Analysis of the ethidium bromide bound to DNA by photoacoustic and FTIR spectroscopy

Under physiological conditions B-form DNA is an exceedingly stable structure. However, experimental evidences obtained through nuclear magnetic resonance and fluorescence anisotropy suggest that the structure of the double helix fluctuates substantially. We describe photoacoustic phase modulation frequency measurements of ethidium bromide (Eb) with calf thymus, DNA. As in fluorescence phase modulation measurements, we used an intercalating dye as a probe; however, we monitored the triplet excited state lifetime at different ionic strengths. The triplet lifetime of Eb varied from about 0.30 ms, with no DNA present, to 20 ms, (at a DNA:Eb molar ratio of 5). With salt titration, this value falls, to about 2.0 ms. This result suggests, a strong coupling between the phenantridinium ring of the ethidium and the base pairs because of the stacking movement of the DNA molecule under salt effect. This, effect may be understood considering DNA as a polyelectrolyte. The counterions, in the solution shield the phosphate groups, reducing the electrostatic repulsion force between them, hence compacting the DNA molecule. The results from Fourier transform infrared demonstrated two important bands: 3187 cm(-1) corresponding to the symmetric stretching of the NH group of the bases, and 1225 cm(-1) corresponding to the asymmetric stretching of phosphate groups shifted toward higher wavenumbers, suggesting a proximity between the intercalant and base pairs and a modification of the DNA backbone state, both induced by salt accretion.

Oscillating holograms recorded in photorefractive crystals by a frequency detuned feedback loop

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Experimental observation of infrared spectral enlargement in As 2S3 suspended core microstructured fiber

The development of chalcogenide glasses fibers for application in the infrared wavelength region between 1 and 10 μm is a big opportunity. More particularly, the possibility to generate efficient non linear effects above 2 μm is a real challenge. We present in this work the elaboration and optical characterizations of suspended core microstructured optical fibers elaborated from the As2S3 chalcogenide glass. As an alternative to the stack and draw process a mechanical machining has been used to the elaboration of the preforms. The drawing of these preforms into fibers allows reaching a suspended core geometry, in which a 2.5 μm diameter core is linked to the fiber clad region by three supporting struts. The zero dispersion wavelength is thus shifted towards 2 μm. At 1.55 μm our fibers exhibit a dispersion around -250 ps/nm/km. Their background level of losses is below 0,5 dB/m. By pumping them at 1.55 μm with a ps source, we observe self phase modulation as well as Raman generation. Finally a strong spectral enlargement is obtained with an average output power of - 5 dbm. © 2010 SPIE.

Coupling rate measurement of a novel multi-actuated piezoelectric device using optical interferometry

The class of piezoelectric actuators considered in this paper consists of a multi-flexible structure actuated by two or more piezoceramic devices that must generate different output displacements and forces at different specified points of the domain and in different directions. The devices were modeled by finite element using the software ANSYS and the topology optimization method. The following XY actuators were build to achieve maximum displacement in the X and Y directions with a minimum crosstalk between them. The actuator prototypes are composed of an aluminum structure, manufactured by using a wire Electrical Discharge Machining, which are bonded to rectangular PZT5A piezoceramic blocks by using epoxy resin. Multi-actuator piezoelectric device displacements can be measured by using optical interferometry, since it allows dynamic measurements in the kHz range, which is of the order of the first resonance frequency of these piezomechanisms. A Michelson-type interferometer, with a He-Ne laser source, is used to measure the displacement amplitudes in nanometric range. A new optical phase demodulation technique is applied, based on the properties of the triangular waveform drive voltage applied to the XY piezoelectric nanopositioner. This is a low-phase-modulation-depth-like technique that allows the rapid interferometer auto-calibration. The measurements were performed at 100 Hz frequency, and revealed that the device is linear voltage range utilized in this work. The ratio between the generated and coupled output displacements and the drive voltages is equal to 10.97 nm/V and 1.76 nm/V, respectively, which corresponds to a 16% coupling rate. © 2010 IEEE.

