230,381 research outputs found
Clustering properties of a type-selected volume-limited sample of galaxies in the CFHTLS
(abridged) We present an investigation of the clustering of i'AB<24.5
galaxies in the redshift interval 0.2<z<1.2. Using 100,000 precise photometric
redshifts in the four ultra-deep fields of the Canada-France Legacy Survey, we
construct a set of volume-limited galaxy catalogues. We study the dependence of
the amplitude and slope of the galaxy correlation function on absolute B-band
rest-frame luminosity, redshift and best-fitting spectral type. We find: 1. The
comoving correlation length for all galaxies decreases steadily from z~0.3 to
z~1. 2. At all redshifts and luminosities, galaxies with redder rest-frame
colours have clustering amplitudes between two and three times higher than
bluer ones. 3. For bright red and blue galaxies, the clustering amplitude is
invariant with redshift. 4. At z~0.5, less luminous galaxies have higher
clustering amplitudes of around 6 h-1 Mpc. 5. The relative bias between
galaxies with red and blue rest-frame colours increases gradually towards
fainter absolute magnitudes. One of the principal implications of these results
is that although the full galaxy population traces the underlying dark matter
distribution quite well (and is therefore quite weakly biased), redder, older
galaxies have clustering lengths which are almost invariant with redshift, and
by z~1 are quite strongly biased.Comment: 16 pages, 18 figures, accepted for publication in Astronomy and
Astrophysic
Grading Exams: 100, 99, 98,...or A, B, C?
We introduce grading into games of status. Each player chooses effort, producing a stochastic output or score. Utilities depend on the ranking of all the scores. By clustering scores into grades, the ranking is coarsened, and the incentives to work are changed. We apply games of status to grading exams. Our main conclusion is that if students care primarily about their status (relative rank) in class, they are often best motivated to work not by revealing their exact numerical exam scores (100, 99, ...,1), but instead by clumping them into coarse categories (A,B,C). When student abilities are disparate, the optimal absolute grading scheme is always coarse. Furthermore, it awards fewer A’s than there are alpha-quality students, creating small elites. When students are homogeneous, we characterize optimal absolute grading schemes in terms of the stochastic dominance between student performances (when they shirk or work) on subintervals of scores, showing again why coarse grading may be advantageous. In both the disparate case and the homogeneous case, we prove that absolute grading is better than grading on a curve, provided student scores are independent.Status, Grading, Incentives, Education, Exams
AI controlled simulation based environmental assessment
Environmental assessment as complex assignment usually needs to use substitute economical methodologies to estimate environmental state instead of using direct valuing, since there are no absolute points of references and cross-couplings of causes and impacts are not transparent. In cases, when quantifying and clustering is ambiguous usage of FUZZY set theory can be suggested. AI controlled simulation assists in identifying of unknown cross-couplings, and in determining of relative importances from different points of views. This article highlights a complex simulation based environmental assessment methodology
The VIMOS Ultra Deep Survey. Luminosity and stellar mass dependence of galaxy clustering at z~3
We present the study of the dependence of galaxy clustering on luminosity and
stellar mass in the redshift range 2z3.5 using 3236 galaxies with robust
spectroscopic redshifts from the VIMOS Ultra Deep Survey (VUDS). We measure the
two-point real-space correlation function for four volume-limited
stellar mass and four luminosity, M absolute magnitude selected,
sub-samples. We find that the scale dependent clustering amplitude
significantly increases with increasing luminosity and stellar mass indicating
a strong galaxy clustering dependence on these properties. This corresponds to
a strong relative bias between these two sub-samples of b/b=0.43.
Fitting a 5-parameter HOD model we find that the most luminous and massive
galaxies occupy the most massive dark matter haloes with
M = 10 h M. Similar to the
trends observed at lower redshift, the minimum halo mass M depends on
the luminosity and stellar mass of galaxies and grows from M
=10 hM to M=10 hM
from the faintest to the brightest among our galaxy sample, respectively. We
find the difference between these halo masses to be much more pronounced than
is observed for local galaxies of similar properties. Moreover, at z~3, we
observe that the masses at which a halo hosts, on average, one satellite and
one central galaxy is M4M over all luminosity ranges,
significantly lower than observed at z~0 indicating that the halo satellite
occupation increases with redshift. The luminosity and stellar mass dependence
is also reflected in the measurements of the large scale galaxy bias, which we
model as b(L)=1.92+25.36(L/L). We conclude our study
with measurements of the stellar-to-halo mass ratio (SHMR).Comment: 20 pages, 11 figures, A&A in press, v2. revised discussion in sec.
5.5, changed Fig. 4 and Fig. 11, added reference
Kernelization for Balanced Graph Clustering
The problems of Balanced Graph Clustering ask whether it is possible to modify a graph such that it becomes a cluster graph where no cluster has a size larger than a given multiplicative factor or absolute difference relative to any other cluster in the graph, by at most k graph modifications. In this thesis we study the problems with respect to the graph modification operations vertex deletion, edge addition and edge deletion. We will show NP-completeness and give polynomial kernels for each version.Masteroppgave i informatikkINF399MAMN-INFMAMN-PRO
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