Stemness factor Sall4 is required for DNA damage response in embryonic stem cells.

Mouse embryonic stem cells (ESCs) are genetically more stable than somatic cells, thereby preventing the passage of genomic abnormalities to their derivatives including germ cells. The underlying mechanisms, however, remain largely unclear. In this paper, we show that the stemness factor Sall4 is required for activating the critical Ataxia Telangiectasia Mutated (ATM)-dependent cellular responses to DNA double-stranded breaks (DSBs) in mouse ESCs and confer their resistance to DSB-induced cytotoxicity. Sall4 is rapidly mobilized to the sites of DSBs after DNA damage. Furthermore, Sall4 interacts with Rad50 and stabilizes the Mre11-Rad50-Nbs1 complex for the efficient recruitment and activation of ATM. Sall4 also interacts with Baf60a, a member of the SWI/SNF (switch/sucrose nonfermentable) ATP-dependent chromatin-remodeling complex, which is responsible for recruiting Sall4 to the site of DNA DSB damage. Our findings provide novel mechanisms to coordinate stemness of ESCs with DNA damage response, ensuring genomic stability during the expansion of ESCs

Seismic Reliability Analysis of Energy-dissipation Structures by PDEM-ETDM

Energy-dissipation devices have been widely used for improving the performance of civil structures exposed to seismic hazard. In this study, a hybrid approach, which combines the probability density evolution method (PDEM) and the explicit time-domain method (ETDM), is proposed for the seismic reliability analysis of large-scale energy-dissipation structures with uncertain parameters of nonlinear energy-dissipation devices subjected to random seismic excitations. To demonstrate the feasibility of the proposed approach, a dynamic reliability analysis under random seismic excitations is carried out for a suspension bridge with a main span of 1,200 m equipped with 4 nonlinear viscous dampers with uncertain parameters.The research is funded by the National Natural Science Foundation of China (51678252) and the Science and Technology Program of Guangzhou, China (201804020069)

Beauty of Cryptography: the Cryptographic Sequences and the Golden Ratio

In this paper, the authors construct a new type of cryptographic sequence which is named an extra-super increasing sequence, and give the definitions of the minimal super increasing sequence {a[1], a[2], ..., a[n]} and minimal extra-super increasing sequence {z[1], z[2], ..., z[n]}. Prove that the minimal extra-super increasing sequence is the odd-positioned subsequence of the Fibonacci sequence, namely {z[1], z[2], ..., z[n], ...} = {F[1], F[3], ..., F[2n-1], ...}, which indicates that the approach to the golden ratio phi through the term difference ratio (z[n+1] - z[n]) / z[n] is more smooth and expeditious than through the term ratio (F[n+1] / F[n]). Further prove that the limit of the term ratio difference between the two cryptographic sequences equals the golden ratio conjugate PHI, namely lim (n to infinity) (z[n+1] / z[n] - a[n+1] / a[n]) = PHI, which reveals the beauty of cryptography

Evolution of the class C GPCR Venus flytrap modules involved positive selected functional divergence

<p>Abstract</p> <p>Background</p> <p>Class C G protein-coupled receptors (GPCRs) represent a distinct group of the GPCR family, which structurally possess a characteristically distinct extracellular domain inclusive of the Venus flytrap module (VFTM). The VFTMs of the class C GPCRs is responsible for ligand recognition and binding, and share sequence similarity with bacterial periplasmic amino acid binding proteins (PBPs). An extensive phylogenetic investigation of the VFTMs was conducted by analyzing for functional divergence and testing for positive selection for five typical groups of the class C GPCRs. The altered selective constraints were determined to identify the sites that had undergone functional divergence via positive selection. In order to structurally demonstrate the pattern changes during the evolutionary process, three-dimensional (3D) structures of the GPCR VFTMs were modelled and reconstructed from ancestral VFTMs.</p> <p>Results</p> <p>Our results show that the altered selective constraints in the VFTMs of class C GPCRs are statistically significant. This implies that functional divergence played a key role in characterizing the functions of the VFTMs after gene duplication events. Meanwhile, positive selection is involved in the evolutionary process and drove the functional divergence of the VFTMs. Our results also reveal that three continuous duplication events occurred in order to shape the evolutionary topology of class C GPCRs. The five groups of the class C GPCRs have essentially different sites involved in functional divergence, which would have shaped the specific structures and functions of the VFTMs.</p> <p>Conclusion</p> <p>Taken together, our results show that functional divergence involved positive selection and is partially responsible for the evolutionary patterns of the class C GPCR VFTMs. The sites involved in functional divergence will provide more clues and candidates for further research on structural-function relationships of these modules as well as shedding light on the activation mechanism of the class C GPCRs.</p

Seismic Reliability Analysis of Complex Nuclear Power Plants by Explicit Time Domain Method

Seismic reliability evaluation is of great importance in nuclear power engineering. The task remains an open challenge since it will involve the dynamic reliability analysis of large-scale complex structures of nuclear power plants on a global structure level under random seismic excitations, and in particular in the presence of structural uncertainties. The traditional random vibration methods with coupling treatment of the physical and the probabilistic evolution mechanism are hardly capable of executing such a difficult task. In this study, the explicit time-domain method (ETDM) developed in recent years is applied to the seismic global reliability analysis of complex nuclear power plants in consideration of structural uncertainties. The time-domain explicit expressions of the critical responses involved are first constructed based on the impulse response functions, and on this basis, the subsequent random vibration and reliability analysis can then be conducted just focusing on the selected critical responses. The uncoupling treatment of the two sets of mechanism in ETDM will lead to a real-sense dimensional reduction in terms of degrees of freedoms and time instants involved in random vibration analysis of structures, and thus a high efficiency in dynamic reliability analysis even in the presence of large-scale structural models. The engineering application to a nuclear power plant with over 2 million degrees of freedom, which is now being built in China, shows the feasibility of the present approach.The research is funded by the National Natural Science Foundation of China (51678252) and the Science and Technology Program of Guangzhou, China (201804020069)

Organic carbon deposition flux on the North Chukchi Sea shelf based on 210Pb radioactivity dating

Deposition of organic carbon forms the final net effect of the ocean carbon sink at a certain time scale. Organic carbon deposition on the Arctic shelves plays a particularly important role in the global carbon cycle because of the broad shelf area and rich nutrient concentration. To determine the organic carbon deposition flux at the northern margin of the Chukchi Sea shelf, the 210Pb dating method was used to analyze the age and deposition rate of sediment samples from station R17 of the third Chinese National Arctic Research Expedition. The results showed that the deposition rate was 0.6 mm∙a-1, the apparent deposition mass flux was 0.72 kg∙m-2∙a-1, and the organic carbon deposition flux was 517 mmol C∙m-2∙a-1. It was estimated that at least 16% of the export organic carbon flux out of the euphotic zone was transferred and chronically buried into the sediment, a value which was much higher than the average ratio (~10%) for low- to mid-latitude regions, indicating a highly effective carbon sink at the northern margin of the Chukchi Sea shelf. With the decrease of sea ice coverage caused by warming in the Arctic Ocean, it could be inferred that the Arctic shelves will play an increasingly important role in the global carbon cycle