Método de detecção interferométrica de fase, com baixa profundidade de modulação, aplicado à medição de deslocamentos nanométricos em atuadores e mini-manipuladores piezoelétricos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Interferometria óptica aplicada à medição de amplitudes de vibração nanométricas em piezoatuadores flextensionais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Novas técnicas de detecção de fase óptica em interferômetros homódinos aplicadas à caracterização de atuadores piezoelétricos flextensionais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estratégia de projeto de atribuição de comprimento de onda com restrição de camada física em redes WDM

O sistema WDM (Wavelength Division Multiplexing) é considerado como uma tecnologia madura para ser usada no backbone de redes ópticas. Entretanto, encontrar uma solução ótima para o algoritmo de atribuição de comprimento de onda no projeto e operação destas redes, ainda é uma questão em aberto. A pesquisa realizada nesta tese aborda os principais aspectos relacionados ao processo de atribuição de comprimento de onda em sistemas WDM, e como resultado foi proposta uma metodologia que minimiza a degradação do sinal óptico gerada pela modulação de fase cruzada (XPM – Cross-Phase Modulation). Esta proposta é composta por uma metodologia híbrida baseada em Coloração de Grafo e Algoritmo Genético (AG), sendo que o primeiro tem a função de reduzir o número de comprimentos de onda necessários para atender a matriz de tráfego (que é fornecida a priori) e o último tem a função de encontrar a ordem de ativação de canais na grade de comprimentos de onda, com o objetivo de reduzir o efeito XPM. A proposta foi comparada com o algoritmo First-Fit em diferentes cenários e topologias de redes, e demonstrou uma considerável redução na probabilidade de bloqueio.

Use of a Single L1 GPS Receiver for Monitoring Structures: First Results of the Detection of Millimetric Dynamic Oscillations

This paper presents preliminary results to determine small displacements of a global positioning system (GPS) antenna fastened to a structure using only one L1 GPS receiver. Vibrations, periodic or not, are common in large structures, such as bridges, footbridges, tall buildings, and towers under dynamic loads. The behavior in time and frequency leads to structural analysis studies. The hypothesis of this article is that any large structure that presents vibrations in the centimeter-to-millimeter range can be monitored by phase measurements of a single L1 receiver with a high data rate, as long as the direction of the displacement is pointing to a particular satellite. Within this scenario, the carrier phase will be modulated by antenna displacement. During a period of a few dozen seconds, the relative displacement to the satellite, the satellite clock, and the atmospheric phase delays can be assumed as a polynomial time function. The residuals from a polynomial adjustment contain the phase modulation owing to small displacements, random noise, receiver clock short time instabilities, and multipath. The results showed that it is possible to detect displacements of centimeters in the phase data of a single satellite and millimeters in the difference between the phases of two satellites. After applying a periodic nonsinusoidal displacement of 10 m to the antenna, it is clearly recovered in the difference of the residuals. The time domain spectrum obtained by the fast Fourier transform (FFT) exhibited a defined peak of the third harmonic much more than the random noise using the proposed third-degree polynomial model. DOI: 10.1061/(ASCE)SU.1943-5428.0000070. (C) 2012 American Society of Civil Engineers.

Focusing surface plasmons on Er3+ ions through gold planar plasmonic lenses

Gold plasmonic lenses consisting of a planar concentric rings-groove with different periods were milled with a focused gallium ion beam on a gold thin film deposited onto an Er3+-doped tellurite glass. The plasmonic lenses were vertically illuminated with an argon ion laser highly focused by means of a 50x objective lens. The focusing mechanism of the plasmonic lenses is explained using a coherent interference model of surface plasmon-polariton (SPP) generation on the circular grating due to the incident field. As a result, phase modulation can be accomplished by the groove gap, similar to a nanoslit array with different widths. This focusing allows a high confinement of SPPs that can excite the Er3+ ions of the glass. The Er3+ luminescence spectra were measured in the far-field (500-750 nm wavelength range), where we could verify the excitation yield via the plasmonic lens on the Er3+ ions. We analyze the influence of the geometrical parameters on the luminescence spectra. The variation of these parameters results in considerable changes of the luminescence spectra.

