Impact of Si nanocrystals in a-SiOx<Er> in C-Band emission for applications in resonators structures

Si nanocrystals (Si-NC) in a-SiOx were created by high temperature annealing. Si-NC samples have large emission in a broadband region, 700nm to 1000nm. Annealing temperature, annealing time, substrate type, and erbium concentration is studied to allow emission at 1550 nm forsamples with erbium. Emission in the C-Band region is largely reduced by the presence of Si-NC. This reduction may be due to less efficient energy transfer processes from the nanocrystals than from the amorphous matrix to the Er3+ ions, perhaps due to the formation of more centro-symmetric Er3+ sites at the nanocrystal surfaces or to very different optimal erbium concentrations between amorphous and crystallized samples.Comment: 3 pages, 4 figure

O uso da argumentação na montagem de um modelo

Trabalhos recentes na área de Ensino de ciência têm tratado a argumentação como parte imprescindível das aulas de ciência, pois argumentar seria uma das características da ciência. A forma de análise recorrente em tais trabalhos é o padrão criado por Toulmin, que permite uma divisão do argumento e a identificação de seus elementos constituintes. Foi analisada uma seqüência didática com as turmas de 3º ano da escola de Aplicação da Universidade de São Paulo que culminou na montagem de um modelo de DNA. Tal montagem foi feita em grupos e as discussões ocorridas durante a tarefa foram gravadas e transcritas. A análise dos discursos mostrou argumentos simples compostos basicamente por dados e conclusão. A atividade se mostra diferente da ciência já que não são defendidos pontos de vista sobre uma questão aberta, mas sim opiniões sobre algo já estabelecido

A argumentação a partir da leitura e interpretação de dados experimentais

Uma das dificuldades encontradas nas atividades investigativas de biologia é a utilização de modelos experimentais, muitas vezes a coleta e o desenvolvimento de atividades com material vivo pode ter dificuldade acentuada. Outro aspecto a se observar é que em geral as atividades são de difícil execução no tempo estabelecido das aulas. Diante disso este estudo analisou se uma aula de biologia baseada na leitura e interpretação de dados experimentais viabiliza a formulação de argumentos conforme o modelo teórico de Toulmin (1958) e, quais são as características de tais falas quanto ao emprego e utilização de justificativas e de conhecimentos básicos. O presente estudo observou argumentos com a utilização de garantias que expressam em alguns casos o resgate de conceitos e em outros a utilização do desenho experimental do cientista como base para apoiar as conclusões dos alunos

The epidthelial sodium channel ENaC and its regulators in the epidermal permeability barrier function

The highly amiloride-sensitive epithelial sodium channel ENaC is well known to be involved in controlling whole body sodium homeostasis and lung liquid clearance. ENaC expression has also been detected in the skin of amphibians and mammals. Mice lacking ENaC expression lose rapidly weight associated with an epidermal barrier defect that develops following birth. This dehydration is accompanied with a highly abnormal lipid matrix composition and an impaired skin surface acidification. This strongly suggests a role of ENaC in the maturation of barrier function rather than in the prenatal generation of the barrier, and may be as such an important modulator for skin hydration. In parallel, gene targeting experiments of regulators of ENaC activity, membrane serine proteases, also termed channel activating proteases, like CAP1/Prss8 and matriptase/MT-SP1 by themselves have been shown to be crucial for the epidermal barrier function. In our review, we mainly focus on the role of ENaC and its regulators in the skin and discuss their importance in the epidermal permeability barrier function

The function and regulation of acid-sensing ion channels (ASICs) and the epithelial Na(+) channel (ENaC): IUPHAR Review 19.

