The Structure of the Hadron-Quark Combustion Zone

Hadron-quark combustion in dense matter is a central topic in the study of phases in compact stars and their high-energy astrophysics. We critically reviewed the literature on hadron-quark combustion, dividing them into a “first wave” that treats the problem as a steady-state burning with or without constraints of mechanical equilibrium, and a “second wave” which uses numerical techniques to resolve the burning front and solves the underlying partial differential equations for the chemistry of the burning front under less restrictive conditions. We detailed the inaccuracies that the second wave amends over the first wave and highlight crucial differences between various approaches in the second wave. We also include results from time-dependent simulations of the reaction zone that include a hadronic EOS, neutrinos, and self-consistent thermodynamics without using parameterized shortcuts.

Self-propagating high-temperature synthesis in a thin-layer CuO–B–glass system

The paper provides experimental research and mathematical models of wave synthesis and thermal explosion in a thin-layer CuO–B–glass system. It is found that burning front propagation has a multi-source behavior and its rate depends on reacting layer thickness by the parabolic law with a maximum at d = 4·10–4m. Increased reacting layer thickness improves thermal explosion properties in this system, and dilution with an inert component makes it possible to obtain copper coatings featuring good electrical conductivity. X-ray phase analysis and optical microscopy demonstrated that the coating consists of metallic copper drops fused together and surrounded by boron-lead silicate glass melt. Coatings have high electrical conductivity comparable with that of metals. It is found that layer thickness increased over 4·10–4m results in a significantly reduced layer propagation rate due to initial mixture loosening under the evaporation effect of water vapors and gases adsorbed on powders, and, as a consequence, it results in reduced heat transfer in the burning front. These coatings are not electrically conductive. Mathematical models of wave synthesis and thermal explosion in a thin-layer CuO–B–glass system using macroscopic approximation. Process dynamics are numerically calculated. Theoretical estimates correspond satisfactorily to experimental values. Thermophysical and thermokinetic process constants are determined by the inverse problem method. Experimental data obtained and mathematical models developed made it possible to obtain prototypes of electric film heaters with high electrical conductivity and operating temperature.

3D geostatistical inversion of induced polarization data and its application to coal seam fires

We applied the principal component geostatistical approach (PCGA) to the inversion of time-domain induced polarization data in terms of resistivity and chargeability distributions. The PCGA presents two major advantages over standard methods: (1) It avoids the storage of the usually large covariance matrix, which contains the geostatistical information, by factorizing it in a product of low-rank matrices. (2) It does not assemble the Jacobian matrix per se. We determine the robustness of this approach with three examples. We first reconstruct the electrical conductivity and chargeability fields of two synthetic models generated using the geostatistical software Stanford Geostatistical Modeling Software. The PCGA approach performs better than the Tikhonov-based regularization approach when the true fields are very heterogeneous and the amount of data is limited. The third example is devoted to a field study over the former Lewis coal mine in Colorado (USA). We perform a 3D localization of the burning front of this coal seam fire by applying our geostatistical inverse methodology to a time-domain induced-polarization data set. In this case, the horizontal components of the semivariogram are determined from a self-potential map and the correlation length scale for the vertical component is determined from the known thickness of the coal bed. The tomogram presents a high normalized chargeability associated with the burning front. We evaluate the high normalized chargeability of the burning front in terms of the physical mechanism associated with the cation exchange capacity of the coal and the effect of temperature. This demonstrates the potential of the geostatistical inversion and its suitability for inverting geophysical data, especially when the data density is sparse. In the case of coal seam fires, we determine the suitability of the induced polarization method to localize the burning front and the effect of temperature on the normalized chargeability.

Thermoelectric self-potential and resistivity data localize the burning front of underground coal fires

Self-potential signals and resistivity data can be jointly inverted or analyzed to track the position of the burning front of an underground coal-seam fire. We first investigate the magnitude of the thermoelectric coupling associated with the presence of a thermal anomaly (thermoelectric current associated with a thermal gradient). A sandbox experiment is developed and modeled to show that in presence of a heat source, a negative self-potential anomaly is expected at the ground surface. The expected sensitivity coefficient is typically on the order of [Formula: see text] in a silica sand saturated by demineralized water. Geophysical field measurements gathered at Marshall (near Boulder, CO) show clearly the position of the burning front in the electrical resistivity tomogram and in the self-potential data gathered at the ground surface with a negative self-potential anomaly of about [Formula: see text]. To localize more accurately the position of the burning front, we developed a strategy based on two steps: (1) We first jointly invert resistivity and self-potential data using a cross-gradient approach, and (2) a joint interpretation of the resistivity and self-potential data is made using a normalized burning front index (NBI). The value of the NBI ranges from 0 to 1 with 1 indicating a high probability to find the burning front (strictly speaking, the NBI is, however, not a probably density). We validate first this strategy using synthetic data and then we apply it to the field data. A clear source is localized at the expected position of the burning front of the coal-seam fire. The NBI determined from the joint inversion is only slightly better than the value determined from independent inversion of the two geophysical data sets.