Characterizing particle deposition in the airways of the human lungs is essential to evaluate the health effects of particulate air pollution. However, lung deposition is rather complicated, and its ...main influencing factors remain unclear. Hence, this study applied computational fluid dynamics (CFD) to investigate the roles of airflow (Reynolds number Re = 100-2000) and particle size (1-10 μm) in deposition using a human tracheobronchial airway model (G3-G6). We calculated the deposition efficiency (DE) based on two mechanisms, inertial impaction (DE_i) and gravitational sedimentation (DE_g), which produced hot spots around the bifurcations and uniform distributions along the tube, respectively. Furthermore, as the particle size increased, DE_i grew rapidly, whereas DE_g grew log-linearly. Particles that were less than 2 μm in diameterμ only penetrated deep in the lungs where the airflow rate was low, but 3 μm particles were more likely to settle in this region owing to the combination of gravitational sedimentation and inertial impaction. Larger particles, on the other hand, mainly deposited in the proximal bifurcations as a result of inertial impaction. Additionally, the deposition due to inertial impaction and that due to gravitational sedimentation primarily depended on the Stokes number (S_t) and the ratio of S_t to Re^2, respectively. The orientation of the human body was another potential factor in the pattern of deposition, although the upright and lateral positions exhibited similar deposition efficiencies for 3 μm particles regardless of Re. These findings identify the critical Reynolds number at which the particle deposition mechanism for a specific size shifts from gravitation to inertia.
An immersed boundary method (IBM) has been developed to handle the solid body embedded flowfield simulation for compressible reactive flows, paving the way of application for a wide range of ...fluid–solid interaction problems. Previously, the Brinkman penalization method (BPM), originated from porous media flows, has been successfully used for incompressible Navier–Stokes equations by adding penalization terms to momentum equations. However, it is nontrivial to solve the compressible form due to the penalized continuity equation that usually poses severe numerical stiffness. In order to circumvent this issue, an extending procedure for relevant variables from the fluid to solid domain is considered, by analyzing the ordinary differential equations remained after operator splitting. Density can be then determined with the help of an equation of state (EoS). Meanwhile, efforts of enforcing the Neumann boundary condition, for example, the adiabatic wall condition, on the fluid–solid interface can be minimized by extending temperature across the interface directly. One more advantage of the extending step lies in that it can quickly reach a steady state when performed within a narrow band around the interface. Implemented into an adaptive Cartesian grid‐based flow solver for compressible Navier–Stokes equations with chemical reaction source terms, the present variable‐extended IBM is validated by numerical examples ranging from single‐species nonreactive to multispecies detonative flows in one‐ and two‐dimensional domains. Numerical results show (1) the successful specification of slip or nonslip, adiabatic or isothermal wall condition on the fluid–solid interface and (2) loss of total energy in the original BPM being avoided and the numerical accuracy being improved especially for energy‐sensitive reactive flows.
This paper investigates the behavioral additionality effects of a unique high‐ and new‐ technology enterprise (HNTE) program in China. The program provides a reduced corporate income tax to ...certificated HNTEs. By distinguishing research expenses from development costs, we examine if the tax incentive program affects firms’ composition of R&D investment, based on a sample of Chinese listed firms. The results indicate that the tax incentive program encourages firms to focus more on development than on research. The effects are also found to be heterogeneous among the first‐time, repeated, and one‐time certification users. The results imply that tax incentives prompt firms to invest in short‐term development opportunities with promising private returns. Conversely, they are less likely to stimulate risky research projects with potential high rates of social and long‐term economic returns. Our study highlights the importance of understanding the behavioral additionality effects for innovation policy evaluations and better policy designs.
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•Supramolecular hydrogels formed using by different construction methods with cucurbitnurils are classified.•The excellent properties possessed by hydrogels, such as biocompatibility, ...self-healing, and stimulus responsiveness, are discussed.•The different hydrogels are classified according to their applications, with a focus on their biomedical use.
Due to their dynamic qualities and potential uses in fields such as biomedicine, tissue engineering, drug delivery, soft materials, and sensing, hydrogels have gained increased attention in recent years. Concurrently, the application of cucurbitnuril-based host-guest interactions has been crucial in advancing the field of supramolecular chemistry. Given this, there has been a growing number of reports in the literature regarding the formation of hydrogels that are mediated by host-guest interactions between various cucurbitnurils and their guests. This review aims to present comprehensive insights into the creation and advancement of supramolecular hydrogels utilizing cucurbitnuril-mediated design strategies. Firstly, supramolecular hydrogels formed via different construction methods with cucurbitnurils are classified, including (i) outer surface interaction construction and (ii) host-guest construction. Next, the excellent properties possessed by hydrogels, namely biocompatibility, stimulus responsiveness, and self-healing, are discussed. Finally, the different hydrogels are classified according to their applications, with a focus on their biomedical use. We believe that this review highlights the potential for further research based on host-guest interaction-mediated hydrogels.
