Component Lifecycle and Concurrency Model in Usage Control (UCON) System

Access control is one of the most challenging issues facing information security. Access control is defined as, the ability to permit or deny access to a particular computational resource or digital information by an unauthorized user or subject. The concept of usage control (UCON) has been introduced as a unified approach to capture a number of extensions for access control models and systems. In UCON, an access decision is determined by three factors: Authorizations, obligations and conditions. Attribute mutability and decision continuity are two distinct characteristics introduced by UCON for the first time. An observation of UCON components indicates that, the components are predefined and static. In this paper, we propose a new and flexible model of usage control for the creation and elimination of some of these components; for example new objects, subjects, attributes and integrate these with the original UCON model. We also propose a model for concurrent usage scenarios in UCON

Natural Dye-Sensitized Solar Cells: Fabrication, Characterization, and Challenges

Bio-inspired dye-sensitized solar cells (DSSCs) from natural plant-based dyes gained importance due to their low cost of manufacturing and environmental friendliness. Not all plants are candidates for DSCCs; they should contain certain pigments such as chlorophyll, anthocyanin, and betalains. Titanium oxide nanoparticles play an important role as electron transporter in the DSSCs. The efficiency is still low in comparison with traditional silicon-based solar cells. There are several challenges to improve the efficiency such as the photodegradation of the dye, the stability of the electrolyte over time, and adhesion of dye with titanium oxide nanoparticles. We reviewed methods for fabricating DSSCs, and the science behind the working principle. Various microscopic and spectroscopic analysis methods such as Fourier transform infrared spectroscopy and confocal microscopy were presented, for investigating optical properties, surface chemistry of the dyes, and in structural characterization of the plant cells. The photoelectrochemical properties such as conversion efficiency measure the performance of the DSSCs. They are usually in the range of 0.05–3.9% depending on the plant dye used, including plant dyes modified. A critical feature in the design of dye-sensitized solar cells is the attachment of the photosensitizing dye to the titanium oxide surface. We reviewed and summarized the design of binding elements that enhance the binding of the sensitizing dye to the titanium dioxide surface. The efficiencies of covalent linkage of the dye to the titanium surface versus non-covalent binding were discussed, including a survey of functional groups and geometries, to determine the most effective reported