Simultaneous 2D flow velocity and gas temperature measurements using thermographic phosphors

In this paper a new approach for simultaneous 2D velocity and temperature measurements using phosphoric particles is presented. The phosphoric particles respond to the temperature changes in the flow while acting as tracers for velocity mapping. The temperature sensitive particles were seeded into a heated flow and were excited by a pulsed UV laser. The subsequent red shifted emission was detected and analyzed to infer temperature using calibration procedures for lifetime and emission spectra against temperature. The diameter of the temperature sensitive particles, usually in the range of 1–10 μm, makes them useful for velocity measurements using particle image velocimetry (PIV). As such, simultaneous measurement of temperature and flow velocity of a gaseous flow were performed and presented. PACS  42.62.-b; 47.80.Cb; 47.80.Fg     

Public perception of nanotechnology

While several studies on the public opinion of nanotechnology have pointed to a rather enthusiastic U.S. public, the public uptake of nanotechnology in Europe is more contained. The results of the Swiss publifocus on nanotechnology reveal a pragmatic attitude of citizens toward the emerging technologies, thus confirming what has been identified as a “balanced approach” in the NanoJury UK.

Ultrabroadband conical emission generated from the ultraviolet up to the far-infrared during the optical filamentation in air

Ultraviolet and infrared conical emissions were observed during the filamentation in air of powerful femtosecond laser pulses produced by a portable terawatt laser system. The broadband spectrum was measured from 200 nm up to 14 microm and covered the complete optical transmission window of the atmosphere. The angularly resolved spectrum showed some X-wave structure across the frequency range analyzed. However, we demonstrated that the strong conical emission observed in the mid- and far-infrared is mainly owing to the four-wave mixing between the pump pulse and its blueshifted conical emission.     

Modeling the sound transmission between rooms coupled through partition walls by using a diffusion model

In this paper, a modification of the diffusion model for room acoustics is proposed to account for sound transmission between two rooms, a source room and an adjacent room, which are coupled through a partition wall. A system of two diffusion equations, one for each room, together with a set of two boundary conditions, one for the partition wall and one for the other walls of a room, is obtained and numerically solved. The modified diffusion model is validated by numerical comparisons with the statistical theory for several coupled-room configurations by varying the coupling area surface, the absorption coefficient of each room, and the volume of the adjacent room. An experimental comparison is also carried out for two coupled classrooms. The modified diffusion model results agree very well with both the statistical theory and the experimental data. The diffusion model can then be used as an alternative to the statistical theory, especially when the statistical theory is not applicable, that is, when the reverberant sound field is not diffuse. Moreover, the diffusion model allows the prediction of the spatial distribution of sound energy within each coupled room, while the statistical theory gives only one sound level for each room.     

Modeling urban street patterns

Urban street patterns form planar networks whose empirical properties cannot be accounted for by simple models such as regular grids or Voronoi tesselations. Striking statistical regularities across different cities have been recently empirically found, suggesting that a general and detail-independent mechanism may be in action. We propose a simple model based on a local optimization process combined with ideas previously proposed in studies of leaf pattern formation. The statistical properties of this model are in good agreement with the observed empirical patterns. Our results thus suggest that in the absence of a global design strategy, the evolution of many different transportation networks indeed follows a simple universal mechanism.     

3D elemental distribution images in biological samples by XRFµCT

An X‐ray transmission microtomography (CT) system combined with an X‐ray fluorescence microtomography (XRFµCT) system was implemented in the Brazilian Synchrotron Light Laboratory (LNLS), Campinas, Brazil. The aim of this work was to determine the elemental distribution in biological samples (breast, prostate and lung samples) in order to verify the concentration of some elements correlated with characteristics and pathology of each tissue observed by the transmission CT. The experiments were performed at the X‐ray fluorescence beamline (D09B‐XRF) of the Brazilian Synchrotron Light Laboratory, Campinas, Brazil. A quasi‐monochromatic beam produced by a multilayer monochromator was used as an incident beam. The sample was placed on a high‐precision goniometer and translation stages that allow rotating as well as translating it perpendicularly to the beam. The fluorescence photons were collected with an energy dispersive HPGe detector placed at 90° to the incident beam, while transmitted photons were detected with a fast Na(Tl) scintillation counter placed behind the sample on the beam path. The CT images were reconstructed using a filtered‐back projection algorithm and the XRFµCT images were reconstructed using a filtered‐back projection algorithm with absorption corrections. The 3D images were reconstructed using the 3D‐DOCTOR software. Results from the 3D visualization showed that the distribution of iron, copper and zinc is different and heterogeneous from the analyzed samples. Copyright © 2011 John Wiley & Sons, Ltd.     

Self-imaging by a volume grating

The self-image phenomenon by a volume grating is proposed and theoretically analyzed. A theoretical model based on a path integral formulation to describe wave propagation through the grating inhomogeneous medium is applied. A modified version of the scalar diffraction theory Fresnel propagator is obtained which allows calculating the diffracted field amplitude by the grating. The proposed model is applied to amplitude and/or phase volume gratings. Remarkable features appear, in particular at the fractional Talbot distance 0.125z_T. In this case, if an in-phase real and imaginary grating modulation is considered a self-image intensity profile is observed for determined values of the absorptive and refractive parameters. On the other hand, a spatial comb intensity profile for a near half period shift between the real and imaginary grating modulations is found.     

Dual-fibre stretcher and coma as tools for independent 2nd and 3rd order tunable dispersion compensation in a fibre-based ‘scan-free’ time domain optical coherence tomography system

Dispersion compensation up to the third order is experimentally demonstrated by using a dual-fibre stretcher combined with the coma of an imaging lens, in a fibre-based scan-free time domain optical coherence tomography system, leading to an axial resolution of less than 3 μm.     

La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> thin films on SrTiO<Subscript>3</Subscript> and CaTiO<Subscript>3</Subscript> buffered Si substrates: structural,static, and dynamic magnetic properties

Nearly 50-nm thick La_0.7Sr_0.3MnO₃ (LSMO) films were grown on Si substrates using molecular beam epitaxy on (001) Si substrates over-layered by a 20 nm thick SrTiO₃ (STO) or by a 20 nm thick CaTiO₃ (CTO) film. In addition, a reference LSMO film was directly deposited on a (001) STO substrate by pulsed laser deposition. For all the samples, X-ray diffraction revealed an excellent epitaxy of the LSMO film and small mosaicity around (001), with in-plane [100] and [010] cubic axes. The LSMO/CTO films are in-plane compressed while the LSMO/STO ones are in-plane extended. The temperature dependence of their static magnetic properties was studied using a SQUID, showing a Curie temperature overpassing 315 K for all the samples. Hysteresis loops performed at room temperature (294 K) with the help of a vibrating sample magnetometer (VSM) are also discussed. At 294 K Micro-strip ferromagnetic resonance (MS-FMR) was used to investigate the dynamic magnetic properties. It allows concluding to a strong anisotropy perpendicular to the films and to a weak fourfold in-plane anisotropy with easy axes along the [110] and [1[`1]0 1\bar{1}0 ] directions. Their values strongly depend on the studied sample and are presumably related to the strains suffered by the films.