- León, Guanajuato, Mexico
Research Interests:
Research Interests:
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... more
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.
Research Interests:
The collinear mirage technique is widely used to measure the thermal diffusivity of semi-transparent materials. However, in a recent paper [A. Salazar, M. Gateshki and A. Sánchez-Lavega: Appl. Phys. Lett. 76, 2665 (2000)], it was shown... more
The collinear mirage technique is widely used to measure the thermal diffusivity of semi-transparent materials. However, in a recent paper [A. Salazar, M. Gateshki and A. Sánchez-Lavega: Appl. Phys. Lett. 76, 2665 (2000)], it was shown that for isotropic materials, because of the influence of photoelastic effect, the method was sensitive to the polarization state of the probe beam. The present paper extends the previous work to include anisotropic materials. In particular, we focus on the experimental conditions under which the thermal diffusivity of each crystal system can be measured using the phase method. Our theoretical model indicates that while the thermal diffusivity of isotropic materials can be measured using an unpolarized probe beam, for anisotropic materials, even the use of an unpolarized probe beam does not guarantee the validity of the method in all crystal systems. Experimental measurements performed on cubic, hexagonal and monoclinic crystals confirm the validity of the model.
Research Interests:
The dynamics of blood and hemolymph sedimentation is studied in real time using the photoacoustic technique. A modified configuration of a conventional photoacoustic cell is used, where the advantage of this methodology is that the sample... more
The dynamics of blood and hemolymph sedimentation is studied in real time using the photoacoustic technique. A modified configuration of a conventional photoacoustic cell is used, where the advantage of this methodology is that the sample is not illuminated directly and that the process can be monitored through the measurement of the thermal contact between a reference material and the
Research Interests:
Research Interests:
In this article, we present a new photoacoustic technique, based on the conventional photoacoustic configuration, to characterize the thermal effusivity of liquid samples. This new technique is applicable for all kind of liquid samples,... more
In this article, we present a new photoacoustic technique, based on the conventional photoacoustic configuration, to characterize the thermal effusivity of liquid samples. This new technique is applicable for all kind of liquid samples, including the nontransparent ones. In order to show the usefulness of this new technique, we measured the thermal effusivity of a variety of liquid samples including: distilled water, ethanol, methanol, chloroform, glycerol, and car oil. The comparison with literature values shows a remarkable agreement. Also, we show measurements of the thermal effusivity of acetone in distilled water mixtures, showing the graphical dependence of this thermal property with the concentration of one of the components.
Research Interests:
Research Interests:
We report a novel method for measurements in vivo of the penetration of topically applied substances by inverse photopyroelectric configuration. This configuration was used to obtain the thermal effusivity, as a function of time, of in... more
We report a novel method for measurements in vivo of the penetration of topically applied substances by inverse photopyroelectric configuration. This configuration was used to obtain the thermal effusivity, as a function of time, of in vivo human skin with ointments. This thermal magnitude was employed to characterize the penetration on the anterior-face of the volunteers forearm. This thermal effusivity was fitted with an exponential function in order to obtain a parameter (characteristic time) for the penetration. The substances used were a sunscreen and Vick Vaporub ointment. We found that the sunscreen have a characteristic time bigger that the Vick Vaporub ointment. The feasibility of skin hydration studies are discussed.
Research Interests:
The impedance spectroscopy technique (IST) was used for studying the effect of a 0.5 T magnetic field on the electrical properties of whole human blood. A Solartron SI 1260 spectrometer was used to measure the impedance spectra of... more
The impedance spectroscopy technique (IST) was used for studying the effect of a 0.5 T magnetic field on the electrical properties of whole human blood. A Solartron SI 1260 spectrometer was used to measure the impedance spectra of magnetic field exposed blood samples compared to non-exposed samples. An equivalent electrical circuit model, consisting in a resistance Rs in series with a parallel circuit formed by a constant phase element (CPE) and another resistance Rp, is proposed to fit the data in both cases. The experiment used 3 ml human blood samples from 160 healthy donors. A Wilcoxon matched pairs statistical test was applied to the data. The data analysis seems to show a statistically significant increase of the values of resistance Rp (Z = 5.06, P < 0.001) and capacitance CT (Z = 3.32, P < 0.001) of the blood exposed to magnetic field, by approximately 10.4% and 1.9%, respectively. Bioelectromagnetics 26:564–570, 2005. © 2005 Wiley-Liss, Inc.
Research Interests:
The metrological aspects related to the sensitivity and signal-to-noise ratio of the auto-normalized front pyroelectric technique for the measurement of thermal effusivity in liquids are investigated. The effect of the thermally thick... more
The metrological aspects related to the sensitivity and signal-to-noise ratio of the auto-normalized front pyroelectric technique for the measurement of thermal effusivity in liquids are investigated. The effect of the thermally thick approximation in the theoretical expressions for the photopyroelectric signal and its effect on the sensitivity of the technique are discussed. It is shown that the sensitivity of the technique decreases with frequency. In contrast, the signal-to-noise ratio increases for higher frequencies.
