Alfredo Cruz-Orea

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

Basic data on thermal, structural and rheological properties of cooked maize tortillas were investigated, with the aim of understanding the role of the slaked lime [Ca(OH)2] that is incorporated during the alkaline cooking process. The changes in the thermal parameters, such as thermal conductivity, thermal diffusivity and specific heat, measured by photoacoustic techniques, as well as the changes in texture and X-ray patterns are presented as a function of the Ca(OH)2 concentration. The results show strong evidence that there is a threshold concentration of Ca(OH)2 of 0.25%, above and below which there are different behaviour patterns of the measured properties of the tortillas.

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.

Growth and characterization of GaInNxAs1−x thin films with band-gap energies in the red-blue portion of the visible spectrum

Using the radio-frequency (rf) sputtering deposition technique, we have grown GaInNxAs1−x thin films on glass substrates at room temperature. The concentration of nitrogen in the films was found to depend mainly on the rf power used to excite the growth plasma. X-ray diffractograms show that the films have small grain sizes and present a broad diffraction band centered close to the (002) diffraction peak of hexagonal GaN. Electron dispersive spectroscopy measurements report N concentrations of x∼0.8 and In concentrations of about 3% indicating that we have grown GaInNxAs1−x alloys in the GaN-rich side. The absorption spectra measured by the photoacoustic technique show that these semiconductor films have band-gap energies ranging between 1.69 and 2.56 eV, when the rf sputtering power is varied in the range 30–80 W. Thus, we show the feasibility to grow GaInNxAs1−x thin films with high N concentrations in which we can tune the band-gap energy in the red-blue portion of the visible spectrum, by a careful co...

Photoacoustic monitoring of the thermal expansion coefficient of amorphous silicon on glass

Using the open photoacoustic cell technique the thermal conductivity, thermal diffusivity, heat capacity, and thermal expansion coefficient of amorphous silicon on glass are investigated. It is shown that in this two layer system a thermal resistance‐electrical resistance phenomenological model can successfully account for the amorphous silicon thermal and thermomechanical properties.

Efficiency Of The Photodynamic Therapy Using Gold Nanoparticles (np‐Au) And PpIX Induced And Not Induced

The use of gold nanoparticles (np‐Au) to eliminate cancer has proved to be very effective due to the fact that cancerous cells accumulate it 600% more than healthy cells. In addition they have a high capacity of absorption and dispersion of light. Therefore, the effectiveness of photodynamic therapy (PDT) could be improved by the simultaneous use of np‐Au and photosensitizes (Ps), emphasizing the high efficiency of the PDT to diagnose and to treat pre‐malignant and malignant processes. The aim of this work was to determine the efficiency of PDT using np‐Au and protoporphyrin IX (PpIX) induced and not induced by the δ‐aminolevulinic acid (ALA). It were found the conditions of synthesis of hydrosoluble np‐Au, and were characterized by transmission electronic microscopy (TEM) and UV‐VIS spectroscopy. It was realized a kinetic by TEM to determine the cellular incorporation time of np‐Au, the maximum incorporation of np‐Au was of 16 h. PDT was applied using different doses of np‐Au and photosensitizers. It was...