arXiv subjects
Publications and source records attributed to Chun Li.
With the help of a summation of basic hypergeometric series, the creative microscoping method recently introduced by Guo and Zudilin, and the Chinese remainder theorem for coprime polynomials, we find some new $q$-supercongruences. Especially, we give a $q$-analogue of a formula due to Liu [J. Math. Anal. Appl. 497 (2021), Art.~124915].
Star clusters are good tracers for formation and evolution of galaxies. We compared different fitting methods by using spectra (or by combining photometry) to determine the physical parameters. We choose a sample of 17 star clusters in M33, which previously lacked spectroscopic observations. The low-resolution spectra were taken with the Xinglong 2.16-m reflector of NAOC. The photometry used in the fitting includes $\rm u_{SC}$ and $\rm v_{SAGE}$ bands from the SAGE survey, as well as the published $UBVRI$ and $ugriz$ photometry. We firstly derived ages and metallicities with the {\sc ULySS} (Vazdekis et al. and {\sc pegase-hr}) SSP model and the Bruzual \& Charlot (2003) (BC03) stellar population synthesis models for the full-spectrum fitting. The fitting results of both the BC03 and {\sc ULySS} models seem consistent with those of previous works as well. Then we add the SAGE $\rm u_{SC}$ and $\rm v_{SAGE}$ photometry in the spectroscopic fitting with the BC03 models. It seems the results become much better, especially for the Padova 2000+Chabrier IMF set. Finally we add more photometry data, $UBVRI$ and $ugriz$, in the fitting and we found that the results do not improve significantly. Therefore, we conclude that the photometry is useful for improving the fitting results, especially for the blue bands ($λ<4000$ Å), e.g., $\rm u_{SC}$ and $\rm v_{SAGE}$ band. At last, we discuss the "UV-excess" for the star clusters and we find five star clusters have UV-excess, based on the $GALEX$ FUV, NUV photometry.
Colloidal cadmium chalcogenide nanoplates are two-dimensional semiconductors that have shown great application prospect for light-emitting technologies. Self-trapped state (STS), a special localized state originated from strong electron-phonon coupling (EPC), has great potential in one-step white light luminance owing to its broadband emission linewidth. However, achieving STS in cadmium chalcogenide nanocrystals is extremely challenging due to their intrinic weak EPC nature. By building hybrid superlattice (SL) structures via self-assembly of colloidal CdSe nanoplates (NPLs), we demonstrated an emergence of zone-folded longnitude acoustic phonons (ZFLAP) differ from monodispersed NPLs, and observed a broadband STS emission in spectra range of 450-600 nm. Through femtosecond transient absorption and impulsive vibrational spectroscopy, we revealed that STS is generated in time scale of ~500 fs and is driven by strong coupling of excitons and ZFLAPs with Huang-Rhys parameter as large as ~22.7. Our findings provide a new avenue for generating and manipulating STS emission by artificially designing and building hybrid periodic structures superior to single material optimization.
Despite the impressive performance of random forests (RF), its theoretical properties have not been thoroughly understood. In this paper, we propose a novel RF framework, dubbed multinomial random forest (MRF), to analyze the \emph{consistency} and \emph{privacy-preservation}. Instead of deterministic greedy split rule or with simple randomness, the MRF adopts two impurity-based multinomial distributions to randomly select a split feature and a split value respectively. Theoretically, we prove the consistency of the proposed MRF and analyze its privacy-preservation within the framework of differential privacy. We also demonstrate with multiple datasets that its performance is on par with the standard RF. To the best of our knowledge, MRF is the first consistent RF variant that has comparable performance to the standard RF.
Two-dimensional (2D) multiferroics exhibit cross-control capacity between magnetic and electric responses in reduced spatial domain, making them well suited for next-generation nanoscale devices; however, progress has been slow in developing materials with required characteristic properties. Here we identify by first-principles calculations robust 2D multiferroic behaviors in decorated Fe2O3 monolayer, showcasing N@Fe2O3 as a prototypical case, where ferroelectricity and ferromagnetism stem from the same origin, namely Fe d-orbit splitting induced by the Jahn-Teller distortion and associated crystal field changes. The resulting ferromagnetic and ferroelectric polarization can be effectively reversed and regulated by applied electric field or strain, offering efficient functionality. These findings establish strong materials phenomena and elucidate underlying physics mechanism in a family of truly 2D multiferroics that are highly promising for advanced device applications.
