208 research outputs found
Photon recycling in Fabry-Perot micro-cavities based on SiN waveguides
We present a numerical analysis and preliminary experimental results on
one-dimensional Fabry-Perot micro-cavities in SiN waveguides. The
Fabry-Perot micro-cavities are formed by two distributed Bragg reflectors
separated by a straight portion of waveguide. The Bragg reflectors are composed
by a few air slits produced within the SiN waveguides. In order to
increase the quality factor of the micro-cavities, we have minimized, with a
multiparametric optimization tool, the insertion loss of the reflectors by
varying the length of their first periods (those facing the cavity). To explain
the simulation results the coupling of the fundamental waveguide mode with
radiative modes in the Fabry-Perot micro-cavities is needed. This effect is
described as a recycling of radiative modes in the waveguide. To support the
modelling, preliminary experimental results of micro-cavities in SiN
waveguides realized with Focused Ion Beam technique are reported.Comment: 5 pages, 5 figure
Schwartz - Zippelov teorem i neke njegove primjene
U ovom radu izloĆŸen je rezultat poznat pod nazivom Schwartz - Zippelova lema ili Schwartz - Zippelov teorem. Tema rada pripada preteĆŸno algebri, ali ima znaÄajne primjene u drugim matematiÄkim podruÄjima kao ĆĄto je na primjer teorija algoritama, te kombinatorika. Rad se sastoji od tri poglavlja. U uvodu je ukratko opisana tema i cilj rada. Prvo poglavlje sadrĆŸi kratku povijest nastanka teorema, razliÄite oblike rezultata pojedinih autora, te kratki opis pojmova koriĆĄtenih u samom radu. Drugo poglavlje sastoji se od iskaza i dokaza Schwartz - Zippelovog teorema, a u treÄem poglavlju izloĆŸene su neke primjene tog teorema na probleme koji se mogu svesti na testiranje jednakosti polinoma. Takvi su, primjerice, problem postojanja savrĆĄenog sparivanja u grafu i ispitivanje svojstva asocijativnosti u grupoidu. Uz svaku primjenu navedeni su i prikladni primjeri.In this diploma thesis we present the result usually called the Schwartz-Zippel lemma or the Schwartz-Zippel theorem. The nature of this theorem is basically algebraic, but it has significant applications in other areas of mathematics, such as the theory of algorithms and combinatorial theory. The thesis consists of three chapters. The main theme and objective are briefly described in the introduction. The first chapter contains a short history of the theoremâs origins, various forms of the main results by different authors and some comments of basic concepts related to this topic. The statement and a proof of the Schwartz-Zippel theorem are given in the second chapter, together with the general outline of its applications. The third and final chapter consists of some applications to problems which can be reduced to polynomial identity testing, including the existence of a perfect matching in a graph and testing of the associativity property in a groupoi
Instalative art as a teaching resource for environmental education in Childhood Education
RESUMEN El niño aprende haciendo, manipulando los objetos y la realidad que se encuentra. Mediante la creaciĂłn artĂstica se puede abrir la puerta a nuevos aprendizajes, algunos de ellos pueden ser los siguientes: psicomotriz, emocional, cognitivo, artĂstico, lĂłgico-matemĂĄtico, lingĂŒĂsticoâŠ
Con el trabajo centrado en la instalaciĂłn artĂstica se le da al niño un espacio fĂsico que le permite pensar mediante la actividad. De este modo, la manipulaciĂłn de objetos durante el juego, ayuda al niño a descubrir y a experimentar a travĂ©s del manejo de los materiales de dicha composiciĂłn artĂstica. La propuesta escogida en este caso ha sido la utilizaciĂłn de materiales presentes en la naturaleza. Con esta elecciĂłn se intenta acercar la educaciĂłn medioambiental a los niños a travĂ©s del arte.
Este trabajo, diseñado para aulas de educaciĂłn infantil (2-6 años), consta de dos partes diferenciadas y relacionadas entre sĂ. Por un lado, se hace un recorrido teĂłrico por los antecedentes del arte de la instalaciĂłn enmarcada en el arte contemporĂĄneo, donde se verĂĄn algunos de los autores que han contribuido al desarrollo de esta disciplina artĂstica. De igual manera se revisa la importancia de la educaciĂłn en contenidos de naturaleza y medio ambiente. En una segunda parte del trabajo, se desarrolla una parte mĂĄs prĂĄctica para ilustrar a maestros y maestras acerca de cĂłmo se lleva al espacio fĂsico esta idea de instalaciĂłn artĂstica. Para ello, se mostrarĂĄn tres ejemplos de ellas y se llevarĂĄ a cabo el anĂĄlisis de su montaje, desarrollo y documentaciĂłn de la actividad.ABSTRACT The child learns by doing, manipulating the objects and the reality arround them. Through artistic creation he will be able to access new learnings, such as: psychomotor, emotional, cognitive, artistic, logical-mathematical, linguistic,...
Such work focused on the artistic installation, allows children to enjoy a place that gives them the chance to think while they are active. Thereby, object manipulation during the game helps them to learn through the handling of the materials of such artistic trend. The chosen approach in this case has been the usage of the materials which are found in nature. Along with this, we try to bring the environment friendly education close to the clindren through art.
