A decades-long fast-rise-exponential-decay flare in low-luminosity AGN NGC 7213

We analysed the four-decades-long X-ray light curve of the low-luminosity active galactic nucleus (LLAGN) NGC 7213 and discovered a fast-rise-exponential-decay (FRED) pattern, i.e. the X-ray luminosity increased by a factor of $\approx 4$ within 200d, and then decreased exponentially with an $e$-folding time $\approx 8116$d ($\approx 22.2$ yr). For the theoretical understanding of the observations, we examined three variability models proposed in the literature: the thermal-viscous disc instability model, the radiation pressure instability model, and the tidal disruption event (TDE) model. We find that a delayed tidal disruption of a main-sequence star is most favourable; either the thermal-viscous disk instability model or radiation pressure instability model fails to explain some key properties observed, thus we argue them unlikely.Comment: Accepted for publication in MNRAS, updated version after proof correction

Sound generated by rubbing objects

In the present paper, we investigate the properties of the sound generated by rubbing two objects. It is clear that the sound is generated because of the rubbing between the contacting rough surfaces of the objects. A model is presented to account for the role played by the surface roughness. The results indicate that tonal features of the sound can be generated due to the finiteness of the rubbing surfaces. In addition, the analysis shows that with increasing rubbing speed, more and more high frequency tones can be excited and the frequency band gets broader and broader, a feature which appears to agree with our intuition or experience.Comment: 3 pages, 2 figure

Localization of U(1)U(1) gauge vector field on flat branes with five-dimension (asymptotic) AdS5_{5} spacetime

In order to localize $U(1)$ gauge vector field on Randall-Sundrum-like braneworld model with infinite extra dimension, we propose a new kind of non-minimal coupling between the $U(1)$ gauge field and the gravity. We propose three kinds of coupling methods and they all support the localization of zero mode. In addition, one of them can support the localization of massive modes. Moreover, the massive tachyonic modes can be excluded. And our method can be used not only in the thin braneword models but also in the thick ones.Comment: Added acknowledgments to the refree. Appeared on JHE

Roles of Wrky proteins in mediating the crosstalk of hormone signaling pathways: An approach integrating bioinformatics and experimental biology

The goal of my research is to understand the molecular mechanism by which hormones control seed germination. Gibberellins (GA) promote, while abscisic acid (ABA) and salicylic acid (SA) inhibit seed germination. Key molecules in these signaling pathways include receptors, secondary messengers, protein kinases and phosphatases, and transcription factors. My study focuses on how WRKY transcription factors modulate the expression of an alpha-amylase gene (Amy32b), which is up-regulated by GA, but down-regulated by ABA and SA in the aleurone cells of germinating seeds; Chapter 2 started with the annotation and phylogenetic analyses of the WRKY gene superfamily, followed by functional studies of WRKY proteins in mediating ABA responses. Eighty-one WRKY genes were identified in the rice genome through computational analyses. Phylogenetic analyses based on WRKY domain sequences suggest that extensive duplications and losses of the WRKY domain occurred during evolution of this gene family. Transient expression studies suggest that among four WRKY genes that are ABA-inducible in aleurone cells, OsWRKY72 and OsWRKY77 function as transcription activators while OsWRKY24 and OsWRKY45 are repressors of the ABA-inducible HVA22 gene; Chapter 3 presents cellular and biochemical data to support a novel model that two transcription repressors OsWRKY51 and OsWRKY71 mediate the crosstalk of GA and ABA signaling. Both genes are ABA-inducible, but GA-repressible in the embryos and aleurone cells of germinating rice seeds. The interaction of OsWRKY51 and OsWRKY71 synergistically represses the GA-induced Amy32b expression, likely by functionally interfering with the GA-inducible transactivator, GAMYB; The mechanism underlying the crosstalk of SA, ABA and GA is reported in Chapter 4. Similar to ABA, SA blocks seed germination likely through repressing the expression of alpha-amylase genes such as Amy32b. Over-expression of the SA-inducible and GA repressible HvWRKY38 in aleurone cells blocks GA-induced Amy32b expression. Therefore, HvWRKY38 might mediate the crosstalk of SA, ABA and GA signaling in regulating alpha-amylase expression and seed germination; My research demonstrates the high efficiency of the approach integrating bioinformatics and experimental biology in addressing the cell-biological signaling network. The finding derived from this research helps advance towards achieving our long-term goal: to improve the yield and quality of rice and other cereals

Development of Manganese-Based Nanoparticles as Contrast Probes for Magnetic Resonance Imaging

MRI is one of the most important imaging tools in clinics. It interrogates nuclei of atoms in a living subject, providing detailed delineation with high spatial and temporal resolutions. To compensate the innate low sensitivity, MRI contrast probes were developed and widely used. These are typically paramagnetic or superparamagnetic materials, functioning by reducing relaxation times of nearby protons. Previously, gadolinium(Gd)-based T1 contrast probes were dominantly used. However, it was found recently that their uses are occasionally associated with nephrogenic system fibrosis (NSF), which suggests a need of finding alternatives. Among the efforts, manganese-containing nanoparticles have attracted much attention. By careful engineering, manganese nanoparticles with comparable r1 relaxivities can be yielded. Moreover, other functionalities, be a targeting motif, a therapeutic agent or a second imaging component, can be loaded onto these nanoparticles, resulting in multifunctional nanoplatforms