Research of Small Kuiper Belt Objects by Stellar Occultations

Fast photometric observations of target stars in the ecliptic are a powerful tool to detect small objects in the Kuiper Belt. The various parameters involved in such observations are described. Meter-sized telescopes are able to detect sub-kilometer KBO (Kuiper Belt Objects). A campaign of research of KBO by stellar occultations, organized at the Pic du Midi Observatory is presented. These observations bring the first constraint on the small end of the size distribution of the KBOs.     

Polarization in the young cluster NGC 6611: circumstellar, interstellar, or ... both?

We obtained linear polarization observations of 82 A/B-type stars in the young cluster NGC 6611, in order to probe the circumstellar material and to search for any evidence of intracluster or interstellar material that could also contribute to the polarization. We found linear polarization values that reach up to 14%. We consider the distribution of the polarization, its position angle, correlations with extinction and membership probability, polarization variability and wavelength distribution to identify the origin of the polarization toward NGC 6611. The polarization is found to be dominated by interstellar polarization, although some stars also have some circumstellar polarization. There is no evidence for intracluster dust. Rather, the dust must be located in a low density cloud toward the general line of sight to NGC 6611 and in front of it. The depth of that cloud along the line of sight increases slowly from the south–east to the north–west. The cloud is threaded by a very uniform magnetic field.     

A porous media finite element approach for soil instability including the second-order work criterion

This paper deals with the hydromechanical modelling of the initiation of failure in soils with particular reference to landslides. To this end, localized and diffused failure modes are simulated with a finite element model for coupled elasto-plastic variably saturated porous geomaterials, in which the material point instability is detected with the second-order work criterion based on Hill’s sufficient condition of stability. Three different expressions of the criterion are presented, in which the second-order work is expressed in terms of generalized effective stress, of total stress and thirdly by taking into account the hydraulic energy contribution for partially saturated materials. The above-mentioned computational framework has been applied to study two initial boundary value problems: shear failure of a plane strain compression test of globally undrained water-saturated dense sand (where cavitation occurs at strain localization) and isochoric grain matter, and the onset of a flowslide from southern Italy due to rainfall (Sarno-Quindici events, May 5–6 1998). It is shown that the second-order work criterion applied at the material point level detects the local material instability and gives a good spatial indication of the extent of the potentially unstable domains in both the localized and diffused failure mechanisms of the cases analyzed, is able to capture the instability induced by cavitation of the liquid water and gives results according to the time evolution of plastic strains and displacement rate.     

Partitioning Stakeholders for the Economic Valuation of Ecosystem Services: Examples of a Mangrove System

Although the importance of ecosystem services provided by natural forests, especially mangroves, is well known, the destruction of these environments is still ubiquitous and therefore protection measures are urgently needed. The present study compares the current approach of economic valuation of ecosystem services to a proposed one, using a study case of a mangrove system as an example. We suggest that a cost-benefit analysis for economically valuing environmental services should be performed with three additional modifications consisting of (i) a categorization of local stakeholders as demanders of particular ecosystem services, (ii) acknowledgement of the government as one of these demander groups, and (iii) the inclusion of opportunity costs in the valuation. The application of this approach to the mangrove area in the east portion of Great Abaco Island, the Bahamas, reveals that not only the ecosystem services received differ between demander groups, but the monetary benefits and costs are also specific to each of these groups. We show that the economic valuation of the ecosystem should be differentiated for each category, instead of being calculated as a net ‘societal value’ as it is currently. Applying this categorization of demanders enables a better understanding of the cost and benefit structure of the protection of a natural area. The present paper aims to facilitate discussions regarding benefit and cost sharing related to the protection of natural areas.     

Impact of the Nocturnal Low-Level Jet and Orographic Waves on Turbulent Motions and Energy Fluxes in the Lower Atmospheric Boundary Layer

The nocturnal low-level jet (LLJ) and orographic (gravity) waves play an important role in the generation of turbulence and pollutant dispersion and can affect the energy production by wind turbines. Additionally, gravity waves have an influence on the local mixing and turbulence within the surface layer and the vertical flux of mass into the lower atmosphere. On 25 September 2017, during a field campaign, a persistent easterly LLJ and gravity waves were observed simultaneously in a coastal area in the north of France. We explore the variability of the wind speed, turbulent eddies, and turbulence kinetic energy in the time–frequency and space domain using an ultrasonic anemometer and a scanning wind lidar. The results reveal a significant enhancement of the turbulence-kinetic-energy dissipation (by?50%) due to gravity waves in the LLJ shear layer (below the jet core) during the period of wave propagation. Large magnitudes of zonal and vertical components of the shear stress (approximately 0.4 and 1.5 m² s^?2, respectively) are found during that period. Large eddies (scales of 110 to 280 m) matching the high-wind-speed regime are found to propagate the momentum downwards, which enhances the mass transport from the LLJ shear layer to the roughness layer. Furthermore, these large-scale eddies are associated with the crests while comparatively small-scale eddies are associated with the troughs of the gravity wave.

