Abstract This paper investigated the formation of crosslinks in natural rubber compounds in the vulcanization systems: conventional (CV), semi-efficient (SEV), and efficient (EV), processed with three types of accelerators: MBTS (dibenzothiazole disulfide), TMTD (tetramethylthiuram disulfide) and CBS (n-cyclohexyl 2-benzothiazole sulfenamide). The cross-linked densities were determined by organic solvent swelling, dynamic mechanical analysis (DMA), stress vs strain, and low-field nuclear magnetic resonance, the latter being the reference technique for comparison with the other results. It was found that the choice of accelerator type influences the processing time and the cross-linked density of the vulcanizate. The four techniques showed close values of cross-linked density for natural rubber compounds, demonstrating that the analytical techniques studied can be applied to determine cross-linked density.

Abstract Objective: to investigate whether the caloric and protein deficits, the diagnosis and the NUTRIC score, behaved as risk factors associated to the survival time. Methods: prospective study with 82 critically ill patients in intensive care unit (ICU), with exclusive enteral nutritional therapy (EENT). We investigated the calorie and protein deficiencies of EENT, the NUTRIC score, and the inflammatory-nutritional index by the C-reactive protein-CRP/albumin. The data were analyzed using the Chi-square, Fisher, Mann-Whitney, Kruskal-Wallis, univariate and multiple Cox regressions and the Kaplan-Meyer method. Results: in the univariate Cox regression, one-year increase in age increased the risk of death by 4.1% (p=0.0009; HR=1.041) and one-day increase with intercurrent events, by 1.8% (p = 0.0485; HR = 1.018). In the multiple Cox regression, the clinical diagnosis (p = 0.0462, HR = 2.091) and the NUTRIC score ≥ 5 (p < 0.0001; HR = 5.740) were the variables that together were associated with the survival time. The critical caloric and protein deficits did not behave as death risk factors in this population. Kaplan-Meier curves showed that the probability of survival in 40 days was 28.1% with clinical diagnosis and 40.2% with surgical diagnosis. The mean survival time with NUTRIC score ≥ 5 was 17.4 days. The probability of survival at 40 days was 72.8% with NUTRIC score < 5 and 6.4% with NUTRIC score ≥ 5. Conclusion: caloric and protein deficits are not risk factors for mortality. Only the diagnosis and the NUTRIC score were considered risk factors associated with the survival time.

Resumen Introducción: la hipovitaminosis D tiene una prevalencia del 50,4% en personas mayores, población en aumento a nivel mundial, en la cual la deficiencia de vitamina D (< 30 mg/dl) podría ser un factor de riesgo para disminuir la sobrevida de esta población. Objetivo: determinar si niveles séricos de vitamina D menores a 30 ng/ml tienen impacto en la sobrevida, medida a través de la mortalidad general y por causas específicas, considerando un periodo de seguimiento de nueve años en personas mayores autovalentes con capacidades cognitivas adecuadas. Método: corresponde a un estudio retrospectivo longitudinal, con un seguimiento de nueve años. Se realizó el seguimiento a 418 personas mayores de la comuna de Santiago, los cuales fueron incorporados el año 2004 para participar en un estudio referente a la suplementación de vitamina D y fuerza muscular. Resultados: niveles de vitamina D bajo 30 ng/dl aumentan en casi tres veces la probabilidad de fallecer (OR = 2,77; IC = 1,81-3,85), mientras que igual nivel de vitamina D se asocia a un doble riesgo de morir por causas cardiovasculares (OR = 1,78; IC = 1,21-2,09) en el modelo no ajustado. Para la mortalidad por cáncer y por caídas no se obtuvo ningún resultado significativo. La vitamina D no actuaría como factor protector ante la mortalidad. Conclusión: el poseer niveles de vitamina D bajo 30 ng/dl podría ser un factor de riesgo de mortalidad general.

In this study we have explored the behavior and the damage mechanisms of a laminate panel composed of polymeric and ceramic materials, submitted to the impact of a metallic projectile. The design of a system with the impact side in ceramic material (SiC) was made, with a support of an ultra-high molecular weight polyethylene (UHMWPE), plaques made with 200 mm square geometry and 5 mm thick, and polymeric tissue cuts with equal area dimensions. The (NIJ) Standard 0101.06 was taken as reference for testing the ballistic impact essay; crater formation was identified in the ceramic material; using optical microscopy and scanning fractures and delamination were identified as predominant failure mechanisms; in the polymeric material, fibrillation twist, fiber fusion, conical deformation and delamination were observed and then samples were analyzed using "Morye, Smith and Retch e Ipson" kinetic energy balance models. The result showed that the most influential to dissipate energy, is the panel made with dual ceramic plate (SiC) and double-layer polymeric tissue as a backup.

En este trabajo se exploró el comportamiento y los mecanismos de daño de un panel laminado compuesto a partir de materiales poliméricos y cerámicos, ante el impacto de un proyectil metálico. Se realizó el diseño de un sistema con la cara de impacto en material cerámico (SiC), con respaldo elaborado en polietileno de peso molecular ultra alto (UHMWPE), placas elaboradas con geometría cuadrada de 200 mm de lado y 5 mm de espesor, y cortes de tejido polimérico con iguales dimensiones de área. Se tomó como referencia el montaje de la norma (NIJ) Standard 0101.06 para el ensayo a impacto balístico; en el material cerámico se identificó la formación de cráter, fracturas y delaminación como mecanismos de falla predominantes, utilizando microscopia óptica y de barrido; en el material polimérico se observó fibrilación, torsión, fusión de fibras, delaminación y deformación cónica y posteriormente se analizaron las muestras empleando los modelos de balance de energía cinética de "Morye, Smith y de Retch e Ipson". El resultado evidenció que el arreglo con mayor influencia para disipar energía, es el panel elaborado con doble placa cerámica (SiC) y doble capa de tejido polimérico como respaldo.