Split-screen single-camera stereoscopic PIV application to a turbulent confined swirling layer with free surface

An annular liquid wall jet, or vortex tube, generated by helical injection inside a tube is studied experimentally as a possible means of fusion reactor shielding. The hollow confined vortex/swirling layer exhibits simultaneously all the complexities of swirling turbulence, free surface, droplet formation, bubble entrapment; all posing challenging diagnostic issues. The construction of flow apparatus and the choice of working liquid and seeding particles facilitate unimpeded optical access to the flow field. A split-screen, single-camera stereoscopic particle image velocimetry (SPIV) scheme is employed for flow field characterization. Image calibration and free surface identification issues are discussed. The interference in measurements of laser beam reflection at the interface are identified and discussed. Selected velocity measurements and turbulence statistics are presented at Re_λ = 70 (Re = 3500 based on mean layer thickness)

Magnetic Force Microscopy study of layered superconductors in vectorial magnetic fields

This thesis is focused on the set-up and use of a cryogenic magnetic force microscope (MFM) in a three axis vector magnet. We have studied superconducting layered and quasi-two dimensional compounds. In particular, we address the superconducting properties of graphene deposited on an isotropic s-wave superconductor β−Bi2Pd, of a layered cuprate superconductor (BiSr2CaCu2O8), of a layered iron based material (Ca(Fe0.965Co0.035)2As2) and of the s-wave superconductor β−Bi2Pd.Por último, me gustaría agradecer a los proyectos de investigación Anisometric permanent hybrid magnets based on inexpensive and non-critical materials (AMPHIBIAN) (Ref. NMBP-03-2016) y Graphene Flagship (Grant No. 604391) financiados por la Unión Europea, gracias a los cuales he podido realizar mi tesis doctoral.Peer reviewe

EXTREME DYNAMICS OF NANOMATERIALS UNDER HIGH-RATE MECHANICAL STIMULI

Nanomaterials demonstrate novel mechanical properties attributed to the extremely large interfacial area. At quasi-static rates, the interfacial interactions are crucial in mechanical behaviors, however, materials under extreme mechanical stimuli are rarely studied at nanoscale. With an advanced laser-induced projectile impact test, we perform supersonic impact of micro-projectiles on polymer films, multilayer graphene, carbon- based nanocomposites membranes as well as individual micro-fibers, to study the interface interactions in the high-rate regime, and develop a simplified model to characterize the ballistic performance of materials

Magnetic Force Microscopy study of layered superconductors in vectorial magnetic fields

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de la Materia Condensada. Fecha de lectura: 22-01-201

Magnetic Force Microscopy study of layered superconductors in vectorial magnetic fields

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de la Materia Condensada. Fecha de lectura: 22-01-201

Free-space and near-wall dynamics of a flexible sheet sedimenting in Stokes flow

We present a numerical study of a thin elastic sheet with small extensibility freely sedimenting in a viscous fluid. Two scenarios are investigated: sedimentation in free space and near an infinite wall, where the wall may be vertical or tilted. Elastic sheets with a rest shape of a square are modeled with a finite-element-based continuum model that accounts for in-plane stretching and out-of-plane bending. The fluid motion is computed by the method of regularized Stokeslets in free space and regularized Blakelets near a wall. During sedimentation, the interplay between gravity and the elastic response of sheets gives rise to complex deformation and reorientation dynamics, measured by a dimensionless elasto-gravitational number. In free space, sheets attain a stable orientation by aligning perpendicular to gravity. Sheets with larger deformability adopt more compact conformations and experience smaller hydrodynamic drag, thereby sedimenting faster. A sheet with a random initial orientation reorients to align perpendicular to gravity, accompanied by lateral drift due to the symmetry-breaking in conformations. We identified two reorientation mechanisms depending on flexibility. When a sheet is placed near an infinite wall, sedimentation is hindered compared to that in free space due to wall-induced hydrodynamic drag. Near a vertical wall, sheets exhibit asymmetric conformations that cause the sheet to drift, with the drifting dynamics determined by elasto-gravitational number. The difference in flexibility leads to a non-monotonic trend in the evolution of wall-normal distance. Near a tilted wall, sheets show qualitatively different dynamics when the wall angle is large: they either deposit on or slide along the wall with a fixed wall-normal distance.Comment: 29 pages, 8 figure