Publisher：Building and Environment  

This study numerically assessed the impact of human crowd density and outdoor wind conditions (average velocity, its profile, and direction) on the convective heat transfer and drag coefficients (hc and Cd). Five different configurations of standing computer-simulated persons (CSPs) were tested in a semi-outdoor environment. A single isolated CSP, nine CSPs in a block array (with three representative crowd densities), and eighteen randomly allocated CSPs were used. The results indicated a significant impact of crowd density on the overall and local hc values. As the density increases, the body's obstruction against wind increases, resulting in lower heat loss. Newly proposed formulas for hc as a function of the average wind velocity (UAVE.) are (7.56 × UAVE.0.65), (8.02 × UAVE.0.64), and (8.26 × UAVE.0.63) for the high, medium, and low crowd densities, respectively. This reveals an overestimation of hc when an isolated human body is used. The hc values of the upper segments were the most affected by a 22 % reduction in the predicted hc. Moreover, when the crowd density increased, local hc and Cd decreased simultaneously, particularly in the chest, pelvis, and thigh segments. Oblique wind angles (60° and 150°) resulted in the highest hc and Cd values compared to other angles. The chest and pelvis were most affected by shifting the wind direction, indicating the dominance of these segments in concurrently controlling the thermal and drag performances. These results provide valuable insights into the optimization of human thermal and physical comfort models.

DOI： 10.1016/j.buildenv.2024.111983

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Scopus

Publisher：Building and Environment  

Understanding human contact behavior plays a crucial role in improving the design of indoor environments, for example, by enhancing thermal comfort, workplace performance and productivity, and controlling infection transmission. Although baseline information for indoor environmental design is available, data on person-to-person contact behavior are limited, especially in populations of diverse nationalities, genders, and age ranges. In this study, we used high-resolution video cameras to collect close contact data for five consecutive school days in a multinational graduate school student office in Japan with a reserved cultural background. We characterized human close-contact behavior using stochastic interactions in terms of interpersonal distance, assortativity, posture, duration, and frequency of contact in a multinational population. Our results showed a remarkable difference compared to the study results from person-to-person contact behavior in an ethnically homogenous population. The interpersonal distance averaged 0.75 m, and the close contact frequency was notably lower, but the close contact duration was significantly longer. Nationality showed stronger homophily. We considered the degree centrality measures of the nodes in the observed networks. The observed contact network links were dense with high reciprocity. High contact heterogeneity was observed in twenty-five percent of the nodes. These data can be used to improve targeted epidemiological analyses for indoor occupant health decision-making, and infection spread prevention strategies.

DOI： 10.1016/j.buildenv.2024.112015

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Scopus

Publisher：Building and Environment  

To enhance the realism and precision of indoor environment assessments and the evaluation of human health risks using computational fluid dynamics (CFD), it is crucial to accurately replicate human shape and physiological functions. This study investigates the influence of micro-movements resulting from posture control on the human breathing zone (BZ) using CFD analysis. A Computer-Simulated Person (CSP) incorporating a sophisticated nasal cavity model and multi-node thermoregulation was employed to precisely predict the microclimate around the human body, including the BZ. Two types of movements were considered to replicate micro-movements of a standing human body: angular and linear movements. The BZs were evaluated based on the Scale for Ventilation Efficiency (SVE) 4 and 5 for exhalation and inhalation modes, respectively. While the distribution of exhaled air remained generally consistent, distinct differences were observed in inhaled air distribution. In a representative case with a maximum angular velocity of 4°/s, the horizontal length increased by 12 cm, and the vertical distance of the SVE5>10 % distribution decreased by 14 cm compared to the stationary case. Linear movement, particularly in the mediolateral (ML) direction, led to a horizontal expansion of the inhaled air distribution. The findings of this study suggest that replicating human micro-movements has a minimal impact on general indoor climate analysis but significantly enhances the accuracy of predicting breathing air quality.

DOI： 10.1016/j.buildenv.2024.111916

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Scopus

Language：English   Publisher：Computer Methods and Programs in Biomedicine  

Background and objective: Viral respiratory infections stand as a considerable global health concern, presenting significant risks to the health of both humans and animals. This study aims to conduct a preliminary analysis of the time series of viral load in the nasal cavity-nasopharynx (NC-NP) of the human and rhesus macaque (RM). Methods: Taking into account the random uniform distribution of virus-laden droplets with a diameter of 10 μm in the mucus layer, this study applies the computational fluid dynamics-host cell dynamics (CFD-HCD) method to 3D-shell NC-NP models of human and RM, analyzing the impact of initial distribution of droplets on the viral dynamics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), estimating parameters in the HCD model based on experimental data, integrating them into simulations to predict the time series of viral load and cell counts, and being visualized. The reproductive number (R0) are calculated to determine the occurrence of infection. The study also considers cross-parameter combinations and cross-experimental datasets to explore potential correlations between the human and RM. Results: The research findings indicate that the uniform distribution of virus-laden droplets throughout the whole NC-NP models of human and RM is reasonable for simulating and predicting viral dynamics. The visualization results offer dynamic insights into virus infection over a period of 20 days. Studies involving parameter and dataset exchanges between the two species underscore certain similarities in predicting virus infections between the human and RM. Conclusions: This study lays the groundwork for further exploration into the parallels and distinctions in respiratory virus dynamics between humans and RMs, thus aiding in making more informed decisions in research and experimentation.

DOI： 10.1016/j.cmpb.2024.108354

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Scopus

PubMed

Publisher：Building and Environment  

In a typical house with a mechanical ventilation system, a ventilation duct with a certain installation length is placed along the exterior walls or in the ceiling shed space. To effectively use this ventilation duct, we aimed to develop a novel ventilation duct system with sensible heat exchange and passive air purification mechanisms. The proposed ventilation duct comprises multiple layers of a counterflow heat recovery ventilator (HRV). Baffles were installed in the middle of the flow channel to collect particles in the outdoor air by forming a circulating flow associated with the separation flow and gravitational settling in a local domain in the flow channel. To optimize the design of this new ventilation duct concept in terms of particle removal and heat exchange efficiencies, we conducted a computational fluid and particle dynamics analysis as a function of design parameters such as airflow rate, particle size, and air temperature. Through a series of numerical analyses, differences in the heat exchange efficiency and effectiveness of particle removal corresponding to different baffle designs were quantitatively evaluated, and finally, the optimal design for the air channel as an HRV was determined.

DOI： 10.1016/j.buildenv.2024.111773

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Scopus

Publisher：Building and Environment  

Engineers have integrated general ventilation systems with personalized ventilation (PV) to achieve energy efficiency while providing good indoor air quality (IAQ) and thermal comfort. Previous studies conducted parametric analyses of PV by varying its flow rate and temperature, analyzing energy, IAQ, and thermal comfort while keeping main ventilation settings constant, even though the latter significantly affect the general flow field. Therefore, computational fluid dynamics simulation is performed to simultaneously optimize the above-mentioned three outputs in an office with displacement ventilation (DV) and PV by varying the DV supply flow rate and temperature, the fraction of outlet air being resupplied to inlet or DV recirculation, and PV supply flow rate and temperature. We utilize the Taguchi design to minimize the number of simulations as well as use the “technique for order preference by similarity to ideal solution” (TOPSIS) coupled with Taguchi's signal-to-noise ratio analysis for optimization. Four optimization cases are investigated by varying the thermal comfort and IAQ parameters from volume-averaged to occupant-centric values, such as the skin temperature and inhaled concentration. Results show that occupant-centric optimization presents low energy requirements with acceptable IAQ and thermal comfort compared with volume-averaged optimization, which can be attributed to imperfect mixing conditions. Furthermore, the DV settings and thermal plumes significantly affect the direction of jet released by the PV, which does not improve the IAQ. This underscores the importance of considering the aforementioned effects in maximizing the PV potential. Nevertheless, the PV system functions as intended under a flow rate of 6 L/s.

DOI： 10.1016/j.buildenv.2024.111837

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Scopus

Publisher：Building and Environment  

Natural ventilation offers significant advantages, especially in terms of energy conservation. However, most published articles have focused on the ventilation flow rate to determine the average contaminant concentration, while few have examined local ventilation distributions. Therefore, isothermal steady-state Reynolds-averaged Navier–Stokes simulations were conducted to analyze the airflow and scalar concentration fields of a cross-ventilation model sheltered by buildings. Based on these fields, we generated the spatial distributions of ventilation indices, namely, the net escape velocity (NEV), point-to-point indices transfer probability (TP), and travel time (TT), to discuss the dispersion of scalars emitted from local points in a room with natural ventilation. The NEV, which indicates the direction of the scalar discharge from each cell, exhibited a distribution distinct from the advection velocity because of concentration gradient effect. Higher TPs were observed when evaluated from a contaminant source to a target point following the NEV streamlines. Meanwhile, lower TTs were observed when evaluated in a point near the source and also from a contaminant source to a target point following the NEV streamlines. Although TP and TT are independent ventilation indices, a negative correlation between them was observed. Instead of the ventilation flow rate, the detailed structure of scalar dispersion can now be described by simultaneously analyzing the ventilation efficiency indices, which provide information on the general contaminant transport direction, and the probability and duration of transfer from a source to a target point. This potentially helps in the design of ventilation system especially in room lay-out to avoid cross-contamination.

