2,384 research outputs found
Handling congestion in crowd motion modeling
We address here the issue of congestion in the modeling of crowd motion, in
the non-smooth framework: contacts between people are not anticipated and
avoided, they actually occur, and they are explicitly taken into account in the
model. We limit our approach to very basic principles in terms of behavior, to
focus on the particular problems raised by the non-smooth character of the
models. We consider that individuals tend to move according to a desired, or
spontanous, velocity. We account for congestion by assuming that the evolution
realizes at each time an instantaneous balance between individual tendencies
and global constraints (overlapping is forbidden): the actual velocity is
defined as the closest to the desired velocity among all admissible ones, in a
least square sense. We develop those principles in the microscopic and
macroscopic settings, and we present how the framework of Wasserstein distance
between measures allows to recover the sweeping process nature of the problem
on the macroscopic level, which makes it possible to obtain existence results
in spite of the non-smooth character of the evolution process. Micro and macro
approaches are compared, and we investigate the similarities together with deep
differences of those two levels of description
First results from the CALYPSO IRAM-PdBI survey. I. Kinematics of the inner envelope of NGC1333-IRAS2A
The structure and kinematics of Class 0 protostars on scales of a few hundred
AU is poorly known. Recent observations have revealed the presence of Keplerian
disks with a diameter of 150-180 AU in L1527-IRS and VLA1623A, but it is not
clear if such disks are common in Class 0 protostars. Here we present
high-angular-resolution observations of two methanol lines in NGC1333-IRAS2A.
We argue that these lines probe the inner envelope, and we use them to study
the kinematics of this region. Our observations suggest the presence of a
marginal velocity gradient normal to the direction of the outflow. However, the
position velocity diagrams along the gradient direction appear inconsistent
with a Keplerian disk. Instead, we suggest that the emission originates from
the infalling and perhaps slowly rotating envelope, around a central protostar
of 0.1-0.2 M. If a disk is present, it is smaller than the disk of
L1527-IRS, perhaps suggesting that NGC1333-IRAS2A is younger.Comment: Accepted for publication in A&A letter
String Shooter's overall shape in ambient air
In this article, we study the behaviour of a looped string launched in
ambient air using motorised wheels. We show that the loop, once it reaches its
stationary state, is either in the pulley or the air-lifted state. The
transition between these two distinct states occurs at the so-called takeoff
speed. We prove that this speed differs from one string to another based on its
characteristics. However, it is independent from the loop's length and its
initial launch angle. This speed indeed corresponds to the threshold where air
drag starts compensating for the weight of the string.Comment: 8 pages, 12 figure
Glycolaldehyde in Perseus young solar analogs
Aims: In this paper we focus on the occurrence of glycolaldehyde (HCOCH2OH)
in young solar analogs by performing the first homogeneous and unbiased study
of this molecule in the Class 0 protostars of the nearby Perseus star forming
region. Methods: We obtained sub-arcsec angular resolution maps at 1.3mm and
1.4mm of glycolaldehyde emission lines using the IRAM Plateau de Bure (PdB)
interferometer in the framework of the CALYPSO IRAM large program. Results:
Glycolaldehyde has been detected towards 3 Class 0 and 1 Class I protostars out
of the 13 continuum sources targeted in Perseus: NGC1333-IRAS2A1,
NGC1333-IRAS4A2, NGC1333-IRAS4B1, and SVS13-A. The NGC1333 star forming region
looks particularly glycolaldehyde rich, with a rate of occurrence up to 60%.
The glycolaldehyde spatial distribution overlaps with the continuum one,
tracing the inner 100 au around the protostar. A large number of lines (up to
18), with upper-level energies Eu from 37 K up to 375 K has been detected. We
derived column densities > 10^15 cm^-2 and rotational temperatures Trot between
115 K and 236 K, imaging for the first time hot-corinos around NGC1333-IRAS4B1
and SVS13-A. Conclusions: In multiple systems glycolaldehyde emission is
detected only in one component. The case of the SVS13-A+B and IRAS4-A1+A2
systems support that the detection of glycolaldehyde (at least in the present
Perseus sample) indicates older protostars (i.e. SVS13-A and IRAS4-A2), evolved
enough to develop the hot-corino region (i.e. 100 K in the inner 100 au).
