A review on massive e-learning (MOOC) design, delivery and assessment

MOOCs or Massive Online Open Courses based on Open Educational Resources (OER) might be one of the most versatile ways to offer access to quality education, especially for those residing in far or disadvantaged areas. This article analyzes the state of the art on MOOCs, exploring open research questions and setting interesting topics and goals for further research. Finally, it proposes a framework that includes the use of software agents with the aim to improve and personalize management, delivery, efficiency and evaluation of massive online courses on an individual level basis.Peer ReviewedPostprint (author's final draft

An event-based resource management framework for distributed decision-making in decentralized virtual power plants

The Smart Grid incorporates advanced information and communication technologies (ICTs) in power systems, and is characterized by high penetration of distributed energy resources (DERs). Whether it is the nation-wide power grid or a single residential building, the energy management involves different types of resources that often depend on and influence each other. The concept of virtual power plant (VPP) has been proposed to represent the aggregation of energy resources in the electricity market, and distributed decision-making (DDM) plays a vital role in VPP due to its complex nature. This paper proposes a framework for managing different resource types of relevance to energy management for decentralized VPP. The framework views VPP as a hierarchical structure and abstracts energy consumption/generation as contractual resources, i.e., contractual offerings to curtail load/supply energy, from third party VPP participants for DDM. The proposed resource models, event-based approach to decision making, multi-agent system and ontology implementation of the framework are presented in detail. The effectiveness of the proposed framework is then demonstrated through an application to a simulated campus VPP with real building energy data

Design study of OER-CC ontology: a semantic web approach to describe open educational resources

Through the application of semantic technologies to describe Open Educational Resources, any agent (human or software-based) could process and understand its contents; therefore, the agent could perform tasks autonomously or in a more effective way. In this paper, we describe the design and validation of the OER-CC ontology, which models the domain knowledge of educational resources licensed under Creative Commons Licenses. One of the most important contributions of this work is that we implement different rules and axioms to identify inconsistencies between rights provided by a licensed on an learning material and particular uses that are performed on it

Reactor design, reaction engineering and cocatalyst development for photocatalytic water splitting half-reactions

