Explosive Behavior Research Articles

Dynamic analysis of flame propagation velocity at the initial stage of gasoline-air explosion in a tube with an open end

Gasoline-air explosion in confined space is a process involving complex fluid mechanics and explosion mechanics. The flame behavior of gasoline-air explosion in a tube with an open end is mainly discussed in this paper. Firstly, on the basis of experimental observation and theoretical analysis, the axial position of the flame front, the flame velocity and the duration of the spherical flame are deduced and calculated. Then, the validity of the theoretical analysis is verified by comparing the theoretical calculation with the experimental data. The results show that the flame velocity is about 2.29m/s at the initial stage of gasoline-air explosion in the tube. The duration of the spherical flame is about 11.7ms. The conclusions of this paper can not only provide valuable data reference for combustible gas explosion safety engineering, fire protection design and evaluation, but also lay a foundation for further research on the flame behavior of gasoline-air explosion in the tubes with an open end.

Multiple Venting Behavior of Inner Dust Explosions

Multiple Venting Behavior of Inner Dust Explosions

Impact of Elevated Temperatures on the Performance of High-Strength Engineered Cementitious Composite

Engineered cementitious composite (ECC) is a relatively recent construction material with characteristics of high ductility and energy dissipation capacity. Such ductility is fulfilled by adding polymeric fibers, such as polypropylene (PP), polyethylene (PE), and polyvinyl alcohol (PVA) fibers, which would inevitably experience fusion under fire. This paper focuses on the behavior deterioration of postexposure high-strength engineered cementitious composite (HSECC). Color change, surface cracking, and spalling phenomena of HSECC specimens were inspected after specimens exposed to 200°C, 400°C, 600°C, 800°C, and 1,200°C for 1 h. Weight loss, residual compressive/flexural strength, and failure modes of cubes were evaluated correspondingly. Experimental results indicated that the threshold temperature for HSECC to crack is lowered in comparison with ECC of normal strength, whereas explosive spalling behavior could still be prevented effectively with 2.0 vol% PVA fiber. The loss ratio of weight and strength in HSECC was lower than that in ECC, but the failure modes under compression were found to be more catastrophic. HSECC exhibits lower intensity in an X-ray diffraction (XRD) curve than that of ECC. Apparent needle-like channels were observed beyond 400°C, then were gradually filled with reaction products ascribed to the synergistic effect of thermal expansion, volume increase caused by chemical reactions and pore-structure coarsening, and manifested by the results of mercury intrusion porosimetry (MIP).

Thermal explosion characteristics of a combustible gas containing fuel droplets

This paper investigated the critical ignition conditions of combustible gas containing liquid fuel droplets. The analysis is done based on the criteria of the thermal explosion theory. It includes analytical and numerical solutions of modeling equations of fuel droplets heating and evaporation by convection and radiation from the surrounding reactive hot gas. The exothermic reaction is usually modeled as a single-step reaction obeying an Arrhenius temperature dependence. The thermal conductivity of the fuel droplet is dependent on temperature. The analytical solution produced relations between the main critical characteristic parameters in all planes of the solution. The results obtained from investigating the effect of the characteristic parameters on the explosion behavior of gas and fuel droplets and the thermal radiation proved that both of them are significant. The study proved that the criticality definitions of the thermal explosion of a single-phase system can be used effectively and efficiently to determine the critical conditions of a multi-phase system. Finally, the application of the numerical solutions of the modeling equations was used to analyze the explosion characteristics of a diesel fuel spray system.

Experimental Study on Electrical Explosion Behavior of Six Metal Wires in Air and Vacuum

Experimental investigations have been carried out to establish a correlation of energy coupling efficiency in fast electrical explosion of different metals with known electrical and thermophysical properties. To cover a wide range of metal properties, in the present study, five metals (Au, Cu, Al, W, and Ti) are considered from two well-known groups (refractory and non refractory) and palladium is included as sixth metal having intermediate properties between these two. Comparative study is carried out for the same circuit parameters (current rate <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx 90 \times 10^{9}$ </tex-math></inline-formula> A/s) to explore electrically exploding wire (EEW) behavior of these metals in two different media: air and vacuum. Temporal evolution of self-emitted light around these metal wires is analyzed as a qualitative measure for energy diversion from the metal core to outer corona and is recorded using streak camera for both media. In air, refractory and non refractory metals are seem to exhibit different behavior as inferred from voltage profiles, time of burst, temporal optical emission profiles, and overheating factor (the ratio of energy deposited till burst to the enthalpy of atomization). Overheating in air is found to depend inversely on the enthalpy of atomization and resistivity for refractory and non refractory metals, respectively. Pd has shown mixed electrical and optical characteristics of both groups (refractory and non refractory) in air as well as in vacuum. On changing the surrounding medium from air to vacuum, overheating is found to decrease for all metals; interestingly, their drop is observed to depend on the speed of sound at room temperature in that particular metal. Using these experimental outcomes, the possible mechanisms responsible for energy diversion in the explosion of wires of different materials along with their correlation to surrounding medium are discussed in this work. In the present study, the electrical characteristics of gold have been found to be most favorable for efficient energy coupling and hence for high-energy-density applications irrespective of the surrounding medium.