Although airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been recognized, the condition of ventilation for its occurrence is still being debated. We analyzed ...a coronavirus disease 2019 (COVID-19) outbreak involving three families in a restaurant in Guangzhou, China, assessed the possibility of airborne transmission, and characterized the associated environmental conditions. We collected epidemiological data, obtained a full video recording and seating records from the restaurant, and measured the dispersion of a warm tracer gas as a surrogate for exhaled droplets from the index case. Computer simulations were performed to simulate the spread of fine exhaled droplets. We compared the in-room location of subsequently infected cases and spread of the simulated virus-laden aerosol tracer. The ventilation rate was measured using the tracer gas concentration decay method. This outbreak involved ten infected persons in three families (A, B, C). All ten persons ate lunch at three neighboring tables at the same restaurant on January 24, 2020. None of the restaurant staff or the 68 patrons at the other 15 tables became infected. During this occasion, the measured ventilation rate was 0.9 L/s per person. No close contact or fomite contact was identified, aside from back-to-back sitting in some cases. Analysis of the airflow dynamics indicates that the infection distribution is consistent with a spread pattern representative of long-range transmission of exhaled virus-laden aerosols. Airborne transmission of the SARS-CoV-2 virus is possible in crowded space with a ventilation rate of 1 L/s per person.
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•This outbreak involved ten infected persons in three families.•Full video recording at time of infection allows restoration of the scene.•Time-averaged ventilation rates were only 0.9 L/s per person in the restaurant.•Insufficient ventilation played a role in this outbreak of COVID-19.
Osthole (also known as Osthol) is the main anti‐inflammatory coumarin found in Cnidium monnieri and severs as the exclusive quality‐controlled component according the Chinese Pharmacopoeia. However, ...its underlying anti‐inflammatory mechanism remains unknown. In this study, we demonstrated that Osthole treatment significantly inhibited the generation of TNF‐α, but not IL‐6 in the classical LPS‐stimulated RAW264.7 macrophage model. In addition, LPS induced the activation of both MAPK and NF‐κB signalling pathways, of which the former was dose‐dependently restrained by Osthole via suppressing the phosphorylation of JNK and P38 proteins, while the phosphorylation of IκB and P65 proteins remained unaffected. Interestingly, Osthole dose‐dependently up‐regulated the expression of the key cholinergic anti‐inflammatory pathway regulator α7nAChR, and the TNF‐α inhibition effect of Osthole was also significantly alleviated by the treatment of α7nAChR antagonist methylbetaine. These results demonstrate that Osthole may regulate TNF‐α by promoting the expression of α7nAChR, thereby activate the vagus nerve‐dependent cholinergic anti‐inflammatory pathway.
Improving city breathability has been confirmed as one feasible measure to improve pollutant dilution in the urban canopy layer (UCL). Building height variability enhances vertical mixing, but its ...impacts remain not completely explored. Therefore, both wind tunnel experiments and computational fluid dynamic (CFD) simulations are used to investigate the effect of building height variations (six height standard deviations σH = 0%–77.8%) associated to building packing densities namely λp/λf = 0.25/0.375 (medium-density) and 0.44/0.67 (compact) on city breathability. Two bulk variables (i.e. the in-canopy velocity (UC) and exchange velocity (UE)) are adopted to quantify the horizontal and vertical city breathability respectively, which are normalized by the reference velocity (Uref) in the free flow, typically set at z = 2.5H0 where H0 is the mean building height.
Both flow quantities and city breathability experience a flow adjustment process, then reach a balance. The adjustment distance is at least three times longer than four rows documented in previous literature. The medium-density arrays experience much larger UC and UE than the compact ones. UE is found mainly induced by vertical turbulent fluxes, instead of vertical mean flows. In height-variation cases, taller buildings experience larger drag force and city breathability than lower buildings and those in uniform-height cases. For medium-density and compact models with uniform height, the balanced UC/Uref are 0.124 and 0.105 respectively, moreover the balanced UE/Uref are 0.0078 and 0.0065. In contrast, the average UC/Uref in height-variation cases are larger (115.3%–139.5% and 125.7%–141.9% of uniform-height cases) but UE/Uref are smaller (74.4%–79.5% and 61.5%–86.2% of uniform-height cases) for medium-density and compact models.
