Three-dimensional petrographical investigations on borehole rock samples: a comparison between X-ray computed- and neutron tomography

Technical difficulties associated with excavation works in tectonized geological settings are frequent. They comprise instantaneous and/or delayed convergence, sudden collapse of gallery roof and/or walls, outpouring of fault-filling materials and water inflows. These phenomena have a negative impact on construction sites and their safety. In order to optimize project success, preliminary studies on the reliability of rock material found on site are needed. This implies in situ investigations (surface mapping, prospective drilling, waterflow survey, etc.) as well as laboratory investigations on rock samples (permeability determination, moisture and water content, mineralogy, petrography, geochemistry, mechanical deformation tests, etc.). A set of multiple parameters are then recorded which permit better insight on site conditions and probable behavior during excavation. Because rock formations are by nature heterogeneous, many uncertainties remain when extrapolating large-scale behavior of the rock mass from analyses of samples order of magnitudes smaller. Indirect large-scale field investigations (e.g. geophysical prospecting) could help to better constrain the relationships between lithologies at depth. At a much smaller scale, indirect analytical methods are becoming more widely used for material investigations. We discuss in this paper X-ray computed tomography (XRCT) and neutron tomography (NT), showing promising results for 3D petrographical investigations of the internal structure of opaque materials. Both techniques record contrasts inside a sample, which can be interpreted and quantified in terms of heterogeneity. This approach has the advantage of combining genetic parameters (physico-chemical rock composition) with geometric parameters resulting from alteration or deformation processes (texture and structure). A critical analysis of such 3D analyses together with the results of mechanical tests could improve predictions of short- and long-term behavior of a rock unit. Indirect methods have the advantage of being non-destructive. However, as it is the case with large-scale geophysical surveying, XRCT and NT are affected by several error factors inherent to the interaction of a radiation modality (X-ray or neutron beam) with the atomic structure of the investigated materials. Recorded signals are therefore in particular cases not artifact-free and need to be corrected in a subsequent stage of data processin

Additional file 1: Figure S1. of Plasmid pPCP1-derived sRNA HmsA promotes biofilm formation of Yersinia pestis

Characterization of sRNA HmsA in Y. pestis. a) Promoter analysis and HmsA expression determined by RNA-seq data. b) Primer extension analysis of HmsA in Y. pestis WT and ∆hfq mutant strains. c) Growth curves of the WT and Pdr1 mutant strains. (TIFF 833 kb

Additional file 2: Figure S2. of Plasmid pPCP1-derived sRNA HmsA promotes biofilm formation of Yersinia pestis

Predicted interactions of HmsA with HmsB, hmsC and hmsT. The interaction between HmsA and HmsB predicted by IntaRNA is shown in a). Predicted structures of the 5′ UTR of hmsC and hmsT mRNA are shown in b) and c), respectively. The start codon is boxed and the ribosomal binding site is underlined. The numbers in the figure indicate the position relative to the start codon (+1) of mRNA. Regions that potentially base pair with HmsA are underlined in blue. (TIFF 1118 kb