The effect of sonication on glass electrodes

This communication describes observations made on the disturbing effect of ultrasound on the functioning of glass electrodes. It was observed that the signal of glass electrodes drops significantly, with as much as several pH units, if sonication is applied to the sample solution. The effect was studied for a variety of electrolyte solutions and for several glass electrode makes, and was always found to be reversible and reproducible. The quality and the concentration of the electrolyte, as well as the ultrasonic power applied were seen to strongly influence the magnitude of the effect. These findings suggests that (i) if a glass electrode is being used to follow chemical reactions in sonicated solutions, irradiation should be intermitted for the time of measurements, and (ii) the phenomenon may provide an alternative method for sensing ultrasound or mapping ultrasound energy distribution.     

Thioglycosides in sequential glycosylation strategies

This tutorial review surveys the use of thioglycosides in the development of sequential glycosylation methodologies, with a focus on chemoselective, orthogonal and iterative glycosylation strategies reported since the beginning of this century. Both fundamental aspects of glycosidic bond formation and ingenious state-of-the-art methodologies are presented.     

Substituent effects on the mass spectrometric fragmentations of 4-aryl-3,3-dichlorooxetan-2-ones

The electron impact mass spectrometric fragmentation pathways for a series of 4-aryl-3,3-di-chlorooxetan-2-ones were investigated. It was found that cleavage to radical cations of dichloroketene and/or the substituted benzaldehyde is preferred by a large measure to cleavage to radical cations of carbon dioxide and/or the substituted β,β-dichlorostrene. Furthermore, it was demonstrated that the nature of the substituent has a significant influence on the localization of charge in the preferred direction of cleavage.     

Near-millimetre wave emission from trioxan

The laser-emission spectrum of trioxan, when pumped by a CO₂ laser, has been extended. The lowest frequency obtained from this molecule has been measured at 144.86(2) GHz.     

Electronic-structure calculations for complex crystals

Summary We discuss some new ideas for improving first-principle muffin-tin orbital-type electronic-structure calculations for complex crystals such as ternary and multinary compounds. The new ideas include construction of generalized muffin-tin orbitals and energy-dependent double MTO basis sets, cellular decomposition based on strongly overlapping atomic spheres and evaluation of matrix elements in the residual interstitial region by extrapolation. Supported in part by the Office of Naval Research, Contract Number N00014-79-C-0814.     

Physics and logic: Thales

Thales's protophysics is reconstructed with the help of the Steiner quasigroup. A three-valued logic is proposed, equivalent to it. The discovered connection between physics and logic is used to discuss the natural form of the logic of quantum mechanics.     

Statistical multi-step compound emission in (n, 2n) reactions

The multi-step compound-emission (MSC) theory has been used to analyse the preequilibrium effects in the neutron-emission spectra and excitation curves of the (n, 2n) reactions. Cross sections for the ¹⁹¹Ir(n, 2n) and ¹⁹³Ir(n, 2n) reactions are reported in the neutron-energy range from 13 MeV to 18 MeV and analysed in terms of combined compound-nucleus and MSC theory.     

A potentiometric study of the water-soluble silver(I) complexes of n,n'-bis(2-hydroxyethyl)dithio-oxamide : Part II. Determination of the mean composition -p and -q

A method is described for determining the mean composition of the complex compounds of silver(I) and HEDTO. The values obtained do not agree with those calculated on the assumption that only B(AB)_n complexes are formed. It is concluded that besides the complexes B(AB)_n other complexes with formula (AB)_n are present.     

Measuring charge transport from transient photovoltage rise times. A new tool to investigate electron transport in nanoparticle films

Charge transport rate at open-circuit potential (V(oc)) is proposed as a new characterization method for dye-sensitized (DS) and other nanostructured solar cells. At V(oc), charge density is flat and measurable, which simplifies quantitative comparison of transport and charge density. Transport measured at V(oc) also allows meaningful comparison of charge transport rates between different treatments, temperatures, and types of cells. However, in typical DS cells, charge transport rates at V(oc) often cannot be measured by photocurrent transients or modulation techniques due to RC limitations and/or recombination losses. To circumvent this limitation, we show that charge transport at V(oc) can be determined directly from the transient photovoltage rise time using a simple, zero-free-parameter model. This method is not sensitive to RC limitation or recombination losses. In trap limited devices, such as DS cells, the comparison of transport rates between different devices or conditions is only valid when the Fermi level in the limiting conductor is at the same distance from the band edge. We show how to perform such comparisons, correcting for conduction band shifts using the density of states (DOS) distribution determined from the same photovoltage transients. Last we show that the relationship between measured transport rate and measured charge density is consistent with the trap limited transport model.