It is of great significance to study the force model of flake and spherical particles in a two-phase flow system for reducing dust hazards. In present work, the correspondence between drag ...coefficient Cd and Re for spherical particle is specified by a new CFD method. Moreover, 144 kinds distribution states for flake particle with equal probability are summarized into 7 kinds stress state models with different occurrence probabilities, and the corresponding relationship between the equivalent drag coefficient Cd and the equivalent Reynolds number Re is further obtained. A series of ventilation and dust removal experiments and full-scale numerical simulation in a large space are carried out, and the maximum error of peak dust concentration between the simulation results and the experimental results for flake powder is 17.4%. In addition, the size effect of flake powder is more obvious than that of spherical powder, and the fluidity of flake powder with equal particle size is obviously better than that of spherical powder, so flake powder can be removed from the production workshop faster. However, in the process of ventilation and dust removal, the diffusion risk of spherical dust larger than 100 μm do not change much during the ventilation process.
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•The correspondence between the drag coefficient Cd and Re is specified by CFD.•The distribution states for flake particle are summarized into 7 stress models.•The ventilation experiments and full-scale simulations are carried out.•Flake powder has obvious advantages in dust removal and recovery efficiency.
The chigger mites Leptotrombidium deliense (L. deliense) and Leptotrombidium scutellare (L. scutellare) are two main vectors of mite-borne diseases in China. However, the associated environmental ...risk factors are poorly understood, and the potential geographic ranges of the two mite species are unknown.
We combined an ensemble boosted regression tree modelling framework with contemporary records of mites and multiple environmental factors to explore the effects of environmental variables on both mites, as well as to predict the current and future environmental suitability distributions of both species. Additionally, the human population living in the potential spread risk zones of each species was also estimated across mainland China.
Our results indicated that climate, land cover, and elevation are significantly associated with the spatial distributions of the two mite species. The current environmental suitability distribution of L. deliense is mainly concentrated in southern China, and that of L. scutellare is mainly distributed in southern and eastern coastal areas. With climate warming, the geographical distribution of the two mites generally tends to expand to the north and northwest. In addition, we estimated that 305.1–447.6 and 398.3–430.7 million people will inhabit the future spread risk zones of L. deliense and L. scutellare, respectively, in mainland China.
Our findings provide novel insights into understanding the current and future risks of spread of these two mite species and highlight the target zones for helping public health authorities better prepare for and respond to future changes in mite-borne disease risk.
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•Spatial distributions of L. deliense and L. scutellare were mapped.•Climate is the main factor that influences the distributions of the two mite species.•Future distributions of both species were predicted.•The distributions of the two mites tend to expand in the future.
The severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) is highly contagious, and the coronavirus disease 2019 (COVID-19) pandemic caused by it has forced many countries to adopt ‘lockdown’ ...measures to prevent the spread of the epidemic through social isolation of citizens. Some countries proposed universal mask wearing as a protection measure of public health to strengthen national prevention efforts and to limit the wider spread of the epidemic. In order to reveal the epidemic prevention efficacy of masks, this paper systematically evaluates the experimental studies of various masks and filter materials, summarises the general characteristics of the filtration efficiency of isolation masks with particle size, and reveals the actual efficacy of masks by combining the volume distribution characteristics of human exhaled droplets with different particle sizes and the SARS-CoV-2 virus load of nasopharynx and throat swabs from patients. The existing measured data show that the filtration efficiency of all kinds of masks for large particles and extra-large droplets is close to 100%. From the perspective of filtering the total number of pathogens discharged in the environment and protecting vulnerable individuals from breathing live viruses, the mask has a higher protective effect. If considering the weighted average filtration efficiency with different particle sizes, the filtration efficiencies of the N95 mask and the ordinary mask are 99.4% and 98.5%, respectively. The mask can avoid releasing active viruses to the environment from the source of infection, thus maximising the protection of vulnerable individuals by reducing the probability of inhaling a virus. Therefore, if the whole society strictly implements the policy of publicly wearing masks, the risk of large-scale spread of the epidemic can be greatly reduced. Compared with the overall cost of social isolation, limited personal freedoms and forced suspension of economic activities, the inconvenience for citizens caused by wearing masks is perfectly acceptable.
The rafting behaviour of the red imported fire ant, Solenopsis invicta, in response to flooding events is well documented, although studies generally have focussed on the mechanisms of raft assembly ...and the behaviour of the raft's occupants. Flooding as a means of dispersal of S. invicta is frequently mentioned in the literature, although there are few data on the distances travelled or how effective it is compared to natural flight. In Australia, S. invicta is a priority invasive species with a national eradication program operating for 23 years, focussed on the population in southeast Queensland, which currently encompasses more than 700 000 ha. Flooding presents a risk to the success of the program through extending the infestation area or recolonising successfully treated areas. We used the program's extensive spatiotemporal dataset of known fire ant colony locations to assess the effects of two significant flood events on the dispersal or displacement of S. invicta in Queensland. Results indicated that flooding did not spread S. invicta beyond the known boundaries of infestation but contributed to localised spread, particularly for sites with known polygyne infestations. This situation could change if the ant spreads to new river catchments. A novel method developed to assess the risk of S. invicta dispersal through flooding is presented, alongside program actions that can be applied to mitigate this risk.
