Microstructure and mechanical property of a high-strength Mg-10Gd-6Y-1.5Zn-0.5Zr alloy prepared by multi-pass equal channel angular pressing

In this work,a high-strength Mg–10Gd–6Y–1.5Zn–0.5Zr(wt.%)alloy was fabricated by successive multi-pass equal channel angular pressing(ECAP).The microstructure and mechanical property of as-cast and ECAP alloys were systematically researched by X-ray diffractometer,scanning electron microscopy,transmission electron microscopy and compression test.The results show that the microstructure of as-cast alloy consists ofα-Mg grains,Mg24Y5 networks,18R blocks,fine 14H lamellas,and fewY-rich particles.After 8 passes ECAP,dynamic recrystallization ofα-Mg is developed and their average grain size decreases to about 1μm.The network Mg_(24)Y_(5) phase at grain boundaries is broken into small particles with average diameter lower than 0.5μm.Moreover,18R blocks are kinked and delaminated,or broken into small particles and blended with Mg24Y5 particles.14H lamellas grow gradually or are dynamically precipitated within certainα-Mg grains.Compression tests indicate that 8p ECAP alloy exhibits excellent mechanical property with compressive strength of 537 MPa and fracture strain of 17.0%.The significant improvement for both strength and ductility of deformed alloy could be ascribed to DRX grains,refined Mg24Y5 particles,18R kinking and dynamical precipitation of 14H.

ANAC087 transcription factor positively regulates age-dependent leaf senescence through modulating the expression of multiple target genes in Arabidopsis

Leaf senescence is the final stage of leaf development and appropriate onset and progression of leaf senescence are critical for reproductive success and fitness.Although great progress has been made in identifying key genes regulating leaf senescence and elucidating the underlining mechanisms in the model plant Arabidopsis,there is still a gap to understanding the complex regulatory network.In this study,we discovered that Arabidopsis ANAC087 transcription factor(TF)positively modulated leaf senescence.Expression of ANAC087 was induced in senescing leaves and the encoded protein acted as a transcriptional activator.Both constitutive and inducible overexpression lines of ANAC087 showed earlier senescence than control plants,whereas T-DNA insertion mutation and dominant repression of the ANAC087 delayed senescence rate.A quantitative reverse transcription-polymerase chain reaction(qRT-PCR)profiling showed that the expression of an array of senescence-associated genes was upregulated in inducible ANAC087 overexpression plants including BFN1,NYE1,CEP1,RbohD,SAG13,SAG15,and VPEs,which are involved in programmed cell death(PCD),chlorophyll degradation and reactive oxygen species(ROS)accumulation.In addition,electrophoretic mobility shift assay(EMSA)and chromatin immunoprecipitation-quantitative polymerase chain reaction(ChIP-qPCR)assays demonstrated that ANAC087 directly bound to the canonical NAC recognition sequence(NACRS)motif in promoters of its target genes.Moreover,mutation of two representative target genes,BFN1 or NYE1 alleviated the senescence rate of ANAC087-overexpression plants,suggesting their genetic regulatory relationship.Taken together,this study indicates that ANAC087serves as an important regulator linking PCD,ROS,and chlorophyll degradation to leaf senescence.

RNA生物标志物体外检测方法研究进展

RNA生物标志物主要包括编码蛋白的mRNA和非编码蛋白的microRNA(miRNA)、环状RNA(circula rRNA,circRNA)及长链非编码RNA(lncRNA)等.RNA生物标志物种类多,生物信息量丰富,相比DNA更能动态反映细胞生物学功能和调控过程,因此,RNA生物标志物的定量检测和表达分析对于细胞功能研究、疾病的诊断和治疗及预后监测等具有重要意义.本文重点介绍了常见RNA生物标志物mRNA、miRNA、circRNA和lncRNA体外检测方法的原理及研究进展,并对RNA生物标志物检测面临的挑战及发展趋势进行了展望.

Effect of Multi-Pass Equal Channel Angular Pressing on the Microstructure and Mechanical Properties of a Heterogeneous Mg_(88)Y_8Zn_4 Alloy

The microstructure evolutions and mechanical properties of a heterogeneous Mg88Y8Zn4（in at.%） alloy during multi-pass equal channel angular pressing（ECAP） were systematically investigated in this work.The results show that four phases,i.e.α-Mg,18 R long period stacking ordered（LPSO） phase,Mg24Y5 and Y-rich phase,are present in cast alloy.During ECAP,dynamic recrystallization（DRX） occurs and the diameter of DRXedα-Mg grains decreases to 0.8 μm.Moreover,precipitation of lamellar 14 H LPSO structure is developed withinα-Mg phase.Both the refinement of α-Mg grains and precipitation of 14 H LPSO contribute to the increase in micro-hardness from 98 HV to 135 HV for α-Mg.In addition,a simplified model describing the evolution of 18 R LPSO phase is established,which illustrates that 18 R undergoes a four-step morphological evolution with increasing strains during ECAP,i.e.original lath → bent lath → cracked lath → smaller particles.Compression test results indicate that the alloy has been markedly strengthened after multi-pass ECAP,and the main reason for the significantly enhanced mechanical properties could be ascribed to the DRXed α-Mg grains,newly precipitated 14 H lamellas,18 R kinking and refined 18 R particles.

Quantifying the characteristics of particulate matters captured by urban plants using an automatic approach

It is widely accepted that urban plant leaves can capture airborne particles. Previous studies on the particle capture capacity of plant leaves have mostly focused on particle mass and/or size distribution. Fewer studies, however, have examined the particle density, and the size and shape characteristics of particles, which may have important implications for evaluating the particle capture efficiency of plants, and identifying the particle sources. In addition, the role of different vegetation types is as yet unclear. Here, we chose three species of different vegetation types, and firstly applied an object-based classification approach to automatically identify the particles from scanning electron microscope（SEM）micrographs. We then quantified the particle capture efficiency, and the major sources of particles were identified. We found（1） Rosa xanthina Lindl（shrub species） had greater retention efficiency than Broussonetia papyrifera（broadleaf species） and Pinus bungeana Zucc.（coniferous species）, in terms of particle number and particle area cover.（2） 97.9% of the identified particles had diameter ≤10 μm, and 67.1% of them had diameter ≤2.5 μm. 89.8% of the particles had smooth boundaries, with 23.4% of them being nearly spherical.（3） 32.4%–74.1% of the particles were generated from bare soil and construction activities, and 15.5%–23.0% were mainly from vehicle exhaust and cooking fumes.