Revealing the role of pyramidal slip in the high ductility of Mg-Li alloy

The high ductility of Mg-Li alloy has been mainly ascribed to a high activity of pyramidal<c+a>slip to accommodate plastic strain.In the present study,however,a quantitative analysis reveals that Li-addition can only slightly stimulate the activation of pyramidal<c+a>slip under compression along the normal direction of a hot-rolled Mg-4.5 wt.%Li plate,with a relative activity of approximately 18%.Although the limited activity of pyramidal<c+a>slip alone cannot accommodate a large plastic strain,it effectively reduces the number of{10.11}−{10.12}double twins,which are believed to be favorable sites for crack initiation.The evidently reduced activity of double twins leads to a lower cracking tendency,and therefore improves ductility.

Causal effects of circulating vitamin levels on the risk of heart failure:a Mendelian randomization study

BACKGROUND Observational studies suggest inverse associations between serum vitamin levels and the risk of heart failure(HF). However, the causal effects of vitamins on HF have not been fully elucidated. Here, we conducted a Mendelian randomization(MR) study to investigate the causal associations between genetically determined vitamin levels and HF.METHODS Genetic instrumental variables for circulating vitamin levels, including vitamins A, B, C, D, and E, which were assessed as either absolute or metabolite levels were obtained from public genome-wide association studies. Summary statistics for single-nucleotide-polymorphisms and HF associations were retrieved from the HERMES Consortium(47,309 cases and 930,014controls) and FinnGen Study(30,098 cases and 229,612 controls). Two-sample MR analyses were implemented to assess the causality between vitamin levels and HF per outcome database, and the results were subsequently combined by meta-analysis.RESULTS Our MR study did not find significant associations between genetically determined circulating vitamin levels and HF risk. For absolute vitamin levels, the odds ratio for HF ranged from 0.97(95% confidence interval [CI]: 0.85–1.09, P = 0.41) for vitamin C to 1.05(95% CI: 0.61–1.82, P = 0.85) for vitamin A. For vitamin metabolites, the odds ratio ranged between 0.94(95% CI:0.75–1.19, P = 0.62) for α-tocopherol and 1.11(95% CI: 0.98–1.26, P = 0.09) for γ-tocopherol.CONCLUSION Evidence from our study does not support the causal effects of circulating vitamin levels on HF. Therefore,there may be no direct beneficial effects of vitamin intake on the prevention of primary HF.

Effect of Twin Boundary–Dislocation–Solute Interaction on Detwinning in a Mg–3Al–1Zn Alloy

In the present study,the influence of solute atoms together with dislocations at {1012} twin boundary(TB) on mechanical behavior of a detwinning predominant deformation in a Mg alloy AZ31 plate was systematically studied.The results show that a large number of {1012} twins disappear during recompression along the normal direction.Both the TB–dislocation interaction and TB–solute–dislocation interaction can greatly enhance the yield stress of the recompression along the normal direction(ND).However,the solute segregation at {1012} TBs with an intensive interaction with <a> dislocations cannot further enhance the yield stress of ND recompression.The samples with TB–dislocation interaction show a similar working hardening performance with that subjected to a TB–solute–dislocation interaction.Both the TB–dislocation interaction and TB–solute–dislocation interaction greatly reduce the value of work hardening peaks during a detwinning predominant deformation.

二维磁性材料的研究进展

二维材料依靠其超薄的厚度在诸多领域中展现出独特的性能,如电子学和催化领域.作为二维材料中的一员,二维磁性材料是物理学基础研究和磁性器件发展的理想平台.因此,二维磁性材料受到了广泛的关注和研究.本文综述了二维磁性材料的研究进展,总结了磁性的表征方法,讨论了常见的二维磁性材料的分类及对二维磁性调控的方法,并介绍了二维磁性材料的应用.最后,展望了二维磁性材料在未来发展中将面临的挑战和机遇.

