The development of creep damage constitutive equations for low Cr-Mo alloy steel and its weldment at low stress

The ultimate objective of this research project is to develop creep damage constitutive equations for low Cr-Mo alloy and its weldment under low stress (0.2-0.4 yield stress,σ_Y). This paper summarizes a critical analysis on the cavity nucleation and growth and the deformation mechanisms and creep damage evolution characteristics at low stress with temperature ranging from 450 °C to 650 °C, in order to firmly establish the physical base for the theoretical constitutive modeling work. Moreover, it covers the influence of the stress level on the development of cavity nucleation and growth, leading to the final rupture, and proposes and discusses a new idea for failure criterion to be used in the constitutive equations under uni-axial stress state. This paper contributes to knowledge and the development of methodology

Development of Advanced Creep Damage Constitutive Equations for Low CR Alloy Under Long-Term Service

Low Cr alloys are mostly utilized in structural components such as steam pipes, turbine generators and reactor pumps operating at high temperatures from 400℃ to 700℃ in nuclear power plants. For safe operation, it is necessary at the design stage to predict and understand the creep damage behaviour of low Cr alloys under long-term service conditions but under low stress levels. Laboratory creep tests can be utilized in the investigation of creep damage behaviour, however, these are usually expensive and time-consuming. Thus, constitutive modelling is considered here for both time and economic efficiency. Existing constitutive equations for describing creep are mostly proposed based on experimental data for materials under high stresses. For low stress levels, the computational determination of a current state is extrapolated from those constitutive equations by simply using a powerlaw or sinh law. However, experimental observation has shown that this method is not satisfactory. The aim of the current research is to utilize continuum damage mechanics (CDM) to improve the constitutive equations for low Cr alloys under long-term service. This project provides three main contributions. The first is a more accurate depiction of the relationship between minimum creep rate and stress levels. The predicted creep rates show good agreement with creep data observed experimentally for both 2.25Cr-1Mo steel and 0.5Cr-0.5Mo- 0.25V steel creep specimens. Secondly, it gives a more comprehensive description of the relationship between creep damage and creep cavitation. The CDM approach has been used and a reasonable agreement has also been achieved between predicted creep strain and experimental data for 0.5Cr-0.5Mo-0.25V base material under the critical stress of 40MPa at 640℃. Thirdly, it proposes a more accurate creep rupture criterion in the creep damage analysis of low Cr alloys under different stress levels. Based on investigation of creep cavitation for 2.25Cr-1Mo steel, the area fraction of cavitation at rupture time obviously differs under different stress levels. This thesis contributes to computational creep damage mechanics in general and in particular to the design of a constitutive model for creep damage analysis of low Cr alloys. The proposed constitutive equations are only valid at low and intermediate stress levels. Further work needs to be undertaken when more experimental data are available

Optical spin pumping induced pseudo-magnetic field in two dimensional heterostructures

Two dimensional heterostructures are likely to provide new avenues for the manipulation of magnetization that is crucial for spintronics or magnetoelectronics. Here, we demonstrate that optical spin pumping can generate a large effective magnetic field in two dimensional MoSe2/WSe2 heterostructures. We determine the strength of the generated field by polarization-resolved measurement of the interlayer exciton photoluminescence spectrum: the measured splitting exceeding 10 milli-electron volts (meV) between the emission originating from the two valleys corresponds to an effective magnetic field of ~ 30 T. The strength of this optically induced field can be controlled by the excitation light polarization. Our finding opens up new possibilities for optically controlled spintronic devices based on van der Waals heterostructures

Causes and classification of EMD mode mixing

At present, the lack of insight into the problem of mode mixing in Empirical Mode Decomposition (EMD) hinders the development of solutions to the problem. Starting with the phenomenon that the EMD decomposition cannot be accomplished when the number of signal extrema is abnormal, the causes of mode mixing were investigated and the conclusion was reached that there are only two basic types of mode mixing. In light of this finding, the mechanisms of the three typical mode mixing solutions and their limitations were analyzed. It was found from the analysis process and results that the findings of this study regarding the causes and types of mode mixing were correct

Modeling and simulation of sintering process across scales

Sintering, as a thermal process at elevated temperature below the melting point, is widely used to bond contacting particles into engineering products such as ceramics, metals, polymers, and cemented carbides. Modelling and simulation as important complement to experiments are essential for understanding the sintering mechanisms and for the optimization and design of sintering process. We share in this article a state-to-the-art review on the major methods and models for the simulation of sintering process at various length scales. It starts with molecular dynamics simulations deciphering atomistic diffusion process, and then moves to microstructure-level approaches such as discrete element method, Monte--Carlo method, and phase-field models, which can reveal subtle mechanisms like grain coalescence, grain rotation, densification, grain coarsening, etc. Phenomenological/empirical models on the macroscopic scales for estimating densification, porosity and average grain size are also summarized. The features, merits, drawbacks, and applicability of these models and simulation technologies are expounded. In particular, the latest progress on the modelling and simulation of selective and direct-metal laser sintering based additive manufacturing is also reviewed. Finally, a summary and concluding remarks on the challenges and opportunities are given for the modelling and simulations of sintering process.Comment: 45 pages, 38 figure

Circ-CCS regulates oxaliplatin resistance via targeting miR-874-3p/HK2 axis in colorectal cancer

