Effect of thermal convection on columnar-toequiaxed transition during solidification of Al-Cu alloy

To investigate the effect of three-dimension(3 D) thermal convection on columnar-to-equiaxed transition(CET), the CET transition during the solidification of an Al-Cu alloy was simulated by 3 D cellular automaton model coupled with the finite element method(CAFE). The thermal convection in the liquid phase was considered. The results show that the thermal convection in the liquid phase promotes the CET. When the convection is present, the temperature gradient at the start position of CET increases and the growth velocity of columnar dendrite decreases. The convection influences the formation of elongated equiaxed grain through changing the local temperature gradient and dendritic growth velocity.

Three dimensional phase-field simulation for non-isothermal binary alloy solidification: Comparison with LKT theory

Using the advanced algorithm combining parallel computing,adaptive mesh re-griding and multigrid methods,quantitative 3D phase-field simulations of non-isothermal solidification of binary alloy were carried out.The 3D phase-field simulation results were compared with the analytical LKT(Lipton,Kurz and Trivedi)theory.For comparison,the simulation and analytical results for 2D cases were also given.The 3D phase-field simulation results support the transport portion of the LKT theory.However,the tip radius and tip velocity predicted by the simulations are not in good agreement with the LKT theory over the whole range of undercooling.The stability parameter calculated from phase-field simulations varies significantly with the Peclet number,indicating that the stability criterion,which assumes that the stability parameter is constant,is invalid.

Effect of Mn and Mo on microstructure and mechanical properties of Al-Si-Cu-Mg-0.6Fe alloy

Effect of different Mn and Mo contents on microstructure and mechanical properties of Al-Si-Cu-Mg-0.6Fe alloy was studied.Results indicate that the increase of Mo and decrease of Mn lead to a decrease in the size of theα-Al_(15)(FeMnMo)_(3)Si_(2) phase formed during solidification.Theα-Al_(15)(FeMnMo)_(3)Si_(2) phase reaches a minimum value of about 16.3μm at 0.2wt.%Mo and 0.1wt.%Mn addition.After solution treatment,theα-Al(FeMnMo)Si dispersed phase is precipitated.When only Mn is added,theα-Al(FeMnMo)Si dispersed phase mainly distributes near the grain boundaries,while when only Mo is added,it primarily distributes in the central region of the matrix.When both Mn and Mo are added,the dispersed phase has a larger and denser dispersed region and is uniformly distributed near the Al matrix and grain boundaries.Moreover,the best overall mechanical properties of the alloy are obtained with the combined addition of 0.1wt.%Mn and 0.2wt.%Mo,due to the smaller size ofα-Al_(15)(FeMnMo)_(3)Si_(2) phase and the larger area fraction and higher density of theα-Al(FeMnMo)Si dispersed phase.The yield strength,ultimate tensile strength,and elongation are respectively improved 67.7 MPa,48.5 MPa and 5.3%,respectively,compared to that of the alloy with only 0.3wt.%Mn.

超深井压裂对管内瞬态波动压力的影响研究

在压裂过程中,由于压裂液流量大且压力高,油管容易失效。如果压裂液流动边界瞬间发生变化,将直接影响油管内压力和速度的突变,导致油管失效甚至断裂,造成严重的井筒完整性问题。该文针对超深井高泵压大排量压裂过程中瞬时停泵工况,建立了压裂管柱内流体水击计算模型,讨论了采用不同直径和壁厚的管柱组合造成的局部摩阻影响,得到了变截面处局部摩阻、停泵时间以及压裂液排量变化对井口压力的影响。研究发现,停泵后,井口压力下降,在平衡压力值附近发生波动,波动幅值逐渐减小,直至衰减至平衡压力。若不考虑局部摩阻,压力波传播速度较快,幅度偏大,稳定至平衡压力所需时间滞后。压裂液的排量增大时,压力波速增加,会提前出现压力首波。排量越大,压力首波的波动幅度就越大。停泵时间越短,压力变化越大,压力首波出现越快,压力峰值越大。

Co-participation of paternal and maternal genomes before the blastocyst stage is not required for full-term development of mouse embryos

Dear Editor,The development of all the mammalian species begins from fertilization of a sperm and an egg into a diploid state.The maternal and paternal genomes are not functionally equivalent in term of their differential contributions to the imprinting gene expressions,and they are complementary and both essential for embryonic and postnatal development(McGrath and Solter,1984;Surani et al.,1986).

Pharmacological regulation of tissue fibrosis by targeting the mechanical contraction of myofibroblasts

Fibrosis can occur in almost all tissues and organs and affects normal physiological function,which may have serious consequences,such as organ failure.However,there are currently no effective,broad-spectmm drugs suitable for clinical application.Revealing the process of fibrosis is an important prerequisite for the development of new therapeutic targets and drugs.Studies have shown that the limiting of myofibroblast activation or the promoting of their elimination can ameliorate fibrosis.However,it has not been reported whether a direct decrease in cell contraction can inhibit fibrosis in vivo.Here,we have shown that(-)-blebbistatin(Ble),a non-muscle myosin II inhibitor,displayed significant inhibition of liver fibrosis in different chronic injury mouse models in vivo.We found that Ble reduced the stiffness of fibrotic tissues from the early stage,which reduced the extent of myofibroblast activation induced by a stiffer extracellular matrix(ECM).Moreover,Ble also reduced the activation of myofibroblasts induced by TGF-β1,which is the most potent pro-fibrotic cytokine.Mechanistically,Ble reduced mechanical contraction,which inhibited the assembly of stress fibers,decreased the F/G-actin ratio,and led to the exnucleation of YAPJ and MRTF-A.Finally,we verified its broad-spectrum antifibrotic effect in multiple models of organ fibrosis.Our results highlighted the important role of mechanical contraction in myofibroblast activation and maintenance,rather than just a characteristic of activation,suggesting that it may be a potential target to explore broad-spectrum drugs for the treatment of fibrotic diseases.