Marcelo Gomes da Silva

Ammonia detection by using quantum-cascade laser photoacoustic spectroscopy

A pulsed quantum-cascade distributed-feedback laser, temperature tunable from -41 degrees C to +31.6 degrees C, and a resonant differential photoacoustic detector are used to measure trace-gas concentrations to as low as 66 parts per 10(9) by volume (ppbv) ammonia at a low laser power of 2 mW. Good agreement between the experimental spectrum and the simulated HITRAN spectrum of NH3 is found in the spectral range between 1046 and 1052 cm(-1). A detection limit of 30 ppbv ammonia at a signal-to-noise ratio of 1 was obtained with the quantum-cascade laser (QCL) photoacoustic (PA) setup. Concentration changes of approximately 50 ppbv were detectable with this compact and versatile QCL-based PA detection system. The performance of the PA detector, characterized by the product of the incident laser power and the minimum detectable absorption coefficient, was 4.7 x 10-9 W cm(-1).

Nutrient release by a Brazilian sedimentary zeolite

This report describes the characterization of a sedimentary occurrence from the Parnaiba Basin, Brazil, containing the zeolite stilbite intertwined with smectitic clay mineral. The head samples from different sites present a wide content range of the zeolitic phase – 15% to 50%. The use of simple separation techniques – conventional gravitic treatments – yields concentrates containing about 67% of the zeolitic component. Assays with the amendments of these concentrates with plant nutrients yield release rates matching those reported for similar commercial products.

Water and vapor permeability at different temperatures of poly (3-Hydroxybutyrate) dense membranes

Polyhydroxyalkanoates (PHAs) are polymers produced from renewable resources with biodegradability and biocompatibility, being therefore attractive for medical and pharmaceutical purposes. Poly (3-hydroxybutyrate) (PHB) is the most important polymer of this family by considering the biotechnology process of its synthesis. In the present study, dense films of PHB were prepared by casting from chloroform solutions (1% m/m). Permeability studies with water, methanol, ethanol and n-propanol were performed using the gravimetric method at different temperatures (from 50 °C to 65 °C). Results provide new data on permeability coefficients of PHB membranes.

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.

Responses of 1-MCP applications in 'Golden' papaya fruits on differents maturation stages.

The study of factors that influence the process of ripening is critical for planning the marketing process, mainly in standard breathing climacteric and perishing fruits, as it is the case of papaya. In this work it was evaluated the effect of the application of 1-MCP (1- methylcyclopropene) in the pattern of fruit ripening of papaya at the maturation stages 0, 1 and 2. The 1-MCP delayed the production of ethylene (≈79%) and the respiratory rate (≈45%) mainly in fruit maturation stages 0. The use of the inhibitor of the ethylene action delayed the degreening of the fruits, especially in fruit maturation stages 0 and 1. With 1-MCP application there was a reduction in loss of flesh and fruit firmness in stages 1 and 2. However, in fruit maturation stage 0, the flesh firmness showed excessively high, which may decrease the acceptance for consumer of these fruits. The solid soluble content was not influenced by the application of the 1-MCP. The effect of 1-MCP in the reduction of the activity of the enzymes PME and PG was bigger in fruit maturation stages 0 and 1 than fruit maturation stage 2. The PME enzyme activity demonstrated an increasing over the shelf life; however, the PG enzyme activity remained low during the first five days of shelf life, increasing later. The results showed that the PME enzyme exerts significant influence on loss of flesh firmness, and the PG acting later. The 1-MCP was effective delaying the process of ripening of papaya fruits being more efficient when associated with initial maturation stages.

Photothermal Characterization of Low Density Polyethylene Food Packages

The present work discuss the applicability of photothermal techniques for determining diffusion coefficients of oxygen and carbon dioxide of commercial low-density polyethylene (LDPE). The methodology involves the monitoring of diffused gas by a photoacoustic analyzer. Diffusion coefficients measured for CO2 and O2 were 2.77 x 10-8 cm2/s and 1.68 x 10-7 cm2/s, respectively. To support the gas diffusion results, thermal properties were studied using photoacoustic spectroscopy and crystallinity was determined using X-ray diffraction. Values obtained for thermal diffusivity and specific heat capacity were 1.65 x 10-3cm2/s and 2.33 J.cm-3K-1, which are in good agreement with values available in the literature for pure LDPE and thus assure reliability of diffusion coefficients values.

Involvement of brassinosteroids and ethylene in the control of mitochondrial electron transport chain in postharvest papaya fruit

The plant hormones brassinosteroids (BR) and ethylene (ET) act together to regulate plant metabolism. We used BR and 1-methylcyclopropene (1-MCP, an ET action inhibitor) to elucidate the interactions between both hormones for the regulation of mitochondrial respiratory pathways in papaya fruit. The exogenous application of the 24-epibrassinolide (epiBR) enhanced the alternative oxidase (AOX) capacity. While treatment with Brz2001 (Brz is a specific inhibitor of the BR synthesis) also enhanced AOX capacity, these effects lacked in fruit treated simultaneously with epiBR and Brz. Changing the BR level had no effect on ET emission rate in the first 24 h, but a reduction in ET emission was observed in Brz-treated fruit on the fifth day. Together with Brz, epiBR increased the ET production on the fifth day, following the day in which the treatment was carried out. When the ET sensitivity of fruit was inhibited by the application of 1-MCP, the effects of epiBR and Brz were opposite to those obtained without 1-MCP. AOX capacity was slightly inhibited by epiBR in fruit pre-treated with 1-MCP. Data suggest that BR and ET act antagonistically, therefore regulating, directly or indirectly, AOX capacity during papaya fruit ripening.

Structural impact of hydroxyvalerate in polyhydroxyalkanoates (PHAscl) dense film monitored by XPS and photothermal methods

Poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) polymer dense films with thickness of 90 µm were obtained by the casting method and characterized using X-ray photoelectron spectroscopy, differential scanning calorimetric and photo-thermal methods. The HV molar fractions in the copolymer structure were 8, 14 and 22 mol %. The measured specific thermal capacity and the glass transition temperature of the P3(HB-co-x%HV) decrease for increasing hydroxyvalerate content following a similar trend.

Effects of ozone exposure on ‘Golden’ papaya fruit by photoacoustic phase-resolved method: Physiological changes associated with carbon dioxide and ethylene emission rates during ripening

This work addresses the effects of ozone activity on the physiology of ‘Golden’ papaya fruit. Depth profile analysis of double-layer biological samples was accomplished using the phase-resolved photoacoustic spectroscopy. The feasibility of the method was demonstrated by singling out the spectra of the cuticle and the pigment layers of papaya fruit. The same approach was used to monitor changes occurring on the fruit during ripening when exposed to ozone. In addition, one has performed real time studies of fluorescence parameters and the emission rates of carbon dioxide and ethylene. Finally, the amount of pigments and the changes in waxy cuticle have been monitored. Results indicate that a fruit deliberately subjected to ozone at a level of 6 ppmv underwent ripening sooner (at least 24-48 h) than a fruit stored at ambient conditions. Moreover, ozone caused a reduction in the maximum quantum yield of photosynthetic apparatus located within the skin of papaya fruit.

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.