Controller HIL testing of real-time distributed frequency control for future power systems

With the evolution of power system components and structures driven mainly by renewable energy technologies, reliability of the network could be compromised with traditional control methodologies. Therefore, it is crucial to thoroughly validate and test future power system control concepts before deployment. In this paper, a Controller Hardware in the Loop (CHIL) simulation for a real-time distributed control algorithm concept developed within the ELECTRA IRP project is performed. CHIL allows exploration of many real-world issues such as noise, randomness of event timings, and hardware design issues that are often not present on a simulation-only system. Octave has been used as the programming language of the controller in order to facilitate the transition between software simulation and real-time control testing. The distributed controller achieved frequency restoration with a collaborative response between different controllers very fast after the unbalanced area is located

Is There a Role for Adversariality in Teaching Critical Thinking?

Although there has been considerable recent debate on the topic of adversariality in argumentation, this debate has rarely found its way into work on critical thinking theory and instruction. This paper focuses on the implications of the adversariality debate for teaching critical thinking. Is there a role for adversarial argumentation in critical thinking instruction? Is there a way to incorporate the benefits of adversarial argumentation while mitigating the problems

HelexKids:a word frequency database for Greek and Cypriot primary school children

In this article, we introduce HelexKids, an online written-word database for Greek-speaking children in primary education (Grades 1 to 6). The database is organized on a grade-by-grade basis, and on a cumulative basis by combining Grade 1 with Grades 2 to 6. It provides values for Zipf, frequency per million, dispersion, estimated word frequency per million, standard word frequency, contextual diversity, orthographic Levenshtein distance, and lemma frequency. These values are derived from 116 textbooks used in primary education in Greece and Cyprus, producing a total of 68,692 different word types. HelexKids was developed to assist researchers in studying language development, educators in selecting age-appropriate items for teaching, as well as writers and authors of educational books for Greek/Cypriot children. The database is open access and can be searched online at www.helexkids.org

Throttling On-Disk Schedulers to Meet Soft-Real-Time Requirements ∗

Many contemporary disk drives have built-in queues and schedulers. These features can improve I/O performance, by offloading work from the system’s main processor, avoiding disk idle time, and taking advantage of vendor-specific disk characteristics. At the same time, they pose challenges for scheduling requests that have real-time requirements, since the operating system has less visibility and control over service times. While it may be possible for an operating system to obtain more predictable real-time performance by bypassing the on-disk queue and scheduler, the diversity and continuing evolution of disk drives make it difficult to extract the necessary detailed timing characteristics of a specific disk, and to generalize that approach to all hard drives. This paper demonstrates three techniques we developed in the Linux operating system to bound real-time request response times for disks with internal queues and schedulers. The first technique is to use the disk’s built-in starvation prevention scheme. The second is to prevent requests from being sent to the disk when real-time requests are waiting to be served. The third is to limit the length of the on-disk queue in addition to the second technique. Our results show the ability to guarantee a wide range of desired response times while still allowing the disk to perform scheduling optimizations. These techniques can be generalized to disks from different vendors

Modeling device driver effects in real-time schedulability analysis: Study of a network driver ∗

Device drivers are integral components of operating systems. The computational workloads imposed by device drivers tend to be aperiodic and unpredictable because they are triggered in response to events that occur in the device, and may arbitrarily block or preempt other time-critical tasks. This characteristic poses significant challenges in real-time systems, where schedulability analysis is essential to guarantee system-wide timing constraints. At the same time, device driver workloads cannot be ignored. Demand-based schedulability analysis is a technique that has been successful in validating the timing constraints in both single and multiprocessor systems. In this paper we present two approaches to demand-based schedulability analysis of systems that include device drivers. First, we derive load-bound functions using empirical measurement techniques. Second, we modify the scheduling of network device driver tasks in Linux to implement an algorithm for which a load-bound function can be derived analytically. We demonstrate the practicality of our approach through detailed experiments with a network device under Linux. Our results show that, even though the network device driver does not conform to conventional periodic or sporadic task models, it can be successfully modeled using hyperbolic load-bound functions that are fitted to empirical performance measurements