• Strong spiral arms drive secular growth of pseudo bulges in disk galaxies

    分类: 天文学 >> 天文学 提交时间: 2023-02-19

    摘要:Spiral-driven instabilities may drive gas inflow to enhance central star formation in disk galaxies. We investigate this hypothesis using the Sloan Digital Sky Survey (SDSS) in a sample of 2779 nearby unbarred star-forming main-sequence spiral galaxies. The strength of spiral arms is quantified by their average Fourier amplitude relative to the axisymmetric disk. The star formation properties in the central 1--3\,kpc region were derived from the SDSS spectra. We show that galaxies with stronger spiral arms not only tend to have more intense central specific star formation rate (sSFR), larger Balmer absorption line index, and lower 4000-\AA\ break strength, but also have enhanced central sSFR relative to sSFR measured for the whole galaxy. This link is independent of redshift, stellar mass, surface density, and concentration. There is a lack of evidence for strong spiral arms being associated with a significant fraction of starburst or post-starburst galaxies, implying that the spiral-induced central star formation is likely continuous rather than bursty. We also show that stronger spiral arms tend to have an increasing fraction of pseudo bulges, a relatively unchanged fraction of star-forming classical bulges, and a decreasing fraction of quenched classical bulges. Moreover, the concentration of galaxies hosting pseudo bulges mildly increases with stronger spiral arms, implying that spirals help pseudo bulges grow. The connection between spirals and the bulge type is partly attributed to the suppression of spirals by classical bulges and partly to the enhanced central star formation driven by spirals. We explain our results in a picture where spiral arms transport cold gas inward to trigger continuous central star formation, which facilitates the build-up of pseudo bulges. Spiral arms thus play a role in the secular evolution of disk galaxies.

  • Downregulation of THBS2 suppresses tumorigenicity and liver metastasis of gastric cancer and

    分类: 医学、药学 >> 基础医学 提交时间: 2023-09-28

    摘要:Objective: Liver metastasis is one of the major causes of cancer-related death in gastric cancer (GC) patients. This study was to investigate the roles of THBS2 in the tumorigenesis and liver metastasis of GC and the sensitivity of GC to trastuzumab.
    Methods: Sequencing was employed to identify the differentially expressed genes in the GC. The THBS2 expression was detected in GC tissues and GC cell lines, its relationships with clinicopathological characteristics were further assessed, and its roles in the malignant behaviors of GC were further investigated in vitro and in vivo, by up-regulating or down-regulating THBS2 expression. The PTEN and its downstream AKT and FAK signaling pathways were investigated in the GC aiming to explore the potential mechanism underlying the regulatory effects of THBS2.
    Results: THBS2 expression increased significantly in the GC as compared to the normal gastric tissues, which was related to the distal metastasis and poor prognosis of GC patients. THBS2 expression also increased in the primary GC cells and human gastric cell line NCI-N87. THBS2 downregulation induced mesenchymal-epithelial transition (MET) and PTEN nuclear translocation, which inhibited the metastasis of GC cells. Carmofur promoted PTEN nuclear translocation, inhibiting the metastases and THBS2 downregulation together with carmofur improved the sensitivity of GC to trastuzumab.
    Conclusions: THBS2 is overexpressed in GC tissues of patients with synchronous liver metastases and its overexpression is associated with poor prognosis. THBS2 downregulation inhibits the metastases of GC. THBS2 down-regulation and carmofur can be used as a new treatment for the advanced GC with metastases.

  • Robust Ultraviolet to Near-infrared Quantum Emitters in Hexagonal Boron Nitride up to 1100 K

    分类: 光学 >> 量子光学 提交时间: 2023-02-19

    摘要:A stable single-photon source working at high temperatures with high brightness and covering full band emission from one host material is critically important for quantum technologies. Here, we find that the certain hBN single-photon emissions (SPEs) can be significantly enhanced by lasers with special wavelengths, which largely broaden the wavelength range of the hBN emitters, down to ultraviolet (357 nm) and up to near-infrared (912 nm). Importantly, these hBN SPEs are still stable even at the temperature up to 1100 Kelvin. The decoupling between single-photon and acoustic phonon is observed at high temperatures. Our work suggests that hBN can be a good host material for generating single-photon sources with ultrabroad wavelength range.