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Mechanical and Electro-Mechanical Properties of Crystalline Organic Semiconductors
The study of the physical properties of organic crystalline semiconductors has allowed the advent of a new generation of high-performance organic electronic devices. Exceptional charge-transport properties and recent developments in large-area patterning techniques make organic single crystals (OSCs) excellent candidates for their utilization in the next-generation of electronic technologies, including flexible and conformable organic thin-film devices. In spite of the profound knowledge of the structural and electrical properties of OSCs, knowledge of the mechanical properties and the effects of mechanical strain is almost non-existent. This dissertation aims to bring new understanding of the intrinsic mechanical properties and the effect of mechanical strains in charge transport phenomena in organic semiconductors.
The wrinkling instability is chosen as the metrology tool for the effective in-plane elastic constants of OSCs. We demonstrate that the wrinkling instability can be used to obtain the elastic constants of single crystals of rubrene, tetracene, PDIF-CN (N,N\u27-1H,1H-perfluorobutyldicyanoperylene-carboxydi-imide) and perylene. We demonstrate that wrinkling is a practical method to map the in-plane mechanical anisotropy in OSCs. In addition, we utilize wrinkling to characterize how the elastic modulus of pBTTT (poly(2,5-bis(3-alkylthiophen- 2-yl)thieno[3,2-b]thiophene)) changes with increasing molecular weight, from the monomer to the pentamer and the high molecular weight polymer.
To elucidate the effects of mechanical strain on charge transport, we first demonstrate and quantify the existence of a piezoresistive effect in rubrene crystals by the application of bending strains along its b [010] axis. A piezoresistive coefficient of approximately 11.26 is determined and confirmed through density functional theory (DFT) calculations. Second, we take advantage of wrinkling as a unique way to strain the conducting channel of field-effect transistors in a non-destructive, reversible, and predictable manner. We observe field-effect mobility modulation upon wrinkling and establish that it is controlled by the strain experienced by the insulator-semiconductor interface upon deformation. Finally, we propose a model based on plate bending to quantify the net strain at the insulator-semiconductor interface and predict the change in mobility. These contributions are the first to quantitatively correlate the crystal structure and the mechanical properties of OSCs, as well as the first to study electro-mechanical behavior in OSCs
Integrated Sachs-Wolfe map recovery from NVSS and WMAP 7yr data
We present a map of the Cosmic Microwave Background (CMB) anisotropies
induced by the late Integrated Sachs Wolfe effect. The map is constructed by
combining the information of the WMAP 7-yr CMB data and the NRAO VLA Sky Survey
(NVSS) through a linear filter. This combination improves the quality of the
map that would be obtained using information only from the Large Scale
Structure data. In order to apply the filter, a given cosmological model needs
to be assumed. In particular, we consider the standard LCDM model. As a test of
consistency, we show that the reconstructed map is in agreemet with the assumed
model, which is also favoured against a scenario where no correlation between
the CMB and NVSS catalogue is considered.Comment: 6 pages, 4 figures. Minor revision, accepted for publication in MNRA
NCBO Ontology Recommender 2.0: An Enhanced Approach for Biomedical Ontology Recommendation
Biomedical researchers use ontologies to annotate their data with ontology
terms, enabling better data integration and interoperability. However, the
number, variety and complexity of current biomedical ontologies make it
cumbersome for researchers to determine which ones to reuse for their specific
needs. To overcome this problem, in 2010 the National Center for Biomedical
Ontology (NCBO) released the Ontology Recommender, which is a service that
receives a biomedical text corpus or a list of keywords and suggests ontologies
appropriate for referencing the indicated terms. We developed a new version of
the NCBO Ontology Recommender. Called Ontology Recommender 2.0, it uses a new
recommendation approach that evaluates the relevance of an ontology to
biomedical text data according to four criteria: (1) the extent to which the
ontology covers the input data; (2) the acceptance of the ontology in the
biomedical community; (3) the level of detail of the ontology classes that
cover the input data; and (4) the specialization of the ontology to the domain
of the input data. Our evaluation shows that the enhanced recommender provides
higher quality suggestions than the original approach, providing better
coverage of the input data, more detailed information about their concepts,
increased specialization for the domain of the input data, and greater
acceptance and use in the community. In addition, it provides users with more
explanatory information, along with suggestions of not only individual
ontologies but also groups of ontologies. It also can be customized to fit the
needs of different scenarios. Ontology Recommender 2.0 combines the strengths
of its predecessor with a range of adjustments and new features that improve
its reliability and usefulness. Ontology Recommender 2.0 recommends over 500
biomedical ontologies from the NCBO BioPortal platform, where it is openly
available.Comment: 29 pages, 8 figures, 11 table
Ratchet universality in the bidirectional escape from a symmetric potential well
The present work discusses symmetry-breaking-induced bidirectional escape from a symmetric metastable potential well by the application of zero-average periodic forces in the presence of dissipation. We characterized the interplay between heteroclinic instabilities leading to chaotic escape and breaking of a generalized parity symmetry leading to directed ratchet escape to an attractor either at infinity or at -infinity. Optimal enhancement of directed ratchet escape is found to occur when the wave form of the zero-average periodic force acting on the damped driven oscillator matches as closely as possible to a universal wave form, as predicted by the theory of ratchet universality. Specifically, the optimal approximation to the universal force triggers the almost complete destruction of the nonescaping basin for driving amplitudes which are systematically lower than those corresponding to a symmetric periodic force having the same period. We expect that this work could be potentially useful in the control of elementary dynamic processes characterized by multidirectional escape from a potential well, such as forced chaotic scattering and laser-induced dissociation of molecular systems, among others
Hot-melt extrusion (HME) formulations of Albendazole for increasing dissolution properties
Hot-Melt-Extrusion (HME) is a flexible process that uses high temperature and pressure conditions to pump raw materials such as an Active Pharmaceutical Ingredient (API) and a pharmaceutical grade polymer through a barrel. The material is conveyed and mixed using intermeshing co-rotating twin-screws and then pushed through a die to form a well-shaped strand. Due to the high mixing degree provided by the twin-screws, the drug is transformed from crystalline to amorphous form. The use of twin-screw extruders is currently being implemented within continuous manufacturing platforms (Crowley, 2007)
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