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Self-Assembly behavior of amphiphilic janus dendrimers in water: a combined experimental and coarse-grained molecular dynamics simulation approach(Instituto Tecnológico y de Estudios Superiores de Monterrey, 2018-05-14)Amphiphilic Janus dendrimers (JDs) are repetitively branched molecules with hydrophilic and hydrophobic components that self-assemble in water to form a variety of morphologies, including vesicles analogous to liposomes with potential pharmaceutical and medical application. To date, the self-assembly of JDs has not been fully investigated thus it is important to gain insight into its mechanism and dependence on JDs’ molecular structure. In this study, a series of amphiphilic JDs with variations in their core and branching pattern was synthesized and its aggregation behavior in water was evaluated using experimental and computational methods. JDs were obtained from 2,2-bis(hydroxymethyl)propionic acid, myristic acid and different glycols. Dispersions of JDs in water were carried out using the thin-film hydration, solvent injection methods and by microfluidics, using double emulsion drops with ultrathin shells as templates. Furthermore, a coarse-grained molecular dynamics (CG-MD) simulation was performed to study the mechanism of JDs aggregation. The resulting assemblies were characterized by optical microscopy, dynamic light scattering, confocal microscopy, and atomic force microscopy. The obtaining of assemblies in water with no interdigitated bilayers was confirmed by the experimental characterization and CG-MD simulation for one of the dendrimers. Assemblies with dendrimersome characteristics were obtained using the solvent injection method. Also, monodisperse nanometric assemblies were obtained by this method. The use of microfluidics enables the production of giant dendrimersomes from highly hydrophobic JDs, even when the dendrimers did not form vesicles using the thin-film hydration method. The results of this study establish a relationship between the molecular structure of the JDs and the properties of its aggregates in water. These results could be relevant for the design of novel JDs with tailored assemblies suitable for drug delivery systems. In addition, this study offers an approach to produce dendrimersomes in a more controlled way.
Capital structure in publicly held family firms: a behavioral agency theory analysis(Instituto Tecnológico y de Estudios Superiores de Monterrey, 2018-05-24)This dissertation proposes behavioral agency theory as a theoretical approach that, through its family firm variant (socioemotional wealth), can offer an alternative explanation for the capital structure decisions of family firms. Behavioral agency theory states that individuals frame their problems by comparing anticipated outcomes to a reference point: when the framed prospects are positive, decision makers will exhibit risk-averse preferences; and when the framed prospects are negative they will exhibit risk-seeking preferences (Wiseman & Gomez-Mejia, 1998). To accomplish the purpose of the study, this dissertation proposes a conceptual model and presents and tests, using econometric techniques, the derived research hypothesis using a sample constituting publicly held Mexican firms from 2012 to 2017. The conceptual model proposes that, in order to make decisions, family principals take into account both financial and socioemotional wealth, using a mixed gamble perspective (Gomez-Mejia, et al., 2015; Gomez-Mejia, Campbell, Martin, Hoskisson, Makri, and Sirmon, 2013). Under a mixed gamble perspective, firms take their decisions by weighting the preservation of current socioemotional endowment versus future financial wealth. Preserving socioemotional wealth is a high priority for family firms. In terms of capital structure, higher levels of leverage imply preserving current socioemotional endowment, because higher levels of leverage contribute to preserving control in the hands of the family (Ellul, 2009), which is one of the most important objectives of socioemotional wealth (Berrone, et al., 2012). In contrast, preserving future financial wealth means incurring lower levels of leverage, because this reduces the risk of financial distress (Anderson, Mansi, & Reeb, 2003) The results of this dissertation show that family firms are more leveraged than non-family firms, as they want to keep the control in the hands of the family. There is a negative relationship between family ownership and leverage because as family ownership increases, the overlapping between business and family spheres increases, so family firms will be more willing to preserve their financial wealth through lower levels of leverage. Family generation weakens the negative relationship between family ownership and leverage, whereas the variable, family members, strengthens this relationship. Implications for the Mexican context are also discussed
OntoOAI : modelo semántico para el descubrimiento selectivo de conocimiento sobre contenidos estructurados con OAI-PMHEl principio fundamental en la Web es la comunidad abierta: cualquiera puede contribuir sus ideas al todo. Esta apertura a la colaboración, su flexibilidad y tolerancia son factores que le han permitido convertirse en un recurso universal. Sin embargo, la masa creciente, dinámica y muchas veces poco estructurada de información en la Web impone retos importantes, uno de ellos: el descubrimiento de conocimiento. El descubrimiento de conocimiento, uno de los productos finales más interesantes de la computación, resulta particularmente relevante en la tarea de un investigador, profesor o alwnno, que usan la información científica para su quehacer profesional. Entre los esfuerzos que se han dado para organizar y estructurar la masa de datos, se ubica el Protocolo para Cosecha de Metadatos de la Iniciativa de Archivos Abiertos (OAIPMH ), estándar para los repositorios de información científica y académica.