Publicaciones

Permanent URI for this collectionhttps://dspace.ucuenca.edu.ec/handle/123456789/45860

Browse

Now showing 1 - 20 of 1170

Financing technological improvements and firm competitive advantage through the kyoto protocol's clean development mechanism (CDM): a Latin American ex...
(2006) Petersen, Henry; Escobar, Luis Fernando; Espinoza Abad, Juan Leonardo; Vredenburg, Harrie
For nations of the global south there has been an overall dismissal of emissions reduction practices surrounding global warming, and perhaps rightfully so. Developed countries have been identified as the primary contributor towards the climate change issue, and many countries perceive that the curbing of emissions will lead to the stagnation of economic growth and prosperity. For developing nations, embracing emission reductions or carbon emission offsets appear to make little sense if in fact such actions would result in the economic contraction expected. However, we suggest that the climate change issue, although perceived as an obstacle to growth and prosperity, holds several strategic competitive advantages for first movers. Three factors are discussed regarding first mover advantage and we use the energy industry of the Latin American and Caribbean (LAC) region as our example.
Optimization of sensor location by static and dynamic slope stability analysis
(Springer, Dordrecht, 2007) Maertens, Jan; Roeck, Guido de; Bojorque Iñeguez, Jaime Asdrúbal
This paper derives the best location of field sensor for landslide monitoring based on static, pseudostatic and dynamic finite element slope stability analysis. Use is made of the finite element technique as not to constrain the analysis by the assumptions required in classical approaches. Numerical techniques in general, easily handle the strain-stress relationship, the non-linear soil behaviour, and complex geometries. The present methodology is implemented in a potential landslide site at km 27 along the Cuenca-Machala highway, Ecuador. This site has a cut slope of about 40 degrees with a length of 130 m and it is 100 m wide, given an approximated landslide volume of 240,000 m3 with an average depth of 18.5 m. The soils behaviour is represented as elastic-plastic soil material with a Mohr-Coulomb failure criterion for which the soil strength parameters were derived from in-situ and laboratory tests. The changes of static and/or dynamic stresses, geometry and soil properties will cause a variation where the highest displacements are developed. The location of the highest total, vertical and horizontal displacements are used to judge the best location for installing sensors for landslide monitoring. Different scenarios are analyzed to evaluate the effect of introducing remedial measures and different transient conditions. The results of the numerical simulation enabled definition of the most efficient and cost-effective location of the sensors to alert for potential landslides.
Effect of cation substitution on magnetic properties in Mn1−xA’xCr2S4 (A’ = Cd, Zn) thiospinel series
(2007) Moure, Carlos; Cruzat Contreras, Christian Américo; Raison, Ch; Manríquez Castro, Víctor; Galdámez Silva, Antonio César; Barahona Huenchumil, Patricia Mabel; Le Coz, Xavier; Peña, Octavio
Colossal magnetoresistance (CMR) materials such as REMnO3 perovskites and AB2S4 thiospinels have been well studied in the past. The authors present thiospinel compounds with A = Mn, since they may be viewed as a link to REMnO3 CMR perovskites. Ferrimagnetic MnCr2S4 is known to present a T c of 65 K and a magnetic transition towards a non-collinear Yafet-Kittel state. The (Mn1−xA’x)Cr2S4 series (A = Cd, Zn) was synthesised at 850°C. This series crystallises in the space group Fd3m with a close to 10 Å. When A’ = Cd (T c ranging from 68 K, x = 0·2, to 79 K, x = 0·6), the ferromagnetic features are enhanced, indicating that antiferromagnetism between Mn spins is progressively lost. For A’ = Zn, two magnetic transitions take place, one at 15 K, which is reminiscent of the antiferromagnetic state of ZnCr2S4 and another one at T c = 115 K. Impurities which could be responsible of these two magnetic states are excluded.
Variation in the expression of insulin-like growth factor-1 in human pulp tissue according to the root-development stage
(2007) Díaz, Eduardo; Lombana Sanchez, Nelson Jose; Álvarez Vásquez, José Luis; Orozco, María Patricia; Díaz Perez, Alberto; Angel Londoño, Patricia; Caviedes Bucheli, Javier Fernando; Muñoz, Hugo Roberto
Insulin-like growth factor-1 (IGF-1) plays an important role in cell proliferation and differentiation. It actively participates during odontogenesis and mineralization of dental hard tissues. The purpose of this study is to use a radioimmunoassay (RIA) to determine whether there are differences in the expression of IGF-1 in human pulp from teeth having incomplete or complete root development. Twenty-six pulp samples were obtained from freshly extracted human third molars, half of them from teeth with incomplete root development. All of the samples were processed and labeled using an IGF-1 RIA kit. Results showed IGF-1 presence in all human pulp samples with a statistically significant higher expression in pulps having complete root development. The present findings are consistent with the hypothesis that IGF-1 contributes toward forming and mineralizing dental tissues in teeth with incomplete root development as well as in pulp-repairing process in teeth with complete root development.
