Para asombrarse y aprender

Este trabajo presenta la fundamentación, diseño y resultados de un proyecto realizado en el marco de un programa institucional en la UNAM, relacionado con la innovación de la enseñanza experimental. Como producto de este proyecto se elaboró un libro con 30 experimentos de aula dirigidos a profesores de los niveles bachillerato y universitario. Los experimentos elaborados presentan propuestas experimentales novedosas que nos permitan reconceptualizar y diversificar el trabajo práctico

Síntesis y caracterización de óxidos mixtos precursores de bronces tetragonales de W de potencial actividad en la oxidación de difenilsulfuro

Fases de heteropolioxometalatos (HPOM), a base de heteropolitungstatos complejos derivados de tipo Keggin de la serie [M4(H2O)2(PW9O34)2]10- (PWM) con M(II) = Cu y su precursor Na8H(PW9O34) (PW9), se han modificado químicamente mediante reacción hidrotermal, con iones Nb y V en el gel de síntesis, dando lugar a la formación de materiales del tipo (KNaCu)xP0.11WV0,2NbOx y (Na)xPWV0,2NbOx. Tanto los materiales de síntesis como los tratados a 500ºC (en atmosfera de N2) son pseudocristalinos (que tras tratamiento a 800º C, conduce a una estructura típica de bronce tetragonal). Los materiales tratados térmicamente a 500ºC se han caracterizado y estudiado como catalizadores en la oxidación parcial de difenilsulfuro. Los resultados catalíticos se han comparado con los obtenidos con los HPOM de partida, observándose que los bronces metálicos presentan una mayor actividad catalítica (con una drástica disminución del tiempo de reacción) y un marcado aumento de la selectividad a difenil-sulfona.Phases based on complex heteropolytungstates (HPOM), derived from series Keggin type [M4 (H2O)2 (PW9O34)2] 10-(PWM) with M(II) = Cu and its precursor Na8H (PW9O34) (PW9), have been chemically modified by hydrothermal reaction, with Nb and V ions in the synthesis gel, giving place materials as (KNaCu)xP0.11WV0,2NbOx and (Na)xPWV0,2NbOx. The as-synthesized and the heat-treated at 500ºC (in N2) are pseudocrystalline (although they are transformed to tetragonal bronze after heattreatment at 800ºC). The samples heat-treated at 500ºC have been characterized and tested in the partial oxidation of diphenylsulfide. The catalytic results have been compared to those achieved over pure HPOM. It has been observed that these metal oxides bronzes show a higher both catalytic activity (with a drastic reduction of the reaction time) and selectivity to diphenyl-sulfone

Simultaneous estimation of the nutritional contribution of fish meal, soy protein isolate and corn gluten to the growth of Pacific white shrimp (Litopenaeus vannamei) using dual stable isotope analysis

The nutritional contribution of the dietary nitrogen, carbon and total dry matter supplied by fish meal (FM), soy protein isolate (SP) and corn gluten (CG) to the growth of Pacific white shrimp Litopenaeus vannamei was assessed by means of isotopic analyses. As SP and CG are ingredients derived from plants having different photosynthetic pathways which imprint specific carbon isotope values to plant tissues, their isotopic values were contrasting. FM is isotopically different to these plant meals in regards to both, carbon and nitrogen. Such natural isotopic differences were used to design experimental diets having contrasting isotopic signatures. Seven isoproteic (36% crude protein), isoenergetic (4.7 Kcal gr-1) diets were formulated; three diets consisted in isotopic controls manufactured with only one main ingredient supplying dietary nitrogen and carbon: 100 % FM (diet 100F), 100% SP (diet 100S) and 100% CG (diet 100G). Four more diets were formulated with varying mixtures of these three ingredients, one included 33% of each ingredient on a dietary nitrogen basis (diet 33FSG) and the other three included a proportion 50:25:25 for each of the three ingredients (diets 50FSG, 50SGF and 50GFS). At the end of the bioassay there were no significant differences in growth rate in shrimps fed on the four mixed diets and diet 100F (k = 0.215-0.224). Growth rates were significantly lower (k = 0.163-0.201) in shrimps grown on diets containing only plant meals. Carbon and nitrogen stable isotope values (δ13C and δ15N) were measured in experimental diets and shrimp muscle tissue and results were incorporated into a three-source, two-isotope mixing model. The relative contributions of dietary nitrogen, carbon and total dry matter from FM, SP and CG to growth were statistically similar to the proportions established in most of the diets after correcting for the apparent digestibility coefficients of the ingredients. Dietary nitrogen available in diet 33FSG was incorporated in muscle tissue at proportions representing 24, 35 and 41% of the respective ingredients. Diet 50GSF contributed significantly higher amounts of dietary nitrogen from CG than from FM. When the level of dietary nitrogen derived from FM was increased in diet 50FSG, nutrient contributions were more comparable to the available dietary proportions as there was an incorporation of 44, 29 and 27% from FM, SP and CG, respectively. Nutritional contributions from SP were very consistent to the dietary proportions established in the experimental diets