Effect of ion motion on breaking of longitudinal relativistically strong plasma waves: Khachatryan mode revisited

The effect of ion motion on the spatiotemporal evolution of a relativistically strong space charge wave is studied using a 1D fluid simulation code. In our simulation, these waves are excited in the wake of a rigid electron beam propagating through a cold homogeneous plasma with a speed close to the speed of light. It is observed that the excited wave is a mode as described by Khachatryan [Phys. Rev. E 58, 7799–7804 (1998)] whose profile gradually sharpens and the wave eventually breaks after several plasma periods exhibiting explosive behavior. It is found that breaking occurs at amplitudes, which is far below the breaking limit analytically derived by Khachatryan [Phys. Rev. E 58, 7799–7804 (1998)]. This phenomenon of wave breaking, at amplitudes well below the breaking limit, is understood in terms of phase mixing of the excited wave. It is further found that the phase mixing time (wave breaking time) inversely scales with the energy density of the wave.

Bubbles in Ethereum

We apply the (Phillips et al., 2015a,b) methodology to date-stamp bubbles in the Ethereum blockchain. Our analysis of the drivers of fundamental value suggests that the explosive behavior documented in ether prices does not constitute speculative bubbles but reflects the abrupt rally of demand for the use of the Ethereum Virtual Machine tied to the development of the decentralized application (dApp) ecosystem.

Price Appreciation and Roughness Duality in Bitcoin: A Multifractal Analysis

Since its launch in 2009, bitcoin has thrived, attracting the attention of investors, regulators, academia, and the public in general. Its price dynamics, characterized by extreme volatility, severe jumps, and impressive long-term appreciation, suggest that bitcoin is a new digital asset. This study presents a comprehensive overview of the fractality of bitcoin in a high-frequency framework, namely by applying Multifractal Detrended Fluctuation Analysis (MF-DFA) and a Multifractal Regime Detecting Method (MRDM) to Bitstamp 1 min bitcoin returns from January 2013 to July 2020. The results suggest that bitcoin is multifractal, with smaller and larger fluctuations being persistent and anti-persistent, respectively. Multifractality comes from significant long-range correlations, which cast some doubts on the informational efficiency at this frequency, but mainly comes from fat-tails, which highlights the significant risks undertaken by investors in this market. Our most important result is that the degree and richness of multifractality is time-varying and increased after 2017, when volumes and prices experienced an explosive behaviour. This complexity puts into perspective the duality of bitcoin: while it is characterized by long-run attractiveness and increasing valuation, it also has a high short-run instability. Hence, this study provides some empirical evidence supporting the relationship between these two observable features.

Experimental research on the spalling behaviour of ultra-high performance concrete under fire conditions

Explosive spalling is a severe risk for ultra-high performance concrete (UHPC) structures exposed to fire, fundamentally obstructing the comprehensive study of fire safety and the extensive engineering application of UHPC. In contrast to previous studies on the optimisation of components and mixture properties, this paper proposes a new curing regime, two-stage hot air curing (THAC), to inhibit the explosive spalling of UHPC in a high stress state and under an extreme heating rate. Two hundred and twenty-eight UHPC cubes with variations in parameters such as curing regime, fibre type, and water-binder ratio were tested under the ISO 834 fire standard. The influence of THAC on the mechanical properties and explosive spalling of the samples was investigated, and scanning electron microscopy (SEM) was utilised to observe the microstructures of the tested cubes. On this basis, twelve full-scale UHPC beams with various curing regimes and load ratios were tested under thermal–mechanical coupling conditions. The explosive spalling behaviour of the beams was observed, and the influence of spalling on the fire resistance was analysed. The test results indicated that UHPC formed a dense microstructure during the first stage of 50 °C curing. With hot air curing at 150 °C, further hydration and pozzolanic reaction of residual cement and mineral admixtures could be activated, generating massive calcium-silica-hydrate (C-S-H) gels. Moreover, almost all the free water could be consumed and evaporated after THAC curing, dramatically improving the explosive spalling resistance of UHPC. THAC could completely prevent the fire-induced explosive spalling of UHPC of different sizes and with varying stress states and improve the mechanical properties. This occurred despite conventional curing such as standard curing, water curing, and steam curing potentially leading to more serious spalling and a significant reduction in fire resistance, even possibly affecting the failure mode of UHPC beams.

