Assaying Total Carotenoids in Flours of Corn and Sweetpotato by Laser Photoacoustic Spectroscopy

This study describes the application of the laser photoacoustic spectroscopy (PAS) for quantification of total carotenoids (TC) in corn flours and sweetpotato flours. Overall, thirty-three different corn flours and nine sweetpotato flours were investigated. All PAS measurements were performed at room temperature using 488-nm argon laser radiation for excitation and mechanical modulation of 9 and 30 Hz. The measurements were repeated within a run and within several days or months. The UV–Vis spectrophotometry was used as the reference method. The concentration range that allows for the reliable analysis of TC spans a region from 1 to 40 mg kg−1 for corn flours and from 9 to 40 mg kg−1 for sweetpotato flours. In the case of sweetpotato flours, the quantification may extend even to 240 mg kg−1 TC. The estimated detection limit values for TC in corn and sweetpotato flours were 0.1 and 0.3 mg kg−1, respectively. The computed repeatability (n = 3–12) and intermediate precision (n = 6–28) RSD values at 9 and 30 Hz are comparable: 0.1–17.1% and 5.3–14.7% for corn flours as compared with 1.4–9.1% and 4.2–23.0% for sweetpotato flours. Our results show that PAS can be successfully used as a new analytical tool to simply and rapidly screen the flours for their nutritional potential based on the total carotenoid concentration

Thermal diffusivity measurement for p-Si and Ag/p-Si by photoacoustic technique

Thermal diffusivity (TD) of p-Si and Ag/p-Si samples were measured by photoacoustic technique using open photoacoustic cell (OPC). The samples were annealed by heating them at 960, 1050, 1200, and 1300 °C for 3 h in air. The thermal diffusivity of Ag-coated samples was obtained by fitting the photoacoustic experimental data to the thermally thick equation for Rosencwaig and Gersho (RG) theory. For the single layer samples, the thermal diffusivity can be obtained by fitting as well as by obtaining the critical frequency f c . In this study, the thermal diffusivity of the p-Si samples increased with increasing the annealing temperature. The thermal diffusivity of the Ag/p-Si samples, after reaching the maximum value of about 2.73 cm2/s at a temperature of 1200 °C, decreased due to the silver complete melt in the surface of the silicon

On the criterion for neglecting convective effects in photoacoustic experiments

The first step in the theoretical modeling of photoacoustic experiments is the calculation of the Temperature within the sample and/or its environment. For solids it is usually calculated by solving the heat diffusion equation. The same equation is used often for liquid samples, as well as for the gas filling the PA chamber, neglecting the role played by hydrodynamic effects. In the present work we will briefly describe how the Theory of Similarity shows that the heat diffusion equation, in its usual formulation, can be only applied for fluids when the product of Grashof (Gr) and Prandtl (Pr) numbers, the so-called Rayleigh, Ra, number, is lower than 1000

Similarity theory and dimensionless numbers in heat transfer

We present basic concepts underlying the so-called similarity theory that in our opinion should be explained in basic undergraduate general physics courses when dealing with heat transport problems, in particular with those involving natural or free convection. A simple example is described that can be useful in showing a criterion for neglecting convection heat transfer effects in a given experimental situation

Specific Heat Measurements by a Thermal Relaxation Method: Influence of Convection and Conduction

This paper involves the well-known thermal relaxation method for measurement of the specific heat (c) of thin solid samples. Although this method was applied successfully in recent years for the characterization of different materials, in this work some aspects that must be taken into account in order to avoid problems based on satisfying the required experimental conditions of heat flux imposed by the physical model used for data analysis and processing will be discussed. For this purpose, for a given experimental geometry, the heat diffusion equation will be solved in order to obtain the sample’s requirements for reliable measurements of c, regarding its thickness and thermal conductivity. An experimental device is described that can be used for the study of the influence of heat dissipation by convection on the method. A computer simulation was performed for comparing the simple model with one that takes to in account the gradient of temperature inside the sample. The results of measurements are presented

Heat capacity measurement in solids by means of the photoacoustic technique

We report a method for determining the specific heat capacity in solids by means of the photoacoustic (PA) technique in a heat transmission configuration. This method involves a modulation frequency range where the samples are thermally thin and a liquid (i.e., distilled water) as a reference sample. It is free of PA cell parameters and was tested in some metals and semiconductors. The results agree very well with literature reported values for these samples

High sensitivity thermal lens microscopy: Cr-VI trace detection in water

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPIn this work, a low detection limit for hexavalent chromium in water of parts per trillions (21 ng/L) was achieved using a micro -spatial thermal lens spectroscopy setup with coaxial counter -propagating pump and probe laser beams and an integrated passive optical Fabry-Perot resonator, aided with a well -established diphenyl carbazide colorimetric method. Cr-VI concentrations in the range of mu g/L, i.e. well -below the toxicity thresholds in humans and animals (26 and 190 mg/L respectively) and below those delimited by international regulations for drink water (similar to 0.05-0.5 mg/L), have been obtained by measurements in bottled and tap water samples. The developed thermal lens microscope is also capable to detect Cr-VI directly in potassium dichromate solutions using pump beam wavelengths within the very low optical absorption region in the visible part of the spectrum, i.e., without the use of any calorimetric method.170260265CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPSem informaçãoSem informaçãoThis work was supported by Research Grants SIP-IPN 2014006, 20150390, 20160144 and CONACyT 2015-02-1042 and 264093. H. Cabrera gratefully acknowledges ICTP TRIL as well as the Associateship Programs. A. M. M. acknowledges the support of the Brazilian Agencies CNPq and FAPESP. The support of COFAA-IPN by the SIBE and BEIFI programs is also acknowledged

DETERMINACION DE LA CONCENTRACION DE HIERRO EN HARINA DE MAIZ UTILIZANDO LA TECNICA FOTOACUSTICA

We report on the use of the photoacoustic technique for the determination of low concentrations of total iron in corn meal samples. This is of considerable interest because several foods are currently enriched with this element at proper levels in order to increase the resistance of people, after their consume, to several diseases such as anemia. The proposed technique is based in an open cell configuration in conjunction with a suitable colorimetric method. The results of the measurements agree very well with those obtained using a conventional spectrophotometric method, showing the possibilities of new photothermal experimental methodologies to perform this kind of studies

Specific heat of the Ba0.7Sr0.3Ti1–yZryO (y = 0, 0.03, 0.05, 0.1) ferroelectric ceramics obtained by the temperature relaxation method

In the last few years great interest has developed around Ba1–xSrxTiO3 (BST) or BST-based materials due to their great potential for technological applications such as integrated capacitors, ferroelectric memory and many others [1–3]. Thermal properties of materials used in the design and construction of electronic devices must be taken into account since heat will be unavoidably generated in a working electronic circuit. The behavior of the devices as their temperature change and their ability to store and dissipate heat will affect their performance and lifetime therefore their thermal properties cannot be neglected. Despite the extended use of the BST ceramic system, knowledge of the thermal properties is still scarc