DOI： 10.1016/j.buildenv.2024.111668

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Scopus

Language：English   Publisher：Computer Methods and Programs in Biomedicine  

Background and objective: Respiratory diseases caused by respiratory viruses have significantly threatened public health worldwide. This study presents a comprehensive approach to predict viral dynamics and the generation of stripped droplets within the mucus layer of the respiratory tract during coughing using a larynx-trachea-bifurcation (LTB) model. Methods: This study integrates computational fluid-particle dynamics (CFPD), host-cell dynamics (HCD), and the Eulerian wall film (EWF) model to propose a potential means for seamless integrated analysis. The verified CFPD-HCD coupling model based on a 3D-shell model was used to characterize the severe acute respiratory syndrome, coronavirus 2 (SARS-CoV-2) dynamics in the LTB mucus layer, whereas the EWF model was employed to account for the interfacial fluid to explore the generation mechanism and trace the origin site of droplets exhaled during a coughing event of an infected host. Results: The results obtained using CFPD delineated the preferential deposition sites for droplets in the laryngeal and tracheal regions. Thus, the analysis of the HCD model showed that the viral load increased rapidly in the laryngeal region during the peak of infection, whereas there was a growth delay in the tracheal region (up to day 8 after infection). After two weeks of infection, the high viral load gradually migrated towards the glottic region. Interestingly, the EWF model demonstrated a high concentration of exhaled droplets originating from the larynx. The coupling technique indicated a concurrent high viral load in the mucus layer and site of origin of the exhaled droplets. Conclusions: This interdisciplinary research underscores the seamless analysis from initial exposure to virus-laden droplets, the dynamics of viral infection in the LTB mucus layer, and the re-emission from the coughing activities of an infected host. Our efforts aimed to address the complex challenges at the intersection of viral dynamics and respiratory health, which can contribute to a more detailed understanding and targeted prevention of respiratory diseases.

DOI： 10.1016/j.cmpb.2024.108073

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Scopus

PubMed

Publisher：Sustainable Cities and Society  

This paper presents a comprehensive numerical investigation to predict the human breathing zones (BZs) in crowded semi-outdoor environments. The computational domain consisted of a nine-human block array with integrated nasal cavities subjected to the lower part of the atmospheric boundary layer. Five crowding levels, seven wind directions, and inflow ambient air temperatures (ranging from 10 to 31 °C) were tested to examine the horizontal and vertical formations of the BZs. Validation and verification tests were performed through comparisons with experimental results, a grid independence test, and an evaluation of various randomized distribution scenarios to minimize the uncertainties of the computational fluid dynamics analyses. The horizontal extension of the BZs tripled as the crowding level increased from 0.325 to 4.0 m2/capita. However, the lateral extension was insensitive and remained within 10 cm of the nostrils. Human models can inhale air close to the cheek, neck, and shoulders when an oblique flow is assumed. As the air temperature increased, individuals tended to inhale air from the upper regions, which was influenced by the interrelated thermal properties of the human body. Consequently, under high-temperature conditions, there may be an increased probability of gas-phase contaminant inhalation over greater horizontal distances.

DOI： 10.1016/j.scs.2024.105274

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Scopus

Publisher：Building and Environment  

The assessment of potential health risks from exposure to airborne contaminants and the inhalability of microparticles through human nasal breathing is crucial for the design of ventilation systems. In this study, using a standing computer-simulated person (CSP) directly linked to a numerical model of the respiratory tract, we investigated the aspiration efficiency (AE) of microparticles ranging between 1 and 80 μm under steady and transient breathing conditions. Two ventilation scenarios with displacement and mixed ventilation systems (DV and MV) were assumed for AE calculations. To determine the appropriate particle injection location, we investigated the position of highly inhaled particles corresponding to the breathing zone using a reverse particle-tracking simulation with reversed time progression. Additionally, the total and regional deposition fractions (TDF and RDF) of the inhaled microparticles on the respiratory wall surfaces were evaluated using the Lagrangian approach. The results indicate that the transient breathing cycle showed relatively higher AE and TDF rates compared to the assumed steady inhalation conditions, particularly for the size range 1–10 μm. An insignificant variation was observed in the AE and RDF results between different ventilation systems. However, microparticles in the MV room showed slightly higher AE than the DV system. Moreover, AE and penetration ratio were highly sensitive to the initially assumed particle density. For a comprehensive and accurate assessment of inhalation exposure to microparticles, we should predict the heterogeneous flow field formed around the human body and then analyze the AE and TDF in the respiratory tract during realistic transient breathing.

DOI： 10.1016/j.buildenv.2023.111114

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Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1371/journal.pone.0295954

Publisher：Building and Environment  

There is a growing demand for more advanced and diverse computer-simulated persons (CSPs) to accurately evaluate the indoor environmental quality and analyze the human body interactions with environmental factors. This study aimed to develop a CSP targeting the ANDI thermal manikin, which regulates skin temperature and thermal functions through a multi-node thermoregulation model, that is, the development of a digital twin for the ANDI thermal manikin. Additionally, to ensure the prediction reliability of the numerical thermoregulation model applied to the CSP using computational fluid dynamics (CFD) analysis, the CFD results were compared with those from the chamber experiment using an ANDI thermal manikin. We conducted integrated analyses of the CSP using the Fiala thermoregulation model to calculate the metabolic heat production, at transfer between different layers and sections, and skin surface temperature. The CFD analysis was performed using the CSP under the same environmental conditions as those used in the experiment. The CSP analysis results reproduced the experimental results obtained using the thermal manikin in the thermal comfort evaluation with acceptable accuracy, and the root mean square deviation of the predicted mean skin temperature was approximately 0.195. Furthermore, the importance of detailed clothing geometry was highlighted by confirming that the thickness of the ventilation layer between the skin and clothing has a significant effect on the thermal performance. The comprehensive prediction method for indoor environments based on the advanced CSP developed in this study can contribute to human-centered indoor environmental planning through parametric analyses under various environmental scenarios.

DOI： 10.1016/j.buildenv.2023.111105

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Scopus

Publisher：18th Conference of the International Society of Indoor Air Quality and Climate, INDOOR AIR 2024 - Conference Program and Proceedings  

Utilizing CFD-CSP coupled analysis, the breathing zone was evaluated considering the micro-movement of CSP. To accurately reproduce the human body functions that may affect the indoor climate, we applied the multi-node thermoregulation model, transient breathing model and single-segment inverted pendulum model. The breathing zone of the case without micro-movement was distributed from around the nasal opening to the upper abdomen, however, in the case with micro-movement, the zone changed significantly to a relatively small area near the face. These results suggest that micro-movement may have some effect on the dimensions of the breathing zone, which is critical for assessing airborne transmission and inhalation exposure.

Scopus

Publisher：18th Conference of the International Society of Indoor Air Quality and Climate, INDOOR AIR 2024 - Conference Program and Proceedings  

The overarching objective of this study is to create an in silico ocular model to evaluate chemical exposure via the eye. As a first step, in this study, we create a model to predict lacrimal fluid evaporation and ocular surface temperature distribution. Computer Simulated Person (CSP) is created to reproduce detailed ocular geometry, and numerical analysis is conducted under different indoor temperature and humidity conditions. We quantitatively evaluate the effects of indoor thermal conditions on ocular surface temperature and evaporation of lacrimal fluid.

Scopus

Publisher：18th Conference of the International Society of Indoor Air Quality and Climate, INDOOR AIR 2024 - Conference Program and Proceedings  

This study examined the impact of background carbon dioxide (CO2) concentration on CO2 emission rates from humans. Twelve volunteers (nine males and three females) stayed in a small chamber. Three background CO2 concentration conditions determined by two different schemes: controlling ventilation rate and dosing pure CO2, were examined: 800, 1400, and 3000ppm. Indirect calorimetry was used to measure CO2 emission rates and additionally respiratory parameters. Increasing the background CO2 concentration from 800 ppm to 1400 ppm and 3000 ppm significantly reduced the CO2 emission rate.

Scopus

Publisher：18th Conference of the International Society of Indoor Air Quality and Climate, INDOOR AIR 2024 - Conference Program and Proceedings  

In a multinational graduate school student laboratory, we investigated human close contact behaviours through high-resolution video camera data collected for five consecutive school days. We characterize close contact behaviour from stochastic interactions in terms of interpersonal distance (IPD), homophily, posture, duration, and frequency of contact in a non-homogenous population. This data can be used to improve targeted epidemiological analyses for indoor occupant health decision-making as well as strategies at diverse community levels.

Scopus

Publisher：18th Conference of the International Society of Indoor Air Quality and Climate, INDOOR AIR 2024 - Conference Program and Proceedings  

This study aims to propose the exhaled droplet properties during coughing and associated viral load (viral RNA copies/mL) under distinct geometric oral cavities. The coupling method of Eulerian Wall Film (EWF)-Discrete Phase (DP) - Host Cell Dynamics (HCD) models was employed in addition to Computational Fluid and Particle Dynamics (CFPD) analysis methods. Obtained results indicate that alternations in the oral structure directly impact exhaled number concentration and emission trend. This study initially proposed the coupling method to correlate the site origin of exhaled droplets and viral RNA copies within the mucus.

Scopus

Language：English   Publisher：PLoS ONE  

The COVID-19 pandemic has remarkably heightened concerns regarding the prediction of communicable disease spread. This study introduces an innovative agent-based modeling approach. In this model, the quantification of human-to-human transmission aligns with the dynamic variations in the viral load within an individual, termed “within-host” and adheres to the susceptible–infected–recovered (SIR) process, referred to as “between-host.” Variations in the viral load over time affect the infectivity between individual agents. This model diverges from the traditional SIR model, which employs a constant transmission probability, by incorporating a dynamic, time-dependent transmission probability influenced by the viral load in a host agent. The proposed model retains the time-integrated transmission probability characteristic of the conventional SIR model. As observed in this model, the overall epidemic size remains consistent with the predictions of the standard SIR model. Nonetheless, compared to predictions based on the classical SIR process, notable differences existed in the peak number of the infected individuals and the timing of this peak. These nontrivial differences are induced by the direct correlation between the time-evolving transmission probability and the viral load within a host agent. The developed model can inform targeted intervention strategies and public health policies by providing detailed insights into disease spread dynamics, crucial for effectively managing epidemics.

