Redox behaviour of thermally activated platinum electrodes with particular reference to operation at elevated temperature

The present work is a continuation of an earlier investigation of the effect of severe thermal pretreatment on the redox properties of platinum electrodes in aqueous media. The most interesting observation was that raising the solution temperature to ca. 75 °C resulted in a dramatic anodic response in the positive sweep at ca. 0.25 V (RHE). Such behaviour was noted earlier at room temperature but only when the thermally pretreated sample was further activated by cathodic polarization. This transition at 0.25 V was partially reversed on the negative sweep, but the cathodic process involved was subject to severe inhibition. There is independent evidence for similar behaviour for gold in aqueous acid solution. The relevance of the present results to the operation of fuel cell anodes is outlined. Received: 2 December 1999 / Accepted: 24 February 2000     

An investigation of the electrochemical responses of superactivated gold electrodes in alkaline solution

It is now well established that gold, in the form of oxide-supported microparticles or even as conventional macroelectrodes, displays inexplicably high catalytic activity for some reactions. In the present work, gold surfaces were superactivated by a combination of thermal and cathodic pretreatment and such electrodes in base yielded up to five distinct, and quite marked, premonolayer oxidation responses within the double layer region, over the range 0.0–1.0 V (RHE). As outlined in earlier publications, such unusual behaviour is important from an electrocatalytic (and heterogeneous catalysis) viewpoint. A new mode of active site adsorption, involving highly localized electron transfer from active surface atoms to either the external circuit (in electrocatalysis) or an adsorbing reactant (in heterogeneous catalysis), is proposed. Such localized (active site) adsorption, which is based on surface quantum confinement effects, is virtually independent of (or only indirectly related to) the electronic properties of the bulk metal.     

Viscoelastic property mapping with contact resonance force microscopy

We demonstrate the accurate nanoscale mapping of near-surface loss and storage moduli on a polystyrene-polypropylene blend with contact resonance force microscopy (CR-FM). These viscoelastic properties are extracted from spatially resolved maps of the contact resonance frequency and quality factor of the AFM cantilever. We consider two methods of data acquisition: (i) discrete stepping between mapping points and (ii) continuous scanning. For point mapping and low-speed scanning, the values of the relative loss and storage modulus are in good agreement with the time-temperature superposition of low-frequency dynamic mechanical analysis measurements to the high frequencies probed by CR-FM.     

Quantum mechanics: cleaning up metaphysical baggage

The dynamic electronic structure of atoms and molecules can be directly observed by means of the (e, 2e) reaction, which measures the distribution of energies and momenta of two electrons in coincidence after a knockout reaction initiated by an electron beam of known momentum incident on a molecular gas target. The molecular state for each event is identified by the electron separation energy. The recoil momentum for each event is known from the difference of measured initial and final momenta. It has been verified that values of this momentum are equal under suitable conditions to the momentum of the electron in the target immediately before knockout. Thus the spherically-averaged electron momentum distribution for each molecular orbital is measured. This is directly related to molecular orbitals calculated by the methods of quantum chemistry. Properties obtained by this method for different types of molecules are discussed.     

Nachweis und colorimetrische Bestimmungsmethoden des Molybd?ns

Ohne Zusammenfassung     

Isolation and Structure of a New Antibiotic Related to Rubiflavin A

A novel antibiotic, PD 121,222, was isolated from a complex of pluramycin-like compounds containing mostly kidamycin and neopluramycin. Spectral analyses showed that this compound is the 14,16-dihydroxy analog of rubiflavin A.     

The Plot-Data Interface in Statistical Graphics

Abstract

Statistical software systems include modules for manipulating data sets, model fitting, and graphics. Because plots display data, and models are fit to data, both the model-fitting and graphics modules depend on the data. Today's statistical environments allow the analyst to choose or even build a suitable data structure for storing the data and to implement new kinds of plots. The multiplicity problem caused by many plot varieties and many data representations is avoided by constructing a plot-data interface. The interface is a convention by which plots communicate with data sets, allowing plots to be independent of the actual data representation. This article describes the components of such a plot-data interface. The same strategy may be used to deal with the dependence of model-fitting procedures on data.