Natural Science

Preparation of lignin derivatives and their application as protease adsorbent

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)

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)

Multi-axial creep-fatigue life prediction considering history-dependent damage evolution : a new numerical procedure and experimental validation

In this paper, a new numerical procedure based on a cycle-by-cycle analysis has been constructed for creep-fatigue behavior and life prediction of high-temperature structures under multi-axial stress states. Within this framework, a modified unified viscoplastic constitutive model with isotropic hardening and modified kinematic hardening rules is developed to simulate the cycle-by-cycle stress-strain responses.Moreover, the newly constructed creep-fatigue approach calculates fatigue and creep damage variables using the critical plane method (CPM) and the modified strain energy density exhaustion (SEDE) model, respectively. The multi-axial ductility factor and elastic follow-up factor are also introduced into the modified SEDE model to accommodate the special multi-axial and mixed controlled modes, which are widely existed in practical structures. In order to validate the feasibility of the proposed numerical procedure, a series of creep-fatigue tests of notched specimens made from nickel-based GH4169 superalloy were carried out at 650 °C. The predicted numbers of cycles to crack initiation agree well with the experimental data. Evidence of crack initiation under various loading conditions was observed via the electron backscatter diffraction (EBSD) technique, indicating location-dependent crack initiations depending on loading conditions. In detail, the crack initiation sites shifting from surface to subsurface with increasing hold times can be well simulated by the proposed numerical procedure due to a reasonable description of the creep- fatigue damage evolution

Zigzag magnetic order in a novel tellurate compound Na4−δ_{4-\delta}NiTeO6_{6} with S\mathit{S} = 1 chains

Na$_{4-\delta}$NiTeO$_{6}$ is a rare example in the transition-metal tellurate family of realizing an $S$ = 1 spin-chain structure. By performing neutron powder diffraction measurements, the ground-state magnetic structure of Na$_{4-\delta}$NiTeO$_{6}$ is determined. These measurements reveal that below $T\rm_{N}$ ${\sim}$ 6.8(2) K, the Ni$^{2+}$ moments form a screwed ferromagnetic (FM) spin-chain structure running along the crystallographic $a$ axis but these FM spin chains are coupled antiferromagnetically along the $b$ and $c$ directions, giving rise to a magnetic propagation vector of $k$ = (0, 1/2, 1/2). This zigzag magnetic order is well supported by first-principles calculations. The moment size of Ni$^{2+}$ spins is determined to be 2.1(1) $\mu$$\rm_{B}$ at 3 K, suggesting a significant quenching of the orbital moment due to the crystalline electric field (CEF) effect. The previously reported metamagnetic transition near $H\rm_{C}$ ${\sim}$ 0.1 T can be understood as a field-induced spin-flip transition. The relatively easy tunability of the dimensionality of its magnetism by external parameters makes Na$_{4-\delta}$NiTeO$_{6}$ a promising candidate for further exploring various types of novel spin-chain physics.Comment: 10 pages, 6 figure

Layer-specific strain in patients with cardiac amyloidosis using tissue tracking MR

BackgroundCardiac infiltration is the major predictor of poor prognosis in patients with systemic amyloidosis, thus it becomes of great importance to evaluate cardiac involvement.PurposeWe aimed to evaluate left ventricular myocardial deformation alteration in patients with cardiac amyloidosis (CA) using layer-specific tissue tracking MR.Material and MethodsThirty-nine patients with CA were enrolled. Thirty-nine normal controls were also recruited. Layer-specific tissue tracking analysis was done based on cine MR images.ResultsCompared with the control group, a significant reduction in LV whole layer strain values (GLS, GCS, and GRS) and layer-specific strain values was found in patients with CA (all P < 0.01). In addition, GRS and GLS, as well as subendocardial and subepicardial GLS, GRS, and GCS, were all diminished in patients with CA and reduced LVEF, when compared to those with preserved or mid-range LVEF (all P < 0.05). GCS showed the largest AUC (0.9952, P = 0.0001) with a sensitivity of 93.1% and specificity of 90% to predict reduced LVEF (<40%). Moreover, GCS was the only independent predictor of LV systolic dysfunction (Odds Ratio: 3.30, 95% CI:1.341–8.12, and P = 0.009).ConclusionLayer-specific tissue tracking MR could be a useful method to assess left ventricular myocardial deformation in patients with CA

S1PR1 regulates ovarian cancer cell senescence through the PDK1-LATS1/2-YAP pathway