Pulse-shaping assisted multidimensional coherent electronic spectroscopy

Understanding nuclear and electronic dynamics of molecular systems has advanced considerably by probing their nonlinear responses with a suitable sequence of pulses. Moreover, the ability to control crucial parameters of the excitation pulses, such as duration, sequence, frequency, polarization, slowly varying envelope, or carrier phase, has led to a variety of advanced time-resolved spectroscopic methodologies. Recently, two-dimensional electronic spectroscopy with ultrashort pulses has become a more and more popular tool since it allows to obtain information on energy and coherence transfer phenomena, line broadening mechanisms, or the presence of quantum coherences in molecular complexes. Here, we present a high fidelity two-dimensional electronic spectroscopy setup designed for molecular systems in solution. It incorporates the versatility of pulse-shaping methods to achieve full control on the amplitude and phase of the individual exciting and probing pulses. Selective and precise amplitude- and phase-modulation is shown and applied to investigate electronic dynamics in several reference molecular systems.

Estudio de limitaciones en sistemas WDM

Los avances tecnológicos de los últimos años han modificado el panorama de las comunicaciones ópticas. Los amplificadores EDFA (Erbium-Doped Fiber Amplifier) han alterado dos aspectos fundamentales de los sistemas WDM (Wavelength Division Multiplexing): el aumento considerable de las distancias de regeneración y además, la tecnología WDM es un medio más económico de incrementar la capacidad de los sistemas que la tecnología TDM (Time Division Multiplexing). Sin embargo, la implementación de sistemas WDM con grandes tramos sin regeneración de señal óptica trae consigo la aparición de nuevos problemas, entre los que se encuentran las no-linealidades en fibra óptica. Estas no-linealidades en fibras de sílice se pueden clasificar en dos categorías: dispersión estimulada (de Raman y de Brillouin) y efectos debidos al índice no lineal de refracción (automodulación y modulación cruzada de fase y mezcla de cuatro ondas). Este Proyecto Fin de Carrera pretende ser un estudio teórico que refleje el actual Estado del Arte de los principales efectos no-lineales que se producen en los sistemas WDM: dispersión estimulada de Raman (SRS, Stimulated Raman Scattering), dispersión estimulada de Brillouin (SBS,Stimulated Brilfouin Scattering), automodulación de fase (SPM, Self-Phase Modulation), modulación cruzada de fase (XPM, Cross-Phase Modulation) y mezcla de cuatro ondas (FWM, Four-Wave Mixing).

Envelope amplifier based on switching capacitors for high efficiency RF amplifiers

Modern transmitters usually have to amplify and transmit signals with simultaneous envelope and phase modulation. Due to this property of the transmitted signal, linear power amplifiers (class A, B, or AB) are usually used as a solution for the power amplifier stage. These amplifiers have high linearity, but suffer from low efficiency when the transmitted signal has high peak-to-average power ratio. The Kahn envelope elimination and restoration technique is used to enhance the efficiency of RF transmitters, by combining highly efficient, nonlinear RF amplifier (class E) with a highly efficient envelope amplifier in order to obtain a linear and highly efficient RF amplifier. This paper presents a solution for the envelope amplifier based on a multilevel converter in series with a linear regulator. The multilevel converter is implemented by employing voltage dividers based on switching capacitors. The implemented envelope amplifier can reproduce any signal with a maximum spectral component of 2 MHz and give instantaneous maximum power of 50 W. The efficiency measurements show that when the signals with low average value are transmitted, the implemented prototypes have up to 20% higher efficiency than linear regulators used as a conventional solution.

UWB doublet generation employing non-linear effects of a Semiconductor Optical Amplifier Mach-Zehnder inteferometer

In this article, a novel method to generate an ultra-wideband (UWB) doublet using the cross-phase modulation (XPM) effect is proposed and experimentally demonstrated. The main component of the submitted architecture is a SOA-Mach-Zehnder interferometer (MZI) pumped with a modulated Gaussian pulse. Maximum and minimum conversion points are analyzed through the systems transfer function in order to determinate the most effective operation stage. By tuning different values for the SOAs currents, it is possible to identify a conversion step in which the input pulse is enough large to saturate the SOAMZI, leading to the generation of a UWB doublet pulse.

UWB doublet generation in an integrated semiconductor optical amplifier Mach-Zehnder interferometer

In this paper, we propose and experimentally demonstrate a novel technique to generate ultrawideband (UWB) doublet pulses by exploiting the cross-phase modulation (XPM) in a semiconductor optical amplifier (SOA). The key component in the proposed system consists on an integrated SOA Mach-Zehnder interferometer (MZI) pumped with a Gaussian pulse modulated optical carrier. The transfer function of the nonlinear conversion process leads to the generation of UWB doublet pulses through the control of the biasing point of the SOA-MZI.