Una visión empresarial del turismo comunitario en el Ecuador
(Universidad de Cuenca, Abya Yala, 2007) Farfán Pacheco, Lourdes Karina; Serrano López, Ana Lucía
Delimitation of safety zones by finite element analysis
(Taylor & Francis, 2008) Maertens, Johanna; Bojorque Iñeguez, Jaime Asdrúbal; De Roeck, Guido; Bojorque Iñeguez, Jaime Asdrúbal
This paper deals with the determination of safety zones and local minima by using finite element analysis. Used is made of finite element method in order not to constraint the analysis by neither the assumptions in the location of the sliding surface nor in the interslice force function. It is known, that only the most critical failure mechanism and global minimum are evaluated by the strength reduction method, in such approach local minima most of the time are unnoticed. Here, it is proposed that the safety zones and the local minima can be detected by keeping the information generated in the strength reduction process. In addition, the importance of soil properties in the location of the failure mechanism is highlighted. The methodology is presented in an artificial case study and in a real natural slope. The safety zones should be considered in landslide stabilization and remediation.
Comments on ‘two-dimensional slope stability analysis by limit equilibrium and strength reduction methods
(2008) De Roeck, Guido; Maertens, Johanna; Bojorque Iñeguez, Jaime Asdrúbal
This article presents comments to the document 'Two-dimensional slope stability analysis by limit equilibrium and strength reduction methods'
Synthesis and study of photoacoustic properties of (Pd/TiO2)/polystyrene nanocomposites
(2008) Cruzat Contreras, Christian Américo; Meléndrez Castro, Manuel F.; Cárdenas Triviño, Galo; Morales, Juan; Díaz Visurraga, Judith Antonieta
In this work, nanocomposites (Ncs) from Pd nanoparticles and TiO2 (Pd-Nps-TiO2) were supported on a polystyrene matrix (PS). Chemical liquid deposition, solvated metal atom dispersion and in situ polymerization were used in order to synthesize these Ncs. Colloid and nanocomposite characterization were performed by TEM, SEM, EDX, SAED and TGA. TEM analysis revealed a particle size of 7 nm for Coll-Styrene and 11 nm for Pd-Nps supported on TiO2 after radical polymerization. SAED showed phases corresponding to both metallic Pd and TiO2 anatase in the polymeric matrix. Molecular weight (MW) was determined by viscosimetric method. MW varies according to the initiator concentration and nanoparticle amount used for polymerization. The amount of nanoparticles increased the decomposition temperature of the Ncs by 10 °C, improving the thermal stability of these hybrid materials. Photoacoustic properties were evaluated in order to determine the effect of nanoparticles on thermal diffusivity (α) inside the matrix. Significant values of (α) were found for Ncs with Pd-Nps in contrast to PS and Pd/TiO2 Ncs. Structural aspects and colloidal aggregation of Ncs were also studied.
Nonisothermal crystallization and melting behavior of syndiotactic polypropylenes of different microstructure
(2008) Vanegas Peña, María Eulalia; Quijada, Raúl; Serafini, Daniel; Galland, Griselda B.; Palza, Humberto
Syndiotactic polypropylenes and their copolymers with 1-olefins were synthesized using two metallocene/MAO catalytic systems, and the effect of the different microstructures on nonisothermal crystallization and subsequent melting was studied. Using differential scanning calorimetry (DSC) it was observed that samples with lower content of defects showed crystallization on cooling from the melt, and a double melting peak in the subsequent heating scan, the latter associated with melt, recrystallization and remelt processes that it was confirmed by its nonreversing exothermic process found by means of temperature modulated DSC (MDSC). However, polymers with high amount of defects showed cold crystallization on heating followed by a melting process, that it was observed by MDSC. Wide angle X-ray diffraction was used for characterizing the changes of crystalline forms in relationship with crystallization process.
Los juegos deportivos ecuatorianos. Su historia
([Editor no identificado], 2009) Barreto Andrade, Jorge Antonio; Sichel González, John
The work is a compilation of the results of the different national sports games held in Ecuador. Explains in detail each one of the results obtained in the eleven editions of the most important national sports games in our country, indicating venues, participants, sports, times and brands, locations and then, the qualitative and quantitative analyses, which makes it a reference text of great value for those of us who are looking for some information.
