119,357 research outputs found
Comparative model accuracy of a data-fitted generalized Aw-Rascle-Zhang model
The Aw-Rascle-Zhang (ARZ) model can be interpreted as a generalization of the
Lighthill-Whitham-Richards (LWR) model, possessing a family of fundamental
diagram curves, each of which represents a class of drivers with a different
empty road velocity. A weakness of this approach is that different drivers
possess vastly different densities at which traffic flow stagnates. This
drawback can be overcome by modifying the pressure relation in the ARZ model,
leading to the generalized Aw-Rascle-Zhang (GARZ) model. We present an approach
to determine the parameter functions of the GARZ model from fundamental diagram
measurement data. The predictive accuracy of the resulting data-fitted GARZ
model is compared to other traffic models by means of a three-detector test
setup, employing two types of data: vehicle trajectory data, and sensor data.
This work also considers the extension of the ARZ and the GARZ models to models
with a relaxation term, and conducts an investigation of the optimal relaxation
time.Comment: 30 pages, 10 figures, 3 table
Afterpulsing studies of low noise InGaAs/InP single-photon negative feedback avalanche diodes
We characterize the temporal evolution of the afterpulse probability in a
free-running negative feedback avalanche diode (NFAD) over an extended range,
from 300 ns to 1 ms. This is possible thanks to an extremely low
dark count rate on the order of 1 cps at 10% efficiency, achieved by operating
the NFAD at a temperatures as low as 143 K. Experimental results in a large
range of operating temperatures (223-143 K) are compared with a legacy
afterpulsing model based on multiple trap families at discrete energy levels,
which is found to be lacking in physical completeness. Subsequently, we expand
on a recent proposal which considers a continuous spectrum of traps by
introducing well defined edges to the spectrum, which are experimentally
observed.Comment: 9 pages, 5 figure
Planetary Migration and Extrasolar Planets in the 2/1 Mean-Motion Resonance
We analyze the possible relationship between the current orbital elements
fits of known exoplanets in the 2/1 mean-motion resonance and the expected
orbital configuration due to migration. It is found that, as long as the
orbital decay was sufficiently slow to be approximated by an adiabatic process,
all captured planets should be in apsidal corotations. In other words, they
should show a simultaneous libration of both the resonant angle and the
difference in longitudes of pericenter.
We present a complete set of corotational solutions for the 2/1
commensurability, including previously known solutions and new results.
Comparisons with observed exoplanets show that current orbital fits of three
known planetary systems in this resonance are either consistent with apsidal
corotations (GJ876 and HD82943) or correspond to bodies with uncertain orbits
(HD160691).
Finally, we discuss the applicability of these results as a test for the
planetary migration hypothesis itself. If all future systems in this
commensurability are found to be consistent with corotational solutions, then
resonance capture of these bodies through planetary migration is a working
hypothesis. Conversely, If any planetary pair is found in a different
configuration, then either migration did not occur for those bodies, or it took
a different form than currently believed.Comment: Submitted to MNRA
Hopf bifurcations to quasi-periodic solutions for the two-dimensional plane Poiseuille flow
This paper studies various Hopf bifurcations in the two-dimensional plane
Poiseuille problem. For several values of the wavenumber , we obtain
the branch of periodic flows which are born at the Hopf bifurcation of the
laminar flow. It is known that, taking , the branch of periodic
solutions has several Hopf bifurcations to quasi-periodic orbits. For the first
bifurcation, previous calculations seem to indicate that the bifurcating
quasi-periodic flows are stable and go backwards with respect to the Reynolds
number, . By improving the precision of previous works we find that the
bifurcating flows are unstable and go forward with respect to . We have
also analysed the second Hopf bifurcation of periodic orbits for several
, to find again quasi-periodic solutions with increasing . In this
case the bifurcated solutions are stable to superharmonic disturbances for
up to another new Hopf bifurcation to a family of stable 3-tori. The proposed
numerical scheme is based on a full numerical integration of the Navier-Stokes
equations, together with a division by 3 of their total dimension, and the use
of a pseudo-Newton method on suitable Poincar\'e sections. The most intensive
part of the computations has been performed in parallel. We believe that this
methodology can also be applied to similar problems.Comment: 23 pages, 16 figure
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