Estimating crustal thickness in Belgium using Moho-reflected waves

We present the results of the determination of the Moho depth underneath Belgium using reflected P and S-waves (PmP- and SmS-waves). Previous studies suggest differences of the Moho depth in the different parts of the region. In the lower Rhine Embayment in the northeast, the Moho depth is considered to be shallow (25 km). In the Brabant Massif in the west the crustal thickness is supposed to be larger (up to 38 km). The southeast of Belgium is characterised by the Variscan allochtone, where the Moho depth is around 30 km. In this study, PmP/SmS-waves of ~150 well-located local earthquakes and explosions in the North Sea registered by 37 stations of the permanent seismic network and by mobile stations installed by the Royal Observatory of Belgium were used. More than 750 PmP/SmS-waves were modelled to determine the Moho depth with the following procedure. PmP-arrivals are picked and the locations of the PmP-bounce points are determined and mapped. Over this map a 20 x 20 km grid is placed and for each grid cell an iteration is performed to determine the Moho depth. The thickness of the crust varies between 25 and 36 km and is slightly shallower in the northeast of Belgium (28–30–32 km) than to the southwest (33-34 km). Underneath the Brabant massif however Moho depths of 31 km are found, which is in contradiction with previous results

Local seismic tomography in Belgium: implications for the geological structure

We present the results of a local seismic tomography in Belgium using well-located local earthquakes registered by 37 stations of the permanent seismic network and by mobile stations installed by the Royal Observatory of Belgium. Previous studies did not offer a lot of information on the middle and lower crust. The seismic profiles shot in the region (Belcorp, Decorp, Ecors, . . . ) all show an unreflective middle and lower crust. The gravimetric and magnetic data show the presence of a sharp transition between the Brabant Massive and the Ardennes allochtone, furthermore, a broad positive gravimetric anomaly, is interpreted as a Moho uplift underneath the Campine region. Our results confirm the sharp transition between the Brabant Massif (higher than expected velocities) and the Ardennes allochtone (lower than expected velocities). At 27 km of depth lower crust – upper mantle velocities (7.50 km/s) are found underneath the Campine region and the Eifelplume region, confirming the Moho uplifts to 28 km underneath these regions. At 13 km similar velocities (7.50 km/s) are seen underneath the Eifelplume, they correspond to a lower crust-upper mantle that trusted in the crust during the Variscan orogeny

To respond or not to respond - a personal perspective of intestinal tolerance

For many years, the intestine was one of the poor relations of the immunology world, being a realm inhabited mostly by specialists and those interested in unusual phenomena. However, this has changed dramatically in recent years with the realization of how important the microbiota is in shaping immune function throughout the body, and almost every major immunology institution now includes the intestine as an area of interest. One of the most important aspects of the intestinal immune system is how it discriminates carefully between harmless and harmful antigens, in particular, its ability to generate active tolerance to materials such as commensal bacteria and food proteins. This phenomenon has been recognized for more than 100 years, and it is essential for preventing inflammatory disease in the intestine, but its basis remains enigmatic. Here, I discuss the progress that has been made in understanding oral tolerance during my 40 years in the field and highlight the topics that will be the focus of future research

A study of the structure of the Belgian crust by Moho determination and local seismic tomography

In Belgium not much is known about the extension of the different crustal structures into the middle and lower crust. Until now, only seismic profiles and gravimetric and magnetic data gave some insights. The general aim of this thesis is to improve the understanding of the lower/middle crustal structure of Belgium. This will be achieved by determining the Moho depth and performing a local seismic tomography. The Moho is rather flat underneath Belgium with Moho depths ranging from 31 km underneath the Brabant Massif (BM) over 31-33 km underneath the Roer Valley Graben (RVG) and the Ardennes Allochthon (AA) to 28 km underneath the Eifel Volcanic Province (EVP). These results are comparable to the results of other studies, like seismic reflection profiles and receiver function analysis. The degree of precision obtained underneath the Belgian onshore part of the BM, however, has not been reached before. At the southeast of Grand-Duchy of Luxemburg, two seismic reflection phases are observed on the seismograms. The origin of the first reflection (at 15 to 24 km) is not clear yet, but this problem will be solved with the results of the seismic tomography. The second reflection is interpreted as the current Moho interface. The local seismic tomography confirmed the Moho uplift to 28 km of depth underneath the Campine Bassin and the EVP. Furthermore, the inversion enables to determine the cause of the intra-crustal reflection mentioned in the previous paragraph. Lower crust velocities are observed at 13.5 km depth at this location. The reflector represents thus a lower crust/upper mantle being upthrusted in the middle crust during the Variscan Orogeny. Superficial geology is also recognizable, like the BM, the AA, the Rocroi and Stavelot Inliers, the sediment infill of the RVG and the Trier Graben. There is a velocity contrast over the entire crust between the AA and the BM. The cause of this contrast is not clear, yet. It either is a crustal separation or a mid-crustal deformation due to the Variscan Orogeny. Fractured regions like the Midi overthrust and the RVG show up on the Vp/Vs results of the tomography