Mechanical and Corrosion Behavior of a Biomedical Mg–6Zn–0.5Zr Alloy Containing a Large Number of Twins

The strong texture of Mg alloys can lead to strong tension–compression yield asymmetry and corrosion anisotropy,and this will consequently affect the effectiveness of hard tissue implants.A biomedical Mg–6Zn–0.5Zr alloy containing a large number of{1012}primary twins and{1012}–{1012}secondary twins is successfully prepared by cross compression.The dual twin structure not only removes the tension–compression yield asymmetry completely,but effectively reduces the corrosion anisotropy without compromise of corrosion resistance.The difference between the largest corrosion rate and smallest one is~1.2 times compared to~1.6 times of the original materials.It is found that the reduced corrosion anisotropy is related to re-distribution of crystallographic orientations by twins.

Detachable and hierarchical assemblies for recyclable and highly efficient oil-fouling removal

Large-scale use of detergents to remove oil-fouling in industry continuously generates tremendous amounts of wastewater and thus leads to both economic and environmental problems.To develop recyclable oil-fouling removal strategy is an appealing solution but a challenging task.Herein,a kind of dynamic imine-based surfactant has been constructed by 2-formylbenzenesulfonic acid sodium salt(FBSS)and linear amines(CnNH_(2),n=6,7,8,10,and 12).Owing to high interfacial activity and strong assembly ability,dynamic FBSS/C8NH_(2)system can remove oil-fouling on multiple substrates for at least 10 cycles,largely reducing the toxicity to ecosystem.At basic pH,the hierarchical assemblies(from vesicle to network and hollow sphere)are formed and boost surfactant molecule enrichment around oil-fouling,leading to highly efficient emulsification.When pH is changed to acidic condition,the surfactant molecules dissociate due to the breaking of imine bonds,and accordingly the emulsion is destroyed and the released oil droplets float to the top layer.After removing the oil-fouling and adjusting the solution back to basic pH,the surfactant assemblies are reconstructed and used for the next oil-fouling cleaning cycle.This study provides a recyclable,efficient and eco-friendly oil-fouling removal approach,satisfying the need of sustainable development.

Regioregular Asymmetric Diketopyrrolopyrrole Copolymers with Good Molecular Ordered Assembly Ability for High-performance Polymer Transistors

Introduction of asymmetric units into conjugated polymers is an important strategy to regulate the photophysical and electronic properties of polymers,as asymmetric units can not only regulate solubility and energy levels,but also molecular stacking and orientation,thus giving much higher optoelectronic properties.However,very few studies have been reported in this field.The semiconducting properties of conjugated polymers could be regulated through regioregularity adjustment.Here,we took the asymmetric thiophene/pyridine side group DPP as core and developed the regioregular monomer T-Py-DPP through three steps:alkyl chain introduction,tin monomer coupling and NBS double bromination.The T-Py-DPP monomer was polymerized into reg-PPy TDPP-2FBT with a head-to-head structure.The regioregularity of T-Py-DPP unit endowed reg-PPy TDPP-2FBT with backbone planarity,self-assembly orientation,network-like morphology and high crystallinity in films,thus the superior bipolar transport properties.The highest hole and electron mobilities of reg-PPy TDPP-2FBT were 0.93 and 0.57 cm^(2)·V^(-1)·s^(-1),respectively,with 40%improvement relative to the regiorandom polymer.

Efficient electrocatalytic CO_(2)reduction to C_(2+)chemicals on internal porous copper

To improve the electrocatalytic conversion of carbon dioxide(CO_(2))into C_(2+)products(such as ethylene(C_(2)H_(4))and ethanol(CH_(3)CH_(2)OH),etc.)is of great importance,but remains challenging.Herein,we proposed a strategy that directs the C–C coupling pathway through enriching and confining the carbon monoxide(CO)intermediate to internal pores of Cu nanocubes,for electrocatalytic reduction of CO_(2)into C_(2+)chemicals.In H-type cell,the Faraday efficiency(FE)for ethylene and ethanol reaches 70.3%at−1.28 V versus the reversible hydrogen electrode(vs.RHE),with a current density of 47.9 mA·cm^(−2).In flow cell,the total current density is up to 340.3 mA·cm^(−2)at^(−2).38 V(vs.RHE)and the FE for C_(2+)products is 67.4%.Experimental and theoretical studies reveal that both the CO intermediate adsorption and C–C coupling reaction on such an internal porous catalyst are facilitated,thus improving CO_(2)-to-C_(2+)conversion efficiency.