Top–down control on eruptive style at Masaya volcano inferred from melt composition

Highly explosive Plinian eruptions of basaltic magma are enigmatic because low melt viscosities should inhibit such eruptive style. Masaya volcano, Nicaragua, is a persistently active basaltic system capable of a wide range of eruptive styles, from open-conduit lava lake activity to voluminous Plinian eruptions; it is thus an ideal natural laboratory to constrain potential controls on basaltic eruption style. Here we report the major, trace, and volatile (CO2, H2O, S, Cl, F) element composition of olivine-, plagioclase- and clinopyroxene-hosted melt inclusions as well as matrix glasses from lava lake ejecta and two Plinian tephra deposits—the 2.1 ka Masaya Triple Layer and the 1.8 ka Ticuantepe Lapilli—to test whether pre-eruptive volatile contents and degassing history may be linked to eruptive style. All samples display a relatively narrow and largely overlapping basaltic–basaltic andesitic compositional range (51.7±1.0 wt.% SiO2, 4.8±0.4 wt.% MgO) with similar trace element signatures (e.g., Ce/Y=0.82±0.10, Ba/La=74±11). However, lava lake and Plinian samples show systematic differences in pre-eruptive volatile contents, forming distinct groups with mean H2O contents of 0.6±0.2 wt.% (lava lake), 1.1±0.2 wt.% (Masaya Triple Layer), and 1.9±0.3 wt.% (Ticuantepe Lapilli). Together, these groups generate broad positive correlations between S, Cl and H2O concentrations, with maximum values reaching 920 ppm, 1300 ppm and 2.3 wt.%, respectively, which are low compared to typical Central American arc magmas. Magma temperature estimates overlap and average at 1115±30°C, while volatile saturation pressures are low, mainly <100 MPa, although only lava lake samples record pressures <31 MPa. These observations reiterate the compositionally buffered state of the volcano's magmatic system highlighted by previous work and demonstrate that — regardless of eruption style — all Masaya magmas undergo variable, but extensive, pre-eruptive degassing at low pressure. Geohygrometry, gas emissions, and H2O/Ce–Ba/La systematics suggest initial, undegassed H2O contents on the order of 3.9–5.5 wt.%. Our results imply that pre-eruptive volatile contents are not the culprit for Plinian events at Masaya. Instead, we propose that the volcano's vigorous magma supply is modulated in a top–down manner to produce a wide range of eruptive styles, whereby temporary sealing of the conduit may instigate a transition to explosive behavior. In this model, rapid magma ascent is triggered when the seal eventually breaks from degassing-induced pressurization, yielding high degrees of undercooling, rapid microlite growth, and a dramatic increase in magma viscosity and explosive eruption potential. There may thus be a thin line between open-conduit conditions and Plinian eruptions at Masaya.

Influence of the Oxide gas on thermal decomposing explosion of methyl nitrite based on instantaneous flame characterization

The decomposing explosion behavior and characteristics of methyl nitrite (MN) were investigated by analyzing the instantaneous flame of MN decomposition explosion in this work. The lowest explosion limit of MN decreases with the addition of nitric oxide, nitrous oxide and oxygen. The ternary diagrams of the explosive range for “methyl nitrite/nitrogen/oxide gas” mixtures at 40℃ and 100 kPa were acquired. The transient explosion process was characterized by high-speed video image and emission spectrum at 40℃ and 40 kPa. The results demonstrate that the decomposing explosion mainly includes dehydrogenation and oxidation of the carbonaceous species, reduction of nitric oxide and conversion of the OH radical, which can be divided into two reaction stages. The first stage is transient and lasts less than 50 ms, basically involving the generation of nitric oxide, methanol and formaldehyde, and most reactions of dehydrogenation and nitric oxide reduction. The second stage lasts more than 300 ms, and develops from the cool flame to the yellow flame, mainly involving the combustion reactions of hydrogen and carbon monoxide with the OH radical. The type and concentration of oxide gases affect the generation of key species HNO and OH radicals which in turn have an important impact on the evolution of the explosion.

