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91.
We present a non-linear symplectic map that describes the alterations of the magnetic field lines inside the tokamak plasma due to the presence of a robust torus (RT) at the plasma edge. This RT prevents the magnetic field lines from reaching the tokamak wall and reduces, in its vicinity, the islands and invariant curve destruction due to resonant perturbations. The map describes the equilibrium magnetic field lines perturbed by resonances created by ergodic magnetic limiters (EMLs). We present the results obtained for twist and non-twist mappings derived for monotonic and non-monotonic plasma current density radial profiles, respectively. Our results indicate that the RT implementation would decrease the field line transport at the tokamak plasma edge. 相似文献
92.
93.
量子隧穿效应在实际技术中具有重要应用,本文首先展示了如何求解一维任意边界非对称以及对称双方势垒的透射系数,然后研究了对称双方势垒透射系数对垒宽、垒间距以及微观粒子入射能量与垒高比值(E/U 0)的变化依赖关系.最终得出以下结论,随着双方势垒垒宽的增加,透射系数从最大值1衰减至最小值0.随着垒间距的增加,透射系数呈现周期振荡,本文首次推导得出透射系数最大时对应的垒间距解析表达式,并给出振荡的周期,进一步证明得到它等于微观粒子的德布罗意波长.当垒宽越小时,随着E/U 0的增大,透射系数更容易达到1,并且保持不变,当垒间距越大时,随着E/U 0的增大,透射系数振荡周期变大,而振幅变小,粒子更容易实现共振隧穿. 相似文献
94.
密度泛函理论作为多相催化研究中的一个强有力工具,常被用于获得催化过程中关键的热力学及动力学参数,如吸附能、反应焓、活化能垒和速率常数等. 理解密度泛函交换关联近似方法对于揭示催化剂的催化性能及机理至关重要. 本文报道了六种不同的交换关联泛函近似方法,包括PBE、RPBE、BEEF+vdW、optB86b+vdW、SCAN和SCAN+rVV10,对金属Ru(0001)和Ru(1011)表面上甲烷和乙烷形成过程中涉及到的中间体的吸附能、反应能和活化能垒的影响. 当基元反应中反应物和产物与表面的配位数不同时,理论计算的反应能大小强烈依赖于交换关联密度泛函的选择. 对于涉及多个基元步骤的总反应,反应能的计算偏差会逐渐累积,从而导致不同的交换关联泛函近似方法之间的巨大差异. 由于不同泛函对反应涉及到的中间体吸附能之间存在差异,交换关联泛函近似方法的选择显著地影响Ru(0001)表面上甲烷、乙烯和乙烷的选择性. 然而,不同泛函近似方法对于Ru(0001) 和Ru(1011)表面上基元反应的能垒以及结构敏感性影响不大. 本工作不仅揭示了交换关联密度泛函近似方法在理论计算研究催化领域的局限性,也强调了选择合适的交换关联泛函方法对于正确评估催化剂活性和选择性的重要性. 相似文献
95.
Asja Kozak 《Molecular physics》2013,111(20):2345-2356
It has been shown that if reorientational jumps of molecules or their parts take place through inequivalent potential barriers, it is possible to draw information on the multiplicity of the axis of reorientation from the spin-lattice T 1 time measurements in the NMR experiment. For the model of n potential wells of which one is deeper than the others, for n = 2, 3, 4, 6 the analytical formulae have been derived for the T 1 relaxation time as a function of the correlation time and n. The recurrent form of the formulae for the conditional probability of the well population has been obtained, which permits calculation of the relaxation time for any n. 相似文献
96.
97.
采用基于密度泛函理论的第一性原理方法对锂离子电池负极材料黑磷在嵌锂过程中的产物LiP5,Li3P7以及LiP的晶体结构与电子结构进行了研究与分析.通过计算这几种材料的电子结构,发现黑磷嵌锂后的这几种相均为半导体能带结构,其带隙均比黑磷嵌锂前的带隙大,表明黑磷嵌锂后的电子电导性能降低了.利用弹性能带方法模拟了Li离子在LiP5,Li3P7和LiP材料中的扩散,从理论上得到了Li离子的扩散势垒,并与其他电极材料进行了比较,发现Li离子在各种嵌锂态的材料中都能够比较快速的扩散.计算结果表明,Li在LiP5中的扩散系数大约为10^-4cm2/s,扩散通道是一维的;Li在Li3P7中的扩散系数为10^-7-10^-6cm2/s,扩散通道是三维的;Li在LiP中的扩散系数为10^-8-10^-5cm2/s,扩散通道是三维的. 相似文献
98.
Juan M. Ramírez‐Anguita Àngels González‐Lafont José M. Lluch 《Journal of computational chemistry》2009,30(9):1477-1489
The production of dimethyl sulfoxide (DMSO) and dimethyl sulfone (DMSO2) in the dimethyl sulfide (DMS) degradation scheme initiated by the hydroxyl (OH) radical has been shown to be very sensitive to nitrogen oxides (NOx) levels. In the present work we have explored the potential energy surfaces corresponding to several reaction pathways which yield DMSO2 from the CH3S(O)(OH)CH3 adduct [including the formation of CH3S(O)(OH)CH3 from the reaction of DMSO with OH] and the reaction channels that yield DMSO or/and DMSO2 from the CH3S(O2)(OH)CH3 adduct are also studied. The formation of the CH3S(O2)(OH)CH3 adduct from CH3S(OH)CH3 (DMS‐OH) and O2 was analyzed in our previous work. All these pathways due to the presence of NOx (NO and NO2) and also due to the reactions with O2, OH and HO2 are compared with the objective of inferring their kinetic relevance in the laboratory experiments that measure DMSO2 (and DMSO) formation yields. In particular, our theoretical results clearly show the existence of NOx‐dependent pathways leading to the formation of DMSO2, which could explain some of these experimental results in comparison with experimental measurements carried out in NOx‐free conditions. Our results indicate that the relative importance of the addition channel in the DMS oxidation process can be dependent on the NOx content of chamber experiments and of atmospheric conditions. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 相似文献
99.
Basem A. Moosa Mohamed I. M. Wazeer Mohammed B. Fettouhi Shaikh A. Ali 《Journal of Physical Organic Chemistry》2009,22(3):212-220
The diastereoselectivity in the cycloaddition reactions of several mono‐ and disubstituted alkenes with a (‐)norephedrine‐derived methylenenitrone has been investigated. The stereochemical analysis of the addition products (i.e., isoxazolidines) has been carried out by X‐ray, NMR, and chemical conversions. The NMR spectra of the isoxazolidines at low temperatures indicated the presence of either a single or a predominant invertomer. The stereochemistry of the invertomers and nitrogen inversion barriers are determined using complete line‐shape analysis and their dependence on solvent is discussed. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
100.
Ultrasound can be used as a carrier to realize wireless communication to and from a metal-enclosed space, which has the characteristics such as immunity to the electromagnetic shielding effect and non-destructive penetration
of metal obstacles. This paper firstly reviews the previous studies in the field of ultrasonic wireless communication through metal barriers, and summarizes their achievements and the existing problems. Secondly, an overview of the research methods involved in studying the characteristic of acoustic-electric channel is presented, and the principles are introduced for the actual measurement method, equivalent circuit method, ABCD parameter method, finite element analysis method and time-domain finite difference method. Then, an overview of the communication algorithms are presented such as orthogonal frequency division multiplexing (OFDM), single-carrier frequency domain equalization and multiple input multiple output OFDM. Finally, the potential future study are proposed in light of the trend of development and unsolved problems. 相似文献