58 research outputs found
AT2018dyk Revisited: a Tidal Disruption Event Candidate with Prominent Infrared Echo and Delayed X-ray Emission in a LINER Galaxy
The multiwavelength data of nuclear transient AT2018dyk, initially discovered
as a changing-look low-ionization nuclear emission-line region (LINER) galaxy,
has been revisited by us and found being in agreement with a tidal disruption
event (TDE) scenario. The optical light curve of AT2018dyk declines as a
power-law form approximately with index -5/3 yet its X-ray emission lags behind
the optical peak by days, both of which are typical characteristics
for TDEs. The X-ray spectra are softer than normal active galactic nuclei
(AGNs) although they show a slight trend of hardening. Interestingly, its
rising time scale belongs to the longest among TDEs while it is nicely
consistent with the theoretical prediction from its relatively large
supermassive black hole (SMBH) mass (). Moreover, a
prominent infrared echo with peak luminosity
has been also detected in
AT2018dyk, implying an unusually dusty subparsec nuclear environment in
contrast with other TDEs. In our sample, LINERs share similar covering factors
with AGNs, which indicates the existence of the dusty torus in these objects.
Our work suggests that the nature of nuclear transients in LINERs needs to be
carefully identified and their infrared echoes offer us a unique opportunity
for exploring the environment of SMBHs at low accretion rate, which has been so
far poorly explored but is crucial for understanding the SMBH activity.Comment: 9 pages, 6figures, 1 table. Accepted for publication in MNRA
Dwarf galaxies with the highest concentration are not thicker than ordinary dwarf galaxies
The formation mechanism of high-concentration dwarf galaxies is still a
mystery. We perform a comparative study of the intrinsic shape of nearby
low-mass galaxies with different stellar concentration. The intrinsic shape is
parameterized by the intermediate-to-major axis ratios B/A and the
minor-to-major axis ratios C/A of triaxial ellipsoidal models. Our galaxies
( < < ) are selected to have
spectroscopic redshift from SDSS or GAMA, and have broadband optical images
from the HSC-SSP Wide layer survey. The deep HSC-SSP images allow to measure
the apparent axis ratios at galactic radii beyond the central star-forming
area of our galaxies. We infer the intrinsic axis ratios based on the
distributions. We find that 1) our galaxies have typical intrinsic shape
similarly close to be oblate ( 0.9--1), regardless of the
concentration, stellar mass, star formation activity, and local environment
(being central or satellite); 2) galaxies with the highest concentration tend
to have intrinsic thickness similar to or (in virtually all cases) slightly
thinner (i.e. smaller mean or equivalently lower triaxiality) than
ordinary galaxies, regardless of other properties explored here. This appears
to be in contrast with the expectation of the classic merger scenario for
high-concentration galaxies. Given the lack of a complete understanding of
dwarf-dwarf merger, we cannot draw a definite conclusion about the relevance of
mergers in the formation of high-concentration dwarfs. Other mechanisms such as
halo spin may also play important roles in the formation of high-concentration
dwarf galaxies.Comment: 12 pages, 8 figures, 2 tables, accepted for publication in Ap
AT 2023clx: the Faintest and Closest Optical Tidal Disruption Event Discovered in Nearby Star-forming Galaxy NGC 3799
We report the discovery of a faint optical tidal disruption event (TDE) in
the nearby star-forming galaxy NGC 3799. Identification of the TDE is based on
its position at the galaxy nucleus, a light curve declining as t^-5/3, a blue
continuum with an almost constant blackbody temperature of ~12,000K, and broad
(~15,000kms^-1) Balmer lines and characteristic He~II 4686A emission. The light
curve of AT 2023clx peaked at an absolute magnitude of -17.16mag in the g-band
and a maximum blackbody bolometric luminosity of 4.56*10^42 ergs^-1, making it
the faintest TDE discovered to date. With a redshift of 0.01107 and a
corresponding luminosity distance of 47.8Mpc, it is also the closest optical
TDE ever discovered to our best knowledge. Furthermore, our analysis of
Swift/XRT observations of AT 2023clx yields a very tight 3 sigma upper limit of
9.53*10^39 ergs^-1 in the range 0.3--10keV. AT 2023clx, together with very few
other faint TDEs such as AT 2020wey, prove that there are probably a large
number of faint TDEs yet to be discovered at higher redshifts, which is
consistent with the prediction of luminosity functions (LFs). The upcoming
deeper optical time-domain surveys, such as the Legacy Survey of Space and Time
(LSST) and the Wide-Field Survey Telescope (WFST) will discover more TDEs at
even lower luminosities, allowing for a more precise constraint of the low-end
of the LF.Comment: 9 pages, 6 figures; Accepted for ApJL (July, 2023
Global research landscape and trends of papillary thyroid cancer therapy: a bibliometric analysis