DOI： 10.1371/journal.pone.0295954

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Scopus

PubMed

Publisher：Building and Environment  

We numerically analyzed odorant transportation from a sniffing device (funnel) to the olfactory region of the nasal cavity during breathing. We followed the procedure for the perceived air quality evaluations described in the ISO 16000-28 standard, and used acetone defined as the standard test substance for pi-scale evaluations in this standard; we also used ammonia and acetic acid, as acetone also emitted by humans. We modelled two breathing conditions: normal breathing (through nose) and sniffing. We evaluated olfactory receptor access under these breathing conditions. The acetone absorption flux to the olfactory epithelial tissues was analyzed using a computer-simulated person with a numerical respiratory tract model and a physiologically based pharmacokinetic model that was used to validate the prediction accuracy. The absorption flux and sensible/latent heat flux to the olfactory epithelial tissue were analyzed quantitatively. We also analyzed the impact of flow through the ortho- and retro-nasal pathways on the absorption flux to the olfactory region. The transient inhalation/exhalation airflow profile, breathing, and sniffing conditions had a significant impact on the absorption flux to the olfactory region of the nasal cavity. We observed two peaks of odorant absorption flux in one breath one during inhalation and one during exhalation. For example, 0.5μg/(m2s) of peak acetone absorption flux in the olfactory region during inhalation and 0.1μg/(m2s) during exhalation was observed.

DOI： 10.1016/j.buildenv.2023.110868

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Scopus

Language：English   Publisher：Physics of Fluids  

Infectious respiratory diseases have long been a serious public health issue, with airborne transmission via close person-to-person contact being the main infection route. Coughing episodes are an eruptive source of virus-laden droplets that increase the infection risk of susceptible individuals. In this study, the droplet generation process during a coughing event was reproduced using the Eulerian wall film (EWF) model, and the absorption/expulsion of droplets was tracked using the discrete phase model (DPM). A realistic numerical model that included the oral cavity with teeth features and the respiratory system from the throat to the first bifurcation was developed. A coughing flow profile simulated the flow patterns of a single coughing episode. The EWF and DPM models were coupled to predict the droplet formation, generation, absorption, and exhalation processes. The results showed that a large droplet number concentration was generated at the beginning of the coughing event, with the peak concentration coinciding with the peak cough rate. Analysis of the droplet site of origin showed that large amounts of droplets were generated in the oral cavity and teeth surface, followed by the caudal region of the respiratory system. The size of the expelled droplets was 0.25–24 μm, with the peak concentration at 4–8 μm. This study significantly contributes to the realm on the site of origin and localized number concentration of droplets after a coughing episode. It can facilitate studies on infection risk assessment, droplet dispersion, and droplet generation mechanisms from other sneezing or phonation activities.

DOI： 10.1063/5.0174014

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Scopus

CiNii Research

Publisher：Building and Environment  

To address the problem of airborne transmission caused by droplets/droplet nuclei containing infectious viruses such as influenza A, tuberculosis, and SARS-CoV-2, the transmission dynamics of infectious droplets in indoor environments, from the generation/emission from an infected subject to the exposure of the target subject via indoor air, must be comprehended seamlessly and accurately. Research on indoor airborne transmission requires rigorous prior ethical review, and experimental studies on humans (in vivo and/or in vitro) are severely limited. Therefore, research methods based on in silico models; i.e., numerical modeling and analysis approaches, are preferred, owing to their flexibility for case and sensitivity analyses. In this study, assuming airborne transmission of SARS-CoV-2 in an indoor environment, we develop and perform a seamless and continuous numerical analysis of infectious droplet dispersion from a coughing infected subject and the subsequent inhalation exposure of a target subject (via the respiratory tract) through transient breathing. We focus on the effects of respiration patterns, particle-size changes due to evaporation, and indoor physical distance between the subjects, on the exposure concentration and distribution of inhaled droplets in the respiratory tract. The results show that, when an infected person coughs within a physical distance of 1 m, inhalation exposure results in significant differences in the inhalation–exhalation timing of breathing, and local environmental conditions have a dominant effect on the inhalation exposure. In short-range airborne transmission, the particle-size change due to evaporation has a dominant effect on the estimation of the inhalation exposure concentration in the respiratory tract.

DOI： 10.1016/j.buildenv.2023.110748

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Scopus

Publisher：Building and Environment  

This study investigates outdoor public health by predicting the airflow fields and probabilistic size of breathing zones. Computational fluid dynamics (CFD) simulations were performed in a simplified semi-outdoor domain, utilizing a validated computer-simulated person (CSP) with an integrated nasal cavity. The simulations were conducted for eight wind orientations (0°, 90°, 180°, 270°, 45°, 135°, 225°, and 315°), four wind velocities (Uref = 0.25, 0.5, 0.75, and 1.0 m/s), and one inhalation flow rate (18.7 L/min), considering both steady and transient conditions. The RANS-based equations were solved using the SST k-omega turbulence model. Breathing zones were computed and visualized using the scale for ventilation efficiency 5 (SVE5) and reverse time-traced vector techniques. The results indicated that wind orientation influenced the air velocity, temperature, and breathing zone distribution. The steady-state condition tended to overestimate breathing zones, whereas, under transient conditions, they assumed a semi-cylindrical form that extended horizontally, with a slight slope from the nostrils towards the direction of the wind source. The horizontal extension of the breathing regions increased at high wind speeds and with a smaller cylinder radius compared to calm conditions. Eventually, this study proposed new definitions of the breathing zone in the semi-outdoor environment in different SVE5 values. These findings can contribute to air quality management and aid in assessing the probability of airborne transmission in public spaces.

DOI： 10.1016/j.buildenv.2023.110672

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Scopus

Language：English   Publisher：Computer Methods and Programs in Biomedicine  

Background and Objective: Respiratory diseases caused by viruses are a major human health problem. To better control the infection and understand the pathogenesis of these diseases, this paper studied SARS-CoV-2, a novel coronavirus outbreak, as an example. Methods: Based on coupled computational fluid and particle dynamics (CFPD) and host-cell dynamics (HCD) analyses, we studied the viral dynamics in the mucus layer of the human nasal cavity-nasopharynx. To reproduce the effect of mucociliary movement on the diffusive and convective transport of viruses in the mucus layer, a 3D-shell model was constructed using CT data of the upper respiratory tract (URT) of volunteers. Considering the mucus environment, the HCD model was established by coupling the target cell-limited model with the convection-diffusion term. Parameter optimization of the HCD model is the key problem in the simulation. Therefore, this study focused on the parameter optimization of the viral dynamics model, divided the geometric model into multiple compartments, and used Monolix to perform the nonlinear mixed effects (NLME) of pharmacometrics to discuss the influence of factors such as the number of mucus layers, number of compartments, diffusion rate, and mucus flow velocity on the prediction results. Results: The findings showed that sufficient experimental data can be used to estimate the corresponding parameters of the HCD model. The optimized convection-diffusion case with a two-layer multi-compartment low-velocity model could accurately predict the viral dynamics. Conclusions: Its visualization process could explain the symptoms of the disease in the nose and contribute to the prevention and targeted treatment of respiratory diseases.

DOI： 10.1016/j.cmpb.2023.107622

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Scopus

PubMed

Language：English   Publisher：Computer Methods and Programs in Biomedicine  

Background and objectives: Suspended respirable airborne particles are associated with human health risks and especially particles within the range of ultrafine (< 0.1 μm) or fine (< 2.5 μm) have a high possibility of penetrating the lung region, which is concerned to be closely related to the bronchial or alveoli tissue dosimetry. Nature complex structure of the respiratory system requires much effort to explore and comprehend the flow and the inhaled particle dynamics for precise health risk assessment. Therefore, this study applied the computational fluid-particle dynamics (CFPD) method to elucidate the deposition characteristics of ultrafine-to-coarse particles in the human respiratory tract from nostrils to the 16th generation of terminal bronchi. Methods: The realistic bronchi up to the 8th generation are precisely and perfectly generated from computed tomography (CT) images, and an artificial model compensates for the 9th-16th bronchioles. Herein, the steady airflow is simulated at constant breathing flow rates of 7.5, 15, and 30 L/min, reproducing human resting-intense activity. Then, trajectories of the particle size ranging from 0.002 – 10 μm are tracked using a discrete phase model. Results: Here, we report reliable results of airflow patterns and particle deposition efficiency in the human respiratory system validated against experimental data. The individual-related focal point of ultrafine and fine particles deposition rates was actualized at the 8th generation; whilst the hot-spot of the deposited coarse particles was found in the 6th generation. Lobar deposition characterizes the dominance of coarse particles deposited in the right lower lobe, whereas the left upper-lower and right lower lobes simultaneously occupy high deposition rates for ultrafine particles. Finally, the results indicate a higher deposition in the right lung compared to its counterpart. Conclusions: From the results, the developed realistic human respiratory system down to the terminal bronchiole in this study, in coupling with the CFPD method, delivers the accurate prediction of a wide range of particles in terms of particle dosimetry and visualization of site-specific in the consecutive respiratory system. In addition, the series of CFPD analyses and their results are to offer in-depth information on particle behavior in human bronchioles, which may benefit health risk assessment or drug delivery studies

DOI： 10.1016/j.cmpb.2023.107589

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Scopus

PubMed

Publisher：E3S Web of Conferences  

Respiratory diseases, such as COVID-19 (coronavirus disease 2019) caused by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), have posed a threat to human health. For infection control and a better understanding of the pathogenesis, this study mainly focused on elucidating the virus dynamics in the mucus layer of the human nasal cavity-nasopharynx, using coupled computational fluid-particle dynamics (CFPD) and host-cell dynamics (HCD) analyses. To reproduce virus transportation in the mucus layer by mucociliary motion, a three-dimensional-shell model was created using the data obtained from computed tomography (CT) of the human upper airway. By considering the mucus milieu, the target-cell-limited model was coupled with the convection-diffusion term to develop the HCD model. Parameter optimization has been shown to have a great impact on the accuracy of model prediction; therefore, this study proposes a method that divides the geometric model into multiple regions and uses Monolix for nonlinear mixed effects modeling for pharmacometrics. The results showed that data from human inoculation challenge trials could be used to estimate the corresponding parameters. The models developed and used with optimized parameters can provide relatively accurate predictions of virus dynamics, which could contribute to the prevention and treatment of respiratory diseases.

