Raman Spectroscopy and DFT calculations for the Electronic Structure Characterization of Conjugated Polymers

In the last three decades, there has been a broad academic and industrial interest in conjugated polymers as semiconducting materials for organic electronics. Their applications in polymer light-emitting diodes (PLEDs), polymer solar cells (PSCs), and organic field-effect transistors (OFETs) offer opportunities for the resolution of energy issues as well as the development of display and information technologies1. Conjugated polymers provide several advantages including low cost, light weight, good flexibility, as well as solubility which make them readily processed and easily printed, removing the conventional photolithography for patterning2. A large library of polymer semiconductors have been synthesized and investigated with different building blocks, such as acenes or thiophene and derivatives, which have been employed to design new materials according to individual demands for specific applications. To design ideal conjugated polymers for specific applications, some general principles should be taken into account, including (i) side chains (ii) molecular weights, (iii) band gap and HOMO and LUMO energy levels, and (iv) suited morphology.3-6 The aim of this study is to elucidate the impact that substitution exerts on the molecular and electronic structure of π-conjugated polymers with outstanding performances in organic electronic devices. Different configurations of the π-conjugated backbones are analyzed: (i) donor-acceptor configuration, (ii) 1D lineal or 2D branched conjugated backbones, and (iii) encapsulated polymers (see Figure 1). Our combined vibrational spectroscopy and DFT study shows that small changes in the substitution pattern and in the molecular configuration have a strong impact on the electronic characteristics of these polymers. We hope this study can advance useful structure-property relationships of conjugated polymers and guide the design of new materials for organic electronic applications.

Relevance or irrelevance of capital structure?

In this paper we examine the effects of asymmetric information on the nature of financial equilibrium and on the capital structure of firms. In the first model presented, the financial contracts on offer involve pooling equilibrium with no adverse selection. However, in the special case analyzed, where contracts are of mixed form, there may be a separating equilibrium and also equilibrium may not exist. Interesting result is that the separating equilibrium found is not economically efficient since aggregate investments falls short of first-best level. More importantly, capital structure does matter. The relative magnitude of outside equity makes a real difference to the quantity of aggregate investment in equilibrium.

Predicting water permeability in sedimentary rocks from capillary imbibition and pore structure

In this paper, absolute water permeability is estimated from capillary imbibition and pore structure for 15 sedimentary rock types. They present a wide range of petrographic characteristics that provide degrees of connectivity, porosities, pore size distributions, water absorption coefficients by capillarity and water permeabilities. A statistical analysis shows strong correlations among the petrophysical parameters of the studied rocks. Several fundamental properties are fitted into different linear and multiple expressions where water permeability is expressed as a generalized function of the properties. Some practical aspects of these correlations are highlighted in order to use capillary imbibition tests to estimate permeability. The permeability–porosity relation is discussed in the context of the influence of pore connectivity and wettability. As a consequence, we propose a generalized model for permeability that includes information about water fluid rate (water absorption coefficient by capillarity), water properties (density and viscosity), wetting (interfacial tension and contact angle) and pore structure (pore radius and porosity). Its application is examined in terms of the type of pores that contribute to water transport and wettability. The results indicate that the threshold pore radius, in which water percolates through rock, achieves the best description of the pore system. The proposed equation is compared against Carman–Kozeny's and Katz–Thompson's equations. The proposed equation achieves very accurate predictions of the water permeability in the range of 0.01 to 1000 mD.

Natural plant polyphenols for alleviating oxidative damage in man: Current status and future perspectives

The balance between oxidation and reduction is important for maintaining a healthy biological system. Oxidative stress results from an imbalance between excessive formation of reactive oxygen species (ROS) and/or reactive nitrogen species (RNS) and limited endogenous defense systems, and this imbalance can adversely alter lipids, proteins and DNA, causing a number of human diseases. Thus, exogenous antioxidants that can neutralize the effect of free radicals are needed to diminish the cumulative effects of oxidative damage over human life span. Current research reveals that phenolic compounds in plants possess high antioxidant activity and free radical scavenging capacity and can prevent the body from oxidative damage over human life span. This review focuses on the present understanding of free radicals and antioxidants and their importance in human health and disease. Information about the chemical features of free radicals as well as their deleterious effects on cell structures is reviewed. The chemical structure and anti-oxidative mechanisms of essential polyphenols and their potential health benefits are presented. In addition, the limitation of natural antioxidants and a perspective on likely future trends in this field are also discussed.

