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The impact of policy timing on the spread of COVID-19

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Infectious Disease Modelling 2021年第1期6卷 942-954页

作者： Moshe Elitzur Scott Kaplan Zeljko Ivezic David Zilberman Department of Astronomy Univ of CaliforniaBerkeleyCA94720USA Dept of Agricultural&Resource Economics Univ of CaliforniaBerkeleyCA94720USA Dept of Astronomy University of WashingtonSeattleWA98195USA Dept of Economics United States Naval AcademyAnnapolisMD 21402USA

We model COVID-19 data for 89 nations and US states with a recently developed formalism that describes mathematically any pattern of growth with the minimum number of *** results show that the disease has a typical duration of 18 days,with a significant increase in fatality when it lasts longer than about 4 *** for correlations between“flattening of the curve”and preventive public policies,we find strong statistical evidence for the impact of the first implemented policy on decreasing the pandemic growth rate;a delay of one week in implementation nearly triples the size of the infected population,on *** any government action,the initial outburst still slows down after 36 days,possibly thanks to changes in public behavior in response to the pandemic ***-at-home(lockdown)was not the first policy of any sample member,and we could not find statistically meaningful evidence for its added impact,similar to a recent study that employed an entirely different ***,lockdown was mostly imposed only shortly before the exponential rise was arrested by other measures,too late for a meaningful impact.A third of the sample members that did implement lockdown imposed it only after the outburst had already started to slow *** possibility remains that lockdown might have significantly shortened the initial exponential rise had it been employed as first resort rather than last.

关键词： COVID-19 Pandemic Exponential growth Growth hindering

ANALYSIS AND SIMULATION ON THE MECHANISM OF A NOVEL DUAL-WAVE SHOCK TEST MACHINE

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Chinese Journal of Mechanical Engineering 2008年第1期21卷 94-100页

作者： WANG Gongxian ZHANG Zhiyi CHU Deying SHEN Rongying institute of Vibration Shock and Noise Shanghai Jiaotong University Shanghai 200240 China School of Logistics Engineering Wuhan University of Technology Wuhan 430063 China

For qualifying the anti-shock performance of shipboard equipments and simulating actual underwater explosion environments, a novel dual-wave shock test machine is proposed to increase testing capability of shock test machines as well as to meet certain shock testing specification. The machine can generate a double-pulse acceleration shock for test articles according to specification defined in BV043/85. On the basis of the impact theory, a nonlinear dynamic model of the hydraulically-actuated test machine is established with thorough analysis on its mechanism which involves conversion of gas potential energy and dissipation of kinetic energy. Simulation results have demonstrated that the machine can produce a double-pulse acceleration shock in the time domain or a desired shock response spectrum in the frequency domain, which sets a theoretical base for the construction of the proposed machine.

关键词： Shock test machine Underwater explosion Velocity generator Pulse generator

Deep Learning-Based Numerical Methods for High-Dimensional Parabolic Partial Differential Equations and Backward Stochastic Differential Equations

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Communications in Mathematics and Statistics 2017年第4期5卷 349-380页

作者： Weinan E Jiequn Han Arnulf Jentzen Beijing institute of Big Data Research BeijingChina Princeton University PrincetonNJUSA Peking University BeijingChina ETH Zurich ZurichSwitzerland

We study a new algorithm for solvingparabolic partial differential equations(PDEs)and backward stochastic differential equations(BSDEs)in high dimension,which is based on an analogy between the BSDE and reinforcement learning with the gradient of the solution playing the role of the policy function,and the loss function given by the error between the prescribed terminal condition and the solution of the *** policy function is then approximated by a neural network,as is done in deep reinforcement *** results using TensorFlow illustrate the efficiency and accuracy of the studied algorithm for several 100-dimensional nonlinear PDEs from physics and finance such as the Allen–Cahn equation,the Hamilton–Jacobi–Bellman equation,and a nonlinear pricing model for financial derivatives.

关键词： PDEs High dimension Backward stochastic differential equations Deep learning Control Feynman-Kac

The Russian Navy is Adrift in the Syrian Doldrums

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International Relations and Diplomacy 2017年第11期5卷 643-649页

作者： Pavel K. Baev Peace Research institute Oslo (PRIO) Oslo Norway

America＇s Rethinking of Sea Power and Its policy Impact

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China International Studies 2017年第4期62卷 112-128页

作者： Xie Xiaodong Zhao Qinghai Bohai University’s School of Politics and History the Center for Maritime Security and Cooperation China Institute of International Studies (CIIS)

A new debate over sea power and a new understanding of it has emerged in the US, highlighting the increasing domestic anxiety about a rising East and a declining West. The return to sea control as the focus of US nava... 详细信息

关键词：海权美国海上安全科技创新决定性发源地全球化

Discrete-time dynamic graphical games:model-free reinforcement learning solution

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Control Theory and Technology 2015年第1期13卷 55-69页

作者： Mohammed I.ABOUHEAF Frank L.LEWIS Magdi S.MAHMOUD Dariusz G.MIKULSKI Systems Engineering Department King Fahd University of Petroleum & Mineral UTA Research institute University of Texas at ArlingtonFort Worth Texas U.S.A. State Key Laboratory of Synthetical Automation for Process Industries Northeastern University Ground Vehicle Robotics (GVR) U.S. Army TARDEC Warren MI U.S.A.

This paper introduces a model-free reinforcement learning technique that is used to solve a class of dynamic games known as dynamic graphical games. The graphical game results from to make all the agents synchronize to the state of a command multi-agent dynamical systems, where pinning control is used generator or a leader agent. Novel coupled Bellman equations and Hamiltonian functions are developed for the dynamic graphical games. The Hamiltonian mechanics are used to derive the necessary conditions for optimality. The solution for the dynamic graphical game is given in terms of the solution to a set of coupled Hamilton-Jacobi-Bellman equations developed herein. Nash equilibrium solution for the graphical game is given in terms of the solution to the underlying coupled Hamilton-Jacobi-Bellman equations. An online model-free policy iteration algorithm is developed to learn the Nash solution for the dynamic graphical game. This algorithm does not require any knowledge of the agents＇ dynamics. A proof of convergence for this multi-agent learning algorithm is given under mild assumption about the inter-connectivity properties of the graph. A gradient descent technique with critic network structures is used to implement the policy iteration algorithm to solve the graphical game online in real-time.

关键词： Dynamic graphical games Nash equilibrium discrete mechanics optimal control model-free reinforcementlearning policy iteration

Editorial Statement——Action and policy

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Advances in Atmospheric Sciences 2004年第3期21卷 382-382页

作者： WU Guoxiong, WANG Huijun, and Da-Lin ZHANG Co-Chief Editors institute of Atmospheric Physics Chinese Academy of Sciences Beijing Department of Meteorology University of Maryland

On 16 March 2004, we received an appeal from Dr. Qing WANG of the United States’ naval Postgraduate School questioning the legitimacy of the paper entitled, Modeling Marine Stratocumulus with a Detailed Micro physical Scheme, that was published by ZHAO Chunsheng and Yutaka Ishizaka in the January 2004 issue of the Advances in Atmospheric Sciences (AAS). She pointed out that the modei described in the paper was developed by her group in which the first author, Dr. Zhao, worked as a visiting scholar during February 1997-February 1998. The authors should not have claimed in the paper that they developed the modei. In particular, they should not have published her group’s work as their own. Thus, Dr. Wang requested that the paper be retracted from AAS.

关键词： AAS Action and policy Editorial Statement