DOI： 10.1051/e3sconf/202339601008

Scopus

Language：English   Publisher：Computer Methods and Programs in Biomedicine  

Background and objective: From various perspectives (e.g. inhalation exposure and drug delivery), it is important to provide insights into the behavior of inhaled particles in the human respiratory system. Although most of the experimental and numerical studies have relied on an assumption of steady inhalation, the transient breathing profile is a key factor in particle deposition in the respiratory tract. In this study, particle transportation and deposition were predicted in a realistic human airway model during a breathing cycle and the effects of steady-state and transient flows on the deposition fraction were observed using computational fluid dynamics. Methods: Two transient breathing cycles with different respiratory durations were considered to evaluate the effects of respiration duration on particle transport and deposition characteristics. Two types of steady breathing conditions with corresponding steady-state respiratory volumes were reproduced. The Lagrangian discrete phase model approach was used to investigate particle transportation and deposition under transient breathing conditions. Additionally, the Eulerian approach was used to analyze the transport of nanoparticles in the gas phase. A total of >50,000 monodispersed particles with aerodynamic diameters ranging between 2 nm and 10 μm were selected for comprehensive deposition predictions for particle sizes ranging from the nano- to microscale. Results: The predicted results were compared with the experimental data. The particle deposition fraction in the nasal cavity and tracheal regions showed differences between the steady and transient simulations. In addition, particle analysis under steady inhalation conditions cannot accurately predict particle transportation and deposition in the lower airway. Furthermore, the breathing cycle had a significant effect on the deposition fraction of the particles and the behavior of the inhaled particles. Conclusions: Transient simulation mimicking the breathing cycle was observed to be an important factor in accurately predicting the transportation and deposition of particles in the respiratory tract.

DOI： 10.1016/j.cmpb.2023.107501

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Scopus

PubMed

Publisher：Environmental Science and Engineering  

The purpose of this study was to accurately predict the dynamics of SARS-CoV-2 infection–based on a 3D shell model and combining computational fluid and particle dynamics (CFPD) and host-cell dynamics–along the mucus layer of the upper airway. Assuming that a healthy person inhaled droplets coughed up by an infected individual via nasal inhalation, we focused on the infection dynamics of the virus deposited in the nasal cavity and nasopharynx. The distribution of the cough droplets deposited was preliminarily analyzed using CFPD. Using this distribution as an initial condition, we predicted the time series distribution for SARS-CoV-2 concentration in the mucus milieu depending on diffusion, mucociliary motion, and virus production. These results form an initial elucidation of an aspect of the virus’ transmission mechanism in the upper airway.

DOI： 10.1007/978-981-19-9822-5_170

Scopus

Publisher：Environmental Science and Engineering  

Inhalation exposure to various types of airborne particles is an important risk factor for human health. This study predicted particle transport and deposition in a realistic human airway model during breathing and observed the effects of steady-state flow and transient flow on the deposition fraction using computational fluid dynamics (CFD). To evaluate the effect of the transient breathing profile on particle transport and deposition in the respiratory tract, we reproduced two unsteady breathing cycles with different breathing time scales. The particle dispersion analysis targeted approximately 50,000 or 75,000 particles, with aerodynamic diameters ranging from 2 nm to 10 µm, randomly placed near the nostril. Under transient breathing conditions, a total of approximately 50,000 or 75,000 particles were continuously released at each time step during the inhalation period. As a result, a significant difference in particle deposition and transport to the lower airway region was confirmed for different breathing patterns.

DOI： 10.1007/978-981-19-9822-5_173

Scopus

Publisher：Environmental Science and Engineering  

This study focused on the impact of the reproduction of oral cavity shape on the droplets dispersion dynamics, and compared the coughing dynamics between human models with and without oral cavity by using computational fluid dyanmics (CFD) technique. In this analysis, droplets were released from mouth opening surface or from the trachea via oral cavity. The results showed these models made differences of exhaled airflow pattern, the droplets dispersion and the rate of inhalation and deposition depending on the oral cavity shape. In conclusion, the droplets dispersion dynamics with consideration of oral cavity shape might contribute to accurately predict the dispersion characteristics of droplets and infection risk caused by coughing.

DOI： 10.1007/978-981-19-9822-5_169

Scopus

Publisher：Environmental Science and Engineering  

The purpose of this study is to reproduce CO2 emission from a human in the chamber experiment and investigate a relationship between CO2 emission rate and indoor air environment. A “digital-twin” model of the experiments for estimation of CO2 emission rate was developed by CSP integrated with CFD technique. As a result, the inhaled CO2 level depended on the flow patterns around the occupants. Additionally, the reasonable reduction of tidal volume by low IAQ could explain the reduction of CO2 emission rate in the chamber experiment.

DOI： 10.1007/978-981-19-9822-5_210

Scopus

Publisher：Healthy Buildings 2023: Asia and Pacific Rim  

To better understand the infection dynamics of respiratory viruses, this study conducted a comparative analysis of the factors affecting the SARS-CoV-2 infection dynamics through the mucociliary movement of the human nasal cavity-nasopharynx based on coupled computational fluid and particle dynamics (CFPD) and host-cell dynamics (HCD) analysis. The viral infection dynamics were predicted by combining a 3D shell model with the mucus layer, droplet deposition distribution, droplet virus content, and developed HCD model. The findings showed that the diffusive rate, mucus flow velocity, and layer mode have a significant influence, which may contribute to the accurate prediction of viral dynamics and disease prevention.

Scopus

Publisher：Environmental Science and Engineering  

The purpose of this study was to analyze the transport dynamics of inhaled gaseous odorants in the respiratory tract and investigate the characteristics of the adsorption flux on the olfactory epithelium tissue. Following the procedure of the perceptive air quality test described in ISO 16000–28, we analyzed the adsorption flux on the olfactory epithelium tissue under transient breathing conditions using a coupled computational fluid dynamics and physiologically based pharmacokinetic (CFD-PBPK) model. In the calculations, a comprehensive model that integrates human body geometry with realistic airway geometry was used. Through the analysis, we obtained the following results: (1) The inhaled odorant concentration varied with the unsteady breathing cycle. (2) The adsorption flux on the olfactory epithelium tissue was low compared to that in the other nasal regions. (3) The difference in the adsorption fraction in the olfactory epithelium region was confirmed between the orthonasal and retronasal pathways. Thus, the two different pathways might have a significant impact on the efficiency of odorant transportation to the olfactory epithelial region.

DOI： 10.1007/978-981-19-9822-5_186

Scopus

Publisher：Healthy Buildings 2023: Asia and Pacific Rim  

Although the current ventilation design is defined only by the time-averaged flow rate, turbulence intensity of airflow at the supply inlet may be one of the major factors forming the concentration distribution of contaminants. In this study, we investigated the effects of turbulent intensity at the supply inlet on the indoor flow field and contaminant concentration distribution for three different contaminant generation methods. As a result, the turbulence intensity at the supply inlet affected the separation point of the airflow from the inlet. In both uniform and regional spatial generation, the peak contaminant concentrations and the effect of the turbulent intensity on the emission rate from the wall surfaces were dependent on the turbulent intensity at the inlet. In conclusion, we should consider not only the time-averaged ventilation rate but also the turbulent inlet boundary condition for indoor contamination control.

Scopus

Publisher：Healthy Buildings 2023: Asia and Pacific Rim  

In this study, we investigated the aspiration efficiency of microparticles in both steady and transient breathing in a ventilated room with a displacement ventilation system. The flow patterns in the vicinity of the CSP and the effects of the thermal plume on the particle aspiration by the CSP were simulated using the computational fluid dynamics (CFD) technique. In order to set the appropriate particle injection position, the high inhaled particle position corresponding to the breathing zone was investigated using the reverse particle tracking method. In addition, the overall and regional deposition efficiencies of inhaled microparticles on the respiratory wall surfaces were evaluated. As a result, the thermal plume around the CSP and the assumption of breathing conditions (steady vs transient) significantly affect the aspiration efficiency of microparticles, the high inhaled particle position, and the overall and regional deposition efficiencies of particles in the respiratory surface depending on the particle size.

Scopus

Language：English   Publisher：Applied Mathematics and Computation  

COVID-19 has emphasized that a precise prediction of a disease spreading is one of the most pressing and crucial issues from a social standpoint. Although an ordinary differential equation (ODE) approach has been well established, stochastic spreading features might be hard to capture accurately. Perhaps, the most important factors adding such stochasticity are the effect of the underlying networks indicating physical contacts among individuals. The multi-agent simulation (MAS) approach works effectively to quantify the stochasticity. We systematically investigate the stochastic features of epidemic spreading on homogeneous and heterogeneous networks. The study quantitatively elucidates that a strong microscopic locality observed in one- and two-dimensional regular graphs, such as ring and lattice, leads to wide stochastic deviations in the final epidemic size (FES). The ensemble average of FES observed in this case shows substantial discrepancies with the results of ODE based mean-field approach. Unlike the regular graphs, results on heterogeneous networks, such as Erdős–Rényi random or scale-free, show less stochastic variations in FES. Also, the ensemble average of FES in heterogeneous networks seems closer to that of the mean-field result. Although the use of spatial structure is common in epidemic modeling, such fundamental results have not been well-recognized in literature. The stochastic outcomes brought by our MAS approach may lead to some implications when the authority designs social provisions to mitigate a pandemic of un-experienced infectious disease like COVID-19.

