280 research outputs found
Competition between shared autonomous vehicles and public transit: A case study in Singapore
Emerging autonomous vehicles (AV) can either supplement the public
transportation (PT) system or compete with it. This study examines the
competitive perspective where both AV and PT operators are profit-oriented with
dynamic adjustable supply strategies under five regulatory structures regarding
whether the AV operator is allowed to change the fleet size and whether the PT
operator is allowed to adjust headway. Four out of the five scenarios are
constrained competition while the other one focuses on unconstrained
competition to find the Nash Equilibrium. We evaluate the competition process
as well as the system performance from the standpoints of four stakeholders --
the AV operator, the PT operator, passengers, and the transport authority. We
also examine the impact of PT subsidies on the competition results including
both demand-based and supply-based subsidies. A heuristic algorithm is proposed
to update supply strategies for AV and PT based on the operators' historical
actions and profits. An agent-based simulation model is implemented in the
first-mile scenario in Tampines, Singapore. We find that the competition can
result in higher profits and higher system efficiency for both operators
compared to the status quo. After the supply updates, the PT services are
spatially concentrated to shorter routes feeding directly to the subway station
and temporally concentrated to peak hours. On average, the competition reduces
the travel time of passengers but increases their travel costs. Nonetheless,
the generalized travel cost is reduced when incorporating the value of time.
With respect to the system efficiency, the bus supply adjustment increases the
average vehicle load and reduces the total vehicle kilometer traveled measured
by the passenger car equivalent (PCE), while the AV supply adjustment does the
opposite
Early Abnormal Temperature Structure of X-ray Looptop Source of Solar Flares
This Letter is to investigate the physics of a newly discovered phenomenon --
contracting flare loops in the early phase of solar flares. In classical flare
models, which were constructed based on the phenomenon of expansion of flare
loops, an energy releasing site is put above flare loops. These models can
predict that there is a vertical temperature gradient in the top of flare loops
due to heat conduction and cooling effects. Therefore, the centroid of an X-ray
looptop source at higher energy bands will be higher in altitude, for which we
can define as normal temperature distribution. With observations made by {\it
RHESSI}, we analyzed 10 M- or X-class flares (9 limb flares). For all these
flares, the movement of looptop sources shows an obvious U-shaped trajectory,
which we take as the signature of contraction-to-expansion of flare loops. We
find that, for all these flares, normal temperature distribution does exist,
but only along the path of expansion. The temperature distribution along the
path of contraction is abnormal, showing no spatial order at all. The result
suggests that magnetic reconnection processes in the contraction and expansion
phases of these solar flares are different.Comment: 11 pages, 4 figure
WavJourney: Compositional Audio Creation with Large Language Models
Large Language Models (LLMs) have shown great promise in integrating diverse
expert models to tackle intricate language and vision tasks. Despite their
significance in advancing the field of Artificial Intelligence Generated
Content (AIGC), their potential in intelligent audio content creation remains
unexplored. In this work, we tackle the problem of creating audio content with
storylines encompassing speech, music, and sound effects, guided by text
instructions. We present WavJourney, a system that leverages LLMs to connect
various audio models for audio content generation. Given a text description of
an auditory scene, WavJourney first prompts LLMs to generate a structured
script dedicated to audio storytelling. The audio script incorporates diverse
audio elements, organized based on their spatio-temporal relationships. As a
conceptual representation of audio, the audio script provides an interactive
and interpretable rationale for human engagement. Afterward, the audio script
is fed into a script compiler, converting it into a computer program. Each line
of the program calls a task-specific audio generation model or computational
operation function (e.g., concatenate, mix). The computer program is then
executed to obtain an explainable solution for audio generation. We demonstrate
the practicality of WavJourney across diverse real-world scenarios, including
science fiction, education, and radio play. The explainable and interactive
design of WavJourney fosters human-machine co-creation in multi-round
dialogues, enhancing creative control and adaptability in audio production.
WavJourney audiolizes the human imagination, opening up new avenues for
creativity in multimedia content creation.Comment: Project Page: https://audio-agi.github.io/WavJourney_demopage
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