bluuebunny/crossref_metadata_2025 huggingface dataset:
La noción de policía en los trabajos de Michel Foucault: objeto, límites, antinomias
Authors: Castro Edgardo
Published: June 2019

El presente trabajo se ocupa de la noción de policía en los escritos de Michel Foucault, tanto en sus libros publicados en vida, como en los cursos y textos editados póstumamente. Establece que las referencias sobre el tema dispersas en sus libros encuentran una formulación articulada en las clases de sus cursos, que conforman una especie de breve tratado sobre la policía en los siglos xvii y xviii, respecto de su objeto, sus límites y sus antinomias. Muestra, además, la relevancia que le concede el autor al dispositivo policial de estos siglos, en la medida en que, a través de él, sobre todo por sus antinomias, tomó forma la racionalidad a partir de la cual pensamos todavía nuestra política. Finalmente, este trabajo subraya la importancia del análisis foucaultiano de la policía para la comprensión del concepto de biopolítica.
Renán Silva. Cuestiones disputadas. Ensayos sobre Marx, Freud, Foucault, Bourdieu y Bloch.
Authors: Little Roch
Published: June 2019

Lo primero que se puede decir de este libro es que su autor cumple a cabalidad con lo anunciado en el título. Son cuatro ensayos sobre cuatro grandes pensadores contemporáneos, los cuales pueden leerse de forma independiente y en el orden que se quiera. La razón por la cual Silva los asocia está claramente expresada en los primeros renglones: “se relacionan con mi trabajo académico como profesor y como investigador” (p. xi). Además, todos ellos pretenden responder a inquietudes respecto del “estatuto cambiante de las ciencias sociales y del análisis histórico” (énfasis del autor), como expresa al inicio del siguiente parágrafo. A primera vista, se podría pensar que nos encontramos ante otro libro sobre Karl Marx, Sigmund Freud, Michel Foucault, Pierre Bourdieu o Marc Bloch, pero el caso está lejos de ser este. En efecto, Silva aborda a los autores desde un ángulo diferente, examinando textos o escritos que se salen del mainstream, como por ejemplo la correspondencia de Freud y La extraña derrota de Bloch. Por otro lado, el historiador insiste reiterativamente en el hecho de que no los abordará como “especialista”, lo que le permite un abordaje “no-ortodoxo” de sus escritos, sin ninguna pretensión de defender cualquier especie de purismo.
El monocultivo de la caña de azúcar en el valle geográfi co del río Cauca (Valle del Cauca, Colombia): un enclave que desnaturaliza la vida ecosistémica
Authors: Ayala-Osorio Germán
Published: June 2019

En el artículo se hace un recorrido histórico acerca del proceso de dominación y domesticación de la naturaleza, que sirvió a los propósitos de la agroindustria cañicultora instalada en el Valle del Cauca y que extendió sus dominios al valle geográfi co del río Cauca (Colombia). La lectura crítica la asume el autor desde la ecología política, y desde ese campo se le propone llamar al agroecosistema de la caña de azúcar como Enclave Artifi cial Desnaturalizante (EAD). Con estas categorías se expone un ejercicio refl exivo y crítico, con el que se confrontan el discurso con el que se valida a diario la plantación de caña de azúcar y la propia lógica que está detrás del monocultivo de dicha gramínea. Se trata de un artículo de reflexión, anclado en las disquisiciones propias de la ecología política, en la búsqueda de encontrar consensos y provocar discusiones no solo alrededor de la nueva categoría nominativa para el cultivo de la caña de azúcar, sino sobre la sostenibilidad, alejada, por supuesto, de toda lógica de plantación, por los efectos conflictos socioambientales que de tiempo atrás viene provocando dicho cultivo y sus prácticas industrializadas.
Abriendo caminos. Los procesos de participación ciudadana promovidos a nivel institucional en el ámbito local, como escuela de profundización democrática
Authors: García-Montes Néstor
Published: June 2019

Las administraciones, los gobernantes y los responsables políticos tienen en su mano la capacidad de generar espacios de democracia directa en sus ámbitos de actuación, especialmente a nivel local, abriendo caminos que van más allá de la democracia representativa. El objetivo de este artículo es hacer un análisis de la participación ciudadana, promovida desde el ámbito institucional, así como de sus potencialidades, difi cultades y requisitos, para facilitar las prácticas de profundización democrática desde el marco de las políticas locales. Una participación que es diferente a la que surge de abajo arriba, pero que ofrece un espacio idóneo para convertirse en una escuela de ciudadanía y de democracia directa.
Tratamiento farmacológico de la enfermedad de Kawasaki
Authors: Escobar Hellmann Adrián , Meneses-Gaviria Gyhill , Ijají-Piamba Jhon Edison , Triana-Murcia Héctor Mauricio , Molina-Bolaños Jaime Alexander , Vidal-Martínez Juan Felipe , Correa-Gallego Cristian Felipe , Cedeño-Burbano Anuar Alonso
Published: June 2019

