very rare complication post-caesarean section (CS). Herniation of small bowel through the rectus muscle with an intact sheath is extremely rare. We present a case of SBO after an uncomplicated c-section and an uneventful early postoperative cours
Modeling and Optimal Design of Machining-Induced Residual Stresses in Aluminium Alloys Using a Fast Hierarchical Multiobjective Optimization Algorithm
The residual stresses induced during shaping and machining play an important role in determining the integrity and durability of metal components. An important issue of producing safety critical components is to find the machining parameters that create compressive surface stresses or minimise tensile surface stresses. In this paper, a systematic data-driven fuzzy modelling methodology is proposed, which allows constructing transparent fuzzy models considering both accuracy and interpretability attributes of fuzzy systems. The new method employs a hierarchical optimisation structure to improve the modelling efficiency, where two learning mechanisms cooperate together: NSGA-II is used to improve the model’s structure while the gradient descent method is used to optimise the numerical parameters. This hybrid approach is then successfully applied to the problem that concerns the prediction of machining induced residual stresses in aerospace aluminium alloys. Based on the developed reliable prediction models, NSGA-II is further applied to the multi-objective optimal design of aluminium alloys in a ‘reverse-engineering’ fashion. It is revealed that the optimal machining regimes to minimise the residual stress and the machining cost simultaneously can be successfully located
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