2,530 research outputs found
Model and method to predict the turbulent kinetic energy induced by tidal currents, application to the wave-induced turbulence
A prediction model for the turbulent kinetic energy (TKE) induced by
tidal-currents is proposed as a function of the barotropic velocity only, along
with a robust method evaluating the different parameters involved using
Acoustic Doppler Current Profiler (ADCP) measurements from Alderney Race. We
find that the model is able to reproduce correctly the TKE profiles with
coefficients of correlation on average higher than 0.90 and normalised
root-mean-square errors (NRMSE) less than 14%. Different profiles are also
tested for the mean velocity, no satisfactory prediction model is found but we
are able to have decent estimates of the velocity shear and friction velocity.
Two applications are then carried out. First the turbulent budget terms are
estimated and discussed. We identify the turbulent production and dissipation
of TKE as the most important mechanisms, then we discuss the validity of
several theoretical results derived for isotropic turbulence for this
application. A strong departure for the estimation of the turbulent dissipation
is notably found and explained by the turbulent anisotropy. At last the
prediction model for the TKE is used to infer the wave-induced TKE. We show the
importance of removing the tidal component, waves can have a strong influence
down to mid-depth
Palladized silver as new cathode material: Evidence of a one-electron scission for primary alkyl iodides
Silver electrodes modified by ââpalladizationâ thanks to an immersion in acidic solutions of Pd2+ salts, exhibit exceptional catalytic capabilities especially in the cleavage of primary alkyl halides used as standard
systems in order to evaluate the catalytic activity. Such chemically modified surfaces characterized by the formation of an Ag/Pd-based alloy showed large potential shifts compared to the use of glassy carbon or even smooth silver cathodes. Specifically, these palladium-doped silver surfaces were successfully used for cleaving carbonâiodine bonds. Thus, preliminary results have revealed that palladized silver electrodes behave quite differently from smooth silver and showed exceptional catalytic capabilities.
Cathodic reductions were achieved in dimethylformamide, acetonitrile, and propylene carbonate. While smooth silver cathodes generally entailed two-electron cleavage reactions (evidence of two clearly separated steps in propylene carbonate), palladized silver interfaces always yield catalytic cleavages of carbonâiodine bonds according to single one-electron processes with the transient formation of a free alkyl radical leading to homo-coupling processes
Electrodeposited Cu2Sb as anode material for 3-dimensional Li-ion microbatteries
An increasing demand on high energy and power systems has arisen not only with the development of electric vehicle (EV), hybrid electric vehicle (HEV), telecom, and mobile technologies, but also for specific applications such as powering of microelectronic systems. To power those microdevices, an extra variable is added to the equation: a limited footprint area. Three-dimensional (3D) microbatteries are a solution to combine high-density energy and power. In this work, we present the formation of Cu2Sb onto three-dimensionally architectured arrays of Cu current collectors. Sb electrodeposition conditions and annealing post treatment are discussed in light of their influence on the morphology and battery performances. An increase of cycling stability was observed when Sb was fully alloyed with the Cu current collector. A subsequent separator layer was added to the 3D electrode when optimized. Equivalent capacity values are measured for at least 20 cycles. Work is currently devoted to the identification of the causes of capacity fading
The one-electron cleavage and reductive homo-coupling of alkyl bromides at silverâpalladium cathodes
We have previously demonstrated that ââpalladizedâ silver electrodes obtained by displacement reaction, thanks to an immersion in acidic PdII-based solutions, display quite interesting capabilities in the cleavage of alkyl halides. Such chemically modified surfaces by an AgâPd alloy lead to large potential shifts compared to the use of glassy carbon or smooth silver cathodes as well. The present article now gives preliminary results focused on the particular electrochemical activity of primary and secondary alkyl bromides. Experimental data show that such electrodes may behave quite differently from smooth silver, especially, when acetonitrile and dimethylformamide are used as solvent. While smooth silver cathodes generally entail two-electron cleavage reactions, palladized silver interfaces always yield catalytic cleavages of CâBr bonds according to single one-electron reactions. The homo-coupling processes may generally occur with a rather high efficiency
