Relation entre température et intensité des circulations d'eau souterraine dans les massifs alpins: outil de prévision des venues d'eau dans les tunnels

Un nombre important de grands tunnels profonds ont été, ou seront à l'avenir, percés dans les massifs montagneux. Le suivi de l'évolution de la température des venues d'eau dans cinq grands tunnels alpins (Vereina, Gothard-N2, Mont-Blanc, Simplon et Gothard-AT) montre que la température de l'eau dans les ouvrages est fortement influencée par la perméabilité des massifs et les circulations d'eau souterraine qui s'y produisent. Les eaux froides qui s'infiltrent à haute altitude possèdent un effet réfrigérant sur le massif. Dès lors, la mesure de la température de l'eau en cours d'avancement d'un ouvrage souterrain constitue un outil de prévision efficace et peu coûteux des venues d'eau. Celles-ci peuvent être très localisées et provoquer une diminution de la température dans une zone du massif ou être diffuses et provoquer une diminution globale du gradient thermique des eaux dans le massif. Une corrélation négative a été mise en évidence entre le gradient thermique des eaux dans chacun des massifs étudiés et l'intensité des venues d'eau qui ont été ensuite observées dans les ouvrages les traversant.Numerous long tunnels have been and will be drilled at great depths in mountainous alpine massifs. Water inflow temperatures in five existing long alpine tunnels (Vereina, Gothard-N2, Mont-Blanc, Simplon and Gothard-AT) have been studied and compared with the volume of water inflows.The Vereina railway tunnel drilled in Austroalpine nappes encountered little water inflow. The linear discharge rates vary between 0.003 and 0.006 L/s/m. Water temperatures series have been observed in both the northern and southern parts of the tunnel trace: the northern thermal gradient is equal to 0.018 °C/m, whereas the southern thermal gradient is not very different with a value equal to 0.016 °C/m. No special thermal anomaly has been observed at this site.The Gothard-N2 road tunnel (National route number two) intersects the Aar and Gothard External Crystalline Massifs. A general thermal gradient equal to 0.015°C/m is observed in the southern part of the tunnel trace in the Monte Prosa massif. Positive thermal anomalies have been measured in both the northern and central parts of the tunnel trace. They are due to topographical effects: in this region, the tunnel is situated beneath the Reuss river valley. Water inflows are weak in this tunnel: about 0.020 L/s/m in the Monte Prosa zone, for example.The Mont-Blanc road tunnel intersects the Mont-Blanc External Crystalline Massif. A water thermal gradient equal to 0.016 °C/m has been observed on the northern part of the massif, at depths less than 1000 meters. This region corresponds to a low-permeability crystalline schist zone. The linear discharge rate is equal to 0.008 L/s/m in this zone. A large negative thermal anomaly was measured during the drilling of this tunnel. The water temperatures decreased from 32°C to 11.5°C beneath the Pointe Helbronner. This decrease corresponds to large water inflows (about 1000 L/s) in a strongly fractured zone. A second water thermal gradient (very weak: 0.007 °C/m) corresponds to the granitic unit which is globally more permeable than the schist with a linear discharge rate equal to 0.193 L/s/m.The Simplon railway tunnel, drilled through the Penninic nappes, is also characterized by a negative thermal anomaly situated in the very permeable marbles of the Teggiolo zone. In this tunnel, the water temperatures decrease from 55°C in the Berisal gneissic zone to less than 15°C in the Teggiolo zone. The water thermal gradient in the northern part is high, in conformity with the weak water inflows (linear discharge rate less than 0.001 L/s/m). A third zone is observed in the Veglia marbles: it is characterized by a water thermal gradient equal to 0.010 °C/m for a linear discharge rate equal to 0.203 L/s/m.The Gothard-AT gallery has been drilled in Penninic gneiss. A water thermal gradient equal to 0.013 °C/m has been measured over the first 3000 m. A negative thermal anomaly was encountered at the end of the gallery, due to the presence of very permeable metasedimentary rocks with important water circulation.These results show that the water temperature in underground works is strongly dependent on the massif permeability and the existence of groundwater flows. Cold waters coming from high infiltration zones have a refrigerating effect on the massif. Thus, measuring water temperature during drilling constitutes a prediction tool for eventual water inflows. Two cases are possible: the observation of a local thermal anomaly due to a very localized aquifer zone, or the decrease of the water thermal gradient due to diffuse water inflows in the massif.Local thermal anomalies, correlated with large water inflows along discrete zones, have been shown in the Simplon, Mont-Blanc and Gothard-AT tunnels. Such thermal anomalies can be measured hundreds of meters before the intersection of the tunnel with the aquifer zone: temperature monitoring thus constitutes a prediction tool for large water inflows localized in a particular aquifer zone. The use of 3D numerical simulations allows one to improve the prediction quantitatively, by taking into account the problem geometry, the heterogeneity and anisotropy of the thermal and hydrogeological properties of rocks, and the boundary conditions.The comparison of water thermal gradients at the massif scale with linear discharge rates in the tunnels through the massif allows us to determine a mathematical relationship between these characteristics of the massif. This relation permits one to predict the water quantity expected during drilling, knowing the water thermal gradient.These results show that water temperature measurements during drilling of an underground work constitute an efficient and cheap predicting tool for water inflows. Anomalies due to relief must be taken into account; these can be very important in such mountainous massifs. A 3D modeling of heat transfer in the massif is, in all cases, necessary to improve the precision of predictions

