130 research outputs found
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
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 1990â1995 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
The fragmentation threshold of pyroclastic rocks
In response to rapid decompression, porous magma may fragment explosively. This occurs when the melt can no
longer withstand forces exerted upon it due to the overpressure in included bubbles. This occurs at a critical pressure
difference between the bubbles and the surrounding magma. In this study we have investigated this pressure threshold
necessary for the fragmentation of magma. Here we present the first comprehensive, high temperature experimental
quantification of the fragmentation threshold of volcanic rocks varying widely in porosity, permeability, crystallinity, and
chemical composition. We exposed samples to increasing pressure differentials in a high temperature shock tube apparatus
until fragmentation was initiated. Experimentally, we define the fragmentation threshold as the minimum pressure
differential that leads to complete fragmentation of the pressurized porous rock sample. Our results show that the
fragmentation threshold is strongly dependent on porosity; high porosity samples fragment at lower pressure differentials
than low porosity samples. The fragmentation threshold is inversely proportional to the porosity. Of the other factors,
permeability likely affects the fragmentation threshold at high porosity values, whereas chemical composition, crystallinity
and bubble size distribution appear to have minor effects. The relationship for fragmentation threshold presented here can
be used to predict the minimum pressure differential necessary for the initiation or cessation of the explosive fragmentation
of porous magma
Intranasal oxytocin reduces provoked symptoms in female patients with posttraumatic stress disorder despite exerting sympathomimetic and positive chronotropic effects in a randomized controlled trial
Background: Posttraumatic stress disorder (PTSD) is a severe psychiatric disease accompanied by neuroendocrine changes such as adrenergic overdrive and hence an elevated cardiovascular morbidity. Current pharmacotherapeutic options for PTSD are less than suboptimal, necessitating the development of PTSD-specific drugs. Although the neuropeptide oxytocin has been repeatedly suggested to be effective in PTSD treatment, there are, to our knowledge, only three studies that have assessed its efficacy on the intensity of PTSD symptoms in PTSD patients - among them one symptom provocation study in male veterans. Methods: To evaluate for the first time how oxytocin influences the intensity of provoked PTSD symptoms and, furthermore, cardiac control in female PTSD patients, we assessed their psychic and cardiac response to trauma-script exposure with and without oxytocin pretreatment in a double-blind randomized placebo-controlled study. We used a within-subject design to study 35 female PTSD patients who received oxytocin and placebo in a 2-week interval. Furthermore, we performed a small pilot study to get an idea of the relation of the stress-modulated endogenous oxytocin levels and heart rate - we correlated oxytocin serum levels with the heart rate of 10 healthy individuals before and after exposure to the Trier Social Stress Test (TSST). Results: Intranasal oxytocin treatment was followed by a reduction of provoked total PTSD symptoms, in particular of avoidance, and by an elevation in baseline and maximum heart rate together with a drop in the pre-ejection period, a marker for sympathetic cardiac control. Furthermore, we found a positive correlation between endogenous oxytocin levels and heart rate both before and after TSST challenge in healthy control subjects. Conclusions: This study provides the first evidence that oxytocin treatment reduces the intensity of provoked PTSD symptoms in female PTSD patients. The small size of both samples and the heterogeneity of the patient sample restrict the generalizability of our findings. Future studies have to explore the gender dependency and the tolerability of the oxytocin- mediated increase in heart rate
Combination of SAR remote sensing and GIS for monitoring subglacial volcanic activity – recent results from Vatnajökull ice cap (Iceland)
This paper presents latest results from the combined use of SAR (Synthetic Aperture Radar) remote sensing and GIS providing detailed insights into recent volcanic activity under Vatnajökull ice cap (Iceland). Glaciers atop active volcanoes pose a constant potential danger to adjacent inhabited regions and infrastructure. Besides the usual volcanic hazards (lava flows, pyroclastic clouds, tephra falls, etc.), the volcano-ice interaction leads to enormous meltwater torrents (icelandic: jökulhlaup), devastating large areas in the surroundings of the affected glacier. The presented monitoring strategy addresses the three crucial questions: When will an eruption occur, where is the eruption site and which area is endangered by the accompanying jökulhlaup. Therefore, sufficient early-warning and hazard zonation for future subglacial volcanic eruptions becomes possible, as demonstrated for the Bardårbunga volcano under the northern parts of Vatnajökull. Seismic activity revealed unrest at the northern flanks of Bardårbunga caldera at the end of September 2006. The exact location of the corresponding active vent and therefore a potentially eruptive area could be detected by continuous ENVISAT-ASAR monitoring. With this knowledge a precise prediction of peri-glacial regions prone to a devastating outburst flood accompanying a possible future eruption is possible
Aging and Error Processing: Age Related Increase in the Variability of the Error-Negativity Is Not Accompanied by Increase in Response Variability
Background: Several studies report an amplitude reduction of the error negativity (Ne or ERN), an event-related potential occurring after erroneous responses, in older participants. In earlier studies it was shown that the Ne can be explained by a single independent component. In the present study we aimed to investigate whether the Ne reduction usually found in older subjects is due to an altered component structure, i.e., a true alteration in response monitoring in older subjects. Methodology/Principal Findings: Two age groups conducted two tasks with different stimulus response mappings and task difficulty. Both groups received fully balanced speed or accuracy instructions and an individually adapted deadline in both tasks. Event-related potentials, Independent Component analysis of EEG-data and between trial variability of the Ne were combined with analysis of error rates, coefficients of variation of RT-data and ex-Gaussian fittings to reaction times. The Ne was examined by means of ICA and PCA, yielding a prominent independent component on error trials, the Ne-IC. The Ne-IC was smaller in the older than the younger subjects for both speed and accuracy instructions. Also, the Ne-IC contributed to a much lesser extent to the Ne in older than in younger subjects. RT distribution parameters were not related to Ne/ERP-variability. Conclusions/Significance: The results show a genuine reduction as well as a different component structure of the Ne in older compared to young subjects. This reduction is not reflected in behaviour, apart from a general slowing of olde
Strong interface-induced spin-orbit coupling in graphene on WS2
Interfacial interactions allow the electronic properties of graphene to be
modified, as recently demonstrated by the appearance of satellite Dirac cones
in the band structure of graphene on hexagonal boron nitride (hBN) substrates.
