This paper presents a systematical and progressive appraisal of the technology since the inception of AC-AC conversion, which is seen to be an indispensable and vital for the advancement of the Solid State Transformer (SST) in a distribution system. Special attention is given to the concepts/topologies and architecture of the SST, the DC-DC conversion devices in the isolation facet, the inversion gadget in the bridge arrangement and their integration in the development of an economically viable and efficient SST design. For the purpose of this article, a number of research papers, research proposals and research dissertations/studies have been accessed that mostly cover work related to this device and brief discussions about several aspects. The various sections of this article are correspondingly devoted to the review of SST design and its various configurations, the significant stages of the DC-DC converter from a transformer-specific perspective and lastly the high-frequency inverter. In critical appraisal, the SST in a three-stage perspective, the dual half-bridge converter and high-frequency half-bridge inverter are the most viable and promising means, offering tremendous advantages over other configurations with emphasis on economy, high flexibility and control performance; thereby weighed as the most workable, practical and realistic solutions. The foremost potential application of this expedient includes a vital component of the power grid.

Access control management is an important area of research within the security field. Several models have been proposed to manage the access rights of users over restricted resources, which are mainly based on defining rules between specific entities and concrete resources. Though these approaches are enough to manage organizations involving a limited number of entities and resources, the specification of rules or constraints for large and heterogeneous scenarios may imply a considerable burden to the administrators. To palliate this problem, we propose a generic ontology-based solution to manage the access control that can greatly simplify and speed up the definition of rules in complex scenarios and that can also improve the interoperability between heterogeneous settings. Moreover, we show its potential by applying it in two highly dynamic and large scenarios, i.e., Online Social Networks (OSNs) and the Cloud.

In online social networks (OSN), users quite usually disclose sensitive information about themselves by publishing messages. At the same time, they are (in many cases) unable to properly manage the access to this sensitive information due to the following issues: i) the rigidness of the access control mechanism implemented by the OSN, and ii) many users lack of technical knowledge about data privacy and access control. To tackle these limitations, in this paper, we propose a dynamic, transparent and privacy-driven access control mechanism for textual messages published in OSNs. The notion of privacy-driven is achieved by analyzing the semantics of the messages to be published and, according to that, assessing the degree of sensitiveness of their contents. For this purpose, the proposed system relies on an automatic semantic annotation mechanism that, by using knowledge bases and linguistic tools, is able to associate a meaning to the information to be published. By means of this annotation, our mechanism automatically detects the information that is sensitive according to the privacy requirements of the publisher of data, with regard to the type of reader that may access such data. Finally, our access control mechanism automatically creates sanitized versions of the users' publications according to the type of reader that accesses them. As a result, our proposal, which can be integrated in already existing social networks, provides an automatic, seamless and content-driven protection of user publications, which are coherent with her privacy requirements and the type of readers that access them. Complementary to the system design, we also discuss the feasibility of the system by illustrating it through a real example and evaluate its accuracy and effectiveness over standard approaches.

In 5G cellular communication systems, achieving low latency is crucial to support the ‘tactile’ Internet with response times of less than one millisecond. Traditional initial synchronization methods face challenges due to high delays. This manuscript presents a novel approach using an EXtrinsic Information Transfer (EXIT) chart-aided method to investigate the concurrence of $m$ -sequences using Iterative Soft Sequence Estimation (ISSE) in a communication channel. The ISSE technique leverages the concept of an Automatic Gain Controller (AGC), which gradually increases the gain as the number of chips in the $m$ -sequence generator grows, both at the transmitter and the receiver. Our ISSE method stands out by achieving sequence synchronization at the receiver with as few as $F$ successive chips for a sequence of ( $2^{F}-1$ ) chips. We base our work on the EXIT chart, eliminating the need for interleavers, which introduce transmission delays. To address the delay issue, we exploit the inherent interrelationship of the $m$ -sequence generator’s concern chips, which have a duration of ( $2^{F}-1$ ), as influenced by the Linear Feedback Shift Register (LFSR) in our ISSE model. We observe that low-order Primitive Polynomials (PPs) exhibit lower Erroneous Loading Probability ( $P_{e}$ ) than higher-order PPs at a specific Signal-to-Noise Ratio (SNR). PPs with identical order but fewer connection taps outperform those with more connection taps. The EXIT chart analysis reveals that lower-order PPs exhibit a larger opening tunnel between the outer and inner curves, resulting in higher achievable rates in our proposed system. Moreover, PPs with lower order achieve higher Mutual Information (MI) more efficiently with the assistance of our ISSE system compared to higher-order PPs.