The risk of fire spread in informal settlements is significant and can be analysed as a function of the spatial arrangement of dwellings. Spatial metrics representing density and shape of dwellings ...are proposed as a method to identify settlements at high risk of fire spread. LiDAR data is used to map dwelling roofs for informal settlements in the City of Cape Town, South Africa. The LiDAR roof dataset is validated against a visually interpreted dataset digitised from 6 cm resolution aerial photography and is found to have an overall completeness and correctness accuracy of greater than 75% with systematic underrepresentation of roofs in the LiDAR dataset. Correlation analysis of metrics derived from the LiDAR dataset and the reference dataset indicates that only the edge density and landscape density metrics could be applied with confidence to all the settlements. These two metrics are then applied to the informal settlements of Kosovo and Imizamo Yethu. A high landscape density in combination with a low edge density is found to be indicative of fire spread risk. This study represents a first step in the development of spatial metrics for understanding informal settlement fire spread risk.
•Spatial metrics proposed for fire spread risk in informal settlements.•LiDAR dataset used to map dwellings in informal settlement in Cape Town.•LiDAR derived spatial metrics of landscape density and edge density reliable.•High landscape density with low edge density may indicate high fire spread risk.
Large scale of fires spreading could occur in urban areas where are consisted of dense wooden buildings. Although it’s urgent need to minimize the fire spreading risks, historical buildings are also ...precious for preserving area’s characteristics. Kanazawa is one of historical cities and has a lot of historical building in its central area. This study estimates fire spreading risks in those historical area and evaluates effectiveness of the disaster prevention projects by the Kanazawa municipality. As the result of the study, it is found the risks are still remain after the projects. We propose some methodologies for minimizing the risks.
Identifying the main environmental drivers of SARS‐CoV‐2 transmissibility in the population is crucial for understanding current and potential future outbursts of COVID‐19 and other infectious ...diseases. To address this problem, we concentrate on the basic reproduction number R0, which is not sensitive to testing coverage and represents transmissibility in an absence of social distancing and in a completely susceptible population. While many variables may potentially influence R0, a high correlation between these variables may obscure the result interpretation. Consequently, we combine Principal Component Analysis with feature selection methods from several regression‐based approaches to identify the main demographic and meteorological drivers behind R0. We robustly obtain that country's wealth/development (GDP per capita or Human Development Index) is the most important R0 predictor at the global level, probably being a good proxy for the overall contact frequency in a population. This main effect is modulated by built‐up area per capita (crowdedness in indoor space), onset of infection (likely related to increased awareness of infection risks), net migration, unhealthy living lifestyle/conditions including pollution, seasonality, and possibly BCG vaccination prevalence. Also, we argue that several variables that significantly correlate with transmissibility do not directly influence R0 or affect it differently than suggested by naïve analysis.
Plain Language Summary
While numerous studies tried to assess the correlations of different factors with the SARS‐CoV‐2, the next step should be predicting the environmental risk of the high transmissibility in a certain population. Specifically, a relatively small number of the most influential meteorological and demographic factors should be selected for a predictive risk measure that is accurate enough and practical for use. To achieve this, we here utilize a combination of Principal Component Analysis and feature selection techniques. We identify that the main drivers behind COVID‐19 transmissibility are the country's wealth/development level corrected by the available indoor space per person and net migration; pollution levels, and some of the unhealthy living factors; spontaneous behavior change due to developing epidemics; weather seasonality; (less significantly) BCG vaccination. On the other hand, we show that several variables that appear significantly related to the disease progression through naive pairwise correlation analysis do not directly influence transmissibility. These results may provide useful guidelines for future strategies of imposing epidemic mitigation measures.
Key Points
Machine learning techniques are utilized to select the most influential environmental factors behind COVID‐19 transmissibility
The country's wealth/development level is identified as the main global predictor of SARS‐CoV‐2 spread in a population
Other important factors are indoor space per person, unhealthy living determinants, spontaneous behavior change, and weather seasonality
Large scale of fires spreading could occur in urban areas where are consisted of dense wooden buildings. Although it’s urgent need to minimize the fire spreading risks, historical buildings are also ...precious for preserving area’s characteristics. Kanazawa is one of historical cities and has a lot of historical building in its central area. This study estimates fire spreading risks in those historical area and evaluates effectiveness of the disaster prevention projects by the Kanazawa municipality. As the result of the study, it is found the risks are still remain after the projects. We propose some methodologies for minimizing the risks.
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