     

Measurement of 34S/32S Ratios of NBS 120c and BCR 32 Phosphorites Using Purge and Trap EA‐IRMS Technology

Measurements of sulfur stable isotope ratios (³⁴S/³²S) have suffered from technical difficulties in analysing low‐S materials reducing their use despite their undeniable scientific interest. The measurement of ³⁴S/³²S ratios is a powerful tool for deciphering problems such as determining the sources of environmental pollutants, to detect adulteration, tracking the evolution of the redox state of the oceans and quantifying the role of the bacterial activity in sulfide minerals genesis. We have used a high‐precision method of sulfur isotope determination using a new type of elemental analyser based on ‘purge and trap’ technology. This new technique demonstrates the high quality of ³⁴S/³²S measurements for samples with S concentrations lower than 1% m/m. International calibrated references of diverse sulfur‐bearing materials were used to calibrate two low (< 1%) S‐bearing phosphorites used as compositional reference material for future use as isotopic references: BCR 32 and NBS 120c. δ³⁴S_CDT values of, respectively, 18.2‰ (1s = 0.3; n = 23) and 18.3‰ (1s = 0.4; n = 20) are proposed for these. Calibration of both phosphorites with international reference materials led to calculation of a mean standard error close to 0.4‰. The demonstration of a capability to reliably measure S isotope ratios in low‐S phosphate minerals or rocks opens up new fields of palaeoenvironmental reconstructions.     

Seismic‐stratigraphic record of a deglaciation sequence: from the marine Laflamme Gulf to Lake Saint‐Jean (late Quaternary,Québec,Canada)

The stratigraphy of the last deglaciation sequence is investigated in Lake Saint‐Jean (Québec Province, Canada) based on 300 km of echo‐sounder two dimensional seismic profiles. The sedimentary archive of this basin is documented from the Late Pleistocene Laurentidian ice‐front recession to the present‐day situation. Ten seismic units have been identified that reflect spatio‐temporal variations in depositional processes characterizing different periods of the Saint‐Jean basin evolution. During the postglacial marine flooding, a high deposition rate of mud settling, from proglacial glacimarine and then prodeltaic plumes in the Laflamme Gulf, produced an extensive, up to 50 m thick mud sheet draping the isostatically depressed marine basin floor. Subsequently, a closing of the water body due to glacio‐isostatic rebound occurred at 8.5 cal. ka BP, drastically modifying the hydrodynamics. Hyperpycnal flows appeared because fresh lake water replaced dense marine water. River sediments were transferred towards the deeper part of the lake into river‐related sediment drifts and confined lobes. The closing of the water body is also marked by the onset of a wind‐driven internal circulation associating coastal hydrodynamics and bottom currents with sedimentary features including shoreface deposits, sediment drifts and a prograding shelf‐type body. The fingerprints of a forced regression are well expressed by mouth‐bar systems and by the shoreface–shelf system, the latter unexpected in such a lacustrine setting. In both cases, a regressive surface of lacustrine erosion (RSLE) has been identified, separating sandy mouth‐bar from glaciomarine to prodeltaic muds, and sandy shoreface wedges from the heterolithic shelf‐type body, respectively. The Lake Saint‐Jean record is an example of a regressive succession driven by a glacio‐isostatic rebound and showing the transition from late‐glacial to post‐glacial depositional systems.     

A numerical model for foundation settlements due to deformation accumulation in granular soils under repeated small amplitude dynamic loading

Repeated small amplitude dynamic loading of the soil in the vicinity of buildings, as arising from traffic or construction activities, may cause differential foundation settlements and structural damage. In this paper, a numerical model for soils under repeated dynamic loading is formulated. It is assumed that the dynamic part of the loading is small with respect to the static part, reflecting the stress conditions in the soil underneath buildings. As the plastic deformation in the soil is only observed after a considerable amount of dynamic loading cycles, only the accumulation of the average plastic deformation is considered. The model accounts for the dependency of the deformation on the stress conditions and the dynamic loading amplitude. The accumulation model is implemented in a finite element framework, using a consistent tangent approach in combination with a backward Euler integration scheme. A triaxial test is considered in a first numerical example. The available analytical solution for this problem allows to validate the numerical implementation. Second, the differential settlement of a two‐storey building founded on loose sandy soil under repeated vehicle passages is considered. The differential foundation settlement causes the stresses to increase at the bottom of the wall, which may result in damage. Copyright © 2009 John Wiley & Sons, Ltd.