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动力学蒙特卡洛方法验证碰撞脱附效应
Alternative TitleThe kinetic Monte Carlo model to verify the encounter desorption
郑旭丽
Subtype硕士
Thesis Advisor常强
2019
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Name理学硕士
Degree Discipline天体物理
Keyword天体化学,物种丰度,数值模拟,加速算法 Astrochemistry,Abundance,Simulation,Algorithm
Abstract尘埃表面反应对于研究宇宙中重要物种的形成有重大意义,是历来研究者的研究热点。尘埃表面的脱附反应将尘埃表面的物种脱附到气相中,其与吸附反应(将气相物种吸附到尘埃表面上)共同成为连接气相和尘埃表面的桥梁。水冰被认为是尘埃上的物种脱附的基质。但在低温的环境下,尘埃表面的gH2的丰度非常大,仅仅考虑g20作为基质并不符合实际情况,H2的碰撞脱附在这个基础上被提出。H2的碰撞脱附是尘埃表面的gH2分子在遇到另一个gH2分子时,其中一个gH2分子从尘埃表面脱附。其已经通过速率方程模型的方法在一个包含气尘反应的大反应网络验证过,但是在尘埃表面物种的个数小于1时,速率方程的方法并不准确。而更为准确的蒙特卡洛模型,由于所耗费的计算机时间过长,而一直不能用来验证这个效应。本文提出一种新的金字塔数据结构,通过跳过一些速率不变的反应提高了查找效率,从而在验证碰撞脱附使用的网络中节约了80%的时间。本文同时使用了加速Gillespie算法以及改进的数据结构加速算法,使用两相动力学蒙特卡洛模型验证了碰撞脱附效应,得到了尘埃表面gH2丰度降低的效果。在此基础上,又验证了关于H的碰撞脱附(gH原子在遇到gH2分子时将从尘埃上脱附到气相中),结果发现加入H的碰撞脱附后,尘埃表面水冰的变化不大,但一些物种的丰度发生了超过3个数量级的变化。碰撞脱附效应对于一些物种的丰度的确定,提供了新的思路并可以对一些物种的丰度造成重大影响。
Other AbstractThe surface reactions are important for forming the fatal species in the space, so grain-surface reactions(on the grain mantle) draw much attention from the researchers for a long time. The grain-surface desorption reaction, which cause the grain-surface species to move to the gaseous phase, become the bind to connect the gas and grain along with the absorption reaction. The water ice is considered as the substrate for the grain-surface species to desorb from. Whereas the abundance of gH is rather high when the environment is cold, only taking account of the gH2O substrate is incomplete. The encounter desorption for Ha is put forward under the circumstances. The encounter desorption for H2 is such a mechanism: when one gH2 molecule on the grain come across another gH2, one of them will desorb from the grain to the gas phase. It has been verified by the rate-equation model already, however the results of the rate-equation is not precise when the abundance of a particular grain-surface species is below one unit. The more suitable model, Monte Carlo model is too time-consuming computationally to verify the mechanism. In the thesis,a pyramid data structure is promoted to save 80 percent of the computing time in the network to evaluate encounter desoption. The data structure improved accelerating method and accelerated Gillespie algorithm are both used to the grain-gas phase kinetic Monte Carlo model to verify the encounter desoption. In the model it shows that the encounter desorption will decrease the abundance of gH2. Furthermore, the encounter desorption for H, in which a gH atom will desorb from the gH2, is verified as well. The results shows that the abundance of the species forming water ice is slightly changed, nevertheless some of the abundance of the species change remarkably about more than 3 magnitude. The encounter desorption provide a new thinking about the detemination of some grain-surface species' abundance and would change some of their abundance in a large scale.
Pages40
Language中文
Document Type学位论文
Identifierhttp://ir.xao.ac.cn/handle/45760611-7/2716
Collection研究生
Affiliation中国科学院新疆天文台
First Author AffilicationXinjiang Astronomical Observatory, Chinese Academy of Sciences
Recommended Citation
GB/T 7714
郑旭丽. 动力学蒙特卡洛方法验证碰撞脱附效应[D]. 北京. 中国科学院大学,2019.
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