Carlos E.N. Gatts

Measurement of the thermal properties of liquids using a thermal wave interferometer

In this paper we discuss the use of an alternative photothermal technique for measurements of thermal properties of liquids. The proposed technique is based upon the concept of thermal wave interferometry. The liquid sample is confined between two thin pyroelectric detectors. One of these detectors acts as a modulated absorber of light while the other is used for sensing the temperature fluctuations transmitted through the liquid layer. The good agreement between the values of the thermal properties we got with the present technique and those reported in the literature demonstrates the capability of the technique for full characterization of the thermal properties of liquids.

On the use of the thermal wave resonator cavity sensor for monitoring hydrocarbon vapors

A gas sensing device based on a thermal wave resonator cavity is outlined. It is experimentally tested by monitoring the presence of several hydrocarbon vapors in air via the measurement of the thermal diffusivity. It is also shown that its time-dependent response may be used to follow the vapor diffusion. It is shown that its characteristic response time is linearly correlated to the thermal diffusivity value of the mixture. The steps toward the development of a practical sensing device are further discussed.

Neural pattern recognition and multivariate data: water typology of the Paraı́ba do Sul River, Brazil

Abstract Modelling environmental processes is a complicated task, for the number of variables involved is usually high. This paper considers the use of neural pattern recognition to analyze structures within large data sets related to the study of ecological phenomena. The purpose is to use the information obtained with the aid of an unsupervised clustering step in a pattern recognition algorithm to obtain insight into the processes occurring along the period of observation. Once the processes are identified, more reliable models can be derived. The method proved to be helpful to highlight the major fluctuations in river water chemistry, and to identify complementary characteristics relevant to understanding the processes involved in the transport of dissolved nutrients in the Paraiba do Sul River basin outlet.

Tuning methyl 4,6-O-benzylidene α-D-glucopyranosides' gelation ability by minor group modifications.

Ten methyl 4,6-O-benzylidene α-D-glucopyranosides were synthesized for the purpose of studying systematically the effect of small group changes at position 4 of the aromatic ring on the ability to gelate organic solvents. The gelation properties are discussed on the basis of small angle X-ray scattering (SAXS), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) measurements, and scanning electron microscopy (SEM) observations. Sol-gel transition temperatures were determined simultaneously by DSC and temperature-dependent FTIR measurements. The current study emphasizes that carbohydrates furnish not only valuable information about structural requirements for organogelator design, but also for molecular assembly systems in general.

Photoacoustic Monitoring of Internal Plastification in Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Copolymers: Measurements of Thermal Parameters

Propriedades termofisicas de copolimeros poli(3-hidroxibutirato-co-3-hidroxivalerato) poli(3HB-co-3HV) foram investigadas com o objetivo de entender a influencia das unidades monomericas de 3-hidroxivalerato (3HV) incorporadas durante a copolimerizacao aleatoria. Os resultados mostram forte evidencia de que uma plastificacao interna e introduzida no copolimero pelas unidades de 3HV. Foi observado que a condutividade termica do copolimero aumentou linearmente com a concentracao de 3HV. Por outro lado, a difusividade termica foi muito sensivel as mudancas de composicao do copolimero, apresentou um aumento brusco inicial e atingiu um plato de saturacao. Os graficos de amplitude contra frequencia indicam a predominância de um mecanismo termoelastico. Neste trabalho e apresentando uma nova montagem fotoacustica para as medidas de efusividade termica.

On the Use of the Optothermal Window Technique for the Determination of Low Concentrations of Chromium (VI) and Phosphorus in Water

Abstract In this work we report about the use of the Optothermal Window (OW) technique, actually a variant of Photoacoustic Spectroscopy, combined with well-proven colorimetric methods to the determination of low concentrations of pollutants in water. As a first approach, chromium (VI) and phosphorus were determined in distilled water samples. The determination of Cr (VI) and P species in environmental and biological systems is currently of considerable interest due to the toxicity of their compounds to live organisms. Their maximum allowed values in drinking water were well discriminated in our experiments as well as the limits of optical spectrophotometric measurements. The detection limit in our measurements was 0.1 μmol/L P-PO4 3- for phosphorus at 632.8 nm and 0.2 μmol/L for chromium (VI) at 514 nm.