Atomic-level structure and deformation in metallic glasses

Metallic glasses (MGs) are a relatively new class of materials discovered in 1960 and lauded for its high strengths and superior elastic properties. Three major obstacles prevent their widespread use as engineering materials for nanotechnology and industry: 1) their lack of plasticity mechanisms for deformation beyond the elastic limit, 2) their disordered atomic structure, which prevents effective study of their structure-to-property relationships, and 3) their poor glass forming ability, which limits bulk metallic glasses to sizes on the order of centimeters. We focused on understanding the first two major challenges by observing the mechanical properties of nanoscale metallic glasses in order to gain insight into its atomic-level structure and deformation mechanisms. We found that anomalous stable plastic flow emerges in room-temperature MGs at the nanoscale in wires as little as ~100 nanometers wide regardless of fabrication route (ion-irradiated or not). To circumvent experimental challenges in characterizing the atomic-level structure, extensive molecular dynamics simulations were conducted using approximated (embedded atom method) potentials to probe the underlying processes that give rise to plasticity in nanowires. Simulated results showed that mechanisms of relaxation via the sample free surfaces contribute to tensile ductility in these nanowires. Continuing with characterizing nanoscale properties, we studied the fracture properties of nano-notched MGnanowires and the compressive response of MG nanolattices at cryogenic (~130 K) temperatures. We learned from these experiments that nanowires are sensitive to flaws when the (amorphous) microstructure does not contribute stress concentrations, and that nano-architected structures with MG nanoribbons are brittle at low temperatures except when elastic shell buckling mechanisms dominate at low ribbon thicknesses (~20 nm), which instead gives rise to fully recoverable nanostructures regardless of temperature. Finally, motivated by understanding structure-to-property relationships in MGs, we studied the disordered atomic structure using a combination of in-situ X-ray tomography and X-ray diffraction in a diamond anvil cell and molecular dynamics simulations. Synchrotron X-ray experiments showed the progression of the atomic-level structure (in momentum space) and macroscale volume under increasing hydrostatic pressures. Corresponding simulations provided information on the real space structure, and we found that the samples displayed fractal scaling (r^d ∝ V, d < 3) at short length scales (< ~8 Å), and exhibited a crossover to a homogeneous scaling (d = 3) at long length scales. We examined this underlying fractal structure of MGs with parallels to percolation clusters and discuss the implications of this structural analogy to MG properties and the glass transition phenomenon.

Structural and functional interaction between polyamine related molecules and biological membranes

Changes induced by PA on nucleic acid (NA) conformation and synthesis is proven to be a major reason for PA essentiality (1-3). However, PA interactions with other polyanions, for instance polyanionic membrane lipid bilayers and glyosaminoglycans have received less attention (3-4). The functional importance of these interactions still is an obscure but interesting area of cell and molecular biology, especially in mammalian cells for which specific PA transport systems are not fully characterized (5). In mammals, activity and turnover of the polyamine (PA) synthesis key enzyme is controlled by a set of proteins: Antizymes (OAZ1-3) and antizyme inhibitors (AZIN1 and 2). It is demonstrated that AOZ modulate polyamine uptake (6), and that PA transport to mitochondria is linked to the respiratory chain state and modulates mitochondrial permeability transition (7). Antizyme expression variants have been located in mitochondria, being proposed as a proapoptotic factor (7-8). AZIN 2 is only expressed in a reduced set of tissues that includes mast cells, where it is associated to mast cell granules membrane (9). This fact, together to the abnormalities observed in bone marrow derived mast cell granules when they are differentiated under restricted PA synthesis conditions (10 and unpublished results), point out to important roles of PA and their related proteins in structure and function of mast cell granules. We will also present novel biophysical results on tripartite interactions of PA that remark the interest of the characterization of PA interactions with lipid bilayers for biomedicine and biotechnology. Thus, the information reported in this paper integrates previously reported information with our still unpublished results, all indicating that PA and their related proteins also are important factors for structure and dynamics of biological membranes and their associated functions essential in human physiology; for instance, solute interchange with the environment (uptake and secretion), oxidative metabolism and apoptosis. The importance of these involved processes for human homeostasis claim for further research efforts. 1. Ruiz-Chica J, Medina MA, Sánchez-Jiménez F and Ramírez FJ (2001) Fourier Transform Raman study of the structural specificities on the interaction between DNA and biogenic polyamines. Biophysical J. 80:443-454. 2. Lightfoot HL, Hall J (2014) Endogenous polyamine function--the RNA perspective. Nucleic Acids Res. 42:11275-11290. 3. Igarashi K, Kashiwagi K (2010) Modulation of cellular function by polyamines. Int J Biochem Cell Biol. 42:39-51. 4. Finger S, Schwieger C, Arouri A, Kerth A, Blume A (2014) Interaction of linear polyamines with negatively charged phospholipids: the effect of polyamine charge distance. Biol Chem. 395:769-778. 5. Poulin R, Casero RA, Soulet D. (2012) Recent advances in the molecular biology of metazoan polyamine transport. Amino Acids. 42:711-723. 6. Kahana C (2009) Regulation of cellular polyamine levels and cellular proliferation by antizyme and antizyme inhibitor. Essays Biochem. 4:47-61. 7. Agostinelli E, Marques MP, Calheiros R, Gil FP, Tempera G, Viceconte N, Battaglia V, Grancara S, Toninello A (2010) Polyamines: fundamental characters in chemistry and biology. Amino Acids 38:393-403. 8. Liu GY, Liao YF, Hsu PC, Chang WH, Hsieh MC, Lin CY, Hour TC, Kao MC, Tsay GJ, Hung HC (2006) Antizyme, a natural ornithine decarboxylase inhibitor, induces apoptosis of haematopoietic cells through mitochondrial membrane depolarization and caspases' cascade. Apoptosis 11:1773-1788. 9. Kanerva K, Lappalainen J, Mäkitie LT, Virolainen S, Kovanen PT, Andersson LC (2009). Expression of antizyme inhibitor 2 in mast cells and role of polyamines as selective regulators of serotonin secretion. PLoS One 31:e6858. 10. García-Faroldi G, Rodríguez CE, Urdiales JL, Pérez-Pomares JM, Dávila JC, Pejler G, Sánchez-Jiménez F, Fajardo I (2010) Polyamines are present in mast cell secretory granules and are important for granule homeostasis. PLoS One 30:e15071.

