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"Garzón, Luis"
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Analysis of Acoustic and Perceptual Variables in Three Heritage Churches in Quito Using Structural Equation Modeling
Acoustic quality is one of the aspects that contribute to the heritage of cultural and religious spaces. It is increasingly common to find scientific literature detailing the sound characteristics of places of worship, especially those with cultural and historical significance. This article presents a comprehensive acoustic characterization of three colonial heritage churches in Quito. It examines the relationship between objective and subjective parameters that influence the valuation of a space or sound environment. To analyze this relationship, we employed structural equation modeling (SEM) to evaluate three latent variables using perceptual acoustic indicators. The SEM results highlighted significant associations between physical acoustic parameters, emotional responses, and evaluative judgments, underscoring that traditional intelligibility metrics alone may not fully capture acoustic quality in these contexts. These findings provide a robust interdisciplinary framework that spans objective measures and human perception, offering valuable guidance for future heritage conservation efforts.
Journal Article
Comparative Mechanical Response of PLA Nanocomposites Reinforced with Multi-Walled Carbon Nanotubes and Halloysite Nanotubes Processed by Injection Moulding
Polylactic acid (PLA) is a biodegradable polymer with an ever-increasing number of applications, although its inherent brittleness limits its performance somewhat in structural applications. In this study, we analysed the influence of incorporating multi-walled carbon nanotubes (MWCNTs) and halloysite nanotubes (HNTs) at different concentrations (0.5, 0.75 and 1 wt%) on the mechanical properties of injection-moulded PLA nanocomposites. The effects of the nanofillers were characterised by tensile, flexural, and impact tests, hardness measurements, and FESEM examination. The results showed that MWCNTs increased the flexural strength and stiffness by up to 60% compared to neat PLA (84.3 vs. 52.6 MPa), although this was accompanied by a reduction in elongation at break (from 2.30% to 1.57%) due to agglomeration. Conversely, HNTs improved the elongation at break up to 6.39%, enhanced flexural strength by approximately 62% (85.1 MPa), and maintained stiffness around 3.0 GPa, indicating a better balance between strength and ductility. The FESEM micrographs confirmed the presence of clusters in MWCNTs and a more homogeneous dispersion in HNTs, thus explaining the differences in behaviour. Overall, MWCNTs are more suitable for applications requiring high stiffness and strength, whereas HNTs are preferable when greater ductility and impact resistance are required.
Journal Article
Study of thermal and rheological properties of PLA loaded with carbon and halloysite nanotubes for additive manufacturing
Purpose
This paper aims to propose using polylactic acid (PLA) as an alternative to nanocomposites in additive manufacturing processes in fusion deposition modelling (FDM) systems and describe its thermal and rheological conditions with multi-wall carbon nanotube (PLA/MWCNT) and halloysite nanotube (PLA/HNT) composites for possible applications in additive manufacturing processes.
Design/methodology/approach
PLA/MWCNTs and PLA/HNTs were obtained through fusion in a co-rotating twin-screw extruder. PLA was mixed with different percentages of MWCNTs and HNTs at concentrations of 0.5 Wt.%, 0.75 Wt.% and 1 Wt.%. Differential scanning calorimetry (DSC) and capillary rheometry were used to characterise these products, together with an analysis of the melt flow index (MFI).
Findings
The DSC data revealed that the nanocomposites had a glass transition temperature Tg = 65 ± 2°C and a melting temperature Tm = 169 ± 1°C. The crystallisation temperature of PLA/MWCNTs and PLA/HNTs was between 107 ± 2°C and 129°C, respectively. The viscosity data of PLA/MWCNTs and PLA/HNTs obtained by capillary rheometry indicated that the viscosity of the materials is the same as that of neat PLA. These results were confirmed by the higher fluidity index in the MFI analysis.
Originality/value
This paper presents an alternative for the applications of nanocomposites in additive manufacturing processes in FDM systems.