However, only two systems do not allow us to firmly conclude whether the
primary factor leading to the detection of glycolaldehyde emission is the
environments hosting the protostars, evolution (e.g. low value of Lsubmm/Lint),
or accretion luminosity (high Lint).Comment: A&A, in pres
First results from the CALYPSO IRAM-PdBI survey - III. Monopolar jets driven by a proto-binary system in NGC1333-IRAS2A
Context: The earliest evolutionary stages of low-mass protostars are
characterised by hot and fast jets which remove angular momentum from the
circumstellar disk, thus allowing mass accretion onto the central object.
However, the launch mechanism is still being debated. Aims: We would like to
exploit high-angular (~ 0.8") resolution and high-sensitivity images to
investigate the origin of protostellar jets using typical molecular tracers of
shocked regions, such as SiO and SO. Methods: We mapped the inner 22" of the
NGC1333-IRAS2A protostar in SiO(5-4), SO(65-54), and the continuum emission at
1.4 mm using the IRAM Plateau de Bure interferometer in the framework of the
CALYPSO IRAM large program. Results: For the first time, we disentangle the
NGC1333-IRAS2A Class 0 object into a proto-binary system revealing two
protostars (MM1, MM2) separated by ~ 560 AU, each of them driving their own
jet, while past work considered a single protostar with a quadrupolar outflow.
We reveal (i) a clumpy, fast (up to |V-VLSR| > 50 km/s), and blueshifted jet
emerging from the brightest MM1 source, and (ii) a slower redshifted jet,
driven by MM2. Silicon monoxide emission is a powerful tracer of
high-excitation (Tkin > 100 K; n(H2) > 10^5 cm-3) jets close to the launching
region. At the highest velocities, SO appears to mimic SiO tracing the jets,
whereas at velocities close to the systemic one, SO is dominated by extended
emission, tracing the cavity opened by the jet. Conclusions: Both jets are
intrinsically monopolar, and intermittent in time. The dynamical time of the
SiO clumps is < 30-90 yr, indicating that one-sided ejections from protostars
can take place on these timescales.Comment: Astronomy & Astrophysics Letter, in pres
Generalized Wasserstein distance and its application to transport equations with source
In this article, we generalize the Wasserstein distance to measures with
different masses. We study the properties of such distance. In particular, we
show that it metrizes weak convergence for tight sequences.
We use this generalized Wasserstein distance to study a transport equation
with source, in which both the vector field and the source depend on the
measure itself. We prove existence and uniqueness of the solution to the Cauchy
problem when the vector field and the source are Lipschitzian with respect to
the generalized Wasserstein distance
Formation of the compact jets in the black hole GX 339-4
Galactic black hole binaries produce powerful outflows with emit over almost
the entire electromagnetic spectrum. Here, we report the first detection with
the Herschel observatory of a variable far-infrared source associated with the
compact jets of the black hole transient GX 339-4 during the decay of its
recent 2010-2011 outburst, after the transition to the hard state. We also
outline the results of very sensitive radio observations conducted with the
Australia Telescope Compact Array, along with a series of near-infrared,
optical (OIR) and X-ray observations, allowing for the first time the
re-ignition of the compact jets to be observed over a wide range of
wavelengths. The compact jets first turn on at radio frequencies with an
optically thin spectrum that later evolves to optically thick synchrotron
emission. An OIR reflare is observed about ten days after the onset of radio
and hard X-ray emission, likely reflecting the necessary time to build up
enough density, as well as to have acceleration (e.g. through shocks) along an
extended region in the jets. The Herschel measurements are consistent with an
extrapolation of the radio inverted power-law spectrum, but they highlight a
more complex radio to OIR spectral energy distribution for the jets.Comment: Accepted for publication in MNRAS Letter, 6 pages, 3 Figures + 1
online Tabl
Dissipative structure formation in cold-rolled Fe and Ni during heavy ion irradiation
We report 4-probe resistivity measurements of cold-rolled Ni and Fe during
100 MeV oxygen ion irradiation, at 300K. The resistivity shows increase and
saturation, marked by jumps. Employing 200 MeV silver ion irradiation of Fe and
Si(100) and topographically identifying strain at an artificial interface in
the latter, we assign the resistivity behavior to atomic rearrangements arising
from dissipation of incident ion energy at internal interfaces of Ni and Fe,
with positive feedback.}Comment: RevTex+ 7 Postscript figures; Fig 2 (topograph) available on demand
to [email protected]. To appear in Phys Rev Let
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