512 research outputs found
The Coarse Geometry of Merger Trees in \Lambda CDM
We introduce the contour process to describe the geometrical properties of
merger trees. The contour process produces a one-dimensional object, the
contour walk, which is a translation of the merger tree. We portray the contour
walk through its length and action. The length is proportional to to the number
of progenitors in the tree, and the action can be interpreted as a proxy of the
mean length of a branch in a merger tree.
We obtain the contour walk for merger trees extracted from the public
database of the Millennium Run and also for merger trees constructed with a
public Monte-Carlo code which implements a Markovian algorithm. The trees
correspond to halos of final masses between 10^{11} h^{-1} M_sol and 10^{14}
h^{-1} M_sol. We study how the length and action of the walks evolve with the
mass of the final halo. In all the cases, except for the action measured from
Markovian trees, we find a transitional scale around 3 \times 10^{12} h^{-1}
M_sol. As a general trend the length and action measured from the Markovian
trees show a large scatter in comparison with the case of the Millennium Run
trees.Comment: 7 pages, 5 figures, submitted to MNRA
Distributed static linear Gaussian models using consensus
Algorithms for distributed agreement are a powerful means for formulating distributed versions of existing centralized algorithms. We present a toolkit for this task and show how it can be used systematically to design fully distributed algorithms for static linear Gaussian models, including principal component analysis, factor analysis, and probabilistic principal component analysis. These algorithms do not rely on a fusion center, require only low-volume local (1-hop neighborhood) communications, and are thus efficient, scalable, and robust. We show how they are also guaranteed to asymptotically converge to the same solution as the corresponding existing centralized algorithms. Finally, we illustrate the functioning of our algorithms on two examples, and examine the inherent cost-performance tradeoff
Tracing the Filamentary Structure of the Galaxy Distribution at z~0.8
We study filamentary structure in the galaxy distribution at z ~ 0.8 using
data from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Redshift Survey
and its evolution to z ~ 0.1 using data from the Sloan Digital Sky Survey
(SDSS). We trace individual filaments for both surveys using the Smoothed
Hessian Major Axis Filament Finder, an algorithm which employs the Hessian
matrix of the galaxy density field to trace the filamentary structures in the
distribution of galaxies. We extract 33 subsamples from the SDSS data with a
geometry similar to that of DEEP2. We find that the filament length
distribution has not significantly changed since z ~ 0.8, as predicted in a
previous study using a \LamdaCDM cosmological N-body simulation. However, the
filament width distribution, which is sensitive to the non-linear growth of
structure, broadens and shifts to smaller widths for smoothing length scales of
5-10 Mpc/h from z ~ 0.8 to z ~ 0.1, in accord with N-body simulations.Comment: 10 pages, 8 figures, accepted for the publication in MNRA
Effect of Intergalactic Medium on the Observability of Lyman Alpha Emitters during Cosmic Reionization
We perform a systematic study of how the inhomogeneities in the
Inter-Galactic Medium (IGM) affect the observability of Lyman Alpha Emitters
(LAEs) around the Epoch of Reionization. We focus on the IGM close to the
galaxies as the detailed ionization distribution and velocity fields of this
region could significantly influence the scattering of Ly-alpha photons off
neutral H atoms as they traverse the IGM after escaping from the galaxy. We
simulate the surface brightness (SB) maps and spectra of more than 100 LAEs at
z=7.7 as seen by an observer at z=0. To achieve this, we extract the source
properties of galaxies and their surrounding IGM from cosmological simulations
of box sizes 5-30 Mpc/h and follow the coupled radiative transfer of ionizing
and Ly-alpha radiation through the IGM using CRASH-alpha. We find that the
simulated SB profiles are extended and their detailed structure is affected by
inhomogeneities in the IGM, especially at high neutral fractions. The
detectability of LAEs and the fraction of the flux observed depend heavily on
the shape of the SB profile and the SB threshold (SB_th) of the observational
campaign. Only ultradeep observations (e.g. SB_th ~ 10^-23
ergs/s/cm^2/arcsec^2) would be able to obtain the true underlying
mass-luminosity relation and luminosity functions of LAEs. The details of our
results depend on whether Ly-alpha photons are significantly shifted in the
galaxy to longer wavelengths, the mean ionization fraction in the IGM and the
clustering of ionizing sources. These effects can lead to an easier escape of
Ly-alpha photons with less scattering in the IGM and a concentrated SB profile
similar to the one of a point source. Finally, we show that the SB profiles are
steeper at high ionization fraction for the same LAE sample which can
potentially be observed from the stacked profile of a large number of LAEs.Comment: 22 pages, 23 figures, 2 tables, Accepted by MNRAS. Minor change
CLARA's view on the escape fraction of Lyman-Alpha photons in high redshift galaxies
Using CLARA (Code for Lyman Alpha Radiation Analysis) we constrain the escape
fraction of Lyman-Alpha radiation in galaxies in the redshift range 5<z<7,
based on the MareNostrum High-z Universe, a SPH cosmological simulation with
more than 2 billion particles. We approximate Lyman-Alpha Emitters (LAEs) as
dusty gaseous slabs with Lyman-Alpha radiation sources homogeneously mixed in
the gas. Escape fractions for such a configuration and for different gas and
dust contents are calculated using our newly developed radiative transfer code
CLARA. The results are applied to the MareNostrum High-z Universe numerical