Cell senescence deters the activation of various oncogenes. Induction of senescence is, therefore, a potentially effective strategy to interfere with vital processes in tumor cells. Sphingosine-1-phosphate receptor 1 (S1PR1) has been implicated in various cancer types, including ovarian cancer. The mechanism by which S1PR1 regulates ovarian cancer cell senescence is currently elusive. In this study, we demonstrate that S1PR1 was highly expressed in human ovarian cancer tissues and cell lines. S1PR1 deletion inhibited the proliferation and migration of ovarian cancer cells. S1PR1 deletion promoted ovarian cancer cell senescence and sensitized ovarian cancer cells to cisplatin chemotherapy. Exposure of ovarian cancer cells to sphingosine-1-phosphate (S1P) increased the expression of 3-phosphatidylinositol-dependent protein kinase 1 (PDK1), decreased the expression of large tumor suppressor 1/2 (LATS1/2), and induced phosphorylation of Yes-associated protein (p-YAP). Opposite results were obtained in S1PR1 knockout cells following pharmacological inhibition. After silencing LATS1/2 in S1PR1-deficient ovarian cancer cells, senescence was suppressed and S1PR1 expression was increased concomitantly with YAP expression. Transcriptional regulation of S1PR1 by YAP was confirmed by chromatin immunoprecipitation. Accordingly, the S1PR1-PDK1-LATS1/2-YAP pathway regulates ovarian cancer cell senescence and does so through a YAP-mediated feedback loop. S1PR1 constitutes a druggable target for the induction of senescence in ovarian cancer cells. Pharmacological intervention in the S1PR1-PDK1-LATS1/2-YAP signaling axis may augment the efficacy of standard chemotherapy.</p

Novel AroA from Pseudomonas putida Confers Tobacco Plant with High Tolerance to Glyphosate

Glyphosate is a non-selective broad-spectrum herbicide that inhibits 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS, also designated as AroA), a key enzyme in the aromatic amino acid biosynthesis pathway in microorganisms and plants. Previously, we reported that a novel AroA (PpAroA1) from Pseudomonas putida had high tolerance to glyphosate, with little homology to class I or class II glyphosate-tolerant AroA. In this study, the coding sequence of PpAroA1 was optimized for tobacco. For maturation of the enzyme in chloroplast, a chloroplast transit peptide coding sequence was fused in frame with the optimized aroA gene (PparoA1optimized) at the 5′ end. The PparoA1optimized gene was introduced into the tobacco (Nicotiana tabacum L. cv. W38) genome via Agrobacterium-mediated transformation. The transformed explants were first screened in shoot induction medium containing kanamycin. Then glyphosate tolerance was assayed in putative transgenic plants and its T1 progeny. Our results show that the PpAroA1 from Pseudomonas putida can efficiently confer tobacco plants with high glyphosate tolerance. Transgenic tobacco overexpressing the PparoA1optimized gene exhibit high tolerance to glyphosate, which suggest that the novel PpAroA1 is a new and good candidate applied in transgenic crops with glyphosate tolerance in future

Genomewide association study of leprosy.

BACKGROUND: The narrow host range of Mycobacterium leprae and the fact that it is refractory to growth in culture has limited research on and the biologic understanding of leprosy. Host genetic factors are thought to influence susceptibility to infection as well as disease progression. METHODS: We performed a two-stage genomewide association study by genotyping 706 patients and 1225 controls using the Human610-Quad BeadChip (Illumina). We then tested three independent replication sets for an association between the presence of leprosy and 93 single-nucleotide polymorphisms (SNPs) that were most strongly associated with the disease in the genomewide association study. Together, these replication sets comprised 3254 patients and 5955 controls. We also carried out tests of heterogeneity of the associations (or lack thereof) between these 93 SNPs and disease, stratified according to clinical subtype (multibacillary vs. paucibacillary). RESULTS: We observed a significant association (P<1.00x10(-10)) between SNPs in the genes CCDC122, C13orf31, NOD2, TNFSF15, HLA-DR, and RIPK2 and a trend toward an association (P=5.10x10(-5)) with a SNP in LRRK2. The associations between the SNPs in C13orf31, LRRK2, NOD2, and RIPK2 and multibacillary leprosy were stronger than the associations between these SNPs and paucibacillary leprosy. CONCLUSIONS: Variants of genes in the NOD2-mediated signaling pathway (which regulates the innate immune response) are associated with susceptibility to infection with M. leprae