Synthesis and aggregation study of tin nanoparticles and colloids obtained by chemical liquid deposition
(2009) Cruzat Contreras, Christian Américo; Arbiol, Jordi; Meléndrez, Manuel F; Cárdenas Triviño, Galo T; Díaz, Jordi
Tin colloids (Sn-Colls) and nanoparticles were synthesized by a chemical liquid deposition method (CLD). Sn0 was evaporated and codeposited with acetone, 2-propanol, and tetrahydrofurane vapors at 77 K to obtain colloidal dispersions. Sn-Coll were characterized by UV spectroscopy, transmission electron microscopy (TEM), high resolution transmission electron microscopy, selected area electron diffraction, thermal analysis, infrared spectroscopy [Fourier transform infrared (FTIR)], and light scattering. TEM micrographs of tin nanoparticles (Sn-Nps) revealed a particle size distribution between 2 and 4 nm for the three solvents used in the synthesis. UV studies showed strong absorption bands in the UV region, suggesting that the Sn-Nps obtained by CLD exhibit quantum confinement and typical bands of plasmons corresponded to aggregated particles. Electrophoresis measurement indicated a significant tendency of particle aggregation along time, which was verified by light scattering studies. The diffraction patterns revealed phases corresponding to metallic tin and FTIR studies showed the interaction Sn-solvent in the metal surface by Sn-O bonds, indicating a solvatation of metallic clusters. Thermal analysis revealed a good thermal stability of Sn-Nps. The mechanism of tin nanoparticles formation was also examined.
Colloidal Cu nanoparticles/chitosan composite film obtained by microwave heating for food package applications
(2009) Cárdenas Triviño, Galo; Díaz, Jordi V; Meléndrez, Manuel F; Cruzat Contreras, Christian Américo; García Cancino, Apolinaria A
In this paper, we describe the preparation and characterization of colloidal Cu nanoparticles/chitosan composite film (composite film) by solution-casting technique with microwave heating. Effects of the incorporation of colloidal Cu nanoparticles on structure, thermal behavior, surface, barrier properties and light transmission of composite film were investigated. The antimicrobial activity of films against Staphylococcus aureus and Salmonella enterica serovar Typhimurium, were also tested. Incorporation of colloidal Cu nanoparticles on chitosan matrix improved the barrier properties of films, decreasing the oxygen permeability as well as water vapor permeability and increasing the protection against UV light. The composite film was effective in alteration of cell wall and reduction of microbial concentration in the liquid culture for both bacteria tested.
Microporous membranes prepared via thermally induced phase separation from metallocenic syndiotactic polypropylenes
(2009) Vanegas Peña, María Eulalia; Quijada, Raúl; Serafini, Daniel
Microporous membranes were prepared by thermally induced phase separation (TIPS) using different tailor-made syndiotactic polypropylenes (sPP) synthesized by metallocene catalysts. The phase diagrams of sPP samples in diphenyl ether (DPE) were determined. The cloud points were found to be slightly affected by molecular weight (Mw) and the influence of syndiotacticy was negligible. The dynamic crystallization curves depended solely on the syndiotacticity of the samples, shifting to lower temperatures as the stereoregularity of the sPP decreased, and no relation with Mw was found. The viscosity of sPP–DPE solutions increased with Mw and stereoregularity of the sPP. Membrane pore sizes were correlated with droplet growth period, crystallization behaviour, and sample viscosity, the latter being an important parameter for low polymer solution concentration (15 wt%) but not so at higher concentration (40 wt%).
Syndiotactic polypropylene copolymer membranes and their performance for oxygen separation
(2010) Quijada, Raúl; Vanegas Peña, María Eulalia
Syndiotactic poly(propylene- -olefin) copolymers with controlled microstructure and desired properties for oxygen enrichment have been synthesized via metallocene catalysts. The controlled incorporation of comonomers as pendant branch mainly improved the oxygen permeability, but the oxygen/nitrogen selectivity dropped around 20%. By controlling the amount and length of the branches in the syndiotactic polypropylene, the permeability of the membrane was enhanced up to 12-fold and it is comparable to typical commercial polymers used for this application. In contrast with conventional commercial polypropylene, copolymers with a large amount of comonomer were soluble in cyclohexane, allowing the manufacture of composite membranes with high permeance.
