Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

The influence of environmental conditions on wood material properties is known. Temperature is one of them and its effect on poplar wood has been examined in a limited way which this study tried to figure out this issue in a limited context. The influence of heat treatment (110 °C, 160 °C, and 210 °C for 3 h and 6 h) on the density, ultrasonic wave velocity, modulus of rupture, and modulus of elasticity of poplar wood was evaluated. A 2,25 MHz longitudinal ultrasonic wave was used to determine both the ultrasonic wave velocity and the dynamic modulus of elasticity. A three-point bending test was conducted to determine the static modulus of elasticity and the modulus of rupture. The average values for the control samples were 350 kg/m³ for density, 3 598 m/s for ultrasonic wave velocity, 4 552 MPa for dynamic modulus of elasticity, 5 864 MPa for static modulus of elasticity, and 64,1 MPa for modulus of rupture. When samples were treated at 210 °C for 6 h, these properties decreased by 14,3 %, 3 %, 18,7 %, 25 %, and 50,2 %, respectively. In general, the dynamic modulus of elasticity values were lower than the static ones across all treatment conditions. The greatest difference between dynamic and static modulus (34 %) was observed at 110 °C for 6 h, while the smallest difference (18,8 %) occurred at 210 °C for 6 h. Improvements of up to 8,9 %, 2,4 %, and 0,85 % were observed in the modulus of rupture, static modulus of elasticity, and ultrasonic wave velocity, respectively, at 110 °C treatments.

In Brazil, thermal and electric power generation from wood chips and agroforestry residues has expanded in regions favored by biomass availability and transportation logistics. Globally, wood stands out as a strategic renewable source, with potential for integration into cogeneration systems to enhance energy efficiency. The development and selection of new genotypes that meet the requirements for forest productivity and wood quality are important strategies for companies aiming to ensure a wood supply for bioenergy. The primary objective of this study was to investigate the differences in energy potential of new Corymbia and Eucalyptus clones intended for direct combustion in thermal and electrical energy cogeneration systems. We utilized the Scott-Knott hierarchical cluster analysis to classify the genetic materials based on the similarity of the evaluated properties. The study analyzed 16 genotypes of Corymbia spp., Eucalyptus spp., and their hybrids. In each treatment, corresponding to a genotype, three trees were harvested at 81 months of age with a medium diameter, spaced 6 m x 1,5 m totaling 48 sample units. We determined the basic and energy densities, elemental chemical composition, higher, lower, and useful heating values, and available energy. Among the Eucalyptus genus, clone 2 Eucalyptus cloeziana (gympie messmate) excelled in basic and energy densities, and useful heating value. Within the Corymbia hybrids and across all genetic materials evaluated, clone 4 exhibited the best performance in providing quality wood to meet the needs of bioenergy projects intended for thermal and electrical energy cogeneration systems. This superiority is attributed to its high basic and energy densities, available energy, and useful heating value, coupled with the best results in the combined analysis of average annual increase and wood dry weight increase.

El conocimiento de la variación anatómica y física de la madera es esencial para comprender su calidad y comportamiento tecnológico. En Pinus montezumae, especie de importancia ecológica y económica en México, la falta de información sobre la relación entre las características morfométricas de las traqueidas y la densidad básica limita la evaluación objetiva de su calidad. La predicción de variables anatómicas a partir de la densidad básica representa una alternativa eficiente que reduce tiempo y recursos. El objetivo del estudio fue evaluar la variación radial de las dimensiones de las traqueidas y la densidad básica de la madera de P. montezumae y generar modelos de predicción para las variables morfométricas. Se analizaron 42 árboles mediante muestras de barreno obtenidas a 1,30 m de altura. Se observaron patrones radiales con tendencia creciente de médula a corteza para la densidad básica, longitud total, diámetro total y espesor de pared celular de las traqueidas, mientras que el diámetro de lumen presentó un comportamiento irregular. Se obtuvieron correlaciones positivas entre la densidad básica y las variables morfométricas (R2= 0,90- 0,95), siendo la densidad básica un buen predictor de la longitud, diámetro total y espesor de la pared celular de las traqueidas.

The research responds to the limited availability of technical data on native Brazilian woods, which constrains their industrial application and sustainable management. The commercial use of timber from native Brazilian species is hindered by a scarcity of data on fundamental properties related to wood quality, limiting its use in the wood industry. This study sought to characterize the timber of ten native Brazilian species using X-ray densitometry and colorimetric analysis. Timber samples of various ages and 2 mm thickness were evaluated. The X-ray images enabled the identification of anatomical characteristics such as wood porosity and parenchyma. Densitometric profiles showed woods with high densities (ranging between 550 kg/m³ and 1000 kg/m³). Variations were identified in each sample due to transitions between earlywood and latewood, with latewood presenting higher density, and parenchyma and pore areas showing lower density values. Standard deviation values ranging from 84,6 (Tabebuia) to 162,8 (Bowdichia) indicated differing homogeneity in wood density across the samples. Colorimetric characterization using the CIELAB system allowed the identification of desirable visual characteristics, with species ranging from lighter (L*46,7) to darker (L*25,7) tones and significantly different colors from yellow to purple. Thus, the techniques used in this study proved effective in characterizing native timber through novel analytical methods, contributing to their better utilization.

