Effect of electron inertia on large amplitude solitary waves in presence of kinematic viscosity in dusty plasma

Nonlinear dust acoustic solitary waves in a dusty plasma are studied for nonzero kinematic viscosity. Sagdeev’s potential can be obtain upto any order in ϕ. The existence of soliton solution is determined by pseudopotential approach. It is seen that the electron inertia has a significant effect on the existence of solitary waves in presence of kinematic viscosity.     

Ion acoustic solitary waves with adiabatic ions in magnetized electron-positron-ion plasmas

Linear and nonlinear ion acoustic waves in the presence of adiabatically heated ions in magnetized electron-positron-ion plasmas are studied. The Sagdeev potential approach is employed to obtain the energy integral equation in such a mulitcomponent plasma using fluid theory. It is found that electron density humps are formed in the subsonic region in magnetized electron-positron-ion plasmas. The amplitude of electron density hump is decreased with the increase of hot ion temperature in electron-positron-ion plasmas. However, the increase in positron concentration and obliqueness of the wave increases the amplitude of nonlinear structure. The increase in positron concentration also reduces the width of the nonlinear structure in a magnetized multicomponent plasma. The numerical solutions in the form of solitary pulses are also presented for different plasma cases. The results may be applicable to astrophysical plasma situations, where magnetized electron-positron-ion plasma with hot ions can exist.     

Bound states and resonance states of the plasma-embedded tdμ and ddμ molecular ions

We have investigated the bound states and resonance states of plasma-embedded tdμ and ddμ molecular ions using accurate correlated basis functions. The plasma effect has been taken care of by considering the Debye shielding approach of plasma modeling which admits a variety of plasma conditions. The density of resonance states are calculated using the stabilization method. The ground and excited states energies, and the S-wave resonance energies of tdμ and ddμ molecular ions immersed in plasmas are reported for various shielding parameters, along with the 1S and 2S threshold energies of the tμ and dμ atoms.     

Oscillator strengths and polarizabilities of the hot-dense plasma-embedded helium atom

The effect of weakly coupled hot plasma environment on the oscillator strengths of the ultraviolet and visible series and the polarizabilities of helium has been investigated using variational highly correlated wave functions within the non-relativistic framework. The Debye shielding approach that admits a variety of plasma conditions is used to simulate the plasma effects. For each shielding parameter, dipole oscillator strengths are calculated for the 1 ¹S-n¹P (n=2, 3), 2 ¹S-2 ¹P, 2 ³S-n³P (n=2, 3) and 2 ^1,3P-n^1,3D (n=3, 4) transitions. The dipole and quadrupole polarizabilities for the ground He (1s²¹S) state are also reported for each screening parameter. Results obtained are useful in plasma diagnostic purposes besides several other applications.     

氮化硼催化低碳烷烃氧化脱氢的活性起源探讨（英文）

页岩气的急速开采推动了以天然气替代石油的资源革命.除主组分甲烷外,天然气、页岩气中还包含大量乙烷、丙烷等低碳烷烃资源,将这些储量丰富的碳资源直接转化为烯烃等基础化学品有望革新以原油为基础的化学工业.现有烷烃催化脱氢制烯烃工艺中,直接脱氢过程吸热、热力学受限,且存在催化剂迅速失活的难题;而氧化脱氢是放热过程、无平衡限制,也无积碳等引发催化剂失活的问题,有利于提高反应效率、降低能耗,代表了更为高效和经济的新路线.但作为一个热力学爬坡过程,目前金属氧化物催化剂上烯烃产物很容易深度氧化到CO_2,选择性仍有待提高.非金属氮化硼能够有效活化低碳烷烃中的C-H键,促进烷烃氧化脱氢,并能够有效抑制深度氧化产物的生成,解决低碳烷烃临氧脱氢过程中产物易深度氧化的固有难题.本文综述了近期氮化硼在乙烷、丙烷、丁烷等低碳烷烃氧化脱氢制烯烃反应中的研究进展.以丙烷氧化脱氢为例,通过比较文献报道的几种氮化硼材料的氧化脱氢性能,发现羟基化氮化硼显示了最高的烯烃选择性和时空收率,以20.6%的丙烷转化率为基准,烯烃选择性超过90%,而时空收率可达6.8 golefin gcat~(-1) h~(-1).在此基础上,本文重点讨论了对于氮化硼材料催化活性起源的认识.主要实验事实和结论包括:氮化硼自身几乎没有氧化脱氢活性,而在烷烃氧化脱氢反应条件下存在活性诱导期;活性诱导期伴随着氮化硼边沿氧官能团化过程;氮化硼边沿B-O官能团没有脱氢活性,而B-OH官能团参与了氧化脱氢过程,辅助分子氧引发低碳烷烃脱氢反应;分子氧在羟基氮化硼边沿解离活化,反应过程中与边沿结构氧存在动态交换;氮化硼边沿羟基化定向合成过程可显著增强氧化脱氢反应活性.氮化硼作为一类新型烷烃氧化脱氢催化剂,目前正处于研究的初始阶段.因此,本文最后总结了一些关于氮化硼烷烃脱氢催化体系仍需深入研究的科学问题.     