Testing for exuberance in house prices using data sampled at different frequencies

AbstractWe undertake Monte Carlo simulation experiments to examine the effect of changing the frequency of observations and the data span on the Phillips, P. C. B., S. Shi, and J. Yu. 2015. “Testing for Multiple Bubbles: Historical Episodes of Exuberance and Collapse in the S&amp;P 500.”International Economic Review56 (4): 1043–78 generalised supremum ADF (GSADF) test for explosive behaviour via Monte Carlo simulations. We find that when a series is characterised by multiple bubbles (periodically collapsing), decreasing the frequency of observations is associated with profound power losses for the test. We illustrate the effects of temporal aggregation by examining two real house price data bases, namely the S&amp;P Case–Shiller real house prices and the international real house price indices available at the Federal Reserve Bank of Dallas.

Spectroscopic evidence for a gold-coloured metallic water solution.

Insulating materials can in principle be made metallic by applying pressure. In the case of pure water, this is estimated1 to require a pressure of 48megabar, which is beyond current experimental capabilities and may only exist in the interior of large planets or stars2-4. Indeed, recent estimates and experiments indicate that water at pressures accessible in the laboratory will at best be superionic with high protonic conductivity5, but not metallic with conductive electrons1. Here we show that a metallic water solution can be prepared by massive doping with electrons upon reacting water with alkali metals. Although analogous metallic solutions of liquid ammonia with high concentrations of solvated electrons have long been known and characterized6-9, the explosive interaction between alkali metals and water10,11 has so far only permitted the preparation of aqueous solutions with low, submetallic electron concentrations12-14. We found that the explosive behaviourof the water-alkali metal reaction can be suppressed by adsorbing water vapour at a low pressure of about 10-4millibar onto liquid sodium-potassium alloy drops ejected into a vacuum chamber. This set-up leads to the formation of a transient gold-coloured layer of a metallic water solution covering the metal alloy drops. The metallic character of this layer, doped with around5×1021electrons per cubic centimetre, is confirmed using optical reflection and synchrotron X-ray photoelectron spectroscopies.

A time-varying parameter model for local explosions

Financial and economic time series can feature locally explosive behaviour when bubbles are formed. We develop a time-varying parameter model that is capable of describing this behaviour in time series data. Our proposed dynamic model can be used to predict the emergence, existence and burst of bubbles. We adopt a flexible observation driven model specification that allows for different bubble shapes and behaviour. We establish stationarity, ergodicity, and bounded moments of the data generated by our model. Furthermore, we obtain the consistency and asymptotic normality of the maximum likelihood estimator. Given the parameter estimates in the model, the implied filter is capable of extracting the unobserved bubble process from the observed data. We study finite-sample properties of our estimator through a Monte Carlo simulation study. Finally, we show that our model compares well with existing noncausal models in a financial application concerning the Bitcoin/US dollar exchange rate.

On the explosion characteristics for central and end-wall ignition in hydrogen-air mixtures: A comparative study

To demonstrate the influence of different ignition positions on the explosion characteristics of H2-Air mixtures, a series of experiments at central and end-wall ignition under turbulent and quiescent conditions are carried out in a constant volume spherical container. Three explosion characteristics including explosion time τe, maximum explosion pressure rise rate (dp/dt)max, and maximum explosion pressure pmax are measured and derived from the explosion overpressure curve. The experimental results demonstrate that the explosion hazard with the central ignition is generally stronger than that with the end-wall ignition under quiescent conditions. At lower initial pressure, the difference between two ignition cases is greater. The results show that for central ignition, the energy loss is small, and the explosion behavior is similar to the ideal constant volume explosion. While for end-wall ignition, the interaction between supersonic blast wave and cooling rough wall consumes a large amount of explosive energy. Under turbulent conditions, the increase of the jet pressure pjet and the jet time Tjet leads to the increase of turbulence intensity and duration, which enhances the explosion hazard of central ignition, but restrains the explosion process of end-wall ignition. The difference between the two ignition locations increases with the increase of pjet and Tjet.

