O USO DE UM SENSOR DE LUZ LINEAR COMO RECURSO DIDÁTICO PARA DEMONSTRAR PRINCÍPIOS DE DIFRAÇÃO E ESPECTROSCOPIA

This article presents a discussion on light diffraction by slits and grids as well as the development of an experimental apparatus which provides quantitative observation of the phenomenon. We conducted a brief historical survey on the evolution of the wave theory of light and the role of diffraction in the context of optical spectroscopy. We also reviewed the use of Huygens’ principle to calculate the intensity pattern obtained when light is diffracted by slits and compared the predictions with experimental results obtained using the apparatus developed. Finally, the use of the apparatus in an optical spectroscopy experiment was demonstrated.

Determination of hydroquinone in a square wave voltammetry procedure using a graphite-polyurethane composite electrode

In order to a better characterization of a graphite-polyurethane composite intended to be used as a voltammetric sensor, the performance in a square wave voltammetric procedure was investigated. Using hydroquinone (HQ) as a probe, the electrode showed to be useful in square wave voltammetry with limit of detection of 0.28 µmol L-1, with recoveries between 99.1 and 101.5%. The results of the proposed method agreed with HPLC ones within 95% confidence level.

Square Wave Voltammetric Determination of Various Pharmaceuticals

Cochin University of Science & Technology

Optimization of the Mechanical and Optical Properties of Tunable Optical Sensor Arrays (TOSA) for a Nanospectrometer in the Visible and Near Infrared Spectral Range

Tunable Optical Sensor Arrays (TOSA) based on Fabry-Pérot (FP) filters, for high quality spectroscopic applications in the visible and near infrared spectral range are investigated within this work. The optical performance of the FP filters is improved by using ion beam sputtered niobium pentoxide (Nb2O5) and silicon dioxide (SiO2) Distributed Bragg Reflectors (DBRs) as mirrors. Due to their high refractive index contrast, only a few alternating pairs of Nb2O5 and SiO2 films can achieve DBRs with high reflectivity in a wide spectral range, while ion beam sputter deposition (IBSD) is utilized due to its ability to produce films with high optical purity. However, IBSD films are highly stressed; resulting in stress induced mirror curvature and suspension bending in the free standing filter suspensions of the MEMS (Micro-Electro-Mechanical Systems) FP filters. Stress induced mirror curvature results in filter transmission line degradation, while suspension bending results in high required filter tuning voltages. Moreover, stress induced suspension bending results in higher order mode filter operation which in turn degrades the optical resolution of the filter. Therefore, the deposition process is optimized to achieve both near zero absorption and low residual stress. High energy ion bombardment during film deposition is utilized to reduce the film density, and hence the film compressive stress. Utilizing this technique, the compressive stress of Nb2O5 is reduced by ~43%, while that for SiO2 is reduced by ~40%. Filters fabricated with stress reduced films show curvatures as low as 100 nm for 70 μm mirrors. To reduce the stress induced bending in the free standing filter suspensions, a stress optimized multi-layer suspension design is presented; with a tensile stressed metal sandwiched between two compressively stressed films. The stress in Physical Vapor Deposited (PVD) metals is therefore characterized for use as filter top-electrode and stress compensating layer. Surface micromachining is used to fabricate tunable FP filters in the visible spectral range using the above mentioned design. The upward bending of the suspensions is reduced from several micrometers to less than 100 nm and 250 nm for two different suspension layer combinations. Mechanical tuning of up to 188 nm is obtained by applying 40 V of actuation voltage. Alternatively, a filter line with transmission of 65.5%, Full Width at Half Maximum (FWHM) of 10.5 nm and a stopband of 170 nm (at an output wavelength of 594 nm) is achieved. Numerical model simulations are also performed to study the validity of the stress optimized suspension design for the near infrared spectral range, wherein membrane displacement and suspension deformation due to material residual stress is studied. Two bandpass filter designs based on quarter-wave and non-quarter-wave layers are presented as integral components of the TOSA. With a filter passband of 135 nm and a broad stopband of over 650 nm, high average filter transmission of 88% is achieved inside the passband, while maximum filter transmission of less than 1.6% outside the passband is achieved.

Use of a portable topographic mapping millimetre wave radar at an active lava flow

A ground-based millimetre wave radar, AVTIS (All-weather Volcano Topography Imaging Sensor), has been developed for topographic monitoring. The instrument is portable and capable of measurements over ranges up to similar to 7 km through cloud and at night. In April and May 2005, AVTIS was deployed at Arenal Volcano, Costa Rica, in order to determine topographic changes associated with the advance of a lava flow. This is the first reported application of mm-wave radar technology to the measurement of lava flux rates. Three topographic data sets of the flow were acquired from observation distances of similar to 3 km over an eight day period, during which the flow front was detected to have advanced similar to 200 m. Topographic differences between the data sets indicated a flow thickness of similar to 10 m, and a dense rock equivalent lava flux of similar to 0.20 +/- 0.08 m(3) s(-1).

