51 research outputs found
Vehicle Dispatching and Routing of On-Demand Intercity Ride-Pooling Services: A Multi-Agent Hierarchical Reinforcement Learning Approach
The integrated development of city clusters has given rise to an increasing
demand for intercity travel. Intercity ride-pooling service exhibits
considerable potential in upgrading traditional intercity bus services by
implementing demand-responsive enhancements. Nevertheless, its online
operations suffer the inherent complexities due to the coupling of vehicle
resource allocation among cities and pooled-ride vehicle routing. To tackle
these challenges, this study proposes a two-level framework designed to
facilitate online fleet management. Specifically, a novel multi-agent feudal
reinforcement learning model is proposed at the upper level of the framework to
cooperatively assign idle vehicles to different intercity lines, while the
lower level updates the routes of vehicles using an adaptive large neighborhood
search heuristic. Numerical studies based on the realistic dataset of Xiamen
and its surrounding cities in China show that the proposed framework
effectively mitigates the supply and demand imbalances, and achieves
significant improvement in both the average daily system profit and order
fulfillment ratio
Online Relocating and Matching of Ride-Hailing Services: A Model-Based Modular Approach
This study proposes an innovative model-based modular approach (MMA) to
dynamically optimize order matching and vehicle relocation in a ride-hailing
platform. MMA utilizes a two-layer and modular modeling structure. The upper
layer determines the spatial transfer patterns of vehicle flow within the
system to maximize the total revenue of the current and future stages. With the
guidance provided by the upper layer, the lower layer performs rapid
vehicle-to-order matching and vehicle relocation. MMA is interpretable, and
equipped with the customized and polynomial-time algorithm, which, as an online
order-matching and vehicle-relocation algorithm, can scale past thousands of
vehicles. We theoretically prove that the proposed algorithm can achieve the
global optimum in stylized networks, while the numerical experiments based on
both the toy network and realistic dataset demonstrate that MMA is capable of
achieving superior systematic performance compared to batch matching and
reinforcement-learning based methods. Moreover, its modular and lightweight
modeling structure further enables it to achieve a high level of robustness
against demand variation while maintaining a relatively low computational cost
Ammonia observations towards the Aquila Rift cloud complex
We surveyed the Aquila Rift complex including the Serpens South and W40
region in the NH(1,1) and (2,2) transitions making use of the Nanshan 26-m
telescope. The kinetic temperatures of the dense gas in the Aquila Rift complex
range from 8.9 to 35.0K with an average of 15.36.1K. Low gas temperatures
associate with Serpens South ranging from 8.9 to 16.8K with an average
12.31.7K, while dense gas in the W40 region shows higher temperatures
ranging from 17.7 to 35.0K with an average of 25.14.9 K. A comparison of
kinetic temperatures against HiGal dust temperatures indicates that the gas and
dust temperatures are in agreement in the low mass star formation region of
Serpens South. In the high mass star formation region W40, the measured gas
kinetic temperatures are higher than those of the dust. The turbulent component
of the velocity dispersion of NH(1,1) is found to be positively correlated
with the gas kinetic temperature, which indicates that the dense gas may be
heated by dissipation of turbulent energy. For the fractional total-NH3
abundance obtained by a comparison with Herschel infrared continuum data
representing dust emission we find values from 0.1 to 21 with
an average of 6.9. Serpens South also shows a
fractional total-NH3 abundance ranging from 0.2 to 21 with an
average of 8.6(. In W40, values are lower, between 0.1
and 4.3 with an average of 1.6(. Weak
velocity gradients demonstrate that the rotational energy is a negligible
fraction of the gravitational energy. In W40, gas and dust temperatures are not
strongly dependent on the projected distance to the recently formed massive
stars. Overall, the morphology of the mapped region is ring-like, with strong
emission at lower and weak emission at higher Galactic longitudes
Cloud-cloud collision and star formation in G323.18+0.15
We studied the cloud-cloud collision candidate G323.18+0.15 based on
signatures of induced filaments, clumps, and star formation. We used archival
molecular spectrum line data from the SEDIGISM CO(\,=\,2--1) survey,
from the Mopra southern Galactic plane CO survey, and infrared to radio data
from the GLIMPSE, MIPS, Hi-GAL, and SGPS surveys. Our new result shows that the
G323.18+0.15 complex is 3.55kpc away from us and consists of three cloud
components, G323.18a, G323.18b, and G323.18c. G323.18b shows a perfect U-shape
structure, which can be fully complemented by G323.18a, suggesting a collision
between G323.18a and the combined G323.18bc filamentary structure. One dense
compressed layer (filament) is formed at the bottom of G323.18b, where we
detect a greatly increased velocity dispersion. The bridge with an intermediate
velocity in a position-velocity diagram appears between G323.18a and G323.18b,
which corresponds to the compressed layer. G323.18a plus G323.18b as a whole
are probably not gravitationally bound. This indicates that high-mass star
formation in the compressed layer may have been caused by an accidental event.