Kinetic Study of Oxidative Dehydrogenation of Ethane over MoVTeNb Mixed-Oxide Catalyst

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Industrial & Engineering Chemistry Research, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see [insert ACS Articles on Request author-directed link to Published Work, see http://doi.org/10.1021/ie402447h[EN] A MoVTeNb multimetallic mixed oxide was studied for the oxidative dehydrogenation of ethane, a promising alternative for catalytic ethylene production. Lab-scale steady-state experimental reaction data were obtained according to a 3(k) experimental design to investigate the simultaneous effect of temperature (400-480 degrees C) and space time [23-70 g(cat) h (mol of ethane) I]. A fixed-bed reactor at atmospheric pressure was employed, feeding a mixture of ethane, oxygen, and nitrogen. Ethane conversion varied from 17 to 85%, whereas selectivity for ethylene and COx varied from 94 to 76% and from 4.0 to 24%, respectively. These types of analyses are useful for determining the optimum reaction conditions to enhance the catalytic performance of the mixed oxides presented herein.This work was financially supported by the Instituto Mexicano del Petroleo. Technical support from Eng. G. Alonso-Ramirez is gratefully acknowledged.Valente, J.; Quintana-Solorzano, R.; Armendariz-Herrera, H.; Barragan-Rodriguez, G.; López Nieto, JM. (2014). Kinetic Study of Oxidative Dehydrogenation of Ethane over MoVTeNb Mixed-Oxide Catalyst. Industrial and Engineering Chemistry Research. 53(5):1775-1786. doi:10.1021/ie402447hS1775178653

Experimental Investigation on Wind Energy Harvesting by Aeroelastic Excitation of a Semi-Circular Cylinder with Flat Side Parallel to the Incoming Flow

In this work, the performance of a semicircular cylinder with the flat side parallel to the incoming flow has been studied experimentally in a wind-excited energy harvester. Preliminary sectional model wind tunnel tests have allowed the identification of the reduced velocity ranges howing appreciable wind-induced oscillations. Interestingly, vortex-induced vibration-galloping interferences have been identified for both heave and pitch degrees of freedom at low reduced wind speeds, as well as coupled galloping in the higher ranges of flow velocities. The impact on the aeroelastic response caused by the attachment of a small-diameter rod at different positions has been studied, finding an enhancement in the amplitude of the oscillations and an enlargement in the vortex-induced vibration excitation range for some of them. Based on these preliminary results, an energy harvester has been designed adopting a cantilever beam supporting the semicircular cylinder. The device has showed a good performance reaching 2.5 mW of averaged harvested power for the configuration with a small-diameter rod attached at γ=85º for 8 m/s flow speed

Understanding the kinetic behavior of a Mo-V-Te-Nb mixed oxide in the oxydehydrogenation of ethane

