Singlet Sigma: The "Other" Singlet Oxygen in Solution

The lowest excited electronic state of molecular oxygen, O₂(a^1-DL_g), is often called simply singlet oxygen. This singlet delta state is an acknowledged and well-studied intermediate in many solution-phase photosystems. However, the second excited electronic state of oxygen, O₂(b¹δ_g+), is also a singlet. It has recently become possible to monitor this singlet sigma state in solution, which, in combination with studies of the singlet delta state, contributes to a better understanding of a variety of general problems in chemistry.     

All-optical wavelength converters for optical switching applications

We present the latest results about all-optical wavelength conversion obtained within the European Union—funded RACE ATMOS project. In particular, solutions based on carrier depletion in Distributed Brag Reflector lasers have reached penalty-free polarization-insensitive operation at up to 2.5 Gbit/s, while solutions based on Semiconductor Optical Amplifiers (SOAS) under cross-gain modulation have been demonstrated at more than 20 Gbit/s. The study of cross-phase modulation in SOAs has also been performed, leading to the monolithic integration of SOAs within an interferometer, according to structures proposed by the project. Penalty-free operation at up to 10 Gbit/s as well as signal reshaping have been obtained with such devices. Besides the study of components, wavelength converters have been used in several demonstrators assessing their maturity and compatibility with photonic-switching applications.     

One-dimensional PtO2 at Pt steps: formation and reaction with CO

Using core-level spectroscopy and density functional theory we show that a one-dimensional (1D) oxide structure forms at the steps of the Pt(332) surface after exposure. The 1D oxide is found to be stable in an oxygen pressure range, where bulk oxides are only metastable, and is therefore argued to be a precursor to the Pt oxidation. As an example of the consequences of such a precursor exclusively present at the steps, we investigate the reaction of CO with oxygen covered Pt(332). Albeit more strongly bound, the oxidic oxygen is found to react more easily with CO than oxygen chemisorbed on the Pt terraces.     

Se-Ga23Se phase equilibria: a regular associated solution model for the Ga-Se liquid

Se vapor pressures were measured by the dew point method for the binary system Ga_1·xSe_x, 0.60 < x < 1.00 (Ga₂Se₃-Se), between 700 and 1050°C. The Se vapor pressure was found to decrease rapidly near x = 60 atomic% Se. The T-X and P-X liquidus curves are thermodymanically modelled by a regular associated solution model for the liquid phase, with the associate, Ga₂Se₃. The best fit to the data was obtained with 4000 cal/mole of Ga₂Se₃ for the regular solution interaction parameter and 0.10 for the degree of dissociation in the stoichiometric liquid (x = 0.60).     

Anisotropic conductivity in a channel-structured superionic conductor: Li2Ti3O7

From measurements on single crystals of Li₂Ti₃O₇, the conductivity is determined to be predominately ionic with an anisotropy of $\text{σ}{}_{\mathrm{b}}\text{σ}{}_{\mathrm{a}}\text{≈4}$ and $\text{σ}{}_{\mathrm{c}}\text{σ}{}_{\mathrm{b}}\text{≈7}$. This anisotropy is significant but is not sufficient to classify this channel-structured ramsdellite material as a one-dimensional conductor. A conduction path through the ramsdellite crystal structure consistent with the determined anisotropy is presented.     

Flow diagnostics downstream of a tribladed rotor model

This paper presents results of a study of vortex wake structures and measurements of instantaneous 3D velocity fields downstream of a triblade turbine model. Two operation modes of flow around the rotor with different tip speed ratios were tested. Initially the wake structures were visualized and subsequently quantitative data were recorded through velocity field restoration from particle tracks using a stereo PIV system. The study supplied flow diagnostics and recovered the instantaneous 3D velocity fields in the longitudinal cross section behind a tribladed rotor at different values of tip speed ratio. This set of data provided a basis for testing and validating assumptions and hypothesis regarding classical theories of rotors.     

Frequency dependence of the shear moduli of spectrin studied using a multiple lumped resonator viscoelastometer

The frequency dependence (119-7860 Hz) of the storage and loss shear moduli, G' and G', of human erythrocyte spectrin dimer crude solutions at 22.5 degrees C has been measured using a Birnboim-Schrag multiple lumped resonator viscoelastometer. The measurements were carried out on solutions of ionic strength 1 mM containing 1.1-3.7 mg ml-1 spectrin. This corresponds to the terminal zone for G' and G'. Analysis of the data using the standard theory of hybrid relaxation spectra yields a relaxation time of 22.5 +/- 1 microseconds. The pure spectrin dimer relaxation time is estimated to be 16 +/- 3 microseconds. This result suggests that at an ionic strength of 1 mM, the spectrin dimers are extended and that the main relaxation process is simple end-over-end rotation.     

Molecular properties of molecules between electrodes

We consider methods for determining properties of molecules between electrodes. We utilize a heterogeneous and structured solvation model for describing the physical situation of a molecule located between electrodes. This method includes directly the polarization terms of the surrounding environment in the quantum mechanical equations.Contribution to the Jacopo Tomasi Honorary Issue     

The Raman spectra and structure of pure vitreous P2O5

We report the polarized Raman spectra of pure anhydrous vitreous P₂O₅ and conclude that this glass is a 3-connected network in which each P atom is surrounded almost tetrahedrally by three bridging O atoms and one double-bonded O terminator. Vibrational calculations on an anchored fragment are used to determine atomic motions in the higher frequency modes; these calculations confirm that the dominant Raman modes involve in-phase compression of neighboring PO bonds.