3,328 research outputs found
Gas expulsion in highly substructured embedded star clusters
We investigate the response of initially substructured, young, embedded star
clusters to instantaneous gas expulsion of their natal gas. We introduce
primordial substructure to the stars and the gas by simplistically modelling
the star formation process so as to obtain a variety of substructure
distributed within our modelled star forming regions. We show that, by
measuring the virial ratio of the stars alone (disregarding the gas
completely), we can estimate how much mass a star cluster will retain after gas
expulsion to within 10% accuracy, no matter how complex the background
structure of the gas is, and we present a simple analytical recipe describing
this behaviour. We show that the evolution of the star cluster while still
embedded in the natal gas, and the behavior of the gas before being expelled,
are crucial processes that affect the timescale on which the cluster can evolve
into a virialized spherical system. Embedded star clusters that have high
levels of substructure are subvirial for longer times, enabling them to survive
gas expulsion better than a virialized and spherical system. By using a more
realistic treatment for the background gas than our previous studies, we find
it very difficult to destroy the young clusters with instantaneous gas
expulsion. We conclude that gas removal may not be the main culprit for the
dissolution of young star clusters.Comment: 19 pages, 8 figures, 2 tables. Accepted for publication in MNRA
Life and death of a hero - Lessons learned from modeling the dwarf spheroidal Hercules: an incorrect orbit?
Hercules is a dwarf spheroidal satellite of the Milky Way, found at a
distance of about 138 kpc, and showing evidence of tidal disruption. It is very
elongated and exhibits a velocity gradient of 16 +/- 3 km/s/kpc. Using this
data a possible orbit of Hercules has previously been deduced in the
literature. In this study we make use of a novel approach to find a best fit
model that follows the published orbit. Instead of using trial and error, we
use a systematic approach in order to find a model that fits multiple
observables simultaneously. As such, we investigate a much wider parameter
range of initial conditions and ensure we have found the best match possible.
Using a dark matter free progenitor that undergoes tidal disruption, our
best-fit model can simultaneously match the observed luminosity, central
surface brightness, effective radius, velocity dispersion, and velocity
gradient of Hercules. However, we find it is impossible to reproduce the
observed elongation and the position angle of Hercules at the same time in our
models. This failure persists even when we vary the duration of the simulation
significantly, and consider a more cuspy density distribution for the
progenitor. We discuss how this suggests that the published orbit of Hercules
is very likely to be incorrect.Comment: accepted by MNRAS; 19 pages, 19 figures, 2 table
Topological confinement in graphene bilayer quantum rings
We demonstrate the existence of localized electron and hole states in a
ring-shaped potential kink in biased bilayer graphene. Within the continuum
description, we show that for sharp potential steps the Dirac equation
describing carrier states close to the K (or K') point of the first Brillouin
zone can be solved analytically for a circular kink/anti-kink dot. The
solutions exhibit interfacial states which exhibit Aharonov-Bohm oscillations
as functions of the height of the potential step and/or the radius of the ring
Ursa Major II - Reproducing the observed properties through tidal disruption
Recent deep photometry of the dwarf spheroidal Ursa Major II's morphology,
and spectroscopy of individual stars, have provided a number of new constraints
on its properties. With a velocity dispersion 6 km s, and under
the assumption that the galaxy is virialised, the mass-to-light ratio is found
to be approaching 2000 - apparently heavily dark matter dominated. Using
N-Body simulations, we demonstrate that the observed luminosity, ellipticity,
irregular morphology, velocity gradient, and the velocity dispersion can be
well reproduced through processes associated with tidal mass loss, and in the
absence of dark matter. These results highlight the considerable uncertainty
that exists in measurements of the dark matter content of Ursa Major II. The
dynamics of the inner tidal tails, and tidal stream, causes the observed
velocity dispersion of stars to be boosted to values of 5 km s (20
km s at times). This effect is responsible for raising the velocity
dispersion of our model to the observed values in UMaII. We test an iterative
rejection technique for removing unbound stars from samples of UMaII stars
whose positions on the sky, and line-of-sight velocities, are provided. We find
this technique is very effective at providing an accurate bound mass from this
information, and only fails when the galaxy has a bound mass less than 10 of
its initial mass. However when mass remains bound, mass overestimation by
3 orders of magnitude are seen. Additionally we find that mass measurements
are sensitive to measurement uncertainty in line-of-sight velocities.
