Marcos Calle

Deformability properties of timolol-loaded transfersomes based on the extrusion mechanism. Statistical optimization of the process

Abstract The purpose of this work was to analyze the deformability properties of different timolol maleate (TM)-loaded transfersomes by extrusion. This was performed because elastic liposomes may contribute to the elevation of amount and rate of drug permeation through the corneal membrane. This paper describes the optimization of a transfersome formulation by use of Taguchi orthogonal experimental design and two different statistical analysis approaches were utilized. The amount of cholesterol (F1), the amount of edge-activator (F2), the distribution of the drug into the vesicle (F3), the addition of stearylamine (F4) and the type of edge-activator (F5) were selected as causal factors. The deformability index, the phosphorous recovery, the vesicle size, the polydispersity index, the zeta potential and percentage of drug entrapped were fixed as the dependent variables and these responses were evaluated for each formulation. Two different statistical analysis approaches were applied. The better statistical approach was determined by comparing their prediction errors, where regression analysis provided better optimized responses than marginal means. From the study, an optimized formulation of TM-loaded transfersomes was prepared and obtained for the proposed ophthalmic delivery for the treatment of open angle glaucoma. It was found that the lipid to surfactant ratio and type of surfactant are the main key factors for determining the flexibility of the bilayer of transfersomes. From in vitro permeation studies, we can conclude that TM-loaded transfersomes may enhance the corneal transmittance and improve the bioavailability of conventional TM delivery.

A DTD for an XML-based mathematical modeling language

This paper contains a proposal for an XML-based modeling language aimed at operations research problems. It has been called Operations Research Markup Language (ORML). There are a number of mathematical modeling languages developed by different companies, but they are proprietary and each one has its own syntax. ORML tries to bring to this field the standardization and interoperability benefits of XML.

Impact of the customer demand on order fulfilment strategies based on floating decoupling point: a simulation analysis

Order Fulfilment Strategies have become more and more popular, thanks to their capability of improving the delivery times and reducing the inventory levels. Among the postponement strategies of Mass Customisation are the Virtual Build-To-Order (VBTO) and i-Virtual Build-To-Order (i-VBTO) systems which are two systems with the ability to serve customers from anywhere in the inventory (Work-in-Process and Finished Goods Inventory) showing an interesting potential of adaptation to the variability of the demand. This study is aimed at testing the suitability of the basis of the i-VBTO system against the VBTO system through the study of the influence of characteristics of demand that are common in real environments. Regarding the contribution of this work, some weaknesses of the VBTO system can be highlighted (e.g. under certain demand conditions it loses the efficiency), and some benefits of the i-VBTO system (e.g. it turns out to be more robust and stable regarding changes in demand than the VBTO system).

Job shop management of products under internal lifespan and external due date

Deteriorating items are found in a wide variety of productive environments and have been extensively reported in the literature. However, the evolution of markets demand the development of new products and new forms of work are made necessary to adapt production systems to those changes. The present work focuses on the production control of perishable products in a job shop environment. Specifically, in those products that have an expiration date within the production interval (internal caducity) that must be delivered before a certain date. As far as we know, there are no previous works that focus on the internal caducity of products at the production-control level. Two systems of different nature have been compared: Workload Control (WLC) and Kanban. WLC is usually a benchmark in job shop and made to order environments. Recent studies show that Kanban, traditionally used in JIT (Just in Time) environments, performs similarly or even better than WLC. The study was performed by discrete events simulation using Python© language, SimPy© and DEAP© modules, and considering several responses of the systems. The results show that both systems have a good performance in a variety of scenarios, with overall performance of Kanban in terms of internal caducity and tardy deliveries.

Genetic Neighborhood Search

The Genetic Neighborhood Search (GNS) is a hybrid method for combinatorial optimization problems. A main feature of the approach is the iterative use of local search on extended neighborhoods, where the better solution will be the center of a new extended neighborhood. We propose using a genetic algorithm to explore the extended neighborhoods. Computational experiences show that this approach is robust with respect to the starting point and that high quality solutions are obtained in reasonable time.