Modeling and simulation of bulk gallium nitride power semiconductor devices

Bulk gallium nitride (GaN) power semiconductor devices are gaining significant interest in recent years, creating the need for technology computer aided design (TCAD) simulation to accurately model and optimize these devices. This paper comprehensively reviews and compares different GaN physical models and model parameters in the literature, and discusses the appropriate selection of these models and parameters for TCAD simulation. 2-D drift-diffusion semi-classical simulation is carried out for 2.6 kV and 3.7 kV bulk GaN vertical PN diodes. The simulated forward current-voltage and reverse breakdown characteristics are in good agreement with the measurement data even over a wide temperature range.

Fabrication, Optical Analysis and Photonic Applications of Certain Metallic Nanostructure-Integrated Dye Doped Polymer Optical Fibers” submitted by Ms. Suneetha Sebastian

Polymer Optical Fibers have occupied historically a place for large core flexible fibers operating in short distances. In addition to their practical passive application in short-haul communication they constitute a potential research field as active devices with organic dopants. Organic dyes are preferred as dopants over organic semiconductors due to their higher optical cross section. Thus organic dyes as gain media in a polymer fiber is used to develop efficient and narrow laser sources with a tunability throughout the visible region or optical amplifier with high gain. Dyes incorporated in fiber form has added advantage over other solid state forms such as films since the pump power required to excite the molecules in the core of the fiber is less thereby utilising the pump power effectively. In 1987, Muto et.al investigated a dye doped step index polymer fiber laser. Afterwards, numerous researches have been carried out in this area demonstrating laser emission from step index, graded index and hollow optical fibers incorporating various dyes. Among various dyes, Rhodamine6G is the most widely and commonly used laser dye for the last four decades. Rhodamine6G has many desirable optical properties which make it preferable over other organic dyes such as Coumarin, Nile Blue, Curcumin etc. The research focus on the implementation of efficient fiber lasers and amplifiers for short fiber distances. Developing efficient plastic lasers with electrical pumping can be a new proposal in this field which demands lowest possible threshold pump energy of the gain medium in the cavity as an important parameter. One way of improving the efficiency of the lasers, through low threshold pump energy, is by modifying the gain of the amplifiers in the resonator/cavity. Success in the field of Radiative Decay Engineering can pave way to this problem. Laser gain media consisting of dye-nanoparticle composites can improve the efficiency by lowering the lasing threshold and enhancing the photostability. The electric field confined near the surface of metal nanoparticles due to Localized Surface Plasmon Resonance can be very effective for the excitation of active centers to impart high optical gain for lasing. Since the Surface Plasmon Resonance of nanoparticles of gold and silver lies in the visible range, it can affect the spectral emission characteristics of organic dyes such as Rhodamine6G through plasmon field generated by the particles. The change in emission of the dye placed near metal nanoparticles depend on plasmon field strength which in turn depends on the type of metal, size of nanoparticle, surface modification of the particle and the wavelength of incident light. Progress in fabrication of different types of nanostructures lead to the advent of nanospheres, nanoalloys, core-shell and nanowires to name a few. The thesis deals with the fabrication and characterisation of polymer optical fibers with various metallic and bimetallic nanostructures incorporated in the gain media for efficient fiber lasers with low threshold and improved photostability.

Photochemical dynamics of laser-irradiated semiconductor nanostructures

Thesis (Ph.D.)--University of Washington, 2016-08

Matematik i det mångkulturella klassrummet : En litteraturstudie om flerspråkiga elevers problemlösningsförmåga

