Electrical and electro-chemical characterisation of La0.99Fe1−x Ni x O3−δ perovskites

(LFN, 0<x<0.6) perovskites were synthesised by a solid-state route and were characterised by powder XRD, dilatometry, four-point DC conductivity measurements and electro-chemical impedance spectroscopy (EIS) on cone-shaped electrodes using a Ce_1.9Gd_0.1O_1.95 (CGO10) electrolyte. All the compounds were of single phase, and they belong to either the cubic or the hexagonal crystal system. The thermal expansion coefficient (TEC) was in the range 10.7*10⁻⁶ K⁻¹ to 13.4*10⁻⁶ K⁻¹, which continued to increase with increasing nickel content. The highest electronic conductivity was measured for the composition giving a value of 670 S/cm at 380 °C. The highest electro-chemical performance was measured for the composition giving an area specific resistance as low as 5.5 Ωcm² at 600 °C based on EIS measurements on a cone-shaped electrode. Composite cathodes made from and CGO10 revealed a rather low performance due to an un-optimised micro-structure.

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Coupled cluster and density functional theory studies of the vibrational contribution to the optical rotation of (S)-propylene oxide

In a previous study (Chemical Physics Letters 2005, 401 , 385) we computed the optical rotatory dispersion of (S)-propylene oxide in gas phase and solution using the hierarchy of coupled cluster models CCS, CC2, CCSD, and CC3. Even for the highly correlated CC3 model combined with a flexible basis set, the theoretical gas-phase specific rotation at 355 nm was found to be negative in contrast to the experimental result. We argued that vibrational contributions could be crucial for obtaining a complete understanding of the experimental result. Here, we show that this indeed is the case by using coupled cluster models and density functional theory methods to calculate the vibrational contributions to the gas-phase specific rotation at 355, 589.3, and 633 nm. While density functional theory (B3LYP and SAOP functionals) overestimates the specific rotation at 355 nm by approximately 1 order of magnitude and yields an incorrect sign at 589.3 and 633 nm, the coupled cluster results are in excellent agreement with the experimentally measured optical rotations. We find that all vibrational modes contribute significantly to the optical rotation and that temperature effects must be taken into account.     

Voltammetric procedure for trace metal analysis in polluted natural waters using homemade bare gold-disk microelectrodes

Voltammetric procedures for trace metals analysis in polluted natural waters using homemade bare gold-disk microelectrodes of 25- and 125-μm diameters have been determined. In filtered seawater samples, square wave anodic stripping voltammetry (SWASV) with a frequency of 25 Hz is applied for analysis, whereas in unfiltered contaminated river samples, differential pulse anodic stripping voltammetry (DPASV) gave more reliable results. The peak potentials of the determined trace metals are shifted to more positive values compared to mercury drop or mercury-coated electrodes, with Zn always displaying 2 peaks, and Pb and Cd inversing their positions. For a deposition step of 120 s at ?1.1 V, without stirring, the 25-μm gold-disk microelectrode has a linear response for Cd, Cu, Mn, Pb and Zn from 0.2 μg L^?1 (1 μg L^?1 for Mn) to 20 μg L^?1 (30 μg L^?1 for Zn, Pb and 80 μg L^?1 for Mn). Under the same analytical conditions, the 125-μm gold-disk microelectrode shows linear behaviour for Cd, Cu, Pb and Zn from 1 μg L^?1 (5 μg L^?1 for Cd) to 100 μg L^?1 (200 μg L^?1 for Pb). The sensitivity of the 25-μm electrode varied for different analytes from 0.23 (±0.5%, Mn) to 4.83 (±0.9%, Pb) nA L μmol^?1, and sensitivity of the 125-μm electrode varied from 1.48 (±0.7%, Zn) to 58.53 (±1.1%, Pb  nA L μmol^?1. These microelectrodes have been validated for natural sample analysis by use in an on-site system to monitor Cu, Pb and Zn labile concentrations in the Deûle River (France), polluted by industrial activities. First results obtained on sediment core issued from the same location have shown the ability of this type of microelectrode for in situ measurements of Pb and Mn concentrations in anoxic sediments.      