PeacoQC : peak-based selection of high quality cytometry data

In cytometry analysis, a large number of markers is measured for thousands or millions of cells, resulting in high-dimensional datasets. During the measurement of these samples, erroneous events can occur such as clogs, speed changes, slow uptake of the sample etc., which can influence the downstream analysis and can even lead to false discoveries. As these issues can be difficult to detect manually, an automated approach is recommended. In order to filter these erroneous events out, we created a novel quality control algorithm, Peak Extraction And Cleaning Oriented Quality Control (PeacoQC), that allows for automated cleaning of cytometry data. The algorithm will determine density peaks per channel on which it will remove low quality events based on their position in the isolation tree and on their mean absolute deviation distance to these density peaks. To evaluate PeacoQC's cleaning capability, it was compared to three other existing quality control algorithms (flowAI, flowClean and flowCut) on a wide variety of datasets. In comparison to the other algorithms, PeacoQC was able to filter out all different types of anomalies in flow, mass and spectral cytometry data, while the other methods struggled with at least one type. In the quantitative comparison, PeacoQC obtained the highest median balanced accuracy and a similar running time compared to the other algorithms while having a better scalability for large files. To ensure that the parameters chosen in the PeacoQC algorithm are robust, the cleaning tool was run on 16 public datasets. After inspection, only one sample was found where the parameters should be further optimized. The other 15 datasets were analyzed correctly indicating a robust parameter choice. Overall, we present a fast and accurate quality control algorithm that outperforms existing tools and ensures high-quality data that can be used for further downstream analysis. An R implementation is available

IRF8 Transcription Factor Controls Survival and Function of Terminally Differentiated Conventional and Plasmacytoid Dendritic Cells, Respectively

International audienceInterferon regulatory factor-8 (IRF8) has been proposed to be essential for development of monocytes, plasmacytoid dendritic cells (pDCs) and type 1 conventional dendritic cells (cDC1s) and remains highly expressed in differentiated DCs. Transcription factors that are required to maintain the identity of terminally differentiated cells are designated `' terminal selectors.'' Using BM chimeras, conditional Irf8(fl/fl) mice and various promotors to target Cre recombinase to different stages of monocyte and DC development, we have identified IRF8 as a terminal selector of the cDC1 lineage controlling survival. In monocytes, IRF8 was necessary during early but not late development. Complete or late deletion of IRF8 had no effect on pDC development or survival but altered their phenotype and gene-expression profile leading to increased T cell stimulatory function but decreased type 1 interferon production. Thus, IRF8 differentially controls the survival and function of terminally differentiated monocytes, cDC1s, and pDCs

Genomic programming of IRF4-expressing human Langerhans cells

Langerhans cells (LC) can prime tolerogenic as well as immunogenic responses in skin, but the genomic states and transcription factors (TFs) regulating these context-specific responses are unclear. Bulk and single-cell transcriptional profiling demonstrates that human migratory LCs are robustly programmed for MHC-I and MHC-II antigen presentation. Chromatin analysis reveals enrichment of ETS-IRF and AP1-IRF composite regulatory elements in antigen-presentation genes, coinciding with expression of the TFs, PU.1, IRF4 and BATF3 but not IRF8. Migration of LCs from the epidermis is accompanied by upregulation of IRF4, antigen processing components and co-stimulatory molecules. TNF stimulation augments LC cross-presentation while attenuating IRF4 expression. CRISPRmediated editing reveals IRF4 to positively regulate the LC activation program, but repress NF2EL2 and NF-kB pathway genes that promote responsiveness to oxidative stress and inflammatory cytokines. Thus, IRF4-dependent genomic programming of human migratory LCs appears to enable LC maturation while attenuating excessive inflammatory and immunogenic responses in the epidermis