基于流固耦合方法的两自由度水翼流激振动特性研究

The flutter of a hydrofoil can cause structural damage and failure,which is a dangerous situation that must be avoided.In this work,based on computational fluid dynamics and structural finite element methods,a co-simulation framework for the flow-induced vibration of hydrofoil was established to realize fluid-structure interaction.Numerical simulation research was conducted on the flow-induced vibration characteristics of rigid hydrofoil with 2-DOF under uniform flow,and the heave and pitch vibration responses of hydrofoil were simulated.The purpose is to capture the instability of hydrofoil vibration and evaluate the influence of natural frequency ratio and inertia radius on vibration state to avoid the generation of flutter.The results indicate that when the inflow velocity increases to a certain critical value,the hydrofoil will enter the flutter critical state without amplitude attenuation.The attack angle of a hydrofoil has a significant impact on the vibration amplitude of heave and pitch.Additionally,the natural frequency ratio and inertia radius of the hydrofoil significantly affect the critical velocity of the flutter.Adjusting the natural frequency ratio by reducing the vertical stiffness or increasing the pitch stiffness can move the vibration from a critical state to a convergent state.

Topological magnetotransport and electrical switching of sputtered antiferromagnetic Ir_(20)Mn_(80)

Topological magnetotransport in non-collinear antiferromagnets has attracted extensive attention due to the exotic phenomena such as large anomalous Hall effect(AHE),magnetic spin Hall effect,and chiral anomaly.The materials exhibiting topological antiferromagnetic physics are typically limited in special Mn_3X family such as Mn_3Sn and Mn_3Ge.Exploring the topological magnetotransport in common antiferromagnetic materials widely used in spintronics will not only enrich the platforms for investigating the non-collinear antiferromagnetic physics,but also have great importance for driving the nontrivial topological properties towards practical applications.Here,we report remarkable AHE,anisotropic and negative parallel magnetoresistance in the magnetron-sputtered Ir_(20)Mn_(80)antiferromagnet,which is one of the most widely used antiferromagnetic materials in industrial spintronics.The ab initio calculations suggest that the Ir_4Mn_(16)(IrMn_4)or Mn_3Ir nanocrystals hold nontrivial electronic band structures,which may contribute to the observed intriguing magnetotransport properties in the Ir_(20)Mn_(80).Further,we demonstrate the spin–orbit torque switching of the antiferromagnetic Ir_(20)Mn_(80)by the spin Hall current of Pt.The presented results highlight a great potential of the magnetron-sputtered Ir_(20)Mn_(80)film for exploring the topological antiferromagnet-based physics and spintronics applications.

High-cycle Fatigue Fracture Behavior of Ultrahigh Strength Steels

The fatigue fracture behavior of four ultrahigh strength steels with different melting processes and therefore different inclusion sizes were studied by using a rotating bar two-point bending fatigue machine in the high-cycle regime up to 107 cycles of loading. The fracture surfaces were observed by field emission scanning electron microscopy （FESEM）. It was found that the size of inclusion has significant effect on the fatigue behavior. For AtSI 4340 steel in which the inclusion size is smaller than 5.5 μm, all the fatigue cracks except one did not initiated from inclusion but from specimen surface and conventional S-N curve exists. For 65Si2MnWE and Aermet 100 steels in which the average inclusion sizes are 12.2 and 14.9 μm, respectively, fatigue cracks initiated from inclusions at lower stress amplitudes and stepwise S-N curves were observed. The S-N curve displays a continuous decline and fatigue failures originated from large oxide inclusion for 60Si2CrVA steel in which the average inclusion size is 44.4 pro. In the case of internal inclusion-induced fractures at cycles beyond about 1×10^6 for 65Si2MnWE and 60Si2CrVA steels, inclusion was always found inside the fish-eye and a granular bright facet （GBF） was observed in the vicinity around the inclusion. The GBF sizes increase with increasing the number of cycles to failure Nf in the long-life regime. The values of stress intensity factor range at crack initiation site for the GBF are almost constant with Nf, and are almost equal to that for the surface inclusion and the internal inclusion at cycles lower than about 1×10^6. Neither fish-eye nor GBF was observed for Aermet 100 steel in the present study.

High-efficiency Brillouin lasing in a planar GeSbS spiral-ring resonator

Stimulated Brillouin scattering in planar integrated circuits promises to realize compact and highly coherent lasers.Here we report efficient Brillouin lasing at telecommunication wavelength from a planar Ge_(25)Sb_(10)S_(65) chalcogenide(ChG)resonator with a high quality factor above 106.A low lasing threshold of 24.8 mW is achieved with a slope efficiency of 8.3%.An 8-kHz linewidth is measured for 1.56-mW on-chip output power.This work offers a good opportunity to enrich the versatility and functionality of the ChG photonics on account of their intrinsic advantages of low loss,high third-order nonlinearity,and potential capacity for wafer-scale fabrication.

The early signal substances induced by heat stress in brains of mice

To study the effects of early signal substances induced by heat stress in brains of Kunming mice,six-month-old mice(n 572)were pretreated with heat stress and subsequent ischemia/reperfusion by clipping of their bilateral cervical common arteries for 7 min.According to different treatments,animals were randomly divided into four groups:(1)normal control group;(2)heat stress pre-treatment followed by ischemia and reperfusion group(HS/IR);(3)ischemia and reperfusion group(IR);(4)heat stress group(HS).Animals in the later three groups were subdivided into 3 subgroups(1 day,4 days,14 days),respectively.The changes in the expression of cAMP res-ponse element binding protein(CREB)and calcitonin gene-related peptide(CGRP)were detected by immuno-histochemistry and computer image analysis methods.The results showed that compared with the normal group,the expressions of CREB in the hippocampal CA1 region increased significantly in the HS,HS/IR and IR groups(P,0.05).Compared to the normal group,heat stress could result in CGRP excretion and redistribution in the cerebrum,with the highest level in the 4 d HS/IR group.Following heat stress,CGRP immunoreactivity was observed in varicose fibers and neuronal perikarya within the CA1 region.The results indicate that heat stress can induce CREB expression,which in turn stimulates CGRP secretion.