Forskning visar att flerspråkiga elevers matematikresultat sjunker i takt med att antalet flerspråkiga elever ökar i klassrummen. Forskningsresultaten visar att flerspråkiga elever framförallt har svårt för problemlösningsuppgifter med mycket text. Frågan är om lärare har tillräckligt med kunskaper och resurser för att tillgodose alla elevers behov. Syftet med vår litteraturstudie är att undersöka vilka strategier lärare kan använda för att stödja flerspråkiga elever. Vidare tar litteraturstudien upp vad som är betydelsefullt för att flerspråkiga elever ska kunna utveckla sin problemlösningsförmåga. I denna litteraturstudie har vetenskapligt granskade texter sökts och upptäckts via användning av olika söktekniker och därefter analyserats. Sökmetoderna vi har använt är slumpmässig sökning, systematisk sökning och kedjesökning. I litteraturstudien förekommer avhandlingar, konferensbidrag, empiriska undersökningar och artiklar i vetenskapligt granskade tidskrifter. Resultatet av vår litteraturstudie visar att flerspråkiga elever påverkas av flera olika faktorer. Lärare har en betydande roll för att eleverna ska kunna utveckla problemlösningsförmågan i ämnet matematik. Vårt resultat tar upp aspekter som lärare i ett mångkulturellt klassrum bör ta hänsyn till i undervisningen. De aspekter som tas upp i litteraturstudien är huruvida lärare tar hänsyn till elevernas tidigare erfarenheter och deras kultur. Ett viktigt begrepp inom detta område som behandlas i litteraturstudien är det etnomatematiska perspektivet. Vidare visar litteraturstudiens resultat att de flerspråkiga elevernas tillgång till sitt modersmål är en väsentlig del för att utveckla matematiska färdigheter. Fortsättningsvis visar resultatet att lärares val av kontextanknutna uppgifter är avgörande för att flerspråkiga elever ska kunna se en helhet i matematiska textuppgifter. Slutligen visar resultatet att det är viktigt att flerspråkiga elever måste ges möjlighet att tala matematik och att lärare belyser viktiga matematiska begrepp i klassrummet. 

El funcionamiento de las empresas solidarias de salud (ESS) : recomendaciones para mejorar su eficacia y eficiencia, resultantes de un estudio evaluativo

Las ESS son organizaciones creadas en 1993 con el fin de cumplir dos propósitos fundamentales: gestionar la adquisición por parte de las comunidades de servicios de salud financiadosmediante el subsidio directo otorgado por el Estado para este fin, yfacilitar la organización y desarrollo de las comunidades a través de la difusión de la cultura de la solidaridad. En el primer semestre de 1998, el Centro de Investigaciones en Desarrollo, Cimder, adscrito a la Universidad del Valle, ganó un concurso público para adelantar una evaluación comprensiva del funcionamiento de este tipo de organizaciones. En este documento se presentan algunas reflexiones de uno de los autores de la evaluación citada.

Role of substrate quality on the performance of semipolar (11 2 - 2) InGaN light-emitting diodes

We compare the optical properties and device performance of unpackaged InGaN/GaN multiple-quantum-well light-emitting diodes (LEDs) emitting at ∼430 nm grown simultaneously on a high-cost small-size bulk semipolar (11 2 - 2) GaN substrate (Bulk-GaN) and a low-cost large-size (11 2 - 2) GaN template created on patterned (10 1 - 2) r-plane sapphire substrate (PSS-GaN). The Bulk-GaN substrate has the threading dislocation density (TDD) of ∼ and basal-plane stacking fault (BSF) density of 0 cm-1, while the PSS-GaN substrate has the TDD of ∼2 × 108cm-2 and BSF density of ∼1 × 103cm-1. Despite an enhanced light extraction efficiency, the LED grown on PSS-GaN has two-times lower internal quantum efficiency than the LED grown on Bulk-GaN as determined by photoluminescence measurements. The LED grown on PSS-GaN substrate also has about two-times lower output power compared to the LED grown on Bulk-GaN substrate. This lower output power was attributed to the higher TDD and BSF density.

Biståndshandläggare inom äldreomsorgens upplevelse av sin arbetssituation : En kvalitativ studie ur ett salutogent perspektiv

Syftet med denna uppsats var att genom ett salutogent perspektiv få en ökad förståelse för, inom äldreomsorgen verksamma, biståndshandläggares arbetssituation samt att undersöka vad som kan bidra till att biståndshandläggares arbetssituation upplevs som lättare och mindre påfrestande. Metoden som använts är kvalitativa intervjuer där sex biståndshandläggare verksamma i Värmland har intervjuats. Intervjuerna analyserades genom teman ur KASAM och resulterade i kategorier under varje tema. Under temat begriplighet framkom att biståndshandläggare får stöd från sina kollegor men att de också önskar att det fanns mer resurser för handledning. Biståndshandläggare utför mer än vad som ingår i arbetsbeskrivningen. Under temat hanterbarhet framgår att hög arbetsbelastning hanteras genom att biståndshandläggarna måste planera, strukturera och prioritera. Kollegornas stöd gör arbetet lättare att hantera då de genom att prata med varandra bearbetar känslomässigt påfrestande delar av arbetet. De uttryckte olika behov av att reflektera över sitt arbete. Biståndshandläggare har en stor frihet att planera sin egen arbetsdag och de samverkar med andra professioner. Under temat meningsfullhet framgår att biståndshandläggare finner mening i att göra skillnad för den enskilde. Vårt resultat visar att biståndshandläggarna är utsatta för stress i sitt arbete och att de också har förmåga att möta stressen, men förmågan att möta stressen minskar när arbetsbelastningen blir för hög. 