Three Essays on Dual-Class Stock Structure

Dual-class stock structure is characterized by the separation of voting rights and cash flow rights. The departure from a common “one share-one vote” configuration creates ideal conditions for conflicts of interest and agency problems between controlling insiders (the holders of voting rights) and remaining shareholders. The owners of voting rights have the opportunity to extract private benefits and act in their personal interest; as a result, dual-class firms are often perceived to have low transparency and high information asymmetry. This dissertation investigates the quality of information and the information environment of firms with two classes of stock. The first essay examines the quality of information by studying accruals in dual-class firms in comparison to firms with only one class of stock. The results suggest that the quality of accruals is better in dual-class firms than in single-class firms. In addition, the difference in the quality of accruals between firms that abolish their dual-class share structure by unification and singe-class firms disappears in the post-unification period. The second essay investigates the earnings informativeness of dual-class firms by examining the explanatory power of earnings for returns. The results indicate that the earnings informativeness is lower for dual-class firms as compared to single-class firms. Earnings informativeness improves in firms that unify their shares. The third essay compares the level of information asymmetry between dual-class firms and single-class firms. It is documented that the information environment for dual-class firms is worse than for single-class firms. Also, the finding suggests that the difference in information environment between dual-class firms and single-class firms disappears after dual-class stock unification.

A Kaleidoscope Perspective: Change in the Semantics and Structure of Facets and Isolates in Analytico-Synthetic Classification

Examines the limitations of the dynamic theory of classification in accommodating the changes and rapid growth of new topics in the universe of knowledge. Change in an analytico-synthetic scheme for classification is much more a web of connections and mapping these changes is a complex process. Suggests that there is need for exploration of this complexity for both improving systems, and revisiting our theory.

Evidence of Term-Structure Differences among Folksonomies and Controlled Indexing Languages

With the advent of Internet-based technologies for information organization, many groups have constructed their own indexing languages. Biologists, Library and Information Science practitioners, and now social taggers have worked together to create large and many times complex indexing languages. In this environment of diversity, two questions surface: (1) what are the measurable characteristics of these indexing languages, and (2) do measurements of these indexing languages speciate along these characteristics? This poster presents data from this exploratory work.