Global warming concerns have brought energy conversion into the spotlight. The conversion of renewable energy into chemical energy carriers has required keen inventiveness of the scientific community to find feasible solutions within today´s global economy. The success of such solutions requires collective efforts of multiple stakeholders, but from a purely technical perspective, this translates to the search for materials that can readily split water using a renewable energy input. For example, by using the right combination of light absorbing and catalytically active materials — or simply photocatalysts — that can simultaneously harvest sunlight and catalyze water splitting (aka artificial photosynthesis). An efficient water splitting photocatalyst aims to transform as much power of the solar spectrum as possible into chemical energy stored in the form of hydrogen and oxygen. The efficiency of this conversion is the result of multiple steps ultimately related to the sequence of light absorption, charge separation and transport, and electron transfer reactions. A photocatalyst is a semiconductor material with properties (i.e., optical band gap and crystallinity) that facilitate that sequence. Photocatalyst optimization is the process of tweaking the rate of those multiple steps (i.e., through material properties) such that the losses along the sequence are minimized. This work focuses on the optimization of the photocatalytic performance of TiO2, WO3, and covalent organic frameworks (COFs). Energy conversion efficiencies using these, and state of the art photocatalysts remain far from the target set for commercial feasibility. However, since the first water splitting experience on TiO2, various materials have been also demonstrated promising photocatalytic properties for water splitting half reactions, like WO3 and COFs. While both WO3 and TiO2 (band gap ~ 2.75 and 3.2 eV, respectively) are n-type semiconductors with valence bands that provide enough thermodynamic driving force for the oxygen evolution reaction (OER), WO3 allows additional harvesting of the visible solar spectrum. COFs are crystalline organic semiconductors that can be synthesized from earth abundant elements which have demonstrated the photocatalytic hydrogen evolution reaction (HER). Differently to the existing myriad of inorganic HER photocatalysts, the superior chemical tunability of COFs allows rational design and almost unlimited options for the tailoring of their photocatalytic properties. Multiple strategies can be found in the literature to optimize the photocatalytic performance of TiO2, WO3 and COFs by the modification of the light harvester material properties. The workflow presented herein differs from those, because it zooms to other aspects that are equally crucial to explain photocatalyst performance but that are typically less explored by material researchers. These are the increase of material photocatalytic performance upon decoration with cocatalysts (HER or OER electrocatalyst), and the intricate interplay between that performance and the nanoparticulate suspensions' multiphysics (optics, transport phenomena, and colloidal suspension stabilization). The latter rationalizes the photoreactor design presented along this work, which simplifies persisting instrumental problems and uncertainties of the artificial photosynthesis field related to reaction modeling, and the accuracy, reproducibility, and sensitivity of the quantification of photocatalyst performance. Commercial TiO2 (P25) is a standardized photocatalyst with the potential to benchmark photocatalytic OER rates among different laboratories, but it requires the addition of an OER catalyst to overcome water oxidation kinetic limitations. In this work a RuOx cocatalyst is developed in-situ on P25 for such purpose. With the instrumentals developed for sensitive O2 detection, the P25@RuO2 benchmark is optimized in terms of activity and reproducibility (at simulated sunlight, AM1.5G) and its resulting external (0.2%) and internal photonic efficiency (16%) is presented. Along with the establishment of this OER benchmark, this work also drafts good practices for reporting OER rates (i.e., adventitious O2 control), and innovative photoreactor engineering and optical modelling for the disentangling of the multiple factors determining photocatalysis physics. Using the same instrumentals for OER detection and a more elaborated cocatalyst tuning approach, a novel 2D RuOx electrocatalyst (ruthenium oxide nanosheet, RONS) is added to WO3 nanoparticles to enhance photocatalytic OER rates. First, the tuning of a top-down method to produce size-controlled unilamellar RONS is developed. Then, the composites resulting from RONS impregnation on WO3 are compared to conventionally impregnated RuO2 nanoparticles (RONP) on WO3, the former displaying a 5-fold increase in photonic efficiency. These results are explained from the electrocatalytic properties at the RONS edges, and the optical properties of the resulting 2D/0D morphology of the RONS/WO3 that decreases the optical losses due to parasitic cocatalyst light absorption. COFs have enormous potential as photocatalysts by design. In this work the photocatalytic performance of a TpDTz COF is analyzed in terms of its interaction with a molecular HER cocatalyst (Ni-ME) and reaction modeling. The TpDTz COF/Ni-ME system, which is one of the few existing COF-molecular cocatalyst known to date that can produce hydrogen, shows relatively high HER photocatalytic activity (~1 mmol h-1 g-1, AM1.5G) compared to other organic visible light responsive semiconductor benchmarks (i.e., like g-C3N4) and it operates in aqueous suspension (containing triethanolamine as electron donor). The TpDTz COF/Ni-ME surprisingly overperforms Pt modified TpDTz COF. Nonetheless, the COFs' charge transport properties are not well understood and most likely short-ranged. This blurs the experimental access to COFs' photocatalytic performance bottlenecks, including the prominent case of the TpDTz COF/Ni-ME system. Regardless of such difficulties, this work deepens the HER reaction understanding of the TpDTz COF/Ni-ME by analyzing dynamic HER reaction trends detected using the aforesaid photoreactor designs and instrumentals. From the modeled HER cycle kinetics and rapid dark step, the HER rate limiting step of the TpDTz COF/Ni-ME is placed at the electron transfer to the resting Ni-ME state. These HER mechanisms on COFs are experimentally challenging to access and are herein partially accessed in-situ from a reaction engineering and modelling perspective. On the whole, this work is the culmination of a multidisciplinary effort to find new opportunities to understand and optimize materials used for energy conversion processes, ranging from fundamental material research, solid-state and optics physics, applied catalysis, to reactor engineering

Enhancing electrochemical intermediate solvation through electrolyte anion selection to increase nonaqueous Li-O2_2 battery capacity

Among the 'beyond Li-ion' battery chemistries, nonaqueous Li-O$_2$ batteries have the highest theoretical specific energy and as a result have attracted significant research attention over the past decade. A critical scientific challenge facing nonaqueous Li-O$_2$ batteries is the electronically insulating nature of the primary discharge product, lithium peroxide, which passivates the battery cathode as it is formed, leading to low ultimate cell capacities. Recently, strategies to enhance solubility to circumvent this issue have been reported, but rely upon electrolyte formulations that further decrease the overall electrochemical stability of the system, thereby deleteriously affecting battery rechargeability. In this study, we report that a significant enhancement (greater than four-fold) in Li-O$_2$ cell capacity is possible by appropriately selecting the salt anion in the electrolyte solution. Using $^7$Li nuclear magnetic resonance and modeling, we confirm that this improvement is a result of enhanced Li$^+$ stability in solution, which in turn induces solubility of the intermediate to Li$_2$O$_2$ formation. Using this strategy, the challenging task of identifying an electrolyte solvent that possesses the anti-correlated properties of high intermediate solubility and solvent stability is alleviated, potentially providing a pathway to develop an electrolyte that affords both high capacity and rechargeability. We believe the model and strategy presented here will be generally useful to enhance Coulombic efficiency in many electrochemical systems (e.g. Li-S batteries) where improving intermediate stability in solution could induce desired mechanisms of product formation.Comment: 22 pages, 5 figures and Supporting Informatio