Reddening law and interstellar dust properties along Magellanic sight-lines

This study establishes that SMC, LMC and Milky Way extinction curves obey the same extinction law which depends on the 2200 Å bump size and one parameter, and generalizes the Cardelli, Clayton and Mathis (Cardelli et al., Astrophys. J. 345, 245, 1989) relationship. This suggests that extinction in all three galaxies is of the same nature. The role of linear reddening laws over all the visible/UV wavelength range, particularly important in the SMC but also present in the LMC and in the Milky Way, is also highlighted and discussed.     

Pb,Hf and Nd isotope compositions of the two Réunion volcanoes (Indian Ocean): A tale of two small-scale mantle “blobs”?

Pb, Hf, Nd and Sr isotopes of basaltic lavas from the two Réunion Island volcanoes are reported in order to examine the origin of the sources feeding these volcanoes and to detect possible changes through time. Samples, chosen to cover the whole lifetime of the two volcanoes (from 2 Ma to present), yield a chemically restricted (compared to OIB lavas) but complex distribution. Réunion plume isotopic characteristics have been defined on the basis of the composition of uncontaminated shield-building lavas from the Piton de la Fournaise volcano. The average ?_Nd, ?_Hf, ⁸⁷Sr/⁸⁶Sr and ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb isotope ratios calculated for this component are + 4.4, + 9.1, 0.70411, 18.97, 15.59 and 39.03, respectively. In Pb–Pb isotope space, each volcano defines a distinct linear trend but slight variations are also detected within the various volcanic sequences. The Piton des Neiges volcano yields a distinct and significantly more scattered isotopic distribution than Piton de la Fournaise for both Pb, Hf and Nd isotope tracers. A principal component analysis of the Pb isotope data from Piton de la Fournaise reveals a major contribution of the C and EM-1 components (with a clear Dupal flavor) as main components for the modern Réunion plume. The same components have been identified for Piton des Neiges but with a stronger participation of a depleted mantle component and a weaker EM-1 contribution. The compositional change of the lavas erupted by the Piton des Neiges and Piton de la Fournaise volcanoes is attributed to the impingement of two small-scale blobs of plume material at the base of the Réunion lithosphere. Compared to other hot-spots worldwide, in particular Hawaii and Kerguelen, magmas beneath Réunion are generated from a considerably more homogeneous, compositionally more primitive plume higher in ²⁰⁶Pb. Although shallow-level contamination processes have been locally detected they did not alter significantly the composition of the plume magmas. This is tentatively attributed to mantle dynamics producing small, high-velocity blobs that ascend rapidly through the lithosphere, and to the lack of a well-developed magma chamber at depth in the lithosphere.     

On type-I migration near opacity transitions. A generalized Lindblad torque formula for planetary population synthesis

We give an expression for the Lindblad torque acting on a low-mass planet embedded in a protoplanetary disk that is valid even at locations where the surface density or temperature profile cannot be approximated by a power law, such as an opacity transition. At such locations, the Lindblad torque is known to suffer strong deviation from its standard value, with potentially important implications for type I migration, but the full treatment of the tidal interaction is cumbersome and not well suited to models of planetary population synthesis. The expression that we propose retains the simplicity of the standard Lindblad torque formula and gives results that accurately reproduce those of numerical simulations, even at locations where the disk temperature undergoes abrupt changes. Our study is conducted by means of customized numerical simulations in the low-mass regime, in locally isothermal disks, and compared to linear torque estimates obtained by summing fully analytic torque estimates at each Lindblad resonance. The functional dependence of our modified Lindblad torque expression is suggested by an estimate of the shift of the Lindblad resonances that mostly contribute to the torque, in a disk with sharp gradients of temperature or surface density, while the numerical coefficients of the new terms are adjusted to seek agreement with numerics. As side results, we find that the vortensity related corotation torque undergoes a boost at an opacity transition that can counteract migration, and we find evidence from numerical simulations that the linear corotation torque has a non-negligible dependency upon the temperature gradient, in a locally isothermal disk.     

