1,721,615 research outputs found
Using Contextual Information with Dynamic Linkbases to Provide Adaptive Hypermedia
No full textThis report provides an overview of the work that the author has conducted into the field of adaptive hypermedia systems. This work produced an agent-based adaptive link augmentation system that was presented at the first adaptive hypermedia conference. The knowledge gained from creating this system has been combined with context research to produce a system for augmenting links based on a document’s spatial context. These links are provided from a collection of linkbases, which are activated on demand. Presented with this work is an overview of the history of AH, including a description of some of the pivotal AH, recommender and knowledge delivery systems. The report concludes with the author’s view of the future for this research, including a work plan covering the next 16 months
Optical properties of lead halide perovskites for optoelectronics
No full textThis thesis presents a collection of work investigating the optical properties of lead halide perovskites for optoelectronic applications. Lead halide perovskites are currently the state-of-the-art in terms of efficiency for thin-film photovoltaics, yet they are not fully understood and require further studies to elucidate their fundamental properties. Firstly in this thesis, the optical constants for lead halide perovskite thin films are determined using spectroscopic ellipsometry, providing important information for future optical modelling and calculations of the electronic structure. Following this, physical insights into the charge carrier dynamics in these materials are provided, revealing the effects of material disorder over a large range of temperatures. In relation to the charge carrier dynamics, the crucial topic of grain boundaries in lead halide perovskites is also investigated, showing their detrimental effects by providing non-radiative recombination centres in perovskite materials. Lastly, an application of colloidal semiconductor nanocrystals for perovskite solar cells is investigated, with the aim to enhance photocurrent in the devices. The prospect of this is shown by the successful dispersion of colloidal CdTe core-type quantum dots in the hole-transporting layer within solution-processed photovoltaic devices. This work is a promising advancement towards perovskite solar cells employing additional light harvesting processes from nanomaterials
An Agent-Based Approach to Adaptive Hypermedia Using a Link Service: VOL. 1892
No full textThis paper describes an approach to adaptive hypermedia by incorporating linkbases into an agent-based system (PAADS). The agents are built on top of an agent framework developed at Southampton University. Personal agents keep a local user model and provide adaptive navigation support. This is accomplished by extracting keywords found in the user model and through the user's browsing history, and by then replacing occurrences of those words with URLs supplied by a linkbase agent. A third agent provides the ability to query these user models through a web browser
High-energy optical transitions and optical constants of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> measured by spectroscopic ellipsometry and spectrophotometry
Full text linkOptoelectronics based on metal halide perovskites (MHPs) have shown substantial promise, following more than a decade of research. For prime routes of commercialization such as tandem solar cells, optical modeling which requires accurate optical data for the materials utilized is essential for engineering device architectures. Additionally, a comprehensive understanding of the fundamental material properties is vital for simulating the operation of devices for design purposes. In this article, we use variable angle spectroscopic ellipsometry (SE) to determine the optical constants of CH3NH3PbI3 (MAPbI3) thin films over a photon energy range of 0.73–6.45 eV. We successfully model the ellipsometric data using six Tauc–Lorentz oscillators for three different incident angles. Following this, we use critical-point analysis of the complex dielectric constant to identify the well-known transitions at 1.59, 2.49, and 3.31 eV but also additional transitions at 4.39 and 5.65 eV, which are observed in both SE and spectrophotometry measurements. This work provides important information relating to optical transitions and the band structure of MAPbI3, which can assist in the development of potential applications of the material
Birefringence data analysis
No full textBailey, Christopher; Chung, Ginmo; Guevara, Alvaro; Hardesty, Sean; Kenney, Joseph; Sircar, Sarthok; Allan, Douglas C.. (2006). Birefringence data analysis. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/3676
An Agent-Based Framework to Support Adaptive Hypermedia
No full textThe field of adaptive hypermedia is a little over a decade old. It has a rich history in a range of fields such as artificial intelligence, user modelling, intelligent tutoring systems and hypertext. Early adaptive hypermedia work concentrated on application-led research; developing a range of systems for specific purposes. In 1996, Peter Brusilovsky reviewed the state-of-the-art and proposed a taxonomy of adaptive hypermedia techniques, thereby providing the means to categorise adaptive hypermedia systems. Since then, several practical frameworks for adaptive hypermedia applications have been produced, in addition to formal models for formalising adaptive hypermedia applications. This thesis presents a new framework for adaptive hypermedia systems based on agent technology, a field of research largely ignored within the adaptive community. Conceptually, this framework occupies a middle ground between the formal reference models for adaptive hypermedia and application-specific frameworks. This framework provides the means to implement formal models using variety of architectural approaches. Three novel adaptive hypermedia applications have been developed around this agent-based framework. Each system employs different architectural structures, they model the user with a variety of profiling techniques, and each provides a different set of adaptive features. The diversity of these three systems emphasises the flexibility and functionality of this proposed agent-based framework
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Phonon-assisted trapping and re-excitation of free carriers and excitons in lead halide perovskites
No full textDespite the advances in solar cells based on lead halide perovskites, the nature of photogenerated charges and trap states within these materials remains unclear. A model describing recombination in CH3NH3PbI3−xClx has been developed that accounts for phonon-assisted free-exciton and free-carrier trapping. We utilize optical spectroscopies and observe significant co-existence of the tetragonal and orthorhombic structural phases at low temperatures. From these measurements, we evaluate the longitudinal−optical phonon energy, exciton binding energy, and temperature-dependent electronic bandgap. We use these parameters to model the temperature- and fluence-dependent time-resolved photoluminescence decays, enabling us to demonstrate how shallow traps from which carriers can be re-excited can account for the delayed recombination in lead halide perovskites. The trap-state density reaches a maximum at the tetragonal to orthorhombic phase transition at ∼140 K, suggesting the formation of disorder-induced trap states, which are shown to dominate the recombination dynamics in CH3NH3PbI3−xClx
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