4,307 research outputs found
Satellites of Simulated Galaxies: survival, merging, and their relation to the dark and stellar halos
We study the population of satellite galaxies formed in a suite of
N-body/gasdynamical simulations of galaxy formation in a LCDM universe. We find
little spatial or kinematic bias between the dark matter and the satellite
population. The velocity dispersion of the satellites is a good indicator of
the virial velocity of the halo: \sigma_{sat}/V_{vir}=0.9 +/- 0.2. Applied to
the Milky Way and M31 this gives V_{vir}^{MW}=109 +/- 22$ km/s and
V_{vir}^{M31} = 138 +/- 35 km/s, respectively, substantially lower than the
rotation speed of their disk components. The detailed kinematics of simulated
satellites and dark matter are also in good agreement. By contrast, the stellar
halo of the simulated galaxies is kinematically and spatially distinct from the
population of surviving satellites. This is because the survival of a satellite
depends on mass and on time of accretion; surviving satellites are biased
toward low-mass systems that have been recently accreted by the galaxy. Our
results support recent proposals for the origin of the systematic differences
between stars in the Galactic halo and in Galactic satellites: the elusive
``building blocks'' of the Milky Way stellar halo were on average more massive,
and were accreted (and disrupted) earlier than the population of dwarfs that
has survived self-bound until the present.Comment: 13 pages, 11 figures, MNRAS in press. Accepted version with minor
changes. Version with high resolution figures available at:
http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm
Cosmic M\'enage \`a Trois: The Origin of Satellite Galaxies On Extreme Orbits
We examine the orbits of satellite galaxies identified in a suite of
N-body/gasdynamical simulations of the formation of galaxies in a LCDM
universe. Most satellites follow conventional orbits; after turning around,
they accrete into their host halo and settle on orbits whose apocentric radii
are steadily eroded by dynamical friction. However, a number of outliers are
also present, we find that ~1/3 of satellites identified at are on
unorthodox orbits, with apocenters that exceed their turnaround radii. This
population of satellites on extreme orbits consists typically of the faint
member of a satellite pair that has been ejected onto a highly-energetic orbit
during its first approach to the primary. Since the concurrent accretion of
multiple satellite systems is a defining feature of hierarchical models of
galaxy formation, we speculate that this three-body ejection mechanism may be
the origin of (i) some of the newly discovered high-speed satellites around M31
(such as Andromeda XIV); (ii) some of the distant fast-receding Local Group
members, such as Leo I; and (iii) the oddly isolated dwarf spheroidals Cetus
and Tucana in the outskirts of the Local Group. Our results suggest that care
must be exercised when using the orbits of the most weakly bound satellites to
place constraints on the total mass of the Local Group.Comment: 10 pages, 6 figures, MNRAS in press. Accepted version with minor
changes. Version with high resolution figures available at:
http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm
Density distribution of particles upon jamming after an avalanche in a 2D silo
We present a complete analysis of the density distribution of particles in a
two dimensional silo after discharge. Simulations through a pseudo-dynamic
algorithm are performed for filling and subsequent discharge of a plane silo.
Particles are monosized hard disks deposited in the container and subjected to
a tapping process for compaction. Then, a hole of a given size is open at the
bottom of the silo and the discharge is triggered. After a clogging at the
opening is produced, and equilibrium is restored, the final distribution of the
remaining particles at the silo is analyzed by dividing the space into cells
with different geometrical arrangements to visualize the way in which the
density depression near the opening is propagated throughout the system. The
different behavior as a function of the compaction degree is discussed.Comment: 11 pages, 10 figure
Satellite Galaxies and Fossil Groups in the Millennium Simulation
We use a semianalytic galaxy catalogue constructed from the Millennium
Simulation to study the satellites of isolated galaxies in the LCDM cosmogony.
This sample (~80,000$ bright primaries, surrounded by ~178,000 satellites)
allows the characterization, with minimal statistical uncertainty, of the
dynamical properties of satellite/primary galaxy systems in a LCDM universe. We
find that, overall, the satellite population traces the dark matter rather
well: its spatial distribution and kinematics may be approximated by an NFW
profile with a mildly anisotropic velocity distribution. Their spatial
distribution is also mildly anisotropic, with a well-defined ``anti-Holmberg''
effect that reflects the misalignment between the major axis and angular
momentum of the host halo. The isolation criteria for our primaries picks not
only galaxies in sparse environments, but also a number of primaries at the
centre of ''fossil'' groups. We find that the abundance and luminosity function
of these unusual systems are in reasonable agreement with the few available
observational constraints. We recover the expected L_{host} \sigma_{sat}^3
relation for LCDM models for truly-isolated primaries. Less strict primary
selection, however, leads to substantial modification of the scaling relation.
Our analysis also highlights a number of difficulties afflicting studies that
rely on blind stacking of satellite systems to constrain the mean halo mass of
the primary galaxies.Comment: 18 pages, 14 figures, MNRAS in press. Accepted version with minor
changes. Version with high resolution figures available at:
http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm
Avaliação do desempenho produtivo de bovinos de corte, em pastos puros e consorciados com o amendoim forrageiro cultivar Mandobi, no Acre.
