Aluminium/tin (IV) oxide thermite composite: sensitivities and reaction propagation

ABSTRACT

Thermites are energetic composites made of metal and oxidizer particles that react according to an exothermic reaction and release large amounts of energy. Many possible metal and oxidizer couples exist in the literature. Here, the performance of the aluminum reducing metal and tin (IV) oxide (SnO₂) combination was reported as a function of the fuel/oxidizer mass ratio. The Al/SnO₂ energetic composite, in stoichiometric conditions, was insensitive to impact, sensitive to friction and extremely sensitive to electrostatic discharge. The combustion velocity was determined to be close to 600 m/s. Changing the stoichiometry affected both the sensitivity thresholds to the friction test (160 N to > 360 N) and flame propagation velocity (480–588 m/s) of the Al/SnO₂ composite. These results are reported for the first time.     

Bootstrap procedures for detecting multiple persistence shifts in heteroskedastic time series

This article proposes new bootstrap procedures for detecting multiple persistence shifts in a time series driven by non-stationary volatility. The assumed volatility process can accommodate discrete breaks, smooth transition variation as well as trending volatility. We develop wild bootstrap sup-Wald tests of the null hypothesis that the process is either stationary [I(0)] or has a unit root [I(1)] throughout the sample. We also propose a sequential procedure to estimate the number of persistence breaks based on ordering the regime-specific bootstrap p-values. The asymptotic validity of the advocated procedures is established both under the null of stability and a variety of persistence change alternatives. A comparison with existing tests that assume homoskedasticity illustrates the finite sample improvements offered by our methods. An application to OECD inflation rates highlights the empirical relevance of the proposed approach and weakens the case for persistence change relative to existing procedures.     

Comparative analysis of formaldehyde and toluene sorption on indoor floorings and consequence on Indoor Air Quality

Indoor surfaces may be adsorptive sinks with the potential to change Indoor Air Quality. To estimate this effect, the sorption parameters of formaldehyde and toluene were assessed on five floorings by an experimental method using solid-phase microextraction in an airtight emission cell. Adsorption rate constants ranged from 0.003 to 0.075 m·h⁻¹, desorption rate constants from 0.019 to 0.51 h⁻¹, and the partition coefficient from 0.005 to 3.9 m, and these parameters vary greatly from one volatile organic compound/material couple to another indicating contrasted sorption behaviors. A rubber was identified as a sink of formaldehyde characterized by a very low desorption constant close to 0. For these sorbent floorings identified, the adsorption rates of formaldehyde are from 2 to 4 times higher than those of toluene. Two models were used to evaluate the sink effects of floorings on indoor pollutant concentrations in one room from different realistic conditions. The scenarios tested came to the conclusion that the formaldehyde sorption on one rubber (identified as a sink) has a maximum contribution from 15% to 21% for the conditions of low air exchange rate. For other floorings, the sorption has a minor contribution less than or equal to 5%, regardless of the air exchange rate.     

Autonomous car decision making and trajectory tracking based on genetic algorithms and fractional potential fields

Intelligent Service Robotics - This article deals with the issue of trajectory optimization of autonomous terrestrial vehicles on a specific range handled by the human driver. The main...     

Potential of the crude glycerol and citric acid mixture as a binder in medium-density fiberboard manufacturing

European Journal of Wood and Wood Products - Urea–formaldehyde (UF) resin is the main commercial adhesive used for medium-density fiberboard (MDF) manufacturing. UF resin is used to produce...     

