One and two degrees-of-freedom Vortex-Induced Vibration experiments with yawed cylinders

Vortex-Induced Vibration (VIV) experiments were carried out with yawed cylinders. The purpose was to investigate the validity of the Independence Principle (IP) for properly describing the flow characteristics and the dynamics of structures subjected to oblique flow. Five yaw angles in relation to the direction perpendicular to the free stream velocity were tested, namely View the MathML sourceθ=0°,10°,20°,30° and 45°. Both the upstream and downstream orientations were tested. The models were mounted on a leaf spring apparatus that allows experiments with one or two degrees of freedom. The Reynolds numbers based on the component normal to the cylinder axis fell in the interval 3×103

Computational simulation of the flow-induced vibration of a circular cylinder subjected to wake interference

In this work, we considered the flow around two circular cylinders of equal diameter placed in tandem with respect to the incident uniform flow. The upstream cylinder was fixed and the downstream cylinder was completely free to move in the cross-stream direction, with no spring or damper attached to it. The centre-to-centre distance between the cylinders was four diameters, and the Reynolds number was varied from 100 to 645. We performed two- and three-dimensional simulations of this flow using a Spectral/hp element method to discretise the flow equations, coupled to a simple Newmark integration routine that solves the equation of the dynamics of the cylinder. The differences of the behaviours observed in the two- and three-dimensional simulations are highlighted and the data is analysed under the light of previously published experimental results obtained for higher Reynolds numbers.

The role of wake stiffness on the wake-induced vibration of the downstream cylinder of a tandem pair

When a pair of tandem cylinders is immersed in a flow the downstream cylinder can be excited into wake-induced vibrations (WIV) due to the interaction with vortices coming from the upstream cylinder. Assi, Bearman & Meneghini ( J. Fluid Mech. , vol. 661, 2010, pp. 365–401) concluded that the WIV excitation mechanism has its origin in the unsteady vortex–structure interaction encountered by the cylinder as it oscillates across the wake. In the present paper we investigate how the cylinder responds to that excitation, characterising the amplitude and frequency of response and its dependency on other parameters of the system. We introduce the concept of wake stiffness , a fluid dynamic effect that can be associated, to a first approximation, with a linear spring with stiffness proportional to Re and to the steady lift force occurring for staggered cylinders. By a series of experiments with a cylinder mounted on a base without springs we verify that such wake stiffness is not only strong enough to sustain oscillatory motion, but can also dominate over the structural stiffness of the system. We conclude that while unsteady vortex–structure interactions provide the energy input to sustain the vibrations, it is the wake stiffness phenomenon that defines the character of the WIV response

X-ray absorption spectroscopy study on La0.6Sr0.4CoO3 and La0.6Sr0.4Co1¡yFeyO3 nanotubes and nanorods for IT-SOFC cathodes.

In the last years, extensive research has been devoted to develop novel materials and structures with high electrochemical performance for intermediate-temperatures solid-oxide fuel cells (IT-SOFCs) electrodes. In recent works, we have investigated the structural and electrochemical properties of La0:6Sr0:4CoO3 (LSCO) and La0:6Sr0:4Co1¡yFeyO3 (LSCFO) nanostructured cathodes, finding that they exhibit excellent electrocatalytic properties for the oxygen reduction reaction [1,2]. These materials were prepared by a pore-wetting technique using polycarbonate porous membranes as templates. Two average pore sizes were used: 200 nm and 800 nm. Our scanning electronic microscopy (SEM) study showed that the lower pore size yielded nanorods, while nanotubes were obtained with the bigger pore size. All the samples were calcined at 1000oC in order to produce materials with the desired perovskite-type crystal structure. In this work, we analyze the oxidation states of Co and Fe and the local atomic order of LSCO and LSCFO nanotubes and nanowires for various compositions. For this pur- pose we performed XANES and EXAFS studies on both Co and Fe K edges. These measurements were carried out at the D08B-XAFS2 beamline of the Brazilian Synchrotron Light Laboratory (LNLS). XANES spectroscopy showed that Co and Fe only change slightly their oxidation state upon Fe addition. Surprisingly, XANES results indicated that the content of oxygen vacancies is low, even though it is well-known that these materials are mixed ionic-electronic conductors. EXAFS results were consistent with those expected according to the rhombohedral crystal structure determined in previous X-ray powder dffraction investigations. [1] M.G. Bellino et al, J. Am. Chem. Soc. 129 (2007) 3066 [2] J.G. Sacanell et al., J. Power Sources 195 (2010) 1786

Two-degree-of-freedom vortex-induced vibration of circular cylinders with very low aspect ratio and small mass ratio

