Effects of a closed-loop system against SARS-CoV-2 at the Beijing 2022 Olympic Winter Games:a descriptive and modeling study

BACKGROUND:To assess the efficacy of the epidemic prevention measures of the“closed-loop”system adopted by the Beijing 2022 Olympic Winter Games(BOWG).METHODS:We retrospectively collected and analyzed information,including age,sex,nationality,vaccination status,date of diagnosis,and date of entry,from 280 SARS-CoV-2-positive individuals identified during the BOWG.A susceptibility-exposed-infectious-remove model was employed to evaluate the effectiveness of epidemic prevention strategies on controlling the spread of SARS-CoV-2 under different scenarios during the BOWG.RESULTS:Regarding SARS-CoV-2-positive cases,97.9%were imported,and 96.4%were asymptomatic.The median age was 37 years(range:29–47 years),and 73.9%were male,with the majority of cases being broadcasters and European attendees.Regarding vaccination status,93.5%were fully vaccinated,and six cases were considered to have been infected in the closed-loop system during the BOWG.Assuming that the BOWG adopted a semi-closed-loop management system,the cumulative number of confirmed cases would be 1,137 for quick quarantine measures(3 d later)implemented and 5,530 for delayed quarantine measures(9 d later)implemented.This modeling revealed that stringent pandemic prevention measures and closed-loop management effectively controlled the spread of SARS-CoV-2 during the BOWG.CONCLUSION:Imported cases are considered the main risk factor for SARS-CoV-2 transmission during mass gatherings,but a comprehensive closed-loop system could minimize transmission among attendees and general personnel.

Deep reinforcement learning and 3D physical environments applied to crowd evacuation in congested scenarios

To avoid crowd evacuation simulations depending on 2D environments and real data,we propose a framework for crowd evacuation modeling and simulation by applying deep reinforcement learning(DRL)and 3D physical environments(3DPEs).In 3DPEs,we construct simulation scenarios from the aspects of geometry,semantics and physics,which include the environment,the agents and their interactions,and provide training samples for DRL.In DRL,we design a double branch feature extraction combined actor and critic network as the DRL policy and value function and use a clipped surrogate objective with polynomial decay to update the policy.With a unified configuration,we conduct evacuation simulations.In scenarios with one exit,we reproduce and verify the bottleneck effect of congested crowds and explore the impact of exit width and agent characteristics(number,mass and height)on evacuation.In scenarios with two exits and a uniform(nonuniform)distribution of agents,we explore the impact of exit characteristics(width and relative position)and agent characteristics(height,initial location and distribution)on agent exit selection and evacuation.Overall,interactive 3DPEs and unified DRL enable agents to adapt to different evacuation scenarios to simulate crowd evacuation and explore the laws of crowd evacuation.

Modeling and analysis of landing collision dynamics for a shipborne helicopter

A Lagrange dynamic model is established based on small-angle approximation to improve the simulation model for shipborne helicopter landing collision.To describe fuselage motion effectively,the proposed model considers ship motion,the interaction of the tires with the deck,and tire slippage.A mechanism of sliding motion is built,and a real-time reliability analysis of the algorithm is implemented to validate the proposed model.Numerical simulations are also conducted under different operation conditions.Results show that the proposed dynamic model can simulate the collision motion of helicopter landing in real time.Several suggestions for helicopter pilot landing are likewise provided.

Improved Cubemap model for 3D navigation in geo-virtual reality

Due to advances in rendering techniques and hardware capability,stereoscopic 3D(s3D)visualization is becoming increasingly common in daily life.However,this does not change the fact that stereo effects and visual comfort depend greatly on how the related parameters are controlled during the production of the s3D images.In geovirtual reality systems,which are important browsers for Digital Earth,the maintenance of these parameters is deeply related to the navigation process.Therefore,the navigation method in such systems requires special care.This paper presents a new flying method based on a Cubemap structure.The method defines a Vehicle model and modifies the original Cubemap structure by adding a front view camera during the navigation;it allows the users to fly through a virtual geographic environment with automatic speed control,smooth collision resolution,and dynamic adjustment of the s3D-related parameters.A user test was conducted to compare this new method with the original method based on the Cubemap structure.The results show that the new method performs better than the former one for it provides a convenient interaction experience with improved stereoscopic effect,and diminishes visual discomfort.

A stream-based Parasitic Model for implementing Mobile Digital Earth

A Parasitic Model is proposed in this study for Digital Earth running on mobile phones through a mobile network.Because of mobile phones’limited capabilities in high-performance computing,rendering,storing,and networking(CRSN),these functions are accomplished by a superior host computer in this model.Rendered virtual scenes are compressed in a time-series as a data stream and are sent to the mobile phone through a mobile network,thus allowing Digital Earth to be operated on a mobile phone.This study examines a prototype and shows that a Mobile Digital Earth based on a Parasitic Model can achieve functionality beyond the mobile phone’s actual hardware capabilities and can reduce network traffic.These results demonstrate quasi-real-time interactions,but with bandwidth increases in next-generation mobile networks such as 4G and 5G,there is potential for real-time interactions in the near future.