To investigate in more details of Stellar Abundance and Galactic Evolution (SAGE) and in a huge sample, we are performing a northern sky photometric survey named SAGES with the SAGE photometric system, which consists of 8 filters: Strömgren-$u$, SAGE-$v$, SDSS $g$, $r$, $i$, DDO-$51$, $Hα_{wide}$, and $Hα_{narrow}$, including three Sloan broadband filters, three intermediate-band filters and two narrow-band filters, and one newly-designed narrow-band filter. SAGES covers $\sim$12,000 square degrees of the northern sky with $δ> -5 ^{\circ}$, excluding the Galactic disk ($|b|<10^{\circ}$) and the sky area of 12 hr $<$ R.A. $<$ 18\,hr. The photometric detection limit depth at signal-to-noise ratio $5σ$ can be as deep as $V\sim$20\,mag. The SAGES will produce a depth-uniformed photometric catalogue for $\sim$500 million stars with atmospheric parameters including effective temperature $T_{\rm eff}$, surface gravity log\,g, and metallicity [Fe/H], as well as interstellar extinction to each individual target. In this work, we will briefly introduce the SAGE photometric system, the SAGE survey, and a preliminary test field of the open cluster NGC\,6791 and around.
Sky survey is one of the most important motivations to improve the astrophysics development, especially when using new photometric bands. We are performing the SAGE (Stellar Abundance and Galactic Evolution) survey with a self-designed SAGE photometric system, which is composed of eight photometric bands. The project mainly aims to study the stellar atmospheric parameters of $\sim$0.5 billion stars in the $\sim12,000$ deg$^2$ of the northern sky, which mainly focuses on the Galactic sciences, as well as some extragalactic sciences. This work introduces the detailed data reduction process of the testing field NGC\,6791, including the data reduction of single-exposure image and stacking multi-exposure images, and properties of the final catalogue.
The probability-scale residual (PSR) is well defined across a wide variety of variable types and models, making it useful for studies of HIV/AIDS. In this manuscript, we highlight some of the properties of the PSR and illustrate its application with HIV data. As a residual, it can be useful for model diagnostics; we demonstrate its use with ordered categorical data and semiparametric transformation models. The PSR can also be used to construct tests of residual correlation. In fact, partial Spearman's rank correlation between $X$ and $Y$ while adjusting for covariates $Z$ can be constructed as the correlation between PSRs from models of $Y$ on $Z$ and of $X$ on $Z$. The covariance of PSRs is also useful in some settings. We apply these methods to a variety of HIV datasets including 1) a study examining risk factors for more severe forms of cervical lesions among 145 women living with HIV in Zambia, 2) a study investigating the association between 21 metabolomic biomarkers among 70 HIV-positive patients in the southeastern United States, and 3) a genome wide association study investigating the association between single nucleotide polymorphisms and tenofovir clearance among 501 HIV-positive persons participating in a multi-site randomized clinical trial.
The internal structures of pulsating white dwarfs can be explored only with asteroseismology. Time series photometric observations were made for the pulsating DA white dwarf (ZZ Ceti star) WD~0246+326 during 9 nights in 2014 with a bi-site observation campaign. Eleven frequencies were detected including 1 triplet, 2 doublets, and 4 single modes, which are identified as either $l=1$ or $l=2$ modes with the complementarity of frequencies present in the literature. From the multiplets, the rotation period of \astrobj{WD~0246+326} is derived as $3.78\pm 0.11$ days. The average period spacing of the l=1 modes $ΔP=29.3\pm 0.2s$, implies that \astrobj{WD~0246+326} may be a massive ZZ Ceti star concerning the $ΔP-M_*$ relationship for the DAVs. Preliminary analysis derives the stellar parameters of $M_*=0.98\pm0.01$~${\rm M_\odot}$ and $T_{\rm eff}=11700\pm100$~K by fitting the theoretical frequencies of the eigen modes to the observed ones.
The present work carries out molecular dynamics simulations to compute the thermal conductivity of the borophene nanoribbon and the borophene nanotube using the Muller-Plathe approach. We investigate the thermal conductivity of the armchair and zigzag borophenes, and show the strong anisotropic thermal conductivity property of borophene. We compare the results of the borophene nanoribbon and the borophene nanotube, and find the thermal conductivity of the borophene is structure dependent.