Introducción. La enfermedad de Kawasaki corresponde a una vasculitis sistémica de origen desconocido y su principal complicación es la formación de aneurismas coronarios.Objetivo. Realizar una revisión actualizada de la literatura acerca del tratamiento farmacológico de la enfermedad de Kawasaki.Materiales y métodos. Se realizó una búsqueda estructurada de la literatura en las bases de datos ProQuest, EBSCO, ScienceDirect, PubMed, LILACS, Embase, Trip Database, SciELO y Cochrane Library con los términos “Kawasaki disease AND therapeutics”, “Kawasaki disease AND treatment” y “Mucocutaneous Lymph Node Syndrome AND therapeutics”, en inglés y con sus equivalentes en español.Resultados. Se encontraron 51 artículos con información relevante para el desarrollo de la presente revisión.Conclusiones. El diagnóstico y el tratamiento oportuno de la enfermedad de Kawasaki son fundamentales para la prevención de las complicaciones coronarias. El tratamiento incluye la terapia combinada de ácido acetilsalicílico más inmunoglobulina G, la cual reduce la incidencia de aneurismas coronarios. Por su parte, las terapias con corticosteroides y otros fármacos inmunosupresores son alternativas utilizadas en el tratamiento de la enfermedad de Kawasaki resistente a inmunoglobulina.
Etapas de cambio comportamental frente al consumo de sustancias psicoactivas en escolares de 9 a 17 años de Bogotá D.C., Colombia
Authors: Núñez Oscar , Ramirez-Vélez Robinson , Correa-Bautista Jorge Enrique
Published: June 2019

Introducción. El consumo de sustancias psicoactivas (SPA) es una problemática que afecta a estudiantes desde edades tempranas.Objetivo. Describir las etapas de cambio de comportamiento frente al consumo de SPA en escolares de Bogotá D.C., Colombia.Materiales y métodos. Estudio transversal en 6 965 escolares de Bogotá D.C. El cambio de comportamiento se evaluó por autoreporte a través de un cuestionario estructurado a partir del Modelo Transteórico en las etapas de precontemplación, contemplación, preparación y acción/mantenimiento.Resultados. 58.4% fueron mujeres con edad promedio de 12.7±2.3 años. Frente al consumo de drogas alucinógenas, 6% de los escolares se ubicaron en la categoría de precontemplación, 44% en contemplación, 30% en preparación y 20% en acción/mantenimiento. Respecto al consumo de alcohol, 5% se encontraban en precontemplación, 36% en contemplación, 12% en preparación y 46% en acción/mantenimiento. El tabaquismo mostró prevalencias de 4% para precontemplación, 33% para contemplación, 12% para preparación y 51% para acción/mantenimiento.Conclusiones. El consumo de SPA es una problemática que se presenta cada vez con mayor frecuencia en población escolar. La mayoría de entrevistados se ubican en etapa de mantenimiento en el consumo de tabaco y alcohol y en la etapa de contemplación de consumo de drogas alucinógenas. Se requieren esfuerzos gubernamentales que fomenten programas preventivos de consumo de SPA en el ámbito escolar.
Características clínicas de los niños con hipotiroidismo congénito en Santander, Colombia
Authors: Acevedo-Rojas Melina , Mendoza-Rojas Víctor Clemente
Published: June 2019

Introducción. El hipotiroidismo congénito (HC) es la primera causa de retraso mental prevenible. El inicio temprano de su tratamiento con la hormona tiroidea garantiza un desarrollo neurológico normal.Objetivos. Describir la etiología y las manifestaciones clínicas del HC y relacionar la discapacidad cognitiva con el inicio del tratamiento en una serie de casos de niños con esta enfermedad en el departamento de Santander, Colombia.Materiales y métodos. Estudio descriptivo a través de serie de casos. La información se recolectó de historias clínicas de pacientes con HC diagnosticado entre 1999 y 2013 y atendidos por el Servicio de Endocrinología Pediátrica del Hospital Universitario de Santander Empresa Social del Estado. Se analizaron 15 variables en el programa Microsoft Excel 2013.Resultados. Se recolectaron 59 casos, con una relación sexo femenino/masculino de 1.7:1. En el 49.2% de los casos se realizó tamizaje neonatal. Las disgenesias tiroideas fueron la etiología más común; la ictericia neonatal prolongada, la hernia umbilical y la hipotonía fueron las características más frecuentes. El retraso mental se presentó en el 64.4% de los casos.Conclusiones. El tamizaje neonatal es la mejor estrategia para captar la mayoría de los casos e iniciar tratamiento oportuno. En Colombia, la ictericia neonatal prolongada debe alertar un posible caso de HC.
Enfermería según la perspectiva deconstructivista de Derrida
Authors: Rebolledo Malpica Dinora Margarita
Published: June 2019

Introducción. El enfoque de la dialéctica deconstruccionista planteada por Derrida consiste en mostrar cómo se ha construido una idea a partir de procesos históricos y acumulaciones metafóricas, mostrando que lo que parece ser claro y evidente no lo es.Objetivo. Propiciar una reconstrucción del concepto de enfermería según la perspectiva deconstructivista de DerridaMateriales y métodos. Se trata de un diseño cualitativo contextualizado en las divisiones de los cuerpos directivos de enfermería de dos centros sanitarios. La muestra estuvo conformada por 13 informantes a quienes se les realizó una observación participante por un lapso de 6 meses y se les preguntó por relatos de vida para recoger los datos.Resultados. La evolución histórica de la mujer ha dejado una herencia al concepto de enfermería, al tiempo que se reflexiona sobre el desarrollo académico, científico y de investigación de esta disciplina en la actualidad, propiciando la reconstrucción de su concepto.Conclusiones. La enfermería debe asumir que la herencia de su evolución histórica le ha dejado importantes marcas en su pasado, pero al mismo tiempo le ha aportado su objeto epistémico: el cuidado.
Prescripción del ejercicio físico y sus implicaciones en adultos que han sufrido quemaduras
Authors: Betancourt-Cárdenas Paula Andrea , Camargo-Caldas Nubia Esperanza , Rodríguez-Camacho Diego Fabricio , Lozano-Rivera Estefanía , Correa Juan Felipe
Published: June 2019