The investigation of vortex-induced vibration on very short cylinders with two degrees of freedom has drawn the attention of a large number of researchers. Some investigations on such a problem are carried out in order to have a better understanding of the physics involved in vortex-induced motions of floating bodies such as offshore platforms. In this paper, experiments were carried out in a recirculating water channel over the range of Reynolds number 6000

Bilipid membrane phase characterization by reflectance anisotropy spectroscopy (RAS)

In this work we propose the use of experimental and theoretical reflectance anisotropy spectra (RAS) as a new tool to identify structural and dynamical aspects of the bilipid membrane and its various constituent molecules. The role of geometric details at the atomic level and macroscopic quantities, such as the membrane curvature and tilt for the different gel phases, in the theoretical RAS spectra (using Kohn-Sham density functional theory (KS-DFT)) are presented. Then the results are compared to the experimentally measured spectra taken from other techniques.

Shape resonance spectra of uracil, 5-fluorouracil, and 5-chlorouracil.

We report on the shape resonance spectra of uracil, 5-fluorouracil, and 5-chlorouracil, as obtained from fixed-nuclei elastic scattering calculations performed with the Schwinger multichannel method with pseudopotentials. Our results are in good agreement with the available electron transmission spectroscopy data, and support the existence of three π* resonances in uracil and 5-fluorouracil. As expected, the anion states are more stable in the substituted molecules than in uracil. Since the stabilization is stronger in 5-chlorouracil, the lowest π* resonance in this system becomes a bound anion state. The present results also support the existence of a low-lying σ ∗ CCl shape resonance in 5- chlorouracil. Exploratory calculations performed at selected C–Cl bond lengths suggest that the σ ∗ CCl resonance could couple to the two lowest π* states, giving rise to a very rich dissociation dynamics. These facts would be compatible with the complex branching of the dissociative electron attachment cross sections, even though we cannot discuss any details of the vibration dynamics based only on the present fixed-nuclei results.

New Improved Version of J 1 ...J 4 Interferometry Method and its Application to Nanometric Vibration Measurements

Piezoelectric ceramics, such as PZT, can generate subnanometric displacements, bu t in order to generate multi- micrometric displacements, they should be either driven by high electric voltages (hundreds of volts ), or operate at a mechanical resonant frequency (in narrow band), or have large dimensions (tens of centimeters). A piezoelectric flextensional actuator (PFA) is a device with small dimensions that can be driven by reduced voltages and can operate in the nano- and micro scales. Interferometric techniques are very adequate for the characterization of these devices, because there is no mechanical contact in the measurement process, and it has high sensitivity, bandwidth and dynamic range. A low cost open-loop homodyne Michelson interferometer is utilized in this work to experimentally detect the nanovi brations of PFAs, based on the spectral analysis of the interfero metric signal. By employing the well known J 1 ...J 4 phase demodulation method, a new and improved version is proposed, which presents the following characteristics: is direct, self-consistent, is immune to fading, and does not present phase ambiguity problems. The proposed method has resolution that is similar to the modified J 1 ...J 4 method (0.18 rad); however, differently from the former, its dynamic range is 20% larger, does not demand Bessel functions algebraic sign correction algorithms and there are no singularities when the static phase shift between the interferometer arms is equal to an integer multiple of  /2 rad. Electronic noise and random phase drifts due to ambient perturbations are taken into account in the analysis of the method. The PFA nanopositioner characterization was based on the analysis of linearity betw een the applied voltage and the resulting displacement, on the displacement frequency response and determination of main resonance frequencies.

Positron annihilation spectroscopy techniques applied to the study of an HPGe detector.

Doppler Broadening Spectroscopy of the large Ge crystal of an HPGe detector was perforrned using positrons from pair production of 6.13 MeV ϒ-rays from the 19F(p,αϒ) 16O reaction. Two HPGe detectors facing opposite sides of the Ge crystal acting as target provided both coincidence and singles spectra. Changes in the shape of the annihilation peak were observed when the high voltage applied to the target detector was switched on or off, amounting to somewhat less than 20% when the areas of equivalent energy intervals in the corresponding normalized spectra are compared.

Bilipid Membrane Phase Characterization by Reflectance Anisotropy Spectroscopy (RAS)

In this work we propose the use of experimental and theoretical reflectance anisotropy spectra (RAS) as a new tool to identify structural and dynamical aspects of the bilipid membrane and its various constituent molecules. The role of geometric details at the atomic level and macroscopic quantities, such as the membrane curvature and tilt for the different gel phases, in the theoretical RAS spectra (using Kohn-Sham density functional theory (KS-DFT)) are presented. Then the results are compared to the experimentally measured spectra taken from other techniques.

História da propagação das citações originais do artigo do Journal of Quantitative Spectroscopy & Radiative Transfer 102/441/2006.