Objetivou-se avaliar o efeito da consorciação de pastos de Brachiaria humidicola com Arachis pintoi cv. Mandobi sobre o desempenho produtivo de novilhos Nelore. O experimento foi realizado em uma fazenda particular no Estado do Acre, de novembro de 2013 a fevereiro de 2014. As unidades experimentais foram seis piquetes de 1,42 ha cada, em um delineamento inteiramente casualizado, com dois tratamentos e três repetições. Foram utilizados seis novilhos Nelore, não castrados, com idade e peso médio iniciais de 16 meses e 282 kg, como testes. Novilhos adicionais foram alocados ou retirados dos piquetes para a manutenção da altura do pasto, em 15 cm. Os animais foram pesados a cada 28 dias, após um jejum de 16 horas, para determinar o ganho de peso médio diário (GMD). A capacidade de suporte foi calculada de acordo com o peso médio e número de animais/dia em cada unidade experimental. A produtividade animal foi calculada com base no GMD dos animais teste e o número de animais/dia utilizados durante todo experimento. As médias dos quadrados mÃnimos foram comparadas usando o teste de Tukey com 5% de probabilidade. A taxa de lotação durante o perÃodo experimental foi de 3,97 UA/ha nos pastos consorciado e 3,81 nos pastos puros (P = 0,8255). O ganho de peso médio diário dos animais foi 17,7% superior (P = 0,0465) para o pasto consorciado (0,597 x 0,479 kg/animal/dia) e a produtividade animal aumentou 18,7% (P = 0,1010) pelo uso de A. pintoi cv. Mandobi (330 kg/ha x 278 kg/ha). Este estudo mostra que apenas 7,7% desta leguminosa em pastagens consorciadas com Brachiaria humidicola pode afetar positivamente a produtividade animal
Possible mechanism for achieving glass-like thermal conductivities in crystals with off-center atoms
In the filled Ga/Ge clathrate, Eu and Sr are off-center in site 2 but Ba is
on-center. All three filler atoms (Ba,Eu,Sr) have low temperature Einstein
modes; yet only for the Eu and Sr systems is there a large dip in the thermal
conductivity, attributed to the Einstein modes. No dip is observed for Ba. Here
we argue that it is the off-center displacement that is crucial for
understanding this unexplained difference in behavior. It enhances the coupling
between the "rattler" motion and the lattice phonons for the Eu and Sr systems,
and turns on/off another scattering mechanism (for 1K < T < 20K) produced by
the presence/absence of off-center sites. The random occupation of different
off-center sites produces a high density of symmetry-breaking defects which
scatters phonons. It may also be important for improving our understanding of
other glassy systems.Comment: 4 pages, 1 figure (2 parts) -- v2: intro broadened; strengthened
arguments regarding need for additional phonon scattering mechanis
Lattice dynamics and reduced thermal conductivity of filled skutterudites
The great reduction in thermal conductivity of skutterudites upon filling the
``void'' sites with Rare Earth (RE) ions is key to their favorable
thermoelectric properties but remains to be understood. Using lattice dynamic
models based on first principles calculations, we address the most popular
microscopic mechanism, reduction via rattling ions. The model withstands
inelastic neutron scattering and specific heat measurements, and refutes
hypotheses of an anharmonic RE potential and of two distinct localized RE
vibrations of disparate frequencies. It does indicate a strong hybridization
between bare La vibrations and certain Sb-like phonon branches, suggesting
anharmonic scattering by harmonic RE motions as an important mechanism for
suppression of heat conductivity.Comment: modified version resubmitted to PRB. Results unchanged, text changed
substantiall
Sharing of hand kinematic synergies across subjects in daily living activities
The motor system is hypothesised to use kinematic synergies to simplify hand control. Recent studies suggest that there is a large set of synergies, sparse in degrees of freedom, shared across subjects, so that each subject performs each action with a sparse combination of synergies. Identifying how synergies are shared across subjects can help in prostheses design, in clinical decision-making or in rehabilitation. Subject-specific synergies of healthy subjects performing a wide number of representative daily living activities were obtained through principal component analysis. To make synergies comparable between subjects and tasks, the hand kinematics data were scaled using normative range of motion data. To obtain synergies sparse in degrees of freedom a rotation method that maximizes the sum of the variances of the squared loadings was applied. Resulting synergies were clustered and each cluster was characterized by a core synergy and different indexes (prevalence, relevance for function and within-cluster synergy similarity), substantiating the sparsity of synergies. The first two core synergies represent finger flexion and were present in all subjects. The remaining core synergies represent coordination of the thumb joints, thumb-index joints, palmar arching or fingers adduction, and were employed by subjects in different combinations, thus revealing different subject-specific strategies
Avaliação de produtividade de novas linhagens de mamoeiro.
O mamoeiro é uma cultura de expressiva importância para o Brasil, um dos principais produtores da fruta, com produção de 1,9 milhão de toneladas em 2008, participando com 20,8% do mercado mundial, de cerca 9,1 milhões de toneladas. Todavia, a sustentabilidade e expansão da cultura dependem do desenvolvimento de novos genótipos com caracterÃsticas superiores. Apenas três cultivares dos grupos Solo ou Formosa ocupam a maior parte dos plantios comerciais, o que tem prejudicado o desenvolvimento da cultura, pelo aumento da vulnerabilidade ao ataque de pragas e doenças.PDF. 096_11
Free mobility, locked rights: the posting of construction workers from Portugal
Mobility has become a cornerstone of the contemporary social world. In the European Union, the removal of barriers aimed at promoting the free movement of the labour force is a major goal of the integration process. This article investigates the political economy of posting, analysing the working and living conditions of Portuguese construction workers posted to other EU Member States. It highlights a set of abusive and exploitative practices involved in posting and the role those practices play in the (de)regulation of labour within the construction sector. In spite of the access to a pan-European labour market and the general principle of equal treatment, posted workers have restricted social rights in the host country. The study presented is based on research developed within the ‘EU Post Lab’ project, aimed at promoting activities of cooperation and awareness raising in the field of posting. The methodology adopted includes document analysis and interviews.info:eu-repo/semantics/acceptedVersio
- …