Introducción. La prescripción del ejercicio físico y sus implicaciones en pacientes que han sufrido quemaduras es objeto de estudio en diferentes investigaciones debido al impacto físico, psicológico y social que tiene en las personas.Objetivo. Describir la prescripción de ejercicio físico y sus implicaciones en la población adulta que ha sufrido quemaduras.Materiales y métodos. Se realizó una revisión de tema por medio de exploración de artículos de manera electrónica con filtros de búsqueda en distintas bases de datos con términos DeCS y MeSH.Resultados. Se seleccionaron 11 artículos con intervención de ejercicio físico en fases aguda y crónica. Se incluyeron estrategias sobre la fuerza muscular en cinco de los artículos: tres de resistencia cardiovascular; dos de rango de movimiento, flexibilidad y características tróficas de la piel, y uno de dolor.Conclusiones. Las variables de la prescripción se determinan de acuerdo a las características propias que presenta la persona con quemadura, las cuales se resumen en esta revisión.
Optically Stable Biocompatible Flame-made SiO2-coated Y2O3:Tb3+ Nanophosphors for Cell Imaging
Authors: Sotiriou G.A. , Franco D. , Poulikakos D. , Ferrari A.
Published: June 2019

Nanophosphors are a promising new class of inorganic labels for bio-imaging applications, possessing a narrow emission bandwidth, good photostability and low toxicity. The effect of crystallinity of the host matrix on the phosphorescence of Tb-doped (1-5 at% Tb) Y2O3 nanophosphors is explored. Nanophosphors with different crystal phase (cubic and monoclinic) and morphology (uncoated and SiO2-coated) but with similar sizes were prepared by flame spray synthesis. That allowed the direct comparison of their phosphorescence performance excluding any observed size effect. The as prepared nanophosphors were characterized by X-ray diffraction, high resolution electron microscopy and photoluminescence spectroscopy. The meta-stable monoclinic crystal structure of Y2O3:Tb3+ nanophosphors favors their green phosphorescence.
Nano and micro- structural self-organization of implant surface from nitinol, fabricated by laser control SHS
Authors: Shishkovsky Igor V. , Morozov Yuri G.
Published: June 2019

Topology of the surface micro- and nano- structures induced by the synthesis of NiTi intermetallic phases under Selective Laser Sintering is studied by Scanning Electron Microscopy. According previously developed us method, those data were analysed by image processing software for identification and discussion of common features and peculiarities of the phase and structural transformations. It was shown, that fine substructures have self- ordering nature. Geometric similarity of synthesizing structures expects their fractal nature. The dependence between the fractal dimension -D of low-dimensional nanostructures and laser energy input -A was found. The change of the fractal dimension of low dimensional structures clearly correlates with the change of roughness, while the increase of the laser energy input influences the fractal dimension - D in different ways. Shown that particularities of phase structural transformations at the intermetallic synthesis in the Ni-Ti system have been defined an appearance of nano sized and self-ordering substructures of cellular, dendrite or mosaic types. A sharp variation of the D orientation indicates about of change of the phase-formation mechanism.
Simulation of Particle Synthesis by Premixed Laminar Stagnation Flames
Authors: Modak Abhijit , Puduppakkam Karthik , Naik Chitralkumar , Meeks Ellen
Published: June 2019

A sectional method for determining particle size distributions has been implemented within the particle tracking module included with CHEMKIN-PRO. The module is available for use with many types of reactor models, ranging from 0-D batch reactors to laminar flame simulations. Coupled with the Burner-stabilized Stagnation Flame (BSSF) Model, the sectional model offers a high-fidelity, robust, and efficient computational framework for simulating flame synthesis of particles in a laminar, premixed stagnation flame environment. The CHEMKIN-PRO coupling allows inclusion of detailed gas-phase chemistry that determines key particle-formation precursors, along with physical processes such as nucleation and coagulation of particles. These capabilities are demonstrated for two flame-particle systems of practical importance, viz. nanocrystalline titania synthesis and soot formation. The results are compared with experimental data obtained at the University of Southern California (USC) flame facility. Computed particle size distributions show good agreement with experimental data. Simulations have led to exploration of the parameter space for particle production and particle-size influences.
Valence Band Offset at Amorphous Boron Carbide / Silicon Interfaces
Authors: King Sean W. , French Marc , Jaehnig Milt , Kuhn Markus
Published: June 2019

In order to understand the fundamental charge transport in a-B4-5C:H/Si heterostructure devices, we have utilized x-ray photoelectron spectroscopy to determine the valence band offset at interfaces formed by Plasma Enhanced Chemical Vapor Deposition of a-B4-5C:H on (100) Si. For such interfaces, we observed relatively small valence band offset values of ± 0.25 eV.
The Viability of Nanotechnology-based InGaN Solar Photovoltaic Devices for Sustainable Energy Generation
Authors: Pearce Joshua M. , Zhang Chenlong , Rozario Joseph , Gwamuri Jephias
Published: June 2019

The unrestrained combustion of fossil fuels has resulted in vast pollution at the local scale throughout the world, while contributing to global warming at a rate that seriously threatens the stability of many of the world's ecosystems. Solar photovoltaic (PV) technology is a clean, sustainable and renewable energy conversion technology that can help meet the energy demands of the world’s growing population. Although PV technology is mature with commercial modules obtaining over 20% conversion efficiency there remains considerable opportunities to improve performance. The nearly global access to the solar resource coupled to nanotechnology innovation-driven decreases in the costs of PV, provides a path for a renewable energy source to significantly reduce the adverse anthropogenic impacts of energy use by replacing fossil fuels. This study explores several approaches to improving indium gallium nitride-based PV efficiency with nanotechnology: optical enhancement, microstructural optimization for electronic material quality and increasing the spectral response via bandgap engineering. The results showing multibandgap engineering with InGaN and impediments to widespread deployment and commercialization are discussed including technical viability, intellectual property laws and licensing, material resource scarcities, and economics. Future work is outlined and conclusions are drawn to overcome these limitations and improve PV device performance using methods that can scale to the necessary terawatt level.
Crystallinity and Mechanical Properties of Polypropylene-based Graphene Nanocomposites Studied with Atomic Force Microscopy and Raman Spectroscopy
Authors: Gronski Kjerstin , Flaig Robinson , Camacho Jorge , Wu Yan , Hamilton James P.
Published: June 2019