Insights into population structure of Diplodus vulgaris along the SW Portuguese coast from otolith elemental signatures

The common two-banded sea bream (Diplodus vulgaris) is an important fish in the marine ecosystems of the NW Atlantic and Mediterranean. In southern Portugal it is a major fishery resource being targeted mainly by the artisanal fleets. Although there is some knowledge of the age, growth and reproductive biology of the species, information about its population structure is scarce and somewhat limited to the Mediterranean Sea. In this study the otolith elemental signatures of 90 specimens of D. vulgaris of the same age group (2+ years) and cohort collected from the important fishery regions of SW Portugal (Sesimbra, Sagres and Faro) have been analysed by inductively coupled plasma mass spectrometry (ICP-MS). Two different methodologies have been applied: solution based analysis of the whole otoliths; representative of the entire life-history prior to capture, and laser ablation analysis of otolith cores; representative of the larval and early post-settlement phase. Whole otolith comparisons utilised Sr/Ca, Ba/Ca, Mn/Ca, Li/Ca and Ni/Ca to demonstrate regional population structure. Classification accuracy rates from linear discriminant function analyses (LDFA) of whole otolith chemistry data were high for each region; Faro - 93%, Sagres - 90% and Sesimbra - 80%. Comparison of the otolith core chemistry utilised Sr/Ca, Ba/Ca, Mn/Ca and Mg/Ca and Zn/Ca. LDFA for the otolith core chemistry also achieved accurate classification for samples from Sesimbra (73%), but there was high overlap of otolith chemistry between samples from Faro and Sagres (47 and 43% classification accuracy respectively). The whole otolith results suggest that D. vulgaris are resident in the regional fishing areas during the juvenile phase. Both the core and whole otolith chemistry data supported separation of the Sesimbra fishery region from the more southern and closely associated Faro and Sagres regions for management purposes. However, while the whole otolith data indicated that the populations at Faro and Sagres likely remained separated in the juvenile stage, the otolith core chemistry data was inconclusive as to whether recruitment to these two areas was derived, or not, from different spawning areas.

Query routing in cooperative semi-structured peer-to-peer information retrieval networks

Conventional web search engines are centralised in that a single entity crawls and indexes the documents selected for future retrieval, and the relevance models used to determine which documents are relevant to a given user query. As a result, these search engines suffer from several technical drawbacks such as handling scale, timeliness and reliability, in addition to ethical concerns such as commercial manipulation and information censorship. Alleviating the need to rely entirely on a single entity, Peer-to-Peer (P2P) Information Retrieval (IR) has been proposed as a solution, as it distributes the functional components of a web search engine – from crawling and indexing documents, to query processing – across the network of users (or, peers) who use the search engine. This strategy for constructing an IR system poses several efficiency and effectiveness challenges which have been identified in past work. Accordingly, this thesis makes several contributions towards advancing the state of the art in P2P-IR effectiveness by improving the query processing and relevance scoring aspects of a P2P web search. Federated search systems are a form of distributed information retrieval model that route the user’s information need, formulated as a query, to distributed resources and merge the retrieved result lists into a final list. P2P-IR networks are one form of federated search in routing queries and merging result among participating peers. The query is propagated through disseminated nodes to hit the peers that are most likely to contain relevant documents, then the retrieved result lists are merged at different points along the path from the relevant peers to the query initializer (or namely, customer). However, query routing in P2P-IR networks is considered as one of the major challenges and critical part in P2P-IR networks; as the relevant peers might be lost in low-quality peer selection while executing the query routing, and inevitably lead to less effective retrieval results. This motivates this thesis to study and propose query routing techniques to improve retrieval quality in such networks. Cluster-based semi-structured P2P-IR networks exploit the cluster hypothesis to organise the peers into similar semantic clusters where each such semantic cluster is managed by super-peers. In this thesis, I construct three semi-structured P2P-IR models and examine their retrieval effectiveness. I also leverage the cluster centroids at the super-peer level as content representations gathered from cooperative peers to propose a query routing approach called Inverted PeerCluster Index (IPI) that simulates the conventional inverted index of the centralised corpus to organise the statistics of peers’ terms. The results show a competitive retrieval quality in comparison to baseline approaches. Furthermore, I study the applicability of using the conventional Information Retrieval models as peer selection approaches where each peer can be considered as a big document of documents. The experimental evaluation shows comparative and significant results and explains that document retrieval methods are very effective for peer selection that brings back the analogy between documents and peers. Additionally, Learning to Rank (LtR) algorithms are exploited to build a learned classifier for peer ranking at the super-peer level. The experiments show significant results with state-of-the-art resource selection methods and competitive results to corresponding classification-based approaches. Finally, I propose reputation-based query routing approaches that exploit the idea of providing feedback on a specific item in the social community networks and manage it for future decision-making. The system monitors users’ behaviours when they click or download documents from the final ranked list as implicit feedback and mines the given information to build a reputation-based data structure. The data structure is used to score peers and then rank them for query routing. I conduct a set of experiments to cover various scenarios including noisy feedback information (i.e, providing positive feedback on non-relevant documents) to examine the robustness of reputation-based approaches. The empirical evaluation shows significant results in almost all measurement metrics with approximate improvement more than 56% compared to baseline approaches. Thus, based on the results, if one were to choose one technique, reputation-based approaches are clearly the natural choices which also can be deployed on any P2P network.

