2,878 research outputs found
Development of a VOR/DME model for an advanced concepts simulator
The report presents a definition of a VOR/DME, airborne and ground systems simulation model. This description was drafted in response to a need in the creation of an advanced concepts simulation in which flight station design for the 1980 era can be postulated and examined. The simulation model described herein provides a reasonable representation of VOR/DME station in the continental United States including area coverage by type and noise errors. The detail in which the model has been cast provides the interested researcher with a moderate fidelity level simulator tool for conducting research and evaluation of navigator algorithms. Assumptions made within the development are listed and place certain responsibilities (data bases, communication with other simulation modules, uniform round earth, etc.) upon the researcher
Tidal disruption of dark matter halos around proto-globular clusters
Tidal disruption of dark matter halos around proto-globular clusters in a
halo of a small galaxy is studied in the context of the hierarchical clustering
scenario by using semi-cosmological N-body/SPH simulations assuming the
standard cold dark matter model (). Our analysis on formation and
evolution of the galaxy and its substructures archives until . In such
a high-redshift universe, the Einstein-de Sitter universe is still a good
approximation for a recently favored -dominated universe, and then our
results does not depend on the choice of cosmology. In order to resolve small
gravitationally-bound clumps around galaxies and consider radiative cooling
below , we adopt a fine mass resolution (m_{\rm SPH} = 1.12 \times
10^3 \Msun). Because of the cooling, each clump immediately forms a
`core-halo' structure which consists of a baryonic core and a dark matter halo.
The tidal force from the host galaxy mainly strips the dark matter halo from
clumps and, as a result, theses clumps get dominated by baryons. Once a clump
is captured by the host halo, its mass drastically decreases each pericenter
passage. At , more than half of the clumps become baryon dominated
systems (baryon mass/total mass ). Our results support the tidal
evolution scenario of the formation of globular clusters and baryon dominated
dwarf galaxies in the context of the cold dark matter universe.Comment: 9page, 13 figures. Accepted for publication in ApJ. A high-resolution
PDF of the paper can be obtained from http://th.nao.ac.jp/~takayuki/ApJ05
Simulations of galaxy formation in a Λ cold dark matter universe : I : dynamical and photometric properties of a simulated disk galaxy.
We present a detailed analysis of the dynamical and photometric properties of a disk galaxy simulated in the cold dark matter (CDM) cosmogony. The galaxy is assembled through a number of high-redshift mergers followed by a period of quiescent accretion after z1 that lead to the formation of two distinct dynamical components: a spheroid of mostly old stars and a rotationally supported disk of younger stars. The surface brightness profile is very well approximated by the superposition of an R1/4 spheroid and an exponential disk. Each photometric component contributes a similar fraction of the total luminosity of the system, although less than a quarter of the stars form after the last merger episode at z1. In the optical bands the surface brightness profile is remarkably similar to that of Sab galaxy UGC 615, but the simulated galaxy rotates significantly faster and has a declining rotation curve dominated by the spheroid near the center. The decline in circular velocity is at odds with observation and results from the high concentration of the dark matter and baryonic components, as well as from the relatively high mass-to-light ratio of the stars in the simulation. The simulated galaxy lies 1 mag off the I-band Tully-Fisher relation of late-type spirals but seems to be in reasonable agreement with Tully-Fisher data on S0 galaxies. In agreement with previous simulation work, the angular momentum of the luminous component is an order of magnitude lower than that of late-type spirals of similar rotation speed. This again reflects the dominance of the slowly rotating, dense spheroidal component, to which most discrepancies with observation may be traced. On its own, the disk component has properties rather similar to those of late-type spirals: its luminosity, its exponential scale length, and its colors are all comparable to those of galaxy disks of similar rotation speed. This suggests that a different form of feedback than adopted here is required to inhibit the efficient collapse and cooling of gas at high redshift that leads to the formation of the spheroid. Reconciling, without fine-tuning, the properties of disk galaxies with the early collapse and high merging rates characteristic of hierarchical scenarios such as CDM remains a challenging, yet so far elusive, proposition
A Unified Scaling Law in Spiral Galaxies
We investigate the origin of a unified scaling relation in spiral galaxies.
Observed spiral galaxies are spread on a plane in the
three-dimensionallogarithmic space of luminosity L, radius R and rotation
velocity V. The plane is expressed as in I-passband,
where is a constant. On the plane, observed galaxies are distributed
in an elongated region which looks like the shape of a surfboard. The
well-known scaling relations, L-V (Tully-Fisher relation), V-R (also the
Tully-Fisher relation) and R-L (Freeman's law), can be understood as oblique
projections of the surfboard-like plane into 2-D spaces. This unified
interpretation of the known scaling relations should be a clue to understand
the physical origin of all the relations consistently. Furthermore, this
interpretation can also explain why previous studies could not find any
correlation between TF residuals and radius.
In order to clarify the origin of this plane, we simulate formation and
evolution of spiral galaxies with the N-body/SPH method, including cooling,
star formation and stellar feedback. Initial conditions are set to isolated 14
spheres with two free parameters, such as mass and angular momentum. The CDM
(h=0.5, ) cosmology is considered as a test case. The simulations
provide the following two conclusions: (a) The slope of the plane is well
reproduced but the zero-point is not. This zero-point discrepancy could be
solved in a low density ($\Omega_00.5) cosmology.
(b) The surfboard-shaped plane can be explained by the control of galactic mass
and angular momentum.Comment: Accepted for publication in ApJ Letters. 6 pages including 2 figure
Star Formation, Supernovae Feedback and the Angular Momentum Problem in Numerical CDM Cosmogony: Half Way There?
We present a smoothed particle hydrodynamic (SPH) simulation that reproduces
a galaxy that is a moderate facsimile of those observed. The primary failing
point of previous simulations of disk formation, namely excessive transport of
angular momentum from gas to dark matter, is ameliorated by the inclusion of a
supernova feedback algorithm that allows energy to persist in the model ISM for
a period corresponding to the lifetime of stellar associations. The inclusion
of feedback leads to a disk at a redshift , with a specific angular
momentum content within 10% of the value required to fit observations. An
exponential fit to the disk baryon surface density gives a scale length within
17% of the theoretical value. Runs without feedback, with or without star
formation, exhibit the drastic angular momentum transport observed elsewhere.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter
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MEASURING TOURISM ADVERTISING: THE DESTINATION ADVERTISING RESPONSE (DAR) MODEL
This study proposes a facets-based destination advertising response (DAR) model that integrates the principal components or decisions of a trip. The proposed DAR framework is discussed and its adequacy for evaluating destination marketing campaigns is assessed. The results of this study indicate that while most travelers decide where to visit without regard to destination advertising, travel advertising significantly affects many trip-related decisions, which in turn, affect the level of visitor expenditures
In vitro assay for antimicrobial interaction evaluation and risk assessment of antimicrobials in anaerobic digestion of swine manure.
SafePork 2017
Acompanhamento de um biodigestor de fluxo ascendente para tratamento de efluentes da suinocultura.
Projeto/Plano de Ação: 02.07.06.007
Cuidados com os biodigestores para estabilidade e qualidade na geração de biogás.
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