53 research outputs found
Seek for Incantations: Towards Accurate Text-to-Image Diffusion Synthesis through Prompt Engineering
The text-to-image synthesis by diffusion models has recently shown remarkable
performance in generating high-quality images. Although performs well for
simple texts, the models may get confused when faced with complex texts that
contain multiple objects or spatial relationships. To get the desired images, a
feasible way is to manually adjust the textual descriptions, i.e., narrating
the texts or adding some words, which is labor-consuming. In this paper, we
propose a framework to learn the proper textual descriptions for diffusion
models through prompt learning. By utilizing the quality guidance and the
semantic guidance derived from the pre-trained diffusion model, our method can
effectively learn the prompts to improve the matches between the input text and
the generated images. Extensive experiments and analyses have validated the
effectiveness of the proposed method
Simulation of CSSTs astrometric capability
The China Space Station Telescope (CSST) will enter a low Earth orbit around
2024 and operate for 10 years, with seven of those years devoted to surveying
the area of the median-to-high Galactic latitude and median-to-high Ecliptic
latitude of the sky. To maximize the scientific output of CSST, it is important
to optimize the survey schedule. We aim to evaluate the astrometric capability
of CSST for a given survey schedule and to provide independent suggestions for
the optimization of the survey strategy. For this purpose, we first construct
the astrometric model and then conduct simulated observations based on the
given survey schedule. The astrometric solution is obtained by analyzing the
simulated observation data. And then we evaluate the astrometric capability of
CSST by analyzing the properties of the astrometric solution. We find that the
accuracy of parallax and proper motion of CSST is better than 1 mas( yr1) for
the sources of 18-22 mag in g band, and about 1-10 mas( yr1) for the sources of
22-26 mag in g band, respectively. The results from real survey could be worse
since the assumptions are optimistic and simple. We find that optimizing the
survey schedule can improve the astrometric accuracy of CSST. In the future, we
will improve the astrometric capability of CSST by continuously iterating and
optimizing the survey schedule.Comment: 17 pages, 10 figure
Strange Quasar Candidates with Abnormal Astrometric Characteristics from Gaia EDR3 and SDSS (SQUAB-II): Optical Identifications
There are some strange quasars with multiple Gaia detections or observed with
abnormal astrometric characteristics, such as with large proper motions or
significant astrometric noises. Those strange quasars could be potential
candidates of quasar-star pairs, dual quasars (DQs), or lensed quasars (LQs).
Searching for both DQs and LQs is of great importance in many fields of
astrophysics. Here in this work, we select 143 SDSS spectroscopically confirmed
quasars that have multiple Gaia EDR3 detections within 1 arcsec of the SDSS
quasar' position. We apply several optical identification methods to classify
this sample. We firstly exclude 65 quasar-star pairs via their stellar features
including their parallaxes and proper motions, stellar features in the SDSS
spectra, or via the colour-colour diagram. Based on the spectral-fitting
results, we find 2 DQ candidates, one of which presents a double-peaked [O III]
emission line feature and the other shows a broad velocity offset
( 870 ) relative to the [O III] 5007 line. Via the
colour difference method, we further find 56 LQ candidates with similar colours
in their multiple images. We also cross-match 143 objects with the HST archive
and find 19 targets with archival HST images. Our classification results of
those 19 targets are mainly consistent with previous works.Comment: 18 pages, 11figures, accepted for publication in MNRA
Nano selenium-doped TiO2 nanotube arrays on orthopedic implants for suppressing osteosarcoma growth