Measurement uncertainties of 1-4 km s result in mass overestimates by a
factor of 1.3-5.7.Comment: 17 pages, 12 figures, accepted to MNRAS: 23rd, May, 201
Optimization of the transmission of observable expectation values and observable statistics in Continuous Variable Teleportation
We analyze the statistics of observables in continuous variable quantum
teleportation in the formalism of the characteristic function. We derive
expressions for average values of output state observables in particular
cumulants which are additive in terms of the input state and the resource of
teleportation. Working with Squeezed Bell-like states, which may be optimized
in a free parameter for better teleportation performance we discuss the
relation between resources optimal for fidelity and for different observable
averages. We obtain the values of the free parameter which optimize the central
momenta and cumulants up to fourth order. For the cumulants the distortion
between in and out states due to teleportation depends only on the resource. We
obtain optimal parameters for the second and fourth order cumulants which do
not depend on the squeezing of the resource. The second order central momenta
which is equal to the second order cumulants and the photon number average are
optimized by the same resource. We show that the optimal fidelity resource,
found in reference (Phys. Rev. A {\bf 76}, 022301 (2007)) to depend also on the
characteristics of input, tends for high squeezing to the resource which
optimizes the second order momenta. A similar behavior is obtained for the
resource which optimizes the photon statistics which is treated here using the
sum of the squared differences in photon probabilities of input and output
states as the distortion measure. This is interpreted to mean that the
distortions associated to second order momenta dominates the behavior of the
output state for large squeezing of the resource. Optimal fidelity and optimal
photon statistics resources are compared and is shown that for mixtures of Fock
states they are equivalent.Comment: 25 pages, 11 figure
Estratégia de transferência de tecnologia como forma de apropriação do conhecimento.
Este artigo tem por objetivo apresentar a trajetória inovadora de uma cooperativa de produção de carnes caprina e ovina. Para isso, inicialmente apresenta definições de inovação, transferência de tecnologia, incubação de empresas, territórios da cidadania e arranjos produtivos locais. É apresentada a Cooperativa dos Produtores de Ovinos e Caprinos de Tauá – COOMANTA, arranjo concebido com o intuito de fortalecer a atuação dos produtores e sua inserção na economia local e regional. Ao final, são feitas recomendações para os produtores e para a evolução da cadeia produtiva da caprinocultura e da ovinocultura. [Technology transfer strategy as form a of knowledge apporpiation]
Estratégia de transferência de tecnologia como forma de apropriação do conhecimento: o caso Coomanta.
Analisar a transferência de tecnologia, utilizando o processo de incubação de empresas, como parte do processo de inovação para o desenvolvimento territorial, utilizando a Unidade de Processamento de Carne de Caprinos e Ovinos da Comunidade de Lustal, Tauá, no Território de Inhamuns-Crateús no Estado do Ceará, como estudo de caso, através da metodologia criada a partir do Programa de Apoio ao Desenvolvimento de Novas Empresas de Base Tecnológica Agropecuária e à Transferência de Tecnologia – PROETA, da Embrapa.bitstream/CNPC-2010/23062/1/doc90.pd
Desempenho e número de avaliações necessárias à seleção de hÃbridos de coqueiro.
Objetivou-se avaliar o desempenho de seis hÃbridos de coqueiro e estimar o coeficiente de repetibilidade dos caracteres número de frutos/planta e produtividade de albúmen sólido, por diferentes procedimentos estatÃsticos. Utilizou-se o delineamento experimental de blocos casualizados, com seis repetições e parcelas representadas por 30 plantas em arranjo triangular eqüilátero de 8,5m. Considerando o desempenho dos hÃbridos durante nove anos para produção de frutos e de albúmen sólido, pode-se recomendar para plantio os hÃbridos PB 111, PB 113 e PB 141 nas condições do Estado do Pará, visando atender à s indústrias (albúmen sólido) e também à venda de cocos ?in natura?. Os coeficientes de repetibilidade estimados pelos métodos Anova, componentes principais com base na covariância e na correlação e na análise da estrutura com base na correlação, foram 0,409, 0,655, 0,500 e 0,356 para número de frutos/planta, e de 0,573, 0,774, 0,655 e 0,554 para produtividade de albúmen sólido, respectivamente. Considerando o nÃvel de 90% de predição como ótimo para a tomada de decisão sobre a superioridade relativa dos hÃbridos e tomando como base a estimativa de repetibilidade obtida pelo método de componentes principais (covariância), recomenda-se realizar somente cinco e três avaliações para número de frutos e produção de albúmen sólido, respectivamente.bitstream/item/48945/1/Boletim-PD-20-AMAZ-ORIENTAL.pd
O associativismo como ferramenta para a inclusão de agricultores familiares produtores de caprinos e ovinos no Território de Aracatiaçu (CE).
bitstream/item/93967/1/Midia-O-associativismo-como-ferramenta.pd
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