Growth and characterization of III-V compound semiconductor nanostructures by metalorganic chemical vapor deposition

Planar <110> GaAs nanowires and quantum dots grown by atmospheric MOCVD have been introduced to non-standard growth conditions such as incorporating Zn and growing them on free-standing suspended films and on 10° off-cut substrates. Zn doped nanowires exhibited periodic notching along the axis of the wire that is dependent on Zn/Ga gas phase molar ratios. Planar nanowires grown on suspended thin films give insight into the mobility of the seed particle and change in growth direction. Nanowires that were grown on the off-cut sample exhibit anti-parallel growth direction changes. Quantum dots are grown on suspended thin films and show preferential growth at certain temperatures. Envisioned nanowire applications include twin-plane superlattices, axial pn-junctions, nanowire lasers, and the modulation of nanowire growth direction against an impeding barrier and varying substrate conditions.

Posibilidades y limitaciones de la garantía de depósitos

Un sistema de garantía de depósitos puede contribuir a la estabilidad financiera, siempre que cuente con fondos adecuados y otros mecanismos de salvaguardia, como un sólido programa de supervisión bancaria. En la fábula de Esopo sobre la liebre y la tortuga, la tortuga aceptó echar una carrera con la liebre. La liebre, mucho más veloz que la tortuga, salió corriendo a toda velocidad en el primer tramo de la carrera, pero después se acostó a dormir una siesta, convencida de que podría adelantar a su contrincante. Cuando despertó, la tortuga, que había avanzado lentamente pero con constancia, se estaba acercando a la meta. La liebre no pudo alcanzar a la tortuga y ésta ganó la carrera. Un sistema de garantía de depósitos eficaz se asemeja más a una tortuga que a una liebre. A primera vista parece que puede establecerse rápidamente y con facilidad un sistema nacional de garantía de depósitos que anuncie una garantía pública para los depósitos de los bancos. Algunos países, a fin de evitar el retiro masivo de depósitos que podría llevar a la quiebra a los bancos en situación sólida y a fin de estabilizar un sistema bancario en dificultades, han intentado crear un sistema de garantía de depósitos de esta forma. Lamentablemente, a menos que el sistema cuente con fondos suficientes para hacer frente a una grave crisis financiera y con un sólido programa de supervisión bancaria, este sistema está destinado al fracaso

Image-Guided Precision Manipulation of Cells and Nanoparticles in Microfluidics

Manipulation of single cells and particles is important to biology and nanotechnology. Our electrokinetic (EK) tweezers manipulate objects in simple microfluidic devices using gentle fluid and electric forces under vision-based feedback control. In this dissertation, I detail a user-friendly implementation of EK tweezers that allows users to select, position, and assemble cells and nanoparticles. This EK system was used to measure attachment forces between living breast cancer cells, trap single quantum dots with 45 nm accuracy, build nanophotonic circuits, and scan optical properties of nanowires. With a novel multi-layer microfluidic device, EK was also used to guide single microspheres along complex 3D trajectories. The schemes, software, and methods developed here can be used in many settings to precisely manipulate most visible objects, assemble objects into useful structures, and improve the function of lab-on-a-chip microfluidic systems.