Osteosarcoma, the most common primary malignant bone tumor, is characterized by malignant cells producing osteoid or immature bone tissue. Most osteosarcoma patients require reconstructive surgery to restore the functional and structural integrity of the injured bone. Metal orthopedic implants are commonly used to restore the limb integrity in postoperative patients. However, conventional metal implants with a bioinert surface cannot inhibit the growth of any remaining cancer cells, resulting in a higher risk of cancer recurrence. Herein, we fabricate a selenium-doped TiO2 nanotube array (Se-doped TNA) film to modify the surface of medical pure titanium substrate, and evaluate the anti-tumor effect and biocompatibility of Se-doped TNA film. Moreover, we further explore the anti-tumor potential mechanism of Se-doped TNA film by studying the behaviors of human osteosarcoma cells in vitro. We provide a new pathway for achieving the anti-tumor function of orthopedic implants while keeping the biocompatibility, aiming to suppress the recurrence of osteosarcoma
CHES: a space-borne astrometric mission for the detection of habitable planets of the nearby solar-type stars
The Closeby Habitable Exoplanet Survey (CHES) mission is proposed to discover
habitable-zone Earth-like planets of the nearby solar-type stars ( away from our solar system) via micro-arcsecond relative
astrometry. The major scientific objectives of CHES are: to search for Earth
Twins or terrestrial planets in habitable zones orbiting 100 FGK nearby stars;
further to conduct a comprehensive survey and extensively characterize the
nearby planetary systems. The primary payload is a high-quality,
low-distortion, high-stability telescope. The optical subsystem is a coaxial
three-mirror anastigmat (TMA) with a -aperture, field of view and
working waveband. The camera focal plane is composed of 81 MOSAIC scientific
CMOS detectors each with pixels. The
heterodyne laser interferometric calibration technology is employed to ensure
micro-arcsecond level (1 as) relative astrometry precision to meet the
requirements for detection of Earth-like planets. CHES satellite operates at
the Sun-Earth L2 point and observes the entire target stars for 5 years. CHES
will offer the first direct measurements of true masses and inclinations of
Earth Twins and super-Earths orbiting our neighbor stars based on
micro-arcsecond astrometry from space. This will definitely enhance our
understanding of the formation of diverse nearby planetary systems and the
emergence of other worlds for solar-type stars, and finally to reflect the
evolution of our own solar system.Comment: 39 pages, 37 figures, Invited Review, accepted to Research in
Astronomy and Astrophysic
The Jiao Tong University Spectroscopic Telescope Project
The Jiao Tong University Spectroscopic Telescope (JUST) is a 4.4-meter f/6.0
segmentedmirror telescope dedicated to spectroscopic observations. The JUST
primary mirror is composed of 18 hexagonal segments, each with a diameter of
1.1 m. JUST provides two Nasmyth platforms for placing science instruments. One
Nasmyth focus fits a field of view of 10 arcmin and the other has an extended
field of view of 1.2 deg with correction optics. A tertiary mirror is used to
switch between the two Nasmyth foci. JUST will be installed at a site at Lenghu
in Qinghai Province, China, and will conduct spectroscopic observations with
three types of instruments to explore the dark universe, trace the dynamic
universe, and search for exoplanets: (1) a multi-fiber (2000 fibers)
medium-resolution spectrometer (R=4000-5000) to spectroscopically map galaxies
and large-scale structure; (2) an integral field unit (IFU) array of 500
optical fibers and/or a long-slit spectrograph dedicated to fast follow-ups of
transient sources for multimessenger astronomy; (3) a high-resolution
spectrometer (R~100000) designed to identify Jupiter analogs and Earth-like
planets, with the capability to characterize the atmospheres of hot exoplanets.Comment: 28 pages, 6 figure
A Brief Overview of the Absolute Proper motions Outside the Plane catalog (APOP)
APOP is the first version of an absolute proper motion catalog achieved using the Digitized Sky Survey Schmidt plate material outside the galactic plane (|b|≥ 27(o) ). The resulting global zero point error is less than 0.6 mas/yr, and the precision better than 4.0 mas/yr for objects brighter than R_{F}=18.5, rising to 9.0 mas/yr for objects with magnitude in the range 18.5<R_{F}<20.0. The average position accuracy is about 150 mas (per coordinate) with a systematic deviation from the ICRS around 0.2 mas. The catalog covers 22,525 square degrees and lists 100,777,385 objects to the limiting magnitude of R_{F}̃ 20.8. Although the Gaia mission is poised to set the new standard in catalog astronomy, the methods and procedures used for APOP will be useful in other reductions to dispel astrometric magnitude- and color-dependent systematic errors from the next generation of ground-based surveys
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