Atomic force microscopy (AFM) and Raman spectroscopy were used to characterize the morphology and the local mechanical properties of polypropylene-based graphene nanocomposites. Amplitude Modulated AFM was used to perform phase angle measurements to estimate the loss tangent, along with the local elastic modulus of the nanocomposite’s surface as a function of graphene content. We have observed an increasing trend in phase angle as the graphene content increased. We also identified wrinkled graphene flakes embedded in the polymer matrix. The graphene corrugation and mismatched strain between polymer and graphene sheets show a variation in the phase angle that is corroborated with Raman measurements. Mechanically exfoliated graphene on SiO2 was characterized as a baseline to understand the effect of graphene wrinkles compared to graphene surfaces on phase angle. The Raman results revealed that there are changes in the crystalline morphology of the polymer with the addition of graphene.
Lithium-containing semiconductor crystals for radiation detection
Authors: Stowe Ashley C. , Cochran Joe , Bhattacharya Pijush , Tupitsyn Eugene , Wiggins Brenden , Groza Michael , Burger Arnold
Published: June 2019

Semiconductor materials have shown promise as ionizing radiation detection devices; however, to be used as a neutron detector, these materials require the addition of a nucleus with a large neutron absorption cross section (such as 10B or 6Li) to capture thermal neutrons and convert them into directly detectable particles. A semiconducting material that contains the neutron absorber within its regular stoichiometry has the potential to be more efficient than a layered or heterogeneous device at transferring the kinetic energy of the charged particle into the semiconducting material. One class of materials that has shown promise is Li-containing AIBIIIXVI2 compounds such as LiGaTe2, LiGaSe2, and LiInSe2. These materials have band gaps (2-3.5 eV) appropriate for room-temperature detection of thermal neutrons and would be the first detection material that is simultaneously, exquisitely sensitive to thermal neutrons; is insensitive to gammas; and acts as a direct conversion device. A vacuum distillation process provided high-purity lithium metal for AIBIIIXVI2 synthesis. Single crystals of sufficient bulk resistivity (grown for LiGaSe2 and LiInSe2LiInSe2) showed a distinct photo response as well as a clear response to alpha particles. Additional radiation measurements indicated that a 6 mm x 7 mm x 1.33 mm crystal of LiInSe2 detected gamma rays, and despite being composed of natural abundance lithium, responded to thermal neutrons as well.
Microwave Reflection From The Microwave Photo-Excited High Mobility GaAs/AlGaAs Two-Dimensional Electron System
Authors: Ye Tianyu , Mani R. G. , Wegscheider W.
Published: June 2019

We examine the microwave reflection from the high mobility GaAs/AlGaAs two-dimensional electron system (2DES). Strong correlations have been observed between the microwave induced magnetoresistance oscillations and the microwave reflection oscillations in a concurrent measurement of the microwave illuminated magnetoresistance and the microwave reflection from the 2DES. The correlations were followed as a function of the microwave frequency and the microwave power dependent. Different existing theories are considered to explain the results.
Microstructural evolution during mechanical treatment of ZnO and black NiO powder mixture
Authors: Kakazey M. , Vlasova M. , Vorobiev Y. , Leon I. , Gonzalez M. Cabecera , Urbiola E.A. Chávez
Published: June 2019

Kinetics of the microstructural evolution in ZnO and NiO black powder mixture during prolonged mechanical processing (MP) was investigated by Scanning electron microscopy (SEM), Laser Particle Sizer (LPS), X-ray diffraction, electron paramagnetic resonance (EPR), infrared absorption (FTIR) and UV-Visible diffuse reflection methods.
A new mild synthesis and optical properties of colloidal ZnO nanocrystals in dimethylformamide/ethanol solutions
Authors: Panasyuk Yaroslav V. , Rayevska Oleskandra E. , Stroyuk Oleksandr L. , Kuchmiy Stepan Ya.
Published: June 2019

A green and mild synthesis of colloidal zinc oxide nanocrystals in ethanol/dimethylformamide mixtures was introduced which allows to produce stable crystalline ZnO particles and tailor their average size in the range of 2.8−4.5 nm by varying temperature and duration of post-synthesis ageing. An increase in dimethylformamide fraction in the mixture results in acceleration of ZnO nanocrystals ripening. Colloidal ZnO nanocrystals emit broadband photoluminescence in the range of 2−3 eV with the quantum yields of up to 12 %.
Modeling of the effect of bio-conjugation to anti-interleukin-10 antibodieson the photoluminescence of CdSe/ZnS quantum dots
Authors: Torchynska Tetyana V. , Vorobiev Yuri V. , Horley Paul P.
Published: June 2019