Impact d’une galerie étanche peu profonde sur l’écoulement d’une nappe

While many studies have been achieved on the interactions between groundwater and deep tunnels, in order to identify the evolution of pore pressure around the structure and to characterize the flow to its leaky parts, few studies have dealt with the impact of the carrying out of an impervious gallery in a shallow aquifer. The induced change in the piezometric level of the aquifer and the one in the hydraulic gradient of the flow however can, in this case, have significant consequences, in particular when the linear structure is located in an urban environment. This paper investigates, in steady state, the case of a straight tunnel having a horizontal axis perpendicular to the direction of the regional groundwater flow and a circular or square cross section. The aim is to determine the additional lost head Δh _s due to the tunnel (i.e. additional to that resulting from the regional flow, supposed to be uniform with a hydraulic gradient i ₀). In the context of a horizontal confined aquifer having a thickness 2B and of a tunnel of radius R located in the middle part of the aquifer, an analogy can be established with the flow above a hydraulic threshold resulting from a local rise of the elevation of the base of an aquifer, having a thickness B, on a width 2R and with a vertical maximum amplitude R. When neglecting the vertical component of the hydraulic gradient compared to its horizontal component, analytical solutions are developed for various hydraulic threshold shapes (rectangular, triangular and circular), based on the equivalence with a local change in the transmissivity of an aquifer keeping a constant thickness. The corresponding formulas take the form: $ {\frac{{\Updelta h_{s} - \Updelta h_{0} }}{{\Updelta h_{0} }}} = f(a) $ , with $ a = {\frac{R}{B}} $ and Δh ₀ = 2Ri ₀. The use of these formulas shows that the additional lost head Δh _s due to the hydraulic threshold is proportional to i ₀ and that, for values of the ratio a < 0.5, the change in the piezometric surface is small. These conclusions are therefore limited by the fact that the vertical conductivity is supposed to be very large. In order to remove this hypothesis, numerical simulations are achieved using the MODFLOW code. It is considered a confined aquifer of length 2L = 110 m and thickness B = 10 m, a ratio $ a = {\frac{R}{B}} = 0.25 $ and a horizontal hydraulic conductivity $ K_{H} = 10^{ - 5} \,{\text{m}}\,{\text{s}}^{ - 1} $ . In the case of an isotropic medium ( $ \alpha = {\frac{{K_{H} }}{{K_{V} }}} = 1 $ ), the simulations allow to check the linearity of the relationship between Δh _s and i ₀, with therefore a homogeneous variation in the proportionality coefficient compared to analytical solutions. Simulations also reveal that, in the case considered, the width of influence upstream and downstream L _i , corresponding to a value of the vertical component of the hydraulic gradient <1% of i ₀, is below 5.5R for the three hydraulic threshold shapes, and that it was few influenced by the hydraulic gradient i ₀. In the case of an anisotropy of the horizontal and vertical hydraulic conductivities, simulations reveal the significant importance of the anisotropy ratio $ \alpha = {\frac{{K_{H} }}{{K_{V} }}} $ when it is more than 1, the most common case, and indicate that the proposed analytical solutions give an asymptotic value of $ {\frac{{\Updelta h_{s} }}{{\Updelta h_{0} }}} $ for the isotropic case and for the values of the component α < 1. In the context of an unconfined aquifer, the hydraulic threshold model is not directly applicable. The model studied, using the Dupuit-Forchheimer assumption, is the one of a water table aquifer with a sloped base (slope value: p ₀). The simulations focus on an aquifer of length 2L = 85 m, with a tunnel of circular cross section having a diameter 2R = 5 m, bottom of which is located 5 m above the base of the aquifer, the isotropic hydraulic conductivity being equal to $ K = 10^{ - 5} \,{\text{m}}\,{\text{s}}^{ - 1} $ . The definitions of water heights d ₀ and d between the water table and the top of the tunnel are given in Fig. 7. The water table can be located above (fully submerged tunnel) or below (partially emerged tunnel) the top of the tunnel. The difference d ₀ ? d represents the half of the additional lost head Δh _s due to the tunnel. Simulations are performed for various values of p ₀ and d ₀. They provide the values of i ₀, d and Δh _s . In the case of a fully submerged tunnel (d > 0), a significant rise of the water table upstream of the tunnel is obtained only for high values of the hydraulic gradient (5 and 10%), but, even in this case, it remains less than the tenth of the wetted height of the aquifer h _m . It is also highlighted that the ratio $ {\frac{{\Updelta h_{s} }}{{i_{0} }}} $ varies as a linear function of (R + d) and that, in the studied case, there is no influence of the tunnel for d ≥ 4R. In the case of a partially emerged tunnel (d < 0), the aquifer is locally confined under the tunnel. It is suggested that an equivalence is possible with the case of a confined aquifer having a thickness equal to the wetted height in the unconfined aquifer. This is verified with one of the simulations. In the case of a partially emerged tunnel, the change in the water table due to the tunnel remains low.