Numerical analysis of plasma arc physical characteristics under additional constraint of keyhole

The physical characteristics of a plasma arc affect the stability of the keyhole and weld pool directly during keyhole plasma arc welding(KPAW). There will be significant change for these characteristics because of the interaction between the keyhole weld pool and plasma arc after penetration. Therefore, in order to obtain the temperature field, flow field, and arc pressure of a plasma arc under the reaction of the keyhole, the physical model of a plasma arc with a pre-set keyhole was established. In addition, the tungsten and base metal were established into the calculated domain, which can reflect the effect of plasma arc to weld pool further. Based on magneto hydrodynamics and Maxwell equations, a two-dimensional steady state mathematical model was established. Considering the heat production of anode and cathode, the distribution of temperature field, flow field, welding current density, and plasma arc pressure were solved out by the finite difference method. From the calculated results, it is found that the plasma arc was compressed a second time by the keyhole. This additional constraint results in an obvious rise of the plasma arc pressure and flow velocity at the minimum diameter place of the keyhole, while the temperature field is impacted slightly. Finally, the observational and metallographic experiments are conducted, and the shapes of plasma arc and fusion line agree with the simulated results generally.     

Molecular dynamics simulations of the effects of sodium dodecyl sulfate on lipid bilayer

Molecular dynamics simulations have been performed on the fully hydrated lipid bilayer with different concentrations of sodium dodecyl sulfate(SDS). SDS can readily penetrate into the membrane. The insertion of SDS causes a decrease in the bilayer area and increases in the bilayer thickness and lipid tail order, when the fraction of SDS is less than 28%.Through calculating the binding energy, we confirm that the presence of SDS strengthens the interactions among the DPPC lipids, while SDS molecules act as intermedia. Both the strong hydrophilic interactions between sulfate and phosphocholine groups and the hydrophobic interactions between SDS and DPPC hydrocarbon chains contribute to the tight packing and ordered alignment of the lipids. These results are in good agreement with the experimental observations and provide atomic level information that complements the experiments.     

Electronic structure and optical properties of the red and yellow mercuric iodides

With the help of the ab initio full-potential linearized augmented plane wave (FPLAPW) method, calculations of the electronic structure and linear optical properties are carried out for red HgI₂ and yellow HgI₂. It is found that the red HgI₂ has a direct gap of 1.22834 eV and the yellow HgI₂ has an indirect gap of 2.11222 eV. For the red HgI₂, the calculated optical spectra are qualitatively in agreement with the experimental data. Furthermore, the origins of the different peaks of ε ₂ (ω ) are discussed. Our calculated anisotropic dielectric function of the red HgI₂ is a nice match with the experimental results. Our calculated results are able to reproduce the overall trend of the experimental reflectivity spectra. Although no comparable experimental and theoretical results are available, clearly, the above proves the reliability of our calculations, suggesting that our calculations should be convincing for the yellow HgI₂. Finally, the different optical properties are discussed.     

一类带局部非线性项的静态狄拉克方程的多重周期解

借助于变分方法,该文主要研究了一类带局部非线性项的静态狄拉克方程的多重周期解.在非线性项满足较为宽泛的条件的假设下,该文表明了这类方程一列非平凡周期解的存在性是一种局部现象,该现象仅由非线性项在原点附近的次线性所决定.与此同时,文献中最近的一些相关结果被推广并得到本质的改进.     

内切轧制形变对Bi2223/Ag多芯带材的影响

内切轧制是新的高温超导Bi2223/Ag带材加工方法.本文采用内切轧制进行高温超导Bi2223/Ag多芯带材加工实验,研究不同压下率(εh)的中间形变对带材组织、结构和性能的影响.研究结果表明,内切轧制中带材的形变属于两向延伸、一向压缩形变,其宽展延伸十分明显,随εh增加而增大;XRD分析结果表明,内切轧制中εh变化对带材相组成、Bi2223相含量和织构度影响不显著;SEM观察和Ic测试表明,εh的增加使带材致密性增强并提高Ic,但是这种作用一定程度上因银超界面而受到抑制.     

