Modal and strength analysis of coal mine mobile refuge chamber

Structural strength, stiffness, etc. are essential safety performances of mine refuge chamber. In this article, the safety performance of the chamber which is under the impact load was evaluated by the method of numerical analysis. First of all, according to some relative standards, a chamber model was established by applying numerical modeling software. In this way, a method of finite element analysis (FEA) was instituted and we used AUTODUN to simulate the process of transmission of blast waves in the underworkings. On the basis of Fourier transform theory, the spectrum analysis of the blast waves acting on the chamber has been done. In order to obtain the natural frequency, a model analysis of the chamber was made by applying OPTISTRUCT. Then the main frequency and the natural frequency were compared. The result shows that the resonance will not happen so that the safety performance of the chamber meets the demand of engineering safety. The structural strength of the chamber was analyzed by using LS-DYNA, and the result comes out that the pressure throughout the chamber will not cause damage to the chamber. After that, according to the simulation results, we proposed some pieces of advice which will be meaningful for the design and the improvement of the chamber

Influence of variable heat transfer coefficient of fireworks and crackers on thermal explosion critical ambient temperature and time to ignition

To study the effect of variable heat transfer coefficient of fireworks and crackers on thermal explosion critical ambient temperature and time to ignition, considering the heat transfer coefficient as the power function of temperature, mathematical thermal explosion steady state and unsteady-state model of finite cylindrical fireworks and crackers with complex shell structures are established based on two-dimensional steady state thermal explosion theory. The influence of variable heat transfer coefficient on thermal explosion critical ambient temperature and time to ignition are analyzed. When heat transfer coefficient is changing with temperature and in the condition of natural convection heat transfer, critical ambient temperature lessen, thermal explosion time to ignition shorten. If ambient temperature is close to critical ambient temperature, the influence of variable heat transfer coefficient on time to ignition become large. For firework with inner barrel in example analysis, the critical ambient temperature of propellant is 463.88 K and the time to ignition is 4054.9s at 466 K, 0.26 K and 450.8s less than without considering the change of heat transfer coefficient respectively. The calculation results show that the influence of variable heat transfer coefficient on thermal explosion time to ignition is greater in this example. Therefore, the effect of variable heat transfer coefficient should be considered into thermal safety evaluation of fireworks to reduce potential safety hazard

Temperature and Pressure Dependent Rate Coefficients for the Reaction of C₂H₄ + HO₂ on the C₂H₄O₂H Potential Energy Surface

The potential energy surface (PES) for reaction C₂H₄ + HO₂ was examined by using the quantum chemical methods. All rates were determined computationally using the CBS-QB3 composite method combined with conventional transition state theory­(TST), variational transition-state theory (VTST) and Rice–Ramsberger–Kassel–Marcus/master-equation (RRKM/ME) theory. The geometries optimization and the vibrational frequency analysis of reactants, transition states, and products were performed at the B3LYP/CBSB7 level. The composite CBS-QB3 method was applied for energy calculations. The major product channel of reaction C₂H₄ + HO₂ is the formation C₂H₄O₂H via an OH^···π complex with 3.7 kcal/mol binding energy which exhibits negative-temperature dependence. We further investigated the reactions related to this complex, which were ignored in previous studies. Thermochemical properties of the species involved in the reactions were determined using the CBS-QB3 method, and enthalpies of formation of species were compared with literature values. The calculated rate constants are in good agreement with those available from literature and given in modified Arrhenius equation form, which are serviceable in combustion modeling of hydrocarbons. Finally, in order to illustrate the effect for low-temperature ignition of our new rate constants, we have implemented them into the existing mechanisms, which can predict ethylene ignition in a shock tube with better performance

Temperature and Pressure Dependent Rate Coefficients for the Reaction of C₂H₄ + HO₂ on the C₂H₄O₂H Potential Energy Surface

The potential energy surface (PES) for reaction C₂H₄ + HO₂ was examined by using the quantum chemical methods. All rates were determined computationally using the CBS-QB3 composite method combined with conventional transition state theory­(TST), variational transition-state theory (VTST) and Rice–Ramsberger–Kassel–Marcus/master-equation (RRKM/ME) theory. The geometries optimization and the vibrational frequency analysis of reactants, transition states, and products were performed at the B3LYP/CBSB7 level. The composite CBS-QB3 method was applied for energy calculations. The major product channel of reaction C₂H₄ + HO₂ is the formation C₂H₄O₂H via an OH^···π complex with 3.7 kcal/mol binding energy which exhibits negative-temperature dependence. We further investigated the reactions related to this complex, which were ignored in previous studies. Thermochemical properties of the species involved in the reactions were determined using the CBS-QB3 method, and enthalpies of formation of species were compared with literature values. The calculated rate constants are in good agreement with those available from literature and given in modified Arrhenius equation form, which are serviceable in combustion modeling of hydrocarbons. Finally, in order to illustrate the effect for low-temperature ignition of our new rate constants, we have implemented them into the existing mechanisms, which can predict ethylene ignition in a shock tube with better performance

Genetic Analysis of the Role of Tumor Necrosis Factor Receptors in Functional Outcome after Traumatic Brain Injury in Mice

We previously reported that tumor necrosis factor-α (TNF-α) and Fas receptor induce acute cellular injury, tissue damage, and motor and cognitive deficits after controlled cortical impact (CCI) in mice (Bermpohl et al. 2007); however, the TNF receptors (TNFR) involved are unknown. Using a CCI model and novel mutant mice deficient in TNFR1/Fas, TNFR2/Fas, or TNFR1/TNFR2/Fas, we tested the hypothesis that the combination of TNFR2/Fas is protective, whereas TNFR1/Fas is detrimental after CCI. Uninjured knockout (KO) mice showed no differences in baseline physiological variables or motor or cognitive function. Following CCI, mice deficient in TNFR2/Fas had worse post-injury motor and Morris water maze (MWM) performance than wild-type (WT) mice (p < 0.05 group effect for wire grip score and MWM performance by repeated measures ANOVA). No differences in motor or cognitive outcome were observed in TNFR1/Fas KO, or in TNFR2 or TNFR1 single KO mice, versus WT mice. Additionally, no differences in propidium iodide (PI)-positive cells (at 6 h) or lesion size (at 14 days) were observed between WT and TNFR1/Fas or TNFR2/Fas KO mice. Somewhat surprisingly, mice deficient in TNFR1/TNFR2/Fas also had PI-positive cells, lesion size, and motor and MWM deficits similar to those of WT mice. These data suggest a protective role for TNFR2/Fas in the pathogenesis of TBI. Further studies are needed to determine whether direct or indirect effects of TNFR1 deletion in TNFR2/Fas KO mice mediate improved functional outcome in TNFR1/TNFR2/Fas KO mice after CCI