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

A cadeia produtiva do marolo na região Sul de Minas Gerais.

O presente trabalho tem como objetivo identificar os mecanismos envolvidos na produção e comercialização do marolo, na região de Alfenas, Minas Gerais. Foram entrevistadas no total 70 pessoas, entre produtores rurais, fabricantes de produtos a base de marolo e comerciantes. Os resultados encontrados evidenciam a precariedade do sistema de produção e comercialização do marolo, com predominância do extrativismo, venda informal dos frutos e processamento artesanal de produtos elaborados a partir do mesmo. Por outro lado, demonstram também o potencial dessa cultura como forma de complementar a renda dos pequenos produtores da região. Assim, torna-se necessária a busca por padrões de eficiência técnica e econômica da produção do marolo e seus derivados, além da busca de uma estrutura de coordenação apropriada. Essa eficiência permite não somente o aumento de renda de muitas famílias, mas também assegura o desenvolvimento sustentável das comunidades envolvidas nessa atividade, protegendo o cerrado e seus recursos naturais

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

Comparison between GC-MS-SIM and GC-ECD for the determination of residues of organochlorine and organophosphorus pesticides in Brazilian citrus essential oils.

Óleos essenciais cítricos brasileiros (mandarina, laranja, limão, bergamota e tangerina) foram analisados a fim de determinar resíduos de pesticidas organoclorados (aldrin, clordano, dieldrin e dicofol) e organofosforados (clorpirifós metílico, dimetoato, metidationa e paration metílico). Um estudo comparativo entre cromatografia gasosa acoplada a espectrometria de massas em modo de monitoramento seletivo de íons (CG-EM-MSI) e cromatografia gasosa com detector por captura de elétrons (CG-DCE) foi realizado usando extração em fase sólida (EFS) com fase Florisil® para pré-concentração dos pesticidas. A recuperação média dos pesticidas foi de 71 a 83% por CG-EM-MSI e de 99 a 104% por CG-DCE. O limite de quantificação foi de 0,93 a 3,93 mg L-1 por CG-EM-MSI e de 0,09 a 0,12 mg L-1 por CG-DCE. Quinze amostras comerciais de óleos essenciais cítricos brasileiros foram analisadas e seis amostras apresentaram contaminação com valores acima do limite máximo de resíduos (LMR) permitido pelo Codex Alimentarius

Aspectos biológicos do parasitoide Chelonus insularis (Cresson) (Hymenoptera, braconidae) criados em ovos de Spodoptera frugiperda, noctuidae).

Biological aspects of the parasitoid Chelonus insularis (Cresson) (Hymenoptera, braconidae) reared on eggs of Spodoptera frugiperda(Smith) (Lepidoptera, braconidae). Biological aspects of Chelonus insularis (Cresson, 1865) an egg-larval parasitoid reared on Spodoptera frugiperda (Smith, 1797) eggs helonus insularis (Cresson, 1865) has been cited in the international literature as a promissing biological control agent against the fall armyworm. Spodoptera frugiperda (Smith, 1797). Its field occurrence in Sete Lagoas, Minas Gerais (Brasil) has been increasing in the last years. For these reasons this experiment was conducted in the laboratory, at the National Corn and Sorghum Research Center, of EMBRAPA, under temperature of 25oC, RH of 73% and phophate of 12 hours. Ten couples of the parasitoid were individually placed in a glass jar (5 liters capacity). They were fed on a 10% sugar solution. Each couple received one fall armyworm egg mass to oviposit during a 24 hour period. After hatching, the larvae were fed on artificial bean diet, up to the death caused by the parasitoid larvae. The total biological life cycle was 26,61 days on the average (larval period of 20,42 and pupal period of 6.19 days). The average weight of two days - old pupae was 0.02g. The adult longevity was on average, 10 days (8,4 days for males and 11.6 days for females). The greatest rate of parasitism occurred when the female was three days old, with a maximum of 92 eggs parasitized in that day