A weak texture dependence of Hall–Petch relation in a rare-earth containing magnesium alloy

Hall–Petch slope(k),an important parameter in Hall–Petch relation,describes the efficiency of strengthening effect by grain boundaries.Previously,a highly texture dependent k for Mg alloys is frequently reported,but,in the present study,we report a weak texture dependence of k in a rare-earth containing Mg-2Zn-1Gd plate with two peaks of(0002)poles inclining approximately±30°away from the ND toward the TD.Although there is a strong mechanical anisotropy between tension along the TD and RD,the k for TD-tension(280 MPaμm^(1/2))is quite similar to that for RD-tension(276 MPaμm^(1/2)).Here,RD,TD and ND refer to the rolling direction,transverse direction and normal direction of the plate,respectively.The weak texture dependence of k is well predicted by the compound use of the activation stress difference between neighboring grains(ΔStress)and the geometric compatibility factor(m').By analyzing how the texture affects the values for ΔStress and m,the mechanism for this texture independence of k is ascribed to the activation of a high fraction of additional deformation mode,besides the predominant one for both RD-tension and TD-tension,namely,prismatic slip accompanied by a high fraction of basal slip for RD-tension and basal slip accompanied by a high fraction of prismatic slip for TD-tension.This will lead to multiple deformation transfer modes and,consequently,the effect of texture on the ease of deformation transfer across grain boundaries is weakened.As a result,there is a similar k for TD-tension and RD-tension.

Microstructural Evolution, Mechanical Properties and Thermal Stability of Gradient Structured Pure Nickel

The microstructural evolution of pure nickel treated by deep rolling(DR)technique with different indent depths was investigated by means of optical microscopy and transmission electron microscopy.The surface roughness,hardness and residual stress distribution along the depth from surface were measured.Moreover,the DR-treated sample was annealed at temperatures from 300 to 700℃for 2 h.The results reveal that dislocation movements are the fundamental mechanisms of gradient grain refinement during the DR process.With increasing indent depth of the DR,the gradient microhardness on the cross section of sample significantly increases,the maximum compressive residual stress decreases,and the affecting region of residual stress increases.The results of thermal stability depict that the microstructure can be stable as temperature up to 300℃,and the abnormal grain growth and annealing twins are observed at 600℃.

Association between thyroid hormone levels and frailty in the community-dwelling oldest-old: a cross-sectional study

Background:Changes in thyroid hormone levels are commonly recognized characters among the elderly,which were reported to potentially influence incident frailty.Therefore,we examined the cross-sectional associations of thyroid hormones(THs)with frailty as well as the five components characterizing frailty(fatigue,resistance,ambulation,number ofillnesses,and loss of weight)among the oldest-old.Methods:Four hundred and eighty-seven community-dwelling oldest-old from a local community in Haidian District,Beijing,participated in our recruitment campaign between April 2019 and May 2020.The primary outcomes were a definitive diagnosis of frailty according to the FRAIL scale(Fatigue,Resistance,Ambulation,Illnesses,Loss of weight)and a positive score for each frailty subdomain.Demographic information(age,sex,marital status,and educational status),comorbidities,and details on the participants lifestyles were recorded.Serum THs including free triodothyronin(fT3),triiodothyronine(T3),free thyroxine(fT4),and thyroxine(T4)and thyroid stimulating hormone(TSH)levels were also measured at the beginning of our study.Logistic regressions were conducted to screen for potential risk factors for frailty and its subdomains.Results:Among the total 487 subjects at enrollment,60(12.23%)of them were diagnosed with subclinical hypothyroidism and 110(22.59%)of the total population scored positive for frailty.Logistic regression analyses adjusted for all potential confounders,showed that frailty was significantly associated with the serum TSH concentration(odds ratio[OR]:1.06),fT3 concentration(OR:0.54),and subclinical hypothyroidism score(OR:2.18).The association between fT4 and frailty was absent in our observational study.The fT3/fT4 ratio characterizing peripheral hormone conversion was also tested to be correlated with frailty.Conclusion:Subclinical hypothyroidism,higher TSH level,lower fT3 level,and decreased fT3/fT4 ratio were all associated with frailty assessed by the FRAIL scale among the community-dwelling oldest-old,suggesting a relevant role of thyroid function in aging.Future longitudinal studies are warranted to determine the casual relationship between thyroid dysfunction and frailty in the oldest-old.