Bio-conjugated CdSe/ZnS core/shell quantum dots (QDs) attract essential scientific interest due to their possible nano-medicine applications, including selective highlighting of affected tissues and targeted drug delivery to the certain type of cells. The paper is focused on the theoretical description of the blue shift observed in the luminescence spectra of CdSe/ZnS QDs upon their bio-conjugation with the anti-interleukin-10 antibodies. We propose a model that describes the ground state of the exciton confined in a quantum dot and explaining the bio-conjugation phenomenon by the change of the effective confinement volume.
Using First Principles Thermodynamics to Predict the Shape Surface Structure and Reactivity of Solvated Nanoparticles at High Temperatures and Pressures.
Authors: O’Brien Christopher J. , Brenner Donald W.
Published: June 2019

Hydrothermal nanoparticle synthesis uses high temperature and pressure water to control the chemical processes that lead to specific compositions and structures. Analyses of the chemistry associated with this process have been mainly restricted to bulk thermodynamics in the form of quantities such as solubilities and empirical models based on experimental observations. In this paper we demonstrate for NiO and NiFe2O4 particles how effective reference chemical potentials derived from first principles calculations can be used to predict cluster shapes, nucleation barriers and surface reactivity. Implications for controlling the nanoparticle size and shape by adjusting pH and temperature will be discussed, as well as implications of these results in forming nanostructured materials by cluster condensation.
High-Temperature Dielectric Polyimide Films for Energy Storage Applications
Authors: Wang David H. , Kurish Brian A. , Treufeld Imre , Yang Lianyun , Zhu Lei , Tan Loon-Seng
Published: June 2019

Two new diamines containing three nitriles are synthesized via a 3-step route. They are polymerized with four commercial dianhydrides (i.e. 6FDA, OPDA, BTDA and PMDA) in N,N-dimethylacetamide (DMAc) to afford poly(amic acid)s, which are thermally cured at temperatures up to 300 °C to form tough, creasable films. Most of these polyimides are soluble in common solvents. Their glass transition temperatures range from 216 to 341 °C. The polyimides are stable up to 400 °C. The dielectric constants of these OPDA-based polyimides increase from 2.9 (CP2) to 4.7 as measured by the D-E loops.
High Performance Lithium-ion Battery Electrode: Silicon Coated on Vertically Aligned Carbon Nanofibers
Authors: Klankowski Steven , Rojeski Ronald , Li Jun
Published: June 2019

This study reports a high-performance hybrid lithium-ion anode material using coaxially coated silicon shells on vertically aligned carbon nanofiber (VACNF) cores. The robust bush-like highly conductive VACNFs effectively connect high-capacity silicon shells for lithium-ion storage. Such architecture allows the Si shells to freely expand/contract in the radial direction during lithium-ion insertion/extraction. A high specific capacity of 3000-3650 mAh(gSi)-1 was obtained at C/1 rate, comparable to the maximum value of amorphous Si, and ∼89% of the capacity was retained after 100 charge-discharge cycles. The lithium-ion storage capacity remains nearly the same from C/10 to C/0.5 rates. The ability to obtain high capacity at significantly improved power rates while maintaining the extraordinary cycle stability demonstrates the utilization of the unique properties of such hybrid architecture for lithium-ion batteries.
Role of Inter-Dopant Interactions on the Diffusion of Li and Na Atoms in Bulk Si Anodes
Authors: Tan Teck L. , Malyi Oleksandr I. , Legrain Fleur , Manzhos Sergei
Published: June 2019

We explore, via density functional theory (DFT) calculations, the effect on the barrier height for Li and Na diffusion in bulk Si of the presence of an extra Li/Na atom at the neighboring tetrahedral (T) or hexagonal (H) interstitial site. For both neighboring sites, the lowest diffusion barrier height is reduced, although the magnitude of the reduction depends on the inter-atomic distance between the 2 Li/Na atoms. We further calculate the effective interaction between the 2 atoms and show that it is a strong predictor of diffusion barrier heights for both Li-Si and Na-Si systems. Importantly, the correlation between inter-dopant interaction and barrier height may be used in future work to predict the diffusion barriers at higher concentration of inserted atoms.
Extraction and Characterization of Natural Dyes Applied to ZnO-based DSSC
Authors: Perez Hernandez G. , Pantoja Enriquez J. , Ramos-Villegas C. I. , Gonzalez-Solano M. , Oskam G. , Escobar-Morales B. , Flota-Robledo A. , Ricardez-Jiménez C.
Published: June 2019

The dye-sensitized solar cells (DSSC) are a technological and economical alternative to conventional p-n junction solar cells. The DSSC is composed of a transparent conducting electrode (SnO2:F) coated by a porous, nanocrystalline film of n-ZnO to which dye molecules are attached, an organic electrolyte containing a reduction-oxidation couple, and finally a counter-electrode (glass/SnO2:F) coated by a thin film of platinum. The most efficient dyes for DSSCs are based on Ruthenium polypyridyl complexes, related to the high absorption coefficient in the entire visible range and the efficient injection of electrons into the conduction band of ZnO. However, the ruthenium polypyridyl complex contains a heavy metal of relatively high cost, and synthetic routes are complicated with low yields. Moreover, natural dyes in addition to their availability, are cost-effective, non-toxic and biodegradable materials, and can be extracted by simple procedures. In this paper we report the extraction of natural dyes from the stems of mangrove (D1) and tinto (D2) trees as well as from walnut (D3) shell. First, it was necessary to dehydrate the materials, after which extraction was performed using ethanol, water and sodium hydroxide solution. The dyes were characterized using UV-visible and infrared spectroscopy. The analysis of the infrared spectra shows an intense and broad band related to OH bond stretching vibration at 3393, 3442 and 3390 cm-1 for the mangrove tree, tinto tree and walnut shell, respectively. At 1051, 1123 and 1050 cm-1, there was a very strong absorption due to the stretching vibration of CO group, for the mangrove tree, tinto tree and walnut shell, respectively. These results indicate that the functional group for bonding to the ZnO is -OH for these dyes. The results of the U-Vis spectroscopy show that the strongest absorption in the visible region is provided by dyes of the tinto and mangrove trees. The current - voltage curve of a preliminary ZnO-DSSC sensitized with the natural dye of the mangrove tree bark is presented.
A Comparative Study of Quasi-solid Nanoclay Based Electrolyte and Liquid Electrolyte Dye Sensitized Solar Cells
Authors: Main Laura , Munukutla Lakshmi , Fauss Brian , Curtis Travis , Kannan Arunachalanadar M.
Published: June 2019

