Operations standards for global ATM networks: network element view

The International Telecommunication Union (ITU) has completed work on a series of standards on asynchronous transfer mode (ATM) equipment functional operations and network element management. The objective of these standards is to enable flexible design and interoperability of network elements for use in a global ATM network, independent of any specific implementation. This article discusses these standards with respect to their development and application in planning ATM networks. Specifically, it addresses the following: the modeling approach taken in the development of the ITU standards, key operational features specified in the ATM network element functional model, and the capabilities of the ATM network element management interface. Examples of ATM equipment are provided to illustrate how the functional models specified in the ITU standards may be used by network planners and equipment manufacturers to specify and develop ATM equipment tailored to specific needs, while ensuring network interoperability. The article concludes with some points on the future enhancement of these and related ATM equipment operations standards     

Electrooxidation of methanol at platinum–ruthenium catalysts prepared from colloidal precursors: Atomic composition and temperature effects

The electrocatalytic oxidation of methanol was investigated on PtRu electrodes of different atomic compositions at several temperatures (from 25 to 110 °C). Very active catalyst nanoparticles supported on active carbon (Vulcan XC 72) were obtained using the colloidal synthesis developed by Bönnemann et al. [11], allowing easy variation of the atomic composition. These electrocatalysts were characterized by TEM, EDX and XRD; results indicate that they consist of platinum nanoparticles decorated by ruthenium. Methanol oxidation was studied as a function of composition, temperature and methanol concentration. Two effects were investigated: the effect of the working temperature and the effect of the atomic composition. It appeared that for lower methanol electrooxidation overvoltages, the best catalysts are ruthenium-rich, whereas at higher overvoltages the best one is the Pt + Ru (80:20)/C composition, irrespective of the working temperature, either in half-cell or in a single DMFC.     

Electrochemical and spontaneous deposition of ruthenium at platinum electrodes for methanol oxidation: an electrochemical quartz crystal microbalance study

PtRu electrodes with Ru surface concentration ranging from 20 to 50% were prepared by electrolysis of Ru(NO)(NO₃)₃ at a constant potential and/or by spontaneous Ru deposition performed at open circuit potential from a RuCl₃ solution. The amount of either spontaneously or electrochemically deposited ruthenium on the platinum electrode was determined by means of an electrochemical quartz crystal microbalance (EQCM). The effect of the Ru surface concentration on the rate of methanol electrooxidation was also investigated and correlated to the EQCM measurements.     

Electrodes modified by electrodeposition of CoTAA complexes as selective oxygen cathodes in a direct methanol fuel cell

The oxygen reduction reaction (ORR) at cobalt tetraazaanulene (CoTAA) modified electrodes was investigated. As a first approach, modified electrodes were prepared by electrodeposition of CoTAA on glassy carbon (GC). The modification of the GC surface was monitored by u.v.–vis. differential reflectance spectroscopy (UVDRS). The recorded spectra (i.e., absorbance as a function of wavelength and time) showed that the electrodeposition of CoTAA at 0.8 V vs Ag|AgCl, that is, at a potential where the TAA ligand is oxidized to TAA⁺, seems to produce a thin polymer film. Starting from these preliminary results, porous rotating disc electrodes (RDEs) were prepared by electrodeposition of CoTAA (0.8 V vs Ag|AgCl, 1 min) on graphite powder embedded in a recast Nafion^® film. The use of a porous RDE allowed comparison of the activity and selectivity of Pt nanoparticles and CoTAA for the ORR under experimental conditions close to those of a fuel cell cathode, that is, at the catalyst|Nafion^® interface. The activity towards the ORR of a porous electrode modified by electrodeposition of CoTAA is not affected when methanol is present in the electrolyte phase, whereas a noticeable decrease in the activity of Pt-based oxygen cathodes was observed under the same conditions. Half-cell life tests showed that CoTAA-modified electrodes and Pt-based electrodes have a comparable stability over a period of 90 min.     

