182 research outputs found
Erosion influences the seismicity of active thrust faults
International audienceAssessing seismic hazards remains one of the most challenging scientific issues in Earthsciences. Deep tectonic processes are classically considered as the only persistentmechanism driving the stress loading of active faults over a seismic cycle. Here we show via amechanical model that erosion also significantly influences the stress loading of thrust faultsat the timescale of a seismic cycle. Indeed, erosion rates of about B0.1â20mmyr1, asdocumented in Taiwan and in other active compressional orogens, can raise the Coulombstress by B0.1â10 bar on the nearby thrust faults over the inter-seismic phase. Masstransfers induced by surface processes in general, during continuous or short-lived andintense events, represent a prominent mechanism for inter-seismic stress loading offaults near the surface. Such stresses are probably sufficient to trigger shallow seismicity orpromote the rupture of deep continental earthquakes up to the surface
Exploring IRSL 50 fading variability in bedrock feldspars and implications for OSL thermochronometry
International audienceOptically Stimulated Luminescence (OSL) is a well-established Quaternary dating method, which has recently been adapted to application in low-temperature thermochronometry. The Infra-Red Stimulated Luminescence (IRSL) of feldspar, which so far is the most promising target signal in thermochronometry, is unfortunately prone to anomalous fading. The fading of feldspar IRSL is at times not only challenging to measure, but also laborious to incorporate within luminescence growth models. Quantification of IRSL fading is therefore a crucial step in OSL thermochronometry, raising questions regarding (i) reproducibility and reliability of laboratory measurements of fading, as well as (ii) the applicability of existing fading models to quantitatively predict the level of IRSL field saturation in nature. Here we investigate the natural luminescence signal and anomalous fading of IRSL measured at 50 °C (IRSL50) in 32 bedrock samples collected from a variety of lithologies and exhumation settings (Alaska and Norway). We report a large span of IRSL50 fading rates between samples (g2days ranging from âŒ0.5 to âŒ45%/decade), which further demonstrates (i) a good reproducibility between two common fading measurement protocols, and (ii) the ability of tunnelling models to predict the level of feldspar IRSL50 field saturation in nature. We observe higher IRSL50 fading in feldspar with increasing Ca content, although other factors cannot be dismissed at present. Finally, our dataset confirms that the applicability of feldspar IRSL50 in OSL thermochronometry is limited to rapidly-exhuming settings or warm subsurface environments
Non-BPS Brane Cosmology
We study cosmology on a BPS D3-brane evolving in the 10D SUGRA background
describing a non-BPS brane. Initially the BPS brane is taken to be a probe
whose dynamics we determine in the non-compact non-BPS background. The
cosmology observed on the brane is of the FRW type with a scale factor
. In this mirage cosmology approach, there is no self-gravity on the
brane which cannot inflate. Self-gravity is then included by compactifying the
background space-time. The low energy effective theory below the
compactification scale is shown to be bi-metric, with matter coupling to a
different metric than the geometrically induced metric on the brane. The
geometrical scale factor on the brane is now where
arises from brane self-gravity. In this non-BPS scenario the brane generically
inflates. We study the resulting inflationary scenario taking into account the
fact that the non-BPS brane eventually decays on a time-scale much larger than
the typical inflationary time-scale. After the decay, the theory ceases to be
bi-metric and COBE normalization is used to estimate the string scale which is
found to be of order GeV.Comment: 20 pages, JHEP3.cl
Modelling 3D crack propagation in ageing graphite bricks of Advanced Gas-cooled Reactor power plant
In this paper, crack propagation in Advanced Gas-cooled Reactor (AGR) graphite bricks withageing properties is studied using the eXtended Finite Element Method (X-FEM). A parametric study for crackpropagation, including the influence of different initial crack shapes and propagation criteria, is conducted. Theresults obtained in the benchmark study show that the crack paths from X-FEM are similar to the experimentalones. The accuracy of the strain energy release rate computation in a heterogeneous material is also evaluatedusing a finite difference approach. Planar and non-planar 3D crack growth simulations are presented todemonstrate the robustness and the versatility of the method utilized. Finally, this work contributes to the better understanding of crack propagation behaviour in AGR graphite bricks and so contributes to the extension of the AGR plantsâ lifetimes in the UK by reducing uncertainties
Dirac Born Infeld (DBI) Cosmic Strings
Motivated by brane physics, we consider the non-linear Dirac-Born-Infeld
(DBI) extension of the Abelian-Higgs model and study the corresponding cosmic
string configurations. The model is defined by a potential term, assumed to be
of the mexican hat form, and a DBI action for the kinetic terms. We show that
it is a continuous deformation of the Abelian-Higgs model, with a single
deformation parameter depending on a dimensionless combination of the scalar
coupling constant, the vacuum expectation value of the scalar field at
infinity, and the brane tension. By means of numerical calculations, we
investigate the profiles of the corresponding DBI-cosmic strings and prove that
they have a core which is narrower than that of Abelian-Higgs strings. We also
show that the corresponding action is smaller than in the standard case
suggesting that their formation could be favoured in brane models. Moreover we
show that the DBI-cosmic string solutions are non-pathological everywhere in
parameter space. Finally, in the limit in which the DBI model reduces to the
Bogomolnyi-Prasad-Sommerfield (BPS) Abelian-Higgs model, we find that DBI