Dye sensitized solar cells (DSSCs) are currently being explored as a cheaper alternative to the more common silicon (Si) solar cell technology with improved performance in low light conditions and less sensitivity to varying angles of incident light. One of the major challenges facing DSSCs is loss of the liquid electrolyte, through evaporation or leakage, which lowers stability and leads to increased degradation. To address this, batches of gel electrolyte cells are fabricated with 7 wt% nanoclay gel electrolyte and liquid electrolyte and were evaluated at standard test conditions over time. The gel cells achieved efficiencies as high as 9.18% compared to the 9.65% achieved by the liquid cells. Over a period of 10 days, the liquid cells degraded less than 20% of its maximum efficiency. By contrast, the gel cell's efficiency did not decrease to 20% of its maximum efficiency until 45 days. After several measurements, the liquid cells showed visible signs of leakage through the sealant, whereas the gel cells did not. This resistance to leakage likely contributed to the improved performance of the quasi-solid cells over liquid electrolyte DSSCs.
Modeling the Mechanical Behavior of P3HT/Fullerene Blends For Photovoltaic Applications
Authors: Zhao B. , Awartani O. , O’Connor B.T. , Zikry M. A.
Published: June 2019

Organic solar cells, comprised of P3HT-fullerene blends, have the potential for photovoltaic energy applications. However, there is limited understanding of the mechanical behavior of these devices, and how this behavior can be tailored for optimal organic solar cell performance and device reliability. Therefore, a recently developed computational approach that is based on a constitutive representation of semi-crystalline polymers and fullerenes is used to identify the dominant morphological and microstructural characteristics that would affect the mechanical behavior of the active layer. The predictions indicate that stress and dislocation-density accumulation in interfacial regions and tie molecules play a significant role on the overall behavior.
Examining the crystal growth that influences the electronic device output from vertical arrays of ZnO nanowires
Authors: Lord Alex M. , Ward Michael B. , Walton Alex S. , Evans Jonathan , Smith Nathan , Maffeis Thierry G. , Wilks Steve P.
Published: June 2019

ZnO nanowire (NW) arrays were examined with Transmission Electron Microscopy (TEM) in cross-section after preparation by Focused Ion Beam (FIB) milling. This technique revealed that ZnO nanowires grown using a Au catalyzed vapor technique typically have Au particles at the NW tips, and also randomly dispersed across the base crystal growth that joins adjacent NWs. It is shown the adjacent NWs and the combined base growth is one crystal structure which can be used as a back electrical contact making fabrication of vertical array devices possible. However, the base growth displays detrimental features such as embedded Au particles and lattice defects which can affect the electrical output through depletion regions and scattering centers. In an effort to overcome these problems we investigate a growth method that is nucleated through a minor alteration of the a-plane sapphire surface roughness via a weak chemical etch. Observations of various stages of the growth show the growth nucleates as separate nanoislands that grow in c-plane alignment with Sapphire (1-210), and as growth continues these islands meet and form a polycrystalline film. Further growth initiates nanowire growth and the formation of a single crystal base layer and NW structure that can cover several square millimeter’s. This allows high quality arrays that are relatively free from defects to be formed without any metals contamination and ready for further device processing.
Multi-branched gold nanoparticles for Surface Enhanced Raman scattering characterization
Authors: Johnston Jencilin , Taylor Erik N. , Gilbert Richard J. , Webster Thomas J.
Published: June 2019

Surface enhanced Raman scattering (SERS) is a sensitive and reproducible vibrational spectroscopic technique used to detect and characterize molecules near the surface of noble metals like Au, Ag, Pt, Cu, etc. SERS enhances Raman signals through light-induced plasmonic vibrations occurring on irregular metal surfaces and localized electromagnetic augmentation. To better define nano-scale regions of the Raman signal enhancement, we generated gold nanoparticles with a unique multi-branched configuration along with surface-adsorbed fluorescent reporter molecules. The reporter molecules included a set of near-infra red active fluorescent dyes IR820 (green cyanine, photo electronic dye), DTTC (3, 3'-diethylthiatricarbocyanine iodide) and DTDC (3, 3'- diethylthiadicarbocyanine iodide). We employed a one-pot synthesis method in order to generate a stellate configuration in gold nanoparticles through the reduction of HAuCl4 with Good’s buffer, HEPES, at pH 7.4 and room temperature. A cell viability assay was performed with normal esophageal cells exposed to the multi-branched gold nanoparticles and SERS molecules to assess their toxicity. Our results demonstrate the capacity of multibranched gold nanoparticles linked to Raman reporter molecules to generate distinct signature spectra and, with the exception of the gold nanoparticles functionalized with DTTC, remain non-toxic to normal esophageal cells.
Material Matters in the Physics Classroom
Authors: Chiaverina Chris
Published: June 2019

