纯铜在碱性土壤中的腐蚀行为

采用室内加速腐蚀实验和电化学测试方法,结合腐蚀产物SEM和XRD分析,研究了纯铜接地材料在碱性土壤中的腐蚀行为。结果表明,在碱性土壤中纯铜具有明显的钝化特征,表面形成了一层由CuO、Cu2O和CuSO4·H2O组成的均匀致密的腐蚀产物,腐蚀产物将腐蚀性离子与基体金属隔离,抑制氧的扩散,对基体金属起到良好的保护作用。

Room temperature compressive properties and strengthening mechanism of Mg96.17Zn3.15Y0.50Zr0.18 alloy solidified under high pressure

The microstructures of Mg96.17Zn3.15Y0.50Zr0.18 alloys solidified under 2-6 GPa high pressure were investigated by employing SEM(EDS) and TEM.The strengthening mechanism of experimental alloy solidified under high pressure is also discussed by analyzing the compressive properties and compression fracture morphology.The results show that the microstructure of experimental alloy becomes significantly fine-grained with increasing GPa level high pressure during solidification process,and the secondary dendrite arm spacing reduces from 40 μm at atmospheric pressure to 10 μm at 6 GPa pressure.The morphology of the second phases changes from the net structure by the lamellar-type eutectic structure at atmospheric pressure to discontinuous thin rods or particles at 6 GPa pressure.Besides,the solid solubility of Zn in the Mg matrix is improved with the increase of the solidification pressure.Compared with atmospheric-pressure solidification,high-pressure solidification can improve the strength of the experimental alloy.The compressive stre ngth is improved from 263 to 437 MPa at 6 GPa.The fracture mechanism of the experimental alloy changes from cleavage fracture at atmospheric pressure to quasi-cleavage fracture at high pressure.The main mechanism of the strength improvement of the experimental alloy includes the grain refinement strengthening caused by the refinement of the solidification microstructure,the second phase strengthening caused by the improvement of the morphology and distribution of the second phases,and solid solution strengthening caused by the increase of the solid solubility of Zn in the Mg matrix.

Rectangular dielectric metagrating for high-efficiency diffraction with large-angle deflection

In this Letter,we propose a metagrating consisting of simple rectangular bars for nearly unity anomalous diffraction with a large deflection angle.The analysis performed by the scattering-matrix method shows that such exceptional beam steering derives from the couplings of the two lowest propagation waveguide-array-modes and their constructive interferences.The tolerance of the incident angle for a high diffraction efficiency(e.g.,>90%)is within a range of 33°.We also discuss that such an advantage still exists after considering a reasonable loss and dispersion.We envision that the proposed strategy may have wide use in the field of high-performance wavefront-shaping applications.

Electron back-scattering diffraction preliminary analysis of heterogeneous nuclei in magnesium alloy during solidification process under GPa high pressure

The effective heterogeneous nuclei in Mg-7.92 Zn-1.70 Y alloy during solidification process under high pressure was investigated by EBSD. It is found that the orientation relationship between Mg matrix and MgY phase, [111]_（MgY）//[1210]_（α-Mg） and（101）_（MgY）//（0001）_（α-Mg）, exists between Mg matrix and MgY phase.The MgY phase is the potential heterogeneous nuclei substrate for a-Mg solidified under high pressure. It is calculated by Bramfitt mode that the mismatch between Mg matrix and MgY phase is greater than 12% under atmospheric pressure. When solidified under high pressure of 4 GPa, the solidification pressure can increase the number of the α-Mg nucleus by reducing the size of the nucleus, decreasing interfacial energy of MgY/a-Mg, and changing the wettability between MgY phase and α-Mg from non-wetting under atmospheric pressure to wetting under high pressure. The MgY phase becomes a powerful heterogeneous nuclei for α-Mg crystal. Increasing the number of valid heterogeneous nuclei substrate increases nucleus number and refines the grain of the alloy.

Arabidopsis F-BOX STRESS INDUCED 4 is required to repress excessive divisions in stomatal development

During the terminal stage of stomatal development,the R2 R3-MYB transcription factors FOUR LIPS(FLP/MYB124) and MYB88 limit guard mother cell division by repressing the transcript levels of multiple cell-cycle genes. In Arabidopsis thaliana possessing the weak allele flp-1, an extra guard mother cell division results in two stomata having direct contact.Here, we identified an ethylmethane sulfonatemutagenized mutant, flp-1 xs01 c, which exhibited more severe defects than flp-1 alone, producing gianttumor-like cell clusters. XS01 C, encoding F-BOX STRESS-INDUCED 4(FBS4), is preferentially expressed in epidermal stomatal precursor cells.Overexpressing FBS4 rescued the defective stomatal phenotypes of flp-1 xs01 c and flp-1 mutants. The deletion or substitution of a conserved residue(Proline166) within the F-box domain of FBS4 abolished or reduced, respectively, its interaction with Arabidopsis Skp1-Like1(ASK1), the core subunit of the Skp1/Cullin/F-box E3 ubiquitin ligase complex. Furthermore, the FBS4 protein physically interacted with CYCA2;3 and induced its degradation through the ubiquitin-26 S proteasome pathway. Thus, in addition to the known transcriptional pathway, the terminal symmetric division in stomatal development is ensured at the post-translational level, such as through the ubiquitination of target proteins recognized by the stomatal lineage F-box protein FBS4.