Field-based density measurements as tool to identify preeruption dome structure: set-up and first results from Unzen volcano, Japan

For an improvement in the quality of conduit flow and dome-related explosive eruption models, knowledge of the preeruption or precollapse density of the rocks involved is necessary. As close investigation is impossible during eruption, the best substitute comes from quantitative investigation of the eruption deposits. The porosity of volcanic rocks is of primary importance for the eruptive behaviour and, accordingly, a key-parameter for realistic models of dome stability and conduit flow. Fortunately, this physical property may be accurately determined via density measurements. We developed a robust, battery-powered device for rapid and reliable density measurements of dry rock samples in the field. The density of the samples (sealed in plastic bags at 250 mbar) is determined using the Archimedean principle. We have tested the device on the deposits of the 1990–1995 eruption of Unzen volcano, Japan. Short setup and operation times allow up to 60 measurements per day under fieldwork conditions. The rapid accumulation of correspondingly large data sets has allowed us to acquire the first statistically significant data set of clast density distribution in block-and-ash flow deposits. More than 1100 samples with a total weight of 2.2 tons were measured. The data set demonstrates that the deposits of the last eruptive episode at Unzen display a bimodal density distribution, with peaks at 2.0F0.1 and 2.3F0.1 g/cm3, corresponding to open porosity values of 20 and 8 vol.%, respectively. We use this data set to link the results of laboratory-based fragmentation experiments to field studies at recently active lava domes

Fragmentation efficiency of explosive volcanic eruptions: A study of experimentally generated pyroclasts

Products of magma fragmentation can pose a severe threat to health, infrastructure, environment, and aviation. Systematic evaluation of the mechanisms and the consequences of volcanic fragmentation is very difficult as the adjacent processes cannot be observed directly and their deposits undergo transport-related sorting. However, enhanced knowledge is required for hazard assessment and risk mitigation. Laboratory experiments on natural samples allow the precise characterization of the generated pyroclasts and open the possibility for substantial advances in the quantification of fragmentation processes. They hold the promise of precise characterization and quantification of fragmentation efficiency and its dependence on changing material properties and the physical conditions at fragmentation. We performed a series of rapid decompression experiments on three sets of natural samples from Unzen volcano, Japan. The analysis comprised grain-size analysis and surface area measurements. The grain-size analysis is performed by dry sieving for particles larger than 250 Am and wet laser refraction for smaller particles. For all three sets of samples, the grain-size of the most abundant fraction decreases and the weight fraction of newly generated ash particles (up to 40 wt.%) increases with experimental pressure/potential energy for fragmentation. This energy can be estimated from the volume of the gas fraction and the applied pressure. The surface area was determined through Argon adsorption. The fragmentation efficiency is described by the degree of fineparticle generation. Results show that the fragmentation efficiency and the generated surface correlate positively with the applied energy

Fall-experiments on Merapi basaltic andesite and constraints on the generation of pyroclastic surges

International audienceWe have performed fall-experiments with basaltic andesite rock samples from Merapi volcano, using an apparatus designed to analyze samples heated up to 850°C. Relative pressure changes during impact and fragmentation of the samples were measured by a pressure transducer. From 200°C, dynamic pressure waves were formed on impact and fragmentation. Peak and duration of the pressure signal, and degree of fragmentation were found to strongly increase with increasing temperature of rock samples. The pressure waves are most likely generated by sudden heating of air forcing it to expand. We propose that the observed pressure changes are analogues to pyroclastic surges that may be generated on impact and fragmentation of large blocks during passage of a pyroclastic flow over a steep cliff. We infer that rock temperatures of ca. 400°C are sufficient for this process to occur, a temperature common in pyroclastic flows even in distal reaches

Correlating atom probe tomography with x-ray and electron spectroscopies to understand microstructure-activity relationships in electrocatalysts

The search for a new energy paradigm with net-zero carbon emissions requires new technologies for energy generation and storage that are at the crossroad between engineering, chemistry, physics, surface and materials sciences. To keep pushing the inherent boundaries of device performance and lifetime, we need to step away from a cook-and-look approach and aim to establish the scientific ground to guide the design of new materials. This requires strong efforts in establishing bridges between microscopy and spectroscopy techniques, across multiple scales. Here, we discuss how the complementarities of X-ray- and electron-based spectroscopies and atom probe tomography can be exploited in the study of surfaces and sub-surfaces to understand structure-property relationships in electrocatalysts

Immunotherapeutic targeting of LIGHT/LTβR/HVEM pathway fully recapitulates the reduced cytotoxic phenotype of LIGHT-deficient T cells.