What do fiber optics, superconductors, memory wire, polymers, solid state devices, ferrofluid, rare earth magnets, carbon-based electroacoustic devices, and photonic crystals have in common? They are all products of materials science research. Many of these advances play an important role in improving daily life; all are capable of enhancing the teaching of physics. This paper will address how topics from materials science can be used to ignite student interest by providing the basis for exciting hands-on activities.
Silica Fume, Bond Strength, and the Compressive Strength of Mortar
Authors: Darwin David , Zhenjia Shen , Harsh Shraddhakar
Published: June 2019

The strength and strain-rate sensitivity of cement paste and mortar is studied as a function of water-cementitious material ratio (W/C) and silica fume content. W/C's of 0.30 and 0.35 are used for materials without silica fume, while W/C's ranging from 0.336 to 0.436 are used for material containing silica fume. The volume fractions of cement paste matrix and sand are held at 63 and 37 percent, respectively, for all mortars. Strain rates of 30, 3000, and 300,000 microstrain per second are used. The results indicate that materials with silica fume are less strain-rate sensitive of than materials without silica fume. The replacement of cement by silica fume appears to (1) reduce rather than increase the bond strength between cement paste and sand and (2) increase the compressive strength of mortar primarily by increasing the strength of the cement paste matrix.
Analysis of Synthetic Fiber Pull-Out from a Cement Matrix
Authors: Wang Youjiang , Li Victor C. , Backer Stanley
Published: June 2019

Experiments were conducted on specimens containing nylon or polypropylene monofilaments embedded in a precracked matrix. During pull-out tests, it was generally observed that the pulling force continued to increase after one or both sides of the filament had begun to slip out, even though one or both of the embedded filament lengths were decreasing. This indicated that the fiber/matrix shear stress increased with the fiber slippage distance. Examination of the extracted filaments under a scanning electron microscope (SEM) revealed the increased shear resistance to be the result of fiber surface abrasion. The severity of abrasion was observed to increase with the fiber slippage distance before complete pull-out. A theoretical model has been developed to predict the pull-out force versus displacement relationship based on given fiber/matrix shear strength as an increasing function of the slippage distance. The model gives good prediction in comparison with experimental results.
Study of Fiber Matrix Interfaces in Metakaoline-Opc Blended Cement GRC Composites
Authors: Ambroise J. , Dejean J. , Pera J.
Published: June 2019

Ductility is one of the main requirements of a reliable building material; the traditional LOP and MOR criteria do not reveal this quality. Other criteria based on deflection, energy or bond-slip relationships are presented. They are applied to four very different series of composites: very brittle, very ductile, and intermediate. The results point out that only the criteria based on the flexural test up to splitting, at a constant deflection rate, can reveal the higher ductility of the metakaoline-OPC blended matrix associated with AR glass. From this test, the bond-slip relationship can be determined. This leads to the definition of a comparative parameter which describes the mechanical interfacial compatibility of the matrix versus the fibers.
Analytical Prediction of the Pull-Out Behavior of Steel Fibers in Cement1tious Matrices
Authors: Nammur George , Naaman Antoine E. , Clark Samuel K.
Published: June 2019

While typical pull-out tests have been, and still are carried out extensively in materials and structural research, the results of such tests are often incapacitated by a lack of understanding of the pull-out behavior. This shortcoming is the source of numerous basic mistakes in the interpretation of pull-out curves.
Bonding in Cementitious Composites: How Important is it?
Authors: Mindess Sidney
Published: June 2019

A number of different types of interfacial bonding occur in concrete, including:

i) bonding between various phases (including anhydrous cement) in the hydrated cement paste (hcp) system

ii) bonding between cement and aggregates

iii) bonding between cement or mortar and the fibres in fibre-reinforced concrete; and

iv) bonding between concrete and steel reinforcing bars or prestressing cables.

The importance of these types of bonds with respect to the mechanical behaviour of concrete is discussed. It is concluded that in some systems, the mechanical properties are governed primarily by the interfacial bond; in other systems, however, this bond has only a secondary effect.
The Effect of Bond Characteristics between Steel Slag Fine Aggregate and Cement Paste on Mechanical Properties of Concrete and Mortar
Authors: Yuji Wang
Published: June 2019

The ordinary fine aggregate in concrete has been replaced by ground and sieved steel slag fine aggregate, treated and exposed to air for three months. Compared with concrete made from natural sand, properties such as compressive strength, flexural strength, elastic modulus, permeability and abrasion resistance are considerably improved. The improvement increases with a decrease in w/c ratio, an increase in curing time and an increase in the replacement weight of sand. These results are due to the fact that the steel slag contains some active minerals such as C3S, C2S, C4AF, etc., and shows favorable surface physical characteristics that improve the bond between steel slag particles and cement paste. The results of XRD, SEM and EPM microhardness showed that there are heavier concentration of ions, with finer crystals and a lower degree of CH orientation at the interfacial zone between steel slag particles and cement paste. The study also found small cementitious and fibrous C-S-H crystals growing from the fine aggregate, which are linked with hydrated products from cement paste making the bond and structural characteristic more favorable with cement. The steel slag fine aggregate is an active mineral similar to cement. The bond between the aggregate and cement paste is strengthened both physically and chemically.
Synthesis and Characterization of T12Ba2CaCu2O8 and T12Ba2Ca2Cu3O10
Authors: McMills Lauren E. H. , Li Shu , Zhang Zhen , Greenblatt Martha
Published: June 2019

Single-phase samples of T12Ba2CaCu2O8 and T12Ba2Ca2Cu3O10 have been prepared using a reliable and simple synthetic method. Samples were characterized by x-ray powder diffraction, magnetic susceptibility and four probe resistivity methods. The TcR=0 values for T12Ba2CaCu2O8 ranged from 100 to 105K, whereas those for T12Ba2Ca2Cu3O10 ranged from 96 to 107K. The relationship between the superconducting properties and the various preparation conditions are discussed.
Electron Cyclotron Resonance Hydrogenation of Poly-Si Thin Film Transistors on SiO2/Si Substrates
Authors: Liu Gand , Ditizio Robert A. , Fonash Stephen J. , Tran Nang
Published: June 2019

