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Nanocomposites are multiphase structures with at least one phase dimension of nanometric order size. Polymer-based materials mixed with low proportions of titanium dioxide nanoparticles (NPs-TiO2) are a versatile alternative in different industrial applications, considering the optimization of mechanical and thermal properties with respect to pure polymers and conventional materials. In this work, the synthesis and thermal characteristics measurement of a nanocomposite formed by anatase phase Nps-TiO2 of 5 nm particle size in a polyurethane matrix is reported. The polymeric matrix was obtained through the reaction between the self-condensation of castor oil and diphenylmethane diisocyanate (MDI), while sol-gel technique was used in the synthesis of NPs-TiO2, using titanium (IV)-bis(acetylacetonate) diisopropoxide as precursor. Specific heat (Cp) of the samples was measured by means of the thermal relaxation method and thermal diffusivity (α) was determined with the photoacoustic technique. Cp of the nanocomposite increased by 12.98 % due to addition of the NPs, while α decreased by 98.63 %, compared to corresponding values of the polyurethane matrix. With a concentration of 3 wt % of NPs-TiO2 in the matrix, these thermal parameters were found below average values of conventional plastics. [ABSTRACT FROM AUTHOR]

En la presente tesis se investigó el cambio de morfología y tamaño de las nanopartículas de oro obtenidos por ablación láser, con diferentes métodos de reconfiguración. En el caso del oro, el blanco fue ablacionado con un láser pulsado de Nd: YAG, (1064 nm, 37.48 mJ/p, 10 Hz, durante 10 minutos), los espectros de absorción presentan un solo máximo de absorción a 521 nm característica de las nanopartículas esféricas de oro. Se aplicó la técnica PLI a los coloides con pulsos láser de 532 nm de longitud de onda, 25.8 mJ de energía durante 6 minutos. El análisis por dispersión dinámica de la luz (DLS) mostró que las NpsAu con PLI fueron de 21 nm de diámetro, además, se comprobó que la amplitud de la señal fotoacústica está relacionada directa y proporcionalmente con la concentración de NpsAu en el coloide evidenciando que a mayor concentración la respuesta fotoacústica es mayor. De la investigación se concluyó que la técnica PLI focalizada aplicada a los coloides con NpsAg presenta nuevas morfologías. En el caso del oro se encontró un cambio de tamaño.

En las últimas décadas se ha intensificado la búsqueda de materia prima proveniente de recursos renovables para la producción de polímeros, elastómeros, resinas, espumas, etc., que disminuyan el uso industrial de compuestos petroquímicos. En este trabajo se usó el aceite extraído de la semilla de higuerilla (Ricinus communis) por su contenido de ácido ricinoleico (92,3 %), por su fácil producción y por no ser comestible; la síntesis del poliuretano adhesivo se hizo a través de reacciones de transesterificación y polimerización; con él se pegaron láminas de Guadua angustifolia Kunth y se determinaron las características mecánicas de la estructura; se obtuvo que la resistencia a la compresión paralela a la fibra es de 43±3 (MPa), y la cortante paralela a la fibra es de 5,9±0,9 (MPa). La determinación de la relación molar adecuada y el seguimiento de la reacción durante la síntesis se hicieron con espectroscopía infrarroja con transformada de Fourier y la estructura del producto final se analizó con difracción de rayos X. A través de calorimetría diferencial de barrido se obtuvo la temperatura de transición vítrea del producto de -26.4 °C y se usó la técnica de relajación térmica para medir su calor específico, mientras que su difusividad térmica y el coeficiente de dilatación térmica se estimaron con la técnica fotoacústica.