Syndiotactic poly (propene-co-norbornene): synthesis and properties at low norbornene incorporation
(2010) Vanegas Peña, María Eulalia; Quijada, Raúl; Galland, Griselda B.
Copolymerizations of propene with norbornene were carried out using a syndiotactic metallocene catalyst at low initial comonomer concentrations for different polymerization times. The influence of the norbornene concentration on the catalytic activity and on the resulting material properties has been analyzed. The copolymer molecular weight decreased drastically when small amounts of norbornene were added in reactions which lasted 30 min. When longer reaction times were used the molecular weight increased with time, however living polymerizationwas ruled out because the polydispersity was ca. 2. The DSC measurements showed copolymers with low crystallinity or which were completely amorphous.
Towards a model of wind energy industry development in industrial and emerging economies
(2010) Espinoza Abad, Juan Leonardo
Through the development and analysis of four in-depth case studies of the emergence of wind power industries in two industrialised and two emerging economies, the authors develop a model of sustainable energy industry development. The model demonstrates that fundamental economic indicators are insufficient for explaining new industry development. Environmental, institutional and cultural factors idiosyncratic to individual jurisdictions play important roles in the emergence of renewable energy industries in both industrialised and emerging economies. The model makes contributions to institutional and strategic change theories and has implications for policy makers and managers.
Analyzing the impact of strategy-based instruction on vocabulary acquisition and the listening skill
(2011) Abad Célleri, Mónica Patricia; Carr, Anne
Validación de modelos computacionales de flujo dinámico con pruebas de trazadores en lagunas de gran escala
(2011) Cedillo Galarza, Juan Sebastián; Matailo Quituisaca, María Magdalena; Alvarado Martínez, Andrés Omar; Alvarado Martínez, Andrés Omar
Synthesis, characterization and properties of magnetic colloids supported on chitosan
(2011) Meléndrez, Manuel Francisco; Peña, Octavio; Cruzat Contreras, Christian Américo; Cárdenas Triviño, Galo; Díaz Visurraga, Judith
This work proposes the synthesis, characterization and investigation of the stabilization capabilities of chitosan doped with magnetic nanoparticles. Nanoparticles of Fe, Co, Co(II,III) oxide, Ni and Ni/Ag mixture in 2-propanol were synthesized by chemical liquid deposition and the incorporation on the polymeric matrix was performed by solvated metal atom dispersion. Colloids and nanoparticles supported on chitosan were characterized by ultraviolet, Fourier-transform infrared, thermogravimetric analysis, electron diffraction X-ray and magnetic behaviour; transmission and field electronic scanning electron microscopy. The particle size distribution of colloids ranges from 6 to 50 nm with low particle stability due to flocculation after 120 days. The nanoparticles supported on chitosan had a particle size distribution of approximately between 10 and 80 nm, with low particle distribution; however, these particles do not flocculate because the matrix increases the stabilization of nanoparticles. All compounds present superparamagnetic behaviour at low temperature.
Percepciones sobre la diversidad sexual en adolescentes escolarizados de la ciudad de Cuenca
(2011) Palacios Madero, María Dolores; Pinos Vélez, Verónica Patricia; Pinos Abad, Guido Marcelo
Lesbian, gay, bisexual and transgender(LGBT) people are a minority group,whose recognition awakens emotional reactions, perceptions and attitudes;the majority with negative tendence. The perceptions and attitudes of rejection are due in large part to the prejudice against this group, which often leads to a stigmatizationof LGBT people. Assessment of the perceptions of adolescents towards LGBT individuals was the main purpose of the research.A survey, consisting of aseries of qualitative and quantitative questions offering the surveyed people the possibility of providing to the questions personal comments and observations, was applied to 1130 college students and 31 teachers. The students in general stated that it isincorrect mistreating LGBT people. They strongly perceive that family, school and especially the society as hostile environments for LGBT.Moreover, most of thesurveyed adolescents expressed serious concern that if they were LGBT, they would worry about the emotional reaction of family, friends, teachers and peers. In the worst case, they even expect being rejected by friends and peers, experience pressure from their family to change attitude, and likely be confronted by an indifferent attitude of their teachers as the latter usually seldom care about the personal situation of students. Given the widespread public opinion and the risk to become the target of strong negative attitudes some adolescents stated to be very reluctant to make public their sexual orientation. It is believed that for achieving social equity for LGBT people one has to work towards the liberation for the broader society from sexual oppression, requiring the initiation of a series of activities, such as the initiation of educational programs aiming de-ligitimization of the prejudice and the opening of people’s mind.

Browse

Browsing Publicaciones by Issue Date