Tumor necrosis factor (TNF)/TNF receptor (TNFR) superfamily members play essential roles in the development of the different phases of the immune response. Mouse LIGHT (TNFSF14) is a type II transmembrane protein with a C-terminus extracellular TNF homology domain (THD) that assembles in homotrimers and regulates the course of the immune responses by signaling through 2 receptors, the herpes virus entry mediator (HVEM, TNFSFR14) and the lymphotoxin β receptor (LTβR, TNFSFR3). LIGHT is a membrane-bound protein transiently expressed on activated T cells, natural killer (NK) cells and immature dendritic cells that can be proteolytically cleaved by a metalloprotease and released to the extracellular milieu. The immunotherapeutic potential of LIGHT blockade was evaluated in vivo. Administration of an antagonist of LIGHT interaction with its receptors attenuated the course of graft-versus-host reaction and recapitulated the reduced cytotoxic activity of LIGHT-deficient T cells adoptively transferred into non-irradiated semiallogeneic recipients. The lack of LIGHT expression on donor T cells or blockade of LIGHT interaction with its receptors slowed down the rate of T cell proliferation and decreased the frequency of precursor alloreactive T cells, retarding T cell differentiation toward effector T cells. The blockade of LIGHT/LTβR/HVEM pathway was associated with delayed downregulation of interleukin-7Rα and delayed upregulation of inducible costimulatory molecule expression on donor alloreactive CD8 T cells that are typical features of impaired T cell differentiation. These results expose the relevance of LIGHT/LTβR/HVEM interaction for the potential therapeutic control of the allogeneic immune responses mediated by alloreactive CD8 T cells that can contribute to prolong allograft survival

The role of external broadcasting in a closed political system

This article investigates the role and impact of external broadcasting (radio and television) on a closed political system, through the example of the two post-war German states: the West German Federal Republic of Germany (FRG) and the East German German Democratic Republic (GDR). The aim is to debunk myths about the influence of external broadcasting on the events that led to German reunification in 1990. The study follows a historical approach and discusses what role external media played during the years of a divided Germany. The findings are based on several historical sources, research reports from the 1950s and 1960s and over 100 biographical interviews with former residents of the German Democratic Republic (GDR). The article analyses the impact of external broadcasting on citizens and the political elite in times of crisis as well as during everyday life

Cation exchange synthesis and optoelectronic properties of type II CdTe-Cu2-xTe nano-heterostructures

Rod-shaped CdTe-Cu2-xTe nano-heterostructures with tunable dimensions of both sub-units and a type II band alignment were prepared by Cd2+/Cu+ cation exchange. The light absorption properties of the heterostructures are dominated by the excitonic and plasmonic contributions arising, respectively, from the CdTe and the Cu2-xTe sub-units. These results were confirmed over a wide range of sub-unit length fractions through optical modelling based on the discrete dipole approximation (DDA). Although assuming electronically independent sub-units, our modelling results indicate a negligible ground state interaction between the CdTe exciton and the Cu2-xTe plasmon. This lack of interaction may be due to the low spectral overlap between exciton and plasmon, but also to localization effects in the vacancy-doped sub-unit. The electronic interaction between both sub-units was evaluated with pump-probe spectroscopy by assessing the relaxation dynamics of the excitonic transition. In particular, the CdTe exciton decays faster in the presence of the Cu2-xTe sub-unit, and the decay gets faster with increasing its length. This points towards an increased probability of Auger mediated recombination due to the high carrier density in the Cu2-xTe sub-unit. This indication is supported through length-fraction dependent band structure calculations, which indicate a significant leakage of the CdTe electron wavefunction into the Cu2-xTe sub-unit that increases along with the shortening of the CdTe sub-unit, thus enhancing the probability of Auger recombination. Therefore, for the application of type II chalcogenide-chalcogenide heterostructures based on Cu and Cd for photoenergy conversion, a shorter Cu-based sub-unit may be advantageous, and the suppression of high carrier density within this sub-unit is of high importance

A 3D insight on the catalytic nanostructuration of few-layer graphene

The catalytic cutting of few-layer graphene is nowadays a hot topic in materials research due to its potential applications in the catalysis field and the graphene nanoribbons fabrication. We show here a 3D analysis of the nanostructuration of few-layer graphene by iron-based nanoparticles under hydrogen flow. The nanoparticles located at the edges or attached to the steps on the FLG sheets create trenches and tunnels with orientations, lengths and morphologies defined by the crystallography and the topography of the carbon substrate. The cross-sectional analysis of the 3D volumes highlights the role of the active nanoparticle identity on the trench size and shape, with emphasis on the topographical stability of the basal planes within the resulting trenches and channels, no matter the obstacle encountered. The actual study gives a deep insight on the impact of nanoparticles morphology and support topography on the 3D character of nanostructures built up by catalytic cutting