La espinaca es consumida por su valioso aporte nutricional. Sin embargo, en Colombia su baja producción en cultivos, ha sido de poco interés en el área de la investigación. Por otro lado, la nanotecnología que puede ser utilizada en la agricultura para evitar o controlar enfermedades en los cultivos a través de la aplicación de nanopartículas (NPs) se perfila como un tema de alto potencial en nuestro país. En este trabajo, se evaluó la inoculación de suspensiones de NPs de dióxido de titanio con incorporación de plata (TiO2-Ag) en semillas de espinaca. Las NPs se sintetizaron a través del método sol-gel y se caracterizaron por medio de Difracción De Rayos X (DFR). Se obtuvieron muestras en polvo con tamaños de partícula entre 7 y 26 nm que se suspendieron en agua a diferentes concentraciones para la inoculación. En comparación con el grupo control (sin inoculación), se obtuvo un crecimiento de las plantas con NPs del tamaño más bajo y concentración del 2 %, debido a que posiblemente el TiO2-Ag incorporado contribuye al proceso de fotosíntesis y desempeña un papel antimicrobiano. La actividad fotosintética de las plantas tratadas, se midió mediante la técnica fotoacústica y del análisis de los resultados se obtuvo que con el tratamiento hecho con la suspensión de NPs de menor tamaño, a concentración entre 0,25 y 2 %, la Razón de Evolución de Oxígeno (REO) es similar a la que se observó en las plantas del grupo control. Esto indica que el tratamiento con NPs de TiO2-Ag entre 7 y 8 nm puede inducir el crecimiento sin alterar drásticamente la tasa fotosintética de plantas de espinaca a bajas concentraciones, lo que puede ser una alternativa eficiente para la mejora de la producción de este cultivo.

In recent decades, the search for raw from renewable resources to produce polymers, elastomers, resins, foams, etc., has intensified; these materials would reduce the industrial use of petrochemical compounds. In this work, the oil extracted from the castor oil seed (Ricinus communis) was used because of ricinoleic acid content (92.3%), it is of easy production and non-edible vegetable origin. The polyurethane adhesive was synthesized through transesterification and polymerization reactions. Using the corresponding standards, this adhesive was applied to sheets of Guadua angustifolia Kunth for determining its mechanical characteristics, the compressive strength parallel to the fiber was 43±3 (MPa), and shear parallel to the fiber was 5.9±0.9 (MPa). Fourier transform infrared spectroscopy was used for determining the appropriate molar ratio and monitoring the reaction during the synthesis and final product structure was analyzed with X-ray diffraction. Through differential scanning calorimetry, the glass transition temperature of the product was estimated on -24.6 °C; the thermal relaxation technique was used to measure its specific heat, while its thermal diffusivity and thermal expansion coefficient were estimated with the photoacoustic technique. [ABSTRACT FROM AUTHOR]

In this paper we present the study of three sensors, based on piezoelectric polymer thin films, for photoacoustic systems used in the characterization of liquids. Its performance was compared by carrying out measurements on well-known liquids. From the measured data, the sensitivity, noise level and quantification limit of each of the sensors were determined. The device with the best characteristics was used in the determination of the quantum efficiency of two dyes: Rhodamine 6G and Rhodamine B. The measured values agree very well with those reported by other authors.

En este trabajo, reportamos la caracterización de monocristales de Si(100) y GaSb(111) utilizando espectroscopia Raman y fotoacústica (principal interés) en configuración abierta y cerrada, para compuestos semiconductores III-V con estructura tipo zinc blenda, los espectros Raman generalmente muestran dos picos, un pico a baja frecuencia correspondiente a modos fononicos TO y un pico en alta frecuencia correspondiente a modos fononicos LO. Un fuerte pico es mostrado en la posición 226 cm−1 y uno un poco más débil en 237 cm−1, que son los modos TO y LO respectivamente, debido a la orientación cristalina del material. Con el fin de determinar la difusividad térmica de los materiales se utilizaron láseres con longitudes de onda de 650 nm y 535 nm. Los resultados de la difusividad térmica de los monocristales de Si y GaSb, obtenidos a partir del modelo de Rosencwaig y Gersho (RG) se analizaron en función de la orientación cristalográfica. Discutimos la recombinación no-radiativa que se origina en la superficie y en el volumen del cristal, que contribuye a la señal fotoacústica, en términos del tipo de celda y de la línea de excitación.