DOI： 10.1016/j.amc.2022.127328

Web of Science

Scopus

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Statistical Mechanics: Theory and Experiment  

Many epidemic modeling studies rely on the common assumption that the disease transmission rate between individuals is constant. However, in reality, transmission rates depend on the time-varying viral load of the infected individual. The time-dependent transmission rate has the potential to affect the spread of an epidemic. In this study, the influenza and SARS-CoV-2 transmission rate profiles were developed based on the viral load of infected individuals and dose-response curves. In addition, a new epidemic model, the multi-infectious stage edge-based compartment model, was proposed to apply the transmission rate profile to epidemic dynamics in both static and temporal networks. It was determined that in terms of the final epidemic size there is no discrepancy between the constant and time-dependent transmission rates in the static network. However, the time at which the infected fraction peaks, and the peak infection fraction are dependent on the transmission rate profile. However, in temporal networks, the final epidemic size for the constant transmission rate is higher than that for the time-dependent transmission rate. In conclusion, the time-dependent transmission rate strongly affects the epidemic dynamics.

DOI： 10.1088/1742-5468/ac8e59

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

COVID-19 has emphasized that a precise prediction of a disease spreading is one of the most pressing and crucial issues from a social standpoint. Although an ordinary differential equation (ODE) approach has been well established, stochastic spreading features might be hard to capture accurately. Perhaps, the most important factors adding such stochasticity are the effect of the underlying networks indicating physical contacts among individuals. The multi-agent simulation (MAS) approach works effectively to quantify the stochasticity. We systematically investigate the stochastic features of epidemic spreading on homogeneous and heterogeneous networks. The study quantitatively elucidates that a strong microscopic locality observed in one- and two-dimensional regular graphs, such as ring and lattice, leads to wide stochastic deviations in the final epidemic size (FES). The ensemble average of FES observed in this case shows substantial discrepancies with the results of ODE based mean-field approach. Unlike the regular graphs, results on heterogeneous networks, such as Erdős–Rényi random or scale-free, show less stochastic variations in FES. Also, the ensemble average of FES in heterogeneous networks seems closer to that of the mean-field result. Although the use of spatial structure is common in epidemic modeling, such fundamental results have not been well-recognized in literature. The stochastic outcomes brought by our MAS approach may lead to some implications when the authority designs social provisions to mitigate a pandemic of un-experienced infectious disease like COVID-19.

DOI： https://doi.org/10.1016/j.amc.2022.127328

Publisher：Japan Architectural Review  

In the existing ventilation design, the ventilation rate is defined by the time-averaged flow rate, and the fluctuating (turbulence) component is not typically considered. However, inlet turbulent conditions are also assumed to have some influence on the formation of contaminant distributions. Therefore, the influence of turbulent kinetic energy at the inlet boundary on scalar transportation in an indoor environment needs to be elucidated when discussing the ventilation rate setpoint via the supply inlet in terms of local contaminant concentration control. This study discusses the impact of turbulent kinetic energy in the ventilation design on scalar transfer and its distribution within an enclosed space. To understand the influence of various inlet turbulent boundary conditions on scalar transfer, a computational fluid dynamics analysis was conducted using two different room models: a simple room and a room with a ventilation system that creates a large velocity gradient. The results indicate that scalar transfer within the room is not solely dominated by the averaged velocity input at the inlet boundary but is also strongly affected by the turbulence conditions at the inlet boundary. The numerical results indicate the possibility of a new ventilation design strategy that simultaneously considers the transfer of turbulent components and contaminants.

DOI： 10.1002/2475-8876.12299

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

In the existing ventilation design, the ventilation rate is defined by the time-averaged flow rate, and the fluctuating (turbulence) component is not typically considered. However, inlet turbulent conditions are also assumed to have some influence on the formation of contaminant distributions. Therefore, the influence of turbulent kinetic energy at the inlet boundary on scalar transportation in an indoor environment needs to be elucidated when discussing the ventilation rate setpoint via the supply inlet in terms of local contaminant concentration control. This study discusses the impact of turbulent kinetic energy in the ventilation design on scalar transfer and its distribution within an enclosed space. To understand the influence of various inlet turbulent boundary conditions on scalar transfer, a computational fluid dynamics analysis was conducted using two different room models: a simple room and a room with a ventilation system that creates a large velocity gradient. The results indicate that scalar transfer within the room is not solely dominated by the averaged velocity input at the inlet boundary but is also strongly affected by the turbulence conditions at the inlet boundary. The numerical results indicate the possibility of a new ventilation design strategy that simultaneously considers the transfer of turbulent components and contaminants.

DOI： https://doi.org/10.1002/2475-8876.12299

Publisher：E3S Web of Conferences  

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has led to the worldwide spread of coronavirus disease-2019 (COVID-19) since its emergence in 2019. Virus replication and infection dynamics after its deposition on the respiratory tissues require detailed studies for infection control. This study focused primarily on SARS-CoV-2 dynamics in the mucus layer of the nasal cavity and nasopharynx, based on coupled computational fluid-particle dynamics (CFPD) and host-cell dynamics (HCD) analyses. Considering the mucus milieu, we coupled the target-cell limited model with the convection-diffusion term to develop an improved HCD model. The infection dynamics in the mucus layer were predicted by a combination of the mucus flow field, droplet deposition distribution, and HCD. The effect of infection rate, β, was investigated as the main parameter of HCD. The results showed that the time series of SARS-CoV-2 concentration distribution in the mucus layer strongly depended on diffusion, convection, and virus production. β affected the viral load peak, its arrival time, and duration. Although the SARS-CoV-2 dynamics in the mucus layer obtained in this study have not been verified by appropriate clinical data, it can serve as a preliminary study on the virus transmission mode in the upper respiratory tract.

DOI： 10.1051/e3sconf/202235605021

Scopus

Language：Japanese   Publisher：Architectural Institute of Japan  

<p>In this study, following the procedure of the perceptive air quality test described in ISO 16000-28 and ISO 16000-30, we numerically analyzed the odorant transportation from the odorant generator to human breathing zone using acetone which is considered as a standard substance for pi-scale evaluation. For the evaluation of access to olfactory receptors under a transient breathing cycle, the acetone adsorption flux to the olfactory epithelial cells was calculated by using computer simulated person (CSP) with numerical respiratory tract model and physiologically based pharmacokinetic (PBPK) model.</p>

DOI： 10.3130/aije.87.541

Scopus

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Indoor Air  

Accurate prediction of inhaled CO2 concentration and alveolar gas exchange efficiency would improve the prediction of CO2 concentrations around the human body, which is essential for advanced ventilation design in buildings. We therefore, developed a computer-simulated person (CSP) that included a computational fluid dynamics approach. The CSP simulates metabolic heat production at the skin surface and carbon dioxide (CO2) gas exchange at the alveoli during the transient breathing cycle. This makes it possible to predict the CO2 distribution around the human body. The numerical model of the CO2 gas exchange mechanism includes both the upper and lower airways and makes it possible to calculate the alveolar CO2 partial pressure; this improves the prediction accuracy. We used the CSP to predict emission rates of metabolically generated CO2 exhaled by a person and assumed that the tidal volume will be unconsciously reduced as a result of exposure to poor indoor air quality. A reduction in tidal volume resulted in a decrease in CO2 emission rates of the same magnitude as was observed in our published experimental data. We also observed that the predicted inhaled CO2 concentration depended on the flow pattern around the human body, as would be expected.

DOI： 10.1111/ina.13079

Web of Science

Scopus

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Sustainability (Switzerland)  

A thorough understanding of the inhalation dynamics of infectious aerosols indoors and infection dynamics within the host by inhaled viruses such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) plays an important role in the assessment and control of infection risks indoors. Here, by combining computational fluid–particle dynamics (CFPD) and host–cell dynamics (HCD), SARS-CoV-2 infection dynamics in the mucus layer of the human upper airway were studied. To reproduce the diffusive and convective transport of the virus in the nasal cavity–nasopharynx by mucociliary motion, a three-dimensional (3D)-shell model with a mucus layer was developed. The initial virus concentrations for HCD calculation were estimated based on the deposition distribution of droplets with representative sizes analyzed by CFPD. To develop a new HCD model, the target-cell-limited model was integrated with the convection–diffusion equation. Additionally, the sensitivity of the infection rate β to the infection dynamics was systematically investigated. The results showed that the time series of SARS-CoV-2 concentration in the mucus layer strongly depended on diffusion, convection, and β. Although the SARS-CoV-2 dynamics obtained here have not been verified by corresponding clinical data, they can preliminarily reveal its transmission mode in the upper airway, which will contribute to the prevention and treatment of coronavirus disease 2019.

DOI： 10.3390/su14073896

Web of Science

Scopus

Language：English   Publisher：Scientific Reports  

We present the pair approximation models for susceptible–infected–recovered (SIR) epidemic dynamics in a sparse network based on a regular network. Two processes are considered, namely, a Markovian process with a constant recovery rate and a non-Markovian process with a fixed recovery time. We derive the implicit analytical expression for the final epidemic size and explicitly show the epidemic threshold in both Markovian and non-Markovian processes. As the connection rate decreases from the original network connection, the epidemic threshold in which epidemic phase transits from disease-free to endemic increases, and the final epidemic size decreases. Additionally, for comparison with sparse and heterogeneous networks, the pair approximation models were applied to a heterogeneous network with a degree distribution. The obtained phase diagram reveals that, upon increasing the degree of the original random regular networks and decreasing the effective connections by introducing void nodes accordingly, the final epidemic size of the sparse network is close to that of the random network with average degree of 4. Thus, introducing the void nodes in the network leads to more heterogeneous network and reduces the final epidemic size.

