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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]

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]

Spinach is consumed for its valuable nutritional contributions. However, in Colombia, this crop has been of little interest in the research area due to its low production. On the other hand, the nanotechnology that can be used in agriculture to prevent or control diseases in crops through the application of nanoparticles (NPs) is emerging as a high potential subject in our country. In this work, the inoculation of suspensions of titanium dioxide NPs with the incorporation of silver (TiO2- Ag) in spinach seeds was evaluated. The NPs were synthesized through Sol-gel method and characterized by means of X-ray diffraction; suspensions of these powder samples of grain size between 7 and 26 nm were prepared at different concentrations for inoculation. In comparison with the control group (without inoculation), highest plant growth was obtained with NPs of the lowest size and 2 % concentration. It possibly due to the contribution in the photosynthesis process and antimicrobial role of incorporated TiO2-Ag. The photosynthetic activity of the plants from control and treated groups was measured by the photoacoustic technique and it was found that the plants treated with the smallest NPs suspension, at a concentration between 0.25 and 2 %, presented a rate of oxygen evolution similar to control group. These results indicate that the treatment with NPs of TiO2-Ag between 7 and 8 nm at low concentration can improve the growth without drastic alteration of the photosynthetic rate of spinach plants, which can be an efficient alternative for improvement in crop production. [ABSTRACT FROM AUTHOR]

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.)

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 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]