Mixture of time-dependent growth models with an application to blue swimmer crab length-frequency data

Understanding how aquatic species grow is fundamental in fisheries because stock assessment often relies on growth dependent statistical models. Length-frequency-based methods become important when more applicable data for growth model estimation are either not available or very expensive. In this article, we develop a new framework for growth estimation from length-frequency data using a generalized von Bertalanffy growth model (VBGM) framework that allows for time-dependent covariates to be incorporated. A finite mixture of normal distributions is used to model the length-frequency cohorts of each month with the means constrained to follow a VBGM. The variances of the finite mixture components are constrained to be a function of mean length, reducing the number of parameters and allowing for an estimate of the variance at any length. To optimize the likelihood, we use a minorization–maximization (MM) algorithm with a Nelder–Mead sub-step. This work was motivated by the decline in catches of the blue swimmer crab (BSC) (Portunus armatus) off the east coast of Queensland, Australia. We test the method with a simulation study and then apply it to the BSC fishery data.

La Participación comunitaria en la resolución de los problemas de salud parroquia Jerusalén. Cantón Biblián. Provincia del Cañar.1997

En el presente trabajo se parte de un marco teórico, que contempla los conceptos y principios básicos de la Atención Primaria de Salud [APS], de los Sistemas Locales de Salud [SILOS], poniendo énfasis en las formas de Participación Comunitaria por ser uno de los ejes principales en el que se sustenta la APS. Luego mediante la aplicación de la Participación Comunitaria en la parroquia Jerusalén, se obtuvieron los siguientes resultados: El equipo de salud logró concientizarse de los problemas existentes en la comunidad y se incorporó al trabajo comunitario con lo cual se ganó confianza, credibilidad y capacidad de asesoramiento; se identificó, reestructuró y conformó organizaciones comunitarias de acuerdo a las necesidades, con dichas organizaciones se realizó el Diagnóstico Participativo de Salud, que engloba: un censo poblacional y de migración mediante mapas parlantes elaborados por la comunidad, identificación de las patologías más frecuentes y de familias en riesgo y por último se priorizó y seleccionó como problema de acuerdo a la frecuencia, importancia y vulnerabilidad la falta de agua apta para el consumo. Para resolver este problema se utilizó una de las herramientas de la Gerencia de Calidad Total que es el Microproyecto, en donde la comunidad participó en la fase de Planificación, Ejecución y Evaluación, obteniéndose: El mejoramiento de los Conocimientos, Actitudes y Prácticas [CAPs] en la desinfección del agua mediante el método de clorificación; autogestión comunitaria para la compra de un equipo productor de cloro. Racionalización del consumo del agua, por último mediante la coordinación interinstitucional con el municipio del cantón Biblián y la Subsecretaría de Saneamiento Ambiental, se obtuvo una partida presupuestaria para la construcción del desarenador, la comunidad por su parte aportó con mano de obra a través de la organización de mingas.

Fabrication and optimizing of metal nano silicate as toxic metal absorbent from sea water

Pure Water, is a crucial demand of creature life. Following industrial development, extra amount of toxic metals such as chromium enters the environmental cycle through the sewage, which is considered as a serious threat for organisms. One of the modern methods of filtration and removal of contaminants in water, is applying Nano-technology. According to specific property of silicate materials, in this article we try to survey increased power in composites and various absorption in several morphologies and also synthesis of Nano-metal silicates with different morphologies as absorbent of metal toxic ions. At first, we synthesize nano zink silicate with three morphologies considering context and the purpose of this survey. 1) Nano synthesis of zink silicate hollow cavity by hydrothermal method in mixed solvent system of ethanol/glycol polyethylene. 2) Zink nano wires silicate in a water-based system by controlling the amount of sodium silicate. 3) Synthesis of nano zink silicate membrane. After synthesizing, we measured the cadmium ion absorbance by synthesized nano zink silicates. Controlling PH, is the applied absorption method. Next step, we synthesized nano zink-magnesium silicate composite in two various morphologies of nanowires and membrane by different precent of zink and magnesium, in order to optimize synthesized nano metal silicate. We used zink nitrate and magnesium nitrate and also measured cadmium absorption by synthesized nano metal silicates in the same way of PH control absorption. In the 3rd step, in order to determine the impact of the type of metal in nano metal silicate, we synthesized nano magnesium silicate and compared its absorption with nano zink silicate. Furthermore, we calculated the optimal concentration in one of synthesizes. Optimal concentration is the process which has the maximum absorption. While applying two methods of absorption in the test, finally we compared the effect of absorption method on the absorption level. Below you find further steps of synthesis: 1) Using IR, RAMAN, XRD spectroscopy to check the accuracy of synthesis. 2) Checking the dispersion of nano particles in ethanol solution by light microscope. 3) Measuring and observing particles with scanning electron microscope (SEM). 4) Using atomic absorption device for measuring the cadmium concentration in water-based solutions. The nano metal silicates were synthesized successfully. All of synthesized nano absorbents have the cadmium ion absorbency. The cadmium absorption via nano absorbents depend on various factors such as kind of metal in nano silicate and percent of metal in nano metal silicate composite. Meanwhile the absorption and PH control of medium containing the absorbent and solution would affect the cadmium absorption.

