Efficiency of city logistics activities suffers due to conflicting personal preferences and distributed decision making by multiple city logistics stakeholders. This is exacerbated by interdependency of city logistics activities, decision making with limited information and stakeholders’ preference for personal objectives over system efficiency. Accordingly, the key to understanding the causes of inefficiency in the city logistics domain is understanding the interaction between heterogeneous stakeholders of the system. With the capabilities of representing a system in a natural and flexible way, agent based modelling (ABM) is a promising alternative for the city logistics domain. This research focuses on developing a framework for the successful implementation of the ABM approach for the city logistics domain. The framework includes various elements – a multi-perspective semantic data model (i.e. ontology) and its validation, the development of an agent base model using this ontology, and a validation approach for the agent-based model. Conclusively, the framework shows that a rigorous course can be taken to successfully implement agent based modelling approach for the city logistics domain.
In this research, which is part of my PhD research into the influence of the use of social media in higher education, I have lessened the amount of variables, from Tinto’s integration theory. By including only the best-proven predictive variables, based on previous studies, I avoid the capitalization of chance and have built a more easy to use model for teachers and management. The latent variable ‘satisfaction’ is constructed by using just a fraction of the original manifest variables. The simplified model is tested using principal component analysis (PCA), to prove its fit. Furthermore, to better suit students’ contemporary society in the developed world, the model is enriched with the use of social media, in this case Facebook. The purpose of Facebook use (information, education, social and leisure) and the use of different pages amongst students were also measured with PCA. This provided a better insight in the integration/engagement components, which are also included in the new model. According by the measurements of Cronbach’s alpha and Guttman’s lambda-2, the new components showed internal consistency and reliability. In addition, SPSS AMOS was used for testing the fit of the model and showed reasonable values for the normed fit index (NFI), the comparative fit index (CFI), the Tucker-Lewis Index (TLI) and the root mean square error of approximation (RMSEA). This study will compare different background variables within the model to uncover the possible influences upon students’ attrition (and therefor also their success), engagement/satisfaction and social media use. Ultimately this paper will provide jet another piece to the puzzle for a better insight into the factors of students’ attrition and/or success.
The present study deals with the numerical modelling of hybridlaminated composites, which can be proved especially useful in theengineering and maintenance of advanced aerospace primary structures. Thelamina is comprised of continuous carbon fibers, thermosetting epoxypolymer matrix, as well as carbon nanostructures, such as graphene orcarbon nanotubes, inclusions. Halpin-Tsai equations combined with resultsobtained from nanomechanical analysis are employed in order to evaluatethe elastic properties of the carbon nanostructure/polymer matrix. Then, theobtained elastic properties of the hybrid matrix are used to calculate theorthotropic macro-mechanical properties of the unidirectional compositelamina. A hybrid composite plate is modelled as a 2D structure via theutilization of 4-node, quadrilateral, stress/displacement shell finite elementswith reduced integration formulation. The convergence and analysisaccuracy are tested. The mechanical performance of the hybrid compositesis investigated by considering specific configurations and applyingappropriate loading and boundary conditions. The results are compared withthe corresponding ones found in the open literature, where it is possible.