Bis[1,1 '-N,N '-(2-picolyl)aminomethyl]ferrocene as a redox sensor for transition metal ions

The compound bis[1,1'-N,N'-(2-picolyl) aminomethyl] ferrocene, L-1, was synthesized. The protonation constants of this ligand and the stability constants of its complexes with Ni2+, Cu2+, Zn2+, Cd2+ and Pb2+ were determined in aqueous solution by potentiometric methods at 25degreesC and at ionic strength 0.10 mol dm(-3) in KNO3. The compound L-1 forms only 1:1 (M:L) complexes with Pb2+ and Cd2+ while with Ni2+ and Cu2+ species of 2:1 ratio were also found. The complexing behaviour of L-1 is regulated by the constraint imposed by the ferrocene in its backbone, leading to lower values of stability constants for complexes of the divalent first row transition metals when compared with related ligands. However, the differences in stability are smaller for the larger metal ions. The structure of the copper complex with L-1 was determined by single-crystal X-ray diffraction and shows that a species of 2:2 ratio is formed. The two copper centres display distorted octahedral geometries and are linked through the two L1 bridges at a long distance of 8.781(10) Angstrom. The electrochemical behaviour of L-1 was studied in the presence of Ni2+, Cu2+, Zn2+, Cd2+ and Pb2+, showing that upon complexation the ferrocene-ferrocenium half-wave potential shifts anodically in relation to that of the free ligand. The maximum electrochemical shift (DeltaE(1/2)) of 268 mV was found in the presence of Pb2+, followed by Cu2+ (218 mV), Ni2+ (152 mV), Zn2+ (111 mV) and Cd2+ (110 mV). Moreover, L-1 is able to electrochemically and selectively sense Cu2+ in the presence of a large excess of the other transition metal cations studied.

Wave trapping in a two-dimensional sound-soft or sound-hard acoustic waveguide of slowly-varying width

In this paper we derive novel approximations to trapped waves in a two-dimensional acoustic waveguide whose walls vary slowly along the guide, and at which either Dirichlet (sound-soft) or Neumann (sound-hard) conditions are imposed. The guide contains a single smoothly bulging region of arbitrary amplitude, but is otherwise straight, and the modes are trapped within this localised increase in width. Using a similar approach to that in Rienstra (2003), a WKBJ-type expansion yields an approximate expression for the modes which can be present, which display either propagating or evanescent behaviour; matched asymptotic expansions are then used to derive connection formulae which bridge the gap across the cut-off between propagating and evanescent solutions in a tapering waveguide. A uniform expansion is then determined, and it is shown that appropriate zeros of this expansion correspond to trapped mode wavenumbers; the trapped modes themselves are then approximated by the uniform expansion. Numerical results determined via a standard iterative method are then compared to results of the full linear problem calculated using a spectral method, and the two are shown to be in excellent agreement, even when $\epsilon$, the parameter characterising the slow variations of the guide’s walls, is relatively large.

Impact of non-hydrostatic effects and trapped lee waves on mountain wave drag in directionally sheared flow

The orographic gravity wave drag produced in flow over an axisymmetric mountain when both vertical wind shear and non-hydrostatic effects are important was calculated using a semi-analytical two-layer linear model, including unidirectional or directional constant wind shear in a layer near the surface, above which the wind is constant. The drag behaviour is determined by partial wave reflection at the shear discontinuity, wave absorption at critical levels (both of which exist in hydrostatic flow), and total wave reflection at levels where the waves become evanescent (an intrinsically non-hydrostatic effect), which produces resonant trapped lee wave modes. As a result of constructive or destructive wave interference, the drag oscillates with the thickness of the constant-shear layer and the Richardson number within it (Ri), generally decreasing at low Ri and when the flow is strongly non-hydrostatic. Critical level absorption, which increases with the angle spanned by the wind velocity in the constant-shear layer, shields the surface from reflected waves, keeping the drag closer to its hydrostatic limit. While, for the parameter range considered here, the drag seldom exceeds this limit, a substantial drag fraction may be produced by trapped lee waves, particularly when the flow is strongly non-hydrostatic, the lower layer is thick and Ri is relatively high. In directionally sheared flows with Ri = O(1), the drag may be misaligned with the surface wind in a direction opposite to the shear, a behaviour which is totally due to non-trapped waves. The trapped lee wave drag, whose reaction force on the atmosphere is felt at low levels, may therefore have a distinctly different direction from the drag associated with vertically propagating waves, which acts on the atmosphere at higher levels.