Neste artigo procuraremos descrever a história cronológica das citações originais (aquelas que os nomes dos autores aparecem apenas uma vez, portanto, excluídas as autocitações) da publicação do artigo: M. Cattani and J. M. F. Bassalo, Racemization, Chiral Stability and Weak Interactions, Journal of Quantitative Spectroscopy & Radiative Transfer 102, pp. 441-449, 2006 (CB: JQS&RT 102/441/2006). Para realizar essa história, usamos a WEB OF SCIENCE (acessado: 08/02/2013) disponibilizado pela CAPES/UFPA.

Determination of degree of ionization of poly(allylamine hydrochloride) (PAH) and poly[1-[4-(3-carboxy‑4 hydroxyphenylazo)benzene sulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) in layer-by-layer films using vacuum photoabsorption spectroscopy

Electrostatic and hydrophobic interactions govern most of the properties of supramolecular systems, which is the reason determining the degree of ionization of macromolecules has become crucial for many applications. In this paper, we show that highresolution ultraviolet spectroscopy (VUV) can be used to determine the degree of ionization and its effect on the electronic excitation energies of layer-by-layer (LbL) films of poly(allylamine hydrochloride) (PAH) and poly[1-[4-(3-carboxy-4 hydroxyphenylazo)- benzene sulfonamido]-1,2-ethanediyl, sodium salt] (PAZO). A full assignment of the VUV peaks of these polyelectrolytes in solution and in cast or LbL films could be made, with their pH dependence allowing us to determine the p'K IND. a' using the Henderson-Hasselbach equation. The p'K IND. a' for PAZO increased from ca. 6 in solution to ca. 7.3 in LbL films owing to the charge transfer from PAH. Significantly, even using solutions at a fixed pH for PAH, the amount adsorbed on the LbL films still varied with the pH of the PAZO solutions due to these molecular-level interactions. Therefore, the procedure based on a comparison of VUV spectra from solutions and films obtained under distinct conditions is useful to determine the degree of dissociation of macromolecules, in addition to permitting interrogation of interface effects in multilayer films.

Thiosaccharine disulfide: synthesis, crystal structure, spectroscopic characterization and theoretical study

The title compound, (thiosaccharine disulfide), bis[1,10dioxide-2,3-dihidro-1,2-benzoisothiazol]disulfide, (tsac)2 has been synthesized and fully characterized by UV–Visible, IR, Raman, 1H and 13C NMR spectroscopy elemental analysis and structural X-ray crystallography. A DFT theoretical study has been performed and good agreement between experimental and theoretical values of structural parameters and vibration frequencies have been achieved.

Luminescence quantum efficiency at 1.5 µm of Er3+- doped tellurite glass determined by thermal lens spectroscopy

Erbium doped tellurite glasses (TeO2 + Li2O + TiO2) were prepared by conventional melt-quenching method to study the influence of the Er3+ concentration on the luminescence quantum efficiency (η) at 1.5 µm. Absorption and luminescence data were used to characterize the samples, and the η parameter was measured using the well-known thermal lens spectroscopy. For low Er3+ concentration, the measured values are around 76%, and the concentration behavior of η shows Er-Er and Er-OH- interactions, which agreed with the measured lifetime values.

Reaction intermediates of ethanol electro-oxidation on platinum investigated by SFG spectroscopy

Although electrochemical oxidation of simple organic molecules on metal catalysts is the basic ingredient of fuel cells, which have great technological potential as a renewable source of electrical energy, the detailed reaction mechanisms are in most cases not completely understood. Here, we investigate the ethanol-platinum interface in acidic aqueous solution using infrared-visible sum frequency generation (SFG) spectroscopy and theoretical calculations of vibrational spectra in order to identify the intermediates present during the electro-oxidation of ethanol. The complex vibrational spectrum in the fingerprint region imply on the coexistence of several adsorbates. Based on spectra in ultra-high-vacuum (UHV) and electrochemical environment from the literature and our density functional theory (DFT) calculations of vibrational spectra, new adsorbed intermediates, never before observed with conventional infrared (IR) spectroscopy, are proposed here: g2-acetaldehyde, g2-acetyl, ethylidyne, monodentate acetate, methoxy, tertiary methanol derivative, COH residue, g2-formaldehyde, mono and bidentate formate, CH3 and CH2 residues. In addition, we present new evidences for an ethoxy intermediate, a secondary ethanol derivative and an acetyl species, and we confirm the presence of previously observed adsorbates: a tertiary ethanol derivative, bidentate acetate, and COad. These results indicate that the platinum surface is much more reactive, and the reaction mechanism for ethanol electro-oxidation is considerably more complex than previously considered. This might be also true for many other molecule-catalyst systems.