Study of oxygen ion transport in acceptor doped samarium cobalt oxide

Dense samples of the perovskite Sm_1−xSr_xCoO₃ (where x=0, 0.2, 0.4, 0.5 and 0.6) have been prepared. The samples were¹⁸O/¹⁶O isotopically exchanged at a variety of temperatures between 500°C and 900°C. Subsequent analysis of the diffusion profile using Secondary Ion Mass Spectrometry (SIMS) allowed the oxygen self-diffusion coefficient, D*, and surface exchange co-efficient, k, to be determined. From the temperature dependence of these parameters the activation energies for both processes were evaluated. The surface coverage of samarium, cobalt and oxygen in SmCoO₃ was determined from calibration samples using Low Energy Ion Scattering (LEIS). LEIS was used to determine the effect of strontium doping on the surface composition and the¹⁸O-concentration at the surface of a number of the¹⁸O-exchanged samples. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11 – 18 Sept. 1994.     

A simple and selective kinetic spectrophotometric method for the determination of kanamycin using acetylacetone-formaldehyde reagent in N,N′-dimethylformamide medium

A simple, sensitive, and selective kinetic spectrophotometric method for the determination of kanamycin in pure form and pharmaceutical formulations is described. The method is based on the measurement of the intensity of the yellow chromogen formed by the reaction between kanamycin and acetylacetone-formaldehyde reagent in a N,N′-dimethyl formamide medium. The variable-time method was used to evaluate the rate of reaction of the colored chromogen formed at 410 nm. The reaction conditions were optimized and the calibration graph was found to be linear in the range 60–160 μg/mL. The results obtained by the developed and reference methods are in good agreement. Various statistical parameters were evaluated to establish the precision, accuracy, repeatability, and reproducibility of the proposed method. The text was submitted by the authors in English.     

Gas phase radiation chemistry of hexafluoroethane

The Co-60 gamma radiolysis of gaseous C₂F₆ was investigated at 50 Torr pressure, both pure and with 10% oxygen added. For the pure system, the radiolytic products and their respective C values were CF₄, 2.27; C₃F₈, 0.23; C₄F₁₀, 0.09; C₅F₁₂, 0.015; and C₆F₁₄, 0.009. All radiolysis products except for CF₄ (C = 0.61) were eliminated when 10% O₂ was added as scavenger. The results are discussed mainly in terms of the decomposition of excited C₂F₆ into free radicals, which can then combine. The unscavenged CF₄ is accounted for by the ion-molecule reaction CF₃⁺ + C₂F₆ → CF₄ + C₂F₅⁺.     

In situ studies of electrode reactions: The mechanism of lithium intercalation in TiS2

The mechanism of lithium intercalation into TiS₂ is poorly understood even though the system Li_xTiS₂ (0 ? x ? 1) has been extensively studied. This mechanism is critical in the functioning of $\text{Li}\text{TiS}{}_2$ nonaqueous batteries. In this report we describe several techniques which are used to study this mechanism. These methods consist of ex situ and in situ optical and X-ray techniques which yield information regarding the mechanism of lithium intercalation and factors which effect this process during the operation of $\text{Li}\text{TiS}{}_2$ batteries.     

Surface ligands in the imprinting and binding of molecularly imprinted cross-linked micelles

Molecular recognition in water is challenging but water-soluble molecularly imprinted nanoparticle (MINP) receptors were produced readily by double cross-linking of surfactant micelles in the presence of suitable template molecules. When the micellar surface was decorated with different polyhydroxylated ligands, significant interactions could be introduced between the surface ligands and the template. Flexible surface ligands worked better than rigid ones to interact with the polar moiety of the template, especially for those template molecules whose water-exposed surface is not properly solvated by water. The importance of these hydrophilic interactions was examined in the context of different substrates, density of the surface ligands, and surface-cross-linking density of the MINP. Together with the hydrophobic interactions in the core, the surface hydrophilic interactions can be used to enhance the binding of guest molecules in water.     

A soft on/off switch based on the electrochemically reversible H–J interconversion of a floating porphyrin membrane

Soft molecular assemblies that respond reversibly to external stimuli are attractive materials as on/off switches, in optoelectronic, memory and sensor technologies. In this Edge Article, we present the reversible structural rearrangement of a soft porphyrin membrane under an electrical potential stimulus in the absence of solid-state architectures. The free-floating porphyrin membrane lies at the interface between immiscible aqueous and organic electrolyte solutions and is formed through interfacial self-assembly of zinc(ii) meso-tetrakis(4-carboxyphenyl)porphyrins (ZnPor). A potential difference between the two immiscible electrolyte solutions induces the intercalation of bis(triphenylphosphoranylidene)ammonium cations from the organic electrolyte that exchange with protons in the porphyrin membrane. In situ UV/vis absorbance spectroscopy shows that this ionic intercalation and exchange induces a structural interconversion of the individual porphyrin molecules in the membrane from an H- to a J-type molecular configuration. These structural rearrangements are reversible over 30 potential cycles. In situ polarisation-modulation fluorescence spectroscopy further provides clear evidence of structural interconversion of the porphyrin membrane, as intercalation of the organic electrolyte cations significantly affects the latter''s emissive properties. By adjusting the pH of the aqueous phase, additional control of the electrochemically reversible structural interconversion can be achieved, with total suppression at pH 3.

The structural rearrangement of a porphyrin membrane self-assembled at a “soft” liquid|liquid interface from a H- to J-molecular configuration is reversibly modulated by externally manipulating the interfacial Galvani potential difference.     

Shortest Path Problem on a Network with Imprecise Edge Weight

A network with its arc lengths as imprecise number, instead of a real number, namely, interval number and triangular fuzzy number is considered here. Existing ideas on addition and comparison between two imprecise numbers of same type are introduced. To obtain a fuzzy shortest path from a source vertex to all other vertices, a common algorithm is developed which works well on both types of imprecise numbers under consideration. In the proposed algorithm, a decision-maker is to negotiate with the obtained fuzzy shortest paths according to his/her view only when the means are same but the widths are different of the obtained paths. Otherwise, a fuzzy optimal path is obtained to which the decision-maker always satisfies with different grades of satisfaction. All pairs fuzzy shortest paths can be found by repeated use of the proposed algorithm.     

The Role of the Pars Recta and Pars Oblique of Cricothyroid Muscle in Speech Production

To evaluate the functional difference of the pars recta and pars oblique during speech production, the electromyographic activities of these muscles were measured in thyroidectomized patients. The hooked wire electrodes were inserted into the normal side of the bellies of the pars recta and pars oblique bundles. Two kinds of sentences were used to obtain pitch changes, a simple interrogative sentence and a complex sentence with stress contrasts. The pars recta and pars oblique were simultaneously activated for initial lengthening and tensing of vocal folds to produce speech. The pars oblique might be initially more active than the pars recta at the initial task of speech and the pars recta might be more active at the pitch elevation in the interrogative sentence and the stress contrast of the complex sentence. The maximum electromyographic activity range of the pars recta and pars oblique seemed to be nearly equal. These results demonstrated that the patterns of electrical activities of the two bellies are different during speech and the combined activities of the pars recta and pars oblique are important in the adjustment of the vocal fold length during speech.