Predicamento de seguridad yemení

Con el inicio del periodo Post-Guerra Fría el Sistema Internacional comienza a experimentar un incremento en el fortalecimiento de su componente social; la Sociedad de Estados alcanza un mayor nivel de homogenización, el estado, unidad predominante de esta, comienzan atravesar una serie de transformaciones que obedecerán a una serie de cambios y continuidades respecto al periodo anterior. Desde la perspectiva del Realismo Subalterno de las Relaciones Internacionales se destacan el proceso de construcción de estado e inserción al sistema como las variables que determinan el sentimiento de inseguridad experimentado por las elites estatales del Tercer Mundo; procesos que en el contexto de un nuevo y turbulento periodo en el sistema, tomara algunas características particulares que darán un sentido especifico al sentimiento de inseguridad y las acciones a través de las cuales las elites buscan disminuirlo. La dimensión externa del sentimiento de inseguridad, el nuevo papel que toma la resistencia popular como factor determinante del sentimiento de inseguridad y de la cooperación, así como del conflicto, entre los miembros de la Sociedad Internacional, la inserción como promotor de estrategias de construcción de Estado, son alguno de los temas puntuales, que desde la perspectiva subalterna, parecen salir a flote tras el análisis del sistema en lo que se ha considerado como el periodo Post-Guerra Fría. En este sentido Yemen, se muestra como un caso adecuado no solo para poner a prueba las postulados de la teoría subalterna, veinte años después de su obra más prominente (The third world security Predicament), escrita por M. Ayoob, sino como un caso pertinente que permite acercarse más a la comprensión del papel del Tercer Mundo al interior de la Sociedad Internacional de Estados.

El efecto de la definición regulatoria de banda ancha sobre la difusión y la competencia del mercado de servicios de Internet fijo en Colombia

A partir de la dinámica evolutiva de la economía de las Tecnologías de la Información y las Comunicaciones y el establecimiento de estándares mínimos de velocidad en distintos contextos regulatorios a nivel mundial, en particular en Colombia, en el presente artículo se presentan diversas aproximaciones empíricas para evaluar los efectos reales que conlleva el establecimiento de definiciones de servicios de banda ancha en el mercado de Internet fijo. Con base en los datos disponibles para Colombia sobre los planes de servicios de Internet fijo ofrecidos durante el periodo 2006-2012, se estima para los segmentos residencial y corporativo el proceso de difusión logístico modificado y el modelo de interacción estratégica para identificar los impactos generados sobre la masificación del servicio a nivel municipal y sobre las decisiones estratégicas que adoptan los operadores, respectivamente. Respecto a los resultados, se encuentra, por una parte, que las dos medidas regulatorias establecidas en Colombia en 2008 y 2010 presentan efectos significativos y positivos sobre el desplazamiento y el crecimiento de los procesos de difusión a nivel municipal. Por otra parte, se observa sustituibilidad estratégica en las decisiones de oferta de velocidad de descarga por parte de los operadores corporativos mientras que, a partir del análisis de distanciamiento de la velocidad ofrecida respecto al estándar mínimo de banda ancha, se demuestra que los proveedores de servicios residenciales tienden a agrupar sus decisiones de velocidad alrededor de los niveles establecidos por regulación.

Electronic structure and magnetism of Mn-doped GaSb for spintronic applications: A DFT study

We have carried out first-principles spin polarized calculations to obtain comprehensive information regarding the structural, magnetic, and electronic properties of the Mn-doped GaSb compound with dopant concentrations: x¼0.062, 0.083, 0.125, 0.25, and 0.50. The plane-wave pseudopotential method was used in order to calculate total energies and electronic structures. It was found that the MnGa substitution is the most stable configuration with a formation energy of 1.60 eV/Mn-atom. The calculated density of states shows that the half-metallic ferromagnetism is energetically stable for all dopant concentrations with a total magnetization of about 4.0 lB/Mn-atom. The results indicate that the magnetic ground state originates from the strong hybridization between Mn-d and Sb-p states, which agree with previous studies on Mn-doped wide gap semiconductors. This study gives new clues to the fabrication of diluted magnetic semiconductors