Journal Article
Effect of Maleinized Linseed Oil (MLO) on thermal and rheolological properties of PLA/MWCNT and PLA/HNT nanocomposites for additive manufacturing
Purpose
This paper aims to describe the influence of maleinized linseed oil (MLO), when used as a lubricant, on the thermal and rheological properties of PLA/MWCNTs (polylactic acid/multi-walled carbon nanotubes) and PLA/HNT (halloysite nanotubes) nanocomposites, as a reference for application in 3D printing processes.
Design/methodology/approach
Nanocomposites were obtained by melting in a twin-screw extruder, mixing PLA with MWCNTs and HNTs in different percentages of 0.5, 0.75 and 1 Wt.% for subsequent mixing by the same process with 5 phr MLO, for application in additive manufacturing, as analyzed by means of differential scanning calorimetry (DSC), capillary rheometry, melt flow rate (MFL) and field emission scanning electron microscopy (FESEM).
Findings
The results obtained for thermal characterization by using DSC indicate the non-variation of glass transition temperature Tg = 62 ± 2°C and a melting temperature (Tm) around 170°C. Crystallization temperature dropped by approximately 12°C, which should be kept in mind during the transformation processes. The values obtained by capillary rheometry indicate that the material’s viscosity is reduced by the influence of the MLO plasticizer’s lubricant effect on the PLA’s molecular structure. The melt flow index values confirm a rise of approximately 46% in the flow index and back up the capillary rheometry results. The values obtained were as follows: PLA/0.5 Wt.% MWCNT/MLO 5 phr 54.07, PLA/0.75 Wt.% MWCNT/MLO 5 phr 53.46, PLA/1 Wt.% MWCNT/MLO 5 phr 51.84y PLA/0.5 Wt.% HNT/MLO 5 phr 61.8, PLA/0.75 Wt.% HNT/MLO 5 phr 68.3 and PLA/1 Wt.% HNT/MLO 5 phr 71.2 g/10 min. Apart from the nanocharge distribution, the information obtained from the FESEM shows the existence of a cluster, which could have been avoided by more energetic stirring during the nanocompound manufacturing process.
Social implications
This paper presents an analysis of the insertion of plasticizer in nanocomposites for the application in additive manufacturing processes in fusion deposition modelling (FDM) system.
Originality/value
This is a novel original research work.
Journal Article
An artificial-vision- and statistical-learning-based method for studying the biodegradation of type I collagen scaffolds in bone regeneration systems
This work proposes a method based on image analysis and machine and statistical learning to model and estimate osteocyte growth (in type I collagen scaffolds for bone regeneration systems) and the collagen degradation degree due to cellular growth. To achieve these aims, the mass of collagen -subjected to the action of osteocyte growth and differentiation from stem cells- was measured on 3 days during each of 2 months, under conditions simulating a tissue in the human body. In addition, optical microscopy was applied to obtain information about cellular growth, cellular differentiation, and collagen degradation. Our first contribution consists of the application of a supervised classification random forest algorithm to image texture features (the structure tensor and entropy) for estimating the different regions of interest in an image obtained by optical microscopy: the extracellular matrix, collagen, and image background, and nuclei. Then, extracellular-matrix and collagen regions of interest were determined by the extraction of features related to the progression of the cellular growth and collagen degradation (e.g., mean area of objects and the mode of an intensity histogram). Finally, these critical features were statistically modeled depending on time via nonparametric and parametric linear and nonlinear models such as those based on logistic functions. Namely, the parametric logistic mixture models provided a way to identify and model the degradation due to biological activity by estimating the corresponding proportion of mass loss. The relation between osteocyte growth and differentiation from stem cells, on the one hand, and collagen degradation, on the other hand, was determined too and modeled through analysis of image objects’ circularity and area, in addition to collagen mass loss. This set of imaging techniques, machine learning procedures, and statistical tools allowed us to characterize and parameterize type I collagen biodegradation when collagen acts as a scaffold in bone regeneration tasks. Namely, the parametric logistic mixture models provided a way to identify and model the degradation due to biological activity and thus to estimate the corresponding proportion of mass loss. Moreover, the proposed methodology can help to estimate the degradation degree of scaffolds from the information obtained by optical microscopy.