cosmic strings are no longer BPS: rather they have positive binding energy. We
thus argue that, when they meet, two DBI strings will not bind with the
corresponding formation of a junction, and hence that a network of DBI strings
is likely to behave as a network of standard cosmic strings.Comment: 25 pages, 12 figure
Quantifying sediment mass redistribution from joint time-lapse gravimetry and photogrammetry surveys
The accurate quantification of sediment mass redistribution is central to the study of surface processes, yet it remains a challenging task. Here we test a new combination of terrestrial gravity and drone photogrammetry methods to quantify sediment mass redistribution over a 1âkm2 area. Gravity and photogrammetry are complementary methods. Indeed, gravity changes are sensitive to mass changes and to their location. Thus, by using photogrammetry data to constrain this location, the sediment mass can be properly estimated from the gravity data. We carried out three joint gravimetryâphotogrammetry surveys, once a year in 2015, 2016 and 2017, over a 1âkm^2 area in southern Taiwan, featuring both a wide meander of the Laonong River and a slow landslide. We first removed the gravity changes from non-sediment effects, such as tides, groundwater, surface displacements and air pressure variations. Then, we inverted the density of the sediment with an attempt to distinguish the density of the landslide from the density of the river sediments. We eventually estimate an average loss of 3.7â\ub1â0.4â
7â10^9âkg of sediment from 2015 to 2017 mostly due to the slow landslide. Although the gravity devices used in this study are expensive and need week-long surveys, new instrumentation currently being developed will enable dense and continuous measurements at lower cost, making the method that has been developed and tested in this study well-suited for the estimation of erosion, sediment transfer and deposition in landscapes
Quiescent Dense Gas in Protostellar Clusters: the Ophiuchus A Core
We present combined BIMA interferometer and IRAM 30 m Telescope data of N2H+
1-0 line emission across the nearby dense, star forming core Ophiuchus A (Oph
A) at high linear resolution (e.g., ~1000 AU). Six maxima of integrated line
intensity are detected which we designate Oph A-N1 through N6. The N4 and N5
maxima are coincident with the starless continuum objects SM1 and SM2
respectively but the other maxima are not coincident with previously-identified
objects. In contrast, relatively little N2H+ 1-0 emission is coincident with
the starless object SM2 and the Class 0 protostar VLA 1623. The FWHM of the
N2H+ 1-0 line, Delta V, varies by a factor of ~5 across Oph A. Values of Delta
V < 0.3 km/s are found in 14 locations in Oph A, but only that associated with
N6 is both well-defined spatially and larger than the beam size. Centroid
velocities of the line, V_LSR, vary relatively little, having an rms of only
\~0.17 km/s. Small-scale V_LSR gradients of <0.5 km/s over ~0.01 pc are found
near SM1, SM1N, and SM2, but not N6. The low N2H+ abundances of SM2 or VLA 1623
relative to SM1, SM1N, or N6 may reflect relatively greater amounts of N2
adsorption onto dust grains in their colder and probably denser interiors. The
low Delta V of N6, i.e., 0.193 km/s FWHM, is only marginally larger than the
FWHM expected from thermal motions alone, suggesting turbulent motions in the
Oph A core have been reduced dramatically at this location. The non-detection
of N6 in previous thermal continuum maps suggests that interesting sites
possibly related to star formation may be overlooked in such data.Comment: LaTex with 7 figures, produces 36 pages. Accepted for publication in
ApJ. Typo related to Equation 3 fixed, caused derived values of N(N2H+) and
X(N2H+) to be low by factors of ~40%. Conclusions of paper are unchange
A systematic review and an individual patient data meta-analysis of ivermectin use in children weighing less than fifteen kilograms: Is it time to reconsider the current contraindication?
BACKGROUND: Oral ivermectin is a safe broad spectrum anthelminthic used for treating several neglected tropical diseases (NTDs). Currently, ivermectin use is contraindicated in children weighing less than 15 kg, restricting access to this drug for the treatment of NTDs. Here we provide an updated systematic review of the literature and we conducted an individual-level patient data (IPD) meta-analysis describing the safety of ivermectin in children weighing less than 15 kg. METHODOLOGY/PRINCIPAL FINDINGS: A systematic review was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) for IPD guidelines by searching MEDLINE via PubMed, Web of Science, Ovid Embase, LILACS, Cochrane Database of Systematic Reviews, TOXLINE for all clinical trials, case series, case reports, and database entries for reports on the use of ivermectin in children weighing less than 15 kg that were published between 1 January 1980 to 25 October 2019. The protocol was registered in the International Prospective Register of Systematic Reviews (PROSPERO): CRD42017056515. A total of 3,730 publications were identified, 97 were selected for potential inclusion, but only 17 sources describing 15 studies met the minimum criteria which consisted of known weights of children less than 15 kg linked to possible adverse events, and provided comprehensive IPD. A total of 1,088 children weighing less than 15 kg were administered oral ivermectin for one of the following indications: scabies, mass drug administration for scabies control, crusted scabies, cutaneous larva migrans, myiasis, pthiriasis, strongyloidiasis, trichuriasis, and parasitic disease of unknown origin. Overall a total of 1.4% (15/1,088) of children experienced 18 adverse events all of which were mild and self-limiting. No serious adverse events were reported. CONCLUSIONS/SIGNIFICANCE: Existing limited data suggest that oral ivermectin in children weighing less than 15 kilograms is safe. Data from well-designed clinical trials are needed to provide further assurance
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