The construction industry has been seeking materials that have a lower impact on the built environment. For this reason, wood has become an attractive option due to its natural and renewable properties. In the Northeast region of Brazil, the Caatinga biome stands out for its biodiversity as the only entirely national biome. However, the physical and mechanical properties of local tree species are poorly investigated, limiting potential uses as construction material. Therefore, this study aims to characterize the jurema preta Mimosa tenuiflora (jurema preta) species, native to the Caatinga biome, and indicate potential uses in civil construction. To this end, physical tests were conducted to determine moisture content, basic density, bulk density, dimensional stability, thermal conductivity; mechanical tests for parallel-to-grain compression, parallel and perpendicular shear, parallel and perpendicular tension, Janka hardness parallel and perpendicular, and static bending were performed. The Shapiro-Wilk test and Pearson correlation were used between physical and mechanical properties. The results classify the wood in the D20 strength class, with mechanical properties that meet the standards required for civil construction, covering both light and heavy indoor applications.

Twelve elastic constants of Populus × canadensis, previously unavailable in the literature, were determined using ultrasonic testing.Samples were conditioned at a temperature of 20 °C ± 1 °C and 45 %, 65 %, and 85 % relative humidity. An Olympus EPOCH 650 flaw detector was used with V153-RM (1 MHz shear wave), and A133S-RM (2,25 MHz pressure wave) contact transducers. A contact medium was applied. Wave propagation times were measured along the principal directions (L, R, T), the main planes (LR, LT, RT, RL, TL, TR), and the off-axis planes (LR45°, LT45°, RT45°). Ultrasonic wave velocities were calculated across the specified directions and planes. These velocities were then used to estimate moduli (EL, ER, ET, GLR, GLT, GRT) and Poisson’s ratios (µLR, µLT, µRT, µRL, µTL, µTR) via stiffness matrix analysis. Moduli were also calculated using a simple formula multiplying the density and velocity for comparison. Elastic moduli derived from the stiffness matrix were substantially lower than those from the simple density–velocity formula, while shear moduli remained nearly identical. Both moduli steadily decreased with the increase in moisture content. Moisture content significantly affected all moduli. In contrast, Poisson’s ratios showed no consistent trend with moisture. Specifically, µLR and µRL increased linearly with moisture, while the other ratios decreased irregularly. For µRT, the effect of moisture was insignificant. Relationships between density and velocity, moduli, and Poisson’s ratios were assessed using coefficients of determination.The coefficients ranged from 0,23 to 0,56 for velocities, 0,08 to 0,37 for elasticity, 0,23 to 0,31 for shear, and 0 to 0,10 for ratios. When the coefficient was calculated within the humidity groups significant increases were observed. It was assumed that water-related increases in density did not reflect structural solidification, and therefore did not lead to improved elasric properties. This effect is explained by the well-known reduction in wave velocities caused by water, which dominates the calculations.    

Abstract In this paper, several practical methods for modeling and forecasting load demand in the ultra-short term are presented. The proposed methods are: ARIMA and Holt-Winters, which are used for future day demand forecasting, some practical considerations for ultra-short term time windows are evaluated. Load demand data from the National Interconnected System of Ecuador with 30 minute granularity is used for the implementation. An evaluation of the two forecasting methods in two different time contexts is also performed to determine their effectiveness and accuracy in each scenario. The ARIMA method has proven to be highly effective, since it has obtained successful results in the two time contexts evaluated.

In this work, we present for the first time an in-depth study of the relationship between the upper semi-B-Fredholm spectrum and the left Drazin spectrum. This connection leads to the definition of a new spectral property, denoted as (ggaz), which generalizes the previously studied property (gaz). Through the framework of local spectral theory, we derive several characterizations of operators that satisfy the (ggaz) property. Moreover, we demonstrate that the set of operators fulfilling this property constitutes a Banach space, highlighting the structural significance of (ggaz) in operator theory.Key words: Property (gaz), Property (ggaz), semi-B-Fredholm operator, Left-Drazin Operator, SVEP..

Esta investigación tiene como objetivo determinar cuales son los factores que influyen en el abandono del control y tratamiento del asma en pacientes del Hospital Militar de División II D.E. “Libertad” diagnosticados con esta enfermedad durante el periodo 2004 – 2005, de forma específica se investiga cuales son los factores que causan que el paciente abandone el control y tratamiento del asma, además se pretende saber cuales son las características asociadas a este tipo de pacientes. Se utilizó como fuente principal de datos la historia clínica neumológica. Se conoce que un total de 366 pacientes presentaron asma del total de pacientes que acudieron al área de neumología durante este periodo. Se muestra los Análisis Univariados y Bivariados, Análisis de Correspondencias Múltiples o Análisis de Homogeneidad y el Análisis de Regresión Logística. Palabras Claves: Asma, Historia clínica neumológica, Factores que influyen en el control y tratamiento del asma, Análisis de Correspondencias Múltiples, Regresión Logística.

Las universidades presentan estructuras rígidas y son presionadas por el entorno cambiante, lo que afecta la calidad en ellas. Las Tecnologías de la Información (TI) son indiscutiblemente herramientas indispensables para generar ventaja competitiva. Es posible aprovechar las características de las TI y utilizar modelos de autoevaluación para mejorar la gestión de la calidad (Total Quality Management – TQM) en las universidades. Existen varios trabajos que establecen un enlace entre TQM y TI en las organizaciones. En cuanto al estudio de TQM en las universidades, existen varias propuestas pero no se especifica qué TI pueden ser utilizadas para apoyar la toma de decisiones. La Inteligencia de Negocios (Business Intelligence – BI) es un modelo que puede ser aplicado a instituciones de educación superior para mejorar la gestión de la calidad en ellas. En este trabajo se propone un modelo preliminar que implementa la sinergia de los modelos de BI y de TQM, tomando como punto clave la estrecha relación y las características similares que existen entre ellos. Este modelo sería aplicable principalmente en universidades latinoamericanas y sobretodo peruanas, dado las características particulares de éstas. La implementación del modelo permitiría la generación de ventajas competitivas en las universidades. Palabras Claves: inteligencia de negocios, calidad, gestión de la calidad total, universidades