A magnetic lens for cold atoms controlled by a rf field

We report on a new type of magnetic lens that focuses atomic clouds using a static inhomogeneous magnetic field in combination with a radio-frequency field. The experimental study is performed with a cloud of cold cesium atoms. The rf field adiabatically deforms the magnetic potential of a coil and therefore changes its focusing properties. The focal length can be tuned precisely by changing the rf frequency value. Depending on the rf antenna position relative to the DC magnetic profile, the focal length of the atomic lens can be either decreased or increased by the rf field

Antifouling bastadin congeners target blue mussel phenoloxidase and complex copper(II) ions

Synthetically prepared congeners of spongederived bastadin derivatives such as 5,5'-dibromohemibastadin- 1 (DBHB) that suppress the settling of barnacle larvae were identified in this study as strong inhibitors of blue mussel phenoloxidase that is involved in the firm attachment of mussels to a given substrate. The IC50 value of DBHB as the most active enzyme inhibitor encountered in this study amounts to 0.84 mu M. Inhibition of phenoloxidase by DBHB is likely due to complexation of copper(II) ions from the catalytic centre of the enzyme by the a-oxo-oxime moiety of the compound as shown here for the first time by structure activity studies and by X-ray structure determination of a copper(II) complex of DBHB.Biotechnology & Applied MicrobiologyMarine & Freshwater BiologySCI(E)EI0ARTICLE61148-11581

Accumulation and thermalization of cold atoms in a finite-depth magnetic trap

We experimentally and theoretically study the continuous accumulation of cold atoms from a magneto-optical trap (MOT) into a finite depth trap, consisting in a magnetic quadrupole trap dressed by a radiofrequency (RF) field. Chromium atoms (52 isotope) in a MOT are continuously optically pumped by the MOT lasers to metastable dark states. In presence of a RF field, the temperature of the metastable atoms that remain magnetically trapped can be as low as 25 microK, with a density of 10^17 atoms.m-3, resulting in an increase of the phase-space density, still limited to 7.10^-6 by inelastic collisions. To investigate the thermalization issues in the truncated trap, we measure the free evaporation rate in the RF-truncated magnetic trap, and deduce the average elastic cross section for atoms in the 5D4 metastable states, equal to 7.0 10^-16m2.Comment: 9 pages, 10 Figure