Two kinetic models based on Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms were developed to describe the oxydehydrogenation of ethane to yield ethylene over a Mo-V-Te-Nb catalyst. Obtained in a lab-scale fixed-bed reactor, experimental data at the steady-state were used to estimate the kinetic models parameters via a nonisothermal regression. Experiments were performed using an ethane, oxygen and nitrogen mixture as feedstock, spanning temperatures from 673 to 753 K, inlet partial pressures of oxygen and ethane between 5.0 and 22.0 kPa, and space-time from 10 to 70 g(cat) h(molethane)- (1). Ethylene, CO and CO2 were the only detected products, the selectivity for ethylene ranged from 76% to 96% for an ethane conversion interval 4-85%. A series of tests feeding ethylene instead of ethane were also performed at 713 K, varying inlet partial pressures and space-time in the same ranges as was done for ethane. Ethylene conversion was relatively low, 3-14%, the dominant product being CO with CO/CO2 ratios from 0.73 to 0.79. The LH mechanism was found to represent better the experimental data. The oxydehydrogenation of ethane was the reaction with the lowest activation energy, 108-115 kJ mol (1). Except for the conversion of ethane into CO2, deep oxidations were detected as very energetically demanding steps, 156-193 kJ mol (1). Competitive adsorption between reagents and products occurred in the two mechanisms particularly at relatively high reaction severity, water re-adsorption being weaker in comparison with COx re-adsorption. (C) 2014 Elsevier Ltd. All rights reserved.This work was financially supported by the Instituto Mexicano del Petroleo.Quintana-Solorzano, R.; Barragan-Rodriguez, G.; Armendariz-Herrera, H.; López Nieto, JM.; Valente, JS. (2014). Understanding the kinetic behavior of a Mo-V-Te-Nb mixed oxide in the oxydehydrogenation of ethane. Fuel. 138:15-26. doi:10.1016/j.fuel.2014.07.051152613

Carbon dioxide emissions from semi-arid soils amended with biochar alone or combined with mineral and organic fertilizers

Semi-arid soils cover a significant area of Earth s land surface and typically contain large amounts of inorganic C. Determining the effects of biochar additions on CO2 emissions fromsemi-arid soils is therefore essential for evaluating the potential of biochar as a climate change mitigation strategy. Here, we measured the CO2 that evolved from semi-arid calcareous soils amended with biochar at rates of 0 and 20 t ha?1 in a full factorial combination with three different fertilizers (mineral fertilizer, municipal solid waste compost, and sewage sludge) applied at four rates (equivalent to 0, 75, 150, and 225 kg potentially available N ha?1) during 182 days of aerobic incubation. A double exponential model, which describes cumulative CO2 emissions from two active soil C compartments with different turnover rates (one relatively stable and the other more labile), was found to fit verywell all the experimental datasets. In general, the organic fertilizers increased the size and decomposition rate of the stable and labile soil C pools. In contrast, biochar addition had no effects on any of the double exponential model parameters and did not interact with the effects ascribed to the type and rate of fertilizer. After 182 days of incubation, soil organic and microbial biomass C contents tended to increase with increasing the application rates of organic fertilizer, especially of compost, whereas increasing the rate of mineral fertilizer tended to suppress microbial biomass. Biochar was found to increase both organic and inorganic C contents in soil and not to interactwith the effects of type and rate of fertilizer on C fractions. As a whole, our results suggest that the use of biochar as enhancer of semi-arid soils, either alone or combined with mineral and organic fertilizers, is unlikely to increase abiotic and biotic soil CO2 emissions

Shape-invariant quantum Hamiltonian with position-dependent effective mass through second order supersymmetry

Second order supersymmetric approach is taken to the system describing motion of a quantum particle in a potential endowed with position-dependent effective mass. It is shown that the intertwining relations between second order partner Hamiltonians may be exploited to obtain a simple shape-invariant condition. Indeed a novel relation between potential and mass functions is derived, which leads to a class of exactly solvable model. As an illustration of our procedure, two examples are given for which one obtains whole spectra algebraically. Both shape-invariant potentials exhibit harmonic-oscillator-like or singular-oscillator-like spectra depending on the values of the shape-invariant parameter.Comment: 16 pages, 5 figs; Present e-mail of AG: [email protected]

Manuela: tradición, modernidad y violencia política

Disuelta la Gran Colombia e iniciado el proceso de formación del Estado de la Nueva Granada se produjo una temprana división en el grupo que, habiendo derrotado la dictadura del general Urdaneta, convocó al Congreso Constituyente que aprobó la Carta de 1832

Manuela: tradición, modernidad y violencia política

Disuelta la Gran Colombia e iniciado el proceso de formación del Estado de la Nueva Granada se produjo una temprana división en el grupo que, habiendo derrotado la dictadura del general Urdaneta, convocó al Congreso Constituyente que aprobó la Carta de 1832