Copyright of Informador Técnico is the property of Servicio Nacional de Aprendizaje SENA and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Photoacoustic (PA) technique was used to investigate the structural properties (e.g. open porosity and permeability) of open-pore sintered glasses. This work demonstrates that the photoacoustic signal of open-pore sintered glasses, which are produced with different grain sizes and several degrees of open porosity, is sensitive to the morphology of the open-pore samples. The results obtained by the PA technique were related to results obtained by the Pressure Decay technique, and an excellent correlation was obtained. This demonstrates that PA technique, which is non-intrusive and non-destructive, is promising for application in analysis of porous ceramic structures, even if the sample is semi-transparent.A técnica fotoacústica (PA) foi usada para investigar as propriedades estruturais (isto é, porosidade aberta e permeabilidade) de filtros vítreos. Este trabalho demonstra que o sinal fotoacústico de filtros vítreos, os quais foram produzidos com diferentes tamanhos de grãos e vários graus de porosidade, é sensível à morfologia destes. Os resultados obtidos pela técnica PA foram relacionados com resultados de permeabilidade obtidos pela técnica de decaimento de pressão, resultando em uma ótima correlação. Isto demonstra que a técnica fotoacústica, a qual é não intrusiva e não destrutiva, é promissora para análise de estruturas cerâmicas porosas, mesmo sendo essas semi-transparentes.

Copyright of Momento: Revista de Física is the property of Universidad Nacional de Colombia, Departamento de Fisica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Phase transition on ferroelectric ceramics were detected by photoacoustic laser technique which allows the measurement of the Curie temperature and ferro-paraelectric transitions. The photoacoustic signal produced by low energy laser pulses using a piezoelectric transducer attached to the sample by a glass or quartz rod is shown. The developed technique requires nor signal amplification neither special preparation of the sample and have an excellent signal to noise ratio. In order to validate this technique it was applied to the measurement of Curie temperature of the PbSmTiO3 and Pb(MgNb)TiO3 ceramics. These results were compared with those obtained by DTA, DMA and dielectric permittivity.Se presenta una técnica fotoacústica de láser pulsado para detectar las transiciones de fase en cerámicas ferroeléctricas, determinando la temperatura de Curie y el cambio de estructura ferro-paraeléctrico. Se muestran los cambios producidos en las señales fotoacústicas generadas por láser pulsado de baja energía (< 200 μJ), utilizando para la detección un sensor piezoeléctrico pegado a la muestra por medio de una varilla de vidrio o cuarzo. La técnica desarrollada no requiere amplificación de la señal, ni preparación especial de la muestra y presenta una relación señal a ruido excelente. Para demostrar la validez de la técnica se aplicó al estudio de la determinación de la temperatura de Curie de las cerámicas: PbSmTiO3 y Pb(MgNb)TiO3. Los resultados se comparan con los obtenidos por otras técnicas como son DTA, DMA y permitividad dieléctrica.

Copyright of Revista Investigaciones Aplicadas is the property of Universidad Pontificia Bolivariana and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The aim of the present work was to classify and identify skin phototypes through in vivo photoacoustic (PA) measurements. Fifty-seven female volunteers took part in the study, being clinically evaluated and classified according to skin phototype (Fitzpatrick classification). After cleaning the skin area to be measured, the PA signal level was obtained for the inner and outer faces of both forearms. Volunteers were then classified according to the respective PA signal amplitude; subsequently, this classification was compared to the phototype classification and to the recently proposed Baumann classification. Comparison between the PA signal of the inner and outer faces of the forearm shows a highly significant statistical difference (p < 0.005), attributed to the higher pigmentation level of the skin region continuously exposed to solar radiation, demonstrating that skin constitution and aspect are influenced by the level of sun exposure. Comparison among phototypes was performed separately for the inner and outer faces of the forearm. The results show that the PA signal level (amplitude) for the inner forearm tends to scale with skin phototype, also allowing the division of the volunteers in two groups, according to their pigmentation levels and also following the recent Baumann classification. In this way, the photoacoustic methodology presented allows an objective, numerical classification of the skin types. [ABSTRACT FROM AUTHOR]