All-Optical Production of Chromium Bose-Einstein Condensates

We report on the production of ^52Cr Bose Einstein Condensates (BEC) with an all-optical method. We first load 5.10^6 metastable chromium atoms in a 1D far-off-resonance optical trap (FORT) from a Magneto Optical Trap (MOT), by combining the use of Radio Frequency (RF) frequency sweeps and depumping towards the ^5S_2 state. The atoms are then pumped to the absolute ground state, and transferred into a crossed FORT in which they are evaporated. The fast loading of the 1D FORT (35 ms 1/e time), and the use of relatively fast evaporative ramps allow us to obtain in 20 s about 15000 atoms in an almost pure condensate.Comment: 4 pages, 4 figure

Development of probabilistic models for quantitative pathway analysis of plant pest introduction for the EU territory

This report demonstrates a probabilistic quantitative pathway analysis model that can be used in risk assessment for plant pest introduction into EU territory on a range of edible commodities (apples, oranges, stone fruits and wheat). Two types of model were developed: a general commodity model that simulates distribution of an imported infested/infected commodity to and within the EU from source countries by month; and a consignment model that simulates the movement and distribution of individual consignments from source countries to destinations in the EU. The general pathway model has two modules. Module 1 is a trade pathway model, with a Eurostat database of five years of monthly trade volumes for each specific commodity into the EU28 from all source countries and territories. Infestation levels based on interception records, commercial quality standards or other information determine volume of infested commodity entering and transhipped within the EU. Module 2 allocates commodity volumes to processing, retail use and waste streams and overlays the distribution onto EU NUTS2 regions based on population densities and processing unit locations. Transfer potential to domestic host crops is a function of distribution of imported infested product and area of domestic production in NUTS2 regions, pest dispersal potential, and phenology of susceptibility in domestic crops. The consignment model covers the several routes on supply chains for processing and retail use. The output of the general pathway model is a distribution of estimated volumes of infested produce by NUTS2 region across the EU28, by month or annually; this is then related to the accessible susceptible domestic crop. Risk is expressed as a potential volume of infested fruit in potential contact with an area of susceptible domestic host crop. The output of the consignment model is a volume of infested produce retained at each stage along the specific consignment trade chain

Techno-economic evaluation of biomass-to-fuels with solid-oxide electrolyzer

Thermochemical biomass-to-fuel conversion requires an increased hydrogen concentration in the syngas derived from gasification, which is currently achieved by water–gas-shift reaction and CO2 removal. State-of-the-art biomass-to-fuels convert less than half of the biomass carbon with the remaining emitted as CO2. Full conversion of biomass carbon can be achieved by integrating solid-oxide electrolyzer with different concepts: (1) steam electrolysis with the hydrogen produced injected into syngas, and (2) co-electrolysis of CO2 and H2O to convert the CO2 captured from the syngas. This paper investigates techno-economically steam- or co-electrolysis-based biomass-to-fuel processes for producing synthetic natural gas, methanol, dimethyl ether and jet fuel, considering system-level heat integration and optimal placement of steam cycles for heat recovery. The results show that state-of-the-art biomass-to-fuels achieve similar energy efficiencies of 48–51% (based on a lower heating value) for the four different fuels. The integrated concept with steam electrolysis achieves the highest energy efficiency: 68% for synthetic natural gas, 64% for methanol, 63% for dimethyl ether, and 56% for jet fuel. The integrated concept with co-electrolysis can enhance the state-of-the-art energy efficiency to 66% for synthetic natural gas, 61% for methanol, and 54% for jet fuel. The biomass-to-dimethyl ether with co-electrolysis only reaches an efficiency of 49%, due to additional heat demand. The levelized cost of the product of the integrated concepts highly depends on the price and availability of renewable electricity. The concept with co-electrolysis allows for additional operation flexibility without renewable electricity, resulting in high annual production. Thus, with limited annual available hours of renewable electricity, biomass-to-fuel with co-electrolysis is more economically convenient than that with steam electrolysis. For a plant scale of 60 MWth biomass input with the renewable electricity available for 1800 h annually, the levelized cost of product of biomass-to-synthesis-natural-gas with co-electrolysis is 35 $/GJ, 20% lower than that with steam-electrolysis