2,484 research outputs found
Cosmic web alignments with the shape, angular momentum and peculiar velocities of dark matter haloes
We study the alignment of dark matter haloes with the cosmic web
characterized by the tidal and velocity shear fields. We focus on the alignment
of their shape, angular momentum and peculiar velocities. We use a cosmological
N-body simulation that allows to study dark matter halos spanning almost five
orders of magnitude in mass (-) and
spatial scales of - Mpc to define the cosmic web. We find
that the halo shape presents the strongest alignment along the smallest tidal
eigenvector, e.g. along filaments and walls, with a signal that gets stronger
as the halo mass increases. In the case of the velocity shear field only
massive halos tend to have their shapes aligned
along the largest tidal eigenvector; that is, perpendicular to filaments and
walls. For the angular momentum we find alignment signals only for halos more
massive than both in the tidal and velocity shear
webs where the preferences are for it to be parallel to the middle eigenvector;
perpendicular to filaments and parallel to walls. Finally, the peculiar
velocities show a strong alignment along the smallest tidal eigenvector for all
halo masses; halos move along filaments and walls. In the velocity shear the
same alignment is present but weaker and only for haloes less massive than
. Our results clearly show that the two different
algorithms we used to define the cosmic web describe different physical aspects
of non-linear collapse and should be used in a complementary way to understand
the effect of the cosmic web on galaxy evolution.Comment: 14 pages, 5 figures, MNRAS accepte
Dynamic Control Design LQR PI Vectorial of Remotely Operated Underwater Vehicl
Este Documento muestra el control LQR (Lineal Regulador cuadrático)
PI (Integral Proporcional) Diseño vectorial, que está desarrollado para
controlar la dinámica de un vehículo submarino operado remotamente ROV,
para permitir que el vehículo siga una trayectoria horizontal de forma autónoma.
Los resultados se muestran mediante simulaciones de seguimiento de trayectoria
de ROV obteniendo resultados satisfactorios y cumpliendo con el objetivo de controlar
la dinámica mientras sigue una trayectoria.Universidad Libre -- Facultad de ingeniería -- Ingeniería MecánicaThis Document shows the control LQR (Linear
quadratic Regulator) PI (Proportional Integral)Vectorial design,
which is developed to control the dynamic of a remote operated
underwater vehicle ROV, to allow that the vehicle follow a
horizontal trajectory autonomously . The results are showed
through simulations of following the trajectory of ROV obtaining
satisfactory results and complying with the objective to control
the dynamic while follow a trajector
U.S. commercial electricity consumption
Commercial electricity usage exceeds that of industrial usage and is almost as large as residential electricity consumption in the United States. In this study, regional economic, demographic, and climatic data are used to analyze commercial electricity demand in the United States. Results indicate that total commercial demand for electricity is negatively related to price. In addition, the number of businesses and service income positively affect electricity demand for commercial use. The results are similar for equations estimated for kilowatt-hours demanded per business. The regional dummy variables exhibit different signs, which may occur due to climate factors because warm weather regions experience greater volumes of cooling degree-days, while cool weather regions observe larger amounts of heating degree-days. Although coefficients for the price of natural gas are positive, they do not satisfy the 5-percent significance criterion. The latter suggests that natural gas may not be a substitute good for electricity within the commercial sector of the U.S. economy.Commercial Electricity Consumption; Regional Economics
Stochastic angular momentum slews and flips and their effect on discs in galaxy formation models
The angular momentum of galactic discs in semi-analytic models of galaxy
formation is usually updated in time as material is accreted to the disc by
adopting a constant dimensionless spin parameter and little attention is paid
to the effects of accretion with misaligned angular momenta. These effects are
the subject of this paper, where we adopt a Monte-Carlo simulation for the
changes in the direction of the angular momentum of a galaxy disc as it
accretes matter based on accurate measurements from dark-matter haloes in the
Millennium II simulation. In our semi-analytic model implementation, the flips
seen the dark matter haloes are assumed to be the same for the cold baryons;
however, we also assume that in the latter the flip also entails a difficulty
for the disc to increase its angular momentum which causes the disc to become
smaller relative to a no-flip case. This makes star formation to occur faster,
specially in low mass galaxies at all redshifts allowing galaxies to reach
higher stellar masses faster. We adopt a new condition for the triggering of
starbursts during mergers. As these produce the largest flips it is natural to
adopt the disc instability criterion to evaluate the triggering of bursts in
mergers instead of one based on mass ratios as in the original model. The new
implementation reduces the average lifetimes of discs by a factor of 2, while
still allowing old ages for the present-day discs of large spiral galaxies. It
also provides a faster decline of star formation in massive galaxies and a
better fit to the bright end of the luminosity function at z = 0.Comment: 15 pages, 12 figures, MNRAS in pres
Galactic conformity measured in semi-analytic models
We study the correlation between the specific star formation rate of central
galaxies and neighbour galaxies, also known as 'galactic conformity', out to 20
Mpc/h using three semi-analytic models (SAMs, one from L-GALAXIES and other two
from GALFORM). The aim is to establish whether SAMs are able to show galactic
conformity using different models and selection criteria. In all the models,
when the selection of primary galaxies is based on an isolation criterion in
real space, the mean fraction of quenched galaxies around quenched primary
galaxies is higher than that around star-forming primary galaxies of the same
stellar mass. The overall signal of conformity decreases when we remove
satellites selected as primary galaxies, but the effect is much stronger in
GALFORM models compared with the L-GALAXIES model. We find this difference is
partially explained by the fact that in GALFORM once a galaxy becomes a
satellite remains as such, whereas satellites can become centrals at a later
time in L-GALAXIES. The signal of conformity decreases down to 60% in the
L-GALAXIES model after removing central galaxies that were ejected from their
host halo in the past. Galactic conformity is also influenced by primary
galaxies at fixed stellar mass that reside in dark matter haloes of different
masses. Finally, we explore a proxy of conformity between distinct haloes. In
this case the conformity is weak beyond ~ 3 Mpc/h (<3% in L-GALAXIES, <1-2% in
GALFORM models). Therefore, it seems difficult that conformity is directly
related with a long-range effect.Comment: 15 pages, 7 figures. Accepted for publication in MNRA
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