Governments worldwide have implemented non-pharmaceutical interventions(NPIs)to control the spread of coronavirus disease 2019(COVID-19),and it is crucial to accurately assess the effectiveness of such measures.Many s...Governments worldwide have implemented non-pharmaceutical interventions(NPIs)to control the spread of coronavirus disease 2019(COVID-19),and it is crucial to accurately assess the effectiveness of such measures.Many studies have quantified the risk of infection transmission and used simulations to compare the risk before and after the implementation of NPIs to judge policies’effectiveness.However,the choice of metric used to quantify the risk can lead to different conclusions regarding the effectiveness of a policy.In this study,we analyze the correlation between different transmission-risk metrics,pedestrian environments,and types of infectious diseases using simulation-generated data.Our findings reveal conflicting results among five different metric types in specific environments.More specifically,we observe that,when the randomness of pedestrian trajectories in indoor spaces is low,the closeness centrality exhibits a higher correlation coefficient with infection-based metrics than with contact-based metrics.Furthermore,even within the same pedestrian environment,the likelihood of discrepancies between infection-based metrics and other metrics increases for infectious diseases with low transmission rates.These results highlight the variability in the measured effectiveness of NPIs depending on the chosen metric.To evaluate NPIs accurately,facility managers should consider the type of facility and infectious disease and not solely rely on a single metric.This study provides a simulation model as a tool for future research and improves the reliability of pedestrian-simulation-based NPI effectiveness analysis methods.展开更多
The applicability of cement grout （or cement-based grout） has been considered as an alternative to bentonite grout commonly used to backfill closed-loop vertical ground heat exchangers. In a geothermal heat pump sys...The applicability of cement grout （or cement-based grout） has been considered as an alternative to bentonite grout commonly used to backfill closed-loop vertical ground heat exchangers. In a geothermal heat pump system, repeated heating-cooling cycles may cause adverse effects on the integrity of cement grout in the ground heat exchanger. To account for the temperature cycling effect, the strength degradation of cement grout due to temperature cycling has been examined by measuring the unconfined compression strength of cured specimens in a humidity-temperature controlling chamber with applying temperature cycles between -5℃ and 50℃. There is a tendency that the unconfined compression strength decreases with an increase in the number of temperature cycles. On the other hand, an equivalent hydraulic conductivity of a pipe-embedded cement grout specimen was evaluated by carrying out a modified flexible wall permeameter test equipped with a water circulating system to control temperature inside the pipe section. The applied operating temperature range was from 5 to 35℃. After three cycles of heating-cooling circulation, the equivalent hydraulic conductivity becomes asymptotic to a constant value, which implies there is no severe detachment of the pipe from the cement grout.展开更多
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Ministry of Science and ICT(MSIT),Republic of Korea(1711185759).
文摘Governments worldwide have implemented non-pharmaceutical interventions(NPIs)to control the spread of coronavirus disease 2019(COVID-19),and it is crucial to accurately assess the effectiveness of such measures.Many studies have quantified the risk of infection transmission and used simulations to compare the risk before and after the implementation of NPIs to judge policies’effectiveness.However,the choice of metric used to quantify the risk can lead to different conclusions regarding the effectiveness of a policy.In this study,we analyze the correlation between different transmission-risk metrics,pedestrian environments,and types of infectious diseases using simulation-generated data.Our findings reveal conflicting results among five different metric types in specific environments.More specifically,we observe that,when the randomness of pedestrian trajectories in indoor spaces is low,the closeness centrality exhibits a higher correlation coefficient with infection-based metrics than with contact-based metrics.Furthermore,even within the same pedestrian environment,the likelihood of discrepancies between infection-based metrics and other metrics increases for infectious diseases with low transmission rates.These results highlight the variability in the measured effectiveness of NPIs depending on the chosen metric.To evaluate NPIs accurately,facility managers should consider the type of facility and infectious disease and not solely rely on a single metric.This study provides a simulation model as a tool for future research and improves the reliability of pedestrian-simulation-based NPI effectiveness analysis methods.
基金supported by the Fundamental Research and Development Program of the Center of New and Renewable Energy of the Ministry of Knowledge and Economy (Grant No. 2008-N-GE08-R-01)the National Research Foundation of Korea Grant funded by the Korean Government (Grant No. 2010-0011159)
文摘The applicability of cement grout （or cement-based grout） has been considered as an alternative to bentonite grout commonly used to backfill closed-loop vertical ground heat exchangers. In a geothermal heat pump system, repeated heating-cooling cycles may cause adverse effects on the integrity of cement grout in the ground heat exchanger. To account for the temperature cycling effect, the strength degradation of cement grout due to temperature cycling has been examined by measuring the unconfined compression strength of cured specimens in a humidity-temperature controlling chamber with applying temperature cycles between -5℃ and 50℃. There is a tendency that the unconfined compression strength decreases with an increase in the number of temperature cycles. On the other hand, an equivalent hydraulic conductivity of a pipe-embedded cement grout specimen was evaluated by carrying out a modified flexible wall permeameter test equipped with a water circulating system to control temperature inside the pipe section. The applied operating temperature range was from 5 to 35℃. After three cycles of heating-cooling circulation, the equivalent hydraulic conductivity becomes asymptotic to a constant value, which implies there is no severe detachment of the pipe from the cement grout.