galaxies. The model shows a weak redshift evolution and good agreement with
estimations of the escape fraction as a function of reddening from observations
at z \sim 2.2 and z \sim 3. We extend the slab model by including additional
dust in a clumpy component in order to reproduce the UV con- tinuum luminosity
function and UV colours at redshifts z>~5. The LAE Luminosity Function (LF)
based on the extended clumpy model reproduces broadly the bright end of the LF
derived from observations at z \sim 5 and z \sim 6. At z \sim 7 our model
over-predicts the LF by roughly a factor of four, presumably because the
effects of the neutral intergalactic medium are not taken into account. The
remaining tension between the observed and simulated faint end of the LF, both
in the UV-continuum and Lyman-Alpha at redshifts z \sim 5 and z \sim 6 points
towards an overabundance of simulated LAEs hosted in haloes of masses
1.0x10^10h-1Msol < Mh < 4.0x10^10h-1Msol. Given the difficulties in explaining
the observed overabundance by dust absorption, a probable origin of the
mismatch are the high star formation rates in the simulated haloes around the
quoted mass range. A more efficient supernova feedback should be able to
regulate the star formation process in the shallow potential wells of these
haloes.Comment: 17 pages, 9 figures. Accepted for publication in MNRA
SHREC’20 Track:Retrieval of digital surfaces with similar geometric reliefs
International audienceThis paper presents the methods that have participated in the SHREC'20 contest on retrieval of surface patches with similar geometric reliefs and 1 the analysis of their performance over the benchmark created for this challenge. The goal of the context is to verify the possibility of retrieving 3D models only based on the reliefs that are present on their surface and to compare methods that are suitable for this task. This problem is related to many real world applications, such as the classification of cultural heritage goods or the analysis of different materials. To address this challenge, it is necessary to characterize the local "geometric pattern" information, possibly forgetting model size and bending. Seven groups participated in this contest and twenty runs were submitted for evaluation. The performances of the methods reveal that good results are achieved with a number of techniques that use different approaches
Structure of a Chaperone-Usher Pilus reveals the molecular basis of rod uncoiling
Types 1 and P pili are prototypical bacterial cell-surface appendages playing essential roles in mediating adhesion of bacteria to the urinary tract. These pili, assembled by the chaperone-usher pathway, are polymers of pilus subunits assembling into two parts: a thin, short tip fibrillum at the top, mounted on a long pilus rod. The rod adopts a helical quaternary structure and is thought to play essential roles: its formation may drive pilus extrusion by preventing backsliding of the nascent growing pilus within the secretion pore; the rod also has striking spring-like properties, being able to uncoil and recoil depending on the intensity of shear forces generated by urine flow. Here, we present an atomic model of the P pilus generated from a 3.8 Å resolution cryo-electron microscopy reconstruction. This structure provides the molecular basis for the rod’s remarkable mechanical properties and illuminates its role in pilus secretion
Sp1-regulated expression of p11 contributes to motor neuron degeneration by membrane insertion of TASK1
Disruption in membrane excitability contributes to malfunction and differential vulnerability
of specific neuronal subpopulations in a number of neurological diseases. The adaptor protein
p11, and background potassium channel TASK1, have overlapping distributions in the CNS.
Here, we report that the transcription factor Sp1 controls p11 expression, which impacts on
excitability by hampering functional expression of TASK1. In the SOD1-G93A mouse model of
ALS, Sp1-p11-TASK1 dysregulation contributes to increased excitability and vulnerability of
motor neurons. Interference with either Sp1 or p11 is neuroprotective, delaying neuron loss
and prolonging lifespan in this model. Nitrosative stress, a potential factor in human neurodegeneration,
stimulated Sp1 expression and human p11 promoter activity, at least in part,
through a Sp1-binding site. Disruption of Sp1 or p11 also has neuroprotective effects in a
traumatic model of motor neuron degeneration. Together our work suggests the Sp1-p11-
TASK1 pathway is a potential target for treatment of degeneration of motor neurons
Prevalence of asthma in a Portuguese countryside town: repercussions on absenteeism and self-concept
Modified Gravity and Cosmology
In this review we present a thoroughly comprehensive survey of recent work on
modified theories of gravity and their cosmological consequences. Amongst other
things, we cover General Relativity, Scalar-Tensor, Einstein-Aether, and
Bimetric theories, as well as TeVeS, f(R), general higher-order theories,
Horava-Lifschitz gravity, Galileons, Ghost Condensates, and models of extra
dimensions including Kaluza-Klein, Randall-Sundrum, DGP, and higher
co-dimension braneworlds. We also review attempts to construct a Parameterised
Post-Friedmannian formalism, that can be used to constrain deviations from
General Relativity in cosmology, and that is suitable for comparison with data
on the largest scales. These subjects have been intensively studied over the
past decade, largely motivated by rapid progress in the field of observational
cosmology that now allows, for the first time, precision tests of fundamental
physics on the scale of the observable Universe. The purpose of this review is
to provide a reference tool for researchers and students in cosmology and
gravitational physics, as well as a self-contained, comprehensive and
up-to-date introduction to the subject as a whole.Comment: 312 pages, 15 figure
- …