Notes on some Late Cretaceous goniasterid starfish (Echinodermata, Asteroidea) from Belgium and Germany

Both partially articulated specimens and dissociated marginal ossicles form the basis for erection of two new species of Late Cretaceous goniasterids from the Mons and Liège-Limburg basins (Belgium) and the Hannover area (Germany). Chomataster breizh sp. nov., which recalls the type species, Chomataster acules Spencer, 1913, but differs in several respects, is based on a partial external mould of the marginal frame of disc and arms in flint (upper Campanian Spiennes Chalk Formation; Mons Basin), as well as on a more or less complete individual, preserving small, spherical spines and granules and encased in a flint nodule from the upper Maastrichtian Nekum Member (Maastricht Formation; Liège-Limburg Basin). In Ch. breizh sp. nov., supero- and inferomarginals bear close-set granule pits, of varying sizes, as well as bivalved alveolar scars of pedicellariae; median superomarginals and all inferomarginals lack large, crater-shaped spine pits – such are found only in the disc/arm transition and along the arms. Dissociated supero- and inferomarginal ossicles from the lower and upper Campanian of the Hannover area and the upper Campanian of northeast Belgium, previously recorded either as indeterminate astropectinids or as Nymphaster obtusus (Forbes, 1848) var. nov. and as Nymphaster sp., respectively, here are assigned to Nymphaster mudzborgh sp. nov. This species is characterised by a row of 3–5 large spine pits on the aboral and lateral surfaces of superomarginals; inferomarginals have an angular profile and a close cover of granule pits. Nymphaster tethysiensis Villier, 2001, from the upper Campanian of Landes (southwest France; Villier and Odin, 2001) appears best accommodated in Chomataster as well, because in the arm superomarginals alternate rather than meet over the mid-radial line.

Relativistic free fermions in spiral dislocation space–time with a distortion of a radial line into a spiral

Relativistic quantum mechanics of free fermions in the presence of the spiral dislocation of space–time with a distortion of a radial line into a spiral is studied within the Katanaev–Volovich geometric approach. The generalized Dirac equation in this background is constructed. Exact closed-form solutions are found by reducing the problem to that of a nonrelativistic two-dimensional [Formula: see text]-problem with a complex coupling constant. The influence of the defect parameter related to the spiral dislocation on these solutions is investigated. We also study the charge density of free fermions in the presence of such a spiral dislocation in space–time. Based on the Bender–Boettcher approach for non-Hermitian Hamiltonians we study, in addition, bound-state solutions of the system.

Study on the Radial Displacement Law and Permeability Enhancement Effect of Coal Body around Hydraulic Flushing Drilling

Hydraulic flushing drilling technology can not only improve the efficiency of high-pressure and low-permeability geological reservoir coalbed methane drainage but also effectively reduce the probability of coal and gas outburst disasters through pressure relief. The main mechanism of this technology is to expand the borehole diameter through hydraulic flushing measures, increase the strain of the coal around the borehole, and increase the development of cracked pores, to improve the permeability of the coal seam and realize the dual reduction of ground and gas pressure. However, in the actual application process, the interaction mechanism among the stress field, the structure field, and the seepage field is still not clear, and there is no clear method to accurately determine the pressure relief range based on the pressure relief mechanism in order to carry out reasonable drilling arrangements. Therefore, this article comprehensively uses laboratory experiments, numerical simulations, and field practices to fully explain the hydraulic flushing pressure relief mechanism and proposes a method to accurately determine the pressure relief range based on the radial line strain law. The results based on radial line strain showed that the effective relief radius expands to 0.86 m once adopting the Φ579 mm hydraulic flushing borehole compared to Φ160 mm; the borehole’s equivalent diameter of drilling field #11 is 2 to 3 times than that of #10 and 1.2 times the average CBM extraction amount. Therefore, as the borehole diameter increases, the permeability and radial line strain of the coal around the borehole increase significantly, but the tendency of the increase in permeability decreases with increasing vertical stress. The findings of this study can help for a better understanding of the pressure relief and permeability enhancement mechanism of hydraulic flushing, and the method of determining the pressure relief range based on radial strain can also provide a new way for other mines to practice ideas.