This work designed for preschool classrooms (2-6 years), consists of two different parts which are related to each other. The first one, consists in a theoretical journey through the background of the art of the installation framed in contemporary art, where we will talk about some of the authors who have contributed to the development of this artistic style. As well, the importance of education in content of nature and environment is reviewed. In the second part of the work, the development of a more practical part will be done to illustrate teachers about how the idea of artistic installation is taken to the physical space. Three examples of it will be shown and the analysis will be carried out, as well the development and the documentation of the activity.Grado en Magisterio en EducaciĂłn Infanti
Effect of thermal treatment on the growth, structure and luminescence of nitride-passivated silicon nanoclusters
Silicon nanoclusters (Si-ncs) embedded in silicon nitride films have been studied to determine the effects that deposition and processing parameters have on their growth, luminescent properties, and electronic structure. Luminescence was observed from Si-ncs formed in silicon-rich silicon nitride films with a broad range of compositions and grown using three different types of chemical vapour deposition systems. Photoluminescence (PL) experiments revealed broad, tunable emissions with peaks ranging from the near-infrared across the full visible spectrum. The emission energy was highly dependent on the film composition and changed only slightly with annealing temperature and time, which primarily affected the emission intensity. The PL spectra from films annealed for duration of times ranging from 2 s to 2 h at 600 and 800°C indicated a fast initial formation and growth of nanoclusters in the first few seconds of annealing followed by a slow, but steady growth as annealing time was further increased. X-ray absorption near edge structure at the Si K- and L3,2-edges exhibited composition-dependent phase separation and structural re-ordering of the Si-ncs and silicon nitride host matrix under different post-deposition annealing conditions and generally supported the trends observed in the PL spectra
Si solid-state quantum dot-based materials for tandem solar cells
The concept of third-generation photovoltaics is to significantly increase device efficiencies whilst still using thin-film processes and abundant non-toxic materials. A strong potential approach is to fabricate tandem cells using thin-film deposition that can optimise collection of energy in a series of cells with decreasing band gap stacked on top of each other. Quantum dot materials, in which Si quantum dots (QDs) are embedded in a dielectric matrix, offer the potential to tune the effective band gap, through quantum confinement, and allow fabrication of optimised tandem solar cell devices in one growth run in a thin-film process. Such cells can be fabricated by sputtering of thin layers of silicon rich oxide sandwiched between a stoichiometric oxide that on annealing crystallise to form Si QDs of uniform and controllable size. For approximately 2-nm diameter QDs, these result in an effective band gap of 1.8 eV. Introduction of phosphorous or boron during the growth of the multilayers results in doping and a rectifying junction, which demonstrates photovoltaic behaviour with an open circuit voltage (VOC) of almost 500 mV. However, the doping behaviour of P and B in these QD materials is not well understood. A modified modulation doping model for the doping mechanisms in these materials is discussed which relies on doping of a sub-oxide region around the Si QDs
Atomic characterization of Si nanoclusters embedded in SiO2 by atom probe tomography
Silicon nanoclusters are of prime interest for new generation of optoelectronic and microelectronics components. Physical properties (light emission, carrier storage...) of systems using such nanoclusters are strongly dependent on nanostructural characteristics. These characteristics (size, composition, distribution, and interface nature) are until now obtained using conventional high-resolution analytic methods, such as high-resolution transmission electron microscopy, EFTEM, or EELS. In this article, a complementary technique, the atom probe tomography, was used for studying a multilayer (ML) system containing silicon clusters. Such a technique and its analysis give information on the structure at the atomic level and allow obtaining complementary information with respect to other techniques. A description of the different steps for such analysis: sample preparation, atom probe analysis, and data treatment are detailed. An atomic scale description of the Si nanoclusters/SiO2 ML will be fully described. This system is composed of 3.8-nm-thick SiO layers and 4-nm-thick SiO2 layers annealed 1 h at 900°C
Silicon and Germanium Nanostructures for Photovoltaic Applications: Ab-Initio Results
Actually, most of the electric energy is being produced by fossil fuels and great is the search for viable alternatives. The most appealing and promising technology is photovoltaics. It will become truly mainstream when its cost will be comparable to other energy sources. One way is to significantly enhance device efficiencies, for example by increasing the number of band gaps in multijunction solar cells or by favoring charge separation in the devices. This can be done by using cells based on nanostructured semiconductors. In this paper, we will present ab-initio results of the structural, electronic and optical properties of (1) silicon and germanium nanoparticles embedded in wide band gap materials and (2) mixed silicon-germanium nanowires. We show that theory can help in understanding the microscopic processes important for devices performances. In particular, we calculated for embedded Si and Ge nanoparticles the dependence of the absorption threshold on size and oxidation, the role of crystallinity and, in some cases, the recombination rates, and we demonstrated that in the case of mixed nanowires, those with a clear interface between Si and Ge show not only a reduced quantum confinement effect but display also a natural geometrical separation between electron and hole
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