6,937 research outputs found
Dynamic User Equilibrium (DUE)
The quantitative analysis of road network traffic performed through static
assignment models yields the transport demand-supply equilibrium under
the assumption of within-day stationarity. This implies that the relevant
variables of the system (i.e. user flows, travel times, costs) are assumed to
be constant over time within the reference period. Although static
assignment models satisfactorily reproduce congestion effects on traffic flow
and cost patterns, they do not allow to represent the variation over time of
the demand flows (i.e. around the rush hour) and of the network
performances (i.e. in presence of time varying tolls, lane usage, signal plans,
link usage permission); most importantly, they cannot reproduce some
important dynamic phenomena, such as the formation and dispersion of
vehicle queues due to the temporary over-saturation of road sections, and
the spillback, that is queues propagation towards upstream roads
HALOGAS: HI Observations and Modeling of the Nearby Edge-on Spiral Galaxy NGC 4565
We present 21-cm observations and models of the neutral hydrogen in NGC 4565,
a nearby, edge-on spiral galaxy, as part of the Westerbork Hydrogen Accretion
in LOcal GAlaxieS (HALOGAS) survey. These models provide insight concerning
both the morphology and kinematics of HI above, as well as within, the disk.
NGC 4565 exhibits a distinctly warped and asymmetric disk with a flaring layer.
Our modeling provides no evidence for a massive, extended HI halo. We see
evidence for a bar and associated radial motions. Additionally, there are
indications of radial motions within the disk, possibly associated with a ring
of higher density. We see a substantial decrease in rotational velocity with
height above the plane of the disk (a lag) of -40 +5/-20 km/s/kpc and -30
+5/-30 km s/kpc in the approaching and receding halves, respectively. This lag
is only seen within the inner ~4.75' (14.9 kpc) on the approaching half and
~4.25' (13.4 kpc) on the receding, making this a radially shallowing lag, which
is now seen in the HI layers of several galaxies. When comparing results for
NGC 4565 and those for other galaxies, there are tentative indications of high
star formation rate per unit area being associated with the presence of a halo.
Finally, HI is found in two companion galaxies, one of which is clearly
interacting with NGC 4565.Comment: 17 pages, 16 figures, accepted for publication in the Astrophysical
Journal, modified affiliatio
Mass models from high-resolution HI data of the dwarf galaxy NGC 1560
We present HI observations performed at the GMRT of the nearby dwarf galaxy
NGC 1560. This Sd galaxy is well-known for a distinct "wiggle" in its rotation
curve. Our new observations have twice the resolution of the previously
published HI data. We derived the rotation curve by taking projection effects
into account, and we verified the derived kinematics by creating model
datacubes. This new rotation curve is similar to the previously published one:
we confirm the presence of a clear wiggle. The main differences are in the
innermost ~100 arcsec of the rotation curve, where we find slightly (<~ 5 km/s)
higher velocities. Mass modelling of the rotation curve results in good fits
using the core-dominated Burkert halo (which however does not reproduce the
wiggle), bad fits using the a Navarro, Frenk & White halo, and good fits using
MOND (Modified Newtonian Dynamics), which also reproduces the wiggle.Comment: Accepted for publication in MNRAS. 11 pages, 13 figures.
High-resolution version available at
http://users.ugent.be/~ggianfra/1560_final.pd
Analysis of cool DO-type white dwarfs from the Sloan Digital Sky Survey Data Release 10
We report on the identification of 22 new cool DO-type white dwarfs (WD)
detected in Data Release 10 (DR10) of the Sloan Digital Sky Survey (SDSS).
Among them, we found one more member of the so-called hot-wind DO WDs, which
show ultrahigh excitation absorption lines. Our non-LTE model atmosphere
analyses of these objects and two not previously analyzed hot-wind DO WDs,
revealed effective temperatures and gravities in the ranges Teff=45-80kK and
log g= 7.50-8.75. In eight of the spectra we found traces of C (0.001-0.01, by
mass). Two of these are the coolest DO WDs ever discovered that still show a
considerable amount of C in their atmospheres. This is in strong contradiction
with diffusion calculations, and probably, similar to what is proposed for DB
WDs, a weak mass-loss is present in DO WDs. One object is the most massive DO
WD discovered so far with a mass of 1.07 M_sun if it is an ONe-WD or 1.09 M_sun
if it is a CO-WD. We furthermore present the mass distribution of all known hot
non-DA (pre-) WDs and derive the hot DA to non-DA ratio for the SDSS DR7
spectroscopic sample. The mass distribution of DO WDs beyond the wind limit
strongly deviates from the mass distribution of the objects before the wind
limit. We address this phenomenon by applying different evolutionary input
channels. We argue that the DO WD channel may be fed by about 13% by
post-extreme-horizontal branch stars and that PG1159 stars and O(He) stars may
contribute in a similar extent to the non-DA WD channel.Comment: 13 pages, accepted for publication in A&
Assessing Environmental Impacts of Earthquake-Induced-Damage for an Italian Case-study Building
This study assesses environmental impacts due to the repair of earthquake-induced damage considering an old reinforced concrete (RC) frame representative of those built in Italy before the 1970s. Such impacts, expressed in terms of embodied carbon, represent a considerable component of buildingsďľ’ life-cycle embodied carbon in seismically-prone regions. Embodied carbon is the term for greenhouse gas emissions associated with manufacturing and using a product/service. In the case of materials for building repairs, this includes extraction, manufacturing, transporting, construction, maintenance, and disposal. The seismic damage sustained by the case-study frame is first evaluated using the FEMA P-58 methodology. Specifically, the frameďľ’s nonlinear response is analysed against increasing ground-shaking intensities, followed by estimating the damage incurred by its individual components via ad-hoc fragility models. Damage is then converted to embodied carbon by calibrating consequence models specifically developed for Italian structural and non-structural building components. This is accomplished by: 1) collecting environmental-impact data from Italian manufacturers of relevant construction materials and; 2) defining suitable structure-specific damage levels and the required repair work for every component. Results show that the embodied carbon induced by seismic damage throughout the case-study buildingďľ’s life cycle might exceed 25% of that generated during its initial construction (pre-use phase)
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