基于γ-H2AX检测的两种基因毒性体外测试方法的比较研究

以7种基因毒性化合物(GCs)及7种非DNA损伤作用化合物(Non-DCs)为模型,分别采用质谱技术与高内涵技术在两种人源细胞株即肝癌细胞HepG2和宫颈癌细胞HeLa中检测磷酸化组蛋白γ-H2AX,对化合物孵育细胞后的基因毒性进行分析检测,进而对基于γ-H2AX检测的两种基因毒性体外测试方法进行比较。结果表明,两种技术均具有高通量检测的优点,均可在2天内完成实验流程。对于本研究所考察的5个GCs,两种技术测定的细胞γ-H2AX水平显著变化的最低起效浓度(MEC)值相同;针对其余2个GCs,质谱测定的MEC值比高内涵技术低。其中,质谱技术在浓度低至10μmol/L苯丁酸氮芥及0.1μmol/L丝裂霉素C时,即可检测到γ-H2AX水平发生显著变化;而高内涵技术需在100μmol/L苯丁酸氮芥及1μmol/L丝裂霉素C浓度下才能检测到γ-H2AX水平发生显著变化,表明质谱技术具有更高的灵敏度。本研究还表明,质谱技术可特异性检测GCs所诱导的γ-H2AX水平变化;而高内涵技术无法区分检测GCs与Non-DCs导致的γ-H2AX焦点,即高内涵技术对于Non-DCs易呈现假阳性结果。本研究通过比...     

一类新芥子气损伤生物标志物的体外高分辨质谱鉴定研究

芥子气(SM)具有亲电性,是典型的高反应活性烷基化毒剂,人体经其暴露后,体内会生成多种水解氧化代谢产物和蛋白质、核酸加合物等,其中,二乙烯砜(Divinyl Sulfone, DVS)是近期发现的一种重要氧化代谢产物,具有类芥子气的反应活性和更高的毒性。以DVS及其谷胱甘肽(Glutathione, GSH)的二相代谢产物DVS-GSH分别染毒人血清白蛋白(HSA)与人源血浆,经蛋白酶K酶解和HLB小柱固相萃取净化后,采用UPLC-Q-Exactive Orbitrap高分辨质谱分析检测,鉴定出3种全新结构的白蛋白加合物:DVS-Cys-Pro-Phe(DVS-CPF)、 Phe-Pro-Cys-DVS-Cys-Pro-Phe(FPC-DVS-CPF)和GSH-DVS-Cys-Pro-Phe(GSH-DVS-CPF)。研究结果表明,含有高反应活性烯键的DVS分子可与白蛋白的Cys-34残基发生特异性加合反应,并且其二相代谢产物DVS-GSH仍可继续发生加合反应,形成一类新的白蛋白加合物。鉴定的新结构加合物不仅为确证SM暴露和中毒诊断提供了新的损伤生物标志物,也为从新的角度阐述SM的损伤...     

电化学混合电容器用新型β-Ni(OH)2/CNTs纳米复合物

采用水热合成法制备出一种新型β-Ni(OH)2/碳纳米管(CNTs)纳米复合物,Ni(OH)2微晶粒径控制在50～80 nm之间,与CNTs直径相当,CNTs与Ni(OH)2质量比为1:15.将纳米复合物应用于活性炭(AC)/NiOOH电化学混合电容器,电化学测试表明:在0.4 A/g电流条件下,其放电比容量达279 mAh/g,是β-Ni(OH)2理论容量的96.5%;当电流密度从0.4 A/g增加至8 A/g时,电容器的容量保持率在76.5%以上,高倍率充放电特性优异.此外,纳米复合物良好的电化学可逆性使AC/NiOOH电化学混合电容器更易活化,并具有较高的充放电效率和良好的循环稳定性能.     

α—AlPO_4单晶的压电和弹性性质研究

用缓慢升温法在高压釜中生长了α-AlPO_4单晶体;用传输法测量了室温下α-AlPO_4单晶体的压电、弹性和介电常数,研究了晶体中缺陷对电性能的影响。