Contextualized Word Representations for Reading Comprehension

Reading a document and extracting an answer to a question about its content has attracted substantial attention recently. While most work has focused on the interaction between the question and the document, in this work we evaluate the importance of context when the question and document are processed independently. We take a standard neural architecture for this task, and show that by providing rich contextualized word representations from a large pre-trained language model as well as allowing the model to choose between context-dependent and context-independent word representations, we can obtain dramatic improvements and reach performance comparable to state-of-the-art on the competitive SQuAD dataset.Comment: 6 pages, 1 figure, NAACL 201

A Fully Attention-Based Information Retriever

Recurrent neural networks are now the state-of-the-art in natural language processing because they can build rich contextual representations and process texts of arbitrary length. However, recent developments on attention mechanisms have equipped feedforward networks with similar capabilities, hence enabling faster computations due to the increase in the number of operations that can be parallelized. We explore this new type of architecture in the domain of question-answering and propose a novel approach that we call Fully Attention Based Information Retriever (FABIR). We show that FABIR achieves competitive results in the Stanford Question Answering Dataset (SQuAD) while having fewer parameters and being faster at both learning and inference than rival methods.Comment: Accepted for presentation at the International Joint Conference on Neural Networks (IJCNN) 201

Carbon-based polymer nanocomposites with enhanced conductive properties

Nowadays the development of new technologies requires materials with unconventional combination of properties. Polymers are classified as electrical and thermal insulating materials, which limits their use for several important technological applications. However, conductive polymers could be used in order to overcame drawbacks in the use of metals, metal alloys and ceramic materials as conductive media. Thermal conductive polymers could be profitably exploited in heat management applications (e.g. heat sink, heat exchangers), while electrical conductive polymers could be used in different fields depending on their electrical conductive values. To enhance the conductive properties of polymers, several approaches has been reported in literature. However, the most established way to achieve this goal consists in the development of suitable composite materials by means of the incorporation of conductive fillers within the polymeric matrix. The choice of the conductive filler is a crucial point in the development of the final material. Due to their extremely high thermal and electrical conductivity, coupled with the low density, the nano-metric scale and the outstanding mechanical properties, carbon-based nanomaterials are the most promising fillers suitable for processing conductive polymers. Since graphene nanoplatelets (GNPs) are considered young materials with potentials not yet fully exploited, multiwall carbon nanotubes (MWCNTs) are nowadays the most established materials used as conductive filler. In this thesis work thermally and electrically conductive polymer composites, filled with carbon-based nanomaterials were investigated. In the first part of the experimental work, particular attention was devoted to the development of GNPs-based thermally conductive polymers. By properly selecting several polymeric matrices and comparing several available processing techniques it was possible to outline a guideline in the use of GNPs as thermally conductive fillers. A strong filler characterization reveals that, in spite to the amount of defects and to the filler purity, the main GNPs properties able to enhance the thermal conductivity of polymers is the lateral dimension. With the aim of developing metal-free circuits integrated in nanocomposite, a laser printing process was successfully exploited in order to obtain electrical conductive paths on the surface of a polymeric materials containing MWCNTs. Starting from the literature knowhow and new experimental results, a complete comprehension of the parameters that affect the laser printing process was achieved by applying a statistical approach. By analysing the experimental outcomes with a statistical approach, it was possible to focus the attention on the main laser parameters that govern the process, thus obtaining multifunctional and multidirectional conductive materials with surface electrical resistance per unit length (inside the tracks) lower than 1 kΩ/cm at 0.5 wt.% of MWCNTs loading content. Finally, by combining outcomes obtained as described above, hybrid carbon-based nanocomposites were developed, with the purpose of enhancing contemporaneously thermal and electrical conductivity. Hybrid materials, obtained starting from a commercial masterbatch containing MWCNTs, demonstrated the possibility to partially replace the high amounts of carbon nanotubes with low cost carbon based materials without worsening the good conductive properties. Not only conductive properties were investigated, but all the studied materials were also characterized by means of mechanical and thermal stability tests, thus demonstrating the possibility of adopting carbon-based polymer nanocomposites as multifunctional materials

Flexibility of Flexible Perovskite Solar Cells Investigated by Nanomechanics

Department of Materials Science and EngineeringOrganic-inorganic halide perovskite solar cells hold promise for next-generation photovoltaic devices because of their remarkable optical properties and high light-absorption coefficient. Mechanical flexibility of the perovskite solar cells together with high photovoltaic efficiency has been attracting attentions because processing temperatures are so low that all the constituent materials can be flexible unlike rigid inorganic solar cells. While various flexible materials used for transparent electrodes and hole- and electron-transport layers have been introduced, irreplaceable perovskite materials have organic-inorganic crystalline structures that can be brittle. In most previous researches, flexibility of the perovskite solar cells has been evaluated empirically; for example, decrease in photovoltaic efficiency by cyclic bending deformation for a certain bending radius. Beyond the empirical studies determining flexibility of the perovskite solar cells based on repeatable bending tests, investigations on mechanical properties of perovskite materials which can be the weakest material among the constituent materials have been conducted by nanoindentations and computational simulations. Because nanoindentations are measured only for local volume, mechanical properties measured by nanoindentations may not represent mechanical properties of film-type perovskite materials including various defects.Computational simulations can be restricted to perfect crystalline structures also. The best way to overcome limitations of nanoindentations and computational studies is to measure uni-axial tensile properties of free-standing perovskite materials because (1) gauge section can include all possible defects that tensile properties represent real mechanical properties of the perovskite materials and (2) deformation and fracture behavior of the perovskite materials at any deformed states of the solar cell can be predicted by solid mechanics with their tensile properties. There has been a computational study on tensile behavior of single- and poly-crystalline perovskite materials, but experimental measurement of tensile properties of free-standing perovskite materials has not been reported so far as far as we know. This is possibly because perovskite materials are so sensitive to environments such as humidity and oxygen that sample preparation and testing procedure are challenging. Therefore, this work contains dedications to explain mechanical flexibility as followings; 1. To fabricate the ultra-flexible perovskite solar cells via ITO-free transparent bottom electrode. 2. To measure the mechanical properties of constituent materials in flexible PSCs 3. To design the innovated mechanical testing method for vulnerable perovskite materials using in-situ nanoindentation system. 4. To measure direct tensile properties of organic-inorganic perovskite materials via in-situ tensile testing. The major contribution of this dissertation is to expand our insight into what truly happens in flexibility of flexible perovskite solar cells. New systematic approaches will be discussed in detail in the body of this dissertation.clos