Research Interests:
Serum samples were studied using Raman spectroscopy and analyzed through the multivariate statistical methods of principal component analysis (PCA) and linear discriminant analysis (LDA). The blood samples were obtained from 11 patients... more
Serum samples were studied using Raman spectroscopy and analyzed through the multivariate statistical methods of principal component analysis (PCA) and linear discriminant analysis (LDA). The blood samples were obtained from 11 patients who were clinically diagnosed with breast cancer and 12 healthy volunteer controls. The PCA allowed us to define the wavelength differences between the spectral bands of the control and patient groups. However, since the differences in the involved molecules were in their tertiary or quaternary structure, it was not possible to determine what molecule caused the observed differences in the spectra. The ratio of the corresponding band intensities were analyzed by calculating the p values and it was found that only seven of these band ratios were significant and corresponded to proteins, phospholipids, and polysaccharides. These specific bands might be helpful during screening for breast cancer using Raman Spectroscopy of serum samples. It is also shown that serum samples from patients with breast cancer and from the control group can be discriminated when the LDA is applied to their Raman spectra.
Research Interests:
One of the best-known methods to measure the heat capacity of solids consists in the illumination of the sample and the analysis of the thermal relaxation when the illumination is stopped. In this work, the energy balance equation with... more
One of the best-known methods to measure the heat capacity of solids consists in the illumination of the sample and the analysis of the thermal relaxation when the illumination is stopped. In this work, the energy balance equation with heat losses due to radiation is solved exactly. This is used to establish the limits of the usual approximations used to obtain the heat capacity from the experimental data. It is shown that large temperature changes, induced by the heat source during the experiment can generate errors in the calculation of heat capacity when the traditional approach is used.
Research Interests:
Research Interests:
Research Interests: Acoustics, Biomedical Engineering, Humans, Photometry, Physiological, and 12 moreSkin, Terpenes, Medical Physiology, Plant extracts, Constant Time Delay, Topical Drug Administration, Skin Temperature, Theoretical Model, Electrical And Electronic Engineering, Exponential Function, Emollients, and Forearm
In this work, we show a particular setup, which is based on the conventional photoacoustic cell, to measure thermal effusivity of human skin in-vivo and in-situ. We measure the changes of thermal effusivity due to the absorption of... more
In this work, we show a particular setup, which is based on the conventional photoacoustic cell, to measure thermal effusivity of human skin in-vivo and in-situ. We measure the changes of thermal effusivity due to the absorption of sunscreen into the skin and these values are compared with those from an adjacent sample of clean skin. This experiment was performed on a volunteer's forearm and stainless steel as the thermally thin absorption surface. The values for this parameter are in good agreement with those reported in the literature. Besides the measurements described above, with the same setup we got the thermal effusivity of the sunscreen itself as a reference parameter. R
Research Interests:
Research Interests:
Research Interests:
The thermal diffusivity and thermal expansion coefficient of teeth and three of their most common restorative materials (Amalgam Phase Alloy, Ionomer Fuji II LC, and Resin 3MFPITEK Lutine TMZ250) were studied by means of the open... more
The thermal diffusivity and thermal expansion coefficient of teeth and three of their most common restorative materials (Amalgam Phase Alloy, Ionomer Fuji II LC, and Resin 3MFPITEK Lutine TMZ250) were studied by means of the open photoacoustic technique. These results were then used as a basis for the theoretical simulation of the photothermal process taking place as a consequence of modulated illumination of a two-layer system formed by the tooth and the restorative material. The model accounts for the coupling of thermal waves and thermoelastic vibration in the two-layer system.
Research Interests:
The open photoacoustic cell technique was used to measure tomato leaves from plants with and without mycorrhizal fungi (Glomus fasciculatum). Based on measurement of the photobaric contribution of the photoacoustic signal, the exponential... more
The open photoacoustic cell technique was used to measure tomato leaves from plants with and without mycorrhizal fungi (Glomus fasciculatum). Based on measurement of the photobaric contribution of the photoacoustic signal, the exponential parameter of the diffusion behavior for this contribution was calculated. From this value, the oxygen diffusion coefficient was derived. The changes in the oxygen- diffusion-coefficient-dependent exponential parameter are statistically significant (p < 0.05) and are consistent with the expected benefits of mycorrhizal symbiosis. Potentially similar results obtained from the photothermal contribution are discussed.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
We describe an optical system in which a vibration induced to a laser probe beam combined with a half-blocked photodiode allows determination of the position and width of objects buried in turbid media. Our system is based on the... more
We describe an optical system in which a vibration induced to a laser probe beam combined with a half-blocked photodiode allows determination of the position and width of objects buried in turbid media. Our system is based on the detection of an AC signal which drastically decreases under the presence of an obstructing buried object. We describe the technique and include experimental results showing that the system is capable of detecting 2 mm wide objects buried at depths up to 3 cm from the front surface of a sample simulating scattering properties of soft tissue.