BRASIL: HACIA UN NUEVO BLOQUE HISTÓRICO

La coalición de fuerzas políticas que sostuvo el gobierno Fernando Henrique Cardoso durante cerca de ocho años entró definitivamente en crisis. El origen de esta crisis se encuentra en el agotamiento de una política económica que parecía exitosa en su comienzo pero que llevó de hecho el país a una de las más graves crisis de su historia.Esta fue la historia de las experiencias neoliberales de los años 90. Salinas duró seis años de esplendor, hasta la crisis del 94. Menen alcanzó reelegirse una vez pero no logró la segunda reelección hasta que su país entró en la dramática crisis actual. Fujimori también logró una reelección y cayó cuando quiso imponer su tercer mandato. En Venezuela la crisis explotó en el “Caracazo”, con Andrés Pérez en el gobierno, pero fue suplantada con más diez años de consenso neoliberal, que ganó la mayoría de la izquierda y pasó el bastión de la oposición al líder del intento insurreccional que se ligara al “Caracazo”: Hugo Chávez.

Mesoscale Optoelectronic Design of Wire-Based Photovoltaic and Photoelectrochemical Devices

The overarching theme of this thesis is mesoscale optical and optoelectronic design of photovoltaic and photoelectrochemical devices. In a photovoltaic device, light absorption and charge carrier transport are coupled together on the mesoscale, and in a photoelectrochemical device, light absorption, charge carrier transport, catalysis, and solution species transport are all coupled together on the mesoscale. The work discussed herein demonstrates that simulation-based mesoscale optical and optoelectronic modeling can lead to detailed understanding of the operation and performance of these complex mesostructured devices, serve as a powerful tool for device optimization, and efficiently guide device design and experimental fabrication efforts. In-depth studies of two mesoscale wire-based device designs illustrate these principles—(i) an optoelectronic study of a tandem Si|WO3 microwire photoelectrochemical device, and (ii) an optical study of III-V nanowire arrays.

The study of the monolithic, tandem, Si|WO3 microwire photoelectrochemical device begins with development and validation of an optoelectronic model with experiment. This study capitalizes on synergy between experiment and simulation to demonstrate the model’s predictive power for extractable device voltage and light-limited current density. The developed model is then used to understand the limiting factors of the device and optimize its optoelectronic performance. The results of this work reveal that high fidelity modeling can facilitate unequivocal identification of limiting phenomena, such as parasitic absorption via excitation of a surface plasmon-polariton mode, and quick design optimization, achieving over a 300% enhancement in optoelectronic performance over a nominal design for this device architecture, which would be time-consuming and challenging to do via experiment.

The work on III-V nanowire arrays also starts as a collaboration of experiment and simulation aimed at gaining understanding of unprecedented, experimentally observed absorption enhancements in sparse arrays of vertically-oriented GaAs nanowires. To explain this resonant absorption in periodic arrays of high index semiconductor nanowires, a unified framework that combines a leaky waveguide theory perspective and that of photonic crystals supporting Bloch modes is developed in the context of silicon, using both analytic theory and electromagnetic simulations. This detailed theoretical understanding is then applied to a simulation-based optimization of light absorption in sparse arrays of GaAs nanowires. Near-unity absorption in sparse, 5% fill fraction arrays is demonstrated via tapering of nanowires and multiple wire radii in a single array. Finally, experimental efforts are presented towards fabrication of the optimized array geometries. A hybrid self-catalyzed and selective area MOCVD growth method is used to establish morphology control of GaP nanowire arrays. Similarly, morphology and pattern control of nanowires is demonstrated with ICP-RIE of InP. Optical characterization of the InP nanowire arrays gives proof of principle that tapering and multiple wire radii can lead to near-unity absorption in sparse arrays of InP nanowires.