Type

Database

Creator

Date

Thumbnail

Search results

7 records were found.

The bare and cultivated indurated pyroclastic formations of the Equatorian Sierra (Cangahuas) are strongly susceptible to pluvial erosion. Their reincorporation to agriculture allows a partial control of ground loss and offers an alternative solution for agriculture management. Rain simulation gives information about imbibition, infiltration, runoff and erodibility. The "quadrat point" method enabled us to observe the evolution of surface features (rugosity, crusting and sealing of porosity). We make three campaignsof simulation just after the soil preparation, before and after the harrowing. We observed the variations of hydrodynamic parameters and the evolution of superficial structural features. A rough soil preparation (coarse particle size) enhance the infiltration rate and reduce the soil loss. On the contrary, a fine sized prepa...
In Mexico, there is very few informations about the soil surface crusting in relation to the rain. When creating a new soil from a indurated volcanic tuff, it is important to study the behaviour and dynamics of the new structure under the action of rain and cultivation practices. We followed 6 terraces during 3 years on different kinds of soil and tepetate, as well as different kinds of soil tillage and crops. We used the rugosimeter and a crop covermeter of 2 m2 with a precision of 10 cm2 for each mesure. We measured the humidity and thecrusting of the soil after every runoff-producing event and the vegetation covering once a week. At the same time, we followed the state of the row and their ruptures along every terrace. This study confirms and details the 4 different kinds of crusting of this new soil. They are following this dynamic...
Due to the increasing importance of modified electrodes for many applications in nanotechnology, including molecular electronics, bioelectronics, and sensors, there is a need to find ways to chemically attach suitable molecular films onto the electrodes. Combining the electroreduction of aryl diazonium salts with the Sonogashira cross-coupling reaction, a new modular technique to modify electrodes is presented. The new technique allows a wide range of functional groups to be introduced onto electrode surfaces with high surface coverage by the functional subunit. Various organic subunits, including redox chromophores, are successfully attached to platinum electrodes. The corresponding films are characterized using cyclic voltammetry, X-ray photoelectron spectroscopy, atomic force microscopy, and contact-angle measurements. The electrore...
The electroreduction of functionalized aryldiazonium salts combined with a protection-deprotection method was evaluated for the fabrication of organized mixed layers covalently bound onto carbon substrates. The first modification consists of the grafting of a protected 4-((triisopropylsilyl)ethynyl)benzene layer onto the carbon surface on which the introduction of a second functional group is possible without altering the first grafted functional group. After deprotection, we obtained an ultrathin robust layer presenting high densities of both active ethynylbenzene groups (available for "click" chemistry) and the second functional group. The strategy was successfully demonstrated using azidomethylferrocene to react with ethynyl moieties in the binary film by "click" chemistry, and NO(2)-phenyl as the second functional group. Two possib...
L'érodibilité des tepetates (horizons indurés de sols volcaniques mis à nu par érosion du sol) réhabilités en sols agricoles, a été étudiée dans la vallée de Mexico au cours de deux programmes successifs (1989-92 et à partir de 1994) de l'Union Européenne au Mexique. Outre la mesure des pluies, du ruissellement et des pertes en terre, une observation a été faite de l'évolution des états de surface sur des parcelles de tepetate et de sol billonnées et plantées en maïs, ou laissées à nu. Ces observations, sur des peties parcelles "Wischmeier" (44 m2) en 1991 ou des terrasses de 500 m2 en 1994, ont été faites selon la méthode de Casenave et Valentin (1989). Elles montrent une évolution maintenant bien connue des états de surface du tepetate et du sol cultivés par suite de la "fonte" des agrégats, à savoir : la formation successive de croû...
Herein, we report the variation of localized surface plasmon resonance (LSPR) of gold nanoparticle (NP) arrays covered by poly(3,4-ethylenedioxythiophene) (PEDOT) as a function of the electronic state of the polymer. Giant shifts and fine-tuning of the LSPR of gold NPs surrounded by PEDOT/sodium docecyl sulfate have been achieved. The color variations of plasmonic/conducting polymer (CP) devices are given not only by changes of the optical properties of the CP upon doping but also by a close synergy of the optical properties of CP and NP. Such systems can considerably extend the field of CP-based electrochromic devices.
Redox-active dithiolated tetrathiafulvalene derivatives (TTFdT) were inserted in two-dimensional nanoparticle arrays to build interlinked networks of molecular junctions. Upon oxidation of the TTFdT to the dication state, we observed a conductance increase of the networks by up to 1 order of magnitude. Successive oxidation and reduction cycles demonstrated a clear switching behavior of the molecular junction conductance. These results show the potential of interlinked nanoparticle arrays as chemical sensors.
Want to know more?If you want to know more about this cutting edge product, or schedule a demonstration on your own organisation, please feel free to contact us or read the available documentation at http://www.keep.pt/produtos/retrievo/?lang=en