Magma sources involved in the 2002 Nyiragongo eruption, as inferred from an InSAR analysis

International audienceOn 17 January 2002, Nyiragongo volcano erupted along a 20 km-long fracture network extending from the volcano to the city of Goma. The event was captured by InSAR data from the ERS-2 and RADARSAT-1 satellites. A combination of 3D numerical modeling and inversions is used to analyze these displacements. Using Akaike Information Criteria, we determine that a model with two subvertical dikes is the most likely explanation for the 2002 InSAR deformation signal. A first, shallow dike, 2 km high, is associated with the eruptive fissure, and a second, deeper dike, 6 km high and 40 km long, lies about 3 km below the city of Goma. As the deep dike extends laterally for 20 km beneath the gas-rich Lake Kivu, the interaction of magma and dissolved gas should be considered as a significant hazard for future eruptions. A likely scenario for the eruption is that the magma supply to a deep reservoir started ten months before the eruption, as indicated by LP events and tremor. Stress analysis indicates that the deep dike could have triggered the injection of magma from the lake and shallow reservoir into the eruptive dike. The deep dike induced the opening of the southern part of this shallow dike, to which it transmitted magma though a narrow dike. This model is consistent with the geochemical analysis, the lava rheology and the pre- and post-eruptive seismicity. We infer low overpressures (1-10 MPa) for the dikes. These values are consistent with lithostatic crustal stresses close to the dikes and low magma pressure. As a consequence, the dike direction is probably not controlled by stresses but rather by a reduced tensile strength, inherited from previous rift intrusions. The lithostatic stresses indicate that magmatic activity is intense enough to relax tensional stresses associated with the rift extension

A General Approach to the Geostationary Transfer Orbit Mission Recovery

This paper discusses recovery scenarios for geosynchronous satellites injected in a non-nominal orbit due to a launcher underperformance. The theory on minimum-fuel orbital transfers is applied to develop an operational tool capable to design a recovery mission. To obtain promising initial guesses for the recovery three complementary techniques are used: p-optimized impulse function contouring, a numerical impulse function minimization and the solutions to the switching equations. The tool evaluates the feasibility of a recovery with the on-board propellant of the spacecraft and performs the complete mission design. This design takes into account for various mission operational constraints such as e.g., the requirement of multiple finite-duration burns, third-body orbital perturbations, spacecraft attitude constraints and ground station visibility. In a final case study, we analyze the consequences of a premature breakdown of an upper rocket stage engine during injection on a geostationary transfer orbit, as well as the possible recovery solution with the satellite on-board propellant

The 2007 rifting event in Northern Tanzania studied by C and L-band interferometry

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Model of fibrolamellar hepatocellular carcinomas reveals striking enrichment in cancer stem cells

The aetiology of human fibrolamellar hepatocellular carcinomas (hFL-HCCs), cancers occurring increasingly in children to young adults, is poorly understood. We present a transplantable tumour line, maintained in immune-compromised mice, and validate it as a bona fide model of hFL-HCCs by multiple methods. RNA-seq analysis confirms the presence of a fusion transcript (DNAJB1-PRKACA) characteristic of hFL-HCC tumours. The hFL-HCC tumour line is highly enriched for cancer stem cells as indicated by limited dilution tumourigenicity assays, spheroid formation and flow cytometry. Immunohistochemistry on the hFL-HCC model, with parallel studies on 27 primary hFL-HCC tumours, provides robust evidence for expression of endodermal stem cell traits. Transcriptomic analyses of the tumour line and of multiple, normal hepatic lineage stages reveal a gene signature for hFL-HCCs closely resembling that of biliary tree stem cells-newly discovered precursors for liver and pancreas. This model offers unprecedented opportunities to investigate mechanisms underlying hFL-HCCs pathogenesis and potential therapies

Clinical burden of hepatitis E virus infection in a tertiary care center in Flanders, Belgium

Background: Hepatitis E virus (HEV) infection is increasingly recognized as a cause of hepatitis in developed countries. A high HEV IgG seroprevalence in humans and pigs is reported as well as sporadic clinical cases of autochtonous HEV but there are currently no data available on the clinical burden of HEV in Belgium. Objectives: The objective of the current study was to evaluate the actual clinical burden of HEV infections in our tertiary care center in Flanders, Belgium. Study design: In the setting of Ghent University Hospital, patients were assessed for the presence of HEV IgG and IgM as well as HEV RNA if no other cause was found for one of the following clinical presentations: a) elevation of liver enzymes in post-liver transplant; b) suspicion of acute or toxic hepatitis; c) unexplainable elevation of liver enzymes; d) cirrhosis with acute-on-chronic exacerbation. Results: In a period of 39 months (January 2011-April 2014) 71 patients were enrolled. HEV IgG was found positive in 13 (18,3%) patients; HEV IgM in 6 patients (8,5%) and HEV RNA in 4 (5,6%) patients. All HEV IgM/ RNA positive patients were male, aged 41-63, and classified in the clinical groups a), b) or d). HEV IgG seroprevalence was slightly higher but not significantly different from the seroprevalence in the general population in this region in Belgium previously reported to be 14% (p-value 0.41) by our group. Conclusions: HEV should be considered as a cause of liver pathology especially in middle-aged men with elevation of liver enzymes

A Greedy Homotopy Method for Regression with Nonconvex Constraints

Constrained least squares regression is an essential tool for high-dimensional data analysis. Given a partition $\mathcal{G}$ of input variables, this paper considers a particular class of nonconvex constraint functions that encourage the linear model to select a small number of variables from a small number of groups in $\mathcal{G}$. Such constraints are relevant in many practical applications, such as Genome-Wide Association Studies (GWAS). Motivated by the efficiency of the Lasso homotopy method, we present RepLasso, a greedy homotopy algorithm that tries to solve the induced sequence of nonconvex problems by solving a sequence of suitably adapted convex surrogate problems. We prove that in some situations RepLasso recovers the global minima of the nonconvex problem. Moreover, even if it does not recover global minima, we prove that in relevant cases it will still do no worse than the Lasso in terms of support and signed support recovery, while in practice outperforming it. We show empirically that the strategy can also be used to improve over other Lasso-style algorithms. Finally, a GWAS of ankylosing spondylitis highlights our method's practical utility