Explosion behaviors of hydrogen-nitrous oxide mixtures at reduced initial pressures

In this study, we report the explosion characteristics of H2/N2O mixtures at fuel-lean side and stoichiometric condition in a 113 L cylindrical vessel. Experiments were performed at different sub-atmospherical pressures (P0 =10 kPa–40 kPa). Explosion pressure traces were obtained by a pressure transducer mounted on the wall. Meanwhile, the flame morphology was recorded using schlieren visualization. The maximum explosion pressure (Pmax) and maximum pressure rise rate ((dp/dt)max) were derived and discussed. Results show that two competitive effects (i.e., the adiabatic flame temperature and the molecular number) make the maximum Pmax occurring at φ =0.5—0.6. Linear correlations were found between Pmax and P0. Except the adiabatic flame temperature and flame propagation speed, the flame instability was found to participate in dominating the maximum pressure rise rate. For increased initial pressure, the equivalence ratio of the maximum (dp/dt)max switches to the lean side due to the enhanced flame instability. Depending on different equivalence ratios, both linear and quadratic correlations were found between (dp/dt)max and P0.

Psychopharmacology of Treating Explosive Behavior.

Explosive and aggressive behavior in children can pose safety risks, disturb family functioning, and lead to significant impairments. Pharmacologic management should be based on the first-line treatment of the primary psychiatric diagnoses of the patient and initiated in combination with appropriate psychosocial interventions. Review of the literature suggests that risperidone has the most supporting evidence in the treatment of explosive behavior. Stimulants have been shown to be helpful in the treatment of explosive behavior in attention-deficit/hyperactivity disorder. Medication treatment can be associated with significant side effects and therefore the risks and benefits of medication management must be weighed carefully.

Volatility Spillover and International Contagion of Housing Bubbles

This paper provides new empirical evidence on housing bubble timing, volatility spillover, and bubble contagion between Japan and its economic partners, namely, the United States, the Eurozone, and the United Kingdom. First, we apply a generalized sup ADF (GSADF) test to the quarterly price-to-rent ratio from 1970Q1 to 2018Q4 to detect explosive behaviors in housing prices. Second, we analyze the volatility spillover in housing prices between Japan and its economic partners using the multivariate time-varying DCC-GARCH model. Third, we assess bubble contagion by estimating a non-parametric model of bubble migration with time-varying coefficients. We document two historical bubble episodes from 1970 to 2018 in Japan’s housing market. Moreover, we find evidence of volatility spillover effects and bubble contagion between Japan’s real estate market and its most important economic partners during several periods. In this context of market integration, countries need to develop coordinated real estate policies to address the risk of global real estate bubbles.

Modeling Time-Varying Random Objects and Dynamic Networks

Samples of dynamic or time-varying networks and other random object data such as time-varying probability distributions are increasingly encountered in modern data analysis. Common methods for time-varying data such as functional data analysis are infeasible when observations are time courses of networks or other complex non-Euclidean random objects that are elements of general metric spaces. In such spaces, only pairwise distances between the data objects are available and a strong limitation is that one cannot carry out arithmetic operations due to the lack of an algebraic structure. We combat this complexity by a generalized notion of mean trajectory taking values in the object space. For this, we adopt pointwise Fréchet means and then construct pointwise distance trajectories between the individual time courses and the estimated Fréchet mean trajectory, thus representing the time-varying objects and networks by functional data. Functional principal component analysis of these distance trajectories can reveal interesting features of dynamic networks and object time courses and is useful for downstream analysis. Our approach also makes it possible to study the empirical dynamics of time-varying objects, including dynamic regression to the mean or explosive behavior over time. We demonstrate desirable asymptotic properties of sample based estimators for suitable population targets under mild assumptions. The utility of the proposed methodology is illustrated with dynamic networks, time-varying distribution data and longitudinal growth data.

Government Supervision on Explosive Enterprises’ Immoral Behaviors in E-Commerce Enterprises: An Evolutionary Game Analysis

Explosive enterprises’ immoral behaviors in the online shopping market are widespread and have not been effectively solved. Especially in developing countries, there is a direct relationship between massive immoral behaviors and the inefficiency of government supervision. Using an evolutionary game, this paper finds that immoral behavior is more likely to spread in online markets than in traditional markets. Only when government supervision and punishment are large enough and government’s punishment for the illegal enterprise exceeds extra supervision costs that government pays, explosive immoral behaviors can be curbed. Additionally, consumer support is an essential factor in improving the efficiency of government supervision. This study sorts out the interactions between e-commerce market participants and the government, obtains a path to achieve efficient government regulation, and offers management insights. The findings can serve as a reference for ensuring order in the emerging online shopping market and can also provide theoretical references for future related research.