DOI： 10.1038/s41598-022-07985-9

Web of Science

Scopus

PubMed

Publisher：Building and Environment  

We determined carbon dioxide (CO2) emission rates from sedentary subjects performing light work on tablets or smartphones in controlled chamber exposures. Five groups, each consisting of four people (four groups with two females and two males and one with three males and one female), stayed in a 22.5 m3 stainless steel chamber under different environmental conditions for 3 h in the morning and then 2,5 h in the afternoon after having a light lunch. Three groups consisted of young adults (college students), one of seniors, and one of teenagers. The chamber was ventilated with outdoor air at 3.2 h−1 (per person rate was 5 L/s). The CO2 emission rates per person were calculated using a single-zone mass-balance equation and the measured CO2 concentration once steady state had been reached. Per person emission rates varied between 14.1 and 16.8 L/h in the morning and 15.9–17.8 L/h in the afternoon; higher levels in the afternoon were probably caused by the increased metabolism from diet-induced thermogenesis (DIT). Emission rates were higher with increased temperature when the participants felt warm, but did not change with increased relative humidity or ozone concentration. They differed to some extent from those estimated using ISO 8996 and ASTM DS 6245, but were similar to published measured CO2 emission rates. The present results require confirmation with more people and measurements of CO2 emission rates using the calorimetric method.

DOI： 10.1016/j.buildenv.2021.108735

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

We present the pair approximation models for susceptible–infected–recovered (SIR) epidemic dynamics in a sparse network based on a regular network. Two processes are considered, namely, a Markovian process with a constant recovery rate and a non-Markovian process with a fixed recovery time. We derive the implicit analytical expression for the final epidemic size and explicitly show the epidemic threshold in both Markovian and non-Markovian processes. As the connection rate decreases from the original network connection, the epidemic threshold in which epidemic phase transits from disease-free to endemic increases, and the final epidemic size decreases. Additionally, for comparison with sparse and heterogeneous networks, the pair approximation models were applied to a heterogeneous network with a degree distribution. The obtained phase diagram reveals that, upon increasing the degree of the original random regular networks and decreasing the effective connections by introducing void nodes accordingly, the final epidemic size of the sparse network is close to that of the random network with average degree of 4. Thus, introducing the void nodes in the network leads to more heterogeneous network and reduces the final epidemic size.

DOI： https://doi.org/10.1038/s41598-022-07985-9

Language：English   Publishing type：Research paper (scientific journal)  

We determined carbon dioxide (CO2) emission rates from sedentary subjects performing light work on tablets or smartphones in controlled chamber exposures. Five groups, each consisting of four people (four groups with two females and two males and one with three males and one female), stayed in a 22.5 m3 stainless steel chamber under different environmental conditions for 3 h in the morning and then 2,5 h in the afternoon after having a light lunch. Three groups consisted of young adults (college students), one of seniors, and one of teenagers. The chamber was ventilated with outdoor air at 3.2 h−1 (per person rate was 5 L/s). The CO2 emission rates per person were calculated using a single-zone mass-balance equation and the measured CO2 concentration once steady state had been reached. Per person emission rates varied between 14.1 and 16.8 L/h in the morning and 15.9–17.8 L/h in the afternoon; higher levels in the afternoon were probably caused by the increased metabolism from diet-induced thermogenesis (DIT). Emission rates were higher with increased temperature when the participants felt warm, but did not change with increased relative humidity or ozone concentration. They differed to some extent from those estimated using ISO 8996 and ASTM DS 6245, but were similar to published measured CO2 emission rates. The present results require confirmation with more people and measurements of CO2 emission rates using the calorimetric method.

DOI： https://doi.org/10.1016/j.buildenv.2021.108735

Publisher：Building and Environment  

Ten healthy young adults slept one by one in a specially designed and constructed sleep capsule located in a climate chamber at two temperatures (24 °C and 28 °C) and two ventilation rates that ensured that the resulting CO2 concentrations were 800 and 1700 ppm. Subjectively rated sleep quality was reduced at 28 °C and reduced ventilation, while sleep onset latency was longer under these conditions. Sleep efficiency was lower at 28 °C. Subjectively rated fatigue and sleepiness decreased after sleeping under all conditions but less so after sleeping at 28 °C. The subjects indicated that their work performance improved after sleeping at 24 °C but not when ventilation was reduced and the temperature increased. Both objectively measured and subjectively rated work performance was worse after sleeping in the condition with increased temperature. The subjects felt warmer at 28 °C although the thermal environment was still rated as acceptable but the air in the capsule was rated stuffier, the acceptability of the air quality decreased and the rated odour intensity increased at this condition. The wrist skin temperature was always higher at 28 °C with reduced ventilation but only during the sleep onset latency period. The subjects felt slightly warm and rated the air stuffier when ventilation was reduced. The present results, albeit from a small exploratory pilot study, show that increased temperature and reduced ventilation both have negative effects on sleep quality, which may have consequences for next-day work performance. These pilot experiment results require validation due to the low number of subjects.

DOI： 10.1016/j.buildenv.2021.108666

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

The breathing zone of an individual indoors is usually defined as a finite region steadily formed in front of a face. Assuming the steady formation of the breathing zone, we propose a procedure for quantitatively identifying a breathing zone formed in front of a human face in the transient condition. This assumption is reasonable considering that the ventilation time scale of human respiration is sufficiently short compared to the ventilation time scale of a room. We used steady-state computational fluid dynamics (CFD) and a computationally simulated person (CSP). We present the probabilistic size of the breathing zone for various postures and breathing conditions. By analyzing unsteady inhalation and exhalation airflow characteristics via a CSP with a respiratory system, we also estimated the direct re-inhalation rate of the exhaled air. The results can be used for developing methods to control the long-term and low-contaminant concentration exposures.

DOI： https://doi.org/10.1111/ina.13003

Language：English   Publishing type：Research paper (scientific journal)  

Ten healthy young adults slept one by one in a specially designed and constructed sleep capsule located in a climate chamber at two temperatures (24 °C and 28 °C) and two ventilation rates that ensured that the resulting CO2 concentrations were 800 and 1700 ppm. Subjectively rated sleep quality was reduced at 28 °C and reduced ventilation, while sleep onset latency was longer under these conditions. Sleep efficiency was lower at 28 °C. Subjectively rated fatigue and sleepiness decreased after sleeping under all conditions but less so after sleeping at 28 °C. The subjects indicated that their work performance improved after sleeping at 24 °C but not when ventilation was reduced and the temperature increased. Both objectively measured and subjectively rated work performance was worse after sleeping in the condition with increased temperature. The subjects felt warmer at 28 °C although the thermal environment was still rated as acceptable but the air in the capsule was rated stuffier, the acceptability of the air quality decreased and the rated odour intensity increased at this condition. The wrist skin temperature was always higher at 28 °C with reduced ventilation but only during the sleep onset latency period. The subjects felt slightly warm and rated the air stuffier when ventilation was reduced. The present results, albeit from a small exploratory pilot study, show that increased temperature and reduced ventilation both have negative effects on sleep quality, which may have consequences for next-day work performance. These pilot experiment results require validation due to the low number of subjects.

DOI： https://doi.org/10.1016/j.buildenv.2021.108666

Language：English   Publisher：Indoor Air  

The breathing zone of an individual indoors is usually defined as a finite region steadily formed in front of a face. Assuming the steady formation of the breathing zone, we propose a procedure for quantitatively identifying a breathing zone formed in front of a human face in the transient condition. This assumption is reasonable considering that the ventilation time scale of human respiration is sufficiently short compared to the ventilation time scale of a room. We used steady-state computational fluid dynamics (CFD) and a computationally simulated person (CSP). We present the probabilistic size of the breathing zone for various postures and breathing conditions. By analyzing unsteady inhalation and exhalation airflow characteristics via a CSP with a respiratory system, we also estimated the direct re-inhalation rate of the exhaled air. The results can be used for developing methods to control the long-term and low-contaminant concentration exposures.

DOI： 10.1111/ina.13003

Web of Science

Scopus

PubMed

Publisher：17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022  

This study examined the impact of room temperature on carbon dioxide (CO2) emission rates from humans at three different physical activity levels: sitting, standing, and walking. Six volunteers (four males and two females) stayed in a temperature-controlled classroom. Four room temperature conditions were examined: 15, 20, 25, and 28℃. Indirect calorimetry was used to measure CO2 emission rates and additionally respiratory parameters such as ETCO2 and respiration rate. CO2 emission rates increased significantly with the physical activity level increased, and it was lower when thermally neutral compared to thermally warm and cool. The room temperature effect on CO2 emission rate depended on the physical activity levels.

Scopus

Publisher：17th International Conference on Indoor Air Quality and Climate, INDOOR AIR 2022  

We summarize our three recent studies that determined CO2 emission rates from humans using the mass-balance model and the measured steady-state CO2 concentration. One study determined CO2 emission rates from sleeping adults; they were on average 11 L/h/person, 30-45% than for awake people at a light activity. They were relatively stable and similar to the published work and estimations using models. Two studies determined CO2 emission rates from the sedentary awake people at a light activity; they were on average 12.9-17.8 L/h/person. They were not significantly different between teenagers, young adults, and the elderly, nor when ozone and relative humidity increased. Reduced ventilation and increased CO2 significantly reduced CO2 emission rates; the changes in respiration could be the plausible reason. CO2 emission rates increased at thermal sensation departing from neutrality; increased metabolic activity could be the plausible reason. The emission rates were different from published results and estimations using models.