•City breathability is assessed by in-canopy velocity (UC) and exchange velocity (UE).•Six building height variations withλp/λf = 0.25/0.375 and 0.44/0.67 are studied.•Flow adjustment distance is much longer than the literature (more than 10 units).•Urban model with λp/λf = 0.25/0.375 produces larger UC and UE than λp/λf = 0.44/0.67.•Taller buildings attain better ventilation but lower ones obtain smaller UC -UE.
By performing unsteady CFD simulations using RNG k–ɛ model and dynamic mesh technique, this paper investigates how the walking motion of health care worker (HCW) influences gaseous dispersion in a ...six-bed isolation room with nine downward supplies and six ceiling-level or floor-level exhausts. The flow near and behind HCW is easily affected by HCW motion. The flow disturbance induced by HCW walking with swinging arms and legs is a mixing process. The walking HCW displaces air in front of it and carries air in the wake forwardly, meanwhile pressure difference drives air from two lateral sides into the wake. HCW motion (0–5.4 s) indeed induces a little gaseous dispersion, but the residual flow disturbance after HCW stops (5.4 s–25.4 s) induces more gaseous agent spread and it requires more than 30–60 s to approximately recover to the initial state after HCW stops.
Although HCW motion indeed affects airborne transmission, but its effect is less important than ventilation design. No matter with or without HCW motion, the ceiling-level exhausts perform much better in controlling airborne transmission than the floor-level exhausts with the same air change rate (12.9 ACH). Smaller air change rate of 6 ACH experiences higher concentration and more gaseous spread than 12.9 ACH. In contrast to the realistic human walking, the simplified motion of a rectangular block produces stronger flow disturbance. Finally surface heating of HCW produces a stronger thermal body plume and enhances turbulence near HCW, thus slightly strengthens airborne transmission.
•Human motion indeed affects airflows and airborne spread in a six-bed isolation room.•But ventilation design is more significant than human motion for gaseous spread.•The flow near and behind HCW is easily affected by HCW motion with a mixing process.•The residual flow after HCW motion induces more gaseous spread than during it.•The simplified motion of a rectangular block produces stronger flow disturbance.
Virus-laden droplets dispersion may induce transmissions of respiratory infectious diseases. Existing research mainly focuses on indoor droplet dispersion, but the mechanism of its dispersion and ...exposure in outdoor environment is unclear. By conducting CFD simulations, this paper investigates the evaporation and transport of solid-liquid droplets in an open outdoor environment. Droplet initial sizes (dp = 10 μm, 50 μm, 100 μm), background relative humidity (RH = 35%, 95%), background wind speed (Uref = 3 m/s, 0.2 m/s) and social distances between two people (D = 0.5 m, 1 m, 1.5 m, 3 m, 5 m) are investigated.
Results show that thermal body plume is destroyed when the background wind speed is 3 m/s (Froude number Fr ~ 10). The inhalation fraction (IF) of susceptible person decreases exponentially when the social distance (D) increases from 0.5 m to 5 m. The exponential decay rate of inhalation fraction (b) ranges between 0.93 and 1.06 (IF=IF0e-b(D-0.5)) determined by the droplet initial diameter and relative humidity. Under weak background wind (Uref = 0.2 m/s, Fr ~ 0.01), the upward thermal body plume significantly influences droplet dispersion, which is similar with that in indoor space. Droplets in the initial sizes of 10 μm and 50 μm disperse upwards while most of 100 μm droplets fall down to the ground due to larger gravity force. Interestingly, the deposition fraction on susceptible person is ten times higher at Uref = 3 m/s than that at Uref = 0.2 m/s. Thus, a high outdoor wind speed does not necessarily lead to a smaller exposure risk if the susceptible person locating at the downwind region of the infected person, and people in outdoors are suggested to not only keep distance of greater than 1.5 m from each other but also stand with considerable angles from the prevailing wind direction.
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•Droplet evaporation and transport in open outdoor space are studied by CFD.•Impacts of relative humidity (RH = 35%,95%) and droplet size (10–100 μm) are tested.•Thermal body plume is destroyed as Uref = 3 m/s while significant as Uref = 0.2 m/s.•Social distances (D = 0.5-5 m) for two face-to-face patients downwind are studied.•Exposure risk exponentially reduces with D at Uref = 3 m/s but exceeds that at 0.2 m/s.
Co(II)-catalyzed C–H C2 selective arylation of indoles with boronic acids through monodentate chelation assistance has been achieved for the first time. The unique features of this methodology ...include mild reaction conditions, highly C2 regioselectivity, and employment of a Grignard reagent-free catalytic system. A wide range of substrates, including unreactive arenes, are well tolerated, which enables the construction of the coupling products efficiently. This new strategy provides an alternative and versatile approach to construct biaryls using inexpensive cobalt catalyst.
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