44 research outputs found
Helps tourists to customize travel plans easily with local experience: Dotrips app
Traveling with group tours can no longer meet the needs of tourists. In-depth tourism has become a new choice for Chinese tourists, especially middle- and high-income groups. Outbound travel, tourists need to find far away from the hustle and bustle of the city and to deeply understand the cultural heritage and folklore origins. Pursue a personal experience of natural beauty and artistic style or a bold exploration of the way of life and the essence of life. The rapid development of the tourism industry and the proliferation of user-shared content have made the problem of information overload in the field of tourism increasingly prominent. How to help tourists quickly develop personalized tour routes while improving the travel experience has become the key to the current research on tourism route planning. The fear of visiting a new, unfamiliar place could lead to stress of travel, making travel plans can also make travel anxiety. Searching for an efficient and local travel experience is very important
Circumstellar Material Ejected Violently by A Massive Star Immediately before its Death
Type II supernovae represent the most common stellar explosions in the
Universe, for which the final stage evolution of their hydrogen-rich massive
progenitors towards core-collapse explosion are elusive. The recent explosion
of SN 2023ixf in a very nearby galaxy, Messier 101, provides a rare opportunity
to explore this longstanding issue. With the timely high-cadence flash spectra
taken within 1-5 days after the explosion, we can put stringent constraints on
the properties of the surrounding circumstellar material around this supernova.
Based on the rapid fading of the narrow emission lines and luminosity/profile
of emission at very early times, we estimate that the progenitor
of SN 2023ixf lost material at a mass-loss rate over the last 2-3 years before explosion.
This close-by material, moving at a velocity , accumulates a compact CSM shell at the radius smaller than cm from the progenitor. Given the high mass-loss rate and
relatively large wind velocity presented here, together with the pre-explosion
observations made about two decades ago, the progenitor of SN 2023ixf could be
a short-lived yellow hypergiant that evolved from a red supergiant shortly
before the explosion.Comment: 10 pages, 6 figures in main body, accepted for publication in Science
Bulleti
Photoacoustic Identification of Laser-induced Microbubbles as Light Scattering Centers for Optical Limiting in Liquid Suspension of Graphene Nanosheets
Liquid suspensions of carbon nanotubes, graphene and transition metal
dichalcogenides have exhibited excellent performance in optical limiting.
However, the underlying mechanism has remained elusive and is generally
ascribed to their superior nonlinear optical properties such as nonlinear
absorption or nonlinear scattering. Using graphene as an example, we show that
photo-thermal microbubbles are responsible for the optical limiting as strong
light scattering centers: graphene sheets absorb incident light and become
heated up above the boiling point of water, resulting in vapor and microbubble
generation. This conclusion is based on direct observation of bubbles above the
laser beam as well as a strong correlation between laser-induced ultrasound and
optical limiting. In-situ Raman scattering of graphene further confirms that
the temperature of graphene under laser pulses rises above the boiling point of
water but still remains too low to vaporize graphene and create graphene plasma
bubbles. Photo-thermal bubble scattering is not a nonlinear optical process and
requires very low laser intensity. This understanding helps us to design more
efficient optical limiting materials and understand the intrinsic nonlinear
optical properties of nanomaterials
RITA: Boost Autonomous Driving Simulators with Realistic Interactive Traffic Flow
High-quality traffic flow generation is the core module in building
simulators for autonomous driving. However, the majority of available
simulators are incapable of replicating traffic patterns that accurately
reflect the various features of real-world data while also simulating
human-like reactive responses to the tested autopilot driving strategies.
Taking one step forward to addressing such a problem, we propose Realistic
Interactive TrAffic flow (RITA) as an integrated component of existing driving
simulators to provide high-quality traffic flow for the evaluation and
optimization of the tested driving strategies. RITA is developed with
consideration of three key features, i.e., fidelity, diversity, and
controllability, and consists of two core modules called RITABackend and
RITAKit. RITABackend is built to support vehicle-wise control and provide
traffic generation models from real-world datasets, while RITAKit is developed
with easy-to-use interfaces for controllable traffic generation via
RITABackend. We demonstrate RITA's capacity to create diversified and
high-fidelity traffic simulations in several highly interactive highway
scenarios. The experimental findings demonstrate that our produced RITA traffic
flows exhibit all three key features, hence enhancing the completeness of
driving strategy evaluation. Moreover, we showcase the possibility for further
improvement of baseline strategies through online fine-tuning with RITA traffic
flows.Comment: 8 pages, 5 figures, 3 table
Mid-infrared Fe2+:ZnSe semiconductor saturable absorber mirror for passively Q-switched Er3+-doped ZBLAN fiber laser
A mid-infrared (mid-IR) semiconductor saturable absorber mirror (SESAM) based on Fe2+:ZnSe for passively Q-switched Er3+-doped ZBLAN fiber laser has been demonstrated. Fe2+:ZnSe SESAM was fabricated by electron beam evaporation method. Fe2+ was innovatively doped into the reflective Bragg stack, in which ZnSe layer served as both doped matrix and high refractive layer during the fabricating process. By using the Fe2+:ZnSe SESAM, stable passively Q-switched pulses with the minimum pulse width of 0.43 μs under a repetition rate of 160.82 kHz were obtained. The recorded maximum average output power of 873 mW with a peak power of 12.59 W and pulse energy of 5.43 μJ were achieved. The results demonstrated a new method for fabricating Fe2+:ZnSe SESAM, which can be used in compact mid-IR Q-switched fiber laser
The effects of the impurity distribution on the electrical and optical properties of Cr2+:ZnSe nanowires: First-principles study
The structural, electrical and mid-infrared optical properties of wurtzite structured ZnSe nanowires with different Chromium impurity distribution are investigated using first-principles calculation based on density-functional theory (DFT). The formation energies have been calculated to study the relative stabilities of different Cr doping positions. It is shown that when the Cr doping position shifted from the center to the edge, the splitting energy between 5T2 and 5E levels of Cr d-orbitals is decreased and a redshift is observed in the calculated infrared absorption spectra. A probable reason for these effects of the impurity distribution is discussed. Keywords: First-principles, Nanowires, Impurity distribution, Cr-doped ZnS