The effect of tissue porosity on ion (sodium, potassium, and chloride) diffusivity in agarose gels and porcine intervertebral disc tissues was investigated using an electrical conductivity method. An empirical, constitutive model for diffusivity (D) of solutes in porous fibrous media was proposed: D/Do = exp[-alpha(r(s)/k(1/2))beta] where r(s) is the Stokes radius of a solute, kappa is the Darcy permeability of the porous medium, Do is the diffusivity in free solution, alpha and beta are two positive parameters whose values depend on material structure. It is found that alpha = 1.25 +/- 0.138, beta = 0.681 +/- 0.059 (95% confidence interval, R2 = 0.92, n = 72) for agarose gels and alpha = 1.29 +/- 0.171 and beta = 0.372 +/- 0.088 (95% confidence interval, R2 = 0.88, n = 86) for porcine annulus fibrosus. The functional relationship between solute diffusivity and tissue deformation was derived. Comparisons of our model prediction with experimental data on diffusion coefficients of macromolecules (proteins, dextrans, polymer beads) in agarose gels in the literature were made. Our results were also compared to the data on ion diffusivity in charged gels and in cartilaginous tissues reported in the literature. There was a good agreement between our model prediction and the data in the literature. The present study provides additional information on solute diffusivity in uncharged gels and charged tissues, and is important for understanding nutritional transport in avascular cartilaginous tissues under different mechanical loading conditions.

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A series of novel polyamides containing diacetylene groups as side chains were prepared by Cadiot-Chodkiewcz-coupling of polymer precursors bearing 2-propynyloxy side groups with 4-bromo-3-butyn-1-01. The conversion of the acetylenic groups was in the range of 87.5-96.5% depending on the chemical structure of the polymer backbone. The polymers are highly amorphous and undergo random cross-linking on heating. Thermally treated polymer films show third-order nonlinear optical susceptibility x (3) of the order of lo-'' esu (= lo-'* m5N2).

ResumenEl objetivo del artículo es analizar las actividades para el aprendizaje organizacional en medianas empresas. El artículo analiza las actividades de exploración y explotación de conocimiento. La investigación considera un estudio de tipo descriptivo, de campo, no experimental. Se aplicó un cuestionario de recolección de datos a una muestra de 44 medianas empresas en Valledupar, Colombia. Los resultados destacan la presencia de actividades de exploración y explotación de conocimiento en las empresas analizadas. Adicionalmente, los resultados indican que no existen diferencias significativas en el desarrollo de estas actividades en las empresas objeto del presente estudio. Palabras AbstractThe paper aims to analyze the activities for organizational learning in medium-size companies. This paper studies the activities of knowledge exploration and knowledge exploitation. The research considers a descriptive approach, of field type, and not experimental form. A data collection questionnaire was applied to 44 medium-sized companies in Valledupar, Colombia. The results highlight the strong presence of activities about knowledge exploration and knowledge exploitation in the companies analyzed. Additionally, the results indicate the absence of statistical differences in the development of these activities inside the companies analyzed in this work.

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El objetivo del presente artículo es analizar las redes de colaboración entre las Instituciones de Educación Superior (IES) en Colombia de acuerdo con el parámetro de “Top collaborating institutions” en ResearchGate. El artículo efectúa una comparación entre las redes de las Instituciones de Educación Superior acreditadas en alta calidad y las no acreditadas, de acuerdo con los lineamientos del Sistema Nacional de Acreditación en Colombia. El análisis de la colaboración institucional se realiza mediante la construcción de redes de trabajo conjunto, en el programa UCINET; se considera la primera universidad registrada en el “Top collaborating institutions” publicado en perfil de ResearchGate de cada Institución de Educación Superior. Los resultados demuestran que las instituciones acreditadas poseen una red de colaboración bien conectada e integrada. Por el contrario, las instituciones no acreditadas poseen una red de colaboración débil y poco interconectada. Además, las instituciones no acreditadas buscan colaborar principalmente con IES acreditadas y no entre ellas. De esta manera, los esfuerzos de las instituciones no acreditadas no están bien coordinados y se diluyen en la distribución de sus relaciones colaborativas.

Specific electrical conductivity, a material property of biological tissues, has been found to be greater in tumor tissue than in normal tissue on account of its higher water content [1]. Its value is related to water content, ion concentrations, and ion diffusivities within biological tissues [e.g., 1,2,3]. The variation in conductivity with water content is hypothesized to be related to the change in ion diffusivities [5,6]. The objective of this study is to investigate the relationship between conductivity and water content in hydrogels. The main goal is to develop a similar relationship for biological tissues and to understand deformation-dependent ion diffusivity in tissues under mechanical loading.