EFECTOS SOCIOTERRITORIALES DE LAS POLÍTICAS NEOLIBERALES EN LA AGRICULTURA DEL MAÍZ: EL CASO DEL DISTRITO DE DESARROLLO RURAL ATLACOMULCO DEL ESTADO DE MÉXICO. 1990-2015

La reestructuración del sector agrario nacional, inducida por las políticas neoliberales implementadas a finales de los años ochenta y principios de los noventa del siglo pasado, lejos de incentivar la siembra de maíz y considerando el principio de las ventajas comparativas, ha tratado de orientar el camino de la agricultura mexicana hacia la producción de cultivos más competitivos en el mercado internacional, entre los cuales no figura el maíz. Aunado a lo anterior, también ha propuesto un esquema de producción en el que sólo los grandes y medianos productores de maíz han logrado insertarse en el nuevo modelo agrícola, dejando un tanto a la deriva a los pequeños productores. El DDR Atlacomulco, ubicado en la porción noroccidental del estado de México, se ha caracterizado por ser un área tradicionalmente importante en la producción de maíz, y a partir del análisis estadístico de sus factores de producción durante el periodo comprendido entre 1990 y 2015, en el presente trabajo se determinan cuáles han sido los principales cambios dentro de la actividad maicera en el marco de la implementación de las políticas neoliberales en la agricultura. Asimismo, se hace una reflexión de la situación del DDR Atlacomulco con respecto a las perspectivas señaladas por algunos autores con relación al posible destino de la agricultura del maíz a nivel nacional como consecuencia del giro neoliberal del campo mexicano. Como resultado del trabajo se observa que la siembra de maíz no ha perdido su papel preponderante dentro de las actividades agrícolas de la región aunque ha sufrido cambios y presenta una ligera, pero constante, disminución, además de que se reconoce que la estructura laboral agrícola se ha reconfigurado con el paso del tiempo

Dual Beam Sinusoidally Modulated Reactance Surface Antenna

In this work, a planar dual beam Sinusoidally Modulated Reactance Surface (SMRS) antenna is presented. Our method is based on the implementation of a surface impedance modulated by the superposition of two sinusoidal functions. In particular, the full process of designing a dual beam antenna that radiates at -14 and 28 off broadside at 10 GHz is described. In a second proposed structure, manipulation of the side lobe level (SLL) is achieved by varying the leakage constant along the antenna with negligible changes in the pointing directions. SLL reductions of 3.4 dB and 1.8 dB for each of the synthesised beams are obtained through full wave simulations, as well as gains 13.4 dBi and 13.6 dBi respectively. An excellent agreement between theoretical and simulated results is observed.This project has received funding from the Spanish Ministerio de Ciencia, Innovación y Universidades (MCIU), the Agencia Estatal de Investigación (AEI) and the Fondo Europeo de Desarrollo Regional (FEDER) (Programa Estatal de I+D+i Orientada a los Retos de la Sociedad) under grant RTI2018-097098-JI00. It has also been undertaken within the context of a Research Collaboration Grant of the I Plan Propio de Investigación y Transferencia of the University of Málaga

Multifunctional microcapsules based on ZnO and n-octadecane: From thermal energy storage to photocatalytic activity

Energy management is one of the most important issues to be addressed in the near future in many fields, one of which is buildings. In this sense, new phase change materials (PCM) are being widely studied for storing energy. Encapsulating PCM is a good way to incorporate these materials into different applications in which energy storage is useful. In this study, microcapsules based on ZnO containing n-octadecane as a phase change material were synthesized and characterized with regard to their structural, morphological and optical properties according to several synthesis parameters, such as the proportion of precursors, stirring rate and ageing time. The microcapsules were characterized using x-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and UV–Vis spectroscopy in diffuse reflectance mode. The presence of n-octadecane inside the capsules was confirmed. Their thermal behaviour was analysed by means of differential scanning calorimetry. Heating/cooling cycles were performed, after which the microcapsules presented good stability. Furthermore, the encapsulation efficiency was estimated from melting and crystallization enthalpy values, reaching a value of 23.1%. Moreover, the isobaric specific heat of the microcapsules is higher than that of ZnO, which means that substituting ZnO with microcapsules in buildings leads to an important increase in the amount of sensible heat stored. Finally, the photocatalytic activity of the microcapsules was analysed by studying the photodegradation of Crystal Violet dye. The degradation rate increased when the microcapsules were present, so the photocatalytic activity of the microcapsules was confirmed under UV and visible irradiation, which is of interest because they can be used to remove organic pollutants from buildings.10 página

Stability and Thermal Properties Study of Metal Chalcogenide-Based Nanofluids for Concentrating Solar Power

Nanofluids are colloidal suspensions of nanomaterials in a fluid which exhibit enhanced thermophysical properties compared to conventional fluids. The addition of nanomaterials to a fluid can increase the thermal conductivity, isobaric-specific heat, diffusivity, and the convective heat transfer coefficient of the original fluid. For this reason, nanofluids have been studied over the last decades in many fields such as biomedicine, industrial cooling, nuclear reactors, and also in solar thermal applications. In this paper, we report the preparation and characterization of nanofluids based on one-dimensional MoS2 and WS2 nanosheets to improve the thermal properties of the heat transfer fluid currently used in concentrating solar plants (CSP). A comparative study of both types of nanofluids was performed for explaining the influence of nanostructure morphologies on nanofluid stability and thermal properties. The nanofluids prepared in this work present a high stability over time and thermal conductivity enhancements of up to 46% for MoS2-based nanofluid and up to 35% for WS2-based nanofluid. These results led to an increase in the efficiency of the solar collectors of 21.3% and 16.8% when the nanofluids based on MoS2 nanowires or WS2 nanosheets were used instead of the typical thermal oil

