562 research outputs found
The effects of degassing on magmatic gas waves and long period eruptive precursors at silicic volcanoes
Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 125 (10), (2020): e2020JB019755, https://doi.org/10.1029/2020JB019755Cyclical ground deformation, associated seismicity, and elevated degassing are important precursors to explosive eruptions at silicic volcanoes. Regular intervals for elevated activity (6–30 hr) have been observed at volcanoes such as Mount Pinatubo in the Philippines and Soufrière Hills in Montserrat. Here, we explore a hypothesis originally proposed by Michaut et al. (2013, https://doi.org/10.1038/ngeo1928) where porosity waves containing magmatic gas are responsible for the observed periodic behavior. We use two‐phase theory to construct a model where volatile‐rich, bubbly, viscous magma rises and decompresses. We conduct numerical experiments where magma gas waves with various frequencies are imposed at the base of the model volcanic conduit. We numerically verify the results of Michaut et al. (2013, https://doi.org/10.1038/ngeo1928) and then expand on the model by allowing magma viscosity to vary as a function of dissolved water and crystal content. Numerical experiments show that gas exsolution tends to damp the growth of porosity waves during decompression. The instability and resultant growth or decay of gas wave amplitude depends strongly on the gas density gradient and the ratio of the characteristic magma extraction rate to the characteristic magma degassing rate (Damköhler number, Da). We find that slow degassing can lead to a previously unrecognized filtering effect, where low‐frequency gas waves may grow in amplitude. These waves may set the periodicity of the eruptive precursors, such as those observed at Soufrière Hills Volcano. We demonstrate that degassed, crystal‐rich magma is susceptible to the growth of gas waves which may result in the periodic behavior.J. S. J. and D. B. were supported by NSF grant EAR‐1645057. C. M. has received financial support of the IDEXLyon Project of the University of Lyon in the frame of the Programme Investissements dAvenir (ANR‐16‐IDEX‐0005)
Modeling multidimensional effects in the propagation of radiative shocks
Radiative shocks (also called supercritical shocks) are high Mach number shock waves that photoionize the medium ahead of the shock front and give rise to a radiative precursor. They are generated in the laboratory using high-energy or high-power lasers and are frequently present in a wide range of astronomical objects. Their modelisation in one dimension has been the subject of numerous studies, but generalization to three dimensions is not straightforward. We calculate analyticaly the absorption of radiation in a grey uniform cylinder and show how it decreases with , the product of the opacity and of the cylinder radius . Simple formulas, whose validity range increases when diminishes, are derived for the radiation field on the axis of symmetry. Numerical calculations in three dimensions of the radiative energy density, flux and pressure created by a stationary shock wave show how the radiation decreases whith . Finally, the bidimensional structures of both the precursor and the radiation field are calculated with time-dependent radiation hydrodynamics numerical simulations and the influence of two-dimensional effects on the electron density, the temperature, the shock velocity and the shock geometry are exhibited. These simulations show how the radiative precursor shortens, cools and slows down when is decreased
Similarity Properties and Scaling Laws of Radiation Hydrodynamic Flows in Laboratory Astrophysics
The spectacular recent development of modern high-energy density laboratory
facilities which concentrate more and more energy in millimetric volumes allows
the astrophysical community to reproduce and to explore, in millimeter-scale
targets and during very short times, astrophysical phenomena where radiation
and matter are strongly coupled. The astrophysical relevance of these
experiments can be checked from the similarity properties and especially
scaling laws establishment, which constitutes the keystone of laboratory
astrophysics. From the radiating optically thin regime to the so-called
optically thick radiative pressure regime, we present in this paper, for the
first time, a complete analysis of the main radiating regimes that we
encountered in laboratory astrophysics with the same formalism based on the
Lie-group theory. The use of the Lie group method appears as systematic which
allows to construct easily and orderly the scaling laws of a given problem.