Journal Article
Thermo-Mechanical and Fungi Treatment as an Alternative Lignin Degradation Method for Bambusa oldhamii and Guadua angustifolia Fibers
Different strategies have been used to degrade the molecular structure of lignins in natural fibers. Both chemical and biological processes can obtain different types of lignins for industrial use. In this study, a variation of the spectral intensity of the thermo-mechanical and fungi-modified Bambusa oldhamii (giant bamboo) and Guadua angustifolia Kunt fibers were examined via Fouriertransform infrared spectroscopy. The giant bamboo and Guadua angustifolia Kunt specimens were modified using a non-chemical alternative steam pressure method for degrading lignins, followed by mechanical sieving to obtain fibers of different lengths. The obtained fibers were treated with the Fusarium incarnatum-equiseti MF18MH45591 strain in a 21 d degradation process. The samples were subjected to Fouriertransform infrared spectroscopy before and after the strain treatment. The intensity variation was found to be in the spectral range of 1200 cm−1 to 1800 cm−1, in which lignin components are commonly found in most plant species. A multivariate analysis of the principal components of the treated and untreated control samples confirmed the changes in the spectral region of interest, which were associated with the thermo-mechanical and fungal treatment.
Journal Article
Justicia transicional, paso del caos a la democracia. Justicia restaurativa, ¿su insignia?
La justicia transicional y la justicia restaurativa, que cuentan con estándares internacionales ya delineados, al menos en su concepto multidimensional son propias de sociedades complejas, diversas, móviles, significativas, pero no encajan en la sociedad colombiana, que insiste en instituciones y estructuras estáticas, hobbesianas, tradicionales y moralmente monistas. De acuerdo con estudios publicados en mayo de 2021, Colombia tiene un alto nivel de impunidad y uno de los más altos índices de criminalidad organizada del planeta. La ley procesal penal de 2004 y el Acuerdo de Paz de 2016 establecen la justicia restaurativa, pero la modalidad de justicia transicional que se aplica es la retributiva. En este estudio se pudo demostrar que, aforismos como: “Justicia transicional: paso del caos a la democracia” o “Justicia restaurativa: insignia de la justicia transicional”, no se pueden aplicar de forma absoluta. La investigación revela que hace falta un giro ontológico y epistemológico que dinamice las estructuras tradicionales dominantes, con aquellas novedosas tendencias sociales, políticas y jurídicas.
Journal Article
Northwesternmost records of Vampyressa thyone Thomas, 1909 (Chiroptera, Phyllostomidae) from Sierra de Atoyac, Guerrero, México
We report new northwesternmost records of the Northern Little Yellow-eared Bat, Vampyressa thyone Thomas, 1909 (Phyllostomidae, Stenodermatinae), from Sierra de Atoyac, Guerrero, Mexico. We identified four individuals using morphological characters; two of the individuals were collected at 1,234 and 1,285 m above sea level, altitudes atypical for this species. Captures were recorded between 19:20 and 23:18 h, and all individuals presented signs of reproductive activity. With these data, we increase the scarce knowledge about this rare frugivorous bat.
Journal Article
Temperature Dependence of Solubility for Ibuprofen in Some Organic and Aqueous Solvents
The thermodynamic functions—Gibbs energy, enthalpy, and entropy of solution—were evaluated from the solubilities of ibuprofen determined at several temperatures in the pure solvents: octanol, isopropyl myristate, chloroform, cyclohexane, and water. The organic solvent-saturated aqueous media and water-saturated organic solvents were also studied, except for cyclohexane. In aqueous media, the solubility was determined at pH = 7.4 and an ionic strength 0.15 mol-L−1 (physiological values). The excess Gibbs energy and the activity coefficients of the solutes were also determined. The solubilities are higher in organic media such as chloroform and octanol than in aqueous media and cyclohexane.
Journal Article