Synthesis and characterization of metal oxide-based microcapsules including phase change materials for energy storage applications

In this study, microcapsules based on Cu2O containing different phase change materials (PCM) were prepared and characterized. The elemental, structural and electronic properties of the Cu2O-based microcapsules were characterized using several techniques such as X-ray diffraction, X-ray photoelectron spectroscopy, scanning and transmission electron microscopy and Fourier-transform infrared spectroscopy. In addition, the thermal properties of the microcapsules prepared were characterized in order to analyse their possible application as a thermal energy storage medium. Heating/cooling cycles using a differential scanning calorimetry technique were performed, and the phase change temperature and enthalpy were estimated. We observed good stability after the cycles. Furthermore, the encapsulation efficiency was estimated from melting and crystallization enthalpy values, reaching a value of 14.8% for the paraffin wax-based microcapsules. Finally, isobaric specific heat was measured to evaluate the storage capability of the encapsulated PCMs with regard to pure Cu2O to evaluate their possible application as a thermal storage system. An increase of around 140% was found in the isobaric specific heat for the microcapsules based on paraffin wax with regard to pure Cu2O. © 2023, The Author(s)

Effect of atomic substitution on the sodium manganese ferrite thermochemical cycle for hydrogen production

This work presents the effect of atomic substitution on the MnFe2O4-Na2CO3 thermochemical cycle for H-2 production. The non-oxidative decarbonation/carbonation reaction of the MnFe2O4-Na2CO3 mixture is investigated as the starting reference. Repeated cycling results in a 30% loss of reversibility due to an overall reduction of the reactive interfaces. The substitution of Na2CO3 for Li2CO3 decreases the decarbonation onset temperature by about 100 degrees C, but almost no reversibility is observed during the cycles due to the irreversible Li+ intercalation. The effect of partial Mn substitution for Ca, Ni, and Zn is presented. The 5% Zn mixture shows the best decarbonation/carbonation reversibility and is tested for H-2 production together with MnFe2O4-Na2CO3. The reference mixture produces more H-2 during the first cycle (asymptotic to 1.1 vs. 0.7 mmol/g), but its production drastically drops by two orders of magnitude upon cycling and becomes negligible after 5 cycles. By contrast, the Zn-doped mixture exhibits a stable H-2 production of 0.22 mmol/g with no decreasing trend observed from cycle 2 to cycle 5. As result, in the fifth cycle, the Zn-doped mixture produces 23 times more H-2 than MnFe2O4-Na2CO3. Thermogravimetry and X-ray diffraction confirm that doping with Zn significantly improves the regeneration of the reactants.Acknowledgment This Project is funded by the Department of Economic Devel-opment, Sustainability and Environment of the Basque Govern-ment (CICe 2019-KK-2019/00097-and H2BASQUE-KK-2021/00054) . The authors express their sincere gratitude to Cristina Luengo and Mikel Intxaurtieta for their technical support

Nanofluidos basados en nanomateriales 2D.

Resumen del proyecto de líneas prioritarias "Nanofluidos basados en nanomateriales 2D" del IMEYMAT

Improving the efficiency of the concentrating solar power plants using heat transfer nanofluids with gold nanoplates: An analysis from laboratory to industrial scale

We report about the remarkable changes in the thermophysical properties of the heat transfer fluid used in concentrating solar power plants with parabolic-trough collectors (Dowtherm A, a mixture of diphenyl oxide and biphenyl) by addition of Au nanoplates in mass fractions around 10−2 wt%. The resulting nanofluids are stable for weeks, and their enhanced physical properties make them good candidates for the application. Particularly, with 4.8·10−2 wt% of Au nanoplates, specific heat increases by 12.0 ± 1.2 % at 523 K and thermal conductivity increases by 24.9 ± 6.1 % at 373 K, with no measurable changes in density or dynamic viscosity. This set of physical properties allows to make a realistic estimation of the performance of a prototypical concentrating solar power plant using these nanofluids for solar-to-thermal energy conversion. We determine, using computational cost-free numerical models available in literature, that the performance of a concentrating solar power plant could increase up to 35.1 %, compared to the predicted 24.7 % with the conventional heat transfer fluid, with neither rheological penalties nor economically prohibitive structural changes. The findings here reported may contribute to encourage the application of heat transfer nanofluids in order to improve the efficiency of concentrating solar power plants, and to consolidate a working scheme that positively promotes the transition from laboratory scale to industrial scale. © 2023 The Author

Uso de dispositivos tecnológicos de los estudiantes de Fima de la Espoch, carrera de Estadística

El principal objetivo de llevar a cabo este proyecto de investigación es conocer el uso de dispositivos tecnológicos que tienen los estudiantes politécnicos de la Escuela de Física y Matemática carrera de Estadística. Para ello tomamos una muestra de población con características similares la cual nos ayudó para el estudio y con ello poder generalizar los resultados obtenidos en la se trata en la realización de encuestas a los estudiantes de estadística, para la recolección y tabulación de datos, de tal manera que podamos determinar cuál es el dispositivo que predomina más en los jóvenes y las consecuencias que consecuencias que del uso excesivo de dispositivos tecnológicos haciendo que los estudiantes deserten la carrera. Por ello, es preciso que la sociedad en general, pero de una manera más directa la familia y la escuela, tomen conciencia de este fenómeno, asumiendo las responsabilidades que les incumben y dotando de la formación y de los mecanismos necesarios a los más jóvenes para que estos hagan un uso correcto y adecuado de las tecnología