A bimodal burst energy distribution of a repeating fast radio burst source.

The event rate, energy distribution and time-domain behaviour of repeating fast radio bursts (FRBs) contain essential information regarding their physical nature and central engine, which are as yet unknown1,2. As the first precisely localized source, FRB 121102 (refs. 3-5) has been extensively observed and shows non-Poisson clustering of bursts over time and a power-law energy distribution6-8. However, the extent of the energy distribution towards the fainter end was not known. Here we report the detection of 1,652 independent bursts with a peak burst rate of 122 h-1, in 59.5 hours spanning 47 days. A peak in the isotropic equivalent energy distribution is found to be approximately 4.8 × 1037 erg at 1.25 GHz, below which the detection of bursts is suppressed. The burst energy distribution is bimodal, and well characterized by a combination of a log-normal function and a generalized Cauchy function. The large number of bursts in hour-long spans allows sensitive periodicity searches between 1 ms and 1,000 s. The non-detection of any periodicity or quasi-periodicity poses challenges for models involving a single rotating compact object. The high burst rate also implies that FRBs must be generated with a high radiative efficiency, disfavouring emission mechanisms with large energy requirements or contrived triggering conditions.

A study on the expression of FGF-21 and NF-κB pathway in the tissues of atherosclerotic mice.

OBJECTIVE: To study the relationship between the expressions of fibroblast growth factor (FGF)-21 and NF-κB signal transduction pathway in the tissues of atherosclerotic mice. MATERIALS AND METHODS: A total of 40 apoE-/- male mice at 8 weeks were selected and randomly divided into 4 groups. 10 mice in group A were normally fed with diet. 10 mice in group B were fed with high-fat diet. 10 mice in group C were fed with high-fat diet + pravastatin. 10 mice in group D were fed with high-fat diet + subcutaneous injection of exogenous recombinant FGF-21 protein. Another 10 C57BL/6J mice at 8 weeks were normally fed with diet (group E). They were killed after 12 weeks to collect retinal venous blood. ELISA method was applied to detect the levels of serum FGF-21, NF-κB, monocyte chemo attractant protein (MCP-1), matrix metalloproteinase (MMP)-9 and TNF-α. Immunohistochemical staining and RT-PCR method were applied to detect the expression of FGF-21 in aortic arch and liver tissues. RT-PCR method and Western blot method were applied to detect the expression of NF-κB, MCP-1, MMP-9 and TNF-α in aortic arch and liver tissues. RESULTS: The levels of serum FGF-21, NF-κB, MCP-1, MMP-9 and TNF-α in group B were higher than those of group A and group E, and those of group C and group D were lower than those of group B (except FGF-21 in group D). The differences had statistical significance (p<0.05). The positive staining rates of FGF-21 in endothelial cells of aortic arch and liver tissues in group B were higher than those group A and group E, and those of group C and group D were lower than those of group B. The differences had statistical significance (p<0.05). The expression levels of FGF-21mRNA, NF-κB, MCP-1, MMP-9, TNF-αmRNA and protein in endothelial cells of aortic arch and liver tissues in group B were higher than those group A and group E, and those of group C and group D were lower than those of group B. The differences had statistical significance (p<0.05). CONCLUSIONS: FGF-21 may participate in the occurrence of atherosclerosis (AS), which is related to the activation of the NF-κB pathway. Lipid-lowering therapy can inhibit the activation of FGF-21 and NF-κB. Exogenous FGF-21 can also lower the activation of NF-κB and interpose in atherosclerosis process.

[Isolation of a metastatic ascitic subpopulation from a human lung adenocarcinoma cell line in nude mice and studies on its biological properties].

An ascitic subpopulation (Anip) was isolated from human lung adenocarcinoma cell line AGZY-83-a through serial intraperitoneal passages in nude mice. Anip manifested a much higher metastatic potential than the parent line. Spontaneous lung metastases occurred in 95% of the mice xenografted intraperitoneally, and the diffuse pattern of the metastases in the lung was very impressive. Anip also differed more or less from the parent line in morphology, growth, rate, electrophoretic mobility, platelet aggregating activity and noticeably in the chromosome histogram. The present model may be used in the study of tumor invasion and metastasis, as large amounts of well dispersed metastatic human carcinoma cells could be reproduced by ascites and much information about the biology of invasion and metastasis of human tumor cells in nude mice could be obtained.