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Item The Demobilization of Protest Campaigns(Oxford University Press, 2017-06) Demirel-Pegg, TijenAll protest campaigns move through cycles of escalation and de-escalation and ultimately demobilize. Some campaigns demobilize quickly as protesters reach their goals. The 2011 Egyptian uprising, when protesters left the streets after they brought down the Mubarak regime, for example, is a case of rapid demobilization. Others, like the 2011 uprising in Bahrain, demobilize over a longer time span before protests come to a complete halt. In Bahrain, the government first cracked down on the opposition by bringing in foreign troops and then continued to repress protesters until the protesters ended the campaign in 2012. Regardless of the length of time it takes for protesters to leave the streets and stop the protests, demobilization is a complex process. Numerous factors, such as severe repression, government concessions, countermobilization of opposition groups, leadership changes, or even unexpected events, can all bring about demobilization. These factors and strategies may occur simultaneously or sequentially, but usually one or a combination of them lead to the demobilization of a protest campaign. Moreover, demobilization is a dynamic process, as it continues to evolve out of the endogenous interactions among governments, challengers, bystanders, and, in some cases, as in Bahrain, external third-party actors.Even though every protest campaign eventually demobilizes one way or another, the demobilization phase has generally attracted less scholarly attention than the onset and escalation of violent and nonviolent forms of collective action. For a long time, most scholars addressed demobilization indirectly within the context of the repression-dissent nexus as they explored why repression backfires and escalates dissent in some cases, while it succeeds in demobilizing the opposition in others. Nonetheless, factors besides state repression contribute to the demobilization of dissent. In other words, a state’s accommodative tactics, as well as individual, organizational, or even regional and systemic factors that interact with the state’s actions, have the potential to shape when and how political dissent demobilizes. More recently, scholars have begun to examine why and how protest campaigns demobilize by stepping out of the repression-dissent nexus and focusing on a variety of other factors related to organizational structures, regime types, individual-level constraints, and contingent events that affect the trajectory of campaigns. At the same time, recent studies on state repression have also begun to focus more heavily on the different causal mechanisms that explain how a state’s repressive tactics can lead to demobilization. While this new line of research has made significant contributions to our understanding of the demobilization of protests, we are still left with important questions about the demobilization process that have yet to be answered.Item Doubly Polarized QM/MM with Machine Learning Chaperone Polarizability(American Chemical Society, 2021) Kim, Bryant; Shao, Yihan; Pu, Jingzhi; Chemistry and Chemical Biology, School of ScienceA major shortcoming of semiempirical (SE) molecular orbital methods is their severe underestimation of molecular polarizability compared with experimental and ab initio (AI) benchmark data. In a combined quantum mechanical and molecular mechanical (QM/MM) treatment of solution-phase reactions, solute described by SE methods therefore tends to generate inadequate electronic polarization response to solvent electric fields, which often leads to large errors in free energy profiles. To address this problem, here we present a hybrid framework that improves the response property of SE/MM methods through high-level molecular-polarizability fitting. Specifically, we place on QM atoms a set of corrective polarizabilities (referred to as chaperone polarizabilities), whose magnitudes are determined from machine learning (ML) to reproduce the condensed-phase AI molecular polarizability along the minimum free energy path. These chaperone polarizabilities are then used in a machinery similar to a polarizable force field calculation to compensate for the missing polarization energy in the conventional SE/MM simulations. Because QM atoms in this treatment host SE wave functions as well as classical polarizabilities, both polarized by MM electric fields, we name this method doubly polarized QM/MM (dp-QM/MM). We demonstrate the new method on the free energy simulations of the Menshutkin reaction in water. Using AM1/MM as a base method, we show that ML chaperones greatly reduce the error in the solute molecular polarizability from 6.78 to 0.03 Å3 with respect to the density functional theory benchmark. The chaperone correction leads to ~10 kcal/mol of additional polarization energy in the product region, bringing the simulated free energy profiles to closer agreement with the experimental results. Furthermore, the solute-solvent radial distribution functions show that the chaperone polarizabilities modify the free energy profiles through enhanced solvation corrections when the system evolves from the charge-neutral reactant state to the charge-separated transition and product states. These results suggest that the dp-QM/MM method, enabled by ML chaperone polarizabilities, provides a very physical remedy for the underpolarization problem in SE/MM-based free energy simulations.