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

Humans emit carbon dioxide (CO2) as a product of their metabolism. Its concentration in buildings is used as a marker of ventilation rate (VR) and degree of mixing of supply air, and indoor air quality (IAQ). The CO2 emission rate (CER) may be used to estimate the ventilation rate. Many studies have measured CERs from subjects who were awake but little data are available from sleeping subjects and the present publication was intended to reduce this gap in knowledge. Seven females (29 ± 5 years old; BMI: 22.2 ± 0.8 kg/m2) and four males (27 ± 1 years old; BMI: 20.5 ± 1.5 kg/m2) slept for four consecutive nights in a specially constructed capsule at two temperatures (24 and 28°C) and two VRs that maintained CO2 levels at ca. 800 ppm and 1700 ppm simulating sleeping conditions reported in the literature. The order of exposure was balanced, and the first night was for adaptation. Their physiological responses, including heart rate, pNN50, core body temperature, and skin temperature, were measured as well as sleep quality, and subjective responses were collected each evening and morning. Measured steady-state CO2 concentrations during sleep were used to estimate CERs with a mass-balance equation. The average CER was 11.0 ± 1.4 L/h per person and was 8% higher for males than for females (P < 0.05). Increasing the temperature or decreasing IAQ by decreasing VR had no effects on measured CERs and caused no observable differences in physiological responses. We also calculated CERs for sleeping subjects using the published data on sleep energy expenditure (SEE) and Respiratory Quotient (RQ), and our measured CERs confirmed both these calculations and the CERs predicted using the equations provided by ASHRAE Standard 62.1, ASHRAE Handbook, and ASTM D6245-18. The present results provide a valuable and helpful reference for the design and control of bedroom ventilation but require confirmation and extension to other age groups and populations.

DOI： https://doi.org/10.1111/ina.12911

Language：Japanese   Publishing type：Research paper (scientific journal)  

With electronic (e)-liquids containing cannabis components easily available, many anecdotal examples of cannabis vaping using electronic cigarette devices have been reported. For electronic cigarette cannabis vaping, there are potential risks of secondary indoor air pollution from vapers. However, quantitative and accurate prediction of the inhalation and dermal exposure of a passive smoker in the same room is difficult to achieve due to the ethical constraints on subject experiments. The numerical method, i.e., in silico method, is a powerful tool to complement these experiments with real humans. In this study, we adopted a computer-simulated person that has been validated from multiple perspectives for prediction accuracy. We then conducted an in silico study to elucidate secondary indoor air pollution and passive smoking associated with cannabis vaping using an electronic cigarette device in an indoor environment. The aerosols exhaled by a cannabis vaper were confirmed to be a secondary emission source in an indoor environment; non-smokers were exposed to these aerosols via respiratory and dermal pathways. Tetrahydrocannabinol was used as a model chemical compound for the exposure study. Its uptake by the non-smoker through inhalation and dermal exposure under a worst-case scenario was estimated to be 5.9% and 2.6% of the exhaled quantity from an e-cigarette cannabis user, respectively.

DOI： https://doi.org/10.1371/journal.pcbi.1009004

Language：Japanese   Publishing type：Research paper (scientific journal)  

The emission rate of carbon dioxide (CO2) depends on many factors but mainly on the activity level (metabolic rate) of occupants. In this study, we examined two other factors that may influence the CO2 emission rate, namely the background CO2 concentration and the indoor temperature. Six male volunteers sat one by one in a 1.7 m3 chamber for 2.5 h and performed light office-type work under five different conditions with two temperature levels (23 vs. 28°C) and three background concentrations of CO2 (800 vs. 1400 vs. 3000 ppm). Background CO2 levels were increased either by dosing CO2 from a cylinder or by reducing the outdoor air supply rate. Physiological responses to warmth, added CO2, and bioeffluents were monitored. The rate of CO2 emission was estimated using a mass-balance equation. The results indicate a higher CO2 emission rate at the higher temperature, at which the subjects were warm, and a lower emission rate in all conditions in which the background CO2 concentration increased. Physiological measurements partially explained the present results but more measurements are needed.

DOI： https://doi.org/10.1111/ina.12852

Language：English   Publishing type：Research paper (scientific journal)  

We successfully establish a theoretical framework of pairwise approximation for the vaccination game in which both the dynamic process of epidemic spread and individual actions in helping prevent social behaviours are quantitatively evaluated. In contrast with mean-field approximation, our model captures higher-order effects from neighbours by using an underlying network that shows how the disease spreads and how individual decisions evolve over time. This model considers not only imperfect vaccination but also intermediate protective measures other than vaccines. Our analytical predictions are validated by multi-agent simulation results that estimate random regular graphs at varying degrees.

DOI： 10.1098/rspa.2020.0769

Language：English   Publishing type：Research paper (scientific journal)  

Electronic (e)‐cigarette smoking is considered to be less harmful than traditional tobacco smoking because of the lack of a combustion process. However, e‐cigarettes have the potential to release harmful chemicals depending on the constituents of the vapor. To date, there has been significant evidence on the adverse health effects of e‐cigarette usage. However, what is less known are the impacts of the chemicals contained in exhaled air from an e‐cigarette smoker on indoor air quality, the second‐hand passive smoking of residents, and the toxicity of the exhaled air. In this study, we develop a comprehensive numerical model and computer‐simulated person to investigate the potential effects of e‐cigarette smoking on local tissue dosimetry and the deterioration of indoor air quality. We also conducted demonstrative numerical analyses for first‐hand and second‐hand e‐cigarette smoking in an indoor environment. To investigate local tissue dosimetry, we used newly developed physiologically based pharmacokinetic/toxicokinetic models that reproduce inhalation exposure by way of the respiratory tract and dermal exposure through the human skin surface. These models were integrated into the computer‐simulated person. Our numerical simulation results quantitatively demonstrated the potential impacts of e‐cigarette smoking in enclosed spaces on indoor air quality.

DOI： 10.1111/ina.12666

Language：English   Publishing type：Research paper (scientific journal)  

A modified susceptible-vaccinated-infected-recovered (SIR/V) with unaware-aware (UA) epidemic model in heterogeneous networks is presented to study the effect of information spreading in the spatial structure of the vaccination game on epidemic dynamics. Two layers SIR/V epidemic model is considered to elucidate information spreading, where the fraction of susceptible, vaccinated and infected individuals are parted as unaware and aware state as each susceptible and vaccinated persons are allied with their infected neighbors by a spatial structure, say, an underlying network. The context deduces epidemic vaccination game with awareness influence dynamics in one single season followed by a strategy update process that refer an individual to take imperfect vaccination or not. We considered two different strategy updating rules: individual based risk assessment (IB-RA) and strategy-based risk assessment (SB-RA) to explore how different underlying network topologies, say, random graph and scale free networks, subsequently giving impact on the final epidemic size, vaccination coverage and average social payoff through the effect of information spreading on epidemic. Thus, it can be seen that, awareness can enhance the epidemic threshold effectiveness and lessen the spreading of infection in a scale free network other than random graph and homogeneous network.

DOI： 10.1016/j.chaos.2019.109548

Language：English   Publishing type：Research paper (scientific journal)  

Industry implies economic growth; however, outdoor and indoor air pollution generated by industrial activities represents a widespread problem for the environment and human beings. In terms of human health, indoor air quality assessment has become essential in a society where people spend most of their time in indoor dwellings, as in the case of industry workers. Because indoor air quality is strongly affected by the outdoor environment, especially under natural ventilation conditions (e.g., cross-ventilation), a comprehensive analysis that includes outdoor atmospheric-urban environment is needed to reproduce realistic scenarios. In this context, computational fluid dynamics (CFD) is a useful tool. To perform a precise analysis of the inhalation exposure of factory workers to potential gas-phase contaminants in the working environment (i.e., inhaled dose of contaminants and potential effects), the human body and respiratory tract need to be integrated in the analysis. Therefore, in this study, we performed an integrated occupational inhalation exposure/toxicology assessment in a factory building that applies a computer simulated person (CSP), a virtual human respiratory tract and integrated physiologically-based toxicokinetic (PBTK) model to predict tissue dosimetry distribution. Outdoor airflow variation was transported into the enclosure through an hourly change in wind pressure coefficient to calculate transient ventilation rate and indoor contaminant concentration between 08:00 and 17:00 h. Thereafter, the time-averaged contaminant concentration calculated at the nares of the human body was employed in a steady state calculation of airflow and contaminant distribution inside the virtual respiratory tract. Subsequently, we predicted adsorbed contaminant in the first layer of tissue of the human airways; highest adsorption took place in the nasal cavity. Finally, based on the results of the comprehensive coupled numerical analysis performed using the CFD-CSP-PBTK model, we quantitatively discussed differences between the inhalation exposure concentration and representative contaminant concentration in the factory space (e.g., time and volume-averaged concentration).

DOI： 10.1016/j.envpol.2019.06.056

Language：English   Publishing type：Research paper (scientific journal)  

We combined the elements of evolutionary game theory and mathematical epidemiology to comprehensively evaluate the performance of vaccination-subsidizing policies in the face of a seasonal epidemic. We conducted multi-agent simulations to, among others, find out how the topology of the underlying social networks affects the results. We also devised a mean-field approximation to confirm the simulation results and to better understand the influences of an imperfect vaccine. The main measure of a subsidy’ performance was the total social payoff as a sum of vaccination costs, infection costs, and tax burdens due to the subsidy. We find two types of situations in which vaccination-subsidizing policies act counterproductively. The first type arises when the subsidy attempts to increase vaccination among past non-vaccinators, which inadvertently creates a negative incentive for voluntary vaccinators to abstain from vaccination in hope of getting subsidized. The second type is a consequence of overspending at which point the marginal cost of further increasing vaccination coverage is higher than the corresponding marginal cost of infections avoided by this increased coverage. The topology of the underlying social networks considerably worsens the subsidy's performance if connections become random and heterogeneous, as is often the case in human social networks. An imperfect vaccine also worsens the subsidy's performance, thus narrowing or completely closing the window for vaccination-subsidizing policies to beat the no-subsidy policy. These results imply that subsidies should be aimed at voluntary vaccinators while avoiding overspending. Once this is achieved, it makes little difference whether the subsidy fully or partly offsets the vaccination cost.