Acid-sensing ion channels (ASICs) and the epithelial Na(+) channel (ENaC) are both members of the ENaC/degenerin family of amiloride-sensitive Na(+) channels. ASICs act as proton sensors in the nervous system where they contribute, besides other roles, to fear behaviour, learning and pain sensation. ENaC mediates Na(+) reabsorption across epithelia of the distal kidney and colon and of the airways. ENaC is a clinically used drug target in the context of hypertension and cystic fibrosis, while ASIC is an interesting potential target. Following a brief introduction, here we will review selected aspects of ASIC and ENaC function. We discuss the origin and nature of pH changes in the brain and the involvement of ASICs in synaptic signalling. We expose how in the peripheral nervous system, ASICs cover together with other ion channels a wide pH range as proton sensors. We introduce the mechanisms of aldosterone-dependent ENaC regulation and the evidence for an aldosterone-independent control of ENaC activity, such as regulation by dietary K(+) . We then provide an overview of the regulation of ENaC by proteases, a topic of increasing interest over the past few years. In spite of the profound differences in the physiological and pathological roles of ASICs and ENaC, these channels share many basic functional and structural properties. It is likely that further research will identify physiological contexts in which ASICs and ENaC have similar or overlapping roles

Modeling quasi-dark states with Temporal Coupled-Mode Theory

Coupled resonators are commonly used to achieve tailored spectral responses and allow novel functionalities in a broad range of applications, from optical modulation and filtering in integrated photonic circuits to the study of nonlinear dynamics in arrays of resonators. The Temporal Coupled-Mode Theory (TCMT) provides a simple and general tool that is widely used to model these devices and has proved to yield very good results in many different systems of low-loss, weakly coupled resonators. Relying on TCMT to model coupled resonators might however be misleading in some circumstances due to the lumped-element nature of the model. In this article, we report an important limitation of TCMT related to the prediction of dark states. Studying a coupled system composed of three microring resonators, we demonstrate that TCMT predicts the existence of a dark state that is in disagreement with experimental observations and with the more general results obtained with the Transfer Matrix Method (TMM) and the Finite-Difference Time-Domain (FDTD) simulations. We identify the limitation in the TCMT model to be related to the mechanism of excitation/decay of the supermodes and we propose a correction that effectively reconciles the model with expected results. A comparison with TMM and FDTD allows to verify both steady-state and transient solutions of the modified-TCMT model. The proposed correction is derived from general considerations, energy conservation and the non-resonant power circulating in the system, therefore it provides good insight on how the TCMT model should be modified to eventually account for the same limitation in a different coupled-resonator design. Moreover, our discussion based on coupled microring resonators can be useful for other electromagnetic resonant systems due to the generality and far-reach of the TCMT formalism.Comment: 7 pages, 4 figure

Spectral Engineering with Coupled Microcavities: Active Control of Resonant Mode-Splitting

Optical mode-splitting is an efficient tool to shape and fine-tune the spectral response of resonant nanophotonic devices. The active control of mode-splitting, however, is either small or accompanied by undesired resonance shifts, often much larger than the resonance-splitting. We report a control mechanism that enables reconfigurable and widely tunable mode-splitting while efficiently mitigating undesired resonance shifts. This is achieved by actively controlling the excitation of counter-traveling modes in coupled resonators. The transition from a large splitting (80 GHz) to a single-notch resonance is demonstrated using low power microheaters (35 mW). We show that the spurious resonance-shift in our device is only limited by thermal crosstalk and resonance-shift-free splitting control may be achieved.Comment: 4 pages, 3 figure

Resonant structures based on amorphous silicon sub-oxide doped with Er3+ with silicon nanoclusters for an efficient emission at 1550 nm

We present a resonant approach to enhance 1550nm emission efficiency of amorphous silicon sub-oxide doped with Er3+ (a-SiOx) layers with silicon nanoclusters (Si-NC). Two distinct techniques were combined to provide a structure that allowed increasing approximately 12x the 1550nm emission. First, layers of SiO2 were obtained by conventional wet oxidation and a-SiOx matrix was deposited by reactive RF co-sputtering. Secondly, an extra pump channel (4I15/2 to 4I9/2) of Er3+ was created due to Si-NC formation on the same a-SiOx matrix via a hard annealing at 1150 C. The SiO2 and the a-SiOx thicknesses were designed to support resonances near the pumping wavelength (~500nm), near the Si-NC emission (~800nm) and near the a-SiOx emission (~1550nm) enhancing the optical pumping process.Comment: 14 pages, 4 figures, in submissio