Radon emanation of heterogeneous basin deposits in Kathmandu Valley,Nepal

Effective radium-226 concentration (EC_Ra) has been measured in soil samples from seven horizontal and vertical profiles of terrace scarps in the northern part of Kathmandu Valley, Nepal. The samples belong to the Thimi, Gokarna, and Tokha Formations, dated from 50 to 14 ky BP, and represent a diverse fluvio-deltaic sedimentary facies mainly consisting of gravelly to coarse sands, black, orange and brown clays. EC_Ra was measured in the laboratory by radon-222 emanation. The samples (n = 177) are placed in air-tight glass containers, from which, after an accumulation time varying from 3 to 18 days, the concentration of radon-222, radioactive decay product of radium-226 and radioactive gas with a half-life of 3.8 days, is measured using scintillation flasks. The EC_Ra values from the seven different profiles of the terrace deposits vary from 0.4 to 43 Bq kg^?1, with profile averages ranging from 12 ± 1 to 27 ± 2 Bq kg^?1. The values have a remarkable consistency along a particular horizon of sediment layers, clearly demonstrating that these values can be used for long distance correlations of the sediment horizons. Widely separated sediment profiles, representing similar stratigraphic positions, exhibit consistent EC_Ra values in corresponding stratigraphic sediment layers. EC_Ra measurements therefore appear particularly useful for lithologic and stratigraphic discriminations. For comparison, EC_Ra values of soils from different localities having various sources of origin were also obtained: 9.2 ± 0.4 Bq kg^?1 in soils of Syabru–Bensi (Central Nepal), 23 ± 1 Bq kg^?1 in red residual soils of the Bhattar-Trisuli Bazar terrace (North of Kathmandu), 17.1 ± 0.3 Bq kg^?1 in red residual soils of terrace of Kalikasthan (North of Trisuli Bazar) and 10 ± 1 Bq kg^?1 in red residual soils of a site near Nagarkot (East of Kathmandu). The knowledge of EC_Ra values for these various soils is important for modelling radon exhalation at the ground surface, in particular in the vicinity of active faults. Importantly, the study also reveals that, above numerous sediments of Kathmandu Valley, radon concentration in dwellings can potentially exceed the level of 300 Bq m^?3 for residential areas; a fact that should be seriously taken into account by the governmental and non-governmental agencies as well as building authorities.     

Mais comment s'écoule donc un glacier ? Aperçu historique

Ice and snow have often helped physicists understand the world. On the contrary it has taken them a very long time to understand the flow of the glaciers. Naturalists only began to take an interest in glaciers at the beginning of the 19th century during the last phase of glacier advances. When the glacier flow from the upslope direction became obvious, it was then necessary to understand how it flowed. It was only in 1840, the year of the Antarctica ice sheet discovery by Dumont d'Urville, that two books laid the basis for the future field of glaciology: one by Agassiz on the ice age and glaciers, the other one by canon Rendu on glacier theory. During the 19th century, ice flow theories, adopted by most of the leading scientists, were based on melting/refreezing processes. Even though the word ‘fluid’ was first used in 1773 to describe ice, more the 130 years would have to go by before the laws of fluid mechanics were applied to ice. Even now, the parameter of Glen's law, which is used by glaciologists to model ice deformation, can take a very wide range of values, so that no unique ice flow law has yet been defined. To cite this article: F. Rémy, L. Testut, C. R. Geoscience 338 (2006).     

High-frequency monitoring of hydrological and biogeochemical fluxes in forested catchments of southern Chile

The variability of rainfall-dependent streamflow at catchment scale modulates many ecosystem processes in wet temperate forests. Runoff in small mountain catchments is characterized by a quick response to rainfall pulses which affects biogeochemical fluxes to all downstream systems. In wet-temperate climates, water erosion is the most important natural factor driving downstream soil and nutrient losses from upland ecosystems. Most hydrochemical studies have focused on water flux measurements at hourly scales, along with weekly or monthly samples for water chemistry. Here, we assessed how water and element flows from broad-leaved, evergreen forested catchments in southwestern South America, are influenced by different successional stages, quantifying runoff, sediment transport and nutrient fluxes during hourly rainfall events of different intensities. Hydrograph comparisons among different successional stages indicated that forested catchments differed in their responses to high intensity rainfall, with greater runoff in areas covered by secondary forests (SF), compared to old-growth forest cover (OG) and dense scrub vegetation (CH). Further, throughfall water was greatly nutrient enriched for all forest types. Suspended sediment loads varied between successional stages. SF catchments exported 455 kg of sediments per ha, followed by OG with 91 kg/ha and CH with 14 kg/ha, corresponding to 11 rainfall events measured from December 2013 to April 2014. Total nitrogen (TN) and phosphorus (TP) concentrations in stream water also varied with rainfall intensity. In seven rainfall events sampled during the study period, CH catchments exported less nutrients (46 kg/ha TN and 7 kg/ha TP) than SF catchments (718 kg/ha TN and 107 kg/ha TP), while OG catchments exported intermediate sediment loads (201 kg/ha TN and 23 kg/ha TP). Further, we found significant effects of successional stage attributes (vegetation structure and soil physical properties) and catchment morphometry on runoff and sediment concentrations, and greater nutrients retention in OG and CH catchments. We conclude that in these southern hemisphere, broad-leaved evergreen temperate forests, hydrological processes are driven by multiple interacting phenomena, including climate, vegetation, soils, topography, and disturbance history.     