BackgroundPapillary thyroid cancer (PTC) is the most common endocrine malignancy worldwide. The treatment of PTC has attracted extensive attention and discussion from the public and scholars. However, no article has systematically assessed the related literature. Therefore, we conducted a bibliometric and knowledge map analysis to reveal the dynamic scientific developments in the PTC therapy field.MethodsWe retrieved publications related to PTC therapy from the Web of Scientific Core Collection (WoSCC) on May 1, 2023. The bibliometric package in R software, VOSviewer and CiteSpace software were used to analyze countries/regions, institutions, journals, authors, references, and keywords. Then, we systematized and summarized the research landscape, global trends and hot topics of research.ResultsThis bibliometric analysis spanned from 2012 to 2022 and involved 18,501 authors affiliated with 3,426 institutions across 87 countries/regions, resulting in the publication of 3,954 papers in 860 academic journals. Notably, the number of publications and citations related to PTC therapy research has exhibited a steady increase over the past decade. China and the United States have emerged as leading contributors in terms of publication count, with the United States also being the most cited country. Furthermore, among the top 10 institutions with the highest number of published papers, half were located in China. Among the journals, Thyroid is ranked first in terms of total publications and citations. The most productive individual author was Miyauchi Akira. While previous research primarily focused on surgery and radioactive iodine therapy, the increasing emphasis on health awareness and advancements in medical technology have led to the emergence of active surveillance, thermal ablation, and genomic analysis as prominent areas of research.ConclusionIn conclusion, this comprehensive and quantitative bibliometric analysis elucidates the research trends and hotspots within PTC therapy, drawing from a substantial body of publications. This study provides valuable insights into the historical and current landscape of PTC therapy research while also offering guidance for future research directions. This study serves as a valuable resource for researchers and practitioners seeking new avenues of exploration in the field
Tailoring MoS2 Valley-Polarized Photoluminescence with Super Chiral Near-Field
Transition metal dichalcogenides with intrinsic spin–valley degrees of freedom hold great potentials for applications in spintronic and valleytronic devices. MoS2 monolayer possesses two inequivalent valleys in the Brillouin zone, with each valley coupling selectively with circularly polarized photons. The degree of valley polarization (DVP) is a parameter to characterize the purity of valley-polarized photoluminescence (PL) of MoS2 monolayer. Usually, the detected values of DVP in MoS2 monolayer show achiral property under optical excitation of opposite helicities due to reciprocal phonon-assisted intervalley scattering process. Here, it is reported that valley-polarized PL of MoS2 can be tailored through near-field interaction with plasmonic chiral metasurface. The resonant field of the chiral metasurface couples with valley-polarized excitons, and tailors the measured PL spectra in the far-field, resulting in observation of chiral DVP of MoS2-metasurface under opposite helicities excitations. Valley-contrast PL in the chiral heterostructure is also observed when illuminated by linearly polarized light. The manipulation of valley-polarized PL in 2D materials using chiral metasurface represents a viable route toward valley-polaritonic devices
Initialization of nanowire or cluster growth critically controlled by the effective V/III ratio at the early nucleation stage
For self-catalyzed nanowires (NWs), reports on how the catalytic droplet initiates successful NW growth are still lacking, making it difficult to control the yield and often accompanying a high density of clusters. Here, we have performed a systematic study on this issue, which reveals that the effective V/III ratio at the initial growth stage is a critical factor that governs the NW growth yield. To initiate NW growth, the ratio should be high enough to allow the nucleation to extend to the entire contact area between the droplet and substrate, which can elevate the droplet off of the substrate, but it should not be too high in order to keep the droplet. This study also reveals that the cluster growth between NWs is also initiated from large droplets. This study provides a new angle from the growth condition to explain the cluster formation mechanism, which can guide high-yield NW growth
Sciences for The 2.5-meter Wide Field Survey Telescope (WFST)
The Wide Field Survey Telescope (WFST) is a dedicated photometric survey
facility under construction jointly by the University of Science and Technology
of China and Purple Mountain Observatory. It is equipped with a primary mirror
of 2.5m in diameter, an active optical system, and a mosaic CCD camera of 0.73
Gpix on the main focus plane to achieve high-quality imaging over a field of
view of 6.5 square degrees. The installation of WFST in the Lenghu observing
site is planned to happen in the summer of 2023, and the operation is scheduled
to commence within three months afterward. WFST will scan the northern sky in
four optical bands (u, g, r, and i) at cadences from hourly/daily to
semi-weekly in the deep high-cadence survey (DHS) and the wide field survey
(WFS) programs, respectively. WFS reaches a depth of 22.27, 23.32, 22.84, and
22.31 in AB magnitudes in a nominal 30-second exposure in the four bands during
a photometric night, respectively, enabling us to search tremendous amount of
transients in the low-z universe and systematically investigate the variability
of Galactic and extragalactic objects. Intranight 90s exposures as deep as 23
and 24 mag in u and g bands via DHS provide a unique opportunity to facilitate
explorations of energetic transients in demand for high sensitivity, including
the electromagnetic counterparts of gravitational-wave events detected by the
second/third-generation GW detectors, supernovae within a few hours of their
explosions, tidal disruption events and luminous fast optical transients even
beyond a redshift of 1. Meanwhile, the final 6-year co-added images,
anticipated to reach g about 25.5 mag in WFS or even deeper by 1.5 mag in DHS,
will be of significant value to general Galactic and extragalactic sciences.