Ongoing research strives to explore interfacial interactions in a broader class
of materials in order to engineer targeted electronic properties. Here we show
that at an interface with a tungsten disulfide (WS2) substrate, the strength of
the spin-orbit interaction (SOI) in graphene is very strongly enhanced. The
induced SOI leads to a pronounced low-temperature weak anti-localization (WAL)
effect, from which we determine the spin-relaxation time. We find that
spin-relaxation time in graphene is two-to-three orders of magnitude smaller on
WS2 than on SiO2 or hBN, and that it is comparable to the intervalley
scattering time. To interpret our findings we have performed first-principle
electronic structure calculations, which both confirm that carriers in
graphene-on-WS2 experience a strong SOI and allow us to extract a
spin-dependent low-energy effective Hamiltonian. Our analysis further shows
that the use of WS2 substrates opens a possible new route to access topological
states of matter in graphene-based systems.Comment: Originally submitted version in compliance with editorial guidelines.
Final version with expanded discussion of the relation between theory and
experiments to be published in Nature Communication
Neutrino Masses, Mixing, and Oscillations
The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 2,873 new measurements from 758 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Among the 118 reviews are many that are new or heavily revised, including a new review on Neutrinos in Cosmology. Starting with this edition, the Review is divided into two volumes. Volume 1 includes the Summary Tables and all review articles. Volume 2 consists of the Particle Listings. Review articles that were previously part of the Listings are now included in volume 1. The complete Review (both volumes) is published online on the website of the Particle Data Group (http://pdg.lbl.gov) and in a journal. Volume 1 is available in print as the PDG Book. A Particle Physics Booklet with the Summary Tables and essential tables, figures, and equations from selected review articles is also available. The 2018 edition of the Review of Particle Physics should be cited as: M. Tanabashi (Particle Data Group), Phys. Rev. D 98, 030001 (2018)
Review of Particle Physics: Particle Data Group
The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 2,873
new measurements from 758 papers, we list, evaluate, and average measured properties of gauge bosons and the
recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical
particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. Particle properties and search
limits are listed in Summary Tables. We give numerous tables, figures, formulae, and reviews of topics such as Higgs
Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology,
Particle Detectors, Colliders, Probability and Statistics. Among the 118 reviews are many that are new or heavily
revised, including a new review on Neutrinos in Cosmology.
Starting with this edition, the Review is divided into two volumes. Volume 1 includes the Summary Tables
and all review articles. Volume 2 consists of the Particle Listings. Review articles that were previously part of the
Listings are now included in volume 1.
The complete Review (both volumes) is published online on the website of the Particle Data Group
(http://pdg.lbl.gov) and in a journal. Volume 1 is available in print as the PDG Book. A Particle Physics Booklet
with the Summary Tables and essential tables, figures, and equations from selected review articles is also available
Review of Particle Physics
The Review summarizes much of particle physics and cosmology. Using data from previous editions, plus 3,062 new measurements from 721 papers, we list, evaluate, and average measured properties of gauge bosons and the recently discovered Higgs boson, leptons, quarks, mesons, and baryons. We summarize searches for hypothetical particles such as supersymmetric particles, heavy bosons, axions, dark photons, etc. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as Higgs Boson Physics, Supersymmetry, Grand Unified Theories, Neutrino Mixing, Dark Energy, Dark Matter, Cosmology, Particle Detectors, Colliders, Probability and Statistics. Among the 117 reviews are many that are new or heavily revised, including those on Pentaquarks and Inflation. The complete Review is published online in a journal and on the website of the Particle Data Group (http://pdg.lbl.gov). The printed PDG Book contains the Summary Tables and all review articles but no longer includes the detailed tables from the Particle Listings. A Booklet with the Summary Tables and abbreviated versions of some of the review articles is also available
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