Effects of computational domain on numerical simulation of building fires

Computational fluid dynamics (CFD) modeling (or field modeling) is becoming the main method for numerical simulation of building fires. Among many factors that influence the validity and accuracy of CFD simulation results, the computational domain is sometimes overlooked. In this article, the effects of computational domain on simulation results are analyzed. Simulation results from the use of different domains are compared with experimental data reported in the literature. A parametric study is then conducted to reveal a relationship between the effective domain extension and the heat release rate of the enclosure fire. The effect of computational domain extension in relation to vent opening is also investigated. It is found that the selection of computational domain can have a significant effect on the outcome of enclosure fire simulations. Determination of the appropriate computational domain without unduly sacrificing computational efficiency is also discussed

Combustion of laminar non-premixed acetylene jet at two different altitudes

In this article, the influence of pressure variation due to altitude change on flames is studied. A series of largely buoyancy-driven acetylene jet fire experiments was conducted at two places in China, namely Lhasa and Hefei, with altitudes of 3658 m and 50 m, respectively. A range of parameters, including flame height, flame and plume centerline temperatures, transmittance through smoke, and irradiance were measured and compared. The flame height at low altitude is higher than that at high altitude. The centerline temperatures of the flame and plume regions exhibit opposite variations with pressure. The soot mass concentration resolved by transmittance measurement follows a weaker power-law dependence on pressure under substandard atmospheric pressure than under pressure greater than standard atmospheric pressure. The radiation heat flux produced from flames of the same burning rate displays a positive proportionality to pressure

Differential bone remodeling mechanism in hindlimb unloaded and hibernating Daurian ground squirrels: a comparison between artificial and natural disuse within the same species

International audienceLoss of bone mass can occur in mammals after prolonged disuse but the situation for hibernators that are in a state of torpor for many months of the year is not yet fully understood. The present study assesses the bone remodeling mechanisms present in Daurian ground squirrels (Spermophilus dauricus) during hibernation as compared with a model of hindlimb disuse. Differences in microstructure, mechanical properties, bone remodeling-related proteins (Runx2, OCN, ALP, RANKL, CTK and MMP-9) and key proteins of Wnt/beta-catenin signaling pathway (GSK-3 beta and phospho-beta-catenin) were evaluated in ground squirrels under 3 conditions: summer active (SA) vs. hibernation (HIB) vs. hindlimb unloaded (HLU). The results indicated that the body weight in HLU ground squirrels was lower than the SA group, and the middle tibia diameter in the HLU group was lower than that in SA and HIB groups. The thickness of cortical and trabecular bone in femurs from HLU ground squirrels was lower than in SA and HIB groups. Most parameters of the tibia in the HLU group were lower than those in SA and HIB groups, which indicated cortical bone loss in ground squirrels. Moreover, our data showed that the changes in microscopic parameters in the femur were more obvious than those in the tibia in HLU and HIB ground squirrels. The levels of Runx2 and ALP were lower in HLU ground squirrels than SA and HIB groups. The protein levels of OCN were unchanged in the three groups, but the protein levels of ALP were lower in the HLU group than in SA and HIB groups. RANKL, CTK and MMP-9 protein levels were significantly decreased in tibia of HLU ground squirrels as compared with SA and HIB groups. In addition, the protein expression levels of RANKL, CTK and MMP-9 showed no statistical difference between SA and HIB ground squirrels. Thus, the mechanisms involved in the balance between bone formation and resorption in hibernating and hindlimb unloading ground squirrels may be different. The present study showed that in femur, the Wnt signaling pathway was inhibited, the protein level of GSK-3 beta was increased, and the protein expression of phospho-beta-catenin was decreased in the HIB group as compared with the SA group, which indicates that the Wnt signaling pathway has a great influence on the femur of the HIB group. In conclusion, the natural anti-osteoporosis properties of Daurian ground squirrels are seasonal. The squirrels do not experience bone loss when they are inactive for a long time during hibernation, but the mechanisms of anti-osteoporosis did not work in HLU summer active squirrels