The column density in the compressed layer of about cm and most of the dense clumps and high-mass stars are located
there. The average surface density of classI and classII young stellar objects
(YSOs) inside the G323.18+0.15 complex is much higher than the density in the
surroundings. The timescale of the collision between G323.18a and G323.18b is
Myr. This is longer than the typical lifetime of classI YSOs and is
comparable to the lifetime of classII YSOs
Gravitational collapse and accretion flows in the hub filament system G323.46-0.08
We studied the hub filament system G323.46-0.08 based on archival molecular
line data from the SEDIGISM 13CO survey and infrared data from the GLIMPSE,
MIPS, and Hi-GAL surveys. G323.46-0.08 consists of three filaments, F-north,
F-west, and F-south, that converge toward the central high_mass clump AGAL
323.459-0.079. F-west and Part 1 of the F-south show clear large-scale velocity
gradients 0.28 and 0.44 km s-1 pc-1, respectively. They seem to be channeling
materials into AGAL 323.459-0.079. The minimum accretion rate was estimated to
be 1216 M Myr-1. A characteristic V-shape appears around AGAL 323.459-0.079 in
the PV diagram, which traces the accelerated gas motions under gravitational
collapse. This has also been supported by model fitting results. All three
filaments are supercritical and they have fragmented into many dense clumps.
The seesaw patterns near most dense clumps in the PV diagram suggests that mass
accretion also occurs along the filament toward the clumps. Our results show
that filamentary accretion flows appear to be an important mechanism for
supplying the materials necessary to form the central high-mass clump AGAL
323.459-0.079 and to propel the star forming activity taking place therein
The JCMT BISTRO Survey: multiwavelength polarimetry of bright regions in NGC 2071 in the far-infrared/submillimetre range, with POL-2 and HAWC+
Polarized dust emission is a key tracer in the study of interstellar medium and of star formation. The observed polarization, however, is a product of magnetic field structure, dust grain properties, and grain alignment efficiency, as well as their variations in the line of sight, making it difficult to interpret polarization unambiguously. The comparison of polarimetry at multiple wavelengths is a possible way of mitigating this problem. We use data from HAWC+ /SOFIA and from SCUBA-2/POL-2 (from the BISTRO survey) to analyse the NGC 2071 molecular cloud at 154, 214, and 850 μm. The polarization angle changes significantly with wavelength over part of NGC 2071, suggesting a change in magnetic field morphology on the line of sight as each wavelength best traces different dust populations. Other possible explanations are the existence of more than one polarization mechanism in the cloud or scattering from very large grains. The observed change of polarization fraction with wavelength, and the 214-to-154 μm polarization ratio in particular, are difficult to reproduce with current dust models under the assumption of uniform alignment efficiency. We also show that the standard procedure of using monochromatic intensity as a proxy for column density may produce spurious results at HAWC+wavelengths. Using both long-wavelength (POL-2, 850 μm) and short-wavelength (HAWC+, ≲200μm) polarimetry is key in obtaining these results. This study clearly shows the importance of multi-wavelength polarimetry at submillimetre bands to understand the dust properties of molecular clouds and the relationship between magnetic field and star formation
The JCMT BISTRO Survey: Studying the Complex Magnetic Field of L43
We present observations of polarized dust emission at 850 μm from the L43 molecular cloud, which sits in the Ophiuchus cloud complex. The data were taken using SCUBA-2/POL-2 on the James Clerk Maxwell Telescope as a part of the BISTRO large program. L43 is a dense (NH 10
22 2 ~ –1023 cm−2) complex molecular cloud with a submillimeter-bright starless core and two protostellar sources. There appears to be an evolutionary gradient along the isolated filament that L43 is embedded within, with the most evolved source closest to the Sco OB2 association. One of the protostars drives a CO outflow that has created a cavity to the southeast. We see a magnetic field that appears to be aligned with the cavity walls of the outflow, suggesting interaction with the outflow. We also find a magnetic field strength of up to ∼160 ± 30 μG in the main starless core and up to ∼90 ± 40 μG in the more diffuse, extended region. These field strengths give magnetically super- and subcritical values, respectively, and both are found to be roughly trans-Alfvénic. We also present a new method of data reduction for these denser but fainter objects like starless cores
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