Improving the accuracy of phase-shifting techniques

The traditional phase-shifting profilometry technique is based on the projection of digital interference patterns and computation of the absolute phase map. Recently, a method was proposed that used phase interpolation to the corner detection, at subpixel accuracy in the projector image for improving the camera–projector calibration. We propose a general strategy to improve the accuracy in the search for correspondence that can be used to obtain high precision three-dimensional reconstruction. Experimental results show that our strategy can outperform the precision of the phase-shifting method

Mixing in convective thermal fluxes in unsteady nonhomogeneous flows generating complex three dimensional vorticity patterns

Diffusion and scaling of the velocity and vorticity in a thermoelectric driven heating and cooling experimental device is presented in order to map the different patterns and transitions between two and three dimensional convection in an enclosure with complex driven flows. The size of the water tank is of 0.2 x 0.2 x 0.1 m and the heat sources or sinks can be regulated both in power and sign [1-3]. The thermal convective driven flows are generated by means of Peltier effects in 4 wall extended positions of 0.05 x 0.05 cm each. The parameter range of convective cell array varies strongly with the Topology of the boundary conditions. Side heat and momentum fluxes are a function of Rayleigh, Peclet and Nusselt numbers, [4-6] Visualizations are performed by PIV, Particle tracking and shadowgraph. The structure of the flow is shown by setting up a convective flow generated by buoyant heat fluxes. The experiments described here investigate high Prandtl number mixing using brine and fresh water in order to form a density interface and low Prandtl number mixing with temperature gradients. The evolution of the mixing fronts are compared and the topological characteristics of the merging of the convective structures are examined for different configurations. Based on two dimensional Vorticity spectral analysis, new techniques can be very useful to determine the evolution of scales considering the multi-fractal structure of the convective flows.Peer ReviewedPostprint (published version

Multiscaling properties on sequences of turbulent plumes images

A multifractal analysis on a finite-range-scale of the plume concentration images at different experimental conditions (the height of the source Ho), where the measure is the grey value of the image (from 0 to 255), was applied to study its structure through time. The multifractal spectrum showed the characteristic inverse U-shape and a similar evolution in all Ho. The variation of the Hölder exponent (¿a) presented different amplitudes at different moments and increased with time. The symmetry of the spectrum (¿f) decreased with time achieving negative values (from left hand asymmetry evolving to right asymmetry). We show the different behaviour of axial velocity (W) with ¿a and ¿f. There is a linear relation of entrainment coefficient (ae) and the entropy dimension (a1). Therefore, the multifractal spectrum and the derived parameters can be used as markers of plume evolution as well as to study the effect of experimental conditions.Postprint (published version

Evolution of the Thorpe and Ozmidov scales at the lower atmospheric and planetary boundary layer

Turbulence affects the dynamics of atmospheric processes by enhancing the transport of mass, heat, humidity and pollutants. The global objective of our work is to analyze some turbulent descriptors which reflect the mixing processes in the atmospheric boundary layer (ABL). In this paper we present results related to the Thorpe displacements dT, the maximum Thorpe displacement (dT)max, the Thorpe scale LT and the Ozmidov scale, LO, and their time evolution in the ABL during a day cycle. A tethered balloon was used to obtain vertical profiles of the atmospheric physical magnitudes up to 1000 m. We discuss their vertical and time variability, and also their relationships.Postprint (author’s final draft

SPICE compact modeling of bipolar/unipolar memristor switching governed by electrical thresholds

In this work we propose a physical memristor/resistive switching device SPICE compact model, that is able to accurately fit both unipolar/bipolar devices settling to its current-voltage relationship. The proposed model is capable of reproducing essential device characteristics such as multilevel storage, temperature dependence, cycle/event handling and even the evolution of variability/parameter degradation with time.The developed compact model has been validated against two physical devices, fitting unipolar and bipolar switching. With no requirement of Verilog-A code, LTSpice and Spectre simulations reproduce distinctive phenomena such as the preforming state, voltage/cycle dependent<br/

SAR measurements of coastal features in the NW Mediterranean

Peer ReviewedPostprint (published version

Percolation experiments in complex fractal media

Postprint (published version

Thermocapilarity and radiative heat flux oscillations

We present a detailled experimental study of the thermocapillary motion of an aniline drop in an stably stratified fluid sytem driven by a laser beam. The thermocapillary motion of drops is the result of the temperature dependence of the interfacial tension. If the surface of the drop is subject to thermal gradients, then non-equilibrium surface tension effects appear, which in some cases can move the drop. We measure some of the velocity induced fields , vorticity, oscilations and intermittency of this complex flow. The source of the no uniformity of the temperature of the surface can be, as is in this experiment, the non uniform heating of the floating drop by a laser beam. In recent years, the thermocapillary movement of bubbles and drops under the influence of laser radiation has received more experimental attention thanks to the improvement in the flow visualization techniques.Peer ReviewedPostprint (published version

Convective thermal fluxes in unsteady non-homogeneous flows

In this paper we describe a novel experimental apparatus consisting of a thermoelectric driven heating and cooling device that could be used in didactic laboratories and research. Is possible to model common environmental flows by means of convective cooling and/or heating. We describe here a four cell device, in a 3D enclosure, but furthermore, it is possible to generate a convective flow of complex profiles using an array of thermoelectric devices (Peltier/Seebeck cells) controlled by a thermal proportional-integral-derivative controller generating a multisource buoyant flux. When convective heating and cooling takes place the combination of internal waves and buoyant turbulence is much more complicated if the Rayleigh and Reynolds numbers are high in order to study entrainment and mixing. The experiments made by our thermoelectric driven device could be used to analyze complex mixing, in either low or high Prandtl numbers, using scalar or heat transport in different liquids. From the varied experiments carried out with our device, we can compute and visualize the fields of velocity, vorticity, density and their gradients, here just a few configurations and the corresponding flows will be shown.This work was partially supported by the company BEROTZA S.L. under Grant No. UPC-BEROTZA-2014-0880 We would also like to thank FLUMEN-UPC and ERCOFTAC and the PELNoHT for travel support for J.T.. Technology Transfer Centre of Technical University of Catalonia (CTT-UPC) grant supported the implementation and analyses of the experiments. Sincere gratitude is extended to Dr. H. Takeda and Masao Kuramitsu from Hokaido Univ.Peer ReviewedPostprint (author's final draft