Integrated transcriptomics and metabolomics reveal protective effects on heart of hibernating Daurian ground squirrels

International audienceAbstract Hibernating mammals are natural models of resistance to ischemia, hypoxia‐reperfusion injury, and hypothermia. Daurian ground squirrels ( spermophilus dauricus ) can adapt to endure multiple torpor‐arousal cycles without sustaining cardiac damage. However, the molecular regulatory mechanisms that underlie this adaptive response are not yet fully understood. This study investigates morphological, functional, genetic, and metabolic changes that occur in the heart of ground squirrels in three groups: summer active (SA), late torpor (LT), and interbout arousal (IBA). Morphological and functional changes in the heart were measured using hematoxylin‐eosin (HE) staining, Masson staining, echocardiography, and enzyme‐linked immunosorbent assay (ELISA). Results showed significant changes in cardiac function in the LT group as compared with SA or IBA groups, but no irreversible damage occurred. To understand the molecular mechanisms underlying these phenotypic changes, transcriptomic and metabolomic analyses were conducted to assess differential changes in gene expression and metabolite levels in the three groups of ground squirrels, with a focus on GO and KEGG pathway analysis. Transcriptomic analysis showed that differentially expressed genes were involved in the remodeling of cytoskeletal proteins, reduction in protein synthesis, and downregulation of the ubiquitin‐proteasome pathway during hibernation (including LT and IBA groups), as compared with the SA group. Metabolomic analysis revealed increased free amino acids, activation of the glutathione antioxidant system, altered cardiac fatty acid metabolic preferences, and enhanced pentose phosphate pathway activity during hibernation as compared with the SA group. Combining the transcriptomic and metabolomic data, active mitochondrial oxidative phosphorylation and creatine‐phosphocreatine energy shuttle systems were observed, as well as inhibition of ferroptosis signaling pathways during hibernation as compared with the SA group. In conclusion, these results provide new insights into cardio‐protection in hibernators from the perspective of gene and metabolite changes and deepen our understanding of adaptive cardio‐protection mechanisms in mammalian hibernators

Underestimated health risks: polystyrene micro- and nanoplastics jointly induce intestinal barrier dysfunction by ROS-mediated epithelial cell apoptosis

Abstract Background Micro- and nanoplastic pollution has become a global environmental problem. Nanoplastics in the environment are still hard to detect because of analysis technology limitations. It is believed that when microplastics are found in the environment, more undetected nanoplastics are around. The current “microplastic exposure” is in fact the mixture of micro- and nanoplastic exposures. Therefore, the biological interaction between organisms among different sizes of micro- and nanoplastics should not be neglected. Results We measured the biodistribution of three polystyrene (PS) particles (50 nm PS, PS50; 500 nm PS, PS500; 5000 nm PS, PS5000) under single and co-exposure conditions in mice. We explored the underlying mechanisms by investigating the effects on three major components of the intestinal barrier (the mucus layer, tight junctions and the epithelial cells) in four intestine segments (duodenum, jejunum, ileum and colon) of mice. We found that the amounts of both PS500 and PS5000 increased when they were co-exposed with PS50 for 24 h in the mice. These increased amounts were due primarily to the increased permeability in the mouse intestines. We also confirmed there was a combined toxicity of PS50 and PS500 in the mouse intestines. This manifested as the mixture of PS50 and PS500 causing more severe dysfunction of the intestinal barrier than that caused by PS50 or PS500 alone. We found that the combined toxicity of PS micro- and nanoplastics on intestinal barrier dysfunction was caused primarily by reactive oxygen species (ROS)-mediated epithelial cell apoptosis in the mice. These findings were further confirmed by an oxidants or antioxidants pretreatment study. In addition, the combined toxicity of PS micro- and nanoplastics was also found in the mice after a 28-day repeated dose exposure. Conclusions There is a combined toxicity of PS50 and PS500 in the mouse intestines, which was caused primarily by ROS-mediated epithelial cell apoptosis in the mice. Considering that most recent studies on PS micro- and nanoplastics have been conducted using a single particle size, the health risks of exposure to PS micro- and nanoplastics on organisms may be underestimated