We report the results of an ECR hydrogenation time-behavior study on polycrystalline silicon thin film transistors. The device characteristics, such as mobility, subthreshold slope, threshold voltage, off current and on/off current ratio, were measured as a function of the passivation time. It was found that there is an optimal passivation time for this particular TFT structure, and overexposure to ECR hydrogen plasma may cause the degradation of some device parameters.
Low Energy Ar Ion Bombardment of (001) Si: Defects and Surface Morphology
Authors: Murty M. V. R. , Atwater Harry A. , Watson Thomas J.
Published: June 2019

The interaction of low energy Ar+ ions with several surface defect structures on (001) Si has been investigated using molecular dynamics simulation. The simulations suggest that ions with energy less than 20 eV selectively displace surface atoms without causing bulk damage, and that the displacement energies for different defect structures is different. The most important effect of ion bombardment on surface morphology is the increased formation rate of single adatoms, which may lead to smoother surfaces by enhanced coarsening at typical epitaxial temperatures. Simulations results also imply that the migration component of adatom diffusion is not significantly enhanced by ion bombardment at typical epitaxial temperatures (600 – 800 K).
The Role of Oxygen In the CF2Cl2 Reactive Ion Etching of Pecvd Films
Authors: Kuo Yue
Published: June 2019

An extensive study on 02 effects on RIE of PECVD a-Si:H and SiNx has been carried out. Mixtures of CF2Cl2/HCI and CF2Cl2/CF3Cl were used as base gases. The addition of O2 into these gases changed the film etch rate and etch selectivity in different ways. Process results were interpreted by examining the plasma phase chemistry, the ion bombardment energy, and ESCA surface chemical states.
The Influence of HBr Discharge Ambience on Poly-Si/SiO2 Etching Selectivity
Authors: Ikawa E. , Tokashiki K. , Kikkawa T. , Teraoka Y. , Nishiyama I.
Published: June 2019

The influence of HBr discharge ambience on SiO2 etching is investigated. A batch type parallel-plate reactive ion etching (RIE) dry etcher was used. The discharge ambience was changed by changing the numbers of poly-Si and SiO2 wafers in the same chamber. It is found that as the number of poly-Si wafers increased, the poly-Si etch rate slightly decreased due to a loading effect and SiO2 etching rate drastically increased. The selectivity of poly-Si / SiO2 decreased with increasing the ratio of the loaded poly-Si number in the same chamber. When A12O3 wafers instead of poly-Si wafers were loaded with SiO2 substrates, SiO2 etching rate enhancement did not occur. Therefore, increase of SiO2 etch rate could not be explained using a loading effect. From the results of mass analysis during etching in Si contained HBr plasma, etching products SiBrx (x=1,2,3) peaks were observed. Namely, when the Si etching products were supplied to SiO2 surface, SiO2 etch rate increased. In order to suppress the enhancement of SiO2 etch rate, the etch temperature must be reduced.
Ion Effects in Optical Films
Authors: Gibson U. J.
Published: June 2019

Ion bombardment during growth of thin films has been shown to be a powerful technique for alteration of a wide variety of film properties from index of refraction and stoichiometry to density and abrasion resistance. A brief review of the deposition processes and ion effects of relevance to the production of optical films is presented. Application of the technique to some particular problems in films with both optical and protective roles, and the use of ion beams to alter the chemical composition and hence index of films will be discussed. Both homogeneous and spatially non-uniform coatings will be discussed, including generation of multilayer filters and gradient index structures in waveguiding films.
Modification Of Properties Of Ion-Beam-Sputtered Yttrium-Oxide Thin Films By Low-Energy Ion Bombardment
Authors: Klemm K. A. , Johnson L. F. , Moran M. B.
Published: June 2019

The effect of low-energy ion bombardment on ion-beam-sputtered yttrium-oxide films was studied. Yttria films were subjected to argon ions accelerated by a potential of up to 500 V with current densities of up to 8 μA/cm2 and were deposited at differing substrate temperatures. Yttria films bombarded during deposition were found to be amorphous, and trends observed with increased ion energy include reduced amount of residual compressive stress, increased argon content, and decreased refractive index, depending on deposited energy and substrate temperature.
Dynamic Monte Carlo Simulation of Ion Beam and Plasma Techniques
Authors: Möller W.
Published: June 2019

A multiprojectile version of TRIDYN has been employed to simulate ion-induced effects which occur during ion-beam assisted deposition (IBAD) or plasma-assisted chemical vapour deposition (PECVD) of thin films.

Simulations of the formation of boron nitride films deposited from evaporated boron and energetic nitrogen show an excellent agreement with experimental results for nitrogen concentrations below the stoichiometric limit. For high N/B flux ratios, non-collisional mechanisms (ion-induced outdiffusion, surface trapping of outdiffusing nitrogen) have been included in the simulations, again producing good agreement with the experimental results.

Simulations of the PECVD of hydrocarbon films suffer from the poor knowledge of the neutral and ionic fluxes which contribute to the growth of the layers. Nevertheless, the composition of the films and its dependence on ion energy can be predicted with satisfactory agreement with experimental findings. A simple model of preferential displacement yields a reasonable average ratio of sp2and sp3coordinated carbon atoms. The energy dependence of the bond ratio is in contradiction to experimental observation.