J. Bernal‐Alvarado

Thermal diffusivity measurements in vegetable oils with thermal lens technique

Using a thermal lensing experimental setup the thermal properties of several vegetable oils were obtained. The samples were oils from Amazonian species and olive (the popular identifications are piqui, copaiba, buriti, and babacu). The two lasers mismatched mode experimental configuration was used, with a He–Ne laser as the probe and an Ar+ laser as the excitation one. The time resolved spectra were measured using an automatic system, and fitting the aberrant theoretical model to the data, the characteristic relaxation time were obtained, and knowing this value, the thermal property of each oil was solved.

Understanding the magnetic susceptibility measurements by using an analytical scale

A description of the measurement procedure, related theory and experimental data analysis of the magnetic susceptibility of materials is given. A short review of previous papers in the line of this subject is presented. This work covers the whole experimental process, in detail, and presents a pragmatic approach for pedagogical sake.

Gastric activity studies using a magnetic tracer

A magnetic pulse generator has been set up in order to study gastric activity. Two coils 1.05 m in diameter, arranged in a Helmholtz configuration, were used. The system generated magnetic field pulses higher than 15 mT, of duration 17.3+/-1.2 ms. Measurements were performed in 11 male volunteers, with average age 29.3+/-6.4 years and body mass index 26.0+/-4.8 kg m(-2). Magnetite (Fe3O4) particles with diameters from 75 to 125 microm were used as magnetic tracers, which were mixed in 250 ml of yogurt in concentrations from 2 to 5 g. Signals were registered by using a high speed 3 axis fluxgate digital magnetometer and processed to determine the relaxation of the magnetic tracers by fitting a first-order exponential function to the data, a mean relaxation constant K = 116+/-40 s(-1) was obtained. Also, an average gastric peristaltic frequency was measured; a value of 3.2+/-0.3 cpm was determined.

Mismatched Mode Thermal Lens for Assessing Thermal Diffusivity of Serum and Plasma from Human Blood

Abstract Thermal diffusivity of human serum and plasma were measured by means of thermal lens spectroscopy. Several samples were studied and results were reported as averages, including standard deviations. The serum and plasma were obtained by random sampling of healthy adult donors at the Guanajuato State Transfusion Center, Mexico; the donors were free of hepatitis, AIDS, and other infectious diseases, all clinically tested. The parameters reported were obtained using the thermal lens aberrant model with the lasers arranged in the mismatched mode.

In vivo measurement of human skin absorption of topically applied substances by a photoacoustic technique

A photoacoustic technique is used for studying topically applied substance absorption in human skin. The proposed method utilizes a double-chamber PA cell. The absorption determination was obtained through the measurement of the thermal effusivity of the binary system substance-skin. The theoretical model assumes that the effective thermal effusivity of the binary system corresponds to that of a two-phase system. Experimental applications of the method employed different substances of topical application in different parts of the body of a volunteer. The method is demonstrated to be an easily used non-invasive technique for dermatology research. The relative concentrations as a function of time of substances such as ketoconazol and sunscreen were determined by fitting a sigmoidal function to the data, while an exponential function corresponds to the best fit for the set of data for nitrofurazona, vaseline and vaporub. The time constants associated with the rates of absorption, were found to vary in the range between 10 and 58 min, depending on the substance and the part of the body.

Cr Localization and Speciation in Roots of Chromate Fed Helianthus annuus L. Seedlings Using Synchrotron Techniques

In order to gain knowledge on the potential use of Helianthus annuus L. for the remediation of Cr(VI) polluted waters, hydroponics experiments were set up to determine Cr uptake and tolerance in different Cr(VI)-sulfate conditions, and Cr biotransformations. Results indicated that Cr(VI) promoted seed germination, and plant tolerance was higher at younger plant stages. Cr uptake was dependent on sulfate concentrations. The highest Cr levels in roots and shoots (13,700 and 2,500 mg kg–1dry weight (DW), respectively) were obtained in 1 mM sulfate. The lowest Cr uptake in roots (10,600 mg kg–1DW) was observed in seedlings treated with no sulfate. In shoots, Cr concentration was of 1,500 mg kg–1DW for the 1 mM sulfate treatment, indicating a different level of interaction between chromate and sulfate in both tissues. For the first time, using micro X-ray florescence (μXRF), we demonstrated Cr reaches the root stele and is located in the walls of xylem vessels. Bulk and micro X-ray Absorption Near-Edge Structure (μXANES) results showed that Cr in the roots is mostly in the form of Cr(III) phosphate (80%), with the remainder complexed to organic acids. Our results suggest this plant species may serve for Cr(VI) rhizofiltration purposes.

16-channel magnetoresistive scanner for magnetic surface imaging

A multichannel scanning system for magnetic surface imaging composed of 16 magnetoresistive sensors has been developed. A gray scale, from 0 to 255, was used to represent the magnetic signal detected by each sensor when the sample was moved above the scanner. Measurements and calibration were performed using magnetic surfaces with different shapes and samples with similar profiles, but different magnetization intensities. The system was sufficiently sensitive to detect gradients and discontinuities on the magnetic map. The 16 channel images were numerically processed to obtain a smooth representation of the magnetic map using the LabView™ Image Vision package.

Characterization of Human Blood Tissue by Impedance Spectroscopy and Study of Erythrocyte Sedimentation

The use of the Impedance Spectroscopy (IS) technique has increased since the middle of 20th century for the characterization of materials which exhibit a frequency dependent behavior over the applied electric field; this behavior is correlated to the substance composition, its structural organization and the interactions between its components. In this work, the human whole blood electrical properties are studied, as well as that of its separated components (plasm, leukocytes, erythrocytes), using an harmonic voltage from 1Hz to 10MHz. The impedance modulus response |Z| and the angular phase lag were registered as functions of the frequency swept. Also, it was studied the variation of the same electrical parameters during sedimentation of blood cells as a function of time. It was found that the use of IS, as a characterization tool for human blood tissue, is an important instrument for the diagnosis and disease tracking of certain pathologies, which could be identified by its correspondent impedance “footprint” in the complex coordinate system.

Dielectric Characterization of Leukocytes from Human Blood

The impedance spectroscopy technique was used to perform a comparative study on blood samples from leukemia and from healthy people. An electric circuit model was used to determine the numerical parameters of each sample. The capacitive properties, reflected in the constant phase element of a Cole model, show the capability to analyze the dielectric and spectral behavior of blood cells, in particular, with cells from leukemia. The spectra and the capacitive parameters are shown, as well as de model fitted to the experimental data.

Electrical Characterization of Human Blood as a Function of Temperature

Impedance spectroscopy has become an important characterization technique in the last years due to the necessity of finding new non‐invasive techniques to study biological materials. In this work, the electrical properties of human blood as a function of temperature were studied, varying in a controlled way the temperature of the sample and, simultaneously, obtaining the impedance spectra. The resistive parameters of the impedance show a decreasing behaviour as a function of temperature. A mathematical model, in the form of a power of the temperature, was used to characterize the blood samples and the results for the parameters are reported.