The use of coffee growing technical methods in Colombia began in fifties due to the high demand of the bean in the international market; this fact prioritized the chemical fertilizers utilization. This process turned out to be unsustainable by the chemical products economical costs and the environmental negative effects. Recently, some communities of small producers have retaken the ancestral cultivation techniques with the composting use in order to protect the soil and to obtain independence of the fertilizers and pesticides business. This change needs the support of natural and social sciences to make agile the process of such form that is profitable and efficient. In this way, the photosynthesis study is interesting what is linked with the acceptance of nutrients. In this work the photoacoustic technique was used to measure the photobaric processes, used in plants with biofertilizers and with chemical agents to compare the photosynthetic activity. [ABSTRACT FROM AUTHOR]

The physical and chemical processes are complexes during the coffee roasting. These processes depend of the roasting time and temperature besides the movement and water content of the bean. The heat and mass transfer are unstable processes, and the concentration and time dependent temperature profiles from the bean core have not been well elucidated. The thermal characterization results of different way farmed coffee and depth profiles are shown in this work, which serves to better understanding of roasting process. Since the thermal diffusivity and thermal effusivity depend directly of the material composition, the differences between these parameters corresponding to organic and traditionally farmed coffee are studied, which help to certify the first one. This benefits the commerce of a product that has greater price in the international market and positive impact in the environment. [ABSTRACT FROM AUTHOR]

Despite of intense searching about coffee roasting mechanisms, these are not being completely understood due to the subject complex. Still it is necessary to combine and compares different results, considering parameters as: fruit origin, grain size, grain mass, moisture, color, appearance, roasting time, used gas temperature in the roasting process, roaster system, etc. The data about coffee thermal conductivity are few credible and there are not temperatures profiles in the bean interior. Bean volume change mechanisms, the structural resistance, and bean layer elasticity, are not being well understood, too. The bean cellular structure knowledge is very important, because the ground and roasting coffee solubility is due to breaking of this structure, it allows the free solution without needing of molecules and colloids diffusion out cell. In this work, was studied the correlation between thermal diffusivity, measured using photoacoustic technique, and the bean cellular structure looked through of optical microcopy, for fruits cultivated with and without the chemicals using. The presented results will allow a possible method for certify organic coffee. [ABSTRACT FROM AUTHOR]

Half century ago the food industry introduced in the home around all word the coffee consume considering the different tastes, for this cause the coffee producers has seen in the flavors diversification a excellent commercial opportunity. It is a complex subject due to the characteristics and organoleptic properties of coffee changing according to soil kind and cultivation, geographic high, variety, etc. For this reason it is necessary to obtain a statistical quantification of the thermal parameters diffusivity and effusivity related to the structural and chemical composition of a material, for doing the thermal characterization of this product that allows to identify the origin that classifies as special with certification objective. In this work the thermal characterization of coffee from Quindío region with different characteristics, using the photoacoustic technique is reported. A deep profile in the bean was made too for understanding better the heat conduction inside. For the effussivity and diffusivity measurements was used a close an open cell, respectively. [ABSTRACT FROM AUTHOR]

Nowadays the globalization brings the opportunity of markets interaction and in spite of the excellent sensorial quality that the growing conditions in Colombia supplies to the coffee, the international commercialization of ground and roasted coffee is very complicated by market monopolization and absence of technology and exhaustive quality control. For this reason, the roasting process study is necessary loocking for tools that contribute to the determination of product taste quality. In this work the photoacoustic technique was used for obtaining proportional spectrum to the optical absorption of coffee powder of samples classified previously according to bean quality. These spectra were compared through its form and using the first derivative criteria and was defined the base for a discrimination method after roasting and ground process. [ABSTRACT FROM AUTHOR]