Emission Spectrum and Resistivity of Low Power Plasma Weld Arcs

Emission spectra from plasma arc welds were observed under a variety of current, voltage, polarity, and standoffs. If reverse polarity (welding torch positive) welds are struck below 50 amperes most of the power is deposited at the electrode rather than the workpiece because of low carrier density within the arc. Straight polarity, on the other hand, suffers no such limitation because of electrons created in the pilot arc used to start the weld process.     

Ultrasonic irradiation and its application for improving the corrosion resistance of phosphate coatings on aluminum alloys

In this paper, ultrasonic irradiation was utilized for improving the corrosion resistance of phosphate coatings on aluminum alloys. The chemical composition and morphology of the coatings were analyzed by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The effect of ultrasonic irradiation on the corrosion resistance of phosphate coatings was investigated by polarization curves and electrochemical impedance spectroscopy (EIS). Various effects of the addition of Nd₂O₃ in phosphating bath on the performance of the coatings were also investigated. Results show that the composition of phosphate coating were Zn₃(PO₄)₂ · 4H₂O(hopeite) and Zn crystals. The phosphate coatings became denser with fewer microscopic holes by utilizing ultrasonic irradiation treatment. The addition of Nd₂O₃ reduced the crystallinity of the coatings, with the additional result that the crystallites were increasingly nubby and spherical. The corrosion resistance of the coatings was also significantly improved by ultrasonic irradiation treatment; both the anodic and cathodic processes of corrosion taking place on the aluminum alloy substrate were suppressed consequently. In addition, the electrochemical impedance of the coatings was also increased by utilizing ultrasonic irradiation treatment compared with traditional treatment.     

Experimental and quantum chemical studies of cooperative enhancement of three-photon absorption, optical limiting, and stabilization behaviors in multibranched and dendritic structures

This paper reports on cooperative enhancement of three-photon absorption (3PA) cross section, studied by nonlinear transmission method, in going from a one-branched to a three-branched and then to a dendritic structure. Experimentally, we observe a 72% enhanced 3PA cross-section value in going from the one-branched chromophore to the dendritic chromophore, and a 49% enhanced 3PA cross-section value in going from the one-branched chromophore to the three-branched chromophore, when the 3PA cross-section values are normalized per structure unit. Quantum chemical calculation for the one- and three-branched structures, using the cubic response (CR) theory applied to a single determinant self-consistent field (SCF) reference state, also predicts such an enhancement. Two-dimensional pi-delocalization, resulting in extended charge-transfer network in the case of the multibranched structures, is the main cause of the cooperative enhancement. Owing to the increased 3PA cross-section value for the dendritic chromophore, improved optical limiting performance at an optical communication wavelength of 1310 nm was observed, compared with the one-branched (or three-branched) chromophore, using comparable structure-unit-based concentrations. Optical stabilization capability of the dendritic chromophore was also observed at this wavelength.     

Initial value problems for fractional differential equations involving Riemann-Liouville sequential fractional derivative

In this paper, we shall discuss the properties of the well-known Mittag-Leffler function, and consider the existence and uniqueness of solution of the initial value problem for fractional differential equation involving Riemann-Liouville sequential fractional derivative by using monotone iterative method.     

Hierarchical Cu precipitation in lamellated steel after multistage heat treatment

Abstract

The hierarchical distribution of Cu-rich precipitates (CRPs) and related partitioning and segregation behaviours of solute atoms were investigated in a 1.54 Cu-3.51 Ni (wt.%) low-carbon high-strength low-alloy (HSLA) steel after multistage heat treatment by using the combination of electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and atom probe tomography (APT). Intercritical tempering at 725 °C of as-quenched lathlike martensitic structure leads to the coprecipitation of CRPs at the periphery of a carbide precipitate which is possibly in its paraequilibrium state due to distinct solute segregation at the interface. The alloyed carbide and CRPs provide constituent elements for each other and make the coprecipitation thermodynamically favourable. Meanwhile, austenite reversion occurs to form fresh secondary martensite (FSM) zone where is rich in Cu and pertinent Ni and Mn atoms, which gives rise to a different distributional morphology of CRPs with large size and high density. In addition, conventional tempering at 500 °C leads to the formation of nanoscale Cu-rich clusters in α-Fe matrix. As a consequence, three populations of CRPs are hierarchically formed around carbide precipitate, at FSM zone and in α-Fe matrix. The formation of different precipitated features can be turned by controlling diffusion pathways of related solute atoms and further to tailor mechanical properties via proper multistage heat treatments.     