Study of a gold electrode modified by trans-[Ru(NH(3))(4)(Ist)SO(4)](+) to produce an electrochemical sensor for nitric oxide

The modification of a gold electrode surface by electropolymerization of trans-[Ru(NH(3))(4)(Ist)SO(4)](+) to produce an electrochemical sensor for nitric oxide was investigated. The influence of dopamine, serotonin and nitrite as interferents for NO detection was also examined using square-wave voltammetry (SWV). The characterization of the modified electrode was carried out by cyclic voltammetry, electrochemical quartz crystal microbalance (EQCM) and SERS techniques. The gold electrode was successfully modified by the trans-[Ru(NH(3))(4)(Ist)SO(4)](+) complex ion using cyclic voltammetry. The experiments show that a monolayer of the film is achieved after ten voltammetric cycles, that NO in solution can coordinate to the metal present in the layer, that dopamine, serotonin and nitrite are interferents for the detection of NO, and that the response for the nitrite is much less significant than the responses for dopamine and serotonin. The proposed modified electrode has the potential to be applied as a sensor for NO. (C) 2011 Elsevier Ltd. All rights reserved.

Voltammetric sensor for amoxicillin determination in human urine using polyglutamic acid/glutaraldehyde film

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

Approach on the Electrochemical Reactivity of Poly-L-Glutamic Acid Against Doxorubicin and Its Application in the Development of a Voltammetric Sensor

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

Relation between ambient humidity and ionic conductivity of poly(thionaphtheneindole): Behaviour as an amperometric humidity sensor

The electrical characteristics of oxidized poly(thionaphtheneindole) were investigated as a function of ambient relative humidity (r.h.). The current flowing through a pressed pellet of material between two massive gold electrodes plotted against voltage gives a wave-shaped curve with a halfwave potential at V = similar to 3 V. The current recorded at 4 V (plateau of the wave) is a sigmoidal function of r.h, with the inflexion point at similar to 60%. An interpretation of these findings is given, based on the influence of water on the dielectric constant of the material and on acid-base equilibrium between poly(thionaphtheneindole) and water, from which protons are produced. The behaviour of poly (thionaphtheneindole) as the active component of an amperometric humidity sensor is also reported.

Detection of buried pipes using a shear wave ground surface vibration technique

A major UK initiative, entitled 'Mapping the Underworld', is seeking to address the serious social, environmental and economic consequences arising from an inability to locate the buried utility service infrastructure without resorting to extensive excavations. Mapping the Underworld aims to develop and prove the efficacy of a multi-sensor device for accurate remote buried utility service detection, location and, where possible, identification. One of the technologies to be incorporated in the device is low-frequency vibro-acoustics, and the application of this technology for detecting buried infrastructure is currently being investigated. Here, a shear wave ground vibration technique for detecting buried pipes is described. For this technique, shear waves are generated at the ground surface, and the resulting ground surface vibrations measured, using geophones, along a line traversing the anticipated run of the pipe. Measurements were made at a test site with a single pressurized polyethylene mains water pipe. Time-extended signals were employed to generate the illuminating wave. Cross-correlation functions between the measured ground velocities and a reference measurement adjacent to the excitation were then calculated and summed using a stacking method to generate a cross-sectional image of the ground. The wide cross-correlation peaks caused by high ground attenuation were partially compensated for by using a generalized cross-correlation function called the smoothed coherence transform. To mitigate the effects of other potential sources of vibration in the vicinity, the excitation signal was used as an additional reference when calculating the generalized cross-correlation functions. For two out of three tests, the pipe was detected, indicating that this technique will be a valuable addition to the Mapping the Underworld armoury.

Sensitive voltammetric sensor for fast detection of mycolic acids present in mycobacteria

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

Wave equation depth migration using complex Padé approximation

Propomos um novo método de migração em profundidade baseado na solução da equação da onda com densidade constante no domínio da freqüência. Uma aproximação de Padé complexa é usada para aproximar o operador de evolução aplicado na extrapolação do campo de ondas. Esse método reduz as imprecisões e instabilidades devido às ondas evanescentes e produz imagens com menos ruídos numéricos que aquelas obtidas usando-se a aproximação de Padé real para o operador exponencial, principalmente em meios com fortes variações de velocidades. Testes em dados de afastamento nulo do modelo de sal SEG/EAGE e nos dados de tiro comum 2-D Marmousi foram realizados. Os resultados obtidos mostram que o método de migração proposto consegue lidar com fortes variações laterais e também tem uma boa resposta para refletores com mergulhos íngremes. Os resultados foram comparados àqueles resultados obtidos com os métodos split-step Fourier (SSF), phase shift plus interpolarion (PSPI) e Fourier diferenças-finitas (FFD).