Modeling the Porosity Evolution of a Powder under Uniaxial Compression

The purpose of this work is to present a new model describing the evolution of powder porosity versus applied pressure during uniaxial compression. This model is based on quasi‐chemical treatments and population balances. It is generally admitted that compression is composed of four steps: a first reorganization of the initial particles, a fragmentation of some initial particles, a second rearrangement of the initial and secondary particle mixture and a plastic deformation stage. So the model is constructed around these four steps. Experimental results on eighteen different powders show a fair agreement with theoretical results and material physical constant values. The use of this model can allow classifying the reorganization, fragmentation and plastic deformation abilities of the products and it will be useful in order to optimize the elaboration process.     

Salivary Amylase Induction by Tannin-Enriched Diets as a Possible Countermeasure Against Tannins

Tannins are characterized by protein-binding affinity. They have astringent/bitter properties that act as deterrents, affecting diet selection. Two groups of salivary proteins, proline-rich proteins and histatins, are effective precipitators of tannin, decreasing levels of available tannins. The possibility of other salivary proteins having a co-adjuvant role on host defense mechanisms against tannins is unknown. In this work, we characterized and compared the protein profile of mice whole saliva from animals fed on three experimental diets: tannin-free diet, diet with the incorporation of 5% hydrolyzable tannins (tannic acid), or diet with 5% condensed tannins (quebracho). Protein analysis was performed by one-dimensional gel electrophoresis combined with Matrix-Assisted Laser Desorption Ionization-Time of Flight mass spectrometry to allow the dynamic study of interactions between diet and saliva. Since abundant salivary proteins obscure the purification and identification of medium and low expressed salivary proteins, we used centrifugation to obtain saliva samples free from proteins that precipitate after tannin binding. Data from Peptide Mass Fingerprinting allowed us to identify ten different proteins, some of them showing more than one isoform. Tannin-enriched diets were observed to change the salivary protein profile. One isoform of α-amylase was overexpressed with both types of tannins. Aldehyde reductase was only identified in saliva of the quebracho group. Additionally, a hypertrophy of parotid salivary gland acini was observed by histology, along with a decrease in body mass in the first 4 days of the experimental period. G. da Costa and E. Lamy have contributed equally to this work.     

Enhancement of the electrooxidation of ethanol on a Pt–PEM electrode modified by tin. Part I: Half cell study

The direct platinisation of a solid polymer electrolyte (Nafion^® membrane) was realized by chemical reduction of a platinum salt. The Pt–PEM electrodes thus obtained were modified by tin to improve the electrocatalytic activity towards the electrooxidation of ethanol. The Pt–PEM and Pt–Sn–PEM electrodes were characterized by TEM, EDX and XRD analysis, cyclic voltammetry, and their polarisation curves for the electrooxidation of ethanol were determined under quasisteady state conditions.     

Direct electrooxidation of methanol on highly dispersed platinum-based catalyst electrodes: temperature effect

The direct electrooxidation of methanol in acid medium was studied on electrodes made of a perfluorinated membrane with small amounts of metal catalysts incorporated by chemical reduction. Platinum is a good electrocatalyst for this reaction, but needs to be modified by other metals in order to obtain oxidation potentials much more compatible with a working anode in a direct methanol fuel cell. Ruthenium and tin appear to give encouraging results, leading to a negative shift of more than 250 mV as compared to the potential obtained with pure platinum. Other parameters were investigated in this work, such as the working temperature, and the manner of introduction of the methanol into the cell. By gaseous supply, it was possible to carry out measurements at higher temperatures than with methanol in solution, and consequently to greatly improve the performance of the catalytic electrode.     

Optimization of platinum dispersion in Pt–PEM electrodes: application to the electrooxidation of ethanol

Nafion® can be used as a solid polymer electrolyte in a PEM fuel cell. Direct platinization of the membrane was realized by chemical reduction of a platinum compound. The platinization procedure was modified to enhance the roughness factor and thus to improve the electrocatalytic activity towards ethanol electrooxidation. The Pt–PEM electrodes were characterized by TEM, atomic absorption analysis, cyclic voltammetry and their polarization curves for ethanol electrooxidation.