Langmuir–Blodgett films of pyridinium-dicyanomethanide dyes mixtures with photobleachable absorption bands

We report on Langmuir-Blodgett (LB) films characterization of 4-[5-dicyanomethanido)thien-2-y1]-N-(n-hexadecyl)pyridinium (C₁₆H₃₃-PDCNT), and 1-(N-(n-hexadecy]-4-pyridinio)-2-[5-(dicyanomethanido)thien-2-yl]ethene (C₁₆H₃₃-PDCNTE); LB films of the pure compounds and of the mixtures of the two compounds were prepared at 291 K: UV-vis investigation revealed the presence of photobleachable absorption bands, the ones at about 530 nm and 640 nm were due to charge transfer transitions of the monomer of C16H33-PDCNT and C₁₆H₃₃-PDCNTE, respectively; the sharp, photobleachable ones shifted to shorter wavelengths were due to H-aggregates of the two compounds. By changing the molar ratios of the two compounds in the mixtures and in other cases by annealing the LB films, the absorption maxima of the sharp, photobleachable bands due to H-aggregates could be tuned in the range 415–467 nm. These LB films are thus very promising in view of optical data storage applications.     

Dynamical systems and numerical analysis: the study of measures generated by uncountable I.F.S.

Measures generated by Iterated Function Systems composed of uncountably many one-dimensional affine maps are studied. We present numerical techniques as well as rigorous results that establish whether these measures are absolutely or singular continuous.     

A graphical approach to redox titrations

Summary A method for drawing a logarithmic diagram which gives a correct representation of the equilibrium concentrations of the various species taking part in a redox titration is described. The use of this kind of diagrams for evaluating the titration error and for calculating the titration curve is illustrated. The symmetry properties of titration curves and the linearity range of Gran plots are also discussed on the basis of the logarithmic diagrams.

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Graphische Behandlung von Redox-Titrationen

Zusammenfassung Ein Verfahren wird beschrieben zur Aufstellung eines logarithmischen Diagramms, das eine korrekte Darstellung der Gleichgewichtskonzentrationen der verschiedenen Teilnehmer an einer Redoxtitration bietet. Der Gebrauch eines solchen Diagramms zur Auswertung des Titrationsfehlers und zur Berechnung der Titrationskurve wird gezeigt. Aufgrund der logarithmischen Diagramme werden auch die Symmetrieeigenschaften von Titrationskurven und der Linearitätsbereich von Gran-Diagrammen diskutiert.

     

Accuracy of suboptimal solutions to kernel principal component analysis

For Principal Component Analysis in Reproducing Kernel Hilbert Spaces (KPCA), optimization over sets containing only linear combinations of all n-tuples of kernel functions is investigated, where n is a positive integer smaller than the number of data. Upper bounds on the accuracy in approximating the optimal solution, achievable without restrictions on the number of kernel functions, are derived. The rates of decrease of the upper bounds for increasing number n of kernel functions are given by the summation of two terms, one proportional to n ^−1/2 and the other to n ⁻¹, and depend on the maximum eigenvalue of the Gram matrix of the kernel with respect to the data. Primal and dual formulations of KPCA are considered. The estimates provide insights into the effectiveness of sparse KPCA techniques, aimed at reducing the computational costs of expansions in terms of kernel units.     

A complete treatment of a steady-state four-level model for the interpretation of OH laser-induced fluorescence measurements in atmospheric pressure flames

In order to obtain OH concentration measurements in atmospheric pressure flames from saturated fluorescence signal, we have developed a stationary four-level model. A general relationship between the measured upper state population and the total number density has been derived. The effects of the imbalance between the rotational transfer rates in the upper and ground states is analyzed. We show that in the case of comparable rotational rates, the results of our treatment are similar to the ones obtained with the balanced cross rate model. A set of complementary data which should facilitate absolute OH concentration measurements is also pointed out.     

Use of 2,2-dimethoxypropane for the direct gas chromatographic-mass spectrometric determination of some organic compounds in water

The well known reaction between 2,2-dimethoxypropane and water allows for the conversion of an aqueous into an organic solution ready to be injected directly into a gas chromatographic-mass spectrometric (GC-MS) system. Only time, temperature and water/ketal ratio were the parameters studied among those which influence the equilibrium reaction. The reaction environment is not suitable for all compounds: acids, esters, alcohols, amines, ketones and phenols may react with methanol, acetone and ketal owing to Amberlyst being present as catalyst. This method is proposed for the GC-MS analysis of aqueous solutions containing hydrocarbons, halogenated hydrocarbons and ethers. The determination of some pesticides in water is reported.     

A boundary-integral equation method for free surface viscous flows

Summary A boundary integral equation method is proposed for the solution of viscous recirculating flows with free surfaces. In particular the method is applied to thermocapillary convection and to drop formation, both in micro-gravity conditions, the latter to test its capability to handle real unsteady problems.The presence of non linear terms in Navier-Stokes equations leads to a volume integral, which has to be approximated by a linearization procedure.Several numerical results for thermocapillary flows, both with fixed and moving free surface, are discussed in comparison with previously obtained finite difference solutions. Some preliminary results, and in particular the time evolution of the free surface shape, are also presented for the drop formation problem. Only plane two dimensional fields are considered for both problems.

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Sommario Si propone un metodo basato sulla soluzione di equazioni integrali di contorno per flussi viscosi con superficie libera. Tale metodo è applicato allo studio della convezione termocapillare ed al processo di formazione di una goccia, entrambi in condizioni di microgravità. La presenza dei termini non lineari nell'equazione di Navier-Stokes comporta un integrale di volume che viene approssimato mediante un processo di linearizzazione.Risultati numerici per flussi termocapillari con superficie libera sia fissa che mobile sono confrontati con altri ottenuti in precedenza con un metodo alle differenze finite. Si presentano inoltre alcuni risultati preliminari sul problema della formazione della goccia ed in particolare l'evoluzione nel tempo della configurazione geometrica della superficie libera. Nei due casi si analizzano solo campi bidimensionali.

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Presented at the VII National Conference AIDAA, Naples, September 1983.

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In leave of absence from Tianjin University, China.