DOI： 10.1016/j.jtbi.2019.02.013

Language：English   Publishing type：Research paper (scientific journal)  

We build a new analytic scheme that competently reproduces the decision-making process of choosing an imperfect provision based on the evolutionary game theory dovetailed with the SIR model for epidemic spreading dynamics. Aside from considering the two extreme options whether or not taking vaccination, we consider an ‘intermediate defense measure’ (IDM) that emulates hand-washing, masking, gargling, and taking energy drinks, defined as the third strategy while taking vaccination as well as IDM at the same time as the fourth strategy. In the present study, each of the proposed three imperfect provisions is able to oppress infectious diseases like Flu, Influenza, Ebola, and SARS during an epidemic season with certain extent. Considering an infinite and well-mixed population, a new analytic framework is built to take care of those three cases instead of perfect vaccination. Unlike MAS (multi-agent simulation) approach we conduct our study throughout using the so-called theoretical approach. Besides that, three different strategy updating rules based on evolutionary game theory have also been considered in our proposed model. We successfully obtain phase diagrams showing the final epidemic size, social average payoff and the respective fractions of the different strategy holders using various values of effectiveness and efficiency coefficients. Finally, a comprehensive discussion is made with comparison among the two-, three- and four- strategy models to get a holistic idea justifying how imperfect provisions work during an epidemic spreading.

DOI： 10.1016/j.amc.2018.10.015

Language：English   Publishing type：Research paper (scientific journal)  

The information spreading of awareness can prompt the manners of human to ease the infectious possibility and assist to recover swiftly. A dynamic system of Susceptible-Infected-Recovered (SIR) with Unaware-Aware (UA) process (SIR-UA) is newly developed by using compartment model through analytical approach with assumption of an infinite and well-mixed population. Moreover, individuals in a population can be classified into six states as unaware susceptible(SU), aware susceptible(SA), unaware infected(IU), aware infected(IA), unaware recovered(RU), and aware recovered(RA). Compared with previous models, the new dynamic set of equations described the more widespread situation and incorporated all possible states of Unaware-Aware (UA) with SIR process. The effect of awareness is explored carefully to show the significance on epidemic model with time steps. Consequently, the properties of parameters on the epidemic awareness model are studied to deliberate different physical situations. Finally, full phase diagrams are explored to show the epidemic sizes of susceptible and recovered individuals for various parameters.

DOI： 10.1016/j.chaos.2018.12.017

Language：English   Publishing type：Research paper (scientific journal)  

The information awareness about contagious diseases have an influential effect on an individual's decision to suppress the diffusion of infections. In this work, a new mathematical framework for a vaccination game combined with susceptible-infected-recovered (SIR) and unaware-aware (UA) situation is considered. Altering wearing mask or taking protection against diseases, we consider the information spreading effect that might be represented the situation of self-protection. The information spreading is supposed only for local situation for a season, but has a very significant effect to reduce the infection through a generation. Within this concept, unaware and aware states are taken for susceptible, infected and vaccinated individuals for an infinite and well mixed population. Moreover, three different strategy updating rules concerning whether an individual committing or not vaccination: individual based, strategy based and direct selection are studied to show the comparison by depicting as full phase diagram. Finally, it can be seen that information spreading can subdue the spreading of epidemic within a population.

DOI： 10.1016/j.chaos.2018.12.023

Language：English   Publishing type：Research paper (scientific journal)  

We explore a mathematical framework of the vaccination game taking into account spatial structure, say, and degree distribution amid individuals. The framework presumes SIR/V dynamics in a season, which is followed by a strategy update process that estimates whether an individual will take a protecting measure, considering imperfect vaccination or defense against contagion. The numerical result based on multi-agent simulations (MAS) validates our theory, suggesting that a more heterogeneous spatial structure is vulnerable to an epidemic. This conclusion is consistent with the qualitative knowledge that a pandemic arises more easily in a scale-free network than in homogeneous networks because of the negative contribution of hub agents acting as super spreaders.

DOI： 10.1088/1742-5468/aae84f

Language：English   Publishing type：Research paper (scientific journal)  

The purpose of this study was to investigate, in the human respiratory tract, the flow patterns and adsorption flux (deposition flux) distributions of volatile organic compounds (VOCs) generated by the use of electronic cigarettes (e-cigarettes) through the application of a three-dimensional computational fluid dynamics (CFD) analysis. Two types of human respiratory tract models, which give detailed respiratory tract geometries were reproduced in this study using computed tomography data, for the CFD analysis of inhalation exposure. Complicated flow patterns, nonuniform distributions of VOC concentrations, and heterogeneous adsorption flux distributions were determined within the human respiratory tract models, and individual specificity was confirmed. The CFD simulation results of adsorption flux distributions on the epithelium tissue surfaces of airways denoted the probability distributions of inhalation exposure in respiratory tracts, and high adsorption flux sites representing ‘hot spots’ were delineated for tissue doses of VOCs generated from smoking e-cigarettes. Furthermore, dispersion and diffusion of VOCs in an indoor environment due to exhalation of the vapour phase of e-cigarette emissions were analysed by using a computer-simulated person with a numerical respiratory tract model through an integrated and contiguous analysis of inhalation and exhalation modes during e-cigarette smoking.

DOI： 10.1177/1420326X17694476

Language：Japanese   Publishing type：Research paper (scientific journal)  

In the recent decades, stricter regulation for cigarette industry has been established due to serious health effect of tobacco smoke which contains various harmful chemical compounds, and electric cigarette (e-cigarette, vape) which is composed of e-liquid and heating device has been widely popularized throughout the world. Although e-liquid mainly contains nicotine and some additives, it was reported that aldehydes occurred by heating e-liquid cause health risks for e-cigarette users (first-hand smokers) and second-hand smokers. The purpose of this research is to develop a comprehensive prediction method for quantitative estimation of respiratory exposure risks to e-cigarette smoke. Previously, we have developed in silico computer simulated person(CSP) which is reproduced actual shape of human body and respiratory tract in detail. The CSP, which was prepared for the numerical analysis, was integrated with CFD analysis in order to predict contaminant transfer in indoors and inside human airway. Moreover, physiologically based pharmacokinetic(PBPK) model was adopted in the airway part of CSP. This PBPK model enables to estimate contaminant adsorption at airway wall surface and contaminant reaction/transfer phenomenon inside airway tissue. Assuming e-cigarette smoker and the other occupant in the simple room, first-hand/second-hand exposure risks of inhaled formaldehyde was estimated under the unsteady breathing condition.
As a result, it was revealed that 39% of inhaled formaldehyde was adsorbed into airway wall surface, and 47% was reached to the lungs through the bronchioles. 11% of inhaled formaldehyde was re-discharged from the airway when the breathing cycle is in the exhalation mode. This formaldehyde was reached to the other occupant, and 2% of the exhaled formaldehyde from e-cigarette smoker was inhaled into occupant's airway.
This study demonstrated a comprehensive analysis of inhalation exposure, especially first-hand/second-hand exposure risks in indoor space. The movement of first-hand e-cigarette smoke in the human airway and its health risk was quantitatively analyzed by using PBPK-CFD hybrid analysis. Moreover, transfer phenomenon of the second-hand e-cigarette smoke in indoor space, and second-hand exposure risk were simultaneously estimated. We believe the in silico human model(CSP) integrated with PBPK-CFD hybrid analysis has great potential for inhalation exposure risks assessment of e-cigarette smoke.

DOI： https://doi.org/10.3130/aije.83.1005

Language：English   Publishing type：Research paper (scientific journal)  

We consider two imperfect ways to protect against an infectious disease such as influenza, namely vaccination giving only partial immunity and a defense against contagion such as wearing a mask. We build up a new analytic framework considering those two cases instead of perfect vaccination, conventionally assumed as a premise, with the assumption of an infinite and well-mixed population. Our framework also considers three different strategy-updating rules based on evolutionary game theory: conventional pairwise comparison with one randomly selected agent, another concept of pairwise comparison referring to a social average, and direct alternative selection not depending on the usual copying concept. We successfully obtain a phase diagram in which vaccination coverage at equilibrium can be compared when assuming the model of either imperfect vaccination or a defense against contagion. The obtained phase diagram reveals that a defense against contagion is marginally inferior to an imperfect vaccination as long as the same coefficient value is used.

DOI： 10.1088/1742-5468/aaac3c

Language：English   Publishing type：Research paper (scientific journal)  

In vivo studies involving mammal surrogate models for toxicology studies have restrictions related to animal protection and ethics. Computer models, i.e., in silico models, have great potential to contribute towards essential understanding of heat and mass transfer phenomena in respiratory tracts in place of in vivo and in vitro studies. Here, we developed numerical upper airway models of a rat, a dog, a monkey, and two humans by using computed tomography data and then applied computational fluid dynamics analysis. Convective heat transfer coefficients were precisely analysed as a function of breathing airflow rate. Based on the computational fluid dynamics simulation results, the correlations between Nusselt (Nu) number and the product of the Reynolds (Re) and Prandtl (Pr) numbers were summarized. The heat transfer efficiency (order of hc and correlation of Nu and RePr) in the upper airway of the dog seems to match those of the human models. On the other hand, the results for the rat and monkey showed clear differences compared with those of human models. The identified fundamental qualities of convective heat transfer phenomena in airways for rats, dogs, monkeys, and humans, have enabled discussions about quantitative differences of heat and mass transfer efficiency between different animals/species.

DOI： 10.1177/1420326X16662111

Event date： 2023.5

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Venue：Tenjin   Country：China  

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