Model studies of colloidal silica precipitation using biosilica extracts from<Emphasis Type="Italic"> Equisetum telmateia</Emphasis>

Structural materials containing silicon are produced in single celled organisms through to higher plants and animals. Hydrated amorphous silica is a colloidal mineral of infinite functionality that is formed into structures with microscopic and macroscopic form. Proteins and proteoglycans are suggested to play a critical role in the catalysis of silica polycondensation and in structure direction during the formation of these magnificent structures. This article extends knowledge on the effect of protein containing biosilica extracts from Equisetum telmateia on the kinetics of silica formation and structure regulation. Utilising potassium silicon catecholate as the source of soluble silicon, bioextracts obtained from plant silica by dissolution of the siliceous phase with aqueous HF following extensive acid digestion of the plant cell wall were found to modify the kinetic rate constants for the formation of small silicic acid oligomers under circumneutral pH conditions and to modify the solubility of silicic acid in solution. Addition of the bioextracts at ca. 1 wt% to the reaction medium reduced the sizes and range of sizes of the fundamental silica particles formed and led to the formation of crystalline polymorphs of silica under conditions of ca. neutral pH, room temperature and in the absence of multiply charged cations, conditions assumed to be relevant to the biological mineralization environment. The ability of biological organisms to regulate the formation of silica structures with prevention of crystallinity is discussed as are the implications of this study in terms of the generation of new materials with specific form and function for industrial application.     

The mass spectra of alkyl phenyl tellurides

The mass spectra of several alkyl phenyl tellurides, C₆H₅TeR (R = CH₃, CD₃, C₂H₅, n-C₃H₇, i-C₃H₇ and n-C₄H₉) have been studied with special emphasis on the fragmentation patterns involving cleavage of the alkyl and aryl tellurium–carbon bonds. Each compound exhibited intense parent ions. The rearrangement ions [C₆H₆Te]⁺? and [C₆H₆]⁺? were found in the spectra of phenyl ethyl and higher tellurides. Two other rearrangement ions [HTe]⁺ and [C₇H₇]⁺ were observed in the spectrum of each compound. Examination of the mass spectrum of phenyl methyl-d₃ telluride demonstrated that the [HTe]⁺ ions derive hydrogen from the phenyl group.     

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Magnetic Resonance Microscopy of Heterogeneity in Polymer Electrolyte Membranes

Magnetic resonance microscopy of Nafion 117 is used to measure the spatial variation of solvent dynamics in protonated (acid form) membranes immersed in solvent. Spatial resolution allows determination of membrane material property heterogeneity via T ₂ and diffusion variations to be easily studied in the presence of strong free solvent signal. Variation of T ₂ and diffusion as a function of solvent methanol–water mole fraction is measured. Spatially averaged T ₂ and diffusion data are in general agreement with previous bulk nuclear magnetic resonance studies; however, significant disparities from sample to sample at fixed solvent concentration are present in the spatially averaged data. The variation is determined to be due to changes in solvent mobility within the membrane over scales of the order of 10 mm, indicating macroscale heterogeneity of the solvent saturated membrane morphology. Authors' address: Sarah L. Codd, Department of Mechanical and Industrial Engineering, Montana State University, Bozeman, MT 59717-3800, USA     

Decay time analysis in pulse thermography

Pulse Thermography is being used since several years for rapid detection of subsurface defects. This method is well suited for industrial applications because no physical contact to the test object is needed. Within a short measurement time robust results are obtained. Besides phase evaluation the decay time of surface temperature can be analyzed. In this paper the idea was to investigate the temperature half-life period of each surface point. The sample is assumed to be composed of small elements having the same surface area but different lengths. In a simple model, heat propagation in between these elements is neglected (local one dimensional model). Only changes in mass, heat capacity, and volume are considered. If the material has homogeneous thermal properties, the length (e.g. thickness) has a strong impact on the cooling down process. The concept takes the decay time for each element as a parameter for imaging.     

Drifting convection cells in rotating fluid layers heated from below

It is shown that hexagonal convection cells in a rotating horizontal fluid layer heated from below will in general exhibit a drift in contrast to convection rolls except in the case of a vertical axis of rotation. The direction of the drift is prograde (retrograde) for cells with rising (descending) motion in the center of the convection cell. In addition a mean flow generated by convection is derived. An application to solar convection is discussed.