Defect passivation of CsPbI_2Br perovskites through Zn(Ⅱ) doping:toward efficient and stable solar cells

Defect passivation is an important strategy to achieve perovskite solar cells(PVSCs) with enhanced power conversion efficiencies(PCEs) and improved stability because the trap states induced by defects in the interfaces and grain boundaries of perovskites are harmful to both large open circuit voltage and high photocurrent of devices. Here, zinc cations(Zn~(2+)) were used as a dopant to passivate defects of the CsPbI_2Br perovskite leading to Zn~(2+)-doped CsPbI_2Br film with fewer trap states, improved charge transportation, and enhanced light-harvesting ability. Thus, the best-performance PVSC based on CsPbI2 Br with the optimal Zn~(2+)doping shows a higher PCE of 12.16% with a larger open-circuit voltage(V_(OC)) of 1.236 V, an improved shortcircuit current(J_(SC)) of 15.61 mA cm~(-2) in comparison with the control device based on the pure CsPbI_2Br which exhibits a PCE of 10.21% with a V_(OC)of 1.123 V, a J_(SC)of 13.27 mA cm~(-2). Time-resolved photoluminescence results show that the Zn~(2+)doping leads to perovskite film with extended photoluminescence lifetime which means a longer diffusion length and subsequently enhanced photocurrent and open circuit voltage. This work provides a simple strategy to boost the performance of PVSCs through Zn~(2+)doping.     

基于吸收互补有机半导体本体复合薄膜的高性能柔性光突触晶体管

采用光吸收互补的聚(3-己基噻吩)(P3HT)和引达省并二噻吩-苯并噻二唑共聚物(PIDT-BT), 通过溶液法制备了两者的本体复合异质结构有机半导体薄膜, 并研究了薄膜的表面结构和光电性质. 将PIDT-BT:P3HT复合薄膜作为一类新型光敏沟道层, 与聚电解质介电材料相结合, 制备了高性能柔性低电压光突触晶体管. 考察了不同光刺激条件对光突触晶体管性能的影响及半导体机制, 发现PIDT-BT:P3HT器件具有明显光突触特性, 并且相较于单纯PIDT-BT或P3HT器件具有更高响应的兴奋性突触后电流. 基于PIDT-BT:P3HT薄膜的光突触器件, 在绿红双色光刺激下的响应大于两种单色光分别刺激的响应之和, 表明附加光刺激可调控器件的记忆效率. 该研究为发展高性能光响应半导体薄膜及柔性低功耗光突触器件提供了新策略.     

Conformationally restricted dipyrromethene boron difluoride (BODIPY) dyes: highly fluorescent, multicolored probes for cellular imaging

Novel fluorescent, conformationally restricted dipyrromethene boron difluoride (BODIPY) dyes have been prepared by introducing a naphthalenyl group at the meso position of the BODIPY core. These BODIPY dyes exhibit increased fluorescence quantum yields compared with dyes that have a meso-position phenyl group with internal rotation. The absorption and emission wavelengths of such conformationally restricted BODIPY dyes can be easily tuned to the near-IR range by derivatization through a condensation reaction with benzaldehyde derivatives. The two-photon absorption properties of these BODIPY dyes were also investigated and the results show that they exhibit increased two-photon excited fluorescence compared to analogue dyes that contain a phenyl group. The one- and two-photon fluorescence imaging of living cells by using selected BODIPY dyes has been successfully demonstrated.     

数字状张拉整体结构的构型设计与力学性能模拟

针对大型张拉整体结构的设计问题,选取四棱柱状张拉整体结构和截角正八面体状张拉整体结构作为基本胞元,采用节点连接节点的方式建立球柱组合式数字状张拉整体结构,并使用基于结构刚度矩阵的大变形非线性数值求解方法对其进行力学性能分析.在两类胞元满足各自的自平衡条件和稳定性条件的前提下,组合得到的数字状张拉整体结构亦处于自平衡稳定状态,搭建了实物模型进行验证.以数字8状张拉整体结构为例,模拟研究了结构承受自重等分布载荷和单轴拉压等端部载荷时的静力学响应,以及结构无阻尼振动时的固有频率和模态等动力学性能.结果表明,结构在自重作用下的变形行为受初始预应力、压杆密度和拉索刚度的影响较大,对其进行合理配置方可确保结构具有足够刚度抵抗自重;结构在单轴拉压作用下呈现非线性的载荷-位移曲线,拉伸刚度随变形量的增大而增大,压缩刚度随变形量的增大而减小;结构的固有频率随初始预应力的增大而增大,而模态振型基本不变.研究结果丰富了大型张拉整体结构的外形种类,有望推动此类结构在土木建筑、结构材料等领域的应用.      

桥连双(酮亚胺)和双(二酮亚胺)及其铝配合物的合成与催化活性

通过桥连双β-二酮类化合物与取代苯胺反应, 合成了5个新的桥连双(β-单酮亚胺)化合物(1~5)和2个新的桥连双(β-二酮亚胺)化合物(6,7), 它们与三甲基铝反应, 得到了相应的3个双(β-酮亚胺基)二铝配合物(8~10)和2个双(β-二酮亚胺基)二铝配合物(11,12). 采用核磁共振、 红外光谱和质谱等对这些化合物进行了表征, 通过X射线单晶衍射分析证实了铝配合物的结构, 并考察了这些铝配合物在ε-己内酯开环聚合反应中的催化活性.