The highly uniform legacy surveys of WFST will also serve as an indispensable
complement to those of LSST which monitors the southern sky.Comment: 46 pages, submitted to SCMP
Teachers’ responses to curriculum reform in China: an organizational behavior perspective
Over the past few decades, Chinese teachers have been suffering severe criticism for their conservatism in responding to education reforms. In particular, when curriculum innovation emphasizing students’ cognitive development has become a crucial direction on the China’s educational reform agenda, the public issued a fierce rebuke over teachers’ resistance. Researchers have pointed out many factors hindering the reform success, such as extreme pressure from examination and insufficient administrative supports from governments (Dello-Iacovo, 2009). However, exploration on responses of teachers towards reforms at school level is insufficient, especially in the context of China, where school are under a strong bureaucratic control and facing a substantial stratification of public reputation.
Organization behavior theory serves as the conceptual framework for understanding teachers' responses to curriculum reform in this study. From its perspective, teachers’ attitude and practice towards reform are not developed individually, but formulated collectively at school level and reshaped in an organizational context, such as institutional arrangements and routines. As school’s public reputation is a key indicator of resources accessibility and academic capacity in China, it is considered a critical factor in formulating teachers’ collective ideology and behavior. Therefore, schools with differed public reputation may react differently to the challenges driven by curriculum reform, which in turn shapes teachers’ responses.
The present study tries to contemplate the nature and impact of different institutional choices employed by individual school. More specifically, the study attempts to answer three questions: 1) what is the teachers’ attitude and practice in response to curriculum reform in different schools? 2) what are the possible institutional choices made by schools with different characteristics to respond to the requirements of curriculum reform? 3) How different institutional choices influence teachers’ attitude and practice towards the reform?
This study is based on teachers’ interviews about curriculum reform carried out in 10 senior secondary schools in two cities in China. In each school, a semi-structured open-ended interview was conducted with teachers. In total 28 teachers participated in the interview. Each interview was transcribed verbatim. The interview transcripts were organized by Nvivo 9 and analyzed by within-and cross-case analysis methods.
The results reveal that schools institutional choices have tremendous influence on teachers’ attitude and practice. In the schools encouraging interdisciplinary cooperation, transferring teacher autonomy, and setting up supportive evaluation system, teachers expressed a positive attitude towards the reform, created a sustainable professional community and achieved school development. The interviews also provide some evidence of the deficiency of traditional organizational structure of senior secondary school in China. As the teaching and research group functions as an administrative department rather than a professional community, it is ill-prepared to respond to the requirements of curriculum reform to cultivate student’s creative thinking and problem-solving ability in an interdisciplinary context.
The present study provides the Chinese case to understand teacher resistance towards curriculum reform under the complex indigenous context in terms of a combination of intensive disparity among schools and over-centralized administration system
Bearing Fault Detection Based on Empirical Wavelet Transform and Correlated Kurtosis by Acoustic Emission
Rolling bearings are widely used in rotating equipment. Detection of bearing faults is of great importance to guarantee safe operation of mechanical systems. Acoustic emission (AE), as one of the bearing monitoring technologies, is sensitive to weak signals and performs well in detecting incipient faults. Therefore, AE is widely used in monitoring the operating status of rolling bearing. This paper utilizes Empirical Wavelet Transform (EWT) to decompose AE signals into mono-components adaptively followed by calculation of the correlated kurtosis (CK) at certain time intervals of these components. By comparing these CK values, the resonant frequency of the rolling bearing can be determined. Then the fault characteristic frequencies are found by spectrum envelope. Both simulation signal and rolling bearing AE signals are used to verify the effectiveness of the proposed method. The results show that the new method performs well in identifying bearing fault frequency under strong background noise
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