Effect of the surface thermal radiation on turbulent natural convection in tall cavities of façade elements

The effect of the surface thermal radiation in tall cavities with turbulent natural convection regime was analyzed and quantified numerically. The parameters considered were: the Rayleigh number 10⁹–10¹², the aspect ratio 20, 40 and 80 and the emmisivity 0.0–1.0. The percentage contribution of the radiative surface to the total heat transfer has a maximum value of  15.19% (Ra = 10⁹, A = 20) with emissivity equal to 1.0 and a minimum of 0.5% (Ra = 10¹², A = 80) with ε* = 0.2. The average radiative Nusselt number for a fixed emissivity is independent of the Rayleigh number, but for a fixed Rayleigh number diminishes with the increase of the aspect ratio. The results indicate that the surface thermal radiation does not modify significantly the flow pattern in the cavity, just negligible effects in the bottom and top of the cavity were observed. Two different temperature patterns were observed a conductive regime Ra = 10⁹ and a boundary layer regime Ra = 10¹².     

Use of neural networks and diode-array detection to develop an isocratic HPLC method for the analysis of nitrophenol pesticides and related compounds

Summary We have used an artificial neural network to optimize the composition of the mobile phase for an isocratic HPLC method for the analysis of nitrophenol pesticides and related compounds, on the basic of different response functions, and have compared the results with those obtained by application of response-surface methodology. These studies resulted in the selection the mobile phase 10:30:15:45 methanol-acetonitrile-tetrahydrofuran-buffer solution (0.1m acetic acid and 0.1m sodium perchlorate); the flow-rate was 1 mL min⁻¹. Under these conditions a chromatogram showing twelve well-resolved peaks was obtained in 14 min. Although the peaks corresponding to ethylparathion and medinoterb acetate overlapped severely, it was possible, by use, of a diode-array spectrophotometer for detection, and by combining the absorbance measured at different wavelengths as the signal, to separate the peaks corresponding to one or other of the compounds. Calibration plots were constructed for the concentration range 2–10 ppm. Detection limits, calculated by the method of Clayton et al., were approximately 0.32–0.69 ppm. The method has been applied to the analysis of these compounds in fortified river water samples, after previous preliminary preconcentration by solid-liquid extraction on a C₁₈ cartridge.     

Polarography and artificial neural network for the simultaneous determination of nalidixic acid and its main metabolite (7-hydroxymethylnalidixic acid)

Nalidixic acid (NA) and its main metabolite, 7-hydroxymethylnalidixic acid (OH-NA), are simultaneously determined by applying artificial neural networks (ANNs), to their square wave voltammetric signals. The scores of a PCR model, built with the voltammetric data of a set of standard samples, recorded between −0.70 and −1.0 V, are used as training set for the net for each compound. The trained nets (ANNs) are used for the simultaneous determination of NA and OH-NA in urine. The recovery values are comprised between 91 and 109% for NA and between 82 and 112% for OH-NA, being these results better than the results obtained by application of partial least squares (PLS) multivariate calibration.     

Determination of Mo(VI) with 2-benzylideneiminobenzohydroxamic acid (2-BIBH) in urine by cathodic stripping voltammetry

Summary Controlled adsorptive accumulation of Mo(VI)-2-BIBH at the hanging mercury drop electrode (HMDE) provides the basis for the direct stripping measurement of Mo(VI) in nanomolar concentration. The cathodic stripping response is evaluated with respect to experimental parameters such as preconcentration time, preconcentration potential and others. A differential pulse cathodic stripping voltammetric method for the determination of Mo(VI) with 2-BIBH in urine is proposed. The detection limit is 10^–9 mol/l Mo(VI), standard deviation for 5×10^–8 mol/l is ±1.58×10^–9 mol/l.

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Bestimmung von MolybdÄn(VI) mit 2-BenzylideniminobenzohydroxamsÄure (2-BIBH) in Harn durch kathodische Stripping-Voltammetrie

     

Application of time-domain differentiation of chromatographic peaks in liquid chromatography

The differentiation of chromatographic bands with respect to time is useful for improving the resolution of overlapping peaks owing to the reduced band widths of derivatives in comparison with the original bands. An IBM XT 286 microcomputer was interfaced to a Perkin-Elmer liquid chromatographic system and software was developped to allow the acquisition and digitization of chromatographic data for subsequent manipulation, storage and graphical representation. Smoothing and differentiation of chromatographic bands with respect to time were done by the Savitzky-Golay method. The method was applied to the determination of a mixture of antioxidants used as additives in nutrition. The overlapping peaks corresponding to propyl gallate and tert-butylhydroquinone were resolved by time-domain differentiation.     

Flow and Dynamic Viscoelastic Characterization of Non-Purified and Purified Mucin Dispersions

This study demonstrated that the rheological behavior of mucin, a glycoprotein, mainly depends on the concentration of its dispersions and purity of the sample. Rheological properties were studied under rotational and oscillatory shear and creep curves. The results showed that mucin dispersions display non-Newtonian behavior of the shear thinning type. The mucin dispersion showed an apparent viscosity ranging from 0.22 to 29.29 Pa.s; at 10% concentration it formed macromolecular solutions with G″>G′; these showed viscoelastic liquid behavior, while at 40% it showed viscoelastic solid behavior, characteristic of weak gels, G′>G″. Atomic force microscopy revealed topographical differences on the commercial mucin surface, as in non-purified and purified mucin gels.     

Total synchronous fluorescence spectroscopic data modeled with first- and second-order algorithms for the determination of doxorubicin in human plasma

In this work, we present the development of a method for the determination of doxorubicin in plasma samples in the presence of an unexpected component (riboflavin) by using total synchronous fluorescence spectroscopic data matrices. To the best of our knowledge, this is the first time that the second-order advantage is obtained with this kind of data. Two strategies including unfolding the data and: (a) processing with multivariate curve resolution coupled to alternating least-squares as first-order data or (b) processing with unfolded partial least-squares and exploiting the second-order advantage by the residual bilinearization procedure were considered. The calibration set was built with human plasma samples spiked with doxorubicin, while the validation set was prepared with human plasma samples spiked with both doxorubicin and riboflavin, a drug whose spectrum highly overlaps with the one corresponding to doxorubicin. Both methodologies reached good indicators of accuracy: recoveries of ca. 100?±?8 % and REP of ca. 5 %; and precision: coefficient of variations between 7 and 9 %.