Record of enhanced late Pliocene tectono‐volcanic activity in the Lesser Antilles forearc basin: Insights into the long‐term behaviour of the Lesser Antilles subduction zone

In this study, we investigate the Lesser Antilles forearc basin, focusing on the late Pliocene to Pleistocene sedimentary archives in order to track the occurrence of extreme events triggered by enhanced subduction‐related tectono‐volcanic activity. We identify late Piacenzian deposits covering a major regional erosional surface, displaying sedimentary dykes and large marine boulders embedded in a mixed continental–marine matrix, characteristic of tsunamites. We interpret this episode of platform emersion and the successive cataclysmic deposits as resulting from enhanced tectonic activity at the interface of the subduction zone, synchronous with the initiation of the Lesser Antilles volcanic arc. We then discuss the implications in terms of the mechanical behaviour of the Lesser Antilles subduction zone.     

Die Rheingrabenrandverwerfung im Wattkopftunnel bei Ettlingen (Nordschwarzwald)

The Wattkopftunnel, near Ettlingen (Nordschwarzwald), drives through the eastern margin of the Rheingraben. The tunnel passes cenozoic and mesozoic sediments. Early quarternary and tertiary beds are situated west of the main thrust of the Rheingraben. Fossil record indicates upper Oligocene age (Chatt) for parts of the tertiary sediments. At the eastern border of the Rheingraben, wedges of jurassic and middle triassic series are squeezed. East of the Rheingraben the tunnel drives in the lower triassic Bausandstein. The eastern margin of the Rheingraben was investigated in detail during tunneling. Faults of the Rheingraben margin are distributed in an 130 meter wide fault zone in the tunnel. Total stratigraphic separation by the normal faults reaches more than 2 000 meters. The cenozoic sequence suffered synsedimentary to early diagenetic deformation, while the mesozoic series are characterized by ruptural deformation. The fault- and joint system is directed in the rheinische Richtung (SSW-NNE). East of the Rheingraben a second direction occur, running parallel to the lower Albtal (W-E).

     

Solid–fluid transition modelling in geomaterials and application to a mudflow interacting with an obstacle

Given the contrasting behaviour observed for geomaterials, for example, during landslides of the flow type, this contribution proposes an original constitutive model, which associates both an elasto‐plastic relation and a Bingham viscous law linked by a mechanical transition criterion. This last is defined as the second‐order work sign for each material point, which is a general criterion for divergence instabilities. Finite element method with Lagrangian integration points is chosen as a framework for implementing the new model because of its well‐known ability to deal with both solid and fluid behaviours in large deformation processes. A first boundary model considering a sample of initially stable soil, a slope and an obstacle is performed. The results show the power of the constitutive model because the consistent evolution of initiation, propagation and arrest of the mudflow is described. A parametric study is led on various plastic and viscous parameters to determine their influence on the flow development and arrest. Finally, forces against the obstacle are compared with good agreement with those of other authors for the same geometry and a pure viscous behaviour. Copyright © 2014 John Wiley & Sons, Ltd.     

Defining deep decarbonization pathways for Switzerland: an economic evaluation

This article simulates deep decarbonization pathways for a small open economy that lacks the usual avenues for large CO₂ reductions – heavy industry and power generation. A computable general equilibrium model is used to assess the energy and economic impacts of the transition to only one ton of CO₂ emissions per capita in 2050. This represents a 76% reduction with respect to 1990 levels, while the population is expected to be 46% larger and GPD to increase by 90%. The article discusses several options and scenarios that are compatible with this emissions target and compares them with a reference scenario that extrapolates already-decided climate and energy policy instruments. We show that the ambitious target is attainable at moderate welfare costs, even if it needs very high carbon prices, and that these costs are lower when either CO₂ can be captured and sequestered or electricity consumption can be taxed sufficiently to stabilize it.

Policy relevance

In the context of COP 21, all countries must propose intended contributions that involve deep decarbonization of their economy over the next decades. This article defines and analyses such pathways for Switzerland, taking into consideration the existing energy demand and supply and also already-defined climate policies. It draws several scenarios that are compatible with a target of 1 ton of CO₂ emissions per capita in 2050. This objective is very challenging, especially with the nuclear phase out decided after the disaster in Fukushima and the political decision to balance electricity trade. Nevertheless, it is possible to design several feasible pathways that are based on different options. The economic cost is significant but affordable for the Swiss economy. The insights are relevant not only for Switzerland, but also for other industrialized countries when defining their INDCs.