A research paper of Hossein Sabzian (2019), Theories and Practice of Agent based Modeling: Some practical Implications for Economic Planners, ArXiv, 54p

Abstract

Nowadays, we are surrounded by a large number of complex phenomena such as virus epidemic, rumor spreading, social norms formation, emergence of new technologies, rise of new economic trends and disruption of traditional businesses. To deal with such phenomena, social scientists often apply reductionism approach where they reduce such phenomena to some lower-lever variables and model the relationships among them through a scheme of equations (e.g. Partial differential equations and ordinary differential equations). This reductionism approach which is often called equation based modeling (EBM) has some fundamental weaknesses in dealing with real world complex systems, for example in modeling how a housing bubble arises from a housing market, the whole market is reduced into some factors (i.e. economic agents) with unbounded rationality and often perfect information, and the model built from the relationships among such factors is used to explain the housing bubble while adaptability and the evolutionary nature of all engaged economic agents along with network effects go unaddressed. In tackling deficiencies of reductionism approach, in the past two decades, the Complex Adaptive System (CAS) framework has been found very influential. In contrast to reductionism approach, under this framework, the socio-economic phenomena such as housing bubbles are studied in an organic manner where the economic agents are supposed to be both boundedly rational and adaptive. According to CAS framework, the socio-economic aggregates such as housing bubbles emerge out of the ways agents of a socio-economic system interact and decide. As the most powerful methodology of CAS modeling, Agent-based modeling (ABM) has gained a growing application among academicians and practitioners. ABMs show how simple behavioral rules of agents and local interactions among them at micro-scale can generate surprisingly complex patterns at macro-scale. Despite a growing number of ABM publications, those researchers unfamiliar with this methodology have to study a number of works to understand (1) the why and what of ABMs and (2) the ways they are rigorously developed. Therefore, the major focus of this paper is to help social sciences researchers get a big picture of ABMs and know how to develop them both systematically and rigorously.

Chemistry on Rotating Grain Surfaces: Ro-thermal Desorption of Molecules from Ice Mantles

“…We term this mechanism ro-thermal hopping. Combining the increased rothermal hopping with ro-thermal desorption (Hoang & Tung 2019) due to grain suprathermal rotation, the rate of formation of molecules on rotating surfaces is found to be much higher than predicted by thermal hopping on non-rotating grains.…”

“…where n(A) is the number density of species A in the gas phase, k des is the desorption rate of species A. Following Hoang & Tung (2019), the rate of rothermal desorption in the presence of grain rotation is given by…”

“…Note that individual molecules can be directly ejected by centrifugal forces when the rotational rate is sufficiently high. Following Hoang & Tung (2019), the critical radiation strength for the direct ejection is given by…”

“…The effect of ro-thermal desorption (Hoang & Tung 2019) and rotational desorption can release saturated species such as H 2 O, CH 3 OH, NH 3 , at temperatures below their sublimation limits. Those evaporating species can trigger rich gas-phase chemistry in warming-up phase (see e.g., Tielens 2013).…”

“…The proposed mechanism can disrupt the ice mantle into tiny fragments, subsequently molecules rapidly evaporate from the tiny ice fragments. Later, Hoang & Tung (2019) considered the effect of suprathermal rotation on thermal sublimation of molecules from intact ice mantles. The authors find that centrifugal potential energy can lower the potential barrier for desorption defined by binding energy E b such that molecules can desorb from the ice mantle at temperatures much below their sublimation threshold.…”