Selective Encapsulation and Chiral Induction of C60 and C70 Fullerenes by Axially Chiral Porous Aromatic Cages

Chiral induction has been an important topic in chemistry, not only for its relevance in understanding the mysterious phenomenon of spontaneous symmetry breaking in nature but also due to its critical implications in medicine and the chiral industry. The induced chirality of fullerenes by host–guest interactions has been rarely reported, mainly attributed to their chiral resistance from high symmetry and challenges in their accessibility. Herein, we report two new pairs of chiral porous aromatic cages (PAC), R- PAC-2 , S- PAC-2 (with Br substituents) and R- PAC-3 , S- PAC-3 (with CH₃ substituents) enantiomers. PAC-2 , rather than PAC-3 , achieves fullerene encapsulation and selective binding of C₇₀ over C₆₀ in fullerene carbon soot. More significantly, the occurrence of chiral induction between R- PAC-2 , S- PAC-2 and fullerenes is confirmed by single-crystal X-ray diffraction and the intense CD signal within the absorption region of fullerenes. DFT calculations reveal the contribution of electrostatic effects originating from face-to-face arene-fullerene interactions dominate C₇₀ selectivity and elucidate the substituent effect on fullerene encapsulation. The disturbance from the differential interactions between fullerene and surrounding chiral cages on the intrinsic highly symmetric electronic structure of fullerene could be the primary reason accounting for the induced chirality of fullerene.     

Xylanase Production by Bacillus circulans D1 Using Maltose as Carbon Source

Bacillus circulans D1 is a good producer of extracellular thermostable xylanase. Xylanase production in different carbon sources was evaluated and the enzyme synthesis was induced by various carbon sources. It was found that d-maltose is the best inducer of the enzyme synthesis (7.05 U/mg dry biomass at 48 h), while d-glucose and d-arabinose lead to the production of basal levels of xylanase. The crude enzyme solution is free of cellulases, even when the microorganism was cultivated in a medium with d-cellobiose. When oat spelt xylan was supplemented with d-glucose, the repressive effect of this sugar on xylanase production was observed at 24 h, only when used at 5.0 g/L, leading to a reduction of 60% on the enzyme production. On the other hand, when the xylan medium was supplemented with d-xylose (3.0 or 5.0 g/L), this effect was more evident (80 and 90% of reduction on the enzyme production, respectively). Unlike that observed in the xylan medium, glucose repressed xylanase production in the maltose medium, leading to a reduction of 55% on the enzyme production at 24 h of cultivation. Xylose, at 1.0 g/L, induced xylanase production on the maltose medium. On this medium, the repressive effect of xylose, at 3.0 or 5.0 g/L, was less expressive when compared to its effect on the xylan medium.     

低温等离子体物理进展

概述了低温等离子体物理研究现状、发展及其应用      

第9届国际等离子体化学会议(ISPC-9)

概述了第9届国际等离子体化学会议的论文和活动情况,对这个领域的发展提出了一些看法。