A cyclic dinucleotide with a four-carbon 5'-C-to-5'-C connection; synthesis by RCM, NMR-examination and incorporation into secondary nucleic acid structures

A 5'-C-allylthymidine derivative was prepared from thymidine by the application of a stereoselective allylation procedure and its 5'(S)-configuration was confirmed. From this nucleoside derivative, appropriately protected building blocks were prepared and coupled using standard phosphoramidite chemistry to afford a dinucleotide with two 5'-C-allylgroups. This molecule was used as a substrate for a ring-closing metathesis (RCM) reaction and after deprotection, a 1 : 1 mixture of E- and Z-isomers of a cyclic dinucleotide with an unsaturated 5'-C-to-5'-C connection was obtained. Alternatively, a hydrogenation of the double bond and deprotection afforded a saturated cyclic dinucleotide. An advanced NMR-examination confirmed the constitution of this molecule and indicated a restriction in its overall conformational freedom. After variation of the protecting group strategy, a phosphoramidite building block of the saturated cyclic dinucleotide with the 5'-O-position protected as a pixyl ether and the phosphate protected as a methyl phosphotriester was obtained. This building block was used in the preparation of two 14-mer oligonucleotides with a central artificial bend due to the cyclic dinucleotide moiety. These were found to destabilise duplexes, slightly destabilise bulged duplexes but, to some extent, stabilise a three-way junction in high Mg(2+)-concentrations.     

Competitive clustering in a bidisperse granular gas

A bidisperse granular gas in a compartmentalized system is experimentally found to cluster competitively: Depending on the shaking strength, the clustering can be directed either towards the compartment initially containing mainly small particles or to the one containing mainly large particles. The experimental observations are quantitatively explained within a flux model.     

Automatic gain control of semiconductor laser amplifiers

A new approach to automatic gain control has been demonstrated and a signal polarization independent operation over a 35-nm wavelength range at a gain level of 17 dB has been obtained.     

Experimental evidence for a partially dissociated water bilayer on Ru[0001

Core-level photoelectron spectra, in excellent agreement with ab initio calculations, confirm that the stable wetting layer of water on Ru[0001] contains O-H and H2O in roughly 3:5 proportion, for OHx coverages between 0.25 and 0.7 ML, and T<170 K. Proton disorder explains why the wetting structure looks to low energy electron diffraction (LEED) to be an ordered p(square root of 3 x square root of 3)R30 degrees adlayer, even though approximately 3/8 of its molecules are dissociated. Complete dissociation to atomic oxygen starts near 190 K. Low photon flux in the synchrotron experiments ensured that the diagnosis of the nature of the wetting structure quantified by LEED is free of beam-induced damage.     

Novel instrument for high temperature thermogravimetric measurements in high water vapour contents

Summary A novel instrument for high temperature thermogravimetric measurements in atmospheres containing high water vapour contents was developed in a collaboration between Netzsch and Risø National Laboratory. The development of the instrument was initiated to facilitate the investigation of high temperature corrosion of steels in humidified atmospheres. The instrument consists of a standard thermal analyser unit, including a new water vapour furnace, balance and sample carrier. The design of the instrument is discussed and thermogravimetric measurements on a Fe₇₈Cr₂₂ steel are presented.     

Porous glass electroosmotic pumps: design and experiments

An analytical model for electroosmotic flow rate, total pump current, and thermodynamic efficiency reported in a previous paper has been applied as a design guideline to fabricate porous-structure EO pumps. We have fabricated sintered-glass EO pumps that provide maximum flow rates and pressure capacities of 33 ml/min and 1.3 atm, respectively, at applied potential 100 V. These pumps are designed to be integrated with two-phase microchannel heat exchangers with load capacities of order 100 W and greater. Experiments were conducted with pumps of various geometries and using a relevant, practical range of working electrolyte ionic concentration. Characterization of the pumping performance are discussed in the terms of porosity, tortuosity, pore size, and the dependence of zeta potential on bulk ion density of the working solution. The effects of pressure and flow rate on pump current and thermodynamic efficiency are analyzed and compared to the model prediction. In particular, we explore the important tradeoff between increasing flow rate capacity and obtaining adequate thermodynamic efficiency. This research aims to demonstrate the performance of EOF pump systems and to investigate optimal and practical pump designs. We also present a gas recombination device that makes possible the implementation of this pumping technology into a closed-flow loop where electrolytic gases are converted into water and reclaimed by the system.