Grain-refining and strengthening mechanisms of bulk ultrafine grained CP-Ti processed by L-ECAP and MDF

The microstructural evolution and mechanical properties of ultrafine-grained(UFG)CP-Ti after an innovative large-volume equal channel angular pressing(L-ECAP)and multi-directional forging(MDF)were systematically examined using monotonic tensile tests combined with transmission electron microscope(TEM)and electron backscatter diffraction(EBSD)techniques.Substantially refined and homogeneous microstructures were achieved after L-ECAP(8-pass and 12-pass)and MDF(2-cycle and 3-cycle),respectively,where the grain size distribution conformed to lognormal distribution.The grain refinement of450℃L-ECAP is dominated by dynamic recrystallization(DRX)and dynamic recovery(DRV),while that of MDF is dominated by DRX.The iron impurities promote recrystallization by pinning-induced dislocation accumulation so that DRX is prone to occur at iron segregation regions during L-ECAP.The monotonic tensile results show that the strain hardening rate of CP-Ti increases with the decrease of grain size,while the continuous strain hardening ability decreases.The relationship between the average grain size and yield strength is in accordance with Hall-Petch relationship.Meanwhile,the individual strengthening mechanisms were quantitatively examined by the modified model.The results indicate that the strengthening contribution of dislocation accumulation to yield strength is greater than that of grain refinement.

Strengthening Mechanism and Microstructure of Deformable Ti Particles Reinforced AZ91 Composite

In this study,the deformable titanium(Ti)particles reinforced AZ91 composite was successfully prepared by powder metallurgy and subsequent extrusion.The mechanical properties and microstructural evolution of pure AZ91 and 5 Ti/AZ91 composite were studied.The yield strength,ultimate tensile strength,and elongation of 5 Ti/AZ91 composite are measured to be 212 MPa,323 MPa,and 10.1%,respectively.Microstructure analysis revealed that Ti particles are elongated along the extrusion direction,forming a discontinuous strip Ti particles,fine precipitated Mg_(17)Al_(12) phase inhibits dynamic recrystallization(DRX)behavior through Zener pinning effect and hinders the growth of matrix grains,resulting in refiner grains of 5 Ti/AZ91 composite.Heterogeneous deformed Ti particles and magnesium(Mg)matrix to generate additional heterogeneous deformation-induced(HDI)strengthening.Heterogeneous deformation-induced strengthening mainly contributed to the increment of yield strength for 5 Ti/AZ91 composite.

Achieving ultra-high strength using densely ultra-fine LPSO phase

Long period stacking ordered(LPSO) structures are an effective strengthening phase in Mg alloys.However,the coarse LPSO phases in as-cast alloys are very difficult to refine,and they dramatically reduce the strengthening effect.In the present study,friction stir processing(FSP) was employed to refine the structure of an Mg-12.8 Y-4.7 Zn(wt%) alloy with a very high content of coarse LPSO phases.An optimized FSP regime refined the coarse LPSO phases into densely ultrafine blocks with an average width of ~200 nm and an average length of~1 μm.An ultrahigh yield strength of ~800 MPa was achieved under compression of the FSP region.Theoretical calculations indicated that the strengthening by the densely ultrafine LPSO phases was up to approximately 630 MPa.

紧致闭Riemann流形上带梯度项的完全非线性椭圆方程的二阶导数估计

二阶导数先验估计是研究完全非线性椭圆方程的一个关键步骤,这是本文所关注的重点.本文考虑闭Riemann流形上一类完全非线性二阶椭圆方程,通过引入依赖解本身及其梯度的等位面的无穷远切锥,给出解的二阶导数先验估计.