5,605 research outputs found
II. Apples to apples : cluster selection functions for next-generation surveys
We present the cluster selection function for three of the largest
next-generation stage-IV surveys in the optical and infrared:
Euclid-Optimistic, Euclid-Pessimistic and the Large Synoptic Survey Telescope
(LSST). To simulate these surveys, we use the realistic mock catalogues
introduced in the first paper of this series.
We detected galaxy clusters using the Bayesian Cluster Finder (BCF) in the
mock catalogues. We then modeled and calibrated the total cluster stellar mass
observable-theoretical mass () relation using a power
law model, including a possible redshift evolution term. We find a moderate
scatter of of 0.124, 0.135 and 0.136 for Euclid-Optimistic, Euclid-Pessimistic and LSST, respectively,
comparable to other work over more limited ranges of redshift. Moreover, the
three datasets are consistent with negligible evolution with redshift, in
agreement with observational and simulation results in the literature.
We find that Euclid-Optimistic will be able to detect clusters with
completeness and purity down to up to .
At higher redshifts, the same completeness and purity are obtained with the
larger mass threshold of up to . The
Euclid-Pessimistic selection function has a similar shape with
higher mass limit. LSST shows higher mass limit than
Euclid-Optimistic up to and increases afterwards, reaching values of
at . Similar selection functions with
only completeness threshold have been also computed. The complementarity
of these results with selection functions for surveys in other bands is
discussed.Comment: 13 pages, 10 figures, accepted for publication in MNRA
Thermodynamics of beta-amyloid fibril formation
Amyloid fibers are aggregates of proteins. They are built out of a peptide
called --amyloid (A) containing between 41 and 43 residues,
produced by the action of an enzyme which cleaves a much larger protein known
as the Amyloid Precursor Protein (APP). X-ray diffraction experiments have
shown that these fibrils are rich in --structures, whereas the shape of
the peptide displays an --helix structure within the APP in its
biologically active conformation. A realistic model of fibril formation is
developed based on the seventeen residues A12--28 amyloid peptide, which
has been shown to form fibrils structurally similar to those of the whole
A peptide. With the help of physical arguments and in keeping with
experimental findings, the A12--28 monomer is assumed to be in four
possible states (i.e., native helix conformation, --hairpin, globular
low--energy state and unfolded state). Making use of these monomeric states,
oligomers (dimers, tertramers and octamers) were constructed. With the help of
short, detailed Molecular Dynamics (MD) calculations of the three monomers and
of a variety of oligomers, energies for these structures were obtained. Making
use of these results within the framework of a simple yet realistic model to
describe the entropic terms associated with the variety of amyloid
conformations, a phase diagram can be calculated of the whole many--body
system, leading to a thermodynamical picture in overall agreement with the
experimental findings. In particular, the existence of micellar metastable
states seem to be a key issue to determine the thermodynamical properties of
the system
Understanding the determinants of stability and folding of small globular proteins from their energetics
The results of minimal model calculations suggest that the stability and the
kinetic accessibility of the native state of small globular proteins are
controlled by few "hot" sites. By mean of molecular dynamics simulations around
the native conformation, which simulate the protein and the surrounding solvent
at full--atom level, we generate an energetic map of the equilibrium state of
the protein and simplify it with an Eigenvalue decomposition. The components of
the Eigenvector associated with the lowest Eigenvalue indicate which are the
"hot" sites responsible for the stability and for the fast folding of the
protein. Comparison of these predictions with the results of mutatgenesis
experiments, performed for five small proteins, provide an excellent agreement
Multispectral scleral patterns for ocular biometric recognition
