Model simulations on the long-term dispersal of 137Cs released into the Pacific Ocean off Fukushima

A sequence of global ocean circulation models, with horizontal mesh sizes of 0.5°, 0.25° and 0.1°, are used to estimate the long-term dispersion by ocean currents and mesoscale eddies of a slowly decaying tracer (half-life of 30 years, comparable to that of 137Cs) from the local waters off the Fukushima Dai-ichi Nuclear Power Plants. The tracer was continuously injected into the coastal waters over some weeks; its subsequent spreading and dilution in the Pacific Ocean was then simulated for 10 years. The simulations do not include any data assimilation, and thus, do not account for the actual state of the local ocean currents during the release of highly contaminated water from the damaged plants in March–April 2011. An ensemble differing in initial current distributions illustrates their importance for the tracer patterns evolving during the first months, but suggests a minor relevance for the large-scale tracer distributions after 2–3 years. By then the tracer cloud has penetrated to depths of more than 400 m, spanning the western and central North Pacific between 25°N and 55°N, leading to a rapid dilution of concentrations. The rate of dilution declines in the following years, while the main tracer patch propagates eastward across the Pacific Ocean, reaching the coastal waters of North America after about 5–6 years. Tentatively assuming a value of 10 PBq for the net 137Cs input during the first weeks after the Fukushima incident, the simulation suggests a rapid dilution of peak radioactivity values to about 10 Bq m−3 during the first two years, followed by a gradual decline to 1–2 Bq m−3 over the next 4–7 years. The total peak radioactivity levels would then still be about twice the pre-Fukushima values

Covalent vs. non-covalent redox functionalization of C-LiFePO4 based electrodes

During high rate utilization of porous Li battery, Li+ refuelling from the electrolyte limits the discharge kinetics of positive electrodes. In the case of thick electrodes a strategy to buffer the resulting sharp drop of Li+ concentration gradient would be to functionalize the electrode with anionic based redox molecules (RMR) that would be therefore able to relay intercalation process. The occurrence of these RMR in the electrode should not however, induce adverse effect on Li intercalation processes. In this respect, this work studies the effect of functionalizing LFPC based electrodes by either covalent or non-covalent chemistry, on Li intercalation kinetics. To do so, model molecules containing a nitro group were introduced at the surface of both carbon conducting additives and active material (C-LiFePO4). It is shown that presumably due to formation of sp(3) defects, covalent anchoring using diazonium chemistry inhibits the intercalation kinetics in C-FePO4. On the contrary, if molecules such as pyrene derivatives are immobilized by pi-staking interactions, Li intercalation is not impeded. Therefore non-covalent functionalization of pyrene based RMR appears as a promising route to relay Li intercalation reaction during high power demand. The framework for future development of this strategy is discussed. (C) 2013 Elsevier B.V. All rights reserved

In situ redox functionalization of composite electrodes for high power-high energy electrochemical storage systems via a non-covalent approach

The growing demand for new global resources of clean and sustainable energy emerges as the greatest challenge in today\u27s society. For numerous applications such as hybrid vehicles, electrochemical storage systems simultaneously require high energy and high power. For this reason, intensive researches focus on proposing alternative devices to conventional Li battery and supercapacitors. Here, we report a proof of concept based on non-covalent redox functionalization of composite electrodes that may occur either during the calendar life or during the device functioning. The active material, a multi-redox pyrene derivative, is initially contained in the electrolyte. No additional benchmarking step is therefore required, and it can, in principle, be readily applied to any type of composite electrode (supercapacitors, battery, semi-solid flow cell etc.). Accordingly, a practical carbon fiber electrode that is 10 mg cm(-2) loaded can deliver up to 130 kW kg(electrode)(-1) and 130 Wh kg(electrode)(-1) with negligible capacity loss over the first 60 000 charge/discharge cycles

New Concept to Boost Energy and Power Peformance of Practical Electrochemical Devices

International audienc

New concept and electrochemistry of in situ non-covalent immobilization of redox molecules for energy storage applications

International audienc

Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor. II. Concept validation with ZELDA on VLT/SPHERE

Warm or massive gas giant planets, brown dwarfs, and debris disks around nearby stars are now routinely observed by dedicated high-contrast imaging instruments on large, ground-based observatories. These facilities include extreme adaptive optics (ExAO) and state-of-the-art coronagraphy to achieve unprecedented sensitivities for exoplanet detection and spectral characterization. However, differential aberrations between the ExAO sensing path and the science path represent a critical limitation for the detection of giant planets with a contrast lower than a few $10^{-6}$ at very small separations (<0.3\as) from their host star. In our previous work, we proposed a wavefront sensor based on Zernike phase contrast methods to circumvent this issue and measure these quasi-static aberrations at a nanometric level. We present the design, manufacturing and testing of ZELDA, a prototype that was installed on VLT/SPHERE during its reintegration in Chile. Using the internal light source of the instrument, we performed measurements in the presence of Zernike or Fourier modes introduced with the deformable mirror. Our experimental and simulation results are consistent, confirming the ability of our sensor to measure small aberrations (<50 nm rms) with nanometric accuracy. We then corrected the long-lived non-common path aberrations in SPHERE based on ZELDA measurements. We estimated a contrast gain of 10 in the coronagraphic image at 0.2\as, reaching the raw contrast limit set by the coronagraph in the instrument. The simplicity of the design and its phase reconstruction algorithm makes ZELDA an excellent candidate for the on-line measurements of quasi-static aberrations during the observations. The implementation of a ZELDA-based sensing path on the current and future facilities (ELTs, future space missions) could ease the observation of the cold gaseous or massive rocky planets around nearby stars.Comment: 13 pages, 12 figures, A&A accepted on June 3rd, 2016. v2 after language editin

Influence of bottom topography on integral constraints in zonal flows with parameterized potential vorticity fluxes

An integral constraint for eddy fluxes of potential vorticity (PV), corresponding to global momentum conservation, is applied to two-layer zonal quasi-geostrophic channel flow. This constraint must be satisfied for any type of parameterization of eddy PV fluxes. Bottom topography strongly influence the integral constraint compared to a flat bottom channel. An analytical solution for the mean flow solution has been found by using asymptotic expansion in a small parameter which is the ratio of the Rossby radius to the meridional extent of the channel. Applying the integral constraint to this solution, one can find restrictions for eddy PV transfer coefficients which relate the eddy fluxes of PV to the mean flow. These restrictions strongly deviate from restrictions for the channel with flat bottom topography