Background. Colorectal cancer (CRC) is a malignancy that threatens the patient’s life. Previous reports showed that circular RNAs (circRNAs) can affect CRC development. Herein, we demonstrated the characters of circular RNA copper chaperone for superoxide dismutase (circ-CCS) in CRC tissues and cells. Methods. Circ-CCS, CCS mRNA, microRNA-8743p (miR-874-3p) and hexokinase 2 (HK2) were indicated by qRT-PCR and western blot in CRC. The cell roles were examined. Additionally, the interaction between miR-874-3p and circ-CCS or HK2 was forecasted by the bioinformatics method and assessed by dual-luciferase reporter assay. Finally, the mouse test was implemented to demonstrate the effect of circ-CCS in vivo. Results. Circ-CCS and HK2 were increased, whereas miR-874-3p was diminished in CRC. Circ-CCS lack subdued the IC50 value of oxaliplatin, cell proliferation, migration, invasion and glycolysis metabolism in CRC cells, while it endorsed cell apoptosis. Furthermore, miR-874-3p was validated as having a tumor repressive effect in CRC cells by restraining HK2. The results also showed that HK2 could regulate the development of CRC. In mechanism, circ-CCS targeted miR-874-3p to control HK2. In addition, circ-CCS knock-down also attenuated tumor growth in mice. Conclusion. Circ-CCS expedited CRC through miR874-3p/HK

Alterations in platelet indices link polycyclic aromatic hydrocarbons toxicity to low-grade inflammation in preschool children

Background: Environmental exposure to carcinogenic polycyclic aromatic hydrocarbons (PAHs) can disturb the immune response. However, the effect of PAHs on low-grade inflammation related to platelets in humans is unknown. Objectives: We investigated the association of PAH exposure with low-grade inflammation and platelet parameters in healthy preschoolers. Methods: The present study recruited 239 participants, aged 2-7 years, from an electronic-waste (e-waste)-exposed (n = 118) and a reference (n = 121) area. We measured ten urinary PAH metabolites, four types of immune cells and cytokines, and seven platelet parameters, and compared their differences between children from the two groups. Spearman correlation analysis was performed to explore the potential risk factors for PAH exposure and the associations between urinary monohydroxylated PAHs (OH-PAHs) and biological parameters. Associations between urinary PAH metabolites and platelet indices were analyzed using quantile regression models. Mediation analysis was used to understand the relationship between urinary total hydroxynaphthalene (Sigma OHNa) and interleukin (IL)-1 beta through seven platelet indices, as mediator variables. Results: We found higher urinary monohydroxylated PAH (OH-PAH) concentrations, especially 1-hydroxynaphthalene (1-OHNa) and 2-hydroxynaphthalene (2-OHNa), in children from the e-waste-exposed group than in the reference group. These were closely associated with child personal habits and family environment. A decreased lymphocyte ratio and increased pro-inflammatory cytokines, such as gamma interferon-inducible protein (IP)-10 and IL-1 beta, were found in the e-waste-exposed children. After adjustment for confounding factors, significantly negative correlations were found between levels of mean platelet volume (MPV), platelet distribution width (PDW), platelet-large cell ratio (P-LCR) and ratio of mean platelet volume to platelet count (MPVP) and OH-PAHs. In addition, Sigma OHNa was positively associated with IL-1 beta mediated through MPV, PDW, P-LCR, and ratio of platelet count to lymphocyte count (PLR). Conclusions: Platelet indices were significantly associated with the changes in urinary OH-PAH levels, which may can be regarded as effective biomarkers of low-grade inflammation resulting from low PAH exposure in healthy children

Topological Single Photon Emission from Quantum Emitter Chains

We develop a scheme of generating highly indistinguishable single photons from an active quantum Su-Schrieffer-Heeger chain made from a collection of noisy quantum emitters. Surprisingly, the single photon emission spectrum of the active quantum chain is extremely narrow compared to that of a single emitter or topologically trivial chain. Moreover, this effect becomes dramatically strong close to the non-trivial-to-trivial phase transition point. Using this effect, we show that the single photon linewidth of a long topological quantum chain can become arbitrarily narrow, constituting an ideal source of indistinguishable single photons. Finally, taking specific examples of actual quantum emitters, we provide a microscopic and quantitative analysis of our model and analyze the most important parameters in view of the experimental realization

PAH exposure is associated with enhanced risk for pediatric dyslipidemia through serum SOD reduction

Background: Exposure to polycyclic aromatic hydrocarbons (PAHs) is linked to abnormal lipid metabolism, but evidence regarding PAHs as risk factors for dyslipidemia is lacking. Objective: To investigate the respective role and interaction of PAH exposure and antioxidant consumption in the risk for pediatric dyslipidemia. Methods: We measured the concentrations of serum lipids, superoxide dismutase (SOD) and urinary hydroxylated PAHs (OH-PAHs) in 403 children, of which 203 were from an e-waste-exposed area (Guiyu) and 200 were from a reference area (Haojiang). Biological interactions were calculated by additive models. Results: Guiyu children had higher serum triglyceride concentration and dyslipidemia incidence, and lower serum concentration of high-density lipoprotein (HDL) than Haojiang children. Elevated OH-PAH concentration, and concomitant SOD reduction, were both associated with lower HDL concentration and higher hypo-HDL risk (S3OH-Phes: B for lgHDL = 0.048, P <0.01; OR for hypo-HDL = 3.708, 95% CI: 1.200, 11.453; SOD: BT3 for lgHDL = 0.061, P <0.01; ORT3 for hypo-HDL = 0.168, 95% CI: 0.030, 0.941; all were adjusted for confounders). Biological interaction between phenanthrol exposure and SOD reduction was linked to dyslipidemia risk (RERI = 2.783, AP = 0.498, S = 2.537). Children with both risk factors (higher S3OH-Phes and lower SOD) had 5.594times (95% CI: 1.119, 27.958) the dyslipidemia risk than children with neither risk factors (lower S3OH-Phes and higher SOD). Conclusion: High PAH exposure combined with SOD reduction is recommended for predicting elevated risk for pediatric dyslipidemia. Risk assessment of PAH-related dyslipidemia should take antioxidant concentration into consideration