Electrochemical Method for Direct Deposition of Nanometric Bismuth and Its Electrochemical Properties vs Li
We report that nanometric bismuth can directly be electrodeposited at room temperature without the use of a nanoporous template. The morphology, microstructure, and purity of the as-prepared electrodeposits were characterized by scanning electron microscopy, transmission electron microscopy, and infrared spectroscopy. Typically, well-crystallized nanometer-sized particles of Bi
ranging from 10 to 20 nm are obtained. The key to success of such a process lies in the electrochemical coreduction of pyrocatechol violet during the bismuth deposition, which disturbs the electrocrystallization process. As a first possible application, we show that Bi/Cu nanoarchitectured electrodes exhibit interesting rate capabilities when used as electrode material vs Li
Electrochemical Deposition and Characterization of FeâOâ Films Produced by the Reduction of Fe(III)-triethanolamine
In this paper, we demonstrate that films of magnetite, Fe3O4, can be deposited by the electrochemical reduction of a Fe(III)-triethanolamine complex in aqueous alkaline solution. the films were deposited with a columnar microstructure and a [100] preferred orientation on stainless steel substrates. In-plane electrical transport and magnetoresistance measurements were performed on the films after they were stripped off onto glass substrates. the resistance of the films was dependent on the oxygen partial pressure. We attribute the increase in resistance in O2 and the decrease in resistance in Ar to the oxidation and reduction of grain boundaries. the decrease in resistance in an Ar atmosphere exhibited first-order kinetics, with an activation energy of 0.2 eV. the temperature dependence of the resistance showed a linear dependence of log(R) versus T-1/2, consistent with tunneling across resistive grain boundaries. a room-temperature magnetoresistance of -6.5% was observed at a magnetic field of 9 T
Confirmation of beach accretion by grain-size trend analysis: Camposoto beach, CĂĄdiz, SW Spain
An application of the grain size trend analysis
(GSTA) is used in an exploratory approach to characterize
sediment transport on Camposoto beach (CĂĄdiz, SW Spain).
In May 2009 the mesotidal beach showed a well-developed
swash bar on the upper foreshore, which was associated
with fair-weather conditions prevailing just before and during
the field survey. The results were tested by means of an
autocorrelation statistical test (index I of Moran). Two sedimentological
trends were recognized, i.e. development towards
finer, better sorted and more negatively skewed
sediment (FBâ), and towards finer, better sorted and less
negatively or more positively skewed sediment (FB+). Both
vector fields were compared with results obtained from
more classical approaches (sand tracers, microtopography
and current measurements). This revealed that both trends
can be considered as realistic, the FB+ trend being identified
for the first time in a beach environment. The data demonstrate
that, on the well-developed swash bar, sediment
transported onshore becomes both finer and better sorted
towards the coast. On the lower foreshore, which exhibits a
steeper slope produced by breaking waves, the higherenergy
processes winnow out finer particles and thereby
produce negatively skewed grain-size distributions. The upper
foreshore, which has a flatter and smoother slope, is
controlled by lower-energy swash-backwash and overwash
processes. As a result, the skewness of the grain-size distributions
evolves towards less negative or more positive
values. The skewness parameter appears to be distributed
as a function of the beach slope and, thus, reflects variations
in hydrodynamic energy. This has novel implications for
coastal management
Reply to J.J. Muñoz-Perez et al. Comments on âConfirmation of beach accretion by grain-size trend analysis: Camposoto beach, CĂĄdiz, SWSpainâ by E. Poizot et al. (2013) Geo-Marine Letters 33(4)
In a novel finding for a beach environment, Poizot
et al. (2013) identified an FB+ trend (sediments becoming
finer, better sorted and more positively skewed upshore) on a
well-developed swash bar on the upper foreshore of the
Camposoto beach of CĂĄdiz in SW Spain. In their Discussion
of that paper, Muñoz-Perez et al. (2014) provide some
supporting arguments and also report grain-size, beach profile
and other data from nearby beaches which differ from those of
Poizot and colleagues for Camposoto beach, pointing out that
a trend observed on one beach may not apply to a
neighbouring beach. However, even though the absolute
values differ, the overall trends actually do show the same
general behaviour. In our Reply to their comments, we also
address some difficulties in comparing granulometric datasets
generated by different analytical techniques
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