This powerful tool permits to unify the recent major advances on scaling laws
and to identify new similarity concepts that we discuss in this paper and which
opens important applications for the present and the future laboratory
astrophysics experiments. All these results enable to demonstrate theoretically
that astrophysical phenomena in such radiating regimes can be explored
experimentally thanks to powerful facilities. Consequently the results
presented here are a fundamental tool for the high-energy density laboratory
astrophysics community in order to quantify the astrophysics relevance and
justify laser experiments. Moreover, relying on the Lie-group theory, this
paper constitutes the starting point of any analysis of the self-similar
dynamics of radiating fluids.Comment: Astrophys. J. accepte
Link between laboratory and astrophysical radiative shocks
This work provides analytical solutions describing the post-shock structure
of radiative shocks growing in astrophysics and in laboratory. The equations
including a cooling function are solved for any values of the exponents , and
. This modeling is appropriate to astrophysics as the observed
radiative shocks arise in optically thin media. In contrast, in laboratory,
radiative shocks performed using high-power lasers present a radiative
precursor because the plasma is more or less optically thick. We study the
post-shock region in the laboratory case and compare with astrophysical shock
structure. In addition, we attempt to use the same equations to describe the
radiative precursor, but the cooling function is slightly modified. In future
experiments we will probe the PSR using X-ray diagnostics. These new
experimental results will allow to validate our astrophysical numerical codes
Highlights from the 6th International Society for Computational Biology Student Council Symposium at the 18th Annual International Conference on Intelligent Systems for Molecular Biology
This meeting report gives an overview of the keynote lectures and a selection of the student oral and poster presentations at the 6th International Society for Computational Biology Student Council Symposium that was held as a precursor event to the annual international conference on Intelligent Systems for Molecular Biology (ISMB). The symposium was held in Boston, MA, USA on July 9th, 2010
Hydrodynamic instabilities in a highly radiative environment
In this paper, we present the effects of a radiative shock (RS) on the morphology of jet-like objects subjected to hydrodynamic instabilities. To this end, we used an experimental platform developed to create RSs on high energy laser facilities such as LULI2000 and GEKKO XII. Here, we employed modulated targets to initiate Richtmyer–Meshkov and Rayleigh–Taylor instability (RTI) growth in the presence of an RS. The RS is obtained by generating a strong shock in a dense pusher that expands into a low-density xenon gas. With our design, only a limited RTI growth occurs in the absence of radiative effects. A strongly radiative shock has opposite effects on RTI growth. While its deceleration enhances the instability growth, the produced radiations tend to stabilize the interfaces. Our indirect experimental observations suggest a lower instability growth despite the interface deceleration. In addition, the jets, produced during the experiment, are relevant to astrophysical structures such as Herbig–Haro objects or other radiatively cooling jets
Counter-propagating radiative shock experiments on the Orion laser and the formation of radiative precursors
We present results from new experiments to study the dynamics of radiative
shocks, reverse shocks and radiative precursors. Laser ablation of a solid
piston by the Orion high-power laser at AWE Aldermaston UK was used to drive
radiative shocks into a gas cell initially pressurised between and $1.0 \
bar with different noble gases. Shocks propagated at {80 \pm 10 \ km/s} and
experienced strong radiative cooling resulting in post-shock compressions of {
\times 25 \pm 2}. A combination of X-ray backlighting, optical self-emission
streak imaging and interferometry (multi-frame and streak imaging) were used to
simultaneously study both the shock front and the radiative precursor. These
experiments present a new configuration to produce counter-propagating
radiative shocks, allowing for the study of reverse shocks and providing a
unique platform for numerical validation. In addition, the radiative shocks
were able to expand freely into a large gas volume without being confined by
the walls of the gas cell. This allows for 3-D effects of the shocks to be
studied which, in principle, could lead to a more direct comparison to
astrophysical phenomena. By maintaining a constant mass density between
different gas fills the shocks evolved with similar hydrodynamics but the
radiative precursor was found to extend significantly further in higher atomic
number gases (\sim4$ times further in xenon than neon). Finally, 1-D and 2-D
radiative-hydrodynamic simulations are presented showing good agreement with
the experimental data.Comment: HEDLA 2016 conference proceeding
Parallel In Vivo and In Vitro Melanoma RNAi Dropout Screens Reveal Synthetic Lethality between Hypoxia and DNA Damage Response Inhibition
SummaryTo identify factors preferentially necessary for driving tumor expansion, we performed parallel in vitro and in vivo negative-selection short hairpin RNA (shRNA) screens. Melanoma cells harboring shRNAs targeting several DNA damage response (DDR) kinases had a greater selective disadvantage in vivo than in vitro, indicating an essential contribution of these factors during tumor expansion. In growing tumors, DDR kinases were activated following hypoxia. Correspondingly, depletion or pharmacologic inhibition of DDR kinases was toxic to melanoma cells, including those that were resistant to BRAF inhibitor, and this could be enhanced by angiogenesis blockade. These results reveal that hypoxia sensitizes melanomas to targeted inhibition of the DDR and illustrate the utility of in vivo shRNA dropout screens for the identification of pharmacologically tractable targets
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