L. C. M. Miranda

Photoacoustic monitoring of the influence of arbuscular mycorrhizal infection on the photosynthesis of corn (Zea mays L.)

Abstract The general utility of the photoacoustic effect is demonstrated by examining in vivo and in situ, for the first time, the influence of arbuscular mycorrhizal infection on the photosynthetic activity of intact maize leaves. Experiments correlating the photosynthetic O 2 evolution, after a dark induction period, through the photoacoustic effect in mycorrhizal and non-mycorrhizal maize plants with their field performance show very consistent data. The influence of the arbuscular mycorrhizal infection on the photosynthetic efficiency is discussed. This methodology opens the possibility for early evaluation of the effect of fungi symbiotic adaptation with maize plants. For the arbuscular mycorrhizal-maize plant system, photoacoustics represents an extremely helpful technique for discarding low performance materials.

OPC technique for in vivo studies in plant photosynthesis research

The open photoacoustic cell (OPC) technique is applied to photosynthesis research in leaves, where the leaf is still attached to the plant. It is shown that real in situ and in vivo measurements of photosynthetic activities in leaves can be performed. The dehydration effect after cutting the leaf from the plant was monitored and some qualitative measurements related to photosynthetic activities are reported in order to show the usefulness of this technique in this field.

Effect of lime content on the processing conditions of cooked maize tortillas: changes of thermal, structural, and rheological properties

Basic data on thermal, dielectric, and IR spectral properties of cooked tortillas were investigated with the major aim to understand the role of lime, Ca(OH)2 , incorporated during the alkaline cooking process. The data are further supplemented by x-ray diffraction and texture measurements. The changes in the thermal diffusivities, measured by the photoacoustic technique, as well as the changes in texture, x-ray patterns, dielectric, and IR spectral properties are presented as a function of the lime concentration. The results show strong evidence that there is a marked concentration of lime (around 0.2%) above and below which different behavior patterns of the measured properties of tortilla were observed. In particular, the results for the dielectric constant and thermal diffusivity provide strong evidences for enhanced starch crosslinking taking place for lime content close to 0.2%.

On the use of the open photoacoustic cell technique for studying photosynthetic O2 evolution of undetached leaves: Comparison with Clark‐type O2 electrode

The leaf photosynthetic O2 evolution detected by the open photoacoustic cell (OPC) technique is compared to the measurements using a Clark‐type O2 electrode detector. In vivo and in situ measurements were carried out with undetached maize leaves. From the correlation between these two methods the possibility of a calibration is proposed for the oxygen evolution OPC signal.

Photoacoustic measurements of thermal diffusivity and correlation with viscosity of instant corn dry masa flour

The usefulness of the photoacoustic technique for the characterization of thermal properties and for the monitoring of the pasting effect of added water and lime on instant corn masa flour is discussed. In particular, it is shown that the photoacoustically measured thermal diffusivity follows closely the change in the sample viscosity, as a function of the lime content.

PHOTOACOUSTIC TECHNIQUE FOR MONITORING THE THERMAL PROPERTIES OF POROUS SILICON

The use of the photoacoustic technique to monitor the ther- mal properties of materials that can be obtained only as parts of multi- component samples is illustrated by performing the thermal character- ization of two porous materials: porous silicon obtained from n-type crystalline silicon through the spark process and that obtained through the electrochemical etching method. This nonseparative, and hence nondestructive, approach makes use of an effective thermal diffusivity treatment based on the analogy between thermal and electrical resis- tances, in combination with simplified compositional models for the cor- responding multicomponent systems. The thermal parameters obtained are in agreement with existent studies concerning the composition of these materials. This approach offers the possibility of performing the thermal characterization of other porous semiconductors and analogous materials.

On the use of the photoacoustic technique for the measurement of the thermomechanical properties of semiconductor two-layer systems

Abstract The photoacoustic technique is used in semiconductor two-layer systems for the determination of thermal properties and thermal expansion coefficient. The two-layer systems studied were amorphous silicon-glass and Al0.2Ga0.8AsGaAs. Our results show that the proposed method is a reliable technique for the characterization of other semiconductor two-layers systems.

A new CO2 analyzer for measuring respiration rates in organic material

In this article, we present a new CO2 analyzer which can be used for monitoring respiration rates in organic material. To demonstrate the potentiality of the analyzer, CO2 evolution of soil samples collected from three different edaphic environments were measured. The results obtained with this compact CO2 analyzer were compared with those carried out simultaneously using the chemical method, and the correlation between them has been established.