Normal-mode-vortex interactions

Standing surface waves that interact with a confined, vertical, vorticity field with zero net circulation are studied both analytically and experimentally. The surface waves are generated by vertical vibration, and constant vorticity injection is achieved by a rotating disk flush mounted in the cell. Experimental results are indicative of a local wave-vortex interaction (no dislocation), and a simple theoretical model is able to explain them in quantitative detail.     

Spin concentration in a possible ESR dosimeter: An electron spin echo study on X-irradiated ammonium tartrate

Several single crystals and powder samples of ammonium tartrate, recently proposed as a possible ESR dosimeter, have been X-irradiated with different doses. The total radical concentration has been determined by quantitative cw ESR, by comparison with a standard. The samples have been studied by electron spin echo spectroscopy. The two-pulse echo decay has been obtained and simulated by a single exponential function for different values of the microwave power of the pulses and for different pulse lengths. The dependence of the phase memory time TM on the microwave power has been exploited to get information on the contribution of the instantaneous diffusion to spin dephasing. At room temperature in the range of radical concentrations of 10(18)-10(19) spins/cm3 the instantaneous diffusion is the dominant spin dephasing mechanism. The linear dependence of the instantaneous diffusion on the total concentration of the radicals is in agreement with the theory. From the latter result we conclude that the average radical-radical distance corresponds to a random distribution of the radicals in the matrix. A simple method of measuring the radical concentration by the ESE decays in powder samples of irradiated ammonium tartrate is described.     

Simulation of a Helicon plasma source using a multivariable fuzzymodel

This paper reports work on the development of an automatic control system for a Helicon plasma processing source. The lack of a definitive physical model for the plasma physics of the source and the power coupling mechanism to the plasma precludes the use of traditional control algorithms. This paper develops a fuzzy model that simulates the behavior of the plasma source using the process of genetic algorithms to identify and optimize the parameters of the fuzzy model. This type of model will eventually be used to test a fuzzy control system for the plasma source. In this work, an extensive set of experimental data was acquired where the magnetic field and input power to the plasma source were varied over a wide range while the electron number density was measured. From this learning dataset, the genetic algorithm derived the values of the parameters for the difference equation that describes the system. The fuzzy model so constructed was used to predict the behavior of the source from known input parameters. Comparing the predictions with experimental observations showed that the fuzzy model was generally able to predict the behavior of the plasma as its input parameters were varied with a precision of better than 10%     

D-isotope-labelled n-butane cations in CF3CCl3 and in CF2ClCFCl2: Structure and reactions at low temperature

Cations of n-butane, n-butane-1,4-d₆, -d₄, -d₂ and n-butane-2,3-d4 produced by X-irradiation of CF₂ClCFCl₂ and CF₃CCl₃ 3 matrices containing 1–2 mole% of solute have been investigated by ESR spectroscopy. The measurements have been performed at 77–130 K. The results confirm that the two largest couplings are assigned to two protons on the methyl groups. Smaller couplings have been resolved in CF₃CCl₃ and assigned to specific H atoms. A geometry with a non-planar carbon skeleton is proposed. Partly deuterated methyl groups give rise to rotational isomers. Thermal and photoinduced decompositions producing 2-butyl radicals and 2-butane cations have been further studied.     

The determination of copper,lead and cadmium in an oyster homogenate by anodic stripping voltammetry

Oyster homogenate is digested with nitric and perchloric acids and analyzed by differential pulse anodic stripping voltammetry. The results are compared with the “probable concentrations” obtained from an intercalibration exercise.     

Synthesis and Structure of Ionic Liquids Containing the ­[Al(OC6H4CN)4]– Anion

The synthesis, structure, and physical properties of ionic liquids (IL) bearing the novel [Al(O–C₆H₄–CN)₄]^– ion as counterion to the commonly used [NR₄]⁺, [PR₄]⁺ and imidazolium ions are reported. Both the influence of the alkyl chain length as well as the functionalization with cyano groups is studied. These ILs are easily obtained by reaction of Ag[Al(O–C₆H₄–CN)₄] with the corresponding ammonium, phosphonium, and imidazolium halides. The stability towards electrophilic cations was investigated. All prepared salts have a window for the liquid phase of ca. 200 °C and are thermally stable up to 450 °C. The solid‐state structures reveal only weak cation ··· anion and anion ··· anion interactions in accord with the observed low melting points (glass transition points).     

Anodic stripping voltammetry with the florence mercury film electrode. determination of copper,lead and cadmium in sea water

The use of the rotating glassy carbon electrode mercury plated in situ for anodic stripping voltammetry has been investigated. The choice of electrode material is discussed. The effect of instrumental parameters on the stripping response for copper, lead and cadmium in sea water is studied, the results being in accordance with the theory of thin film electrodes. The variation in the observed sensitivity for the three metals in sea water is discussed in terms of complex-forming ligands. Lastly the performance of the film electrode is compared to that of the hanging mercury drop electrode.     

Self-assembling a molecular pegboard

This paper describes the design, construction, and application of a self-assembled, chemically addressable DNA nanogrid composed of DNA tiles of nanometer dimensions. This self-assembled structure permits precise placement of molecules at predetermined locations on a "molecular pegboard". We used the indexed DNA nanogrids to identify single molecules of DNA that hybridize at particular locations.     

Spatial distribution and decrease of dye solar cell performance induced by electrolyte filling

The spatial performance variation of dye solar cell with standard liquid electrolyte was examined by dividing the cell into segments. Surprisingly large and permanent performance differences were found in different parts of the cell leading to significant losses in the overall cell efficiency. The decrease of open circuit voltage along the electrolyte filling direction suggests that 4-tert-butylpyridine is adsorbed non-uniformly as the electrolyte passes through the dyed TiO₂ layer during the filling process. The result indicates that non-uniform electrolyte adsorption may limit the up-scaling of dye solar cells, which calls for the examination of electrolyte filling techniques and electrolyte compositions less prone to this effect.