Biometrics is the science of recognizing people based on their physical or behavioral traits such as face, fingerprints, iris, and voice. Among the various traits studied in the literature, ocular biometrics has gained popularity due to the significant progress made in iris recognition. However, iris recognition is unfavorably influenced by the non-frontal gaze direction of the eye with respect to the acquisition device. In such scenarios, additional parts of the eye, such as the sclera (the white of the eye) may be of significance. In this dissertation, we investigate the use of the sclera texture and the vasculature patterns evident in the sclera as potential biometric cues. Iris patterns are better discerned in the near infrared spectrum (NIR) while vasculature patterns are better discerned in the visible spectrum (RGB). Therefore, multispectral images of the eye, consisting of both NIR and RGB channels, were used in this work in order to ensure that both the iris and the vasculature patterns are successfully imaged.;The contributions of this work include the following. Firstly, a multispectral ocular database was assembled by collecting high-resolution color infrared images of the left and right eyes of 103 subjects using the DuncanTech MS 3100 multispectral camera. Secondly, a novel segmentation algorithm was designed to localize the spacial extent of the iris, sclera and pupil in the ocular images. The proposed segmentation algorithm is a combination of region-based and edge-based schemes that exploits the multispectral information. Thirdly, different feature extraction and matching method were used to determine the potential of utilizing the sclera and the accompanying vasculature pattern as biometric cues. The three specific matching methods considered in this work were keypoint-based matching, direct correlation matching, and minutiae matching based on blood vessel bifurcations. Fourthly, the potential of designing a bimodal ocular system that combines the sclera biometric with the iris biometric was explored.;Experiments convey the efficacy of the proposed segmentation algorithm in localizing the sclera and the iris. The use of keypoint-based matching was observed to result in the best recognition performance for the scleral patterns. Finally, the possibility of utilizing the scleral patterns in conjunction with the iris for recognizing ocular images exhibiting non-frontal gaze directions was established
Edge-colorings of 4-regular graphs with the minimum number of palettes
A proper edge-coloring of a graph G is an assignment of colors to the edges of G such that adjacent edges receive distinct
colors. A proper edge-coloring defines at each vertex the set of colors of its incident edges. Following the terminology introduced by Hor\u148\ue1k, Kalinowski, Meszka and Wo\u17aniak, we call such a set of colors the palette of the vertex. What is the minimum number of distinct palettes taken over all proper edge-colorings of G? A complete answer is known for complete graphs and cubic graphs. We study in some detail the problem for 4-regular graphs
Collective oscillations in disordered neural networks
We investigate the onset of collective oscillations in a network of
pulse-coupled leaky-integrate-and-fire neurons in the presence of quenched and
annealed disorder. We find that the disorder induces a weak form of chaos that
is analogous to that arising in the Kuramoto model for a finite number N of
oscillators [O.V. Popovych at al., Phys. Rev. E 71} 065201(R) (2005)]. In fact,
the maximum Lyapunov exponent turns out to scale to zero for N going to
infinite, with an exponent that is different for the two types of disorder. In
the thermodynamic limit, the random-network dynamics reduces to that of a fully
homogenous system with a suitably scaled coupling strength. Moreover, we show
that the Lyapunov spectrum of the periodically collective state scales to zero
as 1/N^2, analogously to the scaling found for the `splay state'.Comment: 8.5 Pages, 12 figures, submitted to Physical Review
Effect of different pastures on CLA content in milk and sheep cheese
It is known that milk composition included conjugated linoleic acid (CLA) is affected by animal feeding system (Cabiddu et al., 2001). In Sardinia dairy sheep feeding is mainly based on pastures. Most of them are characterised by self-regenerating species, like annual ryegrass (Lolium rigidum Gaudin) and burr medic (Medicago polymorpha L.). Non conventional species belonging to the Compositae family such as (Chrysanthemum coronarium L.) seem interesting for sheep feeding when other herbages decrease in quality (late spring- early summer). It was observed that C. coronarium establishes rapidly, can be grazed early in the growing season and persist where other pasture species
may disappear; for these reasons it can be considered a valuable source of food. Moreover a preliminary
study with dairy sheep fed fresh forage of C. coronarium showed relatively high levels of CLA in milk
(Molle G. pers. com.) The aim of the present work was to study the influence of different pastures on milk composition, with particular reference to CLA and its precursors
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